Biology subjects

McMahon, L.

Publications and source records attributed to McMahon, L..

13 recordsLinked to original sources

bioRxiv2026

Characterization of Electrophysiological and Transcriptomic Alterations in Patient-Derived Neurons from CHAMP1 Syndrome

Mutations in chromosome alignment maintaining phosphoprotein 1 (CHAMP1) have been linked to neurodevelopmental disorders characterized by intellectual disability, developmental delay, and autism spectrum disorder. However, the cellular and electrophysiological mechanisms by which CHAMP1 mutations disrupt human neuronal development remain poorly understood. In the present study, we used patient-derived induced pluripotent stem cells (iPSCs) carrying two pathogenic CHAMP1 mutations and generated neural progenitor cells (NPCs) and excitatory neurons to investigate the effects of each mutation on neuronal maturation and function, DNA repair, and gene expression. Proliferative capacity declines with CHAMP1 dosage, while DNA repair dysfunction is allele-specific. Whole-cell patch-clamp electrophysiology revealed that CHAMP1 mutant neurons exhibit significant alterations in intrinsic membrane properties during early developmental stages, including depolarized resting membrane potential, reduced action potential firing, and impaired waveform kinetics. These functional deficits were accompanied by reduced sodium and potassium current densities, suggesting impaired ion channel accumulation during neuronal maturation. Furthermore, recordings of spontaneous excitatory postsynaptic currents indicated altered synaptic activity and reduced proportions of synaptically active neurons. Morphological analyses showed that CHAMP1-deficient neurons exhibit impaired neurite outgrowth and branching, supporting a defect in neuronal maturation. Single-nucleus transcriptomic profiling further revealed delayed developmental trajectories and mutation-specific dysregulation of synaptic gene programs enriched for autism, ADHD, and epilepsy risk genes. Together, these findings demonstrate that CHAMP1 mutations disrupt multiple aspects of neuronal development, including homologous recombination (HR) dysfunction in NPCs, membrane excitability, ion channel function, and synaptic connectivity. Our results provide insights into the neurobiological consequences of CHAMP1 mutations and establish patient-derived neurons as a platform to investigate cellular pathophysiology and potential therapeutic strategies for CHAMP1-associated neurodevelopmental disorders.

neuroscience↗

bioRxiv2024

Ketosis Elevates Antioxidants and Enhances Neural Function Through Improved Bioenergetics: A 1H MR Spectroscopy Study

Ketosis is known to alter the balance of neuroactive amino acids and enhance neural function when compared to a glycolytic condition. However, its influence on other metabolites, such as antioxidants and neural energy markers, and the mechanisms by which ketosis improves neural function remain unclear. Here, we measure the neurochemical effects of acute ketosis on the human brain using ultra-high-field 1H MR Spectroscopy (MRS) and investigate the subsequent impact on neural function through resting-state functional magnetic resonance imaging (rsfMRI). In a within-subjects design, N = 63 healthy adults from across the lifespan underwent 1H MRS and rsfMRI scans before and after consuming individually weight-dosed and calorically-matched ketone monoester or glucose drinks. Ketone monoester administration, but not glucose, significantly elevated cerebral antioxidants and energy markers while decreasing GABA, glutamate, and glutamine levels in the posterior cingulate cortex (PCC). Notably, increased bioenergetics, specifically an increase in total creatine, correlated with greater improvements in neural function as measured using rsfMRI. Our results integrate metabolic and functional neuroimaging findings, offering a comprehensive understanding of ketosis-induced changes in brain chemistry and functional network dynamics, yielding valuable insights into potential mechanisms by which ketosis imparts its neural benefits.

neuroscience↗

bioRxiv2024

Forskolin reverses the O-GlcNAcylation dependent decrease in GABAAR current amplitude at hippocampal synapses possibly at a neurosteroid site on GABAARs.

