9-Cis-retinoic acid suppresses inflammatory responses of microglia and astrocytes.

Retinoic acid (RA) regulates a wide range of biologic process, including inflammation. Previously, RA was shown to inhibit the clinical signs of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). The current study investigated the effects of 9-cis-RA on primary mouse microglia and astrocytes, two cell types implicated in the pathology of MS and EAE. The studies demonstrated that 9-cis-RA inhibited the production of nitric oxide (NO) as well as the pro-inflammatory cytokines TNF-alpha, IL-1beta and IL-12 p40 by LPS-stimulated microglia. However, this retinoid had no effect on IL-6 secretion and increased MCP-1 production by LPS-stimulated microglia. In LPS-stimulated astrocytes, 9-cis-RA inhibited NO and TNF-alpha production but had not effect on IL-1beta, IL-6 and MCP-1 secretion. These results suggest that RA modulates EAE, at least in part, by suppressing the production of NO and specific inflammatory cytokines from activated glia and suggests that RA might be effective in the treatment of MS.