ELMO1 Deficiency Reduces Neutrophil Chemotaxis in Murine Peritonitis.

Peritoneal inflammation remains a major cause of treatment failure in patients with kidney failure who receive peritoneal dialysis. Peritoneal inflammation is characterized by an increase in neutrophil infiltration. However, the molecular mechanisms that control neutrophil recruitment in peritonitis are not fully understood. ELMO and DOCK proteins form complexes which function as guanine nucleotide exchange factors to activate the small GTPase Rac to regulate F-actin dynamics during chemotaxis. In the current study, we found that deletion of the Elmo1 gene causes defects in chemotaxis and the adhesion of neutrophils. ELMO1 plays a role in the fMLP-induced activation of Rac1 in parallel with the PI3K and mTORC2 signaling pathways. Importantly, we also reveal that peritoneal inflammation is alleviated in Elmo1 knockout mice in the mouse model of thioglycollate-induced peritonitis. Our results suggest that ELMO1 functions as an evolutionarily conserved regulator for the activation of Rac to control the chemotaxis of neutrophils both in vitro and in vivo. Our results suggest that the targeted inhibition of ELMO1 may pave the way for the design of novel anti-inflammatory therapies for peritonitis.

1,25-Dihydroxyvitamin D deficiency induces sarcopenia by inducing skeletal muscle cell senescence.

To determine if 1,25(OH)2D deficiency can induce age-related sarcopenia, the skeletal muscular phenotype of male wild-type (WT) and Cyp27b1 knockout (KO) mice were compared at 3 and 6 months of age. We found that muscle mass, grip strength and muscle fiber size were significantly decreased in aging Cyp27b1 KO male mice. The expression levels of genes related to mitochondrial metabolic activity, and antioxidant enzymes including SOD1, catalase, Nqo1 and Gcs were significantly down-regulated in skeletal muscle tissue of Cyp27b1 KO male mice; in contrast, the percentage of p16+ and p21+ myofibers, and the expression of p16, p19, p21, p53, TNFα, IL6 and MMP3 at mRNA and/or protein levels were significantly increased. We then injected tibialis anterior muscle of WT and Cyp27b1+/- male mice with BaCl2, and analyzed the regenerative ability of skeletal muscle cells 7 days later. The results revealed that the numbers of newly formed regenerating central nucleated fibers (CNF), the percentage of BrdU+ cells and the expression of MyoD, MyHC and Myf5 at mRNA levels were significantly down-regulated in the injured skeletal muscle tissue of Cyp27b1+/- mice. In summary, our studies indicate that 1,25(OH)2D deficiency can result in the development of age-related sarcopenia by inducing oxidative stress, skeletal muscular cell senescence and SASP, and by inhibiting skeletal muscle regeneration. Cyp27b1 KO mice can therefore be used as an animal model of age-related sarcopenia in order to investigate the pathogenesis of age-related sarcopenia and potentially to test intervention measures for treatment of sarcopenia.

Mesenchymal stem cell treatment improves outcome of COVID-19 patients via multiple immunomodulatory mechanisms.

The infusion of coronavirus disease 2019 (COVID-19) patients with mesenchymal stem cells (MSCs) potentially improves clinical symptoms, but the underlying mechanism remains unclear. We conducted a randomized, single-blind, placebo-controlled (29 patients/group) phase II clinical trial to validate previous findings and explore the potential mechanisms. Patients treated with umbilical cord-derived MSCs exhibited a shorter hospital stay (P = 0.0198) and less time required for symptoms remission (P = 0.0194) than those who received placebo. Based on chest images, both severe and critical patients treated with MSCs showed improvement by day 7 (P = 0.0099) and day 21 (P = 0.0084). MSC-treated patients had fewer adverse events. MSC infusion reduced the levels of C-reactive protein, proinflammatory cytokines, and neutrophil extracellular traps (NETs) and promoted the maintenance of SARS-CoV-2-specific antibodies. To explore how MSCs modulate the immune system, we employed single-cell RNA sequencing analysis on peripheral blood. Our analysis identified a novel subpopulation of VNN2+ hematopoietic stem/progenitor-like (HSPC-like) cells expressing CSF3R and PTPRE that were mobilized following MSC infusion. Genes encoding chemotaxis factors - CX3CR1 and L-selectin - were upregulated in various immune cells. MSC treatment also regulated B cell subsets and increased the expression of costimulatory CD28 in T cells in vivo and in vitro. In addition, an in vivo mouse study confirmed that MSCs suppressed NET release and reduced venous thrombosis by upregulating kindlin-3 signaling. Together, our results underscore the role of MSCs in improving COVID-19 patient outcomes via maintenance of immune homeostasis.

