Investigating the lactate/SLC5A12-induced metabolic signalling network in inflammation

PhDThe tissue microenvironment is a key determinant of pathology in both inflammation and cancer. It is now understood that the tumour microenvironment is a niche that favours tumour growth over anti-tumour immune surveillance. Accumulation of lactate in the tumour microenvironment, largely due to the accelerated metabolism of cancer cells avidly consuming most of the scarcely available nutrients, has been shown to drive regulatory T cell responses favouring tumour growth. Immune cells that infiltrate the tissue microenvironments in inflammatory disorders find similarly harsh conditions, including scarce nutrients and high levels of lactate and other metabolites. Yet opposite to the tumour microenvironment, the inflamed tissue features high levels of inflammatory cytokines with impairment of Treg in favour of Th1 and Th17 immune responses, contributing to the perpetuation of the chronic inflammatory disease process. Indeed, in inflammatory disorders lactate is an amplifier of the inflammatory response. Here, I explored the response of CD4+ T cells to lactate in the context of inflammation. Specifically, the project aimed at characterizing whether the lactate/SLC5A12-induced metabolic signalling pathway modulates inflammatory immune responses. I employed a combination of immunology, mass spectrometry and biochemistry approaches on human peripheral blood mononuclear cells from healthy controls (HC) and rheumatoid arthritis (RA) subjects, as well as mononuclear cells from inflamed arthritic synovia and tonsils. I also used RNA-sequencing and clinical scores from a well-characterized early rheumatoid arthritis cohort and a murine model of CD4+ T cell-driven arthritis. I found that: 1. SLC5A12 is up-regulated by CD4+ but not CD8+ T cells upon T-cell-receptor (TCR) triggering. This expression is higher on CD4+ T cells isolated from RA synovial joints, where lactate is more abundant, as compared to peripheral RA and HC CD4+ T-cells. 2. Lactate-uptake by CD4+ T cells through SLC5A12 causes a reprogramming of intracellular metabolism, including reduced glycolysis and enhanced TCA cycle and fatty acid synthesis substrates. 3. SLC5A12-mediated lactate influx into human CD4+ T cells contributed to reshaping their effector phenotype, leading to increased IL- 4. 17 production via nuclear PKM2/Stat3 signalling and enhanced fatty acid synthesis. 5. SLC5A12-mediated lactate influx caused increased CD4+ T cell retention at the inflamed tissue as a consequence of impaired cell motility caused by reduced glycolysis and enhanced fatty acid synthesis. 6. Antibody-mediated blockade of SLC5A12 ameliorates the clinical course of CD4+ T cell-driven human glucose 6 phosphate isomerase (hG6PI)-induced arthritis. 7. Lactate/SLC5A12-induced metabolic reprogramming in CD4+ T cells is a distinctive mechanism of lymphoid RA pathogenesis. These findings establish lactate as an active signalling metabolite that contributes to the perpetuation of chronic inflammation and provide a novel therapeutic rationale to combat chronic inflammatory diseases.Versus Arthritis Clinical Research Fellowship

Intermediates of Metabolism: From Bystanders to Signalling Molecules

British Heart Foundation Fellowship FS/12/38/2964

Lactate at the crossroads of metabolism, inflammation, and autoimmunity

Supported by a fellowship from the Arthritis Research UK to VP and by a fellowship from the British Heart Foundation, a project grant from the CARIPLO Foundation and a Proof of Concept award from Queen Mary Innovation, Ltd to CM

Metabolic Checkpoints in Rheumatoid Arthritis

Several studies have highlighted the interplay between metabolism, immunity and inflammation. Both tissue resident and infiltrating immune cells play a major role in the inflammatory process of rheumatoid arthritis (RA) via the production of cytokines, adipo-cytokines and metabolic intermediates. These functions are metabolically demanding and require the most efficient use of bioenergetic pathways. The synovial membrane is the primary site of inflammation in RA and exhibits distinctive histological patterns characterized by different metabolism, prognosis and response to treatment. In the RA synovium, the high energy demand by stromal and infiltrating immune cells, causes the accumulation of metabolites, and adipo-cytokines, which carry out signaling functions, as well as activating transcription factors which act as metabolic sensors. These events drive immune and joint-resident cells to acquire pro-inflammatory effector functions which in turn perpetuate chronic inflammation. Whether metabolic changes are a consequence of the disease or one of the causes of RA pathogenesis is still under investigation. This review covers our current knowledge of cell metabolism in RA. Understanding the intricate interactions between metabolic pathways and the inflammatory and immune responses will provide more awareness of the mechanisms underlying RA pathogenesis and will identify novel therapeutic options to treat this disease

Insulin signaling in arthritis

Inflammatory arthritis is burdened by an increased risk of metabolic disorders. Cytokines and other mediators in inflammatory diseases lead to insulin resistance, diabetes and hyperlipidemia. Accumulating evidence in the field of immunometabolism suggests that the cause-effect relationship between arthritis and metabolic abnormalities might be bidirectional. Indeed, the immune response can be modulated by various factors such as environmental agents, bacterial products and hormones. Insulin is produced by pancreatic cells and regulates glucose, fat metabolism and cell growth. The action of insulin is mediated through the insulin receptor (IR), localized on the cellular membrane of hepatocytes, myocytes and adipocytes but also on the surface of T cells, macrophages, and dendritic cells. In murine models, the absence of IR in T-cells coincided with reduced cytokine production, proliferation, and migration. In macrophages, defective insulin signaling resulted in enhanced glycolysis affecting the responses to pathogens. In this review, we focalize on the bidirectional cause-effect relationship between impaired insulin signaling and arthritis analyzing how insulin signaling may be involved in the aberrant immune response implicated in arthritis and how inflammatory mediators affect insulin signaling. Finally, the effect of glucose-lowering agents on arthritis was summarized.Pathophysiology and treatment of rheumatic disease

Lactate Buildup at the Site of Chronic Inflammation Promotes Disease by Inducing CD4(+) T Cell Metabolic Rewiring

Accumulation of lactate in the tissue microenvironment is a feature of both inflammatory disease and cancer. Here, we assess the response of immune cells to lactate in the context of chronic inflammation. We report that lactate accumulation in the inflamed tissue contributes to the upregulation of the lactate transporter SLC5A12 by human CD4+ T cells. SLC5A12-mediated lactate uptake into CD4+ T cells induces a reshaping of their effector phenotype, resulting in increased IL17 production via nuclear PKM2/STAT3 and enhanced fatty acid synthesis. It also leads to CD4+ T cell retention in the inflamed tissue as a consequence of reduced glycolysis and enhanced fatty acid synthesis. Furthermore, antibody-mediated blockade of SLC5A12 ameliorates the disease severity in a murine model of arthritis. Finally, we propose that lactate/SLC5A12-induced metabolic reprogramming is a distinctive feature of lymphoid synovitis in rheumatoid arthritis patients and a potential therapeutic target in chronic inflammatory disorders