Smad proteins mediate TGFbeta1 effects in ALS muscle

Some familiar forms of Amyotrophic Lateral Sclerosis (ALS) are characterized by a dominant mutation in superoxide dismutase (SOD) 1 gene. Many evidence suggested that SOD1 toxicity is non-cell autonomous, involving multiple cell types: motoneurons, glial cells and muscle cells. In particular, muscle might be a primary source of toxicity, since it is reported that in mice the expression of mutated SOD1 in muscle cells is sufficient to induce motorneuron degeneration and muscle abnormalities already at pre-symptomatic stages. TGFbeta1 is a growth factor known to be involved in neuron survival and in muscle development/maintenance. Furthermore, TGFbeta1 levels are increased in ALS patient serum. Therefore we decided to evaluate the expression of TGFbeta1and Smads (which are involved in the main signal transduction pathway) in the skeletal muscles of transgenic mice expressing mutated hSOD1. The results indicate that mutated hSOD1 up-regulates the expression of TGFbeta1already at the pre-symptomatic stage. The expression of mutated hSOD1 correlated with a decrease of Smad 2 and 4, while the Smad 3 mRNA levels increase. Our previous results indicate that proteasomial and autophagic activity are higher in muscle cells than motorneuron. For this reason we decided to evaluate the effect of TGFbeta1 on the protein quality (PQC) systems of the C2C12 myoblasts measuring the gene expression of different markers. The data indicate that TGFbeta1 is able to modulate the expression of p62, HSPB8, and atrogin, without affecting BAG3 and BAG1 mRNA levels. Our results suggest that ALS skeletal muscles have an increased expression of TGFbeta1, but the action of this growth factor could be impaired by the low level of Smad4 that is necessary to import the TGFbeta1 into the nucleus. Moreover we have demonstrated that TGFbeta1 is able to modulate the PQC pathways. Grants: ARISLA, Telethon-Italy, Fondazione Cariplo, AFM.