Description: Background— Recent studies suggest that the oxygen-sensing pathway consisting of transcription factor hypoxia-inducible factor and prolyl hydroxylase domain proteins (PHDs) plays a critical role in glucose metabolism. However, the role of adipocyte PHD in the development of obesity has not been clarified. We examined whether deletion of PHD2 , the main oxygen sensor, in adipocytes affects diet-induced obesity and associated metabolic abnormalities. Methods and Results— To delete PHD2 in adipocyte, PHD2 -floxed mice were crossed with aP2-Cre transgenic mice ( Phd2 f/f /aP2-Cre) . Phd2 f/f /aP2-Cre mice were resistant to high-fat diet–induced obesity (36.7±1.7 versus 44.3±2.0 g in control; P 〈0.01) and showed better glucose tolerance and homeostasis model assessment–insulin resistance index than control mice (3.6±1.0 versus 11.1±2.1; P 〈0.01). The weight of white adipose tissue was lighter (epididymal fat, 758±35 versus 1208±507 mg in control; P 〈0.01) with a reduction in adipocyte size. Macrophage infiltration into white adipose tissue was also alleviated in Phd2 f/f /aP2-Cre mice. Target genes of hypoxia-inducible factor, including glycolytic enzymes and adiponectin, were upregulated in adipocytes of Phd2 f/f /aP2-Cre mice. Lipid content was decreased and uncoupling protein-1 expression was increased in brown adipose tissue of Phd2 f/f /aP2-Cre mice. Knockdown of PHD2 in 3T3L1 adipocytes induced a decrease in the glucose level and an increase in the lactate level in the supernatant with upregulation of glycolytic enzymes and reduced lipid accumulation. Conclusions— PHD2 in adipose tissue plays a critical role in the development of diet-induced obesity and glucose intolerance. PHD2 might be a novel target molecule for the treatment of obesity and associated metabolic abnormalities.

Description: Rationale: Both fusion and fission contribute to mitochondrial quality control. How unopposed fusion affects survival of cardiomyocytes and left ventricular function in the heart is poorly understood. Objective: We investigated the role of dynamin-related protein 1 (Drp1), a GTPase that mediates mitochondrial fission, in mediating mitochondrial autophagy, ventricular function, and stress resistance in the heart. Methods and Results: Drp1 downregulation induced mitochondrial elongation, accumulation of damaged mitochondria, and increased apoptosis in cardiomyocytes at baseline. Drp1 downregulation also suppressed autophagosome formation and autophagic flux at baseline and in response to glucose deprivation in cardiomyocytes. The lack of lysosomal translocation of mitochondrially targeted Keima indicates that Drp1 downregulation suppressed mitochondrial autophagy. Mitochondrial elongation and accumulation of damaged mitochondria were also observed in tamoxifen-inducible cardiac-specific Drp1 knockout mice. After Drp1 downregulation, cardiac-specific Drp1 knockout mice developed left ventricular dysfunction, preceded by mitochondrial dysfunction, and died within 13 weeks. Autophagic flux is significantly suppressed in cardiac-specific Drp1 knockout mice. Although left ventricular function in cardiac-specific Drp1 heterozygous knockout mice was normal at 12 weeks of age, left ventricular function decreased more severely after 48 hours of fasting, and the infarct size/area at risk after ischemia/reperfusion was significantly greater in cardiac-specific Drp1 heterozygous knockout than in control mice. Conclusions: Disruption of Drp1 induces mitochondrial elongation, inhibits mitochondrial autophagy, and causes mitochondrial dysfunction, thereby promoting cardiac dysfunction and increased susceptibility to ischemia/reperfusion.

Description: Objective— BubR1, a cell cycle–related protein, is an essential component of the spindle checkpoint that regulates cell division. Mice with BubR1 expression reduced to 10% of the normal level display a phenotype characterized by progeria; however, the involvement of BubR1 in vascular diseases is still unknown. We generated mice in which BubR1 expression was reduced to 20% ( BubR1 L/L mice) of that in wild-type mice ( BubR1 +/+ ) to investigate the effects of BubR1 on arterial intimal hyperplasia. Approach and Results— Ten-week-old male BubR1 L/L and age-matched wild-type littermates ( BubR1 +/+ ) were used in this study. The left common carotid artery was ligated, and histopathologic examinations were conducted 4 weeks later. Bone marrow transplantation was also performed. Vascular smooth muscle cells (VSMCs) were isolated from the thoracic aorta to examine cell proliferation, migration, and cell cycle progression. Severe neointimal hyperplasia was observed after artery ligation in BubR1 +/+ mice, whereas BubR1 L/L mice displayed nearly complete inhibition of neointimal hyperplasia. Bone marrow transplantation from all donors did not affect the reconstitution of 3 hematopoietic lineages, and neointimal hyperplasia was still suppressed after bone marrow transplantation from BubR1 +/+ mice to BubR1 L/L mice. VSMC proliferation was impaired in BubR1 L/L mice because of delayed entry into the S phase. VSMC migration was unaffected in these BubR1 L/L mice. p38 mitogen–activated protein kinase–inhibited VSMCs showed low expression of BubR1, and BubR1-inhibited VSMCs showed low expression of p38. Conclusions— BubR1 may represent a new target molecule for treating pathological states of vascular remodeling, such as restenosis after angioplasty.

Description: Background— Mitochondrial autophagy is an important mediator of mitochondrial quality control in cardiomyocytes. The occurrence of mitochondrial autophagy and its significance during cardiac hypertrophy are not well understood. Methods and Results— Mice were subjected to transverse aortic constriction (TAC) and observed at multiple time points up to 30 days. Cardiac hypertrophy developed after 5 days, the ejection fraction was reduced after 14 days, and heart failure was observed 30 days after TAC. General autophagy was upregulated between 1 and 12 hours after TAC but was downregulated below physiological levels 5 days after TAC. Mitochondrial autophagy, evaluated by electron microscopy, mitochondrial content, and Keima with mitochondrial localization signal, was transiently activated at 3 to 7 days post-TAC, coinciding with mitochondrial translocation of Drp1. However, it was downregulated thereafter, followed by mitochondrial dysfunction. Haploinsufficiency of Drp1 abolished mitochondrial autophagy and exacerbated the development of both mitochondrial dysfunction and heart failure after TAC. Injection of Tat-Beclin 1, a potent inducer of autophagy, but not control peptide, on day 7 after TAC, partially rescued mitochondrial autophagy and attenuated mitochondrial dysfunction and heart failure induced by overload. Haploinsufficiency of either drp1 or beclin 1 prevented the rescue by Tat-Beclin 1, suggesting that its effect is mediated in part through autophagy, including mitochondrial autophagy. Conclusions— Mitochondrial autophagy is transiently activated and then downregulated in the mouse heart in response to pressure overload. Downregulation of mitochondrial autophagy plays an important role in mediating the development of mitochondrial dysfunction and heart failure, whereas restoration of mitochondrial autophagy attenuates dysfunction in the heart during pressure overload.