The PPARγ-SETD8 axis constitutes an epigenetic, p53-independent checkpoint on p21-mediated cellular senescence

SETD8 inhibition targets cancer cells with increased rates of ribosome biogenesis

SETD8 is a methyltransferase that is overexpressed in several cancers, which monomethylates H4K20 as well as other non-histone targets such as PCNA or p53. We here report novel SETD8 inhibitors, which were discovered while trying to identify chemicals that prevent 53BP1 foci formation, an event mediated by H4K20 methylation. Consistent with previous reports, SETD8 inhibitors induce p53 expression, although they are equally toxic for p53 proficient or deficient cells. Thermal stability proteomics revealed that the compounds had a particular impact on nucleoli, which was confirmed by fluorescent and electron microscopy. Similarly, Setd8 deletion generated nucleolar stress and impaired ribosome biogenesis, supporting that this was an on-target effect of SETD8 inhibitors. Furthermore, a genome-wide CRISPR screen identified an enrichment of nucleolar factors among those modulating the toxicity of SETD8 inhibitors. Accordingly, the toxicity of SETD8 inhibition correlated with MYC or mTOR activity, key regulators of ribosome biogenesis. Together, our study provides a new class of SETD8 inhibitors and a novel biomarker to identify tumors most likely to respond to this therapy.

Urolithin A alleviates cell senescence by inhibiting ferroptosis and enhances corneal epithelial wound healing

Purpose

To analyze the therapeutic effect and mechanism of Urolithin A (UA) on delayed corneal epithelial wound healing.

Methods

The C57BL/6 mice were continuously exposed to hyperosmotic stress (HS) for 7 days followed by the removal of central corneal epithelium to establish a delayed corneal epithelial wound healing model in vivo. In vitro, the human corneal epithelial cell line (HCE-T) was also incubated under HS. UA was administered in vivo and in vitro to study its effects on corneal epithelial cells. Senescence-associated β-galactosidase (SA-β-gal) staining was performed to detect the level of cell senescence. Transcriptome sequencing (RNA-seq) was conducted to elucidate the molecular mechanism underlying the effect of UA on corneal epithelial repair. Additionally, the expression of senescence-related and ferroptosis-related genes and the levels of lipid peroxides (LPO) and malondialdehyde (MDA) were measured.

Results

Hyperosmotic stress (HS) significantly increased the proportion of SA-β-gal staining positive cells in corneal epithelial cells and upregulated the expression of p16 and p21 (p < 0.0001). Topical application of UA decreased the accumulation of senescent cells in corneal epithelial wounds and promoted epithelial wound healing. The results of RNA-seq of HS-induced corneal epithelial cells showed that the ferroptosis pathway was significantly dysregulated. Further investigation revealed that UA decreased the level of oxidative stress in HCE-T cells, including the levels of LPO and MDA (p < 0.05). Inhibition of ferroptosis significantly prevented cellular senescence in HS-induced HCE-T cells.

Conclusion

In this study, UA promoted HS-induced delayed epithelial wound healing by reducing the senescence of corneal epithelial cells through the inhibition of ferroptosis.

BDE-209 induced spermatogenesis disorder by inhibiting SETD8/H4K20me1 related histone methylation in mice

Past studies have observed that decabromodiphenyl ether (BDE-209) induces reproductive and developmental toxicity, but the specific mechanism remains unclear. Based on our previous work, male mice were orally given BDE-209 at 75 mg/kg/d via continuous exposure for one spermatozoon development period (50 days) and then stopping exposure for another 50 days. The mouse spermatocyte line GC-2spd was used to examine the toxic effects of BDE-209 on histone methylation and spermatogenesis. The findings indicated that BDE-209 damaged testis and epididymis structure, induced spermatogenic cell apoptosis, and decreased sperm quantity and quality after the 50-day exposure. Furthermore, BDE-209 lowered the levels of SETD8/H4K20me1 and activated the upstream signaling of DNA damage response (Mre11/Rad50/NBS1), thereby causing spermatogenic cell cycle arrest and apoptosis. Downregulation of meiotic promoter Stra8 was associated with a decrease in SETD8 after BDE-209 exposure. After stopping the exposure for 50 days, reproductive system damage and meiosis and cell cycle inhibition due to histone methylation did not improve. In vitro experiments revealed that Setd8 overexpression upregulated the histone methylation and Stra8 expression but did not promote the cell cycle in GC-2 cells. Therefore, BDE-209 exposure impaired spermatogenesis by affecting SETD8/H4K20me1-linked histone methylation and inhibiting meiosis initiation and cell cycle progression, thereby resulting in long-term male reproductive toxicity.

