Regulation of Gastric Lgr5+ve Cell Homeostasis by Bone Morphogenetic Protein (BMP) Signaling and Inflammatory Stimuli

BACKGROUND & AIMS

Gastric Leucine-rich repeat-containing G-protein-coupled receptor 5 (Lgr5) cells exert important functions during injury and homeostasis. Bone morphogenetic protein (BMP) signaling regulates gastric inflammation and epithelial homeostasis. We investigated if BMP signaling controls the fate of Lgr5^+ve cells during inflammation.

METHODS

The H⁺/K⁺-adenosine triphosphatase β-subunit promoter was used to express the BMP inhibitor noggin (Nog) in the stomach (H⁺/K⁺-Nog mice). Inhibition of BMP signaling in Lgr5 cells was achieved by crossing Lgr5-EGFP-ires-CreERT2 (Lgr5-Cre) mice to mice with floxed alleles of BMP receptor 1A (Lgr5-Cre;Bmpr1a^flox/flox mice). Lgr5/GFP^+ve cells were isolated using flow cytometry. Lineage tracing studies were conducted by crossing Lgr5-Cre mice to mice that express Nog and tdTomato (Lgr5-Cre;H⁺/K⁺-Nog;Rosa26-tdTom). Infection with Helicobacter felis was used to induce inflammation. Morphology of the mucosa was analyzed by H&E staining. Distribution of H⁺/K⁺-adenosine triphosphatase-, IF-, Ki67-, CD44-, CD44v9-, and bromodeoxyuridine-positive cells was analyzed by immunostaining. Expression of neck and pit cell mucins was determined by staining with the lectins Griffonia (Bandeiraea) simplicifolia lectin II and Ulex europaeus agglutinin 1, respectively. Id1, Bmpr1a, Lgr5, c-Myc, and Cd44 messenger RNAs were measured by quantitative reverse-transcription polymerase chain reaction.

RESULTS

Lgr5-Cre;Bmpr1a^flox/flox mice showed diminished expression of Bmpr1a in Lgr5/GFP^+ve cells. Infection of Lgr5-Cre;Bmpr1a^flox/flox mice with H felis led to enhanced inflammation, increased cell proliferation, parietal cell loss, and to the development of metaplasia and dysplasia. Infected Lgr5-Cre;H⁺/K⁺-Nog;Rosa26-tdTom mice, but not control mice, showed the presence of tomato^+ve glands lining the lesser curvature that stained positively with Griffonia (Bandeiraea) simplicifolia lectin II and Ulex europaeus agglutinin 1, and with anti-IF, -CD44, -CD44v9, and -bromodeoxyuridine antibodies.

CONCLUSIONS

Inflammation and inhibition of BMP signaling activate Lgr5^+ve cells, which give rise to metaplastic, dysplastic, proliferating lineages that express markers of mucus neck and zymogenic cell differentiation.

Initiation and Maintenance of Gastric Cancer: A Focus on CD44 Variant Isoforms and Cancer Stem Cells

Gastric cancer is the third most common cause of cancer-related death. Although the incidence of gastric cancer in the United States is relatively low, it remains significantly higher in some countries, including Japan and Korea. Interactions between cancer stem cells and the tumor microenvironment can have a substantial impact on tumor characteristics and contribute to heterogeneity. The mechanisms responsible for maintaining malignant cancer stem cells within the tumor microenvironment in human gastric cancer are largely unknown. Tumor cell and genetic heterogeneity contribute to either de novo intrinsic or the therapy-induced emergence of drug-resistant clones and eventual tumor recurrence. Although chemotherapy often is capable of inducing cell death in tumors, many cancer patients experience recurrence because of failure to effectively target the cancer stem cells, which are believed to be key tumor-initiating cells. Among the population of stem cells within the stomach that may be targeted during chronic Helicobacter pylori infection and altered into tumor-initiating cells are those cells marked by the cluster-of-differentiation (CD)44 cell surface receptor. CD44 variable isoforms (CD44v) have been implicated as key players in malignant transformation whereby their expression is highly restricted and specific, unlike the canonical CD44 standard isoform. Overall, CD44v, in particular CD44v9, are believed to mark the gastric cancer cells that contribute to increased resistance for chemotherapy- or radiation-induced cell death. This review focuses on the following: the alteration of the gastric stem cell during bacterial infection, and the role of CD44v in the initiation, maintenance, and growth of tumors associated with gastric cancer.

Regulation of Gastric Metaplasia, Dysplasia, and Neoplasia by Bone Morphogenetic Protein Signaling

The bone morphogenetic proteins, (BMP)s are regulatory peptides that have significant effects on the growth and differentiation of gastrointestinal tissues. In addition, the BMPs have been shown to exert anti-inflammatory actions in the gut and to negatively regulate the growth of gastric neoplasms. The role of BMP signaling in the regulation of gastric metaplasia, dysplasia and neoplasia has been poorly characterized. Transgenic expression in the mouse stomach of the BMP inhibitor noggin leads to decreased parietal cell number, increased epithelial cell proliferation, and to the emergence of SPEM. Moreover, expression of noggin increases Helicobacter-induced inflammation and epithelial cell proliferation, accelerates the development of dysplasia, and it increases the expression of signal transducer and activator of transcription 3 (STAT3) and of activation-induced cytidine deaminase (AID). These findings provide new clues for a better understanding of the pathophysiological mechanisms that regulate gastric inflammation and the development of both dysplastic and neoplastic lesions of the stomach.

The Development of Spasmolytic Polypeptide/TFF2-Expressing Metaplasia (SPEM) During Gastric Repair Is Absent in the Aged Stomach

BACKGROUND & AIMS

During aging, physiological changes in the stomach result in more tenuous gastric tissue that is less capable of repairing injury, leading to increased susceptibility to chronic ulceration. Spasmolytic polypeptide/trefoil factor 2-expressing metaplasia (SPEM) is known to emerge after parietal cell loss and during Helicobacter pylori infection, however, its role in gastric ulcer repair is unknown. Therefore, we sought to investigate if SPEM plays a role in epithelial regeneration.

METHODS

Acetic acid ulcers were induced in young (2-3 mo) and aged (18-24 mo) C57BL/6 mice to determine the quality of ulcer repair with advancing age. Yellow chameleon 3.0 mice were used to generate yellow fluorescent protein-expressing organoids for transplantation. Yellow fluorescent protein-positive gastric organoids were transplanted into the submucosa and lumen of the stomach immediately after ulcer induction. Gastric tissue was collected and analyzed to determine the engraftment of organoid-derived cells within the regenerating epithelium.

RESULTS

Wound healing in young mice coincided with the emergence of SPEM within the ulcerated region, a response that was absent in the aged stomach. Although aged mice showed less metaplasia surrounding the ulcerated tissue, organoid-transplanted aged mice showed regenerated gastric glands containing organoid-derived cells. Organoid transplantation in the aged mice led to the emergence of SPEM and gastric regeneration.

CONCLUSIONS

These data show the development of SPEM during gastric repair in response to injury that is absent in the aged stomach. In addition, gastric organoids in an injury/transplantation mouse model promoted gastric regeneration.