Ravi Muddashetty - Academia.edu (original) (raw)
Papers by Ravi Muddashetty
IBRO Neuroscience Reports
Experimental Brain Research, Sep 5, 2022
Astrocytic cells are a subtype of glial cells that engulf pathogenic aggregates derived from dege... more Astrocytic cells are a subtype of glial cells that engulf pathogenic aggregates derived from degenerative neurons to facilitate its degradation. Here, we show that exposure to α-SYN protofibrils caused a transient increase in biogenesis of tunneling nanotubes (TNTs) in primary astrocytes and astrocyte-origin cancer cell-lines (U-87 MG, U251). Biogenesis of nascent TNTs corresponds to α-SYN protofibril-induced organelle toxicities, increased reactive oxygen species (ROS), and oxidative stress-induced premature cellular senescence. These TNTs mediate cell-to-cell transfer of α-SYN protofibrils, toxic lysosomes and mitochondria. Biogenesis of TNTs precedes clearance of α-SYN-induced organelle toxicities, cellular ROS levels and reversal of cellular senescence. Consequences of cellular clearance results in enhanced cell proliferation. Further, we have shown α-SYN-induced senescence promotes transient localization of focal adhesion kinase (FAK) in the nucleus. FAK mediated regulation of ...
Frontiers in Neuroscience
Alzheimer’s disease (AD) is the most common cause of dementia, with no current cure. Consequently... more Alzheimer’s disease (AD) is the most common cause of dementia, with no current cure. Consequently, alternative approaches focusing on early pathological events in specific neuronal populations, besides targeting the well-studied amyloid beta (Aβ) accumulations and Tau tangles, are needed. In this study, we have investigated disease phenotypes specific to glutamatergic forebrain neurons and mapped the timeline of their occurrence, by implementing familial and sporadic human induced pluripotent stem cell models as well as the 5xFAD mouse model. We recapitulated characteristic late AD phenotypes, such as increased Aβ secretion and Tau hyperphosphorylation, as well as previously well documented mitochondrial and synaptic deficits. Intriguingly, we identified Golgi fragmentation as one of the earliest AD phenotypes, indicating potential impairments in protein processing and post-translational modifications. Computational analysis of RNA sequencing data revealed differentially expressed g...
Experimental Brain Research
Journal of Cell Science
ABSTRACTPrecise development of the dendritic architecture is a critical determinant of mature neu... more ABSTRACTPrecise development of the dendritic architecture is a critical determinant of mature neuronal circuitry. MicroRNA (miRNA)-mediated regulation of protein synthesis plays a crucial role in dendritic morphogenesis, but the role of miRNA-induced silencing complex (miRISC) protein components in this process is less studied. Here, we show an important role of a key miRISC protein, the GW182 paralog TNRC6A, in the regulation of dendritic growth. We identified a distinct brain region-specific spatiotemporal expression pattern of GW182 during rat postnatal development. We found that the window of peak GW182 expression coincides with the period of extensive dendritic growth, both in the hippocampus and cerebellum. Perturbation of GW182 function during a specific temporal window resulted in reduced dendritic growth of cultured hippocampal neurons. Mechanistically, we show that GW182 modulates dendritic growth by regulating global somatodendritic translation and actin cytoskeletal dyna...
Journal of Cell Science
Stress response pathways protect the lung from the damaging effects of environmental toxicants. H... more 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 injury model, reveals that FMRP-deficient cells exhibit increased expression of markers of oxidative and genotoxic stress and increased cell death. Further inquiry shows 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 cells als...
ABSTRACTStress response pathways protect the lung from the damaging effects of environmental toxi... more ABSTRACTStress 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 fai...
The Journal of Neuroscience, 2021
Apolipoprotein E (APOE), one of the primary lipoproteins in the brain has three isoforms in human... more Apolipoprotein E (APOE), one of the primary lipoproteins in the brain has three isoforms in humans, APOE2, APOE3, and APOE4. APOE4 is the most well-established risk factor increasing the predisposition for Alzheimer's disease (AD). The presence of the APOE4 allele alone is shown to cause synaptic defects in neurons and recent studies have identified multiple pathways directly influenced by APOE4. However, the mechanisms underlying APOE4-induced synaptic dysfunction remain elusive. Here, we report that the acute exposure of primary cortical neurons or synaptoneurosomes to APOE4 leads to a significant decrease in global protein synthesis. Primary cortical neurons were derived from male and female embryos of Sprague Dawley (SD) rats or C57BL/6J mice. Synaptoneurosomes were prepared from P30 male SD rats. APOE4 treatment also abrogates the NMDA-mediated translation response indicating an alteration of synaptic signaling. Importantly, we demonstrate that both APOE3 and APOE4 generate...
