Nicotinic acetylcholine receptor stability at the NMJ deficient in α-syntrophin in vivo.
α-Syntrophin (α-syn), a scaffold protein, links signaling molecules to the dystrophin-glycoprotein complex. Absence of α-syn from the DGC is known to lead to structurally aberrant neuromuscular junctions (NMJs) with few acetylcholine receptors (AChRs) clustered at synaptic sites. Using α-syn knock-out mice, we show that during the first postnatal week, α-syn is not required for synapse formation. However, at postnatal day 6 (P6)-P7, the structural integrity of the postsynaptic apparatus is altered, the turnover rate of AChRs increases significantly, and the number/density of AChRs is impaired. At the adult α-syn(-/-) NMJ, the turnover rate of AChRs is ∼ 4 times faster than wild-type synapses, and most removed receptors are targeted to degradation as few AChRs recycled to synaptic sites. Biochemical analyses show that in muscle cells of adult knock-out α-syn mice, total AChRs and scaffold protein rapsyn are significantly reduced, the 89 kDa and 75 kDa isoforms of tyrosine phosphorylated α-dystrobrevin (α-dbn) 1 (which are required for the maintenance and stability of AChR in α-dbn(-/-) synapses) are barely detectable. Electroporation of GFP-α-dbn1 in α-syn(-/-) muscle cells partially restored receptor density, turnover rate, and the structural integrity of the postsynaptic apparatus, whereas expression of rapsyn-GFP failed to rescue the α-syn(-/-) synaptic phenotype. These results demonstrate that α-syn is required for the maturation and stability of the postsynaptic apparatus and suggest that α-syn may act via α-dbn1.
Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan 48109, USA.
Isabel
I
Martinez-Pena y Valenzuela
Chakib
C
Mouslim
Marcelo
M
Pires-Oliveira
Marvin E
ME
Adams
Stanley C
SC
Froehner
Mohammed
M
Akaaboune
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D002038:Bungarotoxins / Q000493:pharmacokinetics; D002135:Calcium-Binding Proteins / Q000172:deficiency*; D018274:Electroporation / Q000379:methods; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000235:genetics*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006834:Hydrazines / Q000493:pharmacokinetics; D008297:Male; D008565:Membrane Proteins / Q000172:deficiency*; D051379:Mice; D018345:Mice, Knockout; D018613:Microscopy, Confocal; D009124:Muscle Proteins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D009469:Neuromuscular Junction / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism*; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000235:genetics / Q000378:metabolism*
C417561:Alexa 488 hydrazide; D002038:Bungarotoxins; D002135:Calcium-Binding Proteins; D006834:Hydrazines; D008565:Membrane Proteins; D009124:Muscle Proteins; D009479:Neuropeptides; D012333:RNA, Messenger; D011978:Receptors, Nicotinic; C053386:drebrins; C051609:peripheral membrane protein 43K; C091825:syntrophin alpha1; D049452:Green Fluorescent Proteins