The Fondation Weizmann.be pour la science is a non-profit, private entity. Its aim is to promote the Weizmann Institute of Science in Belgium and to support its research projects via appropriate public relations activities as well as selective fund raising, in particular in the form of sponsorships, donations and legacies.
One of the Foundation’s regular activites is the sponsoring of promising students attending Belgian secondary schools, who qualify for participation in the annual 4 weeks International Scientific Summer School (ISSI) on the Weizmann Institute of Science campus, before continuing their tertiary education in science. This year two promising young women have been selected.
The Foundation is chaired by Mr Christian Hendboeg.
Mrs Diane Culer, Prof. Pierre Klees, Prof Maurice Sosnowski, Mr Paul de Schietere de Lophem, Mr Eric Hemeleers and Mr Roland Louis are directors.
The Belgian Foundation was founded in 2006, replacing the Belgian Committee, which had been established in 1973 by Prof. Georges Schnek, who also served as the first Secretary General until 1979. He was succeeded by Mr Louis Culer, who held this position for 20 years until 1999, followed by Prof. Marc van Montagu until June 2006.
Among the former Chairmen of the Committee were the former Belgian Prime Minister Theo Lefèvre (1973-1975), Prof. Piet de Somer, Rector of the “Katolieke Universiteit Leuven” (1975-1980) and Prof. Jean Brachet (1980-1972). Two Nobel Laureates, Prof. Christian de Duve and Prof. Ilya Prigogine, were members of the Academic Council.
A Weizmann Institute method for tracking the effects of drugs on zebrafish may help develop improved therapies for depression and other mood-related disorders
Psychedelics are a hot topic in labs all over the world because they hold great potential for relieving the symptoms of depression, anxiety, PTSD and other mood-related conditions. Still, there is a major hurdle to developing these substances into safe, effective medications: Very little is known about how psychedelic drugs work.
In a study reported recently in Molecular Psychiatry, a team headed by Dr. Takashi Kawashima at the Weizmann Institute of Science has developed a new approach that makes it possible to observe how psychedelics influence behavior and how they affect individual cells in the brain. The method combines powerful optical microscopy, advanced image analysis and artificial intelligence, and uses immature, larval zebrafish as its animal model.
Targeting serotonin for mental health
Psychedelics have been with us for thousands of years, from ancient shamanistic rituals to today’s wild parties. They were placed off limits for scientific study by the Comprehensive Drug Abuse Prevention and Control Act of 1970, which inaugurated the United States’ “war on drugs.” Recently, however, psychedelics have made it to the right side of the law.
According to Kawashima, who in addition to being a research neuroscientist is a medical doctor, psychedelics are now poised to do something that’s truly on the up and up: improve the state-of-the-art for the treatment of mood-related psychiatric conditions. In particular, a number of psychedelics are currently being investigated for their effects on serotonin, a chemical that, among its many other functions, carries messages throughout the brain and nervous system, regulating mood.
“Psychedelics affect serotonin receptors much faster than common antidepressants and appear to act in a more targeted manner”
Kawashima points out, however, that it’s problematic to test psychedelics on humans because of their hallucinogenic side effects, and it’s hard to know what exactly they do to the brain because they may target circuits in the brain’s deep-seated regions, where neural activity is difficult to observe. “Zebrafish larvae, on the other hand, are transparent, making it possible to monitor drugs’ impact on specific brain cells and to correlate this with behavior.”
The present study was launched at the instigation of Dr. Dotan Braun, a psychiatrist who joined Kawashima’s lab in Weizmann’s Brain Sciences Department as a visiting scientist. Inspired by Kawashima’s technology for imaging brain activity in zebrafish and his investigations of the serotonin system, Braun proposed a project that would help clarify the precise effects of psychedelics on serotonin. This in turn might contribute to the development of potential psychedelic alternatives to the widely prescribed class of antidepressants known as serotonin-selective reuptake inhibitors, or SSRIs, which include such drugs as Cipralex and Prozac.
