Biology subjects

Kumar, R.

Publications and source records attributed to Kumar, R..

At least 217 records · Page 12Linked to original sources

bioRxiv2022

The orphan ligand, Activin C, signals through activin receptor-like kinase 7

Activin ligands are formed from two disulfide-linked inhibin {beta} subunit chains. They exist as homodimeric proteins, as in the case of activin A (ActA; Inh{beta}A/Inh{beta}A) or activin C (ActC; Inh{beta}C/Inh{beta}C), or as heterodimers, as with activin AC (ActAC; Inh{beta}A:Inh{beta}C). While the biological functions of ActA and activin B (ActB) have been well-characterized, little is known about the biological function of ActC or ActAC. One thought is that the Inh{beta}C chain functions to interfere with ActA production by forming less active ActAC heterodimers. Here, we assessed and characterized the signaling capacity of ligands containing the Inh{beta}C chain. ActC and ActAC activated SMAD2/3-dependent signaling via the type I receptor, activin receptor-like kinase 7 (ALK7). Relative to ActA and ActB, ActC exhibited lower affinity for the cognate activin type II receptors and was resistant to neutralization by the extracellular antagonist, follistatin. In mature adipocytes, which exhibit high ALK7 expression, ActC elicited a SMAD2/3 response similar to ActB, which can also signal via ALK7. Collectively, these results establish that ActC and ActAC are active ligands that exhibit a distinct signaling receptor and antagonist profile compared to other activins.

biochemistry↗

bioRxiv2022

A pathogenicity locus of Streptococcus gallolyticus subspecies gallolyticus

Streptococcus gallolyticus subspecies gallolyticus (Sgg) is known to be strongly associated with colorectal cancer (CRC). Recent functional studies further demonstrated that Sgg actively stimulates CRC cell proliferation and promotes the development of colon tumors. However, the Sgg factors important for the pro-proliferative and pro-tumor activities of Sgg remain unclear. Here, we identified a chromosomal locus in Sgg strain TX20005. Deletion of this locus significantly reduced Sgg adherence to CRC cells and abrogated the ability of Sgg to stimulate CRC cell proliferation. Thus, we designate this locus as the Sgg pathogenicity-associated region (SPAR). More importantly, we found that SPAR is important for Sgg pathogenicity in vivo. In a gut colonization model, mice exposed to the SPAR deletion mutant showed significantly reduced Sgg load in the colonic tissues and fecal materials, suggesting that SPAR contributes to the colonization capacity of Sgg. In a mouse model of CRC, deletion of SPAR abolished the ability of Sgg to promote the development of colon tumors growth. Taken together, these results highlight SPAR as a critical pathogenicity determinant of Sgg.

microbiology↗

bioRxiv2022

Modulation of the extracellular matrix by Streptococcus gallolyticus subsp. gallolyticus and importance in cell proliferation

