Andrew F Stewart

Mount Sinai School of Medicine, Manhattan, New York, United States

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Publications (60)484.37 Total impact

  • Rohit N Kulkarni, Andrew F Stewart
    Diabetes 12/2014; 63(12):3979-81. · 7.90 Impact Factor
  • Adolfo García-Ocaña, Andrew F Stewart
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    ABSTRACT: Adult human pancreatic β cells are refractory to current therapeutic approaches to enhance proliferation. This reluctance to expand is problematic, especially for people with diabetes who lack sufficient numbers of functional insulin-producing β cells and could therefore benefit from therapies for β cell expansion. In this issue of the JCI, Chamberlain et al. describe a surprising series of observations that involve two downstream arms of the RAS signaling pathway, MAPK and RASSF proteins, which also involve the tumor suppressor menin. The findings of this study may help explain the difficulty of inducing β cell proliferation and may provide leads for therapeutic expansion of human β cells.
    The Journal of clinical investigation. 08/2014;
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    Diabetes 03/2014; 63((3)):819-31.. · 7.90 Impact Factor
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    Aaron Bender, Andrew F Stewart
    Diabetologia 11/2013; · 6.49 Impact Factor
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    ABSTRACT: Parathyroid hormone-related protein (PTHrP)(1-36) increases lumbar spine (LS) bone mineral density (BMD), acting as an anabolic agent when injected intermittently, but has not been directly compared to parathyroid hormone (PTH)(1-34). We performed a three month, randomized, prospective study in 105 postmenopausal women with low bone density or osteoporosis comparing daily subcutaneous injections of PTHrP(1-36) to PTH(1-34). Thirty-five women were randomized to each of three groups: PTHrP(1-36) 400 µg/d; PTHrP(1-36) 600 µg/d; and PTH(1-34) 20 µg/d. The primary outcomes measures were changes in amino-terminal telopeptides of procollagen 1 (PINP) and carboxy-terminal telopeptides of collagen 1 (CTX). Secondary measures included safety parameters, 1,25(OH)2 vitamin D and BMD. The increase in bone resorption (CTX) by PTH(1-34) (92%) (p < 0.005) was greater than for PTHrP(1-36) (30%) (p < 0.05). PTH(1-34) also increased bone formation (PINP) (171%) (p < 0.0005) more than either dose of PTHrP(1-36) (46 & 87%). The increase in PINP was earlier (day 15) and greater than the increase in CTX for all three groups. LS BMD increased equivalently in each group (p < 0.05 for all). Total hip (TH) and femoral neck (FN) BMD increased equivalently in each group but were only significant for the two doses of PTHrP(1-36) (p < 0.05) at the TH, and for PTHrP(1-36) 400 (p < 0.05) at the FN. PTHrP(1-36) 400 induced mild, transient (day 15) hypercalcemia. PTHrP(1-36) 600 required a dose reduction for hypercalcemia in three subjects. PTH(1-34) was not associated with hypercalcemia. Each peptide induced a marked biphasic increase in 1,25(OH)2 D. Adverse events (AE) were similar among the three groups. This study demonstrates that PTHrP(1-36) and PTH(1-34) cause similar increases in LS BMD. PTHrP(1-36) also increased hip BMD. PTH(1-34) induced greater changes in bone turnover than PTHrP(1-36). PTHrP(1-36) was associated with mild transient hypercalcemia. Longer term studies using lower doses of PTHrP(1-36) are needed to define both the optimal dose and full clinical benefits of PTHrP.
