Phosphoinositide 3-kinase accelerates autophagic cell death during glucose deprivation in the rat cardiomyocyte-derived cell line H9c2

Interplay of energy metabolism and autophagy

Macroautophagy/autophagy, is widely recognized for its crucial role in enabling cell survival and maintaining cellular energy homeostasis during starvation or energy stress. Its regulation is intricately linked to cellular energy status. In this review, covering yeast, mammals, and plants, we aim to provide a comprehensive overview of the understanding of the roles and mechanisms of carbon- or glucose-deprivation related autophagy, showing how cells effectively respond to such challenges for survival. Further investigation is needed to determine the specific degraded substrates by autophagy during glucose or energy deprivation and the diverse roles and mechanisms during varying durations of energy starvation.Abbreviations: ADP: adenosine diphosphate; AMP: adenosine monophosphate; AMPK: AMP-activated protein kinase; ATG: autophagy related; ATP: adenosine triphosphate; ER: endoplasmic reticulum; ESCRT: endosomal sorting complex required for transport; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GD: glucose deprivation; GFP: green fluorescent protein; GTPases: guanosine triphosphatases; HK2: hexokinase 2; K phaffii: Komagataella phaffii; LD: lipid droplet; MAP1LC3/LC3: microtubule-associated protein1 light chain 3; MAPK: mitogen-activated protein kinase; Mec1: mitosis entry checkpoint 1; MTOR: mechanistic target of rapamycin kinase; NAD (+): nicotinamide adenine dinucleotide; OGD: oxygen and glucose deprivation; PAS: phagophore assembly site; PCD: programmed cell death; PtdIns3K: class III phosphatidylinositol 3-kinase; PtdIns3P: phosphatidylinositol-3-phosphate; ROS: reactive oxygen species; S. cerevisiae: Saccharomyces cerevisiae; SIRT1: sirtuin 1; Snf1: sucrose non-fermenting 1; STK11/LKB1: serine/threonine kinase 11; TFEB: transcription factor EB; TORC1: target of rapamycin complex 1; ULK1: unc-51 like kinase 1; Vps27: vacuolar protein sorting 27; Vps4: vacuolar protein sorting 4.

Lnc001209 Participates in aluminium-induced apoptosis of PC12 cells by regulating PI3K-AKT-mTOR signalling pathway

Aluminium (Al) is a common environmental neurotoxin, but the molecular mechanism underlying its toxic effects remains unclear. Many studies have shown that aluminium exposure leads to increased neuronal apoptosis. This study aimed to investigate the mechanisms and signalling pathways involved in aluminium exposure-induced neuronal apoptosis. The results showed a decrease in the number of PC12 cells and changes in cell morphology in the aluminium maltol exposure group. The viability of PC12 cells decreased gradually with increasing of exposure doses, and the apoptosis rate increased. The expression of Lnc001209 decreased gradually with an increase in the aluminium exposure dose. After transfection of Lnc001209 siRNA in aluminium-exposed PC12 cells, the protein expression levels of p-Akt Ser473, p-Akt Thr308, p-P85 Tyr467, p-mTOR Ser2448 and CD36 were increased. RNA pull-down MS showed that Lnc001209 interacts with the CD36 protein. Expression of the CD36 protein was increased in PC12 cells exposed to aluminium. The results of the CD36 intervention experiment showed that the protein expression levels of p-Akt Ser473, p-Akt Thr308, p-P85 Tyr467, and p-mTOR Ser2448 likely increased after CD36 overexpression. In addition, the phosphorylation level of AKT had the most significant increase. The enhancement of p-Akt activity promotes neuronal apoptosis.

