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SASH1 SIGNALING CONTRIBUTES TO THE PROGRESSION OF THE ENDOTHELIAL-TO-HEMATOPOIETIC TRANSITION
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Poster Presentations / Experimental Hematology 2019;76 (Suppl):S52−S96
3032 - DISSECTION OF THE PRE-B LEUKAEMIA BONE
MARROW MICROENVIRONMENT Laurence Cheung1,2, Anastasia Hughes3, Ursula Kees3, Jennifer Tickner4 , Rishi Kotecha3 1 School of Pharmacy and Biomedical Sciences, Curtin University, Western Australia, Australia, Perth, Australia; 2Telethon Kids Institute, Western Australia, Australia, Perth, Australia; 3Telethon Kids Institute, Perth, Australia; 4University of Western Australia, Perth, Australia
infancy and was largely influenced by studies of normal developmental processes. Therefore, understanding the regulatory network driving EHT remains essential to develop better strategies for HSC specification.
The microenvironments of leukaemia and cancer are critical for multiple stages of malignancies, and they are an attractive therapeutic target. Clinical studies in children diagnosed with acute lymphoblastic leukaemia (ALL) have clearly demonstrated defects in bone marrow microenvironment, yet little is known about the contribution of the normal bone marrow cells during the development of the disease, progression and relapse. It remains unclear whether the clinical symptoms of increased bone fragility and reduced bone mineral density should be treated at diagnosis, and whether such treatments would have any impact on the leukaemia progression. To elucidate the influence of ALL on haematopoiesis and the microenvironment, we studied the development of pre-B cell ALL (pre-B ALL) in an immunocompetent BCR-ABL1+ model. We found that haematopoiesis was perturbed, B lymphopoiesis was impaired, collagen production was reduced, and the number of osteoblastic cells was decreased in the bone marrow microenvironment. Moreover, the leukaemiabearing mice exhibited severe bone loss during leukaemogenesis, which is consistent with clinical data in paediatric ALL. We showed that leukaemia cells produce receptor activator of nuclear factor kB ligand (RANKL), and observed osteoclast-mediated bone resorption. We demonstrated that inhibition of osteoclasts with zoledronic acid in leukaemia mice significantly reduced disease burden and prolonged survival. Our study reveals the impact of pre-B ALL development on haematopoiesis, bones and bone marrow microenvironment. It provides evidence for targeting leukaemiainduced bone loss as a novel therapeutic strategy for patients.1
Reference 1. Cheung LC, Tickner J, Hughes AM, Skut P, Howlett M, Foley B, et al. New therapeutic opportunities from dissecting the preB leukemia bone marrow microenvironment. Leukemia. 2018;32(11):2326–2338.
3034 - MEIS1 EXPRESSION IN MOUSE EMBRYONIC
3035 - SASH1 SIGNALING CONTRIBUTES TO THE
HEMATOPOIESIS Patrick Coulombe1,2, Ping Xiang3 , Jeremy Parker1, Keith Humphries3 , Aly Karsan1 1 BC Cancer Agency - Genome Sciences Centre, Vancouver, Canada; 2 University of British Columbia, Vancouver, Canada; 3BC Cancer Terry Fox Laboratory, Vancouver, Canada
PROGRESSION OF THE ENDOTHELIAL-TOHEMATOPOIETIC TRANSITION Patrick Coulombe1,2 , Grigorios Paliouras1, Katherine Bilan1, Aly Karsan1 1 BC Cancer Agency - Genome Sciences Centre, Vancouver, Canada; 2 University of British Columbia, Vancouver, Canada
Hematopoietic stem cells (HSCs) originate during embryogenesis and colonize the bone marrow, after expansion in the fetal liver, to sustain adult hematopoiesis. In vivo imaging studies have supported the emergence of HSCs form the ventral endothelium of the dorsal aorta in the aorta-gonado-mesonephros (AGM) region through a process termed endothelial-to-hematopoietic transition (EHT). Generation of HSC is a dynamic process requiring temporal and cell-specific changes within a subset of cells, the hemogenic endothelium, to drive a new cell fate. Although several pathways have been shown to play a critical role in this transition, the molecular programming driving EHT remains elusive. In this study, we aim to understand how the transcription factor Meis1 affects the emergence of HSC by taking advantage of various mouse models. Using a GFP reporter mouse, we mapped Meis1 expression in the developing dorsal aorta and showed that Meis1 expression enriches for the hemogenic endothelium compared to vascular endothelium. We combined these data with observations of endothelial-specific deletion of Meis1 in vivo, using VE-cadherin (VEC)-Cre recombinase, to gain a better understanding of the requirements for Meis1 during this dynamic developmental process. Conditional Meis1-deletion impaired the hematopoietic potential of the AGM endothelium based on specific gene expression and significantly reduce the emergence of cells with hematopoietic surface markers. Our ability to derived HSC in vitro is in its
