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Could A Gut-Brain Connection Help Explain Autism?

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What is Your Big Idea?
Diego Bohórquez/Credit: Duke University, Durham, NC

You might think nutrient-sensing cells in the human gastrointestinal (GI) tract would have no connection whatsoever to autism spectrum disorder (ASD). But if Diego Bohórquez’s “big idea” is correct, these GI cells, called neuropods, could one day help to provide a direct link into understanding and treating some aspects of autism and other brain disorders.

Bohórquez, a researcher at Duke University, Durham, NC, recently discovered that cells in the intestine, previously known for their hormone-releasing ability, form extensions similar to neurons. He also found that those extensions connect to nerve fibers in the gut, which relay signals to the vagus nerve and onward to the brain. In fact, he found that those signals reach the brain in milliseconds [1].

Bohórquez has dedicated his lab to studying this direct, high-speed hookup between gut and brain and its impact on nutrient sensing, eating, and other essential behaviors. Now, with support from a 2019 NIH Director’s New Innovator Award, he will also explore the potential for treating autism and other brain disorders with drugs that act on the gut.

Bohórquez became interested in autism and its possible link to the gut-brain connection after a chance encounter with Geraldine Dawson, director of the Duke Center for Autism and Brain Development. Dawson mentioned that autism typically affects multiple organ systems.

With further reading, he discovered that kids with autism frequently cope with GI issues, including bowel inflammation, abdominal pain, constipation, and/or diarrhea [2]. They often also show unusual food-related behaviors, such as being extremely picky eaters. But his curiosity was especially piqued by evidence that certain gut microbes can influence abnormal behaviors in mice that model autism.

With his New Innovator Award, Bohórquez will study neuropods and the gut-brain connection in a mouse model of autism. Using the tools of optogenetics, which make it possible to activate cells with light, he’ll also see whether autism-like symptoms in mice can be altered or alleviated by controlling neuropods in the gut. Those symptoms include anxiety, repetitive behaviors, and lack of interest in interacting with other mice. He’ll also explore changes in the animals’ eating habits.

In another line of study, he will take advantage of intestinal tissue samples collected from people with autism. He’ll use those tissues to grow and then examine miniature intestinal “organoids,” looking for possible evidence that those from people with autism are different from others.

For the millions of people now living with autism, no truly effective drug therapies are available to help to manage the condition and its many behavioral and bodily symptoms. Bohórquez hopes one day to change that with drugs that act safely on the gut. In the meantime, he and his fellow “GASTRONAUTS” look forward to making some important and fascinating discoveries in the relatively uncharted territory where the gut meets the brain.

References:

[1] A gut-brain neural circuit for nutrient sensory transduction. Kaelberer MM, Buchanan KL, Klein ME, Barth BB, Montoya MM, Shen X, Bohórquez DV. Science. 2018 Sep 21;361(6408).

[2] Association of maternal report of infant and toddler gastrointestinal symptoms with autism: evidence from a prospective birth cohort. Bresnahan M, Hornig M, Schultz AF, Gunnes N, Hirtz D, Lie KK, Magnus P, Reichborn-Kjennerud T, Roth C, Schjølberg S, Stoltenberg C, Surén P, Susser E, Lipkin WI. JAMA Psychiatry. 2015 May;72(5):466-474.

Links:

Autism Spectrum Disorder (National Institute of Mental Health/NIH)

Bohórquez Lab (Duke University, Durham, NC)

Bohórquez Project Information (NIH RePORTER)

NIH Director’s New Innovator Award (Common Fund)

NIH Support: Common Fund; National Institute of Mental Health


Can Organoids Yield Answers to Fatty Liver Disease?

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Liver Organoid
Confocal microscope image shows liver organoid made from iPS cells derived from children with Wolman disease. The hepatocyte cells (red) accumulate fat (blue). Credit: Cincinnati Children’s Hospital Medical Center

With advances in induced pluripotent stem cell (iPSC) technology, it’s now possible to reprogram adult skin or blood cells to form miniature human organs in a lab dish. While these “organoids” closely mimic the structures of the liver and other vital organs, it’s been tough to get them to represent inflammation, fibrosis, fat accumulation, and many other complex features of disease.

Fatty liver diseases are an increasingly serious health problem. So, I’m pleased to report that, for the first time, researchers have found a reliable way to make organoids that display the hallmarks of those conditions. This “liver in a dish” model will enable the identification and preclinical testing of promising drug targets, helping to accelerate discovery and development of effective new treatments.

Previous methods working with stem cells have yielded liver organoids consisting primarily of epithelial cells, or hepatocytes, which comprise most of the organ. Missing were other key cell types involved in the inflammatory response to fatty liver diseases.

To create a better organoid, the team led by Takanori Takebe, Cincinnati Children’s Hospital Medical Center, focused its effort on patient-derived iPSCs. Takebe and his colleagues devised a special biochemical “recipe” that allowed them to grow liver organoids with sufficient cellular complexity.

As published in Cell Metabolism, the recipe involves a three-step process to coax human iPSCs into forming multi-cellular liver organoids in as little as three weeks. With careful analysis, including of RNA sequencing data, they confirmed that those organoids contained hepatocytes and other supportive cell types. The latter included Kupffer cells, which play a role in inflammation, and stellate cells, the major cell type involved in fibrosis. Fibrosis is the scarring of the liver in response to tissue damage.

Now with a way to make multi-cellular liver organoids, the researchers put them to the test. When exposed to free fatty acids, the organoids gradually accumulated fat in a dose-dependent manner and grew inflamed, which is similar to what happens to people with fatty liver diseases.

