Effect of Sildenafil on Autophagy in HL-1 Cells Exposed to Hypoxia

Abstract

Sildenafil, a phosphodiesterase-5 inhibitor more commonly known as Viagra, is shown to have cardioprotective effects. Ischemic cardiomyopathy is the leading type of cardiomyopathy, and heart failure in the U.S. Studies have shown that during an ischemic episode, autophagy is an essential pathway to prevent cell death and survival during conditions of nutrient deprivation of cardiac myocytes. The effects of sildenafil on autophagy are, however, unknown. Using HL-1 cardiac cell line, we treated cultures with varying doses of sildenafil, and bafilomycin, an inhibit autophagosome lysosome fusion. Doing so, LC3-II detection was the best way to detect autophagosome formation and the beginnings of autophagy. Once a sufficient dosage of sildenafil was identified, via a titration of varying concentrations, 10mglmi was chosen as the standard dosage for subsequent experiments. The next step to determine the effect of sildenafil, was to create two groups, a control group and a hypoxia group. The hypoxia group was placed under 0.5% 02 conditions and the control group under normal 02 incubation conditions for 2 hours. A Western blot was carried out and found that LC3-II concentrations were high for those treated with bafilomycin, and under hypoxic conditions sildenafil treated groups showed lower LC3-II concentrations. Furthermore, mTOR, Akt, Ampk, and Erk were probed for, since they are regulatory enzymes involved in autophagy, and it was found that each had a high concentration within both the control group and the hypoxia group. The phosphorylated mTOR, Akt, and Erk also were present. In Conclusion, it can be said that sildenafil is an enhancer of autophagy; yet, the exact mechanism is still unknown. However, our results show that it is most likely an Erk related pathway. Future study of the Erk pathway may yield insight as to how exactly sildenafil affects autophagy.