A cellular senescence-related genes model allows for prognosis and treatment stratification of hepatocellular carcinoma: A bioinformatics analysis and experimental verification

Introduction: Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer with low 5-year survival rate. Cellular senescence, characterized by permanent and irreversible cell proliferation arrest, plays an important role in tumorigenesis and development. This study aims to develop a cellular senescence-based stratified model, and a multivariable-based nomogram for guiding clinical therapy for HCC. Materials and methods: The mRNAs expression data of HCC patients and cellular senescence-related genes were obtained from TCGA and CellAge database, respectively. Through multiple analysis, a four cellular senescence-related genes-based prognostic stratified model was constructed and its predictive performance was validated through various methods. Then, a nomogram based on the model was constructed and HCC patients stratified by the model were analyzed for tumor mutation burden, tumor microenvironment, immune infiltration, drug sensitivity and immune checkpoint. Functional enrichment analysis was performed to explore potential biological pathways. Finally, we verified this model by siRNA transfection, scratch assay and Transwell Assay. Results: We established an cellular senescence-related genes-based stratified model, and a multivariable-based nomogram, which could accurately predict the prognosis of HCC patients in the ICGC database. The low and high risk score HCC patients stratified by the model showed different tumor mutation burden, tumor microenvironment, immune infiltration, drug sensitivity and immune checkpoint expressions. Functional enrichment analysis suggested several biological pathways related to the process and prognosis of HCC. Scratch assay and transwell assay indicated the promotion effects of the four cellular senescence-related genes (EZH2, G6PD, CBX8, and NDRG1) on the migraiton and invasion of HCC. Conclusion: We established a cellular senescence-based stratified model, and a multivariable-based nomogram, which could predict the survival of HCC patients and guide clinical treatment.

MDM2 Aggravates Adipose Tissue Dysfunction through Ubiquitin-mediated STEAP4 Degradation

Healthy adipose tissue is crucial to maintain normal energy homeostasis. Little is known about the role of murine double minute 2 (MDM2), an E3 ubiquitin ligase and has been highlighted in oncopathology, in adipose tissue. Our results indicated that MDM2 expression was associated with nutritional status. Mdm2 adipocyte-specific knock-in (Mdm2-AKI) mice exhibited exacerbated weight gain, insulin resistance, and decreased energy expenditure. Meanwhile, chronic high-fat diet (HFD) exposure caused obvious epididymal white adipose tissue (eWAT) dysfunction, such as senescence, apoptosis, and chronic inflammation, thereby leading to hepatic steatosis in Mdm2-AKI mice. Mechanically, MDM2 could interact with six-transmembrane epithelial antigen of prostate 4 (STEAP4) and inhibit STEAP4 expression through ubiquitin-mediated STEAP4 degradation. Thereinto, the K18 and K161 sites of STEAP4 were ubiquitin-modificated by MDM2. Finally, STEAP4 restoration in eWAT of Mdm2-AKI mice on a HFD rescued MDM2-induced adipose dysfunction, insulin resistance, and hepatic steatosis. Summary, the MDM2-STEAP4 axis in eWAT plays an important role in maintaining healthy adipose tissue function and improving hepatic steatosis.

•

Murine double minute 2 (MDM2) overexpression intensifies high-fat diet-induced adipose tissue dysfunction

•

Adipocyte MDM2 overexpression aggravates insulin resistance and hepatosteatosis

•

MDM2 decreases six-transmembrane epithelial antigen of prostate 4 (STEAP4) expression by ubiquitin-dependent STEAP4 degradation

