Biology subjects

Xu, S.

Publications and source records attributed to Xu, S..

At least 343 records · Page 19Linked to original sources

bioRxiv2021

A base-line cellular antiviral state is maintained by cGAS and its most frequent naturally occurring variant rs610913

Upon recognition of aberrantly located DNA, the innate immune sensor cGAS activates STING/IRF-3-driven antiviral responses. Here we characterized the ability of a specific variant of the cGAS-encoding gene MB21D1, rs610913, to alter cGAS-mediated DNA sensing and viral infection. rs610913 is a frequent G>T polymorphism resulting in a P261H exchange in the cGAS protein. Data from the International Collaboration for the Genomics of HIV suggested that rs610913 nominally associates with HIV-1 acquisition in vivo. Molecular modeling of cGAS(P261H) hinted towards the possibility for an additional binding site for a potential cellular co-factor in cGAS dimers. However, cGAS(WT) or cGAS(P261H)-reconstituted THP-1 cGAS KO cells shared steady-state expression of interferon-stimulated genes (ISGs), as opposed to cells expressing the enzymatically inactive cGAS(G212A/S213A). Accordingly, cGAS(WT) and cGAS(P261H) cells were less susceptible to lentiviral transduction and infection with HIV-1, HSV-1, and Chikungunya virus as compared to cGAS KO- or cGAS(G212A/S213A) cells. Upon DNA challenge, innate immune activation appeared to be mildly reduced upon expression of cGAS(P261H) compared to cGAS(WT). Finally, DNA challenge of PBMCs from donors homozygously expressing rs610913 provoked a trend towards a slightly reduced type I IFN response as compared to PBMCs from GG donors. Taken together, the steady-state activity of cGAS maintains a base-line antiviral state rendering cells more refractory to ISG-sensitive viral infections. Even though rs610913 failed to grossly differ phenotypically from the wild-type gene, its expression potentially results in a slightly altered susceptibility to viral infections in vivo.

immunology↗

bioRxiv2021

Chromosomal rearrangements preserve adaptive divergence in ecological speciation

Despite increasing empirical evidence that chromosomal rearrangements may play an important role in adaptive divergence and speciation, the degree to which divergent genomic regions are associated with chromosomal rearrangements remains unclear. In this study, we provide the first whole-genome analyses of ecological speciation and chromosomal evolution in a Daphnia species complex, using chromosome-scale assemblies and natural-population sequencing of the recently diverged species pair, Daphnia pulicaria and Daphnia pulex, which occupy distinct yet overlapping habitats in North America, and the outgroup species Daphnia obtusa. Our results describe a mixed mode of geographic divergence (isolation with secondary contact) resulting in a heterogeneous landscape of genomic divergence. Large contiguous "continents of divergence" encompass over one third of the genome (36%) and contain nearly all the fixed differences (94%) between the species, while the background genome has been homogenized. Chromosomal rearrangements between species, including inversions and intrachromosomal translocations, are associated with the continents of divergence and capture multiple adaptive alleles in genes and pathways thought to contribute to the species phenotypic differences.

evolutionary biology↗

bioRxiv2021

A bacterium-like particle vaccine displaying Zika virus prM-E induces systemic immune responses in mice

