New insights into the processing of hormones in the human gut

The human gut is the largest mammalian organ to produce hormones. In response to food, the hormone-producing cells in this organ secrete dozens of peptides. Now, researchers from the Organoid group (Hubrecht Institute) and the group of Wei Wu (Utrecht University) have defined the broad spectrum of these peptides and the way they are processed. These data will help characterize potentially new hormones that the gut produces to control key aspects of human physiology, including appetite and bowel movement. The results were published in PNAS on 7 November 2022.

The intestine is the largest organ in the human body to produce hormones. So-called enteroendocrine cells (EECs) are responsible for secreting these hormones. While EECs only comprise 1% of the surface of the intestine, they secrete dozens of peptides in response to food intake. These hormones regulate important physiological responses, including appetite, bowel movement and insulin secretion.

Hormone processing

EECs produce large proteins termed prohormones, from which small peptides that are bioactive are cleaved. The precise role of the enzymes (i.e. proteases) involved in this process, is not understood. Notably, mutations in these enzymes can cause endocrine diseases that result from the lack of some functional hormones. Researchers from the Organoid group teamed up with the group of Wei Wu at Utrecht University to study the role of these enzymes in gut hormone processing and identify potentially novel gut hormones.

Organoids as model system

EECs are rare in human tissue and have therefore been difficult to study. The researchers made use of human intestinal organoids to greatly enrich the number of EECs, allowing them to study these in greater detail. EECs in human organoids resemble their tissue counterparts, and are therefore a great model to study how they function. Moreover, EEC’s in the human gut are in a different state depending on their precise anatomical location. For example, an EEC is in a different state in the crypts than in the villi. In the organoid models, the team was able to reproduce these different states of the EEC’s.

Hormone factories

The researchers turned the organoids into large hormone factories. At will, they were able to induce secretion of hormones and collect them to allow characterization (Figure 1). Joep Beumer explains: ‘’In tissues of humans or animals it is difficult to detect the hormones due to their low abundance. You will never be sure if what you measure is derived from EECs. The massive amounts of hormones that we obtain in organoids make it possible to almost entirely bypass this problem.”

Mutating hormone proteases

Next, the team employed CRISPR-Cas9 to delete the enzymes, or proteases, that could be involved in hormone processing, and that are found to be mutated in endocrine diseases (Figure 2). With an advanced technique (mass spectrometry-based peptidomics), they characterized the peptide hormones produced by healthy EECs and the ones produced by EECs with mutations in the processing enzymes. ‘’This technique allows us to accurately map what kind of hormones healthy and mutant EECs produce’’, explains co-first author Julia Bauzá-Martinez. ‘’Moreover, if specific peptides are depleted in the background of a mutant protease, one can assume it is an important hormone and not a random artefact’’.

Glucagon in the human gut

The researchers succeeded in performing a broad characterization of peptide hormones in normal EECs, as well as in EECs where specific proteases were missing. Against all expectations, the team could measure substantial amounts of glucagon from human EECs. Glucagon is a well-known hormone produced by the human pancreas, but whether the human gut can produce it too is subject of debate. ‘’Glucagon was particularly found when cells were stimulated with specific signals, mimicking the intestinal villus environment,” says Joep Beumer, other co-first author. The enzyme that can generate this glucagon – called PCSK2 – was indeed stimulated by the very same signals

Future directions

Previous work by the same research groups indicated that EECs can change the hormones they produce when migrating from crypt to villus (refer to our 2018 nature cell biology press release?, Nature Cell Biology paper). The current work suggests EECs could potentially also change how they process prohormones into bioactive peptides depending on their location in the gut. Future work could focus on the physiological relevance of the changes in the hormones that EECs produce. “In the future, a more complete understanding of hormone processing could contribute to better therapeutic interventions for endocrine diseases,” Beumer concludes.

Publication

Mapping prohormone processing by proteases in human enteroendocrine cells using genetically engineered organoid models. Joep Beumer, Julia Bauzá-Martinez, Tim S. Veth, Veerle Geurts, Charelle Boot, Hannah Gilliam-Vigh, Steen S. Poulsen, Filip Knop, Wei Wu & Hans Clevers. PNAS, 2022.

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About Hans Clevers

Hans Clevers is advisor/guest researcher at the Hubrecht Institute for Developmental Biology and Stem Cell Research and at the Princess Máxima Center for Pediatric Oncology. He is also University Professor at the University Utrecht and Oncode Investigator. Since March 2022, Hans Clevers is Head of pharma Research and Early Development (pRED) of Roche, Basel Switzerland.

About the Hubrecht Institute

The Hubrecht Institute is a research institute focused on developmental and stem cell biology. Because of the dynamic character of the research, the institute as a variable number of research group, around 20, that do fundamental, multidisciplinary research on healthy and diseased cells, tissues and organisms. The Hubrecht Institute is a research institute of the Royal Netherlands Academy of Arts and Sciences (KNAW), situated on Utrecht Science Park. Since 2008, the institute is affiliated with the UMC Utrecht, advancing the translation of research to the clinic. The Hubrecht Institute has a partnership with the European Molecular Biology Laboratory (EMBL). For more information, visit www.hubrecht.eu.