CHIA DEFICIENCY IN THE CHIEF CELLS PROMOTES SPASMOLYTIC POLYPEPTIDE-EXPRESSING METAPLASIA THROUGH PYROPTOSIS MEDIATED M2 MACROPHAGE POLARIZATION

Aim: Loss of parietal cells causes the development of spasmolytic polypeptide-expressing metaplasia (SPEM) through transdifferentiation of chief cells. However, whether initial chief cell loss cause SPEM needs to be further investigated. Acidic mammalian chitinase (CHIA) belongs to the 18 glycosidase family and is expressed in epithelial cells in various organ, which can degrade chitin-containing pathogens, participate in Th2-mediated inflammation. CHIA is highly expressed in the chief cells, and our previous studies showed that CHIA deficiency in the chief cells is the key event to induces SPEM and progress to gastric cancer, which is independent of parietal cell loss (Zhao et al., DDW 2023; Hu et al., KDDW 2021). However, the exact mechanism of CHIA in the development of SPEM is need further investigated.
Methods: PCR and single-cell sequencing (scRNA-seq) technology, histopathological and immunofluorescence stainning with specific markers were performed in CHIA wild type (WT) mice and knockout (KO) mice. Multiple endoplasmic reticulum stress markers, macrophage polarization markers and cytokine-related markers were detected by qPCR in CHIA WT and KO.
Results: PCR and scRNA-seq technology data showed that increased M2 macrophage infiltration and SPEM formation, but remaining of parietal cells in CHIA KO mice, when compared to CHIA WT mice. Furthermore, deletion of CHIA in mice resulted in release of endoplasmic reticulum stress-triggered, including upregulation of endoplasmic reticulum stress markers (PERK, XBP-1, eIF2α/P- eIF2α, and GRP78), followed with upregulation of pyroptosis-related marker, including NLRP3, ACS, GSDMD, NEK7, Casepase1, Casepase11, IL-1β, and IL-18, as well as significantly increasement of IL33/IL-13 release. Moreover, Double immunofluorescence staining showed that upregulation and colocalization of NLRP3 and IL-33 induced M2 macrophage polarization markers, including F4/80 and CD163⁺ in the gastric mucosal of CHIA KO mice. Notably, immunofluorescence staining showed that CHIA deficiency caused the mucous neck cell marker SOX9 shifted from the cervical isthmus into the SPEM cells, and co-localized with the SPEM markers CD44v, TFF2 and MUC6, suggesting that the origin of SPEM cells may transdifferentiate from mucous neck cell after CHIA gene deletion.
Conclusions: CHIA deficiency casued the initial chief cells loss and followed with pyroptosis mediated M2 macrophage polarization, which is sufficent to induce SPEM. The cellular origin of CHIA deficiency induced SPEM may come from the mucous neck cells transdifferantation.