Paraspeckles as a target for myocardial hypertrophy

BACKGROUND AND AIMS: Pathological cardiac hypertrophy, a key precursor to heart failure (HF), can be triggered by external stimuli such as pressure overload or increased sympathetic activity. While liquid-liquid phase separation (LLPS) is a fundamental mechanism for cellular stress response and is implicated in various diseases, its role in HF remains unclear. Of particular interest are paraspeckles, membraneless organelles formed through the long non-coding RNA Neat1 via LLPS. Therefore, this study aims to investigate the contribution of this specific RNA-mediated LLPS pathway to the development of cardiac hypertrophy and HF. METHODS: RNA fluorescence in situ hybridization (FISH) was employed to evaluate the presence and abundance of paraspeckles in cardiomyocytes under pathological stress-including isoproterenol (ISO) treatment and transverse aortic constriction (TAC) surgery-as well as in heart tissue from patients with HF. Neat1 expression in human HF samples was quantified to establish the association between Neat1 and HF. The functional role of paraspeckles was assessed using Neat1 knockout mice. Subsequent in vivo and in vitro loss-of-function experiments, involving both Neat1 knockout and knockdown models, were conducted to elucidate the underlying mechanisms. Finally, the therapeutic potential of targeting paraspeckles was explored using a viral delivery strategy to disrupt paraspeckle formation in mice subjected to TAC. RESULTS: Paraspeckles were present in cardiomyocytes, and their formation, mediated by lncRNA Neat1, was significantly up-regulated in cardiomyocytes in response to ISO stimulation, pressure overload, and in heart tissue from patients with HF. Functionally, disrupting paraspeckle formation attenuated ISO-induced cardiomyocyte remodelling, whereas genetic ablation of Neat1 prevented pressure overload-induced cardiac dysfunction and hypertrophy. Mechanistically, increased paraspeckle formation drove myocardial remodelling by promoting cardiomyocyte ferroptosis, achieved through the nuclear sequestration of Fth1 mRNA. Importantly, AAV9-mediated cardiomyocyte-specific knockdown of Neat1_2 (the long isoform of Neat1) effectively prevented the development of TAC-induced HF. CONCLUSIONS: These findings revealed that LLPS driven by lncRNA Neat1 promotes pressure-overload cardiac remodelling by regulating iron homeostasis. Targeting this process presents a novel RNA-based therapeutic avenue for preventing pathological cardiac remodelling and HF.