Neuro-immuno-endocrine modulation in marathon runners.

OBJECTIVE: Sports practice alters the homeostasis of athletes. To achieve homeostatic equilibrium, the integrated action of the neuroendocrine and immune systems is necessary. Here we studied the relation between cytokines, hormones and mood states in marathon runners. METHODS: A total of 20 male recreational marathon runners (mean age = 35.7 ± 9 years) and 20 male sedentary individuals (mean age = 35.5 ± 7 years) were recruited. We compared the serum levels of growth hormone (GH), cortisol and interleukins 8 and 10 and the amounts of these two cytokines spontaneously produced by peripheral blood mononuclear cells. Blood samples of the sedentary group were collected at rest. Blood from the marathon runners was collected at rest (baseline: 24 h before the race), immediately after a marathon and 72 h after a marathon. Mood state analysis in both groups was performed using the 24-item Brunel Mood Scale (BRUMS). RESULTS: Our results showed that, at rest, levels of interleukins 8 and 10 in the supernatant of culture cells, the serum concentration of GH, and tension and vigour (evaluated using the BRUMS), were significantly higher in athletes compared to sedentary people. Immediately after the race all serum parameters analysed were statistically higher than baseline values. At 72 h after the marathon, serum levels of hormones and interleukins returned to values at rest, but the concentrations of interleukins in the supernatant of culture cells showed a significant reduction compared to values at rest. CONCLUSION: The higher serum levels of GH in athletes at rest and the higher production of cytokines in culture without previous stimulus suggest that marathon runners present mechanisms that may be associated with preparing the body to perform prolonged strenuous exercise, such as a marathon.

Activation of platelet-activating factor receptor exacerbates renal inflammation and promotes fibrosis.

Platelet-activating factor (PAF) is a lipid mediator with important pro-inflammatory effects, being synthesized by several cell types including kidney cells. Although there is evidence of its involvement in acute renal dysfunction, its role in progressive kidney injury is not completely known. In the present study, we investigated the role of PAF receptor (PAFR) in an experimental model of chronic renal disease. Wild-type (WT) and PAFR knockout (KO) mice underwent unilateral ureter obstruction (UUO), and at kill time, urine and kidney tissue was collected. PAFR KO animals compared with WT mice present: (a) less renal dysfunction, evaluated by urine protein/creatinine ratio; (b) less fibrosis evaluated by collagen deposition, type I collagen, Lysyl Oxidase-1 (LOX-1) and transforming growth factor ß (TGF-ß) gene expression, and higher expression of bone morphogenetic protein 7 (BMP-7) (3.3-fold lower TGF-ß/BMP-7 ratio); (c) downregulation of extracellular matrix (ECM) and adhesion molecule-related machinery genes; and (d) lower levels of pro-inflammatory cytokines. These indicate that PAFR engagement by PAF or PAF-like molecules generated during UUO potentiates renal dysfunction and fibrosis and might promote epithelial-to-mesenchymal transition (EMT). Also, early blockade of PAFR after UUO leads to a protective effect, with less fibrosis deposition. In conclusion, PAFR signaling contributes to a pro-inflammatory environment in the model of obstructive nephropathy, favoring the fibrotic process, which lately will generate renal dysfunction and progressive organ failure.

Clearance of apoptotic cells by macrophages induces regulatory phenotype and involves stimulation of CD36 and platelet-activating factor receptor.

Phagocytosis of apoptotic cells (efferocytosis) induces macrophage differentiation towards a regulatory phenotype (IL-10(high)/IL-12p40(low)). CD36 is involved in the recognition of apoptotic cells (AC), and we have shown that the platelet-activating factor receptor (PAFR) is also involved. Here, we investigated the contribution of PAFR and CD36 to efferocytosis and to the establishment of a regulatory macrophage phenotype. Mice bone marrow-derived macrophages were cocultured with apoptotic thymocytes, and the phagocytic index was determined. Blockage of PAFR with antagonists or CD36 with specific antibodies inhibited the phagocytosis of AC (~70-80%). Using immunoprecipitation and confocal microscopy, we showed that efferocytosis increased the CD36 and PAFR colocalisation in the macrophage plasma membrane; PAFR and CD36 coimmunoprecipitated with flotillin-1, a constitutive lipid raft protein, and disruption of these membrane microdomains by methyl-ß-cyclodextrin reduced AC phagocytosis. Efferocytosis induced a pattern of cytokine production, IL-10(high)/IL-12p40(low), that is, characteristic of a regulatory phenotype. LPS potentiated the efferocytosis-induced production of IL-10, and this was prevented by blocking PAFR or CD36. It can be concluded that phagocytosis of apoptotic cells engages CD36 and PAFR, possibly in lipid rafts, and this is required for optimal efferocytosis and the establishment of the macrophage regulatory phenotype.

Identification of a danger-associated peptide from apolipoprotein B100 (ApoBDS-1) that triggers innate proatherogenic responses.

