Redox-activated protein kinase A Type I (PKA RI) exerts a protective role during pathological pressure overload

Abstract

Abstract Background Phosphorylation of L-type calcium channels (LTCC) by cAMP-dependent protein kinase A (PKA) increases calcium current (ICa). However, it is unclear if PKA-dependent regulation of ICa is impaired in heart failure (HF) despite evidence for impaired β-adrenergic signaling. Recently, a novel PKA activation pathway by oxidation of regulatory subunit I (RI) has been identified. Objective We investigated the impact of redox-activated PKA for regulation of ICa, intracellular calcium (Ca) handling and contractile function in a pressure overload heart failure mouse model. Methods Knock-in mice (KI) that lack redox-dependent PKA activation (exchange of cysteine 17 of RI with serine) were compared to wild-type (WT) at baseline, 7 days and 6 weeks after transverse aortic constriction (TAC). Mouse echocardiography was performed to evaluate in-vivo cardiac function. ICa was measured by whole-cell patch clamp, PKA activity, cAMP levels, and protein levels of central Ca handling proteins were assessed at different time points in vitro. Results At baseline, no alterations of left ventricular (LV) function (echocardiography) were observed between WT and KI. TAC induced a significant RI oxidation in WT but not KI mice. Despite this difference, at 7 days after TAC, development of LV hypertrophy and impairment of systolic LV function in vivo were similar between WT and KI. Compared to baseline, 7 days after TAC a significant stimulation of peak ICa was observed in WT. In contrast to WT, the stimulation of peak ICa was absent in KI mice at 7 days after TAC. This impairment in peak ICa occurred despite a comparable increase in global PKA activity (ELISA), which was most likely due to increased cAMP levels in our TAC model (assessed by FLIM-FRET). Notably, cAMP levels were comparably increased in between groups (ELISA). Importantly, at 6 weeks after TAC, WT mice showed a mild additional deterioration of systolic LV function in vivo. In contrast, LV function was significantly more impaired in KI mice 6 weeks after TAC, which was accompanied by a significant increase in KI mice mortality. Comparing 6 weeks to 7 days after TAC, there was no stimulation of peak ICa in WT and even a significant decrease in peak ICa in KI mice. In accordance, PKA-dependent LTCC phosphorylation was absent in KI mice 6 weeks after TAC (western blotting). Conclusion Redox-activated PKA seems to exert a protective role by stimulation of ICa during pressure overload. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): Deutsche Forschungsgemeinschaft