Cellular senescence: from anti-cancer weapon to anti-aging target

Context-dependent role of SIRT3 in cancer

Sirtuin 3 (SIRT3), an NAD+-dependent deacetylase, plays a key role in the modulation of metabolic reprogramming and regulation of cell death, as well as in shaping tumor phenotypes. Owing to its critical role in determining tumor-type specificity or the direction of tumor evolution, the development of small-molecule modulators of SIRT3, including inhibitors and activators, is of significant interest. In this review, we discuss recent studies on the oncogenic or tumor-suppressive functions of SIRT3, evaluate advances in SIRT3-targeted drug discovery, and present potential avenues for the design of small-molecule modulators of SIRT3 for cancer therapy.

Vemurafenib induces senescence in acute myeloid leukemia and myelodysplastic syndrome by activating the HIPPO signaling pathway: implications for potential targeted therapy

BACKGROUND

The outcome of Acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) remain dismal despite the development of treatment. Targeted therapy is gaining more and more attention in improving prognosis.

METHODS

Expression of BRAF was analyzed by RT-qPCR in AML and MDS patients. Cells viability treated by drugs was measured by CCK-8 assay. Network pharmacology and RNA-sequence were used to analyze the mechanism of drugs and verified in vitro and xenograft tumor model.

RESULTS

Here we showed that BRAF was overexpressed in AML and MDS patients, and correlated with poor prognosis. The BRAF inhibitor-Vemurafenib (VEM) could significantly induce senescence, proliferation inhibition and apoptosis in AML cells, which can be enhanced by Bortezomib (BOR). This inhibitory effect was also verified in CD34 + cells derived from AML patients. Mechanistically, we showed that VEM combined with BOR could turn on HIPPO signaling pathway, thereby inducing cellular senescence in AML cells and xenograft mouse.

CONCLUSIONS

Taken together, our findings demonstrate a significant upregulation of BRAF expression in AML and MDS patients, which is associated with unfavorable clinical outcomes. We also discovered that the BRAF inhibitor Vemurafenib induces cellular senescence through activation of the HIPPO signaling pathway. Analysis of BRAF expression holds promise as a prognostic indicator and potential therapeutic target for individuals with AML and MDS.

Micronano Titanium Accelerates Mesenchymal Stem Cells Aging through the Activation of Senescence-Associated Secretory Phenotype

Stem cell senescence is one of the most representative events of organism aging and is responsible for many physiological abnormalities and disorders. In the scenario of orthopedic disease treatment, stem cell aging may affect the implantation outcome and even lead to operation failure. To explore whether stem cell aging will affect the osteointegration effect of titanium implant, a widely used micronano titanium (MNT) was fabricated. We first verified the expected osteointegration effect of the MNT, which could be attributed to the improvement of stem cell adhesion and osteogenic differentiation. Then, we obtained aged-derived bone marrow mesenchymal stem cells (BMSCs) and studied their biological behaviors on MNT both in vitro and in vivo. We found that compared with normal rats, MNT did not significantly improve the osteointegration in aged rats. Compared with normal rats, fewer endogenous stem cells were observed at the implant-host interface, and the expression of p21 (senescence marker) was also higher. We further confirmed that MNT promoted the nuclear localization of NF-κB in senescent stem cells through the activation of p38 MAPK, thereby inducing the occurrence of the senescence-associated secretory phenotype (SASP) and ultimately leading to the depletion of the stem-cell pool at the implant-host interface. However, the activation of p38 MAPK can still promote the osteogenic differentiation of nonsenescent BMSCs. These results showed an interesting paradoxical balance between osteogenesis and senescence on MNT surfaces and also provided insights for the design of orthopedic implants for aging patients.

