Development of Intrathecal AAV9 Gene Therapy for Giant Axonal Neuropathy

Abstract

An NIH-sponsored phase I clinical trial is underway to test a potential treatment for giant axonal neuropathy (GAN) using viral-mediated GAN gene replacement (https://ichgcp.net/clinical-trials-registry/NCT02362438). This trial marks the first instance of intrathecal (IT) adeno-associated viral (AAV) gene transfer in humans. GAN is a rare pediatric neurodegenerative disorder caused by autosomal recessive loss-of-function mutations in the GAN gene, which encodes the gigaxonin protein. Gigaxonin is involved in the regulation, turnover, and degradation of intermediate filaments (IFs). The pathologic signature of GAN is giant axonal swellings filled with disorganized accumulations of IFs. Herein, we describe the development and characterization of the AAV vector carrying a normal copy of the human GAN transgene (AAV9/JeT-GAN) currently employed in the clinical trial. Treatment with AAV/JeT-GAN restored the normal configuration of IFs in patient fibroblasts within days in cell culture and by 4 weeks in GAN KO mice. IT delivery of AAV9/JeT-GAN in aged GAN KO mice preserved sciatic nerve ultrastructure, reduced neuronal IF accumulations and attenuated rotarod dysfunction. This strategy conferred sustained wild-type gigaxonin expression across the PNS and CNS for at least 1 year in mice. These results support the clinical evaluation of AAV9/JeT-GAN for potential therapeutic outcomes and treatment for GAN patients.

Keywords: AAV9; adeno-associated virus; biodistribution; dorsal root ganglia; fibroblast; gene therapy; giant axonal neuropathy; gigaxonin; intrathecal; sciatic nerve.

Figures

Figure 1

AAV9/JeT-GAN Construct Design for Expressing Human Gigaxonin (A) Schematic diagram of the AAV/JeT-GAN gene transfer cassette using a JeT promoter, the full-length, codon-optimized human GAN cDNA, and the synthetic poly(A) tail (SpA). (B and C) Western blot and densitometry of gigaxonin expression from HEK293 cells transfected with the JeT-GAN plasmid or JeT-GFP control plasmid. (D and E) Western blot and densitometry of AAV9-permissive Lec2 cells treated with the indicated vectors at the indicated amounts per cell. (C and E) Values are mean ± SEM gigaxonin levels normalized to GAPDH or β-actin levels and relative to control (untransfected and GFP-treated) cells. Data were analyzed by one-way ANOVA with Bonerfonni’s post-hoc analysis.

Figure 2

AAV/GAN Vectors Restore Normal IF Morphology in GAN Patient Fibroblasts Cultures of fibroblasts from three patients (GAN-T, GAN-S, and GAN-M) were infected with either vehicle, AAV2/JeT-GFP, AAV2/JeT-FLAG-GAN, or AAV2/CMV-GAN for 72 hr. Cells were then stained for vimentin (red), GFP (green), and DAPI to visualize the nuclei (blue). (A–C) Representative images of GAN-S fibroblasts. Arrows indicate inclusions. (A) Enlarged view of normal (left) and GAN-specific (right) distribution of vimentin in vehicle-treated GAN fibroblasts to illustrate how inclusion-negative and inclusion-positive cells were scored. (B) GFP staining of GFP-treated patient cells shows the relative transduction efficiency of AAV2 in both normal and inclusion-bearing cells. (C) GAN fibroblasts treated with AAV2/FLAG-JeT-GAN show a reduction in the number of cells containing vimentin inclusions. (D) Quantification of the percent of cells containing inclusions for each patient culture. Values are means ± SEM for each group. One-way ANOVA with Bonferonni’s post-hoc analysis of each treatment condition compared to control cells (vehicle and GFP-treated) (**p 

Figure 3

AAV9/JeT-GAN Reduces NF Inclusions in Cortical and Striatal Neurons Twenty-month-old GAN/Y KO mice received a unilateral brain injection into the border of the striatum and cortex of a mix of AAV9/JeT-FLAG-GAN and AAV9/JeT-GFP and harvested 4 weeks post-injection (cohort 1). (A) A representative image of GFP staining shows that AAV9 vector spread decreased with distance from the injection site and was substantially reduced in the uninjected hemisphere. The white hashed box outlines the “control” area that was not efficiently transduced by AAV9, and the white dashed circle shows the injection site. (B) A representative image of NF staining shows that compared to the untreated hemisphere (C), NF inclusions are greatly reduced in the treated side (D). (E) Quantification of NF inclusions in the treated hemisphere, normalized to the number of inclusions in the corresponding area of the untreated hemisphere of each mouse. Data are means ± SEM for each group, n = 3 mice. One-way ANOVA with Bonferonni’s post-hoc analysis. (A and B) Scale bars represent 1 mm. (C and D) Arrows point to examples of NF inclusions, and scale bars represent 0.1 mm.

