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This article reviews the current knowledge on the mechanisms of adaptive response to low doses of ionizing radiation or chemical exposure. A better knowledge of these mechanisms is needed to improve our understanding of health risks at low levels of environmental or occupational exposure and their involvement in cancer or non-cancer diseases. This response is orchestrated through a multifaceted cellular program involving the concerted action of diverse stress response pathways. These evolutionary highly conserved defense mechanisms determine the cellular response to chemical and physical aggression. They include DNA damage repair (p53, ATM, PARP pathways), antioxidant response (Nrf2 pathway), immune/inflammatory response (NF-κB pathway), cell survival/death pathway (apoptosis), endoplasmic response to stress (UPR response), and other cytoprotective processes including autophagy, cell cycle regulation, and the unfolded protein response. The coordinated action of these processes induced by low-dose radiation or chemicals produces biological effects that are currently estimated with the linear non-threshold model. These effects are controversial. They are difficult to detect because of their low magnitude, the scarcity of events in humans, and the difficulty of corroborating associations over the long term. Improving our understanding of these biological consequences should help humans and their environment by enabling better risk estimates, the revision of radiation protection standards, and possible therapeutic advances.

Autophagy is an evolutionarily conserved catabolic process that plays an essential role in maintaining cellular homeostasis by degrading unneeded cell components. When exposed to hostile environments, such as hypoxia or nutrient starvation, cells hyperactivate autophagy in an effort to maintain their longevity. In densely packed solid tumors, such as glioblastoma, autophagy has been found to run rampant due to a lack of oxygen and nutrients. In recent years, targeting autophagy as a way to strengthen current glioblastoma treatment has shown promising results. However, that protective autophagy inhibition or autophagy overactivation is more beneficial, is still being debated. Protective autophagy inhibition would lower a cell’s previously activated defense mechanism, thereby increasing its sensitivity to treatment. Autophagy overactivation would cause cell death through lysosomal overactivation, thus introducing another cell death pathway in addition to apoptosis. Both methods have been proven effective in the treatment of solid tumors. This systematic review article highlights scenarios where both autophagy inhibition and activation have proven effective in combating chemoresistance and radioresistance in glioblastoma, and how autophagy may be best utilized for glioblastoma therapy in clinical settings.

Polydeoxyribonucleotide (PDRN) is a low molecular weight linear polyribonucleotide fragment derived from salmon sperm, known for its potential in tissue regeneration and anti-inflammatory applications. However, its specific function in cellular senescence is yet to be fully understood. Silent information regulator 1 (SIRT1), an NAD + -dependent deacetylase, plays a crucial role in regulating cellular aging and tumorigenesis. Notably, SIRT1 levels decrease with age in both mice and during cellular senescence, highlighting its significance in anti-aging processes. This study assessed the effects of PDRN on cellular aging induced by ultraviolet B (UVB) or hydrogen peroxide (H 2 O 2 ) and investigated the mechanisms of its protective effects against aging at the cellular level. Our data demonstrated that PDRN treatment mitigated the decline in cell viability and inhibited cell aging when exposed to UVB or H 2 O 2 . Furthermore, PDRN ameliorated UVB-induced epidermal thickening in mouse skin. Mechanically, we found that PDRN treatment led to a reduction in nuclear autophagy and the formation of cytoplasmic stress granules by preventing the accumulation of damaged LC3 in the nuclear and inhibiting the degradation of SIRT1 and p62 in the cytoplasm during cellular senescence. In conclusion, PDRN exhibits antioxidant and anti-aging properties by diminishing autophagy and enhancing SIRT1 expression. These results suggest that PDRN has potential as a therapeutic compound for reducing skin aging induced by UVB or H 2 O 2 through the modulation of SIRT1 levels.

