Autophagy and Self-Defense

The role and current research status of resveratrol in the treatment of osteoarthritis and its mechanisms: a narrative review

Osteoarthritis (OA) is a chronic degenerative disease caused by various factors such as aging, obesity, trauma, and genetics. It is a challenging condition faced by orthopedic doctors in clinical practice and places a heavy burden on patients and their families. Currently, the treatment of OA primarily focuses on symptomatic relief and lacks ideal therapeutic methods. Resveratrol is a natural polyphenolic compound with anti-inflammatory and antioxidant properties, and in recent years, it has gained attention as a candidate drug for OA treatment. This article provides an overview of the research status on the role and mechanisms of resveratrol in treating OA. It has been found that resveratrol can prevent the development of OA by inhibiting inflammatory responses, protecting chondrocytes, maintaining cartilage homeostasis, promoting autophagy, and has shown certain therapeutic effects. This process may be related to the regulation of signaling pathways such as nuclear factor-kappa B (NF-κB), Toll-like receptor 4 (TLR4), and silent information regulator 1 (SIRT1). We summarize the current molecular mechanisms of resveratrol in treating OA, hoping to provide a reference for further research and application of resveratrol in OA treatment.

Critical signaling molecules in the temporomandibular joint osteoarthritis under different magnitudes of mechanical stimulation

The mechanical stress environment in the temporomandibular joint (TMJ) is constantly changing due to daily mandibular movements. Therefore, TMJ tissues, such as condylar cartilage, the synovial membrane and discs, are influenced by different magnitudes of mechanical stimulation. Moderate mechanical stimulation is beneficial for maintaining homeostasis, whereas abnormal mechanical stimulation leads to degeneration and ultimately contributes to the development of temporomandibular joint osteoarthritis (TMJOA), which involves changes in critical signaling molecules. Under abnormal mechanical stimulation, compensatory molecules may prevent degenerative changes while decompensatory molecules aggravate. In this review, we summarize the critical signaling molecules that are stimulated by moderate or abnormal mechanical loading in TMJ tissues, mainly in condylar cartilage. Furthermore, we classify abnormal mechanical stimulation-induced molecules into compensatory or decompensatory molecules. Our aim is to understand the pathophysiological mechanism of TMJ dysfunction more deeply in the ever-changing mechanical environment, and then provide new ideas for discovering effective diagnostic and therapeutic targets in TMJOA.

Impact of α-Globin Gene Expression and α-Globin Modifiers on the Phenotype of β-Thalassemia and Other Hemoglobinopathies: Implications for Patient Management

In this short review, we presented and discussed studies on the expression of globin genes in β-thalassemia, focusing on the impact of α-globin gene expression and α-globin modifiers on the phenotype and clinical severity of β-thalassemia. We first discussed the impact of the excess of free α-globin on the phenotype of β-thalassemia. We then reviewed studies focusing on the expression of α-globin-stabilizing protein (AHSP), as a potential strategy of counteracting the effects of the excess of free α-globin on erythroid cells. Alternative processes controlling α-globin excess were also considered, including the activation of autophagy by β-thalassemia erythroid cells. Altogether, the studies reviewed herein are expected to have a potential impact on the management of patients with β-thalassemia and other hemoglobinopathies for which reduction in α-globin excess is clinically beneficial.

Initiation and progression of dental-stimulated temporomandibular joints osteoarthritis

