Reduced AKT activation accompanied with high TP53 expression is implicated in the impaired hematogenesis in Ziegler-Huang syndrome and the Znt7 null mice partially recapitulates the human disease linked to pancytopenia

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BACKGROUND: Inherited bone marrow failure (IBMF) is a life-threatening condition. Excessive expression of TP53 induces cell cycle arrest and apoptosis of hematopoietic cells in individuals with IBMF. We recently discovered two pathogenic variants, NM_001144884:c.21dup;p.(Asp8ArgfsTer3) and NM_001144884:c.842 + 15 T > C, in ZNT7 associated with IBMF (Ziegler-Huang Syndrome; BMF8). However, the pathophysiologic mechanism of IBMF caused by ZNT7 mutations remained unknown. METHOD: We investigated TP53 expression and the activation of its upstream regulator, AKT, in cell lines from affected individuals. We rescued the wild-type phenotype of AKT activation via transduction of wild-type ZNT7 into patient's fibroblasts. We performed fluorescence microscopy to assess co-expression patterns of ZNT7 with hematopoietic cell markers in different human and mouse bone marrow cell types. Finally, we evaluated the hematological features of Znt7 deficient mice. RESULTS: The growth of patient's EBV-transformed B (B-EBV) lymphoblasts was impaired. We observed excessive expression of TP53 in the patient's B-EBV lymphoblasts accompanied by a significant decrease in AKT activation. Importantly, overexpression of wild-type ZNT7 in patient's fibroblasts rescued the activation of the AKT pathway by insulin. Additionally, human ZNT7 was expressed in myeloid and lymphoid lineage cells, whereas mouse ZnT7 was mainly expressed in the nucleated hematopoietic cells in the respective bone marrow. Despite these differences, we observed progressive cytopenia in Znt7KO mice, partially recapitulating BMF8 in humans. CONCLUSION: Excessive expression of TP53 and down-regulation of AKT activation induced by ZNT7 deficiency might impair cell survival, which may contribute to the pathophysiology of bone marrow failure in affected individuals with BMF8.

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