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. 2017 Sep 6;25(9):2038-2052.
doi: 10.1016/j.ymthe.2017.05.017. Epub 2017 Jun 26.

A New AAV10-U7-Mediated Gene Therapy Prolongs Survival and Restores Function in an ALS Mouse Model

Maria Grazia Biferi  1 , Mathilde Cohen-Tannoudji  2 , Ambra Cappelletto  2 , Benoit Giroux  2 , Marianne Roda  2 , Stéphanie Astord  2 , Thibaut Marais  2 , Corinne Bos  2 , Thomas Voit  3 , Arnaud Ferry  4 , Martine Barkats  2
Affiliations

A New AAV10-U7-Mediated Gene Therapy Prolongs Survival and Restores Function in an ALS Mouse Model

Maria Grazia Biferi et al. Mol Ther. .

Abstract

One of the most promising therapeutic approaches for familial amyotrophic lateral sclerosis linked to superoxide dismutase 1 (SOD1) is the suppression of toxic mutant SOD1 in the affected tissues. Here, we report an innovative molecular strategy for inducing substantial, widespread, and sustained reduction of mutant human SOD1 (hSOD1) levels throughout the body of SOD1G93A mice, leading to therapeutic effects in animals. Adeno-associated virus serotype rh10 vectors (AAV10) were used to mediate exon skipping of the hSOD1 pre-mRNA by expression of exon-2-targeted antisense sequences embedded in a modified U7 small-nuclear RNA (AAV10-U7-hSOD). Skipping of hSOD1 exon 2 led to the generation of a premature termination codon, inducing production of a deleted transcript that was subsequently degraded by the activation of nonsense-mediated decay. Combined intravenous and intracerebroventricular delivery of AAV10-U7-hSOD increased the survival of SOD1G93A mice injected either at birth or at 50 days of age (by 92% and 58%, respectively) and prevented weight loss and the decline of neuromuscular function. This study reports the effectiveness of an exon-skipping approach in SOD1-ALS mice, supporting the translation of this technology to the treatment of this as yet incurable disease.

Keywords: AAV; ALS; exon skipping; gene therapy; hSOD1.

