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Deregulation of mRNA translation engenders many human disorders, including obesity, neurodegenerative diseases, and cancer, and is associated with pathogen infections. The role of eIF4E-dependent translational control in macrophage inflammatory responses in vivo is largely unexplored. In this study, we investigated the involvement of the translation inhibitors eIF4E-binding proteins (4E-BPs) in the regulation of macrophage inflammatory responses in vitro and in vivo. We show that the lack of 4E-BPs exacerbates inflammatory polarization of bone marrow-derived macrophages and that 4E-BP-null adipose tissue macrophages display enhanced inflammatory gene expression following exposure to a high-fat diet (HFD). The exaggerated inflammatory response in HFD-fed 4E-BP-null mice coincides with significantly higher weight gain, higher

Chemokine production has been associated with the immunopathology related to malaria. Previous findings indicated that hemozoin (HZ), a parasite metabolite released during schizogeny, might be an important source of these proinflammatory mediators. In this study we investigated the molecular mechanisms underlying HZ-inducible macrophage (Mφ) chemokine mRNA expression. We found that both Plasmodium falciparum HZ and synthetic HZ increase mRNA levels of various chemokine transcripts (MIP-1α/CCL3, MIP-1β/CCL4, MIP-2/CXCL2, and MCP-1/CCL2) in murine B10R Mφ. The cellular response to HZ involved ERK1/2 phosphorylation, NF-κB activation, reactive oxygen species (ROS) generation, and ROS-dependent protein-tyrosine phosphatase down-regulation. Selective inhibition of either IκBα or the ERK1/2 pathway abolished both NF-κB activation and chemokine up-regulation. Similarly, blockage of HZ-inducible Mφ ROS with superoxide dismutase suppressed chemokine induction, strongly reduced NF-κB activation, and restored HZ-mediated Mφ protein-tyrosine phosphatase inactivation. In contrast, superoxide dismutase had no effect on EKR1/2 phosphorylation by HZ. Collectively, these data indicate that HZ triggers ROS-dependent and -independent signals, leading to increased chemokine mRNA expression in Mφ. Overall, our findings may help to better understand the molecular mechanisms through which parasite components, such as HZ, modulate the immune response during malaria infection.

Elevated NO production has been detected in patients suffering from various arthropathies; however, its role and regulation during gouty arthritis remain largely unexplored. Monosodium urate (MSU) crystals, the causative agent of gout, have been shown to induce NO generation in vivo and inducible NO synthase (iNOS) expression in human monocytes. The present study was designed to evaluate the ability of MSU crystals to modulate macrophage (Mφ) iNOS expression and NO synthesis and to investigate the molecular mechanisms underlying these cellular responses. We found that MSU crystals did not induce NO production in murine J774 Mφ. However, a synergistic effect on the level of iNOS expression and NO generation was observed in cells exposed to MSU crystals in combination with IFN-γ. Characterization of the second messengers involved revealed the requirement of IFN-γ-mediated Janus kinase 2/STAT1α activation even though MSU crystals did not modulate this signaling cascade by themselves. MSU crystals exerted their up-regulating effect by increasing extracellular signal-regulated kinase (ERK) 1/2 phosphorylation and NF-κB nuclear translocation in response to IFN-γ. The use of specific inhibitors against either NF-κB or the ERK1/2 pathway significantly reduced MSU + IFN-γ-inducible NF-κB activity, iNOS expression, and NO production. Altogether, these data indicate that MSU crystals exert a potent synergistic effect on the IFN-γ-inducible Mφ NO generation via ERK1/2- and NF-κB-dependent pathways. Understanding the molecular mechanisms through which MSU crystals amplify Mφ responses to proinflammatory cytokines such as IFN-γ will contribute to better define their role in NO regulation during gout, in particular, and inflammation, in general.

During malaria infection, high levels of proinflammatory molecules (e.g., cytokines, chemokines) correlate with disease severity. Even if their role as activators of the host immune response has been studied, the direct contribution of hemozoin (HZ), a parasite metabolite, to such a strong induction is not fully understood. Previous in vitro studies demonstrated that both Plasmodium falciparum HZ and synthetic HZ (sHZ), β-hematin, induce macrophage/monocyte chemokine and proinflammatory cytokine secretion. In the present study, we investigated the proinflammatory properties of sHZ in vivo. To this end, increasing doses of sHZ were injected either i.v. or into an air pouch generated on the dorsum of BALB/c mice over a 24-h period. Our results showed that sHZ is a strong modulator of leukocyte recruitment and more specifically of neutrophil and monocyte populations. In addition, evaluation of chemokine and cytokine mRNA and protein expression revealed that sHZ induces the expression of chemokines, macrophage-inflammatory protein (MIP)-1α/CCL3, MIP-1β/CCL4, MIP-2/CXCL2, and monocyte chemoattractant protein-1/CCL2; chemokine receptors, CCR1, CCR2, CCR5, CXCR2, and CXCR4; cytokines, IL-1β and IL-6; and myeloid-related proteins, S100A8, S100A9, and S100A8/A9, in the air pouch exudates. Of interest, chemokine and cytokine mRNA up-regulation were also detected in the liver of i.v. sHZ-injected mice. In conclusion, our study demonstrates that sHZ is a potent proinflammatory agent in vivo, which could contribute to the immunopathology related to malaria.

NO overproduction has been suggested to contribute to the immunopathology related to malaria infection. Even though a role for some parasite molecules (e.g., GPI) in NO induction has been proposed, the direct contribution of hemozoin (HZ), another parasite metabolite, remains to be established. Therefore, we were interested to determine whether Plasmodium falciparum (Pf) HZ and synthetic HZ, beta-hematin, alone or in combination with IFN-gamma, were able to induce macrophage (Mphi) NO synthesis. We observed that neither Pf HZ nor synthetic HZ led to NO generation in B10R murine Mphi; however, they significantly increased IFN-gamma-mediated inducible NO synthase (iNOS) mRNA and protein expression, and NO production. Next, by investigating the transductional mechanisms involved in this cellular regulation, we established that HZ induces extracellular signal-regulated kinase (ERK)1/2 mitogen-activated protein kinase phosphorylation as well as NF-kappaB binding to the iNOS promoter, and enhances the IFN-gamma-dependent activation of both second messengers. Of interest, cell pretreatment with specific inhibitors against either NF-kappaB or the ERK1/2 pathway blocked the HZ + IFN-gamma-inducible NF-kappaB activity and significantly reduced the HZ-dependent increase on IFN-gamma-mediated iNOS and NO induction. Even though selective inhibition of the Janus kinase 2/STAT1alpha pathway suppressed NO synthesis in response to HZ + IFN-gamma, HZ alone did not activate this signaling pathway and did not have an up-regulating effect on the IFN-gamma-induced Janus kinase 2/STAT1alpha phosphorylation and STAT1alpha binding to the iNOS promoter. In conclusion, our results suggest that HZ exerts a potent synergistic effect on the IFN-gamma-inducible NO generation in Mphi via ERK- and NF-kappaB-dependent pathways.