Orphan Nuclear Receptor ERRγ Is a Novel Transcriptional Regulator of IL-6 Mediated Hepatic BMP6 Gene Expression in Mice

BMP6 participates in the molecular mechanisms involved in APAP hepatotoxicity

Given the lack of accurate diagnostic methods of acetaminophen (APAP)-induced acute liver failure (ALF), the search for new biomarkers for its diagnosis is an urgent need. The aim of this study was to evaluate the role of bone morphogenetic protein 6 (BMP6) in APAP-induced ALF progression and its potential value as a biomarker of ALF. Hepatic and circulating BMP6 expression was assessed in APAP-treated mice and in serum samples from patients with APAP overdose. In addition, BMP6 expression and release was evaluated in hepatocytes after APAP exposure. BMP6 gene was silenced in Huh7 cells prior to APAP treatment and the culture medium (CM) was added to THP1 cells to evaluate the paracrine effects of hepatocyte BMP6 on APAP toxicity. Hepatic and serum BMP6 levels were increased in mice after APAP-induced ALF. In addition, a positive correlation was observed between circulating BMP6 and ALT activity in patients exposed to APAP overdose. Moreover, hepatocytes expressed and released BMP6 to the CM after APAP treatment. Indeed, the CM from APAP-treated Huh7 cells upregulated M1 and M2 markers in THP1 monocytes. The CM from BMP6-silenced Huh7, which was depleted of BMP6, reduced the expression of M2 markers in THP1 cells. In fact, expression of M2 markers was increased in THP1 cells exposed to BMP6. This study reveals that hepatic BMP6 expression is increased in APAP-induced acute liver injury, positioning it as a potential new biomarker of liver damage severity. Moreover, our data indicate that BMP6 might play a role in the hepatocyte-macrophage crosstalk during APAP-induced hepatotoxicity.

Atractylodes macrocephala Rhizoma alleviates blood hyperviscosity induced by high-fat, high-sugar, and high-salt diet by inhibiting gut-liver inflammation and fibrinogen synthesis

ETHNOPHARMACOLOGICAL RELEVANCE

Unhealthy dietary patterns and lifestyle changes have been linked to increased blood viscosity, which is recognized as an important pathogenic factor in cardiovascular and cerebrovascular diseases. The underlying mechanism may involve chronic inflammation resulting from intestinal barrier disruption induced by unhealthy diets. The rhizome of Atractylodes macrocephala Koidz. (Called Baizhu in China), is a well-used "spleen-reinforcing" traditional Chinese medicinal herb used for thousands of years. Previous research has demonstrated its multiple gastrointestinal health benefits and its ability to regulate metabolic disorders. However, the effects of Baizhu on blood hyperviscosity induced by long-term unhealthy diets remain unclear.

AIM OF THE STUDY

This study aimed to investigate the effects of the aqueous extract of Baizhu on blood hyperviscosity induced by unhealthy diet and to explore the possible mechanisms.

MATERIALS AND METHODS

The blood hyperviscosity model in SD rats was established utilizing a high-fat, high-sugar, and high-salt diet (HFSSD). Subsequently, the rats underwent a twelve-week intervention with varying doses of Baizhu and a positive control. To evaluate the efficacy of Baizhu on blood hyperviscosity in model rats, we measured behavioral index, hemorheological parameters, inflammatory cytokines, hematology, adhesion molecules, as well as biochemical indicators in serum and liver. We also assessed the pathological states of the colon and liver. Furthermore, Western blotting, ELISA, IHC, and qRT-PCR were used to determine the effect of Baizhu on the IL-6/STAT3/ESRRG signaling pathway and FIB synthesis.

RESULTS

The intervention of Baizhu showed evident attenuating effects on blood viscosity and microcirculation disorders, and exhibit the capacity to moderately modulate parameters including grip, autonomous activities, vertigo time, TC, TG, LDL-c, inflammatory factors, adhesion factors, hematological indicators, etc. At the same time, it reduces liver lipid droplet deposition, restores intestinal integrity, and lowers LPS level in the serum. Subsequent experimental results showed that Baizhu downregulated the expression of TLR4 and NF-κB in colon tissue, as well as the expression of IL-6, TLR4, p-JAK2, p-STAT3, and ESRRG in liver tissue. Finally, we also found that Baizhu could regulate the levels of FIB in plasma and liver.

CONCLUSION

Baizhu protects HFSSD-induced rats from blood hyperviscosity, likely through repairing the intestinal barrier and inhibiting LPS/TLR4-associated liver inflammatory activation, thus suppressing FIB synthesis through the downregulation of IL-6/STAT3/ESRRG pathway.