Streptococcus gallolyticus subspecies gallolyticus (Sgg) has a strong clinical association with colorectal cancer (CRC) and actively promotes the development of colon tumors. Previous work showed that this organism stimulates CRC cells proliferation and tumor growth. However, the molecular mechanisms underlying these activities are not well understood. Here, we found that Sgg upregulates the expression of several types of collagens in HT29 and HCT116 cells, with type VI collagen (ColVI) being the highest upregulated collagen type. Knockdown of ColVI abolished the ability of Sgg to induce cell proliferation and reduced the adherence of Sgg to CRC cells. The extracellular matrix (ECM) is an important regulator of cell proliferation. Therefore, we further examined the role of decellularized matrix (dc-matrix), which is free of live bacteria or cells, in Sgg-induced cell proliferation. Dc-matrix prepared from Sgg-treated cells showed a significantly higher pro-proliferative activity than that from untreated cells or cells treated with the control bacteria. On the other hand, dc-matrix from Sgg-treated ColVI knockdown cells showed no difference in the capacity to support cell proliferation compared to that from untreated ColVI knockdown cells, suggesting that the ECM by itself is a mediator of Sgg-induced cell proliferation. Furthermore, Sgg-treated CRC cells formed significantly larger tumors in vivo, whereas Sgg treatment had no effect on ColVI knockdown cells, suggesting that ColVI is important for Sgg to promote tumor growth in vivo. These results highlight a dynamic bidirectional interplay between Sgg and the ECM, where Sgg upregulates collagen expression. The Sgg-modified ECM in turn affects the ability of Sgg to adhere to host cells and more importantly, acts as a mediator for Sgg-induced CRC cell proliferation. Taken together, our results reveal a novel mechanism in which Sgg stimulates CRC proliferation through modulation of the ECM. Author SummaryColorectal cancer (CRC) is a leading cause of cancer-related death. The development of CRC can be strongly influenced by specific gut microbes. Understanding how gut microbes modulate CRC is critical to developing novel strategies to improve clinical diagnosis and treatment of this disease. S. gallolyticus subsp. gallolyticus (Sgg) has a strong clinical association with CRC and actively promotes the development of colon tumors. However, the mechanisms Sgg utilizes to promote tumors are not well understood. Our results showed for the first time a dynamic interplay between Sgg and the extracellular matrix. We found that Sgg upregulates the expression of collagens which in turn affects the interaction between Sgg and CRC cells and mediates CRC cell proliferation. These findings draw attention to a previously unrecognized dynamic bidirectional interplay between a CRC-associated microbe and the extracellular matrix (ECM). Given the importance of the ECM in normal homeostasis and in tumor microenvironment, these findings have important implications in the context of microbial contribution to cancer.

microbiology↗

bioRxiv2022

Inter- and intra-Subunit interactions driving the MukBEF ATPase

MukBEF, an SMC-like protein complex, is the bacterial condensin. It is likely that it compacts DNA via an ATP hydrolysis-dependent, DNA loop-extrusion reaction as has been demonstrated for the yeast SMC proteins condensin and cohesin. MukB also interacts with the ParC subunit of the cellular chromosomal decatenase topoisomerase IV, an interaction that is required for proper chromosome condensation and segregation in E. coli, although it suppresses the MukB ATPase activity. We have investigated the MukBEF ATPase activity, identifying inter- and intra-subunit interactions by protein-protein crosslinking and site-specific mutagenesis. We show that interactions between the hinge of MukB and its neck region are essential for the ATPase activity, that the ParC subunit of Topo IV inhibits the MukB ATPase by preventing this interaction, that MukE interaction with DNA is likely essential for viability, and that interactions between MukF and the MukB neck region are necessary for ATPase activity and viability.

biochemistry↗

bioRxiv2022

Hippo Signaling Cofactor, WWTR1, at the Crossroads of Human Trophoblast Progenitor Self-Renewal and Differentiation.

Healthy progression of human pregnancy relies on cytotrophoblast progenitor (CTB) self-renewal and their differentiation towards multi-nucleated syncytiotrophoblasts (STBs) and invasive extravillous trophoblasts (EVTs). However, underlying molecular mechanisms that fine-tune CTB self-renewal or direct their differentiation towards STBs or EVTs during human placentation are poorly defined. Here, we show that hippo signaling cofactor WW Domain Containing Transcription Regulator 1 (WWTR1) is a master regulator of trophoblast fate choice during human placentation. Using human trophoblast stem cells (human TSCs), primary CTBs and human placental explants, we demonstrate that WWTR1 promotes self-renewal in human CTBs and is essential for their differentiation to EVTs. In contrast, WWTR1 prevents induction of STB fate in undifferentiated CTBs. Our single-cell RNA-sequencing analyses in first-trimester human placenta along with mechanistic analyses in human TSCs revealed that WWTR1 fine-tunes trophoblast fate by directly regulating Wnt signaling components. Importantly, our analyses of placentae from pathological pregnancies show that extreme preterm birth (gestational time [≤]28weeks) and intrauterine growth restriction along with preeclampsia (IUGR/PE) are often associated with loss of WWTR1 expression in CTBs. In summary, our findings establish a critical importance of WWTR1 at the crossroads of human trophoblast progenitor self-renewal vs. differentiation. It plays positive instructive roles to promote CTB self-renewal and EVT differentiation and safeguards undifferentiated CTBs from obtaining the STB fate. SIGNIFICANCEHuman pregnancy relies on formation of the transient organ placenta and trophoblast cells are the major building blocks of the placenta. A defect in trophoblast progenitor self-renewal or their differentiation is associated with either pregnancy loss or pathological pregnancies, yet underlying molecular mechanisms that regulate trophoblast differentiation are poorly understood. In this study, we discovered that WWTR1, a transcription cofactor and a component of conserved Hippo signaling pathway, optimizes trophoblast progenitor self-renewal and is essential for their differentiation into the invasive extravillous trophoblast cell lineage. Our findings establish WWTR1 as a critical regulator for success in human placentation and progression of a healthy pregnancy.

