Introduction
Cigarette smoke has a strong correlation with abdominal aortic aneurysm (AAA) formation and is characterized by increased levels of MMP9 in the aorta. We hypothesized that smoke-induced MMP9 regulation is mediated by the Jak/Stat pathway thereby contributing to AAA formation.
Methods
Aqueous extract of cigarette smoke (AEC) was applied to male rat aortic vascular smooth muscle cells (RASMC) for 24 hours (h) in serum free medium (SFM), using SFM alone for controls. Media were collected for MMP2 and MMP9 zymography and proteins extracted from cells for phospho-Stat3 (pStat3), total Stat3 (T-Stat3), phospho-Jak2 (pJak2) and total Jak2 (T-Jak2) western blots. RASMC were transfected by siRNAs for Jak2 and Stat3 before AEC treatment to evaluate induction of MMPs. Coimmunoprecipitation and immunofluorescence microscopy investigated complex formation and cellular distribution of Jak2 and Stat3 following AEC treatment.
Results
MMP9 was increased in the medium of the AEC treated RASMC (P=0.005) and pro-MMP2 slightly elevated (P=0.055) at 24h compared to controls. By western blot protein extracts from AEC treated RASMC showed up regulation of pStat3, pJak2 and T-Jak2 and stable T-Stat3 compared with controls. siRNA transfection of RASMC for Jak2, Stat3 and a combination of Jak2 and Stat3 reduced MMP9 (P<0.005) and pro-MMP2 (P<0.05) in medium of AEC treated RASMC compared with AEC-treated cells transfected with control siRNA. Coimmunoprecipitation of total proteins from RASMC with total Jak2 antibody revealed increased levels of pStat3 in the AEC treated cells compared to controls, while separation of nuclear and cytoplasmic components followed by coimmunoprecipitation revealed more abundant Jak2/T-Stat3 complexes in the nuclear fraction than the cytoplasm following AEC treatment. Immunofluorescence microscopy revealed increased presence of pJak2, T-Jak2, pStat3 and T-Stat3 in the cytoplasm and nucleus of the AEC treated cells compared to the control cells.
Conclusion
This study suggests that cigarette smoke may result in AAA formation through Jak/Stat-mediated MMP9 production. siRNA inhibition of the Jak/Stat pathway greatly reduced AEC-induced MMP9 by RASMC and suggests a potential therapeutic target for the treatment of AAA.
Activation of the JAK-STAT pathway through α1B adrenergic receptor in vascular smooth muscle cells
