Induction of tolerance to human arylsulfatase A in a mouse model of metachromatic leukodystrophy.
A deficiency of arylsulfatase A (ASA) causes metachromatic leukodystrophy (MLD), a lysosomal storage disorder characterized by accumulation of sulfatide, a severe neurological phenotype and early death. The efficacy of enzyme replacement therapy (ERT) has previously been determined in ASA knockout (ASA-/-) mice representing the only available animal model for MLD. Repeated intravenous injection of human ASA (hASA) improved the nervous system pathology and function, but also elicited a progressive humoral immune response leading to treatment resistance, anaphylactic reactions, and high mortality. In contrast to ASA-/- mice, most MLD patients express mutant hASA which may entail immunological tolerance to substituted wildtype hASA and thus protect from immunological complications. To test this notion, a cysteine-to-serine substitution was introduced into the active site of the hASA and the resulting inactive hASA-C69S variant was constitutively expressed in ASA-/- mice. Mice with sub-to supranormal levels of mutant hASA expression were analyzed. All mice, including those showing transgene expression below the limit of detection, were immunologically unresponsive to injected hASA. More than 100-fold overexpression did not induce an overt new phenotype except occasional intralysosomal deposition of minor amounts of glycogen in hepatocytes. Furthermore, long-term, low-dose ERT reduced sulfatide storage in peripheral tissues and the central nervous system indicating that high levels of extracellular mutant hASA do not prevent cellular uptake and lysosomal targeting of substituted wildtype hASA. Due to the tolerance to hASA and maintenance of the MLD-like phenotype, the novel transgenic strain may be particularly advantageous to assess the benefit and risk of long-term ERT.
Institut für Physiologische Chemie, Rheinische Friedrich-Wilhelms-Universität, Nussallee 11, D-5315 Bonn, Germany. matzner@institut.physiochem.uni-bonn.de
Ulrich
U
Matzner
Frank
F
Matthes
Eva
E
Herbst
Renate
R
Lüllmann-Rauch
Zsuzsanna
Z
Callaerts-Vegh
Rudi
R
D'Hooge
Cecilia
C
Weigelt
Carl
C
Eistrup
Jens
J
Fogh
Volkmar
V
Gieselmann
D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D002553:Cerebroside-Sulfatase / Q000008:administration & dosage / Q000235:genetics / Q000378:metabolism / Q000627:therapeutic use* / Q000648:ultrastructure; D006224:Cricetinae; D004195:Disease Models, Animal; D004334:Drug Administration Schedule; D004797:Enzyme-Linked Immunosorbent Assay; D015870:Gene Expression; D006801:Humans; D007108:Immune Tolerance / Q000235:genetics*; D007275:Injections, Intravenous; D007668:Kidney / Q000166:cytology; D007966:Leukodystrophy, Metachromatic / Q000188:drug therapy* / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D008099:Liver / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D051379:Mice; D008822:Mice, Transgenic; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000627:therapeutic use; D012694:Serine / Q000378:metabolism; D019076:Transgenes
D011994:Recombinant Proteins; D012694:Serine; D002553:Cerebroside-Sulfatase