Inclusions in novel perivascular macrophages (Mato's fluorescent granular perithelial cells) and neurons in the cerebral cortex of Hex A- and Hex B-deficient mice.

Abstract

Beta-hexosaminidases are important enzymes for lipid and saccharide metabolism in the brain. In mice deficient in these enzymes, indigestible metabolic intermediates deposit in neurons. Inclusions such as membranous cytoplasmic bodies (MCB) and zebra bodies were seen in neurons of Tay-Sachs (TS) model mice, Sandhoff's disease (SD) model mice, and double knockout (DKO) mice. However, the cerebral perivascular macrophages discovered by Mato are active in the uptake of waste products and regarded as scavenger cells under steady-state conditions. We observed that indigestible components derived from neurons were taken up by the perivascular macrophages of TS mice by pinocytosis, but those of SD and DKO mice contained only pale inclusions and had marked vacuolations, and pinocytosis was rarely observed. Histochemically, the inclusions in the perivascular macrophages of TS mice were positive for the PAS stain, but those of SD and DKO mice were negative. In addition, the perivascular cells of TS mice expressed clear positive immunoreactivity against BM-8 and F4/80, but those of DKO mice had very weak BM-8 and F4/80 immunoreactivity. These differences between TS, SD, and DKO mice are based on their metabolism of oligosaccharides and glycosaminoglycans (GAG). Thus, hexosaminidase B is more important for keeping normal morphology and function of perivascular macrophages than hexosaminidase A. The foamy cells that appeared along the cerebral microvessels in lipidosis and saccharidosis were identified as perivascular macrophages (Mato's fluorescent granular perithelial cells: FGP cells).