REGULATION OF SURFACTANT ENDOCYTOSIS BY FETAL LUNG CELLS

Project: Research project

Description

Structural immaturity and deficiency of surfactant in the fetal lung
cause the respiratory distress syndrome, the major factor contributing
to neonatal death. Although surfactant replacement therapy reduces
morbidity and mortality, it does not represent a cure for RDS. The
cellular fate and metabolism of exogenous surfactant are unknown. Thus,
understanding the mechanisms of cellular trafficking and reuptake in the
developing fetal lung are crucial now that the use of exogenous
surfactant therapy has become widespread. Reuptake of surfactant by adult type II epithelial cells is energy
dependent and probably occurs via receptor-mediated endocytosis.
Reuptake is enhanced by the major surfactant-associated protein (SP-A),
which specifically binds to type II cells with high affinity and
saturability. This is a fundamental process in the clearance, metabolism
and recycling or resecretion of surfactant. All of the in vitro work on surfactant reuptake has utilized type II
cells isolated from adult lung. We have recently shown a developmental
increase in the reuptake of liposomes by type II cells derived from fetal
rat lung concurrent with morphologic differentiation. This proposal will
study the cellular mechanisms involved in the regulation of the
development of surfactant reuptake using cultures of fetal type II cells.
The effects of SP-A on reuptake of labelled surfactant phospholipid will
be examined in undifferentiated fetal, differentiated fetal and neonatal
type II cells to determine if the developmental changes in reuptake are
mediated by changes in the expression of SP-A or binding of SP-A to the
cell surface. The effects of SP-A on the location of internalized
surfactant phospholipid as a function of time will be studied using cell
fractionation techniques. We then plan to isolate and purify the
putative receptor using ligand affinity chromatography. Once the
receptor is purified, monoclonal antibodies and other molecular probes,
such as cDNA, will be generated to study the developmental regulation of
the expression of the gene for this receptor. In addition, we will use
ligand binding assays to determine if developmental differences in uptake
are due to developmental changes in receptor capacity and/or affinity. Information from this project will be used in future studies of the
regulation of the differentiation of the type II cell.
StatusFinished
Effective start/end date7/1/9312/31/97

Funding

  • National Institutes of Health: $103,801.00
  • National Institutes of Health
  • National Institutes of Health
  • National Institutes of Health: $103,144.00

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Endocytosis
Surface-Active Agents
Lung
Developmental Gene Expression Regulation
Phospholipids
Pulmonary Surfactant-Associated Protein A
Molecular Probes
Recycling
Affinity Chromatography
Liposomes
Cell Differentiation
Ligands
Complementary DNA
Epithelial Cells
Monoclonal Antibodies
Mortality
Therapeutics