BACKGROUND: Subendothelial deposited low-density lipoprotein particles are a known inflammatory factor in atherosclerosis. However, the causal components derived from low-density lipoprotein are still poorly defined. Apolipoprotein B100 (ApoB100) is the unexchangeable protein component of low-density lipoprotein, and the progression of atherosclerosis is associated with immune responses to ApoB100-derived peptides. In this study, we analyzed the proinflammatory activity of ApoB100 peptides in atherosclerosis. METHODS AND RESULTS: By screening a peptide library of ApoB100, we identified a distinct native peptide referred to as ApoB100 danger-associated signal 1 (ApoBDS-1), which shows sequence-specific bioactivity in stimulation of interleukin-8, CCL2, and interleukin-6. ApoBDS-1 activates mitogen-activated protein kinase and calcium signaling, thereby effecting the expression of interleukin-8 in innate immune cells. Ex vivo stimulation of carotid plaques with ApoBDS-1 enhances interleukin-8 and prostaglandin E2 release. Furthermore, we demonstrated that ApoBDS-1-positive peptide fragments are present in atherosclerotic lesions using immunoassays and that low-molecular-weight fractions isolated from plaque show ApoBDS-1 activity inducing interleukin-8 production. CONCLUSIONS: Our data show that ApoBDS-1 is a previously unrecognized peptide with robust proinflammatory activity, contributing to the disease-promoting effects of low-density lipoprotein in the pathogenesis of atherosclerosis.

Pivotal role for platelet-activating factor receptor in CD36 expression and oxLDL uptake by human monocytes/macrophages.

The uptake of oxLDL by CD36 is not regulated by intracellular levels of cholesterol, leading to macrophage differentiation into foam cells which play a major role in atherosclerosis. Furthermore, oxLDL competes with PAF in macrophages for binding to PAF receptors (PAFR). Here we investigated the involvement of PAFR in CD36 expression and uptake of oxLDL by human monocytes/macrophages. Adherent peripheral blood mononuclear cells were treated with PAFR-antagonists (WEB2170, CV3988); inhibitors of ERK1/2 (PD98059), p38 (SB203580), JNK (SP600125) or diluents, before stimulation with oxLDL or PAF. After 24 h, uptake of FITC-oxLDL and expression of CD36 was determined by flow cytometry and phosphorylation of MAP-kinases by Western blot. It was shown that the uptake of oxLDL was reduced by PAFR antagonists. CD36 expression was up-regulated by oxLDL, an effect reversed by PAFR antagonists. The up-regulation of CD36 and oxLDL uptake both required MAP-kinases activation. The oxLDL-induced ERK1/2 and JNK but not p38 phosphorylation was reversed by PAFR-antagonists suggesting that oxLDL signalling involves PAFR dependent and independent pathways. In macrophages from PAFR(-/-) mice, oxLDL was unable to up-regulate CD36 expression and the oxLDL uptake was reduced compared to wild type. These results suggest that oxLDL interacts with PAFR in macrophages to increase CD36 expression and oxLDL uptake. Whereas pharmacological intervention at the level of PAFR would be beneficial in atherosclerosis remains to be determined.

Role of PPAR-gamma in the modulation of CD36 and FcgammaRII induced by LDL with low and high degrees of oxidation during the differentiation of the monocytic THP-1 cell line.

Scavenger or Fcgamma receptors are important for capture and clearance of modified LDL particles by monocytes/macrophages. Uptake via scavenger receptors is not regulated by intracellular levels of cholesterol and in consequence, macrophages develop into foam cells in the arterial intima. The levels of scavenger receptor CD36 are increased in atherosclerotic lesions and there is evidence that some components of oxLDL auto-regulate the expression of this receptor. Fcgamma receptor expression is increased in cardiovascular diseases but it is not known weather their expression is regulated by oxLDL. The biological properties of oxLDLs vary depending on the degree of oxidation. In the present study we investigated the effect of LDL particles showing extensive or low oxidation (HoxLDL and LoxLDL) on the expression of CD36 and FcgammaRII in a human monocytic cell line (THP-1), differentiated or not to macrophage, and the involvement of PPARgamma. It was found that both forms of oxLDL are able to increase the expression of CD36 and FcgammaRII and that this effect is dependent on the degree of oxidation and of the stage of cell differentiation (monocyte or macrophage). We also showed that the increased expression of FcgammaRII is dependent on PPARgamma whereas that of the CD36 is independent of PPARgamma.

Athletes with higher VO2max present reduced oxLDL after a marathon race.

