Intestinal Microbiome‐Macrophage Crosstalk Contributes to Cholestatic Liver Disease by Promoting Intestinal Permeability in Mice

Abstract

BaCKgRoUND aND aIMS: Mounting evidence supports an association between cholestatic liver disease and changes in the composition of the microbiome. Still, the role of the microbiome in the pathogenesis of this condition remains largely undefined. appRoaCH aND ReSUltS: To address this, we have used two experimental models, administering alpha-naphtylisocyanate or feeding a 0.1% 3,5-diethoxycarbonyl-1,4-dihydrocollidine diet, to induce cholestatic liver disease in germ-free mice and germ-free mice conventionalized with the microbiome from wild-type, specific pathogen-free animals. Next, we have inhibited macrophage activation by depleting these cells using clodronate liposomes and inhibiting the inflammasome with a specific inhibitor of NOD-, LRR-, and pyrin domain-containing protein 3. Our results demonstrate that cholestasis, the accumulation of bile acids in the liver, fails to promote liver injury in the absence of the microbiome in vivo. Additional in vitro studies supported that endotoxin sensitizes hepatocytes to bile-acid-induced cell death. We also demonstrate that during cholestasis, macrophages contribute to promoting intestinal permeability and to altered microbiome composition through activation of the inflammasome, overall leading to increased endotoxin flux into the cholestatic liver. CoNClUSIoNS: We demonstrate that the intestinal microbiome contributes to cholestasis-mediated cell death and inflammation through mechanisms involving activation of the inflammasome in macrophages. (Hepatology 2020;72:2090-2108). T he intestine is a selective barrier that prevents pathogenic bacteria translocating to the systemic circulation, while simultaneously allowing nutrient absorption. In the intestine, crosstalk regulation among the microbiome, the immune system, and epithelial cells is essential to preserve barrier function. (1,2) Intestinal permeability is tightly regulated by the immune system as inflammatory cytokines (e.g., tumor necrosis factor [TNF] and interferon gamma) modulate the expression of tight junction (TJ) proteins. (3) In the intestine, the microbiome shapes the immune system, rendering a tolerant environment where microbes and host cells can coexist. (1,2) Reciprocally, inflammation can determine the composition of the intestinal microbiome, (4,5) adding another layer of complexity to the regulation of intestinal permeability and barrier function. The "leaky gut" hypothesis proposes that chronic liver disease is associated with breaching of the

The Role of the Microbiome in Liver Cancer

“…Mechanistically, in murine models of ALD, lower abundances of Firmicutes and higher abundances of Verrucomicrobia and Bacteroidetes were observed when compared with those in healthy mice [ 64 ]; the dysbiotic microbiome contributed to the progression of liver disease via the promotion of intestinal inflammation and the resulting reduction in tight junction protein expression, which was similar to our findings in murine models of cholestasis [ 65 ]. Depletion of antimicrobial molecules was also demonstrated in murine models of ALD [ 64 , 66 ].…”

“…Likewise, our knowledge of the mechanisms mediating both the detrimental and the beneficial effects of different bacteria on liver function and disease progression remain scarce. These may include the capacity of specific bacteria to regulate tight junctions and, thus, intestinal permeability [ 65 ], controlling inflammation [ 66 ], or via the direct effects of bacteria-derived metabolites (e.g., phenylacetic acid) on the liver, as it was observed in obese steatotic patients [ 71 ].…”

Hepatic macrophages in liver homeostasis and diseases-diversity, plasticity and therapeutic opportunities

“…113,114 KC depletion by CLDN or treatment with an NLRP3 inhibitor significantly attenuates αnaphtylisocyanate (ANIT)-induced cholestatic liver injury, further supporting a role for macrophage inflammasome activation in the pathogenesis of the disease. 115 Studies investigating whether bile acids play an important role in triggering macrophage inflammasome activation have yielded controversial findings. The hydrophobic bile acids chenodeoxycholic acid and deoxycholic acid have been found to induce macrophage NLRP3 inflammasome activation.…”

Tectorigenin alleviates intrahepatic cholestasis by inhibiting hepatic inflammation and bile accumulation via activation of PPARg

“…A previous study reported that ANIT and DDC treatment could cause intestinal permeability, leading to the translocation of bacteria or their products (LPS) from the leaky intestine into the liver [14] . Additionally, whilst murine experimental models may not fully represent human disease, ANIT and feeding with 0.1% DDC are well-accepted models of sclerosing cholangitis relevant to PSC [27,28] .…”

“…Macrophages, which are composed of resident tissue macrophages and monocyte-derived recruited cells, can differentiate into either classically activated macrophages (a pro-inflammatory phenotype, also called M1 polarity) or alternatively activated macrophages (M2 polarity) which express anti-inflammatory cytokines [13] . Recent studies have demonstrated that the intestinal microbiome leads to the process of cholestasis-mediated cell death and inflammation by activating the mechanisms of the inflammasome in macrophages [14] . Additionally, clinical studies have suggested that in cholestasis patients, the recruitment of monocytes and macrophages in diseased liver is significantly increased [15] .…”