ELMO1 Regulates RANKL-Stimulated Differentiation and Bone Resorption of Osteoclasts.

Bone homeostasis is a metabolic balance between the new bone formation by osteoblasts and old bone resorption by osteoclasts. Excessive osteoclastic bone resorption results in low bone mass, which is the major cause of bone diseases such as rheumatoid arthritis. Small GTPases Rac1 is a key regulator of osteoclast differentiation, but its exact mechanism is not fully understood. ELMO and DOCK proteins form complexes that function as guanine nucleotide exchange factors for Rac activation. Here, we report that ELMO1 plays an important role in differentiation and bone resorption of osteoclasts. Osteoclast precursors derived from bone marrow monocytes (BMMs) of Elmo1-/- mice display defective adhesion and migration during differentiation. The cells also have a reduced activation of Rac1, p38, JNK, and AKT in response to RANKL stimulation. Importantly, we show that bone erosion is alleviated in Elmo1-/- mice in a rheumatoid arthritis mouse model. Taken together, our results suggest that ELMO1, as a regulator of Rac1, regulates osteoclast differentiation and bone resorption both in vitro and in vivo.

Isotope dilution LC/ESI--MS-MS quantitation of urinary 1,4-bis(N-acetyl-S-cysteinyl)-2-butanone in mice and rats as the biomarker of 1-chloro-2-hydroxy-3-butene, an in vitro metabolite of 1,3-butadiene.

1-Chloro-2-hydroxy-3-butene (CHB) is a possible metabolite of 1,3-butadiene, a carcinogenic air pollutant. To demonstrate its formation in vivo, it is desirable to develop a practical biomarker and the corresponding analysis method. CHB can undergo alcohol dehydrogenase- and cytochromes P450 enzymes (P450)-mediated oxidation to yield 1-chloro-3-buten-2-one (CBO), which readily forms glutathione conjugates. We hypothesized that CBO-derived mercapturic acids, which are the expected biotransformed products of CBO-glutathione conjugates, could be used as CHB biomarkers. Thus, in the present study, we investigated the in vivo biotransformation of CHB into CBO-derived mercapturic acids. Because the reaction of CBO with N-acetyl-l-cysteine yields two products, 1,4-bis(N-acetyl-S-cysteinyl)-2-butanone (NC1) and 1-chloro-4-(N-acetyl-S-cysteinyl)-2-butanone (NC2), we first developed an isotope dilution LC/ESI--MS-MS method to quantitate urinary NC1 and NC2, and then determined their concentrations in urine of C57BL/6 mice and Sprague-Dawley rats administered CHB. Since no NC2 was detected in samples, the LC/ESI--MS-MS method was optimized specifically for NC1. NC1 was enriched through solid phase extraction with the recovery being 75-82%. The limits of detection and quantitation were 6.8 and 34 fmol/0.1 mL for mouse urine, and 4.5 and 7.1 fmol/0.1 mL for rat urine, respectively. In urine of animals before CHB administration, no NC1 was detected; in mice administered CHB at 10 and 30 mg/kg, and rats at 5 and 15 mg/kg, NC1 was detected and its concentrations in urine from animals given higher doses were 3-6 fold higher than those given lower doses. Moreover, the NC1 concentrations in urine during 0-8 h were 4-6 fold and 10-11 fold higher than those during 8-24 h for mice and rats, respectively. The results demonstrated that CHB could be in vivo biotransformed into NC1, which could be used as a practical CHB biomarker.

