Biology subjects

Lemaitre, M.

Publications and source records attributed to Lemaitre, M..

7 recordsLinked to original sources

bioRxiv2026

Axonopathy in Duchenne Muscular Dystrophy limits microdystrophin gene therapy efficacy

Duchenne muscular dystrophy (DMD) is classically defined as a primary myopathy, and current AAV-mediated microdystrophin gene therapies are shown to successfully preserve muscle integrity. However, their efficacy in recovering functional outcomes remains to improve. We hypothesized that this limitation stems from an unaccounted vulnerability within the peripheral nerve. Here, we demonstrate that the mdx mouse model exhibits a peripheral axonopathy independently of muscle necrosis. Using single-nucleus RNA sequencing and structural analyses, we have identified an active denervation program and a profound failure of neural repair pathways. Importantly, we revealed that the full-length dystrophin isoform Dp427c is expressed in the healthy peripheral nerve, intimately following the cytoskeletal organization and accumulating at regions of high biomechanical stress, including Schmidt-Lanterman incisures and Nodes of Ranvier. In its absence, nerves of mdx mice loss an essential scaffolding support, leading to localized structural collapse. Furthermore, we showed that muscle-restricted microdystrophin gene therapy rescues sarcolemmal integrity but failed to restore nerve-muscle connectivity or resolved neurotransmission defects. These findings fundamentally redefine DMD as an integrated motor unit pathology, thereby underscoring the absolute necessity of implementing combined therapeutic strategies that target both the muscle and the peripheral nervous system.

physiology↗

bioRxiv2025

Identification of CaVβ1 isoforms required for neuromuscular junction formation and maintenance

Voltage-gated Ca{superscript 2} channels (VGCCs) are regulated by four CaV{beta} subunits (CaV{beta}1-CaV{beta}4), each showing specific expression patterns in excitable cells. While primarily known for regulating VGCC function, CaV{beta} proteins also have channel-independent roles, including gene expression modulation. Among these, CaV{beta}1 is expressed in skeletal muscle as multiple isoforms. The adult isoform, CaV{beta}1D, localizes at the triad and modulates CaV1 activity during Excitation-Contraction Coupling (ECC). In this study, we investigated the lesser-known embryonic/perinatal CaV{beta}1 isoforms and their roles in neuromuscular junction (NMJ) formation, maturation, and maintenance. We found that CaV{beta}1 isoform expression is developmentally regulated through differential promoter activation. Specifically, CaV{beta}1A is expressed in embryonic muscle and reactivated in denervated adult muscle, alongside the known CaV{beta}1E isoform. Nerve injury in adult muscle triggers a shift in promoter usage, resulting in re-expression of embryonic/perinatal Cacnb1A and Cacnb1E transcripts. Functional analyses using aneural agrin-induced AChR clustering on primary myotubes demonstrated that these isoforms contribute to NMJ formation. Additionally, their expression during early postnatal development is essential for NMJ maturation and long-term maintenance. These findings reveal previously unrecognized roles of CaV{beta}1 isoforms beyond VGCC regulation, highlighting their significance in neuromuscular system development and homeostasis.

physiology↗

bioRxiv2024

Divalent siRNA for prion disease

Prion protein (PrP) lowering is effective in animal models of prion disease and is being tested clinically in prion disease patients, but there remains a need for more potent PrP-lowering drug candidates. Inspired by the reported potency and duration of action of divalent short interfering RNA (siRNA), a new oligonucleotide drug modality for the central nervous system, we sought to discover and develop a new PrP-lowering drug candidate. Herein we identify a mouse Prnp-targeting divalent siRNA molecule, 1682-s4, that lowers PrP to 49% residual brain expression in wild-type mice, and, in the context of intracerebral infection with Rocky Mountain Laboratory (RML) prions, achieves a 2.7-fold increase in survival time with pre-symptomatic chronic treatment and 64% increase in survival time with a single dose after symptom onset. We describe the generation of two transgenic mouse lines, Tg25109 and Tg26372, expressing the full human PRNP gene and its non-coding sequence, and demonstrate their utility for in vivo discovery of potent human PRNP-targeting oligonucleotides. We discover siRNA sequence 2439 against human PRNP and compare its potency in different divalent siRNA chemical scaffolds. We determine that both the fixed UU tail and extended nucleic acid linkages of scaffold s4 contribute to superior potency compared to other scaffolds tested, offering 9.4 and 15.9 percentage points respectively of additional PrP knockdown. A single dose of 348 {micro}g of 2439-s4 lowered whole brain hemisphere human PrP in transgenic mice to 17% residual after 30 days, while 52 {micro}g lowered PrP to 49% residual. 1-2% of the dose of 2439-s4 delivered into cerebrospinal fluid is retained in the brain, and the median effective tissue concentration is estimated at 1.2 micrograms per gram of tissue. Good Laboratory Practices toxicology studies identified no significant liabilities, and the U.S. FDA has cleared an Investigational New Drug application to bring 2439-s4 into clinical trials.

