Phosphoinositide 3-Kinase C2alpha controls cardiac contractility through regulation of beta2-adrenergic receptor recycling

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Doctoral fellowship Introduction Phosphoinositide 3-kinase C2α (PI3KC2α) is a ubiquitously expressed class II PI3K isoform, which has been previously shown to be involved in the control of vesicular trafficking. However, its role in the myocardium has not been investigated. The primary aim of this study is to elucidate the mechanism by which mechanism PI3KC2α controls cardiac pathophysiology. Methods Cardiomyocyte-specific PI3KC2α knockout (PI3KC2α KO) animals were generated by crossing mice expressing a tamoxifen-inducible Cre recombinase under the control of the αMHC promoter with PI3KC2αflox/flox mice. Zebrafish embryos were injected with a PI3KC2α (PI3KC2α morphants) or a control morpholino (control morphants) at 1-cell stage. HEK293 with stable overexpression of GFP-tagged β2-AR were generated and transfected with either scramble or PI3KC2α siRNAs. Results Our findings indicate that PI3KC2α KO mice display a reduced cardiac contractility compared to wildtype animals. Similarly, PI3KC2α morphants zebrafish exhibit lower heart rate and fractional shortening compared to controls, both at baseline and after isoproterenol (ISO) stimulation. A similar unresponsiveness to ISO was found in vivo in PI3KC2α KO mice where chronic treatment with the β-adrenergic receptor (β-AR) agonist failed to induce the classical β-AR-mediated remodeling, characterized by an increase of the left ventricular mass and of cardiomyocyte area. These findings suggest that PI3KC2α plays a critical role in the regulation of β-AR signaling. In agreement, cAMP levels failed to increase in response to ISO treatment in PI3KC2α morphants. Furthermore, silencing of PI3KC2α in HEK293-GFP-β2-AR cells resulted in an increased GFP-β2-AR internalization compared to control cells, both at baseline and after ISO stimulation. Interestingly, preliminary findings indicate that overexpression of constitutively active Rab11Q70L induced a redistribution of GFP-β2-AR at the plasma membrane in PI3KC2α-silenced cells. Conclusion Overall, we identify a key role for PI3KC2α in the control of cardiac contractility through the regulation of β2-AR trafficking to the plasma membrane through a Rab11-dependent mechanism.