Activation of AMP-activated Protein Kinase by Metformin Inhibits Dedifferentiation of Platelet-derived Growth Factor-BB-induced Vascular Smooth Muscle Cells to Improve Arterial Remodeling in Cirrhotic Portal Hypertension

Background & Aims

Portal hypertension (PHT) is the potentially deadly complication of liver cirrhosis. Intrahepatic vascular resistance and the splanchnic hyperdynamic circulation are 2 principal driving factors contributing to the maintenance and exacerbation of PHT. However, in the advanced stages of cirrhosis, the fibrotic process in the liver becomes irreversible, leading to persistent and intractable increases in intrahepatic vascular resistance. Arterial remodeling emerges as a crucial mechanism driving the hyperdynamic splanchnic circulation. Therefore, ameliorating the hyperdynamic splanchnic circulation has become an indispensable component of PHT therapeutic strategies.

Methods

Liver cirrhosis with PHT was induced in the rats by common bile duct ligation (BDL). Based on the transcriptomic sequencing of the mesenteric arteries, we investigated the effects and mechanisms of metformin on the arterial remodeling at different stages of cirrhosis. We further validated potential molecular mechanisms through in vitro experiments using the A7r5 smooth muscle cell line and primary vascular smooth muscle cells (VSMCs).

Results

Our findings revealed the beneficial effects of metformin on liver cirrhosis and PHT in rats following BDL for 4 and 6 weeks. Metformin was observed to ameliorate PHT and splanchnic hyperdynamic circulation in BDL rats, even in the advanced stages of liver cirrhosis. This effect was evidenced by reduced portal pressure and cardiac output, decreased superior mesenteric artery (SMA) flow, accompanied by improvements in systemic vascular resistance and SMA resistance. Moreover, chronic inflammation in BDL rats was alleviated by metformin, which might inhibit the driving factors of angiogenesis and arterial remodeling. Notably, SMA dilation and arterial remodeling in BDL rats were potent alleviated following metformin treatment. Metformin ameliorated arterial remodeling in BDL rats by inhibiting the dedifferentiation of contractile VSMCs, resulting in the upregulation of contractile protein expressions such as alpha-smooth muscle actin (α-SMA) and smooth muscle 22α (SM22α). Platelet-derived growth factor-BB (PDGF-BB)/platelet-derived growth factor receptor beta (PDGFR-β) signaling exerted crucial roles in regulating the VSMCs cell phenotype. Activation of AMP-activated protein kinase (AMPK) by metformin blocked the downstream pathway of PDGF-BB/PDGFRβ. Furthermore, in vitro cell experiments, VSMCs were respectively treated with AMPK activator metformin or AMPK inhibitor Compound C. We revealed the molecular mechanism that metformin inhibited the phenotypic switching of A7r5 cells induced by PDGF-BB and primary VSMCs from BDL rats, which was mediated by activating AMPK to enhance the expression of contractile protein α-SMA. These findings suggest that AMPK can ameliorate the progression of arterial remodeling during PHT via suppressing the PDGF-BB/PDGFRβ signaling pathway, thereby offering novel insights into seek PHT treatment approaches.

Conclusions

Our findings revealed that metformin exerts its effects by activating the AMPK pathway, inhibiting the dedifferentiation of contractile VSMCs in the splanchnic arteries, and improving arterial remodeling, thereby ameliorating PHT and splanchnic hyperdynamic circulation in cirrhotic rats.