Biology subjects

Xie, B.

Publications and source records attributed to Xie, B..

At least 55 records · Page 3Linked to original sources

bioRxiv2023

Early life regulatory T cells modulate PPARγ-dependent skin pigmentation

The maintenance of adult tissue homeostasis is dependent on the functional cross-talk between stem cells (SCs) and tissue-resident immune cells. This reciprocal relationship is also essential for tissue organogenesis during early life. The skin harbors a relatively large population of Regulatory T cells (Tregs) that accumulate within the first two weeks after birth. A functional role for early skin seeding Tregs (ETregs) during the first week of life is currently unexplored. Here, we show that skin Tregs are detected early as postnatal day 3 (P3) where they localize to hair follicle (HF) structures and enter a dynamic flux of activation marker expression. Punctual ETreg depletion from P6-P8, but not later, results in defective HF melanocyte SC (MeSC) mediated skin pigmentation in juvenile life. Transcriptomic analysis of the whole skin on P9 exhibited immediate and pronounced changes in MeSC markers and perturbation of Peroxisome proliferator-activated receptor-{gamma} (PPAR{gamma}) target genes in the HF. Accordingly, punctual ETreg depletion combined with short-term PPAR{gamma} agonization restored skin pigmentation. Single cell profiling of P9 skin revealed that PPAR{gamma} signalling activity is preferentially diminished in the HF epithelium upon loss of ETregs. Finally, we explored changes in the single cell transcriptome of the human tissue disorder, vitiligo, characterized by a lack of melanin and consequent skin depigmentation. These analyses showed that the HF cells from lesional vitiligo skin exhibited a significant downregulation in PPAR{gamma} pathway activation, relative to heathy controls. Overall, ETregs in neonatal skin are critical for sustaining HF PPAR{gamma} signaling, which is vital for facilitating MeSC mediated skin pigmentation during postnatal development. One Sentence SummaryPPAR{gamma} pathway functions downstream of neonatal Tregs to regulate melanocyte stem cell function.

immunology↗

bioRxiv2023

Exploring the tumor micro-environment in ovarian cancer histotypes and tumor sites

Ovarian cancer is a highly heterogeneous disease consisting of at least five different histological subtypes with varying clinical features, cells of origin, molecular composition, risk factors, and treatments. While most single-cell studies have focused on High grade serous ovarian cancer, a comprehensive landscape of the constituent cell types and their interactions within the tumor microenvironment are yet to be established in the different ovarian cancer histotypes. Further characterization of tumor progression, metastasis, and various histotypes are also needed to connect molecular signatures to pathological grading for personalized diagnosis and tailored treatment. In this study, we leveraged high-resolution single-cell RNA sequencing technology to elucidate the cellular compositions on 21 solid tumor samples collected from 12 patients with six ovarian cancer histotypes and both primary (ovaries) and metastatic (omentum, rectum) sites. The diverse collection allowed us to deconstruct the histotypes and tumor site-specific expression patterns of cells in the tumor and identify key marker genes and ligand-receptor pairs that are active in the ovarian tumor microenvironment. Our findings can be used in improving precision disease stratification and optimizing treatment options.

cancer biology↗

bioRxiv2023

The molecular mechanism of positive allosteric modulation at the dopamine D1 receptor

The dopamine D1 receptor (D1R) is a promising target for treating various psychiatric disorders. While upregulation of D1R activity has shown potential in alleviating motor and cognitive symptoms, orthosteric agonists have limitations, restricting their clinical applications. However, the discovery of several allosteric compounds specifically targeting the D1R, such as LY3154207, has opened new therapeutic avenues. Based on the cryo-EM structures of the D1R, we conducted molecular dynamics simulations to investigate the binding and allosteric mechanisms of LY3154207. Our simulations revealed that LY3154207 preferred the horizontal orientation above intracellular loop 2 (IL2) and stabilized the helical conformation of IL2. Moreover, LY3154207 binding induced subtle yet significant changes in key structural motifs and their neighboring residues. Notably, a cluster of residues centered around the Na+ binding site became more compact, while interactions involving the PIF motif and its neighboring residues were loosened upon LY3154207 binding, consistent with their role in opening the intracellular crevice for receptor activation. Additionally, we identified an allosteric pathway likely responsible for the positive allosteric effect of LY3154207 in enhancing Gs protein coupling. This mechanistic understanding of LY3154207s allosteric action at the D1R pave the way for the rational design of more potent and effective allosteric modulators.

