Biology subjects

Rhymes, E. R.

Publications and source records attributed to Rhymes, E. R..

6 recordsLinked to original sources

bioRxiv2026

The neuropathy-causing GARS1{triangleup}ETAQ mutation drives pathology in subsets of motor and sensory neurons in mice

Charcot-Marie-Tooth disease type 2D (CMT2D) results from gain-of-function mutations in GARS1, which encodes glycyl-tRNA synthetase (GlyRS), the enzyme responsible for charging transfer RNA (tRNA) with glycine. There are several CMT2D mouse models, but Gars{Delta}ETAQ/+ is the only one that bears a patient-sourced mutation. Created using CRISPR/Cas9 to model a 12-nucleotide de novo GARS1 deletion identified in an unusually severe CMT2D patient, Gars{Delta}ETAQ/+ mice have previously been shown to display several neuromuscular phenotypes; motor axon loss, denervated neuromuscular junctions (NMJs) and reduced muscle function. Here, we extend these analyses to provide a more comprehensive understanding of both motor and sensory nerve deficits across hind- and fore-limbs. At 3 months, Gars{Delta}ETAQ/+ mice possess sex-independent alterations in the levels of neuropathy biomarkers - including decreased NfL and increased periaxin - alongside reduced muscle endurance and strength, and impairments in the sensory modalities of mechanosensation, proprioception and nociception. Underpinning these dysfunctions, we identified site-specific defects comprising altered sensory neuron populations, muscle spindle loss, reduced motor neuron size, disrupted NMJ innervation and maturation, and reduced axonal transport of signalling endosomes in vivo. Together, these experiments show that Gars{Delta}ETAQ/+ mice display robust and selective peripheral nerve pathology that manifests in a general distal-to-proximal fashion, priming this CMT2D allele for testing treatments and evaluating mechanisms underlying peripheral nerve vulnerability. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/736541v1_ufig1.gif" ALT="Figure 1"> View larger version (70K): org.highwire.dtl.DTLVardef@b48a41org.highwire.dtl.DTLVardef@e0c22dorg.highwire.dtl.DTLVardef@1ec2f5forg.highwire.dtl.DTLVardef@11a3311_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2025

CNTF specifically slows down the axonal transport of signalling endosomes

Efficient axonal transport is essential for maintaining neuronal function, enabling the bidirectional delivery of diverse cargoes between the cell body and distal compartments. In the neuromuscular system, neurotrophic factors (NTFs) regulate motor neuron survival, function, and synaptic connectivity, in part, through retrograde trafficking of activated NTF-receptor complexes from the neuromuscular junction (NMJ) to the cell body. We recently demonstrated that brain-derived neurotrophic factor (BDNF) stimulation to muscles selectively enhances retrograde transport of signalling endosomes in fast, but not slow, motor neurons in vivo. Moreover, both axonal endosome transport and its BDNF-mediated regulation are disrupted in mouse models of diseases impacting motor neurons. Here, we examined whether additional NTFs, when applied to distal axon terminals, share this transport-modulating property. Through imaging sciatic nerves in anaesthetised mice, we tracked the in vivo dynamics of signalling endosomes in fast (FMN) and slow motor neurons (SMN) via intramuscular injections of a fluorescently conjugated, atoxic fragment of tetanus neurotoxin (HCT). HCT was co-administered with ciliary neurotrophic factor (CNTF), hepatocyte growth factor (HGF), neurturin (NRTN), or proBDNF - four growth factors with known effects on motor neurons. Compared to vehicle-treated controls, proBDNF, HGF, and NRTN, produced no detectable change in transport dynamics. In contrast, CNTF markedly reduced endosome speeds in both FMNs and SMNs, indicating remarkable selectivity of specific NTFs in the regulation of signalling endosome transport in motor neurons. Understanding this selectivity may aid the development of muscle-targeted NTF-based therapeutic strategies aimed at restoring axonal transport in neurodegenerative disease, peripheral neuropathy, and nerve injury. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=88 SRC="FIGDIR/small/681259v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@10e4229org.highwire.dtl.DTLVardef@119c69aorg.highwire.dtl.DTLVardef@13dd629org.highwire.dtl.DTLVardef@b733ec_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2025

Processivity and BDNF-dependent modulation of signalling endosome axonal transport are impaired in aged mice