The emergence of Zika virus (ZIKV) infection, which is an unexpectedly associated with congenital defects, has prompted the development of safe and effective vaccines. The gram-positive enhancer matrix-protein anchor (GEM-PA) display system has emerged as a versatile and highly effective platform for delivering target proteins for vaccines. In this article, we developed a bacterium-like particle vaccine ZI-{Delta}-PA-GEM based on the GEM-PA system. The fusion protein ZI-{Delta}-PA, which contains the prM-E-{Delta} protein of ZIKV (with a stem-transmembrane region deletion) and the protein anchor PA3, was expressed. The fusion protein was successfully displayed on the GEM surface, forming ZI-{Delta}-PA-GEM. Moreover, when BALB/c mice were immunized intramuscularly with ZI-{Delta}-PA-GEM combined with 201 VG and poly(I:C) adjuvants, durable ZIKV-specific IgG and protective neutralizing antibody responses were induced. Potent B cell/DC activation was also be stimulated early after immunization. Remarkably, splenocyte proliferation, the secretion of multiple cytokines, T/B cell activation and central memory T cell responses were elicited. These data indicate that ZI-{Delta}-PA-GEM is a promising bacterium-like particle vaccine candidate for ZIKV. Author summaryBecause Zika virus (ZIKV) infection is considered as an example of "disease X", the development of a safe and effective ZIKV vaccine is essential. The gram-positive enhancer matrix-protein anchor (GEM-PA) display system has been used in many vaccine studies due to its advantages. In this study, prM-E-{bigtriangleup} protein of ZIKV (with a stem-transmembrane region deletion) and the protein anchor PA3 was fusion expressed, termed ZI-{bigtriangleup}-PA. Then the fusion protein ZI-{bigtriangleup}-PA could be displayed on the surface of GEM, forming ZI-{bigtriangleup}-PA-GEM. The author evaluated the immunogenicity of ZI-{bigtriangleup}-PA-GEM with the 201 VG and poly(I:C) adjuvants. The study demonstrates that ZI-{bigtriangleup}-PA-GEM induced mice to produce neutralizing antibody and specific cellular immune responses. The author believe that the bacterium-like particle vaccine ZI-{bigtriangleup}-PA-GEM has the potential to be used as the ZIKV vaccine.

microbiology↗

bioRxiv2021

Mechanism of hyperproteinemia-induced blood cell homeostasis imbalance in an animal model

Hyperproteinemia is a metabolic disorder associated with increased plasma protein concentration (PPC). It is often clinically complicated by malignant diseases or severe infections. Research on the molecular mechanism of High PPC (HPPC) is scant. Here, an animal model of primary hyperproteinemia was constructed in an invertebrate, Bombyx mori, to investigate the effect of HPPC on circulating blood cells. We showed that HPPC affected blood cell homeostasis and enhanced blood cell phagocytosis, leading to increased reactive oxygen species levels, and induced programmed cell death that depended on the endoplasmic reticulum-calcium ion signaling pathway. HPPC induced the proliferation of blood cells, mainly granulocytes, by activating the JAK/STAT signaling pathway. Supplementation with endocrine hormone active substance 20E significantly reduced the impact of HPPC on blood cell homeostasis. Herein, we reported a novel signaling pathway by which HPPC affected blood cell homeostasis, which was different from hyperglycemia, hyperlipidemia, and hypercholesterolemia. In addition, we showed that down-regulation of gene expression of the hematopoietic factor Gcm could be used as a potential early monitoring index for hyperproteinemia. Highlights* HPPC induced proliferation of circulating blood cells through the JAK/STAT pathway, leading to a significant increase in the proportion of granulocytes. * Supplementing endocrine hormone 20E improved hematopoietic function and restored the homeostasis of circulating blood cells through modulation of the JAK/STAT signaling pathway. * HPPC induced PCD in blood cells through the endoplasmic reticulum-calcium ion release signaling pathway. * Down-regulation of the gene expression of the hematopoietic factor Gcm could be used as a potential early monitoring index for hyperproteinemia.

pharmacology and toxicology↗

bioRxiv2021

Unconventional tonicity-regulated nuclear trafficking of NFAT5 mediated by KPNB1, XPOT and RUVBL2

NFAT5 is the only known mammalian tonicity-responsive transcription factor functionally implicated in diverse physiological and pathological processes. NFAT5 activity is tightly regulated by extracellular tonicity but the underlying mechanisms remain elusive. We demonstrated that NFAT5 enters the nucleus via the nuclear pore complex. We also found that NFAT5 utilizes a non-canonical nuclear localization signal (NFAT5-NLS) for nuclear imports. siRNA screening revealed that karyopherin {beta}1 (KPNB1) drives nuclear import of NFAT5 via directly interacting with NFAT5-NLS. Proteomics analysis and siRNA screening further revealed that nuclear export of NFAT5 under hypotonicity is mediated by Exportin-T, and that it requires RuvB-Like AAA type ATPase 2 (RUVBL2) as an indispensable chaperone. Our findings have identified KPNB1 and RUVBL2 as key molecules responsible for the unconventional tonicity-regulated nucleocytoplasmic shuttling of NFAT5. These findings offer an opportunity for developing novel NFAT5 targeting strategies that are potentially useful for the treatment of diseases associated with NFAT5 dysregulation.