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Figures

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Graphical abstract
Figure 1
Figure 1
hSOD1 Exon Skipping Reduces mRNA Levels In Vitro (A) Schematic representation of E2 skipping in the hSOD1 pre-mRNA induced by specific antisense oligonucleotides (hSOD1-ASO1 to 5). The 9,310-bp hSOD1 gene (Gene ID 6647) comprises five exons separated by four introns, encoding a 153-aa protein. E2 skipping leads to the formation of a premature termination codon (PTC) in exon 4 of the hSOD1-skipped mRNA (ΔE2 hSOD1), 92 nt upstream of the last exon/exon junction (exon 4-exon 5), inducing its degradation by nonsense-mediated decay (NMD) activation. (B) Semiquantitative RT-PCR analysis of HEK293T cells transfected with the five hSOD1-ASOs, showing ΔE2 hSOD1 mRNA production. H2O, non-transfected cells (NT), and a scrambled control (ASO-CTR) were used as negative controls. Arrowheads indicate full-length (355 bp) and ΔE2 (258 bp) hSOD1 mRNA forms (the shown gel is one replicate of the experiment shown in Figure S1B). The bar graph on the right represents results of qRT-PCR analysis of full-length hSOD1 mRNA expression levels from another set of ASO-transfected HEK293T cells. hSOD1 mRNA was amplified using a specific probe mapping within exon 1-2 of the human SOD1 gene. Results correspond to the percent reduction of full-length hSOD1 mRNA induced by the different ASOs relative to NT. Data are expressed as the mean ± SEM of four independent transfection experiments. Differences between groups were analyzed by one-way ANOVA analysis, followed by Tukey’s post hoc test (**p < 0.01; ***p < 0.001; ****p < 0.0001).
Figure 2
Figure 2
AAV-U7-Mediated hSOD1 Exon Skipping Reduces mRNA and Protein Levels In Vivo (A) Design of the AAV vectors used to target hSOD1 (AAV10-U7-hSOD1) or control (AAV10-U7-CTR) sequences. The antisense sequences (ASs) corresponding to ASO1 and ASO4 were embedded into the optimized human U7 small nuclear RNA (snRNA), and cloned between two AAV inverted terminal repeats (ITRs). (B) The upper panel corresponds to a semiquantitative RT-PCR analysis of mRNA extracted from the spinal cord (SC) of SOD1G93A mice, in which the lumbar SC was injected with 4.7 × 1012 vg/kg of AAV10-U7-hSOD1 (n = 3) or AAV10-U7-CTR (n = 2). The lower panel shows results of the corresponding qRT-PCR analysis, showing lower levels of full-length hSOD1 mRNA in SC from AAV10-U7-hSOD1-injected mice than AAV10-U7-CTR-injected controls. Data are expressed as the mean ± SEM. (C) Western blot (WB) analysis of hSOD1 protein expression in SOD1G93A mice, in which the SC was injected with AAV10-U7-hSOD1 (n = 3) or AAV10-U7-CTR (n = 3) (4.7 × 1012 vg/kg). Antibody specificity for the human form of SOD1 was demonstrated by the absence of signal in protein extracts from WT mice. α-Tubulin was used as a loading control. The lower panel corresponds to the densitometric analysis of WB results, showing the significant reduction of hSOD1 levels in the AAV10-U7-hSOD1-injected SCs. Values are expressed as the mean ± SEM, and differences between groups were analyzed by the Student’s t test (**p < 0.01).
Figure 3
Figure 3
Combined i.v./i.c.v. Delivery of AAV10-U7-hSOD1 Prolongs Survival in Neonatal SOD1G93A Mice (A) Schematic representation of AAV10 delivery into the temporal vein (i.v.) and lateral ventricles (i.c.v.) (co-i.v./i.c.v.) of SOD1G93A mice on PND1. The mice were injected with a total dose of 4.5 × 1014 vg/kg of AAV10-U7-hSOD1 or AAV10-U7-CTR vectors (i.v., 4 × 1014 vg/kg, and i.c.v., 5 × 1013 vg/kg). (B) Kaplan-Meier survival curves of SOD1G93A mice co-i.v./i.c.v. injected with either AAV10-U7-SOD1 (red, n = 15) or AAV10-U7-CTR (green, n = 17) and NI mice (blue, n = 12). Differences between the curves were analyzed using the log rank Mantel-Cox test, showing a significant difference between AAV10-U7-SOD1-injected mice and either AAV10-U7-CTR-injected or NI mice (****p < 0.0001). (C) Bar graph indicating a significant difference between the mean survival of AAV10-U7-SOD1- and either AAV10-U7-CTR-injected mice or NI mice (235.6 ± 11 days versus 120.1 ± 2.3 days and 122.9 ± 1.6 days, respectively). Data are expressed as the mean ± SEM, and differences between groups were analyzed by one-way ANOVA analysis followed by Tukey’s post hoc test (****p < 0.0001). (D) Body weight curves of AAV10-U7-hSOD1-injected SOD1G93A mice (red) compared to AAV10-U7-CTR-injected SOD1G93A mice (green), NI SOD1G93A mice (blue), and WT mice (pink) (n = 8 in each sex-balanced group, Student’s t test, *p < 0.05). (E) Kaplan-Meier curves showing the significant delay in median disease onset (based on the age at body-weight peak) in mice injected with either AAV10-U7-hSOD1 (red, n = 14) relative to NI mice (blue, n = 8) and AAV10-U7-CTR-injected mice (green, n = 14). Differences between the curves were analyzed by the log rank Mantel-Cox test (****p < 0.0001). (F) Mean duration of disease of mice injected with either AAV10-U7-hSOD1 (red, n = 14) or AAV10-U7-CTR (green, n = 14) and of NI mice (blue, n = 8), showing the significant extension of disease duration in the AAV10-U7-hSOD1-treated animals. Results are expressed as the mean ± SEM, and the differences between groups were determined by one-way ANOVA, followed by Tukey’s post hoc test (*p < 0.05).
Figure 4
Figure 4
