A molecular link between the loss of function of the enzyme MIP/MTMR14 and the muscle defects in mice is reported online this week in Nature Cell Biology. The finding points towards new potential therapeutic targets for certain types of hereditary muscle disorders.
Autosomal centronuclear myopathy belongs to a class of genetic muscle disorders characterized by severe alteration of skeletal muscle structure and metabolism. Inactivating mutations in the gene that encodes the enzyme MIP/MTMR14 have previously been associated with autosomal centronuclear myopathy. Cheng-Kui Qu and colleagues now show that mice that lack MIP/MTMR14, which is essential for the modification of the signalling molecule phosphatidylinositol phosphate (PIP), displayed muscle weakness and fatigue and their muscles produced less contractile force. Rapid changes in levels of intracellular calcium are essential for muscle contraction, and the team showed that, in the absence of MIP/MTMR14, intracellular calcium was abnormally elevated due to accumulation of unmodified PIPs and their ability to bind and activate the calcium release channel RyR1 on intracellular calcium stores.
By providing evidence that fine regulation of the MIP substrates in muscle cells is crucial for maintenance of proper calcium levels and therefore for muscle performance, this study sheds light onto potential new therapy targets of myopathies associated with loss of MIP/MTMR14 function.