biophysics↗

bioRxiv2023

Strengthening E-cadherin adhesion via antibody mediated binding stabilization.

E-cadherins (Ecads) are a crucial cell-cell adhesion protein with tumor suppression properties. Ecad adhesion can be enhanced by the monoclonal antibody 66E8, which has potential applications in inhibiting cancer metastasis. However, the biophysical mechanisms underlying 66E8 mediated adhesion strengthening are unknown. Here, we use molecular dynamics simulations, site directed mutagenesis and single molecule atomic force microscopy experiments to demonstrate that 66E8 strengthens Ecad binding by stabilizing the primary Ecad adhesive conformation: the strand-swap dimer. By forming electrostatic interactions with Ecad, 66E8 stabilizes the swapped {beta}-strand and its hydrophobic pocket and impedes Ecad conformational changes, which are necessary for rupture of the strand-swap dimer. Our findings identify fundamental mechanistic principles for strengthening of Ecad binding using monoclonal antibodies.

biophysics↗

bioRxiv2023

Co-engagement of TIGIT+ immune cells to PD-L1+ tumours by a bispecific antibody potentiates T-cell response and tumour control

Co-targeting PD-1/PD-L1 and TIGIT/CD226 is being pursued to broaden the efficacy of current immunotherapy. Here we demonstrate that a bispecific antibody (BsAb) targeting PD-L1 and TIGIT, HB0036, shows major advantages over the combination of the two parental monoclonal Abs (mAbs). We demonstrated that HB0036 co-engages PD-L1+ tumour cells and TIGIT+ T cells, and thereby upregulates CD226 on T cells and induces a greater T-cell proliferative response compared to the combination of the parental antibodies in vitro. In vivo, HB0036 recruits greater amounts of TIGIT antibody in PD-L1+ tumours but not in PD-L1- tumours, compared with therapy using the two parental antibodies. We also observed improved tumour control and favourable immunological signatures with HB0036 in syngeneic and xenograft tumour models. Collectively, these findings demonstrate that bispecific antibodies targeting PD-L1 and TIGIT offer superior benefits in cancer immunotherapy compared with therapy using the two parental antibodies. Based on these studies, a phase I clinical trial with HB0036 has been initiated in patients with solid tumours (NCT05417321).

immunology↗

bioRxiv2023

Does the territorial behaviour of the Amur tiger affect the accuracy of occupancy estimation?

1. Accurate estimates of wildlife distributions and population persistence are essential for conservation programs. Occupancy models that account for detection probability have been used to characterize the occupancy and habitat selection of imperilled species. However, failure to distinguish between true-presence and pseudo-presence associated with territorial behaviour can result in the overestimation of the occupancy probability of target species in unsuitable habitats, and this can have major implications for the development of conservation strategies. 2. For highly territorial wildlife species requiring high-quality habitat for survival, occasional Presence in unsuitable areas might be related to dispersal or migration, but this does not reflect actual occupancy and habitat use. True-Presence and Pseudo-Presence should be distinguished for target species to better reflect their actual occupancy and habitat use. 3. To investigate the effect of True-Presence and Pseudo-Presence on wildlife occupancy estimation, we developed a modified model (Mm) that considers the territorial behaviour of the Amur tiger in northeast China, which distinguished between True-Presence and Pseudo-Presence. We compared two models, Mm and M0 (conventional occupancy model), and assessed model performance using goodness-of-fit evaluation, detection and occupancy probability, and favourable variable selection. 4. We found that Mm, which has fewer favourable variables, is more powerful than M0 for estimating detection and occupancy probability, as well as characterizing the effect of various factors on the habitat use of Amur tigers. Furthermore, Mm significantly reduced the overestimation of occupancy probability outside the home range compared with M0, and detection probability estimates did not significantly differ between M0 and Mm. Finally, Mm provided more empirical habitat selection variables for the Amur tiger. 5. Our results revealed how True-Presence and Pseudo-Presence affect the occupancy probability and habitat selection of Amur tigers. Our method improves the accuracy of occupancy models; it can also be used to characterize the habitat selection and distribution of wildlife species and be applied to other territorial species.

