Hematopoiesis and Iron Metabolism - Lectures 3 and 4 Flashcards
1
Q
Where is the major site of hematopoiesis from 6 weeks until 6-7 months of fetal life?
A
Spleen and Liver
2
Q
Where is the major site of hematopoiesis after 6-7 months of fetal life?
A
Bone Marrow
3
Q
Where is the major site of hematopoiesis until 6 weeks of fetal life?
A
Yolk Sac
4
Q
What replaces hematopoietic bone marrow in long bones and in 50% of hematopoietic areas of other bones?
A
Fat
5
Q
Can fatty marrow, spleen, and liver revert to hematopoiesis?
A
Yes
6
Q
Which cell can become any blood cell and can repopulate a bone marrow from which all cells have been eliminated?
A
Hematopoietic Stem Cells (a pluripotent stem cell)
7
Q
What is the general name of the two cells made directly from hematopoietic stem cells, and what is each cell called?
A
Hematopoietic Progenitor Cells
- Common Myeloid Progenitor Cell (CFU-GEMM)
- Common Lymphoid Progenitor Cell
8
Q
How common is the Hematopoietic Stem Cell in the bone marrow?
A
~1 in every 20 million nucleated cells
9
Q
What surface markers do hematopoietic stem cells have?
A
CD34+
10
Q
How many mature cells can one hematopoietic stem cell make?
A
~1 million
11
Q
What are the mature cells?
A
- Red Cells
- Megakaryocytes (platelets)
- Monocytes
- Granulocytes (neutrophils, eosinophils, basophils)
- Lymphocytes (B and T cells)
12
Q
What are the stromal cells, and what do they secrete?
A
Stromal cells include:
- adipocytes, fibroblasts, osteoblasts, endothelial cells, and macrophages
Stromal cells secrete:
- collagen, glycoproteins, and glycosaminoglycans to form an extracellular matrix
- growth factors for stem cell survival
13
Q
What is a niche?
A
The area of the bone marrow that provides a suitable environment for stem cell growth and division formed by stromal cells
14
Q
Mesenchymal stem cells are important in the formation of which cell type?
A
Stromal cells
15
Q
What is present in a niche?
A
Growth factors [like stem cell factor (SCF)], adhesion molecules (like jagged proteins that bind to KIT and NOTCH receptors on stem cells), and cytokines necessary for stem cell growth and differentiation
16
Q
What is mobilization, and what growth factor is important for it to occur?
A
The movement of stem cells across the blood vessel endothelium into the blood which requires granulocyte colony-stimulating factor (G-CSF)
17
Q
What is homing, and what chemokine is important for it to occur?
A
The movement of stem cells across the blood vessel endothelium out of the blood which requires stromal-derived factor 1 (SDF-1)
18
Q
What is the first step of hematopoiesis?
A
Self-renewal (replication of one pluripotent hematopoietic stem cell into another one pluripotent hematopoietic stem cell)
19
Q
What is the major source of growth factors for hematopoiesis, what are the two growth factors not made by this source, and where are these two growth factors made?
A
- Stromal cells (90% of growth factors)
- Erythropoietin - Kidneys
- Thrombopoietin - Liver
20
Q
What type of receptors are the hematopoietic receptor superfamily?
A
JAK-STAT receptors
21
Q
What are the 3 main signal transduction pathways following hematopoietic growth factors binding to their receptors?
A
- JAK/STAT pathway (STAT dimers act as transcription factor in the nucleus)
- Mitogen-activated protein (MAP) kinase pathway (JAK activates RAS/RAF to activate MAP kinase which results in gene expression that acts on cell cycle/proliferation)
- Phosphatidylinositol 3 (PI3) pathway (JAK activates PI3 kinase to block apoptosis)
22
Q
What do Janus-associated kinase (JAK) proteins associate with?
A
The intracellular domain of growth factor receptors
23
Q
What are the two main phases of the cell cycle, and what occurs in each?
