Involvement of TRPC in the abnormal calcium influx observed in dystrophic (mdx) mouse skeletal muscle fibers

Abstract

Duchenne muscular dystrophy results from the lack of dystrophin, a cytoskeletal protein associated with the inner surface membrane, in skeletal muscle. The absence of dystrophin induces an abnormal increase of sarcolemmal calcium influx through cationic channels in adult skeletal muscle fibers from dystrophic (mdx) mice. We observed that the activity of these channels was increased after depletion of the stores of calcium with thapsigargin or caffeine. By analogy with the situation observed in nonexcitable cells, we therefore hypothesized that these store-operated channels could belong to the transient receptor potential channel (TRPC) family. We measured the expression of TRPC isoforms in normal and mdx adult skeletal muscles fibers, and among the seven known isoforms, five were detected (TRPC1, 2, 3, 4, and 6) by RT-PCR. Western blot analysis and immunocytochemistry of normal and mdx muscle fibers demonstrated the localization of TRPC1, 4, and 6 proteins at the plasma membrane. Therefore, an antisense strategy was used to repress these TRPC isoforms. In parallel with the repression of the TRPCs, we observed that the occurrence of calcium leak channels was decreased to one tenth of its control value (patch-clamp technique), showing the involvement of TRPC in the abnormal calcium influx observed in dystrophic fibers.

Noninvasive monitoring of therapeutic gene transfer in animal models of muscular dystrophies

“…[36][37][38] This membrane leakage induces abnormal calcium influx followed by activation of the ubiquitous calpains, leading to an excess of unwanted and untimely proteolysis, and finally necrosis of the muscle fiber. [39][40][41] Accordingly, the high numbers of central nuclei found in both models indicate an ongoing cycle of necrosis and regeneration. The two treatments used alleviated the pathophysiological signs, as demonstrated by improved histology and Evans blue dye exclusion.…”

Regulation of TRPC1 and TRPC4 Cation Channels Requires an α1-Syntrophin-dependent Complex in Skeletal Mouse Myotubes

“…Endogenous TRPC4 Interacts with Sarcolemmal TRPC1 in Muscle and Cultured Myotubes-The formation in skeletal muscle cells of heterotetrameric channels associating TRPC1 and TRPC4 was explored because the use of antisense had suggested previously that store-operated calcium currents recorded in fibers are dependent on the expression level of TRPC1 and TRPC4 channels (22). Moreover, TRPC1 translocation into the plasma membrane has been shown to depend upon the expression of TRPC4 at the membrane (32).…”

“…The activity of MS channels (25)(26)(27) and SOCs (22) is higher in dystrophin-deficient muscle cells. The sarcolemma of dystrophin-deficient muscle also displays cation channels that are active when muscles are at rest, with greater open probability (28), and an antisense strategy suggested that the spontaneously active channels are constituted by TRPC protein (22). These studies and others led to the hypothesis that the DAPC may control TRPC-MS/ SOC channels at the sarcolemma and that is involved in regulating subsarcolemmal calcium concentration.…”

“…At the sarcolemma, TRPC1 and TRPC4 are involved in a cationic channel with activity enhanced by the depletion of calcium stores by thapsigargin (22) and with many biophysical properties similar to those of the mechanosensitive (MS) channels recorded in the same preparation (23). Moreover, a stretch-activated channel, as well as a SOC, was shown to be encoded by the TRPC1 gene (24).…”

“…Because TRPC1 has the ability to form heteromeric channels, the association with other TRPC was explored. Several contributions have shown that TRPC1 and TRPC4 associate to build a cation channel that is permeable to calcium (31) and that reducing TRPC1 and TRPC4 expression decreases the occurrence of store-operated currents recorded at the sarcolemma of muscle fibers (22).…”