Prolonged proteasome inhibition cyclically upregulates Oct3/4 and Nanog gene expression, but reduces induced pluripotent stem cell colony formation

There is ample evidence that the ubiquitin-proteasome system is an important regulator of transcription and its activity is necessary for maintaining pluripotency and promoting cellular reprogramming. Moreover, proteasome activity contributes to maintaining the open chromatin structure found in pluripotent stem cells, acting as a transcriptional inhibitor at specific gene loci generally associated with differentiation. The current study was designed to understand further the role of proteasome inhibition in reprogramming and its ability to modulate endogenous expression of pluripotency-related genes and induced pluripotent stem cells (iPSCs) colony formation. Herein, we demonstrate that acute combinatorial treatment with the proteasome inhibitors MG101 or MG132 and the histone deacetylase (HDAC) inhibitor valproic acid (VPA) increases gene expression of the pluripotency marker Oct3/4, and that MG101 alone is as effective as VPA in the induction of Oct3/4 mRNA expression in fibroblasts. Prolonged proteasome inhibition cyclically upregulates gene expression of Oct3/4 and Nanog, but reduces colony formation in the presence of the iPSC induction cocktail. In conclusion, our results demonstrate that the 26S proteasome is an essential modulator in the reprogramming process. Its inhibition enhances expression of pluripotency-related genes; however, efficient colony formation requires proteasome activity. Therefore, discovery of small molecules that increase proteasome activity might lead to more efficient cell reprogramming and generation of pluripotent cells.

Recruitment of fat cell precursors during high fat diet in C57BL/6J mice is fat depot specific

OBJECTIVE

The study aims to explore long-term dietary effects on increases in body mass and fat depot enlargement through the recruitment of early in life labeled progenitor cells to the adipolineage.

METHODS

Neonate male C57BL/6J (B6) mice were injected intraperitoneally with BrdU. From 4 until 30 weeks of age they were fed either low fat diet (LFD) or high fat diet (HFD). BrdU-labeled cells were analyzed by flow cytometric and immunohistochemical assays after 10 days and 4, 8, 16, and 30 weeks.

RESULTS

Mice fed HFD were heavier than mice fed LFD with the most dramatic disparity recorded between week 16 and 30. BrdU-bearing cells showed the decrease in the percentage content of labeled cells in inguinal (iWAT), epididymal (eWAT) and bone marrow (BM) tissues, regardless diets. However, iWAT collected from animals on HFD showed significant increase in labeled-cells at week 16th, which coincides with robust increase in inguinal but not epididymal fat weight between 16 and 30 weeks age.

CONCLUSIONS

Cells labeled with BrdU during neonate life of B6 mice persist in fat tissues for long period of time and are recruited to the adipocyte lineage in a favorable (obesogenic) environment in iWAT but not in eWAT.

An ethanolic extract of Artemisia dracunculus L. regulates gene expression of ubiquitin-proteasome system enzymes in skeletal muscle: potential role in the treatment of sarcopenic obesity

OBJECTIVE

Obesity is linked to insulin resistance, a primary component of metabolic syndrome and type 2 diabetes. The problem of obesity-related insulin resistance is compounded when age-related skeletal muscle loss, called sarcopenia, occurs with obesity. Skeletal muscle loss results from elevated levels of protein degradation and prevention of obesity-related sarcopenic muscle loss will depend on strategies that target pathways involved in protein degradation. An extract from Artemisia dracunculus, termed PMI 5011, improves insulin signaling and increases skeletal muscle myofiber size in a rodent model of obesity-related insulin resistance. The aim of this study was to examine the effect of PMI 5011 on the ubiquitin-proteasome system, a central regulator of muscle protein degradation.

METHODS

Gastrocnemius and vastus lateralis skeletal muscle was obtained from KK-A(y) obese diabetic mice fed a control or 1% (w/w) PMI 5011-supplemented diet. Regulation of genes encoding enzymes of the ubiquitin-proteasome system was determined using real-time quantitative reverse transcriptase polymerase chain reaction.

RESULTS

Although MuRF-1 ubiquitin ligase gene expression is consistently down-regulated in skeletal muscle, atrogin-1, Fbxo40, and Traf6 expression is differentially regulated by PMI 5011. Genes encoding other enzymes of the ubiquitin-proteasome system ranging from ubiquitin to ubiquitin-specific proteases are also regulated by PMI 5011. Additionally, expression of the gene encoding the microtubule-associated protein-1 light chain 3 (LC3), a ubiquitin-like protein pivotal to autophagy-mediated protein degradation, is down-regulated by PMI 5011 in the vastus lateralis.

