Decreased expression of the NLRP6 inflammasome is associated with increased intestinal permeability and inflammation in obesity with type 2 diabetes.

BACKGROUND: Obesity-associated dysfunctional intestinal permeability contributes to systemic chronic inflammation leading to the development of metabolic diseases. The inflammasomes constitute essential components in the regulation of intestinal homeostasis. We aimed to determine the impact of the inflammasomes in the regulation of gut barrier dysfunction and metabolic inflammation in the context of obesity and type 2 diabetes (T2D). METHODS: Blood samples obtained from 80 volunteers (n = 20 normal weight, n = 21 OB without T2D, n = 39 OB with T2D) and a subgroup of jejunum samples were used in a case-control study. Circulating levels of intestinal damage markers and expression levels of inflammasomes as well as their main effectors (IL-1ß and IL-18) and key inflammation-related genes were analyzed. The impact of inflammation-related factors, different metabolites and Akkermansia muciniphila in the regulation of inflammasomes and intestinal integrity genes was evaluated. The effect of blocking NLRP6 by using siRNA in inflammation was also studied. RESULTS: Increased circulating levels (P < 0.01) of the intestinal damage markers endotoxin, LBP, and zonulin in patients with obesity decreased (P < 0.05) after weight loss. Patients with obesity and T2D exhibited decreased (P < 0.05) jejunum gene expression levels of NLRP6 and its main effector IL18 together with increased (P < 0.05) mRNA levels of inflammatory markers. We further showed that while NLRP6 was primarily localized in goblet cells, NLRP3 was localized in the intestinal epithelial cells. Additionally, decreased (P < 0.05) mRNA levels of Nlrp1, Nlrp3 and Nlrp6 in the small intestinal tract obtained from rats with diet-induced obesity were found. NLRP6 expression was regulated by taurine, parthenolide and A. muciniphila in the human enterocyte cell line CCL-241. Finally, a significant decrease (P < 0.01) in the expression and release of MUC2 after the knockdown of NLRP6 was observed. CONCLUSIONS: The increased levels of intestinal damage markers together with the downregulation of NLRP6 and IL18 in the jejunum in obesity-associated T2D suggest a defective inflammasome sensing, driving to an impaired epithelial intestinal barrier that may regulate the progression of multiple obesity-associated comorbidities.

The Differential Expression of the Inflammasomes in Adipose Tissue and Colon Influences the Development of Colon Cancer in a Context of Obesity by Regulating Intestinal Inflammation.

BACKGROUND: Inflammasomes maintain tissue homeostasis and their altered regulation in the colon, and the adipose tissue (AT) leads to chronic activation of inflammatory pathways promoting colon cancer (CC) development. We aimed to analyze the potential involvement of inflammasomes in obesity-associated CC. METHODS: Ninety-nine volunteers [61 with obesity (OB) and 38 normoponderal (NP)] further subclassified according to the approved protocol for the diagnosis of CC (58 without CC and 41 with CC) were included in the case-control study. RESULTS: CC (P<0.01) and obesity (P<0.01) were accompanied by increased mRNA levels of NLRP3, NLRP6, ASC, IL1B and NOD2 in VAT. Contrarily, patients with CC exhibited a downregulation of NLRP6 and IL18 in their colon. Additionally, we revealed that the decreased Nlrp1 (P<0.05), Nlrp3 (P<0.01) and Nlrp6 (P<0.01) mRNA levels in the colon from obese rats significantly increase (P<0.05) after caloric restriction. Adipocyte-conditioned media obtained from subjects with obesity reduced (P<0.01) the mRNA of NLRP3 as well as molecules involved in maintaining the intestinal integrity (MUC2, CLDN1 and TJP1) and the anti-inflammatory factors FGF21, KLF4, and IL33 and in HT-29 cells. We also found that the knockdown of NLRP6 in HT-29 cells significantly upregulated (P<0.05) the mRNA of NLRP1 and NLRP3 and inhibited (P<0.05) the expression levels of MUC2. Finally, we showed that the incubation of HT-29 with Akkermansia muciniphila influence (P<0.05) the inflammasome expression profile as well as intestinal integrity-related genes and aberrant inflammation. CONCLUSIONS: These findings provide evidence that the downregulated levels of NLRP6 and IL18 in the colon from patients with CC may be responsible for a reduced intestinal-barrier integrity, triggering local inflammation, which in turn acts on the dysfunctional AT in obesity, increasing the expression of different inflammasome components and flaring up a vicious cycle of uncontrollable inflammatory cascades that favours a pro-tumorigenic microenvironment.