Temporomandibular joint (TMJ), a site that is often impacted by osteoarthritis (OA), is biomechanically linked with dental occlusion. Tissue responses in TMJ condyle to biomechanical stimulation could be investigated by intervention of the dental occlusion in animals. Unilateral anterior crossbite, an experimental malocclusion, has been demonstrated to induce TMJ-OA lesions, showing primarily as enhanced cartilage calcification and subchondral cortical bone formation at the osteochondral interface, causing the osteochondral interface thickening and stiffening. The changed interface would worsen the local biomechanical environment. At the cartilage side, the matrix degenerates. In the case of insufficient restoration of the matrix, the cells in the deep zone flow into the ones undergoing autophagy, apoptosis, and terminal differentiation while the cells in the superficial zone are promoted to differentiate to supply the loss of the deep zone cells. At the meantime, the bone marrow stromal cells are stimulated to bone formation in the subchondral cortical region which is uncoupled with the sites of the osteoclast-mediated resorption process that is predominantly observed at the subchondral trabecular bone region. Overall, the thickening and stiffening osteochondral interface, due greatly to the enhanced endochondral ossification in deep zone cartilage, should be a central pathological process that links with cartilage decay and subchondral bone remodelling in OA joints. The residual chondrocytes locating in the cartilage superficial zone have the progenitor-like qualities that can proliferate, and also differentiate into the deep zone chondrocytes, thus should be critical in progression and rehabilitation of TMJ-OA.

Irisin promotes osteogenic differentiation of bone marrow mesenchymal stem cells by activating autophagy via the Wnt//β-catenin signal pathway

Osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) plays a crucial role in osteoporosis. Irisin, an exercise-induced muscle-dependent myokine, has been reported to stimulate the development of brown adipose tissue and regulate energy expenditure. The present study aimed to investigate the effects of irisin on autophagy in BMSCs. Furthermore, the osteogenic differentiation ability was evaluated, as well as the activation of autophagy. It was found that 40 μM irisin for 48 h was an appropriate concentration and time period, with regards to cell viability, which was measured with a Cell Counting Kit-8. Moreover, the increasing expression levels of microtubule-associated protein light chain 3 (Lc3)-I/II and autophagy related 5 (Atg5) by irisin demonstrated the upregulation of autophagy. Mechanistically, bafilomycin A1 and Atg5 small interfering RNA were used to evaluate the possible mechanism of autophagy activated by irisin, and it was identified that irisin may upregulate autophagy by increasing the Atg12-Atg5-Atg16L complex. In addition, with the increasing level of autophagy, osteogenesis and the Wnt/β-catenin signal pathway were also enhanced. However, inhibition of autophagy by bafilomycin A1 negatively regulated osteogenic differentiation. Collectively, the present results suggested that irisin may stimulate autophagy in BMSCs and that osteogenic differentiation may be enhanced by stimulating autophagy.

A research update on the anticancer effects of bufalin and its derivatives

Bufalin (BF) is a cardiotonic steroid that has recently been found to have substantial anticancer activity; however, more efforts should be directed toward clarifying the detailed molecular mechanisms underlying this activity. BF could exert its anticancer effect by inducing apoptosis in various human cancer cells and thus triggering autophagic cancer cell death. The anti-inflammatory activities of BF are potentially important for its anticancer functions. Notably, some promising synthetic BF derivatives, including poly (ethylene glycol)-based polymeric prodrug of BF and BF211, have shown potent anticancer activity. Additionally, clinical trials regarding the use of BF-related agents in patients have supported the positive effect of BF as an anticancer treatment. Currently, large-scale randomized, double-blind, placebo or positive drug parallel controlled studies are required to confirm the anticancer potential of BF in various cancer types in the clinical setting. The present review will evaluate the potential mechanisms mediated by BF in intracellular signaling events in cancer cells and various promising BF derivatives that may have greater anticancer activity, thereby clarifying BF-mediated anticancer effects. The experimental and clinical results reviewed strongly emphasize the importance of this topic in future investigations.