cell biology↗

bioRxiv2021

Gating mechanism of human N-type voltage-gated calcium channel

N-type voltage-gated calcium (CaV) channels mediate Ca2+ influx at the presynaptic terminals in response to action potential and play vital roles in synaptogenesis, neurotransmitter releasing, and nociceptive transmission. Here we elucidate a cryo-electron microscopy (cryo-EM) structure of the human CaV2.2 complex at resolution of 2.8 [A]. This complex structure reveals how the CaV2.2, {beta}1, and 2{delta}1 subunits are assembled. In our structure, the second voltage-sensing domain (VSD) is stabilized at a resting-state conformation, which is distinct from the other three VSDs of CaV2.2 as well as activated VSDs observed in previous structures of CaV channels. The structure also shows that the intracellular gate formed by S6 helices is closed, and a W-helix from the DII-III linker is determined to act as a blocking-ball that causes closed-state inactivation in CaV2.2. Collectively, our structure provides previously unseen structural insights into fundamental gating mechanisms of CaV channels.

neuroscience↗

bioRxiv2021

MPI8 is Potent Against SARS-CoV-2 by Inhibiting Dually and Selectively the SARS-CoV-2 Main Protease and the Host Cathepsin L

A number of inhibitors have been developed for the SARS-CoV-2 main protease (MPro) as potential COVID-19 medications but little is known about their selectivity. Using enzymatic assays, we characterized inhibition of TMPRSS2, furin, and cathepsins B/K/L by more than a dozen of previously developed MPro inhibitors including MPI1-9, GC376, 11a, 10-1, 10-2, and 10- 3. MPI1-9, GC376 and 11a all contain an aldehyde for the formation of a reversible covalent hemiacetal adduct with the MPro active site cysteine and 10-1, 10-2 and 10-3 contain a labile ester to exchange with the MPro active site cysteine for the formation of a thioester. Our data revealed that all these inhibitors are inert toward TMPRSS2 and furin. Diaryl esters also showed low inhibition of cathepsins. However, all aldehyde inhibitors displayed high potency in inhibiting three cathepsins. Their determined IC50 values vary from 4.1 to 380 nM for cathepsin B, 0.079 to 2.3 nM for cathepsin L, and 0.35 to 180 nM for cathepsin K. All aldehyde inhibitors showed similar inhibition levels toward cathepsin L. A cellular analysis indicated high potency of MPI5 and MPI8 in inhibiting lysosomal activity, which is probably attributed to their inhibition of cathepsins. Among all aldehyde inhibitors, MPI8 shows the best selectivity toward cathepsin L. With respect to cathepsins B and K, the selective indices are 192 and 150, respectively. MPI8 is the most potent compound among all aldehyde inhibitors in cellular MPro inhibition potency and anti-SARS-CoV-2 activity in Vero E6 cells. Cathepsin L has been demonstrated to play a critical role in the SARS-CoV-2 cell entry. By selectively inhibiting both SARS-CoV-2 MPro and the host cathepsin L, MPI8 potentiates dual inhibition effects to synergize its overall antiviral potency and efficacy. Due to its high selectivity toward cathepsin L that reduces potential toxicity toward host cells and high cellular and antiviral potency, we urge serious consideration of MPI8 for preclinical and clinical investigations for treating COVID-19.

pharmacology and toxicology↗

bioRxiv2021

Cellular Activities of SARS-CoV-2 Main Protease Inhibitors Reveal Their Unique Characteristics

