Haemopoiesis & Cytokines

Objectives

Haematopoiesis and cytokines dr. veera sekaran nadarajan department of pathology

Lecture contents 1. 2. 3. 4.

1.

Define stem cells and explain its role in haematopoiesis

2.

Describe how mature haematopoietic cells are generated

3.

Illustrate the regulatory processes involved in driving haematopoiesis via transcription factor activations and cytokine regulatory networks

4.

Describe the functions of certain important cytokines in haematopoiesis I.e. EPO, TPO, G-CSF, GM-CSF, IL-3, SCL

Haematopoietic cells

Brief overview on stem cells Haematopoiesis Regulation of haematopoiesis via cytokine and TF pathways Biology and function of key cytokines (assignment)

Normal bone marrow aspirate showing variety of haematopietic cells in varying degrees of maturation

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Sites of Haematopoiesis Foetus 0-2 months - yolk sac 2-7 months - liver, spleen 5 –9 months – bone marrow Infant bone marrow (all bones) True origin of the first HSC is still debated

Metcalf, D. Stem Cells 2007;25:2390-2395

Adults Vertebrae, ribs, sternum, skull, sacrum & pelvis, proximal ends of femur

Metcalf, D. Stem Cells 2007;25:2390-2395

The conventional view of hematopoiesis in which multipotential stem cells are self-generating and also produce precursor cells with increasing restriction of their lineage and proliferative potential

Demonstration of HSC spleen colony assays in rodents long term bone marrow cultures (limiting dilution assays) surrogate markers (CD34, CD38, c-kit, Thy-1, Sca-1)

Earliest recognisable colony on methylcellulose cell culture is CFU-GEMM

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Properties of HSC

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capacity for self renewal/generation

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capable of reconstituting all haematopoietic elements (multipotentiality)

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confer radioprotection

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capable of secondary transfer

The HSC niche •

The fate of HSC to self renew or differentiate is decided by its endosteal or vascular environment

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Signals generated by cytokine network, work within this framework to regulate HSC development

Wilson et al. Nature Reviews Immunology 6, 93–106 (February 2006) | doi:10.1038/nri1779

Transcriptional regulation of HSC

Mechanism of HGF action

The switching on and off with complex interactions within the genetic regulatory network (GRN), mediated by external signals decide on HSC fate and lineage restriction PU.1 and GATA-1 TFs are decisive in lineage commitment of the HSC Other important TF in early HSC development include SCL and GATA-2

Metcalf, D. Blood 2008;111:485-491

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Cytokines regulate haematopoietic differentiation via activation/inactivation of downstream signals and functional pathways May be lineage restricted or act on multiple lineage

http://www.nottingham.ac.uk/genetics/networks /mouse/

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Mechanism of HGF action HGF binding to its cognate receptor causes approximation of the cytoplasmic domain allowing cross phosphorylation and activation of downstream kinases

Multilineage HGF Kit ligand (SCF) Flt-3 (fms-like tyrosine kinase 3) GM-CSF IL2, IL-3,IL-7 Redundancy seen with most of the cytokines except for possible SCF and IL-7

Lineage specific HGF Erythropoietin (EPO) G-CSF Thrombopoietin (TPO)

Assignment Write a ~ 500 word essay on any one of the lineage restricted HGFs, giving brief details on how it it is regulated and how its actions are mediated. Also, briefly discuss how it has been exploited for clinical therapeutic use.

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