“SSRIs elevate serotonin levels throughout the brain,” Braun says. “Psychedelics, in contrast, affect serotonin receptors via a different, much faster mechanism and they appear to act on brain areas in a more targeted manner. A better understanding of their mechanism of action and a mapping of their influence on the brain may lead to more efficient drugs, with fewer side effects.”
Fish on drugs
The scientists designed an experiment that enabled them to “get into the head” of zebrafish soaked in a solution containing psilocybin, a mushroom-derived psychedelic compound being tested for use against depression that is not relieved by other medications. Following a four-hour psilocybin “bath,” the fish dove into Kawashima’s arena for behavioral experiments: a shallow pool of water that has attention-grabbing visual patterns projected onto its glass bottom.
After exposing the fish to a stressful situation – a sudden, temporary drop in water temperature – the researchers compared their behaviors to those of fish that had not taken a preparatory bath. “We wanted to see how psychedelics affect the fish’s stress response,” Kawashima says, adding with a smile: “We found that, similar to what can be true for humans, when you’re heading into a stressful situation, taking a long bath can help.”
Indeed, the psychedelic bath reduced stress-related behaviors in two ways. Following stress exposure, the presoaked fish were more likely to explore the tank, venturing even into its darker domains, compared to fish that were drug-free. The “drugged” fish also darted about faster than the “sober” ones. These differences suggested that psilocybin produced a stimulating effect.
In addition, psilocybin reduced post-stress anxiety. “Fish that had not bathed in psilocybin reacted to the sudden drop in temperature with irregular, zig-zag swimming,” says Ayelet Rosenberg, a research student in Kawashima’s lab who, together with Braun, is a first coauthor of the research paper. “But the fish that had been pretreated with the psychedelic drug stayed calm; they seemed to take this added stress in stride.”
The scientists were able to pick up on these differences in behavior by documenting freely swimming individual zebrafish in minute detail with the help of a high-speed camera that produced 270,000 images for each 15-minute experiment. A subset of this wealth of images was manually annotated for ten zebrafish body parts, including the eyes, nostril, body trunk, and six points along the tail, and used to train a deep neural network – an advanced AI algorithm – to identify the nuances of the fish’s swimming patterns. Once trained, the algorithm was able to identify complex swimming trajectories and map out how behavior changed in fish under the influence of psychedelics.
The scientists were then able to link these behavioral effects to specific neural activation patterns. They relied on a method, previously developed by Kawashima and colleagues, involving the fluorescent tagging of individual zebrafish neurons and neural circuits, which causes them to light up when activated. Because the zebrafish larvae are transparent, the scientists were able to use a powerful optical microscope to image this activation directly, enabling them to identify specific changes in serotonin-related neurons and circuits.
Over 100: number of visits, phone calls and emails to Israel’s Ministry of Health by members of Dr. Kawashima’s team before they received permission to use psilocybin, making theirs the first Israeli lab ever authorized to work with this controlled psychedelic substance.
“Our optical imaging has revealed neural activity patterns in psilocybin-soaked fish that were similar to those seen by other labs in the mammalian brain exposed to psychedelics,” says Kawashima. “This indicates that psilocybin exerts its influence on behavior through neural mechanisms in deep areas of the brain that have been conserved in evolution and are also found in mammals, including humans.”
A “trip” toward better psychiatric treatment
The Kawashima team’s methodology and findings could help advance the development of psychedelics as therapies for mood-related conditions. Kawashima cautions that studying psychedelics in fish has its limits: Despite the fascinating nature of the question, it is unclear, for example, whether zebrafish experience hallucinatory “trips” in the course of these investigations. Still, his method can help advance therapeutic research in psychiatry.
“The practical significance of our work is that it demonstrates a fish-based screening tool for drug discovery,” he says. “Researchers can use our method to test new drug compounds or compare the relative usefulness of the serotonin-targeting drugs already in use. This could lead to discoveries about the mechanics of serotonin-related disorders, something that could generate entirely new approaches to the treatment of depression, anxiety, OCD, PTSD and addiction.”
Dr. Takashi Kawashima is the incumbent of the Birnbach Family Career Development Chair.
His research is supported by the Swiss Society Center for Research on Perception and Action and the Jared M. Drescher Center for Research on Mental and Emotional Health.
