MACF1 controls skeletal muscle function through the microtubule-dependent localization of extra-synaptic myonuclei and mitochondria biogenesis

Skeletal muscles are composed of hundreds of multinucleated muscle fibers (myofibers) whose myonuclei are regularly positioned all along the myofiber's periphery except the few ones clustered underneath the neuromuscular junction (NMJ) at the synaptic zone. This precise myonuclei organization is altered in different types of muscle disease, including centronuclear myopathies (CNMs). However, the molecular machinery regulating myonuclei position and organization in mature myofibers remains largely unknown. Conversely, it is also unclear how peripheral myonuclei positioning is lost in the related muscle diseases. Here, we describe the microtubule-associated protein, MACF1, as an essential and evolutionary conserved regulator of myonuclei positioning and maintenance, in cultured mammalian myotubes, in Drosophila muscle, and in adult mammalian muscle using a conditional muscle-specific knockout mouse model. In vitro, we show that MACF1 controls microtubules dynamics and contributes to microtubule stabilization during myofiber's maturation. In addition, we demonstrate that MACF1 regulates the microtubules density specifically around myonuclei, and, as a consequence, governs myonuclei motion. Our in vivo studies show that MACF1 deficiency is associated with alteration of extra-synaptic myonuclei positioning and microtubules network organization, both preceding NMJ fragmentation. Accordingly, MACF1 deficiency results in reduced muscle excitability and disorganized triads, leaving voltage-activated sarcoplasmic reticulum Ca2+ release and maximal muscle force unchanged. Finally, adult MACF1-KO mice present an improved resistance to fatigue correlated with a strong increase in mitochondria biogenesis.

Assessment of Clinical Meaningfulness of Endpoints in the Generation Program by the Insights to Model Alzheimer's Progression in Real Life (iMAP) Study

We are launching the Insights to Model Alzheimer's Progression in Real Life study in parallel with the Alzheimer Prevention Initiative Generation Program. This is a 5-year, multinational, prospective, longitudinal, non-interventional cohort study that will collect data across the spectrum of Alzheimer's disease. The primary objective is to assess the ability of the Alzheimer's Prevention Initiative Cognitive Composite Test Score and Repeatable Battery for the Assessment of Neuropsychological Status to predict clinically meaningful outcomes such as diagnosis of mild cognitive impairment or dementia due to Alzheimer's disease, and change in Clinical Dementia Rating - Global Score. This study is the first large-scale, prospective effort to establish the clinical meaningfulness of cognitive test scores that track longitudinal decline in preclinical Alzheimer's disease. This study is also expected to contribute to our understanding of the relationships among outcomes in different stages of Alzheimer's disease as well as models of individual trajectories during the course of the disease.

Anti-agrin autoantibodies in myasthenia gravis

OBJECTIVE

Because the extracellular matrix protein agrin is essential for neuromuscular junction formation and maintenance, we tested the hypothesis that autoantibodies against agrin are present in sera from patients with myasthenia gravis (MG).

METHODS

We determined the presence of anti-agrin antibodies in 54 sera from patients with generalized MG using a solid-phase ELISA with purified mini-agrin protein. Thirty of the 54 sera were seronegative for antibodies against the acetylcholine receptor (AChR) or muscle-specific tyrosine kinase (MuSK), 15 had elevated levels of anti-MuSK, and 9 had elevated levels of anti-AChR autoantibodies. Sixteen sera from healthy volunteers served as control.

RESULTS

Five sera with elevated levels of anti-agrin antibodies were identified. The concentration of the antibodies ranged between 0.04 and 0.12 nM. Four of the 5 agrin-positive sera were also positive for anti-MuSK, one was positive for anti-AChR, and 2 had elevated levels of anti-low-density lipoprotein receptor-related protein 4 (LRP4) autoantibodies. Some of the sera stained adult mouse neuromuscular junctions and reacted with native mini-agrin expressed in 293HEK cells.

CONCLUSIONS

The results provide evidence for agrin as a novel target protein for autoantibodies in patients with MG. Anti-agrin antibodies were always detected in combination with autoantibodies against MuSK, LRP4, or AChRs, indicating a high incidence of autoantibodies against several neuromuscular proteins in the agrin-positive MG cases.

Antibodies to clustered acetylcholine receptor: expanding the phenotype

BACKGROUND AND PURPOSE

To provide a detailed phenotypical description of seronegative patients with generalized myasthenia gravis and antibodies to clustered acetylcholine receptors (AChRs) and to assess their frequency amongst a French seronegative generalized myasthenia gravis (SNMG) population.

METHODS

A French SNMG database was created and the sera from the 37 patients included in it were analysed by immunofluorescence of cell-based assays using cotransfection of AChR subunit genes together with rapsyn to densely cluster the AChRs.

RESULTS

Sixteen per cent (n = 6) of the SNMG patients were found to have antibodies to clustered AChR. They presented either with early onset MG and thymic hyperplasia, late onset MG and thymic involution, or thymoma associated MG. They responded well to cholinesterase inhibitors and immunosuppressants.

CONCLUSIONS

Patients with antibodies to clustered AChR account for a significant proportion of SNMG patients and resemble patients with AChR antibodies detected by standard radio-immunoprecipitation.

Identification of a new gene family specifically expressed in chicken embryonic stem cells and early embryo

Chicken embryonic stem (CES) cells are pluripotent cells derived from chicken early blastoderm. In order to identify new genes specifically expressed in these pluripotent cells, we have used a gene trap strategy and cloned a novel gene family called cENS for chicken Embryonic Normal Stem cell gene. The cENS genes expression decreases after induction of CES cells differentiation in culture and is restricted in vivo to the very early embryo. We have characterized three different cENS genes. One, cENS-1, is composed of an open reading frame inserted between two terminal direct repeats which are the common point of the cENS genes. cENS-1 encodes a protein identical to cERNI, a recently described protein. cENS-2 is a truncated form of cENS-1. cENS-3 presents two adjacent open reading frames coding respectively for env and pol related proteins. The presence of conserved direct repeats, of retrovirus related genes and the absence of introns argue in favor of a retroviral origin of the cENS genes. In the cENS we identified a promoter region whose activity is strong in CES cells and decreases after induced differentiation showing a highly specific transcriptional activity specific of undifferentiated chicken embryonic stem cells.