Whey protein isolate inhibits hepatic FGF21 production, which precedes weight gain, hyperinsulinemia and hyperglycemia in mice fed a high-fat diet

Abstract

Insufficient expression of hepatic fibroblast growth factor 21 (FGF21) and stromal cell-derived factor 2 like 1 (Sdf2l1) reportedly leads to insulin resistance and hepatosteatosis in obesity and type 2 diabetes. On the other hand, increased expression of hepatic serotonin receptor 2a (htr2a) in diet-induced obesity contributes to hepatosteatosis. Here we show that increases in circulating FGF21 levels and expression of hepatic FGF21 preceded weight gain, hyperinsulinemia, and hyperglycemia in C57BLJ6 mice fed a high-fat diet. Expression of hepatic htr2a and Sdf2l1 increased in insulin-resistant mice fed a high-fat diet. Intake of whey protein isolate decreased plasma FGF21 levels and expression of hepatic FGF21 in mice fed either a high-fat diet or a chow diet, whereas it only suppressed the overexpression of hepatic Sdf2 and htr2a in insulin-resistant mice fed a high-fat diet. Moreover, intake of whey protein isolate decreased plasma serotonin levels in mice fed either a high-fat diet or a chow diet. Genetic inhibition of tryptophan hydroxylase 1 decreased hepatic FGF21 expression and plasma FGF21 levels in mice. These findings suggest that increased hepatic FGF21 production precedes diet-induced weight gain, hyperinsulinemia, and hyperglycemia, and that intake of whey protein isolate could inhibit hepatic FGF21 production by suppressing peripheral serotonin synthesis.

Figure 1

Expression of hepatic FGF21 (a), plasma FGF21 levels (b), body weight (c), plasma insulin (d) and blood glucose levels (e), expression of hepatic htr2a (f) and Sdf2l1 (g) in C57BL6J mice fed a high-fat diet (HFD) or a chow diet for 13 days. The relative amount of mRNA is shown as fold-change of the mean value of the control group in mice fed a chow diet (a,g,h). Plasma insulin levels were measured after a 6-h fast (h). Glucose tolerance was tested by injection of 1 g/kg d-glucose (i). Open symbols, mice fed a chow diet for 13 days; filled symbols, mice fed a high-fat diet for 13 days. Data are presented as the mean ± SEM (n = 6/group). *P < 0.05.

Figure 2

Effects of intake of whey protein isolate (5 g/100 ml water) on body weight changes (a), daily food intake (b), water intake (c), blood glucose levels (d), plasma insulin (e) and FGF21 (f) levels, expression of hepatic FGF21 (g), htr2a (h), and Sdf2l1 (i) in C57BL6J mice fed a high-fat diet for 6 days and 13 days. Body weights in mice fed a high-fat diet for 6 days were 21.3 g ± 0.3 g (controls) and 21.5 ± 0.2 g (whey group), respectively. Body weights in mice fed a high-fat diet for 13 days were 22.6 g ± 0.3 g (controls) and 22.3 ± 0.2 g (whey group), respectively. The relative amount of mRNA is shown as fold-change of the mean value of the control group in mice fed a high-fat diet (g,h,i). Data are presented as the mean ± SEM (n = 6/group). * P < 0.05. HFD; high-fat diet.

Figure 3

Effects of intake of whey protein isolate (5 g/100 ml water) on body weight changes (a), daily food intake (b), water intake (c), blood glucose levels (d), plasma insulin (e) and FGF21 (f) levels, expression of hepatic FGF21 (g), htr2a (h), and Sdf2l1 (i) in C57BL6J mice fed a chow diet for 13 days. Body weights in mice fed a chow diet for 3 days were 19.9 g ± 0.1 g (controls) and 19.8 ± 0.1 g (whey group), respectively. The relative amount of mRNA is shown as fold-change of the mean value of the control group in mice fed a chow diet (g,h,i). Data are presented as the mean ± SEM (n = 6/group). *P < 0.05.

Figure 4

Expression of hepatic ATF4 in C57BL6J mice fed a high-fat diet or chow fat diet for 13 Days (a). Effects of intake of whey protein isolate (5 g/100 ml water) on expression of hepatic ATF4 in C57BL6J mice fed a high fat diet (b) or a chow diet (c) for 13 days. The relative amount of mRNA is shown as fold-change of the mean value of the control group in mice fed a chow diet. Data are presented as the mean ± SEM (n = 6/group). *P < 0.05.

Figure 5

Effects of intake of whey protein isolate (5 g/100 ml water) on plasma 5-HT levels in mice fed a high-fat diet for 13 days (a) or a chow diet (b) for 13 days. Plasma 5-HT levels in 8-week-old Tph1 mutant mice and wild-type mice fed a chow diet (c). HFD; high-fat diet, Tph1KO; Tph1 mutant mice WT; wild-type mice.

Figure 6

Body weight (a), daily food intake (b), blood glucose levels (c), plasma FGF21 levels (d) and expression of hepatic FGF21 (e), ATF4 (f), Htr2a (g), and Sdf2l1 (h) in Tph1 mutant mice (Tph1KO) and wild-type mice (WT) fed a chow fat diet. The relative amount of mRNA is shown as fold-change of the mean value of the WT group in mice fed a chow diet. Data are presented as the mean ± SEM (n = 6/group). * P < 0.05.

Figure 7

Effects of intraperitoneal injection of TCB-2 (2.5 mg/kg) or saline on body weight changes (a), daily food intake (b), and expression of hepatic htr2a (c), Sdf2l1 (d), FGF21 (e), and ATF4 (f) in C57BL6J mice fed a chow diet. Body weights in mice fed a chow diet for 3 days were 19.0 g ± 0.9 g (controls) and 19.8 ± 0.7 g (TCB-2 group), respectively. The relative amount of mRNA is shown as fold-change of the mean value of the control group in mice fed a chow diet. Data are presented as the mean ± SEM (n = 6/group). *P < 0.05.