Disruption of SM22 Promotes Inflammation After Artery Injury via Nuclear Factor κB Activation

Abstract

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...

Nutritional B vitamin deficiency alters the expression of key proteins associated with vascular smooth muscle cell proliferation and migration in the aorta of atherosclerotic apolipoprotein E null mice

“…Reduced expression of transgelin-1 (sm22a) is related to VSMC proliferation and atherosclerotic plaque formation (Feil et al 2004;Shen et al 2010). Transgelin expression was strongly downregulated in the aorta of mice fed a highfat and combined B vitamin-depleted diet.…”

Molecular Biology of Atherosclerosis

“…VSMC in SM22 KO mice had increased NF-B activation upon carotid arterial injury with greater adhesion molecule expression possibly related to greater ROS production associated with cytoskeletal disruption (1614).…”

Phosphorylation of Smooth Muscle 22α Facilitates Angiotensin II–Induced ROS Production Via Activation of the PKCδ-P47 phox Axis Through Release of PKCδ and Actin Dynamics and Is Associated With Hypertrophy and Hyperplasia of Vascular Smooth Muscle Cells In Vitro and In Vivo

“…These data suggest that disruption of SM22␣ may be responsible for activation of p47 phox and ROS production in VSMCs, as previously shown. 15 Phosphorylation of SM22␣ at Ser181 Mediates P47 phox Activation and ROS Production Via Promoting Interaction of PKC␦ With P47 phox It has been known that Ang II-induced ROS production occurs in early and later 2 phases. 25,26 To confirm the possible roles of SM22␣ in early oxidative stress, based on 3 potential phosphorylation sites in SM22␣, 16 an immunoprecipitation assay was performed to examine the phosphorylation of SM22␣.…”

“…The latest study has revealed that the disruption of smooth muscle (SM) 22␣, an actin-associated protein, induces vascular inflammation through activation of ROS-mediated NF-B pathways. 15 SM22␣ is a member of the calponin family, containing a calponin homology domain conserved from yeast to human. 16,17 The known function of SM22␣ is to bundle and stabilize actin filaments, which is involved in actin filament assembly and cytoskeletal rearrangements.…”

“…21 Because SM22␣ is an actin-associated protein, and NADPH oxidase activation may be affected by change in actin cytoskeleton organization, 22 cytoskeleton remodeling induced by disruption of SM22␣ in VSMCs may activate multiple ROS production machineries. 15 The precise mechanism of SM22␣ in controlling oxidative stress remains to be identified.…”