•

STEAP4 overexpression in eWAT alleviates MDM2-induced metabolic disorder

Roles for the methyltransferase SETD8 in DNA damage repair

Epigenetic posttranslational modifications are critical for fine-tuning gene expression in various biological processes. SETD8 is so far the only known lysyl methyltransferase in mammalian cells to produce mono-methylation of histone H4 at lysine 20 (H4K20me1), a prerequisite for di- and tri-methylation. Importantly, SETD8 is related to a number of cellular activities, impinging upon tissue development, senescence and tumorigenesis. The double-strand breaks (DSBs) are cytotoxic DNA damages with deleterious consequences, such as genomic instability and cancer origin, if unrepaired. The homology-directed repair and canonical nonhomologous end-joining are two most prominent DSB repair pathways evolved to eliminate such aberrations. Emerging evidence implies that SETD8 and its corresponding H4K20 methylation are relevant to establishment of DSB repair pathway choice. Understanding how SETD8 functions in DSB repair pathway choice will shed light on the molecular basis of SETD8-deficiency related disorders and will be valuable for the development of new treatments. In this review, we discuss the progress made to date in roles for the lysine mono-methyltransferase SETD8 in DNA damage repair and its therapeutic relevance, in particular illuminating its involvement in establishment of DSB repair pathway choice, which is crucial for the timely elimination of DSBs.

Integrative bioinformatics analysis the clinical value of KMT5A in different subtypes of lung cancer

To combat cancer disease, The Cancer Genome Atlas (TCGA) collects a large amount of information through high-throughput genome analysis technology. At present, there are only few treatments available for lung squamous cell carcinoma (LUSC). Although lysine methyltransferase 5A (KMT5A) is considered as a new biomarker for LUSC, its functionalities needs to be confirmed clinically in lung adenocarcinoma (LUAD). Therefore, in the current investigation we obtained the expression data of KMT5A in LUSC and LUAD by TCGA database. This study evaluated the prognostic value of KMT5A expression in LUAD and LUSC, and discussed the relevant biological pathways of KMT5A involved in the pathogenesis of LUAD and LUSC. KMT5A was highly expressed in LUAD and LUSC cancer tissues. The overall survival analysis revealed that the prognosis of high expression group was poor for LUAD, but was opposite in LUSC. In LUAD, the expression of KMT5A was significantly correlated with age (P = 0.029), gender (P = 0.001) and m (P = 0.042). Logistic regression showed that gender was significantly correlated with poor prognosis of LUAD (P = 0.00175). Multivariate analysis of Cox proportional hazards model exhibited that KMT5A risk ratio (HR) was 0.97, 95% confidence interval (CI), 0.94-1.0, P = 0.026. Age (P = 0.044), t (P = 0.031), m (P = 0.047) were the independent prognostic factors of LUSC patients, while the stage was the independent prognostic factor of LUAD (P < 0.001). Genome enrichment analysis presented that LUSC was differentially enriched with antigen processing and presentation, cell adhesion molecules, cytokine receptor interaction, ECM receptor interaction, etc. LUAD was differentially enriched with apoptosis, cancer pathway, vascular endothelial growth factor signaling pathway and wnt signaling pathway. Overall, this study presented the clinical value of KMT5A in LUSC and LUAD and suggested the possible pathways involved.

NFATc4 mediates ethanol-triggered hepatocyte senescence

BACKGROUND

Hepatocyte senescence is a core event that mediates the occurrence and development of alcoholic liver disease. Nuclear factor of activated T-cells 4 (NFATc4) is a key driver of nonalcoholic steatohepatitis. However, little was known about the implication of NFATc4 for alcoholic liver disease. This study was aimed to investigate the role of NFATc4 in hepatocyte senescence and further elucidate the underlying mechanism.

METHODS

Real-time PCR, Western blot, immunofluorescence staining, and enzyme-linked immunosorbent assay were performed to explore the role of NFATc4 in hepatocyte senescence.

RESULTS

NFATc4 was induced in ethanol-incubated hepatocytes. NFATc4 knockdown recovered cell viability and reduced the release of aspartate transaminase, alanine transaminase, and lactic dehydrogenase from ethanol-incubated hepatocytes. NFATc4 knockdown protected mice from alcoholic liver injury and inflammation. NFATc4 knockdown counteracted ethanol-induced hepatocyte senescence, evidenced by decreased senescence-associated β-galactosidase positivity and reduced p16, p21, HMGA1, and γH2AX, which was validated in in vivo studies. Peroxisome proliferator-activated receptor (PPAR)γ was inhibited by NFATc4 in ethanol-treated hepatocytes. PPARγ deficiency abrogated the inhibitory effects of NFATc4 knockdown on hepatocyte senescence, oxidative stress, and hepatic steatosis in mice with alcoholic liver disease.