CONCLUSION

PMI 5011 alters the gene expression of ubiquitin-proteasome system enzymes that are essential regulators of skeletal muscle mass. This suggests that PMI 5011 has therapeutic potential in the treatment of obesity-linked sarcopenia by regulating ubiquitin-proteasome-mediated protein degradation.

Cyclosporin A reduces matrix metalloproteinases and collagen expression in dermal fibroblasts from regenerative FOXN1 deficient (nude) mice

Background

Cyclosporin A (CsA), an immunosuppressive agent modifies the wound healing process through an influence on extracellular matrix metabolism. We have compared the effects of CsA on dermal fibroblasts from nude (FOXN1 deficient) mice, a genetic model of skin scarless healing, and from control (C57BL/6 J (B6) mice to evaluate metabolic pathways that appear to have important roles in the process of scarless healing/regeneration.

Results

High levels of matrix metalloproteinases (MMPs) and collagen III expression in dermal fibroblasts from nude (regenerative) mice were down-regulated by CsA treatment to the levels observed in dermal fibroblasts from B6 (non-regenerative) mice. In contrast, dermal fibroblasts from control mice respond to CsA treatment with a minor reduction of Mmps mRNA and 2.5-fold increase expression of collagen I mRNA. An in vitro migratory assay revealed that CsA treatment profoundly delayed the migratory behavior of dermal fibroblasts from both nude and control mice.

Conclusion

The data suggest that by alternation of the accumulation of extracellular matrix components CsA treatment stimulates the transition from a scarless to a scar healing.

The ubiquitin ligase Siah2 regulates PPARγ activity in adipocytes

Moderate reductions in peroxisome proliferator-activated receptor (PPAR)γ levels control insulin sensitivity as effectively as activation of PPARγ in adipocytes by the thiazolidinediones. That observation suggests that PPARγ activity can be regulated by modulating the amount of PPARγ protein in adipocytes. Activation of PPARγ in adipocytes is linked to changes in PPARγ protein levels via increased degradation of PPARγ proteins by the ubiquitin proteasome system. Identification of the ubiquitin ligase or ligases that recognize ligand bound PPARγ is an essential step in determining the physiological significance of the relationship between activation and ubiquitin-dependent degradation of PPARγ. Using an RNA interference-based screen, we identified five RING (really interesting new gene)-type ubiquitin ligases that alter PPARγ protein levels in adipocytes. Here, we demonstrate that Drosophila seven-in-absentia homolog 2 (Siah2), a mammalian homolog of Drosophila seven-in-absentia, regulates PPARγ ubiquitylation and ligand-dependent activation of PPARγ in adipocytes. We also demonstrate that Siah2 expression is up-regulated during adipogenesis and that PPARγ interacts with Siah2 during adipogenesis. In addition, Siah2 is required for adipogenesis. These data suggest that modulation of PPARγ protein levels by the ubiquitin ligase Siah2 is essential in determining the physiological effects of PPARγ activation in adipocytes.

Insulin receptor-independent upregulation of cellular glucose uptake

BACKGROUND

Cellular glucose uptake can be enhanced by up-regulating Ras signaling in either insulin dependent or independent manner. In presence of insulin and intact insulin signaling, Ras plays a negligible role in glucose uptake. Conversely, when insulin signaling is impaired in obesity or diabetes, the insulin-independent Ras pathway may be valuable for enhancing glucose disposal. We previously reported that Ad36, a human adenovirus, enhances cellular glucose uptake by up-regulating the Ras/Glut4 pathway. Here, we investigated if Ad36-up-regulated Ras via the insulin-independent pathway, to enhance glucose uptake. Furthermore, uncontrolled up-regulation of Ras is linked with oncogenic cell transformation, if the tumor suppressor gene p53 is also down regulated. Hence, we determined if up-regulation of Ras by Ad36 would induce oncogenic cell transformation. Finally, we determined the relevance of Ad36 to insulin resistance in humans.

METHODS

Insulin receptor (IR) was knocked down with siRNA in 3T3-L1 adipocytes, to determine if Ad36 increases the Ras/Glut4 pathway and glucose uptake without IR-signaling. Next, the effects of Ad36 on cell transformation and p53 abundance were determined. Finally, overweight or obese women were screened for seropositivty to Ad36, as an indicator of natural Ad36 infection. Associations of Ad36 infection with adiposity and C-Reactive proteins (CRP) –two key markers of insulin resistance, and with glucose disposal, were determined.