ecology↗

bioRxiv2023

Imbalanced gut microbiota predicts and drives the progression of nonalcoholic fatty liver disease and nonalcoholic steatohepatitis in a fast-food diet mouse model

Nonalcoholic fatty liver disease (NAFLD) is multifactorial in nature, affecting over a billion people worldwide. The gut microbiome has emerged as an associative factor in NAFLD, yet mechanistic contributions are unclear. Here, we show fast food (FF) diets containing high fat, added cholesterol, and fructose/glucose drinking water differentially impact short- vs. long-term NAFLD severity and progression in conventionally-raised, but not germ-free mice. Correlation and machine learning analyses independently demonstrate FF diets induce early and specific gut microbiota changes that are predictive of NAFLD indicators, with corresponding microbial community instability relative to control-fed mice. Shotgun metagenomics showed FF diets containing high cholesterol elevate fecal pro-inflammatory effectors over time, relating to a reshaping of host hepatic metabolic and inflammatory transcriptomes. FF diet-induced gut dysbiosis precedes onset and is highly predictive of NAFLD outcomes, providing potential insights into microbially-based pathogenesis and therapeutics. HighlightsO_LIGerm-free mice are protected from fast-food diet-induced NAFLD. C_LIO_LIFast-food diets rapidly shift gut microbiota composition and function. C_LIO_LIIncreasing dietary cholesterol exacerbates hepatic inflammation only in SPF mice. C_LIO_LIFast-food diet-induced gut dysbiosis precedes and predicts late-stage NAFLD severity. C_LI

physiology↗

bioRxiv2022

Multiplex Epigenome Editing of MECP2 to Rescue Rett Syndrome Neurons

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder caused by loss-of-function heterozygous mutations of Methyl CpG-binding Protein 2 (MECP2) on the X chromosome in girls. Reactivation of the silent wild-type MECP2 allele from the inactive X chromosome (Xi) represents a promising therapeutic opportunity for female patients with RTT. Here, we applied a multiplex epigenome editing approach to reactivate MECP2 from Xi in RTT human embryonic stem cells (hESCs) and derived neurons. Demethylation of the MECP2 promoter by dCas9-Tet1 with target sgRNA reactivated MECP2 from Xi in RTT hESCs without detectable off-target effects at the transcriptional level. Neurons derived from methylation-edited RTT hESCs maintained MECP2 reactivation and reversed the smaller soma size and electrophysiological abnormalities, two hallmarks of RTT. In RTT neurons, insulation of the methylation edited MECP2 locus by dCpf1-CTCF with target CRISPR RNA enhanced MECP2 reactivation and rescued RTT-related neuronal defects, providing a proof-of-concept study for epigenome editing to treat RTT and potentially other dominant X-linked diseases. One-Sentence SummaryReactivation of MECP2 from the inactive X chromosome by multiplex epigenome editing rescues Rett syndrome neurons in vitro.

physiology↗

bioRxiv2022

Bright and sensitive red voltage indicators for imaging action potentials in brain slices and pancreatic islets

