Biology subjects

Gokhale, R. S.

Publications and source records attributed to Gokhale, R. S..

10 recordsLinked to original sources

bioRxiv2024

PPARγ mediated enhanced lipid biogenesis fuels Mycobacterium tuberculosis growth in hepatocytes.

Mycobacterium tuberculosis (Mtb) infection of the lungs, besides producing prolonged cough with mucus, also causes progressive fatigue and cachexia with debilitating loss of muscle mass. While anti-tuberculosis (TB) drug therapy is directed toward eliminating bacilli, the treatment regimen ignores the systemic pathogenic derailments that probably dictate TB-associated mortality and morbidity. Presently, it is not understood whether Mtb spreads to metabolic organs and brings about these impairments. Here we show that Mtb creates a replication-conducive milieu of lipid droplets in hepatocytes by upregulating transcription factor PPAR{gamma} and scavenging lipids from the host cells. In hepatocytes, Mtb shields itself against the common anti-TB drugs by inducing drug-metabolizing enzymes. Infection of the hepatocytes in the in vivo aerosol mice model can be consistently observed post-week 4 along with enhanced expression of PPAR{gamma} and drug-metabolizing enzymes. Moreover, histopathological analysis indeed shows the presence of Mtb in hepatocytes along with granuloma-like structures in human biopsied liver sections. Hepatotropism of Mtb during the chronic infectious cycle results in immuno-metabolic dysregulation that could magnify local and systemic pathogenicity, altering clinical presentations.

microbiology↗

bioRxiv2023

A hepatocyte-specific transcriptional program driven by Rela and Stat3 exacerbates experimental colitis in mice by modulating bile synthesis

Hepatic factors secreted by the liver promote homeostasis and are pivotal for maintaining the liver-gut axis. Bile acid metabolism is one such example wherein, bile acid synthesis occurs in the liver and its biotransformation happens in the intestine. Dysfunctional interactions between the liver and the intestine stimulate varied pathological outcomes through its bidirectional portal communication. Indeed, aberrant bile acid metabolism has been reported in inflammatory bowel disease (IBD). However, the molecular mechanisms underlying these crosstalks that perpetuate intestinal permeability and inflammation remain obscure. Here, we identify a novel hepatic gene program regulated by Rela and Stat3 that accentuates the inflammation in an acute experimental colitis model. Hepatocyte-specific ablation of Rela and Stat3 reduces the levels of primary bile acids in both the liver and the gut and shows a restricted colitogenic phenotype. On supplementation of chenodeoxycholic acid (CDCA), knock-out mice exhibit enhanced colitis-induced alterations. This study provides persuasive evidence for the development of multi-organ strategies for treating IBD and identifies a hepatocyte-specific rela-stat3 network as a promising therapeutic target.

immunology↗

bioRxiv2023

Melanocytes Exhibit Distinct Cell States Governed by A Gene Regulatory Network Under Stochastic Influence

Melanocytes serve as a protector of the skin against external stressors such as ultraviolet radiations. While melanocytes remain functional for nearly the entire lifespan of an individual, how they respond efficiently and survive such insults remain elusive. Here, we show the co-existence of multiple distinct states of normal human epidermal melanocytes (NHEMs). Using a progressive pigmentation model, we show that stochasticity in gene expression can lead to the co-existence of multiple melanocyte states. Using active enhancers and gene expression footprint, we identified state-specific transcription factors and constructed a gene regulatory network (GRN). The GRN couples pigmentation and cell cycle regulators and explains the co-existence and transitions of the melanocyte states. Finally, we show that NHEMs respond to external cues by altering the cell state dynamics. These results demonstrate that stochasticity in gene expression followed by epigenetic modification leads to the co-existence of multiple melanocyte states enabling an efficient response to environmental cues.

cell biology↗

bioRxiv2022

Whole exome-sequencing of vitiligo lesions indicate lower burden of somatic variations: implications in risk for non-melanoma skin cancers

Mapping of somatic variations has enabled understanding the progression of clonal variations from healthy skin to cutaneous malignancies. Highlighting, the adaptive nature of pigmentation, germline mutations in albinism amplify skin cancer susceptibility. However, lower incidence of non-melanoma skin cancer among subjects with acquired depigmenting skin disorder vitiligo is enigmatic and a matter of longstanding debate. To address this, we performed high-coverage exome sequencing of matched non-lesional and lesional vitiligo skin along with whole blood to account for germline variations. Our analysis suggests lower burden of somatic cancer-associated variations in exposed depigmented lesional skin compared to the non-lesional skin. A detailed investigation of vitiligo skin transcriptome reveals elevation of DNA repair and cell-proliferation pathways. Validation by comet-assay for DNA damage and cell cycle analysis of epidermal cells suggest undamaged DNA in vitiligo lesions that could be attributed to higher proliferation-coupled repair. Endorsing this, UV-signature variations are not prominent, instead SBS5 associated with endogenous mutational processes is conspicuous in both the vitiligo tissues. Our systematic pilot study indicates lower somatic mutation burden in vitiligo skin and supports the earlier demographic observation on lower risk of non-melanoma skin cancer in vitiligo subjects, providing an opportunity to learn strategies for cancer prevention from vitiligo. Brief SummaryVitiligo skin harbors decreased somatic variation burden in cancer-associated genes and a concomitant augmentation in DNA repair response, explaining the lower incidence of cutaneous malignancies.

