Biology subjects

Gautam, N.

Publications and source records attributed to Gautam, N..

6 recordsLinked to original sources

bioRxiv2026

CTL1 (SLC44A1) regulates myelin lipid composition and architecture in Schwann cells

Myelin formation requires extensive membrane lipid synthesis, yet how myelinating glia acquire the choline needed for this process remains incompletely understood. Choline transporter-like protein 1 (CTL1; SLC44A1) is highly expressed in Schwann cells, and CTL1 deficiency in oligodendrocytes impairs CNS myelination. Here, we examined the role of CTL1 in peripheral nerve myelination using Schwann cell-specific Ctl1 knockout mice. Unexpectedly, loss of Ctl1 did not alter Schwann cell differentiation, the number of myelinated axons, or myelin thickness, but increased myelin abnormalities, including in-foldings and out-foldings. Lipidomic analysis revealed selective alterations in myelin lipid composition, particularly among long-chain lipid species, together with triglyceride accumulation in whole nerves. CTL1 deficiency also increased mTORC1-associated S6 and mTORC2-associated AKT S473 phosphorylation. Transcriptomic analysis revealed downregulation of gene programs associated with fatty acid {beta}-oxidation, triglyceride catabolism, and oxidative phosphorylation. Following peripheral nerve injury, Ctl1-deficient Schwann cells generated a normal repair response and efficiently remyelinated regenerated axons despite altered mTOR signaling. Together, these findings demonstrate that CTL1 is not required for overall peripheral myelin production but contributes to maintaining normal myelin lipid composition and architecture, revealing an unexpected ability of Schwann cells to sustain myelination despite disruption of CTL1-dependent choline metabolism

neuroscience↗

bioRxiv2026

CpG methylation and methionine metabolism account for phenotypic bifurcation of HIV transcription: a unique case of a pure epigenetic phenomenon

HIV transcription is characterized by its stochastic nature, which plays a pivotal role in determining the fate of a provirus--active replication or latent infection--and is therefore a critical determinant of the HIV latency establishment. Building upon our previous work, we identified a unique phenotype of stochastic HIV transcription in a Jurkat T cell clonal model harboring a single lentiviral-based vector, herein referred to as the HIV transcription-sensitized model. A defining feature of this cellular model is that the turnover of HIV transcription shows elevated frequency--a phenomenon designated phenotypic bifurcation--suggesting that, under certain conditions, the regulation of stochastic HIV transcription can be a pure epigenetic phenomenon. In continuation of and to further substantiate this premise, the present study characterizes the contributions of epigenetic regulation of CpG methylation, methionine metabolism that coordinates cell cycle events, and HIV antisense transcription to this phenomenon. This work adds direct causal evidence to the hypothesis that a potential lag prior to the entry of the G2 phase in the bifurcated state of low HIV transcription may serve as one of the underlying mechanisms that lead to the high CpG methylation level compared with that measured in the state of high HIV transcription, contributing to the cyclical turnover of phenotypic bifurcation of HIV transcription.

microbiology↗

bioRxiv2025

Gonadal Hormone Status Dictates Neurobehavioral, Metabolic and Immunological Benefits of Ketogenic Diet in Female Mice through Gut-Metabolic-Brain Axis

The ketogenic diet (KD) is recognized for its broad therapeutic potential across metabolic, neurological, immunological, and aging-related domains; however, its efficacy and durability in females remain underexplored. This study investigated the effects of a short-term, intermittent KD on neurobehavioral function, lipid metabolism, immune response, and gut microbiota composition in sham-operated (intact) and ovariectomized (OVX, estrogen-deficient) female mice, aiming to delineate the interactions between diet and gonadal hormones. In sham females, KD reduced circulating estradiol levels and induced low-grade systemic inflammation, without producing measurable behavioral benefits. Conversely, KD exhibited reduced compulsivity, anxiety, and depression-like behaviors with improved well-being in OVX females, suggesting enhanced neurobehavioral resilience under estrogen-deficient conditions. Biochemical analyses revealed KD-induced hyperlipidemia in both groups, although the lipid load was attenuated in OVX mice. KD further decreased low-density lipoprotein cholesterol but led to uremia and histopathological evidence of hepatic steatosis and fibrosis in OVX females, despite unaltered liver function markers. 16S rRNA sequencing revealed hormone-dependent remodelling of the gut microbiota, characterised by distinct compositional shifts between the sham and OVX cohorts. Correlation analyses linked microbial alterations to improved lipid profiles and reduced anxiodepressive behaviors, implicating the gut-metabolic-brain axis in mediating the effects of KD. Collectively, these findings suggest that KD confers neurobehavioral and metabolic benefits in the absence of ovarian hormones but may also pose risks to the liver and kidneys. These results highlight ketogenic nutrition as a potential non-pharmacological strategy to mitigate menopause- and aging-associated neurobehavioral, metabolic, and immune dysfunctions through modulation of the gut microbiota.

