Interaction between monocytes and vascular endothelial cells induces adrenomedullin production

Lysophosphatidylcholines modulate immunoregulatory checkpoints in peripheral monocytes and are associated with mortality in people with acute liver failure

BACKGROUND & AIMS

Acute liver failure (ALF) is a life-threatening disease characterised by high-grade inflammation and immunoparesis, which is associated with a high incidence of death from sepsis. Herein, we aimed to describe the metabolic dysregulation in ALF and determine whether systemic immune responses are modulated via the lysophosphatidylcholine (LPC)-autotaxin (ATX)-lysophosphatidylcholinic acid (LPA) pathway.

METHODS

Ninety-six individuals with ALF, 104 with cirrhosis, 31 with sepsis and 71 healthy controls (HCs) were recruited. Pathways of interest were identified by multivariate statistical analysis of proton nuclear magnetic resonance spectroscopy and untargeted ultraperformance liquid chromatography-mass spectrometry-based lipidomics. A targeted metabolomics panel was used for validation. Peripheral blood mononuclear cells were cultured with LPA 16:0, 18:0, 18:1, and their immune checkpoint surface expression was assessed by flow cytometry. Transcript-level expression of the LPA receptor (LPAR) in monocytes was investigated and the effect of LPAR antagonism was also examined in vitro.

RESULTS

LPC 16:0 was highly discriminant between ALF and HC. There was an increase in ATX and LPA in individuals with ALF compared to HCs and those with sepsis. LPCs 16:0, 18:0 and 18:1 were reduced in individuals with ALF and were associated with a poor prognosis. Treatment of monocytes with LPA 16:0 increased their PD-L1 expression and reduced CD155, CD163, MerTK levels, without affecting immune checkpoints on T and NK/CD56+T cells. LPAR1 and 3 antagonism in culture reversed the effect of LPA on monocyte expression of MerTK and CD163. MerTK and CD163, but not LPAR genes, were differentially expressed and upregulated in monocytes from individuals with ALF compared to controls.

CONCLUSION

Reduced LPC levels are biomarkers of poor prognosis in individuals with ALF. The LPC-ATX-LPA axis appears to modulate innate immune response in ALF via LPAR1 and LPAR3. Further investigations are required to identify novel therapeutic agents targeting these receptors.

IMPACT AND IMPLICATIONS

We identified a metabolic signature of acute liver failure (ALF) and investigated the immunometabolic role of the lysophosphatidylcholine-autotaxin-lysophosphatidylcholinic acid pathway, with the aim of finding a mechanistic explanation for monocyte behaviour and identifying possible therapeutic targets (to modulate the systemic immune response in ALF). At present, no selective immune-based therapies exist. We were able to modulate the phenotype of monocytes in vitro and aim to extend these findings to murine models of ALF as a next step. Future therapies may be based on metabolic modulation; thus, the role of specific lipids in this pathway require elucidation and the relative merits of autotaxin inhibition, lysophosphatidylcholinic acid receptor blockade or lipid-based therapies need to be determined. Our findings begin to bridge this knowledge gap and the methods used herein could be useful in identifying therapeutic targets as part of an experimental medicine approach.

Adrenomedullin Expression Characterizes Leukemia Stem Cells and Associates With an Inflammatory Signature in Acute Myeloid Leukemia

