DEC1 is involved in circadian rhythm disruption-exacerbated pulmonary fibrosis.

BACKGROUND: The alveolar epithelial type II cell (AT2) and its senescence play a pivotal role in alveolar damage and pulmonary fibrosis. Cell circadian rhythm is strongly associated with cell senescence. Differentiated embryonic chondrocyte expressed gene 1 (DEC1) is a very important circadian clock gene. However, the role of DEC1 in AT2 senescence and pulmonary fibrosis was still unclear. RESULTS: In this study, a circadian disruption model of light intervention was used. It was found that circadian disruption exacerbated pulmonary fibrosis in mice. To understand the underlying mechanism, DEC1 levels were investigated. Results showed that DEC1 levels increased in lung tissues of IPF patients and in bleomycin-induced mouse fibrotic lungs. In vitro study revealed that bleomycin and TGF-ß1 increased the expressions of DEC1, collagen-I, and fibronectin in AT2 cells. Inhibition of DEC1 mitigated bleomycin-induced fibrotic changes in vitro and in vivo. After that, cell senescence was observed in bleomycin-treated AT2 cells and mouse models, but these were prevented by DEC1 inhibition. At last, p21 was confirmed having circadian rhythm followed DEC1 in normal conditions. But bleomycin disrupted the circadian rhythm and increased DEC1 which promoted p21 expression, increased p21 mediated AT2 senescence and pulmonary fibrosis. CONCLUSIONS: Taken together, circadian clock protein DEC1 mediated pulmonary fibrosis via p21 and cell senescence in alveolar epithelial type II cells.

Obstructive sleep apnea-increased DEC1 regulates systemic inflammation and oxidative stress that promotes development of pulmonary arterial hypertension.

Obstructive sleep apnea (OSA), characterized by chronic intermittent hypoxia (CIH), is a common risk factor for pulmonary arterial hypertension (PAH). As a hypoxia-induced transcription factor, differentially expressed in chondrocytes (DEC1) negatively regulates the transcription of peroxisome proliferative activated receptor-γ (PPARγ), a recognized protective factor of PAH. However, whether and how DEC1 is associated with PAH pathogenesis remains unclear. In the present study, we found that DEC1 was increased in lungs and pulmonary arterial smooth muscle cells (PASMCs) of rat models of OSA-associated PAH. Oxidative indicators and inflammatory cytokines were also elevated in the blood of the rats. Similarly, hypoxia-treated PASMCs displayed enhanced DEC1 expression and reduced PPARγ expression in vitro. Functionally, DEC1 overexpression exacerbated reactive oxygen species (ROS) production and the expression of pro-inflammatory cytokines (such as TNFα, IL-1ß, IL-6, and MCP-1) in PASMCs. Conversely, shRNA knockdown of Dec1 increased PPARγ expression but attenuated hypoxia-induced oxidative stress and inflammatory responses in PASMCs. Additionally, DEC1 overexpression promoted PASMC proliferation, which was drastically attenuated by a PPARγ agonist rosiglitazone. Collectively, these results suggest that hypoxia-induced DEC1 inhibits PPARγ, and that this is a predominant mechanism underpinning oxidative stress and inflammatory responses in PASMCs during PAH. DEC1 could be used as a potential target to treat PAH.

Emerging Role of Decoy Receptor-2 as a Cancer Risk Predictor in Oral Potentially Malignant Disorders.

The aim of this study was to evaluate the expression of the senescence markers, Decoy Receptor 2 (DcR2) and Differentiated Embryo-Chondrocyte expressed gen 1 (DEC1), in oral potentially malignant disorders (OPMDs) to ascertain their possible association with oral cancer risk. The immunohistochemical analysis of DcR2 and DEC1 expression (along with p16 and Ki67 expression) was carried out in 60 patients with clinically diagnosed oral leukoplakia. Fifteen cases (25%) subsequently developed an invasive carcinoma. Correlations between protein marker expression, histological grade and oral cancer risk were assessed. DcR2, DEC1 and Ki67 protein expressions were found to correlate significantly with increased oral cancer risk, and also with an increased grade of dysplasia. Multivariate analysis demonstrated that DcR2 and Ki67 expression are independent predictors of oral cancer development. Our results evidence for the first time the potential of DcR2 as an early biomarker to assess oral cancer risk in patients with oral leukoplakia (HR = 59.7, p = 0.015), showing a superior predictive value to histology (HR = 4.225, p = 0.08). These findings reveal that the increased expression of DcR2 and DEC1 occurred frequently in OPMDs. In addition, DcR2 expression emerges as a powerful biomarker for oral cancer risk assessment in patients with oral leukoplakia.

