Long-term Stress with Hyperglucocorticoidemia-induced Hepatic Steatosis with VLDL Overproduction Is Dependent on both 5-HT2 Receptor and 5-HT Synthesis in Liver

Abstract

Hepatic triglycerides production and adipose lipolysis are pivotal for long-term stress (LTS) or hyperglucocorticoidemia-induced insulin resistance. 5-hydroxytryptamine (5-HT) has been demonstrated to induce hepatic lipid metabolic abnormality by activating mammalian target of rapamycin (mTOR). In present study, we explored whether 5-HT is involved in LTS effects in liver using restraint stress-exposed rats and cultured primary rat hepatocytes and HepG2 cells. LTS with hyperglucocorticoidemia induced hepatic 5-HT synthetic increase with tryptophan hydroxylase 1 (Tph1) up-regulation, and 5-HT2 receptor (5-HT2R, including 5-HT2A, 2B receptor) up-regulation in liver and visceral adipose, as well as hepatic mTOR activation with triglycerides and VLDL overproduction with steatosis, and visceral adipose lipolytic increase with high blood free fatty acids (FFAs) level. 5-HT exposure exhibited LTS-like effects in both tissues, and both LTS and 5-HT effects could be abolished significantly by blocking 5-HT2R. In HepG2 cells dexamethasone or palmitate-induced mTOR activation with triglycerides and VLDL overproduction were accompanied by up-regulations of 5-HT synthesis and 5-HT2R, which were significantly abolished by gene silencing Tph1 or 5-HT2R and were almost fully abolished by co-silencing of both, especially on VLDL overproduction. Chemical inhibition of Tph1 or/and 5-HT2R in both hepatocytes exhibited similar abolishment with genetic inhibition on dexamethason-induced effects. 5-HT-stimulated effects in both hepatocytes were fully abolished by blocking 5-HT2R, while 5-HT itself also up-regulated 5-HT2R. In conclusion, up-regulated hepatic 5-HT synthesis and 5-HT2R induced by both glucocorticoid and FFAs are crucial for LTS-induced hepatic steatosis with VLDL overproduction, while 5-HT by acting on 5-HT2R mediates mTOR activation in liver.

Enteric serotonin and oxytocin: endogenous regulation of severity in a murine model of necrotizing enterocolitis

“…If this idea were correct, then deletion of 5-HT from the intestinal mucosa and liver would be expected to protect mice from experimental NEC. Deletion of TPH1 prevents 5-HT biosynthesis in the intestinal mucosa (14) and liver (20). The effects of the NEC protocol on the intestine and liver of WT mice and their TPH1KO littermates were, thus, compared.…”

5-HT 2A receptor deficiency alters the metabolic and transcriptional, but not the behavioral, consequences of chronic unpredictable stress

“…We observed mildly enhanced circulating glucose levels in the 5-$\text{H}{\text{T}}_{2\text{A}}^{-/-}$ mice in our serum profile studies, with a genotype effect noted in both male and female mice. Recent reports using pharmacological approaches indicate a role for peripheral 5-HT 2A receptors in the liver and in adipocytes in mediating metabolic changes evoked by chronic stress, including dyslipidemia and insulin resistance (Fu et al., 2016, Hansson et al., 2016, Oh et al., 2016, Rosmond et al., 2002). Chronic stress is associated with upregulation of liver 5-HT 2A and 5-HT 2B receptors, and a 5-HT 2A/B receptor antagonist sarpogrelate can block stress-evoked dyslipidemia (Fu et al., 2016).…”

“…CUS is known to cause a reduction in body weight and alterations in lipid metabolism ( da Silva et al., 2014 , Fu et al., 2016 ). We did find a CUS-evoked decline in body weight with no significant CUS x genotype interaction for either males or females, although the weight decline did appear attenuated in the knockout mice.…”

“…Recent reports using pharmacological approaches indicate a role for peripheral 5-HT 2A receptors in the liver and in adipocytes in mediating metabolic changes evoked by chronic stress, including dyslipidemia and insulin resistance ( Fu et al., 2016 , Hansson et al., 2016 , Oh et al., 2016 , Rosmond et al., 2002 ). Chronic stress is associated with upregulation of liver 5-HT 2A and 5-HT 2B receptors, and a 5-HT 2A/B receptor antagonist sarpogrelate can block stress-evoked dyslipidemia ( Fu et al., 2016 ). Our results indicate that CUS evokes dyslipidemia, with enhanced serum cholesterol and LDL, which appeared more pronounced in wild-type female mice.…”

Crucial Roles of 5-HT and 5-HT2 Receptor in Diabetes-Related Lipid Accumulation and Pro-Inflammatory Cytokine Generation in Hepatocytes

“…As in a previous study [12], we silenced the expression of Tph1 (siTph1), 5-HT 2A R (si5-HT 2A R), 5-HT 2B R (si5-HT 2B R), and Gαq (siGαq) using a recombinant lentivirus. Target short hairpin RNAs (shRNAs) against human Tph1, 5-HT 2A R, 5-HT 2B R, and Gαq genes for RNA interference were designed and synthesized by GenePharma (Shanghai, China) as follows: Tph1 (5′-CGG GAG GAT AAT ATC CCA CAA-3′), 5-HT 2A R (5′-CCC TGC TCA ATG TGT TTG TTT-3′), 5-HT 2B R (5′-CCG ATA TAT CAC CTG CAA TTA-3′), Gαq (5′-GCA AGA GTA CGT TTA TCA AGC-3′), and the lentiviral vector GV248-negative (shRNA control) (siCtrl): 5′-TTC TCC GAA CGT GTC ACG T-3′ without suppression of the expression of human genes.…”