Biology subjects

Kolthur-Seetharam, U.

Publications and source records attributed to Kolthur-Seetharam, U..

At least 19 recordsLinked to original sources

bioRxiv2026

Conserved Transcriptomic Signatures of Sirt6 Activity: A Cross-Species RNA-seq Meta-analysis

The NAD+-dependent histone deacetylase Sirt6 regulates transcription of multiple classes of genes, including those involved in metabolism, immune response, oxidative stress response, and development. Defining the Sirt6-regulated transcriptome is relevant to understanding the various important physiological roles of Sirt6, such as extending lifespan, maintaining metabolic health, and tumor suppression. Numerous studies have identified Sirt6 target genes, using both targeted and genome-wide approaches; however, consensus is limited and there has yet to be a systematic analysis of gene expression changes induced by altering Sirt6 levels. In the present study, we conducted a meta-analysis of 19 mammalian RNA-seq datasets in which Sirt6 levels were perturbed (knockout, knockdown, or overexpression). Our analyses included Gene Set Enrichment Analysis, pathway analysis of differentially expressed genes, and identification of individual differentially expressed genes. Our analysis identified consistent gene expression changes associated with lowering Sirt6 levels, including increased expression of immune response and ribosomal protein genes and reduced expression of lipid oxidation and oxidative phosphorylation genes. Extracellular Matrix and E2F target genes also had consistently increased expression upon Sirt6 reduction, highlighting novel regulation by Sirt6. To determine the conservation of gene regulation by Sirt6, we performed additional RNA-Seq meta-analysis on tissues from Drosophila melanogaster with Sirt6 deletion and overexpression. The fly datasets produced similar results to the mammal results, except for lipid oxidation genes, which were found to increase in Sirt6-low conditions. These results provide consensus about conserved and novel pathways transcriptionally regulated by Sirt6.

genomics↗

bioRxiv2025

Mammalian mitochondrial polyphosphate is regulated by the 5-InsP7 synthase IP6K1

Inorganic polyphosphate (polyP) is a linear polymer of varying length composed of phosphate residues linked by phosphoanhydride bonds. PolyP remains poorly understood in mammals due to its low abundance and lack of information on its synthesis and regulation. Using synthetic polyP8 as a bait, we identified polyP interacting proteins involved in RNA splicing, transcription, and mitochondrial function. We developed a DAPI fluorescence-based assay to quantify the low levels of polyP present in mammalian cell lines and tissues, and detected a higher concentration of polyP in the mitochondria compared with the nucleus and post-mitochondrial fraction. We observed that mitochondrial polyP synthesis relies on active FoF1 ATP synthase and an intact proton gradient across the inner mitochondrial membrane. Our data shows that orthophosphate (Pi) is required for the generation of mitochondrial polyP and that the presence of ATP enhances Pi-driven polyP synthesis in isolated mitochondria. We discovered that the inositol pyrophosphate 5-InsP7, synthesized by IP6K1, regulates mitochondrial polyP levels. Mice and cells deficient in IP6K1 showed a significant reduction in mitochondrial polyP synthesis compared with wild type controls. Cells lacking IP6K1 also showed impaired mitochondrial respiration and membrane potential. The expression of active IP6K1, but not its catalytically inactive form, restored mitochondrial polyP synthesis and membrane potential in IP6K1 deficient cells, but mitochondrial respiration was rescued by expression of either active or inactive IP6K1. These data show that IP6K1 regulates mitochondrial function and polyP production through both the synthesis of 5-InsP7 and via a catalytic activity-independent mechanism. Our findings uncover a link between 5-InsP7, an energy sensor, and polyP, an energy store, in the regulation of mammalian mitochondrial homeostasis.

biochemistry↗

bioRxiv2025

SIRT1-IDR-Driven Temporal Gating of Sequential Transcription-Factor Recruitment Coordinates Fasting Adaptation

