AAV-Mediated Progranulin Delivery to a Mouse Model of Progranulin Deficiency Causes T Cell-Mediated Toxicity

Abstract

Adeno-associated virus-mediated gene replacement is emerging as a safe and effective means of correcting single-gene mutations affecting the CNS. AAV-mediated progranulin gene (GRN) delivery has been proposed as a treatment for GRNdeficient frontotemporal dementia and neuronal ceroid lipofuscinosis, and recent studies using intraparenchymal AAV-Grn delivery to brain have shown moderate success in histopathologic and behavioral rescue in mouse models. Here, we used AAV9 to deliver GRN to the lateral ventricle to achieve widespread expression in the Grn null mouse brain. We found that, despite a global increase in progranulin, overexpression resulted in dramatic and selective hippocampal toxicity and degeneration affecting neurons and glia. Hippocampal degeneration was preceded by T cell infiltration and perivascular cuffing. GRN delivery with an ependymal-targeting AAV for selective secretion of progranulin into the cerebrospinal fluid similarly resulted in T cell infiltration, as well as ependymal hypertrophy. Interestingly, overexpression of GRN in wild-type animals also provoked T cell infiltration. These results call into question the safety of GRN overexpression in the CNS, with evidence for both a region-selective immune response and cellular proliferative response. Our results highlight the importance of careful consideration of target gene biology and cellular response to overexpression prior to progressing to the clinic.

Materials promoting viral gene delivery

“…Physical methods such as microinjection, 68,69 microfluidic, 70,71 sonication, 72,73 centrifugation, 74 cellular deformation, 75 laser irradiation 76,77 or electroporation 78,79 induce or facilitate cell entry of vectors by mechanical force, mainly through disrupting the plasma membrane. They are commonly applied in non-viral gene delivery because they transport the genetic information easily without the need for carriers and the otherwise low infectivity.…”

Discovery of small molecules that normalize the transcriptome and enhance cysteine cathepsin activity in progranulin-deficient microglia

“…Several therapeutic options are being explored to overcome progranulin haploinsufficiency 19 . A major strategy is to directly enhance progranulin expression level using gene therapy vectors introduced into the medial prefrontal cortex (mPFC) 20,21 , although one study showed that overexpression of GRN in Grn KO mice led to neurodegeneration 22 . Increased progranulin level can also be achieved by enhancing global transcriptional activity using histone deacetylase (HDAC) inhibitors 23,24 or by activating autophagy with trehalose 25 .…”

Age- and stress-associated C. elegans granulins impair lysosomal function and induce a compensatory HLH-30/TFEB transcriptional response

“…As such, efforts to increase progranulin production in patients are underway [62][63][64][65]. However, a more recent study has suggested that progranulin delivery to brain promotes in T-cell infiltration and neuronal and glial degeneration [66]. Progranulin cleavage and granulin levels were not measured in these studies, and may account for differences in the observed results.…”