GATA3 induces the upregulation of UCP-1 by directly binding to PGC-1α during adipose tissue browning

OBJECTIVE

Obesity is recognized as the cause of multiple metabolic diseases and is rapidly increasing worldwide. As obesity is due to an imbalance in energy homeostasis, the promotion of energy consumption through browning of white adipose tissue (WAT) has emerged as a promising therapeutic strategy to counter the obesity epidemic. However, the molecular mechanisms of the browning process are not well understood. In this study, we investigated the effects of the GATA family of transcription factors on the browning process.

METHODS

We used qPCR to analyze the expression of GATA family members during WAT browning. In order to investigate the function of GATA3 in the browning process, we used the lentivirus system for the ectopic expression and knockdown of GATA3. Western blot and real-time qPCR analyses revealed the regulation of thermogenic genes upon ectopic expression and knockdown of GATA3. Luciferase reporter assays, co-immunoprecipitation, and chromatin immunoprecipitation were performed to demonstrate that GATA3 interacts with proliferator-activated receptor-γ co-activator-1α (PGC-1α) to regulate the promoter activity of uncoupling protein-1 (UCP-1). Enhanced energy expenditure by GATA3 was confirmed using oxygen consumption assays, and the mitochondrial content was assessed using MitoTracker. Furthermore, we examined the in vivo effects of lentiviral GATA3 overexpression and knockdown in inguinal adipose tissue of mice.

RESULTS

Gata3 expression levels were significantly elevated in the inguinal adipose tissue of mice exposed to cold conditions. Ectopic expression of GATA3 enhanced the expression of UCP-1 and thermogenic genes upon treatment with norepinephrine whereas GATA3 knockdown had the opposite effect. Luciferase reporter assays using the UCP-1 promoter region showed that UCP-1 expression was increased in a dose-dependent manner by GATA3 regardless of norepinephrine treatment. GATA3 was found to directly bind to the promoter region of UCP-1. Furthermore, our results indicated that GATA3 interacts with the transcriptional coactivator PGC-1α to increase the expression of UCP-1. Taken together, we demonstrate that GATA3 has an important role in enhancing energy expenditure by increasing the expression of thermogenic genes both in vitro and in vivo.

CONCLUSION

GATA3 may represent a promising target for the prevention and treatment of obesity by regulating thermogenic capacity.

A reliable approach for assessing size-dependent effects of silica nanoparticles on cellular internalization behavior and cytotoxic mechanisms

Background

The size of nanoparticles is considered to influence their toxicity, as smaller-sized nanoparticles should more easily penetrate the cell and exert toxic effects. However, conflicting results and unstandardized methodology have resulted in controversy of these size-dependent effects. Here, we introduce a unique approach to study such size-dependent effects of nanoparticles and present evidence that reliably supports this general assumption along with elucidation of the underlying cytotoxic mechanism.

Methods

We prepared and physically characterized size-controlled (20-50 nm) monodispersed silica nanoparticles (SNPs) in aqueous suspensions. Then, a variety of biochemical assessments are used for evaluating the cytotoxic mechanisms.

Results

SNP treatment in three cell lines decreased cell viability and migration ability, while ROS production increased in dose- and size-dependent manners, with SNPs <30 nm showing the greatest effects. 30- and 40-nm SNPs were observed similar to these biological activities of 20- and 50-nm, respectively. Under the conventionally used serum-free conditions, both 20-nm and 50-nm SNPs at the IC₅₀ values (75.2 and 175.2 μg/mL) induced apoptosis and necrosis in HepG2 cells, whereas necrosis was more rapid with the smaller SNPs. Inhibiting endocytosis impeded the internalization of the 50-nm but not the 20-nm SNPs. However, agglomeration following serum exposure increased the size of the 20-nm SNPs to approximately 50 nm, preventing their internalization and cell membrane damage without necrosis. Thus, 20-nm and 50-nm SNPs show different modes of cellular uptake, with smaller SNPs capable of trafficking into the cells in an endocytosis-independent manner. This approach of using non-overlapping size classes of SNPs under the same dose, along with serum-induced agglomeration analysis clarifies this long-standing question about the safety of small SNPs.

