Targeting adipocyte ESRRA promotes osteogenesis and vascular formation in adipocyte-rich bone marrow.

Excessive bone marrow adipocytes (BMAds) accumulation often occurs under diverse pathophysiological conditions associated with bone deterioration. Estrogen-related receptor α (ESRRA) is a key regulator responding to metabolic stress. Here, we show that adipocyte-specific ESRRA deficiency preserves osteogenesis and vascular formation in adipocyte-rich bone marrow upon estrogen deficiency or obesity. Mechanistically, adipocyte ESRRA interferes with E2/ESR1 signaling resulting in transcriptional repression of secreted phosphoprotein 1 (Spp1); yet positively modulates leptin expression by binding to its promoter. ESRRA abrogation results in enhanced SPP1 and decreased leptin secretion from both visceral adipocytes and BMAds, concertedly dictating bone marrow stromal stem cell fate commitment and restoring type H vessel formation, constituting a feed-forward loop for bone formation. Pharmacological inhibition of ESRRA protects obese mice against bone loss and high marrow adiposity. Thus, our findings highlight a therapeutic approach via targeting adipocyte ESRRA to preserve bone formation especially in detrimental adipocyte-rich bone milieu.

Correlation between spherical equivalent and biometry parameters in adult Cynomolgus macaque.

PURPOSE: To characterize the distribution of refractive and ocular biometry parameters and analyze the effect factors of the refractive status in cynomolgus monkey colonies. METHODS: A Population-based cross-sectional study was conducted in adult cynomolgus macaque colonies. Animals were anesthetized with Zoletil 50. Intraocular pressure was measured using the Icare tonometer. Cycloplegic refraction (three drops of 1% tropicamide) and corneal radius of curvature (CRC) were measured using an autorefractor. The spherical equivalent (SE) was calculated. Biometric measurements, including the anterior chamber depth (ACD), lens thickness (LT), and axial length (AL), were obtained by A-scan ultrasonography. The AL-to-CR ratio (AL/CRC) was calculated. Central corneal thickness (CCT) and choroidal thickness (ChT) were measured using the Heidelberg Spectralis HRA OCT. Multiple regression analysis was performed to explore the association between refraction and ocular biometry. RESULTS: Among 263 cynomolgus monkeys (aged 5-26 years), which consisted of 520 eyes, 29.42% had hyperopia, 27.12% had emmetropia, 33.27% had mild-to-moderate myopia and 10.19% had high myopia. The mean SE was -1.27 ± 3.44 Diopters (D). The mean CRC, CCT, AL, and ChT was 5.70 ± 0.22 mm, 454.30 ± 32.40 µm, 18.76 ± 0.89 mm and 188.96 ± 38.19 µm, respectively. The LT was the thickest in the hyperopic eyes. CRC was the lowest, and CCT was the thickest in high myopic eyes. AL increased, while ChT decreased as SE decreased. For the SE variance, AL alone explained 40.5%; age, AL, and CRC together explained 57.5%. CONCLUSIONS: The refractive characteristics and biometry parameters of cynomolgus monkeys are highly comparable to those of humans. AL, CRC, and ChT showed the similar variation tendency in cynomolguses when compared to humans. Cynomolgus monkeys with naturally-occurring refractive errors may be a good animal model for refractive studies.

The mitotic regulator RCC2 promotes glucose metabolism through BACH1-dependent transcriptional upregulation of hexokinase II in glioma.

Weighted gene co-expression network analysis (WGCNA) identified a cell-cycle module that is associated with poor prognosis and aggressiveness of glioma. One of the core members, Regulator of chromatin condensation 2 (RCC2) is a component of the chromosome passenger complex. Accumulating evidence suggests that RCC2 plays a vital role in the mitotic process and that abnormal RCC2 expression is involved in cancer development. Gene silencing experiments show that RCC2 is required for glioma cell proliferation and migration. RNA-Sequencing analysis reveals a dual role of RCC2 in both the cell cycle and metabolism. Specifically, RCC2 regulates G2/M progression via CDC2 phosphorylation at Tyrosine 15. Metabolomic analysis identifies a role for RCC2 in promoting the glycolysis and pentose phosphate pathway. RCC2 exerts effects on metabolism by stabilizing the transcription factor BACH1 at its C-terminus leading to the transcriptional upregulation of hexokinase 2 (HK2). These findings elucidate a novel PTEN/RCC2/BACH1/HK2 signaling axis that drives glioma progression through the dual regulation of mitotic cell cycle and glycolytic events.

