HMGB1 Inhibition Protects Schwann Cells from High Glucose-Induced Cytotoxicity

Objective: Damage to Schwann cells play a crucial role in diabetic peripheral neuropathy (DPN) . To observe whether HMGB1 inhibitor (Glycyrrhizic acid, GA) can prevent diabetic Schwann cells damage and its potential mechanisms. Methods: RSC96 cells were divided into 5 groups: NG group (5.6 mmol/L) and HG group (25.0 mmol/L) , HG+GA (1μM) group, HG+GA (10μM) , HG+GA (100μM) . Small interfering RNA was used to knock out HMGB1. CCK8 assay was used to detect the proliferation of RSC96 cells. The levels of inflammatory factors were determined by ELISA. The mRNA expression of NGF and neuritin-1 was detected by qRT-PCR. The expression levels of NSE, cleaved-caspase-3, RAGE, p38MAPK, ERK, JNK and NF-κBp65 in cells were measured by western blot. Results: GA at the concentration of μM for 24h had significant inhibitory effect on HMGB1 synthesis and secretion (P<0.05) . Schwann cell viability in high glucose was restored due to GA and siHMGB1 (P<0.05) . GA intervention and siHMGB1 potently prevented inflammatory substance generation (TNF-α, IL-1β, IL-6, MCP-1 and ICAM-1) , alleviated the neurotrophic factor reduction (NGF and neuritin-1) , and suppressed cellular apoptosis related protein activation (cleaved caspase-3) in Schwann cells exposed to high glucose ambience (P<0.05) . Moreover, we found that RAGE expression, p38MAPK phosphorylation and nuclear NF-κBp65 expression in high glucose-stimulated Schwann cells was reversed by GA or siRNA interference with HMGB1 (P<0.05) . Conclusions: GA and siHMGB1 can not only inhibit HMGB1 expression in Schwann cells exposed to high glucose, but also enhance cell viability. GA and siHMGB1 restored neurotrophic factors level and reduce cleaved caspase-3 expression in Schwann cell due to its anti-inflammatory ability, which may be related to the inhibition of RAGE/p38MAPK/nuclear NF-κBp65 pathway. HMGB1 may implicate in Schwann cells lesion in high glucose milieu and HMGB1 inhibition protects Schwann cells from high glucose induced cytotoxicity. Funding National Natural Science Foundation of China Grant Award (81700723)