Adrenomedullin (ADM) is a hypotensive and vasodilator peptide belonging to the calcitonin gene-related peptide family. It is secreted in vitro by endothelial cells and vascular smooth muscle cells, and is significantly upregulated by a number of stimuli. Moreover, ADM participates in the regulation of hematopoietic compartment, solid tumors and leukemias, such as acute myeloid leukemia (AML). To better characterize ADM involvement in AML pathogenesis, we investigated its expression during human hematopoiesis and in leukemic subsets, based on a morphological, cytogenetic and molecular characterization and in T cells from AML patients. In hematopoietic stem/progenitor cells and T lymphocytes from healthy subjects, ADM transcript was barely detectable. It was expressed at low levels by megakaryocytes and erythroblasts, while higher levels were measured in neutrophils, monocytes and plasma cells. Moreover, cells populating the hematopoietic niche, including mesenchymal stem cells, showed to express ADM. ADM was overexpressed in AML cells versus normal CD34+ cells and in the subset of leukemia compared with hematopoietic stem cells. In parallel, we detected a significant variation of ADM expression among cytogenetic subgroups, measuring the highest levels in inv(16)/t(16;16) or complex karyotype AML. According to the mutational status of AML-related genes, the analysis showed a lower expression of ADM in FLT3-ITD, NPM1-mutated AML and FLT3-ITD/NPM1-mutated cases compared with wild-type ones. Moreover, ADM expression had a negative impact on overall survival within the favorable risk class, while showing a potential positive impact within the subgroup receiving a not-intensive treatment. The expression of 135 genes involved in leukemogenesis, regulation of cell proliferation, ferroptosis, protection from apoptosis, HIF-1α signaling, JAK-STAT pathway, immune and inflammatory responses was correlated with ADM levels in the bone marrow cells of at least two AML cohorts. Moreover, ADM was upregulated in CD4+ T and CD8+ T cells from AML patients compared with healthy controls and some ADM co-expressed genes participate in a signature of immune tolerance that characterizes CD4+ T cells from leukemic patients. Overall, our study shows that ADM expression in AML associates with a stem cell phenotype, inflammatory signatures and genes related to immunosuppression, all factors that contribute to therapy resistance and disease relapse.

Adrenomedullin in the growth modulation and differentiation of acute myeloid leukemia cells

Adrenomedullin (ADM) is a regulatory peptide endowed with multiple biological effects, including the regulation of blood pressure, cell growth and innate host defence. In the present study, we demonstrated that ADM signaling could be involved in the impaired cellular differentiation of myeloid leukemia cells to mature granulocytes or monocytes by modulating RAMPs/CRLR expression, PI3K/Akt cascade and the ERK/MAPK signaling pathway. When exogenously administered to in vitro cultures of HL60 promyelocytic leukemia cells, ADM was shown to exert a strong proliferative effect with minimal upregulation in the expression level of monocyte antigen CD14. Notably, the experimental inhibition of ADM signaling with inhibitor ADM22-52 promoted a differentiative stimulation towards monocytic and granulocytic lineages. Moreover, based on the expression of CD31 relative to CD38, we hypothesized that an excess of ADM in bone marrow (BM) niche could increase the transendothelial migration of leukemia cells while any inhibitory event of ADM activity could raise cell retention in hyaluronate matrix by upregulating CD38. Taken into consideration the above evidence, we concluded that ADM and ADM22-52 could differently affect the growth of leukemia cells by autocrine/paracrine mechanisms and may have clinical relevance as biological targets for the intervention of tumor progression.

Adrenomedullin expression in coronary circulation after stent implantation as a prognostic factor for restenosis

The authors determined the changes in adrenomedullin (AM) expression in the coronary circulation of patients with ischemic heart disease who underwent coronary stent implantation. Blood samples were drawn from the coronary sinus before, immediately after and four hours after coronary stent implantation, and plasma levels of AM were measured. AM levels in the coronary sinus blood were significantly increased four hours after stent implantation. On the other hand, in the femoral arterial blood, no significant changes in AM levels were observed. A significant positive correlation was found between AM level in the coronary sinus blood four hours after stent implantation and late loss index six months after the procedure. These results suggest that inflammation after coronary stent implantation induces AM expression, which might play an important role in restenosis after stenting.

Thrombin-induced VEGF expression in human retinal pigment epithelial cells

PURPOSE

The purpose of the present study was to investigate the effects of thrombin and thrombin in combination with other proangiogenic factors on VEGF expression in hRPE cells.

METHODS

hRPE cells were stimulated with thrombin TNF-alpha, monocytes, and TGF-beta2. After stimulation, conditioned medium and lysed cells were subjected to ELISA, Western blot analysis, immunocytochemistry, and RT-PCR analyses. Inhibitors specific for various signal transduction pathways were used to determine the signaling pathways involved.

