RBP1 attenuates pathological cardiac hypertrophy via Wnt3a/β-catenin signaling.

BACKGROUND: Pathological cardiac hypertrophy is a central driver of heart failure, yet targeted therapies remain lacking. This study aimed to investigate the role of retinoid homeostasis in cardiac hypertrophy, focusing on retinol-binding protein 1 (RBP1), the primary intracellular regulator of retinol homeostasis. We sought to elucidate the effects and underlying mechanisms of RBP1 in cardiac hypertrophy.

METHODS: Cardiac retinol and all-trans retinoic acid (atRA) levels were quantified using LC-MS. A mouse model of pressure overload-induced cardiac hypertrophy was established via transverse aortic constriction (TAC) surgery. Cardiomyocyte-specific overexpression of RBP1 was achieved by intravenous injection of an adeno-associated virus 9 (AAV9) vector carrying RBP1 under the control of the cardiac troponin T (cTnT) promoter. An in vitro hypertrophy model was established by treating rat neonatal cardiomyocytes (NRCMs) with phenylephrine (PE). Gain- and loss-of-function approaches were applied to evaluate the effect of RBP1 on cardiomyocyte hypertrophy. Transcriptomic changes upon RBP1 knockdown in PE-treated NRCMs were analyzed by RNA sequencing. To dissect the signaling pathways involved, the retinoic acid receptors (RARs) inhibitor AGN193109 (AGN) and the Wnt signaling agonist Wnt3a were administered. A dual-luciferase reporter assay was performed to evaluate whether atRA regulates Wnt3a promoter activity.

RESULTS: Retinol metabolism was impaired in mice subjected to TAC. Supplementation of atRA sufficiently ameliorated cardiac hypertrophy. RBP1 was upregulated in both hypertrophied myocardium and isolated cardiomyocytes. Cardiomyocyte-specific RBP1 overexpression effectively restored myocardial retinol and atRA pools and alleviated cardiac hypertrophy and fibrosis in TAC mice. RBP1 expression was significantly upregulated in PE-induced hypertrophic NRCMs. Knockdown of RBP1 in NRCMs aggravated hypertrophy, whereas its overexpression attenuated hypertrophy induced by PE stimulation. RNA sequencing analyses indicated that RBP1 knockdown disrupted retinol and retinoic acid metabolic processes. Pharmacological inhibition of atRA signaling using AGN partially reversed the protective effect of RBP1 overexpression on cardiomyocyte hypertrophy, indicating that the anti-hypertrophic effect of RBP1 is partially dependent on atRA signaling. Further analyses demonstrated that RBP1 inhibited cardiomyocyte hypertrophy by suppressing Wnt3a/β-catenin signaling. Mechanistically, atRA partially reversed Wnt3a/β-catenin activation induced by RBP1 knockdown, whereas AGN partially abolished the inhibitory effect of RBP1 overexpression on this pathway, indicating that RBP1 regulated Wnt3a/β-catenin signaling in an atRA-dependent manner. Moreover, luciferase reporter assays demonstrated that atRA suppressed Wnt3a promoter activity via retinoic acid response elements (RAREs) within its promoter region.

CONCLUSIONS: RBP1 is upregulated in hypertrophic myocardium and exerts a protective role against cardiac hypertrophy. These results suggest that RBP1 may serve as a potential therapeutic target for cardiac hypertrophy and heart failure, offering a promising strategy to prevent and regress cardiac hypertrophy through RBP1/atRA/Wnt3a/β-catenin signaling.