RESULTS

Unaffected by IR knock-down, Ad36 significantly increased the Ras pathway, Glut4 translocation, and glucose uptake in 3T3-L1 adipocytes. Despite Ras up-regulation, Ad36 did not transform 3T3-L1 cells. This may be because Ad36 significantly increased p53 protein in 3T3-L1 cells or mice adipose tissue. Ad36 seropositivity was associated with greater adiposity and CRP levels, yet a significantly higher systemic glucose disposal rate.

CONCLUSIONS

Overall, the study offers Ras/Glut4 pathway as an alternate to enhance glucose disposal when insulin signaling is impaired, and, importantly, provides Ad36 as a tool to understand the modulation of that pathway.

PPARgamma-independent increase in glucose uptake and adiponectin abundance in fat cells

Although thiazolidinediones (TZD) effectively improve hyperglycemia and increase adiponectin, a proinsulin-sensitizing adipokine, they also increase adipogenesis via peroxisome proliferator-activated receptor (PPAR)γ induction, which may be undesirable. Recent safety concerns about some TZD have prompted the search for next generation agents that can enhance glycemic control and adiponectin independent of PPARγ or adipogenesis. Reminiscent of TZD action, a human adenovirus, adenovirus 36 (Ad36), up-regulates PPARγ, induces adipogenesis, and improves systemic glycemic control in vivo. We determined whether this effect of Ad36 requires PPARγ and/or adipogenesis. Glucose uptake and relevant cell signaling were determined in mock-infected or human adenoviruses Ad36 or Ad2-infected cell types under the following conditions: 1) undifferentiated human-adipose-tissue-derived stem cells (hASC), 2) hASC differentiated as adipocytes, 3) hASC in presence or absence of a PPARγ inhibitor, 4) NIH/3T3 that have impaired PPARγ expression, and 5) PPARγ-knockout mouse embryonic fibroblasts. Mouse embryonic fibroblasts with intact PPARγ served as a positive control. Additionally, to determine natural Ad36 infection, human sera were screened for Ad36 antibodies. In undifferentiated or differentiated hASC, or despite the inhibition, down-regulation, or the absence of PPARγ, Ad36 significantly enhanced glucose uptake and PPARγ, adiponectin, glucose transporter 4, and glucose transporter 1 protein abundance, compared with mock or Ad2-infected cells. This indicated that Ad36 up-regulates glucose uptake and adiponectin secretion independent of adipogenesis or without recruiting PPARγ. In humans, natural Ad36 infection predicted greater adiponectin levels, suggesting a human relevance of these effects. In conclusion, Ad36 provides a novel template to metabolically remodel human adipose tissue to enhance glycemic control without the concomitant increase in adiposity or PPARγ induction associated with TZD actions.

Template to improve glycemic control without reducing adiposity or dietary fat

Drugs that improve chronic hyperglycemia independently of insulin signaling or reduction of adiposity or dietary fat intake may be highly desirable. Ad36, a human adenovirus, promotes glucose uptake in vitro independently of adiposity or proximal insulin signaling. We tested the ability of Ad36 to improve glycemic control in vivo and determined if the natural Ad36 infection in humans is associated with better glycemic control. C57BL/6J mice fed a chow diet or made diabetic with a high-fat (HF) diet were mock infected or infected with Ad36 or adenovirus Ad2 as a control for infection. Postinfection (pi), systemic glycemic control, hepatic lipid content, and cell signaling in tissues pertinent to glucose metabolism were determined. Next, sera of 1,507 adults and children were screened for Ad36 antibodies as an indicator of past natural infection. In chow-fed mice, Ad36 significantly improved glycemic control for 12 wk pi. In HF-fed mice, Ad36 improved glycemic control and hepatic steatosis up to 20 wk pi. In adipose tissue (AT), skeletal muscle (SM), and liver, Ad36 upregulated distal insulin signaling without recruiting the proximal insulin signaling. Cell signaling suggested that Ad36 increases AT and SM glucose uptake and reduces hepatic glucose release. In humans, Ad36 infection predicted better glycemic control and lower hepatic lipid content independently of age, sex, or adiposity. We conclude that Ad36 offers a novel tool to understand the pathways to improve hyperglycemia and hepatic steatosis independently of proximal insulin signaling, and despite a HF diet. This metabolic engineering by Ad36 appears relevant to humans for developing more practical and effective antidiabetic approaches.

