Elucidating the cardioprotective effects of phosphodiesterase 3A in mouse hearts

Background: 

Hypertension and its clinical consequences remain one of the leading causes of death worldwide. Bilginturan syndrome or hypertension with brachydactyly type E (HTNB) represents a subtype of high blood pressure and resembles essential hypertension. The underlying pathophysiology involves hyperproliferation of vascular smooth muscle cells (VSMCs) and hyperactivity of mutant PDE3A enzymes which cause HTNB. However, recent studies showed that gain-of-function PDE3A gene mutations also protect the heart against hypertension-induced cardiac damage. The overall goal of this work is to investigate the underlying mechanisms of the cardioprotective effect of PDE3A. For this purpose, we generated and validated two PDE3A knockout mouse models.  

Methods:

To generate cardiac myocyte-specific knockout of all PDE3A isoforms (PDE3A-CM-KO), we bred PDE3A fl/fl mice with the cardiac-specific α-myosin heavy chain promoter driven Cre line (αMHC-Cre). For vascular smooth muscle cell (VSMC)-specific knockout of all PDE3A isoforms (PDE3A-VSMC-KO), we also crossed PDE3A fl/fl mice with the smooth muscle cell-specific deleter mouse line (SM22-Cre). PDE3A knockout in isolated ventricular cardiomyocytes of these two mouse models was evaluated by immunoblotting.

Results:

Protein analysis of freshly isolated adult ventricular cardiac myocytes revealed comparable strong expression of PDE3A in the wild-type and VSMC-specific knockout mouse line. As expected, PDE3A protein expression in cardiomyocytes from the PDE3A-CM-KO line was completely abolished, as was the PDE3A expression in VSMCs from PDE3A-VSMC-KO mice. The confirmed specific deletion of the enzyme in cardiomyocytes vs. VSMC should dissect individual contributions of both cell types into cardioprotective effect of PDE3A. 

Conclusion:

PDE3A-KO knockout mouse lines (PDE3A-CM-KO and PDE3A-VSMC-KO) were validated and should allow us to study in more detail the cardioprotective effect of HTNB-causing PDE3A mutations. These studies will include phenotypic characterization in cardiac stress models with and without PDE3A hyperactive mutant overexpression, live cell imaging studies to analyze their effects on local cAMP-signaling and assessments of contractility and Ca²⁺ homeostasis in the isolated cardiomyocytes.