Neuroprotective effect of aldose reductase knockout in a mouse model of spinal cord injury involves NF-κB pathway

The inflammatory response following spinal cord injury (SCI) involves the activation of resident microglia and the infiltration of macrophages. Activated microglia/macrophages have either detrimental or beneficial effects on neural regeneration based on their functional polarized M1/M2 subsets. Aldose reductase (AR) has recently been shown to be a key component of the innate immune response. However, the mechanisms involved in AR and innate immune response remain unclear. In this study, wild-type (WT) or AR-deficiency (KO) mice were subjected to SCI by a spinal crush injury model. AR KO mice showed better locomotor recovery and smaller injury lesion areas after spinal cord crushing compared with WT mice. Here, we first demonstrated that AR deficiency repressed the expression level of inducible nitric oxide synthase (iNOS) induced by lipopolysaccharide (LPS) in vitro via the activation of autophagy. AR deficiency caused 4-hydroxy-2-(E)-nonenal (4-HNE) accumulation in LPS-induced macrophages. We also found that exogenous addition of low concentrations of 4-HNE in LPS-induced macrophages had the effect of promoting further activation of NF-κB pathway, whereas high concentrations of 4-HNE had inhibitory effects. Together, these results indicated that autophagy as a mechanism underlying AR and 4-HNE in LPS-induced macrophages.