Interactions of high-density lipoprotein 3 with brain capillary endothelial cells

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Martin-Nizard, Françoise | Meresse, Stéphane | Cecchelli, Roméo | Fruchart, Jean-Charles | Delbart, Christiane

Edité par CCSD ; Elsevier -

International audience. High-density lipoprotein 3 (HDL₃) binds to capillary endothelial cells when their lumen surfaces are exposed to ¹²⁵I-HDL₃ by post-mortem perfusion of whole brain. Kinetic studies of binding of HDL₃ to issolated membranes show that HDL₃ binds only to endothelial membranes with high affinity (K_d=7 μg/ml). Trypsin treatment of membranes abolishes HDL₃ binding. High-affinity binding sites for HDL₃ were recovered when endothetial cells from bovine brain capillaries were maintained in culture (K_d= 13 μg/ml HDL₃ protein). The characteristics of the binding were preserved up to the 6th passage. Competition experiments using isolated luminal membranes or cultured endothelial cells indicate that only HDL₃ and not LDL or methylated LDL, are able to compete binding of ¹²⁵I-HDL₃. Furthermore, the inhibition of ¹²⁵I-HDL₃ binding by lipoprotein A-I and lipoprotein A-I:A-II shongly suggests that apolipoprotein A-I is implicated in the formation of HDl₃-receptor complexes. The binding is increased by loading cells with free cholesterol or LDL cholesterol. In addition, surface-bound ¹²⁵I-HDL₃ remains sensitive to mild trypsin treatment after subsequent incubation of BBCE at 37° C. HDL₃ bound to the cell surface is not endocytose, but rather rapidly released into the medium after binding (t_1/2= 5 min).

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