Biology subjects

Khayachi, A.

Publications and source records attributed to Khayachi, A..

13 recordsLinked to original sources

bioRxiv2026

Sex- and age-dependent control of dopamine function by LRRK2, and rapid reversal of dopamine release deficits in the LRRK2-G2019S knock-in mouse model of Parkinson's Disease.

No disease-modifying therapy exists for Parkinson's disease (PD). At diagnosis (~65y), ~70% of nigrostriatal dopamine (DA) axons may have degenerated, so identifying when and how striatal axon function declines is critical. LRRK2 hyperactivity is observed in LRRK2 and VPS35 familial cases, and also idiopathic PD. Thus suggests LRRK2 hyperfunction is a common pathophysiological feature of PD. LRRK2 inhibitors are currently in human trials, yet their effects on brain circuit function are poorly characterized. By optical imaging of iGluSnFR and dLight we measured striatal glutamate and DA release in WT, LRRK2 G2019S (LKI) and VPS35 D620N (VKI) knock-in mice, across adult ages and sexes, with and without LRRK2 inhibition. In WT mice, ongoing LRRK2 activity regulated DA release in an age- and sex-dependent manner. Acute inhibition reversed basal sex differences in striatal glutamate and DA release in aged mice, and potentiated DA release more in middle-aged females than males. In LKI mice, DA release declined progressively, first in males, then females, after maturation to full adulthood, and remained impaired in very old LKI and VKI mice. Release deficits in aged LKI and VKI mice were resistant to acute LRRK2 inhibition, but 2h inhibition rapidly reversed deficits in middle-aged LKI males and females. We conclude that LRRK2 activity, and inhibition effects, depend on age, sex, and genotype, with direct implications for the design and timing of current LRRK2 inhibitor clinical trials for PD.

neuroscience↗

bioRxiv2026

Neuronal secretome from bipolar patient-derived neurons alters network function and contains candidate biomarkers for diagnosis and lithium response

Delayed diagnosis and treatment are a major burden to patients with bipolar disorder. While lithium is the most effective treatment against mania, depressive episodes, and suicide, only 30% of patients respond to it fully. Currently there are no reliable methods to predict lithium responsiveness. To address these challenges, we aimed to identify potential diagnostic and treatment response biomarkers for BD, in addition furthering understanding of BD pathophysiology. Here, we leveraged human induced pluripotent stem cell (hiPSC) derived neurons from lithium responsive (LR), lithium non-responsive (LNR), and healthy age-matched controls (CTL). We found extracellular vesicle (EV) cargos from hiPSC-derived neurons are indicative of disease state and treatment-response. Unbiased proteomic and miRNA profiling identified 10 proteins and 13 miRNAs that were differentially expressed in BD EVs relative to CTL, as well as distinct molecular signatures separating LR ad LNR groups. These differences converged on pathways related to synaptic function, neurotrophic signalling, and cellular stress responses. Additionally, we found the BD neuronal secretome alters activity in non-BD neuronal networks. Chronic treatment of CTL cultures with BD neuron-conditioned media modified the proportion of active neurons and the frequency and amplitude of calcium transients in individual neurons. We demonstrate that neuronal EVs contain molecular signatures of disease state and treatment response in BD and identify the BD secretome as an active regulator of neuronal network homeostasis. This study provides novel insights into the pathophysiology of BD and candidate biomarkers for personalized BD diagnosis and treatment selection.

neuroscience↗

bioRxiv2025

Lithium partially rescues gene expression and enhancer activity from heterozygous knockout of AKAP11 while inducing novel differential changes

