Nexilin Is a New Component of Junctional Membrane Complexes Required for Cardiac T-Tubule Formation

• DOI: 10.1161/circulationaha.119.039751
• Publication Date: 2019-04-15T09:09:01Z
• Authors: Canzhao Liu; Simone Spinozzi; Jia-Yu Chen; Xi Fang; Wei Feng; Guy Perkins; Paola Cattaneo; Nuno Guimarães-Ca...; Nancy D. Dalton; Kirk L. Peterson; Tongbin Wu; Kunfu Ouyang; Xiang-Dong Fu; Sylvia M. Evans; Ju Chen
• Keywords: Cardiomyopathy, Dilated; junctional membrane complexes; Calcium Channels, L-Type; Cardiomyopathy; Cells; Knockout; Medical Physiology; Clinical Sciences; Muscle Fibers, Skeletal; 610; membrane contact sites; Clinical sciences; Mice, Transgenic; Cardiorespiratory Medicine and Haematology; Cardiovascular; T-tubule, membrane contact sites; Muscle Fibers; Cardiovascular medicine and haematology; Transgenic; Mice; 03 medical and health sciences; Rare Diseases; Dilated; Genetics; 2.1 Biological and endogenous factors; Animals; Myocytes, Cardiac; Cells, Cultured; Mice, Knockout; Myocytes; 0303 health sciences; Cultured; Biomedical and Clinical Sciences; Cell Membrane; Microfilament Proteins; Skeletal; L-Type; 3. Good health; Heart Disease; T-tubule; Intercellular Junctions; Cardiovascular System & Hematology; Public Health and Health Services; Calcium Channels; Sports science and exercise; Cardiac; cardiomyopathy

Background: Membrane contact sites are fundamental for transmission and translation of signals in multicellular organisms. The junctional membrane complexes in the cardiac dyads, where transverse (T) tubules are juxtaposed to the sarcoplasmic reticulum, are a prime example. T-tubule uncoupling and remodeling are well-known features of cardiac disease and heart failure. Even subtle alterations in the association between T-tubules and the junctional sarcoplasmic reticulum can cause serious cardiac disorders. NEXN (nexilin) has been identified as an actin-binding protein, and multiple mutations in the NEXN gene are associated with cardiac diseases, but the precise role of NEXN in heart function and disease is still unknown.

Methods:

Nexn global and cardiomyocyte-specific knockout mice were generated. Comprehensive phenotypic and RNA sequencing and mass spectrometry analyses were performed. Heart tissue samples and isolated single cardiomyocytes were analyzed by electron and confocal microscopy.

Results:

Global and cardiomyocyte-specific loss of Nexn in mice resulted in a rapidly progressive dilated cardiomyopathy. In vivo and in vitro analyses revealed that NEXN interacted with junctional sarcoplasmic reticulum proteins, was essential for optimal calcium transients, and was required for initiation of T-tubule invagination and formation.

Conclusions:

These results demonstrated that NEXN is a pivotal component of the junctional membrane complex and is required for initiation and formation of T-tubules, thus providing insight into mechanisms underlying cardiomyopathy in patients with mutations in NEXN .