Biology subjects

Thakkar, D.

Publications and source records attributed to Thakkar, D..

6 recordsLinked to original sources

bioRxiv2026

A targetable opioid/cancer associated fibroblast axis drives extracellular matrix remodeling and tumor aggressiveness in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is an intractable disease with few effective treatment options. PDAC is characterized by a dense, fibro-inflammatory tumor microenvironment (TME) consisting mainly of cancer-associated fibroblasts (CAFs) and a CAF-generated collagen-rich extracellular matrix (ECM). As the ECM has profound impacts on tumor progression and therapy response, it is critical that we understand the mechanisms underlying ECM deposition and remodeling. In addition to a highly fibrotic and reactive TME, a hallmark of PDAC is pain. 93% of PDAC patients experience pain, and [~]70% are prescribed opioids for pain management during the course of their cancer treatment. Despite epidemiological evidence linking opioid use with diminished patient survival, how opioids impact tumor biology remains largely unknown. We now provide evidence that both endogenous and exogenous opioids drive ECM remodeling in the PDAC TME. We find that the commonly prescribed opioid morphine promotes the development of poorly differentiated tumors and increases collagen bundling and maturation in a mouse model of PDAC. Accordingly, RNA sequencing reveals that morphine induces significant upregulation of ECM genes and collagen modifying enzymes. We developed a morphine-induced gene signature which correlates significantly with the basal/mesenchymal subtypes of human PDAC and predicts worse overall survival in PDAC and other tumor types. Mechanistically, pharmacological inhibition and genetic knockdown of the mu opioid receptor (OPRM1) in CAFs attenuates expression of type 1a and type 3a collagens, and the myofibroblastic CAF marker alpha-SMA, demonstrating that opioid signaling is a direct regulator of CAF biology. Additionally, we provide the first evidence that CAFs produce endogenous opioids capable of activating OPRM1 and driving collagen expression. Finally, treatment with the FDA-approved peripherally restricted OPRM1 antagonist methylnaltrexone (MNTX) reduces desmoplasia, tumor weight, and ascites burden in a mouse model of PDAC. Therefore, we have identified a novel opioid-mediated signaling axis driving PDAC desmoplasia and reveal MNTX as a potential therapeutic to inhibit both exogenous and endogenous opioid-induced ECM remodeling and tumor aggressiveness.

cancer biology↗

bioRxiv2025

Dengue virus suppression by 25-hydroxycholesterol is mediated by a combination of membrane fusion inhibition, innate immune activation and cholesterol biosynthesis dysregulation

Physicochemical properties and composition of cellular membranes are crucial for regulating broad cellular responses including signaling and defense against pathogens. Dengue virus (DENV) exploits cholesterol-rich membranes and host lipid pathways, such as cholesterol biosynthesis, lipid raft organization, and lipid droplet formation, for entry, replication, and assembly. Additionally, lipid-based plasma membrane signaling can trigger innate immune responses that attenuate viral growth, underscoring the dual role of lipids in facilitating and restricting DENV infection. Here, we demonstrate that 25-hydroxycholesterol (25-HC), an oxidized cholesterol metabolite, inhibits DENV infection through a multifaceted mechanism. 25-HC disrupts viral membrane fusion by altering cholesterol distribution and lipid raft organization, impairing the binding and fusion of the DENV envelope (E) protein with host membranes. Additionally, 25-HC modulates host cholesterol metabolism by suppressing biosynthesis pathways essential for viral replication while enhancing lipid droplet formation and stress-response pathways. Transcriptomic analyses reveal that 25-HC primes innate immune responses, activating proinflammatory pathways such as the NLRP3 inflammasome and MAPK signaling, while selectively modulating interferon-stimulated gene expression. Notably, 25-HC exhibits synergistic antiviral effects when combined with direct-acting antivirals like Remdesivir, underscoring its potential in combination therapies. These findings establish 25-HC as a promising candidate for host-directed antiviral strategies against DENV and other enveloped viruses.

