Abstract 131: PDE1 Inhibition Improves Cardiac Protein Quality Control

Abstract

Protein quality control (PQC) functions to minimize the level and toxicity of misfolded proteins in the cell. PQC relies on molecular chaperones and the targeted degradation of misfolded proteins. The latter is currently known to require the ubiquitin-proteasome system (UPS) and the autophagic-lysosomal pathway (ALP). Virtually all cardiovascular diseases end up heart failure (HF), the leading cause of death of our society. UPS function insufficiency is implicated in the genesis of a large subset of HF, making cardiac PQC enhancement via promoting UPS and ALP function a promising therapeutic strategy to treat HF. Previously, we have demonstrated that stimulating protein kinase G (PKG) genetically or via inhibition of the type 5 phosphodiesterase (PDE5) improves UPS performance, facilitates the removal of misfolded proteins in cardiomyocytes and slows down the progression of cardiac proteinopathy in a transgenic mouse model (CryAB R120G ). PKA has also been shown to enhance proteasomal function. Our preliminary studies reveal that myocardial protein levels of PDE1A, which suppresses both PKG and PKA, are remarkably elevated in the CryAB R120G mice. Hence we hypothesize that PDE1 inhibition (PDE1I) stimulates cardiac proteasomes via PKG and PKA activation and thereby protects against cardiac proteotoxicity. To test our hypothesis, we took advantage of a proven surrogate UPS substrate (GFPu or GFPdgn) as well as a bona fide misfolded protein (CryAB R120G ) that is known to induce cardiac proteinopathy in human and mice. In cultured cardiomyocytes, PDE1 inhibitor LSN2790158 dose- and time-dependently decreased GFPu. Cycloheximide (CHX) chase assays further confirmed that PDE1I shortened the half-life of GFPu, indicative of improved UPS performance. Furthermore, PDE1I promoted the degradation of CryAB R120G . Our in vivo findings revealed that GFPdgn mice treated with LSN2790158 (3mg/kg, i.p.) displayed a significant reduction of myocardial GFPdgn protein but not mRNA levels. Taken together, our data strongly indicate that PDE1I improves cardiac UPS performance and PDE1 represents a potential target to treat cardiac diseases with elevated proteotoxicity.