Preliminary Evidences For Regulation Of Autophagy On The Quiescence State Of Hematopoietic Stem Cells

All kinds of blood cells differentiate from the very few long-term hematopoietic stem cells(LT-HSCs, also called pluripotent hematopoietic stem cells). The LT-HSCs differentiate into short-term HSCs(ST-HSCs) in the bone marrow, ST-HSCs subsequently differentiate into different hematopoietic precursor cells and finally differentiate into mature blood cells. As the "seed" of blood cells, the majority of LT-HSCs is located in closed bone marrow tissue and keeps in quiescence state(without proliferation or without differentiation or without apoptosis). Interference of quiescence of LT-HSCs can cause abnormal expansion of hematopoietic stem cells and lead to hematopoiesis dysfunction(exhaustion of HSCs and transformation of leukemia stem cells). Thus, the quiescence state of LT-HSCs is important for the maintenance of hemapotosis in bone marrow in life cycle and abilities to respond to stress.LT-HSCs are located in the hypoxic bone marrow microenvironment(niche). In the absence of oxygen or nutrient deficiency, autophagy provides nutrition and energy support for the survival of HSCs by decomposing the senescence organelles and denatured biological macromolecules. Autophagy is an important conserved biological process of the evolution of the intracellular substances in eukaryotes. More and more studies show that autophagy is involved in the regulation of the self-renewal and differentiation of embryonic stem cells, the growth and development of embryo. However, because of the lack of effective animal and cell model, the mechanisms underlying how autophagy regulates the quiescence state of LT-HSCs remains unknown. On the basis of our previous research, we employed hematopoietic stem cell line EML as the cell model, utilizing the techniques of cell biology, molecular biology and genetics, to explore the association of autophagy with quiescence state of HSCs. We found that autophagy is involved in the regulation of quiescence of hematopoietic stem cells and conversion of quiescence state and proliferative state.The main conclusions of this paper include:1.Two sub-populations of LSKCD34-(CD34-) and LSKCD34+(CD34+) in EML cell line were successfully isolated. We found that CD34- cells are in quiescence state but CD34+ cells in a proliferative state. Interestingly, the two sub-populations are converted to each other.2.The microarray data of gene expression pattern analysis indicated that the autophagy related genes and its upstream of the transcription factors were significantly different expressed between CD34- cells and CD34 + cells. The expression levels of autophagy related genes of CD34- cells was significantly higher than that of CD34 + cells.3.Rapamycin, autophagy activation agent inhibits conversion of CD34- into CD34 + cells. On the contrary, transcription factor Tcf7 of activated Wnt signaling pathway enhanced conversion of CD34 cells into CD34 + cells by inhibiting autophagy.