Bipolar disorder (BD) is a complex psychiatric condition usually requiring long-term treatment. Lithium (Li) remains the most effective mood stabilizer for BD, yet it benefits only a subset of patients, and its precise mechanism of action remains elusive. Exome sequencing has identified AKAP11 (A-kinase anchoring protein 11) as a shared risk gene for BD and schizophrenia (SCZ). Given that both the AKAP11-Protein Kinase A (PKA) complex and Li target and inhibit Glycogen Synthase Kinase-3 beta (GSK3{beta}), we hypothesize that Li may partially normalize the transcriptomic and/or epigenomic alterations observed in heterozygous AKAP11-knockout (Het-AKAP11-KO) iPSC-derived neurons. In this study, we employed genome-wide approaches to assess the effects of Li on the transcriptome and epigenome of human iPSC-derived Het-AKAP11-KO neuronal culture. We show that chronic Li treatment in this cellular model upregulates key pathways that were initially downregulated by Het-AKAP11-KO, several of which have also been reported as downregulated in synapses of BD and SCZ post-mortem brain tissues. Moreover, we demonstrated that Li treatment partially rescues certain transcriptomic alterations resulting from Het-AKAP11-KO, bringing them closer to the WT state. We suggest two possible mechanisms underlying these transcriptomic effects: (1) Li modulates histone H3K27ac levels at intergenic and intronic enhancers, influencing enhancer activity and transcription factor binding, and (2) Li enhances GSK3{beta} serine 9 phosphorylation, impacting WNT/{beta}-catenin signaling and downstream transcription. These findings underscore Lis potential as a therapeutic agent for BD and SCZ patients carrying AKAP11 loss-of-function variants or exhibiting similar pathway alterations to those observed in Het-AKAP11-KO models.

genomics↗

bioRxiv2024

A single-cell eQTL atlas of the human cerebellum reveals vulnerability of oligodendrocytes in essential tremor

Essential tremor (ET) is a movement disorder characterized by an upper-limb postural and action tremor. It is one of the most common neurological disorders, affecting 1% of the worldwide population. Despite strong evidence for genetic factors driving the aetiology of ET, the underlying pathophysiology remains poorly understood. To understand the effects of genetic risk factors in ET on the cerebellum, the brain region thought to be affected by the disease, we built a population-scale single-cell atlas of the human cerebellar cortex comprised of over 1 million cells from 109 individuals. Using single-cell expression quantitative trait loci and mendelian randomization, we found evidence of ET-associated variants in the BACE2 locus causally linked to its downregulation in cerebellar oligodendrocytes. We highlight a genetically vulnerable population of BACE2-expressing immature oligodendrocytes, suggestive of demyelination. We also find dysfunctional processes affecting interactions between Golgi cells, Purkinje layer interneurons, and oligodendrocytes in ET. Our study suggests a crucial role for cerebellar oligodendrocytes in the pathogenesis of ET.

genomics↗

bioRxiv2024

The Effects of Bipolar Disorder Granule Cell Hyperexcitability and Lithium Therapy on Pattern Separation in a Computational Model of the Dentate Gyrus

Induced pluripotent stem cell (iPSC) derived hippocampal dentate granule cell-like neurons from individuals with bipolar disorder (BD) are hyperexcitable and more spontaneously active relative to healthy control (HC) neurons. These abnormalities are normalised after the application of lithium in neurons derived from lithium responders (LR) only. How these abnormalities impact hippocampal microcircuit computation is not understood. We aimed to investigate the impacts of BD-associated abnormal granule cell (GC) activity on pattern separation (PS) using a computational model of the dentate gyrus (DG). We used parameter optimization to fit the parameters of biophysically realistic granule cell (GC) models to electrophysiological data from iPSC GCs from patients with BD. These cellular models were incorporated into DG networks to assess impacts on PS using an adapted spatiotemporal task. Relationships between BD, lithium and spontaneous activity were analysed using linear mixed effects modelling. Lithium and BD negatively impacted PS, consistent with clinical reports of cognitive slowing and memory impairment during lithium therapy. By normalising spontaneous activity levels, lithium improved PS performance in LRs only. Improvements in PS after lithium therapy in LRs may therefore be attributable to the normalisation of spontaneous activity levels, rather than reductions in GC intrinsic excitability as we hypothesised. Our results agree with a hypothesised relationship between behavioural mnemonic discrimination and DG PS, as previous research has suggested that mnemonic discrimination improves after lithium therapy in lithium responders only. Our work can be expanded on in the future by simulating the effects of lithium-induced neurogenesis on PS.

neuroscience↗

bioRxiv2024

Transcriptomic and epigenomic consequences of heterozygous loss of function mutations in AKAP11, the first large-effect shared risk gene for bipolar disorder and schizophrenia