A machine learning model sheds new light on muscle development
Life sciences have never been more digital. To learn more about life processes, biologists are collecting massive quantities of data that computer scientists analyze by means of sophisticated computational models that they develop. Over the past few years, Dr. Ori Avinoam of the Biomolecular Sciences Department at the Weizmann Institute of Science has been grappling with one unresolved biological conundrum: How do stem cells generate new muscle fibers? In his search for an answer, Avinoam turned to his friend Dr. Assaf Zaritsky from the Software and Information Systems Engineering Department at Ben-Gurion University of the Negev, and together they started developing a machine learning model capable of tracking this complex biological process. As the researchers reported recently in Molecular Systems Biology, their model could attach numerical scores to each cell in the course of its unique maturation – and this allowed them to define a novel regulatory checkpoint in this process.
The stem cells from which muscle tissue develops are created in the embryo, but a few of them are still present in adult muscles. These cells are dormant most of the time, but during growth, strenuous physical activity or injury they leap into action. At the first stage, the stem cells divide in order to increase their numbers. They then stop dividing and undergo what is known as differentiation – a part of the maturation process in which cells specialize in performing a unique function and acquire traits necessary to fulfill it. In the case of muscle tissue, the differentiating stem cells become elongated, begin to synthesize the protein fibers that give muscles their characteristic ability to contract and then migrate to wherever the tissue is regenerating. Once they arrive at their destination, they fuse together to form one long cell, known as muscle fiber. A collection of these cells is what makes up the entire muscle. Until now, however, scientists have had difficulty understanding how stem cells progress along this path of specialization and what causes them to move from one stage to another.
Seeking to address these questions, Giulia Zarfati and Adi Hazak from Avinoam’s lab documented in real time how muscle fibers develop from stem cells isolated from mice. They decided to focus on two changes: the movement of the cells and the manufacture of protein fibers inside them, which is essential for generating an adult muscle capable of contracting. To follow the movement of these cells, the researchers fluorescently labeled their nuclei and one of the protein components, called actin, that is essential for making fibers. Throughout a day-long differentiation process, the researchers created numerous videos documenting, down to the level of a single cell, the stages by which hundreds of stem cells become adult muscle cells and fuse into a new fiber.
“The two research groups had to learn each other’s language. Assaf’s team learned what a differentiated muscle cell is and my team had to study the basics of machine learning”
Having collected abundant biological data, the scientists teamed up with research student Amit Shakarchy from Zaritsky’s lab to build a model that would accurately represent this dynamic process. “The two research groups had to learn each other’s language,” Avinoam explains. “Assaf’s team learned what a differentiated muscle cell is and how we know when it has fused with other cells to form muscle fiber. My team had to study the basics of machine learning and how to analyze data collected from a sequence of observations at different times. Then we had to work out together how to translate the biological process into a computational model capable of following its progress.”
Building a computerized model that can monitor a dynamic biological process is a huge challenge. “First, we had to decide how to define the point in time at which a cell was differentiated,” Zaritsky explains. “After that, we had to choose whether and how to use this temporal information. We decided to incorporate it while training a supervised model that follows the movement of the cells and the intensity of the fluorescent light emitted by the actin fibers they contain. The model also examined derivatives of these data, such as changes in the cells’ motion speed and how the actin fibers’ structure changes over time.”
The video shows the unique path followed by several individual muscle cells on their way to fusing and becoming a new muscle fiber
The researchers discovered that, as the differentiation process progressed, the cells’ motility decreased, whereas the strength of the signal from their actin fibers increased. The machine learning model, trained to distinguish between stem cells and adult muscle cells, created a real-time quantitative index that gives a numerical score to each individual cell, based on how far along it has progressed in its differentiation. When the model was tested on experiments for which it had not been trained, the researchers found that most of the stem cells gradually scored higher during the differentiation process, reaching the highest mark when the process was completed. “The model showed us that differentiation is a gradual and decentralized process, so that the cells do not progress together in stages – rather, they follow different patterns of progress,” Avinoam says. “That was an unexpected finding, since we assumed that the cells would display collective behavior.”
