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ABSTRACT: Deposition of islet amyloid polypeptide (IAPP) as amyloid is a pathological hallmark of the islet in type 2 diabetes, which is toxic to β cells. We previously showed that the enzyme neprilysin reduces islet amyloid deposition, and thereby reduces β-cell apoptosis, by inhibiting fibril formation. Two other enzymes, matrix metalloproteinase (MMP)-2 and MMP-9, are extracellular gelatinases capable of degrading another amyloidogenic peptide, Aβ, the constituent of amyloid deposits in Alzheimers disease. We therefore investigated whether MMP-2 and MMP-9 play a role in reducing islet amyloid deposition. MMP-2 and MMP-9 mRNA were present in mouse islets but only MMP-9 activity was detectable. In an islet culture model where human IAPP (hIAPP) transgenic mouse islets develop amyloid but non-transgenic islets do not, a broad-spectrum MMP inhibitor (GM6001) and an MMP-2/9 inhibitor increased amyloid formation and the resultant β-cell apoptosis. In contrast, a specific MMP-2 inhibitor had no effect on either amyloid deposition or β-cell apoptosis. Mass spectrometry demonstrated that MMP-9 degraded amyloidogenic hIAPP but not non-amyloidogenic mouse IAPP. Thus, MMP-9 constitutes an endogenous islet protease that limits islet amyloid deposition and its toxic effects via degradation of hIAPP. As islet MMP-9 mRNA levels are decreased in type 2 diabetic subjects, islet MMP-9 activity may also be decreased in human type 2 diabetes, thereby contributing to increased islet amyloid deposition and β-cell loss. Approaches to increase islet MMP-9 activity could reduce or prevent amyloid deposition and its toxic effects in type 2 diabetes.
Journal of Biological Chemistry 12/2012; · 4.77 Impact Factor
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Catherine A Jurgens,
Mirna N Toukatly,
Corinne L Fligner,
Jayalakshmi Udayasankar,
Shoba L Subramanian,
Sakeneh Zraika, Kathryn Aston-Mourney,
Darcy B Carr,
Per Westermark,
Gunilla T Westermark,
Steven E Kahn,
Rebecca L Hull
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ABSTRACT: Amyloid deposition and reduced β-cell mass are pathological hallmarks of the pancreatic islet in type 2 diabetes; however, whether the extent of amyloid deposition is associated with decreased β-cell mass is debated. We investigated the possible relationship and, for the first time, determined whether increased islet amyloid and/or decreased β-cell area quantified on histological sections is correlated with increased β-cell apoptosis. Formalin-fixed, paraffin-embedded human pancreas sections from subjects with (n = 29) and without (n = 39) diabetes were obtained at autopsy (64 ± 2 and 70 ± 4 islets/subject, respectively). Amyloid and β cells were visualized by thioflavin S and insulin immunolabeling. Apoptotic β cells were detected by colabeling for insulin and by TUNEL. Diabetes was associated with increased amyloid deposition, decreased β-cell area, and increased β-cell apoptosis, as expected. There was a strong inverse correlation between β-cell area and amyloid deposition (r = -0.42, P < 0.001). β-Cell area was selectively reduced in individual amyloid-containing islets from diabetic subjects, compared with control subjects, but amyloid-free islets had β-cell area equivalent to islets from control subjects. Increased amyloid deposition was associated with β-cell apoptosis (r = 0.56, P < 0.01). Thus, islet amyloid is associated with decreased β-cell area and increased β-cell apoptosis, suggesting that islet amyloid deposition contributes to the decreased β-cell mass that characterizes type 2 diabetes.
