Stem Cell Program Labs

The North Lab

Dr. Trista E. North is Principal Investigator at Boston Children’s Hospital and Associate Professor of Pathology, Harvard Medical School. Her laboratory is interested in the identification of regulators of hematopoietic (blood) stem cell formation and function.

Background Training and Research:

Dr. North has had a long-standing impactful role in Hematology research, starting from her initial work as a graduate student in the laboratory of Dr. Nancy A. Speck at Dartmouth College. She was the first to reveal the essential functional requirement for Runx1 (formerly AML1) in definitive HSC formation in the vertebrate embryo (Development 1999), demonstrating that it was necessary for the production of the first blood stem cells with long-term adult repopulating potential in the vertebrate embryo (Immunity 2002). Runx1 is now considered the definitive marker of HSC specification during development, required for transition from an endothelial to hematopoietic state and responsible for initiating life-long hematopoiesis.

During her postdoctoral research fellowship with Dr. Leonard I. Zon at Boston Children’s Hospital, she led the discovery and characterization of Prostaglandin E2 (PGE2) as an essential conserved regulator of hematopoietic stem cell formation and function (Nature 2007). PGE2 enhances the production and proliferation of HSCs during embryonic development and recovery after marrow injury, by enhancing the activity of cAMP and WNT signaling (Cell 2009). PGE2 was subsequently tested in preclinical xenotransplantation studies and in vitro analyses using human umbilical cord blood (hUCB) (Cell Stem Cell 2011), advancing to an FDA-approved clinical trial for patients receiving hUCB transplants to treat leukemia and lymphoma (Blood 2013).

Primary Investigations in the North laboratory:

Utilizing the array of chemical genetic and genomic methods available in the zebrafish model through an unbiased in vivo systems biology approach, members of the North laboratory have discovered several classes of extrinsic, or “environmental”, cues and regulators that influence the timing, location and magnitude of HSC production. The majority of these factors modulate the expression or signaling of key regulatory networks known to specify the HSC niche or HSC population, and have been subsequently determined to exert similar regulatory action in adult zebrafish, murine models and/or human HSC cell culture. Among these environmental regulators, we have found a critical and highly conserved initiating cue resulting from the onset of blood flow and subsequent sheer-force stimulated nitric oxide (NO) production (Cell 2009) which stimulates HSC production in vivo and expansion in vitro. Ongoing work in is focused on how these signals are mediated to direct endothelial-to-hematopoietic transition and subsequent migration to secondary niches, including the mechanism(s) of structural modifications of the endothelium and extracellular matrix necessary to produce HSCs.

Studies in the North laboratory also identified an essential role for glucose metabolism and elevation of reactive oxygen species (ROS) in stimulation of Hypoxia inducible factor 1a (Hif1a)-mediated transcriptional regulation to control the onset and scale of definitive hematopoiesis (Blood 2013). This work was consequently replicated in mammals, and is now regarded to have an essential role in homeostatic regulation in the adult bone marrow. Recently published and ongoing work is focused on the identification of relevant downstream functional regulators of HSC specification and fate (Experimental Hematology, 2016), as well as understanding how this signaling network allows the developing embryo to coordinate blood production to match continuous growth and nutritional inputs to maintain viability (Cell Stem Cell, 2016). As metabolic diseases such as obesity and diabetes are of increasing incidence, these studies are of particular relevance to our understanding of the potential short and long-term impact on the stem cell pool, including acquisition of hematopathology.

