G protein-coupled receptor crosstalk and signaling in hematopoietic stem and progenitor cells

Chronic alcohol consumption enhances the differentiation capacity of hematopoietic stem and progenitor cells into osteoclast precursors

Chronic alcohol consumption (CAC) is associated with an enhanced risk of bone fracture, reduced bone density, and osteoporosis. We have previously shown using a rhesus macaque model of voluntary ethanol consumption that CAC induces functional, transcriptomic, and epigenomic changes in hematopoietic stem and progenitor cells (HSPCs) and their resultant monocytes/macrophages, skewing them towards a hyper-inflammatory response. Here, we extended those studies and investigated alterations in osteoclasts, which, in postnatal life, are differentiated from HSPCs and play a critical role in maintaining bone homeostasis. Analysis using spectral flow cytometry revealed a skewing of HSPCs towards granulocyte-monocyte progenitors (GMPs) with the CAC group that was in concordance with an increased number of colony-forming unit-granulocyte/macrophage (CFU-GM). Additionally, HSPCs from animals in the CAC group incubated with M-CSF and RANKL were more likely to differentiate into osteoclasts, as evidenced by increased Tartrate-Resistant Acid Phosphatase (TRAP) staining and bone resorption activity. Moreover, single-cell RNA sequencing of differentiated HSPCs identified three clusters of osteoclast precursors in the CAC group with enhanced gene expression in pathways associated with cellular response to stimuli, membrane trafficking, and vesicle-mediated transport. Collectively, these data show that CAC-derived hematopoietic progenitor cells exhibit a higher capacity to differentiate into osteoclast precursors. These findings provide critical insights for future research on the mechanisms by which CAC disrupts monopoiesis homeostasis and enhances osteoclast precursors, thereby contributing to reduced bone density.

Functional selective FPR1 signaling in favor of an activation of the neutrophil superoxide generating NOX2 complex

The formyl peptide receptors FPR1 and FPR2 are abundantly expressed by neutrophils, in which they regulate proinflammatory tissue recruitment of inflammatory cells, the production of reactive oxygen species (ROS), and resolution of inflammatory reactions. The unique dual functionality of the FPRs makes them attractive targets to develop FPR‐based therapeutics as novel anti‐inflammatory treatments. The small compound RE‐04‐001 has earlier been identified as an inducer of ROS in differentiated HL60 cells but the precise target and the mechanism of action of the compound was has until now not been elucidated. In this study, we reveal that RE‐04‐001 specifically targets and activates FPR1, and the concentrations needed to activate the neutrophil NADPH‐oxidase was very low (EC₅₀ ∼1 nM). RE‐04‐001 was also found to be a neutrophil chemoattractant, but when compared to the prototype FPR1 agonist N‐formyl‐Met‐Leu‐Phe (fMLF), the concentrations required were comparably high, suggesting that signaling downstream of the RE‐04‐001‐activated‐FPR1 is functionally selective. In addition, the RE‐04‐001‐induced response was strongly biased toward the PLC‐PIP₂‐Ca²⁺ pathway and ERK1/2 activation but away from β‐arrestin recruitment. Compared to the peptide agonist fMLF, RE‐04‐001 is more resistant to inactivation by the MPO‐H₂O₂‐halide system. In summary, this study describes RE‐04‐001 as a novel small molecule agonist specific for FPR1, which displays a biased signaling profile that leads to a functional selective activating of human neutrophils. RE‐04‐001 is, therefore, a useful tool, not only for further mechanistic studies of the regulatory role of FPR1 in inflammation in vitro and in vivo, but also for developing FPR1‐specific drug therapeutics.

An Overview on G Protein-coupled Receptor-induced Signal Transduction in Acute Myeloid Leukemia

BACKGROUND

Acute Myeloid Leukemia (AML) is a genetically heterogeneous disease characterized by uncontrolled proliferation of precursor myeloid-lineage cells in the bone marrow. AML is also characterized by patients with poor long-term survival outcomes due to relapse. Many efforts have been made to understand the biological heterogeneity of AML and the challenges to develop new therapies are therefore enormous. G Protein-coupled Receptors (GPCRs) are a large attractive drug-targeted family of transmembrane proteins, and aberrant GPCR expression and GPCR-mediated signaling have been implicated in leukemogenesis of AML. This review aims to identify the molecular players of GPCR signaling, focusing on the hematopoietic system, which are involved in AML to help developing novel drug targets and therapeutic strategies.

