Deterioration of adult stem cells accounts for much of aging-associated compromised tissue maintenance. How stem cells maintain metabolic homeostasis remains elusive. Here, we identified a regulatory branch of the mitochondrial unfolded protein response (UPRmt), which is mediated by the interplay of SIRT7 and NRF1 and is coupled to cellular energy metabolism and proliferation. SIRT7 inactivation caused reduced quiescence, increased mitochondrial protein folding stress (PFSmt), and compromised regenerative capacity of hematopoietic stem cells (HSCs). SIRT7 expression was reduced in aged HSCs, and SIRT7 up-regulation improved the regenerative capacity of aged HSCs. These findings define the deregulation of a UPRmt-mediated metabolic checkpoint as a reversible contributing factor for HSC aging.

Visceral obesity has been defined as an important element of the metabolic syndrome and contributes to the development of insulin resistance and cardiovascular disease. Increasing endogenous levels of epoxyeicosatrienoic acids (EETs) are known for their analgesic, antihypertensive, and antiinflammatory effects. The availability of EETs is limited primarily by the soluble epoxide hydrolase (sEH, EPHX2), which metabolizes EETs to their less active diols. In this study, we tested the hypothesis that EETs are involved in glucose regulation and in retarding the development of insulin resistance. To address the role of EETs in regulating glucose homeostasis and insulin signaling, we used mice with targeted gene deletion of sEH (Ephx2-null mice) and a subsequent study with a selective sEH inhibitor. When wild-type mice are fed a high fat diet, insulin resistance develops. However, knockout or inhibition of sEH activity resulted in a significant decrease in plasma glucose. These findings are characterized by enhancement of tyrosyl phosphorylation of the insulin receptor, insulin receptor substrate 1, and their downstream cascade. In addition, pancreatic islets were larger when sEH was disrupted. This effect was associated with an increase in vasculature. These observations were supported by pharmacological inhibition of sEH. These data suggest that an increase in EETs due to sEH-gene knockout leads to an increase in the size of islets and improved insulin signaling and sensitivity.type 2 diabetes | pancreas | arachidonic acid pathway

Background & Aims Reactive oxidative species (ROS) are believed to be involved in the progression of non-alcoholic steatohepatitis (NASH). However, little is known about the sources of ROS in hepatocytes or their role in disease progression. We studied the effects of NADPH oxidase 4 (NOX4) in liver tissues from patients with NASH and mice with steatohepatitis. Methods Liver biopsy samples were obtained from 5 patients with NASH, as well as 4 patients with simple steatosis and 5 patients without steatosis (controls) from the University of California, Davis Cancer Center Biorepository. Mice with hepatocyte-specific deletion of NOX4 (NOX4hepKO) and NOX4floxp+/+ C57BL/6 mice (controls) were given fast food diets (supplemented with high-fructose corn syrup) or choline-deficient L-amino acid-defined to induce steatohepatitis, or control diets, for 20 weeks. A separate group of mice were given the NOX4 inhibitor (GKT137831). Liver tissues were collected and immunoblot analyses were performed determine levels of NOX4, markers of inflammation and fibrosis, double-stranded RNA-activated protein kinase (PKR), and phospho-eIF-2alpha kinase (PERK)-mediated stress signaling pathways. We performed hyperinsulinemic-euglycemic clamp studies and immunoprecipitation analyses to determine the oxidation and phosphatase activity of PP1C. Results Levels of NOX4 were increased in patients with NASH, compared with controls. Hepatocyte-specific deletion of NOX4 reduced oxidative stress, lipid peroxidation, and liver fibrosis in mice with diet-induced steatohepatitis. A small molecule inhibitor of NOX4 reduced liver inflammation and fibrosis and increased insulin sensitivity in mice with diet-induced steatohepatitis. In primary hepatocytes, NOX4 reduced the activity of the phosphatase PP1C, prolonging activation of PKR and PERK-mediated stress signaling. Mice with hepatocyte-specific deletion of NOX4 and mice given GKT137831had increased insulin sensitivity. Conclusion NOX4 regulates oxidative stress in the liver and its levels are increased in patients with NASH and mice with diet-induced steatohepatitis. Inhibitors of NOX4 reduce liver inflammation and fibrosis and increase insulin sensitivity, and might be developed for treatment of NASH.

The Src homology 2 domain-containing protein-tyrosine phosphatase Src homology phosphatase 2 (Shp2) is a negative regulator of hepatic insulin action in mice fed regular chow. To investigate the role of hepatic Shp2 in lipid metabolism and energy balance, we determined the metabolic effects of its deletion in mice challenged with a high-fat diet (HFD). We analyzed body mass, lipid metabolism, insulin sensitivity, and glucose tolerance in liver-specific Shp2-deficient mice (referred to herein as LSHKO) and control mice fed HFD. Hepatic Shp2 protein expression is regulated by nutritional status, increasing in mice fed HFD and decreasing during fasting. LSHKO mice gained less weight and exhibited increased energy expenditure compared with control mice. In addition, hepatic Shp2 deficiency led to decreased liver steatosis, enhanced insulin-induced suppression of hepatic glucose production, and impeded the development of insulin resistance after high-fat feeding. At the molecular level, LSHKO exhibited decreased hepatic endoplasmic reticulum stress and inflammation compared with control mice. In addition, tyrosine and serine phosphorylation of total and mitochondrial signal transducer and activator of transcription 3 were enhanced in LSHKO compared with control mice. In line with this observation and the increased energy expenditure of LSHKO, oxygen consumption rate was higher in liver mitochondria of LSHKO compared with controls. Collectively, these studies identify hepatic Shp2 as a novel regulator of systemic energy balance under conditions of high-fat feeding.

Protein-tyrosine phosphatase 1B (PTP1B) and T cell proteintyrosine phosphatase (TCPTP) are closely related intracellular phosphatases implicated in the control of glucose homeostasis. PTP1B and TCPTP can function coordinately to regulate protein tyrosine kinase signaling, and PTP1B has been implicated previously in the regulation of endoplasmic reticulum (ER) stress. In this study, we assessed the roles of PTP1B and TCPTP in regulating ER stress in the endocrine pancreas. PTP1B and TCPTP expression was determined in pancreases from chow and high fat fed mice and the impact of PTP1B and TCPTP overor underexpression on palmitate-or tunicamycin-induced ER stress signaling assessed in MIN6 insulinoma ␤ cells. PTP1B expression was increased, and TCPTP expression decreased in pancreases of mice fed a high fat diet, as well as in MIN6 cells treated with palmitate. PTP1B overexpression or TCPTP knockdown in MIN6 cells mitigated palmitate-or tunicamycininduced PERK/eIF2␣ ER stress signaling, whereas PTP1B deficiency enhanced ER stress. Moreover, PTP1B deficiency increased ER stress-induced cell death, whereas TCPTP deficiency protected MIN6 cells from ER stress-induced death. ER stress coincided with the inhibition of Src family kinases (SFKs), which was exacerbated by PTP1B overexpression and largely prevented by TCPTP knockdown. Pharmacological inhibition of SFKs ameliorated the protective effect of TCPTP deficiency on ER stress-induced cell death. These results demonstrate that PTP1B and TCPTP play nonredundant roles in modulating ER stress in pancreatic ␤ cells and suggest that changes in PTP1B and TCPTP expression may serve as an adaptive response for the mitigation of chronic ER stress.