developmental biology↗

bioRxiv2022

An innovative hematopoietic stem cell gene therapy approach benefits CLN1 disease in the mouse model

Hematopoietic stem and progenitor cells (HSPCs) can lead to the establishment of a long-lasting microglia-like progeny in the brain of properly myeloablated hosts. We exploited this approach to treat the severe CLN1 neurodegenerative disorder, which is the most aggressive form of neuronal ceroid lipofuscinoses, due to deficiency of palmitoyl-protein thioesterase 1 (hPPT1). We here provide first evidence that: i) transplantation of wild type HSPCs exerts a partial but long-lasting mitigation of the symptoms; ii) transplantation of HSPCs over-expressing hPPT1 by lentiviral gene transfer enhances therapeutic benefit as compared to wild type cell transplant, with first demonstration of such a dose-effect benefit for a purely neurodegenerative condition like CLN1 disease; iii) transplantation of hPPT1 over-expressing HSPCs by a novel intracerebroventricular (ICV) approach is sufficient to transiently ameliorate CLN1 disease symptomatology in the absence of hematopoietic tissue engraftment of the transduced cells; and iv) the combinatorial transplantation of transduced HSPCs intravenously and ICV results in the most robust therapeutic benefit among the tested approaches on both pre-symptomatic as well as symptomatic animals. Overall, these findings provide first evidence of the efficacy and feasibility of this novel approach to treat CLN1 disease and possibly other neurodegenerative conditions, paving the way for its future clinical application.

neuroscience↗

bioRxiv2022

Sex differences in insular gyri responses to the cold pressor challenge

IntroductionSex differences in autonomic control may contribute to physiological sex differences in cardiovascular disease, thermoregulation, and the experience of pain. We previously showed sex differences in functional mapping of autonomic responses across the insula, a central autonomic control region. Anterior insula response patterns to sympathetic activation (Valsalva) and parasympathetic withdrawal (handgrip) differed between men and women. We here assessed sex differences in autonomic insula gyrus responses to a cold pressor challenge, which involves temperature and pain regulation. MethodsFunctional MRI (fMRI) involved a 1-minute right-foot cold pressor challenge in 22 women (age; mean{+/-}std: 50{+/-}4 yrs), and 39 men (45{+/-}3 yrs). Regions of interest (ROI) comprised left and right anterior short gyrus (ASG), middle short gyrus (MSG), posterior short gyrus (PSG), anterior long gyrus (ALG), and posterior long gyrus (PLG). Two-second time intervals of fMRI signal responses per ROI and concurrently recorded heart rate and blood oxygen saturation (SaO2) were tested for within- and between-group effects over time (repeated measures ANOVA P[≤]0.05). We tested sex differences in 1) each ROI; 2) lateralization effects; and 3) posterior-to-anterior gradients in responses. ResultsNo sex differences emerged in heart rate or SaO2. Women showed larger signal changes in several gyri than men after cold pressor onset and offset. Most consistently, women showed a greater right-over-left hemisphere dominance in cold pressor response compared to men in the MSG, PSG and ALG. Greater right-over-left hemisphere anterior-to-posterior dominance was more pronounced in men. ConclusionsThe findings confirm anterior and right-hemispheric dominance of insular responses during sympathetic activation that includes pain and cold. Although distinct transient male-female differences in fMRI responses appeared during the cold pressor, unlike the Valsalva and handgrip, no sex differences in ASG lateralization emerged, suggesting that the previously found sex differences may not solely relate to regulating blood pressure responses.

