Biomarkers of cellular senescence and risk of death in humans

A robust and heterogenous secretory phenotype is a core feature of most senescent cells. In addition to mediators of age-related pathology, components of the senescence associated secretory phenotype (SASP) have been studied as biomarkers of senescent cell burden and, in turn, biological age. Therefore, we hypothesized that circulating concentrations of candidate senescence biomarkers, including chemokines, cytokines, matrix remodeling proteins, and growth factors, could predict mortality in older adults. We assessed associations between plasma levels of 28 SASP proteins and risk of mortality over a median follow-up of 6.3 years in 1923 patients 65 years of age or older with zero or one chronic condition at baseline. Overall, the five senescence biomarkers most strongly associated with an increased risk of death were GDF15, RAGE, VEGFA, PARC, and MMP2, after adjusting for age, sex, race, and the presence of one chronic condition. The combination of biomarkers and clinical and demographic covariates exhibited a significantly higher c-statistic for risk of death (0.79, 95% confidence interval (CI): 0.76–0.82) than the covariates alone (0.70, CI: 0.67–0.74) (p < 0.001). Collectively, these findings lend further support to biomarkers of cellular senescence as informative predictors of clinically important health outcomes in older adults, including death.     

How autophagy both activates and inhibits cellular senescence

Autophagy and cellular senescence are stress responses essential for homeostasis. While recent studies indicate a genetic relationship between autophagy and senescence, whether autophagy acts positively or negatively on senescence is still subject to debate. Although autophagy was originally recognized as a nonspecific lysosomal degradation pathway (general autophagy), increasing evidence supports a selective form of autophagy that mediates the degradation of specific targets (selective autophagy). Our recent study revealed distinctive roles of selective autophagy and general autophagy in the regulation of senescence, at least in part resolving apparently contradictory reports regarding the relationship between these 2 important homeostatic stress responses.     

Aging of the cells: Insight into cellular senescence and detection Methods

Cellular theory of aging states that human aging is the result of cellular aging, in which an increasing proportion of cells reach senescence. Senescence, from the Latin word senex, means “growing old,” is an irreversible growth arrest which occurs in response to damaging stimuli, such as DNA damage, telomere shortening, telomere dysfunction and oncogenic stress leading to suppression of potentially dysfunctional, transformed, or aged cells. Cellular senescence is characterized by irreversible cell cycle arrest, flattened and enlarged morphology, resistance to apoptosis, alteration in gene expression and chromatin structure, expression of senescence associated- β-galactosidase (SA-β-gal) and acquisition of senescence associated secretory phenotype (SASP). In this review paper, different types of cellular senescence including replicative senescence (RS) which occurs due to telomere shortening and stress induced premature senescence (SIPS) which occurs in response to different types of stress in cells, are discussed. Biomarkers of cellular senescence and senescent assays including BrdU incorporation assay, senescence associated- β-galactosidase (SA-β-gal) and senescence-associated heterochromatin foci assays to detect senescent cells are also addressed.     

Spatial transcriptomics and proteomics technologies for deconvoluting the tumor microenvironment

The tumor microenvironment (TME) harbors heterogeneous contents and plays critical roles in tumorigenesis, metastasis, and drug resistance. Therefore, the deconvolution of the TME becomes increasingly essential to every aspect of cancer research and treatment. Novel spatially-resolved high-plex molecular profiling technologies have been emerging rapidly as powerful tools to obtain in-depth understanding from TME perspectives due to their capacity to allow high-plex protein and RNA profiling while keeping valuable spatial information. Based on our practical experience, we review a variety of available spatial proteogenomic technologies, including 10X Visium, GeoMx Digital Spatial Profiler (DSP), cyclic immunofluorescence-based CODEX and Multi-Omyx, mass spectrometry (MS)-based imaging mass spectrometry (IMS) and multiplex ion-beam imaging (MIBI). We also discuss FISSEQ, MERFISH, Slide-seq, and HDST, some of which may become commercially available in the near future. In particular, with our experience, we elaborate on DSP for spatial proteogenomic profiling and discuss its unique features designed for immuno-oncology and propose anticipation towards its future direction. The emerging spatially technologies are rapidly reshaping the magnitude of our understanding of the TME.     

细胞衰老与癌症治疗

细胞衰老是生物界普遍存在的现象。肿瘤细胞是一类摆脱细胞周期束缚,突破Hayflick界限,能够无限增殖而不衰老的细胞。癌症是一种与细胞衰老密切相关的疾病。从进化的角度来看,衰老对于生物体是有益的,可以导致细胞不可逆的周期阻滞,被认为是一种自主的肿瘤抑制机制。在恶性增殖的癌细胞中,在胞外及胞内多种刺激下,如端粒缩短、DNA损伤、氧化应激以及化疗药物的处理等,都会出现细胞周期阻滞,生长迟缓等细胞衰老现象。诱导肿瘤细胞衰老也被认为是一种治疗癌症的有效手段。衰老细胞可以向胞外分泌数十种因子,维持细胞自身衰老表型,并影响周围细胞的生长,这种特性被称为衰老相关的分泌表型(SASP)。本文详细综述细胞衰老的形态学特征与分子标记物及检测方法,细胞衰老的信号调控通路（p53-p21,p16-pRB和PTEN-p27）,以及细胞衰老与恶性肿瘤发生发展的关系等。尤其是应激压力诱导下的细胞衰老在癌症治疗中的潜在作用,并进一步讨论当下流行的促衰老癌症治疗的靶点与药物以及存在的问题,以期为今后的研究提供新思路和新方向。     