Inhibition of acid‑sensing ion channel 1a attenuates acid‑induced activation of autophagy via a calcium signaling pathway in articular chondrocytes

Acid-sensing ion channel 1a (ASIC1a), member of the degenerin/epithelial sodium channel protein superfamily, serves a critical role in various physiological and pathological processes. The aim of the present study was to examine the role of ASIC1a in the autophagy of rat articular chondrocytes. Autophagy was induced by acidic stimulation in rat articular chondrocytes and the extent of autophagy was evaluated via the expression levels of microtubule-associated protein 1 light chain 3II, Beclin1 and uncoordinated-51 like kinase1. Suppression of ASIC1a was achieved using small interfering RNA technology and/or inhibitor psalmotoxin-1. The expression levels of autophagy markers were measured by western blot analysis and reverse transcription-quantitative polymerase chain reaction methods. Intracellular calcium ([Ca²⁺]_i) was analyzed using a Ca²⁺-imaging method. Additionally, protein expression levels of the Ca²⁺/calmodulin-dependent protein kinase kinase β (CaMKKβ)/5′-monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) pathway were measured by western blot analysis. The results showed that autophagy was increased in a pH-and time-dependent manner with exposure to an acidic environment. In addition, silencing ASIC1a significantly decreased the expression levels of autophagy makers, accompanied by abrogation of the acid-induced [Ca²⁺]_i increase. Furthermore, silencing of ASIC1a downregulated the levels of CaMKKβ/β-actin and phosphorylated (p-) AMPK/AMPK, and upregulated the levels of p-mTOR/mTOR. These results indicated that ASIC1a is a potent regulator of autophagy in chondrocytes, which may be associated with decreased Ca²⁺ influx and the CaMKKβ/AMPK/mTOR pathway.

Wild-type rabies virus induces autophagy in human and mouse neuroblastoma cell lines

Different rabies virus (RABV) strains have their own biological characteristics, but little is known about their respective impact on autophagy. Therefore, we evaluated whether attenuated RABV HEP-Flury and wild-type RABV GD-SH-01 strains triggered autophagy. We found that GD-SH-01 infection significantly increased the number of autophagy-like vesicles, the accumulation of enhanced green fluorescent protein (EGFP)-LC3 fluorescence puncta and the conversion of LC3-I to LC3-II, while HEP-Flury was not able to induce this phenomenon. When evaluating autophagic flux, we found that GD-SH-01 infection triggers a complete autophagic response in the human neuroblastoma cell line (SK), while autophagosome fusion with lysosomes was inhibited in a mouse neuroblastoma cell line (NA). In these cells, GD-SH-01 led to apoptosis and mitochondrial dysfunction while triggering autophagy, and apoptosis could be decreased by enhancing autophagy. To further identify the virus constituent causing autophagy, 5 chimeric recombinant viruses carrying single genes of HEP-Flury instead of those of GD-SH-01 were rescued. While the HEP-Flury virus carrying the wild-type matrix protein (M) gene of RABV triggered LC3-I to LC3-II conversion in SK and NA cells, replacement of genes of nucleoprotein (N), phosphoprotein (P) and glycoprotein (G) produced only minor autophagy. But no one single structural protein of GD-SH-01 induced autophagy. Moreover, the AMPK signaling pathway was activated by GD-SH-01 in SK. Therefore, our data provide strong evidence that autophagy is induced by GD-SH-01 and can decrease apoptosis in vitro. Furthermore, the M gene of GD-SH-01 may cooperatively induce autophagy.

The protective role of autophagy in experimental osteoarthritis, and the therapeutic effects of Torin 1 on osteoarthritis by activating autophagy

Background

Recent studies have shown that autophagy was associated with the development of osteoarthritis (OA), the purpose of this research was to determine the exact role of autophagy in OA and investigate effective therapeutic drugs to inhibit the pathological progression of OA.

Methods

In this study, a cellular OA model was generated by stimulating SW1353 cells with IL-1β and a rabbit OA model was established by intra-articular injection of collagenase, followed by treatment with Torin 1 or 3-Methyladenine (3-MA). The mRNA expression levels of VEGF, MMP-13 and TIMP-1 were determined by quantitative real-time PCR. The caitilage degeneration was examined by histological evaluation, chondrocytes degeneration and autophagosomes were observed by transmission electron microscopy. Expression levels of Beclin-1 and LC3 were evaluated by western blotting and immunofluorescence.