neuroscience↗

bioRxiv2022

Sensory Schwann cells are required for mechanical nociception and touch perception

That sensory neurons alone transduce mechanical stimuli was challenged by the discovery of nociceptive Schwann cells that can initiate pain. Consistent with the existence of inherently mechanosensitive sensory Schwann cells, we found that the mechanosensory function of almost all nociceptors, including those signaling fast pain, were critically dependent on sensory Schwann cells. Furthermore, in polymodal nociceptors, sensory Schwann cells signal mechanical, but not cold or heat pain. Terminal Schwann cells also surround mechanoreceptor nerve-endings within the Meissners corpuscle and in at hair follicle lanceolate endings that both signal vibrotactile touch. Within Meissners corpuscles, two molecularly and functionally distinct sensory Schwann cells positive for Sox10 and Sox2 differentially modulate rapidly adapting mechanoreceptor function. Using optogenetics we show that Meissners corpuscle Schwann cells are necessary for the perception of low threshold vibrotactile stimuli. These results show that sensory Schwann cells within diverse glio-neural mechanosensory end-organs are sensors for mechanical pain as well as necessary for touch perception. Thus, specialized sensory Schwann are central to the transduction of mechanical forces that underpin somatic sensation.

neuroscience↗

bioRxiv2022

Activity and state dependent modulation of salt taste behavior in Drosophila melanogaster

Sodium present in NaCl is a fundamental nutrient required for many physiological processes. In animals, including Drosophila, low-salt concentrations induce attraction and high-salt concentrations evoke aversive behavior. Although the cellular basis of low and high salt taste detection has been described, the mechanisms regulating high salt consumption and salt taste modulation in animals remain elusive. Thus, we investigated the neural mechanisms behind high NaCl consumption in adult Drosophila, focusing on how flies adjust their acceptance of high salt based on their diet. Our findings show that long-term exposure to high salt increases the taste sensitivity of pharyngeal LSO neurons, which, in turn, enhances high salt intake. Exposing flies to a high NaCl diet for three days shows a decline in high salt aversion under starvation. Our results suggest that this modulation requires active LSO neurons and a starvation state or dopamine as genetic suppression of LSO pharyngeal neuronal activity in high NaCl-fed flies inhibit excessive salt intake. We also found that several independent taste receptor neurons and pathways are involved in such a modulation. Silencing any one of multiple LSO neuronal types inhibits excessive salt intake. Our study suggests that flies can adapt to the amount of salt ingested over several days, indicating the presence of a critical mechanism that resets the salt appetite and related neural circuits.

neuroscience↗

bioRxiv2022

A high-throughput approach to identify reproductive toxicants among environmental chemicals using an in vivo evaluation of gametogenesis in budding yeast Saccharomyces cerevisiae

BackgroundEnvironmental chemical exposures are likely making important contributions to current levels of infertility and its increasing incidence. Yet the US produces high volumes of industrial chemicals for which there is limited data on their potential human reproduction toxicity. Current assays typically used in policy and regulatory settings involve costly and timeconsuming whole-animal rodent tests which limit the rapidity with which one can assess the thousands of chemicals yet to be tested. ObjectiveOur aim was to develop a fast and reliable strategy to evaluate a large number of chemicals for reproductive toxicity by developing a high-throughput toxicity assessment using the yeast S. cerevisiae. MethodsYeast are chronically exposed to each environmental chemical at two doses, 30 M and 100 M, in a 96-well plate-based format throughout gametogenesis. Non-gametes are removed and chemicals are washed away before gamete viability is measured using absorbance at 600 nm to produce growth curves. The difference in time at half-maximal saturation with and without exposure is used to determine the extent of reproductive toxicity. ResultsWe validated our assay using bisphenol A (BPA), a well-established mammalian reproductive toxicant. We find that BPA in yeast has similar detrimental effects in meiosis as shown in worms and mammals. Competition assays with BPA analogs reveal that two of out of 19 BPA analogs examined (bisphenol E and 17{beta}-estradiol) show synergistic effects with BPA at doses tested and none show antagonistic effects. Out of 179 additional environmental chemicals, we designated 57 chemicals as reproductively toxic. Finally, by comparing chemicals in our cohort that have been evaluated for reproductive toxicity in mammalian studies, we find a statistically significant association between toxic chemicals in yeast and mammals. ConclusionWe show that a high-throughput assay using yeast may be a useful approach for rapidly and reliably identifying chemicals that pose a reproductive risk.

