Biology subjects

Spendiff, S.

Publications and source records attributed to Spendiff, S..

6 recordsLinked to original sources

bioRxiv2026

Validation of optogenetic approach to investigate fatigable weakness using a zebrafish model of congenital myasthenic syndrome

Congenital myasthenic syndromes (CMS) are rare inherited diseases of the neuromuscular junction (NMJ). There are 40 identified CMS genes, but many patients go without genetic diagnosis, which suggests new genes have yet to be discovered and characterised. Here, we describe an optogenetic approach to study fatigable muscle weakness and NMJ function in larval zebrafish to facilitate screening approaches for uncovering novel CMS genes. Using blue-light illumination of spinal motoneurons that express channelrhodopsin-2 (ChR2) to induce muscle contraction, we measure motor defects at the behavioural, synaptic, and genetic level through a novel behavioural assay, standard whole-cell electrophysiology of individual muscle fibers and a customized NMJ gene panel. We employ this approach in synaptotagmin-2 (syt2) morphant zebrafish, an identified CMS gene model, to validate its usefulness. Our customized optogenetic behavioural assay successfully demonstrates reduced, fatigable, locomotor response during repeated activation of spinal motoneurons. Whole-cell electrophysiology recordings of optogenetically-elicited endplate currents in muscle fibers reveal similarities to altered properties of NMJ function in syt2 morphants reported in other studies using the standard paired motoneuron-muscle electrophysiology technique. Finally, we develop a genetic panel of CMS and NMJ-related genes to characterize the expression landscape of syt2 morphants to elucidate potential pathomechanisms and novel therapeutic targets. We propose that this three-tiered approach successfully links behaviour, synaptic motor function, and genetic expression and can be used as a tool in the screening of novel genes associated with CMS.

neuroscience↗

bioRxiv2025

Cell-type-specific adaptations to mitochondrial stress underly the neurological presentations of MTRFR mutations

Mitochondrial diseases are a group of heterogeneous genetic disorders that exhibit striking tissue specificity. Neurological involvement is among the most consistent features, yet the mechanisms that determine why selective neuronal populations are particularly vulnerable to mitochondrial dysfunction remain poorly understood. Mutations in MTRFR, a mitochondrial ribosome rescue factor, cause a progressive neuromuscular phenotype, but no relevant disease model exists to explain its cell-type-specific pathology. Here, we established the first human iPSC-derived neuronal model of MTRFR loss and identified mechanisms driving differential vulnerability between cortical and motor neurons. Although knockdown led to comparable deficits in mitochondrial translation and OXPHOS across both subtypes, cortical neurons engaged adaptive programs, including dendritic mitochondrial remodelling and heat-shock response activation, that preserved survival. Motor neurons failed to mount these responses and instead displayed apoptotic and inflammatory priming. Pharmacological enhancement of stress adaptation rescued motor neuron survival, indicating that resilience is programmable. These findings provide the first mechanistic evidence that neuronal susceptibility to mitochondrial translation defects is defined by the capacity to activate mitochondrial and cytoprotective stress-response pathways.

neuroscience↗

bioRxiv2025

Acute AMPK activation does not adequately stimulate insulin signaling in skeletal muscle models of Myotonic Dystrophy Type 1

Myotonic Dystrophy Type 1 (DM1) is a multisystemic neuromuscular disorder characterized by skeletal muscle weakness, muscle atrophy, myotonia, cognitive impairments, gastrointestinal complications, and insulin resistance. While insulin resistance is well characterized in type 2 diabetes, its pathomechanism in DM1 remains unclear. Our study aims to elucidate the pathomechanism of insulin resistance in DM1 and how the pathway responds to AMPK stimulation. Proteomic analysis from sedentary wildtype and sedentary HSA-LR mice, a common DM1 mouse model, revealed downregulation of the AMPK-PGC-1 axis. Analysis of sedentary HSA-LR mice and exercised HSA-LR mice revealed activation of the AMPK-PGC-1 axis in exercised animals. To investigate this pathway, we treated WT and HSA-LR mice with the AMPK activator AICAR to examine the impact of AMPK stimulation on insulin signaling in DM1. This revealed impaired responses in the insulin pathway activation in the HSA-LR mice. Next, we examined whether these differences extended to a human model by treating control and DM1 myotubes with insulin and/or AICAR. In DM1 myotubes, both treatments produced dampened responses of key insulin signaling intermediates compared to controls. Taken together, these results suggest impaired activation of insulin signaling pathways in DM1 models and confirm the presence of insulin resistance with an impaired response to acute AMPK stimulation.

molecular biology↗

bioRxiv2025

Gene-specific response to MuSK agonist antibody in the treatment of Congenital Myasthenic Syndromes