Redox-stress response resistance (RRR) mediated by hyperoxidation of peroxiredoxin 2 in senescent cells

Aging is closely related to redox regulation. In our previous work, we proposed a new concept, "redox-stress response capacity (RRC)," and found that the decline in RRC was a dynamic characteristic of aging. However, the mechanism of RRC decline during aging remains unknown. In this study, using the senescent human fibroblast cell model and Caenorhabditis elegans model, we identified that peroxiredoxin 2 (PRDX2), as a hydrogen peroxide (H2O2) sensor, was involved in mediating RRC. PRDX2 knockdown led to a decline of RRC and accelerated senescence in fibroblasts and prdx-2 mutant C. elegans also showed decreased RRC. The mechanism study showed that the decreased sensor activity of PRDX2 was related to the increase in hyperoxidation of PRDX2 in senescent cells. Moreover, the level of PRDX2 hyperoxidation also increased in old C. elegans. Simultaneous overexpression of both PRDX2 and sulfiredoxin (SRX) rescued the reduced RRC and delayed senescence. The increase in PRDX2 hyperoxidation in senescent cells led to a decrease in its sensor activity, resulting in the decreased cellular response to H2O2, which is similar to the mechanism of insulin resistance due to the lower insulin receptor sensitivity. Treatment of young cells with a high level of H2O2 to induce a higher level of PRDX2-SO3 resulted in mimicking the RRC decline in senescent cells, which is also similar to a model of insulin resistance induced by high levels of insulin. All these results thrillingly indicate that there is an insulin-resistance-like phenomenon in senescent cells, we named it redox-stress response resistance, RRR. RRR in senescent cells is an important new discovery that explains RRC decline during aging and reveals the internal relationship between redox regulation and aging from a new perspective.

LncRNA NEAT1 suppresses cellular senescence in hepatocellular carcinoma via KIF11-dependent repression of CDKN2A

BACKGROUND

Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related deaths worldwide. Therapeutic options for advanced HCC are limited, which is due to a lack of full understanding of pathogenesis. Cellular senescence is a state of cell cycle arrest, which plays important roles in the pathogenesis of HCC. Mechanisms underlying hepatocellular senescence are not fully understood. LncRNA NEAT1 acts as an oncogene and contributes to the development of HCC. Whether NEAT1 modulates hepatocellular senescence in HCC is unknown.

METHODS

The role of NEAT1 and KIF11 in cellular senescence and tumor growth in HCC was assessed both in vitro and in vivo. RNA pulldown, mass spectrometry, Chromatin immunoprecipitation (ChIP), luciferase reporter assays, RNA FISH and immunofluorescence (IF) staining were used to explore the detailed molecular mechanism of NEAT1 and KIF11 in cellular senescence of HCC.

RESULTS

We found that NEAT1 was upregulated in tumor tissues and hepatoma cells, which negatively correlated with a senescence biomarker CDKN2A encoding p16INK4a and p14ARF proteins. NEAT1 was reduced in senescent hepatoma cells induced by doxorubicin (DOXO) or serum starvation. Furthermore, NEAT1 deficiency caused senescence in cultured hepatoma cells, and protected against the progression of HCC in a mouse model. During senescence, NEAT1 translocated into cytosol and interacted with a motor protein KIF11, resulting in KIF11 protein degradation and subsequent increased expression of CDKN2A in cultured hepatoma cells. Furthermore, KIF11 knockdown caused senescence in cultured hepatoma cells. Genetic deletion of Kif11 in hepatocytes inhibited the development of HCC in a mouse model.

CONCLUSIONS

Conclusively, NEAT1 overexpression reduces senescence and promotes tumor progression in HCC tissues and hepatoma cells, whereas NEAT1 deficiency causes senescence and inhibits tumor progression in HCC. This is associated with KIF11-dependent repression of CDKN2A. These findings lay the foundation to develop potential therapies for HCC by inhibiting NEAT1 and KIF11 or inducing senescence.

Evaluation of the Effectiveness of an Innovative Polycomponent Formulation on Adult and Aged Human Dermal Fibroblasts

