Endothelin-1 induces degeneration of motor neurons: a possible pharmacological target for amyotrophic lateral sclerosis.

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease characterized by progressive loss of motor neurons (MNs) and astrogliosis. Factors secreted by activated astrocytes might contribute to MN degeneration. We have found that endothelin-1 (ET-1), a peptide strongly up-regulated in reactive astrocytes under pathological conditions, is abundantly expressed in reactive astrocytes in the spinal cord of SOD-1 G93A mice and ALS patients and exerts a toxic effect on cultured MNs through activation of astrocytic ET receptors (Ranno et al., Neurobiol Dis. 2014; 65:160-71). In this study, we investigated the mechanisms underlying ET-1 toxicity, focusing on cell survival pathways, such as phosphatidylinositide 3-kinase (PI3K) and JAK-STAT pathways, and/or inflammatory processes. To this aim, mixed spinal cord cultures were treated with ET-1 (100 nM for 48 h) with/without LPS (40 ng/ml) or inhibitors of PI3K (LY294002, 50 uM) and JAK-STAT (AG-490, 50mM). The number of surviving MNs was assessed after treatments by direct counting SMI32-positive neurons. We observed that the inhibition of PI3K pathway or JAK-STAT pathway caused MN death, as expected; however, exposure to ET-1 in the presence of LY294002 did not result in a further increase of MN death whereas a treatment with AG-490 in the presence of ET-1 increased the toxic effect of the peptide. We also observed that LPS induced MN death, but its effect was not additive with that of ET-1. Our results suggest that ET-1 may cause neuronal death by a mechanism that involves the PI3K pathway. An inflammatory component may account for the ET-1 toxicity, but this requires further investigation. Considering the toxic effect that ET-1 exerts on MNs, we can assume that the modulation of ET-1 mediated mechanisms might be envisaged as a new therapeutic approach for ALS.