MiRNAs are regulatory molecules that can be packaged into exosomes and secreted from cells. Here, we show that adipose tissue macrophages (ATMs) in obese mice secrete miRNA-containing exosomes (Exos), which cause glucose intolerance and insulin resistance when administered to lean mice. Conversely, ATM Exos obtained from lean mice improve glucose tolerance and insulin sensitivity when administered to obese recipients. miR-155 is one of the miRNAs overexpressed in obese ATM Exos, and earlier studies have shown that PPARγ is a miR-155 target. Our results show that miR-155KO animals are insulin sensitive and glucose tolerant compared to controls. Furthermore, transplantation of WT bone marrow into miR-155KO mice mitigated this phenotype. Taken together, these studies show that ATMs secrete exosomes containing miRNA cargo. These miRNAs can be transferred to insulin target cell types through mechanisms of paracrine or endocrine regulation with robust effects on cellular insulin action, in vivo insulin sensitivity, and overall glucose homeostasis.

SUMMARY The nature of obesity-associated islet inflammation and its impact on β cell abnormalities remains poorly defined. Here, we explore immune cell components of islet inflammation and define their roles in regulating β cell function and proliferation. Islet inflammation in obese mice is dominated by macrophages. We identify two islet-resident macrophage populations, characterized by their anatomical distributions, distinct phenotypes, and functional properties. Obesity induces the local expansion of resident intra-islet macrophages, independent of recruitment from circulating monocytes. Functionally, intra-islet macrophages impair β cell function in a cell-cell contact-dependent manner. Increased engulfment of β cell insulin secretory granules by intra-islet macrophages in obese mice may contribute to restricting insulin secretion. In contrast, both intra- and peri-islet macrophage populations from obese mice promote β cell proliferation in a PDGFR signaling-dependent manner. Together, these data define distinct roles and mechanisms for islet macrophages in the regulation of islet β cells.

Decreased adipose tissue oxygen tension and increased HIF-1α expression can trigger adipose tissue inflammation and dysfunction in obesity. Our current understanding of obesity-associated decreased adipose tissue oxygen tension is mainly focused on changes in oxygen supply and angiogenesis. Here, we demonstrate that increased adipocyte O2 demand, mediated by ANT2 activity, is the dominant cause of adipocyte hypoxia. Deletion of adipocyte Ant2 improves obesity-induced intracellular adipocyte hypoxia by decreasing obesity-induced adipocyte oxygen demand, without effects on mitochondrial number or mass, or oligomycin-sensitive respiration. This led to decreased adipose tissue HIF-1α expression and inflammation with improved glucose tolerance and insulin resistance in both a preventative or therapeutic setting. Our results suggest that ANT2 may be a target for the development of insulin sensitizing drugs and that ANT2 inhibition might have clinical utility.

β1-Integrin, a critical regulator of β cell survival and function, has been shown to protect against cell death and promote insulin expression and secretion in rat and human islet cells in vitro. The aim of the present study was to examine whether the knockout of β1-integrin in collagen I-producing cells would have physiological and functional implications in pancreatic endocrine cells in vivo. Using adult mice with a conditional knockout of β1-integrin in collagen I-producing cells, the effects of β1-integrin deficiency on glucose metabolism and pancreatic endocrine cells were examined. Male β1-integrin-deficient mice display impaired glucose tolerance, with a significant reduction in pancreatic insulin content (p < 0.01). Morphometric analysis revealed a significant reduction in β cell mass (p < 0.001) in β1-integrin-deficient mice, along with a significant decrease in β cell proliferation, Pdx-1 and Nkx6.1 expression when compared with controls. Interestingly, these physiological and morphometric alterations in female β1-integrin-deficient mice were less significant. Furthermore, β1-integrin-deficient mice displayed decreased FAK (p < 0.05) and ERK1/2 (p < 0.001) phosphorylation, reduced cyclin D1 levels (p < 0.001) and increased caspase 3 cleavage (p < 0.01), while no changes in Akt phosphorylation were observed, indicating that the β1-integrin signals through the FAK-MAPK-ERK pathway in vivo. Our results demonstrate that β1-integrin is involved in the regulation of glucose metabolism and contributes to the maintenance of β cell survival and function in vivo.

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Diabetes mellitus is a chronic condition resulting from insufficient β-cell mass, which leads to improper glycemia regulation. Research efforts have focused on expanding islets and β-cells in vitro for use in cell-based therapies to cure diabetes. Collagens are triple-helix extracellular matrix proteins with widespread expression in mammals. With multiple functions, collagen can provide structural integrity in addition to mediating cellular signaling. In the pancreas, collagens I and IV are abundant and support cell structures while also stimulating cell surface receptors to influence pancreatic cell processes. Collagen-based materials and scaffolds have also been used to assist in the maintenance and expansion of islet cells in vitro, primarily through integrin and discoindin domain receptors. Islet transplantation using collagen-based scaffolds may improve long-term glycemic control, but progressive research efforts are required to realize this potential in humans. This review will outline the critical role played by native collagens I and IV and their receptors in maintaining islet function. The advantages of using collagens I and IV as culture gels/scaffolds and islet encapsulation vehicles for transplantation will be described.