GABAergic transmission is influenced by post-translational modifications, like phosphorylation, impacting channel conductance, allosteric modulator sensitivity, and membrane trafficking. O-GlcNAcylation is a post-translational modification involving the O-linked attachment of {beta}-N-acetylglucosamine on serine/threonine residues. Previously we reported an acute increase in O-GlcNAcylation elicits a long-term depression of evoked GABAAR inhibitory post synaptic currents (eIPSCs) onto hippocampal principal cells. Importantly, O-GlcNAcylation and phosphorylation can co-occur or compete for the same residue; whether they interact in modulating GABAergic IPSCs is unknown. We tested this by recording IPSCs from hippocampal principal cells and pharmacologically increased O-GlcNAcylation, before or after increasing serine phosphorylation using the adenylate cyclase activator, forskolin. Although forskolin had no significant effect on baseline eIPSC amplitude, we found that a prior increase in O-GlcNAcylation unmasks a forskolin-dependent increase in eIPSC amplitude, reversing the O-GlcNAc-induced eIPSC depression. Inhibition of adenylate cyclase or protein kinase A did not prevent the potentiating effect of forskolin, indicating serine phosphorylation is not the mechanism. Surprisingly, increasing O-GlcNAcylation also unmasked a potentiating effect of the neurosteroids 5-pregnane-3,21-diol-20-one (THDOC) and progesterone on eIPSC amplitude, mimicking forskolin. Our findings show under conditions of heightened O-GlcNAcylation, the neurosteroid site on synaptic GABAARs is accessible to agonists, permitting strengthening of synaptic inhibition.

neuroscience↗

bioRxiv2024

Divergent trajectories to structural diversity impact patient survival in high grade serous ovarian cancer

Deciphering the structural variation across tumour genomes is crucial to determine the events driving tumour progression and better understand tumour adaptation and evolution. High grade serous ovarian cancer (HGSOC) is an exemplar tumour type showing extreme, but poorly characterised structural diversity. We comprehensively describe the mutational landscape driving HGSOC, exploiting a large (N=324), deeply whole genome sequenced dataset. We reveal two divergent evolutionary trajectories, affecting patient survival and involving differing genomic environments. One involves homologous recombination repair deficiency (HRD) while the other is dominated by whole genome duplication (WGD) with frequent chromothripsis, breakage-fusion-bridges and extra-chromosomal DNA. These trajectories contribute to structural variation hotspots, containing novel candidate driver genes with significantly altered expression. While structural variation predominantly drives tumorigenesis, we also find high mtDNA mutation loads associated with shorter patient survival, and acting in combination with alterations in the nuclear genome to impact prognosis and suggesting new strategies for patient stratification.

cancer biology↗

bioRxiv2023

Disruption of Golgi markers by two RILP-directed shRNAs in neurons: a new role for RILP or a neuron-specific off-target phenotype?

In neurons, degradation of dendritic cargos requires RAB7 and dynein-mediated retrograde transport to somatic lysosomes. In order to test if the dynein adaptor RILP (RAB-interacting lysosomal protein) mediated the recruitment of dynein to late endosomes for retrograde transport in dendrites, we obtained several knockdown reagents which had been previously validated in non-neuronal cells. We found that striking endosomal phenotypes elicited by one shRILP plasmid were not reproduced by another one. Furthermore, we discovered a profound depletion of Golgi/TGN markers for both shRILP plasmids. This Golgi disruption was only observed in neurons and could not be rescued by re-expression of RILP. This Golgi phenotype was also not found in neurons treated with siRILP or gRILP/Cas9. Lastly, we tested if a different RAB protein that interacts with RILP, namely the Golgi-associated RAB34, might be responsible for the loss of Golgi markers. Expression of a dominant-negative RAB34 did indeed cause changes in Golgi staining in a small subset of neurons but manifested as fragmentation rather than loss of markers. Unlike in non-neuronal cells, interference with RAB34 did not cause dispersal of lysosomes in neurons. Based on multiple lines of experimentation, we conclude that the neuronal Golgi phenotype observed with shRILP is likely off-target in this cell type specifically. Any observed disruptions of endosomal trafficking caused by shRILP in neurons might thus be downstream of Golgi disruption. Different approaches will be needed to test if RILP is required for late endosomal transport in dendrites. Cell type-specific off-target phenotypes therefore likely occur in neurons, making it prudent to re-validate reagents that were previously validated in other cell types.

neuroscience↗

bioRxiv2022

Examination of diurnal variation and sex differences in hippocampal neurophysiology and spatial memory