“The ability to continuously follow cells transitioning in real time could help us in the future to monitor the progress of diseases in an unprecedented way. Today, for example, we examine cancerous growths by taking a biopsy, a sampling that is frozen in time and does not provide us with ongoing information about a dynamic biological process,” Zaritsky adds.
Stop before you fuse
Although the model suggested that different cells complete their maturation process at different times, it also found that from the moment of completion on, there is a consistent period of around three hours before they fuse together and become muscle fiber. This led the researchers to postulate that at a certain checkpoint, each cell makes sure that it has indeed finished differentiating, and only then sets the fusion process in motion.
Past studies had suggested that an enzyme called p38 regulates muscle development, but its precise role was unknown. To test whether the enzyme was the crucial component of the checkpoint step, the researchers inhibited its activity and found that, indeed, the cells got stuck: They did not fuse into a new muscle fiber.
When the researchers ran the computational model, they saw that the cells in which the enzyme had been blocked were given a numerical score that continued to rise. In other words, even in the absence of the enzyme, they successfully completed their differentiation process but did not continue to the fusion stage. The researchers concluded that the checkpoint comes at the end of the differentiation process but before the fusion stage. But why did the cells become stuck at this step in the absence of the enzyme?
The human back thigh muscle, biceps femoris, contains more than 37.5 million cell nuclei. It is made up of more than 250,000 muscle fibers, each of which contains an average of 150 cell nuclei after the differentiation and fusion processes.
The model suggested one possible explanation, showing that when the enzyme’s activity was inhibited, actin fibers became organized in a different manner during differentiation. When the researchers measured the level of protein expressed in inhibited cells, the findings confirmed the model’s prediction: The cells expressed a high level of the proteins that are responsible for organizing the actin fibers in the cytoskeleton – an important stage in the differentiation process and in readying the cells for fusion. At the same time, the cells had lower levels of the proteins that are needed for fusion, those that help create adult muscle fibers and allow the muscles to contract. “The cells get stuck in a stage of ‘ready-to-fuse,’” says Avinoam. “So, when the enzyme becomes active again, they can resume the fusion process. In fact, we believe this is the central checkpoint at which the muscle ensures that its cells have completed their preparation for fusing into a new muscle fiber. Beyond shedding new light on muscle development, this discovery shows that computerized models are capable of identifying important checkpoints in dynamic biological processes.”
High levels of defensive proteins offer protection against a hostile takeover by herpes viruses
“Let him who desires peace, prepare for war,” wrote the Roman author Vegetius in the 4th century CE. Our bodies, it seems, live by this dictum: Even in times of peace, some cells express high levels of defensive, antiviral proteins. A new Weizmann Institute of Science study reveals that the higher the routine levels of these proteins in a cell, the greater the chances of preventing a viral takeover.
When a virus enters a cell, it can gain control of the protein production mechanisms, forcing them to make multiple copies of itself. But infection might not lead to all-out war. While an active infection entails the virus killing the cell as it spreads its copies to other cells, at times a virus fails to take over the production mechanisms of the host cell, remaining latent within it, sometimes for decades. Herpes viruses, for example, are notorious for their ability to hide inside the body in a dormant state. What determines whether an active infection occurs, or the virus remains latent?
A team of researchers led by Dr. Michal Schwartz of Prof. Noam Stern-Ginossar’s lab in Weizmann’s Molecular Genetics Department addressed this question by focusing on human cytomegalovirus, a member of the herpes family that infects most of the population. Like other herpes viruses, cytomegalovirus awaits silently in the bodies of carriers, although it might cause an onset of symptomatic illness anytime later in life. The virus often raises its ugly head when a patient is immunosuppressed, following an organ transplant or chemotherapy. Pregnant women contracting the virus can pass it to the fetus, which sometimes suffers from serious illness as a result.
The scientists monitored the process of infection in two groups of immune cells – macrophages and their precursor cells – for 144 hours. At several points in time after infection, they sequenced RNA molecules from individual cells. Since RNA molecules carry the recipes for protein production, sequencing them revealed which proteins are produced, and in what quantities, at each stage of infection.