Andrographolide prevents bone loss via targeting estrogen-related receptor-α-regulated metabolic adaption of osteoclastogenesis.

BACKGROUND AND PURPOSE: Metabolic adaptation driven by oestrogen-related receptor-α (ERRα/NR3B1) is required to meet the increased energy demand during osteoclast differentiation. Here, we hypothesize that natural product, andrographolide, acts as an ERRα inverse agonist to inhibit osteoclastogenesis. EXPERIMENTAL APPROACH: Virtual docking and site-directed mutagenesis analysis were employed to study the binding mode of andrographolide to ERRα. Co-immunoprecipitation, luciferase reporter assay, real-time polymerase chain reaction (PCR) and immunoblot analyses were performed to identify andrographolide as an ERRα inverse agonist. The pharmacological effects of andrographolide in vivo were assessed in mice models of osteopenia induced by either a high-fat diet in male or ovariectomy in female mice. KEY RESULTS: ERRα-dependent expression of glutaminase, a rate-limiting enzyme of mitochondrial glutamine anaplerosis, is required for ex vivo bone marrow osteoclast differentiation. Andrographolide inhibited glutaminase expression induced by ERRα and co-activator peroxisome proliferator-activated receptor γ co-activator-1ß (PGC-1ß), leading to reduction in osteoclastogenesis. Andrographolide acted as an inverse agonist of ERRα by disrupting its interaction with co-activator PGC-1ß. Phenylalanine 232, valine 395 and phenylalanine 399 of ERRα ligand-binding domain were confirmed to be essential for this effect. In contrast, glutaminase overexpression restored the impairment triggered by andrographolide. Accordingly, andrographolide suppressed osteoclastic bone resorption and attenuated bone loss in vivo. CONCLUSIONS AND IMPLICATIONS: These findings demonstrate that andrographolide acts as an ERRα inverse agonist for perturbation of ERRα/PGC-1ß/glutaminase axis-driven metabolic adaption during osteoclast differentiation, implying that andrographolide may be a promising natural compound for preventing physiological and pathological bone loss.

Dysfunction of estrogen-related receptor alpha-dependent hepatic VLDL secretion contributes to sex disparity in NAFLD/NASH development.

Rationale: Men and postmenopausal women are more prone to developing non-alcoholic fatty liver disease/steatohepatitis (NAFLD/NASH) than premenopausal women. However, the pathological links and underlying mechanisms of this disparity are still elusive. The sex-difference in hepatic very low-density lipoprotein (VLDL) assembly and secretion may contribute to NAFLD development. Estrogen-related receptor alpha (ERRα) is a key regulator of several metabolic processes. We hypothesized that ERRα plays a role contributing to the sex-difference in hepatic VLDL assembly and secretion. Methods: VLDL secretion and essential genes governing said process were assessed in male and female mice. Liver-specific ERRα-deficient (ERRαLKO) mice were generated to assess the rate of hepatic VLDL secretion and alteration in target gene expression. Overexpression of either microsomal triglyceride transfer protein (Mttp) or phospholipase A2 G12B (Pla2g12b) by adenovirus was performed to test if the fatty liver phenotype in male ERRαLKO mice was due to defects in hepatic VLDL secretion. Female ERRαLKO mice were put on a diet high in saturated fat, fructose and cholesterol (HFHC) to promote NASH development. Wild type female mice were either ovariectomized or treated with tamoxifen to induce a state of estrogen deficiency or disruption in estrogen signaling. Adenovirus was used to overexpress ERRα in these mice to test if ERRα was sufficient to rescue the suppressed VLDL secretion due to estrogen dysfunction. Finally, wild type male mice on a high-fat diet (HFD) were treated with an ERRα inverse agonist to assess if suppressing ERRα activity pharmacologically would lead to fatty liver development. Results: ERRα is an indispensable mediator modulating hepatic triglyceride-rich very low-density lipoprotein (VLDL-TG) assembly and secretion through coordinately controlling target genes apolipoprotein B (Apob), Mttp and Pla2g12b in a sex-different manner. Hepatic VLDL-TG secretion is blunted in ERRαLKO mice, leading to hepatosteatosis which exacerbates endoplasmic reticulum stress and inflammation paving ways for NASH development. Importantly, ERRα acts downstream of estrogen/ERα signaling in contributing to the sex-difference in hepatic VLDL secretion effecting hepatic lipid homeostasis. Conclusions: Our results highlight ERRα as a key mediator which contributes to the sex disparity in NAFLD development, suggesting that selectively restoring ERRα activity in the liver may be a novel strategy for treating NAFLD/NASH.

