Possible Role of GnIH as a Novel Link between Hyperphagia-Induced Obesity-Related Metabolic Derangements and Hypogonadism in Male Mice

Abstract

Gonadotropin-inhibitory hormone (GnIH) is a reproductive inhibitor and an endogenous orexigenic neuropeptide that may be involved in energy homeostasis and reproduction. However, whether GnIH is a molecular signal link of metabolism and the reproductive system, and thus, regulates reproductive activity as a function of the energy state, is still unknown. In the present study, we investigated the involvement of GnIH in glycolipid metabolism and reproduction in vivo, and in the coupling between these two processes in the testis level. Our results showed that chronic intraperitoneal injection of GnIH into male mice not only increased food intake and altered meal microstructure but also significantly elevated body mass due to the increased mass of liver and epididymal white adipose tissue (eWAT), despite the loss of testicular weight. Furthermore, chronic intraperitoneal administration of GnIH to male mice resulted in obesity-related glycolipid metabolic derangements, showing hyperlipidemia, hyperglycemia, glucose intolerance, and insulin resistance through changes in the expression of glucose and lipid metabolism-related genes in the pancreas and eWAT, respectively. Interestingly, the expression of GnIH and GPR147 was markedly increased in the testis of mice under conditions of energy imbalance, such as fasting, acute hypoglycemia, and hyperglycemia. In addition, chronic GnIH injection markedly inhibited glucose and lipid metabolism of mice testis while significantly decreasing testosterone synthesis and sperm quality, inducing hypogonadism. These observations indicated that orexigenic GnIH triggers hyperphagia-induced obesity-related metabolic derangements and hypogonadism in male mice, suggesting that GnIH is an emerging candidate for coupling metabolism and fertility by involvement in obesity and metabolic disorder-induced reproductive dysfunction of the testes.

Keywords: GnIH; food intake; glucose and lipid metabolism; reproduction; testis.

Figure 1

Chronic intraperitoneally injected GnIH increases male mice obesity and photophase food intake and alters meal microstructure. (A) Effect of GnIH injected intraperitoneally on the structure of first meal in the fasting mice. (B) The food intake and meal frequency were monitored over 21 d during different periods of the photophase and scotophase post-GnIH or vehicle injection in the ad libitum fed mice. (C) The body weight change. (D) Average daily gain and average daily intake of mice intraperitoneally injected with GnIH or vehicle for 14 d. n = 15/group. The data are presented as the mean ± SEM. * p < 0.05, ** p < 0.01, and *** p < 0.001 GnIH 20 μg/100 μL vs. vehicle.

Figure 2

Chronic intraperitoneally injected GnIH alters organ indexes and serum biochemical indexes in male mice. (A) The organ weight and organ index in male mice intraperitoneally injected with GnIH or vehicle for 21 d. (B) The concentration of TG (total triglyceride), GLU (glucose), CHOL (cholesterol), HDL-C (high-density lipoprotein cholesterol), LDL-C (low-density lipoprotein cholesterin), ALT (alanine aminotransferase), and AST (aspartate aminotransferase) in the serum of chronic GnIH or vehicle-treated male mice. n = 15/group. The data are presented as the mean ± SEM. * p < 0.05, ** p < 0.01, and *** p < 0.001 GnIH 20 μg/100 μL vs. vehicle.

Figure 3

Chronic intraperitoneal injection of GnIH impaired glucose homeostasis in male mice. (A) The fasting blood glucose levels were measured at different time points after intraperitoneally injecting GnIH or vehicle into mice that had fasted for 8 h. The upper panel shows the total area under the curve (AUC) for fasting blood glucose after GnIH or vehicle injection from 0 to 120 min. (B) For the intraperitoneal glucose tolerance test, blood glucose concentrations were measured in ad libitum fed mice that had been administered with GnIH or vehicle. The upper panel shows the total AUC values for blood glucose or insulin after the administration of GnIH or vehicle from 0 to 120 min; (C) The blood glucose levels during the insulin tolerance test were measured in mice injected intraperitoneally with GnIH or vehicle. The panel shows the total AUC for blood glucose after the administration of different doses of GnIH or vehicle from 0 to 120 min. (D,E) The mRNA expression of glucose and lipid metabolism-related genes in the pancreas and eWAT of mice administered with GnIH or vehicle for 21 d, respectively. n = 15/group. The data are presented as the mean ± SEM. * p < 0.05, ** p < 0.01, and *** p < 0.001 GnIH 20 μg/100 μL vs. vehicle.

Figure 4

GnIH and its receptor GPR147 are involved in glucolipid metabolic disorder-induced testicular dysfunction. (A) The mRNA expression of GnIH and its receptor GPR147 in the testis of mice under conditions of energy imbalance. (B,C) The mRNA expression of glucose and lipid metabolism-related genes in testis of mice receiving chronic intraperitoneal injection of GnIH or vehicle for 21 d. (D) The morphological changes in testis of mice receiving chronic intraperitoneal injection of GnIH (D1, D3 and D5) or vehicle (D2, D4 and D6) for 21 d. D5 and D6 was magnified from D3 and D4 while D3 and D4 was magnified from D1 and D2, respectively. Scale bar = 50 μm. (E,F) The sperm count and sperm motility of epididymis in mice receiving chronic intraperitoneal injection of GnIH or vehicle for 21 d. (G) The mRNA expression of testosterone synthesis-related genes in mice receiving chronic intraperitoneal injection of GnIH or vehicle for 21 d. n = 15/group. The data are presented as the mean ± SEM. * p < 0.05, ** p < 0.01 and *** p < 0.001 GnIH 20 μg/100 μL vs. vehicle.