neuroscience↗

bioRxiv2025

Themis dominates T cell exhaustion by regulation of TCR and PD-1 signaling

T cell exhaustion is important to protect the host from immunopathology during chronic viral infection, but it also impairs T cell anti-tumor immunity1-5. A fundamental unresolved question is whether and how T cell exhaustion is determined at the onset of TCR signaling6-8. Here we report an unexpected role of Themis, a TCR-proximal signaling molecule9, in T cell exhaustion. Chronic viral infection in mice usually leads to T cell exhaustion and survival of the host. Surprisingly, Themis T-cell conditional knockout mice died from severe CD8+-dependent lung immunopathology in chronic viral infection, showing Themis importance in establishing T cell exhaustion. We found that Themis-deficient CD8+ T cells were hyperactivated at the single-cell level - producing more TNF and IFN{gamma} compared to wild-type counterparts - but defective in population-level expansion. Moreover, TCF-1 and TOX expression were inhibited in Themis-deficient CD8+ T cells, thereby impairing differentiation of exhausted T cell precursors (T-pex) and maintenance of terminally exhausted T cells (T-ex), respectively. Mechanistically, Themis initially promotes TCR signaling to induce PD-1 expression and subsequently mediates PD-1 signaling. In the latter, Themis binds to PD-1 and promotes PD-1 phosphorylation and its recruitment of SHP2, thereby acting as a negative regulator to inhibit T cell effector functions. Without Themis, the orderly regulation of TCR and PD-1 signaling, and therefore exhaustion, is disrupted. Thus, our results unequivocally demonstrate that Themis-mediated early TCR signaling plays a decisive role in T cell exhaustion and provide a novel mechanism of PD-1 signaling through Themis.

immunology↗

bioRxiv2021

A tau class Glutathione-S-Transferase (OsGSTU5) acts as a negative regulator of VirE2 interaction with T-DNA during Agrobacterium infection in rice

During Agrobacterium-mediated transformation (AMT), T-DNA along with several virulence proteins like VirD2, VirE2, VirE3, VirD5, and VirF enter into the plant cytoplasm. VirE2 is supposed to serve as single-stranded DNA binding (SSB) protein and assist the cytoplasmic trafficking of T-DNA inside the host cell. In the present study, a rice glutathione-S-transferase (OsGSTU5) that interacts with VirE2 protein in plant cytoplasm has been identified. OsGSTU5 is observed to be involved in post-translational glutathionylation of VirE2 protein (gVirE2). In silico analysis revealed that gVirE2+ssDNA complex is structurally less stable than VirE2+ ssDNA complex. The gel shift activity confirms the attenuated SSB property of gVirE2 over VirE2 protein under in vitro condition. Moreover, knock-down and overexpression OsGSTU5 phenotypes of rice showed increased and decreased T-DNA expression, respectively after Agrobacterium infection. The present finding convincingly establishes the role of OsGSTU5 as defense protein in rice that can further serve as an important target for modulation of AMT efficiency in rice.

plant biology↗

bioRxiv2021

A photoswitchable GPCR-based opsin for presynaptic silencing

Optical manipulations of genetically defined cell types have generated significant insights into the dynamics of neural circuits. While optogenetic activation has been relatively straightforward, rapid and reversible synaptic inhibition has been far more difficult to achieve. Instead of relying on unpredictable ion manipulations or slow photoactivatable toxins at axon terminals, we took a different approach to leverage the natural ability of inhibitory presynaptic GPCRs to silence synaptic transmission. Here we characterize parapinopsin (PPO), a photoswitchable non-visual opsin from lamprey pineal gland that couples to Gi/o-signaling cascades. PPO can be rapidly activated by pulsed blue light, switched off with amber light, and is effective for repeated or prolonged inhibition. We developed viral vectors for cell-specific expression of PPO, which traffics very effectively in numerous neuron types. At presynaptic terminals, PPO can silence glutamate release and suppress dopamine-dependent reward and cocaine place preference behaviors in vivo. PPO immediately fills a significant gap in the neuroscience toolkit for rapid and reversible synaptic inhibition, and has broader utility for achieving spatiotemporal control of inhibitory GPCR signaling cascades in other biological and pharmacological applications.

neuroscience↗