Influence of the TLR4-mediated p38MAPK signaling pathway on chronic intermittent hypoxic-induced rat's oxidative stress and inflammatory cytokines in rats

Abstract

Objective: To investigate the influence of the TOLL-like receptor 4 (TLR4)-mediated p38MAPK signaling pathway on chronic intermittent hypoxic (CIH)-induced oxidative stress and inflammatory cytokines in rats.

Materials and methods: A total of 120 healthy male Sprague Dawley (SD) rats, aged between 8-10 weeks, were randomly divided into 9 groups (normoxia control group, CIH 2 weeks group, CIH 4 weeks group, CIH 6 weeks group, CIH 8 weeks group, CIH 6 weeks + p38MAPK receptor inhibit group, CIH 6 weeks + Tempol group, CIH 8 weeks + p38MAPK receptor inhibitor group and CIH 8 weeks + Tempol group). The expression of TLR4 and p38MAPK in the adipose tissue was evaluated, as well as the level of serum oxidative stress markers (SOD, TRx-1, MDA) and inflammatory cytokines (adiponectin, TNF-α, hsCRP and IL-6). RT-PCR and Western-blot were conducted to detect the expression of TLR4 and p38MAPK mRNA.

Results: With increased hypoxia, the levels of SOD and adiponectin in the serum of the CIH group decreased significantly, and the levels of TNF-α, hsCRP, IL-8 and IL-6 in serum increased significantly. After the intervention of antioxidant Tempol and p38MAPK inhibitor SB203580, SOD increased significantly but with significant MDA reduction. The levels of TNF-α, hsCRP, IL-8 and IL-6 in serum significantly decreased. The results of RT-PCR and Western-Blot indicated that the P-p38 and TLR4 proteins related to the MAPK pathway were expressed in rat adipose tissue. With the hypoxia intensity, expression of P-p38 decreased after initially increasing. The expression of TLR4 showed a continuously growing trend. After Tempol treatment, the expression of p38MAPK protein decreased, and the expression of TLR4 did not change significantly, indicating the inhibiting effect of Tempol on p38MAPK, without a significant inhibiting effect on TLR4.

Conclusions: The TLR4-mediated p38MAPK signaling pathway was active in adipose tissue and the expression of the corresponding molecules increased as the duration of intermittent hypoxia increased. The expression of TLR4 and p38MAPK components regulated the level of oxidative stress and inflammatory cytokines; the application of p38MAPK inhibitors and antioxidant free radical scavengers improved the levels of oxidative stress and inflammatory cytokines.