Extracellular vesicles derived from cells overexpressing HGSNAT rescue defects in Mucopolysaccharidosis IIIC neurons

Mucopolysaccharidosis III type C (MPS IIIC) is a rare neurological lysosomal storage disorder caused by genetic deficiency of the lysosomal membrane enzyme, heparan--glucosaminide N-acetyltransferase (HGSNAT). To assess the feasibility of therapeutic strategies based on cross-correction of neurons by HGSNAT secreted from transplanted cells overexpressing the enzyme, we generated induced cortical neurons (iCN) from induced pluripotent stem cells (iPSCs) derived from MPS IIIC patients. The neurons were treated with extracellular vesicles (EV) purified from the culture medium conditioned by human endothelial cells transduced with a lentiviral vector encoding EGFP-tagged HGSNAT (LV-HGSNAT-EGFP). The isolated EV showed supraphysiologic HGSNAT activity levels and efficiently delivered the enzyme to the lysosomes of MPS IIIC iCN reducing lysosomal size and restoring normal synaptic protein levels. EV-mediated delivery of HGSNAT to neurons was further confirmed by the analysis of MPS IIIC iCN either co-cultured with iPSC-derived MPS IIIC microglia (iMGL) transduced with LV-HGSNAT-EGFP or treated with the iMGL conditioned medium. MPS IIIC iCN co-cultured with iMGL overexpressing HGSNAT achieved a complete phenotypic rescue, including normalization of lysosomal size, and the levels of heparan sulfate, GM2-ganglioside, synaptic proteins and brain-derived neurotropic factor. Treatment of MPS IIIC iCNs with conditioned medium led to a partial defects correction. Our findings reveal the translational potential of EV-mediated enzyme delivery in MPS IIIC patients treated with LV-mediated haematopoietic progenitor stem cell gene therapy.