Abstract

This study was conducted to present the mechanism of the therapeutic effects of Chlorella vulgaris extract (CV) on the carbon tetrachloride (CCl₄) induced liver fibrosis model. Primarily, the mechanism of antioxidant effects of CV were investigated via measuring the expression of forkhead box protein O1 (FOXO1) and phosphorylated 5′ adenosine monophosphate-activated protein kinase (p-AMPK) as upstream regulators of superoxide dismutase (SOD) and catalase (CAT). Subsequently, we investigated the regulatory effect of CV treatment on the yes-associated protein (YAP) and transcriptional coactivators with a PDZ-binding motif (TAZ) as fibrogenic factors. Male Wistar rats received CCl₄ and olive oil solution 1 ml/kg intraperitoneally for 12 weeks, twice weekly. CV 50 and 100 mg/kg were administered on a daily basis by gavage in the last 4 weeks. Ultimately, liver marker enzymes and hepatic hydroxyproline content were measured. The activity of SOD and CAT and the expression of YAP, TAZ, FOXO1, SOD, and CAT were analyzed. Finally, the protein levels of YAP, TAZ, and p-AMPK were detected. CV administration decreased liver marker enzymes and hydroxyproline content significantly. The expression and protein levels of YAP and TAZ reduced by CV treatment. Furthermore, the augmentation of expression and function of CAT and SOD by CV treatment was followed by an increase in the expression of FOXO1 and protein level of p-AMPK. Our data revealed that the stimulation of expression and function of SOD and CAT by CV treatment could be mediated by FOXO1/p-AMPK axis. Moreover, anti-fibrotic effect of CV might be associated with its inhibitory effect on the hepatic expression of YAP and TAZ.

Graphic Abstract

Chlorella vulgaris treatment ameliorates liver fibrosis via two cellular mechanisms. A) Likely, Chlorella vulgaris treatment increases gene expression of enzymatic antioxidants superoxide dismutase (SOD) and catalase (CAT) via upregulating its upstream regulatory elements i.e. phosphorylated 5′ adenosine monophosphate-activated protein kinase (p-AMPK) and forkhead box protein O1 (FOXO1). These possible regulatory effects maybe lead to reduce reactive oxygen species level (ROS). B) Chlorella vulgaris treatment decreases hepatic protein level and gene expression of key elements of Hippo signaling pathway i.e. Yes-associated protein (YAP) and Transcriptional coactivators with a PDZ-binding motif (TAZ). Figure created with BioRender (https://biorender.com). ROS: Reactive oxygen species, YAP: Yes-associated protein, TAZ: Transcriptional coactivators with a PDZ-binding motif, FOXO1: Fork head Box O1, AMPK: 5′ adenosine monophosphate activated protein kinase, SOD: Superoxide dismutase, CAT: Catalase, P: Phosphate group.