The orphan nuclear receptor small heterodimer partner is required for thiazolidinedione effects in leptin-deficient mice

Pterostilbene targets the molecular oscillator RORγ to restore circadian rhythm oscillation and protect against sleep restriction induced metabolic disorders

BACKGROUND

Considerable researches have directed toward metabolic disorders caused by sleep restriction (SR). SR-induced disruption of circadian metabolic rhythmicity is identified as an important pathophysiological mechanism. The flavonoid pterostilbene (PTE) is abundant in the traditional Chinese medicine dragon's blood with protective efficacy against obesity-related metabolic dysfunctions. Our previous study found that PTE ameliorates exercise intolerance and clock gene oscillation in the skeletal muscles subjected to SR.

PURPOSE

This study aimed to explore whether PTE improves SR-induced metabolic disorders and delineate the relationship between PTE and the circadian clock.

STUDY DESIGN AND METHODS

Two hundred male C57/B6J mice were kept awake for 20 h/d over five consecutive days and concurrently gavaged with 50, 100, or 200 mg/kg·bw/d PTE. Food consumption and body weight were monitored, and the metabolic status of the mice was evaluated by performing OGTT and ITT, measuring the serum lipid profiles and liver histopathology in response to SR. Daily behavior was analyzed by Clocklab™. The circadian rhythms of the liver clock genes and metabolic output genes were evaluated by cosine analysis. Binding between PTE and RORα/γ or NR1D1/2 was investigated by molecular docking. A luciferase reporter assay was used to determine the impact of PTE on Bmal1 transcription in SR-exposed mice co-transfected with Ad-BMAL1-LUC plus Ad-RORγ-mCherry or Ad-NR1D1-EGFP.

RESULTS

PTE significantly ameliorated abnormal glucose and lipid metabolism (p < 0.05) in SR-exposed mice. PTE improved circadian behavior (p < 0.05) and rescued the circadian rhythm oscillation of the liver clock (p < 0.05) and metabolic output genes (p < 0.05) under SR condition. Molecular docking disclosed that PTE might interact with RORs, and PTE was found to increase Bmal1 promoter luciferase activity with RORE elements in the presence of Ad-RORγ-mCherry (p < 0.05).

CONCLUSIONS

PTE may protect against SR-induced metabolic disorders by directly modulating RORγ to maintain circadian metabolic rhythm. The findings provide valuable insights into the potential use of PTE in the treatment of metabolic disorders associated with disruptions in the circadian rhythm.

Hepatocyte Small Heterodimer Partner Mediates Sex-Specific Effects on Triglyceride Metabolism via Androgen Receptor in Male Mice

Mechanisms of sex differences in hypertriglyceridemia remain poorly understood. Small heterodimer partner (SHP) is a nuclear receptor that regulates bile acid, glucose, and lipid metabolism. SHP also regulates transcriptional activity of sex hormone receptors and may mediate sex differences in triglyceride (TG) metabolism. Here, we test the hypothesis that hepatic SHP mediates sex differences in TG metabolism using hepatocyte-specific SHP knockout mice. Plasma TGs in wild-type males were higher than in wild-type females and hepatic deletion of SHP lowered plasma TGs in males but not in females, suggesting hepatic SHP mediates plasma TG metabolism in a sex-specific manner. Additionally, hepatic deletion of SHP failed to lower plasma TGs in gonadectomized male mice or in males with knockdown of the liver androgen receptor, suggesting hepatic SHP modifies plasma TG via an androgen receptor pathway. Furthermore, the TG lowering effect of hepatic deletion of SHP was caused by increased clearance of postprandial TG and accompanied with decreased plasma levels of ApoC1, an inhibitor of lipoprotein lipase activity. These data support a role for hepatic SHP in mediating sex-specific effects on plasma TG metabolism through androgen receptor signaling. Understanding how hepatic SHP regulates TG clearance may lead to novel approaches to lower plasma TGs and mitigate cardiovascular disease risk.

Deciphering the Relationship between Obesity and Various Diseases from a Network Perspective

The number of obesity cases is rapidly increasing in developed and developing countries, thereby causing significant health problems worldwide. The pathologic factors of obesity at the molecular level are not fully characterized, although the imbalance between energy intake and consumption is widely recognized as the main reason for fat accumulation. Previous studies reported that obesity can be caused by the dysfunction of genes associated with other diseases, such as myocardial infarction, hence providing new insights into dissecting the pathogenesis of obesity by investigating its associations with other diseases. In this study, we investigated the relationship between obesity and diseases from Online Mendelian Inheritance in Man (OMIM) databases on the protein–protein interaction (PPI) network. The obesity genes and genes of one OMIM disease were mapped onto the network, and the interaction scores between the two gene sets were investigated on the basis of the PPI of individual gene pairs, thereby inferring the relationship between obesity and this disease. Results suggested that diseases related to nutrition and endocrine are the top two diseases that are closely associated with obesity. This finding is consistent with our general knowledge and indicates the reliability of our obtained results. Moreover, we inferred that diseases related to psychiatric factors and bone may also be highly related to obesity because the two diseases followed the diseases related to nutrition and endocrine according to our results. Numerous obesity–disease associations were identified in the literature to confirm the relationships between obesity and the aforementioned four diseases. These new results may help understand the underlying molecular mechanisms of obesity–disease co-occurrence and provide useful insights for disease prevention and intervention.

