Altered Stra13 and Dec2 circadian gene expression in hypoxic cells

Age-dependent expression changes of circadian system-related genes reveal a potentially conserved link to aging

The circadian clock system influences the biology of life by establishing circadian rhythms in organisms, tissues, and cells, thus regulating essential biological processes based on the day/night cycle. Circadian rhythms change over a lifetime due to maturation and aging, and disturbances in the control of the circadian system are associated with several age-related pathologies.

However, the impact of chronobiology and the circadian system on healthy organ and tissue aging remains largely unknown. Whether aging-related changes of the circadian system’s regulation follow a conserved pattern across different species and tissues, hence representing a common driving force of aging, is unclear.

Based on a cross-sectional transcriptome analysis covering 329 RNA-Seq libraries, we provide indications that the circadian system is subjected to aging-related gene alterations shared between evolutionarily distinct species, such as Homo sapiens, Mus musculus, Danio rerio, and Nothobranchius furzeri. We discovered differentially expressed genes by comparing tissue-specific transcriptional profiles of mature, aged, and old-age individuals and report on six genes (per2, dec2, cirp, klf10, nfil3, and dbp) of the circadian system, which show conserved aging-related expression patterns in four organs of the species examined. Our results illustrate how the circadian system and aging might influence each other in various tissues over a long lifespan and conceptually complement previous studies tracking short-term diurnal and nocturnal gene expression oscillations.

Effects of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors on ageing: Molecular mechanisms

Human ageing is determined by degenerative alterations and processes with different manifestations such as gradual organ dysfunction, tissue function loss, increased population of aged (senescent) cells, incapability of maintaining homeostasis and reduced repair capacity, which collectively lead to an increased risk of diseases and death. The inhibitors of HMG-CoA reductase (statins) are the most widely used lipid-lowering agents, which can reduce cardiovascular morbidity and mortality. Accumulating evidence has documented several pleiotropic effects of statins in addition to their lipid-lowering properties. Recently, several studies have highlighted that statins may have the potential to delay the ageing process and inhibit the onset of senescence. In this review, we focused on the anti-ageing mechanisms of statin drugs and their effects on cardiovascular and non-cardiovascular diseases.

Bhlhe40 differentially regulates the function and number of peroxisomes and mitochondria in myogenic cells

PGC-1α is a key regulator of oxidative metabolism facilitating the expression of genes critical for the function and biogenesis of the two key oxidative organelles, mitochondria and peroxisomes, in skeletal muscle (SKM) and other organs. Our recent studies have found that the transcription factor Bhlhe40 negatively regulates PGC-1α gene expression and its coactivational activity, therefore, this factor should have profound influence on the biogenesis and metabolic activity of mitochondria and peroxisomes. Here we found that both the number and activity of peroxisomes were increased upon knockdown of Bhlhe40 expression but were repressed by its over-expression. Mitochondrial efficiency was significantly reduced by Bhlhe40 knockdown, resulting in the burst of ROS. Over-expression of a constitutively active PGC-1α-interactive domain (named as VBH135) of Bhlhe40 mimicked the effects of its knockdown on peroxisomes but simultaneously reduced ROS level. Furthermore, the efficiency, but not the number, of mitochondria was also increased by VBH135, suggesting differential regulation of peroxisomes and mitochondria by Bhlhe40. Unsaturated fatty acid oxidation, insulin response, and oxidative respiration were highly enhanced in Bhlhe40 knockdown or VBH135 over-expressed cells, suggesting the importance of Bhlhe40 in the regulation of unsaturated fatty acid and glucose oxidative metabolism. Expression profiling of genes important for either organelle also supports differential regulation of peroxisomes and mitochondria by Bhlhe40. These observations have established the important role of Bhlhe40 in SKM oxidative metabolism as the critical regulator of peroxisome and mitochondrion biogenesis and functions, and thus should provide a novel route for developing drugs targeting SKM metabolic diseases.

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Knockout of Bhlhe40 increased ROS but over-expression of Bhlhe40 reduced ROS.

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Peroxisome number was increased by Bhlhe40 knockout or VBH135 overexpression.

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Mitochondrial efficiency was reduced by Bhlhe40 knockout but increased by VBH135.

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Oxidative respiration was enhanced by Bhlhe40 knockdown or VBH135 overexpression.

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Bhlhe40 repressed PGC-1α coactivation of nuclear gene expression.

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.

