Blockade of Toll-like receptor 4 (TLR4) reduces oxidative stress and restores phospho-ERK1/2 levels in Leydig cells exposed to high glucose

Aims: Hyperglycemia in combination with oxidative stress plays a significant pathophysiological role in diabetic testicular dysfunction, often leading to infertility. Activation of Toll-like receptor 4 (TLR4) has been reported to mediate oxidative stress during diabetes. However, engagement of the TLR4 signaling pathway in diabetic testicular dysfunction has not been previously explored. Herein, we investigated the role of TLR4 in reactive oxygen species (ROS) production and in the phosphorylation status of ERK1/2 in primary Leydig cells exposed to high glucose and in testis isolated from diabetic rats. Main methods: Testicular levels of TLR4 and phospho-ERK1/2 were determined by Western blotting. ROS production was detected with a fluorescent probe. Additionally, primary Leydig cells were exposed to normal (5.5 mmol/l) or elevated (33 mmol/l) glucose concentrations and treated with or without a TLR4 inhibitor, CLI095 (10^{− 5} mol/l) for 24 h, followed by evaluation of TLR4 and phospho-ERK1/2 expression levels by Western blotting and immunofluorescence staining, respectively. Key findings: We show that high glucose induces the expression of TLR4 in Leydig cells. Additionally, we demonstrate that blockade of this receptor in this cell population reduces oxidative stress and restores the levels of phospho-ERK1/2. Significance: Our findings provide new insight into TLR4 interaction with ROS and MEK/ERK pathway in Leydig cells exposed to high glucose and present a rationale for the development of new therapeutics for diabetic testicular dysfunction.