The stomach tissue microenvironment is composed of many types of cells. This diversity along with their interactions is involved in the maintenance of homeostasis and the development of tumors. The major players involved are immune cells, fibroblasts, endothelial cells, and the extracellular matrix. All these elements work in unison to maintain the structure, integrity, and functions of the gastric tissue. In the event of the development of a tumor, there are changes in these interactions and signaling thus, altering the microenvironment. The development and metastasis due to altered interactions allow for cancer cells to “escape” detection by the immune system and even therapy.
The interactions between gastric epithelial and stromal cells are yet to be studied in detail even though the functions are so important. Thus, a suitable model to assess the interactions is cell culture. The combination of primary tissue culture with the latest technology emerges as an option to study these aspects in detail. A team led by Chen published an article in Scientific Reports in 2019 of developing primary gastric cultures using the latest approaches.
Primary cultures were developed from mouse gastric tissues using the air-liquid interphase (ALI) system. This system allows for the maintenance of gastrointestinal primary tissue cultures for longer periods of time. It allows for the preservation of the heterogeneous content of cells seen in vivo. It also allows for the introduction of mutations in a wild-type background to engineer cancer models and study the changes in known genes.
Analysis of the culture was done at single-cell level using a droplet-based single-cell RNA sequencing. The markers of thousands of cells were analyzed to identify fibroblasts, epithelial cells, and macrophages. The macrophages were found to be mainly of the M2-type: involved in promoting tumors and healing wounds. Additionally, the use of primary cultures allowed for the identification of Lgr5 in a few cells-known to be a stem cell marker! The exact implication of this requires further analysis given that LGR5 was expressed in the epithelium and stromal cells of healthy colon samples while tumor cells expressed higher levels of LGR5.
The expression of Wnt signaling genes revealed that fibroblasts were found to express Rspo3 while epithelial cells expressed Wnt4. Research by Sigal and colleagues published in a 2017 Nature article showed that Rspo3 from the stroma influences the epithelial cells of the gastric system in mice while also controlling gland homeostasis. Research has also shown that Rspo3 alone could facilitate intestinal homeostasis in mice. Genetic analysis has revealed that some colon cancers expressed RSPO fusions.
Targeting Wnt signaling involving molecules to treat gastric cancer emerges as a promising approach. The use of primary culture highlighted several new aspects of Rspos that are involved in homeostasis and cancer development. Thus, details of intricate biological pathways with clinical applications can be facilitated using primary cultures.
- Chen, J., Lau, B.T., Andor, N. et al. Single-cell transcriptome analysis identifies distinct cell types and niche signaling in a primary gastric organoid model. Scientific Reports 9, 4536 (2019).
2. Sigal, M. et al. Stromal R-spondin orchestrate gastric epithelial stem cells and gland homeostasis. Nature 548, 451–455 (2017).