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Conformational equilibria in GPCRs provides critical clues about activation mechanisms

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A multinational research team led by Dr. Adnan Sljoka (RIKEN), Prof. R. Scott Prosser (Univ. of Toronto) with collaborations with Dr. Duy Phuoc Tran and Prof. Akio Kitao (Tokyo Tech) and Prof. Roger K. Sunahara (Univ. of California San Diego) has carried out experimental and computational studies, revealing key steps associated with the activation of the human adenosine A2A receptor (A2AR). A2AR is a member of superfamily of receptors called G protein-coupled receptors (GPCRs) (major drug targets) which engage the G protein and initiates cell signaling. The research team discovered that A2AR is represented by at least two inactive conformations and three active conformations whose populations are dependent on ligands and activation states of G protein, and that communication between receptor and G-protein is important for activation and signalling. This study is expected to allow researchers to reach new level of insight in GPCR activation and disease mechanism.

Background

GPCRs affect almost every aspect of human physiology, where 35% of all approved drugs act on GPCRs. In most cases, GPCRs are situated in the plasma membrane that surrounds the cell while the drug or ligand (such as hormones and neurotransmitters) that acts on the GPCR binds to an extracellular pocket. Activation is then transduced across the receptor, resulting in complexation with proteins on the cell interior. Since input arrives at the cell exterior and initiates signalling pathways inside the cell, this makes GPCRs useful in pharmacology as the drug in many cases need not enter the cell. However, GPCRs activations relate to dynamic events and key intermediate states that arise between the time that a ligand binds and when the G protein is activated. Capturing conformational dynamics of GPCRs and description of intermediate states and its role in activation and signalling has been a formidable challenge, which has hampered progress in understanding activation mechanisms of GPCRs.

Overview of Research Achievement

Using Fluorine-nuclear magnetic resonance (19F-NMR), mathematical rigidity theory, and molecular dynamics simulations, the international research team has discovered the key mechanism of activation of the human adenosine A2A receptor (A2AR) as it proceeds through signaling pathway. A2AR (also known as caffeine receptor as it is deactivated by caffeine) is a well-known GPCR that is distributed in the nervous system, platelets, immune cells, lungs, heart, and the vasculature. A2AR drugs have been developed to address wound healing, vascular diseases, including atherosclerosis, restenosis, and platelet activation, in addition to inflammation and cancer. Thus, understanding its functional states associated with receptor signaling can yield new opportunities in pharmacology and general understanding of GPCR activation mechanisms. The researchers focused on biasing key conformational states of A2AR by complexing it with G protein and different ligands to better understand signal transduction and receptor activation. F-NMR showed that A2AR is represented by at least two inactive conformations and three active conformations associated with signaling pathway whose populations are dependent on ligands engagement and G protein interactions (Fig2). Research team also used Molecular Dynamics simulations to create a structure of A2AR bound to heterotrimer G-protein complex (performed by Kitao lab), where rigidity theory methods of Sljoka identified an activation pathway where A2AR initiates communication with the G-protein which traverses the receptor’s ligand binding site and G-protein (Fig3). Gβγ subunit was discovered to serve as a critical domain for facilitating signaling and activation. Understanding the activation mechanism and functional states of A2AR signaling may provide new opportunities for drug discovery.

Future Development

While the current study provides unprecedented resolution of key functional states associated with receptor signaling, future studies will no doubt focus on other key domains, providing a more comprehensive picture of the activation process.

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About Tokyo Institute of Technology

Tokyo Tech stands at the forefront of research and higher education as the leading university for science and technology in Japan. Tokyo Tech researchers excel in fields ranging from materials science to biology, computer science, and physics. Founded in 1881, Tokyo Tech hosts over 10,000 undergraduate and graduate students per year, who develop into scientific leaders and some of the most sought-after engineers in industry. Embodying the Japanese philosophy of “monotsukuri,” meaning “technical ingenuity and innovation,” the Tokyo Tech community strives to contribute to society through high-impact research.
https://www.titech.ac.jp/english/

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Source: https://bioengineer.org/conformational-equilibria-in-gpcrs-provides-critical-clues-about-activation-mechanisms/

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USC Stem Cell study identifies molecular ‘switch’ that turns precursors into kidney cells

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Kidney development is a balancing act between the self-renewal of stem and progenitor cells to maintain and expand their numbers, and the differentiation of these cells into more specialized cell types. In a new study in the journal eLife from Andy McMahon’s laboratory in the Department of Stem Cell Biology and Regenerative Medicine at the Keck School of Medicine of USC, former graduate student Alex Quiyu Guo and a team of scientists demonstrate the importance of a molecule called β-catenin in striking this balance.