Congenital myasthenic syndromes (CMS) are a group of rare disorders characterized by fatigable muscle weakness and caused by impaired neuromuscular junction (NMJ) function. CMS symptoms are highly variable, but can be detrimental and lead to death. There are over 40 different genetic subtypes, including Agrn-CMS and ColQ-CMS. Agrn encodes for neural AGRIN, which is released from the nerve terminal and triggers muscle-specific kinase phosphorylation (pMuSK). pMuSK is essential for NMJ development and maintenance, thus AGRIN deficiency causes NMJ impairment. ColQ encodes for collagenous subunit Q (ColQ), which anchors acetylcholinesterase and stabilizes MuSK. As a result, ColQ deficiency results in NMJ degeneration from prolonged transmission signals and decreased pMuSK. Current treatments for Agrn-CMS and ColQ-CMS are limited, highlighting the importance of finding more efficient therapies. Recently, a MuSK agonist antibody with high affinity for the Frizzled-like domain showed remarkable rescue of a Dok7-CMS mouse model. We hypothesized a similar antibody could benefit Agrn- and ColQ-CMS mouse models. Agrn-CMS mice were treated at postnatal day 5 (P5), P15 and P35, and ColQ-CMS mice were treated weekly from P22 to P57. In Agrn-CMS mice, 3B2 treatment rescued survival, bodyweight, fibre type switching and pMuSK levels, and improved grip strength and NMJ morphology. In ColQ-CMS mice, 3B2 treatment was unable to rescue deficits observed. Our findings suggest that MuSK agonists may benefit patients with Agrn-CMS, which should be tested in clinical trials. Our study emphasizes that effective CMS treatment is gene-dependent and relies on an accurate genetic diagnosis.

molecular biology↗

bioRxiv2021

Unbiased Proteomics, Histochemistry, and Mitochondrial DNA Copy Number Reveal Better Mitochondrial Health in Muscle of High Functioning Octogenarians

BackgroundMaster athletes prove that preserving a high level of physical function up to very late in life is possible, but the mechanisms responsible for their high function remain unclear. MethodsWe performed muscle biopsies in 15 octogenarian world class track and field masters athletes (MA) and 14 non-athlete age/sex-matched controls (NA) to provide insights into mechanisms for preserving function in advanced age. Muscle samples were assessed for respiratory compromised fibers, mtDNA copy number, and proteomics by liquid-chromatography mass spectrometry. ResultsMost of the [~]800 differentially represented proteins in MA versus NA pertained to mitochondria structure/function such as electron transport capacity (ETC), cristae formation, mitochondrial biogenesis, and mtDNA-encoded proteins. In contrast, proteins from the spliceosome complex and nuclear pore were downregulated in MA. Consistent with proteomics data, MA had fewer respiratory compromised fibers, higher mtDNA copy number, and an increased protein ratio of the cristae-bound ETC subunits relative to the outer mitochondrial membrane protein voltage dependent anion channel. There was a substantial overlap of proteins overrepresented in MA versus NA with proteins that decline with aging and which are higher in physically active than sedentary individuals. However, we also found 176 proteins related to mitochondria that are uniquely differentially expressed in MA. DiscussionWe conclude that high function in advanced age is associated with preserving mitochondrial structure/function proteins, with under-representation of proteins involved in the spliceosome and nuclear pore complex. Whereas many of these differences in MA appear related to their physical activity habits, others may reflect unique biological (e.g., gene, environment) mechanisms that preserve muscle integrity and function with aging.

physiology↗

bioRxiv2021

Collagen VI regulates motor circuit plasticity and motor performance by cannabinoid modulation

Collagen VI is a key component of muscle basement membranes, and genetic variants can cause monogenic muscular dystrophies. Conversely, human genetic studies recently implicated collagen VI in central nervous system function, with variants causing the movement disorder dystonia. To elucidate the neurophysiological role of collagen VI, we generated mice with a truncation of the dystonia-related collagen 3 (VI) (COL6A3) C-terminal domain (CTD). These Col6a3CTT mice showed a recessive dystonia-like phenotype. We found that COL6A3 interacts with the cannabinoid receptor 1 (CB1R) complex in a CTD-dependent manner. Col6a3CTT mice have impaired homeostasis of excitatory input to the basal pontine nuclei (BPN), a motor control hub with dense COL6A3 expression, consistent with deficient endocannabinoid signaling. Aberrant synaptic input in the BPN was normalized by a CB1R agonist, and motor performance in Col6a3CTT mice was improved by CB1R agonist treatment. Our findings identify a readily therapeutically addressable synaptic mechanism for motor control. SIGNIFICANCE STATEMENTDystonia is a movement disorder characterized by involuntary movements. We previously identified genetic variants affecting a specific domain of the COL6A3 protein as a cause of dystonia. Here, we we created mice lacking the affected domain and observed an analogous movement disorder. Using a protein interaction screen, we found that the affected COL6A3 domain mediates an interaction with the cannabinoid receptor CB1R. Concordantly, our COL6A3-deficient mice showed a deficit in synaptic plasticity linked to a deficit in cannabinoid signaling. Pharmacological cannabinoid augmentation rescued the motor impairment of the mice. Thus, cannabinoid augmentation could be a promising avenue for treating dystonia, and we have identified a possible molecular mechanism mediating this.

neuroscience↗