University of Wisconsin-Madison, Department of Forest and Wildlife Ecology, Madison, WI 53706, USA.
Consejo Nacional de Investigaciones Científicas y Técnicas, Instituto Multidisciplinario de Investigaciones Biológicas de San Luis, 5700 San Luis, Argentina.
J Exp Biol. 2021 Feb 3;224(Pt 3):jeb234708. doi: 10.1242/jeb.234708.
Although dietary flexibility in digestive enzyme activity (i.e. reaction rate) is widespread in vertebrates, mechanisms are poorly understood. When laboratory rats are switched to a higher protein diet, the activities of apical intestinal peptidases increase within 15 h, in some cases by rapid increase in enzyme transcription followed by rapid translation and translocation to the intestine's apical, brush-border membrane (BBM). Focusing on aminopeptidase-N (APN), we studied intestinal digestive enzyme flexibility in birds, relying on activity and mRNA data from the same animals. Our model was nestling house sparrows (), already known to modulate intestinal peptidase activity when switching between lower and higher protein diets. Twenty-four hours after a switch from an adequate, lower protein diet to a higher protein diet, APN activity was increased in both whole intestinal tissue homogenates and in isolated BBM, but not at 12 h post-diet switch. Twenty-four hours after a reverse switch back to the lower protein diet, APN activity was decreased, but not at 12 h post-diet switch. Changes in APN activity in both diet switch experiments were associated with parallel changes in APN mRNA. Although transcriptional changes seem to be an important mechanism underlying dietary modulation of intestinal peptidase in both nestling house sparrows and laboratory rodents, the time course for modulation in nestlings seemed slower (taking approximately twice as long) compared with laboratory rodents. It may be ecologically advantageous if nestlings biochemically restructure their gut in response to a sustained increase in insects and protein intake rather than one or a few lucky insect meals.
尽管脊椎动物的消化酶活性（即反应速率）在饮食上具有灵活性，但机制尚不清楚。当实验室大鼠被切换到高蛋白饮食时，肠道顶端的肽酶活性在 15 小时内增加，在某些情况下，通过快速增加酶的转录，随后快速翻译并转运到肠道的顶端，刷状缘膜（BBM）。我们专注于氨肽酶-N（APN），研究了鸟类肠道消化酶的灵活性，依赖于同一动物的活性和 mRNA 数据。我们的模型是雏麻雀（），已知在从低蛋白饮食切换到高蛋白饮食时会调节肠道肽酶的活性。从充足的低蛋白饮食切换到高蛋白饮食后 24 小时，整个肠道组织匀浆和分离的 BBM 中 APN 活性均增加，但在饮食切换后 12 小时没有增加。在反向切换回低蛋白饮食 24 小时后，APN 活性降低，但在饮食切换后 12 小时没有降低。这两种饮食转换实验中 APN 活性的变化与 APN mRNA 的平行变化相关。尽管转录变化似乎是雏麻雀和实验室啮齿动物饮食调节肠道肽酶的重要机制，但与实验室啮齿动物相比，雏鸟的调节时间似乎较慢（大约需要两倍的时间）。如果雏鸟通过生物化学方式重构肠道，以应对昆虫和蛋白质摄入的持续增加，而不是一两次幸运的昆虫餐，那么这可能在生态上是有利的。
