Polyglutamine disorders are inherited neurodegenerative diseases caused by the accumulation of expanded polyglutamine protein (polyQ). Previously, we identified a new guanosine triphosphatase, CRAG, which facilitates the degradation of polyQ aggregates through the ubiquitin-proteasome pathway in cultured cells. Because expression of CRAG decreases in the adult brain, a reduced level of CRAG could underlie the onset of polyglutamine diseases. To examine the potential of CRAG expression for treating polyglutamine diseases, we generated model mice expressing polyQ predominantly in Purkinje cells. The model mice showed poor dendritic arborization of Purkinje cells, a markedly atrophied cerebellum and severe ataxia. Lentivector-mediated expression of CRAG in Purkinje cells of model mice extensively cleared polyQ aggregates and re-activated dendritic differentiation, resulting in a striking rescue from ataxia. Our in vivo data substantiate previous cell-culturebased results and extend further the usefulness of targeted delivery of CRAG as a gene therapy for polyglutamine diseases.

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Previous studies from our laboratory demonstrated that PVC-211 murine leukemia virus (MuLV), a neuropathogenic variant of Friend MuLV (F-MuLV), had undergone genetic changes which allowed it to efficiently infect rat brain capillary endothelial cells (BCEC) in vivo and in vitro. Two amino acid changes from F-MuLV in the putative receptor binding domain (RBD) of the envelope surface protein of PVC-211 MuLV (Glu-116 to Gly and Glu-129 to Lys) were shown to be sufficient for conferring BCEC tropism on PVC-211 MuLV. Recent examination of the unique RBD of PVC-211 MuLV revealed that the substitution of Lys for Glu at position 129 created a new heparin-binding domain that overlapped a heparin-binding domain common to ecotropic MuLVs. In this study we used heparin-Sepharose columns to demonstrate that PVC-211 MuLV, but not F-MuLV, can bind efficiently to heparin and that one or both of the amino acids in the RBD of PVC-211 MuLV that are associated with BCEC tropism are responsible. We further showed that heparin can enhance or inhibit MuLV infection and that the mode of action is dependent on heparin concentration, sulfation of heparin, and the affinity of the virus for heparin. Our results suggest that the amino acid changes that occurred in the envelope surface protein of PVC-211 MuLV may allow the virus to bind strongly to the surface of BCEC via heparin-like molecules, increasing the probability that the virus will bind to its cell surface receptor and efficiently infect these cells.

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