BACKGROUND: During a session of prolonged and exhaustive exercise, such as a marathon race, large quantities of free radicals are produced and can oxidise (ox) several molecules, such as low-density lipoprotein (LDL). To prevent oxidative damage, athletes present higher antioxidant levels. However, the effect of marathon running on the natural IgM or IgG anti-oxLDL autoantibodies is not understood. Thus, we investigated the effect of a marathon race on oxidative stress and the mechanisms of control of this stress. METHODS: Blood samples of 20 marathon runners were collected 24 hours before, immediately and 72 hours after a marathon race to evaluate: plasma lipid profile; serum levels of oxLDL and anti-oxLDL autoantibodies (IgM and IgG isotype) and total antioxidant capacity (TAC). Maximum oxygen uptake (VO2max) was also determined. RESULTS: Immediately after the race, oxLDL and TAC levels decreased in comparison to the basal levels; however, the IgM or IgG anti-oxLDL levels remain unchanged. Whereas no differences were observed in the IgM or IgG anti-oxLDL levels 72h after the marathon, the oxLDL and TAC levels returned to the basal values. Significant positive correlations were observed between oxLDL and LDL-cholesterol before, and 72h after the marathon. Significant negative correlations were observed between oxLDL and VO2max immediately after the marathon and 72 h later, as well as between oxLDL and TAC 72 h after the race. CONCLUSIONS: Athletes with a higher VO2max and total antioxidant activity presented reduced LDL oxidation. The levels of IgM or IgG anti-oxLDL autoantibodies were not affected by running the marathon.

Activation of PAF-receptor induces regulatory dendritic cells through PGE2 and IL-10.

Activation of the platelet-activating factor receptor (PAFR) in macrophages is associated with suppressor phenotype. Here, we investigated the PAFR in murine dendritic cells (DC). Bone marrow-derived dendritic cells (BALB/c) were cultured with GM-CSF and maturation was induced by LPS. The PAFR antagonists (WEB2086, WEB2170, PCA4248) and the prostaglandin (PG) synthesis inhibitors (indomethacin, nimesulide and NS-398) were added before LPS. Mature and immature DCs expressed PAFR. LPS increased MHCII, CD40, CD80, CD86, CCR7 and induced IL-10, IL-12, COX-2 and PGE2 expression. IL-10, COX-2 and PGE2 levels were reduced by PAFR antagonists and increased by cPAF. The IL-10 production was independent of PGs. Mature DCs induced antigen-specific lymphocyte proliferation. PAFR antagonists or PG-synthesis inhibitors significantly increased lymphocyte proliferation. It is proposed that PAF has a central role in regulatory DC differentiation through potentiation of IL-10 and PGE2 production.

Uptake of oxLDL and IL-10 production by macrophages requires PAFR and CD36 recruitment into the same lipid rafts.

Macrophage interaction with oxidized low-density lipoprotein (oxLDL) leads to its differentiation into foam cells and cytokine production, contributing to atherosclerosis development. In a previous study, we showed that CD36 and the receptor for platelet-activating factor (PAFR) are required for oxLDL to activate gene transcription for cytokines and CD36. Here, we investigated the localization and physical interaction of CD36 and PAFR in macrophages stimulated with oxLDL. We found that blocking CD36 or PAFR decreases oxLDL uptake and IL-10 production. OxLDL induces IL-10 mRNA expression only in HEK293T expressing both receptors (PAFR and CD36). OxLDL does not induce IL-12 production. The lipid rafts disruption by treatment with ßCD reduces the oxLDL uptake and IL-10 production. OxLDL induces co-immunoprecipitation of PAFR and CD36 with the constitutive raft protein flotillin-1, and colocalization with the lipid raft-marker GM1-ganglioside. Finally, we found colocalization of PAFR and CD36 in macrophages from human atherosclerotic plaques. Our results show that oxLDL induces the recruitment of PAFR and CD36 into the same lipid rafts, which is important for oxLDL uptake and IL-10 production. This study provided new insights into how oxLDL interact with macrophages and contributing to atherosclerosis development.

Co-stimulation of PAFR and CD36 is required for oxLDL-induced human macrophages activation.

The oxidative process of LDL particles generates molecules which are structurally similar to platelet-activating factor (PAF), and some effects of oxidized LDL (oxLDL) have been shown to be dependent on PAF receptor (PAFR) activation. In a previous study, we showed that PAFR is required for upregulation of CD36 and oxLDL uptake. In the present study we analyzed the molecular mechanisms activated by oxLDL in human macrophages and the contribution of PAFR to this response. Human adherent monocytes/macrophages were stimulated with oxLDL. Uptake of oxLDL and CD36 expression were determined by flow cytometry; MAP kinases and Akt phosphorylation by Western blot; IL-8 and MCP-1 concentration by ELISA and mRNA expression by real-time PCR. To investigate the participation of the PI3K/Akt pathway, Gαi-coupled protein or PAFR, macrophages were treated with LY294002, pertussis toxin or with the PAFR antagonists WEB2170 and CV3988, respectively before addition of oxLDL. It was found that the addition of oxLDL to human monocytes/macrophages activates the PI3K/Akt pathway which in turn activates the MAPK (p38 and JNK). Phosphorylation of Akt requires the engagement of PAFR and a Gαi-coupled protein. The upregulation of CD36 protein and the uptake of oxLDL as well as the IL-8 production are dependent on PI3K/Akt pathway activation. The increased CD36 protein expression is dependent on PAFR and Gαi-coupled protein. Transfection studies using HEK 293t cells showed that oxLDL uptake occurs with either PAFR or CD36, but IL-8 production requires the co-transfection of both PAFR and CD36. These findings show that PAFR has a pivotal role in macrophages response to oxLDL and suggest that pharmacological intervention at the level of PAFR activation might be beneficial in atherosclerosis.