Ubiquitin carboxyl-terminal hydrolase L1 is required for maintaining the structure and function of the neuromuscular junction

Abstract

The enzyme ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) is one of the most abundant proteins in the mammalian nervous system. In humans, UCH-L1 is also found in the ubiquitinated inclusion bodies that characterize neurodegenerative diseases in the brain, suggesting its involvement in neurodegeneration. The physiologic role of UCH-L1 in neurons, however, remains to be further elucidated. For example, previous studies have provided evidence both for and against the role of UCH-L1 in synaptic function in the brain. Here, we have characterized a line of knockout mice deficient in the UCH-L1 gene. We found that, in the absence of UCH-L1, synaptic transmission at the neuromuscular junctions (NMJs) is markedly impaired. Both spontaneous and evoked synaptic activity are reduced; paired pulse-facilitation is impaired, and synaptic transmission fails to respond to high-frequency, repetitive stimulation at the NMJs of UCH-L1 knockout mice. Morphologic analyses of the NMJs further revealed profound structural defects-loss of synaptic vesicles and accumulation of tubulovesicular structures at the presynaptic nerve terminals, and denervation of the muscles in UCH-L1 knockout mice. These findings demonstrate that UCH-L1 is required for the maintenance of the structure and function of the NMJ and that the loss of normal UCH-L1 activity may result in neurodegeneration in the peripheral nervous system. electrophysiology | knockout mice | neurodegeneration | synaptic transmission

Recessive loss of function of the neuronal ubiquitin hydrolase UCHL1 leads to early-onset progressive neurodegeneration

“…In addition, myokymia was observed in affected subjects, consistent with UCHL1's role in the neuromuscular junction (15). The ataxia and muscular phenotypes in individuals with the homozygous UCHL1 GLU7ALA mutation are consistent with the phenotypes of the gracile axonal dystrophy (gad) mouse, harboring a spontaneous in-frame deletion in Uchl1 that results in a truncated protein, as well as those of the Uchl1 KO mice that lack the entire Uchl1 protein (15)(16)(17).…”

“…Neuropathological findings included nerve fiber loss with astrocytic proliferation and considerable axonal swellings in the gracile fascicles of the spinal cord along with axonal degeneration and formation of spheroid bodies in the nerve terminals (16,18,19). Similarly, recently generated Uchl1 KO mice have been shown to suffer from markedly impaired synaptic transmission at the neuromuscular junction accompanied by structural defects such as loss of synaptic vesicles and accumulation of tubulovesicular structures at the presynaptic nerve terminals in addition to denervation of the muscles (15). The phenotypes of both of these Uchl1 mouse models closely resemble that of our patients, with the exception of lack of optic nerve degeneration in the Uchl1 KO mice, examined at about 4 mo of age.…”

Increased Neurotransmitter Release at the Neuromuscular Junction in a Mouse Model of Polyglutamine Disease

“…To minimize errors in the quantal content estimation, we have corrected the effect of nonlinear summation on EPP amplitude as previously described (McLachlan and Martin, 1981) using a correction factor ( f ϭ 0.8) (see Materials and Methods). The introduction of that factor improves overcorrection introduced by older methods (Martin, 1955), and it has been used in different mouse neuromuscular preparations (Plomp et al, 1992;Wood and Slater, 1997;Bullens et al, 2002;Bewick et al, 2004;Chen et al, 2010). Current-clamp measurements of quantal content could be relatively inaccurate if compared with absolute quantal content values obtained with voltage-clamp recordings as previously described in other preparations (Wood and Slater, 1997).…”

To build a synapse: signaling pathways in neuromuscular junction assembly

“…Direct interactions between nerve terminals and muscle fibers might be mediated by adhesion molecules, including neural cell adhesion molecule [NCAM (Polo-Parada et al, 2004)], CD24 [a glycosylphosphatidylinositol (GPI)-linked protein (Jevsek et al, 2006)], the immunoglobin proteins Syg1 and Syg2 (Shen and Bargmann, 2003;Shen et al, 2004), and embigin (Lain et al, 2009). However, the mechanisms by which NMJ development is regulated by cell adhesion remain to be elucidated.Finally, recent studies have identified several genes the mutation of which leads to NMJ development defects, including the neuronspecific splicing factors Nova1 and Nova2 (Ruggiu et al, 2009), amyloid precursor protein (APP) , dystrophinassociated proteins (Adams et al, 2004; Banks et al, 2009;Grady et al, 2000;Grady et al, 2003), the glycosyltransferase Large , the protein degradation components Fbxo45, Nedd4, Usp14 and Uchl1 (Chen et al, 2009;Chen et al, 2010;Liu et al, 2009;Saiga et al, 2009), the chromatin organization protein HP1 (Aucott et al, 2008) and meltrin b, a metalloprotease (Yumoto et al, 2008). These studies demonstrate that the complexity involved in the formation of this simple, large peripheral synapse is only beginning to be unravelled.…”