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FoxO proteins are major targets of insulin action, and FoxO1 mediates the effects of insulin on hepatic glucose metabolism. We reported previously that serpinB1 is a liver-secreted factor (hepatokine) that promotes adaptive β-cell proliferation in response to insulin resistance in the liver-specific insulin receptor knockout (LIRKO) mouse. Here we report that FoxO1 plays a critical role in promoting serpinB1 expression in hepatic insulin resistance in a non-cell-autonomous manner. Mice lacking both the insulin receptor and FoxO1 (LIRFKO) exhibit reduced β-cell mass compared with LIRKO mice because of attenuation of β-cell proliferation. Although hepatic expression of serpinB1 mRNAand protein levels was increased in LIRKO mice, both the mRNA and protein levels returned to control levels in LIRFKO mice. Furthermore, liver-specific expression of constitutively active FoxO1 in transgenic mice induced an increase in hepatic serpinB1 mRNA and protein levels in refed mice. Conversely, serpinB1mRNAand protein levels were reduced in mice lacking FoxO proteins in the liver. ChIP studies demonstrated that FoxO1 binds to three distinct sites located ~9 kb upstream of the serpinb1 gene in primary mouse hepatocytes and that this binding is enhanced in hepatocytes from LIRKO mice. However, adenoviral expression of WT or constitutively active FoxO1 and insulin treatment are sufficient to regulate other FoxO1 target genes (IGFBP-1 and PEPCK) but not serpinB1 expression in mouse primary hepatocytes. These results indicate that liver FoxO1 promotes serpinB1 expression in hepatic insulin resistance and that non-cell-autonomous factors contribute to FoxO1-dependent effects on serpinB1 expression in the liver. [ABSTRACT FROM AUTHOR]

Abstract There is emerging evidence to support an important role for the transient receptor potential vanilloid type 1 (TRPV1) sensory innervation in glucose homeostasis. However, it remains unknown whether the glucoregulatory action of these afferent neurons is sex-biased and whether it is pancreatic β-cell-mediated. Objective We investigated in male and female mice whether denervation of whole-body or pancreas-projecting TRPV1 sensory neurons regulates adult functional β-cell mass and alters systemic glucose homeostasis. Methods We used a combination of pharmacological and surgical approaches to ablate whole-body or pancreatic TRPV1 sensory neurons and assessed islet β-cell function and mass, aspects of glucose and insulin homeostasis, and energy expenditure. Results Capsaicin-induced chemodenervation of whole-body TRPV1 sensory neurons improved glucose clearance and enhanced glucose-stimulated insulin secretion without alterations in β-cell proliferation and mass, systemic insulin sensitivity, body composition, and energy expenditure. Similarly, denervation of intrapancreatic TRPV1 afferents by pancreas intraductal injection of capsaicin or surgical removal of the dorsal root ganglia projecting into the pancreas lowered post-absorptive glucose levels and increased insulin release upon glucose stimulation. The beneficial effects of TRPV1 sensory denervation on glucose tolerance and β-cell function were observed in male but not female mice. Conclusion Collectively, these findings suggest that TRPV1 neurons regulate glucose homeostasis, at least partly, through direct modulation of glucose-induced insulin secretion and that this regulation operates in a sex-dependent manner. Highlights • Whole-body ablation of TRPV1 neurons increases insulin secretion and glucose clearance in male but not female mice. • Pancreas-selective ablation of TRPV1 neurons enhances insulin secretion and glucose clearance in male but not female mice. • Surgical removal of lower thoracic DRGs improves insulin secretion and glucose clearance in male but not female mice. [ABSTRACT FROM AUTHOR]

Summary Although compensatory islet hyperplasia in response to insulin resistance is a recognized feature in diabetes, the factor(s) that promote β cell proliferation have been elusive. We previously reported that the liver is a source for such factors in the liver insulin receptor knockout (LIRKO) mouse, an insulin resistance model that manifests islet hyperplasia. Using proteomics we show that serpinB1, a protease inhibitor, which is abundant in the hepatocyte secretome and sera derived from LIRKO mice, is the liver-derived secretory protein that regulates β cell proliferation in humans, mice, and zebrafish. Small-molecule compounds, that partially mimic serpinB1 effects of inhibiting elastase activity, enhanced proliferation of β cells, and mice lacking serpinB1 exhibit attenuated β cell compensation in response to insulin resistance. Finally, SerpinB1 treatment of islets modulated proteins in growth/survival pathways. Together, these data implicate serpinB1 as an endogenous protein that can potentially be harnessed to enhance functional β cell mass in patients with diabetes. [ABSTRACT FROM AUTHOR]

Summary The mechanisms underlying the development of complications in type 1 diabetes (T1D) are poorly understood. Disease modeling of induced pluripotent stem cells (iPSCs) from patients with longstanding T1D (disease duration ≥ 50 years) with severe (Medalist +C) or absent to mild complications (Medalist −C) revealed impaired growth, reprogramming, and differentiation in Medalist +C. Genomics and proteomics analyses suggested differential regulation of DNA damage checkpoint proteins favoring protection from cellular apoptosis in Medalist −C. In silico analyses showed altered expression patterns of DNA damage checkpoint factors among the Medalist groups to be targets of miR200, whose expression was significantly elevated in Medalist +C serum. Notably, neurons differentiated from Medalist +C iPSCs exhibited enhanced susceptibility to genotoxic stress that worsened upon miR200 overexpression. Furthermore, knockdown of miR200 in Medalist +C fibroblasts and iPSCs rescued checkpoint protein expression and reduced DNA damage. We propose miR200-regulated DNA damage checkpoint pathway as a potential therapeutic target for treating complications of diabetes. [ABSTRACT FROM AUTHOR]

