Biology subjects

Han, X.

Publications and source records attributed to Han, X..

At least 289 records · Page 16Linked to original sources

bioRxiv2020

Anacardic acid protects against phenylephrine-induced mouse cardiac hypertrophy through JNK signaling-dependent regulation of histone acetylation

Cardiac hypertrophy is a complex process induced by the activation of multiple signaling pathways. We previously reported that anacardic acid (AA), a histone acetylase (HAT) inhibitor, attenuates phenylephrine (PE)-induced cardiac hypertrophy by downregulating histone H3 acetylation at lysine 9 (H3K9ac). Unfortunately, the upstream signaling events remained unknown. The mitogen-activated protein kinase (MAPK) pathway is an important regulator of cardiac hypertrophy. In this study, we explored the role of JNK/MAPK signaling in cardiac hypertrophy. A mouse model of cardiomyocyte hypertrophy was successfully established in vitro using PE. This study showed that p-JNK directly interacts with HATs (P300 and P300/CBP-associated factor, PCAF) and alters H3K9ac. In addition, both the JNK inhibitor SP600125 and the HAT inhibitor AA attenuated p-JNK overexpression and H3K9 hyperacetylation by inhibiting P300 and PCAF during PE-induced cardiomyocyte hypertrophy. Moreover, we demonstrated that both SP600125 and AA attenuate the overexpression of cardiac hypertrophy-related genes (MEF2A, ANP, BNP, and {beta}-MHC), preventing cardiomyocyte hypertrophy and dysfunction. These results revealed a novel mechanism through which AA might protect mice from PE-induced cardiac hypertrophy. In particular, AA inhibits the effects of JNK signaling on HAT-mediated histone acetylation, and could therefore be used to prevent and treat hypertrophic cardiomyopathy.

cell biology↗

bioRxiv2020

A large cross-ancestry meta-analysis of genome-wide association studies identifies 69 novel risk loci for primary open-angle glaucoma and includes a genetic link with Alzheimer's disease

We conducted a large multi-ethnic meta-analysis of genome-wide association studies for primary open-angle glaucoma (POAG) on a total of 34,179 cases vs 349,321 controls, and identified 127 independent risk loci, almost doubling the number of known loci for POAG. The majority of loci have broadly consistent effect across European, Asian and African ancestries. We identify a link, both genome-wide and at specific loci, between POAG and Alzheimers disease. Gene expression data and bioinformatic functional analyses provide further support for the functional relevance of the POAG risk genes. Several drug compounds target these risk genes and may be potential candidates for developing novel POAG treatments.

genetics↗

bioRxiv2020

The stress specific impact of ALKBH1 on tRNA cleavage and tiRNA generation

tiRNAs are small non-coding RNAs produced when tRNA is cleaved under stress. tRNA methylation modifications has emerged in recent years as important regulators for tRNA structural stability and sensitivity to cleavage and tiRNA generation during stress, however, the specificity and higher regulation of such a process is not fully understood. Alkbh1 is a m1A demethylase that leads to destabilization of tRNA and enhanced tRNA cleavage. We examined the impact of Alkbh1 targeting via gene knockdown or overexpression on B35 rat neuroblastoma cell line fate following stresses and on tRNA cleavage. We show that Alkbh1 impact on cell fate and tRNA cleavage is a stress specific process that is impacted by the demethylating capacity of the cellular stress in question. We also show that not all tRNAs are cleaved equally following Alkbh1 manipulation and stress, and that Alkbh1 KD fails to rescue tRNAs from cleavage following demethylating stresses. These findings shed a light on the specificity and higher regulation of tRNA cleavage and should act as a guide for future work exploring the utility of Alkbh1 as a therapeutic target for cancers or ischemic insult.

molecular biology↗

bioRxiv2020

Analysis of metagenome-assembled genomes from the mouse gut microbiota reveals distinctive strain-level characteristics

