Long-Term Mid-onset Dietary Restriction Rejuvenates Hematopoietic Stem Cells And Improves Regeneration Capacity Of Total Bone Marrow From Aged Mice

Background/Aims:Hematopoietic cell transplantation is an important treatment option for many hematopoietic malignancies.HLA haploidentical family members have become an important donor source due to the lack of HLA identical sibling donors and the high expenses of recruiting HLA matched unrelated donor volunteers.However,hematopoietic malignancies（such as acute myeloid leukemia,myelodysplastic syndrome,and other hematopoietic malignancies）mostly occur in the elderly population,which results in older transplant recipients and donors.The function of donor hematopoietic cells is crucial to the prognosis of hematopoietic cell transplantation.However,how to improve the regeneration functionality of old donors in order to improve the engraftment and reconstruction after hematopoietic cell transplantation remains to be elucidated.This study is mainly to study how to improve the regeneration capacity of hematopoietic cells in old donors,and to explore new ways to improve hematopoietic cell transplantation when only old donors are available.Methods:15-18 months old mice（the equivalent change in humans would roughly be50-60 years）were treated with 30%dietary restriction（DR,the daily food intake is70%of the daily intake of the control mice that match the sex,age,and weight）.After 4 months of DR,the aging-related phenotypes of HSCs（Hematopoietic stem cells,HSCs）(the number of phenotypically defined HSC,the ratio of CD150^highCD34^-KSL and CD150^lowCD34^-KSL cell)and HSC cell cycle activity,downstream lineages（lymphoid lineage and myeloid lineage）were analyzed by flow cytometry;immunostaining of p-H2AX（phospho-Histone H2AX,a typical marker of DNA damage induced by DNA double strand breaks）for quantification of DNA damage（γ-H2AX foci）;sorted HSCs and unsorted total bone marrow cells from DR4 month aged mice were subjected to competitive transplantation experiments to analyze the effect of short-term mid-onset DR on HSC and bone marrow cell function.After 9 months of DR,the aging-related phenotypes of HSCs were analyzed by flow cytometry.The bone marrow competitive transplantation experiments were performed to analyze the effect of long-term mid-onset DR on hematopoietic reconstruction of bone marrow transplant.Results:Mid-onset（15-18 months）DR significantly reduced the size of HSC pool（not mediated by apoptosis）,especially myeloid-biased HSCs(CD150^highHSCs),and increased HSCs quiescence and reduced DNA damage.Short-term（4 months）DR derived HSCs led to higher chimerisms in whole white blood cells（WBC）and B lymphocytes in competitive transplantation,while short-term DR derived bone marrow cells have no advantage in chimerism in all lineages.Long-term（9 months）DR derived bone marrow cells led to higher chimerisms in WBC and lymphocytes in competitive transplantation,and the beneficial effect starts as early as 1 month after transplantation.However,analysis of the donor’s hematopoietic system shows that mid-onset DR suppresses B lymphopoiesis while myelopoiesis is negligibly influenced.Conclusion:Long-term mid-onset DR significantly improved hematopoietic reconstruction after bone marrow transplantation in elderly transplant donors.The current study will provide new ideas for exploring possible ways to improve the clinical prognosis of bone marrow transplantation from middle-aged and elderly donors.