AAV10-U7-hSOD1 Injection in Newborn SOD1G93A Mice Rescues the ALS Phenotype (A) Representative transverse sections of the ventral horn of the lumbar spinal cord from SOD1G93A mice injected at birth with AAV10-U7-hSOD1 or AAV10-U7-CTR and processed for immunofluorescence at 112 days of age using anti-ChAT (upper panels), anti-GFAP (middle panels), or anti-Iba1 (lower panels) antibodies. Scale bar, 25 or 75 μm, as indicated. (B) Quantitative analysis of the number of ChAT-positive motor neurons (upper panel, n = 6, 50 sections per mouse), the mean fluorescence intensity of GFAP immunostaining (middle panel, n = 6, three sections per mouse), and the number of Iba1-positive cells (lower panel, n = 6, three sections per mouse) in AAV10-U7-hSOD1- or AAV10-U7-CTR-injected SOD1G93A mice, NI SOD1G93A mice, and WT mice. Data are expressed as the mean ± SEM. ****p < 0.0001, one-way ANOVA followed by Tukey’s post hoc test. (C) Representative NMJ of the EDL muscles from WT mice and SOD1G93A mice, injected at birth with AAV10-U7-hSOD1 or NI, and analyzed for whole mount immunofluorescence at 112 days. Endplates were identified by 594-conjugated BTX (red); terminal axons were identified by anti-NF antibody (green). Full arrowheads indicate innervated endplates; empty arrowheads indicate denervated endplates. Scale bar, 25 μm. (D) Quantification of innervated endplates (left panel) and endplate areas (right panel) in WT, AAV10-U7-hSOD1-injected SOD1G93A mice, or NI SOD1G93A mice (n = 4; ∼50 BTX-positive endplates per animal were randomly chosen and analyzed). Data are expressed as the mean ± SEM. *p < 0.05; **p < 0.01; ***p < 0.001; one-way ANOVA followed by Tukey’s post hoc test. (E) Representative transverse sections of the TA muscle from AAV10-U7-hSOD1- or AAV10-U7-CTR-injected SOD1G93A mice processed for anti-laminin immunofluorescence at 112 days of age. Scale bar, 200 μm. (F) Frequency distribution curves of myofiber areas in the TA muscle of AAV10-U7-hSOD1-or AAV10-U7-CTR-injected SOD1G93A mice, NI mice, and WT mice. N = 3 mice per group. Data are expressed as the mean ± SEM. **p < 0.01, ***p < 0.001, and ****p < 0.0001 for NI compared to WT; ###p < 0.001 and ####p < 0.0001 for AAV10-U7-CTR compared to WT; §p < 0.05 and §§§§p < 0.0001 for AAV10-U7-hSOD1 compared to NI; p < 0.05 and ¶¶¶¶p < 0.0001 for AAV10-U7-hSOD1 compared to AAV10-U7-CTR; two-way ANOVA followed by Bonferroni post hoc test (treatment and frequency).
Figure 5
Figure 5
Combined i.v./i.c.v. Injection of AAV10-U7-hSOD1 Rescues Survival of Adult SOD1G93A Mice (A) Kaplan-Meier survival curves of SOD1G93A mice co-i.v./i.c.v. injected at PND50 with AAV10-U7-SOD1 (4.5 × 1014 vg/kg total, n = 25) or NI (n = 24), sex-balanced group. The median lifespan was significantly longer for mice treated with AAV10-U7-hSOD1 than for NI mice (186 days versus 123 days; ****p < 0.0001, log rank Mantel-Cox test). (B) Comparison of the mean survival of AAV10-U7-SOD1-injected (red, n = 25) and NI mice (blue, n = 24) (195 ± 6.7 days versus 122.8 ± 0.9 days). Data are expressed as the mean ± SEM, ****p < 0.0001, Student’s t test. (C) Comparison of the body weight curves of AAV10-U7-hSOD1-injected and NI SOD1G93A mice (n = 24 per sex-balanced group). **p < 0.01; ****p < 0.0001, Student’s t test. (D) Kaplan-Meier curves illustrating the onset of disease, defined by the age at the peak body weight, for AAV10-U7-hSOD1-injected (red, n = 24) and NI (blue, n = 24) SOD1G93A mice. The median time of disease onset was significantly delayed for the AAV10-U7-hSOD1-injected mice relative to that of NI mice. Differences between the curves were analyzed by the log rank Mantel-Cox test; ****p < 0.0001.
Figure 6
Figure 6
Combined i.v./i.c.v. Injection of AAV10-U7-hSOD1 Preserves Neuromuscular Function in Adult SOD1G93A Mice (A) Photographs illustrating the phenotype of a NI SOD1G93A mouse at 124 days of age displaying kyphosis, closed eyes, self-grooming defects, and lower limb paralysis (upper panel), and of a 174-day-old AAV10-U7-hSOD1-injected SOD1G93A mouse (whose phenotype was similar to WT mice) (lower panel). (B) Absolute and specific maximal forces in response to muscle stimulation (direct stimulation), and maximal activation capacity that was a functional index of neuromuscular transmission measured in 112-day-old AAV10-U7-hSOD1-injected SOD1G93A mice, age-matched WT mice, and 112-day-old NI SOD1G93A mice (n = 3 per group). Data are expressed as the mean ± SEM. **p < 0.01; ***p < 0.001; ****p < 0.0001, one-way ANOVA followed by Tukey’s post hoc test. (C) Grip strength was assessed twice a week from the day of treatment in injected (red) and NI (blue) SOD1G93A mice (n = 24 per group) as well as in age- and sex-matched WT animals (pink, n = 10). Data are expressed as the mean per week ± SEM. The difference between injected and NI mice was statistically significant at 15 weeks of age (*p < 0.05, Student’s t test). (D) Spontaneous motor activity monitored during 12 hr overnight in AAV10-U7-hSOD-injected (n = 17), NI SOD1G93A mice (n = 14), and WT mice (n = 16) (sex-balanced groups) at 120 days of age. The analyzed parameters were the time spent moving (left panel), distance covered (middle panel) (cm), and number of rearings (right panel). Individual data for WT (circles), NI (squares), and AAV10-U7-hSOD1 (triangles) are indicated, as well as the mean values ± SEM. *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001, one-way ANOVA followed by Tukey’s post hoc test.
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