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Naskar, S.

Publications and source records attributed to Naskar, S..

At least 19 recordsLinked to original sources

AlphaGenome informed machine learning for pathogenicity prediction of germline mutations

Accurate interpretation of germline variants remains a central challenge in clinical genomics. Existing in silico pathogenicity predictors often provide incomplete coverage or restricted to missense variants from the coding region, leaving the variants from splice sites, -UTR, and intronic regions under-scored. We present AGVarPred, a gradient-boosted classifier designed to predict the pathogenicity of germline mutants, with a broad consequence-class coverage across SNVs and indels. Here, the population allele frequency from gnomAD, functional consequence annotations from Ensembl VEP, and cell-type-specific functional genomic scores from the AlphaGenome platform were integrated to develop the classifier. Using a gene-level split of 134,002 high-confidence ClinVar variants across 9,222 genes, AGVarPred achieved an AUC-ROC of 0.9753 (95% CI 0.9731-0.9775) and a AUC-PR of 0.9606 on 12,385 scored internal test variants. A paired DeLong analysis showed that the full model significantly outperformed an allele-frequency-plus-VEP model ({Delta}AUC = 0.1539, 95% CI 0.1489-0.1589; p < 1 x 10-300), supporting a substantial incremental contribution from AlphaGenome-derived features. Performance remained strong when restricted to SNVs (AUC-ROC 0.9558) and was also high for indels (AUC-ROC 0.9532). On five external benchmarks, AUC-ROCs ranged from 0.528 on a functional-assay-derived benchmark to 0.977 on a clinically curated deafness database, reflecting its dependence on benchmark composition and label source. A separate analysis of the VIP Database, whose pathogenic labels are ClinVar-derived, showed consistent performance (AUC-ROC of 0.892) in held-out genes. AGVarPred scored 100% of evaluated variants in the external benchmarks, whereas AlphaMissense and REVEL covered only small fractions of non-missense variants. Model interpretation indicated that gnomAD allele frequency was the dominant individual predictor; the 111 AlphaGenome features provided complementary functional signal, with splicing and chromatin assays contributing to the largest share of the AlphaGenome SHAP mass. A web-based interface for AGVarPred is available at https://pankaj357.github.io/AGVarPred/ to facilitate the submission of normalized GRCh38 germline variants and retrieval of pathogenicity predictions using the frozen AGVarPred model.

bioinformatics↗

SUMO paralogues differentially affect phase separation and aggregation of intrinsically disordered proteins

SUMO, the small ubiquitin-like modifier, modulates interactions of folded proteins, but also affects the dynamics of biomolecular condensates. Moreover, SUMO can directly impinge on the biophysical properties of its targets, often increasing their solubility. TDP-43 is an RNA-binding protein containing an intrinsically disordered domain that participates in protein phase separation. Its aggregation, linked to neurodegenerative diseases, is counteracted by SUMOylation, but the underlying principles are poorly understood. We now reveal distinct mechanisms of how the two isoforms, SUMO1 and SUMO2, act on TDP-43. While SUMO1 inhibits phase separation by blocking TDP-43s self-assembly site, SUMO2 enhances phase separation via proximity-induced self-interaction involving its N-terminus and promotes a liquid-like state that prevents aggregation. The latter represents a general principle by which SUMO solubilises other targets. Our findings provide insight into how SUMOylation regulates transitions between soluble, liquid-like and aggregated states.

