BACKGROUND: The objective of this study was to examine specific membrane binding of [125I]-acylation stimulating protein (ASP) in cultured human skin fibroblasts obtained from normal subjects and patients with hyperapoB. ASP is a small basic protein isolated from human plasma that stimulates triglyceride synthesis (TGS) and glucose transport (GT) in human skin fibroblasts and adipocytes. DESIGN: In the present study, three groups were studied: normal (NASP-NB) subjects, hyperapoB subjects with normal plasma ASP (NASP-HB) and hyperapoB subjects with high plasma ASP (HASP-HB). RESULTS: ASP-induced TGS in fibroblasts from HASP-HB subjects was significantly less than in the two control groups with normal plasma ASP (NASP-NB and NASP-HB). Similarly, ASP stimulation of GT was less in HASP-HB fibroblasts than in the NASP-HB fibroblasts or the NASP-NB subjects. Insulin-induced TGS was similar in all three groups as was insulin-stimulated GT. As well, protein kinase C-mediated stimulation was equivalent among the three groups both for GT and for TGS. There was no significant difference in the binding affinity (Kd) of [125I]-ASP to intact cells in any group. By contrast, binding of [125I]-ASP revealed a significantly lower Bmax of the HASP-HB cell lines than the NASP-NB cells and the NASP-HB cells. CONCLUSION: A decrease in the ASP cell-surface receptor concentration is responsible for decreased ASP stimulation of TGS, and GT and may contribute to the inefficient postprandial triglyceride (TG) clearance in HASP-HB subjects.
BACKGROUND: The objective of this study was to examine specific membrane binding of [125I]-acylation stimulating protein (ASP) in cultured human skin fibroblasts obtained from normal subjects and patients with hyperapoB. ASP is a small basic protein isolated from human plasma that stimulates triglyceride synthesis (TGS) and glucose transport (GT) in human skin fibroblasts and adipocytes. DESIGN: In the present study, three groups were studied: normal (NASP-NB) subjects, hyperapoB subjects with normal plasma ASP (NASP-HB) and hyperapoB subjects with high plasma ASP (HASP-HB). RESULTS: ASP-induced TGS in fibroblasts from HASP-HB subjects was significantly less than in the two control groups with normal plasma ASP (NASP-NB and NASP-HB). Similarly, ASP stimulation of GT was less in HASP-HB fibroblasts than in the NASP-HB fibroblasts or the NASP-NB subjects. Insulin-induced TGS was similar in all three groups as was insulin-stimulated GT. As well, protein kinase C-mediated stimulation was equivalent among the three groups both for GT and for TGS. There was no significant difference in the binding affinity (Kd) of [125I]-ASP to intact cells in any group. By contrast, binding of [125I]-ASP revealed a significantly lower Bmax of the HASP-HB cell lines than the NASP-NB cells and the NASP-HB cells. CONCLUSION: A decrease in the ASP cell-surface receptor concentration is responsible for decreased ASP stimulation of TGS, and GT and may contribute to the inefficient postprandial triglyceride (TG) clearance in HASP-HB subjects.