Developmentally regulated mannose 6-phosphate receptor-mediated transport of a lysosomal enzyme across the blood-brain barrier

Abstract

Mucopolysaccharidosis type VII is a lysosomal storage disorder resulting from inherited deficiency of ␤-glucuronidase (GUS). Mucopolysaccharidosis type VII is characterized by glycosaminoglycan storage in most tissues, including brain. In these disorders, enzyme delivery across the blood-brain barrier (BBB) is the main obstacle to correction of lysosomal storage in the CNS. Prior studies suggested mouse brain is accessible to GUS in the first 2 weeks of life but not later. To explore a possible role for the mannose 6-phosphate͞insulin-like growth factor II receptor in GUS transport across the BBB in neonatal mice, we compared brain uptake of phosphorylated GUS (P-GUS) and nonphosphorylated GUS (NP-GUS) in newborn and adult mice. 131 I-P-GUS was transported across the BBB after i.v. injection in 2-day-old mice. The brain influx rate (Kin) of 131 I-P-GUS in 2-day-old mice was 0.21 l͞g⅐min and decreased with age. By 7 weeks of age, transport of 131 I-P-GUS was not significant. Capillary depletion revealed that 62% of the 131 I-P-GUS in brain was in brain parenchyma in 2-day-old mice. In addition, uptake of 131 I-P-GUS into brain was significantly reduced by coinjection of unlabeled P-GUS or M6P in a dose-dependent manner. In contrast, the Kin of 131 I-NP-GUS (0.04 l͞g⅐min) was significantly lower than 131 I-P-GUS in 2-day-old mice. Transcardiac brain perfusion confirmed that neither 131 I-P-GUS nor 131 I-NP-GUS crossed the BBB in adult mice. These results indicate that 131 I-P-GUS transport into brain parenchyma in early postnatal life is mediated by the mannose 6-phosphate͞insulin-like growth factor II receptor. This receptor-mediated transport is not observed in adult mice.␤-glucuronidase ͉ mannose 6-phosphate͞insulin-like growth factor II receptor ͉ central nervous system ͉ lysosomal storage disease ͉ phosphorylated ␤-glucuronidase

Targeted delivery of proteins across the blood–brain barrier

“…injection. To determine the extent of delivery of sGCmApoB and sGFPmApoB to the CNS, adult mice (Ͼ8 weeks) were used to mimic the BBB environment observed in the patient (12).…”

Visualization of targeted transduction by engineered lentiviral vectors

“…To visualize the distribution of endosomal compartments, we used antibodies against early endosome antigen 1 (EEA1) [26][27][28] and cation-independent mannose-6-phosphate receptor (CI-MPR) 26,35 as the early and late endosomal markers, respectively. As shown in Figure 3a, the early and the late endosomal markers were largely separated.…”

Chronic enzyme replacement therapy ameliorates neuropathology in alpha‐mannosidosis mice

“…According to Sly and coworkers using recombinant GUS in preclinical ERT studies with MPSVII mice,24, 34 mannose‐6 phosphate receptors (MPRs) that are responsible for intracellular lysosomal targeting of most lysosomes enzymes and their cellular uptake35, 36 cannot account for the uptake of recombinant lysosomal enzymes into adult brain due to their restricted expression in brain endothelial cells within the perinatal period (2 weeks after birth). In adult animals which lack expression of endothelial MPRs, administration of recombinant enzymes bearing mannose 6‐phosphate (M6P) residues might even diminish their uptake into brain as demonstrated for GUS 24, 30, 34. Of note, recombinant rhLAMAN which, in comparison with other lysosomal enzymes, is highly efficient in clearance of brain primary substrate storage is only marginally phosphorylated, suggesting primarily M6P‐independent uptake 16.…”