The laboratorial mouse harbors a unique gut microbiota with potential value for human microbiota-associated studies. Mouse gut microbiota has been explored at the genus and species levels, but features rarely been showed at the strain level. The identification of 833,051 and 658,438 nonredundant genes of faeces and gut content samples from the laboratorial C57/BL mice showed over half of these genes were newly found compared to the previous mouse gut microbial gene catalogue. Metagenome-assembled genomes (MAGs) was used to reconstruct 46 nonredundant MAGs belonging to uncultured specieses. These MAGs included members across all phyla in mouse gut (i.e. Firmicutes, Bacteroidetes, Proteobacteria, Deferribacteres, Verrucomicrobia, and Tenericutes) and allowed a strain-level delineating of the mouse gut microbiota. Comparison of MAGs with human gut colonies revealed distinctive genomic and functional characteristics of mouses Bacteroidetes and Firmicutes strains. Genomic characteristics of rare phyla in mouse gut microbiota were demonstrated by MAG approach, including strains of Mucispirillum schaedleri, Parasutterella excrementihominis, Helicobacter typhlonius, and Akkermansia muciniphila. ImportanceThe identification of nonredundant genes suggested the existence of unknown microbes in the mouse gut samples. The metagenome-assembled genomes (MAGs) instantiated the specificity of mouse gut species and revealed an intestinal microbial correlation between mouse and human. The cultivation of faeces and gut contents sample validated the existence of MAGs and estimate their accuracy. Full-length 16S ribosomal RNA gene sequencing enabled taxonomic characterization. This study highlighted a unique ecosystem in the gut of laboratorial mice that obviously differed with the human gut flora at the strain level. The outcomes may be beneficial to researches based on laboratorial mouse models.

microbiology↗

bioRxiv2020

The bacterial quorum sensing signal DSF hijacks Arabidopsis thaliana sterol biosynthesis to suppress plant innate immunity

Quorum sensing (QS) is a recognized phenomenon that is crucial for regulating population-related behaviors in bacteria. However, the direct specific effect of QS molecules on host biology is largely under-studied. In this work, we show that the QS molecule DSF (cis-11-methyl-dodecenoic acid) produced by Xanthomonas campestris pv. campestris can suppress pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) in Arabidopsis thaliana, mediated by flagellin-induced activation of flagellin receptor FLS2. The DSF-mediated attenuation of innate immunity results from the alteration of oligomerization states and endocytic internalization of plasma membrane FLS2. DSF altered the lipid profile of Arabidopsis, with a particular increase of the phytosterol species, which impairs the general endocytosis pathway mediated by clathrin and FLS2 nano-clustering on the plasma membrane. The DSF effect on receptor dynamics and host immune responses could be entirely reversed by sterol removal. Together, our results highlighted the importance of sterol homeostasis to plasma membrane organization and demonstrate a novel mechanism by which pathogenic bacteria use their communicating molecule to manipulate PAMP-triggered host immunity. SIGNIFICANCE STATEMENTBacteria rely on small signalling molecules called quorum sensing (QS) signals to communicate and coordinate their behaviors. QS is known to regulate gene expression, production of virulence factors, and biofilm formation for pathogenic bacteria to effectively colonize their hosts and cause diseases. In this work, we found a class of QS molecule called diffusible-signal factor (DSF), produced by devastating phytopathogenic bacteria such as Xanthomonas spp. and Xylella fastidiosa, could communicate directly with plant host and subvert plant innate immunity by inducing plant sterol production and thereby, attenuating receptor signalling through hindering the receptor clustering and plant endocytosis. The results significantly enrich our understanding of the mechanisms in the tug-of-war between bacterial pathogenesis and host immunity.

plant biology↗

bioRxiv2020

Conditioned media from MCF7 and BT474 breast cancer cells induce insulin resistance in skeletal muscle myotubes