Roles for HB-EGF in Mesenchymal Stromal Cell Proliferation and Differentiation During Skeletal Growth.

HB-EGF, a member of the EGF superfamily, plays important roles in development and tissue regeneration. However, its functions in skeletal stem cells and skeleton development and growth remain poorly understood. Here, we used the Cre/LoxP system to ablate or express HB-EGF in Dermo1+ mesenchymal stromal cells and their progenies, including chondrocytes and osteoblast lineage cells, and bone marrow stromal cells (BMSCs). Dermo1-Cre; HB-EGFf/f mice only showed a modest increase in bone mass, whereas Dermo1-HB-EGF mice developed progressive chondrodysplasia, chondroma, osteoarthritis-like joint defects, and loss of bone mass and density, which were alleviated by treatment with EGFR inhibitor AG1478. The cartilage defects were recapitulated in chondrocyte-specific HB-EGF overexpression (Col2-HB-EGF) mice with a lesser severity. Dermo1-HB-EGF mice showed an increase in proliferation but defects in differentiation of chondrocytes and osteoblasts. HB-EGF promoted BMSC proliferation via the Akt1 and Erk pathways but inhibited BMSC differentiation via restraining Smad1/5/8 activation. However, Dermo1-HB-EGF mice showed normal osteoclastogenesis and bone resorption. These results reveal an important function of autocrine or paracrine HB-EGF in mesenchymal stromal cell proliferation and differentiation and suggest that EGF signaling needs to be tightly controlled to maintain bone and articular cartilage integrity. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

Identification of Associated Proteins by Immunoprecipitation and Mass Spectrometry Analysis.

Protein-protein interactions play central roles in intercellular and intracellular signal transduction. Impairment of protein-protein interactions causes many diseases such as cancer, cardiomyopathies, diabetes, microbial infections, and genetic and neurodegenerative disorders. Immunoprecipitation is a technique in which a target protein of interest bound by an antibody is used to pull down the protein complex out of cell lysates, which can be identified by mass spectrometry. Here, we describe the protocol to immunoprecipitate and identify the components of the protein complexes of ElmoE in Dictyostelium discoideum cells.

In vivo Raman measurement of levofloxacin lactate in blood using a nanoparticle-coated optical fiber probe.

Monitoring drug concentrations in vivo is very useful for adjusting a drug dosage during treatment and for drug research. Specifically, cutting-edge "on-line" drug research relies on knowing how drugs are metabolized or how they interact with the blood in real-time. Thus, this study explored performing in vivo Raman measurements of the model drug levofloxacin lactate in the blood using a nanoparticle-coated optical fiber probe (optical fiber nano-probe). The results show that we were able to measure real-time changes in the blood concentration of levofloxacin lactate, suggesting that this technique could be helpful for performing drug analyses and drug monitoring in a clinical setting without repeatedly withdrawing blood from patients.

MiR-130b suppresses prostate cancer metastasis through down-regulation of MMP2.

Prostate cancer (PCa) is the most prevalent malignant carcinoma among males in western countries. Currently no treatments can cure advanced prostate cancers, so new diagnostic and therapeutic strategies are in urgent need. At present limited knowledge is available concerning the roles of dysregulated microRNAs in prostate cancer metastasis. In this study, we found that the expression of miR-130b was significantly down-regulated in prostate cancer cell lines and clinical prostate cancer tissues. Enforced over-expression of miR-130b in prostate cancer cells suppressed whereas knock-down of miR-130b increased cell migration and invasion. Using mouse model, we revealed that miR-130b-expressed prostate cancer cells displayed significant reduction in tumor metastasis. Furthermore, we identified and validated matrix metalloproteinase-2 (MMP2) as a direct target of miR-130b. Ectopic expression of MMP2 rescued miR-130b-suppressed cell migration and invasion, and knock-down of MMP2 antagonized the effect of silencing miR-130b.Taken together, our data reveal for the first time that miR-130b exerts a suppressive effect in prostate cancer metastasis through down-regulation of MMP2.

