Sáez Juan C, Cisterna Bruno A, Vargas Anibal, Cardozo Christopher P
Departamento de Fisiología, Pontificia Universidad Católica de Chile, Santiago, Chile,
Cell Mol Life Sci. 2015 Aug;72(15):2929-35. doi: 10.1007/s00018-015-1968-1. Epub 2015 Jun 18.
Myogenic precursor cells express connexins (Cx) and pannexins (Panx), proteins that form different membrane channels involved in cell-cell communication. Cx channels connect either the cytoplasm of adjacent cells, called gap junction channels (GJC), or link the cytoplasm with the extracellular space, termed hemichannels (HC), while Panx channels only support the latter. In myoblasts, Panx1 HCs play a critical role in myogenic differentiation, and Cx GJCs and possibly Cx HCs coordinate metabolic responses during later steps of myogenesis. After innervation, myofibers do not express Cxs, but still express Panx1. In myotubes and innervated myofibers, Panx1 HCs allow release of adenosine triphosphate and thus they might be involved in skeletal muscle plasticity. In addition, Panx1 HCs present in adult myofibers mediate adenosine triphosphate release and glucose uptake required for potentiation of muscle contraction. Under pathological conditions, such as upon denervation and spinal cord injury, levels of Panx1 are upregulated. However, Panx1(-/-) mice show similar degree of atrophy as denervated wild-type muscles. Skeletal muscles also express Cx HCs in the sarcolemma after denervation or spinal cord injury, plus other non-selective membrane channels, including purinergic P2X7 receptors and transient receptor potential type V2 channels. The absence of Cx43 and Cx45 is sufficient to drastically reduce denervation atrophy. Moreover, inflammatory cytokines also induce the expression of Cxs in myofibers, suggesting the expression of these Cxs as a common factor for myofiber degeneration under diverse pathological conditions. Inhibitors of skeletal muscle Cx HCs could be promising tools to prevent muscle wasting induced by conditions associated with synaptic dysfunction and inflammation.
生肌前体细胞表达连接蛋白(Cx)和泛连接蛋白(Panx),这些蛋白形成参与细胞间通讯的不同膜通道。Cx通道连接相邻细胞的细胞质,称为缝隙连接通道(GJC),或将细胞质与细胞外空间相连,称为半通道(HC),而Panx通道仅支持后者。在成肌细胞中,Panx1半通道在肌源性分化中起关键作用,Cx缝隙连接通道以及可能的Cx半通道在肌生成的后期步骤中协调代谢反应。神经支配后,肌纤维不表达Cx,但仍表达Panx1。在肌管和受神经支配的肌纤维中,Panx1半通道允许三磷酸腺苷释放,因此它们可能参与骨骼肌可塑性。此外,成年肌纤维中存在的Panx1半通道介导增强肌肉收缩所需的三磷酸腺苷释放和葡萄糖摄取。在病理条件下,如去神经支配和脊髓损伤时,Panx1水平上调。然而,Panx1基因敲除小鼠显示出与去神经支配的野生型肌肉相似程度的萎缩。去神经支配或脊髓损伤后,骨骼肌在肌膜中也表达Cx半通道,以及其他非选择性膜通道,包括嘌呤能P2X7受体和瞬时受体电位V2型通道。Cx43和Cx45的缺失足以显著减少去神经支配性萎缩。此外,炎性细胞因子也诱导肌纤维中Cx的表达,表明这些Cx的表达是多种病理条件下肌纤维变性的共同因素。骨骼肌Cx半通道抑制剂可能是预防由与突触功能障碍和炎症相关的疾病引起的肌肉萎缩的有前景的工具。