Relationship between the Hematopoietic Phenotype and the Subtype of Fanconi Anemia Mice.

Fanconi anemia (FA) is a rare inherited disease associated with aplastic anemia and cancer predisposition. Great progress has occurred at a molecular level that allowed the identification of 13 genes involved in the disease. Additionally, several FA mouse models have been developed with the purpose of investigating the biological basis of the disease, and of facilitating the development of new therapies for FA. Because of the genetic heterogeneity of FA, here we have investigated the relevance of different FA genes to preserve the function of the hematopoietic stem cells (HSCs) of the mouse. To this aim, we have comparatively investigated the hematopoietic phenotype of different FA mice: Fanca^−/−, Fancc^−/−, Fancd1/Brca2^Δ27/Δ27and Fancd2^−/−. Normal counts of peripheral blood (PB) cells were observed in the different FA mice. Flow cytometry analyses were also incapable of demonstrating significant changes in the hematopoietic subpopulations present in PB, bone marrow (BM) or spleen of the different FA mice. In contrast to these observations, a reduction in the content of the hematopoietic progenitors was observed both in the BM and the spleen of Fancd1/Brca2^Δ27/Δ27 and Fancd2^−/− mice, either in young or adult. Significantly, a similar reduction in hematopoietic progenitors was only observed in old Fanca^−/− and Fancc^−/− mice. Moreover, hematopoietic colonies from mice defective in FA proteins downstream the FA core complex were smaller, compared to colonies from wild type, Fanca^−/− or Fancc^−/− mice. As expected, hematopoietic progenitors from all studied FA mouse models were highly sensitive to the DNA cross-linking agent, mitomycin C (MMC). Concerning the function of the HSCs of these FA mice, reduced competitive repopulation ability was always observed, compared to WT HSCs. However, in animals defective in FA proteins downstream the FA core, CRA values progressively dropped along the transplantation period. Additionally, a spontaneous chromosomal instability was observed in bone marrow cells from Fancd1/Brca2^Δ27/Δ27. These animals also showed a marked repopulation defect in their HSCs assessed in their natural physiological environment, when wild type cells were transplanted in unconditioned Brca2^Δ27/Δ27 recipients. In summary, our results show a more severe defect in the functionality of the HSC compartment in mice with mutant FA proteins downstream the FA core complex.