Dijk, Theo H. van

High plasma cholesterol levels increase the risk of cardiovascular disease (CVD). Transintestinal Cholesterol Excretion (TICE) is a recently emerged pathway of cholesterol removal and has the potential to lower plasma cholesterol levels and confer protection against CVD. Under control conditions, TICE accounts for about 30% of fecal cholesterol loss in mice. Using a panel of knock-out and transgenic mice as well as pharmacological manipulations we show that in mice TICE is regulated by intestinal activation of the Farnesoid X Receptor (FXR), via its target Fibroblast Growth Factor 15/19 (FGF15/19). Activation of FXR by the agonist PX20606 (PX) resulted in a >10-fold increased fecal cholesterol excretion as well as TICE and 40% reduced plasma cholesterol levels. The induction of fecal cholesterol excretion and TICE was absent in PX-treated intestine-specific FXR-null mice but was regained when those mice were co-treated with FGF19. Moreover, FGF19 treatment alone was sufficient to induce fecal cholesterol loss to a similar extend as was observed in PX-treated wild-type mice. PX treatment resulted in an increased muricholate/cholate-ratio and thereby induced a more hydrophilic bile salt pool. Not surprisingly, cholesterol absorption was reduced in PX-treated mice. However, experiments in which mice were co-treated with PX and the cholesterol absorption inhibitor ezetimibe revealed that the stimulating effect of PX on fecal neutral sterol excretion and TICE were completely independent of differences in cholesterol absorption. Of note, treatment of mice with a combination of PX and ezetimibe stimulated fecal cholesterol loss and TICE so strongly that those mice lost about 60% of their entire estimated body cholesterol content each day. The stimulation of fecal cholesterol loss and TICE by PX and PX/ezetimibe treatment was severely blunted in Abcg8-KO mice and this could not be restored by hepatic reintroduction of Abcg8, indicating a decisive role for intestinal ABCG5/G8 in PX-induced fecal cholesterol loss and TICE. Our data strongly suggest that hydrophilic bile acids stimulate ABCG5/G8 activity in the intestine, leading to an increased flux of cholesterol from the body into the intestinal lumen that is subsequently excreted with the feces.

The evolutionary conserved Wiskott-Aldrich syndrome protein and SCAR homolog (WASH) complex is one of the crucial multiprotein complexes that facilitates endosomal recycling of transmembrane proteins. Defects in WASH components have been associated with inherited developmental and neurological disorders in humans. Here, we show that hepatic ablation of the WASH component Washc1 in chow-fed mice increases plasma concentrations of cholesterol in both LDLs and HDLs, without affecting hepatic cholesterol content, hepatic cholesterol synthesis, biliary cholesterol excretion, or hepatic bile acid metabolism. Elevated plasma LDL cholesterol was related to reduced hepatocytic surface levels of the LDL receptor (LDLR) and the LDLR-related protein LRP1. Hepatic WASH ablation also reduced the surface levels of scavenger receptor class B type I and, concomitantly, selective uptake of HDL cholesterol into the liver. Furthermore, we found that WASHC1 deficiency increases LDLR proteolysis by the inducible degrader of LDLR, but does not affect proprotein convertase subtilisin/kexin type 9–mediated LDLR degradation. Remarkably, however, loss of hepatic WASHC1 may sensitize LRP1 for proprotein convertase subtilisin/kexin type 9–induced degradation. Altogether, these findings identify the WASH complex as a regulator of LDL as well as HDL metabolism and provide in vivo evidence for endosomal trafficking of scavenger receptor class B type I in hepatocytes.

Abstract Adipose tissue inflammation and dysfunction are associated with obesity‐related insulin resistance and diabetes, but mechanisms underlying this relationship are unclear. Although senescent cells accumulate in adipose tissue of obese humans and rodents, a direct pathogenic role for these cells in the development of diabetes remains to be demonstrated. Here, we show that reducing senescent cell burden in obese mice, either by activating drug‐inducible “suicide” genes driven by the p16 Ink4a promoter or by treatment with senolytic agents, alleviates metabolic and adipose tissue dysfunction. These senolytic interventions improved glucose tolerance, enhanced insulin sensitivity, lowered circulating inflammatory mediators, and promoted adipogenesis in obese mice. Elimination of senescent cells also prevented the migration of transplanted monocytes into intra‐abdominal adipose tissue and reduced the number of macrophages in this tissue. In addition, microalbuminuria, renal podocyte function, and cardiac diastolic function improved with senolytic therapy. Our results implicate cellular senescence as a causal factor in obesity‐related inflammation and metabolic derangements and show that emerging senolytic agents hold promise for treating obesity‐related metabolic dysfunction and its complications.