Children with Down Syndrome (DS) have an increased risk of developing acute leukaemia, theorised to occur in a three step process beginning with Trisomy 21 (Tri21), progressing to a Transient Myeloproliferative Disorder (TMD), and culminating in Acute Megakaryoblastic Leukaemia (AMKL). This study aims to determine if key genetic elements on chromosome 21 including ERG, ETS2, and microRNA (miR)-99a and 155, which can directly impact haematopoiesis and regulate downstream genes and pathways (TAL1 and mTOR pathway) to drive abnormal haematopoiesis, are overexpressed in Tri21 cells versus control. Non-Tri21 genes known to be involved in megakaryopoiesis may also be associated with the pathogenesis of DS-AMKL.
Embryoid bodies derived from bona-fide iPSC lines were cultured in defined haematopoietic differentiation medium to produce CD34+ haematopoietic stem cells (HSCs). Assessment of functional haematopoiesis by colony forming assays demonstrated that HSCs derived from Tri21-iPSCs had greater clonogenic potential and generated more CFU-E, BFU-E and CFU-GEMM colonies compared to control cells. Real-time RT-PCR of these pre-leukaemic (Tri21) haematopoietic colonies detected ≥ 1.4 fold increase in relative expression of Tri21 elements ERG and ETS2 compared to their Normal Karyotype (NK) counterparts. This was also observed in a DS-AMKL cell line (CMY) when compared to NK megakaryoblastic cell lines such as MEG-01. Our cell line model of DS-AMKL has also shown a change in other haematopoiesis regulatory gene and miR expressions which are known to be involved in megakaryopoiesis in DS-AMKL compared to non-trisomic megakaryoblasts. To sum up, we have identified specific genes associated with the aberrant Trisomy 21 haematopoiesis and megakaryoblastic leukaemia. The role of these genes in the pathogenesis of this trisomy 21 condition warrants further investigation.