Sickle molecular Flashcards
1
Q
sickle cell mutation
A
- chromosome 11
- pt mutation A to T
- glu to val
2
Q
HbS
A
- reside 6 is now Val
- deoxygenation HbS forms 14 stranded polymers
- when well oxygenated returns to normal tetramers
- some cells remain irreversible
3
Q
hallmarks
A
- cycling b/n biconcave and sickled shape-weakens PM
- resulting RBC hemolysis (anemia) and vasoocclusion-ischemia, pain
- some sickle cells locked in sickle shape even when cell has o2 and in monomer
- 2-40% of circulating RBCs in homozygotes
4
Q
vasooculsion
A
- disease is polygenic on 2,6, and 11
- varies extent of inflammation and vasculopathy
- vasoocclusion is altered RBCs, leukocytes, BV endo cells and plasma factors
- RBCs and WBCs latch to endo and then to each other
5
Q
sickle cell crises
A
- those with less than 1 per year have a much longer life span than those with 1-3 or more than 3 per year
- 15 year difference
- molecular basis and biomarkers?
6
Q
expression of globins
A
- alpha is on 16, beta on 11
- erythropoiesis yolk sac in embyonic development, midway through 1st trimester to liver, then bone marrow at birth
- LCR for beta cluster
- embryonic to fetal gamma and alpha gamma at switch to liver
- feta gamma and alpha gamma to beta at birh
- beta genes are linearly arranged from 5’-3’ with a distal LCR directing expression
7
Q
HbF and sickle cell severity
A
- 3 loci associated with HbF levels and B globin disorder severity
- b cluster itself (cis acting haplotype on 11), HBS1l-MYB, and BCL11A
- bind to other TFs and complexes switch gamma to beta
- variants of the TFs that cause high HbF levels are clinically less severe
8
Q
BCL11A
A
- TF
- trans acting
- gamma globin silencer
- chromosome 2
9
Q
HBS1L-MYB
A
- intergenic interval on chromosome 6
- MYB influences HbF expression
- TF that represses gamma globin
10
Q
SNPs
A
- SNPs on the TFs on chromosomes 2 and 6 can increase HbF
- if around 20%, less severe form of disease
11
Q
haplotypes in the beta globin gene cluster
A
- HbS on 5 different B globin like gene cluster haplotypes which contain a polymorphism acting cis that regulates HbF
- 5 different mutations have different regulations og HbF
- Africa, Middle East, and India
- severe disease order goes Bantu, Benin, Senegal, Arab Indian
- Amount of HbF goes opposite way-most in Arab Indian
12
Q
Inflammation and vasculopathy
A
- ischemia reperfusion cycle
- vasoocclusion and ischemia cause a metabolic change, which leads to a burst of ROS when blood flow restored
- during ischemia, XO increased, upon reperfusion XO converts o2 to superoxide radical
- burst of ROS from endo cells (RBCs), adherent leukocytes and XO on endo surface
- ROS leads to NFkB, IF and cytokines, activation of leukocytes, increased adhesion molecules, further plugging, decreased NO–>abnormal endo dependent vasodilation
13
Q
sickle cell in double jeopary
A
- sickle cell RBCs contain 3x as much o2 radicals compared to normal RBCs
- they also have very low levels of reduced glutathione, particularly in highest density RBCs
- highest density, most damaged, lease antioxidants
14
Q
ROS and antioxidants
A
- RBC susceptible to oxidative damage because always carrying o2 at various po2s
- o2 radical (which comes from Fe II-III, which happens faster in sickle cells, with o2 on- superoxide) changed to h2o2 by super oxide dismutase
- h2o2 degraded by catalase, glutathione peroxidase (GPX), perioxiredoxin2, or reoxidation of Fe (makes OH radical-bad)
- normally radicals degraded to below toxic levels
- RBCs also sink for o2 radicals produced by other cell types
15
Q
metHb
A
- lower affinity for heme
- released hemin and free iron on cytoplasmic surface
- hemin or free FE can convert h2o2 into OH radical by catalyzing Fenton reaction or in concert with o2 radical by Haber Weiss reaction
- this is in sickle cell not as much in normal because Fe II to Fe III slower
