LSD1 controls a nuclear checkpoint in Wnt/ß-Catenin signaling to regulate muscle stem cell self-renewal.

The Wnt/ß-Catenin pathway plays a key role in cell fate determination during development and in adult tissue regeneration by stem cells. These processes involve profound gene expression and epigenome remodeling and linking Wnt/ß-Catenin signaling to chromatin modifications has been a challenge over the past decades. Functional studies of the lysine demethylase LSD1/KDM1A converge to indicate that this epigenetic regulator is a key regulator of cell fate, although the extracellular cues controlling LSD1 action remain largely unknown. Here we show that ß-Catenin is a substrate of LSD1. Demethylation by LSD1 prevents ß-Catenin degradation thereby maintaining its nuclear levels. Consistently, in absence of LSD1, ß-Catenin transcriptional activity is reduced in both MuSCs and ESCs. Moreover, inactivation of LSD1 in mouse muscle stem cells and embryonic stem cells shows that LSD1 promotes mitotic spindle orientation via ß-Catenin protein stabilization. Altogether, by inscribing LSD1 and ß-Catenin in the same molecular cascade linking extracellular factors to gene expression, our results provide a mechanistic explanation to the similarity of action of canonical Wnt/ß-Catenin signaling and LSD1 on stem cell fate.

Homozygous COQ7 mutation: a new cause of potentially treatable distal hereditary motor neuropathy.

Distal hereditary motor neuropathy represents a group of motor inherited neuropathies leading to distal weakness. We report a family of two brothers and a sister affected by distal hereditary motor neuropathy in whom a homozygous variant c.3G>T (p.1Met?) was identified in the COQ7 gene. This gene encodes a protein required for coenzyme Q10 biosynthesis, a component of the respiratory chain in mitochondria. Mutations of COQ7 were previously associated with severe multi-organ disorders characterized by early childhood onset and developmental delay. Using patient blood samples and fibroblasts derived from a skin biopsy, we investigated the pathogenicity of the variant of unknown significance c.3G>T (p.1Met?) in the COQ7 gene and the effect of coenzyme Q10 supplementation in vitro. We showed that this variation leads to a severe decrease in COQ7 protein levels in the patient's fibroblasts, resulting in a decrease in coenzyme Q10 production and in the accumulation of 6-demethoxycoenzyme Q10, the COQ7 substrate. Interestingly, such accumulation was also found in the patient's plasma. Normal coenzyme Q10 and 6-demethoxycoenzyme Q10 levels were restored in vitro by using the coenzyme Q10 precursor 2,4-dihydroxybenzoic acid, thus bypassing the COQ7 requirement. Coenzyme Q10 biosynthesis deficiency is known to impair the mitochondrial respiratory chain. Seahorse experiments showed that the patient's cells mainly rely on glycolysis to maintain sufficient ATP production. Consistently, the replacement of glucose by galactose in the culture medium of these cells reduced their proliferation rate. Interestingly, normal proliferation was restored by coenzyme Q10 supplementation of the culture medium, suggesting a therapeutic avenue for these patients. Altogether, we have identified the first example of recessive distal hereditary motor neuropathy caused by a homozygous variation in the COQ7 gene, which should thus be included in the gene panels used to diagnose peripheral inherited neuropathies. Furthermore, 6-demethoxycoenzyme Q10 accumulation in the blood can be used to confirm the pathogenic nature of the mutation. Finally, supplementation with coenzyme Q10 or derivatives should be considered to prevent the progression of COQ7-related peripheral inherited neuropathy in diagnosed patients.

Expanding the phenotypic variability of MORC2 gene mutations: From Charcot-Marie-Tooth disease to late-onset pure motor neuropathy.