As an essential enzyme of SARS-CoV-2, the pathogen of COVID-19, main protease (MPro) triggers acute toxicity to its human cell host, an effect that can be alleviated by an MPro inhibitor with cellular potency. By coupling this toxicity alleviation with the expression of an MPro-eGFP fusion protein in a human cell host for straightforward characterization with fluorescent flow cytometry, we developed an effective method that allows bulk analysis of cellular potency of MPro inhibitors. In comparison to an antiviral assay in which MPro inhibitors may target host proteases or other processes in the SARS-CoV-2 life cycle to convene strong antiviral effects, this novel assay is more advantageous in providing precise cellular MPro inhibition information for assessment and optimization of MPro inhibitors. We used this assay to analyze 30 literature reported MPro inhibitors including MPI1-9 that were newly developed aldehyde-based reversible covalent inhibitors of MPro, GC376 and 11a that are two investigational drugs undergoing clinical trials for the treatment of COVID-19 patients in United States, boceprevir, calpain inhibitor II, calpain inhibitor XII, ebselen, bepridil that is an antianginal drug with potent anti-SARS-CoV-2 activity, and chloroquine and hydroxychloroquine that were previously shown to inhibit MPro. Our results showed that most inhibitors displayed cellular potency much weaker than their potency in direct inhibition of the enzyme. Many inhibitors exhibited weak or undetectable cellular potency up to 10 M. On contrary to their strong antiviral effects, 11a, calpain inhibitor II, calpain XII, ebselen, and bepridil showed relatively weak to undetectable cellular MPro inhibition potency implicating their roles in interfering with key steps other than just the MPro catalysis in the SARS-CoV-2 life cycle to convene potent antiviral effects. characterization of these molecules on their antiviral mechanisms will likely reveal novel drug targets for COVID-19. Chloroquine and hydroxychloroquine showed close to undetectable cellular potency to inhibit MPro. Kinetic recharacterization of these two compounds rules out their possibility as MPro inhibitors. Our results also revealed that MPI5, 6, 7, and 8 have high cellular and antiviral potency with both IC50 and EC50 values respectively below 1 M. As the one with the highest cellular and antiviral potency among all tested compounds, MPI8 has a remarkable cellular MPro inhibition IC50 value of 31 nM that matches closely to its strong antiviral effect with an EC50 value of 30 nM. Given its strong cellular and antiviral potency, we cautiously suggest that MPI8 is ready for preclinical and clinical investigations for the treatment of COVID-19.

biochemistry↗

bioRxiv2021

Drug Repurposing for the SARS-CoV-2 Papain-Like Protease

As the pathogen of COVID-19, SARS-CoV-2 encodes two essential cysteine proteases that process the pathogens two large polypeptide translates ORF1a and ORF1ab in human host cells to form 15 functionally important, mature nonstructural proteins. One of the two enzymes, papain-like protease or PLpro, also possesses deubiquitination and deISGylation activities that suppresses host innate immune responses toward SARS-CoV-2 infection. Therefore, PLpro is a potential COVID-19 drug target. To repurpose drugs for PLpro, we experimentally screened 33 deubiquitinase and 37 cysteine protease inhibitors on their inhibition of PLpro. Our results showed that 15 deubiquitinase and 1 cysteine protease inhibitors exhibit potent inhibition of PLpro at 200 M. More comprehensive characterizations revealed 7 inhibitors GRL0617, SJB2-043, TCID, DUB-IN-1, DUB-IN-3, PR-619, and S130 with an IC50 value below 60 M and four inhibitors GRL0617, SJB2-043, TCID, and PR-619 with an IC50 value below 10 M. Among four inhibitors with an IC50 value below 10 M, SJB2-043 is the most unique in that it doesnt fully inhibit PLpro but has an outstanding IC50 value of 0.56 M. SJB2-043 likely binds to an allosteric site of PLpro to convene its inhibition effect, which needs to be further investigated. As a pilot study, the current work indicates that COVID-19 drug repurposing by targeting PLpro holds promises but in-depth analysis of repurposed drugs is necessary to avoid omitting allosteric inhibitors.

biochemistry↗

bioRxiv2021

Efficacy of ancestral receptor-binding domain, S1 and trimeric spike protein vaccines against SARS-CoV-2 variants B.1.1.7, B.1.351, and B.1.617.1

The ongoing coronavirus disease 2019 (COVID-19) pandemic is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The current SARS-CoV-2 vaccines are based on spike (S) protein, S1 subunit, or receptor-binding domain (RBD) of prototype strain. Emergence of several novel SARS-CoV-2 variants has raised concern about potential immune escape. In this study, we performed an immunogenicity comparison of ancestral RBD, S1, and S ectodomain trimer (S-trimer) antigens and tested the efficacy of these prototype vaccines against the circulating variants, especially B.1.617 that has been linked to Indias current COVID-19 surge. We found that RBD and S-trimer proteins could induce significantly higher neutralizing antibody titers than S1 protein. For the three vaccines, the neutralizing titers decreased over time, but still remained high for at least five months after immunization. Importantly, the three prototype vaccines were still effective in neutralizing the variants of concern, although B.1.351 and B.1.617.1 lineages showed varying degrees of reduction in neutralization by the immune sera. The vaccines-induced sera were shown to block receptor binding and inhibit S protein-mediated membrane fusion. In addition, the immune sera did not promote antibody-dependent enhancement (ADE) in vitro. Our work provides valuable information for development of SARS-CoV-2 subunit vaccines and also supports the continued use of ancestral RBD or S-based vaccines to fight the COVID-19 epidemic.