pharmacology and toxicology↗

bioRxiv2022

Ocimum sanctum, OscWRKY1, regulates phenylpropanoid pathway genes and promotes resistance to pathogen infection in Arabidopsis

WRKY transcription factor (TF) family regulates various developmental and physiological functions in plants. PAL genes encode enzymes which are involved in plant defense responses, but the direct regulation of PAL genes and phenylpropanoid pathway through WRKY TFs is not well characterized. In the present study, we have characterized an OscWRKY1 gene from O. sanctum which shows induced expression after methyl jasmonate (MeJA), salicylic acid (SA), and wounding. Recombinant OscWRKY1 protein binds to the W-box cis-element TTGAC[C/T] and activates the reporter gene in yeast. Overexpression of OscWRKY1 enhances Arabidopsis resistance towards Pseudomonas syringae pv. tomato Pst DC3000. Upstream activator sequences of PAL and C4H have identified the conserved W-box cis-element (TTGACC) in both O. sanctum and Arabidopsis. OscWRKY1 was found to interact with W-box cis-element present in the PAL and C4H promoters. Silencing of OscWRKY1 using VIGS resulted in reduced expression of PAL, C4H, COMT, F5H and 4CL transcripts. OscWRKY1 silenced plants exhibit reduced PAL activity, whereas, the overexpression lines of OscWRKY1 in Arabidopsis exhibit increased PAL activity. These results revealed that OscWRKY1 positively regulates the phenylpropanoid pathway genes and enhances the resistance against bacterial pathogen in Arabidopsis.

plant biology↗

bioRxiv2022

Comprehensive analysis of disease pathology in immunocompetent and immunocompromised hamster models of SARS-CoV-2 infection

The pathogenesis of SARS-CoV-2 in the context of a specific immunological niche is not fully understood. Here, we used a golden Syrian hamster model to systematically evaluate the kinetics of host response to SARS-CoV-2 infection, following disease pathology, viral loads, antibody responses, and inflammatory cytokine expression in multiple organs. The kinetics of SARS-CoV-2 pathogenesis and genomewide lung transcriptome was also compared between immunocompetent and immunocompromised hamsters. We observed that the body weight loss was proportional to the SARS-CoV-2 infectious dose and lasted for a short time only in immunocompetent hamsters. Body weight loss was more prominent and prolonged in infected immunocompromised hamsters. While the kinetics of viral replication and peak live viral loads were not significantly different at low and high infectious doses (LD and HD), the HD-infected immunocompetent animals developed severe lung disease pathology. The immunocompetent animals cleared the live virus in all tested tissues by 12 days post-infection and generated a robust serum antibody response. In contrast, immunocompromised hamsters mounted an inadequate SARS-CoV-2 neutralizing antibody response, and the virus was detected in the pulmonary and multiple extrapulmonary organs until 16 days post-infection. These hamsters also had prolonged moderate inflammation with severe bronchiolar-alveolar hyperplasia/metaplasia. Consistent with the difference in disease presentation, distinct changes in the expression of inflammation and immune cell response pathways and network genes were seen in the lungs of infected immunocompetent and immunocompromised animals. This study highlights the interplay between the kinetics of viral replication and the dynamics of SARS-CoV-2 pathogenesis at organ-level niches and maps how COVID-19 symptoms vary in different immune contexts. Together, our data suggest that the histopathological manifestations caused by progressive SARS-CoV-2 infection may be a better predictor of COVID-19 severity than individual measures of viral load, antibody response, and cytokine storm at the systemic or local (lungs) levels in the immunocompetent and immunocompromised hosts.

