Mechanisms of pancreatic beta-cell death in type 1 and type 2 diabetes: many differences, few similarities.

Abstract

Type 1 and type 2 diabetes are characterized by progressive beta-cell failure. Apoptosis is probably the main form of beta-cell death in both forms of the disease. It has been suggested that the mechanisms leading to nutrient- and cytokine-induced beta-cell death in type 2 and type 1 diabetes, respectively, share the activation of a final common pathway involving interleukin (IL)-1beta, nuclear factor (NF)-kappaB, and Fas. We review herein the similarities and differences between the mechanisms of beta-cell death in type 1 and type 2 diabetes. In the insulitis lesion in type 1 diabetes, invading immune cells produce cytokines, such as IL-1beta, tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma. IL-1beta and/or TNF-alpha plus IFN-gamma induce beta-cell apoptosis via the activation of beta-cell gene networks under the control of the transcription factors NF-kappaB and STAT-1. NF-kappaB activation leads to production of nitric oxide (NO) and chemokines and depletion of endoplasmic reticulum (ER) calcium. The execution of beta-cell death occurs through activation of mitogen-activated protein kinases, via triggering of ER stress and by the release of mitochondrial death signals. Chronic exposure to elevated levels of glucose and free fatty acids (FFAs) causes beta-cell dysfunction and may induce beta-cell apoptosis in type 2 diabetes. Exposure to high glucose has dual effects, triggering initially "glucose hypersensitization" and later apoptosis, via different mechanisms. High glucose, however, does not induce or activate IL-1beta, NF-kappaB, or inducible nitric oxide synthase in rat or human beta-cells in vitro or in vivo in Psammomys obesus. FFAs may cause beta-cell apoptosis via ER stress, which is NF-kappaB and NO independent. Thus, cytokines and nutrients trigger beta-cell death by fundamentally different mechanisms, namely an NF-kappaB-dependent mechanism that culminates in caspase-3 activation for cytokines and an NF-kappaB-independent mechanism for nutrients. This argues against a unifying hypothesis for the mechanisms of beta-cell death in type 1 and type 2 diabetes and suggests that different approaches will be required to prevent beta-cell death in type 1 and type 2 diabetes.

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Mechanisms of Pancreatic ?-Cell Death in Type 1 and
Type 2 Diabetes
Many Differences, Few Similarities
Miriam Cnop,1,2Nils Welsh,3Jean-Christophe Jonas,4Anne Jo ¨rns,5,6Sigurd Lenzen,6
and Decio L. Eizirik1
Type 1 and type 2 diabetes are characterized by progres-
sive ?-cell failure. Apoptosis is probably the main form of
?-cell death in both forms of the disease. It has been
suggested that the mechanisms leading to nutrient- and
cytokine-induced ?-cell death in type 2 and type 1 diabetes,
respectively, share the activation of a final common path-
way involving interleukin (IL)-1?, nuclear factor (NF)-?B,
and Fas. We review herein the similarities and differences
between the mechanisms of ?-cell death in type 1 and type
2 diabetes. In the insulitis lesion in type 1 diabetes,
invading immune cells produce cytokines, such as IL-1?,
tumor necrosis factor (TNF)-?, and interferon (IFN)-?.
IL-1? and/or TNF-? plus IFN-? induce ?-cell apoptosis via
the activation of ?-cell gene networks under the control of
the transcription factors NF-?B and STAT-1. NF-?B activa-
tion leads to production of nitric oxide (NO) and chemo-
kines and depletion of endoplasmic reticulum (ER)
calcium. The execution of ?-cell death occurs through
activation of mitogen-activated protein kinases, via trig-
gering of ER stress and by the release of mitochondrial
death signals. Chronic exposure to elevated levels of glu-
cose and free fatty acids (FFAs) causes ?-cell dysfunction
and may induce ?-cell apoptosis in type 2 diabetes. Expo-
sure to high glucose has dual effects, triggering initially
“glucose hypersensitization” and later apoptosis, via dif-
ferent mechanisms. High glucose, however, does not induce
or activate IL-1?, NF-?B, or inducible nitric oxide synthase
in rat or human ?-cells in vitro or in vivo in Psammomys
obesus. FFAs may cause ?-cell apoptosis via ER stress,
which is NF-?B and NO independent. Thus, cytokines and
nutrients trigger ?-cell death by fundamentally different
mechanisms, namely an NF-?B–dependent mechanism that
culminates in caspase-3 activation for cytokines and an
NF-?B–independent mechanism for nutrients. This argues
against a unifying hypothesis for the mechanisms of ?-cell
death in type 1 and type 2 diabetes and suggests that
different approaches will be required to prevent ?-cell
death in type 1 and type 2 diabetes. Diabetes 54 (Suppl. 2):
S97–S107, 2005
C
vironmental factors eventually lead to loss of functional
?-cell mass and hyperglycemia. The mechanisms leading
to ?-cell loss may be quite diverse in the various subtypes
of the disease. As our knowledge of disease pathogeneses
increases, better classifications of diabetes may be
proposed.
The two main forms of diabetes are type 1 and type 2
diabetes (1). Both types are characterized by progressive
?-cell failure. In type 1 diabetes, this is typically caused by
an autoimmune assault against the ?-cells, inducing pro-
gressive ?-cell death. The pathogenesis of type 2 diabetes
is more variable, comprising different degrees of ?-cell
failure relative to varying degrees of insulin resistance.
The genetics (i.e., HLA-related in type 1 diabetes vs.
non–HLA-related in type 2 diabetes), putative environmen-
tal triggers (for instance viral infection in type 1 diabetes,
obesity in type 2 diabetes), and natural history of the
disease are different between type 1 and type 2 diabetes.
Because these topics are covered in detail in other articles
in this supplement issue, they will not be discussed further
here.
In type 1 diabetes, ?-cell mass is reduced by 70–80% at
the time of diagnosis. Because of the variable degrees of
insulitis and absence of detectable ?-cell necrosis, it was
suggested that ?-cell loss occurs slowly over years (2).
