Ursolic acid alleviates high starch induced hepatic glucose and lipid metabolism disorders in largemouth bass (Micropterus salmoides) via the CERK/PI3K/AKT signaling pathway

Abstract

Disorders of hepatic glucose and lipid metabolism are a significant factor reducing the economic value of largemouth bass. Ursolic acid (UA) has been shown to regulate such metabolic disorders. This study aimed to investigate the core mechanism of UA in hepatic glucose and lipid metabolism in largemouth bass fed a high starch (HS) diet. A total of 800 healthy largemouth bass with an initial average body weight of 11.00 ± 0.12 g were selected and randomly allocated into four treatment groups in a 2 × 2 factorial design: control (CON) group, UA group, HS group, and HS + UA group. Each group had five replicates with 40 fish per replicate. Fish in the CON group received a basal diet (7.38% starch); the UA group received the basal diet supplemented with UA at 500 mg/kg; the HS group received the HS diet (13.26% starch); and the HS + UA group received the HS diet supplemented with UA at 500 mg/kg. The experiment lasted for 8 weeks. To further validate the direct regulatory effect of UA on the CERK/PI3K/AKT signaling pathway in hepatocytes, this study established an in vitro primary hepatocyte culture model containing five groups: CON, high-glucose (HG), HG + UA, HG + NVP231 (CERK inhibitor), and HG + UA + NVP231. Results showed that the HS diet led to reduced final weight, weight gain ratio and body crude protein content, increased body ether extract content and hepatic collagen area (P < 0.05), while UA intervention reversed these adverse changes in bass (P < 0.05). Transcriptomic sequencing identified cerk and b4galnt1b as key genes regulating hepatic glucose and lipid metabolism, enriched in the glycosphingolipid biosynthesis-ganglio series pathway. Compared with the CON group, hepatic b4galnt1b expression was decreased, while cerk expression was increased in the HS group, and these expression trends were reversed by UA treatment (P < 0.05). Furthermore, UA increased hepatic p-PI3K and p-AKT1 protein levels, and reduced serum triacylglycerol and cholesterol contents (P < 0.05), while improved serum insulin contents, and hepatic phosphofructokinase (PFK) activity (P < 0.05). It also down-regulated hepatic il-1β and tnf-α expression and up-regulated il-10 expression (P < 0.05). In vitro experiments showed that 25 mmol/L glucose induction enhanced cell viability but increased triacylglycerol content and phosphoenolpyruvate carboxykinase activity while decreasing PFK activity (P < 0.05). Treatment with 1 μmol/L UA further improved cell viability, ameliorated these metabolic indicators, and enhanced p-AKT1, AKT1, and p-PI3K protein expression (P < 0.05). The CERK inhibitor NVP231 was applied, the expression of p-PI3K, p-AKT1, and AKT1 was suppressed (P < 0.05), and UA could no longer activate this pathway under HG conditions. In summary, the UA alleviates HS induced hepatic glucose and lipid metabolism disorders in largemouth bass main via the CERK/PI3K/AKT signaling pathway.