Increased phosphatidylcholine production but disrupted glycogen metabolism in fetal type II cells of mice that overexpress CTP:phosphocholine cytidylyltransferase.
CTP:phosphocholine cytidylyltransferase (CCT) is a rate-determining enzyme in the de novo synthesis of phosphatidylcholine (PtdCho). Alveolar type II cells synthesize large quantities of disaturated PtdCho, the surface-active agent of pulmonary surfactant, particularly at late gestation when the lung prepares itself for postnatal air breathing. To clarify the role of CCTalpha in lung surfactant maturation, we overexpressed CCTalpha(1-367) using the surfactant protein-C promoter. Lungs of transgenic mice were analyzed at day 18 of gestation (term = 19 days). Overexpression of CCTalpha(1-367) increased the synthesis and content of PtdCho in fetal type II cells isolated from the transgenic mice. Also, PtdCho content of fetal lung fluid was increased. No changes in surfactant protein content were detected. Interestingly, fetal type II cells of transgenic mice contained more glycogen than control cells. Incorporation studies with [U-(14)C]glucose demonstrated that overexpression of CCTalpha(1-367) in fetal type II cells increased glycogen synthesis without affecting glycogen breakdown. To determine which domain contributes to this glycogen phenotype, two additional transgenes were created overexpressing either CCTalpha(1-239) or CCTalpha(239-367). Glycogen synthesis and content were increased in fetal type II cells expressing CCTalpha(239-367) but not CCTalpha(1-239)(.) We conclude that overexpression of CCTalpha increases surfactant PtdCho synthesis without affecting surfactant protein levels but that it disrupts glycogen metabolism in differentiating type II cells via its regulatory domain.
Ridsdale
Ross
R
Canadian Institutes of Health Research Group in Lung Development, Hospital for Sick Children Research Institute and Institute of Medical Sciences, University of Toronto, 555 University Avenue, Toronto M5G 1X8, Canada.
Tseu
Irene
I
Roth-Kleiner
Matthias
M
Wang
Jinxia
J
Post
Martin
M
D000818:Animals; D015153:Blotting, Western; D002794:Choline / Q000378:metabolism; D019916:Choline-Phosphate Cytidylyltransferase / Q000235:genetics* / Q000502:physiology*; D005838:Genotype; D005947:Glucose / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism*; D015151:Immunoblotting; D007834:Lasers; D008168:Lung / Q000378:metabolism / Q000473:pathology; D013058:Mass Spectrometry; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D008957:Models, Genetic; D010641:Phenotype; D010713:Phosphatidylcholines / Q000737:chemistry* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011663:Pulmonary Surfactants / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D019076:Transgenes
D010713:Phosphatidylcholines; D011663:Pulmonary Surfactants; D012333:RNA, Messenger; D006003:Glycogen; D019916:Choline-Phosphate Cytidylyltransferase; D005947:Glucose; D002794:Choline