Provocative non-canonical roles of p53 and AKT signaling: A role for Thymosin β4 in medulloblastoma

The PI3K/AKT and p53 pathways are key regulators of cancer cell survival and death, respectively. Contrary to their generally accepted roles, several lines of evidence, including ours in medulloblastoma, the most common childhood brain cancer, highlight non-canonical functions for both proteins and show a complex context-dependent dynamic behavior in determining cell fate. Interestingly, p53-mediated cell survival and AKT-mediated cell death can dominate in certain conditions, and these interchangeable physiological functions may potentially be manipulated for better clinical outcomes. This review article presents studies in which p53 and AKT behave contrary to their well-established functions. We discuss the factors and circumstances that may be involved in mediating these changes and the implications of these unique roles of p53 and AKT in devising therapeutic strategies. Lastly, based on our recent finding of Thymosin beta 4-mediated chemosensitivity via an AKT-p53 interaction in medulloblastoma cells, we also discuss the possible implications of Thymosin beta-4 in enhancing drug sensitivity in this deadly childhood disease.

4EBP1 senses extracellular glucose deprivation and initiates cell death signaling in lung cancer

Nutrient-limiting conditions are common during cancer development. The coordination of cellular glucose levels and cell survival is a fundamental question in cell biology and has not been completely understood. 4EBP1 is known as a translational repressor to regulate cell proliferation and survival by controlling translation initiation, however, whether 4EBP1 could participate in tumor survival by other mechanism except for translational repression function, especially under glucose starvation conditions remains unknown. Here, we found that protein levels of 4EBP1 was up-regulated in the central region of the tumor which always suffered nutrient deprivation compared with the peripheral region. We further discovered that 4EBP1 was dephosphorylated by PTPMT1 under glucose starvation conditions, which prevented 4EBP1 from being targeted for ubiquitin-mediated proteasomal degradation by HERC5. After that, 4EBP1 translocated to cytoplasm and interacted with STAT3 by competing with JAK and ERK, leading to the inactivation of STAT3 in the cytoplasm, resulting in apoptosis under glucose withdrawal conditions. Moreover, 4EBP1 knockdown increased the tumor volume and weight in xenograft models by inhibiting apoptosis in the central region of tumor. These findings highlight a novel mechanism for 4EBP1 as a new cellular glucose sensor in regulating cancer cell death under glucose deprivation conditions, which was different from its classical function as a translational repressor.

Blunting TRPML1 channels protects myocardial ischemia/reperfusion injury by restoring impaired cardiomyocyte autophagy

Accumulating evidence suggests that autophagy dysfunction plays a critical role in myocardial ischemia/reperfusion (I/R) injury. However, the underling mechanism of malfunctional autophagy in the cardiomyocytes subjected to I/R has not been well defined. As a result, there is no effective therapeutic option by targeting autophagy to prevent myocardial I/R injury. Here, we used both an in vitro and an in vivo I/R model to monitor autophagic flux in the cardiomyocytes, by exposing neonatal rat ventricular myocytes to hypoxia/reoxygenation and by subjecting mice to I/R, respectively. We observed that the autophagic flux in the cardiomyocytes subjected to I/R was blocked in both in vitro and in vivo models. Down-regulating a lysosomal cationic channel, TRPML1, markedly restored the blocked myocardial autophagic flux induced by I/R, demonstrating that TRPML1 directly contributes to the blocked autophagic flux in the cardiomyocytes subjected to I/R. Mechanistically, TRPML1 is activated secondary to ROS elevation following ischemia/reperfusion, which in turn induces the release of lysosomal zinc into the cytosol and ultimately blocks the autophagic flux in cardiomyocytes, presumably by disrupting the fusion between autophagosomes and lysosomes. As a result, the inhibited myocardial autophagic flux induced by TRPML1 disrupted mitochondria turnover and resulted in mass accumulation of damaged mitochondria and further ROS release, which directly led to cardiomyocyte death. More importantly, pharmacological and genetic inhibition of TRPML1 channels greatly reduced infarct size and rescued heart function in mice subjected to I/R in vivo by restoring impaired myocardial autophagy. In summary, our study demonstrates that secondary to ROS elevation, activation of TRPML1 results in autophagy inhibition in the cardiomyocytes subjected to I/R, which directly leads to cardiomyocyte death by disrupting mitochondria turnover. Therefore, targeting TRPML1 represents a novel therapeutic strategy to protect against myocardial I/R injury.