American Journal Of Pathology 06/2011; 178(6):2632-40. · 4.89 Impact Factor
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ABSTRACT: Deposition of islet amyloid polypeptide (IAPP) as islet amyloid in type 2 diabetes contributes to loss of beta-cell function and mass, yet the mechanism for its occurrence is unclear. Neprilysin is a metallopeptidase known to degrade amyloid in Alzheimer disease. We previously demonstrated neprilysin to be present in pancreatic islets and now sought to determine whether it plays a role in degrading islet amyloid. We used an in vitro model where cultured human IAPP (hIAPP) transgenic mouse islets develop amyloid and thereby have increased beta-cell apoptosis. Islet neprilysin activity was inhibited or up-regulated using a specific inhibitor or adenovirus encoding neprilysin, respectively. Following neprilysin inhibition, islet amyloid deposition and beta-cell apoptosis increased by 54 and 75%, respectively, whereas when neprilysin was up-regulated islet amyloid deposition and beta-cell apoptosis both decreased by 79%. To determine if neprilysin modulated amyloid deposition by cleaving hIAPP, analysis of hIAPP incubated with neprilysin was performed by mass spectrometry, which failed to demonstrate neprilysin-induced cleavage. Rather, neprilysin may act by reducing hIAPP fibrillogenesis, which we showed to be the case by fluorescence-based thioflavin T binding studies and electron microscopy. In summary, neprilysin decreases islet amyloid deposition by inhibiting hIAPP fibril formation, rather than degrading hIAPP. These findings suggest that targeting the role of neprilysin in IAPP fibril assembly, in addition to IAPP cleavage by other peptidases, may provide a novel approach to reduce and/or prevent islet amyloid deposition in type 2 diabetes.
Journal of Biological Chemistry 06/2010; 285(24):18177-83. · 4.77 Impact Factor
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Melkam Kebede,
Jenny Favaloro,
Jenny E Gunton,
D Ross Laybutt,
Margaret Shaw,
Nicole Wong,
Barbara C Fam, Kathryn Aston-Mourney,
Christian Rantzau,
Anthony Zulli,
Joseph Proietto,
Sofianos Andrikopoulos
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ABSTRACT: Fructose-1,6-bisphosphatase (FBPase) is a gluconeogenic enzyme that is upregulated in islets or pancreatic beta-cell lines exposed to high fat. However, whether specific beta-cell upregulation of FBPase can impair insulin secretory function is not known. The objective of this study therefore is to determine whether a specific increase in islet beta-cell FBPase can result in reduced glucose-mediated insulin secretion.
To test this hypothesis, we have generated three transgenic mouse lines overexpressing the human FBPase (huFBPase) gene specifically in pancreatic islet beta-cells. In addition, to investigate the biochemical mechanism by which elevated FBPase affects insulin secretion, we made two pancreatic beta-cell lines (MIN6) stably overexpressing huFBPase.
FBPase transgenic mice showed reduced insulin secretion in response to an intravenous glucose bolus. Compared with the untransfected parental MIN6, FBPase-overexpressing cells showed a decreased cell proliferation rate and significantly depressed glucose-induced insulin secretion. These defects were associated with a decrease in the rate of glucose utilization, resulting in reduced cellular ATP levels.
Taken together, these results suggest that upregulation of FBPase in pancreatic islet beta-cells, as occurs in states of lipid oversupply and type 2 diabetes, contributes to insulin secretory dysfunction.
Diabetes 08/2008; 57(7):1887-95. · 8.29 Impact Factor
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ABSTRACT: Type 2 diabetes is associated with insulin resistance and reduced insulin secretion, which results in hyperglycaemia. This can then lead to diabetic complications such as retinopathy, neuropathy, nephropathy and cardiovascular disease. Although insulin resistance may be present earlier in the progression of the disease, it is now generally accepted that it is the deterioration in insulin-secretory function that leads to hyperglycaemia. This reduction in insulin secretion in Type 2 diabetes is due to both islet beta-cell dysfunction and death. Therefore, interventions that maintain the normal function and protect the pancreatic islet beta-cells from death are crucial in the treatment of Type 2 diabetes so that plasma glucose levels may be maintained within the normal range. Recently, a number of compounds have been shown to protect beta-cells from failure. This review examines the evidence that the existing therapies for Type 2 diabetes that were developed to lower plasma glucose (metformin) or improve insulin sensitivity (thiazolidinediones) may also have islet-protective function. Newer emerging therapeutic agents that are designed to increase the levels of glucagon-like peptide-1 not only stimulate insulin secretion but also appear to increase islet beta-cell mass. Evidence will also be presented that the future of drug therapy designed to prevent beta-cell failure should target the formation of advanced glycation end products and alleviate oxidative and endoplasmic reticulum stress.