Conclusion

Our results highlight the need to revise safety guidelines to account for this demonstrated size-dependent cytotoxicity under serum-free conditions, which may be similar to the microenvironment after tissue penetration.

HDAC11 Inhibits Myoblast Differentiation through Repression of MyoD-Dependent Transcription

Abnormal differentiation of muscle is closely associated with aging (sarcopenia) and diseases such as cancer and type II diabetes. Thus, understanding the mechanisms that regulate muscle differentiation will be useful in the treatment and prevention of these conditions. Protein lysine acetylation and methylation are major post-translational modification mechanisms that regulate key cellular processes. In this study, to elucidate the relationship between myogenic differentiation and protein lysine acetylation/methylation, we performed a PCR array of enzymes related to protein lysine acetylation/methylation during C2C12 myoblast differentiation. Our results indicated that the expression pattern of HDAC11 was substantially increased during myoblast differentiation. Furthermore, ectopic expression of HDAC11 completely inhibited myoblast differentiation, concomitant with reduced expression of key myogenic transcription factors. However, the catalytically inactive mutant of HDAC11 (H142/143A) did not impede myoblast differentiation. In addition, wild-type HDAC11, but not the inactive HDAC11 mutant, suppressed MyoD-induced promoter activities of MEF2C and MYOG (Myogenin), and reduced histone acetylation near the E-boxes, the MyoD binding site, of the MEF2C and MYOG promoters. Collectively, our results indicate that HDAC11 would suppress myoblast differentiation via regulation of MyoD-dependent transcription. These findings suggest that HDAC11 is a novel critical target for controlling myoblast differentiation.

Methyltransferase and demethylase profiling studies during brown adipocyte differentiation

Although brown adipose tissue is important with regard to energy balance, the molecular mechanism of brown adipocyte differentiation has not been extensively studied. Specifically, regulation factors at the level of protein modification are largely unknown. In this study, we examine the changes in the expression level of enzymes which are involved in protein lysine methylation during brown adipocyte differentiation. Several enzymes, in this case SUV420H2, PRDM9, MLL3 and JHDM1D, were found to be up-regulated. On the other hand, Set7/9 was significantly down-regulated. In the case of SUV420H2, the expression level increased sharply during brown adipocyte differentiation, whereas the expression of SUV420H2 was marginally enhanced during the white adipocyte differentiation. The knock-down of SUV420H2 caused the suppression of brown adipocyte differentiation, as compared to a scrambled control. These results suggest that SUV420H2, a methyltransferase, is involved in brown adipocyte differentiation, and that the methylation of protein lysine is important in brown adipocyte differentiation. [BMB Reports 2016; 49(7): 388-393]

Set7/9, a methyltransferase, regulates the thermogenic program during brown adipocyte differentiation through the modulation of p53 acetylation

Brown adipose tissue, which is mainly composed of brown adipocytes, plays a key role in the regulation of energy balance via dissipation of extra energy as heat, and consequently counteracts obesity and its associated-disorders. Therefore, brown adipocyte differentiation should be tightly controlled at the multiple regulation steps. Among these, the regulation at the level of post-translational modifications (PTMs) is largely unknown. Here, we investigated the changes in the expression level of the enzymes involved in protein lysine methylation during brown adipocyte differentiation by using quantitative real-time PCR (qPCR) array analysis. Several enzymes showing differential expression patterns were identified. In particular, the expression level of methyltransferase Set7/9 was dramatically repressed during brown adipocyte differentiation. Although there was no significant change in lipid accumulation, ectopic expression of Set7/9 led to enhanced expression of several key thermogenic genes, such as uncoupling protein-1 (UCP-1), Cidea, peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), and PR domain containing 16 (PRDM16). In contrast, knockdown of endogenous Set7/9 led to significantly reduced expression of these thermogenic genes. Furthermore, suppressed mitochondrial DNA content and decreased oxygen consumption rate were also detected upon Set7/9 knockdown. We found that p53 acetylation was regulated by Set7/9-dependent interaction with Sirt1. Based on these results, we suggest that Set7/9 acts as a fine regulator of the thermogenic program during brown adipocyte differentiation by regulation of p53 acetylation. Thus, Set7/9 could be used as a valuable target for regulating thermogenic capacity and consequently to overcome obesity and its related metabolic diseases.

