Gemma Dulsat1,2, Sonia Palomeras1,2, Eric Cortada1,2, Helena Riuró1,2, Ramon Brugada1,2,3, Marcel Vergés1,2,3. 1. Cardiovascular Genetics Group, Girona Biomedical Research Institute (IDIBGI), Salt, Girona, 17190, Spain. 2. Biomedical Research Networking Center on Cardiovascular Diseases (CIBERCV), ISCIII, Madrid, 28029, Spain. 3. Medical Sciences Department, University of Girona Medical School, Girona, 17003, Spain.
Abstract
BACKGROUND INFORMATION: Cardiac channelopathies arise by mutations in genes encoding ion channel subunits. One example is Brugada Syndrome (BrS), which causes arrhythmias and sudden death. BrS is often associated with mutations in SCN5A, encoding Nav 1.5, the α subunit of the major cardiac voltage-gated sodium channel. This channel forms a protein complex including one or two associated β subunits as well as other proteins. RESULTS: We analysed regulation of Nav 1.5 localisation and trafficking by β2, specifically, Nav 1.5 arrival to the cell surface. We used polarised Madin-Darby canine kidney (MDCK) cells and mouse atria-derived HL-1 cells, which retain phenotypic features of adult cardiomyocytes. In both, Nav 1.5 was found essentially intracellular, mainly in the endoplasmic reticulum, whereas β2 localised to the plasma membrane, and was restricted to the apical surface in MDCK cells. A fraction of β2 interacted with Nav 1.5, despite their limited overlap. Importantly, β2 promoted Nav 1.5 localisation to the cell surface. Both β2 WT and the BrS-associated mutation D211G (substitution of Asp for Gly) effectively reached the plasma membrane. Strikingly, however, β2 D211G was defective in promoting Nav 1.5 surface localisation. CONCLUSIONS: Our data sustain that β2 promotes surface localisation of Nav 1.5, which can be affected due to β2 mutations associated with channelopathies. SIGNIFICANCE: Our findings add to the understanding of β2 role in Nav 1.5 trafficking and localisation, which must influence cell excitability and electrical coupling in the heart. This study will contribute to knowledge on development of arrhythmias.
BACKGROUND INFORMATION: Cardiac channelopathies arise by mutations in genes encoding ion channel subunits. One example is Brugada Syndrome (BrS), which causes arrhythmias and sudden death. BrS is often associated with mutations in SCN5A, encoding Nav 1.5, the α subunit of the major cardiac voltage-gated sodium channel. This channel forms a protein complex including one or two associated β subunits as well as other proteins. RESULTS: We analysed regulation of Nav 1.5 localisation and trafficking by β2, specifically, Nav 1.5 arrival to the cell surface. We used polarised Madin-Darby canine kidney (MDCK) cells and mouse atria-derived HL-1 cells, which retain phenotypic features of adult cardiomyocytes. In both, Nav 1.5 was found essentially intracellular, mainly in the endoplasmic reticulum, whereas β2 localised to the plasma membrane, and was restricted to the apical surface in MDCK cells. A fraction of β2 interacted with Nav 1.5, despite their limited overlap. Importantly, β2 promoted Nav 1.5 localisation to the cell surface. Both β2 WT and the BrS-associated mutation D211G (substitution of Asp for Gly) effectively reached the plasma membrane. Strikingly, however, β2 D211G was defective in promoting Nav 1.5 surface localisation. CONCLUSIONS: Our data sustain that β2 promotes surface localisation of Nav 1.5, which can be affected due to β2 mutations associated with channelopathies. SIGNIFICANCE: Our findings add to the understanding of β2 role in Nav 1.5 trafficking and localisation, which must influence cell excitability and electrical coupling in the heart. This study will contribute to knowledge on development of arrhythmias.