Skin aging is a dynamic process that determines structural alterations in ECM and reduction in dermal fibroblasts. The recent availability on the market of an innovative polycomponent formulation (KARISMA Rh Collagen® FACE, K) containing noncrosslinked high-molecular-weight hyaluronic acid (HMW-HA), a human recombinant polypeptide of collagen-1 alpha chain, and carboxymethyl cellulose (CMC), attracted our scientific interest in evaluating its biomolecular effects on human dermal adult and aged fibroblasts. After treatment with increasing K concentrations, cell proliferation, collagen I, prolyl 4-hydroxylase (P4HA1), an essential protein in collagen biosynthesis, and α-SMA levels were assessed. The fibroblast contractility, TGF-β1 levels, and oxidative stress markers were also evaluated. K formulation exposure led to a significant and dose-dependent increase in the proliferation and migration of adult fibroblasts. Of note, the K exposure counteracted the H2O2-induced aging by promoting cell proliferation, reducing β-galactosidase activity, and neutralizing the aging-associated oxidative damage. Moreover, an increase in collagen I, P4HA1, α-SMA, TGF-β1 levels, and improved contractility of adult and aged fibroblasts were observed after treatment. Overall, our results show evidence that the K treatment is efficacious in improving biological functions in adult fibroblasts and suppressing the biomolecular events associated with H2O2-induced cellular aging, thus supporting the regenerative and bio-revitalizing action of the K formulation helpful in preventing or treating skin aging.

Evolution of Resistance to Irinotecan in Cancer Cells Involves Generation of Topoisomerase-Guided Mutations in Non-Coding Genome That Reduce the Chances of DNA Breaks

Resistance to chemotherapy is a leading cause of treatment failure. Drug resistance mechanisms involve mutations in specific proteins or changes in their expression levels. It is commonly understood that resistance mutations happen randomly prior to treatment and are selected during the treatment. However, the selection of drug-resistant mutants in culture could be achieved by multiple drug exposures of cloned genetically identical cells and thus cannot result from the selection of pre-existent mutations. Accordingly, adaptation must involve the generation of mutations de novo upon drug treatment. Here we explored the origin of resistance mutations to a widely used Top1 inhibitor, irinotecan, which triggers DNA breaks, causing cytotoxicity. The resistance mechanism involved the gradual accumulation of recurrent mutations in non-coding regions of DNA at Top1-cleavage sites. Surprisingly, cancer cells had a higher number of such sites than the reference genome, which may define their increased sensitivity to irinotecan. Homologous recombination repairs of DNA double-strand breaks at these sites following initial drug exposures gradually reverted cleavage-sensitive "cancer" sequences back to cleavage-resistant "normal" sequences. These mutations reduced the generation of DNA breaks upon subsequent exposures, thus gradually increasing drug resistance. Together, large target sizes for mutations and their Top1-guided generation lead to their gradual and rapid accumulation, synergistically accelerating the development of resistance.

CDK4/6 Inhibition Induces Senescence and Enhances Radiation Response by Disabling DNA Damage Repair in Oral Cavity Squamous Cell Carcinoma

Purpose: HPV(−) OCSCC resists radiation treatment. The CDKN2A gene, encoding p16INK4A, is commonly disrupted in OCSCC. p16 inhibits CDK4/CDK6, leading to cell cycle arrest, but the biological sequelae of CDK4/6 inhibition in OCSCC remains understudied. This study examines whether inhibition of CDK4/6 enhances radiation response in OCSCC. Methods: MTT assays were performed in OCSCC cell lines HN5 and CAL27following treatment with palbociclib. Clonogenic survival and synergy were analyzed after radiation (RT-2 or 4Gy), palbociclib (P) (0.5 µM or 1 µM), or concurrent combination treatment (P+RT). DNA damage/repair and senescence were examined. CDK4/6 were targeted via siRNA to corroborate P+RT effects. Three-dimensional immortalized spheroids and organoids derived from patient tumors (conditionally reprogrammed OCSCC CR-06 and CR-18) were established to further examine and validate responses to P+RT. Results: P+RT demonstrated reduced viability and synergy, increased β-gal expression (~95%), and ~two-fold higher γH2AX. Rad51 and Ku80 were reduced after P+RT, indicating impairment of both HR and NHEJ. siCDK4/6 increased senescence with radiation. Spheroids showed reduced proliferation and size with P+RT. CR-06 and CR-18 further demonstrated three-fold reduced proliferation and organoids size with P+RT. Conclusion: Targeting CDK4/6 can lead to improved efficacy when combined with radiation in OCSCC by inducing senescence and inhibiting DNA damage repair.

