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La proliferation des cellules musculaires lisses (CML) de l'artere pulmonaire (AP) contribue largement au remodelage vasculaire qui se produit dans l'hypertension pulmonaire hypoxique chronique. Les premieres manifestations proliferatives des CML en reponse a l'hypoxie apparaissent dans la media externe. Nous avons verifie l'hypothese que le profil de la proliferation des CML induite par l'hypoxie dans l'AP, observe in vivo, est determine, du moins en partie, par des differences intrinseques dans la reponse proliferative de CML isolees de diverses couches de la media a des mitogenes peptidiques pertinents et a l'hypoxie. Des CML d'AP bovines adultes ont ete isolees au niveau du meme site proximal de la media externe (couche 3) et centrale (couche 2). En reponse a une stimulation serique maximale, les CML d'AP de la media externe se sont developpees plus rapidement que les cellules de la media centrale. Les cellules de la media externe ont aussi ete plus sensibles a des nombreux mitogenes peptidiques (IGF-I, PDGF-BB, bFGF et EGF). Nous avons ensuite evalue la reponse a un activateur direct, permeable aux cellules, de la PKC (PMA, phorbol 12-myristate 13-acetate), la proteine kinase C (PKC), une voie pro-proliferative cle de la transduction des signaux, ayant joue un role important dans ce type d'augmentation globale du developpement des CML. Les CML d'AP de la media externe ont eu une plus grande synthese d'ADN en reponse a l'activation selective de la PKC que celles de la media centrale. Etant donne que l'activation de cette kinase est essentielle pour que les CML d'AP proliferent en reponse a l'hypoxie, le potentiel de croissance hypoxique des cellules de la media externe et centrale a donc ete compare. Les CML de la media externe ont eu une reponse proliferative accrue a l'hypoxie comparativement aux CML de la media centrale. Ces resultats ont suggere un role important pour la PKC dans le developpement accru des CML d'AP de la media externe. Ainsi, l'activite cellulaire totale, l'expression et l'activation de la PKC induite par l'hypoxie ont ete determinees dans les deux sous-populations de CML d'AP. Les cellules de la media externe ont eu une activite cellulaire totale, une expression et une activation de la PKC (et particulierement de l'isoenzyme α) induite par l'hypoxie plus importantes que les cellules isolees de la media centrale. Ces resultats confortent l'hypothese qu'il existe une heterogeneite dans la capacite de developpement des CML d'AP dans la media d'AP bovines, que ces differences intrinseques dans le developpement regissent, du moins en partie, le profil de proliferation anormale des CML observe in vivo, et que la voie de la PKC (et en particulier de la PKC-α) joue probablement un role important dans la determination des differences specifiques aux sous-populations identifiees.

Pulmonary artery (PA) smooth muscle cell (SMC) proliferation is an important contributor to the vascular remodeling that occurs in chronic hypoxic pulmonary hypertension. The earliest SMC proliferative changes in response to hypoxia occur in the outer media. We tested the hypothesis that the pattern of hypoxia-induced PA SMC proliferation observed in vivo is determined at least in part by intrinsic differences in proliferative response of SMC isolated from different medial layers to relevant peptide mitogens and hypoxia. Adult bovine PA SMCs were isolated 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 medial cells also had increased responsiveness to multiple peptide mitogens (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, responsiveness to a direct cell-permeable activator of PKC (PMA, phorbol 12-myristate 13-acetate) was then measured. PA SMCs from the outer media had greater DNA synthesis in response to selective PKC activation than middle medial cells. Since activation of this kinase is a requisite step for PA SMCs to proliferate in response to hypoxia, the hypoxic growth potential of cells from the middle and outer media was then compared. SMCs from the outer media had an augmented proliferative response 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 subpopulations of PA SMCs. Outer medial cells had greater total cellular activity, expression, and hypoxia-induced activation of PKC (and the alpha isozyme in particular) than cells isolated from the middle media. These findings support the concept that heterogeneity in growth capacity of PA SMCs exists within the bovine PA media, that these intrinsic differences in growth govern, at least in part, the pattern of abnormal SMC proliferation observed in vivo, and that the PKC pathway (and PKC-alpha in particular) is likely an important determinant of the subpopulation-specific differences found.