L14 Hematopoiesis
Page 1: Introduction
Dr. Vijendra Sharma, Faculty, Department of Biomedical Sciences, University of WindsorTopic: Hematopoiesis, Regenerative Biology, and Disease
Page 3: Learning Objectives
Understand the concept of hematopoiesis, the process through which all blood cells are produced from hematopoietic stem cells (HSCs).
Overview of the blood system, including the different types of blood cells and their functions, as well as the significance of maintaining a balanced hematopoietic system.
Discuss early development related to hematopoiesis, tracing the origins of blood cell formation from embryonic development through to adulthood.
Study properties and characteristics of Hematopoietic stem cells (HSCs) that allow self-renewal and differentiation into various blood cell lineages.
Learn key terminology: LT/ST-SCs (Long-term/Short-term stem cells), highlighting their roles in maintenance and rapid response to need, and CSFs (Colony Stimulating Factors), which are crucial for stimulating the production and differentiation of blood cells.
Explore the bone marrow niche, an essential microenvironment for HSCs, and the various factors that control HSC expansion and differentiation into specialized blood cells.
Erythropoiesis, the precise process for the production of red blood cells, detailing the stages from stem cell to mature erythrocyte.
Define transplant terms, clarifying essential vocabulary related to the process of bone marrow and stem cell transplantation.
Discuss hurdles in bone marrow transplantation such as graft-versus-host disease (GVHD) and current directions in transplantation research aimed at improving outcomes.
Page 4: Principles of Hematopoiesis
Hematopoietic cells are multipotent stem cells capable of giving rise to all types of blood cells, responsible for maintaining homeostasis in the blood system.
These cells have a limited lifespan and are produced continuously throughout the life of an organism, adapting to physiological demands.
All blood cells are derived from a common lineage of stem cells in the bone marrow.
Page 5: Classes of Blood Cells
White Blood Cells (Leukocytes):
Function: Combat infection and digest cellular debris through various immune mechanisms.
Unique ability to migrate actively into tissues through small blood vessels, playing a crucial role in immune surveillance.
Red Blood Cells (Erythrocytes):
Location: Specialized for the transport of oxygen (O2) and carbon dioxide (CO2) within the bloodstream.
Contain hemoglobin, a protein essential for gas transport.
Platelets:
Not entire cells but fragments derived from larger cells called megakaryocytes within bone marrow.
Involved in the coagulation process, playing a vital role in blood clotting and tissue repair during injury.
Page 6: Red Blood Cells (Erythrocytes)
Mature RBCs lack organelles and the nucleus, finding their structure optimized for hemoglobin and gas transport.
The human RBC lifespan is approximately 120 days, with significantly shorter lifespan in smaller mammals, like mice (approximately 55 days).
Emphasizing the need for continuous repopulation through erythropoiesis to maintain adequate oxygen transport capacity in the body.
Page 7: Classes of White Blood Cells
Granulocytes:
Contain lysosomes and secretory vesicles that aid in the immune response.
Monocytes:
These cells exit the bloodstream and mature into macrophages, critical for phagocytosis and antigen presentation.
Lymphocytes:
Essential components of the immune response, including B cells (producing antibodies) and T cells (mediating cellular immunity).
Page 8: Hematopoietic System Tasks
Ensure continuous production of diverse blood cells via a systemic pool of stem cells, maintaining essential immune functions and oxygen transport.
Precise maintenance of specialized cell type ratios (e.g., red vs. white blood cells) is crucial for proper physiological function.
Cytokines and hormones play vital roles in controlling differentiation, division, and migration of blood cells, allowing for adaptability to physiological needs and stressors.
Page 9: Studying Hemopoiesis
Although hematopoiesis presents studying challenges, it remains accessible for experimental analysis through in vivo and in vitro models.
Individual cell behaviors and differentiation can be tracked using advanced tracking techniques and specific markers associated with various stages of cell differentiation.
Page 10: Formation of Blood Islands
Hemangioblasts from the yolk sac give rise to central HSCs and peripheral angioblasts, initiating blood vessel and blood cell formation.
Blood circulation begins around embryonic days 15-17, marking a critical phase of embryonic development.
Migratory cells locate to the aorta-gonads-mesonephros (AGM) region around day 21, setting the stage for definitive hematopoiesis.
Page 11: Adult Hematopoiesis
In adults, blood cells are primarily generated within the bone marrow, a process termed medullary hematopoiesis.
Notably, certain maturation stages for macrophages and lymphocytes can occur outside the marrow, exemplifying the adaptability of the hematopoietic system.