Circadian rhythms are biological processes that cycle across 24 hours and regulate many facets of neurophysiology, including learning and memory. Circadian variation in performance on spatial memory tasks is well-documented; however, the effect of sex across circadian time remains unclear. Additionally, little is known regarding the impact of time-of-day on hippocampal neuronal physiology. Here, we investigated the influence of both sex and time-of-day on hippocampal neurophysiology and memory. Performance on the object location memory (OLM) task depended on both circadian time and sex, with memory enhanced at night in males but during the day in females. Long-term synaptic potentiation (LTP) magnitude at CA3-CA1 synapses was greater at night compared to day in both sexes. Next, we measured spontaneous synaptic excitation and inhibition onto CA1 pyramidal neurons. Frequency and amplitude of inhibition was greater during the day compared to night, regardless of sex. Frequency and amplitude of excitation was larger in females, compared to males, independent of time-of-day, although both time-of-day and sex influenced presynaptic release probability. At night, CA1 pyramidal neurons showed enhanced excitability (action potential firing and/or baseline potential) that was dependent on synaptic excitation and inhibition, regardless of sex. This study emphasizes the importance of sex and time-of-day in hippocampal physiology, especially given that many neurological disorders impacting the hippocampus are linked to circadian disruption and present differently in men and women. Knowledge about how sex and circadian rhythms affect hippocampal physiology can improve the translational relevancy of therapeutics and inform the appropriate timing of existing treatments.

neuroscience↗

bioRxiv2021

KymoMerge: a new tool for analysis of multichannel kymographs

Kymograph analysis is commonly used by researchers to study dynamic processes in cells. Current tools widely available only allow for analysis of one channel kymographs. Here we provide a python-coded, open source program to use as a plug-in for ImageJ which creates one kymograph from the kymographs of two separate channels of one time-lapse movie. This add-in, which we call KymoMerge, therefore allows for analysis of only the co-located tracks in multi-channel movies.

neuroscience↗

bioRxiv2020

Increased Excitability and Heightened Magnitude of Long-term Potentiation at Hippocampal CA3-CA1 Synapses in a Mouse Model of Neonatal Hyperoxia Exposure

Preterm infants exposed to supraphysiological oxygen (hyperoxia) during the neonatal period have hippocampal atrophy and cognitive dysfunction later in childhood and as adolescents. Previously, we reported that 14-week-old adult mice exposed to hyperoxia as newborns had spatial memory deficits and hippocampal shrinkage, findings that mirror those of adolescents who were born preterm. Area CA1 region of the hippocampus that is crucial for spatial learning and memory is highly vulnerable to oxidative stress. In this study, we investigated the long-term impact of neonatal hyperoxia exposure on hippocampal CA3-CA1 synaptic function. Male and female C57BL/6J mouse pups were continuously exposed to either 85% normobaric oxygen or air between postnatal days 2-14. Hippocampal slice electrophysiology at CA3-CA1 synapses was then performed at 14 weeks of age. We observed that hyperoxia exposed mice have heightened strength of basal synaptic transmission measured in input-output curves, increased fiber volley amplitude indicating increased axonal excitability, and heightened LTP magnitude at CA3-CA1 synapses, likely a consequence of increased postsynaptic depolarization during the tetanus. These data demonstrate that supraphysiological oxygen exposure during the critical neonatal developmental period leads to pathologically heightened CA3-CA1 synaptic function during early adulthood which may contribute to hippocampal shrinkage and learning and memory deficits we previously reported. Furthermore, these changes may account for cognitive disorders in children born preterm who were exposed to prolonged oxygen supplementation.

neuroscience↗

bioRxiv2020

Structural variants at the BRCA1/2 loci are a common source of homologous repair deficiency in high grade serous ovarian carcinoma