Development of an efficient expression system with large cargo capacity for interrogation of gene function in bamboo based on bamboo mosaic virus.

Bamboo is one of the fastest growing plants among monocotyledonous species and is grown extensively in subtropical regions. Although bamboo has high economic value and produces much biomass quickly, gene functional research is hindered by the low efficiency of genetic transformation in this species. We therefore explored the potential of a bamboo mosaic virus (BaMV)-mediated expression system to investigate genotype-phenotype associations. We determined that the sites between the triple gene block proteins (TGBps) and the coat protein (CP) of BaMV are the most efficient insertion sites for the expression of exogenous genes in both monopodial and sympodial bamboo species. Moreover, we validated this system by individually overexpressing the two endogenous genes ACE1 and DEC1, which resulted in the promotion and suppression of internode elongation, respectively. In particular, this system was able to drive the expression of three 2A-linked betalain biosynthesis genes (more than 4 kb in length) to produce betalain, indicating that it has high cargo capacity and may provide the prerequisite basis for the development of a DNA-free bamboo genome editing platform in the future. Since BaMV can infect multiple bamboo species, we anticipate that the system described in this study will greatly contribute to gene function research and further promote the molecular breeding of bamboo.

Crosstalk between microRNA-21-5p and the transcription factor Dec1 maintains osteoblast function.

MicroRNAs are associated with pivotal post-transcriptional gene regulation in bone formation. Human differentiated embryonic chondrocyte expressed gene 1 (Dec1) is also involved in regulating osteoblastogenesis. In the present study, we aimed to investigate the distinctive role of miR-21-5p and Dec1 in osteoblast function and to determine their biological functions. MC3T3-E1 pre-osteoblastic cells were used for in vitro analyses. miR-21-5p knockout (KO) mice, Dec1KO mice and age-matched wild-type (WT) mice were used to characterize the influence of miR-21-5p and Dec1 deficiencies on bone formation. Morphological analyses [micro-computed tomography (micro-CT)] were performed, and measurements were collected to validate miR-21-5pKO mice. Histopathological changes in mouse femur tissues were assessed by H-E staining, Azan staining, Masson's Trichrome staining, and Toluidine Blue staining. Quantitative real-time RT-PCR, western blotting and immunohistochemical staining were used to characterize the expression levels of Alkaline Phosphatase, Runx2, Osterix, Osteopontin, Dec1 and miR-21-5p. Bioinformatics analyses and dual-luciferase reporter assays were performed to confirm Dec1 as a target of miR-21-5p. Dec1 expression was gradually increased from day 7 of osteoblast induction, while miR-21-5p showed a peak at day 21. In non-induced osteoblasts, a mechanistically gain-of-function transfection study with a miR-21-5p mimic enhanced Runx2 and Osterix expression but suppressed Dec1. miR-21-5pKO mice had reduced bone growth. Dec1-deficient mice showed advanced bone formation at the age of 12 weeks compared to WT mice. The Dec1 deficiency upregulated Runx2 and Osterix expression in Dec1KO mouse femurs. Those changes, however, were reversed in miR-21-5pKO mouse femurs compared to WT mouse femurs. Dual-luciferase reporter assays showed that Dec1 is a possible downstream target of miR-21-5p. These findings showed that the reduced osteogenic potential due to a miR-21-5p deficiency is achieved by enhanced Dec1 expression and that the miR-21-5p/Dec1 axis is involved in regulating osteoblast function.

Ribosomal Stress Couples with the Hypoxia Response in Dec1-Dependent Orthodontic Tooth Movement.