MicroRNA-206 prevents hepatosteatosis and hyperglycemia by facilitating insulin signaling and impairing lipogenesis

BACKGROUND & AIMS

The paradox of selective hepatic insulin resistance, wherein the insulin-resistant liver fails to suppress glucose production but continues to produce lipids, has been central to the pathophysiology of hepatosteatosis and hyperglycemia. Our study was designed to investigate the mechanism(s) by which microRNA-206 alleviates the pathogenesis of hepatosteatosis and hyperglycemia.

METHODS

Dietary obese mice induced by a high fat diet were used to study the role of microRNA-206 in the pathogenesis of hepatosteatosis and hyperglycemia. A mini-circle vector was used to deliver microRNA-206 into the livers of mice.

RESULTS

Lipid accumulation impaired biogenesis of microRNA-206 in fatty livers of dietary obese mice and human hepatocytes (p<0.01). Delivery of microRNA-206 into the livers of dietary obese mice resulted in the strong therapeutic effects on hepatosteatosis and hyperglycemia. Mechanistically, miR-206 interacted with the 3' untranslated region of PTPN1 (protein tyrosine phosphatase, non-receptor type 1) and induced its degradation. By inhibiting PTPN1 expression, microRNA-206 facilitated insulin signaling by promoting phosphorylation of INSR (insulin receptor) and impaired hepatic lipogenesis by inhibiting Srebp1c transcription. By simultaneously modulating lipogenesis and insulin signaling, microRNA-206 reduced lipid (p=0.006) and glucose (p=0.018) production in human hepatocytes and livers of dietary obese mice (p<0.001 and p<0.01 respectively). Re-introduction of Ptpn1 into livers offset the inhibitory effects of microRNA-206, indicating that PTPN1 mediates the inhibitory effects of microRNA-206 on both hepatosteatosis and hyperglycemia.

CONCLUSIONS

MicroRNA-206 is a potent inhibitor of lipid and glucose production by simultaneously facilitating insulin signaling and impairing hepatic lipogenesis. Our findings potentially provide a novel therapeutic agent for both hepatosteatosis and hyperglycemia.

LAY SUMMARY

The epidemic of obesity is causing a sharp rise in the incidence of insulin resistance and its major complications, type 2 diabetes and non-alcoholic fatty liver disease (NAFLD). However, there are no effective treatments because the mechanisms underlying both disorders are not well described. We identified microRNA-206 as a novel and effective inhibitor for both glucose and lipid production in liver and potentially provide a unique therapeutic drug for both hepatosteatosis and hyperglycemia.

Small heterodimer partner (SHP) contributes to insulin resistance in cardiomyocytes

Small heterodimer partner (SHP) is an atypical nuclear receptor expressed in heart that has been shown to inhibit the hypertrophic response. Here, we assessed the role of SHP in cardiac metabolism and inflammation. Mice fed a high-fat diet (HFD) displayed glucose intolerance accompanied by increased cardiac mRNA levels of Shp. In HL-1 cardiomyocytes, SHP overexpression inhibited both basal and insulin-stimulated glucose uptake and impaired the insulin signalling pathway (evidenced by reduced AKT and AS160 phosphorylation), similar to insulin resistant cells generated by high palmitate/high insulin treatment (HP/HI; 500μM/100nM). In addition, SHP overexpression increased Socs3 mRNA and reduced IRS-1 protein levels. SHP overexpression also induced Cd36 expression (~6.2 fold; p<0.001) linking to the observed intramyocellular lipid accumulation. SHP overexpressing cells further showed altered expression of genes involved in lipid metabolism, i.e., Acaca, Acadvl or Ucp3, augmented NF-κB DNA-binding activity and induced transcripts of inflammatory genes, i.e., Il6 and Tnf mRNA (~4-fold induction, p<0.01). Alterations in metabolism and inflammation found in SHP overexpressing cells were associated with changes in the mRNA levels of Ppara (79% reduction, p<0.001) and Pparg (~58-fold induction, p<0.001). Finally, co-immunoprecipitation studies showed that SHP overexpression strongly reduced the physical interaction between PPARα and the p65 subunit of NF-κB, suggesting that dissociation of these two proteins is one of the mechanisms by which SHP initiates the inflammatory response in cardiac cells. Overall, our results suggest that SHP upregulation upon high-fat feeding leads to lipid accumulation, insulin resistance and inflammation in cardiomyocytes.