CONCLUSIONS

This work discovered that ethanol enhanced NFATc4 expression, which further triggered hepatocyte senescence via repression of PPARγ.

Chromatin dynamics and DNA replication roadblocks

A broad spectrum of spontaneous and genotoxin-induced DNA lesions impede replication fork progression. The DNA damage response that acts to promote completion of DNA replication is associated with dynamic changes in chromatin structure that include two distinct processes which operate genome-wide during S-phase. The first, often referred to as histone recycling or parental histone segregation, is characterized by the transfer of parental histones located ahead of replication forks onto nascent DNA. The second, known as de novo chromatin assembly, consists of the deposition of new histone molecules onto nascent DNA. Because these two processes occur at all replication forks, their potential to influence a multitude of DNA repair and DNA damage tolerance mechanisms is considerable. The purpose of this review is to provide a description of parental histone segregation and de novo chromatin assembly, and to illustrate how these processes influence cellular responses to DNA replication roadblocks.

B7-H3 suppresses doxorubicin-induced senescence-like growth arrest in colorectal cancer through the AKT/TM4SF1/SIRT1 pathway

Emerging evidence suggests that cellular senescence induced by chemotherapy has been recognized as a new weapon for cancer therapy. This study aimed to research novel functions of B7-H3 in cellular senescence induced by a low dose of doxorubicin (DOX) in colorectal cancer (CRC). Here, our results demonstrated that B7-H3 knockdown promoted, while B7-H3 overexpression inhibited, DOX-induced cellular senescence. B7-H3 knockdown dramatically enhanced the growth arrest of CRC cells after low-dose DOX treatment, but B7-H3 overexpression had the opposite effect. By RNA-seq analysis and western blot, we showed that B7-H3 prevented cellular senescence and growth arrest through the AKT/TM4SF1/SIRT1 pathway. Blocking the AKT/TM4SF1/SIRT1 pathway dramatically reversed B7-H3-induced resistance to cellular senescence. More importantly, B7-H3 inhibited DOX-induced cellular senescence of CRC cells in vivo. Therefore, targeting B7-H3 or the B7-H3/AKT/TM4SF1/SIRT1 pathway might be a new strategy for promoting cellular senescence-like growth arrest during drug treatment in CRC.

Identification and validation of three core genes in p53 signaling pathway in hepatitis B virus-related hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is a common cancer and the leading cause is persistent hepatitis B virus (HBV) infection. We aimed to identify some core genes and pathways for HBV-related HCC.

METHODS

Gene expression profiles of GSE62232, GSE121248, and GSE94660 were available from Gene Expression Omnibus (GEO). The GSE62232 and GSE121248 profiles were the analysis datasets and GSE94660 was the validation dataset. The GEO2R online tool and Venn diagram software were applied to analyze commonly differentially expressed genes between HBV-related HCC tissues and normal tissues. Then, functional enrichment analysis using Gene Ontology (GO) and the Kyoto Encyclopedia of Gene and Genome (KEGG) as well as the protein-protein interaction (PPI) network was conducted. The overall survival rates and the expression levels were detected by Kaplan-Meier plotter and Gene Expression Profiling Interactive Analysis (GEPIA). Next, gene set enrichment analysis (GSEA) was performed to verify the KEGG pathway analysis. Furthermore, quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) was performed to validate the levels of these three core genes in tumor tissues and adjacent non-tumor liver tissues from 12 HBV related HCC patients, HBV-associated liver cancer cell lines and normal liver cell lines, and HepG2 with p53 knockdown or deletion, respectively.

RESULTS

Fifteen highly expressed genes associated with significantly worse prognoses were selected and CCNB1, CDK1, and RRM2 in the p53 signaling pathway were identified as core genes. GSEA results showed that samples highly expressing three core genes were all enriched in the p53 signaling pathway in a validation dataset (P < 0.0001). The expression of these three core genes in tumor tissue samples was higher than that in relevant adjacent non-tumor liver tissues (P < 0.0001). Furthermore, we also found that the above genes were highly expressed in liver cancer cell lines compared with normal liver cells. In addition, we found that the expression of these three core genes in p53 knockdown or knockout HCC cell lines was lower than that in negative control HCC cell lines (P < 0.05).