    Journal of bone and mineral research: the official journal of the American Society for Bone and Mineral Research 05/2013; · 6.04 Impact Factor
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    ABSTRACT: Expansion of pancreatic beta cells is a key goal of diabetes research, yet induction of adult human beta cell replication has proven frustratingly difficult. In part, this reflects a lack of understanding of cell cycle control in the human beta cell. Here, we provide a comprehensive immunocytochemical "atlas" of G1/S control molecules in the human beta cell. This "atlas" reveals that the majority these molecules, previously known to be present in islets, are actually present in the beta cell. More importantly, and in contrast to anticipated results, the "human beta cell G1/S atlas" reveals that almost all of the critical G1/S cell cycle control molecules are located in the cytoplasm of the quiescent human beta cell. Indeed, the only nuclear G1/S molecules are the cell cycle inhibitors, pRb, p57, and variably, p21: none of the cyclins or cdks necessary to drive human beta cell proliferation are present in the nuclear compartment. This observation may provide an explanation for the refractoriness of human beta cells to proliferation. Thus, in addition to known obstacles to human beta cell proliferation, restriction of G1/S molecules to the cytoplasm of the human beta cell represents an unanticipated obstacle to therapeutic human beta cell expansion.
    Diabetes 03/2013; · 7.90 Impact Factor
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    ABSTRACT: Harnessing control of human beta cell proliferation has proven frustratingly difficult. Most G1/S control molecules, generally presumed to be nuclear proteins in the human beta cell, are in fact constrained to the cytoplasm. Here, we asked whether G1/S molecules might traffic into and out of the cytoplasmic compartment in association with activation of cell cycle progression. Cdk6 and cyclin D3 were used to drive human beta cell proliferation, and promptly translocated into the nucleus in association with proliferation. In contrast, the cell cycle inhibitors p15, p18 and p19 did not alter their location, remaining cytoplasmic. Conversely, p16, p21, p27 all increased their nuclear frequency. In contrast once again, p57 decreased its nuclear frequency. While proliferating beta cells contained nuclear cyclin D3 and cdk6, proliferation generally did not occur in beta cells that contained nuclear cell cycle inhibitors, except p21. Dynamic cytoplasmic-nuclear trafficking of cdk6 was confirmed using GFP-tagged cdk6 and live-cell imaging. Thus, we provide novel working models describing the control of cell cycle progression in the human beta cell. In addition to known obstacles to beta cell proliferation, cytoplasmic-to-nuclear trafficking of G1/S molecules may represent both an obstacle, as well as a therapeutic opportunity, for human beta cell expansion.
    Diabetes 03/2013; · 7.90 Impact Factor
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    ABSTRACT: Context:The African-American skeleton is resistant to PTH; whether it is also resistant to PTHrP and the hormonal milieu of lactation is unknown.Objectives:The objective of the study was to assess bone turnover markers in African-Americans during lactation vs Caucasians.Design and Participants:A prospective cohort study with repeated measures of markers of bone turnover in 60 African-American women (3 groups of 20: lactating, bottle feeding, and healthy controls), compared with historic Caucasian women.Setting:The study was conducted at a university medical center.Outcome Measures:Biochemical markers of bone turnover and calcium metabolism were measured.Results:25-Hydroxyvitamin D (25-OHD) and PTH were similar among all 3 African-American groups, but 25-OHD was 30%-50% lower and PTH 2-fold higher compared with Caucasians (P < .001, P < .002), with similar 1,25 dihydroxyvitamin D [1,25(OH)(2)D] values. Formation markers [amino-terminal telopeptide of procollagen-1 (P1NP) and bone-specific alkaline phosphatase (BSAP)] increased significantly (2- to 3-fold) in lactating and bottle-feeding African-American women (P1NP, P < .001; BSAP, P < .001), as did resorption [carboxy-terminal telopeptide of collagen-1 (CTX) and serum amino-terminal telopeptide of collagen 1 (NTX), both P < .001). P1NP and BSAP were comparable in African-American and Caucasian controls, but CTX and NTX were lower in African-American vs Caucasian controls. African-American lactating mothers displayed quantitatively similar increases in markers of bone formation but slightly lower increases in markers of resorption vs Caucasians (P = .036).Conclusions:Despite reported resistance to PTH, lactating African-American women have a significant increase in markers of bone resorption and formation in response the hormonal milieu of lactation. This response is similar to that reported in Caucasian women despite racial differences in 25-OHD and PTH. Whether this is associated with similar bone loss in African-Americans as in Caucasians during lactation is unknown and requires further study.