Gender and the circadian pattern of body temperature in normoxia and hypoxia

Circadian patterns are at the core of many physiological processes, and their disruption can have short- and long-term consequences. This essay focuses on one of the best known patterns, the daily oscillation of body temperature (Tb), and the possibility of its difference between genders. From human and animal studies globally considered, the tentative conclusion is reached that differences in Tb circadian pattern between genders are very small and probably limited to the timing of the rhythm, not to its amplitude. Such similarity between genders, despite the differences in hormonal systems, presumably testifies to the importance that the Tb circadian pattern plays in the economy of the organism and its survival against environmental challenges. The second part of the article presents some previously unpublished experimental data from behaving male and female rats during hypoxia in synchronized conditions. In adult rats hypoxia (10.5% O₂ for three days) caused a profound drop of the Tb daily oscillations; by day 3 they were 55% (♀) and 22% (♂) of the normoxic amplitudes, with a statistically significant gender difference. In pre-puberty rats (26-day old) hypoxia caused a major disruption of the circadian pattern qualitatively similar to the adults but not different between genders. Hence, on the basis of this preliminary set of data, it seems that sex-hormones may be a factor in how the Tb daily pattern responds to hypoxia. The implications of the effects of hypoxia on the circadian patterns, and the possibility that such effects may differ between genders, are matters that could have biological and clinical implications and deserve further investigations.

MicroRNA-138 functions as a tumor suppressor in osteosarcoma by targeting differentiated embryonic chondrocyte gene 2

BACKGROUND

MicroRNA-138 (miR-138) has been proven to be a tumor suppressor gene in various types of tumors. However, the expression and the role of miR-138 in human osteosarcoma are still poorly understood. We investigated the function and the underlying mechanism of miR-138 in osteosarcoma.

METHODS

The expression of miR-138 in human osteosarcoma tissues and cell lines was detected by real-time PCR analysis. The gain-of-function and loss-of-function experiments were performed on osteosarcoma cell lines to investigate the effects of miR-138 on osteosarcoma progression, and to determine whether differentiated embryonic chondrocyte gene 2 (DEC2) mediates these effects. Cell proliferation, apoptosis and invasion were assessed by MTT, flow cytometry and transwell-matrigel assays. Dual-luciferase reporter assay was used to identify whether DEC2 is a direct target of miR-138.

RESULTS

MiR-138 was significantly downregulated in human osteosarcoma tissues and cell lines. Moreover, miR-138 expression was significantly lower in metastatic osteosarcoma tissues than that in non-metastatic tissues. The in vitro gain-of-function and loss-of-function experiments demonstrated that miR-138 inhibited cell proliferation and invasion, and promoted cell apoptosis of human osteosarcoma cells. DEC2 was verified as a direct target of miR-138, and DEC2 could reverse the inhibitory effect of miR-138 on osteosarcoma progression.

CONCLUSIONS

These findings suggested that miR-138 acts as a tumor suppressor in osteosarcoma.miR-138 inhibited cell proliferation and invasion, as well as promoted cell apoptosis of human osteosarcoma cells, at least partially, by inhibiting the expression of DEC2. MiR-138/DEC2 may be a novel therapeutic target in osteosarcoma.

Physiological, Diurnal and Stress-Related Variability of Cadmium-Metallothionein Gene Expression in Land Snails

The terrestrial Roman snail Helix pomatia has successfully adapted to strongly fluctuating conditions in its natural soil habitat. Part of the snail’s stress defense strategy is its ability to express Metallothioneins (MTs). These are multifunctional, cysteine-rich proteins that bind and inactivate transition metal ions (Cd²⁺, Zn²⁺, Cu⁺) with high affinity. In Helix pomatia a Cadmium (Cd)-selective, inducible Metallothionein Isoform (CdMT) is mainly involved in detoxification of this harmful metal. In addition, the snail CdMT has been shown to also respond to certain physiological stressors. The aim of the present study was to investigate the physiological and diurnal variability of CdMT gene expression in snails exposed to Cd and non-metallic stressors such as desiccation and oxygen depletion. CdMT gene expression was upregulated by Cd exposure and desiccation, whereas no significant impact on the expression of CdMT was measured due to oxygen depletion. Overall, Cd was clearly more effective as an inducer of the CdMT gene expression compared to the applied non-metallic stressors. In unexposed snails, diurnal rhythmicity of CdMT gene expression was observed with higher mRNA concentrations at night compared to daytime. This rhythmicity was severely disrupted in Cd-exposed snails which exhibited highest CdMT gene transcription rates in the morning. Apart from diurnal rhythmicity, feeding activity also had a strong impact on CdMT gene expression. Although underlying mechanisms are not completely understood, it is clear that factors increasing MT expression variability have to be considered when using MT mRNA quantification as a biomarker for environmental stressors.