molecular biology↗

How the Azadithiolate Ligand Impacts O2-Stability of Group B -Hydrogenase ToHydA

[FeFe]-hydrogenases are metalloenzymes that catalyze the reversible oxidation and production of H2, making them potential candidates for sustainable energy solutions. However, their practical application is restricted by their extreme O2 sensitivity, which leads to irreversible active site degradation. A newly characterized Group B hydrogenase, ToHydA from Thermosediminibacter oceani, has exhibited exceptional O2-stability even after longtime exposure to air. In ToHydA, the highly conserved proton-transporting cysteine (C212) safeguards the H-cluster from O2-induced degradation by formation of the Hinact state. In this study, we investigate the effects of replacing the azadithiolate (ADT) ligand of [2Fe]H with propanedithiolate (PDT), revealing that this substitution prevents the formation of the Hinact and Htrans states observed in ToHydA WT (bearing the ADT ligand). By combining ATR-FTIR spectroscopy and molecular dynamics (MD) simulations, we show that a hydrogen bond between the nitrogen bridgehead of the ADT ligand and the C212 sidechain is crucial for stabilizing these states. The absence of this interaction in ToHydAPDT (bearing the PDT ligand) prevents the C212 sidechain from approaching the Fed center of [2Fe]H, thereby reducing Hinact accumulation. Moreover, as-isolated ToHydAPDT predominantly exhibits the Hhyd state, which is unusual for [FeFe]-hydrogenases with bound PDT ligand. These findings demonstrate how ligand substitution at the [2Fe]H site of ToHydA affects the structural dynamics, offering detailed molecular insights into the ligand-dependent modulation of [FeFe]-hydrogenases.

biophysics↗

Tuning the H2 Production Activity of ToHydA by Molecular Simulation-Informed Protein Engineering

In the context of bio-hydrogen production, the O2-stable Group B [FeFe]-hydrogenase from Thermosediminibacter oceani has attracted significant interest due to its distinctive "TSCCCP" motif near the active site, which contains an additional (third) cysteine residue that is absent in the "TSCCP" motif of standard Group A hydrogenases. The precise role of the additional cysteine residue in H2 production has remained an open question. In this study, we sought to contribute to the understanding of this cysteines role in H2 production by combining molecular dynamics (MD) simulations, site-directed mutagenesis, biochemical assays, and Fourier-transform infrared (FTIR) spectroscopy. Remarkably, a cysteine-to-serine exchange variant (TSSCCP) demonstrated enhanced H2 production activity without compromising the O2-stability of ToHydA, offering new insights into its functional dynamics.

biophysics↗

Regulation of the essential peptidoglycan hydrolytic complex FtsEX-PcsB during Streptococcus pneumoniae cell division

In the human commensal Gram-positive bacterial pathogen Streptococcus pneumoniae, the essential cell-division-associated peptidoglycan (PG) hydrolase PcsB interacts directly with the membrane-bound FtsEX complex (1-3). PcsB contains a cysteine, histidine-dependent amidohydrolase/peptidase (CHAP) domain responsible for PG hydrolysis, and a coiled-coil domain required for interaction with FtsEX (1,4). ATP hydrolysis of FtsE in the cytoplasm drives conformational changes in FtsX in the cytoplasmic membrane, which ultimately regulates the PG hydrolase on the outside of the cell (5). In this work we show that the CHAP domain of PcsB predominately functions as an D-iso-Glutaminyl-Lysyl D,L-endopeptidase, with substrate specificity for Lys-containing, amidated PG. The catalytic activity of PcsB is regulated by conformational changes of the coiled-coil region and by a short helical region immediately adjacent to the CHAP domain, to guard against PcsB hydrolytic activation outside of its cell division specific functional requirement. This work supports a model for the overall biological activity of the FtsEX-PcsB complex, allowing stem peptide cleavage that splits the septal disk and marks a region of the peptidoglycan sacculus for subsequent cell division remodelling.

biochemistry↗

Cannabinoid Modulation of Central Amygdala Population Dynamics During Threat Investigation

Cannabinoids modulate innate avoidance, threat-reactivity, and stress adaptations via modulation amygdala-associated circuits; however, the mechanisms by which cannabinoids modulate amygdala representation of threat-related behavior are not known. We show that cannabinoid administration increases the activity of central amygdala (CeA) somatostatin neurons (SOM) and alters basal network dynamics in a manner supporting generation of antagonistic sub-ensembles within the SOM population. Moreover, diverging neuronal population trajectory dynamics and enhanced antagonistic sub-ensemble representation of threat-related behaviors, and enhanced threat-related location representation, were also observed. Lastly, cannabinoid administration increased the proportion of SOM neurons exhibiting multidimensional representation of threat-related behaviors and behavior-location conjunction. While cannabinoid receptor activation ex vivo suppressed excitatory inputs to SOM neurons, our data suggest preferential suppression of local GABA release subserves cannabinoid activation of CeA SOM neurons. These data provide insight into how cannabinoid-mediated presynaptic suppression transforms postsynaptic population dynamics and reveal cellular mechanisms by which cannabinoids could affect threat-reactivity.