METHODS

We undertook an exhaustive and structured search of bibliographic databases for research focusing on GPCR, GPCR signaling and expression in AML.

RESULTS AND CONCLUSION

Many scientific reports were found with compelling evidence for the involvement of aberrant GPCR expression and perturbed GPCR-mediated signaling in the development of AML. The comprehensive analysis of GPCR in AML provides potential clinical biomarkers for prognostication, disease monitoring and therapeutic guidance. It will also help to provide marker panels for monitoring in AML. We conclude that GPCR-mediated signaling is contributing to leukemogenesis of AML, and postulate that mass spectrometrybased protein profiling of primary AML cells will accelerate the discovery of potential GPCR related biomarkers for AML.

Human Cytomegalovirus UL111A and US27 Gene Products Enhance the CXCL12/CXCR4 Signaling Axis via Distinct Mechanisms

Human cytomegalovirus (HCMV) is a prevalent pathogen that establishes lifelong infection in the host. Virus persistence is aided by extensive manipulation of the host immune system, particularly cytokine and chemokine signaling pathways. The HCMV UL111A gene encodes cmvIL-10, an ortholog of human interleukin-10 that has many immunomodulatory effects. We found that cmvIL-10 increased signaling outcomes from human CXCR4, a chemokine receptor with essential roles in hematopoiesis and immune cell trafficking, in response to its natural ligand CXCL12. Calcium flux and chemotaxis to CXCL12 were significantly greater in the presence of cmvIL-10 in monocytes, epithelial cells, and fibroblasts that express CXCR4. cmvIL-10 effects on CXCL12/CXCR4 signaling required the IL-10 receptor and Stat3 activation. Heightened signaling occurred both in HCMV-infected cells and in uninfected bystander cells, suggesting that cmvIL-10 may broadly influence chemokine networks by paracrine signaling during infection. Moreover, CXCL12/CXCR4 signaling was amplified in HCMV-infected cells compared to mock-infected cells even in the absence of cmvIL-10. Enhanced CXCL12/CXCR4 outcomes were associated with expression of the virally encoded chemokine receptor US27, and CXCL12/CXCR4 activation was reduced in cells infected with a deletion mutant lacking US27 (TB40/E-mCherry-US27Δ). US27 effects were Stat3 independent but required close proximity to CXCR4 in cell membranes of either HCMV-infected or US27-transfected cells. Thus, HCMV encodes two proteins, cmvIL-10 and US27, that exhibit distinct mechanisms for enhancing CXCR4 signaling. Either individually or in combination, cmvIL-10 and US27 may enable HCMV to exquisitely manipulate CXCR4 signaling to alter host immune responses and modify cell trafficking patterns during infection.IMPORTANCE The human chemokine system plays a central role in host defense, as evidenced by the many strategies devised by viruses for manipulating it. Human cytomegalovirus (HCMV) is widespread in the human population, but infection rarely causes disease except in immunocompromised hosts. We found that two different HCMV proteins, cmvIL-10 and US27, act through distinct mechanisms to upregulate the signaling activity of a cellular chemokine receptor, CXCR4. cmvIL-10 is a secreted viral cytokine that affects CXCR4 signaling in both infected and uninfected cells, while US27 is a component of the virus particle and impacts CXCR4 activity only in infected cells. Both cmvIL-10 and US27 promote increased intracellular calcium signaling and cell migration in response to chemokine CXCL12 binding to CXCR4. Our results demonstrate that HCMV exerts fine control over the CXCL12/CXCR4 pathway, which could lead to enhanced virus dissemination, altered immune cell trafficking, and serious health implications for HCMV patients.