BackgroundMetabolic disorders are prevalent in women with breast cancer, increasing mortality and cancer recurrence rates. Despite clinical implications, the cause of breast cancer-associated metabolic dysfunction remains poorly understood. Skeletal muscle is crucial for insulin-stimulated glucose uptake, thus key to whole-body glucose homeostasis. In this study, we determined the effect of breast cancer cell-conditioned media on skeletal muscle glucose uptake in response to insulin. MethodL6 myotubes overexpressing myc-tagged GLUT4 (GLUT4myc-L6) were incubated with 40% conditioned media from tumorigenic MCF7 or BT474, or non-tumorigenic control MCF10A breast cells. Mass-spectrometry-based proteomics was applied to detect molecular rewiring in response to breast cancer in the muscle. Expression of myogenesis and inflammation markers, GLUT4 translocation, [3H]-2-deoxyglucose (2DG) uptake, and intramyocellular insulin signalling were determined. ResultsBreast cancer cell-conditioned media induced proteomic changes in pathways related to sarcomere organisation, actin filament binding, and vesicle trafficking, disrupted myogenic differentiation, activated an inflammatory response via NF-{kappa}B, and induced muscle atrophy. Basal and insulin-stimulated GLUT4 translocation and 2DG uptake were reduced in myotubes treated with breast cancer cell-conditioned media compared to the control. Insulin signalling via the Rho GTPase Rac1 was blocked in breast cancer-treated myotubes, while Akt-TBC1D4 signalling was unaffected. ConclusionConditioned media from MCF7 and BT474 breast cancer cells reduced skeletal muscle glucose uptake via inhibition of GLUT4 translocation and intramyocellular insulin signalling by selectively blocking Rac1 activation and inducing inflammation. These findings indicate that the rewiring of skeletal muscle proteome, inflammation, and insulin signalling could play a role in metabolic dysfunction in patients with breast cancer.

cancer biology↗

bioRxiv2020

From SARS-CoV to Wuhan 2019-nCoV: Will History Repeat Itself?

This manuscript has been withdrawn as it was submitted without the full consent of all the authors. Therefore, the authors do not wish this work to be cited as reference for the project. If you have any questions, please contact the corresponding author.

microbiology↗

bioRxiv2020

Removable cranial window for sustained wide-field optical imaging in mouse neocortex

Attempts to image neocortical regions on the surface of mouse brain typically use a small glass disc attached to the cranial surface. This approach, however, is often challenged by progressive deterioration in optical quality and permits limited tissue access after its initial implantation. Here we describe a design and demonstrate a two-stage cranial implant device developed with a remarkably versatile material, polydimethylsiloxane, which facilitates longitudinal imaging experiments in mouse cortex. The system was designed considering biocompatibility and optical performance. This enabled us to achieve sustained periods of optical quality, extending beyond a year in some mice, and allows imaging at high spatio-temporal resolution using wide-field microscopy. Additionally, the two-part system, consisting of a fixed headplate with integrated neural access chamber and optical insert, allowed flexible access to the underlying tissue offering an expansive toolbox of neuromanipulation possibilities. Finally, we demonstrate the technical feasibility of rapid adaptation of the system to accommodate varying applications requiring long-term ability to visualize and access neural tissue. This capability will drastically reduce wasted time and resources for experiments of any duration, and will facilitate previously infeasible studies requiring long-term observation such as for research in aging or the progression chronic neurological disorders.

bioengineering↗

bioRxiv2020

Pioglitazone rescues mitochondrial lipid remodeling and pyruvate dehydrogenase hyperactivation in hepatic insulin resistance

