Targeting RXRα inhibits foamy macrophage formation and neuroinflammation by promoting cholesterol efflux channels post traumatic spinal cord injury.

Abstract

The formation of foamy cells (FMMs) by excessive engulfment of myelin debris (MD) causes secondary neuroinflammation and chronic neuropathies after traumatic spinal cord injury (SCI). It is unclear what the function and mechanism of retinoid X receptor (RXR) α are in FMMs-induced neuroinflammation and neural improvement post SCI. The present study aims to investigate the effects and underlying mechanisms of RXRα activation on FMMs and SCI mice. We established an in vitro FMMs model by MD stimulation and an in vivo SCI model in mice. Using an agonist 2, 4-Di-tert-butylphenol (2, 4-DTBP), we activated RXRα and examined the inflammation levels by PCR, WB, and Immunofluorescence (IF), then detected lipid accumulation by BODIPY and Oil red O staining, and determined secondary neuropathies using IF and histological staining. The locomotor function recovery was assessed using motor evoked potential (MEP), Basso Mouse Scale (BMS), as well as footprint assay. Activation of RXRα by 2, 4-DTBP reduced the expression of interleukin (IL)-6, IL-1β, and tumor necrosis factor (TNF)-α and the levels of inflammatory mediators iNOS and COX-2. Besides, treatment with 2, 4-DTBP increased the expression of cholesterol efflux channels including Abca1, Abcg1, Apoe, and caused a marked decrease in intracellular cholesterol and lipid accumulation. Blocking the RXRα-induced cholesterol efflux caused an increase in cholesterol and FMMs, reversing the prior decrease, and exacerbated the degree of neuroinflammation. Also, administration of 2, 4-DTBP improved the neuropathies and locomotor function recovery after SCI.Taken together, activation of RXRα decreased the formation of FMMs by promoting cholesterol efflux and inhibited neuroinflammation by inhibition of p38 and NF-κB signaling after SCI. It is a promising target for mitigating FMMs-induced neuroinflammation and locomotor dysfunction.