Pleiotropic effects of sphingosine-1-phosphate signaling to control human chorionic mesenchymal stem cell physiology

Chorionic stem cells represent a promising opportunity for regenerative medicine. A deeper understanding of the stimuli that regulate their physiology, could lead to innovative clinical approaches. We revealed the presence of multiple sphingosine-1-phosphate (S1P) receptor isoforms in chorion-derived mesenchymal stem cells (CMSCs). Their activation simultaneously propagated from the plasma membrane through Gi and other heterotrimeric G proteins and further diverged toward extracellular-signal-regulated kinase 1/2 (ERK1/2), p38 and protein kinase D 1. At a functional level, S1P signaling inhibited CMSC migration, while promoting proliferation. Instead, a reduction of cell density was obtained when S1P was combined to treatments that increased cAMP intracellular concentration. Such surprising reduction of cell viability was relatively specific as it was not observed with stromal stem cells from bone marrow. Neither it was observed by activating analogous G proteins with bradykinin nor by inducing cell death via a cAMP-independent pathway. S1P could thus reveal novel keys to improve CMSC differentiation programs acting on cAMP concentration. Furthermore, S1P receptor agonists/antagonists could become instrumental in favoring CMSC engraftment by controlling cell motility.

Cannabinoid receptor subtype 2 (CB2R) agonist, GW405833 reduces agonist-induced Ca(2+) oscillations in mouse pancreatic acinar cells

Emerging evidence demonstrates that the blockade of intracellular Ca(2+) signals may protect pancreatic acinar cells against Ca(2+) overload, intracellular protease activation, and necrosis. The activation of cannabinoid receptor subtype 2 (CB2R) prevents acinar cell pathogenesis in animal models of acute pancreatitis. However, whether CB2Rs modulate intracellular Ca(2+) signals in pancreatic acinar cells is largely unknown. We evaluated the roles of CB2R agonist, GW405833 (GW) in agonist-induced Ca(2+) oscillations in pancreatic acinar cells using multiple experimental approaches with acute dissociated pancreatic acinar cells prepared from wild type, CB1R-knockout (KO), and CB2R-KO mice. Immunohistochemical labeling revealed that CB2R protein was expressed in mouse pancreatic acinar cells. Electrophysiological experiments showed that activation of CB2Rs by GW reduced acetylcholine (ACh)-, but not cholecystokinin (CCK)-induced Ca(2+) oscillations in a concentration-dependent manner; this inhibition was prevented by a selective CB2R antagonist, AM630, or was absent in CB2R-KO but not CB1R-KO mice. In addition, GW eliminated L-arginine-induced enhancement of Ca(2+) oscillations, pancreatic amylase, and pulmonary myeloperoxidase. Collectively, we provide novel evidence that activation of CB2Rs eliminates ACh-induced Ca(2+) oscillations and L-arginine-induced enhancement of Ca(2+) signaling in mouse pancreatic acinar cells, which suggests a potential cellular mechanism of CB2R-mediated protection in acute pancreatitis.

Proteolytic processing of human serum albumin generates EPI-X4, an endogenous antagonist of CXCR4

The chemokine receptor CXCR4 is an important G protein-coupled receptor. Signaling via CXCL12 regulates a number of important biologic processes, including immune responses, organogenesis, or hematopoiesis. Dysregulation of CXCR4 signaling is associated with a variety of diseases, such as cancer development and metastasis, immunodeficiencies, or chronic inflammation. Here, we review our findings on endogenous peptide inhibitor of CXCR4 as a novel antagonist of CXCR4. This peptide is a 16-residue fragment of human serum albumin and was isolated as an inhibitor of CXCR4-tropic human immunodeficiency virus type 1 from a blood-derived peptide library. Endogenous peptide inhibitor of CXCR4 binds the second extracellular loop of CXCR4, thereby preventing engagement of CXCL12 and antagonizing the receptor. Consequently, endogenous peptide inhibitor of CXCR4 inhibits CXCL12-mediated migration of CXCR4-expressing cells in vitro, mobilizes hematopoietic stem cells, and suppresses inflammatory responses in vivo. We discuss the generation of endogenous peptide inhibitor of CXCR4, its relevance as biomarker for disease, and its role in human immunodeficiency virus/acquired immunodeficiency syndrome pathogenesis and cancer. Furthermore, we discuss why optimized endogenous peptide inhibitor of CXCR4 derivatives might have advantages over other CXCR4 antagonists.