Insulin resistance and altered hepatic mitochondrial function are central features of type 2 diabetes (T2D) and non-alcoholic fatty liver disease (NAFLD), but the etiological role of these processes in disease progression remains unclear. We investigated the molecular links between insulin resistance, mitochondrial remodeling, and hepatic lipid accumulation in a rodent model of T2D / NAFLD. Livers from obese, insulin resistant mice displayed augmented mitochondrial content and increased TCA cycle and pyruvate dehydrogenase (PDH) activities. Insulin sensitization with pioglitazone mitigated pyruvate-driven TCA cycle activity and PDH activation via both covalent (PDK4 and PDP2) and allosteric (intracellular pyruvate availability) mechanisms. Interestingly, improvements in insulin sensitivity and mitochondrial function were entirely dissociated from changes in hepatic triglycerides, diacylglycerides or fatty acids. Instead, we show that the mitochondrial phospholipid cardiolipin undergoes pathological remodeling in livers from obese mice and that this is reversed by insulin sensitization. Our findings identify targetable mitochondrial features of T2D and NAFLD and highlight the benefit of insulin sensitization in managing the clinical burden of obesity-associated disease.

biochemistry↗

bioRxiv2019

Moxifloxacin efficacy against Mycobacterium abscessus in vivo using zebrafish model

Moxifloxacin (MFX) showed good activity in vitro against Mycobacterium abscessus (M. abscessus) and was suggested as one of the antibiotic regimens for adults with M. abscessus disease. However, some other studies showed that MFX showed less or none activity against M. abscessus. In our study we aim to evaluate MFX activity against M. abscessus using zebrafish (ZF) model in vivo. MIC of each drugs were determined by broth microdilution method. M. abscessus labeled by CM-DiI, were micro-injected into ZF. Survival curves were determined by recording dead ZF every day. After 4 days of incubation ZF were lysed. Colony-forming unit (CFU) were enumerated and results are expressed as mean log10 CFU per ZF. Bacteria dissemination and fluorescence intensity in ZF were observed and analyzed. Inhibition rate was also calculated. In our study MFX showed good activity in vitro. But in vivo MFX showed limited restriction to M. abscessus. The association between increased survival and high dose of MFX is not significant. Same results were observed in bacterial fluorescence intensity and inhibition rates, with no significant difference when compared with no drug group (P > 0.05). However, significant difference was observed in azithromycin (AZM) group. MFX showed limited efficacy on Mycobacterium abscessus in vivo using ZF model. MFXs activity in vivo need to be confirmed.

microbiology↗

bioRxiv2019

Tuning antiviral CD8 T-cell response via proline-altered peptide ligand vaccination

Viral escape from CD8+ cytotoxic T lymphocyte responses correlates with disease progression and represents a significant challenge for vaccination. Here, we demonstrate that CD8+ T cell recognition of the naturally occurring MHC-I-restricted LCMV-associated immune escape variant Y4F is restored following vaccination with a proline-altered peptide ligand (APL). The APL increases MHC/peptide (pMHC) complex stability, rigidifies the peptide and facilitates T cell receptor (TCR) recognition through reduced entropy costs. Structural analyses of pMHC complexes before and after TCR binding, combined with biophysical analyses, revealed that although the TCR binds similarly to all complexes, the p3P modification alters the conformations of a very limited amount of specific MHC and peptide residues, facilitating efficient TCR recognition. This approach can be easily introduced in peptides restricted to other MHC alleles, and can be combined with currently available and future vaccination protocols in order to prevent viral immune escape. Author SummaryViral escape mutagenesis correlates often with disease progression and represents a major hurdle for vaccination-based therapies. Here, we have designed and developed a novel generation of altered epitopes that re-establish and enhance significantly CD8+ T cell recognition of a naturally occurring viral immune escape variant. Biophysical and structural analyses provide a clear understanding of the molecular mechanisms underlying this reestablished recognition. We believe that this approach can be implemented to currently available or novel vaccination approaches to efficiently restore T cell recognition of virus escape variants to control disease progression.

immunology↗

bioRxiv2019

CRISPR screening of porcine sgRNA library identified host factors essential for Japanese encephalitis virus replication