Silica nanoparticles inhibit brown adipocyte differentiation via regulation of p38 phosphorylation

Nanoparticles are of great interest due to their wide variety of biomedical and bioengineering applications. However, they affect cellular differentiation and/or intracellular signaling when applied and exposed to target organisms or cells. The brown adipocyte is a cell type important in energy homeostasis and thus closely related to obesity. In this study, we assessed the effects of silica nanoparticles (SNPs) on brown adipocyte differentiation. The results clearly showed that brown adipocyte differentiation was significantly repressed by exposure to SNPs. The brown adipocyte-specific genes as well as mitochondrial content were also markedly reduced. Additionally, SNPs led to suppressed p38 phosphorylation during brown adipocyte differentiation. These effects depend on the size of SNPs. Taken together, these results lead us to suggest that SNP has anti-brown adipogenic effect in a size-dependent manner via regulation of p38 phosphorylation.

Mitofusins deficiency elicits mitochondrial metabolic reprogramming to pluripotency

Cell reprogramming technology has allowed the in vitro control of cell fate transition, thus allowing for the generation of highly desired cell types to recapitulate in vivo developmental processes and architectures. However, the precise molecular mechanisms underlying the reprogramming process remain to be defined. Here, we show that depleting p53 and p21, which are barriers to reprogramming, yields a high reprogramming efficiency. Deletion of these factors results in a distinct mitochondrial background with low expression of oxidative phosphorylation subunits and mitochondrial fusion proteins, including mitofusin 1 and 2 (Mfn1/2). Importantly, Mfn1/2 depletion reciprocally inhibits the p53-p21 pathway and promotes both the conversion of somatic cells to a pluripotent state and the maintenance of pluripotency. Mfn1/2 depletion facilitates the glycolytic metabolic transition through the activation of the Ras-Raf and hypoxia-inducible factor 1α (HIF1α) signaling at an early stage of reprogramming. HIF1α is required for increased glycolysis and reprogramming by Mfn1/2 depletion. Taken together, these results demonstrate that Mfn1/2 constitutes a new barrier to reprogramming, and that Mfn1/2 ablation facilitates the induction of pluripotency through the restructuring of mitochondrial dynamics and bioenergetics.

Chemical constituents from aerial parts of Caryopteris incana and cytoprotective effects in human HepG2 cells

An ethyl acetate fraction of the aerial parts of Caryopteris incana (Verbenaceae) showed potent cytoprotective effects against damage to HepG2 cells induced by tert-butylhydroperoxide (t-BHP). To search for hepatoprotective components of C. incana, various chromatographic separations of the ethyl acetate soluble fraction of C. incana led to isolation of three phenylpropanoid glycosides, 6‴-O-feruloylincanoside D, 6‴-O-sinapoylincanoside D and caryopteroside, and two iridoid glycosides, incanides A and B, together with 17 known compounds. Structures of these compounds were determined by spectroscopic analyses. The absolute stereochemistry of the caryopteroside was established with the help of circular dichroism data and in comparison with literature data. All isolated substances were determined for their cytoprotective effects against t-BHP-induced toxicity in HepG2 cells. Among the tested compounds, 6'-O-caffeoylacteoside exhibited the most potent cytoprotective activity with an IC50 value of 0.8±0.1 μM against t-BHP-induced toxicity. Structure-activity relationships of the assay results indicated an important role of the catechol moiety in phenylpropanoid, iridoid and flavonoid derivatives in eliciting cytoprotective effects.

