Chronic hypercapnia alters lung matrix composition in mouse pups.
BACKGROUND
permissive hypercapnia, a stretch-limiting ventilation strategy, often results in high Pa(CO(2)). This strategy is associated with reduced morbidity and mortality in premature infants and its benefits have been attributed to diminished barotrauma. However, little is known about the independent effect of high CO(2) levels during the lung development.


METHODS
mice were exposed to 8% CO(2) or room air for 2 wk either from postnatal day 2 through 17 or as adults (approximately 2 mo of age). Lungs were excised and processed for protein, RNA, histology, and total lung volumes.


RESULTS
histologic analysis demonstrated that alveolar walls of CO(2)-exposed mouse pups were thinner than those of controls and had twice the total lung volume. Molecular analysis revealed that several matrix proteins in the lung were downregulated in mouse pups exposed to hypercapnia. Interstitial collagen type I alpha1, type III alpha1, elastin and fibronectin protein, and mRNA levels were less than half of controls while collagen IV alpha 5 was unaffected. This decrease in interstitial collagen could thus account for the thinning of the interstitial matrix and the altered lung biomechanics. Matrix metalloproteinase (MMP)-8, a collagenase that has specificity for collagen types I and III, increased in hypercapnic mouse pups, suggesting increased collagen degradation. Moreover, tissue inhibitor of MMP (TIMP)-1, a potent inhibitor of MMP-8, was significantly decreased. However, unlike pups, adult mice exposed to hypercapnia demonstrated only a mild increase in total lung volumes and did not exhibit similar molecular or histologic changes.


CONCLUSIONS
although permissive hypercapnia may prevent lung injury from barotrauma, our study revealed that exposure to hypercapnia may be an important factor in lung remodeling and function, especially in early life.
Ryu
Julie
J
University of California, San Diego, Department of Pediatrics, Section of Respiratory Medicine, 9500 Gilman Dr., MC 0735, La Jolla, CA 92093, USA. J1Ryu@ucsd.edu
Heldt
Gregory P
GP
Nguyen
Mary
M
Gavrialov
Orit
O
Haddad
Gabriel G
GG
D056151:Airway Remodeling; D000818:Animals; D000831:Animals, Newborn; D002245:Carbon Dioxide / Q000378:metabolism*; D002908:Chronic Disease; D016326:Extracellular Matrix Proteins / Q000032:analysis / Q000378:metabolism; D006935:Hypercapnia / Q000378:metabolism / Q000473:pathology*; D008168:Lung / Q000254:growth & development* / Q000378:metabolism / Q000473:pathology*; D008176:Lung Volume Measurements; D008297:Male; D020784:Matrix Metalloproteinase 8 / Q000032:analysis / Q000378:metabolism; D051379:Mice; D019715:Tissue Inhibitor of Metalloproteinase-1 / Q000032:analysis / Q000378:metabolism
D016326:Extracellular Matrix Proteins; D019715:Tissue Inhibitor of Metalloproteinase-1; D002245:Carbon Dioxide; D020784:Matrix Metalloproteinase 8