18ß-Glycyrrhetinic acid acts through hepatocyte nuclear factor 4 alpha to modulate lipid and carbohydrate metabolism.

Hepatocyte nuclear factor 4 alpha (HNF4α) regulates the expression of essential genes involved in very-low-density lipoprotein (VLDL) homeostasis and gluconeogenesis.　18ß-glycyrrhetinic acid (GA) is an active ingredient of Glycyrrhiza uralensis an herbal medicine used for treating liver aliments. In this study, we established that GA functions as a partial antagonist of HNF4α through HNF4α-driven reporter luciferase assay and co-immunoprecipitation experiments with co-activator PGC1α. By virtual docking and site-directed mutagenesis analysis, we confirmed that serine 190 and arginine 235 of HNF4α are both essential for GA to exert its antagonistic action on HNF4α. Importantly, GA suppressed the expression of HNF4α target genes such as apolipoprotein B (ApoB), microsomal triglyceride transfer protein (MTP) and phospholipase A2 G12B (PLA2G12B) modulating hepatic VLDL secretion in mice fed on a high fat diet. In addition, GA also suppressed gluconeogenesis and ameliorated glucose intolerance via down-regulating the expression of HNF4α target genes glucose-6-phosphatase (G6pc) and phosphoenolpyruvate carboxykinase (Pepck). Furthermore, GA significantly lowered blood glucose and improved insulin resistance in db/db mice. In all, we established that GA acts as a partial HNF4α antagonist modulating lipid and carbohydrate metabolism.

Andrographolide modulates HNF4α activity imparting on hepatic metabolism.

Hepatic nuclear factor 4 alpha (HNF4α) drives the expression of apolipoprotein B (ApoB), microsomal triglyceride transfer protein (MTP) and phospholipase A2 G12B (PLA2G12B), governing hepatic very-low-density lipoprotein (VLDL) production and secretion. Andrographolide (AP) is a major constituent isolated from Andrographis paniculata. We found that AP can disrupt the interaction between HNF4α and its coactivator peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α). Virtual docking and mutational analysis indicated that arginine 235 of HNF4α is essential for binding to AP. As a consequence of antagonizing the activity of HNF4α, AP suppresses the expression of ApoB, MTP and PLA2G12B and reduces the rate of hepatic VLDL secretion in vivo. AP additionally reduced gluconeogenesis via down-regulating the expression of HNF4α target genes phosphoenolpyruvate carboxykinase (Pepck) and glucose-6-phosphatase (G6pc). Collectively, our results suggest that AP affects liver function via modulating the transcriptional activity of HNF4α.

Discovery of Farnesoid X Receptor Antagonists Based on a Library of Oleanolic Acid 3-O-Esters through Diverse Substituent Design and Molecular Docking Methods.

The pentacyclic triterpene oleanolic acid (OA, 1) with known farnesoid X receptor (FXR) modulatory activity was modified at its C-3 position to find new FXR-interacting agents. A diverse substitution library of OA derivatives was constructed in silico through a 2D fingerprint similarity cluster strategy. With further docking analysis, four top-scored OA 3-O-ester derivatives were selected for synthesis. The bioassay results indicated that all four compounds 3 inhibited chenodeoxycholic acid (CDCA)-induced FXR transactivation in a concentration-dependent mode. Among them 3b and 3d are more active than the parent compound OA. A molecular simulation study was performed to attempt to explain the structure-activity relationship (SAR) and the antagonistic action. To the best of our knowledge, this is the first report on semi-synthetic pentacyclic triterpenoids with FXR-modulatory activities.

