Regulation of glucose homeostasis in Macrobrachium rosenbergii: Effects of glucose load on glucose metabolism and hormonal response

The aim of this study was to assess the glucose tolerance of the giant freshwater prawn, Macrobrachium rosenbergii, and investigate the underlying mechanisms that regulate glucose homeostasis. A glucose tolerance test was conducted by fasting the giant freshwater prawns for 24 h, followed by an intraperitoneal injection of 1 mg of glucose per gram of body weight. The content of glucose, trehalose (disaccharide composed of two glucose molecules), glycogen, triglyceride, and protein levels in the plasma, hepatopancreas and muscle, as well as the transcriptional level of metabolism-related genes, were examined. Besides, the potential damage caused by glucose injection was evaluated by histological examination. Results showed that plasma glucose and trehalose levels peaked at 0.5 and 1 h after injection, respectively, and returned to baseline levels between 2 and 4 h, indicating a rapid clearance of exogenous glucose. The content of trehalose, glycogen, and triglyceride in both the hepatopancreas and muscle significantly increased at a relatively high speed after the glucose load, while the protein levels remained unchanged. Transcriptional levels of a rate-limiting enzyme in gluconeogenesis (phosphoenolpyruvate carboxykinase), and several enzymes involved in catabolism of trehalose (trehalase), glycogen (glycogen debranching enzyme), and triglyceride (adipose triglyceride lipase), were observed to be downregulated immediately following the glucose injection. In contrast, glycolysis and anabolism were stimulated, as indicated by increased mRNA levels of glucokinase, trehalose-6-phosphate synthase, glycogen branching enzyme, and diacylglycerol acyltransferase. Furthermore, the glucose injection decreased the expression of crustacean hyperglycemic hormone (CHH) and increased the expression of insulin-like peptide 1 (ILP1), while insulin-like peptide 2 (ILP2) expression remained unchanged. No noticeable histopathological damage to the hepatopancreas and muscle was observed after glucose injection. These findings suggest that M. rosenbergii demonstrated a rapid clearance of exogenous glucose. A glucose load may induce the expression of ILP1, stimulate glycolysis and the conversion of glucose to trehalose, glycogen, and triglyceride, while decreasing the expression of CHH and inhibiting gluconeogenesis to aid in the efficient regulation of glucose homeostasis in M. rosenbergii.