Objective The Polycomb Repressive Complexes (PRC) 1 and 2 function to epigenetically repress target genes. The PRC1 component, Bmi1, plays a crucial role in maintenance of glucose homeostasis and beta cell mass through repression of the Ink4a/Arf locus. Here we have explored the role of Bmi1 in regulating glucose homeostasis in the adult animal, which had not been previously reported due to poor postnatal survival of Bmi1 −/− mice. Methods The metabolic phenotype of Bmi1 +/− mice was characterized, both in vivo and ex vivo . Glucose and insulin tolerance tests and hyperinsulinemic-euglycemic clamps were performed. The insulin signaling pathway was assessed at the protein and transcript level. Results Here we report a negative correlation between Bmi1 levels and insulin sensitivity in two models of insulin resistance, aging and liver-specific insulin receptor deficiency. Further, heterozygous loss of Bmi1 results in increased insulin sensitivity in adult mice, with no impact on body weight or composition. Hyperinsulinemic-euglycemic clamp reveals increased suppression of hepatic glucose production and increased glucose disposal rate, indicating elevated glucose uptake to peripheral tissues, in Bmi1 +/− mice. Enhancement of insulin signaling, specifically an increase in Akt phosphorylation, in liver and, to a lesser extent, in muscle appears to contribute to this phenotype. Conclusions Together, these data define a new role for Bmi1 in regulating insulin sensitivity via enhancement of Akt phosphorylation. [ABSTRACT FROM AUTHOR]

Summary: Integrative organ crosstalk regulates key aspects of energy homeostasis, and its dysregulation may underlie metabolic disorders such as obesity and diabetes. To test the hypothesis that crosstalk between the liver and pancreatic islets modulates β cell growth in response to insulin resistance, we used the liver-specific insulin receptor knockout (LIRKO) mouse, a unique model that exhibits dramatic islet hyperplasia. Using complementary in vivo parabiosis and transplantation assays, as well as in vitro islet culture approaches, we demonstrate that humoral, nonneural, non-cell-autonomous factor(s) induces β cell proliferation in LIRKO mice. Furthermore, we report that a hepatocyte-derived factor(s) stimulates mouse and human β cell proliferation in ex vivo assays, independent of ambient glucose and insulin levels. These data implicate the liver as a critical source of β cell growth factor(s) in insulin-resistant states. [ABSTRACT FROM AUTHOR]

The regulation of glucose-stimulated insulin secretion and glucose excursion has a sensory component that operates in a sex-dependent manner. Here, we aim to dissect the basis of the sexually dimorphic interaction between sensory neurons and pancreatic β cells and its overall impact on insulin release and glucose homeostasis. We used viral retrograde tracing techniques, surgical and chemodenervation models, and primary cell-based co-culture systems to uncover the biology underlying sex differences in sensory modulation of pancreatic β-cell activity. Retrograde transsynaptic labeling revealed a sex difference in the density of sensory innervation in the pancreas. The number of sensory neurons emanating from the dorsal root and nodose ganglia that project in the pancreas is higher in male than in female mice. Immunostaining and confocal laser scanning microscopy confirmed the higher abundance of peri-islet sensory axonal tracts in the male pancreas. Capsaicin-induced sensory chemodenervation concomitantly enhanced glucose-stimulated insulin secretion and glucose clearance in male mice. These metabolic benefits were blunted when mice were orchidectomized prior to the ablation of sensory nerves. Interestingly, orchidectomy also lowered the density of peri-islet sensory neurons. In female mice, capsaicin treatment did not affect glucose-induced insulin secretion nor glucose excursion and ovariectomy did not modify these outcomes. Interestingly, same- and opposite-sex sensory-islet co-culture paradigms unmasked the existence of potential gonadal hormone-independent mechanisms mediating the male-female difference in sensory modulation of islet β-cell activity. Taken together, these data suggest that the sex-biased nature of the sensory control of islet β-cell activity is a result of a combination of neurodevelopmental inputs, sex hormone-dependent mechanisms and the potential action of somatic molecules encoded by the sex chromosome complement. • Pancreas-projecting sensory neurons are more abundant in males than in females. • Male sex hormones regulate the density of peri-islet sensory innervation in adulthood. • Male sex hormones regulate sensory modulation of β-cell activity and glucose clearance. • Sex chromosome mechanisms regulate sensory modulation of islet β-cell activity. [ABSTRACT FROM AUTHOR]

Summary Investigation of cell-cycle kinetics in mammalian pancreatic β cells has mostly focused on transition from the quiescent (G0) to G1 phase. Here, we report that centromere protein A (CENP-A), which is required for chromosome segregation during the M-phase, is necessary for adaptive β cell proliferation. Receptor-mediated insulin signaling promotes DNA-binding activity of FoxM1 to regulate expression of CENP-A and polo-like kinase-1 (PLK1) by modulating cyclin-dependent kinase-1/2. CENP-A deposition at the centromere is augmented by PLK1 to promote mitosis, while knocking down CENP-A limits β cell proliferation and survival. CENP-A deficiency in β cells leads to impaired adaptive proliferation in response to pregnancy, acute and chronic insulin resistance, and aging in mice. Insulin-stimulated CENP-A/PLK1 protein expression is blunted in islets from patients with type 2 diabetes. These data implicate the insulin-FoxM1/PLK1/CENP-A pathway-regulated mitotic cell-cycle progression as an essential component in the β cell adaptation to delay and/or prevent progression to diabetes. [ABSTRACT FROM AUTHOR]