Biology subjects

Chattarji, S.

Publications and source records attributed to Chattarji, S..

11 recordsLinked to original sources

bioRxiv2024

The Fragile X Messenger Ribonucleoprotein 1 regulates the morphology and maturation of human and rat oligodendrocytes

The Fragile X Messenger Ribonucleoprotein (FMRP) is an RNA binding protein that regulates the translation of multiple mRNAs and is expressed by neurons and glia in the mammalian brain. Loss of FMRP leads to Fragile X Syndrome (FXS), a common inherited form of intellectual disability and autism. While most research has been focusing on the neuronal contribution to FXS pathophysiology, the role of glia, particularly oligodendro-cytes, is largely unknown. FXS individuals are characterised by white matter changes which imply impairments in oligodendrocyte differentiation and myelination. We hypothesized that FMRP regulates oligodendrocyte maturation and myelination during postnatal development. Using a combination of human pluripotent stem cell - derived oligodendrocytes and an Fmr1 knockout rat model, we studied the role of FMRP on mammalian oligodendrocyte development. We found that the loss of FMRP leads to shared defects in oligodendrocyte morphology in both rat and human systems in vitro which persist in the presence of FMRP expressing axons in chimeric engraftment models. Our findings point to species-conserved, cell-autonomous defects during oligodendrocyte maturation in FXS.

neuroscience↗

bioRxiv2024

Human induced pluripotent stem cell-derived microglia contribute to thepathophysiology of Fragile X syndrome via increased RAC1 signaling

Fragile X syndrome (FXS) is one of the most common monogenic causes of neurodevelopmental disorders characterized by intellectual disability, autism and epilepsy. Emerging evidence suggests a role for immune dysfunction in autism. Using induced pluripotent stem cell (iPSC)-derived microglial cells from FXS patients (mFXS-MG) and FMR1-deficient microglia from FMR1-knock out human embryonic stem cells (FMR1 KO-MG), we show that loss-of-function of Fragile X Messenger Ribonucleoprotein (FMRP) leads to cell autonomous phagocytic deficits and a proinflammatory state in microglia when compared to gene-corrected controls. Moreover, increased RAC1 signaling in mFXS-MG and FMR1 KO-MG results in increased actin polymerization and enhanced activation of NF-{kappa}B signaling. Exposure of control iPSC-derived cortical neuron cultures to conditioned medium from proinflammatory mFXS-MG results in hyperexcitability. Importantly, pharmacological inhibition of RAC1 signaling in mFXS-MG attenuates their proinflammatory profile and corrects the neuronal hyperexcitability caused by the conditioned medium. Our results suggest that microglia impair neuronal function in FXS, which can be prevented by targeting of RAC1 signaling. Significance statementFXS is one of the most common monogenic causes of neurodevelopmental disorders characterized by intellectual disability, autism, epilepsy and has been associated with immune dysfunction. We therefore generated brain macrophages (microglia) from patient-derived induced pluripotent stem cells (mFXS-MG) and an embryonic stem cell line deficient in the Fragile X messenger ribonucleoprotein 1 (FMR1 KO-MG). We find enhanced activation of RAC1 signaling resulting in phagocytic deficits and immune activation of mFXS-MG and FMR1 KO-MG. Exposure of control iPSC-derived cortical neurons to conditioned medium from proinflammatory mFXS-MG results in neuronal hyperexcitability, which can be prevented by pharmacological RAC1 inhibition in mFXS-MG. We conclude that RAC1 signaling in microglia could be a potential therapeutic target in FXS.

neuroscience↗

bioRxiv2023

Administration of the glutamate-modulating drug riluzole after stress reverses its delayed effects on the amygdala