The gene A-kinase anchoring protein 11 (AKAP11) recently emerged as a shared risk factor between bipolar disorder and schizophrenia, driven by large-effect loss-of-function (LoF) variants. Recent research has uncovered the neurophysiological characteristics and synapse proteomics profile of Akap11-mutant mouse models. Considering the role of AKAP11 in binding cAMP-dependent protein kinase A (PKA) and mediating phosphorylation of numerous substrates, such as transcription factors and epigenetic regulators, and given that chromatin alterations have been implicated in the brains of patients with bipolar disorder and schizophrenia, it is crucial to uncover the transcriptomic and chromatin dysregulations following the heterozygous knockout of AKAP11, particularly in human neurons. In this study, we use genome-wide approaches to investigate such aberrations in human induced pluripotent stem cell (iPSC)-derived neurons. We show the impact of heterozygous AKAP11 LoF mutations on the gene expression landscape and profile the methylomic and acetylomic modifications. Altogether we highlight the involvement of aberrant activity of intergenic and intronic enhancers, which are enriched in PBX homeobox 2 (PBX2) and Nuclear Factor-1 (NF1) known binding motifs, respectively, in transcription dysregulations of genes functioning as DNA-binding transcription factors, actin and cytoskeleton regulators, and cytokine receptors, as well as genes involved in G-protein-coupled receptors (GPCRs) binding and signaling. A better understanding of the dysregulations resulting from haploinsufficiency in AKAP11 improves our knowledge of the biological roots and pathophysiology of BD and SCZ, paving the way for better therapeutic approaches.

genomics↗

bioRxiv2023

The Impact of Electrophysiological Diversity on Pattern Completion in Lithium Nonresponsive Bipolar Disorder: A Computational Modelling Approach

Patients with bipolar disorder (BD) demonstrate episodic memory deficits, which may be hippocampal-dependent and may be attenuated in lithium responders. Induced pluripotent stem-cell derived CA3 pyramidal cell-like neurons show significant hyperexcitability in lithium responsive BD patients, while lithium nonresponders show marked variance in hyperexcitability. We hypothesize that this variable excitability will impair episodic memory recall, as assessed by cued retrieval (pattern completion) within a computational model of the hippocampal CA3. We simulated pattern completion tasks using a computational model of the CA3 with different degrees of pyramidal cell excitability variance. Since pyramidal cell excitability variance naturally leads to a mix of hyperexcitability and hypoexcitability, we also examined what fraction (hyper-vs. hypoexcitable) was predominantly responsible for pattern completion errors in our model. Pyramidal cell excitability variance impaired pattern completion (linear model {beta}=-1.94, SE=0.01, p<0.001). The effect was invariant to the number of patterns stored in the network, as well as general inhibitory tone and pyramidal cell sparsity in the network. Excitability variance, and more specifically hyperexcitability, increased the number of spuriously active neurons, increasing false alarm rates and producing pattern completion deficits. Excessive inhibition also induces pattern completion deficits by limiting the number of correctly active neurons during pattern retrieval. Excitability variance in CA3 pyramidal cell-like neurons observed in lithium nonresponders may predict pattern completion deficits in these patients. These cognitive deficits may not be fully corrected by medications that minimize excitability. Future studies should test our predictions by examining behavioural correlates of pattern completion in lithium responsive and nonresponsive BD patients. Author summaryPatients with bipolar disorder experience debilitating cognitive impairments whose mechanisms are unknown, and these deficits may be greater in patients who do not respond to the mood stabilizer lithium. Studies using induced pluripotent stem cell (iPSC) derived neurons have suggested that CA3 pyramidal cells in lithium nonresponders may have wide diversity of excitability. Our study examines how this diversity of neuronal excitability would impact the computation of pattern completion in the CA3. In a computational model of the CA3, we found that variance in pyramidal cell excitability reliably impaired pattern completion abilities. Furthermore, we found that both the hyperexcitable and hypoexcitable fractions of cells were each responsible for distinct pattern completion errors, depending on the overall level of network inhibition. These results suggest that lithium nonresponsive patients with bipolar disorder will have worse performance on behavioural tasks that are sensitive to pattern completion, potentially including cued recall paradigms. Our results also suggest that mood stabilizers that simply reduce cellular hyperexcitability may not be sufficient to correct micro-circuit level computations in lithium nonresponsive bipolar disorder. Rather, these patients may require development of mood stabilizers that normalize the distribution of neuronal hyperexcitability among CA3 pyramidal cells.

neuroscience↗

bioRxiv2023

Molecular signatures of hyperexcitability and lithium responsiveness in bipolar disorder patient neurons provide alternative therapeutic strategies.

