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New gene delivery vehicle shows promise for human brain gene therapy

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New gene delivery vehicle shows promise for human brain gene therapy


In an important step toward more effective gene therapies for brain diseases, researchers from the Broad Institute of MIT and Harvard have engineered a gene-delivery vehicle that uses a human protein to efficiently cross the blood-brain barrier and deliver a disease-relevant gene to the brain in mice expressing the human protein. Because the vehicle binds to a well-studied protein in the blood-brain barrier, the scientists say it has a good chance at working in patients.

Gene therapy could potentially treat a range of severe genetic brain disorders, which currently have no cures and few treatment options. But FDA-approved forms of the most commonly used vehicle for packaging and delivering these therapies to target cells, adeno-associated viruses (AAVs), aren’t able to efficiently cross the blood-brain barrier at high levels and deliver therapeutic cargo. The enormous challenge of getting therapies past this barrier — a highly selective membrane separating the blood from the brain — has stymied the development of safer and more effective gene therapies for brain diseases for decades.

Now researchers in the lab of Ben Deverman, an institute scientist and senior director of vector engineering at the Broad, have engineered the first published AAV that targets a human protein to reach the brain in humanized mice. The AAV binds to the human transferrin receptor, which is highly expressed in the blood-brain barrier in humans. In a new study published in Science, the team showed that their AAV, when injected into the bloodstream in mice expressing a humanized transferrin receptor, crossed into the brain at much higher levels than the AAV that is used in an FDA-approved gene therapy for the central nervous system, AAV9. It also reached a large fraction of important types of brain cells, including neurons and astrocytes. The researchers then showed that their AAV could deliver copies of the GBA1 gene, which has been linked to Gaucher’s disease, Lewy body dementia, and Parkinson’s disease, to a large fraction of cells throughout the brain.

The scientists add that their new AAV could be a better option for treating neurodevelopmental disorders caused by mutations in a single gene such as Rett syndrome or SHANK3 deficiency; lysosomal storage diseases like GBA1deficiency; and neurodegenerative diseases such as Huntington’s disease, prion disease, Friedreich’s ataxia, and single-gene forms of ALS and Parkinson’s disease.

“Since we came to the Broad we’ve been focused on the mission of enabling gene therapies for the central nervous system,” said Deverman, senior author on the study. “If this AAV does what we think it will in humans based on our mouse studies, it will be so much more effective than current options.”

“These AAVs have the potential to change a lot of patients’ lives,” said Ken Chan, a co-first author on the paper and group leader from Deverman’s group who has been working on solving gene delivery to the central nervous system for nearly a decade.

Mechanism first

For years, researchers developed AAVs for specific applications by preparing massive AAV libraries and testing them in animals to identify top candidates. But even when this approach succeeds, the candidates often don’t work in other species, and the approach doesn’t provide information about how the AAVs reach their targets. This can make it difficult to translate a gene therapy using these AAVs from animals to humans.

To find a delivery vehicle with a greater chance of reaching the brain in people, Deverman’s team switched to a different approach. They used a method they published last year, which involves screening a library of AAVs in a test tube for ones that bind to a specific human protein. Then they test the most promising candidates in cells and mice that have been modified to express the protein.

As their target, the researchers chose human transferrin receptor, which has long been the target of antibody-based therapies that aim to reach the brain. Several of these therapies have shown evidence of reaching the brain in humans.

The team’s screening technique identified an AAV called BI-hTFR1 that binds human transferrin receptor, enters human brain cells, and bypasses a human cell model of the blood-brain barrier.

“We’ve learned a lot from in vivo screens but it has been tough finding AAVs that worked this well across species,” added Qin Huang, a co-first author on the study and a senior research scientist in Deverman’s lab who helped develop the screening method to find AAVs that bind specific protein targets. “Finding one that works using a human receptor is a big step forward.”

Beyond the dish

To test the AAVs in animals, the researchers used mice in which the mouse gene that encodes the transferrin receptor was replaced with its human equivalent. The team injected the AAVs into the bloodstream of adult mice and found dramatically higher levels of the AAVs in the brain and spinal cord compared to mice without the human transferrin receptor gene, indicating that the receptor was actively ferrying the AAVs across the blood-brain barrier.

The AAVs also showed 40-50 times higher accumulation in brain tissue than AAV9, which is part of an FDA-approved therapy for spinal muscular atrophy in infants but is relatively inefficient at delivering cargo to the adult brain. The new AAVs reached up to 71 percent of neurons and 92 percent of astrocytes in different regions of the brain.

In work led by research scientist Jason Wu, Deverman’s team also used the AAVs to deliver healthy copies of the human GBA1 gene, which is mutated in several neurological conditions. The new AAVs delivered 30 times more copies of the GBA1 gene than AAV9 in mice and were delivered throughout the brain.

The team said that the new AAVs are ideal for gene therapy because they target a human protein and have similar production and purification yields as AAV9 using scalable manufacturing methods. A biotech company co-founded by Deverman, Apertura Gene Therapy, is already developing new therapies using the AAVs to target the central nervous system.