MORC2 gene encodes a ubiquitously expressed nuclear protein involved in chromatin remodeling, DNA repair, and transcriptional regulation. Heterozygous mutations in MORC2 gene have been associated with a spectrum of disorders affecting the peripheral nervous system such as Charcot-Marie-Tooth (CMT2Z), spinal muscular atrophy-like with or without cerebellar involvement, and a developmental syndrome associated with impaired growth, craniofacial dysmorphism and axonal neuropathy (DIGFAN syndrome). Such variability in clinical manifestations associated with the increasing number of variants of unknown significance detected by next-generation sequencing constitutes a serious diagnostic challenge. Here we report the characterization of an in vitro model to evaluate the pathogenicity of variants of unknown significance based on MORC2 overexpression in a neuroblastoma cell line SH-EP or cortical neurons. Likewise, we show that MORC2 mutants affect survival and trigger apoptosis over time in SH-EP cell line. Furthermore, overexpression in primary cortical neurons increases apoptotic cell death and decreases neurite outgrowth. Altogether, these approaches establish the pathogenicity of two new variants p.Gly444Arg and p.His446Gln in three patients from two families. These new mutations in MORC2 gene are associated with autosomal dominant CMT and with adult late onset proximal motor neuropathy, further increasing the spectrum of clinical manifestations associated with MORC2 mutations.

Severe congenital myasthenic syndromes caused by agrin mutations affecting secretion by motoneurons.

Congenital myasthenic syndromes (CMS) are predominantly characterized by muscle weakness and fatigability and can be caused by a variety of mutations in genes required for neuromuscular junction formation and maintenance. Among them, AGRN encodes agrin, an essential synaptic protein secreted by motoneurons. We have identified severe CMS patients with uncharacterized p.R1671Q, p.R1698P and p.L1664P mutations in the LG2 domain of agrin. Overexpression in primary motoneurons cultures in vitro and in chick spinal motoneurons in vivo revealed that the mutations modified agrin trafficking, leading to its accumulation in the soma and/or in the axon. Expression of mutant agrins in cultured cells demonstrated accumulation of agrin in the endoplasmic reticulum associated with induction of unfolded protein response (UPR) and impaired secretion in the culture medium. Interestingly, evaluation of the specific activity of individual agrins on AChR cluster formation indicated that when secreted, mutant agrins retained a normal capacity to trigger the formation of AChR clusters. To confirm agrin accumulation and secretion defect, iPS cells were derived from a patient and differentiated into motoneurons. Patient iPS-derived motoneurons accumulated mutant agrin in the soma and increased XBP1 mRNA splicing, suggesting UPR activation. Moreover, co-cultures of patient iPS-derived motoneurons with myotubes confirmed the deficit in agrin secretion and revealed a reduction in motoneuron survival. Altogether, we report the first mutations in AGRN gene that specifically affect agrin secretion by motoneurons. Interestingly, the three patients carrying these mutations were initially suspected of spinal muscular atrophy (SMA). Therefore, in the presence of patients with a clinical presentation of SMA but without mutation in the SMN1 gene, it can be worth to look for mutations in AGRN.

Evidence of a dual mechanism of action underlying the anti-proliferative and cytotoxic effects of ammonium-alkyloxy-stilbene-based α7- and α9-nicotinic ligands on glioblastoma cells.

Glioblastomas (GBMs), the most frequent brain tumours, are highly invasive and their prognosis is still poor despite the use of combination treatment. MG624 is a 4-oxystilbene derivative that is active on α7- and α9-containing neuronal nicotinic acetylcholine receptor (nAChR) subtypes. Hybridisation of MG624 with a non-nicotinic resveratrol-derived pro-oxidant mitocan has led to two novel compounds (StN-4 and StN-8) that are more potent than MG624 in reducing the viability of GBM cells, but less potent in reducing the viability of mouse astrocytes. Functional analysis of their activity on α7 receptors showed that StN-4 is a silent agonist, whereas StN-8 is a full antagonist, and neither alters intracellular [Ca2+] levels when acutely applied to U87MG cells. After 72 h of exposure, both compounds decreased U87MG cell proliferation, and pAKT and oxphos ATP levels, but only StN-4 led to a significant accumulation of cells in phase G1/G0 and increased apoptosis. One hour of exposure to either compound also decreased the mitochondrial and cytoplasmic ATP production of U87MG cells, and this was not paralleled by any increase in the production of reactive oxygen species. Knocking down the α9 subunit (which is expressed at relatively high levels in U87MG cells) decreased the potency of the effects of both compounds on cell viability, but cell proliferation, ATP production, pAKT levels were unaffected by the presence of the noncell-permeable α7/α9-selective antagonist αBungarotoxin. These last findings suggest that the anti-tumoral effects of StN-4 and StN-8 on GBM cells are not only due to their action on nAChRs, but also to other non-nicotinic mechanisms.