Functional consequences of perturbed CXCL12 signal processing: analyses of immature hematopoiesis in GRK6-deficient mice

Hematopoietic stem and progenitor cells (HSPCs) reside in bone marrow (BM) in an environment rich in CXCL12, the ligand for CXCR4, which is constitutively expressed on all immature hematopoietic cells in BM. This ligand-receptor pair critically controls HSPC retention and (relative) quiescence in BM. Interestingly, in a chemokine-abundant environment, CXCR4 surface expression and CXCL12 sensitivity of BM-residing HSPCs are continuously maintained. The mechanisms underlying this peculiar pattern of G-protein signal integration by BM-HSPCs are unknown. G-protein receptor kinases (GRKs) control receptor function by phosphorylating the intracellular domains upon ligand-induced activation, which results in receptor internalization and transient refractoriness. Using, therefore, a GRK6-deficient (GRK6(-/-)) mouse, we sought to address how perturbed ligand-induced CXCR4 (in)activation affects HSPC behavior in vitro and in vivo. In vitro, GRK6(-/-) HSPCs were characterized by hyper-responsiveness to CXCL12, as expected. In vivo, GRK6(-/-) immature hematopoiesis was characterized by a marked expansion of immature hematopoiesis in spleens and a modest repopulation defect in serial competitive transplantation. Enforced mobilization with granulocyte colony-stimulating factor (G-CSF) and AMD3100 was normal, as was hematopoietic regeneration after noncompetitive transplantation or pharmacological myelosuppression. These observations illustrate that GRK-mediated restriction of CXCR4 signal input after ligand engagement is largely dispensable for BM-resident HSPCs, which may explain how continuous CXCL12 responsiveness of BM-HSPCs can be maintained.

A tale of two models: mouse and zebrafish as complementary models for lymphatic studies

Lymphatic vessels provide essential roles in maintaining fluid homeostasis and lipid absorption. Dysfunctions of the lymphatic vessels lead to debilitating pathological conditions, collectively known as lymphedema. In addition, lymphatic vessels are a critical moderator for the onset and progression of diverse human diseases including metastatic cancer and obesity. Despite their clinical importance, there is no currently effective pharmacological therapy to regulate functions of lymphatic vessels. Recent efforts to manipulate the Vascular Endothelial Growth Factor-C (VEGFC) pathway, which is arguably the most important signaling pathway regulating lymphatic endothelial cells, to alleviate lymphedema yielded largely mixed results, necessitating identification of new targetable signaling pathways for therapeutic intervention for lymphedema. Zebrafish, a relatively new model system to investigate lymphatic biology, appears to be an ideal model to identify novel therapeutic targets for lymphatic biology. In this review, we will provide an overview of our current understanding of the lymphatic vessels in vertebrates, and discuss zebrafish as a promising in vivo model to study lymphatic vessels.

Zebrafish yap1 plays a role in differentiation of hair cells in posterior lateral line

The evolutionarily conserved Hippo signaling pathway controls organ size by regulating cell proliferation and apoptosis and this process involves Yap1. The zebrafish Yap1 acts during neural differentiation, but its function is not fully understood. The detailed analysis of yap1 expression in proliferative regions, revealed it in the otic placode that gives rise to the lateral line system affected by the morpholino-mediated knockdown of Yap1. The comparative microarray analysis of transcriptome of Yap1-deficient embryos demonstrated changes in expression of many genes, including the Wnt signaling pathway and, in particular, prox1a known for its role in development of mechanoreceptors in the lateral line. The knockdown of Yap1 causes a deficiency of differentiation of mechanoreceptors, and this defect can be rescued by prox1a mRNA. Our studies revealed a role of Yap1 in regulation of Wnt signaling pathway and its target Prox1a during differentiation of mechanosensory cells.