Abstract 350: Bcl-xL-Ser14 Phosphorylation is Critical for Compensatory Cardiac Hypertrophy

Abstract

Cardiac hypertrophy is an adaptive response at least initially since it reduces wall stress. Phosphorylation of Bcl-xL at Serine (Ser) 14, which dissociates Bcl-xL from Bax and promotes apoptosis, is increased in the heart within one hour after transverse aortic constriction (TAC)-induced pressure overload (PO). Here, we investigated how the increased Ser14-phosphorylation affects hypertrophy during PO. The Bcl-xL knock-in (KI) mice, in which Ser14 was replaced with Ala (Ser14Ala), exhibited a significantly greater mortality than wild-type (WT) mice (p=0.001) after TAC, with elevated end diastolic pressure (LVEDP, 34.6 vs 16.5 mmHg, p<0.05), impaired systolic function (EF, 38.2% vs 67.5%, p<0.001), and increased fibrosis (1.6-fold, p<0.001). The level of apoptosis was similar between the KI and WT mice one week after TAC, as assessed by TUNEL staining. The KI mice showed less cardiomyocyte and cardiac hypertrophy (cardiomyocyte size, 0.71-fold; heart weight/tibia length, 0.88-fold, both P<0.001). Adult cardiomyocytes isolated from the KI mice two days after TAC showed significantly lower contractility compared to those isolated from WT mice (0.32-fold, p<0.001). Mechanistically, gene set enrichment analysis using the RNA-seq data obtained from one-day TAC hearts showed that ion channel activity-related gene sets enriched in WT mice are downregulated in the KI mice. In line with this result, angiotensin II (Ang II) increased Ser14-phosphorylation and cytosolic Ca 2+ level in WT-MEFs in vitro , whereas MEFs isolated from the KI mice showed a significantly lower elevation of cytosolic Ca 2+ against Ang II. Proteomics analysis showed that Ankyrin, an anchoring protein that targets and stabilizes ion channels on the membrane, interacts with endogenous Bcl-xL in the heart. Taken together, these data suggest that phosphorylation of Bcl-xL at Ser14 is critical for augmenting Ca 2+ release from the sarcoplasmic reticulum by modulating the ion channel activity in part via Ankyrin against PO or AngII, thereby developing compensatory hypertrophy and maintaining contractile function. Our findings indicate that increasing the Bcl-xL-Ser14 phosphorylation during acute phase PO could be a potential therapeutic strategy for maintaining cardiac function.