HETEROGENEITY IN THE PROLIFERATIVE RESPONSE OF BOVINE PULMONARY-ARTERY SMOOTH-MUSCLE CELLS TO MITOGENS AND HYPOXIA - IMPORTANCE OF PROTEIN-KINASE-C

Pulmonary artery (PA) smooth muscle cell (SMC) proliferation is an imp ortant contributor to the vascular remodeling that occurs in chronic h ypoxic pulmonary hypertension. The earliest SMC proliferative changes in response to hypoxia occur in the outer media. We tested the hypothe sis that the pattern of hypoxia-induced PA SMC proliferation observed in vivo is determined at least in part by intrinsic differences in pro liferative response of SMC isolated from different medial layers to re levant peptide mitogens and hypoxia. Adult bovine PA SMCs were isolate d at the same proximal site from the middle (layer 2) and outer (layer 3) media. In response to maximal serum stimulation, PA SMCs from the outer media grew faster than cells from the middle media. The outer me dial cells also had increased responsiveness to multiple peptide mitog ens (IGF-I, PDGF-BB, bFGF, and EGF). Because protein kinase C (PKC), a key pro-proliferative signal transduction pathway, has been shown to play an important role in this type of global increase in growth, resp onsiveness to a direct cell-permeable activator of PKC (PMA, phorbol 1 2-myristate 13-acetate) was then measured. PA SMCs from the outer medi a had greater DNA synthesis in response to selective PKC activation th an middle medial cells. Since activation of this kinase is a requisite step for PA SMCs to proliferate in response to hypoxia, the hypoxic g rowth potential of cells from the middle and outer media was then comp ared. SMCs from the outer media had an augmented proliferative ie resp onse to hypoxia compared with those from the middle media. These data suggested an important role for PKC in the enhanced growth of PA SMCs from the outer media. Therefore, whole cellular activity, expression, and hypoxia-induced activation of PKC were measured in both subpopulat ions of PA SMCs. Outer medial cells had greater total cellular activit y, expression, and hypoxia-induced activation of PKC (and the a isozym e in particular) than cells isolated from the middle media. These find ings support the concept that heterogeneity in growth capacity of PA S MCs exists within the bovine PA media, that these intrinsic difference s in growth govern, at least in part, the pattern of abnormal SMC prol iferation observed in vivo, and that the PKC pathway (and PKC-a in par ticular) is likely an important determinant of the subpopulation-speci fic differences found.