This study characterized the effects of a deficiency of the hypoxia-responsive gene, differentiated embryonic chondrocyte gene 1 (Dec1), in attenuating the biological function of orthodontic tooth movement (OTM) and examined the roles of ribosomal proteins in the hypoxic environment during OTM. HIF-1α transgenic mice and control mice were used for hypoxic regulation of periodontal ligament (PDL) fibroblasts. Dec1 knockout (Dec1KO) and wild-type (WT) littermate C57BL/6 mice were used as in vivo models of OTM. The unstimulated contralateral side served as a control. In vitro, human PDL fibroblasts were exposed to compression forces for 2, 4, 6, 24, and 48 h. HIF-1α transgenic mice had high expression levels of Dec1, HSP105, and ribosomal proteins compared to control mice. The WT OTM mice displayed increased Dec1 expression in the PDL fibroblasts. Micro-CT analysis showed slower OTM in Dec1KO mice compared to WT mice. Increased immunostaining of ribosomal proteins was observed in WT OTM mice compared to Dec1KO OTM mice. Under hypoxia, Dec1 knockdown caused a significant suppression of ribosomal protein expression in PDL fibroblasts. These results reveal that the hypoxic environment in OTM could have implications for the functions of Dec1 and ribosomal proteins to rejuvenate periodontal tissue homeostasis.

DEC1 regulates the rhythmic expression of PPARγ target genes involved in lipid metabolism in white adipose tissue.

Previously, we found that the basic helix-loop-helix transcriptional repressor DEC1 interacts with the PPARγ:RXRα heterodimer, a master transcription factor for adipogenesis and lipogenesis, to suppress transcription from PPARγ target genes (Noshiro et al., Genes to Cells, 2018, 23:658-669). Because the expression of PPARγ and several of its target genes exhibits circadian rhythmicity in white adipose tissue (WAT), we examined the expression profiles of PPARγ target genes in wild-type and Dec1-/- mice. We found that the expression of PPARγ target genes responsible for lipid metabolism, including the synthesis of triacylglycerol from free fatty acids (FFAs), lipid storage and the lipolysis of triacylglycerol to FFAs, oscillates in a circadian manner in WAT. Moreover, DEC1 deficiency led to a marked increase in the expression of these genes at night (Zeitgeber times 16 and 22), resulting in disruption of circadian rhythms. Serum FFA levels in wild-type mice also showed circadian oscillations, but these were disrupted by DEC1 deficiency, leading to reduced FFA levels. These results suggest that PPARγ:RXRα and DEC1 cooperatively generate the circadian expression of PPARγ target genes through PPAR-responsive elements in WAT.

Loss of Dec1 prevents autophagy in inflamed periodontal ligament fibroblast.

Periodontal ligament fibroblasts (PDLFs) are integral to the homeostasis of periodontal tissue. The transcription factor Dec1 functions to modulate Porphyromonas gingivalis-induced periodontal inflammation. Here, we aimed to characterize the Dec1-mediated autophagy in PDLFs under inflammatory conditions. Human PDLFs were subjected to an inflammatory environment using P. gingivalis Lipopolysaccaride (LPS) along with Dec1 siRNA in vitro. Quantitative real-time polymerase chain reaction and Western blot analyses were used to evaluate the expression levels of autophagy-related genes and their upstream AKT/mTOR signaling pathways. An experimental P. gingivalis-treated Dec1 knockout (Dec1KO) mouse model was used to confirm the expression of autophagy in PDLFs in vivo. Treatment with P. gingivalis LPS induced the expression of ATG5, Beclin1 and microtubule-associated protein 1 light chain 3 (LC3) and elevated the expression of pro-inflammatory cytokine IL-1ß and Dec1 in human PDLFs. Knockdown of Dec1 partly reversed the detrimental influences of LPS on these autophagy markers in human PDLFs. The inhibition of autophagy with Dec1 siRNA suppressed the inflammatory effect of AKT/mTOR signaling pathways following treatment with P. gingivalis LPS. P. gingivalis-treated Dec1KO mice partly reduced autophagy expression. These findings suggest that a Dec1 deficiency can modulate the interaction between autophagy and inflammation in PDLFs.

The Potential Roles of Dec1 and Dec2 in Periodontal Inflammation.

