Waterborne Copper And Zinc Exposure Influencing Hepatic Lipid Deposition And Metabolism In Javelin Goby (Synechogobius Hasta)

Synechogobius hasta is small fish, which widely distributed over the southern coast of Liaoning Province, China. In recent years, commercial farming of this fish has become an increasing interest in northern China because of its euryhalinity, rapid growth, good taste, and high market value. Copper(Cu) and Zinc(Zn) are essential micronutrient required for the various functions in biological development such as cell structure and enzyme activities of fish. However, excessive Cu and Zn in aquatic environment can be toxic. In fish, lipids act as a major energy source and support various physiological, developmental and reproductive processes. At present, in fish, the bioaccumulation of Cu and Zn, and their waterborne exposure effect on survival, growth, reproduction, development, histological changes, enzymatic activity, metal accumulation and oxidative stress have widely been studied. However, relatively low waterborne Cu and Zn concentration and long exposure time influencing hepatic lipid deposition and metabolism remained unexplored. The present study was conducted to determine the time-course effect and mechanism of waterborne chronic Cu and Zn exposure influencing hepatic lipid deposition and metabolism in javelin goby S. hasta. The main results were as follows:1. S. hasta were exposed to four waterborne Cu concentrations(2(control), 18, 38 and 55 g Cu/l) for 60 days. Sampling occurred on day 30 and day 60, respectively. Survival decreased and hepatic Cu content increased with increasing Cu levels. On day 30, Cu exposure increased hepatic lipid content, viscerosomatic index(VSI) and hepatosomatic index(HSI), and activities of lipogenic enzymes: 6-phosphogluconate dehydrogenase(6PGD), Glucose 6-phosphatedehydrogenase(G6PD), Malic enzyme(ME), Isocitrate dehydrogenase(ICDH) and Fatty acid synthase(FAS) in the liver. On day 60, Cu exposure reduced hepatic lipid content, HSI, VSI, activities of G6 PD, ME, ICDH and FAS. Cu exposure for 30 days induced hepatic lipid accumulation by stimulating lipogenesis. However, 60-day Cu exposure reduced hepatic lipid content by inhibiting lipogenesis. To our knowledge, for the first time, the present study provided experimental evidence that waterborne chronic Cu exposure differentially influenced enzymes involved in lipogenic metabolic pathway in a duration-dependent manner in fish, and provided new insight into the relationship between metal toxicity and lipid metabolism.2. S. hasta were exposed to four waterborne Zn concentrations(0.005(control), 0.18, 0.36 and 0.55 mg Zn/l, respectively) for 60 days. Sampling occurred at day 20, 40 and 60, respectively. Zn exposure increased Zn content and declined hepatic lipid content in liver. Zn exposure reduced viscerosomatic index(VSI), hepatosomatic index(HSI) and activities of lipogenic enzymes(6PGD, G6 PD, ME and FAS). At day 20 and 60, Zn exposure decreased hepatic m RNA levels of 6PGD, G6 PD, ME, FAS, acetyl-Co A carboxylase(ACCα and ACCβ), hormone-sensitive lipase(HSLa and HSLb), sterol-regulator element-binding protein-1(SREBP-1), peroxisome proliferators-activated receptor(PPARα and PPARγ). However, the m RNA levels of carnitine palmitoyltransferase 1(CPT 1) and adipose triglyceride lipase(ATGL) increased following Zn exposure. On day 40, Zn exposure reduced hepatic m RNA expression of 6PGD, G6 PD, ME, FAS, ACCα, ACCβ, HSLa, HSLb, SREBP-1 and PPARγ but increased m RNA expression of CPT 1, ATGL and PPARα. The differential Pearson correlation between m RNA levels of transcription factors(SREBP-1, PPARα and PPARγ), and the activities and m RNA expression of enzymes involved in lipogenesis and lipolysis were also observed at day 20, 40 and 60, respectively, indicating that the correlation between transcriptional factors and enzymes was also time-dependent. General speaking, Zn exposure reduced hepatic lipid content by inhibiting lipogenesis and stimulating lipolysis. To our knowledge, for the first time, the present study provided experimental evidence that waterborne chronic Zn exposure differentially influenced m RNA expression and activities of genes and enzymes involved in lipogenic and lipolytic metabolism in a duration-dependent manner in fish, and provided new insight into the relationship between metal elements and lipid metabolism.