Altered Immunomodulatory Responses in the CX3CL1/CX3CR1 Axis Mediated by hMSCs in an Early In Vitro SOD1^G93A Model of ALS

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron (MN) disease characterized by progressive MN loss and muscular atrophy resulting in rapidly progressive paralysis and respiratory failure. Human mesenchymal stem/stromal cell (hMSC)-based therapy has been suggested to prolong MN survival via secretion of growth factors and modulation of cytokines/chemokines. We investigated the effects of hMSCs and a hMSC-conditioned medium (CM) on Cu/Zn superoxidase dismutase 1G93A (SOD1G93A) transgenic primary MNs. We found that co-culture of hMSCs and MNs resulted in slightly higher MN numbers, but did not protect against staurosporine (STS)-induced toxicity, implying marginal direct trophic effects of hMSCs. Aiming to elucidate the crosstalk between hMSCs and MNs in vitro, we found high levels of vascular endothelial growth factor (VEGF) and C-X3-C motif chemokine 1 (CX3CL1) in the hMSC secretome. Co-culture of hMSCs and MNs resulted in altered gene expression of growth factors and cytokines/chemokines in both MNs and hMSCs. hMSCs showed upregulation of CX3CL1 and its receptor CX3CR1 and downregulation of interleukin-1 β (IL1β) and interleukin-8 (IL8) when co-cultured with SOD1G93A MNs. MNs, on the other hand, showed upregulation of growth factors as well as CX3CR1 upon hMSC co-culture. Our results indicate that hMSCs only provide moderate trophic support to MNs by growth factor gene regulation and may mediate anti-inflammatory responses through the CX3CL1/CX3CR1 axis, but also increase expression of pro-inflammatory cytokines, which limits their therapeutic potential