Extracellular glutamate levels are elevated across brain regions immediately after stress. Despite sharing common features in their genesis, the patterns of stress-induced plasticity that eventually take shape are strikingly different between these brain areas. While stress impairs structure and function in the hippocampus, it has the opposite effect on the amygdala. Riluzole, an FDA-approved drug known to modulate glutamate release and facilitate glutamate clearance, prevents stress-induced deficits in the hippocampus. But, whether the same drug is also effective in countering the opposite effects of stress in the amygdala remains unexplored. We addressed this question by using a rat model wherein even a single 2-hour acute immobilization stress causes a delayed build-up, 10 days later, in anxiety-like behavior, alongside stronger excitatory synaptic connectivity in the basolateral amygdala (BLA). This temporal profile - several days separating the acute stressor and its delayed impact - allowed us to test if these effects can be reversed by administering riluzole in the drinking water after acute stress. Post-stress riluzole not only prevented the delayed increase in anxiety-like behavior on the elevated plus-maze, but also reversed the increase in spine-density on BLA neurons 10 days later. Further, stress-induced increase in the frequency of miniature excitatory postsynaptic currents recorded in BLA slices, 10 days later, was reversed by the same post-stress riluzole administration. Together, these findings underscore the importance of therapeutic strategies, aimed at glutamate uptake and modulation, in correcting the delayed behavioral, physiological, and morphological effects of stress on the amygdala. Significance statementStress disorders are characterized by impaired cognitive function alongside enhanced emotionality. Consistent with this, the same stress elicits contrasting effects in the rodent hippocampus versus amygdala. This poses a therapeutic challenge - the same pharmacological intervention against stress has to counter these opposite effects. Yet, the immediate consequence of stress - enhanced extracellular glutamate - is similar across these two areas. To target this common feature, we treated rats with riluzole, a drug that prevents stress-induced glutamate surge. Although the drug was administered after the end of stress, it reversed its delayed impact on amygdalar structure and function. Since riluzole also enhances glutamate-uptake through glial-transporters and is approved for human use, these results highlight the importance of therapeutic strategies focused on neuron-astrocyte interactions.

neuroscience↗

bioRxiv2021

The Fragile X Mental Retardation Protein protects the lung from xenobiotic stress by facilitating the Integrated Stress Response

Stress response pathways protect the lung from the damaging effects of environmental toxicants. Here we investigate the role of the Fragile X Mental Retardation Protein (FMRP), a multifunctional protein implicated in stress responses, in the lung. We report that FMRP is expressed in murine and human lungs, in the airways and more broadly. Analysis of airway stress responses in mice and in a murine cell line ex vivo, using the well-established Naphthalene (Nap) injury model, reveals that FMRP-deficient cells exhibit increased expression of markers of oxidative and genotoxic stress and increased cell death. We find that FMRP-deficient cells fail to actuate the Integrated Stress Response Pathway (ISR) and upregulate the transcription factor ATF4. Knockdown of ATF4 expression phenocopies the loss of FMRP. We extend our analysis of the role of FMRP to human bronchial BEAS-2B cells, using a 9, 10-Phenanthrenequinone air pollutant model, to find that FMRP-deficient BEAS-2B also fail to actuate the ISR and exhibit greater susceptibility. Taken together, our data suggest that FMRP has a conserved role in protecting the airways by facilitating the ISR.

cell biology↗

bioRxiv2020

Heterozygous deletion of SYNGAP enzymatic domains in rats causes selective learning, social and seizure phenotypes

Pathogenic variants in SYNGAP1 are one of the most common genetic causes of nonsyndromic intellectual disability (ID) and are considered a risk for autism spectrum disorder (ASD). SYNGAP1 encodes a synaptic GTPase activating protein that modulates the intrinsic GTPase activity of several small G-proteins and is implicated in regulating the composition of the postsynaptic density. By targeting the deletion of exons encoding the calcium/lipid binding (C2) and GTPase activating protein (GAP) domains, we generated a novel rat model to study SYNGAP related pathophysiology. We find that rats heterozygous for the C2/GAP domain deletion (Syngap+/{Delta}-GAP) exhibit reduced exploration and fear extinction, altered social behaviour, and spontaneous seizures, while homozygous mutants die within days after birth. This new rat model reveals that the enzymatic domains of SYNGAP are essential for normal brain function and provide an important new model system in the study of both ID/ASD and epilepsy.

neuroscience↗

bioRxiv2020

Imbalance of flight-freeze responses and their cellular correlates in the Nlgn3-/y rat model of autism

