Metabolic processes in rheumatoid arthritis CD8+T cells: exploring their diagnostic value and potential as therapeutic targets

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For a long time, the role of CD8+T cells in the (immuno)pathogenesis of rheumatoid arthritis (RA) was considered negligible when compared to CD4+T cells or B cells. However, recent studies carried out by our team and others, focusing on CD8+T cells from either samples from RA patients or animal models of chronic polyarthritis, have challenged those dogmas, and have shown that CD8+T cells in RA have a marked pro-inflammatory, cytotoxic effector phenotype and may, therefore, play a preponderant role in RA initiation, maintenance and/or relapse. The presence of such effector CD8+T cells in the peripheral blood, in the synovial fluid and -as reported by other teams- in the synovial membrane, suggests that they have to adapt their metabolism to sustain their energetic demands for the effector functions in both well oxygenated and in oxygen-deprived environments. In our recent in vitro studies on CD8+T cells under normoxia and using the stable isotope metabolic tracer [U-13C]glucose, we detected high rates of aerobic glycolysis in RA cells at rest, as measured by the extraordinary rise in [U-13C]lactate levels in cell culture media, and a significant increase of those rates upon stimulation, coherent with the prevalence of a glycolytic metabolism in these cells even in a well oxygenated environment. When compared to CD8+ T cells from healthy controls, ankylosing spondylitis (SpA) and psoriatic arthritis (PsA) patients, these changes seem to be rather specific for RA cells. Therefore, we have set as the main objectives of the current proposal: A) Characterization of the metabolic processes in CD8+T cells from RA comparing to other chronic inflammatory autoimmune arthritis patients; B) Explore the potential of those CD8+T cell metabolic processes as new diagnostic tool and/or therapeutic targets in RA. Combining quantification of immunological parameters and 1H- plus 13C-NMR analysis will focus on: 1) Identification and characterization of distinctive metabolic fingerprints in RA CD8+T cells, as compared to SpA, PsA, multiple sclerosis and healthy controls. 2) Phenotypic, functional and metabolic characterization of CD8+T cells infiltrating the RA synovial membrane in comparison to osteoarthritis by MALDI-TOF imaging mass spectrometry. 3) Selection and validation of metabolic targets for in vitro modulation of CD8+T cell responses in RA. In order to transfer the human data in a mouse model of RA, we have planned to validate the metabolic fingerprints from CD8+T cells in the K/BxN mouse model of spontaneous chronic polyarthritis. Our first data hint towards similar metabolic changes also in this animal model of RA. We then will be able to therapeutically modulate CD8+T cell metabolism in the K/BxN mouse model of spontaneous chronic polyarthritis to test whether alteration of metabolism offers a new and innovative therapeutic option.