Expression and localization of C-type natriuretic peptide in human vascular smooth muscle cells

C-type natriuretic peptide (CNP) released by vascular endothelium relaxes smooth muscle and is important in the maintenance of vascular tone. Since it is not known whether other human vascular cell types produce CNP, we investigated its expression in human vascular smooth muscle. CNP expression was examined by RT-PCR in vascular smooth muscle cells (SMC) cultured from human saphenous vein (SV), internal mammary artery (IMA) and radial artery (RA), and CNP protein was probed using immunostaining, in tissue sections and in SMCs cultured from these vessels, respectively. PCR for CNP produced a 334 bp product in all SMC cultures, as expressed in endothelial cells, although the band intensity was markedly less in SMCs. Myocardium from CNP-knockout mouse did not express CNP, while there was expression in wild-type mouse. CNP protein was detected by immunostaining in 100% of SMC cultures. By immunostaining of tissue sections, CNP was detected throughout the medial layer, but not adventitia, of all vessel types. Expression of CNP at gene and protein level by human vascular SMCs suggests that CNP may have the capacity to regulate vascular tone independently of the endothelium.