细胞衰老与癌症治疗

细胞衰老是生物界普遍存在的现象。肿瘤细胞是一类摆脱细胞周期束缚,突破Hayflick界限,能够无限增殖而不衰老的细胞。癌症是一种与细胞衰老密切相关的疾病。从进化的角度来看,衰老对于生物体是有益的,可以导致细胞不可逆的周期阻滞,被认为是一种自主的肿瘤抑制机制。在恶性增殖的癌细胞中,在胞外及胞内多种刺激下,如端粒缩短、DNA损伤、氧化应激以及化疗药物的处理等,都会出现细胞周期阻滞,生长迟缓等细胞衰老现象。诱导肿瘤细胞衰老也被认为是一种治疗癌症的有效手段。衰老细胞可以向胞外分泌数十种因子,维持细胞自身衰老表型,并影响周围细胞的生长,这种特性被称为衰老相关的分泌表型(SASP)。本文详细综述细胞衰老的形态学特征与分子标记物及检测方法,细胞衰老的信号调控通路（p53-p21,p16-pRB和PTEN-p27）,以及细胞衰老与恶性肿瘤发生发展的关系等。尤其是应激压力诱导下的细胞衰老在癌症治疗中的潜在作用,并进一步讨论当下流行的促衰老癌症治疗的靶点与药物以及存在的问题,以期为今后的研究提供新思路和新方向。     

Bazi Bushen alleviates skin senescence by orchestrating skin homeostasis in SAMP6 mice

Bazi Bushen, a Chinese-patented drug with the function of relieving fatigue and delaying ageing, has been proven effective for extenuating skin senescence. To investigate the potential mechanism, senescence-accelerated mouse prone 6 (SAMP6) was intragastrically administered with Bazi Bushen for 9 weeks to induce skin homeostasis. Skin homeostasis is important in mitigating skin senescence, and it is related to many factors such as oxidative stress, SASP, apoptosis, autophagy and stem cell. In our study, skin damage in SAMP6 mice was observed using HE, Masson and SA-β-gal staining. The content of hydroxyproline and the activities of SOD, MDA, GSH-PX and T-AOC in the skin were measured using commercial assay kits. The level of SASP factors (IL-6, IL-1β, TNF-α, MMP2 and MMP9) in skin were measured using ELISA kits. The protein expressions of p16, p21, p53, Bax, Bcl-2, Cleaved caspase-3, LC3, p62, Beclin1, OCT4, SOX2 and NANOG were measured by western blotting. The expression of ITGA6 and COL17A1 was measured by immunofluorescence staining and western blotting. Our findings demonstrated that Bazi Bushen alleviated skin senescence by orchestrating skin homeostasis, reducing the level of oxidative stress and the expression of SASP, regulating the balance of apoptosis and autophagy and enhancing the protein expressions of ITGA6 and COL17A1 to improve skin structure in SAMP6 mice. This study indicated that Bazi Bushen could serve as a potential therapy for alleviating skin senescence.     

Arrested development and the great escape – The role of cellular senescence in pancreatic cancer

The outcomes of pancreatic cancer remain dismal due to late clinical presentation and the aggressive nature of the disease. A heterogeneous combination of genetic mutations, including KRAS, INK4a/CDKN2A and p53, underpin the propensity of pancreatic cancer to rapidly invade and disseminate. These oncogenes and tumour suppressors are strongly associated with cellular senescence, therefore suggesting this process as having a key role in malignant transformation. In the context of cancer, oncogenic stimuli trigger the senescent phenotype resulting in cell cycle growth arrest and prevention of progression of premalignant lesions such as PanINs. However mutations of the aforementioned oncogenes or tumour suppressors result in cells escaping senescence and thus allowing tumours to progress. This review presents current evidence regarding both senescence induction and escape with respect to pancreatic cancer, highlighting the key roles of p19ARF, p53, Rb and P16INK4a. The epigenetic regulatory component is also discussed, with relevance to DNA methylation and HDACs. Lastly the role of the tumour microenvironment, and in particular pancreatic stellate cells, is discussed with regards to the induction of a senescence associated secretory phenotype (SASP), with SASP-associated secretory factors contributing to the pro-tumorigenic effects of the surrounding activated stroma. Further work is required in this field to elucidate the most important pathways relating to cellular senescence that contribute to the belligerent nature of this disease, with the aim of discovering therapeutic targets to improve patient outcomes.     