As fast developing tools for observing cellular membrane potential, red-emitting genetically encoded voltage indicators (GEVIs) reduce auto-fluorescence background, allow multiplexed recordings, and enable all-optical electrophysiology, but have been limited by either insensitivity or dimness. Here, we report a pair of red GEVIs, Cepheid1b/s, with improved sensitivity, brightness, and photostability. Cepheid1 indicators faithfully report cellular excitability in pancreatic islets and neural activity in acute brain slices.

neuroscience↗

bioRxiv2022

G-PROTEIN COUPLED RECEPTOR 19 (GPR19) KNOCKOUT MICE DISPLAY SEX-DEPENDENT METABOLIC DYSFUNCTION

G-protein coupled receptors (GPCRs) mediate signal transduction from the cellular surface to intracellular metabolic pathways. While the function of many GPCRs has been delineated previously, a significant number require further characterization to elucidate their cellular function. G-protein coupled receptor 19 (GPR19) is a poorly characterized class A GPCR which has been implicated in the regulation of circadian rhythm, tumor metastasis, and mitochondrial homeostasis. In this report, we use a novel knockout (KO) mouse model to examine the role of GPR19 in whole-body metabolic regulation. We show that loss of GPR19 promotes increased energy expenditure and decreased activity in both male and female mice. However, only male GPR19 KO mice display glucose intolerance in response to a high fat diet (HFD). Loss of GPR19 expression in male mice, but not female mice, resulted in diet-induced hepatomegaly, which was associated with decreased expression of key fatty acid oxidation genes in male GPR19 KO livers. Overall, our data suggest that loss of GPR19 impacts whole-body energy metabolism in diet-induced obese mice in a sex-dependent manner.

physiology↗

bioRxiv2022

A molecular mechanism for membrane chaperoning by a late embryogenesis abundant protein

Environmental stress can result in substantial damage to proteins, membranes, and genetic material, impacting organismal survival1-3. Stress tolerance can be conferred by intrinsically disordered proteins (IDPs)4 that lack stable tertiary structure. IDPs from the large family of late embryogenesis abundant (LEA) proteins confer a fitness advantage when heterologously expressed5,6. Such protection suggests a general molecular function leading to stress tolerance, although the mechanisms remain unclear. Here, we report that a tardigrade LEA protein that confers stress tolerance in yeast acts as a molecular chaperone for the mitochondrial membrane. This protein, named HeLEA1, localizes to the mitochondrial matrix, and harbors conserved LEA sequence motifs that undergo dynamic disorder-to-helical transition upon binding to negatively charged membranes. Yeast expressing HeLEA1 show increased mitochondrial membrane fluidity, increased membrane potential, and enhanced tolerance to hyperosmotic stress under non-fermentative growth without significantly altering mitochondrial lipid composition or triggering a generic stress response. We demonstrate that membrane binding ameliorates excess surface tension, possibly by stabilizing lipid packing defects. Evolutionary analysis suggests that HeLEA1 homologs localize to different membrane-bound organelles and share similar sequence and biophysical features. We suggest that membrane chaperoning by LEA proteins represents a general biophysical solution that can operate across the domains of life.

biophysics↗

bioRxiv2022

An interaction between betaprime-COP and the ArfGAP, Glo3, maintains post-Golgi cargo recycling

The essential COPI vesicular coat mediates retrieval of key transmembrane proteins at the Golgi and endosomes following recruitment by the small GTPase, Arf1. ArfGAP proteins regulate COPI coats, but molecular details for COPI recognition by ArfGAP proteins remain elusive. Biochemical and biophysical data reveal how {beta}-COP propeller domains directly engage the yeast ArfGAP, Glo3, with a low micromolar binding affinity (KD ~1 {micro}M). Calorimetry data demonstrate both {beta}-COP propeller domains are required to bind Glo3 using electrostatic interactions. An acidic patch on {beta}-COP (D437/D450) interacts with Glo3 lysine residues located within the BoCCS (Binding of Coatomer, Cargo, and SNAREs) region. Targeted point mutations in either Glo3 BoCCS or {beta}-COP abrogate the interaction in vitro, and loss of the {beta}-COP/Glo3 interaction drives Ste2 mis-sorting to the vacuole and aberrant Golgi morphology in budding yeast. Together, these data suggest cells require the {beta}-COP/Glo3 interaction for cargo recycling via endosomes and the TGN, where {beta}-COP may serve as a molecular platform to coordinate binding to multiple protein partners, including Glo3, Arf1, and the COPI F-subcomplex.

