Mitochondrial redox signaling enables repair of injured skeletal muscle cells

Abstract

Strain and physical trauma to mechanically active cells, such as skeletal muscle myofibers, injures their plasma membranes, and mitochondrial function is required for their repair. Here we found that mitochondrial function was also needed for plasma membrane repair in myoblasts as well as nonmuscle cells, which depended on mitochondrial uptake of calcium through the mitochondrial calcium uniporter (MCU). Calcium uptake transiently increased the production of mitochondrial reactive oxygen species (ROS), which locally activated the GTPase RhoA, triggering F-actin accumulation at the site of injury and facilitating membrane repair. Blocking mitochondrial calcium uptake or ROS production prevented injury-triggered RhoA activation, actin polymerization, and plasma membrane repair. This repair mechanism was shared between myoblasts, nonmuscle cells, and mature skeletal myofibers. Quenching mitochondrial ROS in myofibers during eccentric exercise ex vivo caused increased damage to myofibers, resulting in a greater loss of muscle force. These results suggest a physiological role for mitochondria in plasma membrane repair in injured cells, a role that highlights a beneficial effect of ROS.

Cellular mechanisms and signals that coordinate plasma membrane repair

“…Depolymerization of densely packed cortical F-actin is thought to free space for vesicle fusion events to occur near the site of injury [14]. Although early disassembly of the cytoskeleton is beneficial, accumulation of F-actin in the later stages of resealing is required for successful repair by aiding in membrane trafficking, wound closure, and providing structural support to the newly formed membrane [16,18,11,19]. In Xenopus and Drosophila models, actin forms a ring structure around the wound area and aids in closure via a purse-string mechanism involving the motor function of myosin [20,21].…”

“…Chelation by calcium-binding proteins can temporarily curb the excess calcium overload in the moments immediately following injury. However, other compartments, such as mitochondria, can selectively take up calcium at the site of injury and help in stably buffering the calcium increase [19]. …”

“…Calcium-dependent activation of PKC β and η isoforms following injury causes PKC β-mediated activation and PKC η-mediated inhibition of GTPase activity, which creates the positive feedback underlying the acute and coordinated amplification of Rho and Cdc42 leading to closure of the plasma membrane wound [86,87]. RhoA also exhibits activation by calcium-triggered mitochondrial redox signaling and this facilitates F-actin reorganization required for repair [19]. In the sections below, we will discuss the interplay of calcium, ROS and other regulators in coordinating Rho GTPases during wound repair.…”

“…Compared to calcium increase after plasma membrane injury, the lifetime of reactive oxygen generating moieties are measured in fractions of seconds. Thus, ROS increase after plasma membrane damage is transient and highly localized to the site of injury where it can facilitate repair by locally activating proteins such as MG53 and RhoA, which facilitate vesicle fusion and cytoskeletal remodeling, respectively [109–111,19]. Chronic ROS increase appears to prevent plasma membrane repair [112].…”

“…Oxidation of RhoA, which contains a redox-sensitive motif, increases its activity [118]. Redox-dependent activation of RhoA facilitates repair by mediating F-actin reorganization (Figure 4b) [19]. Redox-regulation of Rho GTPases may also occur via different mechanisms.…”