Hormonal and developmental regulation of pulmonary surfactant synthesis in fetal lung. Baillière's Clin
Baillière s Clinical Endocrinology and Metabolism 07/1990; 4(2):351-78. DOI: 10.1016/S0950-351X(05)80055-2
Pulmonary surfactant, a unique developmentally regulated, phospholipid-rich lipoprotein, is synthesized by the type II cells of the pulmonary alveolus, where it is stored in organelles termed lamellar bodies. The principal surface-active component of surfactant, dipalmitoylphosphatidylcholine, a disaturated form of phosphatidylcholine, acts in concert with the surfactant-associated proteins to reduce alveolar surface tension. Relatively large amounts of phosphatidylglycerol also are present in lung surfactants of a number of species, including man. The role of phosphatidylglycerol in surfactant function has not been elucidated; however, its presence in increased amounts in pulmonary surfactant is correlated with enhanced fetal lung maturity. Surfactant glycerophospholipid synthesis in fetal lung tissue is regulated by a number of hormones and factors, including glucocorticoids, prolactin, insulin, oestrogens, androgens, thyroid hormones, and catecholamines acting through cyclic AMP. In studies with human fetal lung in organ culture, we have observed that glucocorticoids, in combination with prolactin and/or insulin, increase the rate of lamellar body phosphatidylcholine synthesis and alter lamellar body glycerophospholipid composition to one reflective of surfactant secreted by the human fetal lung at term.
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ABSTRACT: Infants of diabetic mothers are frequently hyperinsulinemic and have an increased incidence of neonatal respiratory distress syndrome, a disease caused by a deficiency in the production of pulmonary surfactant by alveolar type II cells. It has been hypothesized that insulin inhibits fetal lung type II cell differentiation. We have shown previously that insulin inhibits the accumulation of surfactant protein (SP)-A and SP-B mRNA and has no effect on SP-C mRNA levels in human fetal lung tissue maintained in vitro. We hypothesized that treatment with glucocorticoids, which are used clinically to accelerate human fetal lung maturation, would overcome the inhibitory effects of insulin on human fetal lung development. In the present study, human fetal lung explants were maintained in the presence or absence of cortisol added alone, or in insulin plus cortisol added together. Cortisol significantly decreased SP-A mRNA levels by approximately 50% at the 100 nM concentration and significantly increased levels by approximately 20% at the 1 nM concentration. Cortisol increased SP-B and SP-C mRNA levels in a dose-dependent fashion (5- and 45-fold at 100 nM cortisol, respectively). The combination of 1 nM cortisol and insulin resulted in inhibition of mRNA levels for SP-A, SP-B, and SP-C at the high insulin concentrations (approximately 50% inhibition for SP-A and SP-B and approximately 25% inhibition of SP-C mRNA levels, in the presence of 40 pmol/L x 10(-3) insulin). Surprisingly, 100 nM cortisol plus inhibitory concentrations of insulin increased SP-A mRNA levels (2-fold at 40 pmol/L x 10(-3).(ABSTRACT TRUNCATED AT 250 WORDS)
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ABSTRACT: A new form of cell death has been observed. The death occurs at liquid-air interfaces when Tetrahymena cells are grown in a chemically defined medium (CDM) at low inocula. The cells die by lysis at the liquid-air interface (medium surface), which they reach due to negative gravitaxis as well as positive aerotaxis. When the cells are grown in a closed compartment, with no liquid-air interface, the death is not observed, and the cells proliferate. Cloning of cells in CDM is thus possible. The addition of effectors such as NGF (10(-11) M), EGF (10(-10) M), PDGF (10(-10) M), and insulin (10(-7) M) to cells in CDM prevents the surface mediated death. Since detergents/surfactants like SDS (7 x 10(-5) M), NP-40 (2 x 10(-5) M), Tween 80 (10(-4))% w/v), Pluronic F-68 (10(-7) M), and the biosurfactant surfactin (10(-6) M) have the same effect, we suggest that the effectors act by stimulating the cells to exudate surfactant(s) of their own. Furthermore, lyzed cells and exudates from living cells (pre-conditioned medium) prevent the death. In conditions with liquid-air interfaces, certain physical parameters are of great importance for the survival of cells at low inocula. The parameters are the distance to the surface, the temperature, and the inoculum. By increasing the height of the medium, lowering the temperature, and increasing the inoculum of the culture, the survival can be greatly enhanced. There is no evidence for programmed cell death (PCD) or apoptosis.
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