Delivery of Active Peptides by Self-Healing, Biocompatible and Supramolecular Hydrogels

Supramolecular and biocompatible hydrogels with a tunable pH ranging from 5.5 to 7.6 lead to a wide variety of formulations useful for many different topical applications compatible with the skin pH. An in vitro viability/cytotoxicity test of the gel components demonstrated that they are non-toxic, as the cells continue to proliferate after 48 h. An analysis of the mechanical properties demonstrates that the hydrogels have moderate strength and an excellent linear viscoelastic range with the absence of a proper breaking point, confirmed with thixotropy experiments. Two cosmetic active peptides (Trifluoroacetyl tripeptide-2 and Palmitoyl tripeptide-5) were successfully added to the hydrogels and their transdermal permeation was analysed with Franz diffusion cells. The liquid chromatography-mass spectrometry (HPLC-MS) analyses of the withdrawn samples from the receiving solutions showed that Trifluoroacetyl tripeptide-2 permeated in a considerable amount while almost no transdermal permeation of Palmitoyl tripeptide-5 was observed.

A novel role of Fas in delaying cellular senescence

Fas-mediated apoptosis is a major player of many physiological and pathological cellular processes. Fas-regulated immune regulation exhibits either the beneficial or the harmful effects which is associated with the onset or development of immune disorders. Alterations in apoptosis may contribute to age-associated changes. However, the role of apoptosis in the ageing process remains ambiguous. Here we demonstrated Fas signaling-mediated premature senescence in young mouse embryonic fibroblast (MEF) cells. Activated Fas signaling by agonist Jo-2 resulted in declined senescence in young and aged MEFs. Premature senescence induced the early activation of senescence markers, including the increase in the percentage of SA-β-galactosidase (SA-β-gal) cells, the induction of p53 phosphorylation, and the enhanced expression of p16 and p21 protein and elevated IL-6 pro-inflammatory cytokine in the absence of Fas. The elevated production of reactive oxygen species (ROS) in Fas-deficient MEFs was associated with dysfunctional mitochondria. Further, we determined that the known ROS scavenger NAC (N-acetyl-l-cysteine) could reverse the process of premature senescence in absence of Fas. Therefore, this study signifies a novel role of Fas in the control of cellular senescence.

A pan-cancer analysis of the oncogenic role of leucine zipper protein 2 in human cancer

In this study, we aimed to perform a pan-cancer analysis of leucine zipper protein 2 (LUZP2). A standardized TCGA pan-cancer dataset was downloaded. Differential expression, clinical prognosis, genetic mutations, immune infiltration, epigenetic modifications, tumor stemness and heterogeneity were analyzed. We conducted all analyses through software R 3.6.3 and its suitable packages. Compared to normal samples, we observed that the LUZP2 mRNA expression was significantly upregulated in LGG, PRAD, LUSC and downregulated in KIRC and other eleven cancer species patients. In terms of overall survival, low-expression of LUZP2 was significantly associated with poor prognosis in lower grade glioma (LGG), lung squamous cell carcinoma (LUSC), kidney renal clear cell carcinoma (KIRC) and prostate adenocarcinoma (PRAD). For progression-free survival, we observed that downregulation of LUZP2 was significantly related to LGG, KIRC, LUSC, and PRAD. Our results observed negative correlations of the stemness of LGG and PRAD with the mRNA expression of LUZP2, whose downregulation was closely associated with poor prognosis. The mutation frequencies of LGG, PRAD, KIRC, and LUSC were 0.4%, 0.4%, 0.3%, and 2.1%, respectively. We detected that the LUZP2 level was negatively associated with TILs in most cancers, including LGG, LUSC, PRAD, and KIRC, while the LUZP2 methylation showed the opposite results. In conclusion, the results of our initial pan-cancer investigation provided a somewhat thorough understanding of the functions of LUZP2 on KIRC, LGG, PRAD, and LUSC.

The landscape of aging

Aging is characterized by a progressive deterioration of physiological integrity, leading to impaired functional ability and ultimately increased susceptibility to death. It is a major risk factor for chronic human diseases, including cardiovascular disease, diabetes, neurological degeneration, and cancer. Therefore, the growing emphasis on “healthy aging” raises a series of important questions in life and social sciences. In recent years, there has been unprecedented progress in aging research, particularly the discovery that the rate of aging is at least partly controlled by evolutionarily conserved genetic pathways and biological processes. In an attempt to bring full-fledged understanding to both the aging process and age-associated diseases, we review the descriptive, conceptual, and interventive aspects of the landscape of aging composed of a number of layers at the cellular, tissue, organ, organ system, and organismal levels.

