Rescue of TDP-43 and neuronal pathologies by peripheral AAV-mediated expression of brain-penetrant progranulin in a mouse model of GRN-linked frontotemporal lobar degeneration

Progranulin (PGRN) haploinsufficiency is a major risk factor for Frontotemporal Lobar Degeneration with TDP-43 pathology (FTLD-TDP). Protein replacement therapeutic strategies are currently in clinical development, intended to restore PGRN levels in the central nervous system and slow or halt disease progression. However, such approaches require repeated dosing. Here, we explored the use of adeno-associated virus (AAV) to achieve sustained expression of a brain penetrant PGRN fusion protein, composed of a single chain variable fragment (scFv) recognizing mouse transferrin receptor (TfR) fused to human PGRN (AAV(L):bPGRN). We evaluated this approach for its ability to rescue pathological phenotypes in a double knockout mouse model lacking both PGRN and TMEM106b. A single administration of AAV(L):bPGRN reduced FTLD-TDP associated pathologies including severe motor function deficits, formation of insoluble, abnormally processed and phosphorylated TDP-43, as well as dysfunctional protein degradation, lipid dysregulation and gliosis. Overall design: We generated AAV(L):bPGRN (L = liver, b = brain-penetrant), a liver-targeting adenovirus (AAV) encoding a fusion protein (8D3:PGRN) consisting of a single chain fragment variable (scFv) antibody recognizing mouse TfR (transferrin receptor) fused to human PGRN (hPGRN). To study the effects of AAV(L):bPGRN, we treated 6-week old wildtype or GRN,TMEM106B double knock-out mice with either 1.3 x 10^13 vg/kg AAV or isotonic saline solution (0.9% NaCl) intravenously via tail vain injection. 9-10 weeks after the treatment the animals were sacrificed; they were anesthetized and transcardiacally perfused with PBS. From each animal, one hemibrain (excluding the olfactory bulb, but including cerebellum) was collected, snap frozen on dry ice and pulverized with a pistill. All animal experiments were performed according to German animal welfare law and approved by the government of upper Bavaria.