“As expected, shortly after infection the cells still only produced their own proteins,” says Schwartz. “However, a few hours later, the cells split into two groups. As some kept making their own proteins, others started assembling viral proteins, a step that initiates the multiplication of the viral genome and its spread throughout the body. We found this step to be irreversible: From the moment cells expressed just two initial viral proteins, we couldn’t stop the viral takeover.”
Searching for an explanation as to why the virus took over some cells but not others, the team examined the differences in proteins produced by each group of cells before and during infection. They discovered that the virus failed to take over cells that had already produced more antiviral defenses prior to infection. While the virus stayed as a latent guest within these cells, those with a lower routine production of defense proteins were open to a viral takeover.
“Latent viruses pose an existential threat to immunosuppressed patients and organ transplant recipients”
This local protein “shield,” produced not only by the attacked cell but throughout its environment, had long been recognized as the first line of defense against an ongoing viral infection. It was known to be generated in response to viral invasion, which prompts cells to secrete protein alerts called interferons. These warning signs, in turn, elicit antiviral protein production in nearby cells – a sort of code red to get ready for battle. Following the secretion of interferons, hundreds of genes for defense proteins are activated. The team’s finding showed that these defense proteins play a significant role even before the infection occurs and the warning signs are flagged.
The researchers believe that high levels of routine defense protein production might serve to immunize cells against a potential active infection. This idea suggests a possible solution to a previously unsolved mystery – why do cytomegaloviruses tend to accumulate in a latent state within bone marrow stem cells? Previous research by other scientists had found that stem cells routinely produce relatively high levels of defense proteins, compared to such mature immune cells as macrophages. These proteins’ newly discovered immunizing effect against active infection could explain why the viruses remain latent within the stem cells.
The scientists also discovered that mature macrophages, which had been thought to only play host to active infection, can harbor latent viral infection as well. This means that, contrary to the prevailing view, cells don’t fall into one of two categories – harboring either active or latent infection – but can be host to either, depending on their levels of defense protein production. In other words, various cell types in the body, formerly thought to be subject to active infection alone, might in fact form unknown reservoirs of latent, potentially harmful viruses. Discovering such reservoirs can lead to preventive treatments.
“Latent viruses pose an existential threat to immunosuppressed patients and organ transplant recipients,” says Stern-Ginossar. “A basic understanding of the mechanisms that determine whether an onset of illness occurs or the virus remains latent is crucial to developing effective treatments. If we find ways to activate or deactivate latent viruses on demand, it will allow us to better prepare patients prior to transplant or treatment. I am hopeful that the understanding of cellular self-defense mechanisms will find its way to effective solutions in the clinical field.”
How B-Cell Eaters Clean Their Plates
Parents tell their children to eat all the food on their plate, down to the last crumb. Certain cells within our lymph nodes, like obedient children, diligently follow this instruction. Although these cells – a subtype of macrophages, or “big eaters” – were first described in 1884 by German biologist Walther Flemming, their origin and mode of operation had until now remained a mystery. In a study published in the Journal of Experimental Medicine, a team of researchers headed by Prof. Ziv Shulman of the Weizmann Institute of Science has made discoveries that largely demystify the tingible body macrophages (TBMs). These tingible (i.e., stainable) cells turn out to eat every last morsel of another type of immune cell, to help protect our bodies from harm.
The cells bound for the dinner plate are the antibody-producing B cells, which reside in lymph nodes in readiness for invasion by pathogens such as viruses or bacteria. When an invasion occurs, they become active, divide rapidly and enter transient structures called germinal centers. These centers, situated in designated niches within lymph nodes, are “training camps” in which the B cells hone their defenses against a particular enemy. The B cells undergo an accelerated evolution of sorts, experiencing random mutations a million times faster than normal cells, a process that increases the binding capacity of the antibodies they produce. On rare occasions, however, other B cells may evolve to produce autoantibodies that target and harm the body’s own healthy tissues instead of pathogens.
By the end of the “training program,” cells that have undergone beneficial mutations survive for the most part, whereas those bearing ineffective or even harmful mutations commit “suicide” through a mechanism of programmed cell death. All these dead B cells, though inactive, can still give rise to harmful antibodies. How is this prevented?