Background/Aims: Chloroquine was formerly used as an anti-malarial agent drug but has now been proven to be useful for various diseases. This study aimed to investigate the radiosensitizing effect of chloroquine in bladder cancer, with an emphasis on autophagy inhibition and apoptosis induction. Methods: Bladder cancer cell lines were irradiated with or without chloroquine. Cell proliferation was determined by a Cell Counting Kit 8 assay. The radiosensitization effect of chloroquine was evaluated by clonogenic survival and progression of xenograft tumors. Cell apoptosis was detected by flow cytometry and western blot. Radiation-induced DNA double strand break was measured by the staining of γ-H2AX. In addition, autophagy was detected by western blot, immunofluorescence staining, and electron microscopy. Results: The treatment with chloroquine alone inhibited the proliferation of bladder cancer cells in a dose-dependent manner. Low cytotoxic concentrations of chloroquine enhanced the radiation sensitivity of bladder cancer cells with a sensitization enhancement ratio of 1.53 and 1.40. Chloroquine also obviously weakened the repair of radiation-induced DNA damage. A combination of radiation and chloroquine enhanced the apoptosis rate of EJ and T24 cells and down-regulated the expression of Bcl-2 while up-regulating the expression of caspase-3. Additionally, the relevant markers of autophagy were obviously increased in the combined group, meaning that chloroquine inhibited autophagy induced by irradiation. Furthermore, subcutaneous xenograft tumors displayed that the combination of radiation and chloroquine could impede tumorigenesis in vivo. Conclusion: In summary, these results provided support that by inhibiting autophagy and activating apoptosis, chloroquine might be a potentially promising radiosensitizer in the radiation therapy of bladder cancer.

Autophagy can play a double role in cancerogenesis: it can either inhibit further development of the disease or protect cells, causing stimulation of tumour growth. This phenomenon is called “autophagy paradox”, and is characterised by the features that the autophagy process provides the necessary substrates for biosynthesis to meet the cell’s energy needs, and that the over-programmed activity of this process can lead to cell death through apoptosis. The fight against cancer is a difficult process due to high levels of resistance to chemotherapy and radiotherapy. More and more research is indicating that autophagy may play a very important role in the development of resistance by protecting cancer cells, which is why autophagy in cancer therapy can act as a “double-edged sword”. This paper attempts to analyse the influence of autophagy and cancer stem cells on tumour development, and to compare new therapeutic strategies based on the modulation of these processes.

Intrinsic autophagy is important for the maintenance of intestinal homeostasis and intestinal regeneration. Ionizing radiation suppresses intrinsic autophagy and reduces damage-induced regeneration in the intestine, resulting in intestinal injury. Resveratrol, a sirtuin 1 (SIRT1) agonist, promotes autophagy and exerts radioprotective effect. In this study, the protective effect of resveratrol against radiation-induced intestinal injury and its potential mechanism were investigated. Intestinal epithelial cells (IEC-6) were exposed to 10 Gy ionizing radiation and resveratrol (0.1–40.0 μM). Cell viability was investigated using Cell Counting Kit 8 (CCK8), apoptosis was observed by Annexin V-fluorescein isothiocyanate/propidium iodide (PI) staining and flow cytometry, and the expression of apoptotic and autophagic proteins was determined by western blotting. Resveratrol exerted a high toxicity against IEC-6 cells, but at low concentrations, it inhibited ionizing radiation-induced apoptosis. Resveratrol increased SIRT1 expression after irradiation and inhibited ionizing radiation-induced p53 acetylation and pro-apoptotic protein, Bax, expression. Furthermore, resveratrol promoted autophagy via the phosphoinositide 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway, thereby protecting IEC-6 cells against radiation-induced damage. These results suggest that resveratrol reduces radiation-induced IEC-6 cell damage by inhibiting apoptosis and promoting autophagy via the activation of SIRT1, and that the PI3K/AKT/mTOR signaling pathway is involved in the induction of autophagy.

Autophagy is an evolutionarily conserved cellular response to conditions of stress such as hypoxia, which induce radioresistance in cancer cells. We studied the mechanism of action of hypoxia on autophagy and radiosensitivity in colon cancer cells. In the human colon cancer cell lines SW480 and SW620, autophagosomes were analyzed to evaluate autophagy by flow cytometry. The expression of hypoxia inducible factor-1α (HIF-1α), Bcl-2, and miR-210 was detected by western blotting and quantitative real-time polymerase chain reaction (PCR). HIF-1α and miR-210 inhibition was induced by siRNA transfections. Apoptosis detection and colony assays were performed to determine radiosensitivity. HIF-1α and miR-210 showed a significant increase under hypoxic condition. The inhibition of HIF-1α decreased miR-210 expression and autophagy. Silencing of miR-210 upregulated Bcl-2 expression and reduced the survival fraction of colon cancer cells after radiation treatment. Under hypoxia, HIF-1α induces miRNA-210 which in turn enhances autophagy and reduces radiosensitivity by downregulating Bcl-2 expression in colon cancer cells. Our results imply that autophagy contributes to the reduction of radiosensitivity in hypoxic environment, and the process is mediated through the HIF-1α/miR-210/Bcl-2 pathway in human colon cancer cells.