Haploinsufficiency in SYNGAP1 is implicated in Intellectual Disability (ID) and Autism Spectrum d... more Haploinsufficiency in SYNGAP1 is implicated in Intellectual Disability (ID) and Autism Spectrum disorder (ASD) and affects the maturation of dendritic spines. The abnormal spine development has been suggested to cause disbalance of excitatory and inhibitory (E/I) neurotransmission at distinct developmental periods. In addition, E/I imbalances in Syngap1+/- mice might be due to abnormalities in K+-Cl- co-transporter function (NKCC1, KCC2), in a similar manner as in the murine models of Fragile-X and Rett syndromes. To study whether an altered intracellular chloride ion concentration represents an underlying mechanism of altered function of GABAergic synapses in Dentate Gyrus Granule Cells of Syngap1+/- recordings were performed at different developmental stages of the mice. We observed that neurons at P14-15 of Syngap1+/- mice had depolarised membrane potential and a decreased Cl- reversal potential. The KCC2 expression was decreased compared to Wild-type (WT) mice at P14-15. Further...
The Fragile X Mental Retardation Protein (FMRP) is an RNA Binding Protein that regulates translat... more The Fragile X Mental Retardation Protein (FMRP) is an RNA Binding Protein that regulates translation of mRNAs, essential for synaptic development and plasticity. FMRP interacts with a specific set of mRNAs and aids in their microtubule dependent transport and regulates their translation through its association with ribosomes. However, the biochemical role of individual domains of FMRP in forming neuronal granules and associating with microtubules and ribosomes is currently undefined. Here, we report that the C-terminus domain of FMRP is sufficient to bind to ribosomes as well as polysomes akin to the full-length protein. Furthermore, the C-terminus domain alone is essential and responsible for FMRP-mediated translation repression in neurons. However, FMRP-mediated puncta formation and microtubule association is favored by the synergistic combination of FMRP domains and not by individual domains. Interestingly, we show that the phosphorylation of hFMRP at Serine-500 is important in m...
Experimental Brain Research, 2021
Haploinsufficiency in SYNGAP1 is implicated in intellectual disability (ID) and autism spectrum d... more Haploinsufficiency in SYNGAP1 is implicated in intellectual disability (ID) and autism spectrum disorder (ASD) and affects the maturation of dendritic spines. The abnormal spine development has been suggested to cause a disbalance of excitatory and inhibitory (E/I) neurotransmission at distinct developmental periods. In addition, E/I imbalances in Syngap1 +/− mice might be due to abnormalities in K + –Cl − co-transporter function (NKCC1, KCC2), in a maner similar to the murine models of Fragile-X and Rett syndromes. To study whether an altered intracellular chloride ion concentration represents an underlying mechanism of modified function of GABAergic synapses in Dentate Gyrus Granule Cells of Syngap1 +/− recordings were performed at different developmental stages of the mice. We observed depolarised neurons at P14–15 as illustrated by decreased Cl − reversal potential in Syngap1 +/− mice. The KCC2 expression was decreased compared to Wild-type (WT) mice at P14–15. The GSK-3β inhibitor, 6-bromoindirubin-3ʹ-oxime (6BIO) that crosses the blood–brain barrier, was tested to restore the function of GABAergic synapses. We discovered that the intraperitoneal administration of 6BIO during the critical period or young adolescents [P30 to P80 (4-week to 10-week)] normalised an altered E/I balance, the deficits of synaptic plasticity, and behavioural performance like social novelty, anxiety, and memory of the Syngap1 +/− mice. In summary, altered GABAergic function in Syngap1 +/− mice is due to reduced KCC2 expression leading to an increase in the intracellular chloride concentration that can be counteracted by the 6BIO, which restored cognitive, emotional, and social symptoms by pharmacological intervention, particularly in adulthood.
