CD36/FAT (fatty acid translocase) is associated with human and murine nonalcoholic fatty liver disease, but it has been unclear whether it is simply a marker or whether it directly contributes to disease pathogenesis. Mice with hepatocyte-specific deletion of Janus kinase 2 (JAK2L mice) have increased circulating free fatty acids (FAs), dramatically increased hepatic CD36 expression and profound fatty liver. To investigate the role of elevated CD36 in the development of fatty liver, we studied two models of hepatic steatosis, a genetic model (JAK2L mice) and a high-fat diet (HFD)-induced steatosis model. We deleted Cd36 specifically in hepatocytes of JAK2L mice to generate double knockouts and from wild-type mice to generate CD36L single-knockout mice. Hepatic Cd36 disruption in JAK2L livers significantly improved steatosis by lowering triglyceride, diacylglycerol, and cholesterol ester content. The largest differences in liver triglycerides were in species comprised of oleic acid (C18:1). Reduction in liver lipids correlated with an improvement in the inflammatory markers that were elevated in JAK2L mice, namely aspartate aminotransferase and alanine transaminase. Cd36 deletion in mice on HFD (CD36L-HFD) reduced liver lipid content and decreased hepatic 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene-FA uptake as compared with CON-HFD. Additionally, CD36L-HFD mice had improved whole-body insulin sensitivity and reduced liver and serum inflammatory markers. Therefore, CD36 directly contributes to development of fatty liver under conditions of elevated free FAs by modulating the rate of FA uptake by hepatocytes. In HFD-fed animals, disruption of hepatic Cd36 protects against associated systemic inflammation and insulin resistance.

Objective: Human immunodeficiency virus (HIV) patients on antiretroviral regimens frequently develop a syndrome of abnormal fat distribution, insulin resistance, and dyslipidemia. This lipodystrophic syndrome has been most closely linked to the use of HIV protease inhibitors (PIs). Several mechanisms have been postulated to explain these adverse effects of PIs, based largely on studies of rodent adipocytes. Intriguingly, atazanavir, a newer PI equally effective against HIV, is associated with fewer signs of lipodystrophy. We hypothesized that the less deleterious clinical effects of atazanavir would be reflected in physiological differences observed in PI-treated adipocytes. Research Methods and Procedures:We compared the effects of atazanavir and an older PI associated with lipodystrophy, ritonavir, on differentiation, gene expression, adipocytokine secretion, and insulin signaling in a human adipocyte cell line. Results: Ritonavir inhibited human adipocyte differentiation and induced apoptosis to a greater extent than atazanavir. Treatment of mature adipocytes with ritonavir, but not atazanavir, also selectively decreased insulin signaling. Moreover, ritonavir also selectively decreased expression of adiponectin, an insulin-sensitizing adipocytokine, while inducing interleukin-6, a proinflammatory cytokine implicated in insulin resistance. Discussion: These data suggest that the distinct metabolic side effect profiles of these PIs could be a consequence of their differential effects on adipocyte physiology.

OBJECTIVEPancreatic-derived factor (PANDER, FAM3B) is a pancreatic islet-specific cytokine-like protein that is secreted from β-cells upon glucose stimulation. The biological function of PANDER is unknown, and to address this we generated and characterized a PANDER knockout mouse.RESEARCH DESIGN AND METHODSTo generate the PANDER knockout mouse, the PANDER gene was disrupted and its expression was inhibited by homologous recombination via replacement of the first two exons, secretion signal peptide and transcriptional start site, with the neomycin gene. PANDER−/− mice were then phenotyped by a number of in vitro and in vivo tests to evaluate potential effects on glucose regulation, insulin sensitivity, and β-cell morphology and function.RESULTSGlucose tolerance tests demonstrated significantly higher blood glucose levels in PANDER−/− versus wild-type male mice. To identify the mechanism of the glucose intolerance, insulin sensitivity and pancreatic β-cell function were examined. Hyperinsulinemic-euglycemic clamps and insulin tolerance testing showed similar insulin sensitivity for both the PANDER−/− and wild-type mice. The in vivo insulin response following intraperitoneal glucose injection surprisingly produced significantly higher insulin levels in the PANDER−/− mice, whereas insulin release was blunted with arginine administration. Islet perifusion and calcium imaging studies showed abnormal responses of the PANDER−/− islets to glucose stimulation. In contrast, neither islet architecture nor insulin content was impacted by the loss of PANDER. Interestingly, the elevated insulin levels identified in vivo were attributed to decreased hepatic insulin clearance in the PANDER−/− islets. Taken together, these results demonstrated decreased pancreatic β-cell function in the PANDER−/− mouse.CONCLUSIONSThese results support a potential role of PANDER in the pancreatic β-cell for regulation or facilitation of insulin secretion.