Nutritional components as mitigators of cellular senescence in organismal aging: a comprehensive review

The process of cellular senescence is rapidly emerging as a modulator of organismal aging and disease. Targeting the development and removal of senescent cells is considered a viable approach to achieving improved organismal healthspan and lifespan. Nutrition and health are intimately linked and an appropriate dietary regimen can greatly impact organismal response to stress and diseases including during aging. With a renewed focus on cellular senescence, emerging studies demonstrate that both primary and secondary nutritional elements such as carbohydrates, proteins, fatty acids, vitamins, minerals, polyphenols, and probiotics can influence multiple aspects of cellular senescence. The present review describes the recent molecular aspects of cellular senescence-mediated understanding of aging and then studies available evidence of the cellular senescence modulatory attributes of major and minor dietary elements. Underlying pathways and future research directions are deliberated to promote a nutrition-centric approach for targeting cellular senescence and thus improving human health and longevity.

Single-cell transcriptomics identifies Mcl-1 as a target for senolytic therapy in cancer

Cells subjected to treatment with anti-cancer therapies can evade apoptosis through cellular senescence. Persistent senescent tumor cells remain metabolically active, possess a secretory phenotype, and can promote tumor proliferation and metastatic dissemination. Removal of senescent tumor cells (senolytic therapy) has therefore emerged as a promising therapeutic strategy. Here, using single-cell RNA-sequencing, we find that senescent tumor cells rely on the anti-apoptotic gene Mcl-1 for their survival. Mcl-1 is upregulated in senescent tumor cells, including cells expressing low levels of Bcl-2, an established target for senolytic therapy. While treatment with the Bcl-2 inhibitor Navitoclax results in the reduction of metastases in tumor bearing mice, treatment with the Mcl-1 inhibitor S63845 leads to complete elimination of senescent tumor cells and metastases. These findings provide insights on the mechanism by which senescent tumor cells survive and reveal a vulnerability that can be exploited for cancer therapy.

Cell senescence remains a barrier to tumor elimination in many cancers. Here, the authors use single cell RNA-seq to identify a role for Mcl-1 in senescent cell survival, and show that Mcl-1 inhibition may be an effective therapeutic strategy.

Andrographolide, a diterpene lactone from the Traditional Chinese Medicine Andrographis paniculate, induces senescence in human lung adenocarcinoma via p53/p21 and Skp2/p27

BACKGROUND

Senescence leads to permanent cell-cycle arrest and is a potential target for cancer therapy. Andrographolide (AD) is a diterpene lactone isolated from Traditional Chinese Medicine (TCM) Andrographis paniculate, which has been used as an anti-inflammatory drug in clinical practice with the potential to target senescence in recalcitrant lung cancer.

PURPOSE

To determine whether AD can induce senescence in human lung adenocarcinoma in vitro and in vivo and to elucidate the underlying mechanisms.

METHODS

SA-β-Gal staining was used to detect the expression of senescence-associated β-galactosidase (SA-β-Gal) in human lung adenocarcinoma cells A549 and NCI-H1795. DNA damage was examined by the detection of γH2AX foci. Cell cycle was analyzed by flow cytometry. Cancer cell proliferation was determined by ATPlite assay and clonogenic survival assay in vitro. Tumor growth was determined in a mouse model of A549. The expression level of proteins and mRNA was estimated by Western blotting and Quantitative RT-PCR, respectively. Small interfering RNA (siRNA) was used to knock down p21, p27 and p53 to explore the potential mechanism of AD-induced senescence in human lung adenocarcinoma cells.

RESULTS

AD-induced A549 and NCI-H1795 cell senescence determined by increased cell size, flattened morphology, DNA damage, cell cycle arrest as well as the increased expression of β-galactosidase. AD inhibited cell proliferation in lung cells in vitro and lung cells xenograft growth in nude mice. p21 and p27, the major cell cycle regulators and mediators of senescence, were upregulated at the protein level in AD-treated A549 lung adenocarcinoma in vitro and in vivo. Further studies demonstrated that AD induced cell senescence via p53/p21 and Skp2/p27.