Japanese encephalitis virus (JEV) is a mosquito-borne zoonotic flavivirus that causes encephalitis and reproductive disorders in mammalian species. However, key host genes involved in the JEV life cycle and cell death are poorly understood. Here, we designed 85,674 single guide RNAs (sgRNAs) targeting 17,743 protein-coding genes, 11,053 long ncRNAs (lncRNAs), and 551 microRNAs (miRNAs) in the porcine genome, and subsequently developed a porcine sgRNA library and genome-scale CRISPR/Cas9 knockout (PigGeCKO) system. These sgRNAs were delivered into porcine kidney-15 (PK-15) cells that constitutively express Cas9, positive selection screening of the resulting PigGeCKO cell collection for resistance to JEV-induced cell death led to the identification of several previously unreported genes required for JEV infection. We conducted follow-up studies to verify the dependency of JEV on these genes, and identified functional contributions for six of the many candidate JEV-related host genes, including an endoplasmic reticulum membrane protein complex subunit 3 (EMC3) and calreticulin (CALR). Additionally, we identified that four genes associated with heparan sulfate proteoglycans (HSPGs) metabolism, specifically those responsible for HSPG sulfurylation, facilitated JEV entry into PK-15 cells. Thus, beyond our development of the largest CRISPR-based functional genomic screening platform for pig research to date, this work deepens our basic understanding of flavivirus infection and identifies multiple potentially vulnerable targets for the development of medical and breeding technologies to prevent and treat diseases caused by Japanese encephalitis virus.

genetics↗

bioRxiv2019

Peripheral Serum Metabolomic Profiles InformAntecedent Central Cognitive Impairment in Older Adults

The incidence of Alzheimers disease (AD) increases with age and is a significant cause of worldwide morbidity and mortality. However, the metabolic perturbations behind the onset of AD remains unclear. In this study, we performed metabolite profiling in both brain (n = 109) and matching serum samples (n = 566) to identify differentially expressed metabolites and metabolic pathways associated with neuropathology and cognitive performance and to identify individuals at high risk of developing cognitive impairment. The abundances of six metabolites, GLCA, petroselinic acid, linoleic acid, myristic acid, palmitic acid, and palmitoleic acid as well as the DCA/CA ratio, along with the dysregulation scores of three metabolic pathways, primary bile acid biosynthesis, fatty acid biosynthesis, and biosynthesis of unsaturated fatty acids showed significant differences in diagnostic groups across both brain and serum (P-value < 0.05).Significant associations were observed between the levels of differential metabolites/pathways and cognitive performance, neurofibrillary tangles, and neuritic plaque burden. Metabolites abundances and personalized metabolic pathways scores were used to derive machine learning models that could be used to differentiate cognitively impaired persons from those without cognitive impairment (median of AUC = 0.772 for the metabolite level model; median of AUC = 0.731 for the pathway level model). Utilizing these two models on the entire baseline control group, we identified those who experienced cognitive decline (AUC = 0.804, sensitivity = 0.722, specificity = 0.749 for the metabolite level model; AUC = 0.778, sensitivity = 0.633, specificity = 0.825 for the pathway level model) and demonstrated their pre-AD onset prediction potentials. Our study provides a proof-of-concept that it is possible to discriminate antecedent cognitive impairment in older adults before the onset of overt clinical symptoms using metabolomics. Our findings, if validated in future studies, could enable the earlier detection and intervention of cognitive impairment that may halt its progression.

neuroscience↗

bioRxiv2019

Development of SSR markers related to seed storability traits in maize subjected to artificial seed aging conditions

