BACKGROUND Niemann-Pick disease type A (NPDA), a disease caused by mutations in acid sphingomyelinase (ASM), involves severe neurodegeneration and early death. Intracellular lipid accumulation and plasma membrane alterations are implicated in the pathology. ASM is also linked to the mechanism of plasma membrane repair, so we investigated the impact of ASM deficiency in skeletal muscle, a tissue that undergoes frequent cycles of injury and repair in vivo. METHODS Utilizing the NPDA/B mouse model ASM-/- and wild type (WT) littermates, we performed excitation-contraction coupling/Ca2+ mobilization and sarcolemma injury/repair assays with isolated flexor digitorum brevis fibers, proteomic analyses with quadriceps femoris, flexor digitorum brevis, and tibialis posterior muscle and in vivo tests of the contractile force (maximal isometric torque) of the quadriceps femoris muscle before and after eccentric contraction-induced muscle injury. RESULTS ASM-/- flexor digitorum brevis fibers showed impaired excitation-contraction coupling compared to WT, a defect expressed as reduced tetanic [Ca2+]i in response to electrical stimulation and early failure in sustaining [Ca2+]i during repeated tetanic contractions. When injured mechanically by needle passage, ASM-/- flexor digitorum brevis fibers showed susceptibility to injury similar to WT, but a reduced ability to reseal the sarcolemma. Proteomic analyses revealed changes in a small group of skeletal muscle proteins as a consequence of ASM deficiency, with downregulation of calsequestrin occurring in the three different muscles analyzed. In vivo, the loss in maximal isometric torque of WT quadriceps femoris was similar immediately after and 2 min after injury. The loss in ASM-/- mice immediately after injury was similar to WT, but was markedly larger at 2 min after injury. CONCLUSIONS Skeletal muscle fibers from ASM-/- mice have an impairment in intracellular Ca2+ handling that results in reduced Ca2+ mobilization and a more rapid decline in peak Ca2+ transients during repeated contraction-relaxation cycles. Isolated fibers show reduced ability to repair damage to the sarcolemma, and this is associated with an exaggerated deficit in force during recovery from an in vivo eccentric contraction-induced muscle injury. Our findings uncover the possibility that skeletal muscle functional defects may play a role in the pathology of NPDA/B disease.

中文翻译：

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Niemann-Pick A / B型小鼠模型损伤后肌膜修复和骨骼肌功能的缺陷。

背景技术由酸性鞘磷脂酶（ASM）突变引起的A型尼曼-皮克病（NPDA）涉及严重的神经变性和早期死亡。细胞内脂质蓄积和质膜改变与病理有关。ASM也与质膜修复机制有关，因此我们研究了ASM缺乏对骨骼肌的影响，骨骼肌是在体内经历频繁的损伤和修复循环的组织。方法利用NPDA / B小鼠模型ASM-/-和野生型（WT）同窝仔，我们进行激发-收缩偶联/ Ca2 +动员和肌膜损伤/修复测定，包括分离的屈指短肌，短股四头肌，股指屈肌。布雷维斯 胫骨后胫骨和胫后肌，以及股内四头肌偏心收缩引起的肌肉损伤前后的收缩力（最大等距扭矩）的体内测试。结果与野生型相比，ASM-/-屈指短肌短纤维表现出减弱的兴奋-收缩耦合，这种缺陷表现为响应电刺激而减少了破伤性[Ca2 +] i，并在反复的破伤性收缩期间早期维持[Ca2 +] i失败。当ASM-/-屈指短肌纤维被穿刺针机械损伤时，显示出与WT相似的易感性，但再次密封肉瘤的能力降低。蛋白质组学分析显示，由于ASM缺乏，一小群骨骼肌蛋白质发生了变化，而在所分析的三种不同的肌肉中，降钙素的下调。体内，股四头肌WT的最大等距扭矩的损失在受伤后立即和受伤后2分钟相似。损伤后立即在ASM-/-小鼠中的损失与WT相似，但是在损伤后2分钟明显更大。结论来自ASM-/-小鼠的骨骼肌纤维在细胞内Ca2 +的处理中受到损害，从而导致Ca2 +的动员减少，并且在重复的收缩松弛周期中，峰值Ca2 +瞬变更快地下降。分离的纤维显示出降低的对肌膜损伤的修复能力，这与体内偏心收缩引起的肌肉损伤的恢复过程中的力量过大有关。我们的发现揭示了骨骼肌功能缺陷可能在NPDA / B疾病的病理过程中起作用的可能性。