CONCLUSIONS

CCNB1, CDK1, and RRM2 were enriched in the p53 signaling pathway and could be potential biomarkers and therapeutic targets for HBV-related HCC.

Age-associated deficient recruitment of 53BP1 in G1 cells directs DNA double-strand break repair to BRCA1/CtIP-mediated DNA-end resection

DNA repair mechanisms play a crucial role in maintaining genome integrity. However, the increased frequency of DNA double-strand breaks (DSBs) and genome rearrangements in aged individuals suggests an age-associated DNA repair deficiency. Previous work from our group revealed a delayed firing of the DNA damage response in human mammary epithelial cells (HMECs) from aged donors. We now report a decreased activity of the main DSB repair pathways, the canonical non-homologous end-joining (c-NHEJ) and the homologous recombination (HR) in these HMECs from older individuals. We describe here a deficient recruitment of 53BP1 to DSB sites in G1 cells, probably influenced by an altered epigenetic regulation. 53BP1 absence at some DSBs is responsible for the age-associated DNA repair defect, as it permits the ectopic formation of BRCA1 foci while still in the G1 phase. CtIP and RPA foci are also formed in G1 cells from aged donors, but RAD51 is not recruited, thus indicating that extensive DNA-end resection occurs in these breaks although HR is not triggered. These results suggest an age-associated switch of DSB repair from canonical to highly mutagenic alternative mechanisms that promote the formation of genome rearrangements, a source of genome instability that might contribute to the aging process.

USP17-mediated de-ubiquitination and cancer: Clients cluster around the cell cycle

Eukaryotic cells perform a range of complex processes, some essential for life, others specific to cell type, all of which are governed by post-translational modifications of proteins. Among the repertoire of dynamic protein modifications, ubiquitination is arguably the most arcane and profound due to its complexity. Ubiquitin conjugation consists of three main steps, the last of which involves a multitude of target-specific ubiquitin ligases that conjugate a range of ubiquitination patterns to protein substrates with diverse outcomes. In contrast, ubiquitin removal is catalysed by a relatively small number of de-ubiquitinating enzymes (DUBs), which can also display target specificity and impact decisively on cell function. Here we review the current knowledge of the intriguing ubiquitin-specific protease 17 (USP17) family of DUBs, which are expressed from a highly copy number variable gene that has been implicated in multiple cancers, although available evidence points to conflicting roles in cell proliferation and survival. We show that key USP17 substrates populate two pathways that drive cell cycle progression and that USP17 activity serves to promote one pathway but inhibit the other. We propose that this arrangement enables USP17 to stimulate or inhibit proliferation depending on the mitogenic pathway that predominates in any given cell and may partially explain evidence pointing to both oncogenic and tumour suppressor properties of USP17.

The role of adipose tissue senescence in obesity- and ageing-related metabolic disorders

Adipose tissue as the largest energy reservoir and endocrine organ is essential for maintenance of systemic glucose, lipid and energy homeostasis, but these metabolic functions decline with ageing and obesity. Adipose tissue senescence is one of the common features in obesity and ageing. Although cellular senescence is a defensive mechanism preventing tumorigenesis, its occurrence in adipose tissue causatively induces defective adipogenesis, inflammation, aberrant adipocytokines production and insulin resistance, leading to adipose tissue dysfunction. In addition to these paracrine effects, adipose tissue senescence also triggers systemic inflammation and senescence as well as insulin resistance in the distal metabolic organs, resulting in Type 2 diabetes and other premature physiological declines. Multiple cell types including mature adipocytes, immune cells, endothelial cells and progenitor cells gradually senesce at different levels in different fat depots with ageing and obesity, highlighting the heterogeneity and complexity of adipose tissue senescence. In this review, we discuss the causes and consequences of adipose tissue senescence, and the major cell types responsible for adipose tissue senescence in ageing and obesity. In addition, we summarize the pharmacological approaches and lifestyle intervention targeting adipose tissue senescence for the treatment of obesity- and ageing-related metabolic diseases.

