Calpains Mediate Integrin Attachment Complex Maintenance of Adult Muscle in Caenorhabditis elegans

Timothy Etheridge,Lewis A Jacobson,Susann Lehmann,Nathaniel J Szewczyk,Brandon D Fields,Freya Shephard,Elizabeth A Oczypok,Gregory A Cox

doi:10.1371/journal.pgen.1002471

Timothy Etheridge, Lewis A Jacobson + Show 6 more

Open Access

https://doi.org/10.1371/journal.pgen.1002471

Copy DOI

Abstract

Two components of integrin containing attachment complexes, UNC-97/PINCH and UNC-112/MIG-2/Kindlin-2, were recently identified as negative regulators of muscle protein degradation and as having decreased mRNA levels in response to spaceflight. Integrin complexes transmit force between the inside and outside of muscle cells and signal changes in muscle size in response to force and, perhaps, disuse. We therefore investigated the effects of acute decreases in expression of the genes encoding these multi-protein complexes. We find that in fully developed adult Caenorhabditis elegans muscle, RNAi against genes encoding core, and peripheral, members of these complexes induces protein degradation, myofibrillar and mitochondrial dystrophies, and a movement defect. Genetic disruption of Z-line– or M-line–specific complex members is sufficient to induce these defects. We confirmed that defects occur in temperature-sensitive mutants for two of the genes: unc-52, which encodes the extra-cellular ligand Perlecan, and unc-112, which encodes the intracellular component Kindlin-2. These results demonstrate that integrin containing attachment complexes, as a whole, are required for proper maintenance of adult muscle. These defects, and collapse of arrayed attachment complexes into ball like structures, are blocked when DIM-1 levels are reduced. Degradation is also blocked by RNAi or drugs targeting calpains, implying that disruption of integrin containing complexes results in calpain activation. In wild-type animals, either during development or in adults, RNAi against calpain genes results in integrin muscle attachment disruptions and consequent sub-cellular defects. These results demonstrate that calpains are required for proper assembly and maintenance of integrin attachment complexes. Taken together our data provide in vivo evidence that a calpain-based molecular repair mechanism exists for dealing with attachment complex disruption in adult muscle. Since C. elegans lacks satellite cells, this mechanism is intrinsic to the muscles and raises the question if such a mechanism also exists in higher metazoans.

Highlights

Muscle is a multifunctional tissue [1,2,3,4] with a well appreciated role in locomotion
In fully developed adult worms, acute RNAi treatment against any one of fourteen genes that encode integrin muscle attachment complex components resulted in loss of a transgene-encoded LacZ reporter of muscle protein degradation in the cytosol (Figure 1A)
As RNAi against the core complex components PAT-2, PAT-3, PAT4, PAT-6, UNC-52, UNC-97, and UNC-112 all yielded protein degradation, it appears that protease activation occurs in response to disruption of the core integrin complex

Summary

Introduction

Muscle is a multifunctional tissue [1,2,3,4] with a well appreciated role in locomotion. The regulation of muscle protein content is an area of broad interest owing to the fact that locomotion is an essential part of being human, the general acceptance that muscle is important for athletic prowess, and because specific muscle wasting is a clinical problem. These wasting conditions have substantial negative impact on mortality [7,8], morbidity, and public health expenditure [9,10]. Muscle size is controlled by signals that regulate the balance of muscle protein synthesis and degradation.

Methods

Results

Conclusion