Week 4 Flashcards
What is hypoxia
Insufficient oxygen availability and there is a deficiency in the amount of oxygen delivered to cells or body tissues
How much oxygen does mitochondria use to make ATP
More than 95%
What does a decrease in O2 do
Effects energy production and disrupts cells ability to maintain proper functions
What is oxygen homeostasis
A balance between oxygen consumption and oxygen supply
What is hypoxia linked too
Cancer, Cardiovascular disease , Stroke and COVID-19
What pathway does hypoxia induce
An evolutionary conserved signalling pathway mediated by hypoxia inducible transcriptional factors (HIF)
What is the concentration of moleculaor oxygen in the atmosphere
21% which also coresponds to normal oxygen conditions normoxia
What is the concentration in alveoli and arterial bood
13%
What is concentration of oxygen in tissues
5%
Why is concnetration is tissues and cells so low
en route oxygen consumption
Are vivo cells exposed to a lower concentration of oxygen than atmospheric oxygen
YES
Why might vitro and vivo normoxia not be the same
Vitro in a controlled envinroment like a lab dish they used conditions that mimic normoxic where in vivo a living organism the oxygen levels can differ signficantly due to various factors so vitro studies may not be super accurate
What are cells in vitro usually exposed too
5% CO2 and 95% air
What is the oxygen concentration in these incubators
20%
What are cells in vitro exposed too
Hyperoxic conditions
What is hypoxia considered at
1-5% and require specific chambers
What are erythrocytes
Red blood cells that reansfer oxygen in our body
Where are RBC produced
In the bone marrow
What is erythropiesies controoled by
A hormone erythropoietin which is produced in the kidneys
What happens to people with anemia
It is a chronic kidney diesase which is a deficiency in red blood cells to carry adequated oxygen to bodys tissues
How can anemina be treated
EPO provided efficient thearpy
What is the process of the EPO gene
Has a specific short sequence downstream gene HRE which binds a heterodimer called hypoxia-inducible factor HIF-1
Under hypoxia conditions what are the cells switching from
Oxidative to glycolytic metabolism
What do the glycolytic enzymes do
Convert glucose to pyruvate
What is pyruvate converted too
aceytlye CoA for oxidation in Krebs cycle or lacate in glycolytic end
What does hypoxia activate the expression of
LDHA and PDK1 which inhibits pyruvate dehydrogenase tipping the balance from oxidative to glycolytic metabolism
What is angiogensis
The growth of newly formed blood vessels from pre-existing vasculature
What is angiogenesis induced by
A growth factor called vasular endothelial growth factor which is upregualted by hupoxia
How does cancer use angiogensis
Induces the formation of new blood vessels in tumors under hypoxic conditions for supplying more nutrients in supporting tumor growth
Why is VEGF up-regualted in hypoxia
They have hypoxia response element sequence in their promoter regions for binding the transcription factor HIF-1 which is activated by hypoxia
What is the transcription factor HLF-1 a heterodimer of
HIF-1 alpha and HIF-1B that assembles in the nucleus to make an active HIF-1
What is the difference between HIF-1 alpha and HIF-1B
HIF-1a is a subunit of Ox labile cytoplasmic protein with a half life of under 5 min under normoxia to due to protesomal degradation where HIF-1B is a subunit of a stable nuclear protein
What do both subuntis have
DNA binding domain (bHLH) and a dimerization domain
What domains does HIF-1A have
Transactivation domain at C terminus split into TAD-N and TAD-C subdomains
What amino acid residues are in HIF-1a
Two prolines in TAD-N and one asparagine in TAD-C they can be hydroxylated by two different types of HIF hydroxylases
What are the two hydroxylases and what do they need
PHDs and FIH1 molecular oxygen as a substrate and hydroxylation occurs at normoxia conditons
What happens to HIF-1A under normoxia
VHL binds to the hydroxylated proteins recurits a ubiquitin E3 ligase and protesomal degradation and hydroxylation of asparagine prevents binding of P300 which is reuqired for HIF-1 activation and so it is not available under normal hypoxia signaling pathway
What happens to HIF-1A under hypoxia conditions
HIF-1A can’t be hydroxylated VHL can not bind which prevents protesomal degradation which it can now be moved to the nucleus to pair with HIF-1B dimerization is needed for DNA binding p300 now binds HIF-1 is now active which binds to HRE
What genes are expressed when HIF-1 dimer binds
EPO PDK1 and VEGF
What domains make sure of dimerization
bHLH and PAS
What is VHL
A tumor supressor gene so in its abesnce or mutations it can lead to cancer
What tumors form with VHL disease
Benging or maligant tumors in the eye kideny or other tissues
What are the two characteristics of VHL disease
Angiogenic intensive blood vessel growth elevated production of VEGF and have high hematocrit the proprotion of red blood cells is high
What is in the E3 ubiquitin protein ligase complex
Elongin c ELC elogin B ELB and Cullin 2 (CUL2) and RING-box protien 1 (RBX1)
What happens in VHL disease
It is not target for VHL-protesomal degradation and accumulate in cells resulting activation of hypoxia-related genes cell proliferation and neovascularization of tumors
What enzyme catalyzes protesomal degradation
PHD and needs oxygen but also c-substrate 2-oxoglutrate and FE(II)
What happens if one of the componets are missing
Hydroxylation of prolines will be impaired and HIF-1a will be stabilized and avoid protesomal degradation
So what can hypoxia signaling response be induced by
Low oxygen, iron chelation (replacment with transtion metals) or non metabolix analgouses of 2-oxoglutrate
What are the two majors way to induce hypoxia
Grow cells in the presence of low oxygen or to use chemical inhibitors of HIF1a hydoxylation
What are the methods of inducing hypoxia
Molecualr oxygen in 1-5% or the chemical approach uses inhibitory durgs colbalt cholride which will replace iron ions
What should you see in a western blot under hypoxia stress
HIF-1A are suppose to increase
How else can hypoxia be tested
Cells can be transfected with a reporter gene (luciferase) under the control of HRE which is supposed to activated by binding HIF-1
