Ghaffari Lab - Research

The Ghaffari laboratory investigates mechanisms that regulate blood stem and progenitor cell formation that are implicated in the pathophysiology of blood disorders. To address these questions, we have been focused on the FOXO family of transcription factors, which are key in stress resistance and implicated in enhancing human longevity (FOXO3). In our studies we use cellular and molecular biology and apply genetic tools and biochemistry to investigate the biology of mouse and human cells and various mouse models of human blood disorders.

Hematopoiesis, Hematopoietic Stem Cells and Erythropoiesis

Blood-forming stem cells have unique properties that enable them to live a long life and regenerate blood constantly. The well-being of blood-forming stem cells throughout life is essential for maintaining a healthy life by producing billions of red and white blood cells every day in humans. With aging this regenerative capacity declines which compromises optimum blood production and might also lead to blood malignancies whose incidence increases with age. The primary goal of our laboratory is to dissect the regulatory pathways that maintain the health of blood-forming stem and progenitor cells throughout life. We hope this knowledge will eventually lead to the identification of specific targets and/or development of novel tools that could be used in the clinic to improve therapy and/or to produce healthy blood-forming stem cells in a dish for bone marrow transplantation. In these efforts, we have identified the transcription factor FOXO3 and its regulatory network as critical regulators of blood-forming stem cells and their production of red blood cells.

Erythropoiesis, Red Blood Cells and FOXO3

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. RBC production is dependent mainly on erythropoietin, a hormone that is produced when oxygen levels are low. We found FOXO3, a protein that regulates a response to oxygen levels and whose function is partly

Figure 1

controlled by erythropoietin, as key to physiological regulation of red blood cell production and maturation and the regulation of harmful consequences of oxygen metabolism (oxidative stress) during this process. One of the recently discovered fascinating features of FOXO3 regulation of RBC production is its control of the essential enucleation (removal of the nucleus) process (Figure 1). In order for RBC to fully mature RBC nucleus (chromatin) is condensed and moves to one side of the cell before being released; our results suggest that FOXO3 might be implicated in chromatin condensation and/or RBC precursor cell polarity. We are testing these alternatives in human RBC precursors. FOXO3 also regulates metabolic gene expression during RBC maturation. Overall our findings raise the possibility that modulating FOXO3 may enhance the production of RBCs in a dish and/or might be useful therapeutically in the context of disease.  

Hematopoietic Stem Cells Mitochondria, Oxidative Stress and FOXO3

Quiescence is a fundamental property of most adult stem cells. The regeneration capacity of adult blood-forming stem cells is tightly linked to their quiescence, a property that requires the transcription factor FOXO3. Mitochondria are the center of energy production and critical for blood-forming stem cell activation. One of the byproduct of mitochondrial activation is the generation of reactive oxygen species (ROS) that depending on the levels and/or context might be deleterious (oxidative stress). Cumulative findings raise the possibility that mitochondria are critical for blood-forming stem cell activity although very little is known about mitochondria in adult blood-forming stem cells. Our work indicates that FOXO3 is required for regulating both ROS levels and mitochondrial metabolism in blood-forming stem cells (Figure 2). We are devising a new functional approach to investigate stem cell behavior. Using this and other tools we have acquired or

Figure 2

developed, we are delving deep into mitochondrial metabolism, its regulation of blood-forming stem cells, and the role of FOXO3 in these processes. Our hope is that these combined approaches will enhance our ability to identify molecules that interfere with abnormal mitochondrial metabolism that might eventually be used therapeutically to modulate stem cell function.

Hematopoietic Stem Cells Aging Stem Cells, Sirtuin 1 and FOXO3.

Figure 3

While most mature blood cells have a short half-life, blood-forming stem cells live a long life that leads to their accumulation of damaged DNA, lipids and proteins overtime with age. Aging of blood-forming stem cells is thought to be at the origin of impaired immune competence and some of the blood malignancies whose incidence increase with age. Our recent findings (Rimmelé et al., Stem Cell Reports, 2014, Figure 3) show that the type of mature white blood cells produced from blood-forming stem cells (lineage specification) is skewed in the absence of Sirtuin 1 deacetylase, an epigenetic regulator critical for healthy aging. Our studies also indicate that SIRT1 modification of FOXO3 might be critical for FOXO3 activity in blood-forming stem cells. Overall our findings suggest that SIRT1 and its target FOXO3 might be implicated in the aging process of blood-forming stem cells.   

