Title: T-tubule biogenesis and triad formation in skeletal muscle and implication in human diseases | Skeletal Muscle | Full Text
Headings: T-tubule biogenesis and triad formation in skeletal muscle and implication in human diseases
T-tubule biogenesis and triad formation in skeletal muscle and implication in human diseases
Abstract
Introduction
T-tubule plasticity
Morphological aspects of triad biogenesis
Sarcoplasmic reticulum
Transverse tubule
Molecular mechanisms involved in T-tubule biogenesis and triad formation and maintenance
Table 1 Proteins implicated in triad organization, roles and associated human diseasesa
Caveolin 3
Amphiphysin 2 (BIN1)
Dysferlin
Mitsugumins
Junctophilins
Myotubularin
The RyR-DHPR complex
Conclusion
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Content: In cardiac myofiber, RyR2-mediated calcium release is induced by extracellular calcium entry via DHPR in a mechanism called calcium-induced calcium release (CICR) [ 8 ]. Moreover, in fibers of small diameter, such as the body muscles of Amphioxus, peripheral couplings between SR and the plasmalemma have similar function to triads. In addition, all differentiating muscle fibers pass through a stage where T-tubules are not present and EC coupling is mediated by such peripheral couplings. In this review, we will focus on the molecular mechanisms underlying T-tubules biogenesis and triad formation specifically in skeletal muscle. Triad defects linked to human monogenic diseases will also be highlighted. T-tubule plasticity
The T-tubule membrane possesses a high plasticity which provides the stability required during muscle contraction, and facilitates repair upon damage. In addition to its principal function in EC coupling, the plasticity of T-tubules confers to this system non-related EC functions. It has been reported that the treatment of isolated muscle fibers with glycerol efflux-influx or with other low molecular weight nonelectrolytes (such as sugars) physically affects T-tubules morphology. Such osmotic shock can convert the T-tubule network into many membrane-bound vacuoles, which can either remain interconnected by normal T-tubules, or become separated (Figure 2) [ 9, 10 ]. Surprisingly, this vacuolation which results in 5-15 fold increase in the relative volume of T-tubule system is reversed spontaneously [ 11, 12 ].