Disruption of SM22 promotes inflammation after artery injury via nuclear factor kappaB activation.
BACKGROUND
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.


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-kappaB activator, reactive oxygen species (ROS) increased in primary Sm22(-/-) VSMCs and in PAC1 cells after Sm22 knockdown. ROS scavengers blocked NF-kappaB 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-kappaB pathways. This study provides initial evidence linking VSMC cytoskeleton remodeling with arterial inflammation.
Department of Internal Medicine, Wayne State University, Detroit, MI 48201, USA.
Jianbin
J
Shen
Maozhou
M
Yang
Donghong
D
Ju
Hong
H
Jiang
Jian-Pu
JP
Zheng
Zhonghui
Z
Xu
Li
L
Li
D000818:Animals; D020212:Carotid Artery Injuries / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism; D004195:Disease Models, Animal; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D007249:Inflammation / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D018836:Inflammation Mediators / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008840:Microfilament Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D008931:Mitochondria, Muscle / Q000378:metabolism; D009124:Muscle Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000378:metabolism* / Q000473:pathology; D032389:Myocytes, Smooth Muscle / Q000378:metabolism* / Q000473:pathology; D019255:NADPH Oxidases / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism*; D052003:NF-kappa B p52 Subunit / Q000378:metabolism; D010084:Oxidation-Reduction; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics; D013482:Superoxide Dismutase / Q000378:metabolism; D051996:Transcription Factor RelA / Q000378:metabolism; D000099156:Superoxide Dismutase 2
D018836:Inflammation Mediators; D008840:Microfilament Proteins; D009124:Muscle Proteins; D019255:NADPH Oxidases; D016328:NF-kappa B; D052003:NF-kappa B p52 Subunit; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D013482:Superoxide Dismutase; D051996:Transcription Factor RelA; D000099156:Superoxide Dismutase 2; C498207:Nfkb2 protein, mouse; C498144:Rela protein, mouse; C058992:Tagln protein, mouse; C060505:neutrophil cytosolic factor 1