A
- M phase - cell physically divides
- Interphase - chromosomes (DNA) are duplicated and cell growth occurs
24
Q
What are the two parts of the M phase of the cell cycle, and what occurs in each part?
A
- Mitosis - nuclear division occurs
- Cytokinesis - cell fission occurs
25
What are the three phases of interphase of the cell cycle, and what occurs in each part?
- G1 phase - cell begins to commit to replication
- S phase - DNA content doubles (chromosomes replicate)
- G2 phase - cell organelles are copied and cytoplasmic volume increases
26
Where are the two checkpoints of the cell cycle?
at the end of the G1 and G2 phases
27
Which classes of molecules control the checkpoints of the cell cycle, and how do they act to control the cycle?
- Cyclin-dependent protein kinases (Cdk) - phosphorylate downstream protein targets
- Cyclins - bind to Cdks to regulate their activity
28
What is the morphology of apoptosis?
- Cell shrinkage
- Condensation of nuclear chromatin
- Fragmentation of the nucleus
- Cleavage of DNA
29
Which proteases are responsible for initiating apoptosis?
Caspases
30
Which molecule is released from the mitochondria during intracellular apoptotic activation and activates caspases?
Cytochrome C
| - which binds to APAF-1 to activate the caspases
31
The level of what molecule is increased by p53, and what molecule tightly controls p53 levels?
- p53 increases the level of BAX resulting in apoptosis
| - MDM2 controls p53 levels
32
What are the major pro-apoptotic and anti-apoptotic molecules within a cell?
BAX - pro-apoptotic
| BCL-2 - anti-apoptotic
33
How can BCL-2 result in malignant disease, and what disease is caused?
BCL-2 is translocated from chromosome 18 to the immunoglobulin heavy chain locus on gene 14 in the t(14:18) translocation of follicular lymphoma (result is over-expression of the BCL-2 gene)
Note: (BCL = B Cell Lymphoma)
34
What are the two domains of transcription factors?
- DNA binding domain
| - Activation domain
35
What are the three major families of adhesion molecules, and what do they involve?
- Immunoglobulin superfamily - antigen receptors (TCR, immunoglobulins, antigen-independent surface adhesion molecules)
- Selectins - Leukocyte and platelet adhesion to endothelium in infection or coagulation
- Integrins - Cell adhesion to extracellular matrix
36
Where is hematopoietic tissue confined in adults?
Confined to the central skeleton (skull, vertebrae, sternum, ribs, sacrum, pelvis, and some in proximal femur)
37
What are a large family of glycoproteins that mediate attachment of marrow precursors, mature leukocytes, and platelets to endothelium, extracellular matrix, and to each other?
Adhesion molecules
38
What does CFU-GEMM stand for?
Colony Forming Unit - Granulocyte, Erythrocyte, Monocyte, and Megakaryocyte
39
What are the separate stages of RBC development from pluripotent hematopoietic stem cell to erythrocyte?
- Hematopoietic stem cell
- CFU-GEMM
- BFU-E (Burst-Forming Unit Erythroid)
- CFU-E (Colony-Forming Unit Erythroid)
- Pronormoblast (dark blue cytoplasm)
- Progressively smaller normoblasts with progressively more hemoglobin and a nucleus
- Reticulocyte (no nucleus, but RNA to continue producing hemoglobin)
- Erythrocyte (no nucleus or RNA)
40
How many RBCs can a single pronormoblast give rise to?
16
41
Are nucleated RBCs (pronormoblasts) ever seen in the blood?
Not except in some marrow disease or extramedullary erythropoiesis (erythropoiesis outside the marrow)
42
What regulates erythropoiesis?
Erythropoietin
43
Where is erythropoietin made?
Peritubular interstitial cells of the kidney
44
What stimulates erythropoietin production?
Hypoxia-inducable factors (HIF-2alpha and beta) caused by oxygen tension in the tissues of the kidneys
45
What are some caused of HIF production?
