A new study published in the international journal Nature describes, for the first time, the use of human pluripotent stem cells to create a three-dimensional stomach-like mini-organ. This is the beginning of what might become an unprecedented tool for examining the genesis of diseases such as stomach cancer to diabetes.
Jim Wells and his colleagues at Cincinnati Children’s Hospital Medical Center used human pluripotent stem cells, which are made from mature human cells through a combination of genetic engineering and cell culture techniques, to grow a their miniature stomachs. Wells’ group then used their mini-stomachs also known as gastric organoids, in collaboration with scientists from University of Cincinnati College of Medicine, to study the infection of stomach tissue by the bacterium Helicobacter pylori, which causes peptic ulcer disease and stomach cancer.
According to Wells, a scientist in the divisions of Developmental Biology and Endocrinology at Cincinnati Children’s, this is the first time anyone has succeeded in making three-dimensional human gastric organoids (hGOs). This achievement may present new opportunities for drug discovery, modeling early stages of stomach cancer and studying some of the factors that give rise to obesity related diabetes. This work also represents the first time researchers have produced three-dimensional human embryonic foregut, which is a good starting point for generating other foregut organ tissues such as the lungs and pancreas. “Until this study, no one had generated gastric cells from human pluripotent stem cells (hPSCs),” Wells said. “In addition, we discovered how to promote formation of three-dimensional gastric tissue with complex architecture and cellular composition.”
Wells’ gastric organoids are a significant advance in gastroenterological research because distinct differences in development and architecture of the adult stomach limit the reliability of mouse models for studying human stomach development and disease.
As a research tool, human gastric organoids may help clarify other unknown features of the stomach, such as identifying those biochemical processes in the gut that allow gastric-bypass patients to become diabetes-free soon after surgery before losing significant weight. Medical conditions such as obesity-fueled diabetes and the metabolic syndrome are of great interest to public health workers, given the explosion of global cases in the last few decades. A major challenge to addressing these and other medical conditions that involve the stomach has been a relative lack of reliable laboratory model systems to accurately recapitulate human biology.
The key to growing human gastric organoids was to identify the developmental steps involved in normal stomach formation. Manipulation of these processes in a cell culture system drove human pluripotent stem cells to form immature stomach tissue. In culture and over the course of a month, these steps resulted in the formation of 3D human gastric organoids that were around 3mm (1/10th of an inch) in diameter. Wells and his colleagues also used this approach to identify steps that go awry when the stomach does not form correctly.
In collaboration with his colleagues, Kyle McCracken, an MD/PhD graduate student in Wells’ laboratory, and Yana Zavros, PhD, a researcher at UC’s Department of Molecular and Cellular Physiology, Wells showed that his gastric organoids were rapidly infected by H. pylori bacteria. Within 24 hours of inoculation, the bacteria had triggered significant biochemical changes to the organ, and the human gastric organoids faithfully mimicked the early stages of H. pylori-induced gastric disease. McCracken also noticed activation of a cancer gene called c-Met, which is one of the first stages in the induction of stomach cancer, an important long-term sequel to peptic ulcer disease. McCracken was also surprised by the rapid spread of infection in the tissues of his human gastric organoids.
There is a relative dearth of literature on how the human stomach developments, which was a significant impediment to Wells’ research. Wells and his coworkers had to use a combination of published works and studies from his own lab, to answer a number of basic developmental questions about how the stomach forms. Over the course of two years, by experimenting with different factors to drive the formation of the stomach, Wells and his colleagues came upon a protocol that resulted in the formation of 3D human gastric tissues in culture.
Wells emphasized importance of basic research for the eventual success of this project, adding, “This milestone would not have been possible if it hadn’t been for previous studies from many other basic researchers on understanding embryonic organ development.”
While this does represent a terrific stride toward better model systems for gastric research and pathology, these gastric organoids are very immature and lack several of the cell types found in mature stomach tissue. For example, these organoids lack chief cells, which secrete the stomach enzyme pepsin (in an inactive form called pepsinogen), and parietal cells, which produce stomach acid. This is significant because chronic inflammation of the stomach can cause loss of parietal cells, which decreases chief cell differentiation and induce chief cells to transdifferentiate back into neck cells. This leads to overproduction of mucus cells. This mucus cell metaplasia is known as spasmolytic polypeptide expressing metaplasia (SPEM) that seems to be a precancerous condition for the stomach. Also if parietal cells are lost, mature chief cells do not form. This seems to imply that parietal cells secrete factors that lead to differentiation of chief cells, so if lost. These gastric organoids also do not make ECL cells or enterochromaffin-like cells, which secrete histamine, one of the most important regulators of stomach acid production. A prolonged stimulation of these ECL cells causes increased numbers of them. This is especially important in gastrinomas, which are tumors in which there is an excessive secretion of the stomach hormone gastrin, one of the key factors contributing to Zollinger-Ellison syndrome. The hallmark of this disease is ulceration of the stomach and upper small intestine (duodenum) as a result of excessive and unregulated secretion of gastric acid. Most commonly, hypergastrinemia is the result of these gastrin-secreting tumors or gastrinomas that develop in the pancreas or duodenum. Thus, in only this short discussion, we have noted several diseases of the stomach that cannot be modeled with this particular system because these stomach-specific cells are not present.
Therefore, while this is a fantastic model system for stomach development and H. pylori infection, more work remains in order to make a stomach model that more accurately models the adult stomach.