Sodium nitroprusside induces autophagic cell death in glutathione-depleted osteoblasts

Previous studies reported that high levels of nitric oxide (NO) induce apoptotic cell death in osteoblasts. We examined molecular mechanisms of cytotoxic injury induced by sodium nitroprusside (SNP), a NO donor, in both glutathione (GSH)-depleted and control U2-OS osteoblasts. Cell viability was reduced by much lower effective concentrations of SNP in GSH-depleted cells compared to normal cells. The data suggest that the level of intracellular GSH is critical in SNP-induced cell death processes of osteoblasts. The level of oxidative stress due to SNP treatments doubled in GSH-depleted cells when measured with fluorochrome H2DCFDA. Pretreatment with the NO scavenger PTIO preserved the viability of cells treated with SNP. Viability of cells treated with SNP was recovered by pretreatment with Wortmannin, an autophagy inhibitor, but not by pretreatment with zVAD-fmk, a pan-specific caspase inhibitor. Large increases of LC3-II were shown by immunoblot analysis of the SNP-treated cells, and the increase was blocked by pretreatment with PTIO or Wortmannin; this implies that under GSH-depleted conditions SNP induces different molecular signaling that lead to autophagic cell death. The ultrastructural morphology of SNP-treated cells in transmission electron microscopy showed numerous autophagic vacuoles. These data suggest NO produces oxidative stress and cellular damage that culminate in autophagic cell death of GSH-depleted osteoblasts.

Changes in transcript and protein levels of calbindin D28k, calretinin and parvalbumin, and numbers of neuronal populations expressing these proteins in an ischemia model of rat retina

Excessive calcium is thought to be a critical step in various neurodegenerative processes including ischemia. Calbindin D28k (CB), calretinin (CR), and parvalbumin (PV), members of the EF-hand calcium-binding protein family, are thought to play a neuroprotective role in various pathologic conditions by serving as a buffer against excessive calcium. The expression of CB, PV and CR in the ischemic rat retina induced by increasing intraocular pressure was investigated at the transcript and protein levels, by means of the quantitative real-time reverse transcription-polymerase chain reaction, western blot and immunohistochemistry. The transcript and protein levels of CB, which is strongly expressed in the horizontal cells in both normal and affected retinas, were not changed significantly and the number of CB-expressing horizontal cells remained unchanged throughout the experimental period 8 weeks after ischemia/reperfusion injury. At both the transcript and protein levels, however, CR, which is strongly expressed in several types of amacrine, ganglion, and displaced amacrine cells in both normal and affected retinas, was decreased. CR-expressing ganglion cell number was particularly decreased in ischemic retinas. Similar to the CR, PV transcript and protein levels, and PV-expressing AII amacrine cell number were decreased. Interestingly, in ischemic retinas PV was transiently expressed in putative cone bipolar cell types possibly those that connect with AII amacrine cells via gap junctions. These results suggest that these three calcium binding proteins may play different neuroprotective roles in ischemic insult by their ability to buffer calcium in the rat retina.

Protective effects of vacuolar H+-ATPase c on hydrogen peroxide-induced cell death in C6 glioma cells

We have isolated a gene, the c subunit (ATP6L) of vacuolar H(+)-ATPase, involved in oxidative stress response. In this study, we examined the role of ATP6L and its molecular mechanisms in glial cell death induced by H(2)O(2). Expression of the ATP6L gene was increased by H(2)O(2) treatment in C6 glial cells. ATP6L siRNA-transfected C6 cells treated with H(2)O(2) showed a significant decrease in viability. ATP6L siRNA-transfected cells that were pretreated with MEK1/2 inhibitor completely recovered cell viability. Pretreatment of the transfected cells with zVAD-fmk, a pan-specific caspase inhibitor, did not result in the recovery of cell viability, as determined by a H(2)O(2)-induced cytotoxicity assay. The ultrastructural morphology of the transfected cells as seen by the use of transmission electron microscopy showed numerous cytoplasmic autophagic vacuoles with double membrane. These results suggest that ATP6L has a protective role against H(2)O(2)-induced cytotoxicity via an inhibition of the Erk1/2 signaling pathway, leading to inhibition of autophagic cell death.