neuroscience↗

bioRxiv2024

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

BackgroundExercise 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. MethodsIn 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 3 sessions per week of running 20cm/s for 20 minutes. 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 to those of respective sedentary mice. For all the groups, force measurement, muscle histology and molecular analyses were conducted. ResultsFollowing 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 and enhanced collagen deposition in the exercised A17 OPMD mice. In the resistance overload protocol, we also observed an increased collagen deposition in the A17 OPMD mice which was associated with larger muscle mass and fiber cross sectional area and increased absolute maximal force as well as a reduction in PABPN1 aggregate number. ConclusionsRunning 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.

pathology↗

bioRxiv2021

The beneficial effect of chronic muscular exercise on muscle fragility is increased by Prox1 gene transfer in dystrophic mdx muscle

PurposeGreater muscle fragility is thought to cause the exhaustion of the muscle stem cells during successive degeneration/repair cycles, leading to muscle wasting and weakness in Duchenne muscular dystrophy. Chronic voluntary exercise can partially reduce the susceptibility to contraction induced-muscle injury, i.e., muscle fragility, as shown by a reduced immediate maximal force drop following lengthening contractions, in the dystrophic mdx mice. Here, we studied the effect of Prospero-related homeobox factor 1 gene (Prox1) transfer (overexpression) on fragility in chronically exercised mdx mice, because Prox1 promotes slower type fibres in healthy mice and slower fibres are less fragile in mdx muscle. Methodsmdx mice received or not Prox1 transfer into the tibialis anterior muscle and performed voluntary running into a wheel during 1 month. We also performed Prox1 transfer in sedentary mdx mice. In situ maximal force production of the muscle in response to nerve stimulation was assessed before, during and after 10 lengthening contractions. Molecular and cellular parameters were also evaluated. ResultsInterestingly, Prox1 transfer reduced the force drop following lengthening contractions in exercised mdx mice (p < 0.05 to 0.01), but not in sedentary mdx mice. It also increased the muscle expression of Myh7 (p < 0.001), MHC-2x (p < 0.01) and Trpc1 (p < 0.01), whereas it reduced that one of Myh4 (p < 0.001) and MHC-2b (p < 0.01) in exercised mdx mice. Moreover, Prox1 transfer decreased the maximal force (p < 0.01) before lengthening contraction in exercised mdx mice (p < 0.01), and reduced muscle weight (p < 0.0001) despite increased Mstn expression (p < 0.001). ConclusionOur results indicate that the beneficial effect of Prox1 transfer on muscle fragility is only observed in chronically exercised mdx mice. Thus, Prox1 transfer combined to chronic exercise have the potential to substantially slow the progression of the dystrophic disease in the long term.

physiology↗

bioRxiv2020

Muscle Van Gogh-like 2 shapes the neuromuscular synapse by regulating MuSK signaling activity

The development of the neuromuscular junction (NMJ) requires dynamic trans-synaptic coordination orchestrated by secreted factors, including the morphogens of the Wnt family. Yet, how the signal of these synaptic cues is transduced, and particularly during the regulation of acetylcholine receptor (AChR) accumulation in the postsynaptic membrane remains unclear. We explored the function of Van Gogh-Like protein 2 (Vangl2), a core component of Wnt planar cell polarity signaling. We showed that the conditional genetic ablation of Vangl2 in muscle reproduces the NMJ differentiation defects in mice with constitutive Vangl2 deletion. These alterations persisted into adulthood with NMJs disassembly leading to an impairment of neurotransmission and motor function deficits. Mechanistically, we found that Vangl2 and the muscle-specific kinase MuSK acted in the same genetic pathway and that Vangl2 binds MuSK, thus controlling its signaling activity. Our results identify Vangl2 as a key player of the core complex of molecules shaping neuromuscular synapses and shed light on the molecular mechanisms underlying NMJ assembly.

neuroscience↗

bioRxiv2019

Desmin is a modifier of dystrophic muscle features in Mdx mice

Duchenne muscular dystrophy (DMD) is a severe neuromuscular disease, caused by dystrophin deficiency. Desmin is like dystrophin associated to costameric structures bridging sarcomeres to extracellular matrix that are involved in force transmission and skeletal muscle integrity. In the present study, we wanted to gain further insight into the roles of desmin which expression is increased in the muscle from the mouse Mdx DMD model. We show that a deletion of the desmin gene (Des) in Mdx mice (DKO, Mdx:desmin-/-) induces a marked worsening of the weakness (reduced maximal force production) as compared to Mdx mice. Fragility (higher susceptibility to contraction-induced injury) was also aggravated and fatigue resistance was reduced in DKO mice. Moreover, in contrast to Mdx mice, the DKO mice did not undergo a muscle hypertrophy because of smaller and less numerous fibers, with reduced percentage of centronucleated fibres. Interestingly, Desmin cDNA transfer with adeno-associated virus in 1-month-old DKO mice and newborn Mdx mice improved muscle weakness. Overall, desmin plays important and beneficial roles on muscle performance, fragility and remodelling in dystrophic Mdx mice.

pathology↗