A Novel Functional Role for Cereblon in Cardiac Cell-Cell Junction Protein Homeostasis, Function and Arrhythmias
Authors: Fujita Kyohei , Bradford William , Zhang Jing , Wang Tsui-Min , Gu Yusu , Peterson Kirk , Sheikh Farah 
Published: May 2023

Desmosomes are cell-cell adhesion junctions that function as mechanical anchors between cardiomyocytes. Loss of desmosomal protein levels and integrity due to desmosomal gene mutations are classically linked to arrhythmogenic cardiomyopathy (AC), an inherited cardiac disease characterized by (bi)-ventricular dysfunction and ventricular arrhythmias. However, there is limited information of how loss of desmosomal protein homeostasis and integrity regulates the complex presentation of AC. To identify novel proteins that may drive desmosomal protein homeostasis and disease, we performed a yeast-two-hybrid screen usingthe desmosomal scaffold protein desmoplakin (DSP) as bait to screen an adult human heart cDNA library. Through this screen we identified cereblon (CRBN), thought to regulate protein degradation, as a novel DSP-interacting protein in the adult human heart. To determine the role of CRBN in the postnatal heart in vivo, we generated cardiac-specific inducible CRBN knockout mice (CRBN-iKO) by crossing new CRBN floxed mice to alpha-MHC-MerCreMer mouse line, to assess its impact on desmosomal protein homeostasis and AC disease features. We hypothesize that CRBN loss drives postnatal desmosomal cell-cell junctional protein degradation and AC-related disease features. CRBN co-localizes with DSP at the cell-cell junction in wild type adult mouse hearts, and we show specificity of this interaction as CRBN protein levels and localization are lost in cardiac-specific DSP knockout hearts. Cardiac-specific ablation of CRBN in the adult heart (8 weeks post-tamoxifen injection) resulted in significant reduction in CRBN levels, that triggered specific cell-cell junction deficits, including downregulation of DSP and electrical channel protein, connexin 43. These molecular deficits lead to a significant increase in heart weight and body weight ratios at the same stages, when compared to controls. Surface ECG analyses also revealed cardiac electrical deficits as CRBN-iKO mice exhibited ventricular depolarization delay as exhibited by significantly longer QRS intervals at baseline as well as the presence of premature ventricular contractions (PVCs) after isoproterenol administration, which were distinct from controls. Telemetry ECG analyses at 13 weeks post-tamoxifen injection, revealed worsened cardiac electrical deficits in CRNB-iKO mice, as PVCs and ventricular tachycardia were observed at baseline, unlike controls. Echocardiographic analysis revealed that CRBN-iKO mice had some predisposition to cardiomyopathy at earlier stages (4 weeks post-tamoxifen) as significant decreases in left ventricular fractional shortening and increased left ventricular internal dimension at end-systole (LVIDs) were observed in mice, distinct from controls. We highlight novel roles for CRBN in postnatal cell-cell junctional integrity and function, and showcase that loss of CRBN is a driver of the progressive cardiac (electro)-physiological deficits associated with AC disease. Work in the laboratory of FS is supported by grants from the NIH (HL142251, HL162369) and industry (LEXEO Therapeutics Inc.) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.