Stem Cell Reports, 2021
Summary Frontotemporal dementia type 3 (FTD3), caused by a point mutation in the charged multives... more Summary Frontotemporal dementia type 3 (FTD3), caused by a point mutation in the charged multivesicular body protein 2B (CHMP2B), affects mitochondrial ultrastructure and the endolysosomal pathway in neurons. To dissect the astrocyte-specific impact of mutant CHMP2B expression, we generated astrocytes from human induced pluripotent stem cells (hiPSCs) and confirmed our findings in CHMP2B mutant mice. Our data provide mechanistic insights into how defective autophagy causes perturbed mitochondrial dynamics with impaired glycolysis, increased reactive oxygen species, and elongated mitochondrial morphology, indicating increased mitochondrial fusion in FTD3 astrocytes. This shift in astrocyte homeostasis triggers a reactive astrocyte phenotype and increased release of toxic cytokines, which accumulate in nuclear factor kappa b (NF-κB) pathway activation with increased production of CHF, LCN2, and C3 causing neurodegeneration.
Precise development of the dendritic architecture is a critical determinant of mature neuronal ci... more Precise development of the dendritic architecture is a critical determinant of mature neuronal circuitry. MicroRNA-mediated regulation of protein synthesis plays a crucial role in dendritic morphogenesis but the role of miRISC protein components in this process is less studied. Here, we show an important role of a key miRISC protein GW182 in the regulation of dendritic growth. We have identified a distinct brain region specific Spatio-temporal expression pattern of GW182 during rat postnatal development. We found that the window of peak GW182 expression coincides with the period of extensive dendritic growth, both in the hippocampus and cerebellum. Perturbation of GW182 function during a specific temporal window resulted in reduced dendritic growth of cultured hippocampal neurons. Mechanistically, we show that GW182 modulates dendritic growth by regulating global somato-dendritic translation, and actin cytoskeletal dynamics of developing neurons. Furthermore, we found that GW182 aff...
SYNGAP1, a Synaptic Ras-GTPase activating protein, regulates synapse maturation during a critical... more SYNGAP1, a Synaptic Ras-GTPase activating protein, regulates synapse maturation during a critical developmental window. Heterozygous mutation in SYNGAP1 (SYNGAP1+/-) has been shown to cause Intellectual Disability (ID) in children. Recent studies have provided evidence for altered neuronal protein synthesis in a mouse model of Syngap1+/-. However, the molecular mechanisms behind the same is unclear. Here, we report the reduced expression of a known translation regulator, FMRP, during a specific developmental period in Syngap1+/- mice. Our results demonstrated that FMRP interacts with and regulates the translation of Syngap1 mRNA. We further show that, during development, reduced translation of FMRP and this decrease in FMRP leads to a compensatory increase of Syngap1 translation in Syngap1+/-. These developmental changes are reflected in the altered response of eEF2 phosphorylation downstream of NMDA receptor signalling. We propose a cross-talk between FMRP and SYNGAP1 mediated sign...
Molecular Brain, 2019
Protein synthesis is crucial for maintaining synaptic plasticity and synaptic signalling. Here we... more Protein synthesis is crucial for maintaining synaptic plasticity and synaptic signalling. Here we have attempted to understand the role of RNA binding proteins, Fragile X Mental Retardation Protein (FMRP) and Moloney Leukemia Virus 10 (MOV10) protein in N-Methyl-D-Aspartate Receptor (NMDAR) mediated translation regulation. We show that FMRP is required for translation downstream of NMDAR stimulation and MOV10 is the key specificity factor in this process. In rat cortical synaptoneurosomes, MOV10 in association with FMRP and Argonaute 2 (AGO2) forms the inhibitory complex on a subset of NMDAR responsive mRNAs. On NMDAR stimulation, MOV10 dissociates from AGO2 and promotes the translation of its target mRNAs. FMRP is required to form MOV10-AGO2 inhibitory complex and to promote translation of MOV10 associated mRNAs. Phosphorylation of FMRP appears to be the potential switch for NMDAR mediated translation and in the absence of FMRP, the distinct translation response to NMDAR stimulation is lost. Thus, FMRP and MOV10 have an important regulatory role in NMDAR mediated translation at the synapse.