immunology↗

bioRxiv2021

Tmem138, a photoreceptor connecting cilium (CC) protein, is required for rhodopsin transport across the cilium and outer segment (OS) biogenesis

Photoreceptor connecting cilium (CC) is structurally analogous to the transition zone (TZ) of primary cilia and gates the molecular trafficking between the inner and the outer segment (OS). Retinal dystrophies with underlying CC defects are manifested in a broad array of syndromic conditions known as ciliopathies as well as non-syndromic retinal degenerations. Despite extensive studies, protein trafficking across the photoreceptor CC is largely unknown. Here we genetically inactivated mouse Tmem138, a gene encoding a ciliary membrane protein localized to the ciliary TZ and linked to Joubert syndrome (JBTS). Germline deletion of Tmem138 abolished OS morphogenesis followed by rapid photoreceptor degeneration. Tmem138 was found localized to the photoreceptor CC and, accordingly, the molecular compartments of the CC and axoneme of the mutant photoreceptors were altered despite ciliogenesis proceeding normally at the early stage of photoreceptor development. To gain further insights into Tmem138 function in OS biogenesis, we focused on trafficking of rhodopsin, the most abundant protein of the OS. Mislocalization of rhodopsin was readily observed as early as P5 in the mutant photoreceptors prior to growth of the OS. Ablation of Tmem138 in mature rods recapitulated the molecular changes in the germline mutants, causing well-formed outer segment discs to disintegrate accompanied by mislocalization of rhodopsin in the cell body. Furthermore, Tmem138 interacted with rhodopsin, and two additional CC compartment proteins Ahi1 and Tmem231, which were both altered in the mutant photoreceptors. Taken together, these results suggest that Tmem138 has a distinct role in gating the transport of rhodopsin and likely other OS bound proteins through formation of CC transport complex(es).

cell biology↗

bioRxiv2021

Modulating the selective utilization of carbon sources by engineering the 3rd and 4th helices of the DNA-binding domain of catabolite control protein A (CcpA) in Bacillus licheniformis

The gram-positive bacterium Bacillus licheniformis exhibits obvious selective utilization on carbon sources. This process is mainly governed by the global regulator catabolite control protein A (CcpA), which can recognize and bind to multiple target genes widely distributed in metabolic pathways. Although the DNA-binding domain of CcpA has been predicted, the influence of key amino acids on target gene recognition and binding remains elusive. In this study, the impact of Lys31, Ile42 and Leu56 on in vitro protein-DNA interactions and in vivo carbon source selective utilization was investigated. The results showed that alanine substitution of Lys31 and Ile42, located within the 3rd helices of the DNA-binding domain, significantly weakened the binding strength between CcpA and target genes. These mutations also lead to alleviated repression of xylose utilization in the presence of glucose. On the other hand, the Leu56Arg mutant in the 4th helices exhibited enhanced binding affinity compared with that of the wild-type one. When this mutant was used to replace the native one in B. licheniformis cells, the selective utilization of glucose over xylose increased. The above research results are helpful for a deep understanding of how microorganisms can flexibly sense and adapt to changes in the external environment. Additionally, they can provide important theoretical basis for the rational design of biomass utilization and environmental adaptability of B. licheniformis cell factories. ImportanceBacillus licheniformis is widely used in producing various valuable products, such as enzymes, industrial chemicals and biocides. The carbon catabolite regulation process in the utilization of raw materials is crucial to maximizing the efficiency of this microbial cell factory. CcpA plays an important role in this process. This study represents a new paradigm to investigate the structure-function relationship in CcpA by fluorescence polarization experiments in vitro. The results also uncover key amino acids in the DNA-binding domain that affect the selective utilization of carbon sources. These results provide a theoretical basis for the rational design of industrial microorganisms.

