Nanoscale remodeling of ryanodine receptor cluster size underlies cerebral microvascular dysfunction in Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) results from mutations in the gene encoding dystrophin which lead to impaired function of skeletal and cardiac muscle, but little is known about the effects of the disease on vascular smooth muscle cells (SMCs). Here we used the mouse model to study the effects of mutant dystrophin on the regulation of cerebral artery and arteriole SMC contractility, focusing on an important Ca-signaling pathway composed of type 2 ryanodine receptors (RyR2s) on the sarcoplasmic reticulum (SR) and large-conductance Ca-activated K (BK) channels on the plasma membrane. Nanoscale superresolution image analysis revealed that RyR2 and BKα were organized into discrete clusters, and that the mean size of RyR2 clusters that colocalized with BKα was larger in SMCs from mice (∼62 RyR2 monomers) than in controls (∼40 RyR2 monomers). We further found that the frequency and signal mass of spontaneous, transient Ca-release events through SR RyR2s ("Ca sparks") were greater in SMCs from mice. Patch-clamp electrophysiological recordings indicated a corresponding increase in Ca-dependent BK channel activity. Using pressure myography, we found that cerebral pial arteries and parenchymal arterioles from mice failed to develop appreciable spontaneous myogenic tone. Inhibition of RyRs with tetracaine and blocking of BK channels with paxilline restored myogenic tone to control levels, demonstrating that enhanced RyR and BK channel activity is responsible for the diminished pressure-induced constriction of arteries and arterioles from mice. We conclude that increased size of RyR2 protein clusters in SMCs from mice increases Ca spark and BK channel activity, resulting in cerebral microvascular dysfunction.