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Ammonia-lowering activities and carbamoyl phosphate synthetase 1 (Cps1) induction mechanism of a natural flavonoid.

Nohara K, Shin Y, Park N, Jeong K, He B, Koike N, Yoo SH, Chen Z - Nutr Metab (Lond) (2015)

Bottom Line: Expression of other urea cycle genes was also decreased by HFD relative to RC and again restored by NOB to varying degrees, which, in conjunction with Cps1 promoter reporter analysis, suggested a C/EBP-dependent mechanism for the co-induction of urea cycle genes by NOB.In comparison, HPD markedly increased CPS1 levels relative to RC, yet NOB did not further enrich CPS1 to a significant extent.Using the circadian mouse mutant Clock (Δ19/Δ19) , we also showed that a functional circadian clock, known to modulate C/EBP and CPS1 expression, was required for NOB induction of CPS1 under the HFD condition.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, The University of Texas Health Science Center at Houston, 6431 Fannin Street, MSB 6.200, Houston, TX 77030 USA.

ABSTRACT

Objective: Ammonia detoxification is essential for physiological well-being, and the urea cycle in liver plays a predominant role in ammonia disposal. Nobiletin (NOB), a natural dietary flavonoid, is known to exhibit various physiological efficacies. In the current study, we investigated a potential role of NOB in ammonia control and the underlying cellular mechanism.

Materials/methods: C57BL/6 mice were fed with regular chow (RC), high-fat (HFD) or high-protein diet (HPD) and treated with either vehicle or NOB. Serum and/or urine levels of ammonia and urea were measured. Liver expression of genes encoding urea cycle enzymes and C/EBP transcription factors was determined over the circadian cycle. Luciferase reporter assays were carried out to investigate function of CCAAT consensus elements on the carbamoyl phosphate synthetase (Cps1) gene promoter. A circadian clock-deficient mouse mutant, Clock (Δ19/Δ19) , was utilized to examine a requisite role of the circadian clock in mediating NOB induction of Cps1.

Results: NOB was able to lower serum ammonia levels in mice fed with RC, HFD or HPD. Compared with RC, HFD repressed the mRNA and protein expression of Cps1, encoding the rate-limiting enzyme of the urea cycle. Interestingly, NOB rescued CPS1 protein levels under the HFD condition via induction of the transcription factors C/EBPα and C/EBPβ. Expression of other urea cycle genes was also decreased by HFD relative to RC and again restored by NOB to varying degrees, which, in conjunction with Cps1 promoter reporter analysis, suggested a C/EBP-dependent mechanism for the co-induction of urea cycle genes by NOB. In comparison, HPD markedly increased CPS1 levels relative to RC, yet NOB did not further enrich CPS1 to a significant extent. Using the circadian mouse mutant Clock (Δ19/Δ19) , we also showed that a functional circadian clock, known to modulate C/EBP and CPS1 expression, was required for NOB induction of CPS1 under the HFD condition.

Conclusion: NOB, a dietary flavonoid, exhibits a broad activity in ammonia control across varying diets, and regulates urea cycle function via C/EBP-and clock-dependent regulatory mechanisms.

No MeSH data available.


NOB modulates Cps1 mRNA and protein expression. a Total protein extracts were prepared from liver samples collected from the four diet/treatment groups of wild-type mice at the indicated circadian time points (n = 3). Western blotting analysis was performed using anti-CPS1 antibody. RC regular chow, HFD high-fat diet, Veh vehicle, NOB Nobiletin. The results shown are representative of three independent experiments. See Additional file 1: Figure S1A for quantitative analysis. b Immunohistochemical staining of CPS1 in liver sections from mice with the indicated diet and treatment at ZT2. c Real-time RT-PCR analysis of Cps1 in liver samples collected as in (a). Data are presented as mean ± SEM (n = 3). Two-way ANOVA with Bonferroni post-hoc tests shows significant statistical differences between HFD.Veh and other three groups (p < 0.0001). d Western blotting analysis of protein lysates of liver samples collected at ZT 6 and 18 from mice with the indicated diet and treatment (n = 3). HPD indicates high-protein diet. The images shown to the left are representative of three independent experiments. Quantitation of Western blots was carried out and the results, presented as mean ± SEM, are shown in the lower panel. Two-way ANOVA with Bonferroni post-hoc tests, RC vs. HPD, ***p < 0.001. e Real-time qPCR analysis was carried out using total RNAs extracted from the liver samples described in (d). The results are presented as mean ± SEM. Two-way ANOVA with Bonferroni post-hoc tests, RC vs. HPD, *p < 0.05
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Fig2: NOB modulates Cps1 mRNA and protein expression. a Total protein extracts were prepared from liver samples collected from the four diet/treatment groups of wild-type mice at the indicated circadian time points (n = 3). Western blotting analysis was performed using anti-CPS1 antibody. RC regular chow, HFD high-fat diet, Veh vehicle, NOB Nobiletin. The results shown are representative of three independent experiments. See Additional file 1: Figure S1A for quantitative analysis. b Immunohistochemical staining of CPS1 in liver sections from mice with the indicated diet and treatment at ZT2. c Real-time RT-PCR analysis of Cps1 in liver samples collected as in (a). Data are presented as mean ± SEM (n = 3). Two-way ANOVA with Bonferroni post-hoc tests shows significant statistical differences between HFD.Veh and other three groups (p < 0.0001). d Western blotting analysis of protein lysates of liver samples collected at ZT 6 and 18 from mice with the indicated diet and treatment (n = 3). HPD indicates high-protein diet. The images shown to the left are representative of three independent experiments. Quantitation of Western blots was carried out and the results, presented as mean ± SEM, are shown in the lower panel. Two-way ANOVA with Bonferroni post-hoc tests, RC vs. HPD, ***p < 0.001. e Real-time qPCR analysis was carried out using total RNAs extracted from the liver samples described in (d). The results are presented as mean ± SEM. Two-way ANOVA with Bonferroni post-hoc tests, RC vs. HPD, *p < 0.05

