Abstract 4950: Loss of SM22 Couples Arterial Inflammation With Osteochondrogenesis in a Murine Artery Injury Model
Expression of vascular smooth muscle cell (VSMC) cytoskeleton markers including SM22 is down-regulated in arterial diseases including atherosclerosis where inflammation and calcification are present. However, the role of this down-regulation in arterial pathogenesis is unknown.
Hypothesis: Down-regulation of SM22 may actively contribute to arterial pathogenesis.
Methods: Five Sm22 knockout (Sm22−/−) mice and their wild type littermates were subjected to carotid denudation, an artery injury model. Analyses were conducted on carotids two weeks after injury. 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 osteochondrogenesis 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 COX-2, MCP-1, VCAM-1, ICAM-1 and CX3CL1. The medial osteochondrogenesis was characterized by augmented expression of type II collagen, aggrecan, osteopontin, BMP2, SOX9 and RUNX2. In accordance with the in vivo findings, expression of the aforementioned pro-inflammatory genes and two key osteochondrogenic transcription factors Sox9 and Runx2 was up-regulated 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 osteochondrogenic genes. As an initiator of NF-κB activation, reactive oxygen species (ROS) production was boosted after SM22 knockdown, and ROS scavenging effectively blocked NF-κB activation and induction of these genes. Further, the compromised actin cytoskeleton 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 osteochondrogenesis 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.