These pathology findings are in line with the progressive
decline in first-phase insulin secretion in antibody-positive
individuals, long before the development of overt diabetes
(3). It was later shown that ?-cell apoptosis causes a
gradual ?-cell depletion in rodent models of type 1 diabe-
tes (rev. in 4). In type 2 diabetic subjects, initial patholog-
ical studies suggested a ?-cell loss of 25–50% (2,5), but this
was debated by others (6). Recent studies, which matched
diabetic patients and control subjects for BMI, showed a
significant reduction in ?-cell mass (7,8) and a threefold
increase in ?-cell apoptosis (8). These observations sug-
gest that ?-cell mass is decreased in type 2 diabetes,
secondary to increased rates of ?-cell apoptosis, but it
linical definitions of disease often obscure dif-
ferent mechanistic subtypes. This is particularly
relevant for complex diseases such as diabetes,
where combinations of multiple genes and en-
From the1Laboratory of Experimental Medicine, Faculty of Medicine, Eras-
mus Hospital, Universite ´ Libre de Bruxelles, Brussels, Belgium; the2Division
of Endocrinology, Erasmus Hospital, Universite ´ Libre de Bruxelles, Brussels,
Belgium; the
Biomedicum, Uppsala, Sweden; the4Unit of Endocrinology and Metabolism,
Faculty of Medicine, University of Louvain (UCL), Brussels, Belgium; the
5Centre of Anatomy, Hannover Medical School, Hannover, Germany; and the
6Institute of Clinical Biochemistry, Hannover Medical School, Hannover,
Germany.
Address correspondence and reprint requests to Dr. Miriam Cnop, Labora-
tory of Experimental Medicine, Universite ´ Libre de Bruxelles (ULB), Route de
Lennik 808, CP-618, 1070 Brussels, Belgium. E-mail: mcnop@ulb.ac.be.
Received for publication 23 February 2005 and accepted in revised form 30
March 2005.
This article is based on a presentation at a symposium. The symposium and
the publication of this article were made possible by an unrestricted educa-
tional grant from Servier.
ATF, activating transcription factor; CHOP, C/EBP (CCAAT/enhancer bind-
ing protein) homologous protein; ER, endoplasmic reticulum; ERK, extracel-
lular signal–regulated kinase; FACS, fluorescence-activated cell sorting; FFA,
free fatty acid; GIIS, glucose-induced insulin secretion; I?B, inhibitory ?B;
IFN, interferon; IL, interleukin; iNOS, inducible nitric oxide synthase; JNK,
c-Jun NH2-terminal kinase; MAPK, mitogen-activated protein kinase; NF,
nuclear factor; SOCS, suppressor of cytokine signaling; TNF, tumor necrosis
factor.
© 2005 by the American Diabetes Association.
3Department of Medical Cell Biology, Uppsala University,
DIABETES, VOL. 54, SUPPLEMENT 2, DECEMBER 2005S97

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remains unclear whether this explains the observed func-
tional loss (9).
?-Cell apoptosis may thus be a common feature of type
1 and type 2 diabetes. Recent studies (rev. in 10 and 11)
suggest that both forms of diabetes are characterized by
intra-islet expression of inflammatory mediators (espe-
cially the cytokine interleukin [IL]-1?), triggering a final
common pathway of ?-cell apoptosis, progressive ?-cell
loss, and diabetes. Based on this hypothesis, a unifying
classification of diabetes has been proposed (10). Against
this background, we review herein the experimental evi-
dence on the similarities and differences between the
mechanisms of ?-cell death in type 1 and type 2 diabetes.
MECHANISMS OF ?-CELL DEATH IN TYPE 1 DIABETES
Pancreatic ?-cells are the target of an autoimmune assault
in type 1 diabetes, with invasion of the islets by mononu-
clear cells in an inflammatory reaction termed “insulitis,”
leading to loss of most ?-cells after prolonged periods of
disease (2). ?-Cell death in the course of insulitis is
probably caused by direct contact with activated macro-
phages and T-cells, and/or exposure to soluble mediators
secreted by these cells, including cytokines, nitric oxide
(NO), and oxygen free radicals (4). In vitro exposure of
?-cells to IL-1?, or to IL-1? ? interferon (IFN)-?, causes
functional changes similar to those observed in pre-dia-
betic patients, namely elevated proinsulin/insulin levels
(12) and a preferential loss of first-phase insulin secretion
in response to glucose, caused by an IL-1?–mediated
decrease in the docking and fusion of insulin granules to
the ?-cell membrane (13). After prolonged exposure to
IL-1? ? IFN-? and/or tumor necrosis factor (TNF)-?, but
not to either cytokine alone, this functional impairment
evolves to ?-cell death (4).
Apoptosis, the main cause of ?-cell death at the onset of
type 1 diabetes, is a highly regulated process, activated
and/or modified by extracellular signals, intracellular ATP
levels, phosphorylation cascades, and expression of pro-
and anti-apoptotic genes (4). Cytokines induce stress
response genes that are either protective or deleterious for
?-cell survival. In extensive microarray experiments (14–
17), we have identified ?700 genes and expressed se-
quence tags that are up- or downregulated in purified rat
?-cells or insulin-producing cells after 1–24 h of exposure
to IL-1? and/or IFN-?. The main findings of these studies
are summarized in Fig. 1. A detailed review of the gene
networks activated by cytokines in ?-cells, and on the role
of chemokines produced by ?-cells in the build up of
insulitis, is provided by Eizirik et al. (18), while the
complete list of ?-cell–expressed genes, as detected by
our microarray analyses, is accessible at the Beta Cell
Gene Expression Bank (http://t1dbase.org/cgi-bin/enter_
bcgb.cgi) (19). IL-1? activates the transcription factor
nuclear factor (NF)-?B (Fig. 1) in rodent and human islet
cells (4), and prevention of NF-?B activation by an inhib-
itory ?B (I?B) “super-repressor” (20,21) protects pancre-
atic ?-cells against cytokine-induced apoptosis. In an
additional microarray analysis, we studied IL-1?–treated
?-cells whose NF-?B activation was blocked by adenovi-
rus-mediated expression of the I?B(SA)2super-repressor
(16). A total of 66 cytokine-responsive NF-?B–dependent
genes were identified, including genes coding for cyto-
FIG. 1. The transcription factor and gene networks putatively involved in the cytokine-promoted ?-cell “decision” to undergo apoptosis. The
transcription factors NF-?B and STAT-1 are the main regulators of the pathways triggered by IL-1? and IFN-?, respectively. The figure is based
on Refs. 14–18. MHC-1, major histocompatibility complex 1.