The NSD2/WHSC1/MMSET methyltransferase prevents cellular senescence-associated epigenomic remodeling

Senescent cells may possess the intrinsic programs of metabolic and epigenomic remodeling, but the molecular mechanism remains to be clarified. Using an RNAi-based screen of chromatin regulators, we found that knockdown of the NSD2/WHSC1/MMSET methyltransferase induced cellular senescence that augmented mitochondrial mass and oxidative phosphorylation in primary human fibroblasts. Transcriptome analysis showed that loss of NSD2 downregulated the expression of cell cycle-related genes in a retinoblastoma protein (RB)-mediated manner. Chromatin immunoprecipitation analyses further revealed that NSD2 was enriched at the gene bodies of actively transcribed genes, including cell cycle-related genes, and that loss of NSD2 decreased the levels of histone H3 lysine 36 trimethylation (H3K36me3) at these gene loci. Consistent with these findings, oncogene-induced or replicative senescent cells showed reduced NSD2 expression together with lower H3K36me3 levels at NSD2-enriched genes. In addition, we found that NSD2 gene was upregulated by serum stimulation and required for the induction of cell cycle-related genes. Indeed, in both mouse and human tissues and human cancer cell lines, the expression levels of NSD2 were positively correlated with those of cell cycle-related genes. These data reveal that NSD2 plays a pivotal role in epigenomic maintenance and cell cycle control to prevent cellular senescence.

Molecular avenues in targeted doxorubicin cancer therapy

In recent, intra- and inter-tumor heterogeneity is seen as one of key factors behind success and failure of chemotherapy. Incessant use of doxorubicin (DOX) drug is associated with numerous post-treatment debacles including cardiomyopathy, health disorders, reversal of tumor and formation of secondary tumors. The module of cancer treatment has undergone evolutionary changes by achieving crucial understanding on molecular, genetic, epigenetic and environmental adaptations by cancer cells. Therefore, there is a paradigm shift in cancer therapeutic by employing amalgam of peptide mimetic, small RNA mimetic, DNA repair protein inhibitors, signaling inhibitors and epigenetic modulators to achieve targeted and personalized DOX therapy. This review summarizes on recent therapeutic avenues that can potentiate DOX effects by removing discernible pitfalls among cancer patients.

Anakoinosis: Correcting Aberrant Homeostasis of Cancer Tissue-Going Beyond Apoptosis Induction

The current approach to systemic therapy for metastatic cancer is aimed predominantly at inducing apoptosis of cancer cells by blocking tumor-promoting signaling pathways or by eradicating cell compartments within the tumor. In contrast, a systems view of therapy primarily considers the communication protocols that exist at multiple levels within the tumor complex, and the role of key regulators of such systems. Such regulators may have far-reaching influence on tumor response to therapy and therefore patient survival. This implies that neoplasia may be considered as a cell non-autonomous disease. The multi-scale activity ranges from intra-tumor cell compartments, to the tumor, to the tumor-harboring organ to the organism. In contrast to molecularly targeted therapies, a systems approach that identifies the complex communications networks driving tumor growth offers the prospect of disrupting or "normalizing" such aberrant communicative behaviors and therefore attenuating tumor growth. Communicative reprogramming, a treatment strategy referred to as anakoinosis, requires novel therapeutic instruments, so-called master modifiers to deliver concerted tumor growth-attenuating action. The diversity of biological outcomes following pro-anakoinotic tumor therapy, such as differentiation, trans-differentiation, control of tumor-associated inflammation, etc. demonstrates that long-term tumor control may occur in multiple forms, inducing even continuous complete remission. Accordingly, pro-anakoinotic therapies dramatically extend the repertoire for achieving tumor control and may activate apoptosis pathways for controlling resistant metastatic tumor disease and hematologic neoplasia.

The ubiquitin-specific protease USP17 prevents cellular senescence by stabilizing the methyltransferase SET8 and transcriptionally repressing p21

Su(var)3-9, Enhancer-of-zeste, and Trithorax (SET) domain-containing protein 8 (SET8) is the sole enzyme that monomethylates Lys-20 of histone H4 (H4K20). SET8 has been implicated in the regulation of multiple biological processes, such as gene transcription, the cell cycle, and senescence. SET8 quickly undergoes ubiquitination and degradation by several E3 ubiquitin ligases; however, the enzyme that deubiquitinates SET8 has not yet been identified. Here we demonstrated that ubiquitin-specific peptidase 17-like family member (USP17) deubiquitinates and therefore stabilizes the SET8 protein. We observed that USP17 interacts with SET8 and removes polyubiquitin chains from SET8. USP17 knockdown not only decreased SET8 protein levels and H4K20 monomethylation but also increased the levels of the cyclin-dependent kinase inhibitor p21. As a consequence, USP17 knockdown suppressed cell proliferation. We noted that USP17 was down-regulated in replicative senescence and that USP17 inhibition alone was sufficient to trigger cellular senescence. These results reveal a regulatory mechanism whereby USP17 prevents cellular senescence by removing ubiquitin marks from and stabilizing SET8 and transcriptionally repressing p21.

