Mitigation of Microglia-mediated Acute Neuroinflammation and Tissue Damage by Heme Oxygenase 1 in a Rat Spinal Cord Injury Model

Acute neuroinflammation is the major detrimental factor that causes secondary tissue damage after spinal cord injury (SCI). Curbing neuroinflammation would reduce the neuronal death and benefit functional recovery. In the current study, we used a HO-1-encoding lentivirus to transduce microglia, and adoptively transferred these microglia into injured rat spinal cords. Lentivirus-induced overexpression of exogenous HO-1 significantly inhibited microglia-mediated inflammatory response after SCI, as demonstrated by lower expression of pro-inflammatory mediators in transferred microglia. In addition, the overall post-SCI neuroinflammation was also suppressed by HO-1-overexpressing microglia, as indicated by less leukocyte infiltration and lower pro-inflammatory cytokine production in the spinal cord. Consistently, the tissue damage and neuronal apoptosis were decreased in injured spinal cords, while the locomotor function was moderately improved. We further identified that adenosine 5′-monophosphate-activated protein kinase (AMPK) signaling was involved in the regulatory effect of HO-1 on microglia, because HO-1 overexpression increased the activating phosphorylation of AMPKα. Moreover, the AMPK inhibitor compound C diminished the anti-inflammatory effect of HO-1 in lipopolysaccharide-stimulated microglia in vitro. Taken together, we proved that microglial HO-1 reduced acute post-SCI neuroinflammation. Our study might provide a promising therapeutic approach to benefit SCI recovery.