    The Journal of Clinical Endocrinology and Metabolism 12/2012; · 6.31 Impact Factor
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    ABSTRACT: The transcription factor HNF4α (hepatocyte nuclear factor-4α) is required for increased β-cell proliferation during metabolic stress in vivo. We hypothesized that HNF4α could induce proliferation of human β-cells. We employed adenoviral-mediated overexpression of an isoform of HNF4α (HNF4α8) alone, or in combination with cyclin-dependent kinase (Cdk)6 and Cyclin D3, in human islets. Heightened HNF4α8 expression led to a 300-fold increase in the number of β-cells in early S-phase. When we overexpressed HNF4α8 together with Cdk6 and Cyclin D3, β-cell cycle entry was increased even further. However, the punctate manner of bromodeoxyuridine incorporation into HNF4α(High) β-cells indicated an uncoupling of the mechanisms that control the concise timing and execution of each cell cycle phase. Indeed, in HNF4α8-induced bromodeoxyuridine(+,punctate) β-cells we observed signs of dysregulated DNA synthesis, cell cycle arrest, and activation of a double stranded DNA damage-associated cell cycle checkpoint mechanism, leading to the initiation of loss of β-cell lineage fidelity. However, a substantial proportion of β-cells stimulated to enter the cell cycle by Cdk6 and Cyclin D3 alone also exhibited a DNA damage response. HNF4α8 is a mitogenic signal in the human β-cell but is not sufficient for completion of the cell cycle. The DNA damage response is a barrier to efficient β-cell proliferation in vitro, and we suggest its evaluation in all attempts to stimulate β-cell replication as an approach to diabetes treatment.
    Molecular Endocrinology 07/2012; 26(9):1590-602. · 4.75 Impact Factor
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    ABSTRACT: A major goal in diabetes research is to find ways to enhance the mass and function of insulin secreting β-cells in the endocrine pancreas to prevent and/or delay the onset or even reverse overt diabetes. In this Perspectives in Diabetes article, we highlight the contrast between the relatively large body of information that is available in regard to signaling pathways, proteins, and mechanisms that together provide a road map for efforts to regenerate β-cells in rodents versus the scant information in human β-cells. To reverse the state of ignorance regarding human β-cell signaling, we suggest a series of questions for consideration by the scientific community to construct a human β-cell proliferation road map. The hope is that the knowledge from the new studies will allow the community to move faster towards developing therapeutic approaches to enhance human β-cell mass in the long-term goal of preventing and/or curing type 1 and type 2 diabetes.
    Diabetes 06/2012; 61(9):2205-13. · 7.90 Impact Factor
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    ABSTRACT: Glucose stimulates rodent and human β-cell replication, but the intracellular signaling mechanisms are poorly understood. Carbohydrate response element-binding protein (ChREBP) is a lipogenic glucose-sensing transcription factor with unknown functions in pancreatic β-cells. We tested the hypothesis that ChREBP is required for glucose-stimulated β-cell proliferation. The relative expression of ChREBP was determined in liver and β-cells using quantitative RT-PCR (qRT-PCR), immunoblotting, and immunohistochemistry. Loss- and gain-of-function studies were performed using small interfering RNA and genetic deletion of ChREBP and adenoviral overexpression of ChREBP in rodent and human β-cells. Proliferation was measured by 5-bromo-2'-deoxyuridine incorporation, [(3)H]thymidine incorporation, and fluorescence-activated cell sorter analysis. In addition, the expression of cell cycle regulatory genes was measured by qRT-PCR and immunoblotting. ChREBP expression was comparable with liver in mouse pancreata and in rat and human islets. Depletion of ChREBP decreased glucose-stimulated proliferation in β-cells isolated from ChREBP(-/-) mice, in INS-1-derived 832/13 cells, and in primary rat and human β-cells. Furthermore, depletion of ChREBP decreased the glucose-stimulated expression of cell cycle accelerators. Overexpression of ChREBP amplified glucose-stimulated proliferation in rat and human β-cells, with concomitant increases in cyclin gene expression. In conclusion, ChREBP mediates glucose-stimulated proliferation in pancreatic β-cells.