Calorie restriction reduces biomarkers of cellular senescence in humans

Calorie restriction (CR) with adequate nutrient intake is a potential geroprotective intervention. To advance this concept in humans, we tested the hypothesis that moderate CR in healthy young-to-middle-aged individuals would reduce circulating biomarkers of cellular senescence, a fundamental mechanism of aging and aging-related conditions. Using plasma specimens from the Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE™) phase 2 study, we found that CR significantly reduced the concentrations of several senescence biomarkers at 12 and 24 months compared to an ad libitum diet. Using machine learning, changes in biomarker concentrations emerged as important predictors of the change in HOMA-IR and insulin sensitivity index at 12 and 24 months, and the change in resting metabolic rate residual at 12 months. Finally, using adipose tissue RNA-sequencing data from a subset of participants, we observed a significant reduction in a senescence-focused gene set in response to CR at both 12 and 24 months compared to baseline. Our results advance the understanding of the effects of CR in humans and further support a link between cellular senescence and metabolic health.     

On the evolution of cellular senescence

The idea that senescent cells are causally involved in aging has gained strong support from findings that the removal of such cells alleviates many age‐related diseases and extends the life span of mice. While efforts proceed to make therapeutic use of such discoveries, it is important to ask what evolutionary forces might have been behind the emergence of cellular senescence, in order better to understand the biology that we might seek to alter. Cellular senescence is often regarded as an anti‐cancer mechanism, since it limits the division potential of cells. However, many studies have shown that senescent cells often also have carcinogenic properties. This is difficult to reconcile with the simple idea of an anti‐cancer mechanism. Furthermore, other studies have shown that cellular senescence is involved in wound healing and tissue repair. Here, we bring these findings and ideas together and discuss the possibility that these functions might be the main reason for the evolution of cellular senescence. Furthermore, we discuss the idea that senescent cells might accumulate with age because the immune system had to strike a balance between false negatives (overlooking some senescent cells) and false positives (destroying healthy body cells).     

Tumor immune microenvironment: sanctuary of tumor and target for immunotherapy

The tumor immune microenvironment (TIME) is the cellular environment in which tumors exist. This includes: surrounding blood vessels, immune cells, fibroblasts, bone marrow-derived inflammatory cells, lymphocytes, signaling molecules, immune checkpoint proteins and the extracellular matrix (ECM). The TIME plays a critical role in cancer progression and regulation. Tumors can influence the microenvironment by releasing extracellular signals, promoting tumor angiogenesis and inducing peripheral immune tolerance, while the immune cells in the microenvironment can affect the growth and evolution of cancerous cells. The molecules and cells in the TIME influence disease outcome by altering the balance of suppressive versus cytotoxic responses in the vicinity of the tumor. Having a better understanding of the tumor immune microenvironment will pave the way for identifying new targets for immunotherapies that promote cancer elimination.     

Metabolic regulation of ferroptosis in the tumor microenvironment

Ferroptosis is an iron-dependent, nonapoptotic form of regulated cell death triggered by impaired redox and antioxidant machinery and propagated by the accumulation of toxic lipid peroxides. A compendium of experimental studies suggests that ferroptosis is tumor-suppressive. Sensitivity or resistance to ferroptosis can be regulated by cell-autonomous and non-cell-autonomous metabolic mechanisms. This includes a role for ferroptosis that extends beyond the tumor cells themselves, mediated by components of the tumor microenvironment, including T cells and other immune cells. Herein, we review the intrinsic and extrinsic factors that promote the sensitivity of cancer cells to ferroptosis and conclude by describing approaches to harness the full utility of ferroptotic agents as therapeutic options for cancer therapy.     

The tumor microenvironment: An irreplaceable element of tumor budding and epithelial-mesenchymal transition-mediated cancer metastasis

Tumor budding occurs at the invasive front of cancer; the tumor cells involved have metastatic and stemness features, indicating a poor prognosis. Tumor budding is partly responsible for cancer metastasis, and its initiation is based on the epithelial-mesenchymal transition (EMT) process. The EMT process involves the conversion of epithelial cells into migratory and invasive cells, and is a profound event in tumorigenesis. The EMT, associated with the formation of cancer stem cells (CSCs) and resistance to therapy, results from a combination of gene mutation, epigenetic regulation, and microenvironmental control. Tumor budding can be taken to represent the EMT in vivo. The EMT process is under the influence of the tumor microenvironment as well as tumor cells themselves. Here, we demonstrate that the tumor microenvironment dominates EMT development and impacts cancer metastasis, as well as promotes CSC formation and mediates drug resistance. In this review, we mainly discuss components of the microenvironment, such as the extracellular matrix (ECM), inflammatory cytokines, metabolic products, and hypoxia, that are involved in and impact on the acquisition of tumor-cell motility and dissemination, the EMT, metastatic tumor-cell formation, tumor budding and CSCs, and cancer metastasis, including subsequent chemo-resistance. From our point of view, the tumor microenvironment now constitutes a promising target for cancer therapy.     

A role for cellular senescence in birth timing

Senescence contributes to the local and systemic aging of tissues and has been associated with age-related diseases. Recently, roles for this process during pregnancy have come to light, the dysregulation of which has been associated with adverse pregnancy outcomes such as preterm birth. Here, we summarize recent advances that support a role for senescence in birth timing and propose new aspects of study in this emerging field.