EXPRESSION OF HYDROPHILIC SURFACTANT PROTEINS BY MESENTERY CELLS IN RAT AND MAN

Human peritoneal dialysis effluent (PDE) contains a phosphatidylcholin e-rich compound similar to the surfactant that lines lung alveoli. Thi s material is secreted by mesothelial cells. Lung surfactant is also c haracterized by four proteins essential to its function. After having long been considered as lung-specific, some of them have been found in gastric and intestinal epithelial cells. To explore further the simil arity between lung and peritoneal surfactants, we investigated whether mesothelial cells also produce surfactant proteins. We used rat trans parent mesentery, human visceral peritoneum biopsies and PDE. Surfacta nt proteins were searched for after one-and two-dimensional SDS/ PAGE and Western blotting. On a one-dimensional Western blot, bands at 38 a nd 66 kDa in rat mesentery, and at 38 and 66 kDa in human peritoneal m esothelial cells (in vivo and in vitro) and PDE, corresponded to monom eric and dimeric forms of lung surfactant protein A (SP-A). On two-dim ensional Western blots, the 32 and 38 kDa spots in mesentery and PDE l ocalized at the acidic pH appropriate to the SP-A monomer's isoelectri c point. SP-D was also identified at the same 43 kDa molecular mass as in lung. SP-B was not detected in mesenteric samples. Expression of S P mRNA species was also assessed by reverse transcriptase-PCR, which w as performed with specific primers of surfactant protein cDNA sequence s. With primers of SP-A and SP-D, DNA fragments of the same size were amplified in lung and mesentery, indicating the presence of SP-A and S P-D mRNA species. These fragments were labelled by appropriate probes in a Southern blot. No amplification was obtained for SP-B. These resu lts show that mesentery cells produce SP-A and SPD, although they are of embryonic origin (mesodermal) and are different from those of the l ung and digestive tract (endodermal) that secrete these surfactants.