CLCF1 signaling restrains thermogenesis and disrupts metabolic homeostasis by inhibiting mitochondrial biogenesis in brown adipocytes.

Great progress has been made in identifying positive regulators that activate adipocyte thermogenesis, but negative regulatory signaling of thermogenesis remains poorly understood. Here, we found that cardiotrophin-like cytokine factor 1 (CLCF1) signaling led to loss of brown fat identity, which impaired thermogenic capacity. CLCF1 levels decreased during thermogenic stimulation but were considerably increased in obesity. Adipocyte-specific CLCF1 transgenic (CLCF1-ATG) mice showed impaired energy expenditure and severe cold intolerance. Elevated CLCF1 triggered whitening of brown adipose tissue by suppressing mitochondrial biogenesis. Mechanistically, CLCF1 bound and activated ciliary neurotrophic factor receptor (CNTFR) and augmented signal transducer and activator of transcription 3 (STAT3) signaling. STAT3 transcriptionally inhibited both peroxisome proliferator-activated receptor-γ coactivator (PGC) 1α and 1ß, which thereafter restrained mitochondrial biogenesis in adipocytes. Inhibition of CNTFR or STAT3 could diminish the inhibitory effects of CLCF1 on mitochondrial biogenesis and thermogenesis. As a result, CLCF1-TG mice were predisposed to develop metabolic dysfunction even without external metabolic stress. Our findings revealed a brake signal on nonshivering thermogenesis and suggested that targeting this pathway could be used to restore brown fat activity and systemic metabolic homeostasis in obesity.

Progress on the epigenetic regulation of adipose tissue thermogenesis.

The activation of brown adipose tissues and beige adipose tissues can utilize more substrates, including glucose and fatty acids, regulate the energy balance of the whole body and improve metabolic diseases such as obesity and type Ⅱ diabetes. Elucidating the regulatory mechanisms underlying the thermogenic adipose program may provide excellent targets for therapeutics against metabolic diseases. The current studies have indicated that epigenetic modifications are vital for regulating differentiation and thermogenesis of adipose tissues. In this review, we summarize the recent progress of epigenetic modifications in adipose tissue development and thermogenesis from the aspects of DNA methylation, histone modification, chromatin remodeling, and non-coding RNAs in order to provide new ideas for further studying the activation of adipose tissues.

CHCHD10 Modulates Thermogenesis of Adipocytes by Regulating Lipolysis.

Brown and beige adipocytes dissipate energy in a nonshivering thermogenesis manner, exerting beneficial effects on metabolic homeostasis. CHCHD10 is a nuclear-encoded mitochondrial protein involved in cristae organization; however, its role in thermogenic adipocytes remains unknown. We identify CHCHD10 as a novel regulator for adipocyte thermogenesis. CHCHD10 is dramatically upregulated during thermogenic adipocyte activation by PPARγ-PGC1α and positively correlated with UCP1 expression in adipose tissues from humans and mice. We generated adipocyte-specific Chchd10 knockout mice (Chchd10-AKO) and found that depleting CHCHD10 leads to impaired UCP1-dependent thermogenesis and energy expenditure in the fasting state, with no effect in the fed state. Lipolysis in adipocytes is disrupted by CHCHD10 deficiency, while augmented lipolysis through ATGL overexpression recovers adipocyte thermogenesis in Chchd10-AKO mice. Consistently, overexpression of Chchd10 activates thermogenic adipocytes. Mechanistically, CHCHD10 deficiency results in the disorganization of mitochondrial cristae, leading to impairment of oxidative phosphorylation complex assembly in mitochondria, which in turn inhibits ATP generation. Decreased ATP results in downregulation of lipolysis by reducing nascent protein synthesis of ATGL, thereby suppressing adipocyte thermogenesis. As a result, Chchd10-AKO mice are prone to develop high-fat diet-induced metabolic disorders. Together, our findings reveal an essential role of CHCHD10 in regulating lipolysis and the thermogenic program in adipocytes.

Hepatic Small Ubiquitin-Related Modifier (SUMO)-Specific Protease 2 Controls Systemic Metabolism Through SUMOylation-Dependent Regulation of Liver-Adipose Tissue Crosstalk.