Arrestins function in cAR1 GPCR-mediated signaling and cAR1 internalization in the development of Dictyostelium discoideum.

Oscillation of chemical signals is a common biological phenomenon, but its regulation is poorly understood. At the aggregation stage of Dictyostelium discoideum development, the chemoattractant cAMP is synthesized and released at 6-min intervals, directing cell migration. Although the G protein-coupled cAMP receptor cAR1 and ERK2 are both implicated in regulating the oscillation, the signaling circuit remains unknown. Here we report that D. discoideum arrestins regulate the frequency of cAMP oscillation and may link cAR1 signaling to oscillatory ERK2 activity. Cells lacking arrestins (adcB(-)C(-)) display cAMP oscillations during the aggregation stage that are twice as frequent as for wild- type cells. The adcB(-)C(-) cells also have a shorter period of transient ERK2 activity and precociously reactivate ERK2 in response to cAMP stimulation. We show that arrestin domain-containing protein C (AdcC) associates with ERK2 and that activation of cAR1 promotes the transient membrane recruitment of AdcC and interaction with cAR1, indicating that arrestins function in cAR1-controlled periodic ERK2 activation and oscillatory cAMP signaling in the aggregation stage of D. discoideum development. In addition, ligand-induced cAR1 internalization is compromised in adcB(-)C(-) cells, suggesting that arrestins are involved in elimination of high-affinity cAR1 receptors from cell surface after the aggregation stage of multicellular development.

lncRNA H19/miR-675 axis represses prostate cancer metastasis by targeting TGFBI.

Prostate cancer is a leading cause of cancer-related mortality in men worldwide and there is a lack of effective treatment options for advanced (metastatic) prostate cancer. Currently, limited knowledge is available concerning the role of long non-coding RNAs in prostate cancer metastasis. In this study, we found that long non-coding RNA H19 (H19) and H19-derived microRNA-675 (miR-675) were significantly downregulated in the metastatic prostate cancer cell line M12 compared with the non-metastatic prostate epithelial cell line P69. Upregulation of H19 in P69 and PC3 cells significantly increased the level of miR-675 and repressed cell migration; however, ectopic expression of H19 in M12 cells could not increase the level of miR-675 and therefore had no effect on cell migration. Furthermore, we found that the expression level of either H19 or miR-675 in P69 cells was negatively associated with the expression of transforming growth factor ß induced protein (TGFBI), an extracellular matrix protein involved in cancer metastasis. Dual luciferase reporter assays showed that miR-675 directly bound with 3'UTR of TGFBI mRNA to repress its translation. Taken together, we show for the first time that the H19-miR-675 axis acts as a suppressor of prostate cancer metastasis, which may have possible diagnostic and therapeutic potential for advanced prostate cancer.

Association between Gαi2 and ELMO1/Dock180 connects chemokine signalling with Rac activation and metastasis.

The chemokine CXCL12 and its G-protein-coupled receptor CXCR4 control the migration, invasiveness and metastasis of breast cancer cells. Binding of CXCL12 to CXCR4 triggers activation of heterotrimeric Gi proteins that regulate actin polymerization and migration. However, the pathways linking chemokine G-protein-coupled receptor/Gi signalling to actin polymerization and cancer cell migration are not known. Here we show that CXCL12 stimulation promotes interaction between Gαi2 and ELMO1. Gi signalling and ELMO1 are both required for CXCL12-mediated actin polymerization, migration and invasion of breast cancer cells. CXCL12 triggers a Gαi2-dependent membrane translocation of ELMO1, which associates with Dock180 to activate small G-proteins Rac1 and Rac2. In vivo, ELMO1 expression is associated with lymph node and distant metastasis, and knocking down ELMO1 impairs metastasis to the lung. Our findings indicate that a chemokine-controlled pathway, consisting of Gαi2, ELMO1/Dock180, Rac1 and Rac2, regulates the actin cytoskeleton during breast cancer metastasis.