β-catenin is a key driver at the end of a complex signaling cascade known as the Wnt pathway. Wnt signaling plays critical roles in the embryonic development of multiple organs including the kidneys. By partnering with other Wnt pathway molecules, β-catenin controls the activity of hundreds to thousands of genes within the cell.

The new study builds on the McMahon Lab’s previous discovery that Wnt/β-catenin can initiate progenitor cells to execute a lengthy and highly orchestrated program of forming structures in the kidney called nephrons. A healthy human kidney contains a million nephrons that balance body fluids and remove soluble waste products. Too few nephrons results in kidney disease.

Previous studies from the UT Southwestern Medical Center laboratory of Thomas Carroll, a former postdoctoral trainee in the McMahon Lab, suggested that Wnt/β-catenin signaling plays opposing roles in ensuring the proper number of nephrons: promoting progenitor maintenance and self-renewal, and stimulating progenitor cell differentiation.

“It sounded like Wnt/β-catenin is doing two things–both maintenance and differentiation–that seem to be opposite operations,” said Guo. “Therefore, the hypothesis was that different levels of Wnt/β-catenin can dictate different fates of the nephron progenitors: when it’s low, it works on maintenance; when it’s high, it directs differentiation.”

In 2015, it became more possible to test this hypothesis when Leif Oxburgh, a scientist at the Rogosin Institute in New York and a co-author of the eLife study, developed a system for growing large numbers of nephron progenitor cells, or NPCs, in a Petri dish.

Relying on this game-changing new system, Guo and his collaborators grew NPCs, added different levels of a chemical that activates β-catenin, and saw their hypothesis play out in the Petri dishes.

They observed that high levels of β-catenin triggered a “switch” in part of the Wnt pathway that relies on another family of transcription factors known as TCF/LEF. There are two types of TCF/LEF transcription factors: one type inhibits genes related to differentiation, and the other activates these genes. In response to high levels of β-catenin, the “activating” members of TCF/LEF switched places with the “inhibiting” members, effectively taking charge. This “switch” triggered NPCs to differentiate into more specialized types of kidney cells.

When they looked at low levels of β-catenin, they saw NPCs self-renewing and maintaining their populations, as expected. However, they were surprised to learn that β-catenin was not engaged with any of the known genes related to self-renewal and maintenance.

“β-catenin does something,” said Guo. “That is for sure. But how it does it is kind of mysterious right now.”

After publishing these results in eLife, Guo earned his PhD from USC, and began his postdoctoral training at UCLA. Helena Bugacov, a current PhD student in the McMahon Lab and a co-author of the eLife study, is now taking the lead in continuing the project–which has implications far beyond the kidney field, due to the broad role of Wnt throughout the body.

“Understanding how Wnt regulates these two very distinct cell outcomes of self-renewal and differentiation, which is very important for kidney development, is also important for understanding the development of other organs and adult stem cells, as Wnt signaling plays important roles in almost all developmental systems,” said Bugacov. “There is also a lot of attention from cancer researchers, as this process can go awry in cancer. Many therapeutics are trying to target this process.”

She added, “The more we know about things, the better we can inform work on developing human kidney organoid cultures, which can be more readily used to understand problems in human health, regeneration and development.”

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Additional co-authors of the eLife study include: Albert Kim, Andrew Ransick, Xi Chen, and Nils Lindstrom from USC; Aaron Brown from the Maine Medical Center Research Institute; and Bin Li and Bing Ren from the University of California, San Diego. The research was supported by federal funding from the National Institute of Diabetes and Digestive and Kidney Diseases (grant number R01 DK054364).

https://stemcell.keck.usc.edu/usc-stem-cell-study-identifies-molecular-switch-that-turns-precursors-into-kidney-cells/

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Source: https://bioengineer.org/usc-stem-cell-study-identifies-molecular-switch-that-turns-precursors-into-kidney-cells/

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Evidence of Antarctic glacier’s tipping point confirmed for first time

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Researchers have confirmed for the first time that Pine Island Glacier in West Antarctica could cross tipping points, leading to a rapid and irreversible retreat which would have significant consequences for global sea level

Researchers have confirmed for the first time that Pine Island Glacier in West Antarctica could cross tipping points, leading to a rapid and irreversible retreat which would have significant consequences for global sea level.

Pine Island Glacier is a region of fast-flowing ice draining an area of West Antarctica approximately two thirds the size of the UK. The glacier is a particular cause for concern as it is losing more ice than any other glacier in Antarctica.

Currently, Pine Island Glacier together with its neighbouring Thwaites glacier are responsible for about 10% of the ongoing increase in global sea level.

