Degenerin channel activation causes caspase-mediated protein degradation and mitochondrial dysfunction in adultC. elegansmuscle

Abstract

BackgroundDeclines in skeletal muscle structure and function are found in various clinical populations, but the intramuscular proteolytic pathways that govern declines in these individuals remain relatively poorly understood. The nematode Caenorhabditis elegans has been developed into a model for identifying and understanding these pathways. Recently, it was reported that UNC‐105/degenerin channel activation produced muscle protein degradation via an unknown mechanism.MethodsGeneration of transgenic and double mutant C. elegans, RNAi, and drug treatments were utilized to assess molecular events governing protein degradation. Western blots were used to measure protein content. Cationic dyes and adenosine triphosphate (ATP) production assays were utilized to measure mitochondrial function.Results unc‐105 gain‐of‐function mutants display aberrant muscle protein degradation and a movement defect; both are reduced in intragenic revertants and in let‐2 mutants that gate the hyperactive UNC‐105 channel. Degradation is not suppressed by interventions suppressing proteasome‐mediated, autophagy‐mediated, or calpain‐mediated degradation nor by suppressors of degenerin‐induced neurodegeneration. Protein degradation, but not the movement defect, is decreased by treatment with caspase inhibitors or RNAi against ced‐3 or ced‐4. Adult unc‐105 muscles display a time‐dependent fragmentation of the mitochondrial reticulum that is associated with impaired mitochondrial membrane potential and that correlates with decreased rates of maximal ATP production. Reduced levels of CED‐4, which is sufficient to activate CED‐3 in vitro, are observed in unc‐105 mitochondrial isolations.ConclusionsConstitutive cationic influx into muscle appears to cause caspase degradation of cytosolic proteins as the result of mitochondrial dysfunction, which may be relevant to ageing and sarcopenia.

DRP-1-mediated apoptosis induces muscle degeneration in dystrophin mutants

“…4B ) confirming that CED-3 plays an important role in dystrophin-dependent muscle degeneration. Interestingly, degenerin-dependent muscle degeneration in C. elegans also depends on CED-3 74 . All the RNAi against executors of cell death tested provoked a decrease in the number of abnormal muscle in dys-1(cx18);hlh-1(cc561ts) mutant worms ( dys-1(cx18);hlh-1(cc561ts) mutant worms fed with: cps-6 RNAi: 5,01 +/− 0,32 abnormal muscle cells; wah-1 RNAi: 5,00 +/− 0,37 abnormal muscle cells; crn-2 RNAi: 4,81+/0,19 abnormal muscle cells; nuc-1 RNAi: 6,25 +/− 0,25 abnormal muscle cells; crn-6 RNAi: 6,53 +/− 0,26 abnormal muscle cells; ced-1 RNAi: 5,50 +/− 0,29 abnormal muscle cells; psr-1 RNAi: 5,31 +/− 0,24 abnormal muscle cells vs dys-1(cx18);hlh-1(cc561ts) mutant worms fed with the empty vector L4440: 9,63 +/− 0,24 abnormal muscle cells) (Fig.…”

Functional phosphatome requirement for protein homeostasis, networked mitochondria, and sarcomere structure in C. elegans muscle

“…Far left (green): caspase activation is induced by mitochondrial dysfunction, which can be caused by loss of degenerin channel contact with collagen in the extracellular matrix. 19 Left (violet): degradation by calpains is regulated by integrin attachment to the basement membrane, 18 and a significant portion of the integrin adhesome appears to contribute to this regulation. 16 Middle (yellow): autophagic degradation is controlled by a balance of signal from insulin/insulin-like receptor (negative regulator, green lines) and autocrine fibroblast growth factor signal (positive regulator, red lines).…”

“…20 Right (pink): intracellular calcium controlled by a combination of membrane depolarization, and G-protein signalling events are required to negatively regulate proteasome-based degradation. 15,17 Displayed model is adapted from models published in Shephard et al 17 and Gaffney et al 19 (B) A schematic of the full RNA interference screen can be found in the kinase screen 20 which this phosphatase screen is based upon. Briefly, for identification of phosphatase, genes whose knockdown induced autophagic protein degradation was achieved through four steps: (1) genes for which RNA interference produced decreased amounts of reporter protein in muscle were identified.…”

“…(A) The model is only from studying the degradation of a single transgenically encoded reporter protein. Far left (green): caspase activation is induced by mitochondrial dysfunction, which can be caused by loss of degenerin channel contact with collagen in the extracellular matrix 19. Left (violet): degradation by calpains is regulated by integrin attachment to the basement membrane,18 and a significant portion of the integrin adhesome appears to contribute to this regulation 16.…”

“…Its small size, transparency, and rapid development coupled with the genetic and genomic tools available make it an ideal model for foundational studies. 4 The worm has been used to study muscle development, 5 muscular dystrophy, 6 fat metabolism, 7 sarcopenia, 8 spaceflight-induced changes in muscle, 9 and muscle protein degradation ( Figure 1A); [10][11][12][13][14][15][16][17][18][19] in each instance, the uncovered genes, signals, and/or underlying concepts of control mechanism(s) have been found to have direct relevance to the same processes and/or conditions in humans.…”