Hindle Allyson G, Horning Markus, Mellish Jo-Ann E, Lawler John M
Department of Marine Biology, Texas A&M University at Galveston, 5007 Avenue U, Galveston, TX 77551, USA.
J Exp Biol. 2009 Mar;212(Pt 6):790-6. doi: 10.1242/jeb.025387.
Classic aging theory postulates the absence of pronounced organismal senescence in wild animals since mortality probably occurs first. Large-bodied, long-lived mammals are a recognized exception to this tenet, yet organismal senescence has not been investigated to date in such mammals in the wild. Furthermore, oxidative stress theory of aging supports the suggestion that exercise hypoxia, as regularly incurred during apneustic foraging in diving mammals might lead to cellular dysfunction and accelerated aging. To determine if an aspect of organismal senescence occurs in wild marine mammals, we examined the pattern of skeletal muscle aging (contractile and connective tissue components of longissimus dorsi and pectoralis muscles) in free-ranging adult Weddell seals (9-26 years). The average myocyte cross-sectional area was 22% greater with age in the longissiums dorsi, but no significant increase occurred in the pectoralis. Cross-sectional area was not related to body mass. Changes in myocyte number per area were consistent with the 35-40% age-increase in extracellular space in both muscle groups. Also consistent with extracellular space remodeling, total and relative collagen contents were significantly elevated in older seals (115% in longissimus dorsi; 65% in pectoralis). The ratio of muscle myocyte to collagen declined with age (50-63%) at both sites. Additionally, a shift towards a higher ratio of type I to type III collagen occurred with advancing age in both muscle groups (79% increase in pectoralis; 49% in longissimus dorsi). We reject the classic tenet and null-hypothesis that Weddell seals do not survive to an age where muscular senescence becomes detectable.
经典衰老理论假定野生动物不存在明显的机体衰老，因为死亡可能首先发生。大型长寿哺乳动物是这一原则公认的例外情况，但迄今为止尚未对野生环境中的此类哺乳动物进行过机体衰老研究。此外，衰老的氧化应激理论支持这样一种观点，即潜水哺乳动物在屏气觅食过程中经常出现的运动性低氧可能导致细胞功能障碍和加速衰老。为了确定野生海洋哺乳动物是否存在机体衰老的某个方面，我们研究了自由放养的成年威德尔海豹（9至26岁）骨骼肌衰老的模式（背最长肌和胸肌的收缩和结缔组织成分）。背最长肌中，肌细胞平均横截面积随年龄增长增加了22%，但胸肌中未出现显著增加。横截面积与体重无关。两个肌肉群中每单位面积肌细胞数量的变化与细胞外空间随年龄增长35%至40%的增加一致。同样与细胞外空间重塑一致的是，老年海豹的总胶原蛋白含量和相对胶原蛋白含量显著升高（背最长肌中为115%；胸肌中为65%）。两个部位的肌肉肌细胞与胶原蛋白的比例均随年龄下降（50%至63%）。此外，随着年龄的增长，两个肌肉群中I型胶原蛋白与III型胶原蛋白的比例均向更高水平转变（胸肌中增加79%；背最长肌中增加49%）。我们拒绝接受威德尔海豹不会活到可检测到肌肉衰老的年龄这一经典原则和零假设。
