Human Adenylate Kinase 2 Deficiency Inhibits Hematopoietic Cell Differentiation towards Neutrophil and T Lymphoid Lineages.

Abstract 78

Reticular dysgenesis (RD), an autosomal recessive form of human Severe Combined Immunodeficiency is characterized by the absence of blood neutrophils and T lymphocytes. This pathology is due to biallelic mutations in the adenylate kinase 2 (AK2) gene, resulting in the loss of AK2 protein expression. AK2 is a mitochondrial protein which regulates the homeostasis of cellular adenine nucleotides by converting ADP into ATP and AMP. In order to understand the precise role of AK2 in hematopoiesis, we have developed a RNA interference strategy through lentiviral-mediated gene transfer of AK2 short hairpin RNAs (shAK2). The knock-down of AK2 in human or murine hematopoietic stem cells (HSC) inhibits their capacity to form granulocyte colonies in methycellulose assays and prevents them to generate mature polynucleated cells in liquid culture in the presence of G-CSF. We also determine the ability of shAK2-transduced HSC to differentiate along the T lymphoid lineage after co-culture on a OP9Delta1 stroma cell line. Our data demonstrated that the apparition of CD4+CD8+ cells was profoundly reduced in the presence of shAK2. To delineate the mechanism involved in this defect, we also studied the neutrophil differentiation of the HL60 promyelocytic cell line, following retinoic acid treatment. In this system, the absence of AK2 expression led to an arrest of neutrophil differentiation process, increased cell apoptosis and disrupt the mitochondrial membrane potential. All these data suggest a novel mechanism regulating hematopoietic cell differentiation, and involved in one of the most severe human immunodeficiency syndromes.