Seed storability is an important and complex agronomic trait in maize because annual seed production considerably exceeds consumption. The viability of seeds decreases over time, even when stored at low temperature, until seeds finally lose viability. In our previous study, two inbred lines with significantly different storability, Dong156 with high storage tolerance and Dong237 with low storage tolerance, were selected over six years using a natural seed aging test. In the present study, an F2:3 population and a RIL (recombinant inbred line) population were constructed from these two inbred lines and used to map QTL (quantitative trait loci) with SSR (simple sequence repeat) markers. A phenotypic index of traits related to seed storability that includes germination rate, germination potential, a germination index, a vigor index, seedling weight, and seedling length was generated using the results of an artificial aging treatment. Two consistent regions, cQTL-7 on chromosome 7 and cQTL-10 on chromosome 10, were identified by comparing QTL analysis results from these two populations. After genotyping SSR markers in these two regions, cQTL-7 was remapped to between umc1671 and phi328175 in a 7.97-Mb region, and cQTL-10 was remapped to between umc1648 and phi050 in a 39.15-Mb region. Four SSR markers linked to cQTL-7 and cQTL-10, including umc1671, phi328175, umc1648, and phi050, were identified using a Chi-squared test. The combined selection efficiency of these four markers was 83.94% in 85 RIL lines with high storability, and marker umc1648 exhibited the highest efficiency value of 88.89%. These results indicated that the four SSR markers developed in this study could be used for selection of maize germplasm with high seed storability.

plant biology↗

bioRxiv2019

Improve Protein Solubility and Activity based on Machine Learning Models

Improving catalytic ability of protein biocatalysts leads to reduction in the production cost of biocatalytic manufacturing process, but the search space of possible proteins/mutants is too large to explore exhaustively through experiments. To some extent, highly soluble recombinant proteins tend to exhibit high activity. Here, we demonstrate that an optimization methodology based on machine learning prediction model can effectively predict which peptide tags can improve protein solubility quantitatively. Based on the protein sequence information, a support vector machine model we recently developed was used to evaluate protein solubility after randomly mutated tags were added to a target protein. The optimization algorithm guided the tags to evolve towards variants that can result in higher solubility. Moreover, the optimization results were validated successfully by adding the tags designed by our optimization algorithm to a model protein, expressing it in vivo and experimentally quantifying its solubility and activity. For example, solubility of a tyrosine ammonium lyase was more than doubled by adding two tags to its N- and C-terminus. Its protein activity was also increased nearly 3.5 fold by adding the tags. Additional experiments also supported that the designed tags were effective for improving activity of multiple proteins and are better than previously reported tags. The presented optimization methodology thus provides a valuable tool for understanding the correlation between amino acid sequence and protein solubility and for engineering protein biocatalysts.\n\nContactkang.zhou@nus.edu.sg, chewxia@nus.edu.sg

bioinformatics↗

bioRxiv2019

Selective targeting of an oncogenic KRAS mutant allele by CRISPR/Cas9 induces efficient tumor regression

BackgroundKRAS is one of the most frequently mutated oncogenes in human cancers, but its activating mutations have remained undruggable due to its picomolar affinity for GTP/GDP and its smooth protein structure resulting in the absence of known allosteric regulatory sites. ResultsWith the goal of treating mutated KRAS-driven cancers, two CRISPR systems, CRISPR-SpCas9 genome-editing system and transcription-regulating system dCas9-KRAB, were developed to directly deplete KRAS mutant allele or to repress its transcription in cancer cells, respectively, through guide RNA specifically targeting the mutant but not wild-type allele. The effect of in vitro proliferation and cell cycle on cancer cells as well as in vivo tumor growth was examined after delivery of Cas9 system. SpCas9 and dCas9-KRAB systems with sgRNA targeting the mutant allele both blocked the expression of mutant KRAS gene, leading to an inhibition of cancer cell proliferation. Local adenoviral injections using SpCas9 and dCas9-KRAB systems both suppressed tumor growth in vivo. The gene-depletion system (SpCas9) performed more effectively than the transcription-suppressing system (dCas9-KRAB) on tumor inhibition. Application of both Cas9 systems to wild-type KRAS tumor cells did not affect cell proliferation in vitro and in vivo. Furthermore, through bioinformatic analysis of 31555 SNP mutations of the top 20 cancer driver genes, we showed that our mutant-specific editing strategy could be extended to a list of oncogenic mutations with high editing potentials, and this pipeline can be applied to analyze the distribution of PAM sequence in the genome to survey the best targets for other editing purpose. ConclusionsWe successfully developed both gene-depletion and transcription-suppressing systems to specifically target an oncogenic mutant allele of KRAS which led to significant tumor regression. It provides a promising strategy for the treatment of tumors with driver gene mutations.