More recently, our group was one of several to simultaneously uncover a novel and unexpected role for inflammatory signaling as an essential regulator of HSC production during embryonic development. Inflammatory networks were long understood to modulate expansion and movements of differentiated blood cells in response to infection or injury. Through complimentary investigations in zebrafish and mice, we demonstrated for the first time that interferon gamma signaling was both required for and could actively drive blood stem cell formation in the embryo (Genes and Development, 2014). Our work, along with related studies, uncovered overlapping and/or compensatory roles for additional inflammatory factors. More surprisingly, as primitive macrophages and neutrophils were shown to be an active source of embryonic inflammatory activity, this study also fundamentally changed our understanding of the role of lineage-limited or non-HSC derived primitive hematopoietic populations – moving the primitive myeloid lineage from a transient means to respond to potential pathogens to active participants in establishing lifelong hematopoiesis. This line of research further modified our interpretation of the potential broader context of our investigations into the effect of other classical inflammatory factors, such as PGE2 and NO (described above; Stem Cells, 2015). Ongoing work is focused on understanding the cellular sources and mediators of the embryonic inflammatory network, as well as the direct functional impact on hematovascular and/or HSC biology. In addition, we are examining how inflammatory signals may be involved in mediating the effects of chronic metabolic deregulation on HSCs.

Finally, we have begun to uncover the regulatory impact of nuclear hormone receptor signaling on hematovascular biology. This area is of particular interest as this receptor class, highly expressed on HSCs, appears to be uniquely impacted by extrinsic or environmental factors, including many xenobiotics associated with developmental disorders and cancer. Arising from our prior chemical screen, our initial work in this area showed that estrogen receptor signaling has an impact on hematovascular fate. In particular, we found that estrogen provides the ventral limit of hemogenic endothelial specification in the major axial vessels during the onset of hematopoiesis (Developmental Cell, 2014). In ongoing studies, we are examining the effect of estrogenic regulation on HSCs at later stages in development and in the adult, where it appears to influence HSC self-renewal and lineage decisions; this work may be relevant both to our understanding of differences in hematopoietic volume and regeneration in males verses females as well as the associations of environmental xenoestrogen exposure with childhood leukemia. In parallel investigations, we have examined the impact of Vitamin D on HSC development in vivo and in vitro. Serum Vitamin D levels are well documented to vary widely across the population and insufficiency is associated with a variety of hematologic disease. Our primary investigation uncovered an inhibitory impact of Vitamin D precursor accumulation on Hedgehog signaling in the AGM (Stem Cell Reports, 2015); this work validated in vitro chemical modeling studies and has relevance for disease pathogenesis for Vitamin D deficient patients with CYP mutations. We also illustrated an essential regulatory input of active Vitamin D [1,25(OH)D3] on the scale of developmental HSC production, which can be exploited to expand human HSC numbers in vitro (Cell Reports, 2016). Ongoing work in is focused on exploiting Vitamin D-stimulated HSC expansion to improve HSC transplantation therapy and investigating correlations between Vitamin D status of donor HSC units and subsequent in vivo function.

Future Directions:

Over the next five years, we will continue to focus our work on the discovery and characterization of intrinsic and extrinsic modifiers of hematovascular formation and function. Ongoing investigations are broadly centered around three main topics: 1) metabolic regulation of hemogenic endothelium specification and HSC function, 2) impact of inflammatory mediators on HSC production and cell fate, and 3) influence of environmental modifiers on HSC development and hematopoietic homeostasis. The developing embryo is undergoing constant change with regard to body shape and structure, affecting mechanical and biochemical parameters, cell-cell interactions and fluctuating resources, including local nutrient availability and oxygen content. We will not only further delineate the impact of specific factors on HSC development, but also elucidate the possible interaction of these factors with regard to the spatio-temporal changes experienced during development. We are confident these studies will continue to provide important insight to the broad field of Hematology, including rational targets and compound modifiers for the directed development of blood stem cell populations in vitro as well as the prevention and treatment of hematologic disease.

SELECTED REFERENCES

Distinct Roles for Matrix Metalloproteinase 2 and 9 in Embryonic Hematopoietic Stem Cell Emergence, Migration and Niche Colonization.

Theodore LN*, Hagedorn EJ*, Cortes M*, Natsuhara KH, Liu SY, Perlin JR, Yang S, Daily ML, Zon LI and North TE.

Stem Cell Reports. 2017; 8(5): 1226-1241.

PMCID: PMC5425629.

 

HIF1α-induced PDGFRβ signaling promotes developmental HSC production via IL-6 activation.