Results

The degeneration of SW 1353 cells, cartilage and chondrocytes was related to the loss of autophagy in experimental OA. 3-MA increased the severity of degeneration of cells and cartilage by autophagy inhibition, while Torin 1 reduced that by autophagy activation.

Conclusions

The loss of autophagy is linked with the experimental OA and autophagy may play a protective role in the pathogenesis of OA. Treatment of Torin 1 can inhibit the degenerative changes of experimental OA by activating autophagy and it may be a useful therapeutic drug for OA.

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-016-0995-x) contains supplementary material, which is available to authorized users.

Activation of autophagy via Ca(2+)-dependent AMPK/mTOR pathway in rat notochordal cells is a cellular adaptation under hyperosmotic stress

Nucleus pulposus (NP) cells experience hyperosmotic stress in spinal discs; however, how these cells can survive in the hostile microenvironment remains unclear. Autophagy has been suggested to maintain cellular homeostasis under different stresses by degrading the cytoplasmic proteins and organelles. Here, we explored whether autophagy is a cellular adaptation in rat notochordal cells under hyperosmotic stress. Hyperosmotic stress was found to activate autophagy in a dose- and time-dependent manner. SQSTM1/P62 expression was decreased as the autophagy level increased. Transient Ca(2+) influx from intracellular stores and extracellular space was stimulated by hyperosmotic stress. Activation of AMPK and inhibition of p70S6K were observed under hyperosmotic conditions. However, intercellular Ca(2+) chelation inhibited the increase of LC3-II and partly reversed the decrease of p70S6K. Hyperosmotic stress decreased cell viability and promoted apoptosis. Inhibition of autophagy led to SQSTM1/P62 accumulation, reduced cell viability, and accelerated apoptosis in notochordal cells under this condition. These evidences suggest that autophagy induction via the Ca(2+)-dependent AMPK/mTOR pathway might occur as an adaptation mechanism for notochordal cells under hyperosmotic stress. Thus, activating autophagy might be a promising approach to improve viability of notochordal cells in intervertebral discs.

Electroacupuncture protects against ischemic stroke by reducing autophagosome formation and inhibiting autophagy through the mTORC1-ULK1 complex-Beclin1 pathway

In a previous study by our group, we demonstrated that electroacupuncture (EA) activates the class I phosphoinositide 3-kinase (PI3K)/Akt signaling pathway. There is considerable evidence that the downstream mammalian target of rapamycin complex 1 (mTORC1) plays an important role in autophagy following ischemic stroke. The aim of the present study was to determine whether EA exerts a neuroprotective effect through mTORC1-mediated autophagy following ischemia/reperfusion injury. Our results revealed that EA at the LI11 and ST36 acupoints attenuated motor dysfunction, improved neurological deficit outcomes and decreased the infarct volumes. The number of autophagosomes, autolysosomes and lysosomes was decreased following treatment with EA. Simultaneously, the levels of the autophagosome membrane maker, microtubule-associated protein 1 light chain 3 beta (LC3B)II/I, Unc-51-like kinase 1 (ULK1), autophagy related gene 13 Atg13) and Beclin1 (ser14) were decreased, whereas mTORC1 expression was increased in the peri-infarct cortex. These results suggest that EA protects against ischemic stroke through the inhibition of autophagosome formation and autophagy, which is mediated through the mTORC1-ULK complex-Beclin1 pathway.

