BB-301: a silence and replace AAV-based vector for the treatment of oculopharyngeal muscular dystrophy

Suppression of CNS APOE4 Expression by miRNAs Delivered by the S2 AAVrh.10 Capsid-Modified AAV Vector

The homozygous Apolipoprotein E (APOE4) genotype is the major risk factor for the development of early Alzheimer's disease. Genome engineering studies in mouse models of human APOE4-dependent pathology have established that reduction of APOE4 expression can rescue the phenotype. We hypothesized that APOE4 could be suppressed in the CNS of APOE4 homozygotes using adeno-associated virus (AAV) expression of microRNAs (miRNA) designed to hybridize to APOE mRNA. We screened nine different miRNAs targeting APOE following transfection in HEK293T and Huh7 cells. Optimal APOE suppression was obtained with mir2A (targeting coding region nt330-351) and mirN4 (3' untranslated region nt1142-1162). miRNA expression cassettes were designed with two copies of each of these two miRNAs co-expressed with a mCherry transgene. To optimize delivery of these miRNAs, an engineered AAVrh.10 variant was identified from a screen of multiple peptide insertions into capsid loop IV and substitutions in loop VIII. This led to identifying the AAV.S2 capsid with enhanced transduction of both neurons and glia and enhanced distribution in the brain. The engineered capsid was used to deliver the APOE miRNA suppression cassette to the hippocampus of TRE4 mice (human APOE4 knock-in replacement of the murine apoE locus). Two weeks after intra-hippocampus administration, regional expression of miRNA at the injection site was quantified at the mRNA level relative to an endogenous reference. The AAV.S2 capsid provided 2.31 ± 0.37-fold higher expression of miRNA over that provided by AAVrh.10 (p < 0.05). In the targeted region, a single intra-hippocampus AAV.S2 administration suppressed hippocampal APOE4 mRNA levels by 76.5 ± 3.9% compared with 41.3 ± 3.3% with the same cassette delivered by the wildtype AAVrh.10 capsid (p < 0.0001). We conclude that an expression cassette with two different miRNAs targeting APOE4 delivered by the AAV.S2 capsid will generate highly significant suppression of APOE4 in the CNS.

Different outcomes of endurance and resistance exercise in skeletal muscles of Oculopharyngeal muscular dystrophy

BACKGROUND

Exercise is widely considered to have beneficial impact on skeletal muscle aging. In addition, there are also several studies demonstrating a positive effect of exercise on muscular dystrophies. Oculopharyngeal muscular dystrophy (OPMD) is a late-onset autosomal dominant inherited neuromuscular disorder caused by mutations in the PAPBN1 gene. These mutations consist in short (1-8) and meiotically stable GCN trinucleotide repeat expansions in its coding region responsible for the formation of PAPBN1 intranuclear aggregates. This study aims to characterize the effects of two types of chronic exercise, resistance and endurance, on the OPMD skeletal muscle phenotype using a relevant murine model of OPMD.

METHODS

In this study, we tested two protocols of exercise. In the first, based on endurance exercise, FvB (wild-type) and A17 (OPMD) mice underwent a 6-week-long motorized treadmill protocol consisting in three sessions per week of running 20 cm/s for 20 min. In the second protocol, based on resistance exercise generated by chronic mechanical overload (OVL), surgical removal of gastrocnemius and soleus muscles was performed, inducing hypertrophy of the plantaris muscle. In both types of exercise, muscles of A17 and FvB mice were compared with those of respective sedentary mice. For all the groups, force measurement, muscle histology, and molecular analyses were conducted.

