The neuronal ALAS2/5-ala axis mitigates chemotherapy-induced neurotoxicity via the BACH1/NRF2 pathway

Despite breakthroughs in immunotherapy and targeted therapies, chemotherapy remains indispensable in oncology.

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.

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.

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.