cell biology↗

bioRxiv2025

VISTA-induced tumor suppression by a four amino acid intracellular motif

VISTA is a key immune checkpoint receptor under investigation for cancer immunotherapy; however, its signaling mechanisms remain unclear. Here we identify a conserved four amino acid (NPGF) intracellular motif in VISTA that suppresses cell proliferation by constraining cell-intrinsic growth receptor signaling. The NPGF motif binds to the adapter protein NUMB and recruits Rab11 endosomal recycling machinery. We identify and characterize a class of triple-negative breast cancers with high VISTA expression and low proliferative index. In tumor cells with high VISTA levels, the NPGF motif sequesters NUMB at endosomes, which interferes with epidermal growth factor receptor (EGFR) trafficking and signaling to suppress tumor growth. These effects do not require canonical VISTA ligands, nor a functioning immune system. As a consequence of VISTA expression, EGFR receptor remains abnormally phosphorylated and cannot propagate ligand-induced signaling. Mutation of the VISTA NPGF domain reverts VISTA-induced growth suppression in multiple breast cancer mouse models. These results define a mechanism by which VISTA represses NUMB to control malignant epithelial cell growth and signaling. They also define distinct intracellular residues that are critical for VISTA-induced cell-intrinsic signaling that could be exploited to improve immunotherapy.

cancer biology↗

bioRxiv2022

Intragastric administration of low-dose rotenone post-colitis exacerbates damage to the nigrostriatal dopaminergic system in Parkinson's disease: The pace accelerates even more

BackgroundThe contribution of gastrointestinal (GI) inflammation and local exposure to neurotoxins in the gut offers the most in-depth explanation of Parkinsons disease (PD) etiopathogenesis through abnormal accumulation and spreading of alpha-synuclein (-syn) aggregates from the gut to the brain. ObjectivesThis study was designed to investigate whether dextran sodium sulfate (DSS)-mediated colitis may have lasting effects on dopaminergic pathways in the brain and whether or not colitis exacerbated susceptibility to later exposure to the neurotoxin rotenone. MethodsTo induce chronic colitis, 10 months old C57BL/6 mice were pre-exposed to 3 cycles of 7 days of 1% (w/v) DSS administration in drinking water followed by 14 days of regular drinking water. After colitis-induction, animals received a low dose of intragastric rotenone for the next 8 weeks, followed by testing for Parkinsonian behavior and GI phenotypes of inflammation. At the end of the 8th week after colitis, colon, brain stem, and midbrain tissue were isolated and analyzed for -syn, inflammatory markers, and dopaminergic neuronal loss. Gut microbial composition was assessed by 16S rRNA sequencing analysis. ResultsWe found that local rotenone exposure for 8 weeks did not affect colitis severity and colonic tight junction(TJ) protein expression (ZO-1, Occludin, and Claudin-1). On the other hand, we found that while eight weeks of chronic rotenone administration led to an increase in inflammatory markers, the presence of pre-existing colitis resulted in a considerable change in gut microbiota composition and a decrease in TJs protein expression. In addition, the administration of rotenone in mice post-colitis caused gastrointestinal function impairment and poor behavioral performances. Itworsened rotenone-induced -syn pathology in the colon, which extended upward and resulted in severe dopaminergic neuron loss and significant astroglia activation in the dorsal motor nucleus of the vagus (DMV), locus coeruleus, substantia nigra as well as in striatum. Interestingly, in the case of rotenone alone, we found that -syn induced ChAT+ neuronal death is restricted to the DMV. These findings indicate that long-term rotenone exposure in conjunction with early inflammatory intestinal milieu exacerbates the progression of -syn pathology and aggravates neurodegeneration in the intragastric mouse PD model. ConclusionsThis work provides detailed insight into the involvement of GI inflammation triggered after a neurotoxic insult in the colon and explores their potential to impact central dopaminergic degeneration in PD. This way, we can identify potential therapeutic targets that stop the enteric inflammatory processes involved in progressing PD. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=170 HEIGHT=200 SRC="FIGDIR/small/521569v1_ufig1.gif" ALT="Figure 1"> View larger version (58K): org.highwire.dtl.DTLVardef@e0b5a4org.highwire.dtl.DTLVardef@b556c0org.highwire.dtl.DTLVardef@1526d27org.highwire.dtl.DTLVardef@7c506f_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LILow-dose intragastric rotenone post-colitis aggravates gastrointestinal dysfunction and accelerates the onset of motor impairment. C_LIO_LILow-dose intragastric rotenone did not alter colitis clinical and histological aspects. C_LIO_LILow-dose intragastric rotenone post-colitis exacerbated the progression of -syn pathology from the GI tract to the brain, leading in central dopaminergic neuronal degeneration. C_LI