Mentions: Carbamoyl phosphate synthetase I (CPS1) has been shown to accumulate in a circadian manner; however, CPS1 proteins are exceedingly abundant and discrepancy in circadian pattern exists [26, 27]. We therefore conducted Western blotting to examine CPS1 protein levels in mouse liver over circadian time course. While largely unchanged between Veh and NOB treatment under RC conditions based on 2-way ANOVA, CPS1 levels were significantly reduced in HFD.Veh compared with RC (Fig. 2a and Additional file 1: Figure S1A) [47]. Strikingly, NOB restored CPS1 in HFD to RC levels (Fig. 2a). We also confirmed the above results using Coomassie staining followed by mass spectrometry (Additional file 1: Figure S1B and Table S3). Furthermore, confocal microscopy using anti-CPS1 antibody also clearly showed recovered CPS1 in livers from HFD.NOB mice relative to HFD.Veh (Fig. 2b and Additional file 1: Figure S1C). Real-time qPCR analysis further revealed strong repression of Cps1 messenger levels by HFD relative to RC (Fig. 2c), consistent with its effect on CPS1 proteins. Importantly, NOB restored Cps1 mRNA expression, mirroring the changes in CPS1 protein.Fig. 2


Ammonia-lowering activities and carbamoyl phosphate synthetase 1 (Cps1) induction mechanism of a natural flavonoid.

Nohara K, Shin Y, Park N, Jeong K, He B, Koike N, Yoo SH, Chen Z - Nutr Metab (Lond) (2015)

NOB modulates Cps1 mRNA and protein expression. a Total protein extracts were prepared from liver samples collected from the four diet/treatment groups of wild-type mice at the indicated circadian time points (n = 3). Western blotting analysis was performed using anti-CPS1 antibody. RC regular chow, HFD high-fat diet, Veh vehicle, NOB Nobiletin. The results shown are representative of three independent experiments. See Additional file 1: Figure S1A for quantitative analysis. b Immunohistochemical staining of CPS1 in liver sections from mice with the indicated diet and treatment at ZT2. c Real-time RT-PCR analysis of Cps1 in liver samples collected as in (a). Data are presented as mean ± SEM (n = 3). Two-way ANOVA with Bonferroni post-hoc tests shows significant statistical differences between HFD.Veh and other three groups (p < 0.0001). d Western blotting analysis of protein lysates of liver samples collected at ZT 6 and 18 from mice with the indicated diet and treatment (n = 3). HPD indicates high-protein diet. The images shown to the left are representative of three independent experiments. Quantitation of Western blots was carried out and the results, presented as mean ± SEM, are shown in the lower panel. Two-way ANOVA with Bonferroni post-hoc tests, RC vs. HPD, ***p < 0.001. e Real-time qPCR analysis was carried out using total RNAs extracted from the liver samples described in (d). The results are presented as mean ± SEM. Two-way ANOVA with Bonferroni post-hoc tests, RC vs. HPD, *p < 0.05
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Fig2: NOB modulates Cps1 mRNA and protein expression. a Total protein extracts were prepared from liver samples collected from the four diet/treatment groups of wild-type mice at the indicated circadian time points (n = 3). Western blotting analysis was performed using anti-CPS1 antibody. RC regular chow, HFD high-fat diet, Veh vehicle, NOB Nobiletin. The results shown are representative of three independent experiments. See Additional file 1: Figure S1A for quantitative analysis. b Immunohistochemical staining of CPS1 in liver sections from mice with the indicated diet and treatment at ZT2. c Real-time RT-PCR analysis of Cps1 in liver samples collected as in (a). Data are presented as mean ± SEM (n = 3). Two-way ANOVA with Bonferroni post-hoc tests shows significant statistical differences between HFD.Veh and other three groups (p < 0.0001). d Western blotting analysis of protein lysates of liver samples collected at ZT 6 and 18 from mice with the indicated diet and treatment (n = 3). HPD indicates high-protein diet. The images shown to the left are representative of three independent experiments. Quantitation of Western blots was carried out and the results, presented as mean ± SEM, are shown in the lower panel. Two-way ANOVA with Bonferroni post-hoc tests, RC vs. HPD, ***p < 0.001. e Real-time qPCR analysis was carried out using total RNAs extracted from the liver samples described in (d). The results are presented as mean ± SEM. Two-way ANOVA with Bonferroni post-hoc tests, RC vs. HPD, *p < 0.05
Mentions: Carbamoyl phosphate synthetase I (CPS1) has been shown to accumulate in a circadian manner; however, CPS1 proteins are exceedingly abundant and discrepancy in circadian pattern exists [26, 27]. We therefore conducted Western blotting to examine CPS1 protein levels in mouse liver over circadian time course. While largely unchanged between Veh and NOB treatment under RC conditions based on 2-way ANOVA, CPS1 levels were significantly reduced in HFD.Veh compared with RC (Fig. 2a and Additional file 1: Figure S1A) [47]. Strikingly, NOB restored CPS1 in HFD to RC levels (Fig. 2a). We also confirmed the above results using Coomassie staining followed by mass spectrometry (Additional file 1: Figure S1B and Table S3). Furthermore, confocal microscopy using anti-CPS1 antibody also clearly showed recovered CPS1 in livers from HFD.NOB mice relative to HFD.Veh (Fig. 2b and Additional file 1: Figure S1C). Real-time qPCR analysis further revealed strong repression of Cps1 messenger levels by HFD relative to RC (Fig. 2c), consistent with its effect on CPS1 proteins. Importantly, NOB restored Cps1 mRNA expression, mirroring the changes in CPS1 protein.Fig. 2

