Meeting Abstract

P1.36  Wednesday, Jan. 4  Mechanisms that Underlie Fasting-Associated Growth Cessation and Lipid Catabolism in Rainbow Trout (Oncorhynchus mykiss) BERGAN, H.E.; SHERIDAN, M.A.*; North Dakota St. Univ., Fargo mark.sheridan@ndsu.edu

In this study, we used rainbow trout (Oncorhynchus mykiss) to identify the cellular mechanisms involved with growth cessation and lipid catabolism during periods of fasting. Fish were placed on one of five dietary regimes—fed continuously for 2 or 4 weeks, fasted continuously for 2 or 4 weeks, or fasted 2 weeks then refed 2 weeks—and the effects on organismal growth and lipid catabolism and activation state of signaling elements (e.g., Akt, ERK, JAK-STAT, PKC) in selected tissues were measured. Fasting for either 2 or 4 weeks significantly retarded growth in terms of body weight and body length; refeeding restored growth to near levels seen in continuously fed fish. Fasting activated lipid catabolism by stimulating the catalytic activity and mRNA expression of hormone-sensitive lipase (HSL). In adipose tissue, liver, and white muscle, HSL activity was significantly elevated in 2- and 4-week fasted fish compared to fed animals, whereas in red muscle, HSL activity was significantly elevated compared to fed fish after 4 weeks. Two HSL-encoding mRNAs have been characterized, and the expression of both forms of mRNA in 2- and 4-week fasted fish were significantly elevated over levels in fed fish in all tissues. Refeeding reversed both fasting-associated elevations of HSL activity and HSL mRNA expression. Fasting resulted in the deactivation of Akt, JAK2, and STAT5 in adipose tissue, liver, and red and white muscle. By contrast, fasting activated ERK and PKC in all tissues measured. Refeeding reversed fasting-associated alterations in the activation state of all signal elements. These findings suggest that deactivation of Akt and JAK-STAT in conjunction with the activation of ERK and PKC underlie fasting-associated growth retardation and lipolysis. (Supported by NSF IOS0920116 to M.A.S.)