Excess DHA Induces Cell Cycle Arrest by Activating the P53/Cycling Pathway in Blunt Snout Bream (Megalobrama amblycephala)

A previous study showed that diets with high levels of docosahexaenoic acid (DHA) cause growth retardation in Megalobrama amblycephala. In order to explore the mechanisms involved, a feeding trial and a primary hepatocyte culture experiment were designed. In vivo, fish (average weight 26.40 +/- 0.11 g) were randomly divided into groups and were fed three levels of DHA (0, 0.2, and 1.6% diets, respectively.) for 8 weeks. The results showed that the final body weight and weight gain of fish fed 1.6% DHA were significantly lower than those of fish fed 0.2% DHA (P < 0.05). P53 gene and protein expression levels were significantly increased (P < 0.05), while expression of downstream Cyclin D1 and Cyclin El was significantly inhibited in the 1.6% DHA group when compared with the 0 and 0.2% DHA groups (P < 0.05). In vitro, primary hepatocytes isolated from Megalobrama amblycephala incubated with 500 mu M DHA showed significantly increased cell cycle arrest and apoptosis (P < 0.05), significantly increased P53 gene and protein levels (P < 0.05), and significantly decreased Cyclin D1 and Cyclin El levels (P < 0.05) when compared with other groups. When primary hepatocytes were incubated with DHA and a P53 inhibitor (pifithrin-u), P53 expression and P53-mediated signaling were inhibited, cell cycle progression recovered, and apoptosis was reduced. In summary, high levels of DHA activated the P53/Cyclin pathway to induce cell cycle arrest. Inhibition of P53 activity may be a potential way of reducing the side effects of DHA on the growth of Megalobrama amblycephala.