CONCLUSION

In the present study, we found that the primary anti-inflammatory drug AD could have a potential antitumor effect in lung cancer. We demonstrated that AD induced lung adenocarcinoma senescence in vitro and in vivo via p53/p21 and Skp2/p27 for the first time. AD is therefore a promising senescence-inducing therapeutic for recalcitrant human lung adenocarcinoma.

Targeting cellular senescence in cancer by plant secondary metabolites: A systematic review

Senescence suppresses tumor growth, while also developing a tumorigenic state in the nearby cells that is mediated by senescence-associated secretory phenotypes (SASPs). The dual function of cellular senescence stresses the need for identifying multi-targeted agents directed towards the promotion of cell senescence in cancer cells and suppression of the secretion of pro-tumorigenic signaling mediators in neighboring cells. Natural secondary metabolites have shown favorable anticancer responses in recent decades, as some have been found to target the senescence-associated mediators and pathways. Furthermore, phenolic compounds and polyphenols, terpenes and terpenoids, alkaloids, and sulfur-containing compounds have shown to be promising anticancer agents through the regulation of paracrine and autocrine pathways. Plant secondary metabolites are potential regulators of SASPs factors that suppress tumor growth through paracrine mediators, including growth factors, cytokines, extracellular matrix components/enzymes, and proteases. On the other hand, ataxia-telangiectasia mutated, ataxia-telangiectasia and Rad3-related, extracellular signal-regulated kinase/mitogen-activated protein kinase, phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin, nuclear factor-κB, Janus kinase/signal transducer and activator of transcription, and receptor tyrosine kinase-associated mediators are main targets of candidate phytochemicals in the autocrine senescence pathway. Such a regulatory role of phytochemicals on senescence-associated pathways are associated with cell cycle arrest and the attenuation of apoptotic/inflammatory/oxidative stress pathways. The current systematic review highlights the critical roles of natural secondary metabolites in the attenuation of autocrine and paracrine cellular senescence pathways, while also elucidating the chemopreventive and chemotherapeutic capabilities of these compounds. Additionally, we discuss current challenges, limitations, and future research indications.

Cell aging related genes can be used to characterize clinical prognoses and further stratify diffuse gliomas

Increasing evidence has indicated that senescent cells are associated with the glioma development. Thus, we aimed to explore the relationship between the cellular senescence gene profile and the clinical prognosis of diffuse glioma. In total, 699 gliomas from The Cancer Genome Atlas (TCGA) dataset were used as the training cohort and 693 gliomas from the Chinese Glioma Genome Atlas (CGGA) dataset were used as the validation cohort. Bioinformatics statistical methods are used to develop the risk signature and to study the prognostic value of the risk signature. We identified a 14-gene risk signature and its risk score was an independent prognostic factor (P < 0.001) in the validation dataset. The risk signature had better prognostic value than traditional factors for the 3- and 5-year survival rate. Importantly, the risk signature could further stratify gliomas in specific subgroups of World Health Organization (WHO) classification by the survival rate. Furthermore, the mRNA levels of genes involved in the cell cycle, cell division and other processes were significantly correlated with the risk score. Our study highlighted a 14-gene risk signature for further stratifying the outcomes of patients with gliomas with definite WHO subgroups. These results indicate the potential clinical implications of cell aging-related genes in gliomas.

The Significance of Exosomes in Pathogenesis, Diagnosis, and Treatment of Esophageal Cancer

Esophageal cancer is one of the most common malignancy in China with high mortality. Understanding pathogenesis and identifying early diagnosis biomarkers can significantly improve the prognosis of patients with esophageal cancer. Exosomes are small vesicular structures containing a variety of components (including DNA, RNA, and proteins) mediating cell-to-cell material exchange and signal communication. Growing evidences have shown that exosomes and its components are involved in growth, metastasis and angiogenesis in cancer, and could also be used as diagnostic and prognostic markers. In this review, we summarized recent progress to elucidate the significance of exosomes in the esophageal cancer progression, microenvironment remodeling, therapeutic resistance, and immunosuppression. We also discuss the utility of exosomes as diagnostic and prognostic biomarkers and therapeutic tool in esophageal cancer.