neuroscience↗

An enhancer-AAV toolbox to target and manipulate distinct interneuron subtypes

In recent years, we and others have identified a number of enhancers that, when incorporated into rAAV vectors, can restrict the transgene expression to particular neuronal populations. Yet, viral tools to access and manipulate specific neuronal subtypes are still limited. Here, we performed systematic analysis of single cell genomic data to identify enhancer candidates for each of the telencephalic interneuron subtypes. We established a set of enhancer-AAV tools that are highly specific for distinct cortical interneuron populations and striatal cholinergic interneurons. These enhancers, when used in the context of different effectors, can target (fluorescent proteins), observe activity (GCaMP) and manipulate (opto-genetics) specific neuronal subtypes. We also validated our enhancer-AAV tools across species. Thus, we provide the field with a powerful set of tools to study neural circuits and functions and to develop precise and targeted therapy.

neuroscience↗

PREFRONTAL CORRELATES OF FEAR GENERALIZATION DURING ENDOCANNABINOID DEPLETION

Maladaptive fear generalization is one of the hallmarks of trauma-related disorders. The endocannabinoid 2-arachidonoylglycerol (2-AG) is crucial for modulating anxiety, fear, and stress adaptation but its role in balancing fear discrimination versus generalization is not known. To address this, we used a combination of plasma endocannabinoid measurement and neuroimaging from a childhood maltreatment exposed and non-exposed mixed population combined with human and rodent fear conditioning models. Here we show that 2-AG levels are inversely associated with fear generalization at the behavioral level in both mice and humans. In mice, 2-AG depletion increases the proportion of neurons, and the similarity between neuronal representations, of threat-predictive and neutral stimuli within prelimbic prefrontal cortex ensembles. In humans, increased dorsolateral prefrontal cortical-amygdala resting state connectivity is inversely correlated with fear generalization. These data provide convergent cross-species evidence that 2-AG is a key regulator of fear generalization and suggest 2-AG deficiency could represent a trauma-related disorder susceptibility endophenotype.

neuroscience↗

Mechanism for Vipp1 spiral formation, ring biogenesis and membrane repair

ESCRT-III family proteins build dynamic filaments that remodel membrane. Although the transition of planar filaments into 3D membrane budding structures is fundamental for their function, the geometric changes in polymer architecture driving the transition remain obscure. Here we show how bacterial Vipp1 polymerises into dynamic planar sheets and spirals on membrane. The spirals converge to form a central ring like those known to bud membrane. To probe how Vipp1 morphs between polymers, we determine the architecture of multiple helical filaments. As well as describing filament constriction and membrane tubulation, the geometric relationship between helical and planar lattices enables Vipp1 sheets and spirals to be modelled. Moreover, the helical structures show filaments twisting - a process needed for Vipp1 to transition between planar and 3D architectures. Given the structural conservation between Vipp1 and ESCRT-III, our results may represent the broad changes in geometry required for some ESCRT-III filaments to switch between 2D and 3D forms.

microbiology↗

Loss of Ezh2 in the medial ganglionic eminence alters interneuron fate, cell morphology and gene expression profiles

Enhancer of zeste homolog 2 (Ezh2) is responsible for trimethylation of histone 3 at lysine 27 (H3K27me3), resulting in gene repression. Here, we explore the role of Ezh2 in forebrain GABAergic interneuron development. Loss of Ezh2 increases somatostatin-expressing (SST+) and decreases parvalbumin-expressing (PV+) interneurons in multiple brain regions. We also observe fewer MGE-derived interneurons in the first postnatal week, indicating reduced interneuron production. Intrinsic electrophysiological properties in SST+ and PV+ interneurons are normal, but PV+ interneurons display increased axonal complexity in Ezh2 mutant mice. Single cell multiome analysis revealed differential gene expression patterns in the embryonic MGE that are predictive of these cell fate changes. Lastly, CUT&Tag analysis revealed differential H3K27me3 levels at specific genomic loci, with some genes displaying a relative increase in H3K27me3 indicating they may be resistant to epigenetic modifications. Thus, loss of Ezh2 in the MGE alters interneuron fate, morphology, and gene expression and regulation.