Anemia, hemoglobin can't give up O2, low atmospheric O2, and cardiac, pulmonary, or renal function impairs O2 delivery to the kidneys
46
What are the 2 transcription factors activated by erythropoietin receptor stimulation?
GATA-1 and FOG-1
47
Which cells contain erythropoietin receptors?
BFU-E and CFU-E
48
What is the main indication of (reason for using) recombinant erythropoietin?
End-stage renal disease
49
What is often given with recombinant erythropoietin to maximize its effects?
Iron
50
What, besides erythropoietin is needed for erythropoiesis, and can cause anemia if absent or low?
Iron, cobalt, vitamins (especially B12, folate, C, E, B6, thiamine, and riboflavin) and hormones (androgens and thyroxine)
51
What is the structure of hemoglobin A (Hb A), the dominant hemoglobin 6 months after birth?
4 polypeptide chains (alpha2beta2) each with its own hemoglobin
52
What are the other types of hemoglobin present in small quantities in adults, and what are their 4 chains?
- Hb F (alpha2gamma2)
| - Hb A2 (alpha2delta2)
53
Where is hemoglobin made?
In the mitochondria where 4 heme groups come together to form hemoglobin
54
What happens when O2 is unloaded from hemoglobin?
the beta chains are pulled apart and 2,3-diphosphoglycerate (2,3-DPG) enters, which lowers the affinity of hemoglobin for O2
55
What is the P-50 of hemoglobin?
26.6 mmHg
56
If Hb has a lower affinity for oxygen does the saturation curve shift to the right or to the left?
To the right
57
If Hb has a higher affinity for oxygen does the saturation curve shift to the right or to the left?
To the left
58
What are the normal O2 operating limits for Hb in vivo (both % and mmHg)?
Low (venous) - 40 mmHg at 70% saturation
| High (arterial) - 95 mmHg at 95% saturation
59
What are some molecules that lower the affinity of Hb for O2 (shift to the right)?
2,3-DPG, H+, CO2, HbS
60
What are some molecules that increase the affinity of Hb for O2 (shift to the left)?
HbF, lower 2,3-DPG, lower H+
61
What is the cause of Methemoglobinemia?
Circulating Hb has an iron in the Fe3+ state instead of the normal Fe2+ state (can be caused by methemoglobin reductase deficiency or inherited Hb M, which is a structurally abnormal Hb, or by toxins that oxidize Hb)
- all of these result in cyanosis
62
How do RBCs generate energy?
Glucose enters the RBC via facilitated transfer and glycolysis produces 2 ATP per glucose as well as NADH which is used by methemoglobin reductase to reduce Fe3+
63
What is ATP in RBCs used for?
The Na/K ATPase to maintain the osmotic equilibrium within the RBC despite high amounts of intracellular proteins (i.e., hemoglobin)
64
What produces NADPH within RBCs, and what enzyme is crucial to this process?
The pentose phosphate shunt produces NADPH, and glucose-6-phosphate dehydrogenase (G6PD) is crucial to this process
65
What is NADPH used for in RBCs?
Mainly to reduce disulfide (S-S) groups in glutathione to sulphydril (SH) groups to maintain structure and function of both hemoglobin and the RBC membrane
66
What are the parts of the RBC membrane?
- lipid bilayer
- integral membrane proteins
- membrane skeleton
67
What forms the membrane skeleton?
Structural proteins (alpha and beta spectrin, ankyrin, protein 4.1, and actin)
68
What proteins are important in maintaining the RBC biconcave shape?
alpha and beta spectrin, ankyrin, protein 4.1, and actin
69
What is the most common cause of anemia?
Iron deficiency
70
What causes microcytic hypochromic anemia, and what are the clinical presentations?
- Caused by defect in hemoglobin synthesis
| - decreased mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) (i.e., small, pale red blood cells)
71
What 3 proteins mediate the transport and storage of iron?
transferrin, transferrin receptor 1 (TfR1), and ferritin
72
How is most iron bound to transferrin?
RBCs broken down by macrophages release iron into blood where transferrin picks it up; small amount through dietary absorption
73
Which cells contain transferrin receptors so transferrin can release iron into the RBCs?