Potential role of autophagy in the bactericidal activity of human PMNs for Bacillus anthracis

Bacillus anthracis, the causative agent of anthrax, is acquired by mammalian hosts from the environment, as quiescent endospores. These endospores must germinate inside host cells, forming vegetative bacilli, before they can express the virulence factors that enable them to evade host defenses and disseminate throughout the body. While the role of macrophages and dendritic cells in this initial interaction has been established, the role of polymorphonuclear leukocytes (PMNs) has not been adequately defined. We discovered that while B. anthracis 34F2 Sterne endospores germinate poorly within non-activated human PMNs, these phagocytes exhibit rapid microbicidal activity toward the outgrown vegetative bacilli, independent of superoxide and nitric oxide. These findings suggest that a non-free radical pathway kills B. anthracis bacilli. We also find in PMNs an autophagic mechanism of bacterial killing based on the rapid induction of LC-3 conversion, beclin-1 expression, sequestosome 1 (SQSTM1) degradation and inhibition of bactericidal activity by the inhibitor, 3-methyladenine. These findings extend to PMNs an autophagic bactericidal mechanism previously described for other phagocytes.

Interplay between unfolded protein response and autophagy promotes tumor drug resistance

The endoplasmic reticulum (ER) is involved in the quality control of secreted protein via promoting the correct folding of nascent protein and mediating the degradation of unfolded or misfolded protein, namely ER-associated degradation. When the unfolded or misfolded proteins are abundant, the unfolded protein response (UPR) is elicited, an adaptive signaling cascade from the ER to the nucleus, which restores the homeostatic functions of the ER. Autophagy is a conserved catabolic process where cellular long-lived proteins and damaged organelles are engulfed and degraded for recycling to maintain homeostasis. The UPR and autophagy occur simultaneously and are involved in pathological processes, including tumorigenesis, chemoresistance of malignancies and neurodegeneration. Accumulative data has indicated that the UPR may induce autophagy and that autophagy is able to alleviate the UPR. However, the detailed mechanism of interplay between autophagy and UPR remains to be fully understood. The present review aimed to depict the core pathways of the two processes and to elucidate how autophagy and UPR are regulated. Moreover, the review also discusses the molecular mechanism of crosstalk between the UPR and autophagy and their roles in malignant survival and drug resistance.

Role of autophagy and its significance in cellular homeostasis

Autophagy is a catabolic pathway that regulates homeostasis in cells. It is an exceptional pathway of membrane trafficking. Autophagy is characterized by the formation of double-membrane vesicles; autophagosomes that are responsible for delivering damaged organelle and extra proteins to lysosome for recycling. A series of actions including environmental and genetic factors are responsible for induction of autophagy. In the past few decades, the research on autophagy has been immensely expanded because it is a vital process in maintaining cellular balance as well as deeply connected with pathogenesis of a number of diseases. The aim of this review is to present an overview of modern work on autophagy and highlight some essential genetic role in the induction of autophagy. There is an emerging need to identify, quantify, and manipulate the pathway of autophagy, due to its close relationship with a variety of developmental pathways and functions especially in cancer, diabetes, neurodegenerative disorders, and infectious diseases.

Enhancement of chondrocyte autophagy is an early response in the degenerative cartilage of the temporomandibular joint to biomechanical dental stimulation

Autophagy is a cell protective mechanism for maintaining cellular homeostasis. The present study aimed to investigate whether autophagy is enhanced in the biomechanically induced degenerative cartilage of the temporomandibular joint (TMJ) and the potential role of mitogen-activated protein kinase kinase kinase kinase 3 (MAP4K3) and mammalian Target of rapamycin (mTOR) in this observation. To induce degenerative changes in the TMJs, rats were subjected to biomechanical dental stimulation by moving 4 molars away from their original position as we previously reported. The ultrastructure of autophagosome was observed by transmission electron microscopy. The number of lysosomes was analyzed by flow cytometry. The expression levels of Beclin1 and LC3 and the involvement of MAP4K3 activity were detected by immunohistochemistry, real-time PCR and western blot. The activity of the mTOR pathway indicated by p-mTOR and p-p70S6 K was assayed by western blot. TMJ degeneration, characterized by irregular cell arrangement and cell-free area, was induced in the experimental groups. Under transmission electron microscopy, we observed the presence of autophagosomes, small patches of condensed chromatin, abundant rough endoplasmic reticulum and Golgi apparatus. The number of lysosomes and the expression levels of Beclin1 and LC3 increased, while the activity of mTOR and the expression level of MAP4K3 decreased in the experimental groups. Cartilage in TMJ which was induced to be degenerative biomechanically exhibited autophagy accompanied by reduced mTOR and MAP4K3 activity.

