Search

Macrophages are plastic cell populations that normally adapt to their environment. Cellular adaptation to hypoxia occurs through transcription factors including hypoxia-inducible factors, and hypoxia-inducible transcriptions are further regulated by chromatin response through histone modification including histone methylation. However, the role of histone methylation in the hypoxia response of macrophages is not well understood. As obesity is associated with dysregulated macrophage functions, we investigated whether hypoxia response is cell-intrinsically dysregulated in macrophages in obesity.In mouse bone marrow-derived macrophages (BMDMs), immunoblotting revealed that 1% hypoxia rapidly increases the global levels of histone 3 methylations. We found that hypoxia-induction of histone 3-lysine 4 tri-methylation (H3K4me3) is specifically inhibited in BMDMs from mice fed a high-fat diet (HFD-BMDMs) compared to BMDMs from mice fed a normal diet (ND-BMDMs). Multi-omics approach with ChIP-seq and RNA-seq identified that glycolysis-related pathways and genes includingAldoaare upregulated after prolonged hypoxia along with upregulated H3K4me3 in ND-BMDMs. In contrast, no pathway is associated with hypoxia-upregulated H3K4me3 peaks in HFD-BMDMs and hypoxia-inducedAldoaexpression is decreased in HFD-BMDMs, suggesting both the extent and the genome location of H3K4me3 response to hypoxia is dysregulated in obesity. Consistently, lactate accumulation and induction of histone lactylation under hypoxia are reduced in HFD-BMDMs. Furthermore, HFD-BMDMs exhibited decreased dying cell clearance under hypoxia due to the reduced capacity of anaerobic glycolysis. Competitive bone marrow transplantation of hematopoietic stem cells (HSCs) shows that HFD-induced long-term memory reflects the impaired dying cell clearance in differentiated BMDMs, which is rescued by inhibiting oxidative stress in HSCs.In summary, chromatin response to hypoxia associated with H3K4me3 enrichment governs transcriptions for anaerobic glycolysis and dying cell clearance under hypoxia. Obesity dysregulates the extent and the genome location of H3K4me3 enrichment, glycolysis, and dying cell clearance of BMDMs under hypoxia, which is initiated in HSPCs via oxidative stress.

Although it is well-known that the environment of mitochondria is a densely packed network of macromolecules, the kinetics of the essential metabolic enzyme, citrate synthase, has been studied only under dilute conditions. To understand how this crowded environment impacts the behavior of citrate synthase, Michaelis-Menten kinetics were measured spectrophotometrically in the presence of synthetic crowders as a function of size, concentration, and identity. The largest factor contributing to crowding effects was the overlap concentration (c*), the concentration above which polymers begin to interact. The presence of the crowder dextran decreased the maximum rate of the reaction by ∼20% in the dilute regime ( c*) regardless of polymer size. The disparate effects observed from different crowding agents of similar size also reveal the importance of transient interactions from crowding.