The FMO3/TMAO/HSP90β axis aggravates MAFLD by disrupting mitochondrial protein homeostasis

Trimethylamine N-oxide (TMAO), a metabolite generated through the cooperation of gut microbiota and liver, has been implicated in the pathogenesis of metabolic associated fatty liver disease (MAFLD). However, the underlying molecular mechanisms remain unclear. Here, we found that TMAO promotes lipid deposition in both in vivo and in vitro models. In high-fat diet (HFD)-fed mice, the conversion of TMA to TMAO was increased, and supplementation with TMAO exacerbated lipid accumulation and liver dysfunction. In contrast, flavin-containing monooxygenase 3 (FMO3)-Sh alleviated hepatic steatosis in HFD-fed mice. Furthermore, molecular docking analysis identified heat shock protein 90β (HSP90β) as a potential downstream effector of TMAO. In both HepG2 cells and HFD-fed mice, TMAO upregulated HSP90β expression, perturbing protein homeostasis. FMO3 Sh reduced HSP90β protein activity and mRNA levels. Meanwhile, proteomic analysis revealed that the TMAO/HSP90β axis disrupts mitochondrial protein homeostasis, leading to mitochondrial dysfunction characterized by MPTP opening, MMP decrease, and ROS production. In vivo, activation of the FMO3/TMAO/HSP90β axis aggravated mitochondrial dysfunction, as evidenced by swollen mitochondria with reduced cristae observed via TEM. Notably, FMO3 Sh ameliorated mitochondrial function by suppressing the TMAO/HSP90β axis. In summary, our study demonstrates that the FMO3/TMAO/HSP90β axis promotes MAFLD progression by targeting mitochondrial protein homeostasis and influencing lipid metabolism.