Background: Brown adipose tissue (BAT) is important for cold-and diet-induced thermogenesis. Results: Obesity and chronic exercise antagonistically regulate thermogenic capacity of BAT and subcutaneous white fat (SC WAT). Conclusion: Endurance exercise reduces thermogenic capacity in classical BAT while increasing it in the SC WAT. Significance: Browning of the SC WAT may be potentially used to treat obesity.

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The search for putative precursor cells within the pancreas has been the focus of extensive research. Previously, we identified rare pancreas-derived multipotent precursor (PMP) cells in the mouse with the intriguing capacity to generate progeny in the pancreatic and neural lineages. Here, we establish the embryonic pancreas as the developmental source of PMPs through lineage-labeling experiments. We also show that PMPs express insulin and can contribute to multiple pancreatic and neural cell types in vivo. In addition, we have isolated PMPs from adult human islet tissue that are also capable of extensive proliferation, self-renewal, and generation of multiple differentiated pancreatic and neural cell types. Finally, both mouse and human PMP-derived cells ameliorated diabetes in transplanted mice. These findings demonstrate that the adult mammalian pancreas contains a population of insulin(+) multipotent stem cells and suggest that these cells may provide a promising line of investigation toward potential therapeutic benefit.

OBJECTIVE-An important mechanism in the pathogenesis of type 2 diabetes in obese individuals is elevation of plasma free fatty acids (FFAs), which induce insulin resistance and chronically decrease ␤-cell function and mass. Our objective was to investigate the role of oxidative stress in FFA-induced decrease in ␤-cell function. RESEARCH DESIGN AND METHODS-We used an in vivo model of 48-h intravenous oleate infusion in Wistar rats followed by hyperglycemic clamps or islet secretion studies ex vivo and in vitro models of 48-h exposure to oleate in islets and MIN6 cells.RESULTS-Forty-eight-hour infusion of oleate decreased the insulin and C-peptide responses to a hyperglycemic clamp (P Ͻ 0.01), an effect prevented by coinfusion of the antioxidants N-acetylcysteine (NAC) and taurine. Similar to the findings in vivo, 48-h infusion of oleate decreased glucose-stimulated insulin secretion ex vivo (P Ͻ 0.01) and induced oxidative stress (P Ͻ 0.001) in isolated islets, effects prevented by coinfusion of the antioxidants NAC, taurine, or tempol (4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl). Forty-eight-hour infusion of olive oil induced oxidative stress (P Ͻ 0.001) and decreased the insulin response of isolated islets similar to oleate (P Ͻ 0.01). Islets exposed to oleate or palmitate and MIN6 cells exposed to oleate showed a decreased insulin response to high glucose and increased levels of oxidative stress (both P Ͻ 0.001), effects prevented by taurine. Real-time RT-PCR showed increased mRNA levels of antioxidant genes in MIN6 cells after oleate exposure, an effect partially prevented by taurine. T ype 2 diabetes is characterized by both insulin resistance and defective insulin secretion (1). Obesity is the major predisposing factor for type 2 diabetes and is associated with excessive release of fatty acids from the expanded adipose tissue mass, leading to elevated plasma free fatty acids (FFAs), which are known to induce insulin resistance (2,3). Acute FFA exposure stimulates insulin secretion (4), but studies in vitro and in situ have shown that prolonged FFA exposure decreases glucose-stimulated insulin secretion (GSIS) (5). The effect of prolonged FFA elevation on ␤-cell function in vivo has been more controversial, as absolute GSIS was found to be increased (6 -8), unchanged (9,10), or decreased (11-13) by FFA. However, in most of these studies ␤-cell function was inadequate to compensate for FFA-induced insulin resistance (9 -13), at least in predisposed individuals (14). Although the mechanisms behind FFA-induced decrease in ␤-cell function are unclear, one possibility points toward oxidative stress. Pancreatic ␤-cells have low antioxidant defenses (15) and are thus susceptible to reactive oxygen species (ROS)-induced decrease in function and viability (16,17). Oxidative stress has been implicated in the decrease in GSIS induced by prolonged exposure to glucose (18,19), which is in many respects similar to that induced by prolonged exposure to FFA (4,20). However, whether oxidative stress plays a role in FFA-...

