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alters surfactant lipid metabolism
Department of Internal Medicine and the Department of Veterans Affairs Medical Center, The University of Iowa College of Medicine, Iowa City, Iowa 52242
Tumor necrosis factor
(TNF)-
is a major cytokine implicated in inducing acute and chronic
lung injury, conditions associated with surfactant
phosphatidylcholine (PtdCho) deficiency. Acutely, TNF-
decreases PtdCho synthesis but stimulates surfactant secretion. To investigate chronic effects of TNF-
, we investigated
PtdCho metabolism in a murine transgenic model exhibiting lung-specific TNF-
overexpression. Compared with controls, TNF-
transgenic mice
exhibited a discordant pattern of PtdCho metabolism, with a decrease in
PtdCho and disaturated PtdCho (DSPtdCho) content in the lung, but
increased levels in alveolar lavage. Transgenics had lower activities
and increased immunoreactive levels of cytidylyltransferase (CCT), a
key PtdCho biosynthetic enzyme. Ceramide, a CCT inhibitor, was
elevated, and linoleic acid, a CCT activator, was decreased in
transgenics. Radiolabeling studies revealed that alveolar reuptake of
DSPtdCho was significantly decreased in transgenic mice. These observations suggest that chronic expression of TNF-
results in a
complex pattern of PtdCho metabolism where elevated lavage PtdCho may
originate from alveolar inflammatory cells, decreased surfactant
reuptake, or altered surfactant secretion. Reduced parenchymal PtdCho
synthesis appears to be attributed to CCT enzyme that is
physiologically inactivated by ceramide or by diminished availability
of activating lipids.
disaturated phosphatidylcholine; choline kinase; choline phosphotransferase
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