Senescent cells in the development of cardiometabolic disease

PURPOSE OF REVIEW

Senescent cells have recently been identified as key players in the development of metabolic dysfunction. In this review, we will highlight recent developments in this field and discuss the concept of targeting these cells to prevent or treat cardiometabolic diseases.

RECENT FINDINGS

Evidence is accumulating that cellular senescence contributes to adipose tissue dysfunction, presumably through induction of low-grade inflammation and inhibition of adipogenic differentiation leading to insulin resistance and dyslipidaemia. Senescent cells modulate their surroundings through their bioactive secretome and only a relatively small number of senescent cells is sufficient to cause persistent physical dysfunction even in young mice. Proof-of-principle studies showed that selective elimination of senescent cells can prevent or delay the development of cardiometabolic diseases in mice.

SUMMARY

The metabolic consequences of senescent cell accumulation in various tissues are now unravelling and point to new therapeutic opportunities for the treatment of cardiometabolic diseases.

Quercetin protects against ox‑LDL‑induced injury via regulation of ABCAl, LXR‑α and PCSK9 in RAW264.7 macrophages

Quercetin is a flavonoid that has anti‑inflammatory, anti‑oxidant and lipid metabolic effects. It has also been reported to reduce the risk of cardiovascular disease. The present study measured the effects of quercetin on the expression of ATP‑binding cassette transporter 1 (ABCAl), ATP‑binding cassette sub‑family G member 1 (ABCG1), liver X receptor‑α (LXR‑α), proprotein convertase subtilisin/kexin type 9 (PCSK9), p53, p21 and p16 induced by oxidized low density lipoprotein (ox‑LDL). RAW264.7 macrophages were exposed to ox‑LDL with or without 20 µmol/l quercetin and cell proliferation and senescence were quantified using β‑gal staining. Superoxide dismutase (SOD), malondialdehyde (MDA) and lipid droplets were measured in the cytoplasm using oil red staining, while intracellular and total cholesterol (TC) were measured using filipin staining and a TC kit. Immunofluorescent studies and western blot analysis were performed to quantify the expression of ABCAl, ABCG1, LXR‑α, PCSK9, p53, p21 and p16. Quercetin increased RAW264.7 cell viability and reduced lipid accumulation, senescence, lipid droplets, intracellular cholesterol and TC. It was concluded that quercetin inhibits ox‑LDL‑induced lipid droplets in RAW264.7 cells by upregulation of ABCAl, ABCG1, LXR‑α and downregulation of PCSK9, p53, p21 and p16.

Salidroside slows the progression of EA.hy926 cell senescence by regulating the cell cycle in an atherosclerosis model

Aging is the major risk factor for diseases of the cardiovascular system, such as coronary atherosclerotic heart disease, but little is known about the relationship between atherosclerosis (AS) and age-related declines in vascular structure and function. Here, we used histological analyses in combination with molecular biology techniques to show that lipid deposition in endothelial cell was accompanied by aging and growth arrest. Endothelial cell senescence is sufficient to cause AS; however, we found that salidroside reduced intracellular lipid deposition, slowed the progression of endothelial cell senescence and inhibited the expression of the senescence-related molecules and phosphorylated the retinoblastoma (Rb) protein. Further study confirmed that salidroside increased the percent of S phase cells in oxidized low-density lipoprotein (ox-LDL)-treated endothelial cells. Collectively, vascular endothelial cell function declined with age and AS, and our data suggested that salidroside prevented ox-LDL-treated endothelial cell senescence by promoting cell cycle progression from G0/G1 phase to S phase via Rb phosphorylation. We demonstrated for the first time the complex interactions between AS and endothelial cell senescence, and we believe that salidroside represents a promising therapy for senescence-related AS.