Frontiers in Molecular Neuroscience, 2019
SYNGAP1, a Synaptic Ras-GTPase activating protein, regulates synapse maturation during a critical... more SYNGAP1, a Synaptic Ras-GTPase activating protein, regulates synapse maturation during a critical developmental window. Heterozygous mutation in SYNGAP1 (SYNGAP1 −/+) has been shown to cause Intellectual Disability (ID) in children. Recent studies have provided evidence for altered neuronal protein synthesis in a mouse model of Syngap1 −/+. However, the molecular mechanism behind the same is unclear. Here, we report the reduced expression of a known translation regulator, FMRP, during a specific developmental period in Syngap1 −/+ mice. Our results demonstrate that FMRP interacts with and regulates the translation of Syngap1 mRNA. We further show reduced Fmr1 translation leads to decreased FMRP level during development in Syngap1 −/+ which results in an increase in Syngap1 translation. These developmental changes are reflected in the altered response of eEF2 phosphorylation downstream of NMDA Receptor (NMDAR)-mediated signaling. In this study, we propose a cross-talk between FMRP and SYNGAP1 mediated signaling which can also explain the compensatory effect of impaired signaling observed in Syngap1 −/+ mice.
Neuronal activity is responsible for large energy consumption within the brain. However, the cell... more 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 del...
Journal of Molecular Biology, 2019
MicroRNAs are small non-coding RNAs regulating mRNA translation. They play a crucial role in regu... more MicroRNAs are small non-coding RNAs regulating mRNA translation. They play a crucial role in regulating homeostasis in neurons, especially in regulating local and stimulation dependent protein synthesis. Since activity mediated protein synthesis in neurons is critical for memory and cognition, microRNAs have become key players in modulating these processes. Dementia is a broad term used for symptoms involving decline of memory and cognition. Several studies have implicated the dysregulation of microRNAs in many brain diseases like neurodegenerative diseases, neurodevelopmental disorders, brain injuries and dementia. In this review, we give an overview of microRNA mediated regulation of proteins and cellular processes affected in dementia pathology, hence illustrating the importance of microRNAs in normal functioning. We also focus on a relatively less explored area in dementia pathologythe importance of activity mediated protein synthesis at the synapse and the role of microRNAs in modulating this. Overall, this review will be helpful in looking at the significance of microRNAs in dementia from the perspective of defective regulation of protein synthesis and synaptic dysfunction.
IBRO Neuroscience Reports
Experimental Brain Research, Sep 5, 2022
Astrocytic cells are a subtype of glial cells that engulf pathogenic aggregates derived from dege... more Astrocytic cells are a subtype of glial cells that engulf pathogenic aggregates derived from degenerative neurons to facilitate its degradation. Here, we show that exposure to α-SYN protofibrils caused a transient increase in biogenesis of tunneling nanotubes (TNTs) in primary astrocytes and astrocyte-origin cancer cell-lines (U-87 MG, U251). Biogenesis of nascent TNTs corresponds to α-SYN protofibril-induced organelle toxicities, increased reactive oxygen species (ROS), and oxidative stress-induced premature cellular senescence. These TNTs mediate cell-to-cell transfer of α-SYN protofibrils, toxic lysosomes and mitochondria. Biogenesis of TNTs precedes clearance of α-SYN-induced organelle toxicities, cellular ROS levels and reversal of cellular senescence. Consequences of cellular clearance results in enhanced cell proliferation. Further, we have shown α-SYN-induced senescence promotes transient localization of focal adhesion kinase (FAK) in the nucleus. FAK mediated regulation of ...
Frontiers in Neuroscience
Alzheimer’s disease (AD) is the most common cause of dementia, with no current cure. Consequently... more Alzheimer’s disease (AD) is the most common cause of dementia, with no current cure. Consequently, alternative approaches focusing on early pathological events in specific neuronal populations, besides targeting the well-studied amyloid beta (Aβ) accumulations and Tau tangles, are needed. In this study, we have investigated disease phenotypes specific to glutamatergic forebrain neurons and mapped the timeline of their occurrence, by implementing familial and sporadic human induced pluripotent stem cell models as well as the 5xFAD mouse model. We recapitulated characteristic late AD phenotypes, such as increased Aβ secretion and Tau hyperphosphorylation, as well as previously well documented mitochondrial and synaptic deficits. Intriguingly, we identified Golgi fragmentation as one of the earliest AD phenotypes, indicating potential impairments in protein processing and post-translational modifications. Computational analysis of RNA sequencing data revealed differentially expressed g...