genetics↗

bioRxiv2019

TLR2 signaling pathway combats Streptococcus uberis infection by inducing production of mitochondrial reactive oxygen species

Mastitis caused by Streptococcus uberis is a hazardous clinical disease in dairy animals. In this study, the role of Toll-like receptors (TLRs) and TLR-mediated signaling pathways in mastitis caused by S. uberis was investigated using mouse models and mammary epithelial cells (MECs). We used S. uberis to infect mammary glands of wild type, TLR2-/- and TLR4-/- mice and quantified the adaptor molecules in TLR signaling pathways, proinflammatory cytokines, tissue damage and bacterial count in mammary glands. When compared with TLR4 deficiency, TLR2 deficiency induced more severe pathological changes through myeloid differentiation primary response 88 (MyD88)-mediated signaling pathways during S. uberis infection. In MECs, TLR2 detected S. uberis infection and induced mitochondrial reactive oxygen species (mROS) to assist host control of secretion of inflammatory factors and elimination of intracellular S. uberis. Our results demonstrate that TLR2-mediated mROS have a significant effect on S. uberis-induced host defense responses in mammary glands as well as MECs. Author summaryS. uberis contributes significantly to global mastitis and remains a major obstacle for inflammation elimination due to its ability to form persistent infection in mammary tissue. The Toll-like receptor (TLR) family plays a significant role in identifying infections of intracellular bacteria and further triggering inflammatory reactions in immune cells. However, the detailed molecular mechanism by which TLR is regulated, and whether MECs, as the main cells in mammary gland, are tightly involved in these processes is poorly understood. Here, we used S. uberis to infect mammary glands of wild type, TLR2-/-, TLR4-/- mice and MECs to assess pathogenesis, proinflammatory cytokines, ROS as well as mROS levels during infection. We found that during S.uberis infection, it is TLR2 deficiency that induced more severe pathological changes through MyD88-mediated signaling pathways. In addition, our work demonstrates that mROS mediated by TLR2 has an important role in host defense response to combat S. uberis infection in mammary glands as well as MECs.

pathology↗

bioRxiv2019

Expression and purification of Protease Activated Receptor 4 (PAR4) and analysis with histidine hydrogen deuterium exchange.

Protease activated receptors (PARs) are G-protein coupled receptors (GPCRs) that are activated by proteolyis of the N-terminus, which exposes a tethered ligand that interacts with the receptor. Numerous studies have focused on the signaling pathways mediated by PARs. However, the structural basis for initiation of these pathways is unknown. Here, we describe a strategy for the expression and purification of PAR4. This is the first PAR family member to be isolated without stabilizing modifications for biophysical studies. We monitored PAR4 activation with histidine-hydrogen deuterium exchange (His-HDX). PAR4 has 9 histidines that are spaced throughout the protein allowing a global view of solvent accessible and non-accessible regions. Peptides containing each of the 9 His residues were used to determine the t1/2 for each His residue in apo or thrombin activated PAR4. The thrombin cleaved PAR4 had a 2-fold increase (p > 0.01) in t1/2 values observed for four histidine residues (His180, His229, His240, and His380) demonstrating that these regions have decreased solvent accessibility upon thrombin treatment. In agreement, thrombin cleaved PAR4 also was resistant to thermolysin digestion. In contrast, activation with the PAR4 agonist peptide was digested at the same rate as apo PAR4. Further analysis showed the C-terminus is protected in thrombin activated PAR4 compared to uncleaved or agonist peptide treated PAR4. The studies described here are the first to examine the tethered ligand activation mechanism for a PAR family member using biophysically and shed light on the overall conformational changes that follow activation of PARs by a protease.

biochemistry↗