Biallelic mutations in GBA1 that lead to reduced β-glucocerebrosidase (GCase) activity result in the monogenic lysosomal storage disease Gaucher disease (GD). Variants in one GBA1 allele are the most common genetic risk factor for multiple synucleinopathies including Parkinson’s disease (PD). Therapies to increase GCase activity in the brain hold great promise for the treatment of these diseases. To this end, we have developed blood-brain barrier penetrant therapeutic molecules by fusing antibody moieties that bind the transferrin receptor (TfR) to murine or human GCase (referred to as mGCase-mBS or hGCase-hBS, respectively). We demonstrate that these fusion proteins maintain full enzymatic activity and, while their total cellular uptake is only marginally increased compared to the enzyme alone, they have up to 100-fold better lysosomal uptake and function. Uptake and efficacy of GCase-BS relies primarily on binding to the TfR, rather than to mannose phosphate receptors (M6PRs) as conventional enzyme replacement therapy. In a GD cellular model, GCase-BS rapidly rescues the lysosomal proteome and lipid accumulations beyond known GCase substrates. Intravenous injection of mGCase-mBS leads to significant reduction of brain lysosomal membrane lipids in a GD mouse model which is sustained for four weeks. Monthly dosing over six months shows sustained efficacy and reduces neurofilament-light chain (NFL) plasma levels. Collectively, these findings demonstrate the great potential of TfR-targeted GCase for treating GBA1-associated neurodegeneration, provide insight into candidate biomarkers of GD lysosomal dysfunction, and ultimately may open a new treatment paradigm for lysosomal storage diseases (LSDs) extending beyond the central nervous system (CNS).

Mutations in glucocerebrosidase cause the lysosomal storage disorder Gaucher’s disease and are the most common risk factor for Parkinson’s disease. Therapies to restore the enzyme’s function in the brain hold great promise for treating the neurological implications. Thus, we developed blood-brain barrier penetrant therapeutic molecules by fusing transferrin receptor-binding moieties to β-glucocerebrosidase (referred to as GCase-BS). We demonstrate that these fusion proteins show significantly increased uptake and lysosomal efficiency compared to the enzyme alone. In a cellular disease model, GCase-BS rapidly rescues the lysosomal proteome and lipid accumulations beyond known substrates. In a mouse disease model, intravenous injection of GCase-BS leads to a sustained reduction of glucosylsphingosine and can lower neurofilament-light chain plasma levels. Collectively, these findings demonstrate the potential of GCase-BS for treating GBA1-associated lysosomal dysfunction, provide insight into candidate biomarkers, and may ultimately open a promising treatment paradigm for lysosomal storage diseases extending beyond the central nervous system.