Determination of hypoxic region by hypoxia marker in developing mouse embryos in vivo: a possible signal for vessel development

Hypoxia is a well-known signal for angiogenesis, but the recent proposal that hypoxia exists in developing embryonic tissues and that it induces vascular development remains to be proven. In the present study, we demonstrate the presence of hypoxia in normal developing embryos by means of a hypoxia marker, pimonidazole, and its associated antibody. Our data clearly show that hypoxia marker immunoreactivity was highly detected in developing neural tubes, heart, and intersomitic mesenchyme at an early stage of organogenesis, suggesting that hypoxia may exist in the early stages of embryo development. We also found that hypoxia inducible factor-1alpha (HIF-1alpha) and vascular endothelial growth factor (VEGF) were spatiotemporally co-localized with possible hypoxic regions in embryos. Investigation of platelet endothelial cell adhesion molecule (PECAM) expression provides evidence that endothelial cells proliferate and form the vessels in the hypoxic region in developing organs. Furthermore, we found that hypoxia induced both HIF-1alpha and VEGF in F9 embryonic stem and differentiated cells. Thus, we suggest that hypoxia may exist widely in developing embryonic tissues and that it may act as a signal for embryonic blood vessel formation in vivo.

Egr-1 mediates transcriptional activation of IGF-II gene in response to hypoxia

We have previously reported that the exposure of human HepG2 cells to hypoxic conditions results in the overexpression of human insulin-like growth factor II (IGF-II) mRNA whose size is 6.0 kb. This particular size of IGF-II mRNA is transcribed under the control of the IGF-II P3 promoter. In the present study, to delineate the molecular mechanism for the activation of the IGF-II gene, we examined the induction of P3 promoter activity in HepG2 cells by hypoxia in the transient expression system. In this system, hypoxia induced a linear increase within 24 h in the expression of luciferase that was driven by the IGF-II P3 promoter. To further delineate which factors mediate this response, the expression pattern of regulators of the P3 promoter, Egr-1, Sp1, and WT1, were analyzed by reverse transcription-PCR and Northern blot analysis. We found that hypoxia increased the expression of Egr-1 but not of Sp1. In contrast, the level of WT1, a repressor of IGF-II expression, was markedly decreased during hypoxia. The mRNA stability assay revealed that the induction of transcription is the mechanism of underlying Egr-1 mRNA elevation. We then investigated the effects of hypoxia on the DNA binding activity of Egr-1. Both electrophoretic mobility shift assay and supershift assay demonstrated that the DNA binding activity of the Egr-1 protein was increased by hypoxia. In addition, the level of Egr-1 protein was also increased under the hypoxia as determined by Western blot analysis. Cotransfection of HepG2 cells with an Egr-1 expression vector and an IGF-II P3 promoter-luciferase reporter plasmid showed that the transcription of IGF-II was activated by Egr-1 in a dose-dependent manner. Moreover, the elevation of IGF-II P3 promoter activity was induced synergistically by the cotreatment of hypoxia with Egr-1 overexpression. Deletion of sequences in the IGF-II P3 promoter containing Egr-1 binding sites did not respond to hypoxic stress. Taken together, these data strongly indicate that hypoxia-induced IGF-II expression in HepG2 cells is due to the enhanced activity of Egr-1 on the IGF-II P3 promoter and that the Egr-1 binding site in the IGF-II P3 promoter is essential for the transcriptional regulation of IGF-II under hypoxic conditions.