Bipolar disorder (BD) is a multifactorial psychiatric illness affecting about 1% of the world population. The first line treatment, lithium (Li), is effective in only a subset of patients and its mechanism of action remains largely elusive. In the present study, we used iPSC-derived neurons from BD patients responsive (LR) or not (LNR) to lithium and combined electrophysiology, calcium imaging, biochemistry, transcriptomics, and phosphoproteomics to report mechanistic insights into neuronal hyperactivity in BD, and Lis mode of action. We show a selective rescue of neuronal hyperactivity by Li in BD LR neurons through changes in Na+ currents. The whole transcriptome sequencing revealed altered gene expression in BD neurons in pathways related to glutamatergic transmission, and Li selectively altered those involved in cell signaling and ion transport/channel activity. We found the therapeutic effect of Li in BD LR patients was associated with Akt signaling and confirmed that an Akt activator mimics Li effect in BD LR neurons. Further, we showed that AMP-activated protein kinase (AMPK) reduces neural network activity and sodium currents in BD LNR patients. These findings suggest the potential for novel treatment strategies in BD, such as Akt activators in BD LR cases, and the use of AMPK activators for BD LNR patients.

neuroscience↗

bioRxiv2022

Genetic inactivation of the USP19 deubiquitinase regulates a-synuclein ubiquitination and inhibits accumulation of Lewy body like aggregates in mice

The USP19 deubiquitinase is found in a locus associated with Parkinsons Disease (PD), interacts with heat shock proteins and promotes secretion of a-synuclein (a-syn) through the misfolding associated protein secretion (MAPS) pathway. Since these processes might modulate the processing of a-syn aggregates during the progression of PD, we tested the effect of USP19 knockout (KO) in mice expressing the A53T mutation of a-syn and in whom a-syn preformed fibrils (PFF) had been injected in the striatum. Compared to WT, KO brains showed decreased accumulation of phospho-synuclein (pSyn) positive aggregates. The improved pathology was associated with less activation of microglia, higher levels of synaptic marker proteins and improved performance in a tail suspension test. Exposure of primary neurons from WT and KO mice to PFF in vitro also led to decreased accumulation of pSyn aggregates. KO did not affect uptake of PFF in the cultured neurons. It also did not affect the propagation of aggregates as assessed by exposing WT or KO neurons to PFF and measuring pSyn positive aggregates in non-exposed adjacent neurons separated using a microfluidics device. We conclude that USP19 instead modulates intracellular dynamics of aggregates. Indeed, at the early time following PFF injection when the number of pSyn positive neurons were similar in WT and KO brains, the KO neurons contained less aggregates. KO brain aggregates stained more intensely with anti-ubiquitin antibodies. Immunoprecipitation of soluble proteins from primary neurons exposed to PFF with antibodies to ubiquitin or pSyn showed higher levels of ubiquitinated a-syn oligomeric species in the KO neurons. We propose that the improved pathology in USP19 KO brains may arise from decreased formation or enhanced clearance of the more ubiquitinated aggregates and/or enhanced disassembly towards more soluble oligomeric species. USP19 inhibition may represent a novel therapeutic approach that targets the intracellular dynamics of a-syn complexes.

neuroscience↗

bioRxiv2021

Convergent transcriptomic targets of propranolol and primidone identify potential biomarkers for essential tremor

Essential tremor (ET) is one of the most common movement disorders, affecting nearly 5% of individuals over 65 years old. Despite its high heritability, few genetic risk loci for ET have been identified. Recent advances in pharmacogenomics have generated a wealth of data that led to the identification of molecular signatures in response to hundreds of chemical compounds. Among the different forms of data, gene expression has proven to be quite successful for the inference of drug response in cell models. We sought to leverage this approach in the context of ET where many patients are responsive two drugs: propranolol and primidone. Propranolol- and primidone-specific transcriptomic drug targets, as well as convergent gene targets across both drugs, could provide insights into the pathogenesis of ET and identify possible targets of interest for future treatments. In this study, cerebellar DAOY and neural progenitor cells were treated for 5 days with clinical concentrations of propranolol and primidone, after which RNA-sequencing was used to identify differentially expressed genes. The expression of genes previously implicated in genetic and transcriptomic studies of ET and other movement disorders, such as TRAPPC11, were significantly upregulated by propranolol. Pathway enrichment analysis identified multiple terms related to calcium signalling, endosomal sorting, axon guidance, and neuronal morphology. Convergent differentially expressed genes across all treatments and cell types were also found to be significantly more mutationally constrained, implying that they might harbour rare deleterious variants implicated in disease. Furthermore, these genes were enriched within cell types having high expression of ET related genes in both cortical and cerebellar tissues. Altogether, our results highlight potential cellular and molecular mechanisms associated with tremor reduction and identify relevant genetic biomarkers for drug-responsiveness in ET.

