Progranulin: A Novel Gene in Gaucher Diseases

Project Summary Modifier genes are responsible for the diverse phenotypes among Gaucher disease (GD) patients harboring identical GBA1 mutations. Thus, identification and characterization of new modifier genes in GD will provide invaluable information for understanding the pathogenesis of GD and discovering novel therapeutic targets for GD. We identified progranulin (PGRN), encoded by the gene GRN, as a key modifier of GCase through direct interaction and stimulation of GCase activity. During the original funding period, we generated Grn-/-GbaD409v/null (termed PG9Vn) mice. Initial assays of PG9Vn mice demonstrated that PGRN deficiency markedly exacerbated GD phenotypes. Importantly, PG9Vn mice developed significant neuronopathic GD (nGD). There is an urgent medical need for treating nGD, since Enzyme Replacement Therapy (ERT) and Substrate Reduction Therapy (SRT) for GD cannot penetrate the blood brain barrier (BBB). Excitingly, a PGRN C-terminal domain, ND7, could cross the BBB and act to increase endogenous CNS GCase activity and exhibit potential therapeutic effects against nGD. Further, we isolated C5a as a novel binding partner of PGRN. PGRN inhibited C5a/C5aR1 signaling by blocking the binding of C5a to C5aR1; deletion of C5aR1 reversed the GD phenotypes seen in ovalbumin-challenged Grn-/- mice. Intriguingly, PGRN N-terminal domain mediates PGRN’s interaction with C5a and may act as an SRT through inhibition of C5a/C5aR1 activated UDP-glucose ceramide glucosyltransferase, leading to the suppression of GCase substrate glucosylceramide production. Thus, this continued application is primarily based on 1) the generation of new PG9Vn model and discovery of PGRN derived ND7 as a BBB- penetrating biologic, 2) the isolation of PGRN as an antagonist of C5a/C5aR1 signaling, and 3) the finding that PGRN’s N-terminal and C-terminal domains have SRT- and ERT-like activities, respectively. The central hypothesis of this renewal is that PGRN is a key modifier in GD and its derivatives are therapeutic against GD. The Specific Aims are: (1) To determine the importance of PGRN/GBA1 mutation interplay in GD in vivo and to evaluate the therapeutic effects of PGRN-derived ND7 in treating GD. We will characterize the visceral GD and CNS nGD phenotypes of PG9Vn mice and elucidate the cellular and molecular mechanisms involved (SA#1A, 1B); and we will leverage various GD models, including our newly generated PG9Vn mice, Gba-specific models (Gba9V/null, 4L;C*) and GD patient derived brain organoids, to test the therapeutic effects of ND7 in GD, with special focus on nGD (SA#1C); and (2) To define the importance of PGRN/C5a interplay in the pathogenesis of GD. We will characterize the PGRN/C5a interaction in GD (SA#2A); elucidate the interplay between PGRN and C5a in regulating macrophage and lysosomal function, as well as the molecular events involved (SA#2B); and determine the interplay between PGRN and C5a/C5aR1 signaling and therapeutic potential of inhibiting C5a/C5aR1 signaling through PGRN derivatives to treat GD (SA#2C). The proposed research will not only advance our understanding of GD pathogenesis, but may also lead to novel biologics for GD, in particular nGD.