Scientists have argued for some time that this region of Antarctica could reach a tipping point and undergo an irreversible retreat from which it could not recover. Such a retreat, once started, could lead to the collapse of the entire West Antarctic Ice Sheet, which contains enough ice to raise global sea level by over three metres.

While the general possibility of such a tipping point within ice sheets has been raised before, showing that Pine Island Glacier has the potential to enter unstable retreat is a very different question.

Now, researchers from Northumbria University have shown, for the first time, that this is indeed the case.

Their findings are published in leading journal, The Cryosphere.

Using a state-of-the-art ice flow model developed by Northumbria’s glaciology research group, the team have developed methods that allow tipping points within ice sheets to be identified.

For Pine Island Glacier, their study shows that the glacier has at least three distinct tipping points. The third and final event, triggered by ocean temperatures increasing by 1.2C, leads to an irreversible retreat of the entire glacier.

The researchers say that long-term warming and shoaling trends in Circumpolar Deep Water, in combination with changing wind patterns in the Amundsen Sea, could expose Pine Island Glacier’s ice shelf to warmer waters for longer periods of time, making temperature changes of this magnitude increasingly likely.

The lead author of the study, Dr Sebastian Rosier, is a Vice-Chancellor’s Research Fellow in Northumbria’s Department of Geography and Environmental Sciences. He specialises in the modelling processes controlling ice flow in Antarctica with the goal of understanding how the continent will contribute to future sea level rise.

Dr Rosier is a member of the University’s glaciology research group, led by Professor Hilmar Gudmundsson, which is currently working on a major £4million study to investigate if climate change will drive the Antarctic Ice Sheet towards a tipping point.

Dr Rosier explained: “The potential for this region to cross a tipping point has been raised in the past, but our study is the first to confirm that Pine Island Glacier does indeed cross these critical thresholds.

“Many different computer simulations around the world are attempting to quantify how a changing climate could affect the West Antarctic Ice Sheet but identifying whether a period of retreat in these models is a tipping point is challenging.

“However, it is a crucial question and the methodology we use in this new study makes it much easier to identify potential future tipping points.”

Hilmar Gudmundsson, Professor of Glaciology and Extreme Environments worked with Dr Rosier on the study. He added: “The possibility of Pine Island Glacier entering an unstable retreat has been raised before but this is the first time that this possibility is rigorously established and quantified.

“This is a major forward step in our understanding of the dynamics of this area and I’m thrilled that we have now been able to finally provide firm answers to this important question.

“But the findings of this study also concern me. Should the glacier enter unstable irreversible retreat, the impact on sea level could be measured in metres, and as this study shows, once the retreat starts it might be impossible to halt it.”

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The paper, The tipping points and early warning indicators for Pine island Glacier, West Antarctica, is now available to view in The Cryosphere.

Northumbria is fast becoming the UK’s leading university for research into Antarctic and extreme environments.

As well as the £4m tipping points study, known as TiPPACCs, Northumbria is also the only UK university to play a part in two projects in the £20m International Thwaites Glacier Collaboration – the largest joint project undertaken by the UK and USA in Antarctica for more than 70 years – where Northumbria is leading the PROPHET and GHC projects. This particular study was funded through both TiPPACCs and PROPHET.

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Source: https://bioengineer.org/evidence-of-antarctic-glaciers-tipping-point-confirmed-for-first-time/

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Diversity can prevent failures in large power grids

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Integrated power grids offer benefits, but also pose challenges best addressed by leveraging differences

The recent power outages in Texas brought attention to its power grid being separated from the rest of the country. While it is not immediately clear whether integration with other parts of the national grid would have completely eliminated the need for rolling outages, the state’s inability to import significant amounts of electricity was decisive in the blackout.

A larger power grid has perks, but also has perils that researchers at Northwestern University are hoping to address to expedite integration and improvements to the system.

An obvious challenge in larger grids is that failures can propagate further — in the case of Texas, across state lines. Another is that all power generators need to be kept synchronized to a common frequency in order to transmit energy. The U.S. is served by three “separate” grids: The Eastern interconnection, the Western interconnection and the Texas interconnection, interlinked only by direct-current power lines. Any persistent deviation in frequencies within a region can lead to an outage.

As a result, researchers are searching for ways to stabilize the grid by looking for methods to mitigate deviations in the power generators’ frequencies.

The new Northwestern research shows that counter to assumptions held by some, there are stability benefits to heterogeneity in the power grid. Examining several power grids across the U.S. and Europe, a team led by Northwestern physicist Adilson Motter recently reported that generators operating on different frequencies return to their normal state more quickly when they are damped by “breakers” at different rates than generators around them.

The paper was published March 5 in the journal Nature Communications.

Motter is the Charles E. and Emma H. Morrison Professor in the department of physics and astronomy in the Weinberg College of Arts and Sciences. His research focuses on nonlinear phenomena in complex systems and networks.