Precise temporal control of gene expression is critical for metabolic adaptation, yet how transcriptional regulators coordinate dynamic responses to nutrient stress remains poorly understood. Here, we identify the intrinsically disordered region (IDR) of SIRT1, encoded by exon-2 (E2), as a key determinant of transcriptional timing during fasting. Using global and conditional SIRT1{Delta}E2 mouse model, which mimics an endogenous transcript variant, we demonstrate that loss of the N-terminal IDR disrupts the hierarchical engagement of transcription factors (TFs), leading to premature and exaggerated activation of gluconeogenic genes. Mechanistically, the IDR acts as a "conformational timer," competitively gating SIRT1 interactions with CREB, FOXO1, and PPAR to ensure sequential TF recruitment and resolution. Absence of this regulatory module resulted in "runaway" CREB activity, aberrant hepatic glucose output, and impaired fasting-refeeding transitions, linking IDR-driven temporal control to systemic metabolic homeostasis. Our findings reveal a paradigm wherein IDRs in upstream metabolic sensors orchestrate transcriptional handovers, offering a molecular basis for the dynamic rewiring of gene networks during physiological transitions. This work expands the functional repertoire of disordered regions beyond TFs, positioning them as critical nodes in nutrient-responsive transcriptional circuits and potential targets for metabolic disorders.

physiology↗

bioRxiv2024

Diurnal variation in skeletal muscle mitochondrial function dictates time of day-dependent differences in exercise capacity

Exercise impinges on almost all physiological processes at an organismal level and is a potent intervention to treat various diseases. Exercise performance is well established to display diurnal rhythm, peaking during the late active phase. However, the underlying molecular/metabolic factors and mitochondrial energetics that possibly dictate time-of-day exercise capacity remain unknown. Here, we have unraveled the importance of diurnal variation in mitochondrial functions as a determinant of skeletal muscle exercise performance. Our results show that exercise-induced muscle metabolome and energetics are distinct at ZT3 and ZT15. Importantly, we have elucidated key diurnal differences in mitochondrial functions that are well correlated with disparate time-of-day dependent exercise capacity. Providing causal evidence, we illustrate that loss of Sirtuin4 (SIRT4), a well-known mitochondrial regulator, abrogates diurnal variation in mitochondrial functions and consequently abolishes time-of-day dependent exercise performance. Therefore, our findings unequivocally demonstrate the pivotal role of baseline skeletal-muscle mitochondrial functions in dictating diurnal exercise capacity.

physiology↗

bioRxiv2024

Consumption of human-relevant levels of sucrose-water rewires macronutrient uptake and utilization mechanisms in a tissue specific manner

Consumption of sugar-sweetened beverages (SSBs) have been linked to metabolic dysfunction, obesity, diabetes and enhanced risk of cardiovascular diseases across all age-groups globally. Decades of work that have provided insights into pathophysiological manifestations of sucrose overfeeding have employed paradigms that rarely mimic human consumption of SSBs. Thus, our understanding of multi-organ cross-talk and molecular and/or cellular mechanisms, which operate across scales and drive physiological derangement is still poor. By employing a paradigm of sucrose water feeding in mice that closely resembles chronic SSB consumption in humans (10% sucrose in water), we have unraveled hitherto unknown tissue-specific mechanistic underpinnings, which contribute towards perturbed physiology. Our findings illustrate that systemic impaired glucose homeostasis, mediated by hepatic gluconeogenesis and insulin resistance, does not involve altered gene expression programs in the liver. We have discovered the pivotal role of the small intestine, which in conjunction with liver and muscles, drives dyshomeostasis. Importantly, we have uncovered rewiring of molecular mechanisms in the proximal intestine that is either causal or consequential to systemic ill-effects of chronic sucrose water consumption including dysfunction of liver and muscle mitochondria. Tissue-specific molecular signatures, which we have unveiled, clearly indicate that inefficient utilization of glucose is exacerbated by enhanced uptake by the gut. Besides providing systems-wide mechanistic insights, we propose that consumption of SSBs causes intestinal molecular addiction for deregulated absorption of hexose-sugars, and drives diseases such as diabetes and obesity.