Lim SE, Esain V, Kwan W, Theodore LN, Cortes M, Frost IM, Liu SY, North TE.

Experimental Hematology. 2017; 46: 83- 95.

PMCID: PMC5338611.

 

Developmental Vitamin D Availability Impacts Hematopoietic Stem Cell Production.

Cortes M, Chen MJ, Stachura DL, Liu SY, Kwan W, Wright F, Vo LT, Theodore LN, Esain V, Frost IM, Schlaeger TM, Goessling W, Daley GQ, North TE.

Cell Reports. 2016; 17(2):458-468.

PMID: 27705794

 

The Central Nervous System Regulates Embryonic HSPC Production via Stress-Responsive Glucocorticoid Receptor Signaling.

Kwan W, Cortes M, Frost I, Esain V, Theodore LN, Liu SY, Budrow N, Goessling W, North TE.

Cell Stem Cell. 2016; 19(3):370-82.

PMID: 27424782

 

Accumulation of the Vitamin D Precursor Cholecalciferol Antagonizes Hedgehog Signaling to Impair Hemogenic Endothelium Formation.

Cortes M, Liu SY, Kwan W, Alexa K, Goessling W, North TE.

Stem Cell Reports. 2015; 5(4):471-9.

PMID: 26365513

PMCID: PMC4624955

 

Cannabinoid Receptor-2 Regulates Embryonic Hematopoietic Stem Cell Development via Prostaglandin E2 and P-Selectin Activity.

Esain V, Kwan W, Carroll KJ, Cortes M, Liu SY, Frechette GM, Sheward LM, Nissim S, Goessling W, North TE.

Stem Cells (Dayton, Ohio). 2015; 33(8):2596-612. NIHMSID: NIHMS691951

PMID: 25931248

PMCID: PMC4781665

 

Inflammatory signaling regulates embryonic hematopoietic stem and progenitor cell production.

Li Y, Esain V, Teng L, Xu J, Kwan W, Frost IM, Yzaguirre AD, Cai X, Cortes M, Maijenburg MW, Tober J, Dzierzak E, Orkin SH, Tan K, North TE, Speck NA.

Genes & Development. 2014; 28(23):2597-612.

PMID: 25395663

PMCID: PMC4248291

 

Estrogen defines the dorsal-ventral limit of VEGF regulation to specify the location of the hemogenic endothelial niche.

Carroll KJ, Esain V, Garnaas MK, Cortes M, Dovey MC, Nissim S, Frechette GM, Liu SY, Kwan W, Cutting CC, Harris JM, Gorelick DA, Halpern ME, Lawson ND, Goessling W, North TE.

Developmental Cell. 2014; 29(4):437-53. NIHMSID: NIHMS600095

PMID: 24871948

PMCID:PMC4469361

 

Prostaglandin-modulated umbilical cord blood hematopoietic stem cell transplantation.

Cutler C, Multani P, Robbins D, Kim HT, Le T, Hoggatt J, Pelus LM, Desponts C, Chen YB, Rezner B, Armand P, Koreth J, Glotzbecker B, Ho VT, Alyea E, Isom M, Kao G, Armant M, Silberstein L, Hu P, Soiffer RJ, Scadden DT, Ritz J, Goessling W, North TE, Mendlein J, Ballen K, Zon LI, Antin JH, Shoemaker DD.

Blood. 2013; 122(17):3074-81.

PMID: 23996087

PMCID: PMC3811179

 

Glucose metabolism impacts the spatiotemporal onset and magnitude of HSC induction in vivo.

Harris JM, Esain V, Frechette GM, Harris LJ, Cox AG, Cortes M, Garnaas MK, Carroll KJ, Cutting CC, Khan T, Elks PM, Renshaw SA, Dickinson BC, Chang CJ, Murphy MP, Paw BH, Vander Heiden MG, Goessling W, North TE.

Blood. 2013; 121(13):2483-93.

PMID: 23341543

PMCID: PMC3612858

Giving