Access Type

Open Access Dissertation

Date of Award

January 2012

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Molecular Biology and Genetics

First Advisor

Li Li

Abstract

Background : Expression of vascular smooth muscle cell (VSMC) cytoskeleton markers including SM22 is down-regulated in arterial diseases including atherosclerosis where inflammation and osteochondrogenesis are present. However, the role of this downregulation in arterial pathogenesis is unknown. Hypothesis : Downregulation of SM22 may actively contribute to arterial pathogenesis. Methods : Five Sm22 knockout (Sm22-/-) mice and their wild type littermates were subjected to carotid artery denudation, an artery injury model. Analyses were conducted on carotid arteries 2 weeks after injury. Primary VSMCs were isolated from mouse aortas and investigated individually at passage 2 to 4. Sm22 knockdown was performed in triplicate using siRNA in a VSMC line, PAC1, followed by downstream experiments 3 days after transfection. Results : Sm22-/- mice developed both enhanced arterial inflammatory response and prominent medial chondrogenesis along with remarkable NF-ΚB activation compared to their wild-type littermates. The inflammation was evidenced by excessive artery swelling, macrophage infiltration and high induction of pro-inflammatory molecules including Vcam1, Icam1, Cx3cl1, Ptgs2 and Ccl2. The medial chondrogenesis was characterized by augmented expression of type II collagen, aggrecan, osteopontin, Bmp2 and the key osteochondrogenic transcription factors Sox9. In accordance with the in vivo findings, expression of the aforementioned pro-inflammatory genes and Sox9 was up-regulated in Sm22-/- primary VSMCs and after Sm22 knockdown in PAC1 cells. Interestingly, Sm22 knockdown also led to NF-ΚB activation, and inhibition of NF-ΚB pathway reversed the up-regulation of both pro-inflammatory genes and Sox9. As an initiator of NF-ΚB activation, reactive oxygen species (ROS) production was boosted in Sm22-/- primary VSMCs and after Sm22 knockdown. ROS scavengers effectively blocked NF-ΚB activation and induction of both pro-inflammatory genes and Sox9 after Sm22 knockdown. Further, the altered cell morphology and increased actin dynamics after Sm22 knockdown might contribute to the elevated ROS. Conclusions : These findings suggest that loss of Sm22 in VSMCs coupled injury induced arterial inflammation with chondrogenesis in part via ROS induced NF-ΚB activation and that Sm22 plays both anti-inflammatory and anti-osteochondrogenic roles in arterial diseases partly by maintaining actin cytoskeleton integrity.

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