Signaling network from GPCR to the actin cytoskeleton during chemotaxis.

Chemotaxis is crucial for many physiological processes including the recruitment of leukocytes to sites of infection, trafficking of lymphocytes in the human body, and metastasis of cancer cells. A family of small proteins, chemokines, serves as the signals, and a family of G-protein coupled receptors (GPCRs) detects chemokines and direct cell migration. One of the basic questions in chemotaxis of eukaryotes is how a GPCR transduces signals to control the assembly of the actin network that generates directional force for cell migration. Over the past decade, a variety of signaling components have been implicated to transduce the GPCR signaling to the actin cytoskeleton. Studies in a lower eukaryotic organism, Dictyostelium discoideum, have allowed us to discover evolutionary conversed components involved in the GPCR-controlled actin network during chemotaxis. However, complete pathways linking GPCR to the actin network are still far from clear. Here we first summarize the previous studies on these components, and then update with our finding showing a new pathway, consisting of a GPCR, Gßγ, Elmo/Dock, Rac and Arp2/3 and actin. We suggest that this pathway serves as a direct linkage between the GPCR/G-protein, the chemoattractant sensing machinery, and the actin cytoskeleton, the machinery of cell movement during chemotaxis of eukaryotic cells.

A Gßγ effector, ElmoE, transduces GPCR signaling to the actin network during chemotaxis.

Activation of G protein-coupled receptors (GPCRs) leads to the dissociation of heterotrimeric G-proteins into Gα and Gßγ subunits, which go on to regulate various effectors involved in a panoply of cellular responses. During chemotaxis, Gßγ subunits regulate actin assembly and migration, but the protein(s) linking Gßγ to the actin cytoskeleton remains unknown. Here, we identified a Gßγ effector, ElmoE in Dictyostelium, and demonstrated that it is required for GPCR-mediated chemotaxis. Remarkably, ElmoE associates with Gßγ and Dock-like proteins to activate the small GTPase Rac, in a GPCR-dependent manner, and also associates with Arp2/3 complex and F-actin. Thus, ElmoE serves as a link between chemoattractant GPCRs, G-proteins and the actin cytoskeleton. The pathway, consisting of GPCR, Gßγ, Elmo/Dock, Rac, and Arp2/3, spatially guides the growth of dendritic actin networks in pseudopods of eukaryotic cells during chemotaxis.

Coupling mechanism of a GPCR and a heterotrimeric G protein during chemoattractant gradient sensing in Dictyostelium.

The coupling of heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs) with G proteins is fundamental for GPCR signaling; however, the mechanism of coupling is still debated. Moreover, how the proposed mechanisms affect the dynamics of downstream signaling remains unclear. Here, through experiments involving fluorescence recovery after photobleaching and single-molecule imaging, we directly measured the mobilities of cyclic adenosine monophosphate (cAMP) receptor 1 (cAR1), a chemoattractant receptor, and a G protein ßγ subunit in live cells. We found that cAR1 diffused more slowly in the plasma membrane than did Gßγ. Upon binding of ligand to the receptor, the mobility of cAR1 was unchanged, whereas the speed of a fraction of the faster-moving Gßγ subunits decreased. Our measurements showed that cAR1 was relatively immobile and Gßγ diffused freely, suggesting that chemoattractant-bound cAR1 transiently interacted with G proteins. Using models of possible coupling mechanisms, we computed the temporal kinetics of G protein activation. Our fluorescence resonance energy transfer imaging data showed that fully activated cAR1 induced the sustained dissociation of G protein α and ßγ subunits, which indicated that ligand-bound cAR1 activated G proteins continuously. Finally, simulations indicated that a high-affinity coupling of ligand-bound receptors and G proteins was essential for cAR1 to translate extracellular gradient signals into directional cellular responses. We suggest that chemoattractant receptors use a ligand-induced coupling rather than a precoupled mechanism to control the activation of G proteins during chemotaxis.

