Inducible nitric oxide synthase protects vascular smooth muscle cells from cell death stimulated by cyclic mechanical stretch

[Speaker] Jing Zhao:1
[Co-author] Yoji Kyotani:1, Minoru Isosaki:1, Masanori Yoshizumi:1
1:Department of Pharmacology, Nara Medical University, Japan

Background: The pulsatile nature of blood flow exposes vascular smooth muscle cells (VSMCs) in the vessel wall to cyclic mechanical stretch (CMS), which evokes VSMC proliferation, cell death, phenotypic switching and migration, leading to vascular remodeling. These responses have been observed in many cardiovascular diseases; however, the underlying mechanisms remain unclear so far. We have revealed that CMS caused cell death in rat aortic smooth muscle cells (RASMCs) in JNK and p38-dependent manners and that a calcium channel blocker and an angiotensin2 antagonist decreased CMS-induced phosphorylation of JNK and p38 and subsequently, decreased cell death by CMS. To explore the causal role of CMS in initiating cell death signaling and MAPKs (JNK & p38) events, in the present study, we compared transcript profiles of CMS-induced RASMCs death using cDNA microarrays. Ninety-one genes, including the inducible nitric oxide synthase (iNOS) gene, were identified as having significantly differential expression in response to CMS in RASMCs.
Methods: RASMCs were subjected to CMS (60 cycles/min,15% elongation) for 4 hours, then gene expression were detected by quantitative PCR (qPCR) and nitric oxide (NO) production was measured by NO colorimetric assay. Comparison of the MTT and LDH assays were performed for quantifying cell death 24 hours after CMS treatment.
Results: qPCR analysis further identified that CMS induced iNOS expression 2-fold increase in a p38-dependent manner. The results of Colorimetric assay showed that NO production was increased by a 3-fold vs. unstretched cells, implying that NO was synthesized by CMS-induced iNOS. Moreover, blockade of iNOS by inhibitor (1400W) strongly increased CMS-induced cell death in RASMCs; in contrast, a NO donor NONOate significantly inhibited CMS-induced RASMC death, indicating that iNOS protects RASMCs from CMS-stimulated cell death.
Discussion: Taken together, our results of the present study suggested that iNOS gene expression was induced by CMS, which led to the increase of NO production and thus protected RASMCs from CMS-induced cell death. iNOS may play an important role via a new mechanism in the stress response against CMS caused by hypertension.
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