Exploring the impact of estrogen-related receptor gamma on metabolism and disease

Estrogen-related receptor gamma (ERRγ) is a member of the ERR orphan nuclear receptor family which possesses three subtypes, α, β, and γ. ERRγ is reportedly predominantly expressed in metabolically active tissues and cells, which promotes positive and negative effects in different tissues. ERRγ overexpression in the liver, pancreas, and thyroid cells is related to liver cancer, oxidative stress, reactive oxygen species (ROS) regulation, and carcinoma. Reduced ERRγ expression in the brain, immune cells, tumor cells, and energy metabolism causes neurological dysfunction, gastric cancer, and obesity. ERRγ is a constitutive receptor; however, its transcriptional activity also depends on co-regulators, agonists, and antagonists, which, when after forming a complex, can play a role in targeting and treating diseases. Moreover, ERRγ has proven crucial in regulating cellular and metabolic activity. However, many functions mediated via ERRγ remain unknown and require further exploration. Hence, considering the importance of ERRγ, this review focuses on the critical findings and interactions between ERRγ and co-regulators, agonists, and antagonists alongside its relationship with downstream and upstream signaling pathways and diseases. This review highlights new findings and provides a path to understanding the current ideas and future studies on ERRγ-mediated cellular activity.

ERRγ-inducible FGF23 promotes alcoholic liver injury through enhancing CYP2E1 mediated hepatic oxidative stress

Fibroblast growth factor 23 (FGF23) is a member of endocrine FGF family, along with FGF15/19 and FGF21. Recent reports showed that under pathological conditions, liver produces FGF23, although the role of hepatic FGF23 remains nebulous. Here, we investigated the role of hepatic FGF23 in alcoholic liver disease (ALD) and delineated the underlying molecular mechanism. FGF23 expression was compared in livers from alcoholic hepatitis patients and healthy controls. The role of FGF23 was examined in hepatocyte-specific knock-out (LKO) mice of cannabinoid receptor type 1 (CB1R), estrogen related receptor γ (ERRγ), or FGF23. Animals were fed with an alcohol-containing liquid diet alone or in combination with ERRγ inverse agonist. FGF23 is mainly expressed in hepatocytes in the human liver, and it is upregulated in ALD patients. In mice, chronic alcohol feeding leads to liver damage and induced FGF23 in liver, but not in other organs. FGF23 is transcriptionally regulated by ERRγ in response to alcohol-mediated activation of the CB1R. Alcohol induced upregulation of hepatic FGF23 and plasma FGF23 levels is lost in ERRγ-LKO mice, and an inverse agonist mediated inhibition of ERRγ transactivation significantly improved alcoholic liver damage. Moreover, hepatic CYP2E1 induction in response to alcohol is FGF23 dependent. In line, FGF23-LKO mice display decreased hepatic CYP2E1 expression and improved ALD through reduced hepatocyte apoptosis and oxidative stress. We recognized CBIR-ERRγ-FGF23 axis in facilitating ALD pathology through hepatic CYP2E1 induction. Thus, we propose FGF23 as a potential therapeutic target to treat ALD.

Molecular dynamics of the ERRγ ligand-binding domain bound with agonist and inverse agonist

Estrogen-related receptor gamma (ERRγ), the latest member of the ERR family, does not have any known reported natural ligands. Although the crystal structures of the apo, agonist-bound, and inverse agonist-bound ligand-binding domain (LBD) of ERRγ have been solved previously, their dynamic behavior has not been studied. Hence, to explore the intrinsic dynamics of the apo and ligand-bound forms of ERRγ, we applied long-range molecular dynamics (MD) simulations to the crystal structures of the apo and ligand-bound forms of the LBD of ERRγ. Using the MD trajectories, we performed hydrogen bond and binding free energy analysis, which suggested that the agonist displayed more hydrogen bonds with ERRγ than the inverse agonist 4-OHT. However, the binding energy of 4-OHT was higher than that of the agonist GSK4716, indicating that hydrophobic interactions are crucial for the binding of the inverse agonist. From principal component analysis, we observed that the AF-2 helix conformation at the C-terminal domain was similar to the initial structures during simulations, indicating that the AF-2 helix conformation is crucial with respect to the agonist or inverse agonist for further functional activity of ERRγ. In addition, we performed residue network analysis to understand intramolecular signal transduction within the protein. The betweenness centrality suggested that few of the amino acids are important for residue signal transduction in apo and ligand-bound forms. The results from this study may assist in designing better therapeutic compounds against ERRγ associated diseases.