physiology↗

bioRxiv2024

Biased recruitment of H3.3 by HIRA is dictated by de-/acetylation and determines transcription memory and response

Chromatin plasticity and epigenetic memory, fundamental for eukaryotic biology, are determined by differential/regulated de novo deposition or recycling of pre-existing histones, which in turn dictate transcriptional programs. Recruitment of the histone-H3 variant, H3.3, mediated by the HIRA chaperone complex, is both causally and consequentially associated with transcription. Despite decades of work, endogenous regulatory mechanisms that differentiate between de novo deposition and recycling activities of HIRA are still unknown. Here, we have investigated the pivotal role of HIRA de-/acetylation in regulating its function. Our results unequivocally establish function separation effects of acetyl and deacetyl mimic mutations of lysine-600, vis-a-vis de novo deposition or recycling of H3.3, respectively. Importantly, we demonstrate that HIRA deacetylation-dependent biased H3.3 recycling determines transcriptional output, possibly through preferential enrichment of H3.3-K36me3. Besides unraveling tunable regulatory mechanism that governs HIRA function, we illustrate a causal link between the chaperone activity, biased recruitment of pre-existing histones, and gene expression.

molecular biology↗

bioRxiv2024

Identification of ABHD6 as a regulator of lysophosphatidylserines in the mammalian liver and kidneys

Lysophosphatidylserine (lyso-PS) is a potent hormone-like signaling lysophospholipid, which regulates many facets of mammalian biology and dysregulation in its metabolism is associated with several human neurological and autoimmune diseases. Despite the physiological importance and causal relation with human pathophysiology, little is known about the metabolism of lyso-PS in tissues other than the nervous and immune systems. To address this problem, here, we attempted to identify one (or more) lipase(s) capable of degrading lyso-PS in different mammalian tissues. We found that the membrane proteomic fraction of most mammalian tissues possess lyso-PS lipase activity, yet interestingly, the only bona fide lyso-PS lipase ABHD12 displays this enzymatic activity and has control over lyso-PS metabolism only in the mammalian brain. Using an in vitro inhibitor screen against membrane proteomic fractions of different tissues, we find that another lipase from the metabolic serine hydrolase family, ABHD6, is a putative lyso-PS lipase in the mouse liver and kidney. Finally, using pharmacological tools, we validate the lyso-PS lipase activity of ABHD6 in vivo, and functionally designate this enzyme as a major lyso-PS lipase in primary hepatocytes, and the mammalian liver and kidneys. HIGHLIGHTSO_LILyso-PS lipase enzymatic activity is present in the membrane proteomic fraction of most mammalian tissues C_LIO_LIAn in vitro inhibitor screen identifies ABHD6 as a putative lyso-PS lipase in the liver and kidney C_LIO_LIABHD6 functions as a lyso-PS lipase in primary hepatocytes C_LIO_LIABHD6 also performs lyso-PS lipase activity in vivo and regulates lyso-PS levels in the liver and kidney C_LI

biochemistry↗

bioRxiv2024

ATP-Binding Free Energy Simulations Reveal an Allosteric Link Between the Enzyme Active Site and Multiple Functional Protein-Protein Interaction Interfaces in Cyclin Dependent Kinase-1

