Collaborative Research: Differential Expression of Oxygen-binding Proteins in Antarctic Fishes Affects Nitric Oxide-mediated Pathways of Angiogenesis and Mitochondrial Biogenesis.

目前环绕南极洲的极地海洋是地球上最冷、热稳定的海洋环境。由于氧在海水中的溶解度与温度成反比，寒冷的南极海域是一个特别富氧的水生栖息地。南极鱼亚目（Notothenioidei）中有8个科，主导着南极洲周围的鱼类区系。南极鱼约占南极极锋以南鱼类种类的35%和鱼类生物量的90%。因此，在一组非常不寻常的条件下，密切相关的南极鱼物种的辐射迅速发生：由于绕极洋流和环绕大陆的深海海沟，在海洋学上与其他动物群相对隔绝，长期以来，水温极低，氧气供应非常高，南大洋的生态位竞争水平非常低，在中第三纪到现在之间的某个时间发生了鱼类物种多样性的剧烈崩溃，导致物种减少。这些特征使南极南极南极鱼类成为研究低温生理生化适应性的独特吸引力群体。南极鱼类中很少有像南极冰鱼科（南极冰鱼科）中氧结合蛋白的表达模式那样独特的。所有渠道鱼类冰鱼都缺乏循环氧结合蛋白血红蛋白（Hb）；细胞内氧结合蛋白，肌红蛋白（Mb）在这个科的物种中不均匀表达。这两种蛋白质通常被认为是必需的足够的氧气输送到动物的有氧平衡组织。为了弥补血红蛋白的缺失，冰鱼发育出了大心脏，快速循环大量血液，拥有比红血鱼更大的管腔直径的精细脉管系统。氧化肌中Mb表达的缺失与细胞内线粒体密度的显著升高相关，尽管每个细胞器中呼吸蛋白的密度较低。在氧气运动的框架内，更大的血管密度和线粒体种群的适应性意义是可以理解的，但这些特征的发展机制尚不清楚。答案可能在于Hb和Mb的另一个主要功能，即普遍存在的生物活性化合物一氧化氮（NO）的降解。该研究将验证一种假设，即在冰鱼中血红蛋白表达的丧失导致一氧化氮水平的增加，一氧化氮介导血管系统的修饰和氧化组织中线粒体种群的扩大。该提案的目的是量化+Hb和-Hb南极南极鱼类视网膜的血管密度，表征南极南极鱼类视网膜和心肌中的NOS亚型和催化活性，评估与血管生成（视网膜组织）和线粒体生物生成（心肌）相关的下游因子的表达水平。并确定NOS在体内的抑制是否会导致冰鱼血管生成和线粒体生物生成反应的消退。更广泛的影响包括通过培训青年科学家从基础生物学到加强对临床相关生物医学过程的理解。

The polar ocean presently surrounding Antarctica is the coldest, most thermally stable marine environment on earth. Because oxygen solubility in seawater is inversely proportional to temperature, the cold Antarctic seas are an exceptionally oxygen-rich aquatic habitat. Eight families of a single perciform suborder, the Notothenioidei, dominate the present fish fauna surrounding Antarctica. Notothenioids account for approximately 35% of fish species and 90% of fish biomass south of the Antarctic Polar Front. Radiation of closely related notothenioid species thus has occurred rapidly and under a very unusual set of conditions: relative oceanographic isolation from other faunas due to circumpolar currents and deep ocean trenches surrounding the continent, chronically, severely cold water temperatures, very high oxygen availability, very low levels of niche competition in a Southern Ocean depauperate of species subsequent to a dramatic crash in species diversity of fishes that occurred sometime between the mid-Tertiary and present. These features make Antarctic notothenioid fishes an uniquely attractive group for the study of physiological and biochemical adaptations to cold body temperature. Few distinctive features of Antarctic fishes are as unique as the pattern of expression of oxygen-binding proteins in one notothenioid family, the Channichthyidae (Antarctic icefishes). All channichthyid icefishes lack the circulating oxygen-binding protein, hemoglobin (Hb); the intracellular oxygen-binding protein, myoglobin (Mb) is not uniformly expressed in species of this family. Both proteins are normally considered essential for adequate delivery of oxygen to aerobically poised tissues of animals. To compensate for the absence of Hb, icefishes have developed large hearts, rapidly circulate a large blood volume and possess elaborate vasculature of larger lumenal diameter than is seen in red-blooded fishes. Loss of Mb expression in oxidative muscles correlates with dramatic elevation in density of mitochondria within the cell, although each individual organelle is less densely packed with respiratory proteins. Within the framework of oxygen movement, the adaptive significance of greater vascular density and mitochondrial populations is understandable but mechanisms underlying development of these characteristics remain unknown. The answer may lie in another major function of both Hb and Mb, degradation of the ubiquitous bioactive compound, nitric oxide (NO). The research will test the hypothesis that loss of hemoprotein expression in icefishes has resulted in an increase in levels of NO that mediate modification of vascular systems and expansion of mitochondrial populations in oxidative tissues. The objectives of the proposal are to quantify the vascular density of retinas in +Hb and -Hb notothenioid species, to characterize NOS isoforms and catalytic activity in retina and cardiac muscle of Antarctic notothenioid fishes, to evaluate level of expression of downstream factors implicated in angiogenesis (in retinal tissue) and mitochondrial biogenesis (in cardiac muscle), and to determine whether inhibition of NOS in vivo results in regression of angiogenic and mitochondrial biogenic responses in icefishes. Broader impacts range from basic biology, through training of young scientists, to enhanced understanding of clinically relevant biomedical processes.