Estrogen-related receptor γ (ERRγ) is a key regulator of lysyl oxidase gene expression in mouse hepatocytes

Lysyl oxidase (LOX), the copper-dependent extracellular enzyme, plays a critical role in the regulation of protein cross-linking in the extracellular matrix (ECM). It is also involved in liver regeneration and liver fibrosis. However, the mechanism of LOX regulation in mouse hepatocytes is still unclear. Here, we identify a molecular mechanism showing that orphan nuclear receptor estrogen-related receptor γ (ERRγ) regulates LOX gene expression in the presence of the pro-inflammatory cytokine, interleukin 6 (IL6). IL6 significantly stimulated the expression of ERRγ and LOX in mouse hepatocytes. Overexpression of ERRγ increased LOX mRNA and protein levels. Moreover, knockdown of ERRγ attenuated IL6-mediated LOX gene expression at mRNA and protein levels. Overexpression of ERRγ or IL6 treatment upregulated LOX gene promoter activity, while knockdown of ERRγ decreased the IL6-induced LOX promoter activity. Furthermore, GSK5182, a specific ERRγ inverse agonist, inhibited the induction effect of IL6 on LOX promoter activity and gene expression in mouse hepatocytes. Overall, our study elucidates the mechanism involved in the LOX gene regulation by nuclear receptor ERRγ in response to IL6 in mouse hepatocytes, suggesting that, in conditions such as chronic inflammation, IL6 may contribute to liver fibrosis via inducing LOX gene expression. Thus, LOX gene regulation by the inverse agonist of ERRγ can be applied to improve liver fibrosis.

Distinctive modulation of hepcidin in cancer and its therapeutic relevance

Hepcidin, a short peptide synthesized primarily by hepatocytes in response to increased body iron and inflammation, is a crucial iron-regulating factor. Hepcidin regulates intestinal iron absorption and releases iron from macrophages into plasma through a negative iron feedback mechanism. The discovery of hepcidin inspired a torrent of research into iron metabolism and related problems, which have radically altered our understanding of human diseases caused by an excess of iron, an iron deficiency, or an iron disparity. It is critical to decipher how tumor cells manage hepcidin expression for their metabolic requirements because iron is necessary for cell survival, particularly for highly active cells like tumor cells. Studies show that tumor and non-tumor cells express and control hepcidin differently. These variations should be explored to produce potential novel cancer treatments. The ability to regulate hepcidin expression to deprive cancer cells of iron may be a new weapon against cancer cells.

Estrogen-related receptor gamma regulates mitochondrial and synaptic genes and modulates vulnerability to synucleinopathy

Many studies implicate mitochondrial dysfunction as a key contributor to cell loss in Parkinson disease (PD). Previous analyses of dopaminergic (DAergic) neurons from patients with Lewy-body pathology revealed a deficiency in nuclear-encoded genes for mitochondrial respiration, many of which are targets for the transcription factor estrogen-related receptor gamma (Esrrg/ERRγ). We demonstrate that deletion of ERRγ from DAergic neurons in adult mice was sufficient to cause a levodopa-responsive PD-like phenotype with reductions in mitochondrial gene expression and number, that partial deficiency of ERRγ hastens synuclein-mediated toxicity, and that ERRγ overexpression reduces inclusion load and delays synuclein-mediated cell loss. While ERRγ deletion did not fully recapitulate the transcriptional alterations observed in postmortem tissue, it caused reductions in genes involved in synaptic and mitochondrial function and autophagy. Altogether, these experiments suggest that ERRγ-deficient mice could provide a model for understanding the regulation of transcription in DAergic neurons and that amplifying ERRγ-mediated transcriptional programs should be considered as a strategy to promote DAergic maintenance in PD.

Epigallocatechin-3-Gallate Suppresses BMP-6-Mediated SMAD1/5/8 Transactivation of Hepcidin Gene by Inducing SMILE in Hepatocytes

Hepcidin, a major regulator of systemic iron homeostasis, is mainly induced in hepatocytes by activating bone morphogenetic protein 6 (BMP-6) signaling in response to changes in the iron status. Small heterodimer partner-interacting leucine zipper protein (SMILE), a polyphenol-inducible transcriptional co-repressor, regulates hepatic gluconeogenesis and lipogenesis. Here, we examine the epigallocatechin-3-gallate (EGCG) effect on BMP-6-mediated SMAD1/5/8 transactivation of the hepcidin gene. EGCG treatment significantly decreased BMP-6-induced hepcidin gene expression and secretion in hepatocytes, which, in turn, abated ferroportin degradation. SMILE overexpression significantly decreased BMP receptor-induced hepcidin promoter activity. SMILE overexpression also significantly suppressed BMP-6-mediated induction of hepcidin mRNA and its secretion in HepG2 and AML12 cells. EGCG treatment inhibited BMP-6-mediated hepcidin gene expression and secretion, which were significantly reversed by SMILE knockdown in hepatocytes. Interestingly, SMILE physically interacted with SMAD1 in the nucleus and significantly blocked DNA binding of the SMAD complex to the BMP-response element on the hepcidin gene promoter. Taken together, these findings suggest that SMILE is a novel transcriptional repressor of BMP-6-mediated hepcidin gene expression, thus contributing to the control of iron homeostasis.