MECHANISMS OF ?-CELL DEATH IN DIABETES
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kines and chemokines and stress-related genes such as
GADD153/CHOP [C/EBP (CCAAT/enhancer binding pro-
tein) homologous protein] (a mediator of endoplasmic
reticulum [ER] stress-induced cell death; see below) and
c-myc. NF-?B was also found to downregulate (probably
indirectly, via NO production) the expression of other
transcription factors responsible for ?-cell differentiation
and function (e.g., PDX-1 and Isl-1). NF-?B regulates
expression of inducible nitric oxide synthase (iNOS) in
?-cells (22), and ?50% of the ?-cell genes modified after
12 h of cytokine exposure are secondary to iNOS-mediated
NO formation (15). Of note, it has been recently described
that transgenic expression of an NF-?B inhibitor under the
control of the pdx-1 promoter (blocking NF-?B during
?-cell development) causes defective GLUT2 expression
and glucose-induced insulin secretion (GIIS) later in
mouse life, suggesting that basal NF-?B is required for
normal insulin release (23). In our hands, however, block-
ing basal NF-?B activity for 48–72 h in adult rat ?-cells
affected neither GLUT2 expression nor GIIS (16,21; A.K.
Cardozo, D.L.E., unpublished data), suggesting that the
putative physiological role of basal NF-?B activity is more
relevant during fetal ?-cell development than during adult
life or is only detectable after prolonged NF-?B inhibition.
In summary, IL-1?–induced NF-?B activation plays a cru-
cial role in controlling multiple and distinct gene regula-
tory networks, which affect the ?-cell–differentiated state
and ER Ca2?homeostasis, attract and activate immune
cells, and directly contribute to ?-cell apoptosis.
Exposure of purified human or rodent ?-cells to IL-1?
alone is not sufficient to induce apoptosis, but when IL-1?
is combined with IFN-?, ?50% of these cells undergo
apoptosis after 6–9 days (4). This suggests that IFN-?
signal transduction must synergize with IL-1? signaling to
trigger ?-cell apoptosis (Fig. 1). IFN-? binds to cell surface
receptors and activates the tyrosine kinases JAK1 and
JAK2. These kinases phosphorylate the transcription fac-
tor STAT-1, which dimerizes and translocates to the nu-
cleus to bind to ?-activated sites of diverse genes (4).
STAT-1 mediates the potentiating effect of IFN-? on IL-1?–
induced iNOS expression (22), and our recent observa-
tions showthat fluorescence-activated
(FACS)-purified
?-cellsfrom
(STAT-1?/?) are protected against IL-1? ? IFN-?–induced
apoptosis (C. Gysemans, L. Ladriere, H. Callewaert, J.
Rasschaert, D. Flamez, D.E. Levy, D.L.E., C. Mathieu,
unpublished data). Because excessive activation of JAK/
STAT signaling may lead to cell death, STAT transcrip-
tional activity is regulated by multiple negative feedback
mechanisms. These include dephosphorylation of JAK and
cytokine receptors by SHP, and inhibition of JAK enzy-
matic activities by the suppressor of cytokine signaling
(SOCS) family. Upregulation of SOCS-1 or SOCS-3 pro-
tects ?-cells in vitro and in vivo against cytokine-induced
death (24,25). SOCS-3 also protects insulin-producing cells
against IL-1?–mediated apoptosis via NF-?B inhibition
(26). The results summarized in Fig. 1 indicate that ?-cell
fate after cytokine exposure depends on the duration and
severity of perturbation of key ?-cell gene networks. The
precise identity and regulation of these gene networks
remain to be elucidated, but the available data suggest an
important role for NF-?B and STAT-1.
It is of interest to understand how the cytokine-acti-
vated gene expression patterns described in Fig. 1 actually
result in ?-cell death. Some of the probable mechanisms
cell sorting
mice STAT-1–deficient
are outlined in Fig. 2. They include the following: 1)
activation of the stress-activated protein kinases c-Jun
NH2-terminal kinase (JNK), p38 mitogen-activated protein
kinase (MAPK), and extracellular signal-regulated kinase
(ERK); 2) triggering of ER stress; and 3) the release of
death signals from the mitochondria.
JNK is a member of the MAPK family. Pancreatic ?-cells
exposed to IL-1? have an early and sustained increase in
JNK activity, a phenomenon potentiated by IFN-? or
TNF-? (4,11). Cell-permeable peptide inhibitors of JNK
prevent cytokine-induced apoptosis in insulin-producing
cells (27), but this remains to be confirmed in primary
?-cells. p38 MAPK and ERK are also activated by cyto-
kines, and pharmacological inhibition of these MAPKs
diminished cytokine-induced rat islet cell death (28,29),
possibly by attenuating transcriptional activation of iNOS
(28). However, when purified ?-cells were exposed to
IL-1? ? IFN-? for 6–9 days, ERK, but not p38, inhibitors
provided partial protection against apoptosis (30), sug-
gesting that some of the protection by MAPK inhibitors in
whole islets is mediated via effects on other islet cells
(such as resident macrophages). p38 may also increase the
apoptotic propensity of the ?-cell, since genetic downregu-
lation of p38? results in a lowered sensitivity to cell death
induced by the NO donor DETA/NONOate (N. Makeeva, J.
Myers, N.W., unpublished data). In addition, the tumor
suppressor p53 is activated in response to cytokine-in-
duced NO production (31). It is conceivable that stabiliza-
tion of the pro-apoptotic protein p53 lies downstream of
the NO-induced activation of MAPKs.
Disruption of ER homeostasis, as induced by changes in
ER Ca2?concentrations, triggers accumulation of un-
folded proteins and activation of a specific stress re-
sponse, known as the ER stress response (32). This
cellular response is a coordinated attempt to restore ER
homeostasis and function, and it includes translational
attenuation, upregulation of ER chaperones, and degrada-
tion of misfolded proteins. In case of prolonged and severe
ER stress, the apoptosis program is activated and exe-
cuted by the transcription factor CHOP, the MAPK JNK,
and caspase-12 (although it remains unclear whether
caspase-12 has a role in human cells) (32). Because of their
high rate of protein synthesis, ?-cells are particularly
susceptible to ER stress (33), and NO donors trigger an ER
stress response in ?-cells leading to CHOP expression and
apoptosis (34). We have recently shown that IL-1? ? IFN-?
inhibit SERCA2b expression, via NF-?B activation and NO
production, and deplete ER Ca2?stores. This is followed
by activation of diverse components of the ER stress
response, including activation of IRE-1? and PERK/acti-
vating transcription factor (ATF)-4, xbp1 mRNA process-
ing, and induction of CHOP (35). Different from the ?-cell
response to chemical SERCA2b inhibitors or free fatty
acids (FFAs) (36), cytokines neither activate ATF-6 nor
induce the ER chaperone BiP (35). This defective ATF-6
activation may deprive ?-cells from a crucial defense
against ER stress, contributing to their exquisite vulnera-
bility to cytokines.
