Formaldehyde-induced hematopoietic stem and progenitor cell toxicity in mouse lung and nose

Abstract

Formaldehyde (FA), an economically important and ubiquitous chemical, has been classified as a human carcinogen and myeloid leukemogen. However, the underlying mechanisms of leukemogenesis remain unclear. Unlike many classical leukemogens that damage hematopoietic stem/progenitor cells (HSC/HPC) directly in the bone marrow, FA-as the smallest, most reactive aldehyde-is thought to be incapable of reaching the bone marrow through inhalation exposure. A recent breakthrough study discovered that mouse lung contains functional HSC/HPC that can produce blood cells and travel bi-directionally between the lung and bone marrow, while another early study reported the presence of HSC/HPC in rat nose. Based on these findings, we hypothesized that FA inhalation could induce toxicity in HSC/HPC present in mouse lung and/or nose rather than in the bone marrow. To test this hypothesis, we adapted a commercially available protocol for culturing burst-forming unit-erythroid (BFU-E) and colony-forming unit-granulocyte, macrophage (CFU-GM) colonies from bone marrow and spleen to also enable culture of these colonies from mouse lung and nose, a novel application of this assay. We reported that in vivo exposure to FA at 3 mg/m³ or ex vivo exposure up to 400 µM FA decreased the formation of both colony types from mouse lung and nose as well as from bone marrow and spleen. These findings, to the best of our knowledge, are the first empirically to show that FA exposure can damage mouse pulmonary and olfactory HSC/HPC and provide potential biological plausibility for the induction of leukemia at the sites of entry rather than the bone marrow.

Keywords: Colony; Formaldehyde; HSC/HPC; Leukemogenesis; Toxicity.

Fig. 1

Experimental design and workflow. a Experiment in vivo. b Experiment ex vivo

Fig. 2

BFU-E and CFU-GM colonies cultured from the lung, nose, BM and spleen of BALB/c mice. Based on a guideline from StemCell Technologies™, erythroid cells tend to grow together forming a “wrinkled” cluster (BFU-E) in which individual cells cannot be distinguished. In contrast, in the CFU-GM colonies, individual cells are “phase-bright” or “clear” in appearance, enabling the identification of this colony type

Fig. 3

The formation of both BFU-E and CFU-GM colonies from all four tissues (lung, nose, BM and spleen) of BALB/c mice exposed to vehicle or 3 mg/m³ FA in vivo. The experiments were conducted independently by two researchers and the results are shown as Expt. I and Expt. II. Each tissue type was cultured in duplicate. Each data point represents one replicate of each tissue type. Data are presented as mean ± SEM. *p < 0.05, **p < 0.01 and ***p < 0.001, as compared to control

Fig. 4

The formation of both BFU-E and CFU-GM colonies from all four tissues (lung, nose, BM and spleen) of BALB/c mice exposed to vehicle or FA ex vivo. The experiments were independently repeated 5 times for lung, BM and spleen, and 4 times for nose. Data at each dose were merged from 4–5 repeated experiments. Each tissue type was cultured in duplicate. The average of the duplicate for each tissue type represents each individual experiment. Data are presented as mean ± SEM. *p < 0.05 as compared to control

Fig. 5

Overview of our study hypothesis, testing model and experimental design for detection of HSC/HPC toxicity induced by FA in mouse lung and nose. (Note: The image of human background figure is adapted from https://www.pngwing.com.)