Bhlhe40 Represses PGC-1α Activity on Metabolic Gene Promoters in Myogenic Cells

PGC-1α is a transcriptional coactivator promoting oxidative metabolism in many tissues. Its expression in skeletal muscle (SKM) is induced by hypoxia and reactive oxidative species (ROS) generated during exercise, suggesting that PGC-1α might mediate the cross talk between oxidative metabolism and cellular responses to hypoxia and ROS. Here we found that PGC-1α directly interacted with Bhlhe40, a basic helix-loop-helix (bHLH) transcriptional repressor induced by hypoxia, and protects SKM from ROS damage, and they cooccupied PGC-1α-targeted gene promoters/enhancers, which in turn repressed PGC-1α transactivational activity. Bhlhe40 repressed PGC-1α activity through recruiting histone deacetylases (HDACs) and preventing the relief of PGC-1α intramolecular repression caused by its own intrinsic suppressor domain. Knockdown of Bhlhe40 mRNA increased levels of ROS, fatty acid oxidation, mitochondrial DNA, and expression of PGC-1α target genes. Similar effects were also observed when the Bhlhe40-mediated repression was rescued by a dominantly active form of the PGC-1α-interacting domain (PID) from Bhlhe40. We further found that Bhlhe40-mediated repression can be largely relieved by exercise, in which its recruitment to PGC-1α-targeted cis elements was significantly reduced. These observations suggest that Bhlhe40 is a novel regulator of PGC-1α activity repressing oxidative metabolism gene expression and mitochondrion biogenesis in sedentary SKM.

The transcription factor DEC1 (BHLHE40/STRA13/SHARP-2) is negatively associated with TNM stage in non-small-cell lung cancer and inhibits the proliferation through cyclin D1 in A549 and BE1 cells

The objective of the current study was to investigate the expression pattern and clinicopathological significance of differentiated embryo-chondrocyte-expressed gene 1 (DEC1) in patients with non-small-cell lung cancer (NSCLC). In 118 archived NSCLC tissues, the positive rate of DEC1 was reduced in human lung cancer samples (36/118, 30.5 %) compared with adjacent normal lung tissues (106/118, 89.8 %), as measured by immunohistochemical staining. Loss of DEC1 was correlated with poor differentiation (p=0.005) and high p-TNM stage (p=0.002). Consistently, downregulation of DEC1 by siRNA knockdown promoted the growth and colony formation in the A549 lung cancer cell line, and overexpression of DEC1 inhibited the growth and colony formation in the BE1 lung cancer cell line. In addition, a significant negative correlation was found between DEC1 and cyclin D1 (p=0.014) in 118 cases of NSCLC. Knockdown of DEC1 resulted in the upregulation of cyclin D1, and overexpression of DEC1 led to the downregulation of cyclin D1. Together with the observation that DEC1 bound directly to the promoter region of cyclin D1 in A549 cells, these results indicate that loss of DEC1 may promote tumor progression in NSCLC through upregulation of cyclin D1, and DEC1 might serve as a novel therapeutic target of NSCLC.

Overexpression of the DEC1 protein induces senescence in vitro and is related to better survival in esophageal squamous cell carcinoma

Esophageal squamous cell carcinoma (ESCC) is a leading cause of cancer-related death in China and has limited effective therapeutic options except for early surgery, since the underlying molecular mechanism driving its precursor lesions towards invasive ESCC is not fully understood. Cellular senescence is the state of the permanent growth arrest of a cell, and is considered as the initial barrier of tumor development. Human differentiated embryo chondrocyte expressed gene 1 (Dec1) is an important transcription factor that related to senescence. In this study, DEC1 immunohistochemical analysis was performed on tissue microarray blocks constructed from ESCC combined with adjacent precursor tissues of 241 patients. Compared with normal epithelia, DEC1 expression was significantly increased in intraepithelial neoplasia and DEC1 expression was significantly decreased in ESCC in comparison with intraepithelial neoplasia. In vitro, DEC1 overexpression induced cellular senescence, and it inhibited cell growth and colony formation in ESCC cell line EC9706. Fresh esophagectomy tissue sections from five ESCC patients were detected by immunohistochemistry of DEC1 and senescence-associated β-galactosidase (SA-β-Gal) activity, and strongly positive expression of DEC1 was correlated to more senescent cells in these fresh tissue sections. Kaplan – Meier method analysis of the 241 patients revealed that DEC1 expression levels were significantly correlated with the survival of ESCC patients after surgery. The expression levels of DEC1 were also correlated with age, tumor embolus, depth of invasion of ESCC, lymph metastasis status and pTNMs. These results suggest that DEC1 overexpression in precursor lesions of ESCC is a protective mechanism by inducing cellular senescence in ESCC initiation, and DEC1 may be a potential prognostic marker of ESCC.