Lysosomes are the major degradative compartments within cells, harbouring a wide variety of hydrolytic enzymes within their lumen. Release of lysosomal hydrolases from lysosomes into the cell cytoplasm results in cell death. Here we report that damaged lysosomes undergo autophagic turnover. Using a light-induced lysosome impairing scheme that can be controlled spatially and temporally within a cell, we show that damaged lysosomes are selectively ubiquitinated, recruit autophagic proteins and are eventually incorporated into autolysosomes for degradation. We propose that autophagic removal of lysosomes, which we term lysophagy, is a surveillance mechanism that alleviates cells from the adverse effects of lysosomal damage. We envision our method to induce lysosomal damage will enable detailed molecular studies of the lysophagy pathway in the future. Lysosomes are the major degradative compartments within cells, but little is known about cellular mechanisms that control lysosome quality. Here Hung et al. show that lysosomes damaged by light-induced activation of a photosensitizer are selectively ubiquitinated and subsequently eliminated by autophagy.

Ultraviolet radiation is markedly increased because of pollution and the depletion of the stratospheric ozone layer. Excessive exposure to sunlight can negatively affect the skin, resulting in sunburn, photo-aging, or skin cancer. In this study, we first determined the photoprotective effect of sanshool, a major component in Zanthoxylum bungeanum , on UVB-irradiated responses in human dermal fibroblasts (HDFs) and nude mouse. We found that sanshool treatment can protect cells against the effects of UVB irradiation by (i) increasing cell viability, (ii) inhibiting MMP expression, and (iii) inducing autophagy. We also used the recombinant CSF2 or anti-CSF2 antibody co-cultured with human dermal fibroblasts (HDFs) and found that CSF2 contributes to sanshool-induced autophagy. Sanshool hindered the UVB-induced activation of JAK2-STAT3 signaling in HDFs, thereby inhibiting the expression of MMPs and activation of autophagic flux. Exposure of the dorsal skin of hairless mice to UVB radiation and subsequent topical application of sanshool delayed the progression of skin inflammation, leading to autophagy and inhibiting the activation of JAK2-STAT3 signaling. These results provide a basis for the study of the photoprotective effect of sanshool and suggest that it can be potentially used as an agent against UVB-induced skin damage in humans.

Tumor hypoxia, acidosis, and excessive reactive oxygen species (ROS) were the main characteristics of the bladder tumor microenvironment (TME), and abnormal TME led to autophagy activation, which facilitated cancer cell proliferation. The therapeutic efficacy of autophagy inhibitors might also be impeded by abnormal TME. To address these issues, we proposed a new strategy that utilized manganese dioxide (MnO ) nanoparticles to optimize the abnormal TME and revitalize autophagy inhibitors, and both oxygenation and autophagy inhibition may sensitize the tumor cells to radiation therapy. By taking advantage of the strong affinity between negatively charged MnO and positively charged chloroquine (CQ), the nanoparticles were fabricated by integrating MnO and CQ in human serum albumin (HSA)-based nanoplatform (HSA-MnO -CQ NPs). HSA-MnO -CQ NPs NPs efficiently generated O and increased pH after reaction with H /H O and then released the encapsulated CQ in a H /H O concentration-dependent manner. The NPs restored the autophagy-inhibiting activity of chloroquine in acidic conditions by increasing its intracellular uptake, and markedly blocked hypoxia-induced autophagic flux. studies showed the NPs improved pharmacokinetic behavior of chloroquine and effectively accumulated in tumor tissues. The NPs exhibited significantly decreased tumor hypoxia areas and increased tumor pH, and had remarkable autophagy inhibition efficacy on bladder tumors. Finally, a significant anti-tumor effect achieved by the enhanced autophagy inhibition and radiation sensitization. HSA-MnO -CQ NPs synergistically regulated the abnormal TME and inhibited autophagic flux, and effectively sensitized radiation therapy to treat bladder cancers.