Résumé :
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Fragmentation of the neuromuscular junction (NMJ) and a dramatically shortened halflife of the acetylcholine receptor are hallmarks of dystrophic mdx muscle. Since cyclic AMP (cAMP) mediated signalling is thought to be important for aspects of NMJ maintenance we investigated the role of protein kinase A (PKA) in the muscle postsynapse. In particular, we studied the function of A kinase anchoring protein (AKAP)–mediated PKA microdomain organisation for the integrity of the NMJ. Using GFP–based cAMP sensors targeted to the microdomains of the different PKA regulatory subunit isoforms we found the RI?–sensor to be localised in an AKAP–specific manner in the NMJ of wildtype mice. Conversely, in dystrophic mdx mice, the RI?–sensor was mostly displaced from the NMJ. Measurement of cAMP–levels in the different regulatory subunit microdomains in vivo revealed AKAP–dependent microdomain specific responses to different agonists and a strongly altered cAMP handling in dystrophic versus wildtype muscles. Expression of disruptor peptides in wildtype muscles completely abolished the AKAP–dependent localisation of the RI?–sensor in the NMJ and led to a fragmentation of the NMJs similar to that in dystrophic mdx muscles. In summary, our results suggest an important role of AKAP–mediated PKA microdomain organisation for the maintenance of structural integrity of the NMJ.
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