Mechanism and functional consequences of dietary lipids in lineage specification and tumor growth in oncohistone gliomas - PROJECT SUMMARY: Mechanism and functional consequences of dietary lipids in lineage specification and tumor growth in oncohistone gliomas Diffuse midline gliomas (DMGs) are the most aggressive brain tumors of childhood. Malignant growth of H3K27M DMGs is linked to reduced activity of the histone methyltransferase polycomb repressive complex 2 (PRC2) and diminished H3K27 trimethylation (H3K27me3), a repressive chromatin mark. H3K27M-induced reconfiguration of chromatin architecture suppresses differentiation of cycling glial progenitor cells in the developing brain. This is further accompanied by increased PDGFRA signaling supporting the expansion of these progenitor cells. Nevertheless, the tumor cells retain some latent differentiation potential. We and others have shown that this potential can be unmasked by treatment with serum or pharmacologic remodeling of chromatin, which drive differentiation of these tumor cells to more mature glial cell lineages and reduce their tumorigenic potential. In preliminary studies, we have found that; (i) diet-derived lipids in the form of n3-polyunsaturated fatty acids (n3- PUFAs) are required for serum-induced differentiation of H3K27 DMGs, and (ii) n3-PUFAs’ effect in this setting is associated with increased H3K27me3 marks, enrichment of more differentiated glial cell population, and reduction of cycling glial progenitor cell population. This suggests a previously unappreciated link between these dietary lipids and epigenetic modulation of cell lineage specification. Against this backdrop, our central hypothesis is that the PUFA pathway (specifically n3-PUFA) modulates cell fate decisions and epigenetic programs relevant for H3K27M-mediated gliomagenesis. We test this hypothesis by addressing three fundamental questions. First, what is the functional role of n3-PUFAs in self-renewal and lineage-specific differentiation of H3K27M glial progenitors? Aim 1 addresses this question by interrogating the causal link between n3-PUFAs and H3K27M glioma cell state specification through a combination of loss- and gain-of- function, nutrient rescue assays, and single-cell transcriptomic to rigorously examine the functional contribution of these lipids to cell fate. Second, what is the biochemical mechanism whereby n3-PUFAs influence these cell states? Aim 2 addresses this question by characterizing a mechanistic links between these lipids and the H3K27M DMG chromatin landscape by examining chromatin accessibility of loci specific for distinct cell lineage, and by interrogating PRC2 activity and PDGFRA signaling as biochemical targets of n3-PUFAs. Third, do PUFA enrichment strategies have therapeutic potential in DMGs? Aim 3 addresses this question by testing the anti- tumor effects of n3-PUFA diets or genetic activation of the PUFA pathway in H3K27M DMG PDX models. These studies are aligned with PAR-23-051 in that they test n3-PUFAs as dietary variables that mechanistically link epigenetic modifiers/programs to H3K27M DMG cell fate decisions and tumorigenic potential.
