The GOAT-ghrelin system is not essential for hypoglycemia prevention during prolonged calorie restriction
Authors: Henriette Kirchner
Anupama Joseph
Traci Kruthaupt
Matthias H Tschöp
Nickki Ottaway
Michael O Thorner
Chun-Xia Yi
Harold W Davis
Paul T Pfluger
Bruce D Gaylinn
Martin Bidlingmaier
Kristy M Heppner
Yongmei Zhao
Diego Perez-Tilve
Erin Bartley
Dhiraj Kabra
Maximillian Bielohuby
Kirk M Habegger
Timo D Müller
Stephen C Benoit
Jenny Tong
Journal: PLoS ONE (2012)
Discipline: Multidisciplinary
Keywords: Ghrelin; acylation; GOAT; GHSR; hypoglycemia
Affiliations: Institute for Diabetes and Obesity, Helmholtz Centre Munich, Neuherberg, Germany.

Abstract:  Objective: Ghrelin acylation by ghrelin O-acyltransferase (GOAT) has recently been reported to be essential for the prevention of hypoglycemia during prolonged negative energy balance. Using a unique set of four different genetic loss-of-function models for the GOAT/ghrelin/growth hormone secretagogue receptor (GHSR) system, we thoroughly tested the hypothesis that lack-of-ghrelin activation or signaling would lead to hypoglycemia during caloric deprivation. Methodology: Male and female knockout (KO) mice for GOAT, ghrelin, GHSR, or both ghrelin and GHSR (dKO) were subjected to prolonged calorie restriction (40% of ad libitum chow intake). Body weight, fat mass, and glucose levels were recorded daily and compared to wildtype (WT) controls. Forty-eight hour blood glucose profiles were generated for each individual mouse when 2% or less body fat mass was reached. Blood samples were obtained for analysis of circulating levels of acyl- and desacyl-ghrelin, IGF-1, and insulin. Principal findings: Chronic calorie restriction progressively decreased body weight and body fat mass in all mice regardless of genotype. When fat mass was depleted to 2% or less of body weight for 2 consecutive days, random hypoglycemic events occurred in some mice across all genotypes. There was no increase in the incidence of hypoglycemia in any of the four loss-of-function models for ghrelin signaling including GOAT KO mice. Furthermore, no differences in insulin or IGF-1 levels were observed between genotypes. Conclusion: The endogenous GOAT-ghrelin-GHSR system is not essential for the maintenance of euglycemia during prolonged calorie restriction. 

Retracted: No

PubPeer comments:
 Some unexpected similarities in change of body mass between animals ![file] , 
 We separately compared GOAT KO mice to their respective WT controls, and GHSR KO, Ghrelin KO, Ghr-GHSR dKO to their respective Ghr-GHSR WT controls. To account for the interindividual variance, Fig. 1 shows body weight or fat mass curves for each individual mouse per genotype. Fig. S1 (pasted below) shows average values per group. Displaying the two single KOs (Ghrelin GHSR), the dKOs and the Ghr-GHSR WTs in one panel wouldnu2019t have worked, the graph would have been too convoluted. Accordingly, we split the graph into three panels, each comparing one genotype (i.e. Ghr KO, GHSR KO or dKO) to the Ghr-GHSR WT control. The similarities in change of body mass (or fat mass) in the Ghr-GHSR WTs are thus not unexpected. Rather, the Ghr-GHSR WT mice are identical in the three lower panels of Fig. 1. The same applies to Fig. S1 (see image below). Please also see in our legend for Fig. 1: u201cLines depict body weight and fat mass curves for individual animals from groups of 8 male GOAT WT, 5 female GOAT WT, 9 male GOAT KO, 8 female GOAT KO, 10 male Ghr-GHSR dWT, 20 female Ghr-GHSR dWT, 19 male Ghr KO, 18 female Ghr KO, 7 male GHSR KO, 19 female GHSR KO, 16 male Ghr-GHSR dKO and 7 female Ghr-GHSR dKO miceu201d. ![file] , 
 While I understand the Ghr-GHSR WT triple appearance in #1, I wonder where some mice in the top left image are hidden - I count only 5. ![file] I am also searching a female Ghrelin KO mouse in table 1... ![file] , 
 #3 Your concern is unclear. The image you posted is from Fig 2A, which shows male mice. The curves in the Fig 2A image match those expected from Table 1: there are 5 black lines (= GOAT WT) and 9 purple lines (= GOAT KO). The text you added to the image suggests you expect  9 black lines , which is incorrect according to Table 1. Perhaps you misinterpreted black vs. purple? , 
 Sorry mixed colors in my description but stand by the fact that there is a major discrepancy. ![file] The legend says 8 male GOAT WT (black) and 9 male GOAT KO (purple). Table 1 says 5 male GOAT WT and 9 male GOAT KO. I can only guess how many lines are in FIG1A and FIG2A... What gives the correct male GOAT numbers? Legend 1 legend 2 or FIG1A or FIG2A or table 1? Maybe you didn t comment also on the missing female Ghrelin KO mouse with the red circle in table 1? , 
 #5 RE: * I can only guess how many lines are in FIG1A and FIG2A... * You don t really have to guess; you can simply count them. They are dense, but in most cases it is pretty easy to count the lines. Overall, by checking the data in Figs 1 and 2, it looks to me that the plots agree with the numbers in Table 1. It seems to me that there are errors in the legends, repeated for both Figs 1 and 2. Namely, there are mix-ups between male female for GOAT WT, and the legends say  18 female Ghr KO rather than  8 . Again, by counting lines in the Figs, it seems Table 1 is correct whereas the legends have mistakes. Hopefully the authors can check and correct the following errors suspected in Figs 1 and 2 legends: u2022  8 male GOAT WT should be  5 . u2022u00a0 5 female GOAT WT should be  8 . u2022u00a0 18 female Ghr KO should be  8 . Finally, Table 1 might have an error for Hypoglycemia data in female Ghr KO mice (i.e., 1 of 8 rather than 1 of 7?). ,