Browsing by Author "Esser, Nathalie"

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    Increased Steroidogenic Acute Regulatory Protein Contributes to Cholesterol-induced β-Cell Dysfunction
    (Oxford University Press, 2025) Akter, Rehana; Hogan, Meghan F.; Esser, Nathalie; Barrow, Breanne M.; Castillo, Joseph J.; Boyko, Edward J.; Templin, Andrew T.; Hull, Rebecca L.; Zraika, Sakeneh; Kahn, Steven E.; Medicine, School of Medicine
    Hypercholesterolemia is often observed in individuals with type 2 diabetes. Cholesterol accumulation in subcellular compartments within islet β-cells can result in insulin secretory dysfunction, which is a key pathological feature of diabetes. Previously, we demonstrated that expression of the mitochondrial cholesterol transport protein, steroidogenic acute regulatory protein (StAR), is induced in islets under conditions of β-cell dysfunction. However, whether it contributes to mitochondrial cholesterol accumulation in β-cells and cholesterol-induced β-cell dysfunction has not been determined. Thus, we sought to examine the role of StAR in isolated mouse islets under conditions of excess exogenous cholesterol. Cholesterol treatment of islets upregulated StAR expression, which was associated with cholesterol accumulation in mitochondria, decreased mitochondrial membrane potential and impaired mitochondrial oxidative phosphorylation. Impaired insulin secretion and reduced islet insulin content were also observed in cholesterol-laden islets. To determine the impact of StAR overexpression in β-cells per se, a lentivirus was used to increase StAR expression in INS-1 cells. Under these conditions, StAR overexpression was sufficient to increase mitochondrial cholesterol content, impair mitochondrial oxidative phosphorylation, and reduce insulin secretion. These findings suggest that elevated cholesterol in diabetes may contribute to β-cell dysfunction via increases in StAR-mediated mitochondrial cholesterol transport and accumulation.
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    Insulinotropic Effects of Neprilysin and/or Angiotensin Receptor Inhibition in Mice
    (Frontiers Media, 2022-06-06) Esser, Nathalie; Schmidt, Christine; Barrow, Breanne M.; Cronic, Laura; Hackney, Daryl J.; Mongovin, Stephen M.; Hogan, Meghan F.; Templin, Andrew T.; Castillo, Joseph J.; Hull, Rebecca L.; Zraika, Sakeneh; Medicine, School of Medicine
    Treatment of heart failure with the angiotensin receptor-neprilysin inhibitor sacubitril/valsartan improved glycemic control in individuals with type 2 diabetes. The relative contribution of neprilysin inhibition versus angiotensin II receptor antagonism to this glycemic benefit remains unknown. Thus, we sought to determine the relative effects of the neprilysin inhibitor sacubitril versus the angiotensin II receptor blocker valsartan on beta-cell function and glucose homeostasis in a mouse model of reduced first-phase insulin secretion, and whether any beneficial effects are additive/synergistic when combined in sacubitril/valsartan. High fat-fed C57BL/6J mice treated with low-dose streptozotocin (or vehicle) were followed for eight weeks on high fat diet alone or supplemented with sacubitril, valsartan or sacubitril/valsartan. Body weight and fed glucose levels were assessed weekly. At the end of the treatment period, insulin release in response to intravenous glucose, insulin sensitivity, and beta-cell mass were determined. Sacubitril and valsartan, but not sacubitril/valsartan, lowered fasting and fed glucose levels and increased insulin release in diabetic mice. None of the drugs altered insulin sensitivity or beta-cell mass, but all reduced body weight gain. Effects of the drugs on insulin release were reproduced in angiotensin II-treated islets from lean C57BL/6J mice, suggesting the insulin response to each of the drugs is due to a direct effect on islets and mechanisms therein. In summary, sacubitril and valsartan each exert beneficial insulinotropic, glycemic and weight-reducing effects in obese and/or diabetic mice when administered alone; however, when combined, mechanisms within the islet contribute to their inability to enhance insulin release.
