Rigon L, Maccari F, Salvalaio M, Legnini E, D’Avanzo F, Galeotti F, Mantovani V, Gabrielli O, Marin O, Scarpa M, Volpi N, Tomanin R. Glycosaminoglycan profile in the Mucopolysaccharidosis type II mouse model at baseline and after 6 weeks treatment with ERT

Mucopolysaccharidosis type II is a lysosomal storage disease due to the deficit of the enzyme iduronate 2-sulfatase (IDS) and to the consequent accumulation of heparan (HS) and dermatan (DS) sulfate, with multi-organ involvement. In this study, we characterized uronic acid-bearing glycosaminoglycans (UA-GAGs) profile in different organs (brain, liver, kidney, heart, lung) of the Ids knock-out (Ids-ko) mouse model at 12 weeks of age and after 6 weeks treatment with the human IDS (hIDS) enzyme, by using the capillary electrophoresis-laser induced fluorescence (CE-LIF) technique. As expected, untreated Ids-ko mice showed a heavy accumulation of total GAGs compared to wild-type (wt) mice, ranging from a 4X increase in lung up to 150X in liver. A deeper analysis of the single UA-GAGs (hyaluronic acid, HA; chondroitin sulfate, CS; DS; HS) highlighted that cumulative CS and DS (CS+DS) and, above all, HS contribute to the observed increase in all organs, whereas HA appears slightly increased in the Ids-ko mice only in the kidney (1.2X). The evaluation of the HS chemical groups composition underlined that the 2-O-sulfated (2s) species are always slightly increased (1.6X) in the Ids-ko mice, 6-O-sulfated (6s) species remain unaltered only in the liver, whereas the N-acetyl (Na) reduce slightly in liver and heart. The disaccharide composition of CS-DS was also examined, pointing out that in liver, heart, kidney and lung the non-sulfated (C0S) and the 6-sulfated (C6S) disaccharides are reduced in the Ids-ko mice, while the 4-sulfated (C4S) disaccharide is increased. This confirmed that the greatest contribution to CS+DS is given by DS, that is naturally more sulfated in position 4. Differently, in the brain the C4S remains unchanged, the C0S is decreased and the C6S is increased, indicating a secondary accumulation of CS in the Ids-ko mice, possibly suggesting an involvement of the molecule in the neurological pathology. We conducted the same analysis also in Ids-ko mice treated with 1 mg/kg of hIDS, once a week for 6 weeks. As expected, we observed a huge reduction of CS+DS and HS in all organs (from 1.7X in lung to 16.4X in liver) vs untreated Ids-ko mice. Only in the brain we did not observe a reduction of the different UA-GAGs, confirming the hIDS inability to cross the blood-brain barrier; only a slight increase in HA levels was observed following treatment. These preliminary data pave the way for a clearer understanding of the involvement of different UA-GAGs species in the pathology of MPS II and also underline the potential of CE-LIF analysis, being a more sensitive technique, for monitoring the therapeutic efficacy. This becomes particularly important in the brain, where very low GAG levels can be detected by common biochemical techniques.