Mitochondria are key organelles for ?-cell function and
survival (37). Paradoxically, mitochondria also play an
important role in triggering apoptosis (38). Members of the
Bcl-2 protein family regulate the mitochondrial response
to pro-apoptotic signals (38), preventing release of mito-
chondrial proteins such as cytochrome c, which, when
liberated to the cytosol, sequentially activate caspase-9
and -3 and execute cell death (39). Cytokines disrupt the
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mitochondrial membrane potential in RINm5F cells, which
is prevented by overexpression of the anti-apoptotic pro-
tein Bcl-2 (40). Overexpression of Bcl-2 partially protects
mouse (41) and human (42) islets against cytokine-in-
duced cell death, but does not prevent adenovirus-induced
islet cell death (43) or spontaneous diabetes in nonobese
diabetic (NOD) mice (44). This suggests that other mech-
anisms, bypassing Bcl-2, induce ?-cell death in vivo and/or
that Bcl-2–regulated mitochondrial events and caspase
activation are late steps in the apoptosis process, occur-
ring when the cell fate has already been decided. In line
with the second possibility, blocking caspase-1 (induced in
?-cells by cytokines [45]) decreases ?-cell apoptosis after
4 days of exposure to IL-1? ? IFN-?, but it does not
prevent their subsequent death by necrosis after 9 days (D.
Liu, D.L.E., unpublished data). Other pro-apoptotic genes
that are induced by cytokines, as detected by microarray
analysis (15), are indicated in Fig. 2 and include Bid, Bak,
and caspase-3. An intriguing possibility is that an early
cytokine-induced “dialogue” between the nucleus, mito-
chondria, and ER influences the decision of the ?-cell to
undergo apoptosis or not. In favor of this hypothesis,
overexpression of free radical scavenging enzymes in
mitochondria, but not in the cytosol, prevents IL-1?–
induced NF-?B activation (46).
MECHANISMS OF ?-CELL DEATH IN TYPE 2 DIABETES
Insulin resistance, often associated with obesity, and
insulin secretion defects are major risk factors for type 2
diabetes (9). A progressive decrease of ?-cell function
leads to glucose intolerance, which is followed by type 2
diabetes that inexorably aggravates with time (47). The
alterations of GIIS in human type 2 diabetes may theoret-
ically result from changes in ?-cell function, ?-cell mass,
or both. A decrease in ?-cell mass is likely to play a role in
the pathogenesis of human type 2 diabetes (8,9) as it does
in rodent models of the disease (48,49). However, in
contrast with type 1 diabetes, the 25–50% reduction in
?-cell mass measured postmortem in type 2 diabetic
patients may not be important enough to account for the
observed loss of GIIS. Because ?-cell mass cannot be
measured in vivo, it remains unclear whether type 2
diabetic patients had a lower ?-cell mass early in life,
failed to increase their ?-cell mass in the face of insulin
resistance, or had a progressive ?-cell loss. The question
whether the reduction in human ?-cell mass results from
increased ?-cell apoptosis, reduced cell neogenesis/repli-
cation, or both also remains unsettled (49). Based on
results obtained in rodent models of the disease and in
cultured rodent and human islet cells, it seems reasonable
to assume that dyslipidemia and hyperglycemia negatively
affect ?-cell mass by increasing ?-cell apoptosis in human
FIG. 2. Proposed model for the different pathways contributing to the execution of cytokine-induced ?-cell apoptosis. Arrows indicate genes for
which expression was modified by cytokines in a time course microarray analysis (15). ?-Cell apoptosis is probably mediated by three main
pathways—namely JNK, ER stress, and liberation of pro-apoptotic proteins from the mitochondria.
MECHANISMS OF ?-CELL DEATH IN DIABETES
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type 2 diabetes (10,48). In the following paragraphs, we
discuss recent hypotheses on the mechanisms of glucotox-
icity and lipotoxicity. Readers are directed to another
recent review (49) for information on other potential
agents causing ?-cell dysfunction/death in type 2 diabetes.
Glucotoxicity. Moderate or severe hyperglycemia cannot
be the primum movens in the pathophysiology of type 2
diabetes, but it contributes to the reduction of GIIS (50).
As such, it could contribute to the progression from
glucose intolerance to overt type 2 diabetes (47). The
mechanisms by which hyperglycemia negatively affects
functional ?-cell mass are still debated. Rodent ?-cells
chronically exposed to high glucose display several alter-
ations of their phenotype, including changes in glucose
stimulus-secretion coupling, gene expression, cell sur-
vival, and cell growth (48,49). These alterations could
result from cytokine-, oxidative stress–, or ER stress–
induced changes in gene expression and cell survival
(10,32,51) or from functional changes that are not directly
related to ?-cell apoptosis, such as accumulation of glyco-
gen (52).
Rodent ?-cells display reduced expression of genes
involved in GIIS in in vivo and in vitro models of prolonged
exposure to high glucose. These include insulin, GLUT2,
glucokinase and voltage-dependent Ca2?channels, and
the transcription factors that regulate their expression
(53). These changes, which may play a role in the alter-
ations of GIIS in rodent type 2 diabetes, have some
similarities with those induced by cytokines (17,18). On
the other hand, several genes expressed at low levels in
normal ?-cells are induced by hyperglycemia, including
hexokinase 1, lactate dehydrogenase and glucose-6 phos-
phatase. In addition, pro- and anti-apoptotic factors, anti-
oxidant enzymes, and some transcription factors are
upregulated (53). Some of these genes, such as c-Myc, A20,
and heme-oxygenase 1, are induced by hyperglycemia and
cytokines, suggesting that both conditions share some
common mechanisms to alter the ?-cell phenotype. The
suggestion that hyperglycemia increases ?-cell production
of IL-1? in human islets provides such a unified hypothesis
for ?-cell pathophysiology in type 1 and type 2 diabetes
(10). However, the pattern of hyperglycemia-induced
?-cell genes is only partly similar to that induced by
cytokines (17,18,53). For instance, iNOS and I?B?, two
NF-?B–dependent genes markedly induced by IL-1?, are
not induced in rodent ?-cells exposed to high glucose.