Targeted PI3K/AKT-hyperactivation induces cell death in chronic lymphocytic leukemia

Current therapeutic approaches for chronic lymphocytic leukemia (CLL) focus on the suppression of oncogenic kinase signaling. Here, we test the hypothesis that targeted hyperactivation of the phosphatidylinositol-3-phosphate/AKT (PI3K/AKT)-signaling pathway may be leveraged to trigger CLL cell death. Though counterintuitive, our data show that genetic hyperactivation of PI3K/AKT-signaling or blocking the activity of the inhibitory phosphatase SH2-containing-inositol-5'-phosphatase-1 (SHIP1) induces acute cell death in CLL cells. Our mechanistic studies reveal that increased AKT activity upon inhibition of SHIP1 leads to increased mitochondrial respiration and causes excessive accumulation of reactive oxygen species (ROS), resulting in cell death in CLL with immunogenic features. Our results demonstrate that CLL cells critically depend on mechanisms to fine-tune PI3K/AKT activity, allowing sustained proliferation and survival but avoid ROS-induced cell death and suggest transient SHIP1-inhibition as an unexpectedly promising concept for CLL therapy.

Angiotensin II and hypoxia induce autophagy in cardiomyocytes via activating specific protein kinase C subtypes

Background

The purpose of this study was to explore the role of protein kinase C (PKC) isozymes and reactive oxygen species (ROS) in hypoxia and angiotensin (Ang) II-induced autophagy.

Methods

Primary cardiomyocytes were isolated from Sprague-Dawley (SD) neonatal rats and cultured in hypoxia and/or Ang II conditions. Dihydroethidium fluorescence staining was used to detect the content of ROS. Cardiomyocyte autophagy was determined using Monodansylcadaverine fluorescence staining and Western blot. We also inhibited ROS production to explore the relationship between ROS and autophagy. ELISA was used to detect the contents of PKC δ and PKC ε. After inhibition of PKC δ activation and PKC ε expression by lentiviral siRNA, ROS content and autophagy of cultured cardiomyocytes were detected.

Results

Hypoxia and Ang II stimulation increased autophagy in cardiomyocytes, accompanied by increased intracellular ROS production. Inhibiting ROS following hypoxia or Ang II stimulation significantly suppressed autophagy in comparison with hypoxia or Ang II stimulation group. Inhibiting PKC δ significantly reduced ROS production and autophagy activity following hypoxia or accompanied with Ang II stimulation except Ang II stimulation alone. Knockdown of PKC ε notably decreased ROS production and autophagy in response to Ang II alone and in combination with hypoxia rather than hypoxia alone.

Conclusions

Both hypoxia and Ang II stimulation can induce autophagy in cardiomyocytes through increasing intracellular ROS. However, hypoxia and Ang II stimulation induced myocardial autophagy via PKC δ and PKC ε, respectively.

Research progress of IGF-1 and cerebral ischemia

Cerebral ischemic disease is a group of diseases that cause insufficient blood supply to the cerebrum, cerebellum or brain stem for different reasons, resulting in corresponding nervous system symptoms. Cardiovascular disease is the leading cause of death in the world. Among them, the death caused by cerebral ischemia accounts for the vast majority, and it is one of the fatal diseases in the middle-aged and elderly at present. Epidemiologic studies have projected increasing mortality due to cardiovascular disease worldwide (about 23.3 million people by 2030) because of the aging population. However, related studies have shown that insulin-like growth factor I (IGF-1) is a multifunctional cell proliferation regulator. It plays an important role in cerebral ischemia. It is effective in promoting cell differentiation, proliferation and individual development. Studies have shown that IGF-1 signaling pathway is a key pathway controlling cell growth and survival. There may be five mechanisms in cerebral ischemia: prevention of intracellular calcium overload, inhibition of the upregulation of nNOS, IGF-1upregulations activating HIF-1α, regulation of Bcl-2 to resist apoptosis, and enhancement of vascular endothelial function. Three critical nodes in the IGF-1 signaling pathway have been described in cardiomyocytes: protein kinase Akt/mammalian target of rapamycin (mTOR), Ras/Raf/extracellular signal-regulated kinase (ERK), and phospholipase C (PLC)/inositol 1,4,5-triphosphate (InsP3)/Ca2+. IGF-1 plays an important role in cerebral ischemia and myocardial ischemia, mainly by activating downstream of IGF-1, controlling cell death and differentiation or transcription work, improving the function of heart muscle cells, reducing the myocardial cell apoptosis induced by myocardial infarction, regulating endogenous protection and restoration of cerebral ischemia injury, thus protecting cerebral and myocardial injury. Related studies have shown that bcl-2 exerts great influence on both cerebral ischemia and myocardial ischemia. Therefore, the relevant pathways and targets of cerebral ischemia and myocardial ischemia and the role of IGF-1 in protecting the heart are reviewed in this paper.