Periodontal inflammation is a common inflammatory disease associated with chronic inflammation that can ultimately lead to alveolar attachment loss and bone destruction. Understanding autophagy and pyroptosis has suggested their significant roles in inflammation. In recent years, studies of differentiated embryo-chondrocyte expressed genes 1 and 2 (Dec1 and Dec2) have shown that they play important functions in autophagy and in pyroptosis, which contribute to the onset of periodontal inflammation. In this review, we summarize recent studies on the roles of clock genes, including Dec1 and Dec2, that are related to periodontal inflammation and other diseases.

DEC1 directly interacts with estrogen receptor (ER) α to suppress proliferation of ER-positive breast cancer cells.

Aberrant ERα signaling and altered circadian rhythms are both features of ER-positive breast cancer, however, the molecular interaction between them is still not fully understood. Herein, we analyzed the interplay between the circadian rhythm molecule DEC1 and ERα and its effect on the proliferation of ER-positive breast cancer cells, providing a new clue for clarifying the pathogenesis of breast cancer. In this study, we revealed that DEC1 negatively regulates the proliferation of ER-positive breast cancer MCF-7 cells through interaction with ERα protein. DEC1 co-localized with ERα in the nucleus of MCF7 cells, stabilized ERα protein independently of its transcriptional activity and without affecting by estrogen stimulation and inhibited the degradation of ERα mediated by CHX in a time-dependent manner. Moreover, results from luciferase reporter assay showed that overexpression of DEC1 significantly inhibits ERα-mediated transcriptional activity in a dose-dependent manner. These results together suggested that DEC1 may serve as a co-repressor of ERα in ER-positive breast cancer. Although DEC1 improved the stability of ERα and alleviated protein degradation, DEC1 inhibited the proliferation of MCF7 cells by decreasing ERα-mediated signal transduction.

Deficiency of the basic helix-loop-helix transcription factor DEC1 prevents obesity induced by a high-fat diet in mice.

Obesity is a major public health problem in developed countries resulting from increased food intake and decreased energy consumption and usually associated with abnormal lipid metabolism. Here, we show that DEC1, a basic helix-loop-helix transcription factor, plays an important role in the regulation of lipid consumption in mouse brown adipose tissue (BAT), which is the major site of thermogenesis. Homozygous Dec1 deletion attenuated high-fat-diet-induced obesity, adipocyte hypertrophy, fat volume and hepatic steatosis. Furthermore, DEC1 deficiency increased body temperature during daytime and enhanced the expression of uncoupler protein 1, a key factor of thermogenesis, and various lipolysis-related genes in interscapular BAT. In vitro experiments suggested that DEC1 suppresses the expression of various lipolysis-related genes induced by the heterodimer of peroxisome proliferator-activated receptor γ and retinoid X receptor α (RXRα) through direct binding to RXRα. These observations suggest that enhanced lipolysis in BAT caused by DEC1 deficiency leads to an increase in lipid consumption, thereby decreasing lipid accumulation in adipose tissues and the liver. Thus, DEC1 may serve as an energy-saving factor that suppresses lipid consumption, which may be relevant to managing obesity.

Dec1 Deficiency Suppresses Cardiac Perivascular Fibrosis Induced by Transverse Aortic Constriction.

Cardiac fibrosis is a major cause of cardiac dysfunction in hypertrophic hearts. Differentiated embryonic chondrocyte gene 1 (Dec1), a basic helix-loop-helix transcription factor, has circadian expression in the heart; however, its role in cardiac diseases remains unknown. Therefore, using Dec1 knock-out (Dec1KO) and wild-type (WT) mice, we evaluated cardiac function and morphology at one and four weeks after transverse aortic constriction (TAC) or sham surgery. We found that Dec1KO mice retained cardiac function until four weeks after TAC. Dec1KO mice also revealed more severely hypertrophic hearts than WT mice at four weeks after TAC, whereas no significant change was observed at one week. An increase in Dec1 expression was found in myocardial and stromal cells of TAC-treated WT mice. In addition, Dec1 circadian expression was disrupted in the heart of TAC-treated WT mice. Cardiac perivascular fibrosis was suppressed in TAC-treated Dec1KO mice, with positive immunostaining of S100 calcium binding protein A4 (S100A4), alpha smooth muscle actin (αSMA), transforming growth factor beta 1 (TGFß1), phosphorylation of Smad family member 3 (pSmad3), tumor necrosis factor alpha (TNFα), and cyclin-interacting protein 1 (p21). Furthermore, Dec1 expression was increased in myocardial hypertrophy and myocardial infarction of autopsy cases. Taken together, our results indicate that Dec1 deficiency suppresses cardiac fibrosis, preserving cardiac function in hypertrophic hearts. We suggest that Dec1 could be a new therapeutic target in cardiac fibrosis.