Sash1 acts as a scaffold molecule regulating signal transduction downstream of TLR4. By investigating its function in vivo, our lab showed that deletion of Sash1 in mice leads to developmental defects during embryogenesis, impacting primarily the lung and the hematopoietic system. We observe a significant reduction in hematopoietic stem and progenitor cells (HSPCs), both phenotypically and functionally, in the fetal liver of Sash1-knockout embryos compared to their wildtype littermates at embryonic day (E)14.5. Further investigation of this phenotype revealed that a deficiency is already present as early as E10.5, when the first HSPCs emerge from intra-aortic hematopoietic clusters in the dorsal aorta via a process termed endothelial-to-hematopoietic transition (EHT). Specifically, we found that fewer hematopoietic clusters are formed in the dorsal aorta of Sash1knockout embryos which correlates with a reduced number of pre-HSCs based on surface markers and decreased expression of EHT-related genes. Interestingly, our data suggests that Sash1 plays a cell non-autonomous role, acting on an already specified hemogenic endothelium, to promote the progression of EHT. Therefore, we aim to understand how signaling via Sash1 stimulates definitive hematopoiesis in the early embryo. Developmental studies have largely guided the current effort to derive HSPC in vitro and further investigation of extrinsic signaling pathways involved may provide new insight to support cells undergoing EHT.
Poster Presentations / Experimental Hematology 2019;76 (Suppl):S52−S96
3032 - DISSECTION OF THE PRE-B LEUKAEMIA BONE
MARROW MICROENVIRONMENT Laurence Cheung1,2, Anastasia Hughes3, Ursula Kees3, Jennifer Tickner4 , Rishi Kotecha3 1 School of Pharmacy and Biomedical Sciences, Curtin University, Western Australia, Australia, Perth, Australia; 2Telethon Kids Institute, Western Australia, Australia, Perth, Australia; 3Telethon Kids Institute, Perth, Australia; 4University of Western Australia, Perth, Australia
infancy and was largely influenced by studies of normal developmental processes. Therefore, understanding the regulatory network driving EHT remains essential to develop better strategies for HSC specification.
The microenvironments of leukaemia and cancer are critical for multiple stages of malignancies, and they are an attractive therapeutic target. Clinical studies in children diagnosed with acute lymphoblastic leukaemia (ALL) have clearly demonstrated defects in bone marrow microenvironment, yet little is known about the contribution of the normal bone marrow cells during the development of the disease, progression and relapse. It remains unclear whether the clinical symptoms of increased bone fragility and reduced bone mineral density should be treated at diagnosis, and whether such treatments would have any impact on the leukaemia progression. To elucidate the influence of ALL on haematopoiesis and the microenvironment, we studied the development of pre-B cell ALL (pre-B ALL) in an immunocompetent BCR-ABL1+ model. We found that haematopoiesis was perturbed, B lymphopoiesis was impaired, collagen production was reduced, and the number of osteoblastic cells was decreased in the bone marrow microenvironment. Moreover, the leukaemiabearing mice exhibited severe bone loss during leukaemogenesis, which is consistent with clinical data in paediatric ALL. We showed that leukaemia cells produce receptor activator of nuclear factor kB ligand (RANKL), and observed osteoclast-mediated bone resorption. We demonstrated that inhibition of osteoclasts with zoledronic acid in leukaemia mice significantly reduced disease burden and prolonged survival. Our study reveals the impact of pre-B ALL development on haematopoiesis, bones and bone marrow microenvironment. It provides evidence for targeting leukaemiainduced bone loss as a novel therapeutic strategy for patients.1
Reference 1. Cheung LC, Tickner J, Hughes AM, Skut P, Howlett M, Foley B, et al. New therapeutic opportunities from dissecting the preB leukemia bone marrow microenvironment. Leukemia. 2018;32(11):2326–2338.