genomics↗

bioRxiv2022

Sustained pigmentation causes DNA damage and invokes translesion polymerase Pol κ for repair in melanocytes

The pigment melanin protects skin cells from ultraviolet (UV) radiation induced DNA damage. However, intermediates of eumelanin are highly reactive quinones that are potentially genotoxic. In this study, we systematically investigate the effect of sustained elevation of melanogenesis and map the consequent cellular repair response of melanocytes. Pigmentation increases DNA damage, causes cell cycle arrest, and invokes translesion polymerase Pol {kappa} for DNA repair in primary human melanocytes, as well as mouse melanoma cells. Confirming the causal link, CRISPR-based genetic ablation of tyrosinase, the key melanin synthesizing enzyme results in depigmented cells with low Pol {kappa} levels. However, silencing of Pol {kappa} in pigmenting cells results in unchecked proliferation despite the presence of damaged DNA, that could potentially lead to genome instability. Thereby, our results indicate Pol {kappa} to be a necessary evil to resolve melanin induced damage. Error-prone repair by Pol {kappa} in part explains the mutational landscape observed in human melanoma. Thus, our study illuminates a hitherto unknown dark side of melanin and identifies (eu)melanogenesis as a key missing link between tanning response and mutagenesis mediated via the Pol {kappa}-based low fidelity DNA repair response of melanocytes. Key HighlightsO_LISustained melanogenesis causes DNA damage in melanocytes C_LIO_LIMelanogenesis elicits replication stress and translesion repair by Pol {kappa} C_LIO_LIPol {kappa} resolves melanin-induced DNA damage and suppresses genome instability C_LIO_LIExpression of Pol {kappa} correlates with mutational load in human melanoma C_LI

cell biology↗

bioRxiv2021

A universal pocket in FAALs ensures redirection of fatty acid pool away from CoA-based activation

Fatty acyl-AMP ligases (FAALs) channelize fatty acids towards biosynthesis of virulent lipids in mycobacteria and other pharmaceutically or ecologically important polyketides and lipopeptides in other microbes. They do so by bypassing the ubiquitous coenzyme A-dependent activation and rely on the acyl carrier protein-tethered 4-phosphopantetheine (holo-ACP). The molecular basis of how FAALs strictly reject chemically identical and abundant acceptors like coenzyme A (CoA) and accept holo-ACP unlike other members of the ANL superfamily remains elusive. We show FAALs have plugged the promiscuous canonical CoA-binding pockets and utilize highly selective alternative binding sites. These alternative pockets can distinguish adenosine 3, 5-bisphosphate-containing CoA from holo-ACP and thus FAALs can distinguish between CoA and holo-ACP. These exclusive features helped identify the omnipresence of FAAL-like proteins and their emergence in plants, fungi, and animals with unconventional domain organisations. The universal distribution of FAALs suggests they are parallelly evolved with FACLs for ensuring a CoA-independent activation and redirection of fatty acids towards lipidic metabolites.

biochemistry↗

bioRxiv2021

Temporal resolution of melanogenesis determine fatty acid metabolism as key skin pigment regulator

Therapeutic methods to modulate skin pigmentation has important implications for skin cancer prevention and for treating meta-inflammatory-triggered cutaneous conditions. Modulators of cAMP signalling of melanocyte have met with minimal clinical efficacy. Towards defining new potential targets, we followed temporal dynamics orchestrating melanocyte differentiation by using a cell-autonomous pigmentation model. Our study elucidates three dominant phases of synchronized metabolic and transcriptional reprogramming. The induction phase is concomitant with a paradoxical decrease in MITF levels, reduced proliferation, and increased anabolic metabolism mediated by AKT phosphorylation. The melanogenic phase shows rapid uptake of glucose and fatty acid, transiently forming lipid droplets through SREBF1-mediated regulation of fatty acid metabolism. This heightened bioenergetic activity impairs mitochondria and the recovery phase is marked by a shift to aerobic glycolysis and activation of the NRF2 detoxication pathway. Finally, we show that inhibitors of lipid metabolism indeed resolve hyper-pigmentary conditions in a guinea pig UV-tanning model. Our studies reveal metabolic control mechanisms of melanocytes that could govern the balance between differentiation and proliferation in a variety of cutaneous diseases.