Page 12: Bone Marrow Function
Various stimuli, such as infections or systemic stress, trigger enhanced production of specific blood cells, primarily leukocytes, in response to inflammatory challenges.
Hematopoiesis occurs predominantly in red marrow, while yellow marrow largely consists of adipose tissue.
Page 13: Cell Types in the Bone Marrow
Bone marrow comprises several key cell types including:
Blood cells (including megakaryocytes, the precursors to platelets)
Fat cells that serve as energy reserves
Stromal cells that constitute supportive connective tissue necessary for hematopoietic cell function
Page 15: Rarity of HSCs
HSCs are incredibly rare, representing only 1 in 10,000 cells within the bone marrow, with long-term label retaining HSCs (LT-HSCs) being significantly rarer at approximately 1 in 100,000.
Remarkably, only about 5 HSCs are usually sufficient to rescue a host mouse during transplantation scenarios.
Page 16: Multipotency of HSCs
Techniques such as retroviral marking enable tracing of cell lineage to examine the outcomes of HSCs post-transfusion into mice, showcasing their versatility and role in regeneration.
HSCs contribute to both myeloid and lymphoid blood cells, highlighting their importance in maintaining blood homeostasis and immune functions.
Page 18: HSC Definition
HSCs must exhibit the capability to repopulate the marrow of lethally irradiated animals, showcasing their essential role in regeneration.
They possess the ability to self-renew and expand, demonstrating significant plasticity in differentiating into all lymphomyeloid cell types.
Page 19: LT-HSC Identification
LT-HSCs are characterized by specific cell surface markers (such as CD150 and CD49f) and morphological features that distinguish them from other cell types.
These cells typically reside in hypoxic environments within the marrow and predominantly utilize glycolysis for ATP production, reflecting their unique metabolic demands.
Page 23: Binding of HSCs to Niche
SDF-1, a chemokine secreted by stromal cells, induces the migration of HSCs via the CXCR4 receptor, ensuring proper localization within the niche.
Robo4 is identified as a guidance receptor aiding HSC adhesion to the niche, critical for maintaining stem cell status and functionality.
Page 26: Activated HSC
Stem cell factor (SCF-1) promotes the movement of HSCs away from the niche to initiate differentiation.
Wnt signaling pathways trigger HSCs to enter the cell cycle, signaling a transition from quiescence to activation.
Bmi-1, a polycomb group gene, inhibits cell cycle inhibitors, fostering meaningful proliferation of HSCs under appropriate conditions.
Page 35: Subdivisions of Hematopoiesis
Hematopoiesis comprises various pathways that lead to the formation of specific blood cells, including myelopoiesis (development of myeloid cells) and lymphopoiesis (development of lymphoid cells), essential for sustaining bodily functions.
Page 48: Steps of Erythropoiesis
The process begins with BFU-E in the presence of interleukin-3 (IL-3) and erythropoietin, which promotes the formation of CFU-E.
CFU-E then matures into a pro-normoblast, which is characterized by increased hemoglobin production, essential for oxygen transport.
The normoblast eventually ejects its nucleus to become a reticulocyte, a precursor to the functional red blood cell.
Page 52: Anemia
Anemia can arise from deficits in healthy RBCs due to various causes, leading to symptoms such as fatigue, weakness, and pallor.
Blood transfusions are common treatments that temporarily restore red blood cell counts.
In severe cases of anemia, recombinant erythropoietin is administered to stimulate erythropoiesis and improve RBC production.
Page 54: Hematopoiesis in Therapy
Bone marrow transplants play a crucial role in the treatment of cancer patients, where donor stem cells help replenish the recipient's hematopoietic system post-myeloablation.
Gene therapy trials for conditions such as severe combined immunodeficiency (SCID) illustrate significant advancements, with promising results reported in various studies.
Page 62: GVHD Issues
Graft versus host disease (GVHD) remains a prominent concern following transplantation, where donor immune cells attack recipient tissues.
Different strategies are actively being explored to mitigate GVHD and enhance patient outcomes, focusing on immunosuppressive protocols and targeted therapies.
Page 73: ADA-SCID Treatment Approaches
Emerging treatments for adenosine deaminase deficiency (ADA-SCID) include enzyme replacement therapy and gene therapy strategies, showcasing evolving scientific progress with success reported in several clinical trials.
Page 77: Potential HIV Cure
Bone marrow transplants have exhibited potential as a therapeutic strategy for HIV treatment, particularly in patients expressing the CCR5 mutation, which provides resistance to a common HIV strain.