Targeting PCSK9 and APOA4 for the treatment of TMAO-induced cholelithiasis

Background and aims

Cholesterol synthesis and gallstone formation are promoted by trimethylamine-N-oxide (TMAO), a derivative of trimethylamine, which is a metabolite of gut microbiota. However, the underlying mechanisms of TMAO-induced lithogenesis remain incompletely understood. This study aimed to explore the specific molecular mechanisms through which TMAO promotes gallstone formation.

Methods

Enzyme-linked immunosorbent assays were used to compare serum concentrations of TMAO, apolipoprotein A4 (APOA4), and proprotein convertase subtilisin/kexin type 9 (PCSK9) between patients with cholelithiasis and normal controls. A murine model of TMAO-induced cholelithiasis was employed, incorporating assays of gallstone weight and bile cholesterol content, along with RNA sequencing of murine hepatic tissue. A TMAO-induced AML12 hepatocyte line was constructed and transfected with targeted small interfering RNAs and overexpression plasmids. In vivo and in vitro experiments were performed to determine the expression and regulation of genes related to cholesterol metabolism.

Results

Serum TMAO and PCSK9 levels were elevated, whereas APOA4 levels were reduced in patients with cholelithiasis. Furthermore, our murine model demonstrated that TMAO upregulated hepatic expression of PCSK9, 3-hydroxy-3-methylglutaryl-CoA reductase, and ATP-binding cassette sub-family G member 5/8, while reducing APOA4 expression, thereby modulating cholesterol metabolism and promoting lithogenesis. PCSK9 and APOA4 were identified as key regulatory genes in the cholesterol metabolic pathway. PCSK9 knockdown increased APOA4 expression, while APOA4 overexpression led to reduced PCSK9 expression.

Conclusions

We have discovered that TMAO dysregulates cholesterol metabolism by initiating a feedback loop, upregulating PCSK9 expression, and downregulating APOA4 expression in murine hepatic tissue, thereby promoting gallstone formation. In clinical practice, hyperlipidemia, a risk factor for cardiovascular diseases, also promotes gallstone formation, which should warrant attention. Regulation of blood lipid levels is necessary for patients with cholelithiasis. Targeting PCSK9 and APOA4 may represent a promising approach for the prevention and treatment of cholelithiasis.