Over-expression of DEC1 inhibits myogenic differentiation by modulating MyoG activity in bovine satellite cell.

Differentiated embryo chondrocyte 1 (DEC1), a member of basic-helix-loop-helix transcription factor Bhlhe40, also called stimulated by retinoic acid 13, STRA13, plays an important role in the regulation of adipogenesis, tumorigenesis, peripheral circadian output, response to hypoxia, and development of metabolic syndrome. Previous studies suggested that DEC1 was involved in skeletal muscle development; however, its precise role in myoblast differentiation has not been determined. In the present study, we showed that DEC1 expressed ubiquitously in different bovine tissues and was down-regulated in differentiated bovine satellite cells. Expression of muscle specific transcription factors (Myf5, MyoD, MyoG, and MHC) was significantly down-regulated when DEC1 was over-expressed by both CoCl2 -simulated hypoxia and Adenovirus-mediated transduction in bovine satellite cells. Consistent with that, promoter analyses via luciferase reporter assay also revealed that overexpression of bovine DEC1 could inhibit MyoG promoter activity. In conclusion, overexpression of DEC1 blocked myogenesis by inhibiting MyoG promoter activity in bovine. Our results provided a new mechanism for the muscle growth, which would contribute to increase cattle meat productivity.

Metformin causes cancer cell death through downregulation of p53-dependent differentiated embryo chondrocyte 1.

BACKGROUND: Metformin is the most commonly used first-line medicine for type II diabetes mellitus. Acting via AMP-activated protein kinase, it has been used for more than 60 years and has an outstanding safety record. Metformin also offers protection against cancer, but its precise mechanisms remain unclear. METHODS: We first examined the cytotoxic effects of metformin in the HeLa human cervical carcinoma and ZR-75-1 breast cancer cell lines using assays of cell viability, cleaved poly-ADP-ribose polymerase, and Annexin V-fluorescein isothiocyanate apoptosis, as well as flow cytometric analyses of the cell cycle profile and reactive oxygen species (ROS). We later clarified the effect of metformin on p53 protein stability using transient transfection and cycloheximide chase analyses. RESULTS: We observed that metformin represses cell cycle progression, thereby inducing subG1 populations, and had induced apoptosis through downregulation of p53 protein and a target gene, differentiated embryo chondrocyte 1 (DEC1). In addition, metformin increased intracellular ROS levels, but N-acetyl cysteine, a ROS scavenger, failed to suppress metformin-induced apoptosis. Further results showed that metformin disrupted the electron transport chain and collapsed the mitochondrial membrane potential, which may be the cause of the elevated ROS levels. Examination of the mechanisms underlying metformin-induced HeLa cell death revealed that reduced stability of p53 in metformin-treated cells leads to decreases in DEC1 and induction of apoptosis. CONCLUSION: The involvement of DEC1 provides new insight into the positive or negative functional roles of p53 in the metformin-induced cytotoxicity in tumor cells.

DEC1 is required for anti-apoptotic activity of gastric cancer cells under hypoxia by promoting Survivin expression.

BACKGROUND: Human differentiated embryonic chondrocyte-expressed gene 1 (DEC1), which has been reported to be overexpressed in several types of cancer, is associated with tumorigenesis through participation in several biological processes. However, the complex mechanisms underlying DEC1 during carcinogenesis are controversial, and its roles in the development and malignancy of gastric cancer (GC) remain unclear. METHODS: We measured DEC1 expression in human GC cell lines. DEC1 levels in GC cells were downregulated by shRNA lentivirus infection. We also evaluated the effect of DEC1 downregulation on xenograft growth in vivo. The viability and apoptosis of the cells were assayed using the CCK8 assay and flow cytometry. The levels of DEC1, Survivin, and Bcl-2 were evaluated by Western blotting. Luciferase reporter was used to verify the downstream target of DEC1. The association of DEC1 and Survivin expression with prognosis was investigated by immunohistochemistry. RESULTS: Downregulation of DEC1 inhibits GC cell proliferation in vitro and tumorigenicity in vivo. We observed that hypoxia-induced expression of DEC1 protects GC cells from apoptosis via transcriptional upregulation of Survivin. Furthermore, positive correlations between DEC1 with Survivin expression were observed in tissue sections from GC patients. Notably, GC patients with high expression levels of DEC1 and Survivin showed poor prognosis. CONCLUSIONS: DEC1 acts as an anti-apoptotic regulator in GC cells under hypoxia by promoting Survivin expression. Our study demonstrates the critical role of the DEC1 in oncogenesis and highlights a novel role for DEC1 in the regulation of cell apoptosis in GC.

