Growth retardation of Mato's fluorescent granular perithelial (FGP) cells in scavenger receptor knockout (SRKO) mice.

Mato's fluorescent granular perithelial (FGP) cells are situated between the basal lamina of cerebral microvessels and the glia limitans covering astrocytic processes. Because they are potent enough to take up endo- and exogenous substances in a steady state, they are regarded as scavenger cells in the central nervous system. The scavenger receptor for oxidized low-density lipoprotein (LDL) is also expressed on their cytoplasmic membrane. We studied the differentiation and growth of FGP cells in wild-type and scavenger receptor knockout (SRKO) mice. Wild-type (129 strain) and SRKO mice at 1, 3, 5, 8, 10, 14, and 28 days after birth were employed in this study. Stretch specimens of their cerebral cortices were used for immunohistochemical investigations, and Epon-embedded specimens of the same region were studied with an electron microscope. In wild-type mice, perivascular cells derived from the pial tissue were transformed at approximately 8 days after birth into the FGP cells, which, provided with several epitopes common to macrophage lineages, developed over a period of 14 days. The FGP cells possessed several inclusions and were surrounded by two defined sheets of basal lamina and continuous glia limitans. At 4 weeks, their morphology, enzymatic activity, and epitopes advanced with the aging of the mice. However, in SRKO mice, at 8 days, the perivascular cells took fibroblastoid forms with scarce lysosomal inclusions, and, even at 14 days, glia limitans remained discontinuous and most of FGP cells remained immature in their cytoplasmic organelles. Different from the case with the wild-type, the intensity of the labeling of epitopes remained at a low level. At 4 weeks, some of the FGP cells fell into degeneration, and the others were differentiated to a certain degree. The development of Mato's FGP cells in SRKO mice was retarded in the morphology, enzyme activity, and epitopes. The scavenger receptor, which reacted with the antibody 2F8, seems to be closely associated with the development of Mato's FGP cells.