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Myasthenia gravis (MG) is a chronic and severe disease of the skeletal neuromuscular junction (NMJ) in which the effects of neurotransmitters are attenuated, leading to muscle weakness. In the most common forms of autoimmune MG, antibodies attack components of the postsynaptic membrane, including the acetylcholine receptor (AChR) or muscle-specific kinase (MuSK). MuSK, a master regulator of NMJ development, associates with the low-density lipoprotein-related receptor 4 (Lrp4) to form the signaling receptor for neuronal Agrin, a nerve-derived synaptic organizer. Pathogenic antibodies to MuSK interfere with binding between MuSK and Lrp4, inhibiting the differentiation and maintenance of the NMJ. MuSK MG can be debilitating and refractory to treatments that are effective for AChR MG. We show here that recombinant antibodies, derived from MuSK MG patients, cause severe neuromuscular disease in mice. The disease can be prevented by a MuSK agonist antibody, presented either prophylactically or after disease onset. These findings suggest a therapeutic alternative to generalized immunosuppression for treating MuSK MG by selectively and directly targeting the disease mechanism. [ABSTRACT FROM AUTHOR]

Muscle-specific kinase (MuSK) is essential for the formation, function, and preservation of neuromuscular synapses. Activation of MuSK by a MuSK agonist antibody may stabilize or improve the function of the neuromuscular junction (NMJ) in patients with disorders of the NMJ, such as congenital myasthenia (CM). Here, we generated and characterized ARGX-119, a first-in-class humanized agonist monoclonal antibody specific for MuSK, that is being developed for treatment of patients with neuromuscular diseases. We performed in vitro ligand-binding assays to show that ARGX-119 binds with high affinity to the Frizzled-like domain of human, nonhuman primate, rat, and mouse MuSK, without off-target binding, making it suitable for clinical development. Within the Fc region, ARGX-119 harbors L234A and L235A mutations to diminish potential immune-activating effector functions. Its mode of action is to activate MuSK, without interfering with its natural ligand neural Agrin, and cluster acetylcholine receptors in a dose-dependent manner, thereby stabilizing neuromuscular function. In a mouse model of DOK7 CM, ARGX-119 prevented early postnatal lethality and reversed disease relapse in adult Dok7 CM mice by restoring neuromuscular function and reducing muscle weakness and fatigability in a dose-dependent manner. Pharmacokinetic studies in nonhuman primates, rats, and mice revealed a nonlinear PK behavior of ARGX-119, indicative of target-mediated drug disposition and in vivo target engagement. On the basis of this proof-of-concept study, ARGX-119 has the potential to alleviate neuromuscular diseases hallmarked by impaired neuromuscular synaptic function, warranting further clinical development. Editor's summary: Muscle-specific kinase (MuSK) is required for the formation and maintenance of neuromuscular junctions, the synaptic connections between motor neurons and muscle fibers. Impairments in MuSK signaling cause certain forms of neuromuscular disease such as congenital myasthenic syndrome and myasthenia gravis. Here, Vanhauwaert et al. present the development of ARGX-119, an agonist antibody for MuSK. ARGX-119 activated MuSK in vitro across different species, including humans, and showed no off-target binding. ARGX-119 was safe in healthy mice and rescued motor function, prolonged survival, and reversed disease relapse in a mouse model of congenital myasthenia. These data support further development of ARGX-119 for neuromuscular diseases. —Daniela Neuhofer [ABSTRACT FROM AUTHOR]

Lrp4, the muscle receptor for neuronal Agrin, is expressed in the hippocampus and areas involved in cognition. The function of Lrp4 in the brain, however, is unknown, as Lrp4-/- mice fail to form neuromuscular synapses and die at birth. Lrp4-/- mice, rescued for Lrp4 expression selectively in muscle, survive into adulthood and showed profound deficits in cognitive tasks that assess learning and memory. To learn whether synapses form and function aberrantly, we used electrophysiological and anatomical methods to study hippocampal CA3-CA1 synapses. In the absence of Lrp4, the organization of the hippocampus appeared normal, but the frequency of spontaneous release events and spine density on primary apical dendrites were reduced. CA3 input was unable to adequately depolarize CA1 neurons to induce long-term potentiation. Our studies demonstrate a role for Lrp4 in hippocampal function and suggest that patients with mutations in Lrp4 or auto-antibodies to Lrp4 should be evaluated for neurological deficits.

Motor axons receive retrograde signals from skeletal muscle that are essential for the differentiation and stabilization of motor nerve terminals (1). Identification of these retrograde signals has proved elusive, but [...]