Transcription factor DEC1 is required for maximal experimentally induced periodontal inflammation.

BACKGROUND AND OBJECTIVES: Disruption of transcriptional regulation is a confounding factor associated with a wide range of human inflammatory diseases. To investigate mechanistic links between transcription factor DEC1 and pathways underlying inflammation, wild-type and DEC1 knockout (KO) C57BL/6 mice were treated with Porphyromonas gingivalis (or carboxymethyl cellulose as a control) to induce periodontal inflammation. It provoked an inflammatory response within the oral environment, which showed robust variation in alveolar bone resorption and expression of inflammatory cytokines. MATERIAL AND METHODS: Male DEC1KO mice and their wild-type littermates were used for the experimental periodontitis model. Measurement of alveolar bone resorption, micro-computed tomography, isolation of gingival mononuclear cells (GMCs), flow cytometry and immunohistochemical analysis were used in this study. Human gingival fibroblast cells (HGF-1) were used for DEC1 over-expression and short interference RNA (siRNA) studies and quantitative real-time polymerase chain reaction and western blot analysis were performed. RESULTS: Micro-computed tomography analysis demonstrated that P. gingivalis caused a decrease in bone area of wild-type mice compared with DEC1KO mice. Expression of inflammatory and immune markers in GMCs was significantly decreased in DEC1KO mice after treatment with P. gingivalis. Conversely, interleukin (IL)-4 and IL-10 mRNAs were significantly increased in GMCs isolated from DEC1KO mice. The results show that treatment of DEC1KO mice with P. gingivalis decreased the numbers of CD11b+ F4/80+ and CD4+ RANKL+ T cells. Moreover, expression of CD4, F4/80, RANKL and cathepsin K in inflammatory cell infiltrates was significantly reduced in DEC1KO mice treated with P. gingivalis compared with controls. Furthermore, over-expression of DEC1 in HGF-1 cells increased the expression of IL-1ß and tumor necrosis factor-α mRNAs and their expression levels reached a maximum in response to treatment with lipopolysaccharide. Inhibition of DEC1 by short interference RNA interference suppressed the P. gingivalis-derived lipopolysaccharide-induced expression of IL-1ß, tumor necrosis factor-α and toll-like receptor4. CONCLUSION: These results suggest that transcription factor DEC1 can modulate P. gingivalis-induced periodontitis in the oral mucosa.

Potential Roles of Dec and Bmal1 Genes in Interconnecting Circadian Clock and Energy Metabolism.

The daily rhythm of mammalian energy metabolism is subject to the circadian clock system, which is made up of the molecular clock machinery residing in nearly all cells throughout the body. The clock genes have been revealed not only to form the molecular clock but also to function as a mediator that regulates both circadian and metabolic functions. While the circadian signals generated by clock genes produce metabolic rhythms, clock gene function is tightly coupled to fundamental metabolic processes such as glucose and lipid metabolism. Therefore, defects in the clock genes not only result in the dysregulation of physiological rhythms but also induce metabolic disorders including diabetes and obesity. Among the clock genes, Dec1 (Bhlhe40/Stra13/Sharp2), Dec2 (Bhlhe41/Sharp1), and Bmal1 (Mop3/Arntl) have been shown to be particularly relevant to the regulation of energy metabolism at the cellular, tissue, and organismal levels. This paper reviews our current knowledge of the roles of Dec1, Dec2, and Bmal1 in coordinating the circadian and metabolic pathways.

Circadian rhythmicity: A functional connection between differentiated embryonic chondrocyte-1 (DEC1) and small heterodimer partner (SHP).

