Myeloid cells play a critical role in CNS demyelination and axonal destruction of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). The early phase of the disease is characterized by the presence of pathogenic activated macrophages (M1 type), while the recovery phase is associated with alternatively-activated macrophages (M2 type)? which release anti-inflammatory cytokines that resolve the pathogenic inflammation. Activated M1 macrophages depend on glycolysis to boost biosynthetic pathways to produce inflammatory mediators. However, anti-inflammatory M2 macrophages rely primarily on mitochondrial respiration. Adenosine monophosphate-activated protein kinase (AMPK) regulates energy metabolism, and thus controls the balance between glycolysis and mitochondrial respiration. We reported previously that AMPK?1 knockout (KO) mice develop severe EAE indicating AMPK activation is protective, yet the molecular mechanism by which AMPK regulates EAE disease progression is not known. AMPK?1-KO macrophages exhibit a hyper- inflammatory phenotype and have a lower rate of metabolism. AMPK?1-KO macrophages also show glycolysis- tricarboxylic acid (TCA) cycle remodeling, which results in an imbalance in the levels of the endogenous metabolites, succinate and itaconate, which regulate pro- and anti-inflammatory macrophage functions, respectively. Their levels are tightly controlled by succinate dehydrogenase (SDH) and immune responsive gene 1 (IRG1), respectively. We hypothesize that the loss of AMPK?1 remodels the glycolytic-TCA pathway causing an imbalance in the levels of succinate and itaconate, which promotes an M1 phenotype over an M2 phenotype. This, in turn, promotes Th17 cells and suppresses T regulatory cells leading to a hyperinflammatory CNS immune response and CNS tissue damage. To test our hypothesis, we have generated monocyte-specific AMPK?1 KO and macrophage-specific, constitutively active AMPK?1T172D transgenic mice.
In Aim 1, we will examine how the loss or gain of function of AMPK?1 in macrophages regulates M1 versus M2 macrophage polarization and consequently, Th17 and Tregs differentiation and disease outcomes. Studies under Aim 2 will elucidate the mechanism by which the loss of AMPK?1 reprograms glycolysis-TCA metabolism leading to an imbalance of succinate and itaconate metabolites in macrophages, which in turn, determine the macrophage phenotype. The proposed study is expected to have a positive impact by elucidating the metabolic regulatory mechanism responsible for macrophage plasticity during disease and investigating AMPK?1 as a potential therapeutic target for MS. Our innovative genetic mouse models and precise metabolomics approach will allow us to identify the apparent rewiring of cellular metabolic pathways specific to AMPK?1 in hyperinflammatory cells. Ultimately, this process could be exploited to tailor novel therapeutic strategies to resolve or limit autoimmune inflammation in the CNS.
The proposed research aims to provide a better understanding of the mechanisms by which cell metabolism controls the proinflammatory nature of monocytes/macrophages and thus affects disease outcomes. This work is directly relevant to public health as the findings of this study will help guide the design of precisely targeted therapies and treatments for autoimmune disease such as multiple sclerosis.