Runx1 is required to sustain muscle by preventing denervated myofibers from undergoing myofibrillar disorganization and autophagy, structural defects found in a variety of congenital myopathies. The findings indicate that only 29 genes, encoding ion channels, signaling molecules, and muscle structural proteins, depend upon Runx1 expression, suggesting that their misregulation causes the dramatic muscle wasting.

Results show that neuregulin-1 stimulates phosphorylation of GABPalpha protein at the site of threonine280 residue, which is mediated by MAP kinases. Data corroborate the hypothesis that phosphorylation of GABPalpha is involved in the transcriptional activation of acetylcholine receptors genes by neuregulin-1.

Neuregulin (NRG)-induced and synapse-specific transcription must have an Ets site that can bind GABP alpha/GABP beta. By transfection of some gene fusions into a muscle cell line it has been shown that a potential binding site for Ets proteins is necessary for NRG-induced gene expression. An NRG-response element (NRE) has been shown to be required for synapse-specific transcription in mice. GABP alpha is an Ets protein and GABP beta is a protein that has no Ets domain, but does dimerize with GABP alpha. It seems that GABP alpha/GABP beta mediates transcriptional response of the acetylcholine receptor (AchR) delta-subunit gene to synaptic signals.

Synapses are formed by a series of steps starting from the generation of neurons. The postsynaptic differentiation is induced following the movement of axons to their skeletal muscle cells. There is also the step when presynaptic terminal and postsynaptic membrane are induced. Current knowledge of neuromuscular synapses formation is based on studies of vertebrates.

Agrin activates the MuSK (muscle-specific kinase) receptor to initiate the formation of the neuromuscular junction by signaling cascades. Agrin also activates presynaptic differentiation and synapse-specific transcription through MuSK receptor stimulation. MuSK gene disruption in mice resulted in perinatal death due to the aberrant formation of neuromuscular synapses. These results indicate the importance of MuSK as a signaling component for receptors that respond to neural agrin.

The muscle-specific kinase (MuSK) receptor is activated by agrin to initiate the formation of neuromuscular junctions. The inability of agrin to induce the clustering acetylcholine receptors in MuSK deficient mice also indicates that MuSK acts further downstream in the agrin signaling pathway. The binding of agrin to MuSK receptors requires myotube-specific components that are not expressed in fibroblast or undifferentiated myoblasts.

The aggregation of neuregulins at synaptic sites and the remnants of neuregulins at the synaptic sites when nerve and muscle cells are absent is demonstrated using antibodies. The erbB3 mRNA and the erbB2 mRNA with less erbB4 mRNA are found in the C2 muscle cells. Tyrosine phosphorylation in erbB2 and erbB3 is stimulated by neuregulins, revealing that erbB2 and erbB3 mediate neuregulin signalling in skeletal muscles.

The involvement of tyrosine kinases in the transduction of synapse-inducing signalswas investigated. A muscle homologous but densely innervated tissue, Torpedo californica, was subjected to polymerase chain reaction. Northern blots were probed with antisense RNA probes. A receptor tyrosine kinase specifically expressed in both electric organ and skeletal muscles was isolated.

The mouse acetylcholine receptor (AChR) delta-subunit gene was fused to the human growth hormone (hGH) gene and the construct was transfected into primary rat myoblasts to identify the cis-acting elements in the AChR delta-subunit gene which respond to muscle cell electrical activity. A181-bp 5' flanking segment of the AChR delta subunit gene was identified as theregion which confers electrical activity-dependent gene expression. In additionto the AChR delta-subunit gene, this region also regulates the expression of MyoD and myogenin.

Telomere length dynamics are an established biomarker of health and ageing in animals. The study of telomeres in numerous species has been facilitated by methods to measure telomere length by real‐time quantitative PCR (qPCR). In this method, telomere length is determined by quantifying the amount of telomeric DNA repeats in a sample and normalizing this to the total amount of genomic DNA. This normalization requires the development of genomic reference primers suitable for qPCR, which remains challenging in nonmodel organism with genomes that have not been sequenced. Here we report reference primers that can be used in qPCR to measure telomere lengths in any vertebrate species. We designed primer pairs to amplify genetic elements that are highly conserved between evolutionarily distant taxa and tested them in species that span the vertebrate tree of life. We report five primer pairs that meet the specificity and reproducibility standards of qPCR. In addition, we demonstrate an approach to choose the best primers for a given species by testing the primers on multiple individuals within a species and then applying an established computational tool. These reference primers can facilitate qPCR‐based telomere length measurements in any vertebrate species of ecological or economic interest. [ABSTRACT FROM AUTHOR]

Wnts can affect the structure of presynaptic mossy fiber axons and growth cones in vitro, but further research is necessary to determine whether they remodel axons and growth cones in vivo. Wnts are signaling molecules secreted by postsynaptic cerebellar granule cells.