A transgenic mouse expressing CHMP2Bintron5 mutant in neurons develops histological and behavioural features of amyotrophic lateral sclerosis and frontotemporal dementia.

Mutations in the charged multivesicular body protein 2B (CHMP2B) are associated with frontotemporal dementia (FTD), amyotrophic lateral sclerosis (ALS), and with a mixed ALS-FTD syndrome. To model this syndrome, we generated a transgenic mouse line expressing the human CHMP2Bintron5 mutant in a neuron-specific manner. These mice developed a dose-dependent disease phenotype. A longitudinal study revealed progressive gait abnormalities, reduced muscle strength and decreased motor coordination. CHMP2Bintron5 mice died due to generalized paralysis. When paralyzed, signs of denervation were present as attested by altered electromyographic profiles, by decreased number of fully innervated neuromuscular junctions, by reduction in size of motor endplates and by a decrease of sciatic nerve axons area. However, spinal motor neurons cell bodies were preserved until death. In addition to the motor dysfunctions, CHMP2Bintron5 mice progressively developed FTD-relevant behavioural modifications such as disinhibition, stereotypies, decrease in social interactions, compulsivity and change in dietary preferences. Furthermore, neurons in the affected spinal cord and brain regions showed accumulation of p62-positive cytoplasmic inclusions associated or not with ubiquitin and CHMP2Bintron5 As observed in FTD3 patients, these inclusions were negative for TDP-43 and FUS. Moreover, astrogliosis and microgliosis developed with age. Altogether, these data indicate that the neuronal expression of human CHMP2Bintron5 in areas involved in motor and cognitive functions induces progressive motor alterations associated with dementia symptoms and with histopathological hallmarks reminiscent of both ALS and FTD.

mTOR inactivation in myocardium from infant mice rapidly leads to dilated cardiomyopathy due to translation defects and p53/JNK-mediated apoptosis.

Mechanistic target of rapamycin (mTOR) is a central regulator of cell growth, proliferation, survival and metabolism, as part of mTOR complex 1 (mTORC1) and mTORC2. While partial inhibition of mTORC1 using rapamycin was shown to be cardioprotective, genetic studies in mouse models revealed that mTOR is essential for embryonic heart development and cardiac function in adults. However, the physiological role of mTOR during postnatal cardiac maturation is not fully elucidated. We have therefore generated a mouse model in which cardiac mTOR was inactivated at an early postnatal stage. Mutant mTORcmKO mice rapidly developed a dilated cardiomyopathy associated with cardiomyocyte growth defects, apoptosis and fibrosis, and died during their third week. Here, we show that reduced cardiomyocyte growth results from impaired protein translation efficiency through both 4E-BP1-dependent and -independent mechanisms. In addition, infant mTORcmKO hearts displayed markedly increased apoptosis linked to stretch-induced ANKRD1 (Ankyrin repeat-domain containing protein 1) up-regulation, JNK kinase activation and p53 accumulation. Pharmacological inhibition of p53 with pifithrin-α attenuated caspase-3 activation. Cardiomyocyte death did not result from activation of the MST1/Hippo pro-apoptotic pathway as reported in adult rictor/mTORC2 KO hearts. As well, mTORcmKO hearts showed a strong downregulation of myoglobin content, thereby leading to a hypoxic environment. Nevertheless, they lacked a HIF1α-mediated adaptive response, as mTOR is required for hypoxia-induced HIF-1α activation. Altogether, our results demonstrate that mTOR is critically required for cardiomyocyte growth, viability and oxygen supply in early postnatal myocardium and provide insight into the molecular mechanisms involved in apoptosis of mTOR-depleted cardiomyocytes.

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.

Modeling Charcot-Marie-Tooth Disease In Vitro by Transfecting Mouse Primary Motoneurons.

