Periodic Reporting for period 1 - SPArKLE (New players in immunometabolism: investigating the role of succinate and pyruvate kinase in T cell immunity)
Período documentado: 2018-04-01 hasta 2019-07-31
During the SPArKLE project, the ER investigated the role of the metabolite succinate and the enzyme pyruvate kinase (PK) in CD4+ T cells. Previous reports showed that succinate and PK play an important role in the functionality of certain immune cell subsets and in the development of inflammatory pathologies, but no studies have specifically evaluated if such molecules regulate CD4+ T cell activation and pathogenicity. Therefore, the overall aim of the SPArKLE research programme was to evaluate whether succinate and PK play a role in the activation, polarisation and functionality of murine and human CD4+ T cells, with the final goal to identify novel potential targets with therapeutic utility in inflammatory and autoimmune pathologies. The results obtained during the development of the SPArKLE project indicate that while succinate plays a minor role in the functionality of CD4+ T lymphocytes, modulation of the activity of the enzyme PK, in particular of its isoform PKM2, could limit CD4+ T cell pro-inflammatory activity and the development of autoimmunity. The project thus identified PKM2 as a potential therapeutic target for the treatment of T cell-mediated inflammatory diseases.
In parallel with the above experiments, the expression of different isoforms of the enzyme PK was evaluated in CD4+ T cells. The results indicate that, upon in vitro activation, two different isoforms of PK (PKM1 and PKM2) are upregulated in CD4+ T cells. In particular, the PKM2 isoform undergoes a complex regulation upon activation, which involves its phosphorylation at multiple sites and accumulation in the nucleus of activated CD4+ T cells. Of note, at all phases of activation, this enzyme is present in equilibrium between a monomeric/dimeric form (i.e. one/two enzyme subunits joined together) and a tetrameric form (i.e. four enzyme subunits joined together). Treatment of CD4+ T cells with PKM2 pharmacological activators, which induce the tetramerisation of the PKM2 enzyme, limited PKM2 nuclear translocation and strongly inhibited T cell activation, proliferation and cytokine production. These activators prevented the engagement of glycolysis, a metabolic pathway that was previously shown to be essential for T cell activation. Importantly, this is associated with a block in the generation of both pro-inflammatory Th1 and Th17 cells and parallel induction of anti-inflammatory Tregs in vitro. Finally, treatment with PKM2 activators ameliorated experimental autoimmune encephalomyelitis, the mouse model of human multiple sclerosis, by inhibiting Th1- and Th17-mediated inflammation in the central nervous system. Overall, these results suggest that pharmacological targeting of PKM2 may represent a valuable therapeutic approach in T cell-mediated inflammation and autoimmunity.