Mutations in the postsynaptic transmembrane protein neuroligin-3 are highly correlative with autism spectrum disorders (ASDs) and intellectual disabilities (IDs). Fear learning is well studied in models of these disorders, however differences in fear response behaviours are often overlooked. Whilst examining fear in a rat model of ASD/ID lacking Nlgn3, we observed that they display a greater propensity to exhibit flight responses in contrast to classic freezing seen in wildtypes during fearful situations. Consequently, we examined the physiological underpinnings of this in neurons of the periaqueductal grey (PAG), a midbrain area involved in flight-or-freeze responses. In ex vivo slices from Nlgn3-/y, rats, dorsal PAG (dPAG) neurons showed intrinsic hyperexcitability. Further analysis of this revealed lower magnitude in vivo dPAG stimulation evoked flight behaviour in Nlgn3-/y, rats, indicating the functional impact of the increased cellular excitability. This study provides new insight into potential pathophysiologies leading to emotional disorders in individuals with ASD.

neuroscience↗

bioRxiv2020

Stress enhances hippocampal neuronal synchrony and prolongs sharp-wave ripples

Chronic stress affects hippocampal function at multiple levels of neural organization. However, much of this understanding is derived from postmortem analyses of molecular, morphological, physiological and behavioral changes at fixed time points. Neural signatures of an ongoing stressful experience in the intact brain of awake animals and their links to later hippocampal dysfunction remain poorly understood. Here we used in vivo tetrode recordings to analyze the dynamic impact of 10 days of immobilization stress on neuronal activity in area CA1 of mice. Unexpectedly, there was a net decrease in pyramidal cell activity in stressed animals. Although these results suggest a lack of stress-induced hyperexcitability, more detailed analysis revealed that a greater fraction of spikes occurred specifically during sharp-wave ripples, resulting in an increase in neuronal synchrony. After repeated stress some of these alterations were visible during rest even in the absence of stress. These findings offer new insights into stress-induced alterations in ripple-spike interactions and mechanisms through which chronic stress may interfere with subsequent information processing.

neuroscience↗

bioRxiv2019

A sex difference in the composition of the rodent postsynaptic density

SynGAP is a postsynaptic density (PSD) protein that binds to PDZ domains of the scaffold protein PSD-95. We previously reported that heterozygous deletion of synGAP in mice is correlated with increased steady-state levels of other key PSD proteins that bind PSD-95, although the level of PSD-95 remains constant (Walkup et al., 2016). For example, the ratio to PSD-95 of Transmembrane AMPA-Receptor-associated Proteins (TARPs), which mediate binding of AMPA-type glutamate receptors to PSD-95, was increased in young synGAP+/- mice. Here we show that a highly significant increase in TARP in the PSDs of young synGAP+/- rodents is present only in females and not in males. The data reveal a sex difference in the adaptation of the PSD scaffold to synGAP heterozygosity.

