Nobel Prize in Physiology or Medicine 2019: How cells sense and adapt to oxygen availability

The Nobel Assembly at Karolinska Institutet has today decided to award the 2019 Nobel Prize in Physiology or Medicine jointly to William G. Kaelin Jr., Sir Peter J. Ratcliffe and Gregg L. Semenza for their discoveries of how cells sense and adjust to oxygen handiness. Animals need oxygen for the conversion of food into utilitarian energy. The fundamental importance of oxygen has been understood for centuries, but how cells adapt to changes in levels of oxygen has retentive been unknown .
William G. Kaelin Jr., Sir Peter J. Ratcliffe and Gregg L. Semenza discovered how cells can sense and adapt to changing oxygen handiness. They identified molecular machinery that regulates the bodily process of genes in response to varying levels of oxygen .
The seminal discoveries by this year ‘s Nobel Laureates revealed the mechanism for one of life ‘s most substantive adaptive processes. They established the basis for our understand of how oxygen levels affect cellular metamorphosis and physiologic serve. Their discoveries have besides paved the way for promising new strategies to fight anemia, cancer and many early diseases.

Oxygen at center stage
oxygen, with the formula O2, makes up about one fifth of Earth ‘s standard atmosphere. oxygen is necessity for animal life : it is used by the mitochondrion present in virtually all animal cells in orderliness to convert food into utilitarian energy. Otto Warburg, the recipient of the 1931 Nobel Prize in Physiology or Medicine, revealed that this conversion is an enzymatic summons .


During development, mechanisms developed to ensure a sufficient provide of oxygen to tissues and cells. The carotid soundbox, adjacent to large blood vessels on both sides of the neck, contains specialize cells that sense the blood ‘s oxygen levels. The 1938 Nobel Prize in Physiology or Medicine to Corneille Heymans awarded discoveries showing how blood oxygen sensing via the carotid body controls our respiratory rate by communicating directly with the brain .
HIF enters the scene
In addition to the carotid body-controlled rapid adaptation to low oxygen levels ( hypoxia ), there are other fundamental physiological adaptations. A key physiologic reception to hypoxia is the originate in levels of the hormone erythropoietin ( EPO ), which leads to increased production of red blood cells ( erythropoiesis ). The importance of hormonal control of erythropoiesis was already known at the beginning of the twentieth hundred, but how this work was itself controlled by O2 remained a mystery .
Gregg Semenza studied the EPO gene and how it is regulated by varying oxygen levels. By using gene-modified mouse, specific DNA segments located following to the EPO gene were shown to mediate the reception to hypoxia. Sir Peter Ratcliffe besides studied O2-dependent regulation of the EPO gene, and both inquiry groups found that the oxygen sensing mechanism was stage in about all tissues, not only in the kidney cells where EPO is normally produced. These were authoritative findings showing that the mechanism was general and functional in many different cell types .
Semenza wished to identify the cellular components mediating this response. In civilized liver cells he discovered a protein building complex that binds to the identified DNA segment in an oxygen-dependent manner. He called this building complex the hypoxia-inducible divisor ( HIF ). extensive efforts to purify the HIF complex began, and in 1995, Semenza was able to publish some of his key findings, including designation of the genes encoding HIF. HIF was found to consist of two different DNA-binding proteins, so call transcription factors, now named HIF-1α and ARNT. now the researchers could begin solving the puzzle, allowing them to understand which extra components were involved and how the machinery works .