bioengineering↗

bioRxiv2021

Awareness-dependent normalization framework of visual bottom-up attention

Although bottom-up attention can improve visual performance with and without awareness, whether they are governed by a common neural computation remains unclear. Using a modified Posner paradigm with backward masking, we found that both the attention-triggered cueing effect with and without awareness displayed a monotonic gradient profile (Gaussian-like). The scope of this profile, however, was significantly wider with than without awareness. Subsequently, for each subject, the stimulus size was manipulated as their respective mean scopes with and without awareness while stimulus contrast was varied in a spatial cueing task. By measuring the gain pattern of contrast-response functions, we observed changes in the cueing effect consonant with changes in contrast gain for bottom-up attention with awareness and response gain for bottom-up attention without awareness. Our findings indicate an awareness-dependent normalization framework of visual bottom-up attention, placing a necessary constraint, namely, awareness, on our understanding of the neural computations underlying visual attention.

neuroscience↗

bioRxiv2021

A tandem-repeat dimeric RBD protein-based COVID-19 vaccine ZF2001 protects mice and nonhuman primates

A safe, efficacious and deployable vaccine is urgently needed to control COVID-19 pandemic. We report here the preclinical development of a COVID-19 vaccine candidate, ZF2001, which contains tandem-repeat dimeric receptor-binding domain (RBD) protein with alum-based adjuvant. We assessed vaccine immunogenicity and efficacy in both mice and non-human primates (NHPs). ZF2001 induced high levels of RBD-binding and SARS-CoV-2 neutralizing antibody in both mice and NHPs, and also elicited balanced TH1/TH2 cellular responses in NHPs. Two doses of ZF2001 protected Ad-hACE2-transduced mice against SARS-CoV-2 infection, as detected by reduced viral RNA and relieved lung injuries. In NHPs, vaccination of either 25 g or 50 g ZF2001 prevented infection with SARS-CoV-2 in lung, trachea and bronchi, with milder lung lesions. No evidence of disease enhancement is observed in both models. ZF2001 is being evaluated in the ongoing international multi-center Phase 3 trials (NCT04646590) and has been approved for emergency use in Uzbekistan.

immunology↗

bioRxiv2021

Expansion-Assisted Iterative-FISH defines lateral hypothalamus spatio-molecular organization

Determining the spatial organization and morphological characteristics of molecularly defined cell types is a major bottleneck for characterizing the architecture underpinning brain function. We developed Expansion-Assisted Iterative Fluorescence In Situ Hybridization (EASI-FISH) to survey gene expression in brain tissue, as well as a turnkey computational pipeline to rapidly process large EASI-FISH image datasets. EASI-FISH was optimized for thick brain sections (300 {micro}m) to facilitate reconstruction of spatio-molecular domains that generalize across brains. Using the EASI-FISH pipeline, we investigated the spatial distribution of dozens of molecularly defined cell types in the lateral hypothalamic area (LHA), a brain region with poorly defined anatomical organization. Mapping cell types in the LHA revealed nine novel spatially and molecularly defined subregions. EASI-FISH also facilitates iterative re-analysis of scRNA-Seq datasets to determine marker-genes that further dissociated spatial and morphological heterogeneity. The EASI-FISH pipeline democratizes mapping molecularly defined cell types, enabling discoveries about brain organization. Highlights- EASI-FISH enables robust gene expression profiling in thick brain slices - A turnkey analysis pipeline for facile analysis of large EASI-FISH image datasets - EASI-FISH reveals novel subregions of the lateral hypothalamus - Identification of rare cell types based on morphological and spatial heterogeneity

neuroscience↗

bioRxiv2021

Neutrophils require SKAP2 for reactive oxygen species production following C-type lectin and Candida stimulation