BACKGROUND AND AIMS: NAFLD, characterized by aberrant triglyceride accumulation in liver, affects the metabolic remodeling of hepatic and nonhepatic tissues by secreting altered hepatokines. Small ubiquitin-related modifier (SUMO)-specific protease 2 (SENP2) is responsible for de-SUMOylation of target protein, with broad effects on cell growth, signal transduction, and developmental processes. However, the role of SENP2 in hepatic metabolism remains unclear. APPROACH AND RESULTS: We found that SENP2 was the most dramatically increased SENP in the fatty liver and that its level was modulated by fed/fasted conditions. To define the role of hepatic SENP2 in metabolic regulation, we generated liver-specific SENP2 knockout (Senp2-LKO) mice. Senp2-LKO mice exhibited resistance to high-fat diet-induced hepatic steatosis and obesity. RNA-sequencing analysis showed that Senp2 deficiency up-regulated genes involved in fatty acid oxidation and down-regulated genes in lipogenesis in the liver. Additionally, ablation of hepatic SENP2 activated thermogenesis of adipose tissues. Improved energy homeostasis of both the liver and adipose tissues by SENP2 disruption prompted us to detect the hepatokines, with FGF21 identified as a key factor markedly elevated in Senp2-LKO mice that maintained metabolic homeostasis. Loss of FGF21 obviously reversed the positive effects of SENP2 deficiency on metabolism. Mechanistically, by screening transcriptional factors of FGF21, peroxisome proliferator-activated receptor alpha (PPARα) was defined as the mediator for SENP2 and FGF21. SENP2 interacted with PPARα and deSUMOylated it, thereby promoting ubiquitylation and subsequent degradation of PPARα, which in turn inhibited FGF21 expression and fatty acid oxidation. Consistently, SENP2 overexpression in liver facilitated development of metabolic disorders. CONCLUSIONS: Our finding demonstrated a key role of hepatic SENP2 in governing metabolic balance by regulating liver-adipose tissue crosstalk, linking the SUMOylation process to metabolic regulation.

[The effects of CT120B over-expression on growth suppression and changes of gene expression profiles in lung adenocarcinoma cells].

OBJECTIVE: CT120B gene is a splicing variant of CT120A, which deletes 96 nucleotides and leads to an in-frame loss of 32 amino acids between the codon 136 and 167 as compared with CT120A. This study was undertaken to assess the effects of CT120B expression on lung cancer cell growth and to explore the gene expression profiles. METHODS: CT120B cDNA was transfected into the human lung adenocarcinoma SPC-A-1 cells, and stable cell lines overexpressing CT120B were established. CCK-8 assay and tumorigenecity in a xenograft model were performed to analyze cell proliferation in vitro and in vivo. The differential gene expression induced by overexpressed CT120B was investigated using Atlas cDNA expression array. Flow cytometry was performed to analyze cell cycle and cell apoptosis. RESULTS: Overexpression of CT120B in SPC-A-1 cells resulted in a reduced cell growth rate in vitro, and decrease of the tumorigenicity in nude mice. A total of 38 genes were identified as differential expressions with more than a 2.0-fold change by Atlas cDNA expression array analysis, including downregulated cyclin E1, cdk 2, c-kit, CXCR4 and upregulated caspase 8 gene. Overexpression of CT120B also induced G1 phase arrest, but had no effect on cell apoptosis. CONCLUSION: The G1 cell cycle arrest, but not apoptosis, underlay the growth inhibitory activities of CT120B. The down-regulation of c-kit and CXCR4 expression might also contribute to the suppressive effects on cell growth of CT120B.

Inhibitory effect of CT120B, an alternative splice variant of CT120A, on lung cancer cell growth.

The expression product of ct120a, a novel gene isolated from human chromosome 17p13.3 in our laboratory, was predicted to have seven transmembrane domains and could cause malignant transformation of mouse NIH3T3 cells. There existed an mRNA splicing variant of ct120a, namely ct120b, which had a 96-nucleotide deletion and produced an in-frame loss of 32 amino acids from codon 136 to codon 167 of CT120A. The CT120B protein was predicted to have six transmembrane domains. In this study, we observed that the green fluorescent protein-tagged CT120B was localized on plasma membrane and in cytoplasm in SPC-A-1 cells. The expression of CT120B/A in normal lung tissue and in lung cancer cells was also examined. Results showed that the stable CT120B overexpression in SPC-A-1 cells resulted in a reduction of cell growth rate, and inhibited tumorigenecity and anchorage-independent growth in nude mice. The functions of CT120A and CT120B for cell growth appeared antagonistic. We suggested that the delayed G1/S phase transition might contribute to the inhibitory activities of CT120B on cell growth and that the deleted 32 amino acids missing in CT120B might be essential for the oncogenetic activities of CT120A.

[Down-regulation of CT120A by RNA interference suppresses lung cancer cells growth].

