Calpain Knockdown to minimize damage and deficits following SCI

Spinal cord injury often results in permanent motor, sensory, bladder, bowel, and sexual function deficits. This ~s the result of not only the initial physical damage to the spinal cord, but also the secondary degøneration that occurs exacerbates and expands the injury over the over the next sevSal hours to days. One mechanism strongly implicated in this secondary degeneration is dxcessive levels of calciun½ inside cells, leading to the over-activation of caippins Calpains are a family of calcium-activated proteases that degrade many intracellular proteins. Under normal conditions, palpains participate in cell signaling and are important for the ability of cells to migrate and differentiate However, calpains become excessively activated ~fter irjury and then degrade k~y cellular proteins. Thus, the challenge is to preserve the normal fuiiction of calpains but prevent the cell death resulting from their overactivation The major forms in the spinal cord are `referred to as m-calpain and mu-calpain. We recen$ly found that mu-calpain is located in mitochondria. This is of interest, as mitochondria help tp buff~r cellular calcium and also regulate cell death via the release of death-related proteins1 Mu-dalpain participates in the release of at least one such protein, apoptosis inducing factor Thus, mu-calpain is thoughf to act as a pathologic calpain isoform Selective inhibitors of m- and mu-calpain are not avail~ble We will therefore use molecular methods to selectively~ prevent the production mu- or rh-calpain inside cells. We will test the hypothesis that cells døficient in mu-calpain (or m-calpain) will be protected excitotoxic insult, which is implicated in Oell death following spinal cord ihjury. In addition, we will determine if the reduction in mt-ca~pain (or m-calpain) within the spinal cord reduces the degeneration and motor impairment following experimental spinal cçrd injury. The results of these experiments will help àefine the roles of these individual calpain isoforms in the secondary degeneration following spihal cord injury, and identify specific calpain isoforms as therapeutic targets.