The ATP dependent phosphorylation activity of Cyclin Dependent Kinase 1 (CDK1), an essential enzyme for cell cycle progression, is intrinsically dependent upon interactions with Cyclin-B, substrate, and Cks proteins. A recent joint experimental-computational study from our group showed intriguingly that acetylation at the active site abrogated the binding of CDK with Cyclin-B. These results posit the possibility of a bi-directional communication between the catalytic site and the protein-protein interface(s). Now, we present evidence for a general allosteric link between the CDK1 active site and all three of its protein-protein interaction (PPI) interfaces through atomistic molecular dynamics simulations (MD). Specifically, we examined ATP binding free energies to CDK1 in native non-acetylated (K33wt) and acetylated (K33Ac) forms as well as in two mutant forms of CDK1, the acetyl-mimic K33Q and the acetyl-null K33R which are accessible in-vitro. We find, in agreement with experiments, that ATP binding is energetically more favorable in K33wt relative to all other states wherein the active site lysine is perturbed (K33Ac, K33Q, and K33R). We also develop an entropy decomposition scheme which reveals, in addition to expected local changes in entropy, significant non-local entropy responses to ATP binding/perturbation of K33 from the -helix, activation loop (A-loop), and the -H loop segments in CDK1 which interface with Cyclin-B, substrate, and Cks proteins. Statistical analyses over a large set of MD trajectories reveal that while the local and non-local entropic responses to active site perturbations are on average correlated with dynamical changes in the associated protein segments, such correlations may be lost in about 9-48 % of the dataset depending on the segment. Besides, proving the bi-directional communication between the active site and CDK1:Cyclin-B interface, our study provides new insights into the regulation of ATP binding by multiple PPI interfaces in CDK1.

biophysics↗

bioRxiv2023

Metabolic transitions regulate global protein fatty acylation

Intermediary metabolites and flux through various pathways have emerged as key determinants of post-translational modifications. Independently, dynamic fluctuations in their concentrations are known to drive cellular energetics in a bi-directional manner. Notably, intracellular fatty acid pools that drastically change during fed and fasted states act as precursors for both ATP production and fatty acylation of proteins. Protein fatty acylation is well regarded for its role in regulating structure and functions of diverse proteins, however the effect of intracellular concentrations of fatty acids on protein modification is less understood. In this regard, we unequivocally demonstrate that metabolic contexts, viz. fed and fasted states, dictate the extent of global fatty acylation. Moreover, we show that presence or absence of glucose, that influences cellular and mitochondrial uptake/utilization of fatty acids, affects palmitoylation and oleoylation, which is consistent with their intracellular abundance in fed and fasted states. Employing complementary approaches including click-chemistry, lipidomics and imaging, we show the top-down control of cellular metabolic state. Importantly, our results establish the crucial role of mitochondria and retrograde signaling components like SIRT4, AMPK and mTOR in orchestrating protein fatty acylation at a whole cell level. Specifically, pharmacogenetic perturbations that alter either mitochondrial functions and/or retrograde signaling affect protein fatty acylation. Besides illustrating the cross-talk between carbohydrate and lipid metabolism in mediating bulk post-translational modification, our findings also highlight the involvement of mitochondrial energetics.

physiology↗

bioRxiv2023

Anticipatory Biogenesis of Hepatic Fed MicroRNAs is Regulated by Metabolic and Circadian Inputs

Starvation and refeeding are mostly unanticipated in the wild in terms of duration, frequency, and nutritional value of the refed state. Notwithstanding this, organisms mount efficient and reproducible responses to restore metabolic homeostasis. Hence, it is intuitive to invoke expectant molecular mechanisms that build anticipatory responses to enable physiological toggling during fed-fast cycles. In this regard, we report anticipatory biogenesis of oscillatory hepatic microRNAs, which were earlier shown to peak during a fed state to inhibit starvation-responsive genes. Results presented in this study clearly demonstrate that the levels of primary and precursor microRNA transcripts increase during a fasting state, in anticipation of a fed response. We delineate the importance of both metabolic inputs and circadian cues in orchestrating microRNA homeostasis in a physiological setting, using the most prominent hepatic fed-miRNAs as candidates. Besides illustrating the metabo-endocrine control, our findings provide a mechanistic basis for the overarching influence of starvation on anticipatory biogenesis. Importantly, by employing pharmacological agents that are widely used in the clinics, we point out the high potential of interventions to restore homeostasis of hepatic microRNAs, whose deregulated expression is otherwise well established to cause metabolic diseases.

physiology↗

bioRxiv2021

G9a and Sirtuin6 epigenetically modulate host cholesterol accumulation to facilitate mycobacterial survival