Erythroblasts
74
What in ferritin actually binds iron?
Apoferritin
75
What is iron stored as in macrophages?
ferritin and hemosiderin
76
What is the difference between ferritin and hemosiderin as far as solubility?
Ferritin is a water soluble protein-iron complex while hemosiderin is an insoluble protein-iron complex
77
Is ferritin or hemosiderin visible under light microscopy?
Hemosiderin
78
What is iron in muscle found as?
Myoglobin
79
What happens to ferritin, TfR1, delta-aminolevulinic acid synthase (ALA-S), and divalent metal transporter 1 (DMT-1) levels in times of iron overload?
- tissue ferritin increases
- ALA-S increases
- TfR1 decreases
- DMT-1 decreases
80
What happens to ferritin, delta-aminolevulinic acid synthase (ALA-S), DMT-1 and TfR1 levels in iron deficiency?
- ferritin decreases
- ALA-S decreases
- TfR1 increases
- DMT-1 increases
81
How do iron levels control ferritin, TfR1, ALA-S, and DMT-1 levels?
Iron regulatory protein (IRP) binds to iron response elements (IREs) on ferritin, TfR1, ALA-s, and DMT-1 mRNA, and whether the binding is upstream (5') of the coding region or downstream (3') of the coding region determines whether or not the mRNA is translated to protein
82
If IRP binds upstream of the coding gene, is protein translation of ferritin, TfR1, ALA-S, and DMT-1 increased or decreased?
Decreased
83
If IRP binds downstream of the coding gene, is protein translation of ferritin, TfR1, ALA-S, and DMT-1 increased or decreased?
Increased
84
Does IRP bind to IREs when iron levels are high or low?
Low
85
What causes pathological changes of the liver, endocrine organs, pancreas, and heart when iron levels are high?
Iron is transferred to parenchymal (functional) cells of these organs
86
What organ produces hepcidin?
Liver
87
What is the major hormonal regulator of iron homeostasis?
Hepcidin
88
How does hepcidin regulate iron homeostasis?
Hepcidin inhibits iron release from macrophages and intestinal epithelial cells by interacting with the transmembrane iron exporter ferroportin by accelerating degradation of ferroportin mRNA
89
What is the role of ferroportin?
Iron export from cells, especially in macrophages and intestinal epithelial cells
90
What happens when hepcidin levels are raised?
Iron absorption and release from macrophages is reduced
91
How many molecules of iron can bind to transferrin?
2
92
What stimulates hepcidin expression?
When membrane bound hemojuvelin (HJV) binds to bone morphogenetic protein (BMP)
93
What stimulates HJV binding to BMP?
High diferric transferrin levels block TfR1 binding to HFE, which allows TfR2/HFE binding which stimulates HJV/BMP binding and therefore hepcidin synthesis
94
What digests HJV thus decreasing hepcidin synthesis, and when does this occur?
Matriptase 2 digests membrane bound HJV in iron deficiency thus reducing hepcidin synthesis
95
Which proteins are released from early erythroblasts to suppress hepcidin production?
GDF 15 and TWSG1
96
What is the result of hypoxia and inflammatory cytokines (IL-6) on hepcidin secretion?
- hypoxia suppresses hepcidin secretion
| - IL-6 increases hepcidin secretion
97
Is much iron obtained from diet?
No, most iron is recycled via RBC destruction by macrophages and release of the iron from macrophages via ferroportin to transferrin then to TfR1 on erythroblasts
98
Is heme iron or inorganic iron more absorbable?
heme iron
99
Is ferrous (FE2+) or ferric (Fe3+) iron more absorbable?
Ferrous (Fe2+)
100
Is iron absorption increased or decreased in inflammation and pregnancy?