neuroscience↗

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↗

Sustained release Resolvin D1 liposomes are effective in the treatment of osteoarthritis in obese mice

Osteoarthritis (OA) is the most common joint disorder and currently affects > 500 million patients worldwide, with ~60% of them also suffering from obesity. There is no drug approved for human use that changes the course of OA progression. OA is one of the most common comorbidities of obesity, and obesity-related OA (ObOA) is a serious health concern because it shows heightened severity of tissue damage and also predominantly affects the working population. Unresolved inflammation is a major driver of ObOA, thus, resolving disease-associated inflammation is a viable strategy to treat ObOA. Resolvins are highly potent molecules that play a role in the resolution of inflammation and promote tissue healing. However, small molecules (like Resolvin D1; RvD1) have to be administered frequently or prior to injury because they lose their in vivo activity rapidly either by lymphatic clearance, or oxidation-mediated deactivation. In this study, we have encapsulated RvD1 in liposomes and established its efficacy in the mouse model of ObOA at much lower dosages than freely administered RvD1. Liposomal RvD1 (lipo-RvD1) acted as a source of the RvD1 molecules for ~11 days in vitro in synovial fluid derived from patients. When administered prophylactically or therapeutically, lipo-RvD1 suppressed cartilage damage in male C57BL/6 mice compared to untreated and free RvD1 treatments. This efficacy was achieved by increasing the proportion of the proresolution M2 macrophages over proinflammatory M1 macrophages in the synovial membrane. These results show the potential of lipo-RvD1 as an anti-OA agent. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/525015v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@141d889org.highwire.dtl.DTLVardef@1ef1753org.highwire.dtl.DTLVardef@1e463c1org.highwire.dtl.DTLVardef@15138c6_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical abstract:C_FLOATNO Mechanism of working of lipo-RvD1 in ObOA joint. C_FIG

bioengineering↗

Posteromedial thalamic nucleus activity significantly contributes to perceptual discrimination

Higher-order sensory thalamic nuclei are densely connected with multiple cortical and subcortical areas, yet the role of these nuclei remains elusive. The posteromedial (POm) thalamic nucleus, the higher-order thalamic nucleus in the rodent somatosensory system, is an anatomical hub broadly connected with multiple sensory and motor brain areas, yet weakly responds to passive sensory stimulation and whisker movements. To understand the role of POm in sensory perception, we developed a self-initiated, two-alternative forced-choice task in freely moving mice during active sensing. Using optogenetic and chemogenetic manipulation, we show that POm thalamic nucleus plays a significant role in sensory perception and the projection from the primary somatosensory cortex to POm is critical for the contribution of POm in sensory perception during active sensing.

neuroscience↗

Mechanistic Insights into the Effects of Key Mutations on SARS-CoV-2 RBD-ACE2 Binding

Some recent SARS-CoV-2 variants appear to have increased transmissibility than the original strain. An underlying mechanism could be the improved ability of the variants to bind receptors on target cells and infect them. In this study, we provide atomic-level insight into the binding of the receptor binding domain (RBD) of the wild-type SARS-CoV-2 spike protein and its single (N501Y), double (E484Q, L452R) and triple (N501Y, E484Q, L452R) mutated variants to the human ACE2 receptor. Using extensive all-atom molecular dynamics simulations and advanced free energy calculations, we estimate the associated binding affinities and binding hotspots. We observe significant secondary structural changes in the RBD of the mutants, which lead to different binding affinities. We find higher binding affinities of the double (E484Q, L452R) and triple (N501Y, E484Q, L452R) mutated variants than the wild type and the N501Y variant, which could contribute to the higher transmissibility of recent variants containing these mutations.

biophysics↗

DESIGNER DNA HYDROGELS TO STIMULATE 3D CELL INVASION BY ENHANCED RECEPTOR EXPRESSION AND MEMBRANE ENDOCYTOSIS

DNA has emerged as one of the smartest biopolymers to bridge the gap between chemical science and biology to design scaffolds like hydrogels by physical entanglement or chemical bonding with remarkable properties. We present here a completely new application of DNA based hydrogels in terms of their capacity to stimulate membrane endocytosis, leading to enhanced cell spreading and invasion for cells in ex-vivo 3D spheroids models. Multiscale simulation studies along with DLS data showed that the hydrogel formation was enhanced at lower temperature and it converts to liquid with increase in temperature. DNA hydrogels induced cell spreading as observed by increase in cellular area by almost two-folds followed by increase in receptor expression, endocytosis and 3D invasion potential of migrating cells. Our first results lay the foundation for upcoming diverse applications of hydrogels to probe and program various cellular and physiological processes that can have lasting applications in stem cells programming and regenerative therapeutics.