sure to elevated saturated free fatty acid (FFA) levels has been shown to induce endoplasmic reticulum (ER) stress that may contribute to promoting pancreatic ␤-cell apoptosis. Here, we compared the effects of FFAs on apoptosis and ER stress in human islets and two pancreatic ␤-cell lines, rat INS-1 and mouse MIN6 cells. Isolated human islets cultured in vitro underwent apoptosis, and markers of ER stress pathways were elevated by chronic palmitate exposure. Palmitate also induced apoptosis in MIN6 and INS-1 cells, although the former were more resistant to both apoptosis and ER stress. MIN6 cells were found to express significantly higher levels of ER chaperone proteins than INS-1 cells, which likely accounts for the ER stress resistance. We attempted to determine the relative contribution that ER stress plays in palmitate-induced ␤-cell apoptosis. Although overexpressing GRP78 in INS-1 cells partially reduced susceptibility to thapsigargin, this failed to reduce palmitate-induced ER stress or apoptosis. In INS-1 cells, palmitate induced apoptosis at concentrations that did not result in significant ER stress. Finally, MIN6 cells depleted of GRP78 were more susceptible to tunicamycin-induced apoptosis but not to palmitate-induced apoptosis compared with control cells. These results suggest that ER stress is likely not the main mechanism involved in palmitate-induced apoptosis in ␤-cell lines. Human islets and MIN6 cells were found to express high levels of stearoyl-CoA desaturase-1 compared with INS-1 cells, which may account for the decreased susceptibility of these cells to the cytotoxic effects of palmitate. endoplasmic reticulum; lipotoxicity; palmitate LIPOTOXICITY CONTRIBUTES to ␤-cell dysfunction during the development of type 2 diabetes (19,42,48). Chronically elevated levels of free fatty acids (FFAs), particularly saturated FFAs such as palmitate, have been shown to be cytotoxic to pancreatic ␤-cells (8, 10, 24, 30 -33, 41, 46, 50). The monounsaturated FFA oleate on the other hand has been shown to not cause apoptosis of ␤-cells in some studies (16,17,31,32,35), while other studies (11,24,27,33,50) found that it does, particularly those that used the INS-1 ␤-cell line.Palmitate-induced cytotoxicity can result from multiple mechanisms, such as increases in reactive oxygen species (8,18,33), ceramide, and nitric oxide (NO) levels (30, 45) and mitochondrial perturbations (8,18,33). In addition, recent studies (23-25) have shown that endoplasmic reticulum (ER) stress pathways are activated by chronic palmitate exposure.ER stress is caused when the protein folding capacity of the ER is not sufficient to deal with protein folding demands or when an excess of misfolded or aggregated proteins accumulate. Such conditions activate the unfolded protein response (UPR) that attempts to reduce the amount of new protein synthesis, increase folding capacity, and degrade terminally misfolded proteins (20, 53). Prolonged ER stress can lead to apoptosis induction (37, 53) and thus may contribute to palmitate-induced ␤-c...

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In pancreatic ␤-cells

The pleckstrin homology domain-interacting protein (PHIP) was originally identified as a 902-amino-acid (aa) protein that regulates insulin receptor-stimulated GLUT4 translocation in skeletal-muscle cells. Immunoblotting and immunohistological analyses of pancreatic ␤-cells reveal prominent expression of a 206-kDa PHIP isoform restricted to the nucleus. Herein, we report the cloning of this larger, 1,821-aa isoform of PHIP (PHIP1), which represents a novel WD40 repeat-containing protein. We demonstrate that PHIP1 overexpression stimulates insulin-like growth factor 1-dependent and -independent proliferation of ␤-cells, an event which correlates with transcriptional upregulation of the cyclin D2 promoter and the accumulation of cyclin D2 protein. RNA interference knockdown of PHIP1 in INS-1 cells abrogates insulin receptor substrate 2 (IRS2)-mediated DNA synthesis, providing for a specific role for PHIP1 in the enhancement of IRS2-dependent signaling responses leading to ␤-cell growth. Finally, we provide evidence that PHIP1 overexpression blocks free fatty acid-induced apoptosis in INS-1 cells, which is accompanied by marked activation of phosphoprotein kinase B (PKB)/AKT and the concomitant inhibition of caspase-9 and caspase-3 cleavage. Our finding that the restorative effect of PHIP1 on ␤-cell lipotoxicity can be attenuated by the overexpression of dominant-negative PKB suggests a key role for PKB in PHIP1-mediated cytoprotection. Taken together, these findings provide strong support for PHIP1 as a novel positive regulator of ␤-cell function. We suggest that PHIP1 may be involved in the induction of long-term gene expression programs to promote ␤-cell mitogenesis and survival.Type 1 and type 2 are the two principal forms of diabetes and account for more than 99% of all known forms of this metabolic disorder (29). Type 1 diabetes results from autoimmune destruction of the pancreatic ␤ cells and manifests itself when less than 10 to 20% of functional ␤ cells remain in the islets (13). Type 2 diabetes is characterized by the development of ␤-cell dysfunction and the progressive reduction of ␤-cell mass via reduced proliferation and increased apoptosis, although, unlike type 1 diabetes, it is the result of peripheral insulin resistance and chronic exposure to high levels of glucose and long-chain free fatty acids (FFA), known as glucotoxicity and lipotoxicity, respectively (28, 31).Biochemical and genetic evidence strongly implicate insulin and insulin-like growth factor 1 (IGF-1) as critical factors in ␤-cell function (21). The activated receptors engage and phosphorylate various cellular proteins, including insulin receptor substrate (IRS) protein family members. Recent studies, both in vitro and in transgenic animals, have revealed an important role for IRS2 in the control of ␤-cell growth and survival (15,17,25). There are two signaling cascades downstream of IRS2 in ␤ cells that have been characterized extensively: the phosphatidylinositol 3Ј-kinase (PI3-kinase)/protein kinase B (PKB) pathway and the Ras/Raf...