Background and Purpose Despite breakthroughs in immunotherapy and targeted therapies, chemotherapy remains indispensable in oncology. Experimental Approach This study seeks to pinpoint key pathways in doxorubicin (DOX)-treated mouse hippocampus, utilising comprehensive transcriptomic and metabolomic analyses, and validating the mechanisms in vitro and in vivo. Key Results Our multi-omics investigation revealed that sustained DOX exposure induced significant down-regulation of 5-aminolevulinate synthase 2 (ALAS2) and its catalytic product 5-aminolevulinic acid (5-ALA) in the hippocampal region. ALAS2 deficiency was specific to hippocampal neurons, which were more sensitive to oxidative damage than astrocytes or microglia. In vivo and in vitro studies demonstrated that 5-ALA administration or ALAS2 overexpression protected the brain from DOX-induced neurotoxicity. ALAS2 catalyses the condensation of glycine and succinyl-CoA to form 5-ALA, the key precursor of haem. Beyond its role in erythropoiesis, haem is a metabolite that modulates cellular redox homeostasis through interactions with the BACH1 (BTB and CNC homology 1)/NRF2 (nuclear factor erythroid 2 like 2) pathway. We found that DOX suppressed the ALAS2/5-ALA axis, thereby enhancing BACH1 stability. This stabilised BACH1 competes with NRF2 for binding to antioxidant response elements (AREs) in target gene promoters. Conversely, reinforcing the ALAS2/5-ALA axis elevated intracellular haem levels, promoting BACH1 degradation and enhancing NRF2 activity. Using a zebrafish model, we further highlighted the antioxidant and neuroprotective role of 5-ALA against DOX-induced neurotoxicity. Conclusions and Implications In conclusion, this study elucidates a novel endogenous neuroprotective mechanism wherein the ALAS2/5-ALA axis modulates the BACH1/NRF2 pathway. 5-ALA shows promise for repurposing to mitigate chemotherapy-associated neurotoxicity. Graphical
Background G-quadruplexes (G4s) are unique noncanonical nucleic acid secondary structures, which have been proposed to physically interact with transcription factors and chromatin remodelers to regulate cell type-specific transcriptome and shape chromatin landscapes.Results Based on the direct interaction between G4 and natural porphyrins, we establish genome-wide approaches to profile where the iron-liganded porphyrin hemin can bind in the chromatin. Hemin promotes genome-wide G4 formation, impairs transcription initiation, and alters chromatin landscapes, including decreased H3K27ac and H3K4me3 modifications at promoters. Interestingly, G4 status is not involved in the canonical hemin-BACH1-NRF2-mediated enhancer activation process, highlighting an unprecedented G4-dependent mechanism for metabolic regulation of transcription. Furthermore, hemin treatment induces specific gene expression profiles in hepatocytes, underscoring the in vivo potential for metabolic control of gene transcription by porphyrins.Conclusion sThese studies demonstrate that G4 functions as a sensor for natural porphyrin metabolites in cells, revealing a G4-dependent mechanism for metabolic regulation of gene transcription and chromatin landscapes, which will deepen our knowledge of G4 biology and the contribution of cellular metabolites to gene regulation.
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