Fasting and re-feeding impact on leptin and aquaglyceroporin 9 in the liver of European sea bass (Dicentrarchus labrax)

The aim of the present study was to investigate by histological methods the impact of fasting and re-feeding induced compensatory growth, in the European sea bass (Dicentrarchus labrax) liver. In addition, the presence and distribution of leptin (LEP) and aquaglyceroporin 9 (AQP-9), two proteins involved in lipid storage and mobilization, were investigated in the liver in relation to fish nutritional status with the aim to verify their involvement in the compensatory growth. The histological results showed modifications in liver feature and in hepatic glycogen storage during fasting. Indeed, liver morphology was altered by food deprivation and was characterized by a large spectrum of vacuolization. During re-feeding, liver of the previously fasted fish showed a similar feature to that observed in the control fish, suggesting a recovery at the histomorphological level. The hepatic glycogen store was observed in the control, and in the re-fed fish, but not in the fasted group. Immunostaining showed an up-regulation in both LEP and AQP-9 during fasting and a down-regulation during re-feeding, whereas AQP-9 but not LEP immunoreactivity was higher than that of the controls. The study of fasting and re-feeding induced histological alterations provides additional knowledge on the fish cell and tissue condition, completing the information obtained with growth studies. We also demonstrated that although LEP and AQP-9 were both influenced by nutritional status in sea bass, only AQP-9 was involved in the compensatory growth of this species. Therefore, we suggest AQP-9 may play a role in the process of energy accumulation to lipid storage in sea bass liver during the phase of the compensatory growth.