Neurodegeneration of spinal motoneurons (MNs) is implicated in a large spectrum of neurological disorders including amyotrophic lateral sclerosis, Charcot-Marie-Tooth disease, and spinal muscular atrophy, which are all associated with muscular atrophy. Primary cultures of spinal MNs have been used widely to demonstrate the involvement of specific genes in such diseases and characterize the cellular consequences of their mutations. This protocol models a primary MN culture derived from the seminal work of Henderson and colleagues more than twenty years ago. First, we detail a method of dissecting the anterior horns of the spinal cord from a mouse embryo and isolating the MNs from neighboring cells using a density gradient. Then, we present a new way of efficiently transfecting MNs with expression plasmids using magnetofection. Finally, we illustrate how to fix and immunostain primary MNs. Using neurofilament mutations that cause Charcot-Marie-Tooth disease type 2, this protocol demonstrates a qualitative approach to expressing proteins of interest and studying their involvement in MN growth, maintenance, and survival.

Genome editing in primary cells and in vivo using viral-derived Nanoblades loaded with Cas9-sgRNA ribonucleoproteins.

Programmable nucleases have enabled rapid and accessible genome engineering in eukaryotic cells and living organisms. However, their delivery into target cells can be technically challenging when working with primary cells or in vivo. Here, we use engineered murine leukemia virus-like particles loaded with Cas9-sgRNA ribonucleoproteins (Nanoblades) to induce efficient genome-editing in cell lines and primary cells including human induced pluripotent stem cells, human hematopoietic stem cells and mouse bone-marrow cells. Transgene-free Nanoblades are also capable of in vivo genome-editing in mouse embryos and in the liver of injected mice. Nanoblades can be complexed with donor DNA for "all-in-one" homology-directed repair or programmed with modified Cas9 variants to mediate transcriptional up-regulation of target genes. Nanoblades preparation process is simple, relatively inexpensive and can be easily implemented in any laboratory equipped for cellular biology.

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.

Muscle inactivation of mTOR causes metabolic and dystrophin defects leading to severe myopathy.

Mammalian target of rapamycin (mTOR) is a key regulator of cell growth that associates with raptor and rictor to form the mTOR complex 1 (mTORC1) and mTORC2, respectively. Raptor is required for oxidative muscle integrity, whereas rictor is dispensable. In this study, we show that muscle-specific inactivation of mTOR leads to severe myopathy, resulting in premature death. mTOR-deficient muscles display metabolic changes similar to those observed in muscles lacking raptor, including impaired oxidative metabolism, altered mitochondrial regulation, and glycogen accumulation associated with protein kinase B/Akt hyperactivation. In addition, mTOR-deficient muscles exhibit increased basal glucose uptake, whereas whole body glucose homeostasis is essentially maintained. Importantly, loss of mTOR exacerbates the myopathic features in both slow oxidative and fast glycolytic muscles. Moreover, mTOR but not raptor and rictor deficiency leads to reduced muscle dystrophin content. We provide evidence that mTOR controls dystrophin transcription in a cell-autonomous, rapamycin-resistant, and kinase-independent manner. Collectively, our results demonstrate that mTOR acts mainly via mTORC1, whereas regulation of dystrophin is raptor and rictor independent.

Expression of simian CETP in normolipidemic Fisher rats has a profound effect on large sized apoE-containing HDL.

In order to investigate the direct effect of cholesteryl ester transfer protein (CETP) on the structure and composition of HDL in vivo, simian CETP was expressed in Fisher rat that spontaneously displays high plasma levels of HDL1. In the new CETPTg rat line, the production of active CETP by the liver induced a significant 48% decrease in plasma HDL cholesterol, resulting in a 34% decrease in total cholesterol level (P < 0.01 in both cases). Among the various plasma HDL subpopulations, the largest HDL were those mostly affected by CETP, with a 74% decrease in HDL1 versus a significantly weaker 38% decrease in smaller HDL2 (P < 0.0001). Apolipoprotein E (apoE)-containing HDL1 were selectively affected by CETP expression, whereas apoA content of HDL remained unmodified. The reduction in the apoE content of serum HDL observed in CETPTg rats compared to controls (53%, P < 0.02) suggests that apoE in HDL may constitute in vivo a major determinant of their ability to interact with CETP. These results bring new insight into the lack of HDL1 in plasma from CETP-deficient heterozygotes despite their substantial 50% decrease in CETP activity. In addition, they indicate that HDL1 constitute reliable and practicable sensors of very low plasma CETP activity in vivo.