Aims/hypothesis The receptor tyrosine kinase, c-Kit, and its ligand, stem cell factor, control a variety of cellular processes, including pancreatic beta cell survival and differentiation as revealed in c-Kit Wv mice, which have a point mutation in the c-Kit allele leading to loss of kinase activity and develop diabetes. The present study further investigated the intrinsic role of c-Kit in beta cells, especially the underlying mechanisms that influence beta cell function. Methods We generated a novel transgenic mouse model with c-KIT overexpression specifically in beta cells (c-KitβTg) to further examine the physiological and functional roles of c-Kit in beta cells. Isolated islets from these mice were used to investigate the underlying molecular pathway of c-Kit in beta cells. We also characterised the ability of c-Kit to protect animals from high-fat-diet-induced diabetes, as well as to rescue c-Kit Wv mice from early onset of diabetes. Results c-KitβTg mice exhibited improved beta cell function, with significantly improved insulin secretion, and increased beta cell mass and proliferation in response to high-fat-dietinduced diabetes. c-KitβTg islets exhibited upregulation of: (1) insulin receptor and IRSs; (2) Akt and glycogen synthase kinase 3β phosphorylation; and (3) transcription factors important for islet function. c-KIT overexpression in beta cells also rescued diabetes observed in c-Kit Wv mice. Conclusions/interpretation These findings demonstrate that c-Kit plays a direct protective role in beta cells, by regulating glucose metabolism and beta cell function. c-Kit may therefore represent a novel target for treating diabetes.

Integrin receptors are responsible for integrating extracellular matrix signals inside the cell. The most prominent integrin receptor, b1 integrin, has a role in cell function, survival and differentiation. Recently, we demonstrated a profound in vivo role of b1 integrin expression in the pancreas on glucose homeostasis and islet function. Here, we extend these results by examining the role of b1 integrin in exocrine pancreatic structure and function. Adult C57Bl/6 mice hemizygous for a collagen type Ia2 (Col1a2) promoter-controlled tamoxifen-inducible Cre recombinase gene and homozygous for loxP-b1 integrin were injected with tamoxifen or corn oil to generate mice deleted or not for b1 integrin. Pancreata derived from these male mice were analyzed by quantitative reverse transcriptase-polymerase chain reaction, western blot and immunofluorescence. Our results showed that b1 integrin-deficient mice displayed a significant decrease in pancreas weight with a significant reduction of amylase, regenerating islet-derived protein II and carboxypeptidase-A expression (Po0.05-0.01). Compared with control pancreata, b1 integrin-deficient pancreata showed reduced mRNA expression of extracellular matrix (collagen type Ia2, fibronectin and laminin) genes (Po0.05), detached acini clusters and lost focal adhesion structure. Moreover, b1 integrin-deficient pancreatic acinar cells displayed decreased proliferation (Po0.05) and increased apoptosis (Po0.001). Apoptosis was reduced to that of controls when isolated exocrine clusters were cultured in media supplemented with extracellular matrix proteins. Taken together, these results implicate b1 integrin as an essential component for maintaining exocrine pancreatic structure and function. Integrin receptors have a significant role in cell-cell and cellextracellular matrix (ECM) contacts in many different tissue types. There are 18 a and 8 b receptors capable of forming 24 heterodimeric interactions; yet, half these interactions are made up by b1 integrin receptors. 1 This b1 integrin receptor group is largely responsible for attachment to the ECM. 2 Upon stimulation, b1 integrin has been shown to mediate cell motility, survival, proliferation and differentiation. [2][3][4][5] Pancreatic acini are enclosed round structures that produce digestive enzymes. 6 Basal lamina covers the acini at the basal surface, stimulating acini integrin receptors. 6 Pancreatic stellate cells (PSCs) are identified as periacinar fibroblast-like cells of the pancreas that express glial fibrillary acidic protein (GFAP) and produce ECM proteins in support of surrounding tissue. 7 PSCs are also, in part, responsible for the fibrosis observed in chronic pancreatitis. 8,9 Previous studies have shown that a3b1 integrin is essential for proper apical/ basolateral cell surface receptor organization and basement membrane formation in the submandibular gland. 10 As well, b1 integrin deficiency has shown to interfere with laminin-1 expression and basement membrane synthesis and assembly in embryoid bodies 11 and te...