Survival of motor neuron protein over-expression prevents calpain-mediated cleavage and activation of procaspase-3 in differentiated human SH-SY5Y cells.

Spinal muscular atrophy (SMA), a neurodegenerative disorder primarily affecting motor neurons, is the most common genetic cause of infant death. This incurable disease is caused by the absence of a functional SMN1 gene and a reduction in full length survival of motor neuron (SMN) protein. In this study, a neuroprotective function of SMN was investigated in differentiated human SH-SY5Y cells using an adenoviral vector to over-express SMN protein. The pro-survival capacity of SMN was assessed in an Akt/PI3-kinase inhibition (LY294002) model, as well as an oxidative stress (hydrogen peroxide) and excitotoxic (glutamate) model. SMN over-expression in SH-SY5Y cells protected against Akt/phosphatidylinositol 3-kinase (PI3-kinase) inhibition, but not oxidative stress, nor against excitotoxicity in rat cortical neurons. Western analysis of cell homogenates from SH-SY5Y cultures over-expressing SMN harvested pre- and post-Akt/PI3-kinase inhibition indicated that SMN protein inhibited caspase-3 activation via blockade of calpain-mediated procaspase-3 cleavage. This study has revealed a novel anti-apoptotic function for the SMN protein in differentiated SH-SY5Y cells. Finally, the cell death model described herein will allow the assessment of future therapeutic agents or strategies aimed at increasing SMN protein levels.