neuroscience↗

bioRxiv2020

The Fc-mediated effector functions of a potent SARS-CoV-2 neutralizing antibody, SC31, isolated from an early convalescent COVID-19 patient, are essential for the optimal therapeutic efficacy of the antibody

SARS-CoV-2-neutralizing antibodies are promising therapeutics for COVID-19. However, little is known about the mechanisms of action of these antibodies or their effective dosing windows. We report the discovery and development of SC31, a potent SARS-CoV-2 neutralizing IgG1 antibody, originally isolated from a convalescent patient at day 27 after the onset of symptoms. Neutralization occurs via a binding epitope that maps within the ACE2 interface of the SARS-CoV-2 Spike protein, conserved across all common circulating SARS-CoV-2 mutants. In SARS-CoV-2 infected K18-human ACE2 transgenic mice, SC31 demonstrated potent survival benefit by dramatically reducing viral load concomitant with attenuated pro-inflammatory responses linked to severe systemic disease, such as IL-6. Comparison with a Fc-null LALA variant of SC31 demonstrated that optimal therapeutic efficacy of SC31 requires intact Fc-mediated effector functions that can further induce an IFN{gamma}-driven anti-viral immune response. Dose-dependent efficacy for SC31 was observed down to 5mg/kg when dosed before the activation of lung inflammatory responses. Importantly, despite Fc{gamma}R binding, no evidence of antibody dependent enhancement was observed with the Fc-competent SC31 even at sub-therapeutic doses. Therapeutic efficacy was confirmed in SARS-CoV-2-infected hamsters, where SC31 again significantly reduced viral load, decreased lung lesions and inhibited progression to severe disease manifestations. This study underlines the potential for significant COVID-19 patient benefit for the SC31 antibody that justifies rapid advancement to the clinic, as well as highlighting the importance of appropriate mechanistic and functional studies during development. One Sentence SummaryAnti-SARS-CoV-2 IgG1 antibody SC31 controls infection in vivo by blocking SP:ACE2 binding and triggering a Fc-mediated anti-viral response.

microbiology↗

bioRxiv2018

Estimating Optimal Lysogenic Propensity for Viruses in Stressed Environments

Abstract.Having infected a bacterial cell, a temperate phage has to make a choice between (a) integrating itself into the bacterial genome, i.e. lysogeny, and (b) using the bacterial machinery to create multiple copies of itself and lysing the cell in the process, i.e. lysis. In order to maximize its long-term growth rate, phages need to ensure that they do not wipe off their bacterial hosts. Temperate phages have been observed to exhibit lysogenic propensities dependent on the MoI (Multiplicity of Infection), among other factors. We propose a model to estimate the propensity of lysogeny opted for by the phages in order to maximize coexistence. One possible approach to do so is to adopt a strategy that would help to attain and maintain an approximately equal proportion of phages with respect to their host. We find that the optimal fraction of phages opting for lysogeny follows a sigmoidal relationship with the MoI and is comparable to results obtained experimentally. We further assess the impact of phage and bacterial environmental stresses on the lysogenic propensity. Our results indicate that the optimal value of lysogenic propensity is greatly dependent on the intensity of these stresses.

systems biology↗