Computational Prediction of Binding Affinity for CDK2-ligand Complexes. A Protein Target for Cancer Drug Discovery

BACKGROUND

CDK2 participates in the control of eukaryotic cell-cycle progression. Due to the great interest in CDK2 for drug development and the relative easiness in crystallizing this enzyme, we have over 400 structural studies focused on this protein target. This structural data is the basis for the development of computational models to estimate CDK2-ligand binding affinity.

OBJECTIVE

This work focuses on the recent developments in the application of supervised machine learning modeling to develop scoring functions to predict the binding affinity of CDK2.

METHOD

We employed the structures available at the protein data bank and the ligand information accessed from the BindingDB, Binding MOAD, and PDBbind to evaluate the predictive performance of machine learning techniques combined with physical modeling used to calculate binding affinity. We compared this hybrid methodology with classical scoring functions available in docking programs.

RESULTS

Our comparative analysis of previously published models indicated that a model created using a combination of a mass-spring system and cross-validated Elastic Net to predict the binding affinity of CDK2-inhibitor complexes outperformed classical scoring functions available in AutoDock4 and AutoDock Vina.

CONCLUSION

All studies reviewed here suggest that targeted machine learning models are superior to classical scoring functions to calculate binding affinities. Specifically for CDK2, we see that the combination of physical modeling with supervised machine learning techniques exhibits improved predictive performance to calculate the protein-ligand binding affinity. These results find theoretical support in the application of the concept of scoring function space.

A Novel Biochemical Study of Anti-Dermal Fibroblast Replicative Senescence Potential of Panax Notoginseng Oligosaccharides

Dermal fibroblast replicative senescence that often occurs in aging skin is characterized by loss of cell proliferative capacity, cell cycle arrest, decreased cell elongation, and decreased synthesis of dermal extracellular matrix (ECM) components. Although Panax notoginseng is known for its effectiveness in alleviating many age-related degenerative diseases, few studies have evaluated P. notoginseng components for efficacy or mechanisms of action in delaying cell replicative senescence. In this study, P. notoginseng oligosaccharides (PNO) were isolated using a stepwise purification procedure involving water extraction and alcohol precipitation followed by DEAE Sepharose Fast Flow column chromatography, preparative high performance liquid chromatography, and size-exclusion chromatography. Monosaccharides detected in PNO constituents included mannose, galactose, and sorbitose in relative molar proportions of 14.2:12.3:1, respectively, aligning with PNO absorption spectrum results resembling typical known spectra for sugars. In vitro, PNO treatment of replicative senescent NIH-3T3 fibroblasts significantly promoted cell vitality, inhibited SA-β-galactosidase (SA-β-Gal) activity, and reduced p16 and p21 protein-level expression. Moreover, PNO treatment of senescent fibroblasts led to a lower proportion of G1 phase cells and higher proportion of S phase cells, while also inducing aging NIH-3T3 cells to migrate and synthesize collagen-I (CoL-I). Mechanistically, PNO treatment up-regulated expression of proliferating cell nuclear antigen (PCNA), cyclin E, cyclin D1, and cyclin-dependent kinase 4 (CDK4) proteins and promoted phosphorylation of MEK, p38, and ERK1/2 to trigger cell cycle progression. Additionally, PNO treatment also up-regulated protein-level expression of TGF-β1 and levels of p-Smad2/3, p-FAK, and p-Pax to trigger CoL-I synthesis and cell migration. Taken together, these findings demonstrate that oligosaccharides purified from P. notoginseng could reverse fibroblast replicative senescence by promoting fibroblast cell proliferation, migration, and CoL-I production.