bioengineering↗

Neuronal activity drives pathway-specific depolarization of astrocyte distal processes

Astrocytes are glial cells that interact with neuronal synapses via their distal processes, where they remove glutamate and potassium (K+) from the extracellular space following neuronal activity. Astrocyte clearance of both glutamate and K+ is voltage-dependent, but astrocyte membrane potential (Vm) has been thought to be largely invariant. As a result, these voltage-dependencies have not been considered relevant to astrocyte function. Using genetically encoded voltage indicators enabling the measurement of Vm at distal astrocyte processes (DAPs), we report large, rapid, focal, and pathway-specific depolarizations in DAPs during neuronal activity. These activity-dependent astrocyte depolarizations are driven by action potential-mediated presynaptic K+ efflux and electrogenic glutamate transporters. We find that DAP depolarization inhibits astrocyte glutamate clearance during neuronal activity, enhancing neuronal activation by glutamate. This represents a novel class of sub-cellular astrocyte membrane dynamics and a new form of astrocyte-neuron interaction. One Sentence SummaryGenetically encoded voltage imaging of astrocytes shows that presynaptic neuronal activity drives focal astrocyte depolarization, contributing to activity-dependent inhibition of glutamate uptake.

neuroscience↗

Bacterial Vipp1 and PspA are members of the ancient ESCRT-III membrane-remodelling superfamily

Membrane remodelling and repair are essential for all cells. Proteins that perform these functions include Vipp1/IM30 in photosynthetic plastids, PspA in bacteria, CdvB in TACK archaea and ESCRT-III in eukaryotes. Here, we show that these protein families are homologous and share a common evolutionary origin. Using cryo-electron microscopy we present structures for Vipp1 rings over a range of symmetries. Each ring is built from rungs that stack and spontaneously self-organise to form domes. Rungs are assembled from a polymer that is strikingly similar in structure to ESCRT-III. A tilt between rungs generates the dome-shaped curvature with constricted open ends and an inner membrane-binding lumen. Overall, our results reveal conserved mechanistic principles that underlie Vipp1, PspA and ESCRT-III dependent membrane remodelling across all domains of life. One sentence summaryEvolutionary and structural analyses of Vipp1/IM30 rings reveal ESCRT-III-like polymers that remodel membranes in bacteria.

microbiology↗

Interneuronal mechanisms underlying a learning-induced switch in a sensory response that anticipates changes in behavioural outcomes

How an animal responds to a particular sensory stimulus will to a great extent depend on prior experience associated with that stimulus. For instance, aversive associative learning may lead to a change in the predicted outcomes, which suppresses the behavioural response to an otherwise rewarding stimulus. However, the neuronal mechanisms of how aversive learning can result in the suppression of even a vitally important innate behaviour is not well understood. Here we used the model system of Lymnaea stagnalis to address the question of how an anticipated aversive outcome can alter the behavioural response to a previously effective feeding stimulus. We found that aversive classical conditioning with sucrose as the CS (conditioned stimulus) and strong touch as the aversive US (unconditioned stimulus) reverses the decision so that the same salient feeding stimulus inhibits feeding, rather than activating it. Key to the understanding of the neural mechanism underlying this switch in the behavioural response is the PlB (pleural buccal) extrinsic interneuron of the feeding network whose modulatory effects on the feeding circuit inhibit feeding. After associative aversive training, PlB is excited by sucrose to reverse its effects on the feeding response. Aversive associative learning induces a persistent change in the electrical properties of PlB that is both sufficient and necessary for the switch in the behavioural output. In addition, the strong touch used as the US during the associative training protocol can also serve as a sensitizing stimulus to lead to an enhanced defensive withdrawal response to a mild touch stimulus. This non-associative effect of the strong touch is probably based on the facilitated excitatory output of a key identified interneuron of the defensive withdrawal network, PeD12.

neuroscience↗