Orphan nuclear receptor ERRγ regulates hepatic TGF-β2 expression and fibrogenic response in CCl4-induced acute liver injury

Acute liver injury results from the complex interactions of various pathological processes. The TGF-β superfamily plays a crucial role in orchestrating fibrogenic response. In contrast to TGF-β1, a role of TGF-β2 in hepatic fibrogenic response has not been fully investigated. In this study, we showed that TGF-β2 gene expression and secretion are induced in the liver of CCl₄ (1 ml/kg)-treated WT mice. Studies with hepatocyte specific ERRγ knockout mice or treatment with an ERRγ-specific inverse agonist, GSK5182 (40 mg/kg), indicated that CCl₄-induced hepatic TGF-β2 production is ERRγ dependent. Moreover, IL6 was found as upstream signal to induce hepatic ERRγ and TGF-β2 gene expression in CCl₄-mediated acute toxicity model. Over-expression of ERRγ was sufficient to induce hepatic TGF-β2 expression, whereas ERRγ depletion markedly reduces IL6-induced TGF-β2 gene expression and secretion in vitro and in vivo. Promoter assays showed that ERRγ directly binds to an ERR response element in the TGF-β2 promoter to induce TGF-β2 transcription. Finally, GSK5182 diminished CCl₄-induced fibrogenic response through inhibition of ERRγ-mediated TGF-β2 production. Taken together, these results firstly demonstrate that ERRγ can regulate the TGF-β2-mediated fibrogenic response in a mouse model of CC1₄-induced acute liver injury.

Orphan nuclear receptor ERR-γ regulates hepatic FGF23 production in acute kidney injury

Bone is the main source of fibroblast growth factor 23 (FGF23), which is important for phosphate and vitamin D homeostasis. In acute kidney injury (AKI), high blood levels of FGF23 are positively correlated with disease progression and increased risk of mortality. Reducing adverse plasma FGF23 levels in AKI patients is favorable. We showed here that hepatocytes are the major source of circulating FGF23, and orphan nuclear receptor ERR-γ is a novel transcriptional regulator of hepatic FGF23 production in AKI. Liver-specific depletion of ERR-γ or ERR-γ inverse agonist, GSK5182, significantly reduced plasma levels of FGF23 in AKI. This study reveals liver is the source of FGF23 and a therapeutic strategy to control pathologically adverse plasma FGF23 levels in AKI.

Orphan nuclear receptor ERR-γ regulates hepatic FGF23 production in acute kidney injury

Fibroblast growth factor 23 (FGF23), a hormone generally derived from bone, is important in phosphate and vitamin D homeostasis. In acute kidney injury (AKI) patients, high-circulating FGF23 levels are associated with disease progression and mortality. However, the organ and cell type of FGF23 production in AKI and the molecular mechanism of its excessive production are still unidentified. For insight, we investigated folic acid (FA)-induced AKI in mice. Interestingly, simultaneous with FGF23, orphan nuclear receptor ERR-γ expression is increased in the liver of FA-treated mice, and ectopic overexpression of ERR-γ was sufficient to induce hepatic FGF23 production. In patients and in mice, AKI is accompanied by up-regulated systemic IL-6, which was previously identified as an upstream regulator of ERR-γ expression in the liver. Administration of IL-6 neutralizing antibody to FA-treated mice or of recombinant IL-6 to healthy mice confirms IL-6 as an upstream regulator of hepatic ERR-γ-mediated FGF23 production. A significant (P < 0.001) interconnection between high IL-6 and FGF23 levels as a predictor of AKI in patients that underwent cardiac surgery was also found, suggesting the clinical relevance of the finding. Finally, liver-specific depletion of ERR-γ or treatment with an inverse ERR-γ agonist decreased hepatic FGF23 expression and plasma FGF23 levels in mice with FA-induced AKI. Thus, inverse agonist of ERR-γ may represent a therapeutic strategy to reduce adverse plasma FGF23 levels in AKI.