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Título: Triglyceride synthesis in normal and hyperapoB fibroblasts
Autores: Cianflone, Katherine M
Fecha: 1989
Publicador:
Fuente: Ver documento
Tipo: Thesis
NonPeerReviewed
Tema:
Descripción: The goal of this thesis was to examine the regulation of intracellular triglyceride synthesis from normals and HyperapoB patients using cultured skin fibroblasts as an experimental model. In a medium supplemented with lipoprotein-deficient serum, triglyceride synthesis and cholesterol esterification were reduced in the HyperapoB fibroblasts by 40% and 44% respectively as compared to the normal fibroblasts. These differences were due to differences in de novo synthesis, and not due to re-esterification or hydrolysis. However, unexpectedly, there was no difference in triglyceride synthesis between the cells from normals and HyperapoB when a serum-free supplemented medium was used. The stimulatory factor in lipoprotein-deficient serum was then isolated from human plasma and characterized. The factor responsible is nondialyzable and trypsin sensitive, and its effects are both concentration and time dependent. The protein responsible has been purified to homogeneity and is a small (MW 14,000), basic (pI 9.0) protein. It has been named Acylation Stimulating Protein (ASP) because it markedly stimulates triglyceride synthesis and cholesterol esterification by 80% and 42% in normal human skin fibroblasts. Further ASP is specifically bound with a KD of 9.9 $\times$ 10$\sp{-7}$ and is internalized and degraded by normal human skin fibroblasts. In contrast, ASP has much less effect on triglyceride synthesis in HyperapoB fibroblasts with an average of only 25% triglyceride stimulation. This is consistent with its reduced maximal binding (51% of normal) and subsequent internalization into these cells. Although both cell groups demonstrate the same binding affinity for ASP (Scatchard analysis slope = $-.0725$ ug$\sp{-1}$ normal and $-.080$R ug$\sp{-1}$ HyperapoB) the maximal number of apparent binding sites is reduced in HyperapoB (1.217 mg$\sp{-1}$ normal vs 0.621 mg$\sp{-1}$ HyperapoB). The ASP effect on cells from patients with Familial Hypercholesterolemia, however, is normal with regard to ASP stimulation of triglyceride synthesis (average 55% stimulation) and ASP binding to cells. This research therefore has led to the description of a previously unrecognized protein in human plasma. This protein, ASP, appears to be the most potent stimulant of intracellular triglyceride synthesis yet described
Idioma: No aplica