Other genes, such as lactate dehydrogenase A, the mito-
chondrial uncoupling protein UCP-2, and the transcription
factor CREM, are induced by hyperglycemia (53,54) and
downregulated by cytokines (17,55). Furthermore, hyper-
glycemia induces ?-cell hypertrophy, whereas cytokine
treatment does not, and the induction of ?-cell apoptosis
by high glucose is much lower than that produced by
cytokines. These differences raise questions about the role
of IL-1?–induced NF-?B activation in ?-cell glucotoxicity.
These doubts are strengthened by our observations that,
under various culture conditions, exposure of rat or hu-
man islets or FACS-purified rat ?-cells to high glucose
does not increase IL-1? mRNA expression or NF-?B
DNA-binding activity (56; Fig. 3; see also below).
It is generally assumed that oxidative stress activates
NF-?B activity in ?-cells as in other cell types (53). This
does not seem to be the case, since acute (57) or overnight
exposure to low concentrations of hydrogen peroxide
does not increase rat islet NF-?B activity and iNOS expres-
sion (56). Islet c-Myc and heme-oxygenase 1 expression
are similarly induced by hydrogen peroxide and high
glucose, and these effects are abrogated by the free radical
scavenger N-acetyl-L-cysteine. This suggests that ?-cell
glucotoxicity may, at least in part, result from an increase
in ?-cell oxidative stress and subsequent JNK activation
that is NF-?B independent (51,56). The main source of
reactive oxygen species in the ?-cell is probably the
mitochondrial electron transport chain (58,59). It is there-
fore possible that chronic stimulation of insulin secretion
in states of insulin resistance induces oxidative stress.
Other possible explanations for changes in ?-cell function
and viability before overt hyperglycemia include activation
of the ER stress pathway (also in the context of lipotox-
icity; see below) and sustained elevation of cytosolic Ca2?
concentration (60).
It is well established that chronic hyperglycemia leads
to ?-cell degranulation and reduction in GIIS (48), but the
effect of hyperglycemia on the ?-cell sensitivity to glucose
is controversial. A first group of studies indicates that the
absence of a glucose-induced rise in ATP production,
perhaps due to hyperglycemia-induced expression of un-
coupling protein 2, is responsible for defective GIIS (61).
FIG. 3. High glucose (28 mmol/l) does not induce NF-?B activation
and DNA binding in ?-cells, as assessed by immunofluorescence
using an antibody directed against the p65 NF-?B subunit. FACS-
purified rat ?-cells were exposed to 10 mmol/l (control, A) or 28
mmol/l glucose (B) for 12–24 h. The data at 12 h are shown here;
similar observations were made at 24 h (not shown). As a positive
control, cells were exposed to IL-1? (30 units/ml, in medium
containing 10 mmol/l glucose [C]) during the last 30 min of culture.
NF-?B is located in the cytosol at 10 mmol/l (A) or 28 mmol/l (B)
glucose, whereas it translocates to the nucleus after exposure to
IL-1?, indicating activation (C). Subcellular NF-?B localization
was counted in 200–400 cells using the same experimental condi-
tions as above (D). ?, Cytoplasmic NF-?B localization; f, nuclear
localization. The results are means ? SE of three independent
experiments. *P < 0.001 vs. percent nuclear staining in the control
by two-sided paired t test (D). Original magnification ?200.
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These observations, conceptualized as ?-cell “glucose de-
sensitization,” seem in contradiction with other studies
showing that ?-cells exposed to hyperglycemia become
more sensitive to glucose for the stimulation of mitochon-
drial metabolism, proinsulin biosynthesis, and insulin se-
cretion. This leads to maximal stimulation of triggering
and amplifying pathways of GIIS at low glucose (a concept
we refer to as “glucose hypersensitization”) (62–64). This
glucose hypersensitization, which results from higher ATP
production at low glucose concentrations, may be due to
the accumulation of glycogen in ?-cells (52,64). Glucose
hypersensitization was observed together with a paradox-
ical dissociation between glucose-induced Ca2?influx and
insulin secretion on one hand and a sustained elevation of
cytosolic Ca2?unaffected by glucose on the other, and it is
associated with a strong reduction of GIIS between 5 and
10 mmol/l glucose. This concept of ?-cell glucose hyper-
sensitivity fits with the presence of fasting hyperinsulin-
emia in type 2 diabetic patients and the observation (based
on autopsy material) that their ?-cells are actively engaged
in proinsulin synthesis (65).
Although both ?-cell “glucose desensitization” and “glu-
cose hypersensitization” may explain loss of GIIS at phys-
iological glucose concentrations, these two hypotheses
have different implications for the role of apoptosis in
?-cell glucotoxicity. Thus, ?-cell glucose desensitization is
compatible with the concept that ?-cell dysfunction
(partly) results from ?-cell apoptosis (10,51,61). In con-
trast, ?-cell glucose hypersensitization may result from
changes in the expression of glycolytic enzymes (de-
creased glucokinase and increased hexokinase 1 and
lactate dehydrogenase expression), from the accumula-
tion of glycogen at high glucose and its subsequent degra-
dation at low glucose, or from other functional alterations
of ?-cells (48,62,64), but not from apoptosis. We have
recently observed that overnight exposure of rat islets to
low concentrations of hydrogen peroxide induces glucose
desensitization and ?-cell apoptosis that are both pre-
vented by N-acetyl-L-cysteine. In contrast, a 1-week culture
at 30 mmol/l glucose, compared with 10 mmol/l, induces a
state of glucose hypersensitization and a modest increase
in ?-cell apoptosis that are both unaffected by N-acetyl-L-
cysteine (66). These results suggest that the various facets
of ?-cell glucotoxicity may result from different patho-
physiological mechanisms. Thus, after prolonged expo-
sure to hyperglycemia, part of the surviving ?-cells may
still be “glucose hypersensitive” while apoptosis is already
affecting a small proportion of these cells. These different
pathophysiological mechanisms are compatible with the
observations that 1) after 3 weeks of diet-induced diabetes
in the gerbil Psammomys obesus, a stage at which the
?-cell mass is decreased (67), isolated islets were still
glucose hypersensitive (62); and 2) human islets trans-
planted under the kidney capsule of hyperglycemic nude
mice and maintained in vivo for 4 weeks have severely
impaired GIIS, which can be dissociated from impaired
glucose oxidation or protein synthesis and, under some
conditions, from depleted insulin content or cell death
(68,69).
