Our results suggest that adipocyte JAK2 plays a critical role in the regulation of adipocyte biology and whole-body metabolism. Targeting of the JAK-STAT pathway could be a novel therapeutic option for the treatment of obesity and type 2 diabetes.

Focal adhesion kinase (FAK) plays a central role in integrin signalling, which regulates growth and survival of tumours. Here we show that FAK protein levels are increased in adipose tissue of insulin-resistant obese mice and humans. Disruption of adipocyte FAK in mice or in 3T3 L1 cells decreases adipocyte survival. Adipocyte-specific FAK knockout mice display impaired adipose tissue expansion and insulin resistance on prolonged metabolic stress from a high-fat diet or when crossed on an obese db/db or ob/ob genetic background. Treatment of these mice with a PPARγ agonist does not restore adiposity or improve insulin sensitivity. In contrast, inhibition of apoptosis, either genetically or pharmacologically, attenuates adipocyte death, restores normal adiposity and improves insulin sensitivity. Together, these results demonstrate that FAK is required for adipocyte survival and maintenance of insulin sensitivity, particularly in the context of adipose tissue expansion as a result of caloric excess.

Aims/hypothesis Non-shivering thermogenesis in adipose tissue can be activated by excessive energy intake or following cold exposure. The molecular mechanisms regulating this activation have not been fully elucidated. The Janus kinase (JAK) -signal transducer and activator of transcription (STAT) pathway mediates the signal transduction of numerous hormones and growth factors that regulate adipose tissue development and function, and may play a role in adaptive thermogenesis. Methods We analysed mRNA and protein levels of uncoupling protein 1 (UCP1) and JAK2 in different adipose depots in response to metabolic and thermal stress. The in vivo role of JAK2 in adaptive thermogenesis was examined using mice with adipocyte-specific Jak2 deficiency (A-Jak2 KO). Results We show in murine brown adipose tissue (BAT) that JAK2 is upregulated together with UCP1 in response to highfat diet (HFD) feeding and cold exposure. In contrast to white adipose tissue, where JAK2 was dispensable for UCP1 induction, we identified an essential role for BAT JAK2 in diet-and cold-induced thermogenesis via mediating the thermogenic response to β-adrenergic stimulation. Accordingly, A-Jak2 KO mice were unable to upregulate BAT UCP1 following a HFD or after cold exposure. Therefore, A-Jak2 KO mice were cold intolerant and susceptible to HFD-induced obesity and diabetes. Conclusions/interpretation Taken together, our results suggest that JAK2 plays a critical role in BAT function and adaptive thermogenesis. Targeting the JAK-STAT pathway may be a novel therapeutic approach for the treatment of obesity and related metabolic disorders.

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Aims/hypothesis Diabetes mellitus is characterised by beta cell loss and alpha cell expansion. Analogues of glucagonlike peptide-1 (GLP-1) are used therapeutically to antagonise these processes; thus, we hypothesised that the related cell cycle regulators retinoblastoma protein (Rb) and p107 were involved in GLP-1 action. Methods We used small interfering RNA and adenoviruses to manipulate Rb and p107 expression in insulinoma and alpha-TC cell lines. In vivo we examined pancreas-specific Rb knockout, whole-body p107 knockout and Rb/p107 doubleknockout mice.Results Rb, but not p107, was downregulated in response to the GLP-1 analogue, exendin-4, in both alpha and beta cells. Intriguingly, this resulted in opposite outcomes of cell cycle arrest in alpha cells but proliferation in beta cells. Overexpression of Rb in alpha and beta cells abolished or attenuated the effects of exendin-4 supporting the important role of Rb in GLP-1 modulation of cell cycling. Similarly, in vivo, Rb, but not p107, deficiency was required for the beta cell proliferative response to exendin-4. Consistent with this finding, Rb, but not p107, was suppressed in islets from humans with diabetes, suggesting the importance of Rb regulation for the compensatory proliferation that occurs under insulin resistant conditions. Finally, while p107 alone did not have an essential role in islet homeostasis, when combined with Rb deletion, its absence potentiated apoptosis of both alpha and beta cells resulting in glucose intolerance and diminished islet mass with ageing. Conclusions/interpretation We found a central role of Rb in the dual effects of GLP-1 in alpha and beta cells. Our findings highlight unique contributions of individual Rb family members to islet cell proliferation and survival.

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Keywords: Hypoxia inducible factor b cell glucose homeostasis diabetes mellitus pancreas Abbreviations: ARNT, aryl hydrocarbon receptor nuclear translocator; EPAS1, endothelial PAS domain protein 1; GLUT1 glucose transporter 1; GTT, glucose tolerance test; HFD, high fat diet; HIF, hypoxia inducible factor; HIF-1a, hypoxia inducible factor-1 a; HIF-1b, hypoxia inducible factor-1 b; HIF-2a, hypoxia inducible factor-2 a; i.p., intraperitoneal; ITT, insulin tolerance test; OE, overexpression; VEGF, vascular endothelial growth factor; VHL, von Hippel-Lindau; WT, wild-type.Both type 1 and type 2 diabetes are associated with insufficient functional b-cell mass. Understanding intracellular signaling pathways associated with this decline is important in broadening our understanding of the disease and potential therapeutic strategies. The hypoxia inducible factor pathway (HIF) plays a critical role in cellular adaptation to hypoxic conditions. Activation of this pathway increases expression of numerous genes involved in multiple cellular processes and has been shown to impact the regulation of b-cell function. Previously, deletion of HIF-1a or HIF-1b in pancreatic b-cells, as well as constitutive activation of the HIF pathway in b-cells, was shown to result in glucose intolerance and impaired insulin secretion. The objective of this study was to delineate roles of HIF-2a overexpression in pancreatic b-cells in vivo. We overexpressed HIF-2a in pancreatic b-cells by employing the Cre-loxP system driven by the Pdx1 promoter to delete a stop codon. Our study revealed that pancreatic HIF-2a overexpression does not result in significant differences in glucose tolerance, insulin sensitivity or b-cell area compared to wild-type littermates under basal conditions or after high fat diet. Together, our study shows excess HIF-2a in the pancreatic b-cells does not play a significant role in b-cell function and glucose homeostasis.

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