The role of the specific aldehyde dehydrogenase (aldh) isoforms in theregulation of embryonic hematopoiesis

Abstract

Despite recognition of aldehyde dehydrogenase (Aldh) as a surrogate marker in isolating primitive hematopoietic stem and progenitor cells (HSPC) [1], its role in HSPC regulation, particularly during embryonic development, remains unclear. In this study, we examined the role of Aldh during embryonic hematopoiesis in zebrafish, which has emerged as a model for hematopoietic studies. [2]

Wild--?type and transgenic [Tg(gata1:gfp),Tg(fli1:gfp)] zebrafish embryos were microinjected with anti--?sense morpholinos (MO) at 1--?cell to 4--?cell stage and evaluated by morphology, flow cytometry, in situ hybridization (ISH) and Q-RT-PCR. In addition, human CD34+ cells, which were enriched with hematopoietic stem cells (HSC), were isolated from umbilical cord blood samples for analysis of ALDH16A1 expression. It was subsequently compared with CD34- cells which were devoid of HSC activity.

When aldh16a1 was knocked down by anti-sense morpholino (the embryos were referred herewith aldh16a1MO embryos), gene expression associated with erythropoiesis was significantly reduced at 18hpf .(gata1:0.70±0.03fold; p=0.002) (α-embryonic hemoglobin: 0.48±0.04fold; p=0.003) (β-embryonic hemoglobin: 0.56±0.03fold; p=0.001). Angiogenesis was also perturbed at 48 and 72hpf. Furthermore, human ALDH16A1 was significantly upregulated (4.79±1.00fold; p=0.00006) in CD34+ (enriched with HSC) as compared to CD34- (devoid of HSC) populations in umbilical cord blood.

Aldh16a1 is important for the maintenance of primitive hematopoiesis at early (18hpf) and angiogenesis at later (48,72 hpf) embryonic stages. As angiogenesis plays an important role in pathophysiology of malignancies, novel therapy against ALDH16A1 might be exploited in therapeutic intervention in cancer treatment. Moreover, a specific role of zebrafish aldh16a1 in primitive erythropoiesis and a higher level of ALDH16A1 expression in human HSC-enriched cells suggested a conserved mechanism whereby ALDH regulates hematopoiesis.