Hematopoietic Stem Cells, Malignant Reprogramming, Myeloid Malignancies and FOXO3.

Leukemic stem cells are thought to be rare cells that have stem cell properties, are quiescent and resist therapy, and reestablish the disease sometimes years after remission. Understanding the biology of leukemic stem cells may provide unique therapeutic opportunities. Although FOXO3 is clearly implicated in myeloproliferative neoplasms (MPNs) and acute myeloid leukemia (AML) whether FOXO3 protects or enhance leukemogenesis remains unclear. In collaboration with other laboratories at ISSMS, United States and abroad we are addressing FOXO3 regulation and function in the context of myeloid malignancies.

lab info

Saghi Ghaffari

212-659-8271 (office / lab)
212-803-6740 (fax)

lab members:
Bigarella, Carolina
Campreciós, Genís
Liang, Raymond
Rimmelé, Pauline
see photos and more here.
key publications

Rimmelé P*., Liang R*., Bigarella C*., Zhang A., Sadek H. and S. Ghaffari,
Mitochondrial metabolism in hematopoietic stem cells requires functional FOXO3.
EMBO Reports, 2015 Sep;16(9):1164-76.

Liang R*., Camprecios G*., Kou Y., McGrath K., Nowak R., Catherman S., Bigarella C.L., Rimmelé P., Zhang X.,Gnanapragasam MN, Bieker J.J., Papatsenko D., Ma¹yan A., Bresnick E., Fowler V., Palis J., and S. Ghaffari,
A systems approach identifies essential FOXO3¹s functions at key steps of terminal erythropoiesis.
PLoS Genetics, 2015, Oct 9; 11 (10): e1005526.

Rimmelé P., C. Bigarella, Izac B., R., Dieguez-Gonzalez, M. Donovan, C. Brugnara, D. Sinclair and S. Ghaffari,
SIRT1 controls hematopoietic stem cell longevity and lineage specification.
Stem Cell Reports, 3 (1): 44-59, 2014

Bigarella, C*., Liang R.* and S. Ghaffari.,
Stem cells and the impact of ROS signaling 
Development, 2014; 141(22):4206-18.

T Zhang X., Yalcin S., Lee D.F., Lee S-M, Yeh T.Y.J., Jie S., Kennedy M., Sellers R., Landthaler, M., Tuschl T, Chi N.W., Lemischka I., Keller G. and S. Ghaffari,
FoxO1 is an essential regulator of human ES cell pluripotency. 
Nature Cell Biology, 13 (9): 1092 ­ 99, 2011, Jul 31 (highlighted in Cell Stem Cell: 9 (3), p181, 2011).
Yalcin S, Marinkovic D., Mungamuri SK, Zhang X., Tong W., and S. Ghaffari.,
ROS-mediated amplification of AKT/mTOR signalling pathway leads to myeloproliferative syndrome in Foxo3(-/-) mice.
EMBOJ, 29(24):4118-31, 2010. Epub 2010 Nov 26.

Yalcin S, Zhang X., Marinkovic D., Luciano J.P., Sarkar A., Brugnara C., Vercherat C., Taneja R. and S. Ghaffari,
Foxo3 is essential for the regulation of ataxia telangiectasia mutated and oxidative stress-mediated homeostasis of hematopoietic stem cells.
Journal of Biological Chemistry, 283:25692-25705, 2008.

Marinkovic D., Zhang X., Yalcin S., Brugnara C., Huber T., and S. Ghaffari.,
Foxo3 is required for the regulation of oxidative stress in erythropoiesis.
Journal of Clinical Investigation, 117 (8): 2133-2144, 2007 (Highlighted in Commentary: JCI, 107 (8): 2075-2077, 2007).

Zhao W, Kitidis C, Fleming MD, Lodish HF, Ghaffari S.,
Erythropoietin stimulates phosphorylation and activation of GATA-1 via the PI3-kinase/AKT signaling pathway. 
Blood, 2006 Feb 1;107(3):907-15. Epub 2005 Oct 4. (Highlighted in inside Blood, 2006).

Ghaffari S, Jagani Z, Kitidis C, Lodish HF, Khosravi-Far R.,
Cytokines and BCR-ABL mediate suppression of TRAIL-induced apoptosis through inhibition of forkhead FOXO3a transcription factor. 
Proc Natl Acad Sci U S A, 2003 May 27;100(11):6523-8. Epub 2003 May 15.

see more publications here.