Cellular Senescence Affects Cardiac Regeneration and Repair in Ischemic Heart Disease

Ischemic heart disease (IHD) is defined as a syndrome of ischemic cardiomyopathy. Myogenesis and angiogenesis in the ischemic myocardium are important for cardiomyocyte (CM) survival, improving cardiac function and decreasing the progression of heart failure after IHD. Cellular senescence is a state of permanent irreversible cell cycle arrest caused by stress that results in a decline in cellular functions, such as proliferation, migration, homing, and differentiation. In addition, senescent cells produce the senescence-associated secretory phenotype (SASP), which affects the tissue microenvironment and surrounding cells by secreting proinflammatory cytokines, chemokines, growth factors, and extracellular matrix degradation proteins. The accumulation of cardiovascular-related senescent cells, including vascular endothelial cells (VECs), vascular smooth muscle cells (VSMCs), CMs and progenitor cells, is an important risk factor of cardiovascular diseases, such as vascular aging, atherosclerotic plaque formation, myocardial infarction (MI) and ventricular remodeling. This review summarizes the processes of angiogenesis, myogenesis and cellular senescence after IHD. In addition, this review focuses on the relationship between cellular senescence and cardiovascular disease and the mechanism of cellular senescence. Finally, we discuss a potential therapeutic strategy for MI targeting senescent cells.

Non-Coding RNAs Steering the Senescence-Related Progress, Properties, and Application of Mesenchymal Stem Cells

The thirst to postpone and even reverse aging progress has never been quenched after all these decades. Unequivocally, mesenchymal stem cells (MSCs), with extraordinary abilities such as self-renewal and multi-directional differentiation, deserve the limelight in this topic. Though having several affable clinical traits, MSCs going through senescence would, on one hand, contribute to age-related diseases and, on the other hand, lead to compromised or even counterproductive therapeutical outcomes. Notably, increasing evidence suggests that non-coding RNAs (ncRNAs) could invigorate various regulatory processes. With even a slight dip or an uptick of expression, ncRNAs would make a dent in or even overturn cellular fate. Thereby, a systematic illustration of ncRNAs identified so far to steer MSCs during senescence is axiomatically an urgent need. In this review, we introduce the general properties and mechanisms of senescence and its relationship with MSCs and illustrate the ncRNAs playing a role in the cellular senescence of MSCs. It is then followed by the elucidation of ncRNAs embodied in extracellular vesicles connecting senescent MSCs with other cells and diversified processes in and beyond the skeletal system. Last, we provide a glimpse into the clinical methodologies of ncRNA-based therapies in MSC-related fields. Hopefully, the intricate relationship between senescence and MSCs will be revealed one day and our work could be a crucial stepping-stone toward that future.

[Palbociclib induces cell cycle arrest and senescence of human renal tubular epithelial cells in vitro]

OBJECTIVE

To investigate the effect of palbociclib on cell cycle progression and proliferation of human renal tubular epithelial cells.

METHODS

Human renal tubular epithelial cell line HK-2 was treated with 1, 5, 10, and 20 μmol/L of palbociclib, and the changes in cell proliferation and viability were examined by cell counting and CCK8 assay. EDU staining was used to assess the proliferation of HK-2 cells following palbiciclib treatment at different concentrations for 5 days. The effect of palbociclib on cell cycle distribution of HK-2 cells was evaluated using flow cytometry. SA-β-Gal staining and C12FDG senescence staining were used to detect senescence phenotypes of HK-2 cells after palbociclib treatment at different concentrations for 5 days. The relative mRNA expression levels of P16, P21, and P53 and the genes associated with senescence-related secretion phenotypes were detected by RT-PCR, and the protein expressions of P16, P21 and P53 were detected by Western blotting.

RESULTS

Palbociclib inhibited HK-2 cell proliferation and induced cell cycle arrest in G1 phase. Compared with the control cells, HK-2 cells treated with high-dose (10 μmol/L) palbociclib exhibited significantly suppressed cell proliferation activity, and the inhibitory effect was the most obvious on day 5 (P < 0.01). Palbociclib treatment significantly reduced the number of cells in S phase (P < 0.01) and induced senescence of HK-2 cells. The results of SA-β-Gal and C12FDG senescence staining showed a significantly enhanced activity of intracellular senescence-related galactosidase in palbociclib-treated HK-2 cells, suggesting significant senescence of the cells (P < 0.01). RT-PCR and Western blotting showed that palbociclib treatment significantly increased the mRNA and protein expression levels of P16, P21, and P53 in HK-2 cells (P < 0.01); the mRNA expression levels of senescence-related secretory factors also increased significantly in HK-2 cells after palbociclib treatment (P < 0.01).

CONCLUSIONS

Palbociclib induces HK-2 cell senescence by causing cell growth arrest and delaying cell cycle progression.