Cracking the context-specific PI3K signaling code

Specificity in signal transduction is determined by the ability of cells to "encode" and subsequently "decode" different environmental signals. Akin to computer software, this "signaling code" governs context-dependent execution of cellular programs through modulation of signaling dynamics and can be corrupted by disease-causing mutations. Class IA phosphoinositide 3-kinase (PI3K) signaling is critical for normal growth and development and is dysregulated in human disorders such as benign overgrowth syndromes, cancer, primary immune deficiency, and metabolic syndrome. Despite decades of PI3K research, understanding of context-dependent regulation of the PI3K pathway and of the underlying signaling code remains rudimentary. Here, we review current knowledge on context-specific PI3K signaling and how technological advances now make it possible to move from a qualitative to quantitative understanding of this pathway. Insight into how cellular PI3K signaling is encoded or decoded may open new avenues for rational pharmacological targeting of PI3K-associated diseases. The principles of PI3K context-dependent signal encoding and decoding described here are likely applicable to most, if not all, major cell signaling pathways.

Cancer Treatment Goes Viral: Using Viral Proteins to Induce Tumour-Specific Cell Death

Cell death is a tightly regulated process which can be exploited in cancer treatment to drive the killing of the tumour. Several conventional cancer therapies including chemotherapeutic agents target pathways involved in cell death, yet they often fail due to the lack of selectivity they have for tumour cells over healthy cells. Over the past decade, research has demonstrated the existence of numerous proteins which have an intrinsic tumour-specific toxicity, several of which originate from viruses. These tumour-selective viral proteins, although from distinct backgrounds, have several similar and interesting properties. Though the mechanism(s) of action of these proteins are not fully understood, it is possible that they can manipulate several cell death modes in cancer exemplifying the intricate interplay between these pathways. This review will discuss our current knowledge on the topic and outstanding questions, as well as deliberate the potential for viral proteins to progress into the clinic as successful cancer therapeutics.

IGF-1 Inhibits Apoptosis of Porcine Primary Granulosa Cell by Targeting Degradation of BimEL

Insulin-like growth factor-1 (IGF-1) is an intra-ovarian growth factor that plays important endocrine or paracrine roles during ovarian development. IGF-1 affects ovarian function and female fertility through reducing apoptosis of granulosa cells, yet the underlying mechanism remains poorly characterized. Here, we aimed to address these knowledge gaps using porcine primary granulosa cells and examining the anti-apoptotic mechanisms of IGF-1. IGF-1 prevented the granulosa cell from apoptosis, as shown by TUNEL and Annexin V/PI detection, and gained the anti-apoptotic index, the ratio of Bcl-2/Bax. This process was partly mediated by reducing the pro-apoptotic Bim_EL (Bcl-2 Interacting Mediator of Cell Death-Extra Long) protein level. Western blotting showed that IGF-1 promoted Bim_EL phosphorylation through activating p-ERK1/2, and that the proteasome system was responsible for degradation of phosphorylated Bim_EL. Meanwhile, IGF-1 enhanced the Beclin1 level and the rate of LC3 II/LC3 I, indicating that autophagy was induced by IGF-1. By blocking the proteolysis processes of both proteasome and autophagy flux with MG132 and chloroquine, respectively, the Bim_EL did not reduce and the phosphorylated Bim_EL protein accumulated, thereby indicating that both proteasome and autophagy pathways were involved in the degradation of Bim_EL stimulated by IGF-1. In conclusion, IGF-1 inhibited porcine primary granulosa cell apoptosis via degradation of pro-apoptotic Bim_EL. This study is critical for us to further understand the mechanisms of follicular survival and atresia regulated by IGF-1. Moreover, it provides a direction for the treatment of infertility caused by ovarian dysplasia, such as polycystic ovary syndrome and the improvement of assisted reproductive technology.