Around half of high grade serous ovarian carcinomas (HGSOC) show homologous recombination repair deficiency (HRD), often caused by germline or somatic single nucleotide variant (SNV) mutations or small indels disrupting BRCA1/2. We have uniformly processed the largest collection of whole genome sequencing (WGS) data from HGSOC samples to date (N=205), comprehensively characterising the somatic mutational landscape, and expression at the BRCA1/2 loci. We discover that large structural variants (SV) are a frequent but unappreciated source of BRCA1/2 disruption in these tumours. Somatic structural variation at these loci is dominated by multi-megabase deletions that span the entirety of BRCA1 (median = 4.9Mb) or BRCA2 (median = 6.2Mb), independently affecting a substantial proportion of patients (16%) in addition to those affected by damaging germline or somatic short variants, within the BRCA1/2 coding sequences (24%). In common with previous studies, we show that the presence of damaging somatic SNVs or short indels in BRCA1 (OR=10, 95% CI 1.8-103, p=0.002, adj p=0.027 and BRCA2 (OR=17, 95% CI 2.1-816), p=0.002, adj.p=0.021) was found to influence HRD. For the first time we also study the compound effect of SV and SNV or short indel mutations at both loci, demonstrating that SVs often contribute to compound deficiencies involving SNVs or indels, with large somatic deletions contributing to these compound deficiencies in 15/205 (7%) of samples. Notably the strongest risk of HRD (OR=19 (2.4-896), p=6.6x10-3, adj P=8.5x10-3) is generated by combined large deletions at BRCA1 and BRCA2 in the absence of SNVs or indels, affecting 3% of patients. Overall, we show that HRD is a complex phenotype in HGSOC tumours, affected by the patterns of shorter variants such as SNVs and indels, SVs, methylation and expression seen at multiple loci, and we construct a successful (ROC AUC = 0.75) predictive model of HRD using such variables. In addition, HRD impacts patient survival when conferred by mechanisms other than through the well-understood short variants at BRCA1/2, currently exploited in the clinic. These results alter our understanding of the mutational landscape at the BRCA1/2 loci in highly rearranged tumours, and increase the number of patients predicted to benefit from therapies exploiting HRD in tumours such as PARP inhibition.

cancer biology↗

bioRxiv2019

Early Life Supraphysiological Levels of Oxygen Exposure Permanently Impairs Hippocampal Mitochondrial Function

Preterm infants requiring prolonged oxygen therapy often develop cognitive dysfunction later life. Previously, we reported that 14-week-old young adult mice exposed to hyperoxia as newborns had spatial memory deficits and hippocampal shrinkage. We hypothesized that the underlying mechanism was the induction of hippocampal mitochondrial dysfunction by neonatal hyperoxia. C57BL/6j mouse pups were exposed to 85% oxygen or air from P2 - P14. Hippocampal proteomic analysis was performed in young adult mice (14 weeks). Mitochondrial bioenergetics were measured in neonatal (P14) and young adult mice. We found that hyperoxia exposure reduced mitochondrial ATP-linked oxygen consumption and increased state 4 respiration linked proton leak in both neonatal and young adult mice. Following hyperoxia exposure, complex I function was decreased at P14 but increased in young adult mice. Proteomic analysis revealed that neonatal hyperoxia exposure decreased complex I NDUFB8 and NDUFB11 and complex IV 7B subunits, but increased complex III subunit 9 in young adult mice. In conclusion, neonatal hyperoxia permanently impairs hippocampal mitochondrial function and alters complex I function. These changes may account for memory deficits seen in preterm survivors following prolonged oxygen supplementation and may potentially be a contributing mechanism in other oxidative stress associated cognitive disorders.

neuroscience↗

bioRxiv2018

Tolerance and dependence to Δ9-tetrahydrocannabinol in rhesus monkeys: activity assessments

Cannabis withdrawal upon discontinuation of long-term, heavy Cannabis use is reported in humans; however, methods to establish the nature and intensity of cannabinoid withdrawal, especially directly observable signs, have not been widely established. This study quantified activity in the home cage of rhesus monkeys, and examined the extent to which activity can be used to quantify tolerance to and dependence on {Delta}9-tetrahydrocannabinol ({Delta}9-THC). Home-cage activity was measured in one group that received {Delta}9-THC (1 mg/kg s.c.) every 12 h (i.e., chronic {Delta}9-THC), and a second group that received {Delta}9-THC (0.1 mg/kg i.v.) once every 3 days (i.e., intermittent {Delta}9-THC). Treatment was temporarily discontinued in the chronic {Delta}9-THC group and the effects of rimonabant and {Delta}9-THC were examined in both groups. Activity counts were highest during the day (lights on 0600-2000 h) and were lower at night. Rimonabant (0.1-3.2 mg/kg i.v.) dose-dependently increased activity (maximum 20-fold) in the chronic {Delta}9-THC group, but did not significantly alter activity in the intermittent {Delta}9-THC group. {Delta}9-THC (0.32-3.2 mg/kg i.v.) dose-dependently decreased activity counts (maximum 4-fold) in both groups, but was somewhat more potent in the intermittent as compared with the {Delta}9-THC group. Discontinuation of {Delta}9-THC treatment resulted in an immediate (i.e., within 24 h) and time-related increase in activity. Resumption of {Delta}9-THC treatment (1 mg/kg/12 h) produced hypoactivity that was no longer evident within 9 days of treatment. The time-related increase in home-cage activity upon abrupt discontinuation of chronic {Delta}9-THC treatment, as well as the effects of rimonabant to increase activity in monkeys receiving chronic, but not intermittent, {Delta}9-THC treatment, are consistent with signs of physical dependence on {Delta}9-THC in primates.