Signaling cascades that convert the recognition of pathogens to efficient inflammatory responses by immune cells, specifically neutrophils, are critical for host survival. SKAP2, an adaptor protein, is required for reactive oxygen species (ROS) generation following stimulation by integrins, formyl peptide receptors and gram-negative bacteria Klebsiella pneumoniae and Yersinia pseudotuberculosis in vitro (Nguyen et al., 2020, Shaban et al., 2020, Boras et al., 2017). SKAP2 is also required for the host defense against K. pneumoniae and{Delta} yopH Y. pseudotuberculosis infection in vivo in mouse models (Shaban et al., 2020, Nguyen et al., 2020). Another class of pattern recognition receptors (PRR) is the C-type lectin receptors (CLR), such as Dectin-1, Dectin-2 and Mincle, that are critical to trigger innate immune responses. Using neutrophils from murine HoxB8-immortalized progenitors, we show that SKAP2 is crucial for maximal ROS response to purified CLR agonists and to the fungal pathogens Candida glabrata and C. albicans, as well as for robust killing of C. glabrata. Skap2-/- murine neutrophils failed to generate ROS and exhibited reduced cellular adhesion in response to trehalose-6,6-dibehenate (TDB), furfurman, and curdlan, Mincle, Dectin-2, and Dectin-1 agonists, respectively. TDB, furfurman, and curdlan stimulation also led to SKAP2-independent integrin conformational changes, showing that inside-out signaling by these CLRs to integrin occurs in the absence of SKAP2. Pyk2 phosphorylation was significantly reduced after infection with C. glabrata in Skap2-/- neutrophils, while Syk phosphorylation was unaffected by the loss of SKAP2. These data strengthen the importance of SKAP2 in the activation of neutrophil ROS production by PRRs to include CLRs and extend the role of SKAP2 in host defense beyond antibacterial immunity to include Candida species.

immunology↗

bioRxiv2021

Sulfur limitation increases duckweed starch accumulation without compromising growth

Duckweeds contain relatively high levels of starch and are a potential biomass feedstock for biofuel production. Here, the biomass and starch yield of duckweed under three different nutrient-limited conditions were analyzed to investigate possible ways of further increasing the efficiency of starch production. The results showed that sulfur limitation resulted in the highest starch yield, which was 42% and 73% higher than in nitrogen or phosphorus limitation, respectively. The high yield of sulfur-limited duckweed is largely due to the combinations of little effects on biomass and high accumulations of starch. Although nitrogen limitation led to higher starch content (67.4%), it severely reduced biomass production. The photosynthetic performance indicator Fv/Fm was a simple and sensitive indicator of starch content in nutrient-limited duckweed. Taken together, this study demonstrates that sulfur limitation is a simple and efficient way to increase starch yield, highlighting the great potential of duckweed for biofuel production. We report that sulfur limitation is a practical approach to increase starch yields in duckweed without affecting growth or biomass. HighlightsO_LISulfur limitation induces starch production in a duckweed specie. C_LIO_LINitrogen limitation triggers the highest starch content, but limits growth. C_LIO_LISulfur limitation results in the highest starch yield. C_LIO_LIFv/Fm is a rapid and robust proxy of starch content in nutrient-limited duckweed. C_LI

plant biology↗

bioRxiv2021

KLF2 is a therapeutic target for COVID-19 induced endothelial dysfunction

Coronavirus disease 2019 (COVID-19) is regarded as an endothelial disease (endothelialitis) with its mechanism being incompletely understood. Emerging evidence has demonstrated that the endothelium represents the Achilles' heel in COVID-19 patients and that endothelial dysfunction precipitates COVID-19 and accompanying multi-organ injuries. Thus, pharmacotherapies targeting endothelial dysfunction have potential to ameliorate COVID-19 and its cardiovascular complications. Primary human umbilical vein endothelial cells (HUVECs) and human pulmonary microvascular endothelial cells (HPMECs) were treated with serum from control subjects or COVID-19 patients. Downstream monocyte adhesion and associated gene/protein expression was evaluated in endothelial cells exposed to COVID-19 patient serum in the presence of KLF2 activator (Atorvastatin) or KLF2 overexpression by an adenoviral vector. Here, we demonstrate that the expression of KLF2 was significantly reduced and monocyte adhesion was increased in endothelial cells treated with COVID-19 patient serum due to elevated levels of pro-adhesive molecules, ICAM1 and VCAM1. IL-1{beta} and TNF-, two cytokines observed in cytokine release syndrome in COVID-19 patients, decreased KLF2 gene expression. Next-generation RNA-sequencing data showed that atorvastatin treatment leads to a cardiovascular protective transcriptome associated with improved endothelial function (vasodilation, anti-inflammation, antioxidant status, anti-thrombosis/-coagulation, anti-fibrosis and reduced angiogenesis). Treatment of HPMECs with atorvastatin or KLF2 adenovirus ameliorate COVID-19 serum-induced increase in endothelial inflammation and monocyte adhesion by increasing KLF2 expression. Altogether, the present study demonstrates that genetic and pharmacological activation of KLF2 represses COVID-19 associated endothelial dysfunction, heralding a potentially new direction to treat endothelialitis accompanying COVID-19.

pharmacology and toxicology↗