A progressive reduction in autophagic capacity contributes to induction of replicative senescence in Hs68 cells

Transformed cells maintain survival by downregulating autophagy at a high cell confluency

Autophagy plays a dual role in tumorigenesis by functioning as both a tumor suppressor and promoter, depending on the stage of tumorigenesis. However, it is still unclear at what stage the role of autophagy changes during tumorigenesis. Herein, we investigated the differences in the basal levels and roles of autophagy in five cell lines at different stages of cell transformation. We found that cell lines at higher transformation stages were more sensitive to the autophagy inhibitors, suggesting that autophagy plays a more important role as the transformation progresses. Our ptfLC3 imaging analysis to measure Atg5/LC3-dependent autophagy showed increased autophagic flux in transformed cells compared to untransformed cells. However, the Cyto-ID analysis, which measures Atg5-dependent and -independent autophagic flux, showed high levels of autophagosome formation not only in the transformed cells but also in the initiated cell and Atg5 KO cell line. These results indicate that Atg5-independent autophagy may be more critical in initiated and transformed cell lines than in untransformed cells. Specially, we observed that transformed cells maintained relatively high basal autophagy levels under rapidly proliferating conditions but exhibited much lower basal autophagy levels at high confluency; however, autophagic flux was not significantly reduced in untransformed cells, even at high confluency. In addition, when continuously cultured for 3 weeks without passage, senescent cells were significantly less sensitive to autophagy inhibition than their actively proliferating counterparts. These results imply that once a cell has switched from a proliferative state to a senescent state, the inhibition of autophagy has only a minimal effect. Taken together, our results suggest that autophagy can be differentially regulated in cells at different stages of tumorigenesis under stressful conditions.

Evaluation of Fermented Turmeric Milk by Lactic Acid Bacteria to Prevent UV-Induced Oxidative Stress in Human Fibroblast Cells

The nutrition enhancement of turmeric using lactic acid bacteria (LAB) was studied. Among the 23 different LAB strains, Levilactobacillus brevis BCRC12247 was chosen due to its robustness. The fermentation of a turmeric drink from L. brevis significantly improved DPPH antioxidant activity (from 71.57% to 75.87%) and total reducing capacity (2.94 ± 0.03 mM Trolox/g dw) compared to the unfermented product. The fermented turmeric samples were subjected to liquid–liquid partition, producing four different fractions. An in vitro study was conducted by treating the fractions on human fibroblast cells (Hs68). The results indicated that hexane (Hex) and water residual (WA) samples could significantly attenuate UVA (15 J/cm2)-induced reactive oxygen species (ROS), reducing the oxidative damage from 16.99 ± 3.86 to 3.42 ± 2.53 and 3.72 ± 1.76 times, respectively. Real-time polymerase chain reaction (qPCR) results showed that Hex and WA inhibited the expression of c-jun and c-fos and lowered the mmp-1 value compared to the negative control group (by 2.72 and 2.58 times, respectively). Moreover, the expressions of Nrf2 and downstream antioxidant-related genes were significantly elevated in the Hex fraction. Therefore, fermentation using L. brevis can be an effective method to elevate the nutritional values of turmeric, protecting fibroblast cells from UVA-induced photoaging and oxidative stress.

A new insight into cell biological and biochemical changes through aging

After several years of extensive research, the main cause of aging is yet elusive. There are some theories about aging, such as stem cell aging, senescent cells accumulation, and neuro-endocrine theories. None of them is able to explain all changes that happen in cells and body through aging. By finding out the main cause of aging, it will be much easier to control, prevent and even reverse the aging process. Our cells, regardless of their replicative capacity, get old through aging and they have almost the same epigenetic age. Different cell signaling pathways contribute to aging. The most important one is mTORC1 that becomes hyperactive in cells that undergo aging. Other significant changes with age are lysosome accumulation, impaired autophagy, and mitophagy. Immune system undergoes gradual changes through aging including a shift from lymphoid to myeloid lineage production as well as increased IL-6 and TNF-α which lead to age-related weight loss and meta-inflammation. Additionally, our endocrine system also experiences some changes that should be taken into consideration when looking for the main cause of aging in the human body. In this review, we planned to summarize some of the changes that happen in cells and the body through aging.