MicroRNA-24 protects retina from degeneration in rats by down-regulating chitinase-3-like protein 1

MicroRNAs (miRNAs) have been shown to play critical roles in the pathogenesis and progression of degenerative retinal diseases like age-related macular degeneration (AMD). In this study, we first demonstrated that miR-24 plays an important role in maintaining retinal structure and visual function of rats by targeting chitinase-3-like protein 1 (CHI3L1). In the retinal pigment epithelial (RPE) cells of Royal College of Surgeons (RCS) rats, an animal model of genetic retinal degeneration (RD), miR-24 was found lower and CHI3L1 level was higher in comparison with those in Sprague-Dawley (SD) rats. Other changes in the eyes of RCS rats include activated AKT/mTOR and ERK pathways and abnormal autophagy in the RPE cells. Such roles of miR-24 and CHI3L1 were further confirmed in RCS rats by subretinal injection of agomiR-24, which decreased CHI3L1 level and preserved retinal structure and function. Upstream, NF-κB was identified as the regulator of miR-24 in the RPE cells of these rats. On the other hand, in SD rats, intraocular treatment of antagomiR-24 induced pathological changes similar to those in RCS rats. The results revealed the protective roles for miR-24 to RPE cells and a mechanism for RD in RCS rats was proposed: extracellular stress stimuli first activate the NF-κB signaling pathway, which lowers miR-24 expression so that CHI3L1 increased. CHI3L1 sequentially results in aberrant autophagy and RPE dysfunction by activating AKT/mTOR and ERK pathways. Taken together, although the possibility, that the therapeutic effects in RCS rats are caused by other transcriptional changes regulated by miR-24, cannot be excluded, these findings indicate that miR-24 protects rat retina by targeting CHI3L1. Thus, miR-24 and CHI3L1 might be the targets for developing more effective therapy for degenerative retinal diseases like AMD.

Guidelines for evaluating myocardial cell death

Cell death is a fundamental process in cardiac pathologies. Recent studies have revealed multiple forms of cell death, and several of them have been demonstrated to underlie adverse cardiac remodeling and heart failure. With the expansion in the area of myocardial cell death and increasing concerns over rigor and reproducibility, it is important and timely to set a guideline for the best practices of evaluating myocardial cell death. There are six major forms of regulated cell death observed in cardiac pathologies, namely apoptosis, necroptosis, mitochondrial-mediated necrosis, pyroptosis, ferroptosis, and autophagic cell death. In this article, we describe the best methods to identify, measure, and evaluate these modes of myocardial cell death. In addition, we discuss the limitations of currently practiced myocardial cell death mechanisms.

Role of Endoplasmic Reticulum Stress-Autophagy Axis in Severe Burn-Induced Intestinal Tight Junction Barrier Dysfunction in Mice

