Metabolic and molecular regulation of myeloid cell functions in brain cancer

Glioblastoma (GBM), the most aggressive and lethal form of brain cancer, is characterized by a profound immunosuppressive microenvironment (TME) that restricts the effects of promising immunotherapies. Therefore, there is a pressing need to develop more effective interventions to overcome this mechanism of resistance. Tumor associated macrophages (TAMs) are a mixture of monocyte-derived macrophages (MDM) and microglia (MG), and they are instrumental for the maintenance of the immunosuppressive state of GBM. However, there are no effective approaches to overcome the immunosuppressive activity of TAMs in GBM, mainly due to an incomplete understanding of TAM regulatory functions. Our long term-goal is to dissect targetable metabolic and molecular mechanisms regulating TAM functions in the context of GBM; as these discoveries will facilitate novel therapies to target immunosuppression and improve the dismaying outcome of GBM patients. A recent study demonstrated that TAM are major consumers of glucose and maintain a robust glucose metabolism in the TME. However, it has not yet been determined how GBM supports the adaptation to glucose metabolism in TAMs and the functional consequences of this adaptation also remain elusive. Endoplasmic reticulum (ER) stress activation is associated with the malignant progression of glioma and with the infiltration of anti-inflammatory macrophages. PKR-like ER kinase (PERK), a critical ER stress sensor, was found to be significantly activated in human glioma tissues, and its inhibition altered ATP/lactate production by glioma cells. Our preliminary data expanded these findings indicating that MDM demonstrated highest glucose avidity among MG and neoplastic cells in GBM tumors, and PERK was strongly activated in GBM infiltrating GLUT1+MDM. Contrary to MG, MDM exhibited potent immunosuppressive activity. GLUT1+MDM were the only contributors to the suppressive activity associated with MDM in GBM tumors. GBM-derived factors primed activation of PERK signaling in MDM, which correlated with metabolic reprogramming resulting in high glycolysis, immunosuppressive functions, histone lactylation, and no change in histone acetylation. Based on our crucial observations, we hypothesize that a PERK-driven perturbation of glucose metabolism in MDM governs their immunosuppressive functions via lactate-derived lactylation of histone lysine residues. We will test this hypothesis through the following aims: Aim1: to elucidate underlying mechanisms of how PERK governs glycolysis in MDM in GBM tumors; Aim2: to define glucose-driven epigenetic modifications that regulates immunosuppressive programs in MDM; Aim3: to investigate the therapeutic potential of an epigenetic targeting approach to modulate the functions of TAMs in GBM. The proposed studies are highly innovative because they will elucidate a previously uncharacterized link between ER stress and glucose metabolism that regulates the activity of TAMs via epigenetic mechanisms. Our proposal will provide a mechanistic rationale for the development of novel therapies to target immunosuppressive TAMs and enhance the efficacy of immunotherapy in GBM patients.