Role of AMPK mediated pathways in autophagy and aging

AMPK is an important kinase regulating energy homeostasis and also a key protein involved in a variety of signal transduction pathways. It plays a vitally regulatory role in cellular senescence. Activation of AMPK can delay or block the aging process, which is of great significance in the treatment of cardiovascular diseases and other aging related diseases, and provides a potential target for new indications such as Alzheimer's disease. Therefore, AMPK signaling pathway plays an important role in aging research. The in-depth study of AMPK activators will provide more new directions for the treatment of age-related maladies and the development of innovative drugs. Autophagy is a process that engulfs and degrades own cytoplasm or organelles. Thereby, meeting the metabolic demands and updating certain organelles of the cell has become a hotspot in the field of anti-aging in recent years. AMPK plays an important role between autophagy and senescence. In our review, the relationship among AMPK signaling, autophagy and aging will be clarified through the interaction between AMPK and mTOR, ULK1, FOXO, p53, SIRT1, and NF -κB.

Ameliorating the hallmarks of cellular senescence in skeletal muscle myogenic progenitors in vitro and in vivo

Senescence of myogenic progenitors impedes skeletal muscle regeneration. Here, we show that overexpression of the transcription factor NANOG in senescent myoblasts can overcome the effects of cellular senescence and confer a youthful phenotype to senescent cells. NANOG ameliorated primary hallmarks of cellular senescence including genomic instability, loss of proteostasis, and mitochondrial dysfunction. The rejuvenating effects of NANOG included restoration of DNA damage response via up-regulation of DNA repair proteins, recovery of heterochromatin marks via up-regulation of histones, and reactivation of autophagy and mitochondrial energetics via up-regulation of AMP-activated protein kinase (AMPK). Expression of NANOG in the skeletal muscle of a mouse model of premature aging restored the number of myogenic progenitors and induced formation of eMyHC+ myofibers. This work demonstrates the feasibility of reversing the effects of cellular senescence in vitro and in vivo, with no need for reprogramming to the pluripotent state.

Senescent RAW264.7 cells exhibit increased production of nitric oxide and release inducible nitric oxide synthase in exosomes

Aging cells not only cease growing, but also secrete various proteins such as inflammatory cytokines. This secretory phenomenon is known as the senescence‑associated secretory phenotype (SASP). The aim of the present study was to elucidate the effects of senescence on the differentiation of osteoclast precursors (OCPs) and corresponding SASP. RAW264.7 cells were used as OCPs and were cultured to passage (P)5, P10 and P20. Cell proliferation assays, senescence‑associated β‑galactosidase staining and telomere length quantification were subsequently performed, and it was revealed that replicative senescence was induced at P20. In addition, the level of tartrate‑resistant acid phosphatase activity in P20 cells treated with receptor activator of nuclear factor‑κB ligand was significantly lower than that in P5 and P10 cells. The SASP factors interleukin‑6, tumour necrosis factor‑α and nitric oxide were significantly increased in P20 culture supernatants compared with those in P5 and P10 supernatants. Furthermore, the number of exosomes at P20 was increased compared with that at P5 and P10, and inducible nitric oxide synthase (iNOS) was expressed in exosomes at P20, but not in exosomes at P5. In conclusion, the present study revealed that senescent RAW264.7 cells exhibit increased expression of SASP factors and release iNOS in exosomes.

Graded regulation of cellular quiescence depth between proliferation and senescence by a lysosomal dimmer switch

The reactivation of quiescent cells to proliferate is fundamental to tissue repair and homeostasis in the body. Often referred to as the G0 state, quiescence is, however, not a uniform state but with graded depth. Shallow quiescent cells exhibit a higher tendency to revert to proliferation than deep quiescent cells, while deep quiescent cells are still fully reversible under physiological conditions, distinct from senescent cells. Cellular mechanisms underlying the control of quiescence depth and the connection between quiescence and senescence are poorly characterized, representing a missing link in our understanding of tissue homeostasis and regeneration. Here we measured transcriptome changes as rat embryonic fibroblasts moved from shallow to deep quiescence over time in the absence of growth signals. We found that lysosomal gene expression was significantly up-regulated in deep quiescence, and partially compensated for gradually reduced autophagy flux. Reducing lysosomal function drove cells progressively deeper into quiescence and eventually into a senescence-like irreversibly arrested state; increasing lysosomal function, by lowering oxidative stress, progressively pushed cells into shallower quiescence. That is, lysosomal function modulates graded quiescence depth between proliferation and senescence as a dimmer switch. Finally, we found that a gene-expression signature developed by comparing deep and shallow quiescence in fibroblasts can correctly classify a wide array of senescent and aging cell types in vitro and in vivo, suggesting that while quiescence is generally considered to protect cells from irreversible arrest of senescence, quiescence deepening likely represents a common transition path from cell proliferation to senescence, related to aging.