Nutrition optimization prior to surgery

Optimization of metabolic state prior to major surgery leads to improved surgical outcomes. Nutrition screening protocols should be implemented in the preoperative evaluation, possibly as part of a bundle. Strategies to minimize hyperglycemia and insulin resistance by aggressive preoperative nutrition and carbohydrate loading may promote maintenance of a perioperative anabolic state, improving healing, reducing complications, and shortening the time to recovery of bowel function and hospital discharge. Short courses of preoperative immune-modulating formulas, using combinations of arginine, ω-3 fatty acids, and other nutrients, have been associated with improved surgical outcomes. These immune-modulating nutrients are key elements of metabolic pathways that promote attenuation of the metabolic response to stress and improve both wound healing and immune function. Patients with severe malnutrition and gastrointestinal dysfunction may benefit from preoperative parenteral nutrition. Continuation of feeding through the intraoperative period for severely stressed hypermetabolic patients undergoing nongastrointestinal surgery is another strategy to optimize metabolic state and reduce prolonged nutrition deficits. In this paper, we review the importance of preoperative nutrition and strategies for effective preoperative nutrition optimization.

Folate stress induces apoptosis via p53-dependent de novo ceramide synthesis and up-regulation of ceramide synthase 6

We have investigated the role of ceramide in the cellular adaptation to folate stress induced by Aldh1l1, the enzyme involved in the regulation of folate metabolism. Our previous studies demonstrated that Aldh1l1, similar to folate deficiency, evokes metabolic stress and causes apoptosis in cancer cells. Here we report that the expression of Aldh1l1 in A549 or HCT116 cells results in the elevation of C16-ceramide and a transient up-regulation of ceramide synthase 6 (CerS6) mRNA and protein. Pretreatment with ceramide synthesis inhibitors myriocin and fumonisin B1 or siRNA silencing of CerS6 prevented C16-ceramide accumulation and rescued cells supporting the role of CerS6/C16-ceramide as effectors of Aldh1l1-induced apoptosis. The CerS6 activation by Aldh1l1 and increased ceramide generation were p53-dependent; this effect was ablated in p53-null cells. Furthermore, the expression of wild type p53 but not transcriptionally inactive R175H p53 mutant strongly elevated CerS6. Also, this dominant negative mutant prevented accumulation of CerS6 in response to Aldh1l1, indicating that CerS6 is a transcriptional target of p53. In support of this mechanism, bioinformatics analysis revealed the p53 binding site 3 kb downstream of the CerS6 transcription start. Interestingly, ceramide elevation in response to Aldh1l1 was inhibited by silencing of PUMA, a proapoptotic downstream effector of p53 whereas the transient expression of CerS6 elevated PUMA in a p53-dependent manner indicating reciprocal relationships between ceramide and p53/PUMA pathways. Importantly, folate withdrawal also induced CerS6/C16-ceramide elevation accompanied by p53 accumulation. Overall, these novel findings link folate and de novo ceramide pathways in cellular stress response.

Exposure to titanium dioxide nanoparticles induces autophagy in primary human keratinocytes

Understanding the mechanisms of cell-nanomaterial interactions is vital in harnessing the potential of using nanomaterials in biomedical applications. By immuno-labeling of LC3 and TEM analysis, it is found that titanium dioxide nanoparticles are internalized by human keratinocytes and induce autophagy. Autophagy appears to play a cytoprotective role in response to toxicity influence exerted by the nanoparticles.