    Diabetes 05/2012; 61(8):2004-15. · 7.90 Impact Factor
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    ABSTRACT: Induction of proliferation in adult human β-cells is challenging. It can be accomplished by introduction of cell cycle molecules such as cyclin-dependent kinase 6 (cdk6) and cyclin D1, but their continuous overexpression raises oncogenic concerns. We attempted to mimic normal, transient, perinatal human β-cell proliferation by delivering these molecules in a regulated and reversible manner. Adult cadaveric islets were transduced with doxycycline (Dox)-inducible adenoviruses expressing cdk6 or cyclin D1. End points were cdk6/cyclin D1 expression and human β-cell proliferation, survival, and function. Increasing doses of Dox led to marked dose- and time-related increases in cdk6 and cyclin D1, accompanied by a 20-fold increase in β-cell proliferation. Notably, Dox withdrawal resulted in a reversal of both cdk6 and cyclin D1 expression as well as β-cell proliferation. Re-exposure to Dox reinduced both cdk/cyclin expression and proliferation. β-Cell function and survival were not adversely affected. The adenoviral tetracycline (tet)-on system has not been used previously to drive human β-cell proliferation. Human β-cells can be induced to proliferate or arrest in a regulated, reversible manner, temporally and quantitatively mimicking the transient perinatal physiological proliferation that occurs in human β-cells.
    Diabetes 12/2011; 61(2):418-24. · 7.90 Impact Factor
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    ABSTRACT: A small-molecule inducer of beta-cell proliferation in human islets represents a potential regeneration strategy for treating type 1 diabetes. However, the lack of suitable human beta cell lines makes such a discovery a challenge. Here, we adapted an islet cell culture system to high-throughput screening to identify such small molecules. We prepared microtiter plates containing extracellular matrix from a human bladder carcinoma cell line. Dissociated human islets were seeded onto these plates, cultured for up to 7 days, and assessed for proliferation by simultaneous Ki67 and C-peptide immunofluorescence. Importantly, this environment preserved beta-cell physiological function, as measured by glucose-stimulated insulin secretion. Adenoviral overexpression of cdk-6 and cyclin D(1), known inducers of human beta cell proliferation, was used as a positive control in our assay. This induction was inhibited by cotreatment with rapamycin, an immunosuppressant often used in islet transplantation. We then performed a pilot screen of 1280 compounds, observing some phenotypic effects on cells. This high-throughput human islet cell culture method can be used to assess various aspects of beta-cell biology on a relatively large number of compounds.
    Journal of Biomolecular Screening 12/2011; 17(4):509-18. · 2.21 Impact Factor
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    ABSTRACT: Adult human β-cells replicate slowly. Also, despite the abundance of rodent β-cell lines, there are no human β-cell lines for diabetes research or therapy. Prior studies in four commonly studied rodent β-cell lines revealed that all four lines displayed an unusual, but strongly reproducible, cell cycle signature: an increase in seven G(1)/S molecules, i.e. cyclins A, D3, and E, and cdk1, -2, -4, and -6. Here, we explore the upstream mechanism(s) that drive these cell cycle changes. Using biochemical, pharmacological and molecular approaches, we surveyed potential upstream mitogenic signaling pathways in Ins 1 and RIN cells. We used both underexpression and overexpression to assess effects on rat and human β-cell proliferation, survival and cell cycle control. Our results indicate that cMyc is: 1) uniquely up-regulated among other candidates; 2) principally responsible for the increase in the seven G(1)/S molecules; and, 3) largely responsible for proliferation in rat β-cell lines. Importantly, cMyc expression in β-cell lines, although some 5- to 7-fold higher than normal rat β-cells, is far below the levels (75- to 150-fold) previously associated with β-cell death and dedifferentiation. Notably, modest overexpression of cMyc is able to drive proliferation without cell death in normal rat and human β-cells. We conclude that cMyc is an important driver of replication in the two most commonly employed rat β-cell lines. These studies reverse the current paradigm in which cMyc overexpression is inevitably associated with β-cell death and dedifferentiation. The cMyc pathway provides potential approaches, targets, and tools for driving and sustaining human β-cell replication.