Synthesis and biological evaluations of chalcones, flavones and chromenes as farnesoid x receptor (FXR) antagonists.

Farnesoid X receptor (FXR), a nuclear receptor mainly distributed in liver and intestine, has been regarded as a potential target for the treatment of various metabolic diseases, cancer and infectious diseases related to liver. Starting from two previously identified chalcone-based FXR antagonists, we tried to increase the activity through the design and synthesis of a library containing chalcones, flavones and chromenes, based on substitution manipulation and conformation (ring closure) restriction strategy. Many chalcones and four chromenes were identified as microM potent FXR antagonists, among which chromene 11c significantly decreased the plasma and hepatic triglyceride level in KKay mice.

The roles of protein disulphide isomerase family A, member 3 (ERp57) and surface thiol/disulphide exchange in human spermatozoa-zona pellucida binding.

Study question: Are multimeric sperm plasma membrane protein complexes, ERp57 and sperm surface thiol content involved in human spermatozoa-zona pellucida (ZP) interaction? Summary answer: ERp57 is a component of a multimeric spermatozoa-ZP receptor complex involved in regulation of human spermatozoa-ZP binding via up-regulation of sperm surface thiol content. What is known already: A spermatozoon acquires its fertilization capacity within the female reproductive tract by capacitation. Spermatozoa-ZP receptor is suggested to be a composite structure that is assembled into a functional complex during capacitation. Sperm surface thiol content is elevated during capacitation. ERp57 is a protein disulphide isomerase that modulates the thiol-disulphide status of proteins. Study design, size, duration: The binding ability and components of protein complexes in extracted membrane protein fractions of spermatozoa were studied. The roles of capacitation, thiol-disulphide reagent treatments and ERp57 on sperm functions and sperm surface thiol content were assessed. Participants/materials, setting, methods: Spermatozoa were obtained from semen samples from normozoospermic men. Human oocytes were obtained from an assisted reproduction programme. Blue native polyacrylamide gel electrophoresis, western ligand blotting and mass spectrometry were used to identify the components of solubilized ZP/ZP3-binding complexes. The localization and expression of sperm surface thiol and ERp57 were studied by immunostaining and sperm surface protein biotinylation followed by western blotting. Sperm functions were assessed by standard assays. Main results and the role of chance: Several ZP-binding complexes were isolated from the cell membrane of capacitated spermatozoa. ERp57 was a component of one of these complexes. Capacitation significantly increased the sperm surface thiol content, acrosomal thiol distribution and ERp57 expression on sperm surface. Sperm surface thiol and ERp57 immunoreactivity were localized to the acrosomal region of spermatozoa, a region responsible for ZP-binding. Up-regulation of the surface thiol content or ERp57 surface expression in vitro stimulated ZP-binding capacity of human spermatozoa. Blocking of ERp57 function by specific antibody or inhibitors against ERp57 reduced the surface thiol content and ZP-binding capacity of human spermatozoa. Large scale data: N/A. Limitations, reasons for caution: The mechanisms by which up-regulation of surface thiol content stimulates spermatozoa-ZP binding have not been depicted. Wider implications of the findings: Thiol-disulphide exchange is a crucial event in capacitation. ERp57 modulates the event and the subsequent fertilization process. Modulation of the surface thiol content of the spermatozoa of subfertile men may help to increase fertilization rate in assisted reproduction. Study funding/competing interest(s): This work was supported by The Hong Kong Research Grant Council Grant HKU764611 and HKU764512M to P.C.N.C. The authors have no competing interests.

Activation of farnesoid X receptor promotes triglycerides lowering by suppressing phospholipase A2 G12B expression.

