Regulation of spinal neuron axon outgrowth by calcium influx through mechanosensitive TrpC channels

Intracellular calcium signals regulate the development and regeneration of spinal axons downstream of chemical and mechanical cues. Previously, we identified a novel calcium influx pathway through stretch-activated channels (SACs) that inhibits spinal neuron axon outgrowth. Here we show that TRPC1 functions as a SAC on growth cones, which constitutively suppresses neurite outgrowth. Reducing TRPC1 expression with anti-sense morpholinos prevents changes in the rate of axon outgrowth in response to stimuli that activate or inhibit calcium influx through mechanosensitive ion channels. Further, activating SACs increases calcium signals in nerve growth cones that are dependent on TRPC1 expression. The elastic properties of the substratum also modulate calcium signaling in growth cones and the extension of spinal axons in a TRPC1-dependent manner. Downstream of calcium signals, we find that the protease Calpain is activated by calcium influx through TRPC1 containing channels, which likely inhibits the growth promoting effects of the non-receptor tyrosine kinase Src. Together our results suggest that calcium influx through mechanosensitive channels containing TRPC1 subunits activates calpain, which in turn cleaves Src family kinases to restrict neurite outgrowth by developing spinal cord neurons.