Bottom Line: Expression of other urea cycle genes was also decreased by HFD relative to RC and again restored by NOB to varying degrees, which, in conjunction with Cps1 promoter reporter analysis, suggested a C/EBP-dependent mechanism for the co-induction of urea cycle genes by NOB.In comparison, HPD markedly increased CPS1 levels relative to RC, yet NOB did not further enrich CPS1 to a significant extent.Using the circadian mouse mutant Clock (Δ19/Δ19) , we also showed that a functional circadian clock, known to modulate C/EBP and CPS1 expression, was required for NOB induction of CPS1 under the HFD condition.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, The University of Texas Health Science Center at Houston, 6431 Fannin Street, MSB 6.200, Houston, TX 77030 USA.

ABSTRACT

Objective: Ammonia detoxification is essential for physiological well-being, and the urea cycle in liver plays a predominant role in ammonia disposal. Nobiletin (NOB), a natural dietary flavonoid, is known to exhibit various physiological efficacies. In the current study, we investigated a potential role of NOB in ammonia control and the underlying cellular mechanism.

Materials/methods: C57BL/6 mice were fed with regular chow (RC), high-fat (HFD) or high-protein diet (HPD) and treated with either vehicle or NOB. Serum and/or urine levels of ammonia and urea were measured. Liver expression of genes encoding urea cycle enzymes and C/EBP transcription factors was determined over the circadian cycle. Luciferase reporter assays were carried out to investigate function of CCAAT consensus elements on the carbamoyl phosphate synthetase (Cps1) gene promoter. A circadian clock-deficient mouse mutant, Clock (Δ19/Δ19) , was utilized to examine a requisite role of the circadian clock in mediating NOB induction of Cps1.

Results: NOB was able to lower serum ammonia levels in mice fed with RC, HFD or HPD. Compared with RC, HFD repressed the mRNA and protein expression of Cps1, encoding the rate-limiting enzyme of the urea cycle. Interestingly, NOB rescued CPS1 protein levels under the HFD condition via induction of the transcription factors C/EBPα and C/EBPβ. Expression of other urea cycle genes was also decreased by HFD relative to RC and again restored by NOB to varying degrees, which, in conjunction with Cps1 promoter reporter analysis, suggested a C/EBP-dependent mechanism for the co-induction of urea cycle genes by NOB. In comparison, HPD markedly increased CPS1 levels relative to RC, yet NOB did not further enrich CPS1 to a significant extent. Using the circadian mouse mutant Clock (Δ19/Δ19) , we also showed that a functional circadian clock, known to modulate C/EBP and CPS1 expression, was required for NOB induction of CPS1 under the HFD condition.

Conclusion: NOB, a dietary flavonoid, exhibits a broad activity in ammonia control across varying diets, and regulates urea cycle function via C/EBP-and clock-dependent regulatory mechanisms.

No MeSH data available.