Severe burn injury induces intestinal barrier dysfunction; however, the underlying mechanisms remain elusive. Our previous studies have shown that the intestinal epithelial tight junction (TJ) barrier dysfunction is associated with both endoplasmic reticulum (ER) stress and autophagy in severely burned mice, but the precise role of ER stress and autophagy in the burn-induced intestinal TJ barrier dysfunction needs to be determined. In this study, female C57/BL6 mice were assigned randomly to either sham burn or 30% total body surface area (TBSA) full-thickness burn. The effects of ER stress and autophagy on the intestinal epithelial TJ barrier were validated by inducing or inhibiting both ER stress and autophagy in mice treated with sham burn or burn injury. The intestinal permeability, expression, and localization of TJ proteins, ER stress, and autophagy were assessed by physiological, morphological, and biochemical analyses. The results showed that inducing ER stress with tunicamycin or thapsigargin caused the activation of autophagy, the increase of intestinal permeability, as well as the reduction and reorganization of TJ proteins in the sham-burned mice, and aggravated the burn-induced activation of autophagy, increase of intestinal permeability, as well as the reduction and reorganization of TJ proteins. In contrast, inhibiting ER stress with 4-phenylbutyrate alleviated the burn-induced activation of autophagy, increase of intestinal permeability, as well as the reduction and reorganization of TJ proteins. In addition, inducing autophagy with rapamycin resulted in the increase of intestinal permeability, as well as the reduction and reorganization of TJ proteins in the sham-burned mice, and aggravated the burn-induced increase of intestinal permeability as well as the reduction and reorganization of TJ proteins. However, inhibiting autophagy with 3-methyladenine attenuated the burn-induced increase of intestinal permeability, as well as the reduction and reorganization TJ proteins. It is suggested that the ER stress-autophagy axis contributes to the intestinal epithelial TJ barrier dysfunction after severe burn injury.

Disruption of embryonic ROCK signaling reproduces the sarcomeric phenotype of hypertrophic cardiomyopathy

Sarcomeric disarray is a hallmark of gene mutations in patients with hypertrophic cardiomyopathy (HCM). However, it is unknown when detrimental sarcomeric changes first occur and whether they originate in the developing embryonic heart. Furthermore, Rho kinase (ROCK) is a serine/threonine protein kinase that is critical for regulating the function of several sarcomeric proteins, and therefore, our aim was to determine whether disruption of ROCK signaling during the earliest stages of heart development would disrupt the integrity of sarcomeres, altering heart development and function. Using a mouse model in which the function of ROCK is specifically disrupted in embryonic cardiomyocytes, we demonstrate a progressive cardiomyopathy that first appeared as sarcomeric disarray during cardiogenesis. This led to abnormalities in the structure of the embryonic ventricular wall and compensatory cardiomyocyte hypertrophy during fetal development. This sarcomeric disruption and hypertrophy persisted throughout adult life, triggering left ventricular concentric hypertrophy with systolic dysfunction, and reactivation of fetal gene expression and cardiac fibrosis, all typical features of HCM. Taken together, our findings establish a mechanism for the developmental origin of the sarcomeric phenotype of HCM and suggest that variants in the ROCK genes or disruption of ROCK signaling could, in part, contribute to its pathogenesis.

Disruption of ROCK activity in embryonic cardiomyocytes revealed a developmental origin for hypertrophic cardiomyopathy.

Pinocembrin induces ER stress mediated apoptosis and suppresses autophagy in melanoma cells

Melanoma, one of the toughest tumors to treat, features high metastasis and high lethality. Pinocembrin is a natural flavanone with versatile biological and pharmacological activities. Here, we evaluated the anti-tumor effects of pinocembrin against melanoma in vitro and in vivo. In vitro, pinocembrin inhibited the proliferation of melanoma cells (B16F10 and A375) in a dose-dependent manner. It induced endoplasmic reticulum stress via IRE1α/Xbp1 pathway and triggered caspase-12/-4 mediated apoptosis in both cell lines. Furthermore, we discovered that pinocembrin suppressed autophagy through the activation of PI3K/Akt/mTOR pathway, which serves as a dual mechanism to enhance the pro-death effect of pinocembrin. In vivo, pinocembrin inhibited the growth of B16F10 by inducing apoptosis. Taken together, our results demonstrated that pinocembrin can induce ER stress mediated apoptosis and suppress autophagy in melanoma, indicating its application potential for melanoma therapy.