As a novel mediator of hepatic very low-density lipoproteins (VLDL) secretion, phospholipase A2 G12B (PLA2G12B) is transcriptionally regulated by hepatocyte nuclear factor-4 alpha (HNF-4α). Farnesoid X receptor (FXR) plays a critical role in maintaining bile acids and triglycerides (TG) homeostasis. Here we report that FXR regulates serum TG level in part through PLA2G12B. Activation of FXR by chenodeoxycholic acid (CDCA) or GW4064 significantly decreased PLA2G12B expression in HepG2 cells. PLA2G12B expression was transcriptionally repressed due to an FXR-mediated up-regulation of small heterodimer partner (SHP) which functionally suppresses HNF-4α activity. We found that hepatic PLA2G12B expression was suppressed and serum TG level reduced in high fat diet mice treated with CDCA. Concurrently, CDCA treatment lowered hepatic VLDL-TG secretion. Our data demonstrate that activation of FXR promotes TG lowering, not only by decreasing de novo lipogenesis but also reducing hepatic secretion of TG-rich VLDL particles in part through suppressing PLA2G12B expression.

Intermedin in rat uterus: changes in gene expression and peptide levels across the estrous cycle and its effects on uterine contraction.

BACKGROUND: The present study demonstrates the expression of intermedin (IMD) and its receptor components in the uterus of the female rat during the estrous cycle and its effect on uterine contraction. METHODS: The gene expression level of intermedin and its receptor components and the peptide level of intermedin were studied by real-time RT-PCR and enzyme immunoassay (EIA) respectively. The separation of precursor and mature IMD was studied by gel filtration chromatography and EIA. The localization of IMD in the uterus was investigated by immunohistochemistry. The effect of IMD on in vitro uterine contraction was studied by organ bath technique. RESULTS: Uterine mRNAs of Imd and its receptor components and IMD levels displayed cyclic changes across the estrous cycle. Imd mRNA level was the highest at proestrus while the IMD level was the highest at diestrus. IMD was found in the luminal and glandular epithelia and IMD treatment significantly reduced the amplitude and frequency of uterine contraction but not the basal tone. Both calcitonin gene-related peptide (CGRP) receptor antagonist hCGRP8-37 and adrenomedullin (ADM) receptor antagonist hADM22-52 partially abolished the inhibitory effect of IMD on uterine contraction while the specific IMD receptor antagonist hIMD17-47 completely blocked the actions. The enzyme inhibitors of NO (L-NAME) and PI3K (Wortmannin) pathways diminished the IMD effects on uterine contraction while the cAMP/PKA blocker, KT5720, had no effect, indicating an involvement of NO and PI3K/Akt but not PKA. CONCLUSIONS: IMD and the gene expression of its receptor components are differentially regulated in the uterus during the estrous cycle and IMD inhibits uterine contraction by decreasing the amplitude and frequency.

Enrichment analysis of miRNA targets.

MicroRNAs (miRNAs) are a class of ∼22-nucleotide endogenous noncoding RNAs which regulate target gene expression via repressing translation or promoting mRNAs degradation. Any individual mammalian miRNA often has more than a hundred predicted mRNA targets and that close to one thirds of all mRNA transcripts bear one or more conserved miRNA binding sites in their 3'-untranslated region. Enrichment analysis of miRNA targets has become a standard technique to elucidating hierarchical functions of miRNAs in gene regulatory networks. In this protocol, we discuss analytical methods and use of computational tools in a step-by-step manner. Important details are also provided to help researchers choose more appropriate tools for a given type of analysis. Available Web-based resources for enrichment analysis of miRNA targets are summarized.

Protein kinase C epsilon affects mitochondrial function through estrogen-related receptor alpha.