Lipotoxicity. Physical inactivity, energy-dense diets rich
in saturated fat, and central obesity predispose individuals
to type 2 diabetes. Prospective studies in subjects at risk
for diabetes have shown that the development of abdom-
inal obesity is correlated with loss of ?-cell function and
hence glucose intolerance (70; M.C., J. Vidal, R.L. Hull,
K.M. Utzschneider, D.B. Carr, E.J. Boyko, W. Fujimoto,
S.E. Kahn, unpublished data). Autopsy data suggest that
the progressive decline in insulin secretion in type 2
diabetes is accompanied by a decrease in ?-cell mass and
that this is secondary to increased ?-cell apoptosis. Thus,
it is conceivable that circulating adipose tissue–derived
products, such as FFAs and adipokines, play a direct role
in pancreatic ?-cell dysfunction and death. A high plasma
concentration of FFAs is indeed a risk factor for the
development of type 2 diabetes, independently of its
effects on insulin sensitivity (71).
Circulating FFAs are solubilized and transported in
millimolar concentrations, by virtue of their tight binding
to albumin. Unbound FFA levels measure in the nanomo-
lar range (5–20 nmol/l), a concentration at which they are
rapidly taken up via a protein-mediated transport. FFAs
acutely stimulate insulin secretion, but prolonged ?-cell
exposure to high FFA levels reduces GIIS in vitro (72) and
in vivo, especially in individuals genetically predisposed to
type 2 diabetes (73). Studies in the ZDF rat indicate that
high circulating FFAs and triglyceride levels induce tri-
glyceride accumulation in pancreatic islets (74). The asso-
ciated rise in cytoplasmic FFA levels would increase
ceramide formation and induce iNOS, resulting in NO-
mediated ?-cell apoptosis (75).
In our in vitro experiments (36,76,77), we used physio-
logical concentrations of palmitate and oleate. FFAs are
toxic to FACS-purified rat ?-cells (36,76) and insulin-
producing INS-1E cells (36). Cytotoxicity depends on the
unbound FFA concentration and is greater for palmitate
than oleate. FFA-induced cell damage results in apoptosis
and, to a lesser extent, necrosis in ?-cells (76) and mostly
in apoptosis in INS-1E cells (36). The toxic effects of FFAs
are potentiated when ?-cells are concomitantly exposed to
high glucose levels (78,79). FFA cytotoxicity does not
depend on mitochondrial FFA oxidation, because eto-
moxir, an inhibitor of carnitine palmitoyltransferase I, did
not alter FFA-induced ?-cell death, and bromopalmitate, a
nonmetabolizable analog, was as toxic as palmitate (76).
FFA-induced cell death occurred in the absence of iNOS
expression or NO production (36,76), and it was not
counteracted by antioxidant or free radical scavenging
compounds (76), suggesting that oxidative stress is not its
main mediator. Moreover, oleate or palmitate did not
activate NF-?B in INS-1E or ?-cells (36), at low (6.1
mmol/l), medium (10 mmol/l), or high (28 mmol/l) glucose
levels (36; I. Kharroubi, D.L.E., M.C., unpublished data). It
was suggested that FFA cytotoxicity could be counter-
acted by the peroxisome proliferator–activated receptor-?
agonist troglitazone through lowering islet triglyceride
content (80). In our hands, however, troglitazone did not
improve survival of FFA-exposed ?-cells, but rather sensi-
tized them to necrosis and apoptosis at low FFA concen-
trations (77). Furthermore, FFA-induced cytoplasmic
triglyceride accumulation was inversely correlated to
?-cell death (76). A mixture of oleate and palmitate caused
the lowest cell death and the highest triglyceride accumu-
lation, whereas bromopalmitate, which did not increase
cellular triglycerides, exerted the highest toxicity (76).
These findings suggest that storage of excess FFAs as
triglycerides protects the cell against accumulation of
potentially deleterious fatty acyl-CoA.
FFA-induced ?-cell toxicity might also occur at the ER
level, where FFA esterification takes place. Using electron
microscopy, we observed that the ER of FFA-exposed
?-cells is dilated (M.C., unpublished data), and we there-
fore examined whether FFAs induce ER stress. Both
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Page 7

oleate and palmitate caused alternative splicing of XBP-1,
activation of ATF-6, and induction of the ER chaperone
BiP in INS-1E cells (36). In addition to these specific ER
stress markers, there was induction of ATF-4 and CHOP
(36). It is thus conceivable that a high FFA load, that
exceeds the ?-cell’s esterification capacity, impairs ER
functions and triggers an ER stress response, thus contrib-
uting to ?-cell toxicity. The mechanism by which FFAs
cause ER stress remains to be elucidated, but (over)stimu-
lation of FFA esterification in the ER might result in
delayed processing and export of newly synthesized pro-
teins, whereas saturated triglycerides may precipitate at
their site of synthesis in the ER because of their high
melting point. FFAs might also impair ER Ca2?handling
(81), whereas conditions that increase ?-cell secretory
demand, such as insulin resistance or high glucose, might
amplify ER stress and ?-cell death. ER stress has been
recently proposed as the cellular/molecular mechanism
linking obesity with insulin resistance (82,83). FFAs might
thus be responsible for the ER stress response observed in
the hepatocytes and adipocytes of obese mice (82,83),
while hampering in parallel pancreatic ?-cell function/
viability (36). If that is the case, these intriguing novel
observations (36,82,83) place ER stress as a common
molecular pathway for the two main causes of type 2
diabetes—namely insulin resistance and loss of ?-cell
mass.
SIMILARITIES AND DIFFERENCES BETWEEN THE
MECHANISMS OF ?-CELL DEATH IN TYPE 1 DIABETES
The development of novel approaches to prevent ?-cell
death in diabetes depends on our knowledge of the
mechanisms leading to ?-cell demise. Thus, if the mecha-
nisms of ?-cell apoptosis were similar in type 1 and type 2
diabetes, it would be logical to search for common inter-
ventions in both forms of diabetes. Let us therefore
examine the evidence pointing to the differences and
similarities between the mechanisms of ?-cell death and
analyze whether sufficient information is available to sup-
port a similar “etiological” intervention in type 1 and type
2 diabetes.