cell biology↗

bioRxiv2022

Molecular mechanism for strengthening E-cadherin adhesion using a monoclonal antibody

E-cadherin (Ecad) is an essential cell-cell adhesion protein with tumor suppression properties. The adhesive state of Ecad can be modified by the monoclonal antibody 19A11, which has potential applications in reducing cancer metastasis. Using x-ray crystallography, we determine the structure of 19A11 Fab bound to Ecad and show that the antibody binds to the first extracellular domain of Ecad near its primary adhesive motif - the strand-swap dimer interface. Molecular dynamics simulations and single molecule atomic force microscopy demonstrate that 19A11 interacts with Ecad in two distinct modes, one that strengthens the strand-swap dimer and one that does not alter adhesion. We show that adhesion is strengthened by the formation of a salt bridge between 19A11 and Ecad, which in turn stabilizes the swapped {beta}-strand and its complimentary binding pocket. Our results identify mechanistic principles for engineering antibodies to enhance Ecad adhesion.

biophysics↗

bioRxiv2022

Improved mammalian retromer cryo-EM structures reveal a new assembly interface

Retromer (VPS26/VPS35/VPS29 subunits) assembles with multiple sorting nexin (SNX) proteins on membranes to mediate endosomal recycling of transmembrane protein cargoes. Retromer has been implicated in other cellular events, including mitochondrial homeostasis, nutrient sensing, autophagy, and fission events. Mechanisms for mammalian retromer assembly remain undefined, and retromer engages multiple sorting nexin proteins to sort cargoes to different destinations. Published structures demonstrate mammalian retromer forms oligomers in vitro, but several structures were poorly resolved. We report here improved retromer oligomer structures using single particle cryo-electron microscopy (cryo-EM) by combining data collected from tilted specimens with multiple improvements in data processing, including using a three-dimensional (3D) starting model for improved automated particle picking in RELION. A retromer mutant (3KE retromer) that breaks VPS35-mediated interfaces was used to determine a structure of a new assembly interface formed by the VPS26A and VPS35 N-termini. The interface reveals how an N-terminal VPS26A arrestin saddle can link retromer chains by engaging a neighboring VPS35 N-terminus, on the opposite side from the well-characterized C-VPS26/N-VPS35 interaction observed within heterotrimers. The new interaction interface exhibits substantial buried surface area ([~]7,000 [A]2) and further suggests metazoan retromer may serve as an adaptable scaffold.

biochemistry↗

bioRxiv2021

Ubiquitination drives COPI priming and Golgi SNARE localization

Deciphering mechanisms controlling SNARE localization within the Golgi complex is crucial to understanding protein trafficking patterns within the secretory pathway. SNAREs are also thought to prime COPI assembly to ensure incorporation of these essential cargoes into vesicles but the regulation of these events is poorly understood. Here we report a roles for ubiquitin recognition by COPI in SNARE trafficking and in stabilizing interactions between Arf, COPI, and Golgi SNAREs. The ability of COPI to bind ubiquitin through its N-terminal WD repeat domain of {beta}COP or through an unrelated ubiquitin-binding domain (UBD) is essential for the proper localization of Golgi SNAREs Bet1 and Gos1. We find that COPI, the ArfGAP Glo3 and multiple Golgi SNAREs are ubiquitinated. Notably, the binding of Arf and COPI to Gos1 is markedly enhanced by ubiquitination of these components. Glo3 is thought to prime COPI-SNARE interactions; however, Glo3 is not enriched in the ubiquitin-stabilized SNARE-Arf-COPI complex but is instead enriched with COPI complexes that lack SNAREs. These results support a new model for how posttranslational modifications drive COPI priming events crucial for Golgi SNARE localization.

