Abstract Body: Background:
Left ventricular noncompaction cardiomyopathy (LVNC) is defined by excessive ventricular trabeculation. It can manifest in both pediatric and adult populations, with mortality rates of 35–38% and a median follow-up of 5–11 years. Despite its clinical importance, the mechanisms underlying LVNC pathogenesis remain unclear.
Methods:
We generated cardiomyocyte-specific Numb (Nb) and Numbl (Nl) double knockout (ADKO) mice using αMHC-Cre. Structural and functional progression was assessed by echocardiography (ECHO). Histology and ECHO were used to define disease evolution, and telemetry was used to evaluate arrhythmias. Numb subcellular localization was examined using two Numb knock-in mouse lines. Numb-interacting proteins were identified by mass spectrometry. mRNA deep sequencing was performed to identify pathways associated with disease progression. Autophagy regulation was assessed using autophagic reporter mouse lines, electron microscopy, and molecular and biochemical approaches. Therapeutic rescue experiment was performed using ECHO-guided intracavitary injection of Numb-enriched endosomes.
Results:
ADKO mice did not exhibit LVNC features during embryonic stages or at young adult stage, and they survived to adulthood without obvious defects. However, as they aged, ADKO progressively developed prominent trabeculation with a NC/C ratio greater than 3, reduced systolic function, ventricular dilation, recapitulating hallmark clinical features of LVNC. Proteomic analysis revealed that Numb interacts with proteins involved in endocytosis and localizes to endosomes and autolysosomes. mRNA deep sequencing showed abnormal cellular homeostasis in ADKO hearts. Loss of NFPs impaired autophagic flux, leading to arrest at the autolysosome stage and the accumulation of ubiquitin-conjugated proteins. Importantly, restoring autophagic flux via administration of exogenous Numb-enriched endosomes improved autophagic processing and rescued LVNC phenotypes in ADKO hearts.
Conclusion:
Numb family proteins are critical regulators of left ventricular compaction. Cardiomyocyte-specific depletion of NFPs results in LVNC that can develop progressively during postnatal life, providing a model for acquired LVNC associated dilated cardiomyopathy. NFP-mediated autophagy is essential for cardiac homeostasis and structural remodeling, restoring autophagic flux represents a potential therapeutic strategy for preventing or treating LVNC.