Circadian rhythm misalignment has been increasingly recognized to pose health risk for a wide range of diseases, particularly metabolic disorders. The liver maintains metabolic homeostasis and expresses many circadian genes, such as differentiated embryo chondrocyte-1 (DEC1) and small heterodimer partner (SHP). DEC1 is established to repress transcription through E-box elements, and SHP belongs to the superfamily of nuclear receptors and has multiple E-box elements in its promoter. Importantly, DEC1 and SHP are inversely oscillated. This study was performed to test the hypothesis that the SHP gene is a target gene of DEC1. Cotransfection demonstrated that DEC1 repressed the SHP promoter and attenuated the transactivation of the classic circadian activator complex of Clock/Bmal1. Site-directed mutagenesis, electrophoretic mobility shift assay and chromatin immunoprecipitation established that the repression was achieved through the E-box in the proximal promoter. Transfection of DEC1 suppressed the expression of SHP. In circadian-inducing cells, the epileptic agent valproate inversely altered the expression of DEC1 and SHP. Both DEC1 and SHP are involved in energy balance and valproate is known to induce hepatic steatosis. Our findings collectively establish that DEC1 participates in the negative loop of SHP oscillating expression with potential implications in metabolic homeostasis.

Differentiated embryo chondrocyte 1 (DEC1) is a novel negative regulator of hepatic fibroblast growth factor 21 (FGF21) in aging mice.

Human differentiated embryo chondrocyte expressed gene 1 (DEC1) is frequently used as a marker of senescence in vivo. Fibroblast growth factor 21 (FGF21), a novel endocrine-like member of the FGF superfamily, is highly expressed in the liver, and FGF21-transgenic mice have extended lifespans. Thus, we hypothesized that FGF21 may play a role in the DEC1-mediated aging process. In this study, DEC1 knockout (KO) mice were used to characterize the mechanism by which FGF21 protects mice from aging. Aging is strongly diminished in DEC1 KO mice, which is reflected by decreased lipid levels and oxidative stress, leading to an amelioration of liver function and structure. The expression of FGF21 decreased with aging in wild-type (WT) mice, whereas ATF4, Phospho-ERK and Phospho-p38 expression was maintained and was accompanied by a compensatory rise of FGF21 mRNA and protein expression in DEC1 KO mice. Over-expression of DEC1 markedly abolished the hepatic expression of FGF21, and siRNA-mediated inhibition of endogenous DEC1 increased the expression of FGF21. DEC1 further diminished the expression of ATF4 in HepG2 cells over-expressing DEC1. The induction of FGF21 and ATF4 at the mRNA and protein levels during the course of aging supports the view that DEC1 KO mice are able to restore the age-related imbalance of metabolism. Collectively, the data obtained in this study suggest that DEC1 is a novel negative regulator of hepatic FGF21 expression.

Fluoxetine reduces CES1, CES2, and CYP3A4 expression through decreasing PXR and increasing DEC1 in HepG2 cells.

1. This study investigated the mechanisms of the decreases of carboxylesterases (CES) and cytochrome P4503A4 (CYP3A4) and the enzymatic activities induced by fluoxetine (FLX) in HepG2 cells. We found that FLX decreased the carboxylesterase 1 (CES1) and carboxylesterase 2 (CES2) expression and the hydrolytic activity. 2. FLX decreased the pregnane X receptor (PXR) expression which regulated the target genes such as CYP3A4, whereas increased the differentiated embryonic chondrocyte-expressed gene 1 (DEC1) expression. 3. FLX repressed the PXR at transcriptional level. 4. Overexpression of PXR alone increased the expression of CES1, CES2, and CYP3A4 and attenuated the decreases of CES1, CES2, and CYP3A4 induced by FLX. On the contrary, knockdown of PXR alone decreased the expression of CES1, CES2, and CYP3A4 and almost abolished the decreases of CES1, CES2, and CYP3A4 induced by FLX. 5. Knockdown of DEC1 alone increased the expression of PXR and CYP3A4 and almost abolished the decreases of CES1, CES2, and CYP3A4 induced by FLX. 6. Taken together, the decreases of CES and CYP3A4 expression and enzymatic activities induced by FLX are through decreasing PXR and increasing DEC1 in HepG2 cells.