A healthy nervous system is reliant upon an efficient transport network to deliver essential cargoes throughout the extensive and polarised architecture of neurons. The trafficking of cargoes, such as organelles and proteins, is particularly challenging within the long projections of neurons, which, in the case of axons, can be more than four orders of magnitude longer than cell bodies. It is therefore unsurprising that disruptions in axonal transport have been reported across neurological diseases. A decline in this essential process has also been identified in many aging models, perhaps compounding age-related neurodegeneration. Via intravital imaging, we recently determined that, despite a reduction in overall motility, the run speed and displacement of anterograde mitochondrial transport were unexpectedly enhanced in aged mouse peripheral nerves. Here, to determine how aging impacts a different axonal cargo, we evaluated in vivo trafficking of signalling endosomes in motor axons of mouse sciatic nerves from 3 to 22 months. Contrasting with mitochondria, we did not detect alterations in signalling endosome speed, but found a consistent rise in pausing that manifested after 18 months. We then treated muscles with brain-derived neurotrophic factor (BDNF), which regulates axonal transport of signalling endosomes in motor neurons; however, we observed no change in the processivity defect at 22 months, consistent with downregulation of the BDNF receptor TrkB at the neuromuscular junction. Together, these findings indicate that aging negatively impacts signalling endosome trafficking in motor axons likely through dampened BDNF signalling at the motor neuron-muscle interface. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=195 SRC="FIGDIR/small/635507v1_ufig1.gif" ALT="Figure 1"> View larger version (84K): org.highwire.dtl.DTLVardef@d5fe63org.highwire.dtl.DTLVardef@13033c2org.highwire.dtl.DTLVardef@19621dcorg.highwire.dtl.DTLVardef@189121a_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2023

Boosting BDNF in muscle rescues impaired in vivo axonal transport in a mouse model of DI-CMTC peripheral neuropathy

Charcot-Marie-Tooth disease (CMT) is a genetic peripheral neuropathy caused by mutations in many functionally diverse genes. The aminoacyl-tRNA synthetase (ARS) enzymes, which transfer amino acids to partner tRNAs for protein synthesis, represent the largest protein family genetically linked to CMT aetiology, suggesting pathomechanistic commonalities. Dominant intermediate CMT type C (DI-CMTC) is caused by YARS1 mutations driving a toxic gain-of-function in the encoded tyrosyl-tRNA synthetase (TyrRS), which is mediated by exposure of consensus neomorphic surfaces through conformational changes of the mutant protein. In this study, we first showed that human DI-CMTC-causing TyrRSE196K mis-interacts with the extracellular domain of the BDNF receptor TrkB, an aberrant association we have previously characterised for several mutant glycyl-tRNA synthetases linked to CMT type 2D (CMT2D). We then performed temporal neuromuscular assessments of YarsE196K mice modelling DI-CMT. We determined that YarsE196K homozygotes display a selective, age-dependent impairment in in vivo axonal transport of neurotrophin-containing signalling endosomes, phenocopying CMT2D mice. This impairment is replicated by injection of recombinant TyrRSE196K, but not TyrRSWT, into muscles of wild-type mice. Augmenting BDNF in DI-CMTC muscles, through injection of recombinant protein or muscle-specific gene therapy, resulted in complete axonal transport correction. Therefore, this work identifies a non-cell autonomous pathomechanism common to ARS-related neuropathies, and highlights the potential of boosting BDNF levels in muscles as a therapeutic strategy.

neuroscience↗

bioRxiv2022

Bimodal regulation of axonal transport by the GDNF-RET signalling axis in healthy and diseased motor neurons

Deficits in axonal transport are one of the earliest pathological outcomes in several models of amyotrophic lateral sclerosis (ALS), including SOD1G93A mice. Evidence suggests that rescuing these deficits prevents disease progression, stops denervation, and extends survival. Kinase inhibitors have been previously identified as transport enhancers, and are being investigated as potential therapies for ALS. For example, inhibitors of p38 mitogen-activated protein kinase and insulin growth factor receptor 1 have been shown to rescue axonal transport deficits in vivo in symptomatic SOD1G93A mice. In this work, we investigated the impact of RET, the tyrosine kinase receptor for glial cell-line-derived neurotrophic factor (GDNF), as a modifier of axonal transport. We identified fundamental interplay between RET signalling and axonal transport in both wild type and SOD1G93A motor neurons in vitro. We demonstrated that blockade of RET signalling using pharmacological inhibitors and genetic knockdown enhances signalling endosome transport in wild type motor neurons and uncovered a divergence in the response of primary motor neurons to GDNF compared with cell lines. Finally, we demonstrated that inhibition of the GDNF-RET signalling axis rescues in vivo transport deficits in early symptomatic SOD1G93A mice, promoting RET as a potential therapeutic target in the treatment of ALS.

neuroscience↗

bioRxiv2021

BDNF-dependent modulation of axonal transport is selectively impaired in ALS

Axonal transport ensures long-range delivery of essential cargoes between proximal and distal compartments of neurons, and is needed for neuronal development, function, and survival. Deficits in axonal transport have been detected at pre-symptomatic stages in mouse models of amyotrophic lateral sclerosis (ALS), suggesting that impairments are fundamental for disease pathogenesis. However, the precise mechanisms responsible for the transport deficits and whether they preferentially affect -motor neuron (MN) subtypes remain unresolved. Here, we report that stimulation of wild-type neurons with brain-derived neurotrophic factor (BDNF) enhances trafficking of signalling endosomes specifically in fast MNs (FMNs). In early symptomatic SOD1G93A mice, FMNs display selective impairment of axonal transport and develop an insensitivity to BDNF stimulation, with pathology upregulating classical non-pro-survival receptors in muscles and sciatic nerves. Altogether, these data indicate that cell- and non-cell autonomous BDNF signalling is impaired in vulnerable SOD1G93A MNs, thus identifying a new key deficit in ALS amenable for future therapeutic interventions.

neuroscience↗