Experimental Brain Research
Journal of Cell Science
ABSTRACTPrecise development of the dendritic architecture is a critical determinant of mature neu... more ABSTRACTPrecise development of the dendritic architecture is a critical determinant of mature neuronal circuitry. MicroRNA (miRNA)-mediated regulation of protein synthesis plays a crucial role in dendritic morphogenesis, but the role of miRNA-induced silencing complex (miRISC) protein components in this process is less studied. Here, we show an important role of a key miRISC protein, the GW182 paralog TNRC6A, in the regulation of dendritic growth. We identified a distinct brain region-specific spatiotemporal expression pattern of GW182 during rat postnatal development. We found that the window of peak GW182 expression coincides with the period of extensive dendritic growth, both in the hippocampus and cerebellum. Perturbation of GW182 function during a specific temporal window resulted in reduced dendritic growth of cultured hippocampal neurons. Mechanistically, we show that GW182 modulates dendritic growth by regulating global somatodendritic translation and actin cytoskeletal dyna...
Journal of Cell Science
Stress response pathways protect the lung from the damaging effects of environmental toxicants. H... more 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 injury model, reveals that FMRP-deficient cells exhibit increased expression of markers of oxidative and genotoxic stress and increased cell death. Further inquiry shows 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 cells als...
ABSTRACTStress response pathways protect the lung from the damaging effects of environmental toxi... more ABSTRACTStress 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 fai...
The Journal of Neuroscience, 2021
Apolipoprotein E (APOE), one of the primary lipoproteins in the brain has three isoforms in human... more Apolipoprotein E (APOE), one of the primary lipoproteins in the brain has three isoforms in humans, APOE2, APOE3, and APOE4. APOE4 is the most well-established risk factor increasing the predisposition for Alzheimer's disease (AD). The presence of the APOE4 allele alone is shown to cause synaptic defects in neurons and recent studies have identified multiple pathways directly influenced by APOE4. However, the mechanisms underlying APOE4-induced synaptic dysfunction remain elusive. Here, we report that the acute exposure of primary cortical neurons or synaptoneurosomes to APOE4 leads to a significant decrease in global protein synthesis. Primary cortical neurons were derived from male and female embryos of Sprague Dawley (SD) rats or C57BL/6J mice. Synaptoneurosomes were prepared from P30 male SD rats. APOE4 treatment also abrogates the NMDA-mediated translation response indicating an alteration of synaptic signaling. Importantly, we demonstrate that both APOE3 and APOE4 generate...
Haploinsufficiency in SYNGAP1 is implicated in Intellectual Disability (ID) and Autism Spectrum d... more Haploinsufficiency in SYNGAP1 is implicated in Intellectual Disability (ID) and Autism Spectrum disorder (ASD) and affects the maturation of dendritic spines. The abnormal spine development has been suggested to cause disbalance of excitatory and inhibitory (E/I) neurotransmission at distinct developmental periods. In addition, E/I imbalances in Syngap1+/- mice might be due to abnormalities in K+-Cl- co-transporter function (NKCC1, KCC2), in a similar manner as in the murine models of Fragile-X and Rett syndromes. To study whether an altered intracellular chloride ion concentration represents an underlying mechanism of altered function of GABAergic synapses in Dentate Gyrus Granule Cells of Syngap1+/- recordings were performed at different developmental stages of the mice. We observed that neurons at P14-15 of Syngap1+/- mice had depolarised membrane potential and a decreased Cl- reversal potential. The KCC2 expression was decreased compared to Wild-type (WT) mice at P14-15. Further...
The Fragile X Mental Retardation Protein (FMRP) is an RNA Binding Protein that regulates translat... more The Fragile X Mental Retardation Protein (FMRP) is an RNA Binding Protein that regulates translation of mRNAs, essential for synaptic development and plasticity. FMRP interacts with a specific set of mRNAs and aids in their microtubule dependent transport and regulates their translation through its association with ribosomes. However, the biochemical role of individual domains of FMRP in forming neuronal granules and associating with microtubules and ribosomes is currently undefined. Here, we report that the C-terminus domain of FMRP is sufficient to bind to ribosomes as well as polysomes akin to the full-length protein. Furthermore, the C-terminus domain alone is essential and responsible for FMRP-mediated translation repression in neurons. However, FMRP-mediated puncta formation and microtubule association is favored by the synergistic combination of FMRP domains and not by individual domains. Interestingly, we show that the phosphorylation of hFMRP at Serine-500 is important in m...