VHL: an unexpected partner
When oxygen levels are eminent, cells contain very little HIF-1α. however, when oxygen levels are first gear, the measure of HIF-1α increases so that it can bind to and frankincense regulate the EPO gene equally well as early genes with HIF-binding DNA segments. several research groups showed that HIF-1α, which is normally quickly degraded, is protected from abasement in hypoxia. At convention oxygen levels, a cellular machine called the proteasome, recognized by the 2004 Nobel Prize in Chemistry to Aaron Ciechanover, Avram Hershko and Irwin Rose, degrades HIF-1α. Under such conditions a belittled peptide, ubiquitin, is added to the HIF-1α protein. Ubiquitin functions as a rag for proteins destined for degradation in the proteasome. How ubiquitin binds to HIF-1α in an oxygen-dependent manner remained a central interrogate .
The answer came from an unexpected management. At about the lapp time as Semenza and Ratcliffe were exploring the rule of the EPO gene, cancer research worker William Kaelin, Jr. was researching an inherit syndrome, von Hippel-Lindau ‘s disease ( VHL disease ). This genic disease leads to dramatically increase risk of certain cancers in families with inherit VHL mutations. Kaelin showed that the VHL gene encodes a protein that prevents the attack of cancer. Kaelin besides showed that cancer cells lacking a running VHL gene carry abnormally high levels of hypoxia-regulated genes ; but that when the VHL gene was reintroduced into cancer cells, normal levels were restored. This was an authoritative clue showing that VHL was somehow involved in controlling responses to hypoxia. Additional clues came from several research groups showing that VHL is separate of a complex that labels proteins with ubiquitin, marking them for degradation in the proteasome. Ratcliffe and his inquiry group then made a key discovery : prove that VHL can physically interact with HIF-1α and is required for its degradation at normal oxygen levels. This conclusively linked VHL to HIF-1α .
Oxygen sHIFts the balance
many pieces had fallen into place, but what was calm lacking was an understand of how O2 levels regulate the interaction between VHL and HIF-1α. The research focused on a specific part of the HIF-1α protein known to be significant for VHL-dependent abasement, and both Kaelin and Ratcliffe suspected that the cardinal to O2-sensing resided somewhere in this protein domain. In 2001, in two simultaneously published articles they showed that under normal oxygen levels, hydroxyl groups are added at two specific positions in HIF-1α. This protein modification, called prolyl hydroxylation, allows VHL to recognize and bind to HIF-1α and therefore explained how normal oxygen levels control rapid HIF-1α abasement with the help of oxygen-sensitive enzymes ( alleged prolyl hydroxylases ). farther inquiry by Ratcliffe and others identified the responsible prolyl hydroxylases. It was besides shown that the gene activating function of HIF-1α was regulated by oxygen-dependent hydroxylation. The Nobel Laureates had now elucidated the oxygen sensing mechanism and had shown how it works .
Oxygen shapes physiology and pathology
Thanks to the groundbreaking workplace of these Nobel Laureates, we know much more about how different oxygen levels regulate fundamental physiological processes. Oxygen sensing allows cells to adapt their metabolism to low oxygen levels : for example, in our muscles during intense exercise. other examples of adaptive processes controlled by oxygen sensing include the generation of newfangled blood vessels and the production of red blood cells. Our immune system and many other physiologic functions are besides fine-tuned by the O2-sensing machinery. Oxygen sense has even been shown to be necessity during fetal development for controlling normal blood vessel formation and placenta exploitation .
oxygen sensing is cardinal to a large numeral of diseases. For example, patients with chronic nephritic bankruptcy much suffer from severe anemia due to decrease EPO expression. EPO is produced by cells in the kidney and is essential for controlling the constitution of loss blood cells, as explained above. furthermore, the oxygen-regulated machinery has an crucial role in cancer. In tumors, the oxygen-regulated machinery is utilized to stimulate lineage vessel formation and reshape metamorphosis for effective proliferation of cancer cells. Intense ongoing efforts in academic laboratories and pharmaceutical companies are now focused on developing drugs that can interfere with different disease states by either energizing, or obstruct, the oxygen-sensing machinery.

William G. Kaelin, Jr. was born in 1957 in New York. He obtained an M.D. from Duke University, Durham. He did his specialist train in inner medicine and oncology at Johns Hopkins University, Baltimore, and at the Dana-Farber Cancer Institute, Boston. He established his own research lab at the Dana-Farber Cancer Institute and became a wax professor at Harvard Medical School in 2002. He is an research worker of the Howard Hughes Medical Institute since 1998 .
Sir Peter J. Ratcliffe was born in 1954 in Lancashire, United Kingdom. He studied medicine at Gonville and Caius College at Cambridge University and did his specialist train in nephrology at Oxford. He established an autonomous research group at Oxford University and became a full professor in 1996. He is the Director of Clinical Research at Francis Crick Institute, London, Director for Target Discovery Institute in Oxford and Member of the Ludwig Institute for Cancer Research .
Gregg L. Semenza was born in 1956 in New York. He obtained his B.A. in Biology from Harvard University, Boston. He received an MD/PhD academic degree from the University of Pennsylvania, School of Medicine, Philadelphia in 1984 and trained as a specialist in pediatrics at Duke University, Durham. He did postdoctoral trail at Johns Hopkins University, Baltimore where he besides established an autonomous research group. He became a full professor at the Johns Hopkins University in 1999 and since 2003 is the Director of the Vascular Research Program at the Johns Hopkins Institute for Cell Engineering .

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