Spotlight on NLRP6 and Tumor Research Situation: A Potential Cancer Participant

Inflammasomes in Intestinal Disease: Mechanisms of Activation and Therapeutic Strategies

NOD-like receptors (NLRs) are a family of cytosolic pattern recognition receptors (PRRs) implicated in the innate immune sensing of pathogens and damage signals. NLRs act as sensors in multi-protein complexes called inflammasomes. Inflammasome activity is necessary for the maintenance of intestinal homeostasis, although their aberrant activation contributes to the pathogenesis of several gastrointestinal diseases. In this review, we summarize the main features of the predominant types of inflammasomes involved in gastrointestinal immune responses and their implications in intestinal disease, including Irritable Bowel Syndrome (IBS), Inflammatory Bowel Disease (IBD), celiac disease, and Colorectal Cancer (CRC). In addition, we report therapeutic discoveries that target the inflammasome pathway, highlighting promising novel therapeutic strategies in the treatment of intestinal diseases. Collectively, our understanding of the mechanisms of intestinal inflammasome activation and their interactions with other immune pathways appear to be not fully elucidated. Moreover, the clinical relevance of the efficacy of inflammasome inhibitors has not been evaluated. Despite these limitations, a greater understanding of the effectiveness, specificity, and reliability of pharmacological and natural inhibitors that target inflammasome components could be an opportunity to develop new therapeutic options for the treatment of intestinal disease.

[Nlrp6 overexpression inhibits lipid synthesis to suppress proliferation of hepatocellular carcinoma cells by regulating the AMPK-Srebp1c axis]

OBJECTIVE

To investigate the mechanism of Nlrp6 for regulating hepatocellular carcinoma (HCC) progression in light of lipid synthesis regulation.

METHODS

Nlrp6 expression level in HCC tissues of different pathological grades was investigated using RNA-seq data from The Cancer Genome Atlas (TCGA) database, and its correlation with the patients' survival was analyzed with Kaplan-Meier survival analysis. HepG2 cells with adenovirus-mediated Nlrp6 overexpression or knockdown were treated with palmitic acid (PA), and the changes in lipid deposition and cell proliferation were evaluated using Oil Red O staining, CCK-8 assay, EdU staining, and colony formation assay. RT-qPCR and Western blotting were used to detect the changes in expression of lipid synthesis-related genes and the proteins in the AMPK-Srebp1c axis. In a mouse model of hepatic steatosis established in liver-specific Nlrp6 knockout mice by high-fat diet feeding for 24 weeks, liver fibrosis was examined with histological staining, and the changes in expressions of HCC markers and the AMPK-Srebp1c signaling pathway were detected.

RESULTS

Nlrp6 expression was significantly reduced in HCC tissues with negative correlations with the pathological grades and the patients' survival (P < 0.0001). In HepG2 cells, Nlrp6 overexpression significantly inhibited lipid deposition and cell proliferation, whereas Nlrp6 knockdown produced the opposite effects. Nlrp6 overexpression strongly suppressed the expression of lipid synthesis-related genes, promoted AMPK phosphorylation, and inhibited Srebp1c expression. The mice with liver-specific Nlrp6 knockout and high-fat feeding showed increased hepatic steatosis, collagen deposition, and AFP expression with reduced AMPK phosphorylation and increased Srebp1c expression.

CONCLUSION

Nlrp6 overexpression inhibits lipid synthesis in HCC cells by regulating the AMPK-Srebp1c axis, which might be a key pathway for suppressing HCC cell proliferation.

NLRP6 deficiency suppresses colorectal cancer liver metastasis growth by modulating M-MDSC-induced immunosuppressive microenvironment

Colorectal cancer liver metastasis (CRLM) a profound influence on the prognosis of patients with colorectal cancer (CRC), prompting a comprehensive inquiry into its underlying mechanisms. Amidst the multifaceted tumor microenvironment, myeloid-derived suppressor cells (MDSCs) have emerged as pivotal orchestrators of immune modulation. However, their specific contributions to the CRLM have not been explored. The role of NLRP6, a member of the NOD-like receptor family, is of interest. Employing a liver metastasis model, our investigation revealed a heightened accumulation of monocytic MDSCs (M-MDSCs) within metastatic sites, culminating in an immunosuppressive milieu characterized by depleted CD8+ T cell populations. Remarkably, the absence of NLRP6 disrupts this intricate immunosuppressive network, highlighting its nuanced role in sculpting the trajectory of CRLM. This study elucidates the interplay between NLRP6 and MDSCs, potentially guiding novel therapeutic strategies to recalibrate the immune microenvironment in CRLM and enhance patient outcomes.