ERRα inhibitor acts as a potential agonist of PPARγ to induce cell apoptosis and inhibit cell proliferation in endometrial cancer

Two transcriptional factors, peroxisome proliferator-activated receptor-γ (PPARγ) and estrogen-related receptor-α (ERRα), have been reported to be key regulators of cellular energy metabolism. However, the relationship between ERRα and PPARγ in the development of endometrial cancer (EC) is still unclear. The expression levels of PPARγ and ERRα in EC were evaluated by quantitative real-time PCR, western blot, tissue array and immunohistochemistry. A significant negative correlation was identified between PPARγ and ERRα expression in women with EC (ρ=-0.509, P<0.001). Bioinformatics analyses showed that PPARγ and ERRα can activate or inhibit the same genes involved in cell proliferation and apoptosis through a similar ModFit. ERRα activation or PPARγ inhibition could promote proliferation and inhibit apoptosis through the Bcl-2/Caspase3 pathways. Both PPARγ and ERRα can serve as serum tumor markers. Surprisingly, as evaluated by receiver operating characteristic (ROC) curves and a logistic model, a PPARγ/ERRα ratio≤1.86 (area under the ROC curve (AUC)=0.915, Youden index=0.6633, P<0.001) was an independent risk factor for endometrial carcinogenesis (OR=14.847, 95% CI= 1.6-137.748, P=0.018). EC patients with PPARγ(-)/ERRα(+) had the worst overall survival and disease-free survival rates (both P<0.001). Thus, a dynamic imbalance between PPARγ and ERRα leads to endometrial carcinogenesis and predicts the EC prognosis.

Epigallocatechin-3-gallate regulates mitofusin 2 expression through the peroxisome proliferator-activated receptor-γ coactivator-1α and estrogen-related receptor-α pathway

Our previous study showed that epigallocatechin-3-gallate (EGCG) inhibition of human aortic smooth muscle cell (HASMC) proliferation might be mediated via upregulation of mitofusin 2 (Mfn-2). Studies on the mechanism of Mfn-2 inhibition of cell proliferation have mainly focused on downstream signaling. However, it is still not clear how upstream signaling molecules regulate Mfn-2. The promoter region of the Mfn-2 gene contains cis-acting elements of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and estrogen-related receptor-α (ERR-α), suggesting a possible link between EGCG, Mfn-2, and PGC-1α/ERR-α. However, the effect of EGCG on PGC-1α/ERR-α remains unknown. In this study, we investigated the role of PGC-1α/ERR-α in the regulation of Mfn-2 induced by EGCG and assessed the underlying mechanisms. The effects of EGCG on cell proliferation of cultured HASMCs were observed by a cell counting kit-8 (CCK8) and 5-ethynyl-2-deoxyuridine (EdU) incorporation assay. Mfn-2, PGC-1α, and ERR-α gene and protein levels were determined by quantitative real-time polymerase chain reaction (PCR) and Western blot analysis. PGC-1α gene-silencing (PGC-1α small interfering RNA [siRNA]) was achieved by RNA interference and Mfn-2 promoter and peroxisome proliferator response element (PPRE) functional activity was achieved by a luciferase transfection assay. The results showed that the ERR-α-specific antagonist XCT-790 and PGC-1α siRNA decreased the expression of Mfn-2, thus antagonizing the inhibition of HASMC proliferation induced by EGCG. EGCG enhanced Mfn-2 promoter (-352 to 459) activity, while XCT-790 and PGC-1α siRNA abrogated this effect. PGC-1α stimulating Mfn-2 expression was dependent on intact ERR-α binding in the Mfn-2 promoter. The transcriptional effect of PGC-1α on the Mfn-2 promoter required the integrity of the -432 to 459 region and supported that Mfn-2 was a key target gene of PGC-1α. These results imply that PGC-1α/ERR-α played important physiological roles in inhibiting the proliferation of HASMCs by modulating Mfn-2 gene expression. Hence, EGCG regulated Mfn-2 expression likely through the PGC-1α/ERR-α pathway.

