PV-1 is a component of the fenestral and stomatal diaphragms in fenestrated endothelia

Abstract

PV-1 is a novel endothelial protein shown by immunocytochemical tests to be specifically associated with the stomatal diaphragms of caveolae in lung endothelium. Although the highest expression levels of both mRNA and protein are in the lung, PV-1 also has been found to be expressed in other organs. Using a specific antibody to the extracellular domain of PV-1, we have extended the survey on the presence of this protein at light and electron microscope level in several rat organs. Here we show that by immunofluorescence the antibody recognizes with high specificity the endothelium of the fenestrated peritubular capillaries of the kidney and those of the intestinal villi, pancreas, and adrenals. By immunolocalization at electron microscope level, the antibody recognizes specifically the diaphragms of the fenestrae and the stomatal diaphragms of caveolae and transendothelial channels in the endothelia of these vascular beds. No signal was detected in the continuous endothelium of the heart, skeletal muscle, intestinal muscularis, or brain capillaries or the nondiaphragmed fenestrated endothelium of kidney glomeruli. Taken together, our findings define the only antigen to be localized thus far in fenestral diaphragms. They also show that the stomatal diaphragms of caveolae and transendothelial channels and the fenestral diaphragms might be biochemically related, in addition to being morphologically similar structures.

PV1 Is a Key Structural Component for the Formation of the Stomatal and Fenestral Diaphragms

“…A strong correlation between the presence of PV1 and the presence of SDs and FDs has been determined in situ where PV1 was basically found only where the diaphragms are found (Stan et al, 1999a(Stan et al, , 1999b. Thus, PV1 antibodies stain only the introits of caveolae provided with SDs and not the caveolae lacking SDs.…”

“…Immunogold labeling was performed by a pre-embedding method as in our past work (Stan et al, 1999a(Stan et al, , 1999b. Cells were either PMA treated or transfected with huPV-FLAG, followed by fixation (30 min, RT) in 2% paraformaldehyde in 0.1 M PB, pH 7.4.…”

“…The extracellular domain contains four N-glycosylation sites near the membrane, a proline-rich region near the C-terminus, and two large coiled-coil domains, suggesting a rodlike protein (Stan et al, 2001). From the studies done so far, PV1 seems to be endothelium specific and moreover to be specifically associated with the SDs of caveolae and TEC and the FDs, at both fronts of ECs (Stan et al, 1999a(Stan et al, , 1999b. PV1 forms homodimers in situ as well as in culture (Stan, 2003).…”

“…PV1 is a single-span, 60-kDa, type II membrane N-glycosylated glycoprotein with a short intracellular tail and a long extracellular domain (Stan et al, 1999b). There is no conserved known consensus site in the intracellular domain across mammalian species.…”

“…Recently, we have shown that the SDs of caveolae and TEC and the FDs of fenestrae share at least one protein, namely PV1 (Stan et al, 1999a(Stan et al, , 1999b. PV1 is a single-span, 60-kDa, type II membrane N-glycosylated glycoprotein with a short intracellular tail and a long extracellular domain (Stan et al, 1999b).…”