Experimental Brain Research, 2021
Haploinsufficiency in SYNGAP1 is implicated in intellectual disability (ID) and autism spectrum d... more Haploinsufficiency in SYNGAP1 is implicated in intellectual disability (ID) and autism spectrum disorder (ASD) and affects the maturation of dendritic spines. The abnormal spine development has been suggested to cause a disbalance of excitatory and inhibitory (E/I) neurotransmission at distinct developmental periods. In addition, E/I imbalances in Syngap1 +/− mice might be due to abnormalities in K + –Cl − co-transporter function (NKCC1, KCC2), in a maner similar to the murine models of Fragile-X and Rett syndromes. To study whether an altered intracellular chloride ion concentration represents an underlying mechanism of modified function of GABAergic synapses in Dentate Gyrus Granule Cells of Syngap1 +/− recordings were performed at different developmental stages of the mice. We observed depolarised neurons at P14–15 as illustrated by decreased Cl − reversal potential in Syngap1 +/− mice. The KCC2 expression was decreased compared to Wild-type (WT) mice at P14–15. The GSK-3β inhibitor, 6-bromoindirubin-3ʹ-oxime (6BIO) that crosses the blood–brain barrier, was tested to restore the function of GABAergic synapses. We discovered that the intraperitoneal administration of 6BIO during the critical period or young adolescents [P30 to P80 (4-week to 10-week)] normalised an altered E/I balance, the deficits of synaptic plasticity, and behavioural performance like social novelty, anxiety, and memory of the Syngap1 +/− mice. In summary, altered GABAergic function in Syngap1 +/− mice is due to reduced KCC2 expression leading to an increase in the intracellular chloride concentration that can be counteracted by the 6BIO, which restored cognitive, emotional, and social symptoms by pharmacological intervention, particularly in adulthood.
Stem Cell Reports, 2021
Summary Frontotemporal dementia type 3 (FTD3), caused by a point mutation in the charged multives... more Summary Frontotemporal dementia type 3 (FTD3), caused by a point mutation in the charged multivesicular body protein 2B (CHMP2B), affects mitochondrial ultrastructure and the endolysosomal pathway in neurons. To dissect the astrocyte-specific impact of mutant CHMP2B expression, we generated astrocytes from human induced pluripotent stem cells (hiPSCs) and confirmed our findings in CHMP2B mutant mice. Our data provide mechanistic insights into how defective autophagy causes perturbed mitochondrial dynamics with impaired glycolysis, increased reactive oxygen species, and elongated mitochondrial morphology, indicating increased mitochondrial fusion in FTD3 astrocytes. This shift in astrocyte homeostasis triggers a reactive astrocyte phenotype and increased release of toxic cytokines, which accumulate in nuclear factor kappa b (NF-κB) pathway activation with increased production of CHF, LCN2, and C3 causing neurodegeneration.
Precise development of the dendritic architecture is a critical determinant of mature neuronal ci... more Precise development of the dendritic architecture is a critical determinant of mature neuronal circuitry. MicroRNA-mediated regulation of protein synthesis plays a crucial role in dendritic morphogenesis but the role of miRISC protein components in this process is less studied. Here, we show an important role of a key miRISC protein GW182 in the regulation of dendritic growth. We have identified a distinct brain region specific Spatio-temporal expression pattern of GW182 during rat postnatal development. We found that the window of peak GW182 expression coincides with the period of extensive dendritic growth, both in the hippocampus and cerebellum. Perturbation of GW182 function during a specific temporal window resulted in reduced dendritic growth of cultured hippocampal neurons. Mechanistically, we show that GW182 modulates dendritic growth by regulating global somato-dendritic translation, and actin cytoskeletal dynamics of developing neurons. Furthermore, we found that GW182 aff...
