Hindle Allyson G, Lawler John M, Campbell Kevin L, Horning Markus
Department of Marine Biology, Texas A&M University at Galveston, Galveston, Texas, USA.
J Exp Zool A Ecol Genet Physiol. 2009 Jun 1;311(5):358-67. doi: 10.1002/jez.534.
Red-toothed (soricine) shrews are consummate predators exhibiting the highest energy turnovers and shortest life spans (ca. 18 months) of any mammal, yet virtually nothing is known regarding their physiological aging. We assessed the emerging pattern of skeletal muscle senescence (contractile/connective tissue components) in sympatric species, the semi-aquatic water shrew (WS), Sorex palustris, and the terrestrial short-tailed shrew (STS), Blarina brevicauda, to determine if muscle aging occurs in wild, short-lived mammals (H(0): shrews do not survive to an age where senescence occurs), and if so, whether these alterations are species-specific. Gracilis muscles were collected from first-year (n=17) and second-year (n=17) field-caught shrews. Consistent with typical mammalian aging, collagen content (% area) increased with age in both species (S. palustris: approximately 50%; B. brevicauda: approximately 60%). Muscle was dominated by stiffer Type I collagen, and the ratio of collagen Type I:Type III more than doubled with age. The area ratio of muscle:collagen decreased with age in both species, but was considerably lower in adult STS, suggesting species-specificity of senescence. Extracellular space was age-elevated in B. brevicauda, but was preserved in S. palustris ( approximately 50 vs. 10% elevation). Though juvenile interspecific comparisons revealed no significance, adult WS myocytes had 68% larger cross-sectional area and occurred at 28% lower fibers/area than those of adult STS. We demonstrate that age-related muscle senescence does occur in wild-caught, short-lived mammals, and we therefore reject this classic aging theory tenet. Our findings moreover illustrate that differential age adjustments in contractile/connective tissue components of muscle occur in the two species of wild-caught shrews.
红齿（鼩鼱科）鼩鼱是技艺高超的捕食者，其能量转换率最高，寿命最短（约18个月），是所有哺乳动物中最短的，但关于它们的生理衰老几乎一无所知。我们评估了同域分布物种——半水生水鼩（WS），即湿地鼩鼱（Sorex palustris）和陆生短尾鼩鼱（STS），即短尾鼩（Blarina brevicauda）骨骼肌衰老（收缩性/结缔组织成分）的新出现模式，以确定肌肉衰老是否发生在野生、寿命短的哺乳动物中（原假设：鼩鼱不会活到衰老发生的年龄），如果是，这些变化是否具有物种特异性。从野外捕获的一岁（n = 17）和两岁（n = 17）鼩鼱身上采集股薄肌。与典型的哺乳动物衰老一致，两种物种（湿地鼩鼱：约50%；短尾鼩：约60%）的胶原蛋白含量（%面积）均随年龄增加。肌肉以更硬的I型胶原蛋白为主，I型与III型胶原蛋白的比例随年龄增加而增加一倍多。两种物种的肌肉与胶原蛋白的面积比均随年龄降低，但成年短尾鼩鼱的该比例要低得多，表明衰老具有物种特异性。短尾鼩鼱的细胞外空间随年龄增加，但湿地鼩鼱的细胞外空间保持不变（升高约50%对10%）。尽管幼年种间比较没有显著差异，但成年水鼩鼱的肌细胞横截面积比成年短尾鼩鼱大68%，且每单位面积的纤维数量比成年短尾鼩鼱少28%。我们证明，与年龄相关的肌肉衰老确实发生在野外捕获的、寿命短的哺乳动物中，因此我们拒绝这一经典衰老理论原则。此外，我们的研究结果表明，在两种野外捕获的鼩鼱中，肌肉收缩性/结缔组织成分的年龄差异调整是存在的。
