SARS‐CoV‐2, the agent that causes COVID‐19, invades epithelial cells, including those of the respiratory and gastrointestinal mucosa, using angiotensin‐converting enzyme‐2 (ACE2) as a receptor. Subsequent inflammation can promote rapid virus clearance, but severe cases of COVID‐19 are characterized by an inefficient immune response that fails to clear the infection. Using primary epithelial organoids from human colon, we explored how the central antiviral mediator IFN‐γ, which is elevated in COVID‐19, affects epithelial cell differentiation, ACE2 expression, and susceptibility to infection with SARS‐CoV‐2. In mouse and human colon, ACE2 is mainly expressed by surface enterocytes. Inducing enterocyte differentiation in organoid culture resulted in increased ACE2 production. IFN‐γ treatment promoted differentiation into mature KRT20+ enterocytes expressing high levels of ACE2, increased susceptibility to SARS‐CoV‐2 infection, and resulted in enhanced virus production in infected cells. Similarly, infection‐induced epithelial interferon signaling promoted enterocyte maturation and enhanced ACE2 expression. We here reveal a mechanism by which IFN‐γ‐driven inflammatory responses induce a vulnerable epithelial state with robust replication of SARS‐CoV‐2, which may have an impact on disease outcome and virus transmission.

Helicobacter pylori causes gastric inflammation, gland hyperplasia and is linked to gastric cancer. Here, we studied the interplay between gastric epithelial stem cells and their stromal niche under homeostasis and upon H. pylori infection. We find that gastric epithelial stem cell differentiation is orchestrated by subsets of stromal cells that either produce BMP inhibitors in the gland base, or BMP ligands at the surface. Exposure to BMP ligands promotes a feed-forward loop by inducing Bmp2 expression in the epithelial cells themselves, enforcing rapid lineage commitment to terminally differentiated mucous pit cells. H. pylori leads to a loss of stromal and epithelial Bmp2 expression and increases expression of BMP inhibitors, promoting self-renewal of stem cells and accumulation of gland base cells, which we mechanistically link to IFN-γ signaling. Mice that lack IFN-γ signaling show no alterations of BMP gradient upon infection, while exposure to IFN-γ resembles H. pylori-driven mucosal responses.

The stomach corpus epithelium is organized into anatomical units that consist of glands and pits. Mechanisms that control the cellular organiza�on of corpus glands and enable its recovery upon injury are not well understood. R-spondin 3 (RSPO3) is a WNT signaling enhancer that regulates stem cell behavior in different organs. Here we inves�gated the func�on of RSPO3 in the corpus during homeostasis, upon chief and/or parietal cell loss, and chronic H. pylori infec�on.Using organoid culture and condi�onal mouse models, we demonstrate that RSPO3 is a cri�cal driver of secretory cell differen�a�on in the corpus gland towards parietal and chief cells, while its absence promoted pit cell differen�ation. Acute loss of chief and parietal cells induced by high dose tamoxifen -or merely the deple�on of LGR5+ chief cells -caused an upregulation of RSPO3 expression, which was required for the ini�a�on of a coordinated regenera�ve response via the ac�vation of yes-associated protein (YAP) signaling. This response enabled a rapid recovery of the injured secretory gland cells. However, in the context of chronic H. pylori infec�on, the R-spondin-driven regenera�on was maintained long-term, promo�ng severe glandular hyperprolifera�on and the development of premalignant metaplasia.

Helicobacter pylori is a pathogen that colonizes the stomach and causes chronic gastritis. Helicobacter pylori can colonize deep inside gastric glands, triggering increased R-spondin 3 (Rspo3) signaling. This causes an expansion of the "gland base module," which consists of self-renewing stem cells and antimicrobial secretory cells and results in gland hyperplasia. The contribution of Rspo3 receptors Lgr4 and Lgr5 is not well explored. Here, we identified that Lgr4 regulates Lgr5 expression and is required for H. pylori-induced hyperplasia and inflammation, while Lgr5 alone is not. Using conditional knockout mice, we reveal that R-spondin signaling via Lgr4 drives proliferation of stem cells and also induces NF-jB activity in the proliferative stem cells. Upon exposure to H. pylori, the Lgr4driven NF-jB activation is responsible for the expansion of the gland base module and simultaneously enables chemokine expression in stem cells, resulting in gland hyperplasia and neutrophil recruitment. This demonstrates a connection between R-spondin-Lgr and NF-jB signaling that links epithelial stem cell behavior and inflammatory responses to gland-invading H. pylori.