Expression Pattern of L-Type Calcium Channel Subunits in Human and Murine Atherosclerosis

Abstract

Cardiovascular L-type Ca2+-channels (LTCC) are heteromeric protein complexes consisting of a pore-forming Cav1.2 (α1C) and several auxiliary subunits. Major determinants of channel function include the composition of the heteromeric complex, but also subunit transcript regulation by splicing. This is of particular importance since splicing patterns may change under pathophysiological conditions, such as atherosclerosis. In human atherosclerosis, arterial smooth muscle Cav1.2 isoforms containing exon 21 were reported to be replaced by a single isoform containing the alternative exon 22. We have recently shown that this splice shift has major effects on LTCC: co-expressing a β3-subunit together with α1C70 (containing exon 21) led to markedly reduced current density compared to α1C77 (containing exon 22). Co-expression of a β2-subunit with either α1C70 or α1C77 had the opposite effect. In the present work we sought to determine the expression pattern of LTCC subunits in both murine and human atherosclerotic arterial tissue. Murine aorta was isolated from wild-type and atherosclerotic apoE-knockout mice. Samples of human atherosclerotic arteries were obtained from patients undergoing arterial bypass surgery, and vascular smooth muscle cells were isolated by laser microdissection. qRT-PCR was used to determine LTCC subunit expression. In murine aortic tissue we were able to detect exon 21- as well as exon 22-containing Cav1.2 subunit mRNA. Furthermore, we detected β1-, β2- and β3-subunit mRNA with expression of β1-subunits being significantly reduced in atherosclerotic aortic tissue compared to non-atherosclerotic tissue. In human atherosclerotic tissue samples, we found mRNA expression of all four β-subunits, β1-4, with a trend towards β2-subunit mRNA being more abundant than that of other β-subunit isoforms. Given the functional impact of LTCC composition, our data support the idea that altered expression profiles of b-subunits might affect channel function in atherosclerosis.