genomics↗

bioRxiv2020

Chronic lithium treatment alters the excitatory/inhibitory balance of synaptic networks and reduces mGluR5-PKC signaling

Bipolar disorder (BD) is characterized by cyclical alternations between mania and depression, often comorbid with psychosis, and suicide. The mood stabilizer lithium, compared to other medications, is the most efficient treatment for prevention of manic and depressive episodes. The pathophysiology of BD, and lithiums mode of action, are yet to be fully understood. Evidence suggests a change in the balance of excitatory/inhibitory activity, favouring excitation in BD. Here, we sought to establish a holistic appreciation of the neuronal consequences of lithium exposure in mouse cortical neurons and identify underlying mechanisms. We found that chronic (but not acute) lithium treatment significantly reduced intracellular calcium flux, specifically through the activation of the metabotropic glutamatergic receptor mGluR5. This was associated with altered phosphorylation of PKC and GSK3 kinases, reduced neuronal excitability, and several alterations to synapse function. Consequently, lithium treatment shifts the excitatory/inhibitory balance in the network toward inhibition. Together, the results revealed how lithium dampens neuronal excitability and glutamatergic network activity, which are predicted to be overactive in the manic phase of BD. Our working model of lithium action enables the development of targeted strategies to restore the balance of overactive networks, mimicking the therapeutic benefits of lithium, but with reduced toxicity.

neuroscience↗

bioRxiv2020

Abnormal AMPAR-mediated synaptic plasticity, cognitive and autistic-like behaviors in a missense Fmr1 mutant mouse model of Fragile X syndrome

Fragile X syndrome (FXS) is the most frequent form of inherited intellectual disability and the best-described monogenic cause of autism. FXS is usually caused by a CGG-repeat expansion in the FMR1 gene leading to its silencing and the loss-of-expression of the Fragile X Mental Retardation Protein (FMRP). Missense mutations were also identified in FXS patients, including the recurrent FMRP-R138Q mutation. To investigate the mechanisms underlying FXS in these patients, we generated a knock-in mouse model (Fmr1R138Q) expressing the FMRP-R138Q protein. We demonstrate that the Fmr1R138Q hippocampus has an increased spine density associated with postsynaptic ultrastructural defects and increased AMPA receptor surface expression. Combining biochemical assays, high-resolution imaging and electrophysiological recordings, we also show that the mutation impairs the hippocampal long-term potentiation (LTP) and leads to socio-cognitive deficits in Fmr1R138Q mice. These findings reveal that the R138Q mutation impacts the synaptic functions of FMRP and highlight potential mechanisms causing FXS in FMRP-R138Q patients.

neuroscience↗

bioRxiv2019

SUSD4 Controls Activity-Dependent Degradation of AMPA Receptor GLUA2 and Synaptic Plasticity

Fine control of protein stoichiometry at synapses underlies brain function and plasticity. How proteostasis is controlled independently for each type of synaptic protein in a synapse-specific and activity-dependent manner remains unclear. Here we show that SUSD4, a complement-related transmembrane protein, binds the AMPA receptor subunit GLUA2 and controls its activity-dependent degradation. Several proteins with known roles in the regulation of AMPA receptor turnover, in particular ubiquitin ligases of the NEDD4 subfamily, are identified as SUSD4 binding partners. SUSD4 is expressed by many neuronal populations starting at the time of synapse formation. Loss-of-function of Susd4 in the mouse prevents long-term depression at cerebellar synapses, and leads to impairment in motor coordination adaptation and learning. Our findings reveal that activity-dependent synaptic plasticity relies on a transmembrane CCP domain-containing protein that regulates the degradation of specific substrates. This mechanism potentially accounts for the role of SUSD4 mutations in neurodevelopmental diseases.

neuroscience↗