Novel in vivo evidence for the in situ expression of
mediators of ?-cell death in animal models of diabe-
tes. The NOD mouse and the BB rat are the most used
animal models of type 1 diabetes (84), but a new model for
type 1 diabetes has been recently described—the IDDM
(LEW.1AR1/Ztm-iddm) rat (85,86). This latter model is of
particular interest, since IDDM rats have a well-preserved
cellular immune system, there is no sex bias in the
incidence of diabetes, and detailed studies of the events
leading to ?-cell death are possible (see below).
ED1?macrophages are the predominant infiltrating
immune cell species during the early stages of insulitis for
all three animal models of type 1 diabetes. This is followed
by an increasing infiltration by cytotoxic CD8?lympho-
cytes, predominating at the onset of diabetes. Other im-
mune cells participating in the insulitis are CD4?
lymphocytes, NK cells, and B-cells (rev. in 4,84). These
immune cells are activated (87) and express proinflamma-
tory cytokines such as IL-1?, TNF-?, and IFN-? (88,89).
IL-1? and TNF-?, but not IFN-?, are detected in the
infiltrating immune cells in the IDDM rat, but the pancre-
atic ?-cells do not express these cytokines at any of the
stages leading to overt diabetes (90; Fig. 4A and B; A.J., A.
Gu ¨nther, H.-J. Hedrich, D. Wedekind, M. Tiedge, S.L.,
unpublished data). Data from other models suggest that
?-cells express chemokines such as MCP-1 and IP-10,
which may contribute to the buildup of insulitis (91).
Detailed morphological studies in the IDDM rat, using
both in situ PCR and immunohistochemistry (A.J., A.
FIG. 4. Morphology of an islet from a diabetic
IDDM (LEW.1AR1/Ztm-iddm) rat (A–C) exhibit-
ing hyperglycemia (21.4 mmol/l) and hypoinsu-
linemia (0.5ng/ml)1
manifestation and of an islet from a type 2
diabetes Psammomys obesus (sand rat) (D–F)
exhibiting hyperglycemia (17.5 mmol/l) and hy-
perinsulinemia (1.8 ng/ml) after 3 weeks on a
high-energy diet. The sections were immuno-
stained for IL-1? (A and D), iNOS (B and E), and
activated caspase-3 (C and F) and show cyto-
plasmic immunoreactivities only in the infil-
trated islets of the type 1 diabetic animal (A–C).
Infiltrating immune cells in the diabetic IDDM
rat (A–C) are mostly ED1?macrophages (ar-
rows) and CD8?T-cells (arrowheads). These
cells express immunoreactivity for IL-1? (A)
and iNOS (B) but not for activated caspase-3
(C). Pancreatic ?-cells undergoing apoptosis
(thick arrows), in contrast, express immunore-
activity for iNOS and activated caspase-3, but
not for IL-1?. The few infiltrating immune cells
in the islet of a diabetic Psammomys obesus
(D–F) are exclusively ED1?macrophages (ar-
rows). These cells show no signs of immunore-
activity for IL-1? (D), iNOS (E), or activated
caspase-3 (F). ?-Cells (thick arrows) of Psam-
momys showed signs of necrotic destruction
including intra- and intercellular vacuolization
without expression of IL-1? (D), iNOS (E), or
activated caspase-3 (F). These ?-cells showed
no signs of nuclear heterochromatin condensa-
tion. The same findings were made after 1 week
of a high-energy diet. ED1?macrophages, CD8?
T-cells, and pancreatic ?-cells were identified by
sequential sections immunostained with specific
antibodies against the given cell type as previ-
ously described (67,86) (data not shown). Orig-
inal magnification ?400.
day afterdiabetes
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Gu ¨nther, H.-J. Hedrich, D. Wedekind, M. Tiedge, S.L.,
unpublished data), suggest the following sequence of
events: 1) islets are initially infiltrated by macrophages,
followed by CD8?and CD4?cells; 2) this infiltration is
accompanied by a high IL-1? (Fig. 4A) and TNF-? expres-
sion in the invading immune cells (but not in the ?-cells)
and iNOS expression (Fig. 4B) in both immune cells and
?-cells; and 3) the ?-cells under attack progressively
express procaspase-3 (Fig. 4C) and undergo apoptosis.
These observations suggest that proinflammatory cyto-
kines are synthesized and released by the activated infil-
trating immune cells, but not by the ?-cells themselves,
leading to apoptotic ?-cell death in a paracrine fashion.
Loss of pancreatic ?-cell mass is slow in type 2 diabetes,
and there is no evidence for mononuclear cell infiltration
(2). This is well documented in a number of type 2 diabetes
animal models, including the Psammomys obesus (sand
rat) (92) and the GK rat (93). When Psammomys are
placed on a high-carbohydrate diet, they rapidly evolve to
a diabetic state because of the loss of endocrine pancreas
function and ?-cell destruction (48,67). In contrast to the
type 1 diabetes models (see above), ?-cell demise occurs
mostly by necrosis (67). The necrotic cells are removed by
scavenger macrophages, which, at variance from the type
1 diabetes situation, are not activated and do not express
the proinflammatory cytokines IL-1?, IFN-?, or TNF-?
(Fig. 4D; A.J., S.L., unpublished data). Importantly, the
?-cells from these animals do not express IL-1?, iNOS, or
caspase-3, as evaluated by immunohistochemistry (Fig. 4E
and F) and in situ PCR over the course of high-energy
diet-induced metabolic changes (1–3 weeks; A.J., S.L.,
unpublished data). As a positive control, IL-1? mRNA
expression was confirmed by in situ PCR using immune
cells of pancreas draining lymph nodes.
The same sequence of events seems to take place in the
physiological situation, where ?-cells undergoing apopto-
sis during their cell renewal cycle are removed by nonac-
tivated macrophages (94). Even when the ?-cell turnover
rate is increased by administration of thyroid hormones
(67,95), the increased demand for removal of apoptotic
cells does not trigger macrophage activation or cytokine
expression (A.J., S.L., unpublished data). These observa-
tions suggest a sequence of events that is different in type
1 and type 2 diabetes models. Thus, ?-cells die by necrosis
or apoptosis in type 2 diabetes, but the cause of death is
not related to cytokine production by infiltrating mononu-
clear cells or the ?-cells themselves. The dead ?-cells
attract scavenger macrophages, which in this case are the
consequence rather than the cause of ?-cell death (Fig. 5).
