Butyrylcholinesterase regulates central ghrelin signaling and has an impact on food intake and glucose homeostasis

Abstract

Background: Ghrelin is the only orexigenic hormone known to stimulate food intake and promote obesity and insulin resistance. We recently showed that plasma ghrelin is controlled by butyrylcholinesterase (BChE), which has a strong impact on feeding and weight gain. BChE knockout (KO) mice are prone to obesity on high-fat diet, but hepatic BChE gene transfer rescues normal food intake and obesity resistance. However, these mice lack brain BChE and still develop hyperinsulinemia and insulin resistance, suggesting essential interactions between BChE and ghrelin within the brain.

Methods: To test the hypothesis we used four experimental groups: (1) untreated wild-type mice, (2) BChE KO mice with LUC delivered by adeno-associated virus (AAV) in combined intravenous (i.v.) and intracerebral (i.c.) injections, (3) KO mice given AAV for mouse BChE (i.v. only) and (4) KO mice given the same vector both i.v. and i.c. All mice ate a 45% calorie high-fat diet from the age of 1 month. Body weight, body composition, daily caloric intake and serum parameters were monitored throughout, and glucose tolerance and insulin tolerance tests were performed at intervals.

Results: Circulating ghrelin levels dropped substantially in the KO mice after i.v. AAV-BChE delivery, which led to normal food intake and healthy body weight. BChE KO mice that received AAV-BChE through i.v. and i.c. combined treatments not only resisted weight gain on high-fat diet but also retained normal glucose and insulin tolerance.

Conclusions: These data indicate a central role for BChE in regulating both insulin and glucose homeostasis. BChE gene transfer could be a useful therapy for complications linked to diet-induced obesity and insulin resistance.

Figure 1

BChE activity in brains of wild-type and BChE KO mice with and without BChE gene transfer. (a) Overview of BChE activity in coronal brain sections from 7-month-old mice with the indicated treatments given 5 months previously. Note that even wild-type mice express very moderate BChE activity. (b) Higher-magnification images of cortex, triangular septal nucleus, striatum, thalamus and hypothalamus from the double injections of AAV–BChE from i.v. and i.c. Ts, triangular septal nucleus; SFO, subfornical organ; CPu, caudate putamen; GP, globus pallidus; PVA, paraventribular thalamic nucleus; PT, paratenial thalamic nucleus; VMHC, ventromedial hypothalamic nucleus; ARC, arcuate hypothalamic nucleus.

Figure 2

Effect of high-fat diet on weight and body composition in wild-type and BChE KO mice fed a 45-calorie high-fat diet from the age of 4 weeks and given vectors at 10 weeks. (a) Time course of body weight in mice transduced with BChE or AAV-Luc by single i.v. injection or combined i.v.–i.c. injections. (b) Body weights at time of necropsy (7 months). (c) Terminal fat and lean mass across entire body. (d) Terminal fat mass in key adipose tissues. Results are means±s.e.m. (n=10 per group). **P<0.01, ***P<0.001 versus wild-type control; ^###P<0.001 versus BChE KO treated with AAV-Luc control.

Figure 3

Daily caloric intake in single-housed mice. (a) Caloric intake of individual 5-month-old mice was measured every day for 14 days. (b) Cumulative food intake for 1 week. Results are means±s.e.m. (n=10 per group). **P<0.01, ***P<0.001 versus wild-type control; ^#P<0.05 versus BChE KO treated with AAV-Luc control; n.s., not significant.

Figure 4

Blood glucose and glucose tolerance. (a) Blood glucose in 6-month-old mice on random feeding (measured at 1000 hours) or after 6 h of fasting (1400 hours). (b–d) Blood glucose levels, area under the curve (AUC) and blood insulin levels during glucose tolerance testing (intraperitoneal (i.p.) 1.0 g kg⁻¹ glucose) when mice were 5 months of age. **P<0.01 versus wild-type control; ^#P<0.05 versus BChE KO treated with AAV-Luc control.

Figure 5

Insulin levels and insulin tolerance. (a) Plasma insulin in 6-month-old random-fed animals was measured at 1000 hours or after 6 h fasting (1400 hours). (b, c) Blood glucose response to bolus insulin (0.75 U kg⁻¹, i.p.) and corresponding area under the curve. *P<0.05 versus wild-type control; **P<0.01 versus wild-type control; ^#P<0.05, ^##P<0.01 versus BChE KO treated with AAV-Luc control.