Tongguan Capsule Mitigates Post-myocardial Infarction Remodeling by Promoting Autophagy and Inhibiting Apoptosis: Role of Sirt1

Left ventricular (LV) adverse remodeling and the concomitant functional deterioration contributes to the poor prognosis of patients with myocardial infarction (MI). Thus, a more effective treatment strategy is needed. Tongguan capsule (TGC), a patented Chinese medicine, has been shown to be cardioprotective in both humans and animals following ischemic injury, although its precise mechanism remains unclear. To investigate whether TGC can improve cardiac remodeling in the post-infarct heart, adult C57/BL6 mice underwent coronary artery ligation and were administered TGC or vehicle (saline) for 6 weeks. The results demonstrated that the TGC group showed significant improvement in survival ratio and cardiac function and structure as compared to the vehicle group. Histological and western blot analyses revealed decreased cellular inflammation and apoptosis in cardiomyocytes of the TGC group. Furthermore, TGC upregulated the Atg5 expression and LC3II-to-LC3I ratio but downregulated autophagy adaptor p62 expression, suggesting that TGC led to increased autophagic flux. Interestingly, with the administration of 3-methyladenine, an autophagy inhibitor, in conjunction with TGC, the aforesaid effects significantly decreased. Further mechanistic studies revealed that TGC increased silent information regulator 1 (Sirt1) expression to reduce the phosphorylation of the mammalian target of rapamycin and its downstream effectors P70S6K and 4EBP1. Moreover, the induction of Sirt1 by TGC was inhibited by the specific inhibitor EX527. In the presence of EX527, TGC-induced autophagy-specific proteins were downregulated, while apoptotic and inflammatory factors were upregulated. In summary, our results demonstrate that TGC improved cardiac remodeling in a murine model of MI by preventing cardiomyocyte inflammation and apoptosis but enhancing autophagy through Sirt1 activation.

Severe Burn-Induced Intestinal Epithelial Barrier Dysfunction Is Associated With Endoplasmic Reticulum Stress and Autophagy in Mice

The disruption of intestinal barrier plays a vital role in the pathophysiological changes after severe burn injury, however, the underlying mechanisms are poorly understood. Severe burn causes the disruption of intestinal tight junction (TJ) barrier. Previous studies have shown that endoplasmic reticulum (ER) stress and autophagy are closely associated with the impairment of intestinal mucosa. Thus, we hypothesize that ER stress and autophagy are likely involved in burn injury-induced intestinal epithelial barrier dysfunction. Mice received a 30% total body surface area (TBSA) full-thickness burn, and were sacrificed at 0, 1, 2, 6, 12 and 24 h postburn. The results showed that intestinal permeability was increased significantly after burn injury, accompanied by the damage of mucosa and the alteration of TJ proteins. Severe burn induced ER stress, as indicated by increased intraluminal chaperone binding protein (BIP), CCAAT/enhancer-binding protein homologous protein (CHOP) and inositol-requiring enzyme 1(IRE1)/X-box binding protein 1 splicing (XBP1). Autophagy was activated after burn injury, as evidenced by the increase of autophagy related protein 5 (ATG5), Beclin 1 and LC3II/LC3I ratio and the decrease of p62. Besides, the number of autophagosomes was also increased after burn injury. The levels of p-PI3K(Ser191), p-PI3K(Ser262), p-AKT(Ser473), and p-mTOR were decreased postburn, suggesting that autophagy-related PI3K/AKT/mTOR pathway is involved in the intestinal epithelial barrier dysfunction following severe burn. In summary, severe burn injury induces the ER stress and autophagy in intestinal epithelia, leading to the disruption of intestinal barrier.