RESULTS

Following the endurance exercise protocol, we did not observe any major changes in the muscle physiological parameters, but an increase in the number of PABPN1 intranuclear aggregates in both tibialis anterior (+24%, **P = 0.0026) and gastrocnemius (+18%, ****P < 0.0001) as well as enhanced collagen deposition (+20%, **P = 0.0064 in the tibialis anterior; +35%, **P = 0.0042 in the gastrocnemius) in the exercised A17 OPMD mice. In the supraphysiological resistance overload protocol, we also observed an increased collagen deposition (×2, ****P < 0.0001) in the plantaris muscle of A17 OPMD mice which was associated with larger muscle mass (×2, ****P < 0.0001) and fibre cross sectional area (×2, ***P = 0.0007) and increased absolute maximal force (×2, ****P < 0.0001) as well as a reduction in PABPN1 aggregate number (-16%, ****P < 0.0001).

CONCLUSIONS

Running exercise and mechanical overload led to very different outcome in skeletal muscles of A17 mice. Both types of exercise enhanced collagen deposition but while the running protocol increased aggregates, the OVL reduced them. More importantly OVL reversed muscle atrophy and maximal force in the A17 mice. Our study performed in a relevant model gives an indication of the effect of different types of exercise on OPMD muscle which should be further evaluated in humans for future recommendations as a part of the lifestyle of individuals with OPMD.

Emerging and established biomarkers of oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is a rare, primarily autosomal dominant, late onset muscular dystrophy commonly presenting with ptosis, dysphagia, and subsequent weakness of proximal muscles. Although OPMD diagnosis can be confirmed with high confidence by genetic testing, the slow progression of OPMD poses a significant challenge to clinical monitoring and a barrier to assessing the efficacy of treatments during clinical trials. Accordingly, there is a pressing need for more sensitive measures of OPMD progression, particularly those which do not require a muscle biopsy. This review provides an overview of progress in OPMD biomarkers from clinical assessment, quantitative imaging, histological assessments, and genomics, as well as hypothesis-generating "omics" approaches. The ongoing search for biomarkers relevant to OPMD progression needs an integrative, longitudinal approach combining validated and experimental approaches which may include clinical, imaging, demographic, and biochemical assessment methods. A multi-omics approach to biochemical biomarker discovery could help provide context for differences found between individuals with varying levels of disease activity and provide insight into pathomechanisms and prognosis of OPMD.

Quantitative vs qualitative muscle MRI: Imaging biomarker in patients with Oculopharyngeal Muscular Dystrophy (OPMD)

Oculopharyngeal muscular dystrophy (OPMD) is a genetic muscle disease causing ptosis, severe swallowing difficulties and progressive limb weakness, although atypical presentations may be difficult to diagnose. Sensitive biomarkers of disease progression in OPMD are needed to enable more effective clinical trials. This study was designed to test the feasibility of using MRI to aid OPMD diagnosis and monitor OPMD progression. Twenty-five subjects with Dixon whole-body muscle MRI were enrolled: 10 patients with genetically confirmed OPMD, 10 patients with non-OPMD muscular dystrophies, and 5 controls. Using the MRI Dixon technique, muscle fat replacement was evaluated in the tongue, serratus anterior, lumbar paraspinal, adductor magnus, and soleus muscles using quantitative and semi-quantitative rating methods. Changes were compared with muscle strength testing, dysphagia severity, use of gait aids, and presence of dysarthria. Quantitative MRI scores of muscle fat replacement in the tongue could differentiate OPMD from other muscular dystrophies and from controls. Moreover, fat fraction in the tongue correlated with clinical severity of dysphagia. This study provides preliminary support for the use of Dixon-based quantitative MRI images as outcome measures for monitoring disease progression in clinical trials and provides rationale for future prospective studies aimed at methodological refinement and covariate identification.

[Nuclear aggregates in oculopharyngeal muscular dystrophy]

Oculopharyngeal muscular dystrophy (OPMD) is one of the diseases related to pathological expansions of trinucleotides. Its pathogenesis remains unclear although the presence of aggregates within the nuclei of the muscle fiber seems to play an important role. The basic research studies presented here help understand their composition and their deleterious role. These elements may result in new therapeutic avenues.