Up-regulation of orphan nuclear estrogen-related receptor alpha expression during long-term caloric restriction in mice

The estrogen-related receptor alpha (ERRα) is an orphan receptor belonging to the nuclear receptor superfamily that regulates a number of target genes encoding enzymes that participate in various metabolic pathways involved in maintaining energy balance in animals. In this study, whether long-term caloric restriction (alternate days of fasting for 3 months) in mice modulates the expression of ERRα in various tissues was investigated. Western blot analyses showed positive immunoreactive ERRα protein (53 kDa) band in various mice tissue extracts, though at varying levels. Heart, kidney, and skeletal muscles expressed significant levels of ERRα, with a comparatively lower level detected in the intestine, brain, and liver. Cardiac ERRα expression was the highest, with the least detected in the liver. Caloric restricted mice exhibited a significant increase in ERRα level in the heart (5.45-fold), kidney (3.70-fold), skeletal muscle (3.0-fold), small intestine (2.72-fold), and liver (2.44-fold) extracts as compared to ad libitum fed. However, caloric restriction could not evoke any detectable receptor level change in the brain. Notably, the highest ERRα up-regulation was detected in the heart. This up-regulation in ERRα level especially in highly oxidative tissues such as heart, kidney, small intestine, and skeletal muscle of caloric restricted mice may be helpful in modulating ERRα responsive genes that participates in maintaining energy balance. This may potentially strengthen the metabolic and biochemical adaptation in such tissues, which is necessary for animal survival under long-term caloric restriction.     

Peroxisome proliferator-activated receptor-gamma coactivator-1alpha activation of CYP7A1 during food restriction and diabetes is still inhibited by small heterodimer partner

Cholesterol 7alpha-hydroxylase (CYP7A1) catalyzes the rate-limiting step in the classic pathway of hepatic bile acid biosynthesis from cholesterol. During fasting and in type I diabetes, elevated levels of peroxisome proliferator-activated receptor gamma-coactivator-1alpha (PGC-1alpha) induce expression of the Cyp7A1 gene and overexpression of PGC-1alpha in hepatoma cells stimulates bile acid synthesis. Using Ad-PGC-1alpha-RNA interference to induce acute disruption of PGC-1alpha in mice, here we show that PGC-1alpha is necessary for fasting-mediated induction of CYP7A1. Co-immunoprecipitation and promoter activation studies reveal that the induction of CYP7A1 is mediated by direct interaction between PGC-1alpha and the AF2 domain of liver receptor homolog-1 (LRH-1). In contrast, the very similar PGC-1beta could not substitute for PGC-1alpha. We also show that transactivation of PGC-1alpha and LRH-1 is repressed by the small heterodimer partner (SHP). Treatment of mice with GW4064, a synthetic agonist for farnesoid X receptor, induced SHP expression and decreased both the recruitment of PGC-1alpha to the Cyp7A1 promoter and the fasting-induced expression of CYP7A1 mRNA. These data suggest that PGC-1alpha is an important co-activator for LRH-1 and that SHP targets the interaction between LRH-1 and PGC-1alpha to inhibit CYP7A1 expression. Overall, these studies provide further evidence for the important role of PGC-1alpha in bile acid homeostasis and suggest that pharmacological targeting of farnesoid X receptor in vivo can be used to reverse the increase in CYP7A1 associated with adverse metabolic conditions.     

Key regulators of mitochondrial biogenesis are increased in kidneys of growth hormone receptor knockout (GHRKO) mice

