Muscle-Derived Collagen XIII Regulates Maturation of the Skeletal Neuromuscular Junction

Abstract

Formation, maturation, stabilization, and functional efficacy of the neuromuscular junction (NMJ) are orchestrated by transsynaptic and autocrine signals embedded within the synaptic cleft. Here, we demonstrate that collagen XIII, a nonfibrillar transmembrane collagen, is another such signal. We show that collagen XIII is expressed by muscle and its ectodomain can be proteolytically shed into the extracellular matrix. The collagen XIII protein was found present in the postsynaptic membrane and synaptic basement membrane. To identify a role for collagen XIII at the NMJ, mice were generated lacking this collagen. Morphological and ultrastructural analysis of the NMJ revealed incomplete adhesion of presynaptic and postsynaptic specializations in collagen XIII-deficient mice of both genders. Strikingly, Schwann cells erroneously enwrapped nerve terminals and invaginated into the synaptic cleft, resulting in a decreased contact surface for neurotransmission. Consistent with morphological findings, electrophysiological studies indicated both postsynaptic and presynaptic defects in Col13a1 ؊/؊ mice, such as decreased amplitude of postsynaptic potentials, diminished probabilities of spontaneous release and reduced readily releasable neurotransmitter pool. To identify the role of collagen XIII at the NMJ, shed ectodomain of collagen XIII was applied to cultured myotubes, and it was found to advance acetylcholine receptor (AChR) cluster maturation. Together with the delay in AChR cluster development observed in collagen XIII-deficient mutants in vivo, these results suggest that collagen XIII plays an autocrine role in postsynaptic maturation of the NMJ. Altogether, the results presented here reveal that collagen XIII is a novel muscle-derived cue necessary for the maturation and function of the vertebrate NMJ.

Multiple roles of integrin-α3 at the neuromuscular junction

“…6). Similar defects are also observed in mutants for laminin-α4, collagen IV (the α5 chain), collagen XIII and nidogen-2, suggesting that interactions between a range of basal lamina proteins and integrins may be important for synaptic maintenance (Fox et al, 2007(Fox et al, , 2008Latvanlehto et al, 2010;Samuel et al, 2012). Consistent with this finding is altered autophagy (Fig.…”

“…Using these mice, and also heterozygotes, which survive after birth, we demonstrate that integrin-α3 plays a role in the localisation of AZ components and synaptic vesicle release at the NMJ. In addition, the NMJs of heterozygous mice progressively accumulate morphological features that are found in aged (∼2 year old) wild-type (WT) animals, and in a number of mouse models with neurodegeneration or NMJ defects, suggesting a role in synaptic maintenance (Fox et al, 2007(Fox et al, , 2008Latvanlehto et al, 2010;Samuel et al, 2012). Surprisingly, we also observed instances of localised detachment of presynaptic terminals from the basal lamina, suggesting that integrin-α3 mediates anchorage of the pre-and postsynaptic elements at the NMJ.…”

“…Data are mean±s.e.m., Student's t-test. detachment phenotype (Latvanlehto et al, 2010;Maselli et al, 2009). Intriguingly, the basal lamina always remained localised at the postsynaptic region (Fig.…”

“…Previous studies have shown that defects in a number of ECM proteins are associated with reduced nerve adhesion at the NMJ. These proteins include collagen XIII in the mouse, laminin-β2 in humans (who present with congenital myasthenia), and collagen IV and laminin A in Drosophila (Koper et al, 2012;Latvanlehto et al, 2010;Maselli et al, 2009). However, despite comprehensive interrogation by genetic means, no cell surface receptors have been identified (Koper et al, 2012).…”

Amotl2 interacts with LL5β, localizes to podosomes and regulates postsynaptic differentiation in muscle

“…In contrast, relatively little is known about the molecular machinery that orchestrates postnatal postsynaptic maturation, perhaps in part because this process is likely to be more complicated than initial aggregation (Shi et al, 2012). Proteins that have been implicated include components of the extracellular matrix that runs through the synaptic cleft [laminins, collagens and nidogens (Fox et al, 2007;Fox et al, 2008;Latvanlehto et al, 2010;Nishimune et al, 2008;Shi et al, 2012)], the guanine exchange factor (GEF) ephexin-1 (Shi et al, 2010a;Shi et al, 2010b), and components of the dystrophin glycoprotein complex such as dystrobrevin (Grady et al, 2000;Grady et al, 2003). Interestingly, several of these proteins have also been implicated in plasticity of synapses the central nervous system (Fu et al, 2007;Michaluk et al, 2007;Shi et al, 2010b).…”