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Plugging the leaks
SAN DIEGO—Organoids, miniature 3D versions of organs grown in dishes, have been a significant boon for industry research. Being able to recreate mini organs offers the ability to study how organs respond to drugs or inflammation, or how diseases progress and impact organs. Liver organoids have been a particular boon, as they have enabled toxicity testing on human organs without endangering patients.
And now, a research team from the University of California, San Diego (UC San Diego) School of Medicine has developed an organoid model of a close neighbor of the liver: the human gut. The team was able to use the organ-in-a-dish model to mimic leaky gut and possibly highlight a potential treatment using a repurposed drug. The work in question was published in Life Science Alliance under the title “The stress polarity signaling (SPS) pathway serves as a marker and a target in the leaky gut barrier: implications in aging and cancer.”
This work builds on previous research by Drs. Pradipta Ghosh, Soumita Das and colleagues, in which they reported their findings on a molecular mechanism known as the stress-polarity signaling pathway. This mechanism helps to maintain gut lining junctions, and when the pathway is under stress, those junctions weaken and loosen. The team had also found that metformin, an approved diabetes drug, could activate the stress-polarity signaling pathway and help tighten the gut lining junctions, but those results had only been seen in vitro.
Ghosh, professor of cellular and molecular medicine at UC San Diego School of Medicine and the Moores Cancer Center, was first author on this latest study, and Das, associate professor of pathology at UC San Diego School of Medicine, was senior author.
“The intestinal barrier is the largest mucosal surface that separates diverse stressors (trillions of microbes, toxins, and food antigens) on one side from the largest immune system on the other,” the authors explained in the Life Science Alliance paper. “A compromised gut barrier allows microbes and unwanted antigens to cross the epithelium and generate inflammation (systemic endotoxemia), which may contribute to a variety of diseases, ranging from metabolic syndrome and chronic organ dysfunctions to neurodegenerative diseases and cancers.
“The primary factor preventing the free access of stressors to our immune cells is a single layer of polarized intestinal epithelial cells strung together in solidarity by cell-cell junctions. Loss of cell polarity and junctions not only impairs organ development and function but can also serve as one of the first triggers for oncogenesis (Martin-Belmonte & Perez-Moreno, 2012). Establishment, maintenance (at baseline), and augmentation (upon stress) of epithelial barriers are achieved by signaling pathways that regulate polarization of epithelial cells.”
To test these results in a more realistic model, the research team used stem cells taken from patients’ intestines to develop 3D gut organoids. According to a UCSD press release by Dr. Heather Buschman, the cells came from so-called “crypts” in the lining of the gut, and when grown in the lab, differentiated into the four different types of cells that comprise the gut. As they grew, the cells rolled up into balls to form crypts and then miniature guts.
Ghosh, Das and colleagues recreated a leaky gut by unrolling the mini-gut organoids to expose the intestinal lining and then applying different types of bacteria to stress the gut lining junctions. In addition to the junctions weakening when stressed, they also found that the stress-polarity signaling pathway becomes damaged both with age and with the development of colorectal cancer. Increased inflammation biomarkers were also noted, according to Buschman's release.
However, the researchers also confirmed metformin as a potential answer to this damage. Metformin activates the AMPK enzyme, which plays a role in the stress-polarity signaling pathway, and when administered to the mini-guts, the gut lining tightened back up. The team was able to confirm the results by measuring the levels of occludin, which are high when the pathway is functioning properly; metformin resulted in a fivefold to sixfold increase in occludin levels in the mini-guts when compared to untreated cells.
The authors noted in their paper that since the stress-polarity signaling pathway “is silenced early during [colorectal cancer] initiation, these findings suggest that activation of the SPS-pathway may serve as a strategy to prevent polyp-to-cancer progression in the colon.” They added that their results also suggest this pathway could impact other diseases such as “chronic gastrointestinal inflammation, Alzheimer’s, Parkinson’s, multiple sclerosis, autism, chronic heart failure, and obesity and metabolic diseases. All these diseases are characterized by systemic inflammation due to chronic endotoxemia that might be triggered by the translocation of endotoxins from the gut lumen into the host circulation.”
“I think you’d be hard-pressed to find a disease in which systemic inflammation is not a driver,” Das stated in a press release. “That’s why, even though there are so many things we still don’t know, we’re excited about the broad potential this model and these findings open for developing personalized leaky gut therapeutics that target AMPK and the stress-polarity signaling pathway.”
Moving forward, Das and the rest of the research team intend to further explore diseases whose pathology is impacted by leaky gut, as well as looking into other methods of tightening gut lining junctions to evaluate if such an approach can be used to prevent progression of such conditions.