Members of the protein kinase C (PKC) family have been implicated in controlling cell proliferation, differentiation, and motility. Many of these processes are energy demanding. How PKCs affect mitochondrial function to regulate energy production is not well defined. Using an inhibitor Gö6983 with broad specificity, we found that inhibiting PKCs reduced mitochondrial mass and altered mitochondrial function characterized by elevations in mitochondrial membrane potential (Δψm) and reactive oxygen species (ROS) levels. These alterations indicated that Gö6983 suppressed the activities of mitochondrial regulators such as estrogen-related receptor α (ERRα). Indeed, Gö6983 dose-dependently suppressed the expression levels of ERRα-target genes peroxisome proliferator-activated receptor α (PPARα) and medium-chain acyl-CoA dehydrogenase (MCAD). Conversely, PKC activator phorbol ester (PMA) enhanced the expression level of another ERRα-target gene pyruvate dehydrogenase kinase 4 (PDK4). This PMA-mediated induction of PDK4 was blunted by an ERRα inverse agonist XCT-790, suggesting that ERRα plays a role in mediating the effects of PKCs on mitochondrial function. By over-expressing constitutively active forms of PKCs, we found that PKCε preferentially stimulated the transcription activity of ERRα. Through mutating residues on ERRα, we established that this PKCε-induced ERRα activity involves threonine 106, serine 110, and threonine 124 of ERRα. Collectively, these pieces of evidence suggest that ERRα plays an important role down-stream of PKCε to regulate mitochondrial homeostasis.

Mitogen-activated protein kinase kinases promote mitochondrial biogenesis in part through inducing peroxisome proliferator-activated receptor γ coactivator-1ß expression.

Growth factor activates mitogen-activated protein kinase kinases to promote cell growth. Mitochondrial biogenesis is an integral part of cell growth. How growth factor regulates mitochondrial biogenesis is not fully understood. In this study, we found that mitochondrial mass was specifically reduced upon serum starvation and induced upon re-feeding with serum. Using mitogen-activated protein kinase kinases inhibitor U0126, we found that the mRNA expression levels of ATP synthase, cytochrome-C, mitochondrial transcription factor A, and mitofusin 2 were reduced. Since the transcriptional levels of these genes are under the control of peroxisome proliferator-activated receptor γ coactivator-1α and -1ß (PGC-1α and PGC-1ß), we examined and found that only the mRNA and protein levels of PGC-1ß were suppressed. Importantly, over-expression of PGC-1ß partially reversed the reduction of mitochondrial mass upon U0126 treatment. Thus, we conclude that mitogen-activated protein kinase kinases direct mitochondrial biogenesis through selectively inducing PGC-1ß expression.

Hepatocyte nuclear factor-4 alpha regulates liver triglyceride metabolism in part through secreted phospholipase A2 GXIIB.

UNLABELLED: Hepatocyte nuclear factor-4 alpha (HNF-4α) is an important transcription factor governing the expression of genes involved in multiple metabolic pathways. Secreted phospholipase A(2) GXIIB (PLA(2) GXIIB) is an atypical member of a class of secreted phospholipases A(2) . We establish in this study that PLA(2) GXIIB is an HNF-4α target gene. We demonstrate that HNF-4α binds to a response element on the PLA(2) GXIIB promoter. Moreover, HNF-4α agonists induce PLA(2) GXIIB expression in human hepatocarcinoma cells. Importantly, PLA(2) GXIIB-null mice accumulate triglyceride, cholesterol, and fatty acids in the liver and develop severe hepatosteatosis resembling some of the phenotypes of liver-specific HNF-4α-null mice. These defects are in part due to compromised hepatic very low-density lipoprotein secretion. Finally, adenovirus-mediated overexpression of HNF-4α elevates serum triglyceride level in wild-type but not PLA(2) GXIIB-null mice. CONCLUSION: Collectively, these evidences suggest that HNF-4α is a key physiological PLA(2) GXIIB transcriptional regulator and that PLA(2) GXIIB is a novel mediator of triglyceride metabolism in the liver.

Chromatin-modifying drugs induce miRNA-153 expression to suppress Irs-2 in glioblastoma cell lines.

MicroRNAs (miRNAs) are noncoding RNAs that regulate gene expression by inhibiting translation or by promoting mRNA degradation. Previously, we established that microRNA-153 (miR-153) induces apoptosis by downregulating B-cell lymphoma 2 (Bcl-2) and myeloid cell leukemia sequence 1 (Mcl-1) protein expression levels in glioblastoma cell line DBTRG-05MG. In our study, we show that ectopic expression of miR-153 also inhibits the protein kinase B (PKB/Akt) pathway via reducing the protein level of insulin receptor substrate-2 (Irs-2). Moreover, simultaneous treatment with the chromatin-modifying drugs 4-phenylbutyric acid and 5-aza-2'-deoxycytidine induces miR-153 expression to suppress Irs-2, Bcl-2 and Mcl-1 expressions, thus downregulating the survival but upregulating the apoptotic pathways, implying that tumor suppressor miR-153 is a dual life and death regulator.

