Diabetes Metab J.  2018 Jun;42(3):233-243. 10.4093/dmj.2017.0084.

Inhibition of Serotonin Synthesis Induces Negative Hepatic Lipid Balance

• Namkung J
• Shong KE
• Kim H
• Oh CM
• Park S
• Kim H

• KMID: 2413986
• DOI: http://doi.org/10.4093/dmj.2017.0084

Abstract

BACKGROUND
Hepatic steatosis is caused by metabolic stress associated with a positive lipid balance, such as insulin resistance and obesity. Previously we have shown the anti-obesity effects of inhibiting serotonin synthesis, which eventually improved insulin sensitivity and hepatic steatosis. However, it is not clear whether serotonin has direct effect on hepatic lipid accumulation. Here, we showed the possibility of direct action of serotonin on hepatic steatosis.
METHODS
Mice were treated with para-chlorophenylalanine (PCPA) or LP-533401 to inhibit serotonin synthesis and fed with high fat diet (HFD) or high carbohydrate diet (HCD) to induce hepatic steatosis. Hepatic triglyceride content and gene expression profiles were analyzed.
RESULTS
Pharmacological and genetic inhibition of serotonin synthesis reduced HFD-induced hepatic lipid accumulation. Furthermore, short-term PCPA treatment prevented HCD-induced hepatic steatosis without affecting glucose tolerance and browning of subcutaneous adipose tissue. Gene expression analysis revealed that the expressions of genes involved in de novo lipogenesis and triacylglycerol synthesis were downregulated by short-term PCPA treatment as well as long-term PCPA treatment.
CONCLUSION
Short-term inhibition of serotonin synthesis prevented hepatic lipid accumulation without affecting systemic insulin sensitivity and energy expenditure, suggesting the direct steatogenic effect of serotonin in liver.

Keyword

Diabetes mellitus; Fatty liver; Lipogenesis; Obesity; Serotonin

MeSH Terms

Animals
Diabetes Mellitus
Diet
Diet, High-Fat
Energy Metabolism
Fatty Liver
Fenclonine
Gene Expression
Glucose
Insulin Resistance
Lipogenesis
Liver
Mice
Obesity
Serotonin*
Stress, Physiological
Subcutaneous Fat
Transcriptome
Triglycerides
Fenclonine
Glucose
Serotonin
Triglycerides

Figure

• 

  Fig. 1 Serotonin inhibition protected against high fat diet (HFD)-induced hepatic steatosis. Eight-week-old mice were fed a standard chow diet (SCD) or HFD for 12 weeks with vehicle, para-chlorophenylalanine (PCPA), or LP-533401 treatment. (A) H&E staining of liver sections from SCD- or HFD-fed mice with vehicle or PCPA treatment. (B) Quantification of hepatic triglyceride (TG) levels in PCPA-treated mice (n=6). (C–E) H&E staining of liver sections (left) and quantification of hepatic TG levels (right) from HFD-fed mice treated with LP-533401 (C), fat-specific Tph1-knockout (Tph1 FKO) mice (D), and 5-hydroxytryptamine receptor 3A (Htr3a) knockout (KO) mice (E) (n=6). Representative images are shown. Scale bars, 50 µm. Tphfl/fl, tryptophan hydroxylase 1 floxed. aP<0.05, bP<0.01, cP<0.001.

• 

  Fig. 2 Para-chlorophenylalanine (PCPA) treatment suppressed the positive hepatic lipid balance. Eight-week-old mice were fed a standard chow diet (SCD) or high fat diet (HFD) for 12 weeks and treated with vehicle or PCPA treatment. Hepatic expressional profiles of genes related to de novo lipogenesis (A), triglyceride synthesis (B), fatty acid (FA) uptake (C), FA oxidation (D), very low density lipoprotein secretion (E), and transcription factors (F) were assessed by quantitative reverse transcription polymerase chain reaction (n=6). Acaca, acetyl-CoA carboxylase alpha; Fasn, fatty acid synthase; Acly, ATP citrate lyase; Me1, malic enzyme 1; Scd1, stearoyl-CoA desaturase 1; Gpam, glycerol-3-phosphate acyltransferase; Agpat1, 1-acylglycerol-3-phosphate O-acyltransferase 1; Lpin1, lipin 1; Mogat1, monoacylglycerol O-acyltransferase 1; Dgat1, diacylglycerol O-acyltransferase 1; Dgat2, diacylglycerol O-acyltransferase 2; Cpt1a, carnitine palmitoyltransferase 1a; Mttp, microsomal triglyceride transfer protein; Apob, apolipoprotein B; Pparg, peroxisome proliferator activated receptor gamma; Ppargc1a, Pparg coactivator 1 alpha; Srebp1c, sterol regulatory element binding transcription factor 1c; Mlxipl, MLX interacting protein-like (ChREBP, carbohydrate response element binding protein); Nr1h3, nuclear receptor subfamily 1, group H, member 3 (LXR, liver X receptor). aP<0.05, bP<0.01, cP<0.001.

• 

  Fig. 3 Short-term treatment with para-chlorophenylalanine (PCPA) in the context of high carbohydrate diet (HCD) protected against hepatic steatosis independently from energy expenditure and insulin sensitivity. Twelve-week-old mice were fed a standard chow diet (SCD) or HCD for 2 weeks and treated with vehicle or PCPA treatment. Intraperitoneal glucose tolerance tests (A) and insulin tolerance tests (B) were performed (n=4). (C) H&E staining of inguinal white adipose tissue sections from HCD-fed mice with vehicle or PCPA treatment. (D) H&E staining of liver sections from SCD- or HCD-fed mice with vehicle or PCPA treatment. (E) Quantification of hepatic triglyceride levels in PCPA-treated mice (n=6). Representative images are shown. Scale bars, 50 µm. aP<0.05.

• 

  Fig. 4 Para-chlorophenylalanine (PCPA) treatment suppressed the positive hepatic lipid balance via downregulation of Pparg, Srebp1c, and Mlxipl. Twelve-week-old mice were fed a standard chow diet (SCD) or high carbohydrate diet (HCD) for 2 weeks with vehicle or PCPA treatment. Hepatic expressional profiles of genes related to de novo lipogenesis (A), triglyceride synthesis (B), fatty acid (FA) uptake (C), FA oxidation (D), very low density lipoprotein secretion (E), and transcription factors (F) were assessed by quantitative reverse transcription polymerase chain reaction (n=6). Acaca, acetyl-CoA carboxylase alpha; Fasn, fatty acid synthase; Acly, ATP citrate lyase; Me1, malic enzyme 1; Scd1, stearoyl-CoA desaturase 1; Gpam, glycerol-3-phosphate acyltransferase; Agpat1, 1-acylglycerol-3-phosphate O-acyltransferase 1; Lpin1, lipin 1; Mogat1, monoacylglycerol O-acyltransferase 1; Dgat1, diacylglycerol O-acyltransferase 1; Dgat2, diacylglycerol O-acyltransferase 2; Cpt1a, carnitine palmitoyltransferase 1a; Apob, apolipoprotein B; Mttp, microsomal triglyceride transfer protein; Pparg, peroxisome proliferator activated receptor gamma; Ppargc1a, Pparg coactivator 1 alpha; Srebp1c, sterol regulatory element binding transcription factor 1c; Mlxipl, MLX interacting protein-like (ChREBP, carbohydrate response element binding protein); Nr1h3, nuclear receptor subfamily 1, group H, member 3 (LXR, liver X receptor). aP<0.05, bP<0.001.

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