Blood Stem Cells Hibernate via Lysosomes; Liang et al, Cell Stem Cell, 2020. Old yellow leaves in the Winter (the waste of hibernating quiescent blood-forming stem cells) are stored and recycled in the green bin (lysosomes) to produce the blooming tree in the Spring (primed active blood-forming stem cells). Illustrated by: Ni-Ka Ford, Katrina Kapp 2020. 

Old Blood in a Young Body; Rimmelé et al, Stem Cell Reports, 2014The effects of loss of SIRT1 on blood and blood stem cells in the young recapitulates the blood defects of the old. Illustrated by Nazanin Sarbandi 2014.

Foxo3 regulates erythroid cell maturation and enucleation.

Liang et al, PLoS Genetics 2015

Hematopoietic Stem Cells, Organelles and Metabolism Towards Improving Stem Cells’ Function in Transplantation and Longevity

The very few hematopoietic stem cells (HSCs) in the bone marrow produce  over 600 billions of red and white blood cells and platelets that are highly specialized in their functions every day. This massive, diverse and balanced production is tightly regulated to counter daily needs, and to regenerate and intervene in response to injury or loss (as in hemorrhage) during the lifetime. Disruption of this production at any level may lead to disease. This happens particularly with age, when the ability of HSCs to regenerate declines. Ghaffari lab is involved in identifying mechanisms that maintain HSC functions, and that are altered with age and in disease (specifically in blood malignancies).. 

One of the main treatments for disorders of blood – including malignancies – is hematopoietic stem cell transplantation. However, the limited numbers of hematopoietic stem cells restrict the use and success of stem cell transplantation. One approach has been to expand HSC numbers in a dish in the laboratory. A major limitation of this approach is the loss of stem cell capacity once HSCs are outside of the body; also current culture conditions are not optimum for HSC maintenance and expansion ex vivo. To address these questions, we have been focused over the years to identify and characterize redox-mediated and metabolic/mitochondrial-regulated pathways that are implicated in generating blood and blood-forming stem cells and their modulations in cultured HSCs compromise stem cell activity. We are using our knowledge of mitochondria and lysosomes to improve the detection, and enhance (rather than expand) the function, of blood-forming stem cells at the steady state, and under stress and aging conditions. These approaches have led us to our recent discovery of lysosomal modulations as a central mechanism that regulates HSC activity based on which we have devised conditions that promote in vitro maintenance, enhance vigorously in vivo HSC ability and identify human HSCs with superior long-lasting in vivo function.

Our initial identification of the longevity FOXO (FOXO3 in HSCs) transcription factors (Ghaffari et al., 2003; PNAS, 2003; Yalcin et al., JBC 2008, Zhang et al, Nature Cell Biology, 2011) as key regulators of stem cell activity and the subsequent over a decade work towards elucidating their functions led us to the current metabolic and organelle (mitochondrial and lysosomal) studies of hematopoietic stem and progenitor cell activity (Yalcin et al., EMBO 2010; Rimmelé et al., Stem cell Reports, 2014; EMBO Reports, 2015; Liang et al., Cell Cycle 2016; Bigarella et al., JBC, 2017; Liang et al., Cell Stem Cell, 2020; Qiu et al., Blood Adv. 2021; Ghaffari, Cell Stem Cell, 2021).

We are also interested in how metabolism impacts stem cell epigenome and how this regulation is modified with age. We initially found that the NAD-dependent Sirtuin deacetylase SIRT1 – a key regulator of lifespan in many organisms – has a strong impact on HSC health and activity (Rimmelé et al., Stem cell Reports, 2014; Liang et al., Cell Cycle 2016).  The decline of HSC function with age leads to a loss of balanced blood production and other HSC alterations that impact the immune response of the elderly and increase the risk of leukemia. We found that in the absence of SIRT1, blood from young animals looks and behaves very much like blood from old animals. Our current work is partly focused on exploring whether mechanisms that promote aging of HSC can be reverted to a younger state (Manuscript in Preparation).  The hope is that by delaying the aging of blood stem cells, we could delay or even prevent age-related disorders of blood and perhaps of other organs.

Erythropoiesis, Red Blood Cells, Erythroid Disorders and Metabolism

Erythropoiesis is the process of making red blood cells (RBCs) from hematopoietic stem and progenitor cells. RBCs carry oxygen and travel throughout the body to oxygenate all tissues. Anemia or reduced capacity of RBCs to carry oxygen constitutes a major health problem associated with many disorders. In response to loss or reduced production of RBCs, blood-forming stem and progenitor cells are activated to produce RBCs.

Ghaffari lab identified FOXO3 as the main transcription factor that coordinates the maturation process of erythroid cells, mediates their expression of metabolic and redox-related enzymes and regulates their metabolism (Marinkovic et al., JCI, 2007; Yalcin et al., EMBOJ, 2010; Zhang et al., AJH 2014; Liang et al., PLoS Genetics, 2015).  We have used FOXO3 to dissect mechanisms that underlie apoptosis in beta-thalassemia (Menon et al., BioRxiv, 2022). Currently the lab is focused on identifying specific metabolic programs and metabolites that control RBC enucleation (removal of the nucleus) and their impact on erythroid cell epigenetics during this process (Menon and Ghaffari, Exp. Hem, 2021; Liang et al. Blood Adv., 2021). Our goal is to apply our knowledge to improve the outcome in erythroid disorders such as beta-thalassemia.

Leukemia and Leukemic Stem Cells, Organelles and Metabolism

In leukemia, leukemic stem cells are cells that resist therapy and reestablish leukemia in patients up to years after remission. Understanding the biology of leukemic stem cells may provide unique therapeutic opportunities. Our work indicates that deregulation of pathways that protect stem cells from age-associated cellular damages may intersect with pathways that promote leukemia (Bigarella et al., In Submission). We are currently testing this hypothesis in human HSCs and their leukemic [acute myeloid leukemia (AML) and myeloproliferative neoplasm (MPN)] counterparts (Qiu et al., Blood Adv., 2021).