Biomedical Engineering Reference
In-Depth Information
disconnected from reticulocytes, expelled, and then engulfed by macrophages.
Phosphatidylserine, often used as an apoptosis signal, is also used for nucleus
engulfment [
102
].
Enucleation results from asymmetrical cell division during which chromatin
condensates and the nucleus surrounded by a part of the plasma membrane buds off
from the immature precursor (erythroblast). MicroRNA miR191 that has mi-
nor effects on cell proliferation and differentiation is downregulated during this
process [
103
]. In fact, the majority of microRNAs in CFUe erythroid progenitors
are inhibited during terminal erythroid differentiation. In particular, miR144 and
miR451, which are encoded by GATA1 target genes, are required for erythropoiesis,
as they act on erythroid Kr ppel-like factor KLF1 and GATA2, respectively. Gene
transcripts that encode erythroid-enriched RiO kinase RiOK3, which operates in
chromatin condensation and enucleation, and class-C basic helix-loop-helix protein
bHLHc11,
18
a MyC antagonist, are miR191 targets.
Reticulocytes
are slightly immature cells that are characterized by a filament
network and by granules. Reticulocytes amount to 0.5 to 2% of the total RBC count
(more in anemia).
In healthy human adults,
10
11
new red blood cells are released from the
bone marrow into the blood circulation per day, and about the same number are
cleared. In the few days after exit from the bone marrow, erythrocytes undergo a
reduction in both volume and hemoglobin content.
A model of RBC maturation and clearance has been developed [
104
]. This
model relies on the splitting of volume (
V
) and hemoglobin (
Hb
) dynamics of an
average RBC over time into deterministic functions (
∼
2.5
×
φ
) and random fluctuations
(
), using the average cell age and population means to scale time,
V
,and
Hb
quantities. The deterministic component depends on 2 parameters related to fast (
ϕ
β
)
and slow (
dominates until the hemoglobin
concentration is close to the mean corpuscular hemoglobin concentration (MCHC).
The random fluctuation is modeled as a Gaussian random variable with a zero mean
and diffusion (
α
) changes. The effect of parameter
β
D
)-dependent variance.
d
dt
V
(
Hb
)=
φ
+
ϕ
;
(3.1)
α
exp
{
β
V
(
V
−
Hb
)
},
φ
=
α
exp
{
β
Hb
(
Hb
−
V
)
}
;
N
(
0
,
2
D
V
)
,
ϕ
=
D
Hb
)
,
The dynamics of the complete circulating RBC population is described by an
equation for time-dependent drift (
N
(
,
0
2
), and birth (
b
) and death (
d
)
rate of probability density of the joint volume-hemoglobin distribution (
P
ϕ
), diffusion (
D
(
V
,
Hb
,
t
)
)
18
A.k.a. MAX interactor MxI1.
Search WWH ::
Custom Search