RESULTS

Treatment of RPE cells with thrombin resulted in dose- and time-dependent increases in VEGF mRNA levels and protein production. hRPE VEGF expression is predominantly protease-activated receptor (PAR)-1 dependent. Approximately 80% of thrombin-induced VEGF secretion was abrogated by inhibitors of MAPK/ERK kinase (MEK), p38, c-Jun NH2-terminal kinase (JNK), protein tyrosine kinase (PTK), phosphatidylinositol 3-kinase (PI3K), protein kinase C (PKC), nuclear factor-kappaB (NF-kappaB), and reactive oxygen species (ROS). Analyses of VEGF protein production and mRNA synthesis revealed that VEGF induction by thrombin plus TNF-alpha or coculture with monocytes was additive, whereas that by co-incubation with TGF-beta2 was synergistic. The costimulated VEGF production by TGF-beta2 plus thrombin was an average of three times higher than the sum of that induced by each agent alone. Furthermore, BAPTA [bis-(o-aminophenoxy)ethane-N,N',N'-tetraacetic acid], a calcium chelator, blocked the VEGF secretion induced by thrombin and thrombin plus TGF-beta2 by 65% and 20%, respectively, but had no effect on that induced by TGF-beta2 alone.

CONCLUSIONS

Thrombin alone and in combination with TNF-alpha, monocytes, and TGF-beta2 potently stimulated VEGF expression in hRPE cells via multiple signaling pathways. The thrombin-induced calcium mobilization may play an important permissive role in maximizing TGF-beta2-induced VEGF expression in RPE cells.

The role of interleukin-1beta in direct and toll-like receptor 4-mediated neutrophil activation and survival

The regulation of systemic and local neutrophil activation is crucial to the clearance of infections and the successful resolution of inflammation without progress to tissue damage or disseminated inflammatory reactions. Using purified lipopolysaccharide (pLPS) and highly purified neutrophils, we have previously shown that Toll-like receptor 4 signaling is a potent neutrophil activator, but a poor stimulator of survival. In the presence of peripheral blood mononuclear cells (PBMCs), however, pLPS becomes a potent neutrophil survival factor. Interleukin (IL)-1beta has been identified as an important neutrophil activator and prosurvival cytokine, and is produced in abundance by LPS-stimulated PBMCs. We now show that IL-1beta fails to activate highly purified neutrophils or enhance their survival, but in the presence of PBMCs, IL-1beta induces neutrophil survival. We hypothesized that LPS-primed neutrophils might become responsive to IL-1beta, but were unable to demonstrate this. Moreover, IL-1ra failed to prevent pLPS + PBMC-dependent neutrophil survival. In studies of IL-1R1(-/-) mice, we found that LPS was still able to mediate neutrophil survival, and neutrophil survival was enhanced by the addition of monocytic cells. Thus an important paradigm of neutrophil regulation needs to be viewed in the context of a cellular network in which actions of IL-1beta on neutrophils are indirect and mediated by other cells.

Adrenomedullin: Multiple functions in human pregnancy

Adrenomedullin is a 52 amino acid peptide originally isolated from human phaeochromocytoma in 1993. It was initially demonstrated to have profound effects on the vasculature including vasodilatation and subsequently promotion of angiogenesis. Since then it has become apparent that it has a wide range of other biological actions including regulation of cell growth and differentiation. Successful pregnancy outcome relies on establishing and maintaining throughout gestation an efficient blood supply to the fetus. This allows the exchange of nutrients, oxygenation of fetal blood and removal of cytotoxins from the fetus, such as carbon dioxide. One of the most important local adaptations to pregnancy is the change in maternal blood flow to the implantation site. Evidence now points towards a vital role for adrenomedullin in the regulation of placentation. It appears that adrenomedullin may play important roles in the regulation of fetal perfusion both in normal and in compromised pregnancies. However, most studies have focused on measuring adrenomedullin levels and studying its expression as well as that of its receptors. More functional studies are now required to elucidate the underlying mechanisms involved.

Expression of adrenomedullin and its receptor by chondrocyte phenotype cells

For clarifying a process of de-differentiation in culturing chondrocytes, the present study was undertaken to investigate the secretion of adrenomedullin (AM) by chondrocyte phenotype cells and whether or not AM effects this proliferation in a cAMP-dependent fashion. Chondrocyte phenotype cells expressed AM and the AM receptor, and secreted high concentration of AM into the culture medium. When added to cultures, AM increased the intracellular cAMP level and decreased the number of these cells in a similar concentration-dependent fashion. Addition of forskolin and dibutyryl-cAMP caused a significant decrease in the number of these cells. Furthermore, the effect of AM was inhibited by a cAMP-dependent protein kinase A inhibitor (H89). The present findings indicate that AM has an autocrine/paracrine type of anti-proliferative effect on these cells mediated via a cAMP-dependent pathway and raise the possibility that AM plays a role in the local modulation of a process of de-differentiation by culturing chondrocyte phenotype cells.