With more development, the scientists think it’s possible to improve the gene-delivery efficiency of their AAVs to the central nervous system, decrease their accumulation in the liver, and avoid inactivation by antibodies in some patients.

Sonia Vallabh and Eric Minikel, two researchers at the Broad who are developing treatments for prion disease, are excited by the potential of the AAVs to deliver brain therapies in humans.

“When we think about gene therapy for a whole-brain disease like prion disease, you need really systemic delivery and broad biodistribution in order to achieve anything,” said Minikel. “Naturally occurring AAVs just aren’t going to get you anywhere. This engineered capsid opens up a world of possibilities.”



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Prying open the AI black box

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Prying open the AI black box


Artificial intelligence continues to squirm its way into many aspects of our lives. But what about biology, the study of life itself? AI can sift through hundreds of thousands of genome data points to identify potential new therapeutic targets. While these genomic insights may appear helpful, scientists aren’t sure how today’s AI models come to their conclusions in the first place. Now, a new system named SQUID arrives on the scene armed to pry open AI’s black box of murky internal logic.

SQUID, short for Surrogate Quantitative Interpretability for Deepnets, is a computational tool created by Cold Spring Harbor Laboratory (CSHL) scientists. It’s designed to help interpret how AI models analyze the genome. Compared with other analysis tools, SQUID is more consistent, reduces background noise, and can lead to more accurate predictions about the effects of genetic mutations.

How does it work so much better? The key, CSHL Assistant Professor Peter Koo says, lies in SQUID’s specialized training.

“The tools that people use to try to understand these models have been largely coming from other fields like computer vision or natural language processing. While they can be useful, they’re not optimal for genomics. What we did with SQUID was leverage decades of quantitative genetics knowledge to help us understand what these deep neural networks are learning,” explains Koo.

SQUID works by first generating a library of over 100,000 variant DNA sequences. It then analyzes the library of mutations and their effects using a program called MAVE-NN (Multiplex Assays of Variant Effects Neural Network). This tool allows scientists to perform thousands of virtual experiments simultaneously. In effect, they can “fish out” the algorithms behind a given AI’s most accurate predictions. Their computational “catch” could set the stage for experiments that are more grounded in reality.

“In silico [virtual] experiments are no replacement for actual laboratory experiments. Nevertheless, they can be very informative. They can help scientists form hypotheses for how a particular region of the genome works or how a mutation might have a clinically relevant effect,” explains CSHL Associate Professor Justin Kinney, a co-author of the study.

There are tons of AI models in the sea. More enter the waters each day. Koo, Kinney, and colleagues hope that SQUID will help scientists grab hold of those that best meet their specialized needs.

Though mapped, the human genome remains an incredibly challenging terrain. SQUID could help biologists navigate the field more effectively, bringing them closer to their findings’ true medical implications.



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Iron meteorites hint that our infant solar system was more doughnut than dartboard

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Iron meteorites hint that our infant solar system was more doughnut than dartboard


Four and a half billion years ago, our solar system was a cloud of gas and dust swirling around the sun, until gas began to condense and accrete along with dust to form asteroids and planets. What did this cosmic nursery, known as a protoplanetary disk, look like, and how was it structured? Astronomers can use telescopes to “see” protoplanetary disks far away from our much more mature solar system, but it is impossible to observe what ours might have looked like in its infancy — only an alien billions of light years away would be able to see it as it once was.

Fortunately, space has dropped a few clues — fragments of objects that formed early in solar system history and plunged through Earth’s atmosphere, called meteorites. The composition of meteorites tells stories of the solar system’s birth, but these stories often raise more questions than answers.

In a paper published in Proceedings of the National Academy of Sciences, a team of planetary scientists from UCLA and Johns Hopkins University Applied Physics Laboratory reports that refractory metals, which condense at high temperatures, such as iridium and platinum, were more abundant in meteorites formed in the outer disk, which was cold and far away from the sun. These metals should have formed close to the sun, where the temperature was much higher. Was there a pathway that moved these metals from the inner disk to the outer?

Most meteorites formed within the first few million years of solar system history. Some meteorites, called chondrites, are unmelted conglomerations of grains and dust left over from planet formation. Other meteorites experienced enough heat to melt while their parent asteroids were forming. When these asteroids melted, the silicate part and the metallic part separated due to their difference in density, similar to how water and oil don’t mix.

Today, most asteroids are located in a thick belt between Mars and Jupiter. Scientists think that Jupiter’s gravity disrupted the course of these asteroids, causing many of them to smash into each other and break apart. When pieces of these asteroids fall to Earth and are recovered, they are called meteorites.

Iron meteorites are from the metallic cores of the earliest asteroids, older than any other rocks or celestial objects in our solar system. The irons contain molybdenum isotopes that point toward many different locations across the protoplanetary disk in which these meteorites formed. That allows scientists to learn what the chemical composition of the disk was like in its infancy.

