Hematopoiesis - Tissue Functioning and Remodeling in the Circulatory and Ventilatory Systems - page 43

Tabl e 2. 9. Examples of hematopoietic growth factor receptors (Source: [ 85 ]).

Receptor type Ligands

(cytokines and chemookines)

Type-1 cytokine IL1-IL9, IL13, IL18,

receptor gmCSF and gCSF (CSF2-CSF3), Epo, Tpo

Type-2 cytokine IL10, INF

receptor

Type-3 cytokine mCSF (CSF1), SCF

receptor

G-protein-coupled chemokine IL8 (or CXCL8)

receptor (CXCR1/2)

TNFR (or TNFRSF1a) TNF α (or TNFSF1)

Receptors, and 11. Receptors of the Immune System) [ 39 ]. Several factors promote
self renewal of hematopoietic stem cells, such as Notch, Wnt3a, angiopoietin-like
proteins, and prostaglandin-E2.
In addition, hematopoietic stem and progenitor cells move into and then out of
the blood circulation for homing, engraftment, and retention. Their interaction with
bone marrow endothelium for engraftment in bone marrow as well as mobilization
into blood depends on guanine nucleotide-binding protein subunit G s[ 84 ].

However, Gs signaling is not required for retention of hematopoietic stem and
progenitor cells in the bone marrow.
Both growth factors and hormones bind to plasmalemmal receptors (Table 2.9 ).
Many kinds of hematopoeitins ensure a dynamic balance between cell differentia-
tion and proliferation. Hematopoietic stem and progenitor cells in their hematopoi-
etic niches in bone marrow respond to their environment upon engagement of
plasmalemmal receptors that leads to signal transduction.

α

2.4.2.1 Morphogens

Notch and Wnt signaling pathways (Vol. 3 - Chap. 10. Morphogen Receptors)
interact and regulate self-renewal of hematopoietic stem cells. Self-renewal of HSCs
can be regulated via inhibition of differentiation and induction of proliferation.
Signaling by Notch inhibits differentiation, thus maintaining hematopoietic stem
cells in an undifferentiated state [ 86 ]. Notch signaling is required for Wnt-mediated
maintenance of undifferentiated HSCs, but not for entry into the cell cycle in vitro.
Notch is specifically active in vivo in the HSC population of the bone marrow and
in immature thymocytes. It is reduced or absent in more mature differentiated cells.