Figure 4

IT Delivery of AAV9/JeT-GAN in GAN KO Mice Attenuates Rotarod Deficits (A) Study design for GAN/Y KO (cohort 2) and (B) for GAN/J KO mice (cohort 3). (C) Aged GAN/Y KO mice (red) have significantly impaired rotarod performance as compared to normal control littermates (black) beginning at 20 months of age. (D) Treatment with AAV9/JeT-GAN delays a significant rotor deficit in GAN/Y KO mice (blue) as compared to normal control mice (black) until 22 months of age. (E) Over the course of testing, treatment with AAV9/JeT-GAN (blue) significantly improves rotarod performance as compared to vehicle-treated GAN KO mice (red). (F) No difference in rotarod performance was found between aged normal control (black) and vehicle-treated GAN/J KO mice (purple). Treatment with AAV9/JeT-GAN did not affect the motor performance of either control (gray) or GAN KO mice (green). Data are means ± SEM for each group (GAN/Y, n = 18 normal controls, 8 KO + vehicle, and 7 KO + AAV9/GAN; GAN/J, n = 10 normal + vehicle, 9 normal + AAV9/GAN, 10 KO + vehicle, and 11 KO + AAV9/GAN). Two-way ANOVA (age × group); main effect of group, +p 

Figure 5

Gigaxonin Expression Persists in Aged Mice IT-Injected with AAV9/JeT-GAN Gigaxonin gene expression was assessed by measuring the codon-optimized human gigaxonin mRNA in each tissue sample from GAN/Y mice injected at 12 months of age and harvested at 24 months of age (cohort 2) (A) and from GAN/J mice injected at 14–16-months of age and harvested at 24 months of age (cohort 3) (B). Mouse β-actin mRNA was measured as an internal control. β-actin was detected in all samples, and codon-optimized human gigaxonin mRNA was not detected in vehicle-injected animals. Data are means ± SEM for each group (GAN/Y: n = 2 per group; GAN/J: n = 3 per group). Multiple unpaired Student’s t tests were performed on GAN-treated animals, *p < 0.05.

Figure 6

AAV9/JeT-GAN Reduces IF Inclusions in the DRG of GAN/Y KO Mice Representative images of light microscopic evaluation of lumbar DRG in 24-month-old normal control (A), vehicle IT-injected GAN /Y KO mice (B), and AAV9/JeT-GAN IT-injected GAN/Y KO mice (C). H&E staining shows unremarkable DRG neurons in control mice (A) versus abundant, brightly eosinophilic inclusion-bearing neurons of vehicle-treated GAN/Y KO mice (B). Neuronal inclusions in GAN-treated mice were significantly reduced compared to vehicle-treated GAN KO mice (C and D). Scale bar represents 61 μm. Arrows indicate neuronal inclusions. Data was analyzed by unpaired Student’s t test.

Figure 7

AAV9/JeT-GAN Gene Therapy Improves IF Cytoskeleton in GAN Peripheral Nerves EM examination of sciatic nerves from 24-month-old control GAN/Y KO and AAV9/JeT-FLAG-GAN-injected GAN/Y KO mice at 6 months post-IT-injection (cohort 4). (A–C) Control GAN KO mouse and (D–F) GAN-treated GAN KO mouse. Stars indicate intact unmyelinated fibers and associated Schwann cells, arrows indicate normal Schwann cell cytoplasm associated with myelinated fibers, asterisks indicate dense, disorganized accumulations of NFs in fibers, arrowhead indicates increased density of NFs in myelinated fiber, and crosses indicate accumulation of IFs in Schwann cell cytoplasm associated with myelinated fibers. Representative images from n = 6 per group. Scale bar: 5 μm (A and D), 1 μm (B and E), and 0.5 μm (C and F).