Abstract 5311: Proteolysis-resistant Collagen Drives Vascular Smooth Muscle Cell Senescence

Abstract

Senescence of vascular smooth muscle cells (SMCs) has recently been identified as a feature of atherosclerosis. However, the factors that lead to premature SMC senescence are not well understood. Plaque SMCs reside within a milieu of type I collagen fibrils that, over time, can undergo progressive intermolecular cross-linking rendering the collagen resistant to proteol-ysis. We hypothesized that vascular SMC longevity depends on the extent to which the surrounding type I collagen can be proteolytically edited. To test this, we studied mice with a targeted mutation of the 3/4 −1/4 collagenase cleavage site in type I collagen (Col1a1r/r). Mice harboring the Col1a1r/r mutation appeared normal up to 5 months of age but subsequently developed features of premature aging, including shortened lifespan (p<0.01), impaired weight gain (p<0.01), decreased adipose tissue content (p<0.01), and increased kyphosis (p<0.05), the latter two attributes quantified by micro CT imaging. Furthermore, SMCs in the aortic wall of aged, Col1a1r/r mice showed increased accumulation of reactive oxygen species, as assessed by hydroethidine incubation and nuclear fluorescence. To determine if collagenase-resistant collagen directly impacted SMC lifespan, primary human SMCs were cultured on collagen harvested from the tails of wild-type or Col1a1r/r mice. SMCs on mutant collagen displayed a 67% decrease in cumulative population doublings (p<0.01), which was associated with increased senescence-associated beta-galactosidase (SA-β-gal) activity (p<0.05) and increased p21 expression (p<0.05). Furthermore, stress-induced premature senescence, initiated by serum-deprivation and assessed by SA-β-gal activity and p21 expression, was also amplified in cells cultured on collagenase-resistant collagen. Conclusions: Collagenase-resistant type I collagen induces a premature aging-like syndrome in mice and accelerates both replicative and stress-induced senescence of vascular SMCs. These findings identify a novel, extracellular driver of vascular cell senescence that may underlie plaque instability in aging arteries.