OBJECTIVE: To validate our obtained outcomes and clarify the relationship between CT120A, a novel human plasma membrane-associated gene, and proliferation of lung cancer cells. METHODS: A vector-based small hairpin RNA (shRNA) was transfected into the human lung adenocarcinoma SPC-A-1 cells to specifically target CT120A cDNA. RT-PCR and Western blotting were used to analyze the CT120A expression. The cell proliferation rate was analyzed by BrdU-TdR incorporation assay, the ability of cells to grow in soft agarose and the tumorigenicity in nude mice were measured. Flow cytometry was performed to analyze cell apoptosis. RESULTS: When compared with the scrambled control cell line, CT120A transcripts were reduced by 70% and 50% in two shRNA-H stable transfectants, H2 and H3 clones, respectively. The protein of CT120A was reduced by about 80% in both the H2 and H3 clones. By BrdU incorporation assay, up to the 6th day a dramatic decrease in the cell growth rate (30% to 40%) was observed in the shRNA-H2 and shRNA-H3 cell lines. The colony formation rate in soft agarose of the two cell lines was about one half that of the control cells. In addition, a remarkable reduction of tumorigenicity of the two cell lines was observed as compared with that of the control. The suppression of CT120A expression also sensitized cells to ultraviolet-induced apoptosis. CONCLUSION: Down-regulation of CT120A by RNA interference suppresses lung cancer cell growth. The successful knockdown of CT120A expression by RNA interference implicates that CT120A may be a new candidate of drug target for treatment of lung cancers.

[A DNA vector-based RNAi technology to inhibit the activity of the telomerase of cell line HCCLM3].

OBJECTIVE: To develop a DNA vector-based RNA interference (RNAi) technology that inhibits the activity of the telomerase of the hepatocellular carcinoma cell line HCCLM3 in order to suppress the proliferation of the cells. METHODS: Hepatocellular carcinoma cells of the line HCCLM3 were cultured. mRNA interfering double-stranded DNA vector PSG-AS targeting the mRNA of human telomerase reverse transcriptase (hTERT) and the control vector PSG-CTR were constructed respectively, and then were transfected into the HCCLM3 cells. The expression of hTERT of the transfected cells was determined by Western blotting and the activity of telomerase was determined by telomeric repeat amplification-ELISA (TRAP-ELISA). Flow cytometry was used to detect the apoptosis of transfected cells and MTS method was used to measure the growth curve of the cells so as to observe the effect of the PSG-AS on the proliferation of HCCLM3 cell. RESULTS: TRAP-ELISA showed that the inhibition rate of PSG-AS on the telomerase activity was 76%. The apoptotic rate of the PSG-AS group was significantly higher than that of the PSG-CTR group (t = 11.48, P < 0.001). Western blotting showed a remarkable inhibition of hTERT protein in the PSG-AS group. CONCLUSION: Capable of suppressing the hTERT expression and the activity of telomerase, RNA interfering technology can be applied to treatment of tumors.

The antioxidant effects of ribonuclease inhibitor.

Ribonuclease inhibitor (RI) is an acidic cytosolic glycoprotein with molecular weight of about 50 kDa, which contains 32 cysteine residues. It is possibly that RI may have antioxidant effect by thiol-disulfide exchange reaction. We studied the effects of RI over-expression on the rat glial cell line C6 injured with H2O2. The transfected C6 cells with RI cDNA (C6') had higher viability, less LDH leakage and MDA contents, but more GSH contents compare that in the control C6 cells. In transfected C6 cells, the activities of CAT and GST were higher than that in the control C6 cells. Without H202 stress, the activities of CAT and GST in the C6' cells were 1.73 and 3.62 times that in the control C6 cells, respectively; With 1.00 mmol/L H2O2 stress, the activities of CATand GSTin the C6' cells were 3.38 and 2.11 times that in the C6 cells, respectively. These results suggest that the over-expression RI has antioxidant activity and it is able to protect cells from per-oxidative injuries. Moreover, we investigated whether RI has a protective role against mouse hepatic damage in vivo. The mice pretreated with different doses of human RI were injected by CC14. The results show that the SOD activities of therapy groups were significantly higher than that of the control group (p < 0.01), while the contents of MOD and activities of ALT and AST in blood were remarkably lower than that of the control group (p < 0.01). Pathological examination shows that the degree of damage was alleviated with RI therapy. These results suggest that RI has the protective role against mouse hepatic damage induced by CC14. The anti-oxidative effects of RI may play an important role in cell protection from per-oxidative injuries.