    Molecular Endocrinology 09/2011; 25(10):1760-72. · 4.75 Impact Factor
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    ABSTRACT: Thyroid nodules are common in adults, but only a small fraction of them is malignant. Fine-needle aspiration (FNA) cytology provides a definitive diagnosis of benign or malignant disease in many cases, whereas about 25% of nodules are indeterminate, hindering most appropriate management. The objective of the investigation was to study the clinical utility of molecular testing of thyroid FNA samples with indeterminate cytology. Residual material from 1056 consecutive thyroid FNA samples with indeterminate cytology was used for prospective molecular analysis that included the assessment of cell adequacy by a newly developed PCR assay and testing for a panel of mutations consisted of BRAF V600E, NRAS codon 61, HRAS codon 61, and KRAS codons 12/13 point mutations and RET/PTC1, RET/PTC3, and PAX8/PPARγ rearrangements. The collected material was adequate for molecular analysis in 967 samples (92%), which yielded 87 mutations including 19 BRAF, 62 RAS, 1 RET/PTC, and five PAX8/PPARγ. Four hundred seventy-nine patients who contributed 513 samples underwent surgery. In specific categories of indeterminate cytology, i.e. atypia of undetermined significance/follicular lesion of undetermined significance, follicular neoplasm/suspicious for a follicular neoplasm, and suspicious for malignant cells, the detection of any mutation conferred the risk of histologic malignancy of 88, 87, and 95%, respectively. The risk of cancer in mutation-negative nodules was 6, 14, and 28%, respectively. Of 6% of cancers in mutation-negative nodules with atypia of undetermined significance/follicular lesion of undetermined significance cytology, only 2.3% were invasive and 0.5% had extrathyroidal extension. Molecular analysis for a panel of mutations has significant diagnostic value for all categories of indeterminate cytology and can be helpful for more effective clinical management of these patients.
    The Journal of Clinical Endocrinology and Metabolism 08/2011; 96(11):3390-7. · 6.31 Impact Factor
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    ABSTRACT: Thyroid papillary microcarcinoma (TPMC) is an incidentally discovered papillary carcinoma that measures ≤1.0 cm in size. Most TPMCs are indolent, whereas some behave aggressively. The objective of the study was to evaluate whether the combination of v-raf murine sarcoma viral oncogene homolog B1 (BRAF) mutation and specific histopathologic features allows risk stratification of TPMC. A group aggressive TPMCs was selected based on the presence of lymph node metastasis or tumor recurrence. Another group of nonaggressive tumors included TPMCs matched with the first group for age, sex, and tumor size, but with no extrathyroid spread. A molecular analysis was performed, and histologic slides were scored for multiple histopathologic criteria. A separate validation cohort of 40 TPMCs was evaluated. BRAF mutations were detected in 77% of aggressive TPMCs and in 32% of nonaggressive tumors (P = .001). Several histopathologic features differed significantly between the groups. By using multivariate regression analysis, a molecular-pathologic (MP) score was developed that included BRAF status and 3 histopathologic features: superficial tumor location, intraglandular tumor spread/multifocality, and tumor fibrosis. By adding the histologic criteria to BRAF status, sensitivity was increased from 77% to 96%, and specificity was increased from 68% to 80%. In the independent validation cohort, the MP score stratified tumors into low-risk, moderate-risk, and high-risk groups with the probability of lymph node metastases or tumor recurrence in 0%, 20%, and 60% of patients, respectively. BRAF status together with several histopathologic features allowed clinical risk stratification of TPMCs. The combined MP risk stratification model was a better predictor of extrathyroid tumor spread than either mutation or histopathologic findings alone.
