α2-ADRENORECEPTOR ANTAGONIST AMELIORATES SEPSIS-ASSOCIATED PULMONARY FIBROSIS BY SUPPRESSING NOREPINEPHRINE-MEDIATED FIBROBLAST DIFFERENTIATION VIA INHIBITING PKC ACTIVATION

Pulmonary fibrosis is an important factor affecting the prognosis of severe septic patients with acute lung injury. The objective of this study was to explore the effect of norepinephrine (NE) and α2-adrenoreceptor (AR) on sepsis-associated pulmonary fibrosis and the mechanism underlying these effects. We found pulmonary fibrotic changes, and increased NE production and α2A-AR expression in the pulmonary tissue of mice subjected to cecal ligation and puncture surgery. Reserpine and yohimbine alleviated pulmonary fibrosis in mice with sepsis by exhausting NE derived from the lung's adrenergic nerve and blocking α2-AR, respectively. There was no significant difference in the expression of the three α1-AR subtypes. The effect of NE on promoting pulmonary fibroblast differentiation in vitrowas suppressed by yohimbine. Both the protein and mRNA expression levels of α2A-AR were increased in pulmonary fibroblasts treated with LPS. Clonidine, a selective α2-AR agonist, enhanced LPS-induced differentiation in pulmonary fibroblasts, as indicated by the increase in α-smooth muscle actin and collagen I/III, which was mitigated by inhibiting PKC and p38. Further in vivoresults indicated that yohimbine alleviated pulmonary fibrosis and inhibited the phosphorylation of PKC, p38, and Smad2/3 in lung tissue of mice exposed to LPS for 4 weeks. Clonidine showed the opposite effect to yohimbine, which aggravated LPS-induced pulmonary fibrosis. These findings demonstrated that the sepsis-induced increase in NE promoted fibroblast differentiation via activating α2-AR. Blockage of α2-AR effectively ameliorated sepsis-associated pulmonary fibrosis by abolishing NE-induced lung fibroblast differentiation and inhibiting the PKC-p38-Smad2/3 pathway.