Developmental differences between cation-independent and cation-dependent mannose-6-phosphate receptors in rat brain at perinatal stages

Mannose-6-phosphate receptors (MPRs) play a role in the selective transport of macromolecules bearing mannose-6-phosphate residue to lysosomes. To date, two types of MPRs have been described in most of cells and tissues: the cation-dependent (CD-MPR) and cation-independent mannose-6-phosphate receptor (CI-MPR). In order to elucidate their possible role in the central nervous system, the expression and binding properties of both MPRs were studied in rat brain along perinatal development. It was observed that the expression of CI-MPR decreases progressively from fetuses to adults, while the CD-MPR increases around the 10th day of birth, and maintains these values up to adulthood. Binding assays showed differences in the B_max and K_D values between the ages studied, and they did not correlate with the expression levels of both MPRs. Variations in lysosomal enzyme activities and expression of phosphomannosylated ligands during development correlated more with CD-MPR than with CI-MPR expression. These results suggest that both receptors play a different role in rat brain during perinatal development, being CD-MPR mostly involved in lysosome maturation.