Paclitaxel-induced apoptosis is blocked by camptothecin in human breast and pancreatic cancer cells

The combination of paclitaxel (PTX) and topoisomerase I inhibitors such as camptothecin (CPT) constitutes a therapeutic strategy based on anticipated synergism. However, previous in vitro studies have generated contradictory findings for this strategy. The interaction between these drugs can be synergistic or antagonistic, depending on the cell type examined. To gain additional insight into this promising yet controversial strategy, we investigated the interaction between PTX and CPT in three different cell lines (PANC-1, MDA-MB-231 and HL-60) and explored possible underlying mechanisms of synergy or antagonism. Using a novel solubilizing natural compound, rubusoside, water-insoluble PTX and CPT were solubilized to enable the comparison of the effects of single drugs and their combination on cell viability. Intracellular drug concentrations were quantified to examine the effect of CPT on cellular uptake and accumulation of PTX. Flow cytometry and quantitative real-time PCR gene array analyses were used to explore the mechanisms behind the interaction between PTX and CPT. Our studies confirmed that rubusoside-solubilized PTX or CPT maintained cytotoxicity, causing significant reductions in cell viability. However, the efficacy of the combination of PTX and CPT produced varied results based on the cell line tested. CPT antagonistically reduced the cytotoxic activity of PTX in PANC-1 and MDA-MB-231 cells. The effect of CPT on the cytotoxicity of PTX was less pronounced in HL-60 cells, showing neither synergy nor antagonism. Analysis of apoptosis by flow cytometry revealed that upon co-treatment with CPT, apoptosis induced by PTX was attenuated in PANC-1 and MDA-MB-231 cells. In agreement with our cytotoxicity findings, no synergistic or antagonistic effects on apoptosis were observed in HL-60 cells. The antagonism in PANC-1 and MDA-MB-231 cells was not a result of reduced PTX uptake and accumulation because the amount of intracellular PTX was not altered upon co-treatment with CPT. Moreover, higher expression of anti-apoptosis-related transcripts (BCL2L10, CFLAR, HIP1 and TRADD) in PANC-1 cells was observed upon combination treatment over PTX treatment alone. Although exact underlying mechanisms are unknown, the suspected CPT-dependent reduction of intracellular PTX accumulation was ruled out. The findings of antagonism and increased anti-apoptotic gene transcription serve as a precaution to the design of combination drug strategies where a synergistic interaction may not exist.

Infectivity period of mice inoculated with human adenoviruses

Due to non-productive infections, mice are not a good model to study some human adenoviruses. However, mice provide an excellent model to study the metabolic effects of human adenovirus, Ad36. Research interest in Ad36 is increasing rapidly, and consequently an increase in the use of mice as a model is anticipated. However, little is known about the transmission potential of Ad36 from infected mice to other laboratory animals or personnel. While underestimating the infectivity could promote inadvertent spread of Ad36, overstating it could drain valuable laboratory resources and animals. Therefore, we determined the duration of infectivity in female C57BL/6J mice that were experimentally infected with human adenoviruses Ad36 or Ad2. Other uninfected mice were co-housed for one week with the experimentally-infected animals, four or eight weeks postinfection. Additionally, uninfected mice were housed in the cages of mice that were infected with Ad36, 12 weeks earlier. The presence of viral DNA in tissues was used to indicate infection of mice. Although experimentally-infected mice harboured viral DNA at least up to 12 weeks, the horizontal transmission of infection was observed in co-housed mice only up to four weeks postinfection. Thus, Ad36-infected mice should be considered potentially infective for eight weeks and appropriate handling and barrier containment should be used. After eight week postinfection, horizontal transmission appears unlikely. This information may provide guidelines for animal handling, and experimental design using Ad36, which may increase safety for laboratory personnel and reduce the number of mice required for experiments.

Flow cytometric and immunohistochemical detection of in vivo BrdU-labeled cells in mouse fat depots

This study has determined the natural frequency and localization of progenitor/stem cells within fat depots in situ based on their ability to retain DNA nucleotide label (BrdU). Neonate and mature male C57BL6/J mice were injected intraperitoneally with BrdU- and label-retaining cells (LRC) were quantified in fat depots by immunohistochemical, immunofluorescent, and flow cytometric methods. In neonates, LRC constituted 27% of the cells in inguinal fat (iWAT) and 65% in interscapular brown fat (BAT) after Day 10 and 26% of the cells in epididymal fat (eWAT) after Day 28. After 52 days, the LRC accounted for 0.72% of iWAT, 0.53% of eWAT and 1.05% of BAT, respectively. The BrdU-labeled cells localized to two areas: single cells distributed among adipocytes or those adjacent to the blood vessels wall. In mature C57BL6/J mice, flow cytometric analysis determined that a majority of the LRC were also positive for stem cell antigen-1 (Sca-1).