Estrogen-related receptor-α mediates puromycin aminonucleoside-induced mesangial cell apoptosis and inflammatory injury

Glomerular diseases are the leading cause of chronic kidney disease, and mesangial cells (MCs) have been demonstrated to be involved in the pathogenesis. Puromycin aminonucleoside (PAN) is a nephrotoxic drug that induces glomerular injury with elusive mechanisms. The present study was undertaken to investigate the role of PAN in MC apoptosis, as well as the underlying mechanism. Here we found that PAN induced MC apoptosis accompanied by declined cell viability and enhanced inflammatory response. The apoptosis was further evidenced by increments of apoptosis regulator BAX (BAX) and caspase-3 expression. In line with the apoptotic response in MCs following PAN treatment, we also found a remarkable induction of estrogen-related receptor-α (ERRα), an orphan nuclear receptor, at both mRNA and protein levels. Interestingly, ERRα silencing by an siRNA approach resulted in an attenuation of the apoptosis and inflammatory response caused by PAN. More importantly, overexpression of ERRα in MCs significantly triggered MC apoptosis in line with increased BAX and caspase-3 expression. In PAN-treated MCs, ERRα overexpression further aggravated PAN-induced apoptosis. In agreement with the in vitro study, we also observed increased ERRα expression in line with enhanced apoptotic response in renal cortex from PAN-treated rats. These data suggest a detrimental effect of ERRα on PAN-induced MC apoptosis and inflammatory response, which could help us to better understand the pathogenic mechanism of MC injury in PAN nephropathy.

Receptor-interacting Protein 140 represses Sirtuin 3 to facilitate hypertrophy, mitochondrial dysfunction and energy metabolic dysfunction in cardiomyocytes

AIM

The transcriptional cofactor receptor-interacting protein 140 (RIP140) is known as a deleterious regulator of cardiac mitochondrial function and energy metabolic homeostasis. This study revealed that RIP140 repressed Sirtuin 3 (SIRT3), a mitochondrial deacetylase that plays an important role in regulating cardiac function.

METHODS

RIP140 was overexpressed by adenovirus infection or was knocked down by RNA interference in neonatal rat cardiomyocytes.

RESULTS

RIP140 overexpression repressed, while RIP140 silencing elevated the expression and activity of SIRT3. Ad-RIP140 enhanced the expressions of the cardiac hypertrophic markers and increased cardiomyocyte surface area, whereas SIRT3 overexpression prevented the effect of Ad-RIP140. Additionally, SIRT3 overexpression reversed Ad-RIP140-induced mitochondrial dysfunction and energy metabolic dysfunction, such as increase in oxidative stress, decrease in mitochondrial membrane potential and ATP production, as well as downregulation of mitochondrial DNA-encoded genes and genes related to mitochondrial genome replication and transcription, mitochondrial oxidative phosphorylation and fatty acid oxidation. In contrast, SIRT3 silencing exacerbated RIP140-induced cardiomyocyte hypertrophy and mitochondrial dysfunction. Furthermore, the repression of SIRT3 by RIP140 was dependent on estrogen-related receptor-α (ERRα). The involvement of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) was ruled out of SIRT3 suppression by RIP140. RIP140 and PGC-1α might act as functional antagonists on the regulation of SIRT3.

CONCLUSION

This study indicates that suppression of SIRT3 by RIP140 facilitates the development of cardiomyocyte hypertrophy, mitochondrial dysfunction and energy metabolic dysfunction. Strategies targeting inhibition of RIP140 and upregulation of SIRT3 might improve cardiac energy metabolism and suggest therapeutic potential for heart diseases.

