Aldehyde dehydrogenase 2 plays a dispensable role in hematopoiesis in response to DNA damage

Abstract Endogenous formaldehyde is a highly reactive metabolite that can induce DNA damage beyond the capacity of repair pathways, posing a threat to genomic integrity. Aldehyde dehydrogenase 2 (Aldh2) is a key mitochondrial enzyme responsible for detoxifying reactive aldehydes, thereby mitigating their genotoxic effects. A common polymorphism in the Aldh2 gene (rs671), present in 30-40% of the East Asian population, significantly reduces enzymatic activity and is associated with alcohol intolerance and increased aldehyde sensitivity. While deficiency of Aldh2 has been shown to exacerbate bone marrow failure in Fanconi anemia mouse models, its role in broader contexts of hematopoietic stress remains unclear. In the current study, we investigated the impact of Aldh2 deficiency on hematopoiesis under genotoxic stress conditions, employing Aldh2 knockout mice. At steady state, Aldh2 deficiency had no significant effect on peripheral blood counts, bone marrow cellularity, and the frequency and composition of hematopoietic stem and progenitor cells (HSPCs). Following administration of the alkylating agent busulfan (10 mg/Kg, intraperitoneally every other day for 10 doses), Aldh2-deficient mice showed no major hematopoietic abnormalities compared to wild-type controls. However, flow cytometry analysis showed elevated γH2AX expression in myeloid progenitor cells of Aldh2 knockout mice, indicating increased DNA damage despite absence of overt phenotypic defects—possibly due to compensatory activity by other aldehyde-detoxifying enzymes. To further challenge the hematopoietic system, we subjected mice to sublethal irradiation (350 rads) following busulfan treatment. One week post-treatment, Aldh2 knockout mice exhibited significantly reduced white blood cell and lymphocyte counts, as well as diminished bone marrow cellularity, relative to wild-type counterparts. Immunostaining confirmed γH2AX accumulation in bone marrow myeloid progenitor cells of Aldh2-deficient mice, reflecting exacerbated DNA damage. To explore molecular responses, we performed bulk RNA sequencing on sorted bone marrow HSPCs (Lineage-CD117+) from busulfan-only and busulfan + irradiation groups. Transcriptomic profiles of Aldh2 knockout and wild-type HSPCs were similar following busulfan alone, but upon combined exposure there were different gene expression patterns. DNA repair genes including Ccon, Pold4, Taf1c, and Npr2 were significantly upregulated in Aldh2-deficent HSPCs under dual treatment; differential gene expression and pathway analysis showed upregulation of MYC targets, E2F targets, G2/M checkpoint, and DNA repair pathways in Aldh2-deficient cells relative to wild-type cells, consistent with compensatory activation of proliferation and DNA repair programs. Notably, Aldh2-deficient HSPCs also exhibited elevated expression of Aldh18a1, a key metabolic enzyme involved in amino acid biosynthesis, suggesting metabolic adaption to stress. We evaluated the functional consequences of Aldh2 deficiency in vivo using competitive transplantation into CD45.1 recipient mice. While Aldh2-deficient cells initially demonstrated reduced engraftment compared to wild-type cells, this difference diminished over time, indicating a transient defect, consistent with compensatory DNA repair and cell cycling in transcriptomic findings. In conclusion, although Aldh2 deficiency increases DNA damage with severe compounded genotoxic stress, Aldh2 has a dispensable role for steady state hematopoiesis and hematopoietic recovery and stem cell function after milder insults. Compensatory metabolic and DNA repair mechanisms may buffer the effects of ALDH2 loss, which has implications for understanding genetic vulnerability and resilience in hematopoietic disorders.