Previous research using the Atacama Large Millimeter/submillimeter Array in Chile has found many disks around other stars that resemble concentric rings, like a dartboard. The rings of these planetary disks, such as HL Tau, are separated by physical gaps, so this kind of disk could not provide a route to transport these refractory metals from the inner disk to the outer.

The new paper holds that our solar disk likely didn’t have a ring structure at the very beginning. Instead, our planetary disk looked more like a doughnut, and asteroids with metal grains rich in iridium and platinum metals migrated to the outer disk as it rapidly expanded.

But that confronted the researchers with another puzzle. After the disk expansion, gravity should have pulled these metals back into the sun. But that did not happen.

“Once Jupiter formed, it very likely opened a physical gap that trapped the iridium and platinum metals in the outer disk and prevented them from falling into the sun,” said first author Bidong Zhang, a UCLA planetary scientist. “These metals were later incorporated into asteroids that formed in the outer disk. This explains why meteorites formed in the outer disk — carbonaceous chondrites and carbonaceous-type iron meteorites — have much higher iridium and platinum contents than their inner-disk peers.”

Zhang and his collaborators previously used iron meteorites to reconstruct how water was distributed in the protoplanetary disk.

“Iron meteorites are hidden gems. The more we learn about iron meteorites, the more they unravel the mystery of our solar system’s birth,” Zhang said.



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Supermassive black hole appears to grow like a baby star

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Supermassive black hole appears to grow like a baby star


Supermassive black holes pose unanswered questions for astronomers around the world, not least “How do they grow so big?” Now, an international team of astronomers, including researchers from Chalmers University of Technology in Sweden, has discovered a powerful rotating, magnetic wind that they believe is helping a galaxy’s central supermassive black hole to grow. The swirling wind, revealed with the help of the ALMA telescope in nearby galaxy ESO320-G030, suggests that similar processes are involved both in black hole growth and the birth of stars.

Most galaxies, including our own Milky Way have a supermassive black hole at their centre. How these mind-bogglingly massive objects grow to weigh as much as millions or billions of stars is a long-standing question for astronomers.

In search of clues to this mystery, a team of scientists led by Mark Gorski (Northwestern University and Chalmers) and Susanne Aalto (Chalmers) chose to study the relatively nearby galaxy ESO320-G030, only 120 million light years distant. It’s a very active galaxy, forming stars ten times as fast as in our own galaxy.

“Since this galaxy is very luminous in the infrared, telescopes can resolve striking details in its centre. We wanted to measure light from molecules carried by winds from the galaxy’s core, hoping to trace how the winds are launched by a growing, or soon to be growing, supermassive black hole. By using ALMA, we were able to study light from behind thick layers of dust and gas,” says Susanne Aalto, Professor of Radio Astronomy at Chalmers University of Technology.

To zero in on dense gas from as close as possible to the central black hole, the scientists studied light from molecules of hydrogen cyanide (HCN). Thanks to ALMA’s ability to image fine details and trace movements in the gas — using the Doppler effect — they discovered patterns that suggest the presence of a magnetised, rotating wind.

While other winds and jets in the centre of galaxies push material away from the supermassive black hole, the newly discovered wind adds another process, that can instead feed the black hole and help it grow.

“We can see how the winds form a spiralling structure, billowing out from the galaxy’s centre. When we measured the rotation, mass, and velocity of the material flowing outwards, we were surprised to find that we could rule out many explanations for the power of the wind, star formation for example. Instead, the flow outwards may be powered by the inflow of gas and seems to be held together by magnetic fields,” says Susanne Aalto.

The scientists think that the rotating magnetic wind helps the black hole to grow.

Material travels around the black hole before it can fall in — like water around a drain. Matter that approaches the black hole collects in a chaotic, spinning disk. There, magnetic fields develop and get stronger. The magnetic fields help lift matter away from the galaxy, creating the spiralling wind. Losing matter to this wind also slows the spinning disk — that means that matter can flow more easily into the black hole, turning a trickle into a stream.

For Mark Gorski, the way this happens is strikingly reminiscent of a much smaller-scale environment in space: the swirls of gas and dust that lead up to the birth of new stars and planets.

“It is well-established that stars in the first stages of their evolution grow with the help of rotating winds — accelerated by magnetic fields, just like the wind in this galaxy. Our observations show that supermassive black holes and tiny stars can grow by similar processes, but on very different scales,” says Mark Gorski.

Could this discovery be a clue to solving the mystery of how supermassive black holes grow? In the future, Mark Gorski, Susanne Aalto and their colleagues want to study other galaxies which may harbour hidden spiralling outflows in their centres.

“Far from all questions about this process are answered. In our observations we see clear evidence of a rotating wind that helps regulate the growth of the galaxy’s central black hole. Now that we know what to look for, the next step is to find out how common a phenomenon this is. And if this is a stage which all galaxies with supermassive black holes go through, what happens to them next?,” asks Mark Gorski.



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