SYNGAP1, a Synaptic Ras-GTPase activating protein, regulates synapse maturation during a critical... more SYNGAP1, a Synaptic Ras-GTPase activating protein, regulates synapse maturation during a critical developmental window. Heterozygous mutation in SYNGAP1 (SYNGAP1+/-) has been shown to cause Intellectual Disability (ID) in children. Recent studies have provided evidence for altered neuronal protein synthesis in a mouse model of Syngap1+/-. However, the molecular mechanisms behind the same is unclear. Here, we report the reduced expression of a known translation regulator, FMRP, during a specific developmental period in Syngap1+/- mice. Our results demonstrated that FMRP interacts with and regulates the translation of Syngap1 mRNA. We further show that, during development, reduced translation of FMRP and this decrease in FMRP leads to a compensatory increase of Syngap1 translation in Syngap1+/-. These developmental changes are reflected in the altered response of eEF2 phosphorylation downstream of NMDA receptor signalling. We propose a cross-talk between FMRP and SYNGAP1 mediated sign...
Molecular Brain, 2019
Protein synthesis is crucial for maintaining synaptic plasticity and synaptic signalling. Here we... more Protein synthesis is crucial for maintaining synaptic plasticity and synaptic signalling. Here we have attempted to understand the role of RNA binding proteins, Fragile X Mental Retardation Protein (FMRP) and Moloney Leukemia Virus 10 (MOV10) protein in N-Methyl-D-Aspartate Receptor (NMDAR) mediated translation regulation. We show that FMRP is required for translation downstream of NMDAR stimulation and MOV10 is the key specificity factor in this process. In rat cortical synaptoneurosomes, MOV10 in association with FMRP and Argonaute 2 (AGO2) forms the inhibitory complex on a subset of NMDAR responsive mRNAs. On NMDAR stimulation, MOV10 dissociates from AGO2 and promotes the translation of its target mRNAs. FMRP is required to form MOV10-AGO2 inhibitory complex and to promote translation of MOV10 associated mRNAs. Phosphorylation of FMRP appears to be the potential switch for NMDAR mediated translation and in the absence of FMRP, the distinct translation response to NMDAR stimulation is lost. Thus, FMRP and MOV10 have an important regulatory role in NMDAR mediated translation at the synapse.
Frontiers in Molecular Neuroscience, 2019
SYNGAP1, a Synaptic Ras-GTPase activating protein, regulates synapse maturation during a critical... more SYNGAP1, a Synaptic Ras-GTPase activating protein, regulates synapse maturation during a critical developmental window. Heterozygous mutation in SYNGAP1 (SYNGAP1 −/+) has been shown to cause Intellectual Disability (ID) in children. Recent studies have provided evidence for altered neuronal protein synthesis in a mouse model of Syngap1 −/+. However, the molecular mechanism behind the same is unclear. Here, we report the reduced expression of a known translation regulator, FMRP, during a specific developmental period in Syngap1 −/+ mice. Our results demonstrate that FMRP interacts with and regulates the translation of Syngap1 mRNA. We further show reduced Fmr1 translation leads to decreased FMRP level during development in Syngap1 −/+ which results in an increase in Syngap1 translation. These developmental changes are reflected in the altered response of eEF2 phosphorylation downstream of NMDA Receptor (NMDAR)-mediated signaling. In this study, we propose a cross-talk between FMRP and SYNGAP1 mediated signaling which can also explain the compensatory effect of impaired signaling observed in Syngap1 −/+ mice.
Neuronal activity is responsible for large energy consumption within the brain. However, the cell... more 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 del...
Journal of Molecular Biology, 2019
MicroRNAs are small non-coding RNAs regulating mRNA translation. They play a crucial role in regu... more MicroRNAs are small non-coding RNAs regulating mRNA translation. They play a crucial role in regulating homeostasis in neurons, especially in regulating local and stimulation dependent protein synthesis. Since activity mediated protein synthesis in neurons is critical for memory and cognition, microRNAs have become key players in modulating these processes. Dementia is a broad term used for symptoms involving decline of memory and cognition. Several studies have implicated the dysregulation of microRNAs in many brain diseases like neurodegenerative diseases, neurodevelopmental disorders, brain injuries and dementia. In this review, we give an overview of microRNA mediated regulation of proteins and cellular processes affected in dementia pathology, hence illustrating the importance of microRNAs in normal functioning. We also focus on a relatively less explored area in dementia pathologythe importance of activity mediated protein synthesis at the synapse and the role of microRNAs in modulating this. Overall, this review will be helpful in looking at the significance of microRNAs in dementia from the perspective of defective regulation of protein synthesis and synaptic dysfunction.