Cholesterol derived from the host milieu forms a critical factor for mycobacterial pathogenesis. However, the molecular circuitry co-opted by Mycobacterium tuberculosis (Mtb) to accumulate cholesterol in host cells remains obscure. Here, we report that a functional amalgamation of WNT-responsive histone modifiers G9a (H3K9 methyltransferase) and Sirt6 (H3K9 deacetylase) orchestrate cholesterol build-up in in-vitro and in-vivo models of Mtb infection. Mechanistically, G9a, along with SREBP2, drives the expression of cholesterol biosynthesis and uptake genes; while Sirt6 represses the genes involved in cholesterol efflux. The accumulated cholesterol promotes the expression of antioxidant genes leading to reduced oxidative stress, thereby supporting Mtb survival. In corroboration, loss-of-function of G9a in vitro and in vivo by pharmacological inhibition; or utilization of BMDMs derived from Sirt6 KO mice or in vivo infection in Sirt6 heterozygous mice; hampers host cholesterol accumulation and restricts Mtb burden. These findings shed light on the novel roles of G9a and Sirt6 during Mtb infection and highlight the previously unknown contribution of host cholesterol in potentiating anti-oxidative responses for aiding Mtb survival.

microbiology↗

bioRxiv2020

Continuous variable response, kinetic gating and connectivity that govern IS topology are perturbed in hyperinsulinemia

Understanding kinetic control of biological processes is as important as identifying components that constitute pathways. Insulin-signaling (IS) is central for almost all metazoans and its perturbations are associated with various diseases and aging. While temporal phosphorylation changes and kinetic constants have provided some insights, constant or variable parameters that establish and maintain signal topology are poorly understood. Our iterative experimental and mathematical simulation-based approaches reveal novel kinetic parameters that encode concentration and nutrient dependent information. Further, we find that pulsatile fasting insulin rewires IS akin to memory and in anticipation of a fed response. Importantly, selective kinetic gating of signals and maximum connectivity, between metabolic and growth-factor arms under normo-insulinemic states, maintains network topology. In addition to unraveling kinetic constraints that determine cascade architecture, our findings will help in identifying novel therapeutic strategies that conserve coupling between metabolic and growth-factor arms, which is lost in diseases and conditions of hyperinsulinemia.

bioinformatics↗

bioRxiv2020

Continuous variable response, kinetic gating and connectivity that determine topology of insulin signaling are perturbed in hyper-insulinemic states

Understanding kinetic control of biological processes is as important as identifying components that constitute pathways. Insulin signaling (IS) is central for almost all metazoans and its perturbations are associated with various diseases and aging. While temporal phosphorylation changes and kinetic constants have provided some insights, constant or variable parameters that establish and maintain signal topology are poorly understood. Our iterative experimental and mathematical simulation-based approaches reveal novel kinetic parameters of IS that encode concentration and nutrient dependent information. Further, we find that pulsatile fasting insulin rewires IS akin to memory and in anticipation of a fed response. Importantly, selective kinetic gating of signals and maximum connectivity, between metabolic and growth-factor arms under normo-insulinemic states, maintains network topology. In addition to unraveling kinetic constraints that determine cascade architecture, our findings will help in identifying novel therapeutic strategies that conserve coupling between metabolic and growth-factor arms, which is lost in diseases and conditions of hyperinsulinemia.

systems biology↗

bioRxiv2019

NAD+-dependent deacetylase SIRT1 is essential for meiotic progression and controls repair-recombination efficiency

