Eddy Sean F, Morin Pier, Storey Kenneth B
Institute of Biochemistry and Department of Chemistry Carleton University, Ottawa, Ont., Canada K1S 5B6.
J Exp Zool A Comp Exp Biol. 2006 Aug 1;305(8):620-30. doi: 10.1002/jez.a.294.
High rates of non-shivering thermogenesis by brown adipose tissue accompanied by additional shivering thermogenesis in skeletal muscle provide the powerful reheating of body organs that allows hibernating mammals to return from their state of cold torpor back to euthermic function. Previous studies have suggested that changes to brown adipose mitochondria occur during hibernation and are partially responsible for its capacity for non-shivering thermogenesis. The current study shows that selected mitochondrial enzyme activities are elevated and selected genes and proteins are induced during torpor in brown adipose tissue of the little brown bat, Myotis lucifugus. Cytochrome oxidase activity in brown adipose tissue was more than 3-fold higher during torpor than in euthermic animals. Transcript levels of mitochondria-encoded genes, coxII and nad4, were also 3-4-fold higher during torpor, as evidenced by northern blotting. By contrast, transcripts of these genes were unchanged in skeletal muscle during torpor. Protein levels of carnitine palmitoyl transferase-1beta, an enzyme embedded in the outer membrane of the mitochondria that is the rate-limiting step enzyme in beta-oxidation, were also elevated by 2-fold during torpor in brown adipose but were unchanged in skeletal muscle. Cloning and sequencing of a 624 bp segment of cpt-1beta revealed a number of amino acid substitutions in the bat protein as compared to CPT-1beta from other mammals; these may be beneficial for enzyme function at low body temperatures during torpor. This study provides further evidence for a key role of mitochondria in hibernation.
褐色脂肪组织产生的高比率非颤抖性产热，伴随着骨骼肌额外的颤抖性产热，为身体器官提供了强大的再加热功能，使冬眠的哺乳动物能够从冷蛰伏状态恢复到正常体温功能。先前的研究表明，冬眠期间褐色脂肪线粒体发生了变化，这部分解释了其非颤抖性产热的能力。当前的研究表明，在小棕蝠（Myotis lucifugus）的褐色脂肪组织蛰伏期间，特定的线粒体酶活性升高，特定的基因和蛋白质被诱导表达。褐色脂肪组织中的细胞色素氧化酶活性在蛰伏期间比正常体温的动物高出3倍多。通过Northern印迹法证明，线粒体编码基因coxII和nad4的转录水平在蛰伏期间也高出3 - 4倍。相比之下，这些基因的转录本在骨骼肌蛰伏期间没有变化。肉碱棕榈酰转移酶-1β（一种嵌入线粒体外膜的酶，是β-氧化中的限速步骤酶）的蛋白质水平在褐色脂肪组织蛰伏期间也升高了2倍，但在骨骼肌中没有变化。对cpt-1β的一个624 bp片段进行克隆和测序发现，与其他哺乳动物的CPT-1β相比，蝙蝠蛋白质中有许多氨基酸替代；这些替代可能有利于该酶在蛰伏期间低温下的功能。这项研究为线粒体在冬眠中的关键作用提供了进一步的证据。