Hypoxia inducible BHLHB2 is a novel and independent prognostic marker in pancreatic ductal adenocarcinoma

AIMS

The cyclic adenosine monophosphate-inducible basic helix-loop-helix (bHLH) domain containing class-B2 transcriptional factor BHLHB2 is differentially expressed in a number of human malignancies. In the present study, the expression, regulation, functions and prognostic impact of BHLHB2 in pancreatic cancer were investigated.

METHODS

Expression analyses were carried out in tissues of the normal pancreas (n=10) and pancreatic ductal adenocarcinoma (n=77) as well as in eight pancreatic cancer cell lines using quantitative RT-PCR, semiquantitative immunohistochemistry, and immunoblot analyses. In vitro functional experiments were conducted using siRNA transfection, hypoxia, serum starvation, apoptosis induction with gemcitabine and actinomycin-D, and invasion assays. Survival analysis was performed using the Kaplan-Meier method. Prognostic factors were determined in a multivariable analysis using a Cox proportional hazards model.

RESULTS

BHLHB2 mRNA and protein expressions were strongly induced by hypoxia and by serum starvation in pancreatic cancer cell lines. BHLHB2 silencing with RNAi had no significant effects on growth and invasion but increased apoptosis resistance against gemcitabine by reducing caspace-3 cleavage. In BHLHB2 silenced cells the ED50 of gemcitabine increased from 13.95 ± 1.353 to 38.70 ± 5.262 nM (p<0.05). Ex vivo, the weak/absent nuclear staining in normal pancreatic ducts and acinar cells was replaced by moderate to strong nuclear/cytoplasmic staining in PanIN lesions and pancreatic cancer cells. Patients with weak/absent nuclear BHLHB2 staining had significantly worse median survival compared to those with strong staining (13 months vs. 27 months, p=0.03). In a multivariable analysis, BHLHB2 staining was an independent prognostic factor (Hazard-Ratio=2.348, 95% CI=1.250-4.411, p=0.008).

CONCLUSIONS

Hypoxia-inducible BHLHB2 expression is a novel independent prognostic marker in pancreatic cancer patients and indicates increased chemosensitivity towards gemcitabine.

Chronic reduction in cardiac output induces hypoxic signaling in larval zebrafish even at a time when convective oxygen transport is not required

In the present study, the zebrafish breakdance mutant ( bre) was used to assess the role of blood flow in development because it has been previously shown that bre larvae have a chronically reduced cardiac output as a result of ventricular contraction following only every second atrial contraction in addition to an atrial bradycardia. We confirmed a 50% reduction compared with control fish and further showed that blood flow in the caudal part of the dorsal aorta decreased by 80%. Associated with these reductions in blood flow were indications of developmental retardation in bre mutants, specifically delayed hatching, reduced cell proliferation, and a transiently decreased growth rate. Surprisingly, an increased red blood cell concentration and an earlier appearance of trunk vessels in bre larvae indicated some compensation to convective oxygen transport, although in previous studies it has been shown that zebrafish larvae at this stage obtain oxygen by bulk diffusion. In bre animals immunohistochemical analyses showed a significant increase in hypoxia inducible factor 1 (HIF)-α protein expression, comparable with wild-type larvae that were raised under hypoxic conditions. Accordingly, the expression of some hif downstream genes was affected. Furthermore, Affymetrix microarray analyses revealed a large number of genes that were differently expressed comparing control and bre larvae, and the number even increased with proceeding development. The results showed that a chronic reduction in blood flow generated hypoxic molecular signals despite partial compensation by increased oxygen carrying capacity and transiently slowed the overall development of zebrafish bre larvae.

Identification and developmental expression of Dec2 in zebrafish

The involvement of Dec2, a member of the basic helix-loop-helix (bHLH) family, in cellular differentiation, hypoxia response, and circadian regulation has been investigated. Here we report the previously unknown spatiotemporal expression of Dec2 in zebrafish embryogenesis. Dec2 is dynamically expressed in zebrafish pineal gland, tract of the postoptic commissure, brain, notochord, heart, common cardinal vein (CCV), axial vein, pronephric duct, swim bladder, and early somites during embryogenesis, which implies that Dec2 is involved in zebrafish central nervous system development, cardiogenesis, and internal organs and somites formation. The embryonic expression patterns of zebrafish Dec2 and its homolog Dec1 partially overlap, but are distinct from each other. The Dec2 expression level was lower than that of Dec1 during zebrafish embryogenesis. Although Dec1 also contributed to zebrafish somites formation, cardiogenesis, and internal organs and central nervous system development, the two Dec genes were not likely to be simply redundant during zebrafish embryogenesis. Our results imply that Dec2, like its homolog Dec1, is involved in zebrafish cardiogenesis, central nervous system development, and internal organs and somites formation with distinct developmental roles.