Tischler M E, Rosenberg S, Satarug S, Henriksen E J, Kirby C R, Tome M, Chase P
Department of Biochemistry, University of Arizona Health Sciences Center, Tucson.
Metabolism. 1990 Jul;39(7):756-63. doi: 10.1016/0026-0495(90)90113-q.
Mechanisms of accelerated proteolysis were compared in denervated and unweighted (by tail-cast suspension) soleus muscles. In vitro and in vivo proteolysis were more rapid and lysosomal latency was lower in denervated than in unweighted muscle. In vitro, lysosomotropic agents (eg, chloroquine, methylamine) did not lessen the increase in proteolysis caused by unweighting, but abolished the difference in proteolysis between denervated and unweighted muscle. Leucine methylester, an indicator of lysosome fragility, lowered latency more in denervated than in unweighted muscle. 3-Methyladenine, which inhibits phagosome formation, increased latency similarly in all muscles tested. Mersalyl, a thiol protease inhibitor, and 8-(diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride (TMB-8), which antagonizes sarcoplasmic reticulum release of Ca2+, reduced accelerated proteolysis caused by unweighting without diminishing the faster proteolysis due to denervation. Calcium ionophore (A23187) increased proteolysis more so in unweighted than control muscles whether or not Ca2+ was present. Different mechanisms of accelerated proteolysis were studied further by treating muscles in vivo for 24 hours with chloroquine or mersalyl. Chloroquine diminished atrophy of the denervated but not the unweighted muscle, whereas mersalyl prevented atrophy of the unweighted but not of the denervated muscle, both by inhibiting in vivo proteolysis. These results suggest that (1) atrophy of denervated, but not of unweighted, soleus muscle involves increased lysosomal proteolysis, possibly caused by greater permeability of the lysosome, and (2) cytosolic proteolysis is important in unweighting atrophy, involving some role of Ca2(+)-dependent proteolysis and/or thiol proteases.
对去神经支配和失重（通过尾吊悬挂）的比目鱼肌中加速蛋白水解的机制进行了比较。去神经支配的肌肉中，体外和体内蛋白水解都更快，溶酶体潜伏性比失重肌肉更低。在体外，溶酶体促渗剂（如氯喹、甲胺）不会减轻失重引起的蛋白水解增加，但消除了去神经支配肌肉和失重肌肉之间蛋白水解的差异。亮氨酸甲酯是溶酶体脆弱性的指标，在去神经支配的肌肉中比在失重肌肉中更能降低潜伏性。抑制吞噬体形成的3-甲基腺嘌呤在所有测试肌肉中同样增加潜伏性。巯基蛋白酶抑制剂汞撒利和拮抗肌浆网释放Ca2+的盐酸8-（二乙氨基）辛基-3,4,5-三甲氧基苯甲酸酯（TMB-8）减少了失重引起的加速蛋白水解，而不会减少去神经支配导致的更快蛋白水解。无论是否存在Ca2+，钙离子载体（A23187）在失重肌肉中比对照肌肉更能增加蛋白水解。通过在体内用氯喹或汞撒利处理肌肉24小时，进一步研究了加速蛋白水解的不同机制。氯喹减少了去神经支配肌肉的萎缩，但没有减少失重肌肉的萎缩，而汞撒利通过抑制体内蛋白水解防止了失重肌肉的萎缩，但没有防止去神经支配肌肉的萎缩。这些结果表明：（1）去神经支配的比目鱼肌萎缩（而非失重的比目鱼肌萎缩）涉及溶酶体蛋白水解增加，可能是由溶酶体更大的通透性引起的；（2）胞质蛋白水解在失重性萎缩中很重要，并涉及Ca2+依赖性蛋白水解和/或巯基蛋白酶的某种作用。