That’s where the “big eaters” come into play. In the new study the team, led by research student Neta Gurwicz of Weizmann’s Systems Immunology Department, used genetically engineered mice to uncover the TBMs’ eating patterns and diet. Genes for two different fluorescent proteins were used to mark the “big eaters” in shiny green and the B cells in their training camps in bright red. As expected, a week after the mice were vaccinated so as to activate the B cells, training camp sites opened within lymph nodes, and B cells began to multiply, mutate and undergo selection. Through microsurgery, the scientists exposed lymph nodes in the mice’s knees and then attached an advanced microscope with a resolution of one millionth of a meter that enabled them to observe biological processes inside a living body.
“If we figure out how to make TBMs more effective at cleaning up the ‘training camps,’ we may have the key to the treatment of currently incurable diseases”
During this real-time broadcast, the team watched B cells moving constantly inside the training camp, while the “big eaters” stayed put in the vicinity, occasionally reaching out with octopus-like arms to grab dying B cells and engulf them. The TBMs did so at a fairly rapid rate: Each TBM captured a B cell around once every 10 minutes. Using a computer model, the scientists predicted that cleaning a single training camp of all its dying cells would require about 30 TBMs. In the live broadcast, an average of 25 TBMs were observed in each camp, indicating that the cleaning mechanism is indeed effective and thorough.
Lymph node recycle bins
Next, the researchers asked whether TBMs are choosy. Do they digest any B cell passing by, or do they prefer to snack on those within the training camps? The team discovered that when exposed to inactive B cells, TBMs did not “swallow the bait,” focusing solely on the mutating B cells.
Still, one question remained – where do TBMs come from?
To solve that riddle, the scientists replaced the mice’s immune system by first irradiating them, then introducing into their bone marrow progenitor blood cells carrying genes to color the future TBMs green. When training camps emerged in the lymph nodes in response to the vaccination, 75 percent of the nearby TBMs were green, revealing that their origin is indeed in the bone marrow. But the green cells only appeared around those training camps a few weeks after vaccination, raising the possibility that their journey included a stopover.
Cell feast streamed live: TBMs (green) swallow dying B cells (red) inside the lymph node “training camps”
The team repeated the experiment, this time shielding lymph nodes during the irradiation so that only the immune cells within these nodes would survive, while the others were eradicated. Unlike in the previous experiment, most of the TBMs lining up for the feast were not green; they developed from cells that were already in lymph nodes prior to vaccination. The researchers concluded that the TBMs develop from progenitor cells emerging from the bone marrow, but rather than stopping off, they go straight to lymph nodes and wait there for a while.
The scientists also discovered what causes progenitor cells to leave the bone marrow and enter lymph nodes. Five days after vaccination, when small concentrations of mutating B cells appeared in the training camps, substantial quantities of TBMs first emerged nearby. That suggested to the researchers that the timing of TBM arrival is a function of B cell training, and that the TBMs serve the particular purpose of cleaning up after what is a highly effective, but somewhat wasteful, immune system campaign.
Finally, the scientists asked when during the process that ends in their suicide the B cells are digested by TBMs. Surprisingly, they observed B cells being engulfed alive, undergoing their final last gasps inside the TBMs. This shows that the “big eaters” are not only “cleaning workers,” as previously thought, they also constitute a biological “recycle bin” that removes dying cells before they start breaking down, preventing harmful waste from scattering in the first place.
“Impaired TBM cleaning might cause the production of autoantibodies that would be aimed at the dead B cells but actually harm healthy tissues,” says Shulman. “This might be one of the causes for autoimmune diseases such as lupus. Basic understanding of the origin of TBMs and their modes of action could help pave the way for autoimmune disease treatments. If we figure out how to make TBMs more effective at cleaning up the ‘training camps,’ we may have the key to the treatment of currently incurable diseases.”
The following researchers also participated in the study: Dr. Liat Stoler-Barak of Weizmann’s Systems Immunology Department; and Niklas Schwan, Dr. Arnab Bandyopadhyay and Prof. Michael Meyer-Hermann of Braunschweig Integrated Centre of Systems Biology, Germany.