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Am J Physiol Heart Circ Physiol. 2017 May 1;312(5):H943-H958. doi: 10.1152/ajpheart.00029.2017. Epub 2017 Mar 10.

Smooth muscle cell-specific deletion of Col15a1 unexpectedly leads to impaired development of advanced atherosclerotic lesions.

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Robert M. Berne Cardiovascular Research Center, University of Virginia, Charlottesville, Virginia.
Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia.
Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, Virginia.
Department of Laboratory Medicine and Pathobiology, Ted Rogers Centre for Heart Research TBEP, University of Toronto, Toronto, Ontario, Canada; and.
Robert M. Berne Cardiovascular Research Center, University of Virginia, Charlottesville, Virginia;
Department of Psychology, University of Virginia, Charlottesville, Virginia.


Atherosclerotic plaque rupture with subsequent embolic events is a major cause of sudden death from myocardial infarction or stroke. Although smooth muscle cells (SMCs) produce and respond to collagens in vitro, there is no direct evidence in vivo that SMCs are a crucial source of collagens and that this impacts lesion development or fibrous cap formation. We sought to determine how conditional SMC-specific knockout of collagen type XV (COL15A1) in SMC lineage tracing mice affects advanced lesion formation given that 1) we have previously identified a Col15a1 sequence variant associated with age-related atherosclerosis, 2) COL15A1 is a matrix organizer enhancing tissue structural integrity, and 3) small interfering RNA-mediated Col15a1 knockdown increased migration and decreased proliferation of cultured human SMCs. We hypothesized that SMC-derived COL15A1 is critical in advanced lesions, specifically in fibrous cap formation. Surprisingly, we demonstrated that SMC-specific Col15a1 knockout mice fed a Western diet for 18 wk failed to form advanced lesions. SMC-specific Col15a1 knockout resulted in lesions reduced in size by 78%, with marked reductions in numbers and proliferating SMCs, and lacked a SMC and extracellular matrix-rich lesion or fibrous cap. In vivo RNA-seq analyses on SMC Col15a1 knockout and wild-type lesions suggested that a mechanism for these effects is through global repression of multiple proatherogenic inflammatory pathways involved in lesion development. These results provide the first direct evidence that a SMC-derived collagen, COL15A1, is critical during lesion pathogenesis, but, contrary to expectations, its loss resulted in marked attenuation rather than exacerbation of lesion pathogenesis.NEW & NOTEWORTHY We report the first direct in vivo evidence that a smooth muscle cell (SMC)-produced collagen, collagen type XV (COL15A1), is critical for atherosclerotic lesion development. SMC Col15a1 knockout markedly attenuated advanced lesion formation, likely through reducing SMC proliferation and impairing multiple proatherogenic inflammatory processes.


atherosclerosis; collagen; collagen type XV α1-gene; lineage tracing; smooth muscle cells

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