Intracellular two-phase Ca release and apoptosis controlled by TRP-ML1 channel activity in coronary arterial myocytes

Xu M, Li X, Walsh SW, Zhang Y, Abais JM, Boini KM, Li PL. Intracellular two-phase Ca release and apoptosis controlled by TRPML1 channel activity in coronary arterial myocytes. Am J Physiol Cell Physiol 304: C458–C466, 2013. First published January 2, 2013; doi:10.1152/ajpcell.00342.2012.—Activation of the death receptor Fas has been reported to produce a two-phase intracellular Ca release response in coronary arterial myocytes (CAMs), which consists of local Ca bursts via lysosomal transient potential receptor-mucolipin 1 (TRP-ML1) channels and consequent Ca release from the sarcoplasmic reticulum (SR). The present study was designed to explore the molecular mechanism by which lysosomal Ca bursts are coupled with SR Ca release in mouse CAMs and to determine the functional relevance of this lysosome-associated two-phase Ca release to apoptosis, a common action of Fas activation with Fas ligand (FasL). By confocal microscopy, we found that transfection of CAMs with TRP-ML1 small interfering (si)RNA substantially inhibited FasL (10 ng/ml)-induced lysosome Ca bursts and consequent SR Ca release. In contrast, transfection of CAMs with plasmids containing a full-length TRP-ML1 gene enhanced FasL-induced two-phase Ca release. We further demonstrated that FasL significantly increased the colocalization of the lysosomal marker Lamp1 with ryanodine receptor 3 and enhanced a dynamic trafficking of lysosomes to the SR. When CAMs were treated with TRP-ML1 siRNA, FasL-induced interactions between the lysosomes and SR were substantially blocked. Functionally, FasL-induced apoptosis and activation of calpain and calcineurin, the Ca sensitive proteins that mediate apoptosis, were significantly attenuated by silencing TRP-ML1 gene but enhanced by overexpression of TRP-ML1 gene. These results suggest that TRP-ML1 channel-mediated lysosomal Ca bursts upon FasL stimulation promote lysosome trafficking and interactions with the SR, leading to apoptosis of CAMs via a Ca -dependent mechanism.