pathology↗

bioRxiv2021

Size-dependent secondary nucleation and amplification of α-synuclein amyloid fibrils

The size of the amyloid seeds is known to modulate their autocatalytic amplification and cellular toxicity. However, the seed size-dependent secondary nucleation mechanism, toxicity, and disease-associated biological processes mediated by -synuclein (-Syn) fibrils are largely unknown. Using the cellular model and in vitro reconstitution, we showed that the size of -Syn fibril seeds not only dictates its cellular internalization and associated cell death; but also the distinct mechanisms of fibril amplification pathways involved in the pathological conformational change of -Syn. Specifically, small-sized fibril seeds showed elongation possibly through monomer addition at the fibril termini; whereas longer fibrils template the fibril amplification by surface-mediated nucleation as demonstrated by super-resolution microscopy. The distinct mechanism of fibril amplification, and cellular uptake along with toxicity suggest that breakage of fibrils into different sizes of seeds determine the underlying pathological outcome of synucleinopathies.

neuroscience↗

bioRxiv2021

Improved binding affinity of the Omicron's spike protein with hACE2 receptor is the key factor behind its increased virulence

The new variant of SARS-CoV-2, Omicron, has been quickly spreading in many countries worldwide. Compared to the original virus, Omicron is characterized by several mutations in its genomic region, including spike proteins receptor-binding domain (RBD). We have computationally investigated the interaction between RBD of both wild-type and omicron variants with hACE2 receptor using molecular dynamics and MM-GBSA based binding free energy calculations. The mode of the interaction between Omicrons RBD to the human ACE2 (hACE2) receptor is similar to the original SARS-CoV-2 RBD except for a few key differences. The binding free energy difference shows that the spike protein of Omicron has increased binding affinity for the hACE-2 receptor. The mutated residues in the RBD showed strong interactions with a few amino acid residues of the hACE2. More specifically, strong electrostatic interactions (salt bridges) and hydrogen bonding were observed between R493 and R498 residues of the Omicron RBD with D30/E35 and D38 residues of the hACE2, respectively. Other mutated amino acids in the Omicron RBD, e.g. S496 and H505, also exhibited hydrogen bonding with the hACE2 receptor. The pi-stacking interaction was also observed between tyrosine residues (RBD-Tyr501: hACE2-Tyr41) in the complex, which contributes majorly to binding free energies suggesting this as one of the key interactions stabilizing the complex formation. The structural insights of RBD:hACE2 complex, their binding mode information and residue wise contributions to binding free energy provide insight on the increased transmissibility of Omicron and pave the way to design and optimize novel antiviral agents.

microbiology↗

bioRxiv2021

Application of sequence semantic and integrated cellular geography approach to study biogenesis of exonic circular RNA

BackgroundConcurrent existence of lncRNA and circular RNA at both nucleus and cytosol within a cell at different proportion is well reported. Secondly, information on genes transcribing both circular and lncRNAs along with total number of RBP binding sites for both of these RNA types is extractable from databases. This study showed how these apparently unconnected pieces of reports could be put together to build a model leading to biogenesis of circular RNA. ResultsAs a result of this study, a model was built under the premises that, sequences with special semantics were molecular precursors in biogenesis of circular RNA which occurred through catalytic role of some specific RBPs. The model outcome was further strengthened by fulfillment of three logical lemmas which were extracted and assimilated in this work using a novel data analytic approach, Integrated Cellular Geography. Result of the study was found to be in well agreement with proposed model. Furthermore this study also indicated that biogenesis of circular RNA was a post-transcriptional event. ConclusionsOverall, this study provides a novel systems biology based model under the paradigm of Integrated Cellular Geography which can assimilate independently performed experimental results and data published by global researchers on RNA biology to provide important information on biogenesis of exonic circular RNAs considering lncRNAs as precursor molecule.

molecular biology↗

bioRxiv2021

Developing selective FPR2 agonists can be a potential approach to treat moderate to severe asthma.