Phosphatidylinositol 3-kinase affects mitochondrial function in part through inducing peroxisome proliferator-activated receptor γ coactivator-1ß expression.

BACKGROUND AND PURPOSE: Hyperactivation of phosphatidylinositol 3-kinase (PI3K), commonly observed in cancer, is believed to promote cancer cell growth and survival. Appropriate mitochondrial function is an integral part of cellular function. How PI3K affects mitochondrial homeostasis is not fully understood. EXPERIMENTAL APPROACH: Mitochondrial mass, membrane potential and reactive oxygen species (ROS) were quantified by three different fluorogenic probes. Gene expression at the levels of mRNA and protein were measured by quantitative RT-PCR and Western analysis. KEY RESULTS: Using the PI3K inhibitors LY294002 and PI103, we found that suppressing PI3K activity altered mitochondrial function. Specifically, LY294002 and PI103 suppressed the mRNA expression levels of mitochondrial regulators nuclear respiratory factors 1 and 2 (NRF1 and NRF2). As NRF1 and NRF2 are under the transcriptional control of peroxisome proliferator-activated receptor γ coactivators-1α and -1ß (PGC-1α and PGC-1ß), we found that suppressing PI3K activity selectively reduced both the mRNA and protein levels of PGC-1ß but not PGC-1α. Reducing PGC-1ß expression also led to reduced mRNA expression levels of uncoupling protein 1, 2 (UCP1 and UCP2) and superoxide dismutase 2. Correspondingly, mitochondrial membrane potential (Δψ(m)) and ROS levels were increased. Finally, we partially blunted the LY294002-mediated growth suppression by using an antioxidant or over-expressing PGC-1ß. CONCLUSIONS AND IMPLICATIONS: PI3K regulates mitochondrial homeostasis in part through PGC-1ß and blocking this pathway induces ROS to arrest cell growth at the G1 phase.

Troglitazone induces cytotoxicity in part by promoting the degradation of peroxisome proliferator-activated receptor γ co-activator-1α protein.

BACKGROUND AND PURPOSE: Troglitazone (Tro), rosiglitazone (Rosi) and pioglitazone (Pio) are anti-diabetic thiazolidinediones that function as ligands for peroxisome proliferator-activated receptor γ (PPARγ); however, Tro has been withdrawn from the market due to liver toxicity issues. Mitochondrial dysfunction induced by Tro has been suggested to be an important mechanism behind its cytotoxicity. Constitutively active nuclear hormone receptors, oestrogen-related receptor α and γ are thought to regulate mitochondrial mass and oxidative phosphorylation together with their co-activators PPARγ co-activator-1α and -1ß (PGC-1α and PGC-1ß). Hence, in this study, we investigated whether Tro affects the expression and activity levels of these regulators. EXPERIMENTAL APPROACH: Cellular viability was measured by an ATP-based assay. Mitochondrial mass and reactive oxygen species (ROS) were quantified by two different fluorogenic probes. Apoptosis was measured by an Annexin-V-based kit. Gene expression at the levels of mRNA and protein was measured by quantitative RT-PCR and Western analysis. Over-expression of PGC-1α was mediated by an adenovirus. KEY RESULTS: Tro, but not Rosi or Pio, selectively stimulated PGC-1α protein degradation. As a result, Tro reduced mitochondrial mass, and superoxide dismutases 1 and 2 expressions, but induced ROS to initiate apoptosis. Using a ubiquitin-proteasome inhibitor MG132, it was established that blocking PGC-1α degradation partially suppressed the reduction of mitochondrial mass. Importantly, over-expressing PGC-1α partially restored the Tro-suppressed mitochondrial mass and attenuated the cytotoxic effects of Tro. CONCLUSIONS AND IMPLICATIONS: Collectively, these results suggest that PGC-1α degradation is an important mechanism behind the cytotoxic effects of Tro in the liver.