The organoids also showed telltale biochemical signatures of fibrosis. Using a sophisticated imaging method called atomic force microscopy (AFM), the researchers found as the fibrosis worsened, they could measure a corresponding increase in an organoid’s stiffness.

Next, as highlighted in the confocal microscope image above, Takebe’s team produced organoids from iPSCs derived from children with a deadly inherited form of fatty liver disease known as Wolman disease. Babies born with this condition lack an enzyme called lysosomal acid lipase (LAL) that breaks down fats, causing them to accumulate dangerously in the liver. Similarly, the miniature liver shown here is loaded with accumulated fat lipids (blue).

That brought researchers to the next big test. Previous studies had shown that LAL deficiency in kids with Wolman disease overactivates another signaling pathway, which could be suppressed by targeting a receptor known as FXR. So, in the new study, the team applied an FXR-targeted compound called FGF19, and it prevented fat accumulation in the liver organoids derived from people with Wolman disease. The organoids treated with FGF19 not only were protected from accumulating fat, but they also survived longer and had reduced stiffening, indicating a reduction in fibrosis.

These findings suggest that FGF19 or perhaps another compound that acts similarly might hold promise for infants with Wolman disease, who often die at a very early age. That’s encouraging news because the only treatment currently available is a costly enzyme replacement therapy. The findings also demonstrate a promising approach to accelerating the search for new treatments for a variety of liver diseases.

Takebe’s team is now investigating this approach for non-alcoholic steatohepatitis (NASH), a common cause of liver failure and the need for a liver transplant. The hope is that studies in organoids will lead to promising new treatments for this liver condition, which affects millions of people around the world.

Ultimately, Takebe suggests it might prove useful to grow liver organoids from individual patients with fatty liver diseases, in order to identify the underlying biological causes and test the response of those patient-specific organoids to available treatments. Such evidence could one day help doctors to select the best available treatment option for each individual patient, and bring greater precision to treating liver disease.

Reference:

[1] Modeling steatohepatitis in humans with pluripotent stem cell-derived organoids. Ouchi R, Togo S, Kimura M, Shinozawa T, Koido M, Koike H, Thompson W, Karns RA, Mayhew CN, McGrath PS, McCauley HA, Zhang RR, Lewis K, Hakozaki S, Ferguson A, Saiki N, Yoneyama Y, Takeuchi I, Mabuchi Y, Akazawa C, Yoshikawa HY, Wells JM, Takebe T. Cell Metab. 2019 May 14. pii: S1550-4131(19)30247-5.

Links:

Wolman Disease (Genetic and Rare Diseases Information Center/NIH)

Nonalcoholic Fatty Liver Disease & NASH (National Institute of Diabetes and Digestive and Kidney Diseases/NIH)

Stem Cell Information (NIH)

Tissue Chip for Drug Screening (National Center for Advancing Translational Sciences/NIH)

Takebe Lab (Cincinnati Children’s Hospital Medical Center)

NIH Support: National Institute of Diabetes and Digestive and Kidney Diseases


Studying Color Vision in a Dish

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Credit: Eldred et al., Science

Researchers can now grow miniature versions of the human retina—the light-sensitive tissue at the back of the eye—right in a lab dish. While most “retina-in-a-dish” research is focused on finding cures for potentially blinding diseases, these organoids are also providing new insights into color vision.

Our ability to view the world in all of its rich and varied colors starts with the retina’s light-absorbing cone cells. In this image of a retinal organoid, you see cone cells (blue and green). Those labelled with blue produce a visual pigment that allows us to see the color blue, while those labelled green make visual pigments that let us see green or red. The cells that are labeled with red show the highly sensitive rod cells, which aren’t involved in color vision, but are very important for detecting motion and seeing at night.


Study Shows Genes Unique to Humans Tied to Bigger Brains

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cortical organoid

Caption: Cortical organoid, showing radial glial stem cells (green) and cortical neurons (red).
Credit: Sofie Salama, University of California, Santa Cruz

In seeking the biological answer to the question of what it means to be human, the brain’s cerebral cortex is a good place to start. This densely folded, outer layer of grey matter, which is vastly larger in Homo sapiens than in other primates, plays an essential role in human consciousness, language, and reasoning.

Now, an NIH-funded team has pinpointed a key set of genes—found only in humans—that may help explain why our species possesses such a large cerebral cortex. Experimental evidence shows these genes prolong the development of stem cells that generate neurons in the cerebral cortex, which in turn enables the human brain to produce more mature cortical neurons and, thus, build a bigger cerebral cortex than our fellow primates.

That sounds like a great advantage for humans! But there’s a downside. Researchers found the same genomic changes that facilitated the expansion of the human cortex may also render our species more susceptible to certain rare neurodevelopmental disorders.


Snapshots of Life: Growing Mini-Brains in a Dish

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Brain grown in a lab dish

Credit: Collin Edington and Iris Lee, Department of Biomedical Engineering, MIT

Something pretty incredible happens—both visually and scientifically—when researchers spread neural stem cells onto a gel-like matrix in a lab dish and wait to see what happens. Gradually, the cells differentiate and self-assemble to form cohesive organoids that resemble miniature brains!

In this image of a mini-brain organoid, the center consists of a clump of neuronal bodies (magenta), surrounded by an intricate network of branching extensions (green) through which these cells relay information. Scattered throughout the mini-brain are star-shaped astrocytes (red) that serve as support cells.


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