Introduction

Metabolic dysfunction-associated steatotic liver disease (MASLD) is closely related to the metabolic syndrome of chronic liver disease and its pathogenesis involves a variety of cell types of metabolic disorders and inflammatory response, however, treatment is limited. Mas is a G protein-coupled receptor highly expressed by myeloid cells. It may play a key role in regulating myeloid-associated inflammation and metabolic homeostasis in the process of MASLD. However, its specific mechanism of action in MASLD remains unclear.

Aims & Methods

This study aims to explore the regulatory mechanism of MAS in myeloid cells in the occurrence and development of MASLD. In this study, liver tissues of patients with MASLD and animal models of MASLD induced by high-fat diet (HFD) were analyzed. In this study, myeloid-specific Mas1 knockout (Lysm^creMas1^f/f) mice were constructed. Single-cell RNA sequencing and multi-omics analysis were used to explore the role and mechanism of myeloid Mas in HFD-induced MASLD mice.

Results

The study found that the expression of MAS protein on myeloid cells in the livers of MASLD patients and MASLD animal models was significantly increased. Mononuclear phagocyte system（MPs）undergo metabolic disorders in the MASLD model, with elevated glycolysis levels, increased lactic acid production, and at the same time, the expression of cellular senescence markers (such as p16 and p21) is upregulated, and the secretion of inflammatory factors is increased. Single-cell multi-omics analysis revealed that myeloid MAS1 knockout activated the FN1⁺CCR2⁺monocytes first. Pseudo-temporal analysis showed that the FN1⁺CCR2⁺ monocytes had spatiotemporal metabolic responses with the macrophages, significantly involving the activation of glycolysis and inflammatory senescence by myeloid MAS. Non-target metabolomics of MASLD patients also revealed elevated glycolytic metabolism and increased lactic acid secretion. Mass spectrometry revealed that Mas specifically bound to the key glycolytic protein pyruvate kinase M2 (PKM2) and activated the lactylation of transcription factor Spi1-K208 site mediated by PKM2. The lactylation of Spi1-K208 promoted the transcription of senescence-associated secretory phenotype (SASP) -related proteins. Myeloid Mas1 knockout inhibited the nuclear translocation of PKM2 and blocked the lactylation of Spi1, inhibiting the transcriptional initiation of SASP. Screening of over 100,000 small molecule compounds through a virtual drug library revealed that Theaflavin 3,3'-digallate (TFDG) might reduce the protein expression of Mas and PKM2, and block the binding of the MAS-PKM2 complex. We synthesized macrophage membrane to encapsulat PLGA nanoparticles loaded with TFDG (MM@NP-TFDG) and found that MM@NP-TFDG effectively reduced the expression level of Mas-PKM2 complex protein expression in the MASLD mouse model, inhibited the glycolytic - inflammatory senescence axis of FN1⁺CCR2⁺ monocytes and macrophages, and alleviated liver inflammation and tissue damage. While the lipid deposition in the liver is reduced and the fatty acid oxidation is enhanced.

Conclusion

This study reveals that myeloid MAS1 protein participates in the occurrence and development of MASLD by regulating PKM2-mediated Spi1 lactylation and reprogramming the metabolic-inflammatory senescence axis of MPs during the process of MASLD. This discovery provides new potential targets for the treatment of MASLD patients and is expected to offer new clinical treatment strategies for MASLD patients.

Disclosure

The authors declare no conflict of interest.

Introduction

Spasmolytic polypeptide expressing metaplasia (SPEM) is a cell repair lineage and is a very important phenotype of gastric mucosal injury and precancerous lesion.
Previously, parietal cells loss is considered as the first step and followed with chief cells transdiffernation to induce SPEM. But whether chief cells initial loss cause SPEM
needs to be further investigation. Acidic mammalian chitinase (CHIA) belongs to the 18 glycosidase family and is highly expressed in the chief cells. Our previous study showed that CHIA deficiency in the chief cells is the key event to induce SPME to progress to gastric cancer (Liu et al., DDW 2023 and 2024). However, the molecular role of CHIA in the development of SPEM is need further investigated.

Aims & Methods

Electron microscopy, qRT-PCR and single-cell sequencing (scRNA-seq) technology, as well as histopathological and immunofluorescence (IF) stainning with specific markers were performed in chief cells specific CHIA knockout mouse model (CHIA^rox/rox-GIF-Dre) and wild-type mice(CHIA^rox/rox), and in CHIA over - expression mice (CHIA ^rox/rox - GIF - Dre + rAAv - CHIA) and the control group (CHIA ^rox/rox - GIF - Dre + rAAv - control).

Results

Compared with CHIA^rox/rox mice, histological analysis and scRNA-seq technology data showed that loss of chief cells with increased M2 macrophage infiltration and final SPEM formation, but remaining of parietal cells in CHIA^rox/rox-GIF-Dre mice. Electron microscopy showed CHIA deficiency in mice resulted in endoplasmic reticulum was dilated and swollen, as well as the mitochondrial membrane was discontinuous of chief cells, followed with the accumulation of endoplasmic reticulum stress marker, including PERK, XBP-1, eIF2α/P-eIF2α, and GRP78, together with upregulation of pyroptosis-related marker, including NLRP3, ACS, GSDMD, NEK7, Caspase1, Caspase11, IL-1β, and IL-18, which was detected by qRT-PCR. These data indicating that target CHIA deletion caused chief cells pyroptosis. Furthermore, qRT-PCR analysis showed that CHIA deficiency caused the activation of IL33/IL-13 circuit in the mucosa of mice. Moreover, double immunofluorescence staining confirmed that upregulation and colocalization of IL-33 induced M2 macrophage polarization markers, including F4/80 and CD163⁺ with NLRP3 in the base of gastric mucosal of CHIA^rox/rox-GIF-Dre mice when compared with CHIA^rox/rox mice.Notably, CHIA ^rox/rox - GIF - Dre + rAvv - CHIA mice reversed the above process compared with controls.

Conclusion

Chief cells specific CHIA deficiency resulted in endoplasmic reticulum stress mediate NLRP3 inflammasome activation to induce chief cells proptosis.
Chief cells initial loss is sufficient and the key step to activate IL-33/ST2-M2 macrophage polarization axis to induce SPEM, which is independent of parietal cells loss.