cell biology↗

bioRxiv2021

kinesin recruitment by adapter SKIP on melanosomes is dynamically controlled by LC3B phosphorylation

Anterograde melanosome transport is essential for adaptive skin tanning response. However, the molecular components involved, their interplay and regulation by external cues in melanosome transport remain under-explored. Silencing of kinesin motors revealed that several members including the established KIF5B and a novel candidate KIF1B, mediate melanosome movement. The camouflage behaviour of zebrafish embryos induced by incident light or -MSH requires kif1b, suggesting a conserved melanosome transport machinery across vertebrates. Interestingly, the peri-nuclear melanosome accumulation upon kinesin knockdown is recapitulated by the silencing of autophagy effector MAP1LC3B (LC3B). Pull-down assays identified KIF1B, but not KIF5B, to be the LC3B-associated kinesin. LC3B binds the adapter SKIP via its LIR docking region that is proximal to Thr12 residue, a site for phosphorylation by Protein Kinase A. We demonstrate that phosphorylation of LC3B at Thr12 is stimulated by -MSH, which potentiates the anterograde melanosome transport. Thereby, our study, identifies a novel kinesin motor KIF1B for melanosome movement and establishes LC3B as the key molecular component that facilitates -MSH responsive mobilization of melanosomes. Key HighlightsO_LIKinesin screen reveals non-redundant use of KIF5B, KIF1B motors for melanosome transport C_LIO_LIkif1b is required for camouflage response in zebrafish and melanosome movement in mammals C_LIO_LIN-terminal region of LC3B interacts with adapter SKIP and couples kinesin KIF1B C_LIO_LI-MSH activates PKA-mediated phosphorylation of LC3B to potentiate anterograde movement C_LI SignificanceMelanosomes are lysosome related organelles containing melanin pigment, that are synthesized in melanocytes and transferred to the recipient keratinocytes of skin. This involves long range melanosome movement within melanocytes to reach cell periphery for the transfer to follow. Physiologically, UV protection involves local secretion of melanocyte stimulating hormone (-MSH) that acts on melanocytes to promote skin tanning response. Herein, we investigate the components involved in this process and establish that the melanosome movement is dynamically controlled by -MSH through phosphorylation of LC3B. These findings establish the mechanism behind the rapid distribution of melanosomes during tanning response and provide opportunity to intervene for sun protection.

cell biology↗

bioRxiv2019

Histone code dictates fate biasing of neural crest cells to melanocyte lineage

In the neural crest lineage, progressive fate-restriction and stem cell assignment are critical for both development and regeneration. While the fate-commitment events have distinct transcriptional footprints, fate-biasing is often transitory and metastable, and is thought to be moulded by epigenetic programs. Hence molecular basis of specification is difficult to define. In this study, we establish a role of a histone variant H2a.z.2 in specification of melanocyte lineage from multipotent neural crest cells. Silencing of H2a.z.2 reduces the number of melanocyte precursors in developing zebrafish embryos, and from mouse embryonic stem cells in vitro. We demonstrate that this histone variant occupies nucleosomes in the promoter of key melanocyte determinant Mitf, and enhances its induction. CRISPR-Cas9 based targeted mutagenesis of this gene in zebrafish drastically reduces adult melanocytes, as well as their regeneration. Thereby our study establishes a histone based specification code upstream to the core gene regulatory network in the neural crest lineage of melanocytes. This epigenetic code renders a poised state to the promoter of key determinant and enhances activation by external instructive signals thereby establishing melanocyte fate identity.

developmental biology↗

bioRxiv2019

pH controlled histone acetylation amplifies melanocyte differentiation program downstream of MITF

Tanning response and melanocyte differentiation are mediated by the central transcription factor MITF. Enigmatically, these involve rapid and selective induction of melanocyte maturation genes, while concomitantly maintaining the expression of other effectors. In this study using cell-based and zebrafish model systems, we elucidate a pH mediated feed-forward mechanism of epigenetic regulation that enables selective amplification of melanocyte maturation program. We demonstrate that MITF activation directly elevates the expression of Carbonic Anhydrase 14 (Ca14) enzyme. Nuclear localized Ca14 increases the intracellular pH, resulting in the activation of histone acetyl transferase activity of p300/CBP. In turn enhanced H3K27 histone acetylation marks of select differentiation genes facilitates their amplified expression by MITF. CRISPR-mediated targeted missense mutation of CA14 in zebrafish results in immature acidic melanocytes with decreased pigmentation, establishing the centrality of this mechanism in rapidly activating melanocyte differentiation. Thereby we reveal a novel epigenetic control through pH modulation that reinforces a deterministic cell fate by altering chromatin dynamics.

cell biology↗