The pancreas-derived hormones, insulin and glucagon, are the two main regulators of glucose homeostasis. However, their actions can be modulated by the presence of other circulating factors including cytokines. Pancreatic-derived factor (PANDER) is a novel cytokine-like molecule secreted from the endocrine pancreas, but its biological function is currently unknown. To address this, we employed adenoviral gene delivery to develop a novel murine model of PANDER overexpression, which we used to study PANDER's effect on glucose homeostasis. Although serum metabolites in fed mice were unaffected by PANDER overexpression, fasting glucose, insulin, and corticosterone levels were significantly elevated. Additionally, PANDER-overexpressing mice displayed elevated glucose and insulin levels during a glucose tolerance test, indicating that glucose tolerance was impaired. However, there were no defects in glucose-stimulated insulin secretion or peripheral insulin sensitivity. Elevated transcription of hepatic gluconeogenic genes, PEPCK and G6Pase accompanied the fasting hyperglycemia observed in PANDER-overexpressing animals. Similarly, treatment of primary hepatocytes with PANDER-expressing adenovirus or PANDER-enriched conditioned medium elevated gluconeogenic gene expression and glucose output. PANDER treatment also resulted in higher levels of Ser133-phosphorylated cAMP-response element-binding protein in hepatocytes stimulated with 8-bromo-cAMP and dexamethasone and higher levels of intracellular cAMP upon stimulation with forskolin. In summary, we provide the first report that identifies PANDER as a regulator of hepatic glucose metabolism, where it serves as a novel factor that amplifies hepatic cAMP and cAMP-response element-binding protein signaling to induce gluconeogenic gene expression and glucose output.

a b s t r a c tPANDER is a cytokine co-secreted with insulin from islet b-cells. To date, the physiological function of PANDER remains largely unknown. Here we show that PANDER binds to the liver membrane by 125 I-PANDER saturation and competitive binding assays. In HepG2 cells, pre-treatment with PANDER ranging from 4 pM to 4 nM for 8 h resulted in a maximal inhibition of insulin-stimulated activation of insulin receptor and insulin receptor substrate 1 by 52% and 63%, respectively. Moreover, PANDER treatment also reduced insulin-stimulated PI3K and pAkt levels by 55% and 48%, respectively. In summary, we have identified the liver as a novel target for PANDER, and PANDER may be involved in the progression of diabetes by regulating hepatic insulin signaling pathways.

For nearly 100 years, growth hormone (GH) has been known to affect insulin sensitivity and risk of diabetes. However, the tissue governing the effects of GH signaling on insulin and glucose homeostasis remains unknown. Excess GH reduces fat mass and insulin sensitivity. Conversely, GH insensitivity (GHI) is associated with increased adiposity, augmented insulin sensitivity, and protection from diabetes. Here, we induce adipocyte-specific GHI through conditional deletion of (JAK2A), an obligate transducer of GH signaling. Similar to whole-body GHI, JAK2A mice had increased adiposity and extreme insulin sensitivity. Loss of adipocyte augmented hepatic insulin sensitivity and conferred resistance to diet-induced metabolic stress without overt changes in circulating fatty acids. While GH injections induced hepatic insulin resistance in control mice, the diabetogenic action was absent in JAK2A mice. Adipocyte GH signaling directly impinged on both adipose and hepatic insulin signal transduction. Collectively, our results show that adipose tissue governs the effects of GH on insulin and glucose homeostasis. Further, we show that JAK2 mediates liver insulin sensitivity via an extrahepatic, adipose tissue-dependent mechanism.

Pancreatic-Derived Factor (PANDER, FAM3B) is a member of the FAM3 family of cytokine molecules that were initially described in 2002. PANDER expression is primarily localized to the endocrine pancreas and is secreted from both pancreatic α and β-cells. Initial characterization of PANDER revealed a potential role in pancreatic islet apoptosis. However, recent animal models have indicated PANDER functions as a hormone by regulating glucose levels via interaction with both the liver and the endocrine pancreas. An understanding of the function of PANDER can further the insight into the mechanisms of glucose regulation and potentially provide additional therapeutic targets for the treatment of diabetes. This review details the supporting data demonstrating PANDER has a biological function in glycemic regulation.

The recent creation of the PANDER knockout (PANKO) and acute mouse models have revealed a biological function in the regulation of glycemic levels via promotion of hepatic glucose production (HGP) and pancreatic β-cell insulin secretion. Therefore, we hypothesized that the absence of PANDER may afford some degree of protection from high-fat diet (HFD) induced fasting hyperglycemia. On HFD, fasting glycemic levels were significantly lower in the PANKO mice. Also, fasting insulin levels and the in-vivo insulin response following glucose injection were inhibited in PANKO mice. The lowered fasting glycemic levels are attributed to decreased HGP due to the absence of PANDER. Overall, our findings further indicate PANDER impacts glycemic levels and may represent a potential but complicated therapeutic target.