Formyl peptide receptor (FPR) family members have been reported to play important role in the resolution of inflammation. A few FPR2/FPR1 dual agonists are reported in the public domain for their anti-inflammatory properties. None of these molecules, however, have been successful as a therapy yet. Recent reports bring forward the ambiguous role of FPR1 in inflammation. These include both positive and negative outcomes. We, therefore, aimed to develop selective FPR2 agonists and evaluated their potential in mitigating the non-resolving inflammation in mouse models of moderate to severe asthma. Extensive structure-activity-relationship (SAR) studies were conducted on the imidazole and benzimidazole chemotype series to identify potent and selective FPR2 agonists. A few molecules were shortlisted based on their in vitro profile and absorption, distribution, metabolism and excretion (ADME) properties and were further evaluated in mouse models of asthma. We report herewith identification of 3 RCI compounds with low nanomolar potency for FPR2 agonism and >10,000 fold selectivity over FPR1 in Ca2+ release assay. These molecules also showed potency in other in vitro assays and potent efficacy in three distinct animal models of asthma. Our data suggest that FPR2 agonism can be a potential therapeutic approach to treat asthma. Our findings also propose that FPR1 can be spared to achieve the desired pharmacological activity.

pharmacology and toxicology↗

bioRxiv2021

A redox cycle with complex II promotes sulfide quinone oxidoreductase dependent H2S oxidation

The dueling roles of H2S as an endogenously synthesized respiratory substrate and as a toxin, raise questions as to how it is cleared when the electron transport chain is inhibited. Sulfide quinone oxidoreductase (SQOR) is a mitochondrial inner membrane flavoprotein that catalyzes the first step in the H2S oxidation pathway and uses coenzyme Q (CoQ) as an electron acceptor. However, complex IV poisoning by H2S inhibits complex III-dependent recycling of CoQH2, which is needed to sustain H2S oxidation. We have discovered that under these conditions, reversal of complex II activity using fumarate as an electron acceptor, establishes a new redox cycle with SQOR. The purine nucleotide cycle and the malate aspartate shuttle are sources of fumarate in H2S treated cells, which accumulate succinate. Complex II knockdown decreases the efficiency of H2S clearance and increases recovery time to the basal respiration rate in H2S treated cells. In contrast, attenuation of complex I, which is a major competitor for the mitochondrial CoQ pool, has the opposite effects. Targeted knockout of complex II in murine intestinal epithelial cells that are routinely exposed to microbiota derived H2S, decreases serum, urine, and fecal thiosulfate, a product of H2S oxidation. Our study identifies a metabolic reprogramming response to H2S that furnishes fumarate as an alternate electron acceptor and supports H2S oxidation independent of complex IV activity. Complex II-linked redox cycling of SQOR has important implications for gut H2S metabolism as colonocytes are routinely exposed to high concentrations of this gas derived from the microbiota. One Sentence SummaryReversal of complex II sustains and prioritizes H2S oxidation when respiration is poisoned.

biochemistry↗

bioRxiv2021

Probiotic consortia improve anti-viral immunity to SARS-CoV-2 in ferrets

Probiotics have been suggested as one solution to counter detrimental health effects by SARS-CoV-2, however, data so far is scarce. We tested the effect of two probiotic consortia, OL-1 and OL-2, against SARS-CoV-2 in ferrets and assessed their effect on cytokine production and transcriptome in a human monocyte-derived macrophage (Mf) and dendritic cell (DC) model. The results showed that the consortia significantly reduced the viral load, modulated immune response, and regulated viral receptor expression in ferrets compared to placebo. In human Mf and DC model, OL-1 and OL-2 induced cytokine production and genes related to SARS-CoV-2 anti-viral immunity. The study results indicate that probiotic stimulation of the ferret immune system leads to improved anti-viral immunity against SARS-COV-2 and that critical genes and cytokines for anti-SARS-CoV-2 immunity are stimulated in human immune cells in vitro. The effect of the consortia against SARS-CoV-2 warrants further investigations in human clinical trials.

immunology↗