The growth hormone receptor knockout (GHRKO) mice are remarkably long-lived and highly insulin sensitive. Alterations in mitochondrial biogenesis are associated with aging and various metabolic derangements. We have previously demonstrated increased gene expression of key regulators of mitochondriogenesis in kidneys, hearts and skeletal muscles of GHRKO mice. The aim of the present study was to quantify the protein levels of the following regulators of mitochondriogenesis: peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α), AMP-activated protein kinase α (AMPKα), phospho-AMPKα (p-AMPKα), sirtuin-3 (SIRT-3), endothelial nitric oxide synthase (eNOS), phospho-eNOS (p-eNOS), nuclear respiratory factor-1 (NRF-1) and mitofusin-2 (MFN-2) in skeletal muscles and kidneys of GHRKOs in comparison to normal mice. We also were interested in the effects of calorie restriction (CR) and visceral fat removal (VFR) on these parameters. Both CR and VFR improve insulin sensitivity and can extend life span. Results: The renal levels of PGC-1α, AMPKα, p-AMPKα, SIRT-3, eNOS, p-eNOS and MFN-2 were increased in GHRKOs. In the GHRKO skeletal muscles, only MFN-2 was increased. Levels of the examined proteins were not affected by CR (except for PGC-1α and p-eNOS in skeletal muscles) or VFR. Conclusion: GHRKO mice have increased renal protein levels of key regulators of mitochondriogenesis, and this may contribute to increased longevity of these knockouts.     

Calcium signalling in the regulation of PGC-1alpha, PDK4 and HKII mRNA expression

The role of calcium signalling and specific intracellular calcium signalling pathways in regulating skeletal muscle tissue peroxisome proliferator-activated receptor gamma co-activator (PGC)-1alpha, hexokinase (HK)II and pyruvate dehydrogenase kinase (PDK)4 mRNA was examined. Cultured primary rat skeletal muscle cells were incubated for 6 h in caffeine or ionomycin. Because PGC-1alpha mRNA clearly showed greater induction with ionomycin, the latter was chosen for the main experiments, whereby cells were incubated for 6 h with either ionomycin alone or in combination with either cyclosporin A or KN-62. The PGC-1alpha mRNA level was increased (p<0.05) approximately six-fold and HKII mRNA content approximately two-fold by ionomycin relative to the corresponding controls, whereas the PDK4 mRNA content remained unaffected. Cyclosporin A abolished (p<0.05) and KN-62 reduced (p<0.1) the ionomycin-induced increase in PGC-1alpha mRNA. Electrical stimulation of in vitro incubated rat EDL muscle increased (p<0.05) PGC-1alpha mRNA by 2.2-fold after 4 h of recovery relative to a resting control, and this increase was absent when muscles were incubated with KN-62 or cyclosporin A. The present data strongly suggest that calcium signalling is involved in regulating the PGC-1alpha and HKII genes, but not PDK4. Both calcineurin and CaMK signalling seem to be involved in the calcium- and contraction-mediated PGC-1alpha up-regulation in skeletal muscle.     

Apolipoprotein A-IV is regulated by nutritional and metabolic stress: involvement of glucocorticoids, HNF-4 alpha, and PGC-1 alpha

Apolipoprotein A-IV (apoA-IV) is a 46 kDa glycoprotein that associates with triglyceride-rich and high density lipoproteins. Blood levels of apoA-IV generally correlate with triglyceride levels and are increased in diabetic patients. This study investigated the mechanisms regulating the in vivo expression of apoA-IV in the liver and intestine of mice in response to changes in nutritional status. Fasting markedly increased liver and ileal apoA-IV mRNA and plasma protein concentrations. This induction was associated with increased serum glucocorticoid levels and was abolished by adrenalectomy. Treatment with dexamethasone increased apoA-IV expression in adrenalectomized mice. Marked increases of apoA-IV expression were also observed in two murine models of diabetes. Reporter gene analysis of the murine and human apoA-IV/C-III promoters revealed a conserved cooperative activation by the hepatic nuclear factor-4 alpha (HNF-4 alpha) and the peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1 alpha) but no evidence of a direct regulatory role for the glucocorticoid receptor. Consistent with these in vitro data, induction of apoA-IV in response to fasting was accompanied by increases in HNF-4 alpha and PGC-1 alpha expression and was abolished in liver-specific HNF-4 alpha-deficient mice. Together, these results indicate that the induction of apoA-IV expression in fasting and diabetes likely involves PGC-1 alpha-mediated coactivation of HNF-4 alpha in addition to glucocorticoid-dependent actions.