cell biology↗

bioRxiv2021

Diet-induced obese mice are resistant to improvements in cardiac function resulting from short-term adropin treatment

Previous studies have shown that treatment with recombinant adropin, a circulating peptide secreted by the liver and brain, restores glucose utilization in the hearts of diet-induced obese mice. This restoration of fuel substrate flexibility, which is lost in obese and diabetic animals, has the potential to improve contractile function in the diabetic heart. Using an ex vivo approach, we examined whether short-term adropin treatment could enhance cardiac function in a mouse model of diet-induced obesity. Our study showed that acute adropin treatment reduces inhibitory phosphorylation of pyruvate dehydrogenase in primary neonatal cardiomyocytes, and leads to moderate improvements in ex vivo cardiac function in mice fed a low fat diet. Conversely, short-term exposure to adropin led to a small decrease in cardiac function in mice fed a long-term high fat diet. Insulin treatment did not significantly alter cardiac function in adropin treated hearts from either low or high fat diet mice, however acute adropin treatment did moderately restore downstream insulin signaling in high fat diet fed mice. Overall, these data suggest that in an ex vivo setting, acute adropin treatment alone is not sufficient to promote improved cardiac function in obese animals.

physiology↗

bioRxiv2021

Inhibitory Acetylation of Pyruvate Dehydrogenase Promotes Diastolic Dysfunction in Mice

Left ventricular diastolic dysfunction is a structural and functional condition that precedes the development of heart failure with preserved ejection fraction (HFpEF). The etiology of diastolic dysfunction includes alterations in fuel substrate metabolism that negatively impact cardiac bioenergetics, and may precipitate the eventual transition to heart failure. To date, the molecular mechanisms that regulate early changes in fuel metabolism leading to diastolic dysfunction remain unclear. In this report, we use a diet-induced obesity model and quantitative acetylproteomics in aged mice to show that inhibitory lysine acetylation of the pyruvate dehydrogenase (PDH) complex promotes energetic deficits and diastolic dysfunction in mouse hearts. Cardiomyocyte-specific deletion of the mitochondrial lysine acetylation regulatory protein GCN5L1 prevented hyperacetylation of the PDH complex subunit PDHA1, allowing aged obese mice to continue using pyruvate as a bioenergetic substrate in the heart. Our findings suggest that changes in mitochondrial protein lysine acetylation represent a key metabolic component of diastolic dysfunction that precedes the development of heart failure.

physiology↗

bioRxiv2021

The β-cell primary cilium is an autonomous Ca2+ compartment for paracrine GABA signalling

The primary cilium is an organelle present in most adult mammalian cells and is thought of as an antenna for detection of a variety of signals. Here we use intact mouse pancreatic islets of Langerhans to investigate signalling properties of the primary cilium in {beta}-cells. Using cilia-targeted Ca2+ indicators we find that the resting Ca2+ concentration in the cilium is lower than that of the cytosol, and we uncover a Ca2+ extrusion mechanism in the cilium that effectively insulates the cilium from changes in cytosolic Ca2+. Stimuli that give rise to pronounced cytosolic Ca2+ concentration increases, such as glucose- and depolarization-induced Ca2+ influx, and mobilization of Ca2+ from the ER, was accompanied by minor increases in cilia Ca2+ concentrations that were spatially restricted to a small compartment at the base. Conversely, we observe pronounced Ca2+ concentration changes in the primary cilia of islet {beta}-cells that do not propagate into the cytosol and show that paracrine GABA signalling via cilia-localized GABA-B1-receptors is responsible for this Ca2+ signalling. Finally, we demonstrate that the cilia response to GABA involves ligand-dependent transport of GABA-B1 receptors into the cilium.

cell biology↗