    Cancer 08/2011; 118(8):2069-77. · 5.20 Impact Factor
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    ABSTRACT: Human in vivo models of primary hyperparathyroidism (HPT), humoral hypercalcemia of malignancy (HHM), or lactational bone mobilization for more than 48 hours have not been described previously. We therefore developed 7-day continuous-infusion models using human parathyroid hormone(1-34) [hPTH(1-34)] and human parathyroid hormone-related protein(1-36) [hPTHrP(1-36)] in healthy human adult volunteers. Study subjects developed sustained mild increases in serum calcium (10.0 mg/dL), with marked suppression of endogenous PTH(1-84). The maximal tolerated infused doses over a 7-day period (2 and 4 pmol/kg/h for PTH and PTHrP, respectively) were far lower than in prior, briefer human studies (8 to 28 pmol/kg/h). In contrast to prior reports using higher PTH and PTHrP doses, both 1,25-dihydroxyvitamin D(3) [1,25(OH)(2) D(3) ] and tubular maximum for phosphorus (TmP/GFR) remained unaltered with these low doses despite achievement of hypercalcemia and hypercalciuria. As expected, bone resorption increased rapidly and reversed promptly with cessation of the infusion. However, in contrast to events in primary HPT, bone formation was suppressed by 30% to 40% for the 7 days of the infusions. With cessation of PTH and PTHrP infusion, bone-formation markers abruptly rebounded upward, confirming that bone formation is suppressed by continuous PTH or PTHrP infusion. These studies demonstrate that continuous exposure of the human skeleton to PTH or PTHrP in vivo recruits and activates the bone-resorption program but causes sustained arrest in the osteoblast maturation program. These events would most closely mimic and model events in HHM. Although not a perfect model for lactation, the increase in resorption and the rebound increase in formation with cessation of the infusions are reminiscent of the maternal skeletal calcium mobilization and reversal that occur following lactation. The findings also highlight similarities and differences between the model and HPT.
    Journal of bone and mineral research: the official journal of the American Society for Bone and Mineral Research 05/2011; 26(9):2287-97. · 6.04 Impact Factor
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    ABSTRACT: To determine the role of hepatocyte growth factor (HGF)/c-Met on β-cell survival in diabetogenic conditions in vivo and in response to cytokines in vitro. We generated pancreas-specific c-Met-null (PancMet KO) mice and characterized their response to diabetes induced by multiple low-dose streptozotocin (MLDS) administration. We also analyzed the effect of HGF/c-Met signaling in vitro on cytokine-induced β-cell death in mouse and human islets, specifically examining the role of nuclear factor (NF)-κB. Islets exposed in vitro to cytokines or from MLDS-treated mice displayed significantly increased HGF and c-Met levels, suggesting a potential role for HGF/c-Met in β-cell survival against diabetogenic agents. Adult PancMet KO mice displayed normal glucose and β-cell homeostasis, indicating that pancreatic c-Met loss is not detrimental for β-cell growth and function under basal conditions. However, PancMet KO mice were more susceptible to MLDS-induced diabetes. They displayed higher blood glucose levels, marked hypoinsulinemia, and reduced β-cell mass compared with wild-type littermates. PancMet KO mice showed enhanced intraislet infiltration, islet nitric oxide (NO) and chemokine production, and β-cell apoptosis. c-Met-null β-cells were more sensitive to cytokine-induced cell death in vitro, an effect mediated by NF-κB activation and NO production. Conversely, HGF treatment decreased p65/NF-κB activation and fully protected mouse and, more important, human β-cells against cytokines. These results show that HGF/c-Met is critical for β-cell survival by attenuating NF-κB signaling and suggest that activation of the HGF/c-Met signaling pathway represents a novel strategy for enhancing β-cell protection.