Altered mitochondrial biogenesis and its fusion gene expression is involved in the high-altitude adaptation of rat lung

Intermittent hypobaric hypoxia-induced preconditioning (IHH-PC) of rat favored the adaption of lungs to severe HH conditions, possibly through stabilization of mitochondrial function. This is based on the data generated on regulatory coordination of nuclear DNA-encoded mitochondrial biogenesis; dynamics, and mitochondrial DNA (mtDNA)-encoded oxidative phosphorylation (mtOXPHOS) genes expression. At 16th day after start of IHH-PC (equivalent to 5000m, 6h/d, 2w of treatment), rats were exposed to severe HH stimulation at 9142m for 6h. The IHH-PC significantly counteracted the HH-induced effect of increased lung: water content; tissue damage; and oxidant injury. Further, IHH-PC significantly increased the mitochondrial number, mtDNA content and mtOXPHOS complex activity in the lung tissues. This observation is due to an increased expression of genes involved in mitochondrial biogenesis (PGC-1α, ERRα, NRF1, NRF2 and TFAM), fusion (Mfn1 and Mfn2) and mtOXPHOS. Thus, the regulatory pathway formed by PGC-1α/ERRα/Mfn2 axes is required for the mitochondrial adaptation provoked by IHH-PC regimen to counteract subsequent HH stress.

MicroRNA-106b induces mitochondrial dysfunction and insulin resistance in C2C12 myotubes by targeting mitofusin-2

MicroRNA-106b (miR-106b) is reported to correlate closely with skeletal muscle insulin resistance and type 2 diabetes. The aim of this study was to identify an mRNA targeted by miR-106b which regulates skeletal muscle insulin sensitivity. MiR-106b was found to target the 3' untranslated region (3' UTR) of mitofusin-2 (Mfn2) through miR-106b binding sites and to downregulate Mfn2 protein abundance at the post-transcriptional level by luciferase activity assay combined with mutational analysis and immunoblotting. Overexpression of miR-106b resulted in mitochondrial dysfunction and insulin resistance in C2C12 myotubes. MiR-106b was increased in insulin-resistant cultured C2C12 myotubes induced by TNF-α, and accompanied by increasing Mfn2 level, miR-106b loss of function improved mitochondrial function and insulin sensitivity impaired by TNF-α in C2C12 myotubes. In addition, both overexpression and downregulation of miR-106b upregulated peroxisome proliferator-activated receptor gamma coactivator (PGC)-1α and estrogen-related receptor (ERR)-α expression. MiR-106b targeted Mfn2 and regulated skeletal muscle mitochondrial function and insulin sensitivity. Therefor, Inhibition of miR-106b may be a potential new strategy for treating insulin resistance and type 2 diabetes.

Bisphenol A exposure is associated with in vivo estrogenic gene expression in adults

BACKGROUND

Bisphenol A (BPA) is a synthetic estrogen commonly used in polycarbonate plastic and resin-lined food and beverage containers. Exposure of animal and cell models to doses of BPA below the recommended tolerable daily intake (TDI) of 50 μg/kg/day have been shown to alter specific estrogen-responsive gene expression, but this has not previously been shown in humans.

OBJECTIVE

We investigated associations between BPA exposure and in vivo estrogenic gene expression in humans.

METHODS

We studied 96 adult men from the InCHIANTI population study and examined in vivo expression of six estrogen receptor, estrogen-related receptor, and androgen receptor genes in peripheral blood leukocytes.

RESULTS

The geometric mean urinary BPA concentration was 3.65 ng/mL [95% confidence interval (CI): 3.13, 4.28], giving an estimated mean excretion of 5.84 μg/day (95% CI: 5.00, 6.85), significantly below the current TDI. In age-adjusted models, there were positive associations between higher BPA concentrations and higher ESR2 [estrogen receptor 2 (ER beta)] expression (unstandardized linear regression coefficient = 0.1804; 95% CI: 0.0388, 0.3221; p = 0.013) and ESRRA (estrogen related receptor alpha) expression (coefficient = 0.1718; 95% CI: 0.0213, 0.3223; p = 0.026): These associations were little changed after adjusting for potential confounders, including obesity, serum lipid concentrations, and white cell subtype percentages. Upper-tertile BPA excretors (urinary BPA > 4.6 ng/mL) had 65% higher mean ESR2 expression than did lower-tertile BPA excretors (0-2.4 ng/mL).

CONCLUSIONS

Because activation of nuclear-receptor-mediated pathways by BPA is consistently found in laboratory studies, such activation in humans provides evidence that BPA is likely to function as a xenoestrogen in this sample of adults.