- inflammation - decreased
| - pregnancy - increased
101
What part of the GI tract absorbs iron?
duodenum
102
Why is iron absorption in acidic conditions (like with vitamin C or HCl) favorable over alkali conditions?
acidic conditions keep the iron in the reduced ferrous (Fe2+) form
103
What happens to heme iron once it is absorbed into the duodenal enterocyte?
the heme is digested to release iron
104
Which iron transporters are active in iron absorption from the duodenum, and on which surface of the enterocytes are they located?
- DMT-1 - apical (lumen) surface to absorb iron from gut
| - ferroportin - basolateral surface to release iron from enterocytes into plasma
105
What reduces iron from the ferric (Fe3+) to the ferrous (Fe2+) form on the apical (lumen) surface of enterocytes, and what oxidizes iron from the ferrous (Fe2+) to the ferric (Fe3+) form on the basolateral surface so it can be transported by transferrin?
- ferrireductase - apical surface (Fe3+ to Fe2+)
| - ferrioxidase - basolateral surface (Fe2+ to Fe3+)
106
How much iron is typically absorbed via diet?
Only enough to compensate for iron lost from the body, which isn't much
107
Who is at the most risk to develop iron deficiency?
pregnant women, adolescents, and menstruating females
108
What are the two groups of white blood cells (leukocytes)?
- Phagocytes
| - Immunocytes
109
What cells are phagocytes?
Granulocytes (neutrophils, eosinophils, and basophils) and monocytes
110
What cells are immunocytes?
B cells, T cells, and NK cells
111
What are the soluble proteins that are closely associated with the function of phagocytes and lymphocytes?
immunoglobulins and complement
112
What is the lifespan of neutrophils in blood?
6-10 hours
113
What are the stages of neutrophil development, and where is each located?
- myeloblast, promyelocyte, myelocyte, metamyelocyte, band neutrophil, and neutrophil
- all are found in bone marrow, but only bands and neutrophils are found in the blood
114
When do granules appear in neutrophil development?
- primary granules - promyelocyte
| - secondary granules - myelocyte
115
Which neutrophil precursor has a large nucleus, fine chromatin, and 2-5 nucleoli?
myeloblast
116
When do nucleoli disappear in neutrophil precursors?
myelocytes
117
Which neutrophil precursors are non-dividing cells?
metamyelocytes
118
What are the cells in monocyte development and where are they found?
- monoblasts (marrow)
- promonocytes (marrow)
- monocytes (blood)
- macrophage (tissue)
119
What are the two main roles of eosinophils?
- allergic response and defense against parasites
120
What cells become mast cells in tissues?
Basophils
121
Which cells in granulocyte development can undergo mitosis and which cannot?
- Dividing cells:
- myeloid progenitor cells
- myeloblasts
- promyelocytes
- myelocytes
- Non-dividing cells:
- metamyelocytes
- bands
- segmented granulocytes
122
Which contains more granulocytes, blood or marrow?
marrow (10-15x more than blood)
123
Does the marrow contain more erythroid cells or myeloid cells?
myeloid cells (within a 2:1 to 12:1 ratio)
124
What are the two pools of granulocytes in blood?
- circulating (included in blood count)
| - marginating (not included in blood count)
125
How long are granulocytes in blood and in peripheral tissue?
- 6-10 hours in blood
| - 4-5 days in tissues
126
What are the growth factors for granulocytes?
IL-1, IL-3, IL-5, IL-6, IL-11, granulocyte-macrophage colony-stimulating factor (GM-CSF), M-CSF, and G-CSF
127
What cytokines stimulate stromal cells and T lymphocytes to release cytokines that increase granulocyte production during infection?
endotoxin, IL-1, TNF
128
What is the result of G-CSF administration?
increase in circulating neutrophils
129
What are some clinical applications of G-CSF?
- post-chemotherapy, radiotherapy, or stem cell transplantation
- acute myeloid leukemia
- myelodysplasia
- lymphomas
- severe neutropenia
- severe infection
- peripheral blood stem cell harvesting
130
What does G-CSF administration reduce?
infections, hospital stays, and antibiotic usage
131
What is another name for a macrophage?
histiocyte