Expert Opinion on Investigational Drugs 11/2005; 14(10):1241-50. · 5.27 Impact Factor
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ABSTRACT: The increasing production of genetically-modified mouse models has necessitated studies to determine the inherent physiological characteristics of commonly used mouse strains. In this study we examined insulin secretory function in response to an intravenous bolus of glucose or glucose plus arginine in anesthetized C57BL/6, DBA/2 and 129T2 mice fed either a control or high fat diet for 6 weeks. The results show that 129T2 mice had higher fasting plasma glucose levels and lower fasting plasma insulin levels compared with C57BL/6 and DBA/2 mice regardless of diet. Furthermore, 129T2 mice were glucose intolerant and secreted significantly less insulin in response to glucose and glucose plus arginine irrespective of diet compared with the other two strains of mice. DBA/2 mice hypersecreted insulin in response to glucose and glucose plus arginine compared with C57BL/6 and 129T2 mice. Moreover while first phase insulin secretion was appropriately increased in response to the high fat diet in C57BL/6 and 129T2 mice, this was not the case for DBA/2 mice. Mean islet area was decreased in response to a high fat diet in DBA/2 mice, while there was no dietary effect on the other two strains. This study highlights the inherent genetic differences that exist among seemingly normal strains of mice that are commonly used to make transgenic and knockout mice. Understanding these differences will provide researchers with the information to choose the appropriate genetic background on which to express their particular genetic alteration.
Journal of Endocrinology 11/2005; 187(1):45-53. · 3.55 Impact Factor
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Suwattanee Kooptiwut,
Melkam Kebede,
Sakeneh Zraika,
Sherley Visinoni, Kathryn Aston-Mourney,
Jenny Favaloro,
Chris Tikellis,
Merlin C Thomas,
Josephine M Forbes,
Mark E Cooper,
Marjorie Dunlop,
Joseph Proietto,
Sofianos Andrikopoulos
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ABSTRACT: Type 2 diabetes is characterized by islet dysfunction resulting in hyperglycemia, which can then lead to further deterioration in islet function. A possible mechanism for hyperglycemia-induced islet dysfunction is the accumulation of advanced glycation end products (AGE). The DBA/2 mouse develops pancreatic islet dysfunction when exposed to a high glucose environment and/or obesity-induced insulin resistance. To determine the biochemical cause of dysfunction, DBA/2 and C57BL/6 control islets were incubated in 11.1 mM or 40 mM glucose in the absence or presence of the AGE inhibitor aminoguanidine (AG) for 10 days. Basal (2.8 mM glucose) insulin release was increased in both DBA/2 and C57BL/6 islets incubated with 40 mM vs 11.1 mM glucose for 10 days. Chronic exposure to hyperglycemia decreased glucose (20 mM)-stimulated insulin secretion in DBA/2 but not in C57BL/6 islets. AG significantly increased fold-induced insulin release in high glucose cultured DBA/2 mouse islets, but did not affect C57BL/6 islet function. DBA/2 islet glucokinase was significantly reduced following 40 mM glucose culture, compared with 11.1 mM glucose cultured DBA/2 islets and 40 mM glucose cultured C57BL/6 islets. Incubation of islets with AG resulted in a normalization of DBA/2 islet glucokinase levels. In conclusion, chronic high glucose-induced increases in AGE can result in islet dysfunction and this is associated with reduced glucokinase levels in a mouse model with susceptibility to islet failure.
Journal of Molecular Endocrinology 09/2005; 35(1):39-48. · 3.48 Impact Factor
