Rationale: SM22 (or transgelin), an actin-binding protein abundant in vascular smooth muscle cells (VSMCs), is downregulated in atherosclerosis, aneurysm and various cancers. Abolishing SM22 in apolipoprotein E knockout mice accelerates atherogenesis. However, it is unclear whether SM22 disruption independently promotes arterial inflammation. Objective: To investigate whether SM22 disruption directly promotes inflammation on arterial injury and to characterize the underlying mechanisms. Methods and Results: Using carotid denudation as an artery injury model, we showed that Sm22 knockout (Sm22 ؊/؊ ) mice developed enhanced inflammatory responses with higher induction of proinflammatory genes, including Vcam1, Icam1, Cx3cl1, Ccl2, and Ptgs2. Higher expression of these genes was confirmed in primary Sm22 ؊/؊ VSMCs and in PAC1 cells after Sm22 knockdown, whereas SM22 recapitulation in primary Sm22 ؊/؊ VSMCs decreased their expression. NFKB2 was prominently activated in both injured carotids of Sm22 ؊/؊ mice and in PAC1 cells after Sm22 knockdown and may mediate upregulation of these proinflammatory genes. As a NF-B activator, reactive oxygen species (ROS) increased in primary Sm22 ؊/؊ VSMCs and in PAC1 cells after Sm22 knockdown. ROS scavengers blocked NF-B activation and induction of proinflammatory genes. Furthermore, Sm22 knockdown increased Sod2 expression and activated p47phox, reflecting contributions of mitochondria and NADPH oxidase to the augmented ROS production; this may result from actin and microtubule cytoskeletal remodeling. Conclusions: Our findings show that SM22 downregulation can induce proinflammatory VSMCs through activation of ROS-mediated NF-B pathways. This study provides initial evidence linking VSMC cytoskeleton remodeling with arterial inflammation. (Circ Res. 2010;106:1351-1362.)Key Words: VSMC Ⅲ SM22 Ⅲ inflammation Ⅲ NF-B Ⅲ ROS S M22, also known as SM22␣ or transgelin, is a 22 kDa protein abundant in the smooth muscle cells (SMCs) of vertebrates. 1 It belongs to the calponin family because it contains an N-terminal calponin homology domain and a C-terminal calponin-like domain. 2 The basic molecular function of SM22 is to bind actin and facilitate the formation of cytoskeletal structures such as stress fibers. 2 SM22 dysregulation is observed in a variety of human diseases. For instance, expression of SM22 is decreased in several types of cancer. 3 Expression of SM22 is also downregulated in atherosclerotic arteries 4,5 and abdominal aortic aneurysms. 6 These findings suggest a correlation between decreased SM22 expression and arterial diseases. However, it is unclear whether the SM22 downregulation promotes the pathogenesis of arterial diseases or whether it is simply a passive outcome.SM22 has been widely used as a SMC marker during embryogenesis and in adult. 7 Sm22 knockout (Sm22 Ϫ/Ϫ ) mice are viable and fertile with uncompromised vasculature development. 8 -10 This suggests that SM22 may be either functionally redundant or compensated during vasculature development. However, th...

Transdifferentiation of vascular smooth muscle cells (VSMC) into chondrogenic cells contributes significantly to vascular calcification during the pathogenesis of atherosclerosis. However, the transcriptional mechanisms that control such phenotypic switch remain unclear. This process is characterized by the induction of Sox9 and Col2a1 genes accompanied by the repression of myocardin (Myocd) and SMC differentiation markers such as SM22, SM α-actin and SM-MHC. Here we explore the regulatory role of SOX9, the master regulator for chondrogenesis, in modulating SMC marker gene expression. qRT-PCR and luciferase assays show that over-expression of SOX9 inhibits SMC gene transcription and promoter activities induced by myocardin, the master regulator of smooth muscle differentiation. Such suppression is independent of the CArG box in the SMC promoters but dependent on myocardin. EMSA assay further shows that SOX9 neither participates in SRF (serum response factor) binding to the CArG box nor interacts with SRF, while co-immunoprecipitation demonstrates an association of SOX9 with myocardin. Conversely, myocardin suppresses SOX9-mediated chondrogenic gene Col2a1 expression. These findings provide the first mechanistic insights into the important regulatory role of SOX9 and myocardin in controlling the transcription program during SMC transdifferentiation into chondrocytes.

These findings suggest that disruption of SM22 alters the actin cytoskeleton and promotes chondrogenic conversion of VSMCs.

BackgroundThe infrarenal abdominal aorta exhibits increased disease susceptibility relative to other aortic regions. Allograft studies exchanging thoracic and abdominal segments showed that regional susceptibility is maintained regardless of location, suggesting substantial roles for embryological origin, tissue composition and site-specific gene expression.ResultsWe analyzed gene expression with microarrays in baboon aortas, and found that members of the HOX gene family exhibited spatial expression differences. HOXA4 was chosen for further study, since it had decreased expression in the abdominal compared to the thoracic aorta. Western blot analysis from 24 human aortas demonstrated significantly higher HOXA4 protein levels in thoracic compared to abdominal tissues (P < 0.001). Immunohistochemical staining for HOXA4 showed nuclear and perinuclear staining in endothelial and smooth muscle cells in aorta. The HOXA4 transcript levels were significantly decreased in human abdominal aortic aneurysms (AAAs) compared to age-matched non-aneurysmal controls (P < 0.00004). Cultured human aortic endothelial and smooth muscle cells stimulated with INF-γ (an important inflammatory cytokine in AAA pathogenesis) showed decreased levels of HOXA4 protein (P < 0.0007).ConclusionsOur results demonstrated spatial variation in expression of HOXA4 in human aortas that persisted into adulthood and that downregulation of HOXA4 expression was associated with AAAs, an important aortic disease of the ageing population.