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    Islet amyloid polypeptide aggregation exerts cytotoxic and proinflammatory effects on the islet vasculature in mice
    (Springer, 2022) Castillo, Joseph J.; Aplin, Alfred C.; Hackney, Daryl J.; Hogan, Meghan F.; Esser, Nathalie; Templin, Andrew T.; Akter, Rehana; Kahn, Steven E.; Raleigh, Daniel P.; Zraika, Sakeneh; Hull, Rebecca L.; Medicine, School of Medicine
    Aims/hypothesis: The islet vasculature, including its constituent islet endothelial cells, is a key contributor to the microenvironment necessary for normal beta cell health and function. In type 2 diabetes, islet amyloid polypeptide (IAPP) aggregates, forming amyloid deposits that accumulate between beta cells and islet capillaries. This process is known to be toxic to beta cells but its impact on the islet vasculature has not previously been studied. Here, we report the first characterisation of the effects of IAPP aggregation on islet endothelial cells/capillaries using cell-based and animal models. Methods: Primary and immortalised islet endothelial cells were treated with amyloidogenic human IAPP (hIAPP) alone or in the presence of the amyloid blocker Congo Red or the Toll-like receptor (TLR) 2/4 antagonist OxPAPc. Cell viability was determined0 along with mRNA and protein levels of inflammatory markers. Islet capillary abundance, morphology and pericyte coverage were determined in pancreases from transgenic mice with beta cell expression of hIAPP using conventional and confocal microscopy. Results: Aggregated hIAPP decreased endothelial cell viability in immortalised and primary islet endothelial cells (by 78% and 60%, respectively) and significantly increased expression of inflammatory markers Il6, Vcam1 and Edn1 mRNA relative to vehicle treatment in both cell types (p<0.05; n=4). Both cytotoxicity and the proinflammatory response were ameliorated by Congo Red (p<0.05; n=4); whereas TLR2/4-inhibition blocked inflammatory gene expression (p<0.05; n=6) without improving viability. Islets from high-fat-diet-fed amyloid-laden hIAPP transgenic mice also exhibited significantly increased expression of most markers of endothelial inflammation (p<0.05; n=5) along with decreased capillary density compared with non-transgenic littermates fed the same diet (p<0.01). Moreover, a 16% increase in capillary diameter was observed in amyloid-adjacent capillaries (p<0.01), accompanied by a doubling in pericyte structures positive for neuron-glial antigen 2 (p<0.001). Conclusions/interpretation: Islet endothelial cells are susceptible to hIAPP-induced cytotoxicity and exhibit a TLR2/4-dependent proinflammatory response to aggregated hIAPP. Additionally, we observed amyloid-selective effects that decreased islet capillary density, accompanied by increased capillary diameter and increased pericyte number. Together, these data demonstrate that the islet vasculature is a target of the cytotoxic and proinflammatory effects of aggregated hIAPP that likely contribute to the detrimental effects of hIAPP aggregation on beta cell function and survival in type 2 diabetes.
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    Loss of ARC Worsens High Fat Diet-Induced Hyperglycemia in Mice
    (Bioscientifica, 2021-09-20) Templin, Andrew T.; Schmidt, Christine; Hogan, Meghan F.; Esser, Nathalie; Kitsis, Richard N.; Hull, Rebecca L.; Zraika, Sakeneh; Kahn, Steven E.; Medicine, School of Medicine
    Apoptosis repressor with caspase recruitment domain (ARC) is an endogenous inhibitor of cell death signaling that is expressed in insulin-producing β cells. ARC has been shown to reduce β-cell death in response to diabetogenic stimuli in vitro, but its role in maintaining glucose homeostasis in vivo has not been fully established. Here we examined whether loss of ARC in FVB background mice exacerbates high fat diet (HFD)-induced hyperglycemia in vivo over 24 weeks. Prior to commencing 24-week HFD, ARC−/− mice had lower body weight than wild type (WT) mice. This body weight difference was maintained until the end of the study and was associated with decreased epididymal and inguinal adipose tissue mass in ARC−/− mice. Non-fasting plasma glucose was not different between ARC−/− and WT mice prior to HFD feeding, and ARC−/− mice displayed a greater increase in plasma glucose over the first 4 weeks of HFD. Plasma glucose remained elevated in ARC−/− mice after 16 weeks of HFD feeding, at which time it had returned to baseline in WT mice. Following 24 weeks of HFD, non-fasting plasma glucose in ARC−/− mice returned to baseline and was not different from WT mice. At this final time point, no differences were observed between genotypes in plasma glucose or insulin under fasted conditions or following IV glucose administration. However, HFD-fed ARC−/− mice exhibited significantly decreased β-cell area compared to WT mice. Thus, ARC deficiency delays, but does not prevent, metabolic adaptation to HFD feeding in mice, worsening transient HFD-induced hyperglycemia.
