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The coexistence of nocturnal sustained hypoxia and obesity additively increases cardiac apoptosis

¹Department of Physical Therapy, China Medical University, Taichung; ²Department of Biological Science and Technology, China Medical College, Taichung; ³Graduate Institute of Chinese Medical Science, China Medical University, Taichung; ⁴Laboratory of Exercise Biochemistry, Taipei Physical Education College, Taipei; ⁵Department of Pediatrics, Medical Research and Medical Genetics, China Medical University Hospital, Taichung; ⁶Department of Physiology, National Yang-Ming University, Taipei; ⁷Departments of Internal Medicine and Microbiology and Immunology, Chung-Shan Medical University, Taichung; ⁸Institute of Medical Science, China Medical University, Taichung; ⁹Department of Health and Nutrition Biotechnology, Asia University, Taichung, Taiwan

Submitted 5 February 2007 ; accepted in final form 11 December 2007

Background: nocturnal sustained hypoxia during sleeping time has been reported in severe obesity, but no information regarding the cardiac molecular mechanism in the coexistence of nocturnal sustained hypoxia and obesity is available. This study evaluates whether the coexistence of nocturnal sustained hypoxia and obesity will increase cardiac Fas death receptor and mitochondrial-dependent apoptotic pathway. Methods: 32 lean and 32 obese 5- to 6-mo-old rats with or without nocturnal sustained hypoxia were studied and assigned to one of four subgroups: normoxia lean (NL), normoxia obese (NO), hypoxia lean (HL, 12% O₂ for 8 h and 21% O₂ 16 h/day, 1 wk), and hypoxia obese (HO). The heart weight index, tail cuff plethysmography, echocardiography, hematoxylin-eosin staining, TUNEL assays, Western blotting, and RT-PCR were performed. Results: systolic and diastolic blood pressures in HO were higher than those in NL, and fractional shortening in HO was reduced compared with others. The whole heart weight, the left ventricular weight, the abnormal myocardial architecture, and TUNEL-positive apoptotic cells, as well as the activity of cardiac Fas-dependent and mitochondrial-dependent apoptotic pathway, were significantly increased in obese group or nocturnal sustained hypoxia group and were further increased when obesity and nocturnal sustained hypoxia coexisted, the evidence for which is based on decreases in an anti-apoptotic protein Bcl2 level and Bid and increases in Fas, FADD, pro-apoptotic Bad, BNIP3, cytosolic cytochrome c, activated caspase-8, activated caspase-9, and activated caspase-3. Conclusions: The cardiac Fas receptor- and mitochondrial-dependent apoptotic pathways were more activated in obesity with coexistent nocturnal sustained hypoxia, which may represent one possible apoptotic mechanism for the development of heart failure in obesity with nocturnal sustained hypoxia.

Fas receptor; mitochondrial; caspases; cell death; obese