Analysis of the evidence for putative final common
pathways of ?-cell death in type 1 and type 2 diabe-
tes. It has been recently suggested that ?-cells exposed in
vitro to high glucose produce IL-1?, thus activating NF-?B
and Fas signaling and consequently triggering apoptosis
(10,11). Another report indicated that FFAs also activate
NF-?B in ?-cells (96). Because both IL-1? and NF-?? are
crucial mediators of ?-cell death in type 1 diabetes (4), the
IL-1?–NF-?B pathway was suggested as a “common final
FIG. 5. Overview of the putative sequence of events leading to ?-cell death in animal models of type 1 and type 2 diabetes. For additional
information on the mechanisms of ?-cell apoptosis in type 1 diabetes, see Figs. 1 and 2. T1D, type 1 diabetes; T2D, type 2 diabetes.
MECHANISMS OF ?-CELL DEATH IN DIABETES
S104DIABETES, VOL. 54, SUPPLEMENT 2, DECEMBER 2005

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pathway” for ?-cell death in both forms of diabetes (11),
providing a rationale for revising and unifying the classi-
fication and treatment of diabetes (10).
As discussed above, exposure to IL-1? alone is not
sufficient to kill human or rodent ?-cells, and the signal
transduction of IFN-? is also required for ?-cell demise. To
exclude that exposure of ?-cells to high glucose or FFAs
induces the IFN-? pathway, we reviewed the results of five
different microarray analyses of human or rodent islets
exposed to these nutrients (list of microarray studies
provided upon request). We also contacted some of the
authors to make sure that small changes in gene expres-
sion were not overlooked (D. Flamez, D. Melloul, G. Webb,
personal communications). The data were compared with
the gene expression patterns in rat (14) or human (P.
Ylipaasto, B. Kutlu, S. Raisilainen, J. Rasschaert, T. Teeri-
joki, O. Korsgren, R. Lahesmaa, T. Hovi, D.L.E., T. Otokon-
ski, M. Roivainen, unpublished data) islets exposed to
IFN-?. The mRNAs whose expression was most aug-
mented by IFN-? in ?-cells were the transcription factors
STAT-1, IRF-1, and IRF-7 and the chemokine CXCL 10
(IP-10). Glucose or FFAs modified none of these genes in
?-cells, practically excluding the IFN-?–STAT-1 pathway
as a mediator of glucotoxicity or lipotoxicity. We therefore
focused on IL-1?–NF-?B as the putative “common final
pathway” for ?-cell death.
As mentioned above, there is strong evidence that IL-1?
contributes to ?-cell death in type 1 diabetes via activation
of NF-?B. Which is the evidence that FFAs induce IL-1?
production or NF-?B activation in ?-cells? We (36) and
others (97) did not observe FFA-induced NF-?B activation
in ?-cells using three different techniques (gel shift, ELISA,
and immunohistochemistry), and there are no reports of
FFA-induced IL-1? expression in these cells. Moreover,
FFAs do not induce expression of the NF-?B–dependent
genes iNOS and MCP-1 in rodent ?-cells (36,98). What
about high glucose? Most of the in vitro data supporting
glucose-induced IL-1? production and NF-?B activation
were obtained by one group (rev. in 11). Based on their
observations, this group initiated a clinical trial with the
IL-1 receptor antagonist in type 2 diabetic patients (10). Of
concern is that there is no in vivo evidence in animal
models that blocking IL-1? protects ?-cells against gluco-
toxicity. In addition, it has been difficult to reproduce the
key findings of this “unifying hypothesis.” Thus, we could
not detect glucose-induced NF-?B activation or IL-1?
expression in rat islets or FACS-purified ?-cells (Fig. 3;
56). We examined whether this was due to a species
difference between rat (56) and human (10,11) islets.
Exposure of five preparations of human islets to increas-
ing glucose concentrations (11 and 28 vs. 5.6 mmol/l) did
not lead to the expression and release of IL-1? or other
NF-?B–dependent genes, such as I?B? or MCP-1 (99). Of
note, the concentration of IL-1? released by human islets
exposed to 28 mmol/l glucose is negligible, i.e., ?50-fold
below the amount of IL-1? released by human monocytes
(99). Moreover, there was no glucose-induced Fas mRNA
expression (99), the proposed NF-?B–dependent mecha-
nism by which glucose causes ?-cell death (11). In line
with our findings, islets isolated from mice deficient in
either the IL-1 receptor or Fas were not protected against
high glucose–induced ?-cell death, and Fas was not de-
tectable in wild-type mouse islets cultured at high glucose
(100). As a whole, these observations argue against a role
for IL-1?, NF-?B, or Fas in high glucose–induced ?-cell
death.
In conclusion, the suggestion that ?-cells are killed by a
similar mechanism in type 1 and type 2 diabetes is
probably an oversimplification, not supported by convinc-
ing data. This oversimplification may bring confusion to a
difficult and complex field and promote testing of novel
therapeutic approaches in humans without adequate ex-
perimental support.
ACKNOWLEDGMENTS
Work by the authors was supported by the following: the
Juvenile Diabetes Research Foundation Center for Preven-
tion of ?-Cell Destruction in Europe, under grant number
4-2002-457 (D.L.E.); a European Foundation for the Study
of Diabetes/Johnson & Johnson Type 2 Diabetes Research
Grant (M.C. and D.L.E.); the Fonds National de la Recher-
che Scientifique (FNRS), Belgium (M.C., J.-C.J., and
D.L.E.); Actions de Recherche Concerte ´es of the Belgium
French Community (J.-C.J. and D.L.E.); Swedish Medical
Research Council (72P-12995, 12X-11564, 12X-109) (N.W.);
EFSD/Lilly European Diabetes Research Program (N.W.);
the Swedish Diabetes Association (N.W.); the Family Ern-
fors Fund (N.W.); the Deutsche Forschungsgemeinschaft
Grant Jo 395/1-1/2 (A.J.); and National Institutes of Health
Grant 1R21AI55464–01 (S.L.).
We thank Dr. A.K. Cardozo for help in preparing Fig. 1
and I. Kharroubi for performing the NF-?B immunostain-
ing in Fig. 3.
NOTE ADDED IN PROOF
In agreement with the lack of IL-1? expression or release
by human islets exposed to high glucose in vitro (as
discussed in this review), recent data do not support a role
for IL-1? in type 2 diabetes in vivo. Two studies, using
respectively real-time RT-PCR and microarray analysis,
demonstrate that IL-1? and Fas expression in islets iso-
lated from type 2 diabetic patients is not increased as
compared with islets from nondiabetic controls (99,101).
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