3034 - MEIS1 EXPRESSION IN MOUSE EMBRYONIC
3035 - SASH1 SIGNALING CONTRIBUTES TO THE
HEMATOPOIESIS Patrick Coulombe1,2, Ping Xiang3 , Jeremy Parker1, Keith Humphries3 , Aly Karsan1 1 BC Cancer Agency - Genome Sciences Centre, Vancouver, Canada; 2 University of British Columbia, Vancouver, Canada; 3BC Cancer Terry Fox Laboratory, Vancouver, Canada
PROGRESSION OF THE ENDOTHELIAL-TOHEMATOPOIETIC TRANSITION Patrick Coulombe1,2 , Grigorios Paliouras1, Katherine Bilan1, Aly Karsan1 1 BC Cancer Agency - Genome Sciences Centre, Vancouver, Canada; 2 University of British Columbia, Vancouver, Canada
Hematopoietic stem cells (HSCs) originate during embryogenesis and colonize the bone marrow, after expansion in the fetal liver, to sustain adult hematopoiesis. In vivo imaging studies have supported the emergence of HSCs form the ventral endothelium of the dorsal aorta in the aorta-gonado-mesonephros (AGM) region through a process termed endothelial-to-hematopoietic transition (EHT). Generation of HSC is a dynamic process requiring temporal and cell-specific changes within a subset of cells, the hemogenic endothelium, to drive a new cell fate. Although several pathways have been shown to play a critical role in this transition, the molecular programming driving EHT remains elusive. In this study, we aim to understand how the transcription factor Meis1 affects the emergence of HSC by taking advantage of various mouse models. Using a GFP reporter mouse, we mapped Meis1 expression in the developing dorsal aorta and showed that Meis1 expression enriches for the hemogenic endothelium compared to vascular endothelium. We combined these data with observations of endothelial-specific deletion of Meis1 in vivo, using VE-cadherin (VEC)-Cre recombinase, to gain a better understanding of the requirements for Meis1 during this dynamic developmental process. Conditional Meis1-deletion impaired the hematopoietic potential of the AGM endothelium based on specific gene expression and significantly reduce the emergence of cells with hematopoietic surface markers. Our ability to derived HSC in vitro is in its
Sash1 acts as a scaffold molecule regulating signal transduction downstream of TLR4. By investigating its function in vivo, our lab showed that deletion of Sash1 in mice leads to developmental defects during embryogenesis, impacting primarily the lung and the hematopoietic system. We observe a significant reduction in hematopoietic stem and progenitor cells (HSPCs), both phenotypically and functionally, in the fetal liver of Sash1-knockout embryos compared to their wildtype littermates at embryonic day (E)14.5. Further investigation of this phenotype revealed that a deficiency is already present as early as E10.5, when the first HSPCs emerge from intra-aortic hematopoietic clusters in the dorsal aorta via a process termed endothelial-to-hematopoietic transition (EHT). Specifically, we found that fewer hematopoietic clusters are formed in the dorsal aorta of Sash1knockout embryos which correlates with a reduced number of pre-HSCs based on surface markers and decreased expression of EHT-related genes. Interestingly, our data suggests that Sash1 plays a cell non-autonomous role, acting on an already specified hemogenic endothelium, to promote the progression of EHT. Therefore, we aim to understand how signaling via Sash1 stimulates definitive hematopoiesis in the early embryo. Developmental studies have largely guided the current effort to derive HSPC in vitro and further investigation of extrinsic signaling pathways involved may provide new insight to support cells undergoing EHT.