Meiotic components and their functions have been extensively studied. Yet, the interplay between molecular factors and regulation of their functions that is brought about by post-translational modifications, specifically (de)-acetylation, is not well characterized. SIRT1, a NAD+-dependent deacetylase has been previously shown to be necessary for spermatogenesis. However, whether it has any role to play in mammalian meiosis remains to be uncovered. Our findings identify SIRT1 as a key determinant of meiotic progression. Knocking out SIRT1 specifically in meiocytes (SIRT1{Delta}meio) led to a delay in progression through pachytene and repair of double strand breaks. Interestingly, despite these deficits, meiotic loss of SIRT1 did not affect synapsis nor did it lead to pachytene arrest or apoptosis. Moreover, our results demonstrate that SIRT1 is required for regulating crossover frequency and its absence results in higher crossover events. Therefore, our study brings to the fore a novel regulatory factor/mechanism that is necessary for coupling of synapsis and recombination. This is noteworthy since mutations in core meiotic components result in gross defects in synapsis, repair and recombination, and very few studies have reported the differential regulation of these processes. Further, exposing SIRT1{Delta}meio to low/moderate doses of (C)-irradiation indicated that SIRT1 might be involved in eliciting recombination checkpoint arrest and in its absence pachytene cells progress to diplotene stage, unlike in the SIRT1WT mice. Importantly, exogenous damage resulted in enhanced retention of (C)H2AX in SIRT1{Delta}meio diplotene cells, reiterating the critical role that SIRT1 plays in regulating repair efficiency/kinetics. Molecularly, we find that SIRT1 interacts with MRN complex and lack of SIRT1 causes hyperacetylation of several non-histone proteins including the MRN components. Given that SIRT1{Delta}meio mice mimic MRN hypomorphs, we propose that SIRT1-dependent deacetylation of these proteins is crucial for normal meiotic progression. Taken together, our study uncovers a previously unappreciated role of SIRT1 in meiotic progression.\n\nAuthor SummaryMeiosis is a key process in germ cell development that is essential for generating genetic diversity via recombination. It involves precise spatio-temporal orchestration of various molecular events such as chromosomal synapsis, repair and recombination. Whereas the core meiotic components are well known, upstream factors that might be important for regulating their functions and also couple the downstream processes are less explored. In this paper, we report that SIRT1, a NAD+-dependent deacetylase, is necessary for meiotic progression by identifying its role in coupling of synapsis and recombination. By generating a meiosis specific knockout of SIRT1, we show that its absence in spermatocytes leads to inefficient/delayed repair and progression through pachytene. We have also uncovered that SIRT1 exerts control over recombination (cross over) frequency. Interestingly, our findings demonstrate that SIRT1 provides protection against exogenous genotoxic stress possibly by eliciting meiotic checkpoints. Thus, this study provides both cellular and molecular insights into the importance of SIRT1 mediated protein deacetylation in governing meiosis in mammals.

developmental biology↗

bioRxiv2019

Anabolic SIRT4 exerts retrograde control over TORC1 signalling by glutamine sparing in the mitochondria

Anabolic and catabolic signalling mediated via mTOR and AMPK have to be intrinsically coupled to mitochondrial functions for maintaining homeostasis and mitigate cellular/organismal stress. Although, glutamine is known to activate mTOR, if/how differential mitochondrial utilization of glutamine impinges on mTOR signalling is less explored. Mitochondrial SIRT4, which unlike other sirtuins is induced in a fed state, is known to inhibit catabolic signalling/pathways through AMPK-PGC1a/SIRT1-PPARa axis and negatively regulate glutamine metabolism via TCA cycle. However, physiological significance of SIRT4 functions during a fed state is still unknown. Here, we establish SIRT4 as key anabolic factor that activates TORC1 signalling and regulates lipogenesis, autophagy and cell proliferation. Mechanistically, we demonstrate that the ability of SIRT4 to inhibit anaplerotic conversion of glutamine to -ketoglutarate potentiates TORC1. Interestingly, we also show that mitochondrial glutamine sparing or utilization is critical for differentially regulating TORC1 under fed and fasted conditions. Moreover, we conclusively show that differential expression of SIRT4 during fed and fasted states is vital for coupling mitochondrial energetics and glutamine utilization with anabolic pathways. These significant findings also illustrate that SIRT4 integrates nutrient inputs with mitochondrial retrograde signals to maintain a balance between anabolic and catabolic pathways.

physiology↗

bioRxiv2019

Sir2 non-autonomously controls differentiation of germline cells in the ovary of Drosophila melanogaster