Carbonic anhydrases III and IV autoantibodies in rheumatoid arthritis, systemic lupus erythematosus, diabetes, hypertensive renal disease, and heart failure

In the present study, the CA III and IV autoantibodies, CA activity, antioxidant enzymes and cytokines in rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), diabetes, hypertensive renal disease, and heart failure were investigated. The anti-CA III antibody titers in patients with RA, SLE, and type 1 diabetes (T1D) were significantly higher than that in control groups (P < 0.05). The anti-CA IV antibody titers in patients with RA, SLE, type 1 diabetic nephropathy (T1DN), and heart failure were significantly higher than that in control groups (P < 0.05) while anti-CA IV antibody could suppress the total CA activity. The SOD and GPx levels in patients with RA, SLE, and T1DN were significantly lower than that in control groups (P < 0.05). IL-6, IL-17, IFN-γ, and TNF-α levels were significantly higher in SLE group compared with the control group (P < 0.05). Weak but significant correlations were found between anti-CA III antibodies and ESR in RA (r = 0.403, P = 0.013) and SLE patients (r = 0.397, P = 0.007). These results suggested that the generation of CA III and IV autoantibodies, antioxidant enzymes, and cytokines might influence each other and CA autoantibodies might affect the normal physiology function of CA.

GSK3β signaling is involved in ultraviolet B-induced activation of autophagy in epidermal cells

Ultraviolet B (UVB) exposure causes damage to skin and represents the primary etiological agent for skin cancer formation. UVB induces DNA damage and apoptosis in epidermal cells. In this study, we demonstrated that UVB activated autophagy in JB6 epidermal cells, which was evident by the formation of LC3 puncta, the induction of LC3 lipidation, the increase in beclin 1 expression, and the decrease in the levels of p62. Autophagy appeared to be a protective response to UVB-induced damage because inhibition of autophagy exacerbated UVB-induced cell death, and stimulation of autophagy offered protection. Furthermore, we demonstrated that glycogen synthase kinase 3β (GSK3β) was involved in UVB-induced autophagy. UVB inhibited GSK3β activation by simultaneously enhancing phosphorylation at Ser⁹ and suppressing Tyr²¹⁶ phosphorylation. GSK3β negatively regulated autophagy; overexpression of wild-type or S9A (constitutive-active) GSK3β mutant inhibited UVB-mediated autophagy, while overexpression of a dominant-negative K85R mutant enhanced UVB-mediated autophagy. Inhibition of GSK3β also offered protection against UVB-mediated damage. UVB activated AMP-activated protein kinase (AMPK), an important regulator of autophagy through the inhibition of GSK3β. Taken together, our results suggest that UVB-stimulated autophagy is a protective response for epidermal cells and is mediated by the GSK3β/AMPK pathway.

Mitophagy and Parkinson's disease: be eaten to stay healthy

Parkinson's disease (PD) is one of the most prevalent neurodegenerative disorders. Pathologically, it is characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNc). Although most occurrences have an unknown cause, several gene mutations have been linked to familial forms of PD. The discovery of some of the proteins encoded by these genes, including Parkin, PINK1 and DJ-1, at the mitochondria offered a new perspective on the involvement of mitochondria in PD. Specifically, these proteins are thought to be involved in the maintenance of a healthy pool of mitochondria by regulating their turnover by mitochondrial autophagy, or mitophagy. In this review, we discuss recent studies on the role of mitophagy in PD. We present three putative models whereby PINK1 and Parkin may affect mitophagy; 1) by shifting the balance between fusion and fission of the mitochondrial network, 2) by modulating mitochondrial motility and 3) by directly recruiting the autophagic machinery to damaged mitochondria. This article is part of a Special Issue entitled 'Mitochondrial function and dysfunction in neurodegeneration'.

