Annexin-A1: The culprit or the solution?

Annexin-A1 has a well-defined anti-inflammatory role in the innate immune system, but its function in adaptive immunity remains controversial. This glucocorticoid-induced protein has been implicated in a range of inflammatory conditions and cancers, as well as being found to be overexpressed on the T cells of patients with autoimmune disease. Moreover, the formyl peptide family of receptors, through which annexin-A1 primarily signals, has also been implicated in these diseases. In contrast, treatment with recombinant annexin-A1 peptides resulted in suppression of inflammatory processes in murine models of inflammation. This review will focus on what is currently known about annexin-A1 in health and disease and discuss the potential of this protein as a biomarker and therapeutic target.

Recovery training or over-training? The contribution of TLR10 to monocyte fitness.

The concept of trained immunity refers to remodelling of the monocyte and macrophage metabolic and epigenetic landscape, conferring an amplified inflammatory response upon secondary stimulation. This effect is typically modelled in vitro by stimulating monocytes with either Bacillus Calmette Guerin (BCG) or ß-Glucan for 24 hr, before subsequent stimulation with LPS or Pam-3-Cys (P3C) as a secondary stimulus 6 days later. Here, we focus on a recent paper which interrogated the role of the anti-inflammatory TLR, TLR10, on trained immunity. Using both an in vitro model of trained immunity, and analysis of BCG vaccinated individuals, the authors interestingly demonstrate that, despite its ability to regulate aspects of innate immunity, TLR10 does not have a significant role in this process.

The rheumatoid synovial environment alters fatty acid metabolism in human monocytes and enhances CCL20 secretion.

OBJECTIVES: Fatty acid oxidation (FAO) and glycolysis have been implicated in immune regulation and activation of macrophages. However, investigation of human monocyte intracellular metabolism in the context of the hypoxic and inflammatory rheumatoid arthritis (RA) synovium is lacking. We hypothesized that exposure of monocytes to the hypoxic and inflammatory RA environment would have a profound impact on their metabolic state, and potential to contribute to disease pathology. METHODS: Human monocytes were isolated from buffy coats and exposed to hypoxia. Metabolic profiling of monocytes was carried out by LC-MS metabolomics. Inflammatory mediator release after LPS or RA-synovial fluid (RA-SF) stimulation was analysed by ELISA. FAO was inhibited by etomoxir or enhanced with exogenous carnitine supplementation. Transcriptomics of RA blood monocytes and RA-SF macrophages was carried out by microarray. RESULTS: Hypoxia exacerbated monocyte-derived CCL20 and IL-1ß release in response to LPS, and increased glycolytic intermediates at the expense of carnitines. Modulation of carnitine identified a novel role for FAO in the production of CCL20 in response to LPS. Transcriptional analysis of RA blood monocytes and RA-SF macrophages revealed that fatty acid metabolism was altered and CCL20 increased when monocytes enter the synovial environment. In vitro analysis of monocytes showed that RA-SF increases carnitine abundance and CCL20 production in hypoxia, which was exacerbated by exogenous carnitine. CONCLUSION: This work has revealed a novel inflammatory mechanism in RA that links FAO to CCL20 production in human monocytes, which could subsequently contribute to RA disease pathogenesis by promoting the recruitment of Th17 cells and osteoclastogenesis.