Abstract Body:
Introduction: The incidence of calcific aortic stenosis (CAS) increases markedly in individuals over age 60, but how aging itself increases susceptibility to this process is not well understood. An increase in the burden of senescent cells in aged (geronic) tissues contributes to the onset of CAS. Both passive processes (physiological senescence, or aging) and active processes (pathological, or stress-induced cellular senescence) serve as key elements in the pathogenesis of CAS.
Hypothesis: We hypothesized that aging, a passive process, worsens CAS induced by hyperlipidemia, a pathological process, and tested this idea in a CAS model using hyperlipidemic mice of different ages.
Methods: We injected a single dose of adeno-associated virus serotype-8 (AAV8-PCSK9) to decrease low-density lipoprotein (LDL) receptor expression in 4 or 18 month old C57Bl/6 male mice and fed them with high fat diet (HFD) for 4 months. We validated the PCSK9 injection technique and its plasma level by IVIS imaging and ELISA, respectively. [ns1] We
Results: Western blot analysis showed complete loss of LDL receptors in liver tissues of the PCSK9 injected groups, accompanied by marked hyperlipidemia, as expected. Moreover, comparison heart weight between old and young mice fed with high fat diet showed significantly increased (0.30 ±0.21g) (P<0.05) in old group of mice. After 4 months, echocardiographic analysis revealed significantly increased trans-aortic valvular flow velocities (1211 ± 2.31 mm/s) (P<0.0002) with lower ejection fraction (27.09 ± 0.36%) (P<0.0001) in old mice when compared to young. Of note, young mice on HFD showed less aortic valve systolic dysfunction and more aortic regurgitation compared to old mice. The plasma lipid profiles showed higher LDL cholesterol levels (237.10 ± 1.21) (P<0.0065) in old mice compared with young mice on HFD. Histological assessment revealed increased aortic valve thickness (8.9 ± 0.34 cm) (P<0.0001), increased fibrosis and collagen deposition, along with increased calcification via routine H&E staining as well as special staining. We also validated the morphological deterioration that occurs in aortic valve leaflets of old mice fed with high fat diet with our proteomic findings and immunofluorescence analysis.
Conclusions: Our present findings show that aging exacerbates the CAS process when combined with an active pathological process such as HFD-induced stress.