Serum can overcome contact inhibition in confluent human pulmonary artery smooth muscle cells.
Pulmonary artery endothelial cells (PAEC) in an intact vessel are continually exposed to serum, but unless injured, do not proliferate, constrained by confluence. In contrast, pulmonary artery smooth muscle cells (PASMC) attain, and maintain, confluence in the presence of minimal serum, protected from serum's stimulatory effects except when the endothelial barrier becomes more permeable. We hypothesized therefore, that confluent PASMC may be less constrained by contact inhibition in the presence of serum than PAEC and tested this idea by exposing confluent non-transformed human PAEC and PASMC to media containing increasing concentrations of fetal bovine serum (FBS) and determining cell growth over 7 days. PAEC that had attained confluence in low serum did not proliferate even when exposed to 5% serum, the highest concentration tested. In contrast, PASMC that attained confluence in low serum did proliferate once serum levels were increased, an effect that was dose dependent. Consistent with this observation, PASMC had more BrdU incorporation and a greater percentage of cells in S phase in 5% compared to 0.2% FBS, whereas no such difference was seen in PAEC. These results suggest that confluent human PAEC are resistant to the stimulatory effects of serum, whereas confluent PASMC can proliferate when serum levels are increased, an effect mediated in part by differences in phosphoinositide 3-kinase activation. This observation may be relevant to understanding the PASMC hyperplasia observed in humans and animals with pulmonary hypertension in which changes in endothelial permeability due to hypoxia or injury expose the underlying smooth muscle to serum.
Center for Lung Biology, University of South Alabama School of Medicine, Mobile, Alabama, United States of America.
Victor
V
Solodushko
Heba A
HA
Khader
Brian W
BW
Fouty
D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D003260:Contact Inhibition / Q000187:drug effects; D003470:Culture Media / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D006801:Humans; D009131:Muscle, Smooth, Vascular / Q000166:cytology* / Q000502:physiology; D032389:Myocytes, Smooth Muscle / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D051058:Oncogene Protein v-akt / Q000378:metabolism; D011651:Pulmonary Artery / Q000166:cytology* / Q000187:drug effects / Q000502:physiology; D016160:Retinoblastoma Protein / Q000378:metabolism; D044967:Serum / Q000502:physiology*
D003470:Culture Media; D016160:Retinoblastoma Protein; D051058:Oncogene Protein v-akt