neuroscience↗

bioRxiv2019

Distinct Regulaton of Bioenergetics and Translation by Gp I mGluRs and NMDARs

Neuronal activity is responsible for large energy consumption within the brain. However, the cellular mechanisms draining ATP upon the arrival of a stimulus are yet to be explored systematically at the post-synapse. Here we provide evidence that a significant fraction of ATP is consumed upon glutamate stimulation to energize the mGluR-induced protein synthesis. We find that both mGluR and NMDAR alter protein synthesis and ATP consumption with distinct kinetics at the synaptic-dendritic compartments. While mGluR activation leads to a rapid and sustained reduction in the neuronal ATP level, NMDAR activation has no immediate impact on the same. ATP consumption correlates inversely to the kinetics of protein synthesis for both the receptors. We observe a persistent elevation in protein synthesis within 5 minutes of mGluR activation and robust inhibition of the same within 2 minutes of NMDAR activation, assessed by the phosphorylation status of eEF2 and metabolic labeling. However, a delayed protein synthesis-dependent ATP expenditure ensues after 15 minutes of NMDAR activation. We identify a central role for AMPK in this correlation between protein synthesis and ATP consumption. AMPK is dephosphorylated and inhibited upon mGluR activation while it was rapidly phosphorylated upon NMDAR activation. Perturbing AMPK activity disrupts the receptor-specific modulations of eEF2 phosphorylation and protein synthesis. Therefore, our observations suggest that the glutamate receptors required modulating the AMPK-eEF2 signaling axis to alter neuronal protein synthesis and bioenergetics. Short SummaryStimulation of glutamate receptors induces robust protein synthesis within cortical neurons and consumes a significantly large fraction of cellular ATP. Glutamate receptors viz. mGlulR and NMDAR modulate AMPK-eEF2 signaling uniquely leading to the dynamic regulation of protein synthesis and bioenergetics. Key HighlightsO_LIProtein synthesis following glutamate receptor activation is responsible for the bulk of the activity-induced ATP consumption in cortical neurons. C_LIO_LImGluR and NMDAR regulate protein synthesis with distinct kinetics and dictate the subsequent impacts over neuronal ATP level. C_LIO_LIDynamic modulation of AMPK and eEF2 phosphorylation is key to create unique temporal features of receptor-specific protein synthesis and bioenergetics. C_LI

neuroscience↗

bioRxiv2018

Impaired reliability and precision of spiking in adults but not juveniles in a mouse model of Fragile X Syndrome

Fragile X Syndrome (FXS) is the most common source of intellectual disability and autism. Extensive studies have been performed on the network and behavioral correlates of the syndrome but our knowledge about intrinsic conductance changes is still limited. In this study we show a differential effect of FMRP Knock Out (KO) in different sub-sections of hippocampus using whole cell patch clamp in mouse hippocampal slices. We observed no significant change in spike numbers in the CA1 region of hippocampus but a significant increase in CA3, in juvenile mice. However, in adult mice we see a reduction in spike number in the CA1 with no significant difference in CA3. In addition, we see increased variability in spike number in CA1 cells following a variety of steady and modulated current step protocols. This effect emerges in adult (8 weeks) but not juvenile (4 weeks) mice. This increased spiking variability was correlated with reduced spike number and with elevated AHP. The increased AHP arose from elevated SK currents (small conductance calcium activated potassium channels) but other currents involved in mAHP, such as Ih and M, were not significantly different. We obtained a partial rescue of the cellular variability phenotype when we blocked SK current using the specific blocker apamin. Our observations provide a single cell correlate of the network observations of response variability and loss of synchronization, and suggest that elevation of SK currents in FXS may provide a partial mechanistic explanation for this difference.\n\nSignificance StatementFragile-X syndrome leads to a range of intellectual disability effects and autism. We have found differential effect of FMRP KO in different sub sections of hippocampus where it caused an increased spiking in CA3 in juveniles and reduced spiking in CA1, in adults. We have also found that even individual neurons with this mutation exhibit increased variability in their activity patterns. Importantly, this effect emerges after six weeks of age in mice. We showed that a specific ion channel protein, SK channel, was partially responsible, and blockage of these channels led to a partial restoration of cellular activity. This is interesting as it provides a possible molecular link between activity variability in single cells, and reported irregularity in network activity.

neuroscience↗

bioRxiv2018

Extinction recall of fear memories formed before stress is not affected despite amygdalar hyperactivity

Stress is known to exert its detrimental effects not only by enhancing fear, but also by impairing its extinction. However, in earlier studies stress exposure invariably preceded both processes. Thus, compared to unstressed animals, stressed animals had to extinguish fear memories from higher levels of freezing caused by prior exposure to stress. Here we decouple the two processes to examine if stress specifically impairs fear extinction. Strikingly, when fear memories were formed before stress exposure, thereby allowing animals to initiate extinction from comparable levels of fear, recall of fear extinction was unaffected. Despite this we observed a persistent increase in theta activity in the BLA. Theta activity in the mPFC, by contrast, was normal. Stress also disrupted mPFC-BLA theta-frequency synchrony and directional coupling. Thus, in the absence of the fear-enhancing effects of stress, the expression of fear reflects normal regulation of mPFC activity, not stress-induced hyperactivity in the amygdala.

neuroscience↗