Motter compares power grids to a choir: “It’s a little bit like a choir without a conductor. The generators have to listen to others and speak in sync. They react and respond to each other’s frequencies.”

Listen to an out-of-whack frequency, and the result can be a failure. Given the interconnected makeup of the system, a failure can propagate across the network. Historically, these malfunctions have been prevented by using active controllers. However, failures are often caused precisely by control and equipment errors. This points to a need to build additional stability within the design of the system. To achieve that, the team looked into leveraging the natural heterogeneities of the grid.

When the frequencies of the power generators are moved away from the synchronous state, they can swing around for a long time and even become more erratic. To mitigate these fluctuations, they came up with something akin to a door mechanism used to close a door the fastest, but without slamming.

“Mathematically, the problem of damping frequency deviations in a power generator is analogous to the problem of optimally damping a door to get it to close the fastest, which has a known solution in the case of a single door,” Motter said. “But it’s not a single door in this analogy. It’s a network of many doors that are coupled with each other, if you can imagine the doors as power generators.”

When creating an “optimal damping” effect, they discovered that rather than making each damper identical, damping the power generators in a way that is suitably different from each other can further optimize their ability to synchronize to the same frequency as quickly as possible. That is, suitably heterogenous damping across the network can lead to improved stability in the power grids studied by the team.

This discovery could have implications for future grid design as developers work to optimize technology and in considerations to further integrate now separated networks.

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The paper is titled “Asymmetry underlies stability in power grids.” Additional co-authors include former postdoctoral researcher Ferenc Molnar and research professor Takashi Nishikawa.

The study was supported by Northwestern University’s Finite Earth Initiative (supported by Leslie and Mac McQuown) and ARPA-E Award No. DE-AR0000702 and also benefited from logistical support from the Northwestern Institute for Sustainability and Energy.

https://news.northwestern.edu/stories/2021/04/diversity-can-prevent-failures-in-large-power-grids/

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How Fortnite and Zelda can up your surgical game (no joke!)

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Scalpel? Check. Gaming console? Check. Study finds video games can be a new tool on surgical tray for medical students

Video games offer students obvious respite from the stresses of studies and, now, a study from a University of Ottawa medical student has found they could benefit surgical skills training.

Arnav Gupta carries a heavy course load as a third-year student in the Faculty of Medicine, so winding down with a game of Legend of Zelda always provides relief from the rigorous of study. But Zelda may be helping improve his surgical education, too, as Gupta and a team of researchers from the University of Toronto found in a paper they recently published in the medical journal Surgery.

“Given the limited availability of simulators and the high accessibility of video games, medical students interested in surgical specialties should know that video games may be a valuable adjunct training for enhancing their medical education, especially in surgical specialties where it can be critical,” says Gupta, whose findings were deciphered from a systematic review of 16 studies involving 575 participants.

“Particularly, in robotic surgery, being a video gamer was associated with improvements in time to completion, economy of motion, and overall performance. In laparoscopic surgery, video games-based training was associated with improvement in duration on certain tasks, economy of motion, accuracy, and overall performance,” explains Gupta, who has been a gamer since age 8.

This study builds on past reviews and is the first to focus on a specific medical student population where this style of training could be feasibly implemented. Their timely study found some of the most beneficial games for students of robotic surgery and laparoscopy were: Super Monkey Ball, Half Life, Rocket League and Underground. Underground is purposely designed to assist medical students with their robotic surgery training via a video game console.

“While video games can never replace the value of first-hand experience, they do have merit as an adjunctive tool, especially when attempting to replicate important movements to surgery. For example, first-person shooting games require you to translate three dimensional motions onto a two-dimensional screen, which is like the concept of laparoscopic surgery,” says Gupta, whose studies are focused on surgery in ophthalmology, which makes games like Resident Evil 4 or Trauma Center: New Blood fitted for his own ambitions.

“I’m not joking when I say that games such as Fortnite have the potential to enhance those necessary movements, providing stronger motivational components and in a low stakes environment.”

Reports suggest 55 percent of university students are gamers and enjoy proficiency with video consoles. Yet, many medical students don’t admit to owning and using a gaming console.

“I think there definitely is some ambivalence towards video games in medicine,” says Gupta, who is also a fan of Witcher 3. “Given how accessible games have become and how video game technology is advancing, video games definitely are an easy go-to for the students who do love them in some capacity. The hope is that maybe this study can inspire someone to take advantage of video games’ unique capabilities, reduce the general ambivalence towards it, and develop some fun ways to let students engage with surgical education.”

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https://media.uottawa.ca/news/how-fortnite-and-zelda-can-your-surgical-game-no-joke

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