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

Abstract

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.

Meta-analysis towards FSHD reveals misregulation of neuromuscular junction, nuclear envelope, and spliceosome

“…in muscle structure, mitochondria and metabolism, signaling, and splicing. Interestingly, microtubule-associated factor 1 (MACF1), which is a top hit in the meta-analysis (Supplementary Data 1 , sheets 2 and 4) and regulates myonuclear positioning at the NMJ 59 , shows a preference for skipping of exon 116 in FSHD (Ψ-value 0.325). MAJIQ further detects an exon skipping event in ATP1B3 (Ψ-value = 0.359), which encodes a subunit of the Na+/K+-ATPase and is involved in the electrical excitability of muscle and nerves.…”

Enrichment of miR-17-5p enhances the protective effects of EPC-EXs on vascular and skeletal muscle injury in a diabetic hind limb ischemia model

“…The muscle force of mice was evaluated according to a previous study [ 30 ]. Briefly, mice were initially anesthetized using 4% isoflurane and maintained by air inhalation through a facemask continuously supplied with 1.5% isoflurane.…”

Principles of organelle positioning in motile and non-motile cells

“…Conceptually more challenging is the proper distribution of organelles to different intracellular localisation in a spaced manner: for example, in the multinucleated muscle, nuclei are accurately and uniformly distributed and spaced within the syncytium but are enriched underneath the neuromuscular junction (Cadot et al, 2015 ; Ghasemizadeh et al, 2021 ; Roman et al, 2021 ), potentially facilitating the local protein translation of specialised mRNAs. Also, during exercise-induced muscle repair, nuclei move towards the damage site to deliver mRNA (Roman et al, 2021 ).…”