The Elmo family forms an ancient group of actin-regulating proteins.

The Elmo protein family members are important mediators of small G protein activity, regulating actin-mediated processes such as chemotaxis and engulfment. Until recently,1 Elmo function has not been explored in professional phagocytes such as Dictyostelium discoideum. We discuss the significance of this family with respect to pathways that regulate Rac signaling, we present a comparison of Elmo proteins between representative taxa, and discuss our findings on ElmoA, one of six Elmo proteins found in D. discoideum.

How human leukocytes track down and destroy pathogens: lessons learned from the model organism Dictyostelium discoideum.

Human leukocytes, including macrophages and neutrophils, are phagocytic immune cells that capture and engulf pathogens and subsequently destroy them in intracellular vesicles. To accomplish this vital task, these leukocytes utilize two basic cell behaviors-chemotaxis for chasing down infectious pathogens and phagocytosis for destroying them. The molecular mechanisms controlling these behaviors are not well understood for immune cells. Interestingly, a soil amoeba, Dictyostelium discoideum, uses these same behaviors to pursue and injest its bacterial food source and to organize its multi-cellular development. Consequently, studies of this model system have provided and will continue to provide us with mechanistic insights into the chemotaxis and phagocytosis of immune cells. Here, we review recent research in these areas that have been conducted in the Chemotaxis Signal Section of NIAID's Laboratory of Immunogenetics.

In vivo acetylation of CheY, a response regulator in chemotaxis of Escherichia coli.

CheY, the excitatory response regulator in the chemotaxis system of Escherichia coli, can be modulated by two covalent modifications: phosphorylation and acetylation. Both modifications have been detected in vitro only. The role of CheY acetylation is still obscure, although it is known to be involved in chemotaxis and to occur in vitro by two mechanisms--acetyl-CoA synthetase-catalyzed transfer of acetyl groups from acetate to CheY and autocatalyzed transfer from AcCoA. Here, we succeeded in detecting CheY acetylation in vivo by three means--Western blotting with a specific anti-acetyl-lysine antibody, mass spectrometry, and radiolabeling with [(14)C]acetate in the presence of protein-synthesis inhibitor. Unexpectedly, the level and rate of CheY acetylation in vivo were much higher than that in vitro. Thus, before any treatment, 9-13% of the lysine residues were found acetylated, depending on the growth phase, meaning that, on average, essentially every CheY molecule was acetylated in vivo. This high level was mainly the outcome of autoacetylation. Addition of acetate caused an incremental increase in the acetylation level, in which acetyl-CoA synthetase was involved too. These findings may have far-reaching implications for the structure-function relationship of CheY.

Locally controlled inhibitory mechanisms are involved in eukaryotic GPCR-mediated chemosensing.

Gprotein-coupled receptor (GPCR) signaling mediates a balance of excitatory and inhibitory activities that regulate Dictyostelium chemosensing to cAMP. The molecular nature and kinetics of these inhibitors are unknown. We report that transient cAMP stimulations induce PIP3 responses without a refractory period, suggesting that GPCR-mediated inhibition accumulates and decays slowly. Moreover, exposure to cAMP gradients leads to asymmetric distribution of the inhibitory components. The gradients induce a stable accumulation of the PIP3 reporter PHCrac-GFP in the front of cells near the cAMP source. Rapid withdrawal of the gradient led to the reassociation of G protein subunits, and the return of the PIP3 phosphatase PTEN and PHCrac-GFP to their pre-stimulus distribution. Reapplication of cAMP stimulation produces a clear PHCrac-GFP translocation to the back but not to the front, indicating that a stronger inhibition is maintained in the front of a polarized cell. Our study demonstrates a novel spatiotemporal feature of currently unknown inhibitory mechanisms acting locally on the PI3K activation pathway.