Abstract Body: The renin-angiotensin system (RAS) regulates vascular function and maintains blood pressure homeostasis. Angiotensin-II (Ang-II) and angiotensin-1-7 (Ang-1-7) have opposing effects on vascular health. Ang-II promotes vascular senescence and pathophysiological remodeling by inducing oxidative stress, inflammation, vascular hypertrophy, and endothelial dysfunction. In contrast, Ang-1-7, known for its vasodilatory, anti-inflammatory, and antioxidative properties, counteracts these detrimental effects, enhancing endothelial function, reducing oxidative stress, and inhibiting inflammation.

Our laboratory has identified the long non-coding RNA CASC15 as a critical regulatory element within the RAS. CASC15 expression is significantly repressed by Ang-II in aortic vascular smooth muscle cells (SMCs), showing a 59.25% decrease compared to the vehicle control (n=10, p=0.000333). Loss of CASC15 induces cellular senescence, increasing senescent cells from a mean of 14.09% (control inhibitor, n=9, SEM=4.824) to 57.79% (CASC15 inhibitor, n=9, SEM=6.420, p<0.0001), and leads to vascular hypertrophy, with cell area increasing from a mean of 46.89% (control inhibitor, n=8, SEM=9.229) to 221.2% (CASC15 inhibitor, n=9, SEM=67.53, p=0.0300).

We hypothesize that CASC15 repression by Ang-II (1 µM) contributes to vascular senescence and increased DNA damage, while Ang-1-7 (1 µM) preserves CASC15 expression and mitigates these effects. Pro-senescent stressors like hydrogen peroxide and doxorubicin also repress CASC15 expression in SMCs. Using RT-qPCR, we observed decreases in CASC15 expression by 29.56% (hydrogen peroxide vs. vehicle, n=4, p=0.0790) and 44.09% (doxorubicin vs. vehicle, n=3, p=0.0733). Ang-1-7 alone did not significantly change CASC15 expression, but combined with Ang-II, it showed potential recovery from 40% repression to 94% recovery. Further research is needed. Immunofluorescence against gamma-H2AX revealed increased DNA damage in SMCs lacking CASC15, with positive foci increasing from 26.27% (control inhibitor, n=4, SEM=1.459) to 63.71% (CASC15 inhibitor, n=4, SEM=1.806, p=0.0009).

In conclusion, CASC15 is a crucial regulator within the RAS. Its repression by Ang-II promotes vascular senescence, hypertrophy, and DNA damage, effects countered by Ang-1-7. Targeting CASC15 could offer new strategies for mitigating vascular aging and improving vascular health, particularly in chronic kidney disease.