Bufalin increases sensitivity to AKT/mTOR-induced autophagic cell death in SK-HEP-1 human hepatocellular carcinoma cells

Bufalin is the major component of Chan-Su (a traditional Chinese medicine, TCM) extracts from the venom of Bufo bufo gargarizan. In the present study, we investigated the pharmacological mechanisms of cell cycle arrest and autophagic cell death induced by bufalin in SK-HEP-1 human hepatocellular carcinoma cells in vitro. Bufalin inhibited cell survival by MTT assay and increased cell death by trypan blue exclusion assay in a concentration-dependent manner. In addition, bufalin induced G2/M phase arrest by reducing CDK1 activity. Bufalin triggered DNA fragmentation and apoptotic cell death in SK-HEP-1 cells by DNA gel electrophoresis, TUNEL and caspase-3 activity assay, while bufalin induced autophagic cell death by double-membrane vacuoles (transmission electron microscopy, TEM), acidic vesicular organelles (acridine orange staining) and cleavage of microtubule-associated protein 1 light chain 3 (LC3). Protein expression levels of cyclin A and B, CDK1, phospho-CDK1 (Thr161), Cdc25c, phospho-Cdc25c (Ser198), phospho-AKT (Thr308), phospho-AKT (Ser473), phospho‑mTOR (Ser2481) were downregulated. In contrast, protein expression levels of the Chk1, Wee1, LC3-II, Beclin-1, Atg 5, Atg 7 and Atg 12 were upregulated in SK-HEP-1 cells after bufalin treatment. Inhibition of autophagy by 3-methyladenine (an inhibitor of class III phosphatidylinositol-3 kinase; 3-MA) or bafilomycin A1 (an inhibitor of the vacuolar proton pump of lysosomes and endosomes) reduced the effect of bufalin on cell viability and enhanced the effect of bufalin on apoptosis. In conclusion, bufalin triggered autophagic cell death and G2/M phase arrest through the AKT/mTOR signaling pathway in SK-HEP-1 cells. Our findings showed that bufalin may be potentially efficacious in the treatment of human hepatocellular carcinoma.

Oridonin up-regulates expression of P21 and induces autophagy and apoptosis in human prostate cancer cells

Background: Oridonin (ORI) could inhibit the proliferation and induce apoptosis in various cancer cell lines. However, the mechanism is not fully understood.

Methods: Human prostate cancer (HPC) cells were cultured in vitro and cell viability was detected by the CCK-8 assay. The ultrastructure changes were observed under transmission electron microscope (TEM). Chemical staining with acridine orange (AO), MDC or DAPI was used to detect acidic vesicular organelles (AVOs) and alternation of DNA. Expression of LC3 and P21 was detected by Western Blot. Apoptotic rates and cell cycle arrest were detected by FACS.

Results: Our study demonstrated that after ORI treatment, the proliferations of human prostate cancer (HPC) cell lines PC-3 and LNCaP were inhibited in a concentration and time-dependent manner. ORI induced cell cycle arrest at the G2/M phase. A large number of autophagosomes with double-membrane structure and acidic vesicular organelles (AVOs) were detected in the cytoplasm of HPC cells treated with ORI for 24 hours. ORI resulted in the conversion of LC3-I to LC3-II and recruitment of LC3-II to the autophagosomal membranes. Autophagy inhibitor 3-methyladenine (3-MA) reduced AVOs formation and inhibited LC3-I to LC3-II conversion. At 48 h, DNA fragmentation, chromatin condensation and disappearance of surface microvilli were detected in ORI-treated cells. ORI induced a significant increase in the number of apoptotic cells (PC-3: 5.4% to 27.0%, LNCaP: 5.3% to 31.0%). Promoting autophagy by nutrient starvation increased cell viability, while inhibition of autophagy by 3-MA promoted cell death. The expression of P21 was increased by ORI, which could be completely reversed by the inhibition of autophagy.

Conclusions: Our findings indicated that autophagy occurred before the onset of apoptosis and protected cancer cells in ORI-treated HPC cells. P21 was involved in ORI-induced autophagy and apoptosis. Our results provide an experimental basis for understand the anti-tumor mechanism of ORI as treatment for prostate cancer.