HYPEROXIA ALONE CAUSES CHANGES IN LUNG PROTEOGLYCANS AND HYALURONAN IN NEONATAL RAT PUPS

Specific changes in composition and content of lung extracellular matr ix (ECM) proteoglycans (PGs) and hyaluronan (HA) have been observed du ring the acute response to damage in several forms of injury including infant respiratory distress syndrome (IRDS). These ECM components are thought to modulate the healing response. Hyperoxia, a contributing f actor to IRDS, is known to damage both adult and developing lung, howe ver, the extent and pattern of impairment depends on lung maturity. We hypothesized that exposing neonatal rats to hyperoxia alone might res ult in changes in lung HA, as well as in age-specific changes in lung PGs, similar to those shown to occur in IRDS. In control rats, lung HA decreased over the first 10 days of life, whereas rats exposed to hyp eroxia exhibited a time-dependent, time-limited increase in both lung HA and lung wet weight. Histochemistry showed the HA in hyperoxia-expo sed lungs to be accumulated in perivascular cuffs of medium sized arte ries, and in the alveolar walls. Rats were then exposed to normoxia or hyperoxia for 7 days beginning at either 3 days of life (neonatal) or 21 days (adolescent), and lung tissue was cultured in the presence of [S-35]-sulfate to label newly synthesized PGs. Proteoglycans were ext racted, and analyzed by isopycnic CsCl gradient centrifugation, sequen tial enzymatic deglycosylation, size chromatography, and sodium dodecy l sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). When controll ed for total protein extracted, 63% more label was incorporated into l arge molecular weight material in the tissue exposed to hyperoxia, wit h a 95% increase in incorporation in the most dense fraction, D-1. [S- 35]-Suufate incorporation into chondroitin and dermatan sulfate in hyp eroxic tissue specifically increased 116% (242% in the D-1 fraction), while incorporation into heparan sulfate remained essentially unchange d. There was a nearly fivefold increase in [S-35]-sulfate incorporatio n into chondroitin sulfate chains in the D-1 fraction. When the D-1 fr actions of extracts of treated and control rat lungs were compared on SDS-PAGE, a large chondroitin sulfate proteoglycan (CSPG; core protein of 195 kDa) was upregulated in the D-1 fraction from hyperoxic tissue of neonatal rats, but was not detected in the lungs of adolescent ani mals exposed to hyperoxia. This CSPG and four additional large CSPGs w ere noted to be upregulated on western blotting by a polyclonal antibo dy directed against the G1 domain of the aggrecan protein core. We con clude that hyperoxia alone causes an increase in lung HA and lung wate r, and speculate that this contributes significantly to the clinical s yndrome of IRDS. In addition, several large CSPGs are upregulated by h yperoxic exposure in a developmentally specific manner. We speculate t hat this increase in CSPGs may interfere with the normal developmental sequence of events, contributing to hypoalveolarization.