pharmacology and toxicology↗

bioRxiv2018

Unexpected Loss of Sensitivity to the nAChR Antagonist Activity of Mecamylamine and DHβEin Nicotine-Tolerant C57BL/6J Mice

There has always been interest in developing nAChR antagonists as smoking cessation aids, to add to nAChR agonists (e.g., nicotine replacement) already used for that indication. Previous studies have demonstrated that daily nicotine treatment confers tolerance to some of the effects of nicotine, as well as cross-tolerance to other nAChR agonists. The current study assessed the extent to which antagonism of nicotine varies as a function of daily nicotine treatment. The rate-decreasing and hypothermic effects of nicotine, as well as antagonism of those effects, were examined in C57BL/6J mice before, during treatment with, and after discontinuation of three daily injections of 1.78 mg/kg nicotine. The nonselective nAChR antagonist mecamylamine and the {beta}2 nAChR antagonist DH{beta}E were studied in combination with nicotine. The ED50 values of nicotine to produce rate-decreasing and hypothermic effects were, respectively, 0.44 and 0.82 mg/kg prior, 1.6 and 3.2 mg/kg during, and 0.74 and 1.1 mg/kg after discontinuation of daily nicotine treatment. Prior to daily nicotine treatment, mecamylamine decreased response rate and rectal temperature; however, during daily nicotine, mecamylamine (up to 5.6 mg/kg) only decreased rectal temperature. DH{beta}E (up to 5.6 mg/kg) when studied prior to daily nicotine decreased rectal temperature, but that decrease was abolished during chronic nicotine treatment. Mecamylamine and DH{beta}E antagonized the rate-decreasing and hypothermic effects of nicotine before and after daily nicotine; however, during daily nicotine, mecamylamine and DH{beta}E antagonized only the hypothermic effects of nicotine. The differential antagonism of rate-decreasing and hypothermic effects implicates differential involvement of nAChR subtypes. The decreased capacity of mecamylamine and DH{beta}E to antagonize nicotine during chronic nicotine treatment may indicate that their effectiveness as smoking cessations might vary as a function of nicotine tolerance and dependence.

pharmacology and toxicology↗

bioRxiv2017

Bulk degradation of dendritic cargos requires Rab7-dependent transport in Rab7-positive/LAMP1-negative endosomes to somatic lysosomes.

Regulation of protein homeostasis (\"proteostasis\") is necessary for maintaining healthy cells. Disturbances in proteostasis lead to aggregates, cellular stress and can result in toxicity. There is thus great interest in when and where proteins are degraded in cells. Neurons are very large as well as very long-lived, creating unusually high needs for effective regulation of protein turnover in time and space. We previously discovered that the dendritic membrane proteins Nsg1 and Nsg2 are short-lived with half-lives of less than two hours. Their short half-lives enabled us to ask whether these proteins are degraded by local degradative pathways in dendrites. We discovered a striking spatial gradient of late endosomes/lysosomes in dendrites, with late endosomes (Rab7-positive/LAMP1-negative/cathepsinB-negative) found in distal portion of dendrites, and degradative lysosomes (LAMP1-positive/cathepsinB-positive) being overwhelmingly found in the soma and in the proximal portion of dendrites. Surprisingly, the majority of dendritic Rab7-positive late endosomes do not contain LAMP1, unlike Rab7-positive late endosomes in fibroblasts. Secondly, Rab7 activity is required to mobilize these distal pre-degradative dendritic late endosomes for transport to the soma and degradation. We conclude that the vast majority of dendritic LAMP1-positive endosomes are not degradative lysosomes and that bulk degradation of dendritic cargos, such as Nsg1, Nsg2, and DNER, requires Rab7-dependent transport in late endosomes to somatic lysosomes.

cell biology↗