Am. J. Respir. Cell Mol. Biol., Vol 13, No. 6, Dec 1995, 629-638.
Hyperoxia alone causes changes in lung proteoglycans and hyaluronan in neonatal rat pups
SE Juul, RC Krueger Jr, L Scofield, MB Hershenson and NB Schwartz
Department of Pediatrics, University of Florida, Gainesville, USA.
Specific changes in composition and content of lung extracellular matrix
(ECM) proteoglycans (PGs) and hyaluronan (HA) have been observed during 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 factor to IRDS, is
known to damage both adult and developing lung, however, the extent and
pattern of impairment depends on lung maturity. We hypothesized that
exposing neonatal rats to hyperoxia alone might result 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 hyperoxia exhibited a time-dependent,
time- limited increase in both lung HA and lung wet weight. Histochemistry
showed the HA in hyperoxia-exposed lungs to be accumulated in perivascular
cuffs of medium sized arteries, 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 [35S]-sulfate to label newly synthesized PGs. Proteoglycans
were extracted, and analyzed by isopycnic CsCl gradient centrifugation,
sequential enzymatic deglycosylation, size chromatography, and sodium
dodecyl sulfate- polyacrylamide gel electrophoresis (SDS-PAGE). When
controlled for total protein extracted, 63% more label was incorporated
into large molecular weight material in the tissue exposed to hyperoxia,
with a 95% increase in incorporation in the most dense fraction, D1. [35S]-
Sulfate incorporation into chondroitin and dermatan sulfate in hyperoxic
tissue specifically increased 116% (242% in the D1 fraction), while
incorporation into heparan sulfate remained essentially unchanged. There
was a nearly fivefold increase in [35S]-sulfate incorporation into
chondroitin sulfate chains in the D1 fraction. When the D1 fractions 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 D1 fraction from hyperoxic tissue of neonatal rats, but
was not detected in the lungs of adolescent animals exposed to hyperoxia.
This CSPG and four additional large CSPGs were noted to be upregulated on
western blotting by a polyclonal antibody directed against the G1 domain of
the aggrecan protein core. We conclude that hyperoxia alone causes an
increase in lung HA and lung water, and speculate that this contributes
significantly to the clinical syndrome of IRDS. In addition, several large
CSPGs are upregulated by hyperoxic exposure in a developmentally specific
manner. We speculate that this increase in CSPGs may interfere with the
normal developmental sequence of events, contributing to
hypoalveolarization.