In Drosophila ovary, germline stem cells (GSCs) reside in a somatic cell niche that provides them signals necessary for their survival and development. Escort cells (ECs), one of the constituents of the niche, help in differentiation of GSC daughter cells. Since nutritional state is known to affect oogenesis, we set out to address the role of a metabolic sensor. NAD-dependent Sir2 is known to acts as a regulator of organismal life-span in a diet dependent manner. Our current study reveals that Sir2 in somatic cells is necessary for germline differentiation. Specifically, Sir2 in ECs upregulates Dpp signalling giving rise to tumorous germaria. In addition to this non-autonomous role of Sir2 in regulation of the germline cell homeostasis, we have demonstrated that EC-specific Sir2 has a role in attributing the identity of Cap cells as well as in de-differentiation of germline cells. Our study also shows that a genetic interaction between Sir2 and upd2 is important for the development of germline cells. Thus, we provide novel insights into the role of Sir2 in ovary development.

developmental biology↗

bioRxiv2019

Temporal gating of SIRT1 functions by O-GlcNAcylation prevents hyperglycemia and enables physiological transitions in liver

Inefficient fasted-to-refed transitions are known to cause metabolic diseases. Thus, identifying mechanisms that may constitute molecular switches during such physiological transitions become crucial. Specifically, whether nutrients program a relay of interactions in master regulators, such as SIRT1, and affect their stability is underexplored. Here, we elucidate nutrient-dependent O-GlcNAcylation of SIRT1, within its N-terminal domain, as a key determinant of hepatic glucose- and fat-metabolism, and insulin signaling. SIRT1 glycosylation dictates interactions with PPAR/FOXO1/PGC1/SREBP1, to exert a temporal control over transcription of genes during fasted-to-refed transitions. Interestingly, glycosylation-dependent cytosolic export of SIRT1 promotes a transient interaction with AKT and subsequent proteasomal degradation. Loss of glycosylation discomposes these interactions and enhances stability of SIRT1 even upon refeeding, which causes insulin resistance, hyperglycemia and hepatic-inflammation. Aberrant glycosylation of SIRT1 is associated with aging and/or metabolic diseases. Thus, nutrient-dependent glycosylation constrains spatio-temporal dynamics of SIRT1 and gates its functions to maintain metabolic homeostasis.

physiology↗

bioRxiv2018

Serotonin regulates mitochondrial biogenesis and function in rodent cortical neurons via the 5-HT2A receptor and SIRT1-PGC-1α axis

Mitochondria in neurons in addition to their primary role in bioenergetics also contribute to specialized functions including regulation of synaptic transmission, Ca2+ homeostasis, neuronal excitability and stress adaptation. However, the factors that influence mitochondrial biogenesis and function in neurons remain poorly elucidated. Here, we identify an important role for serotonin (5-HT) as a regulator of mitochondrial biogenesis and function in rodent cortical neurons, via a 5-HT2A receptor-mediated recruitment of the SIRT1-PGC-1 axis, which is relevant to the neuroprotective action of 5-HT. 5-HT increased mitochondrial biogenesis, reflected through enhanced mtDNA levels, mitotracker staining, and expression of mitochondrial genes. This was accompanied by increased cellular ATP levels, basal and maximal respiration, as well as spare respiratory capacity. Mechanistically the effects of 5-HT were mediated via the 5-HT2A receptor and master modulators of mitochondrial biogenesis, SIRT1 and PGC-1. SIRT1 was required to mediate the effects of 5-HT on mitochondrial biogenesis and function in cortical neurons. In vivo studies revealed that 5-HT2A receptor stimulation increased cortical mtDNA and ATP levels, in a SIRT1 dependent manner. In cortical neurons, 5-HT enhanced expression of anti-oxidant enzymes, decreased cellular reactive oxygen species, and exhibited neuroprotection against excitotoxic and oxidative stress, an effect that required SIRT1. These findings identify 5-HT as a novel upstream regulator of mitochondrial biogenesis and function in cortical neurons, and implicate the mitochondrial effects of 5-HT in its neuroprotective action.

neuroscience↗