    Diabetes 10/2010; 60(2):525-36. · 7.90 Impact Factor
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    ABSTRACT: Inducing human β-cell growth while enhancing function is a major goal in the treatment of diabetes. Parathyroid hormone-related protein (PTHrP) enhances rodent β-cell growth and function through the parathyroid hormone-1 receptor (PTH1R). Based on this, we hypothesized that PTH1R is expressed in human β-cells and that PTHrP has the potential to enhance human β-cell proliferation and/or function. PTH1R expression, β-cell proliferation, glucose-stimulated insulin secretion (GSIS), and expression of differentiation and cell-cycle genes were analyzed in human islets transduced with adenoviral PTHrP constructs or treated with PTHrP peptides. The effect of overexpression of late G1/S cell cycle molecules was also assessed on human β-cell proliferation. We found that human β-cells express PTH1R. More importantly, overexpression of PTHrP causes a significant approximately threefold increase in human β-cell proliferation. Furthermore, the amino terminus PTHrP(1-36) peptide is sufficient to increase replication as well as expression of the late G1/S cell-cycle proteins cyclin E and cyclin-dependent kinase 2 (cdk2) in human islets. Notably, PTHrP(1-36) also enhances GSIS. Finally, overexpression of cyclin E alone, but not cdk2, augments human β-cell proliferation, and when both molecules are expressed simultaneously there is a further marked synergistic increase in replication. PTHrP(1-36) peptide enhances human β-cell proliferation as well as function, with associated upregulation of two specific cell-cycle activators that together can induce human β-cell proliferation several fold. The future therapeutic potential of PTHrP(1-36) for the treatment of diabetes is especially relevant given the complementary therapeutic efficacy of PTHrP(1-36) in postmenopausal osteoporosis.
    Diabetes 09/2010; 59(12):3131-8. · 7.90 Impact Factor
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    ABSTRACT: Most knowledge on human beta-cell cycle control derives from immunoblots of whole human islets, mixtures of beta-cells and non-beta-cells. We explored the presence, subcellular localization, and function of five early G1/S phase molecules-cyclins D1-3 and cdk 4 and 6-in the adult human beta-cell. Immunocytochemistry for the five molecules and their relative abilities to drive human beta-cell replication were examined. Human beta-cell replication, cell death, and islet function in vivo were studied in the diabetic NOD-SCID mouse. Human beta-cells contain easily detectable cdks 4 and 6 and cyclin D3 but variable cyclin D1. Cyclin D2 was only marginally detectable. All five were principally cytoplasmic, not nuclear. Overexpression of the five, alone or in combination, led to variable increases in human beta-cell replication, with the cdk6/cyclin D3 combination being the most robust (15% versus 0.3% in control beta-cells). A single molecule, cdk6, proved to be capable of driving human beta-cell replication in vitro and enhancing human islet engraftment/proliferation in vivo, superior to normal islets and as effectively as the combination of cdk6 plus a D-cyclin. Human beta-cells contain abundant cdk4, cdk6, and cyclin D3, but variable amounts of cyclin D1. In contrast to rodent beta-cells, they contain little or no detectable cyclin D2. They are primarily cytoplasmic and likely ineffective in basal beta-cell replication. Unexpectedly, cyclin D3 and cdk6 overexpression drives human beta-cell replication most effectively. Most importantly, a single molecule, cdk6, supports robust human beta-cell proliferation and function in vivo.
    Diabetes 08/2010; 59(8):1926-36. · 7.90 Impact Factor

Publication Stats

1k Citations
484.37 Total Impact Points

Institutions

  • 2013
    • Mount Sinai School of Medicine
      • Diabetes, Obesity and Metabolism Institute
      Manhattan, New York, United States
  • 2001–2013
    • University of Pittsburgh
      • • Division of Pediatric Endocrinology
      • • Division of Endocrinology and Metabolism
      • • School of Medicine
      Pittsburgh, PA, United States
  • 2012
    • Joslin Diabetes Center
      • Section on Islet Cell and Regenerative Biology
      Boston, MA, United States