Animals chronically exposed to
hypoxia develop characteristic structural changes in the pulmonary arterial vasculature including cell
hypertrophy,
hyperplasia, and increased deposition of
extracellular matrix proteins. The medial smooth muscle cells' (SMC) increase in
tropoelastin mRNA expression and
elastin deposition as determined by in situ hybridization and histologic examination appears to contribute significantly to this increase in matrix
protein accumulation. The primary stimulus for the increased
tropoelastin production, which persists in vitro, is unknown but mechanical forces and
hypoxia seem to play a role. In order to determine the direct effects of
hypoxia on
tropoelastin production by pulmonary artery SMC, cultured neonatal bovine pulmonary artery SMC were exposed to 3%, 10%, and 21% O2 concentrations for 48, 72, and 120 h and soluble
tropoelastin was measured by direct immunoassay.
Tropoelastin mRNA levels were also determined by Northern and slot blot analysis after 48 h of incubation under hypoxic conditions. SMC cultured in 3% and 10% O2 for 120 h showed dose-dependent decreases (11-fold and 2-fold, respectively) in measured
tropoelastin levels compared with SMC cultured in 21% O2 conditions. This decrease was not due to cell damage or accumulation of toxic metabolites while under hypoxic conditions nor to a change in
tropoelastin partitioning between the cell and media.
Tropoelastin mRNA levels were also decreased under hypoxic conditions. Secreted, cell layer, and total
protein synthesis determined by L-[3H]
leucine incorporation again showed a dose-dependent decrease under hypoxic conditions but not to the same extent as
tropoelastin production.(ABSTRACT TRUNCATED AT 250 WORDS)