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    RIPK3 promotes islet amyloid-induced β-cell loss and glucose intolerance in a humanized mouse model of type 2 diabetes
    (Elsevier, 2024) Mukherjee, Noyonika; Contreras, Christopher J.; Lin, Li; Colglazier, Kaitlyn A.; Mather, Egan G.; Kalwat, Michael A.; Esser, Nathalie; Kahn, Steven E.; Templin, Andrew T.; Biochemistry and Molecular Biology, School of Medicine
    Objective: Aggregation of human islet amyloid polypeptide (hIAPP), a β-cell secretory product, leads to islet amyloid deposition, islet inflammation and β-cell loss in type 2 diabetes (T2D), but the mechanisms that underlie this process are incompletely understood. Receptor interacting protein kinase 3 (RIPK3) is a pro-death signaling molecule that has recently been implicated in amyloid-associated brain pathology and β-cell cytotoxicity. Here, we evaluated the role of RIPK3 in amyloid-induced β-cell loss using a humanized mouse model of T2D that expresses hIAPP and is prone to islet amyloid formation. Methods: We quantified amyloid deposition, cell death and caspase 3/7 activity in islets isolated from WT, Ripk3-/-, hIAPP and hIAPP; Ripk3-/- mice in real time, and evaluated hIAPP-stimulated inflammation in WT and Ripk3-/- bone marrow derived macrophages (BMDMs) in vitro. We also characterized the role of RIPK3 in glucose stimulated insulin secretion (GSIS) in vitro and in vivo. Finally, we examined the role of RIPK3 in high fat diet (HFD)-induced islet amyloid deposition, β-cell loss and glucose homeostasis in vivo. Results: We found that amyloid-prone hIAPP mouse islets exhibited increased cell death and caspase 3/7 activity compared to amyloid-free WT islets in vitro, and this was associated with increased RIPK3 expression. hIAPP; Ripk3-/- islets were protected from amyloid-induced cell death compared to hIAPP islets in vitro, although amyloid deposition and caspase 3/7 activity were not different between genotypes. We observed that macrophages are a source of Ripk3 expression in isolated islets, and that Ripk3-/- BMDMs were protected from hIAPP-stimulated inflammatory gene expression (Tnf, Il1b, Nos2). Following 52 weeks of HFD feeding, islet amyloid-prone hIAPP mice exhibited impaired glucose tolerance and decreased β-cell area compared to WT mice in vivo, whereas hIAPP; Ripk3-/- mice were protected from these impairments. Conclusions: In conclusion, loss of RIPK3 protects from amyloid-induced inflammation and islet cell death in vitro and amyloid-induced β-cell loss and glucose intolerance in vivo. We propose that therapies targeting RIPK3 may reduce islet inflammation and β-cell loss and improve glucose homeostasis in the pathogenesis of T2D.
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    The islet tissue plasminogen activator/plasmin system is upregulated with human islet amyloid polypeptide aggregation and protects beta cells from aggregation-induced toxicity
    (Springer, 2024) Esser, Nathalie; Hogan, Meghan F.; Templin, Andrew T.; Akter, Rehana; Fountaine, Brendy S.; Castillo, Joseph J.; El‑Osta, Assam; Manathunga, Lakshan; Zhyvoloup, Alexander; Raleigh, Daniel P.; Zraika, Sakeneh; Hull, Rebecca L.; Kahn, Steven E.; Medicine, School of Medicine
    Aims/hypothesis: Apart from its fibrinolytic activity, the tissue plasminogen activator (tPA)/plasmin system has been reported to cleave the peptide amyloid beta, attenuating brain amyloid deposition in Alzheimer's disease. As aggregation of human islet amyloid polypeptide (hIAPP) is toxic to beta cells, we sought to determine whether activation of the fibrinolytic system can also reduce islet amyloid deposition and its cytotoxic effects, which are both observed in type 2 diabetes. Methods: The expression of Plat (encoding tPA) and plasmin activity were measured in isolated islets from amyloid-prone hIAPP transgenic mice or non-transgenic control islets expressing non-amyloidogenic mouse islet amyloid polypeptide cultured in the absence or presence of the amyloid inhibitor Congo Red. Plat expression was also determined in hIAPP-treated primary islet endothelial cells, bone marrow-derived macrophages (BMDM) and INS-1 cells, in order to determine the islet cell type(s) producing tPA in response to hIAPP aggregation. Cell-free thioflavin-T assays and MS were used to respectively monitor hIAPP aggregation kinetics and investigate plasmin cleavage of hIAPP. Cell viability was assessed in INS-1 beta cells treated with hIAPP with or without plasmin. Finally, to confirm the findings in human samples, PLAT expression was measured in freshly isolated islets from donors with and without type 2 diabetes. Results: In isolated islets from transgenic mice, islet Plat expression and plasmin activity increased significantly with the process of amyloid deposition (p≤0.01, n=5); these effects were not observed in islets from non-transgenic mice and were blocked by Congo Red (p≤0.01, n=4). In response to hIAPP exposure, Plat expression increased in BMDM and INS-1 cells vs vehicle-treated cells (p≤0.05, n=4), but not in islet endothelial cells. Plasmin reduced hIAPP fibril formation in a dose-dependent manner in a cell-free system, and restored hIAPP-induced loss of cell viability in INS-1 beta cells (p≤0.01, n=5). Plasmin cleaved monomeric hIAPP, inducing a rapid decrease in the abundance of full-length hIAPP and the appearance of hIAPP 1-11 and 12-37 fragments. hIAPP 12-37, which contains the critical amyloidogenic region, was not toxic to INS-1 cells. Finally, PLAT expression was significantly increased by 2.4-fold in islets from donors with type 2 diabetes (n=4) vs islets from donors without type 2 diabetes (n=7) (p≤0.05). Conclusions/interpretation: The fibrinolytic system is upregulated in islets with hIAPP aggregation. Plasmin rapidly degrades hIAPP, limiting its aggregation into amyloid and thus protecting beta cells from hIAPP-induced toxicity. Thus, increasing islet plasmin activity might be a strategy to limit beta cell loss in type 2 diabetes.