S1. HIF and Oxygen Sensing Flashcards
What experiment first demonstrated a ‘humoral’ factor inducing erythropoiesis?
Blood from hypoxic/anaemic rabbits was transferred into normal rabbits, causing erythrocytosis in the latter
What discovery linked hypoxia to erythropoiesis?
The identification of the Erythropoietin (EPO) gene, showing EPO production is induced under hypoxic conditions
How was the EPO-producing cell type identified in the kidney?
Using transgenic mouse models expressing tagged EPO, identifying interstitial fibroblasts as the producers
Which cell lines enabled molecular dissection of the HIF pathway?
Hep3B and HepG2 hepatoma cell lines, which showed hypoxic EPO induction
What region of the EPO gene is critical for hypoxic regulation?
The Hypoxia Response Element (HRE) adjacent to the EPO gene
How was HIF first identified?
By analyzing proteins binding to the HRE, leading to the discovery of HIF as a heterodimer of alpha and beta subunits
What mutation analysis helped explain HIF regulation by oxygen?
Mutations in the oxygen-dependent degradation domain (ODDD) showed its importance for HIF stabilization in hypoxia
What role does the nematode C. elegans play in HIF research?
It helped identify Egl-9, the prolyl hydroxylase responsible for HIF regulation, due to its simpler genetic system
How do PHD enzymes regulate HIF?
They hydroxylate prolines on HIF-alpha in normoxia, marking it for degradation by VHL
What is the role of FIH in HIF regulation?
FIH hydroxylates asparagine residues on HIF-alpha, preventing co-activator binding and limiting transcription in normoxia
What distinguishes HIF-1alpha and HIF-2alpha?
HIF-1alpha is ubiquitous and essential for embryonic development, while HIF-2alpha specializes in adult hypoxic responses like erythropoiesis
What experiment showed HIF-2alpha’s role in erythropoiesis?
Transgenic mice lacking HIF-2alpha failed to show hypoxia-induced erythropoiesis
How is the carotid body involved in hypoxia responses?
It senses arterial oxygen drops, triggering acute ventilatory responses through Type I cell neurotransmitter release
What role does HIF-2alpha play in the carotid body?
It mediates chronic hypoxia-induced carotid body proliferation and ventilatory acclimatization
What is the link between VHL mutations and cancer?
VHL mutations lead to constitutive HIF activation, promoting tumors like renal clear cell carcinoma
How do high-altitude populations demonstrate adaptation to hypoxia?
Genetic studies reveal SNPs in HIF-2alpha and PHD2, associated with reduced erythrocytosis and pulmonary hypertension
What are PHIs and their clinical significance?
Prolyl hydroxylase inhibitors enhance erythropoiesis and are used to treat renal anemia, with potential for other ischemic conditions
What is the mechanism of action for HIF-2alpha antagonists?
They block dimerization of HIF-2alpha with HIF-beta, inhibiting its transcriptional activity
How did experiments with reporter constructs demonstrate HIF ubiquity?
Transfection of HRE-reporter genes into various cell types showed hypoxia responsiveness across diverse tissues
What experiment linked mitochondrial adaptations to HIF-2alpha?
HIF-2alpha was shown to induce atypical mitochondrial subunits like Cox4i2, enhancing oxygen sensing under hypoxia
How might HIF pathways impact COVID-19?
PHIs activating HIF-1alpha impair SARS-CoV-2 infection and replication, suggesting therapeutic potential
What does the term ‘pseudohypoxia’ describe?
Constitutive activation of HIF due to mutations, mimicking hypoxic conditions
What is the role of angiogenesis in hypoxia adaptation?
It involves the formation of new blood vessels, mediated by HIF-induced VEGF expression, to enhance oxygen delivery
Which tumors are commonly associated with VHL mutations?
Renal clear cell carcinomas, hemangioblastomas, and pheochromocytomas
What adaptation allows Tibetans to thrive at high altitudes?
Genetic SNPs in HIF-2alpha reduce erythrocytosis and enhance oxygen delivery efficiency
What is the role of HIF in pulmonary hypertension?
HIF contributes to vascular remodeling and vasoconstriction, leading to increased pulmonary arterial pressure
How does HIF affect glucose metabolism?
HIF induces glycolytic enzymes and glucose transporters, facilitating anaerobic metabolism under hypoxia
What are atypical mitochondrial subunits induced by HIF?
Subunits like Cox4i2 enhance mitochondrial oxygen sensing and efficiency under hypoxia
What experiment linked VHL to HIF regulation?
VHL-deficient renal carcinoma cells showed constitutive HIF activation, revealing VHL’s role in HIF degradation
How does chronic hypoxia affect ventilatory response?
It leads to ventilatory acclimatization, mediated by HIF-2alpha and carotid body adaptations
What is the primary function of PHIs in therapy?
To treat anemia by enhancing erythropoiesis via HIF stabilization
What are the two classes of HIF pharmacological modulators?
Prolyl hydroxylase inhibitors (PHIs) and HIF-2alpha antagonists
What is the main conclusion from hypoxia chamber studies?
HIF-2alpha, not HIF-1alpha, is essential for ventilatory acclimatization and carotid body proliferation
What are the main differences between HIF-1 and HIF-2?
HIF-1 is involved in general metabolic adaptation, while HIF-2 specializes in systemic oxygen control
How do genetic lineage tracers help in hypoxia studies?
They track progenitor cell proliferation and differentiation under hypoxic conditions
What is Monge’s disease?
Chronic mountain sickness characterized by excessive erythrocytosis and pulmonary hypertension
How do PHD inhibitors work?
They inhibit prolyl hydroxylase enzymes, stabilizing HIF to mimic hypoxic conditions therapeutically
What role does the carotid body play in acute oxygen sensing?
It triggers immediate respiratory responses via neurotransmitter release from Type I cells
How is the HIF pathway evolutionary conserved?
It is found across species, from nematodes to humans, highlighting its fundamental role in oxygen sensing
What is the clinical significance of Belzutifan?
A HIF-2alpha antagonist used to treat VHL-associated renal carcinomas and pulmonary hypertension
What does hypoxia-induced proliferation in the carotid body indicate?
It is a hallmark of chronic hypoxia adaptation, mediated by HIF-2alpha