A peptide derived from apoptin inhibits glioma growth

Glioblastoma (GBM) is associated with poor prognosis due to its resistance to surgery, irradiation, and conventional chemotherapy. Thus, efficient therapeutic approaches for the treatment of GBM are urgently needed. HSP70 is an antiapoptotic protein that participates in the inhibition of both mitochondrial and membrane receptor apoptosis pathways and is highly expressed in glioma tissues. Here, we investigated a derivative of apoptin; specifically, a chicken anemia viral protein with selective toxicity toward cancer cells that can inhibit hyperactive molecules, including HSP70. Our earlier studies demonstrated that apoptin directly binds to the promoter of HSP70 and inhibits HSP70 transcription, which contributes to HSP70 downregulation. This study provides the first demonstration of the therapeutic potential of an apoptin-derived peptide for the treatment of GBM by identifying the minimal region of the apoptin domain required for interaction with the heat-shock element (HSE). This apoptin-derived peptide (ADP) inhibits glioma cell proliferation and tumor growth as well as exhibits an increased ability to promote apoptosis in GBM cells compared with rapamycin and temozolomide. ADP treatment inhibited xenograft tumor growth and increased the overall health and survival of nude mice implanted with GBM cells. These effects were measured in tumors obtained from cell lines and were observed in both intracranial and subcutaneous xenografts. In conclusion, we provide the first demonstration that ADP has therapeutic potential for the treatment of human GBM. Specifically, this study suggests that ADP is a potent candidate for drug development based on its favorable toxicity and pharmacokinetic profiles as well as its time- and cost-saving benefits.

Signaling mediators modulated by cardioprotective interventions in healthy and diabetic myocardium with ischaemia-reperfusion injury

Ischaemic heart diseases are one of the major causes of death in the world. In most patients, ischaemic heart disease is coincident with other risk factors such as diabetes. Patients with diabetes are more prone to cardiac ischaemic dysfunctions including ischaemia-reperfusion injury. Ischaemic preconditioning, postconditioning and remote conditionings are reliable interventions to protect the myocardium against ischaemia-reperfusion injuries through activating various signaling pathways and intracellular mediators. Diabetes can disrupt the intracellular signaling cascades involved in these myocardial protections, and studies have revealed that cardioprotective effects of the conditioning interventions are diminished in the diabetic condition. The complex pathophysiology and poor prognosis of ischaemic heart disease among people with diabetes necessitate the investigation of the interaction of diabetes with ischaemia-reperfusion injury and cardioprotective mechanisms. Reducing the outcomes of ischaemia-reperfusion injury using targeted strategies would be particularly helpful in this population. In this study, we review the protective interventional signaling pathways and mediators which are activated by ischaemic conditioning strategies in healthy and diabetic myocardium with ischaemia-reperfusion injury.

Inhibition of autophagy by berberine enhances the survival of H9C2 myocytes following hypoxia

Hypoxia may induce apoptosis and autophagy to promote cardiomyocyte injury. The present study investigated the effect of berberine, a natural extract of Rhizoma Coptidis, on hypoxia‑induced autophagy and apoptosis in the H9c2 rat myocardial cell line. Expression levels of apoptosis and autophagy markers were upregulated in H9c2 myocytes during hypoxia and cell viability was reduced. However, berberine significantly reduced hypoxia‑induced autophagy in H9c2 myocytes, as demonstrated by the ratio of microtubule‑associated proteins 1A/1B light chain 3 I/II and the expression levels of B‑cell lymphoma 2 (Bcl‑2)/adenovirus E1B 19 kDa protein‑interacting protein 3, and promoted cell viability. In addition, expression levels of the Bcl‑2 anti‑apoptotic protein were significantly downregulated, and expression levels of pro‑apoptotic proteins Bcl‑2‑associated X protein and cleaved caspase‑3 were upregulated during hypoxia injury in cardiac myocytes. This was reversed by treatment with berberine or the autophagy inhibitor 3‑methyladenine, whereas the autophagy agonist rapamycin had the opposite effects, suggesting that berberine reduces myocyte cell death via inhibition of autophagy and apoptosis during hypoxia. In addition, Compound C, a 5' adenosine monophosphate‑activated protein kinase (AMPK) inhibitor, reduced apoptosis and autophagy in hypoxic myocytes, suggesting that the activation of the AMPK signaling pathway may be involved in this process. These findings suggested that berberine protects cells from hypoxia‑induced apoptosis via inhibition of autophagy and suppression of AMPK activation. Therefore, berberine may be a potential therapeutic agent for the treatment of patients with cardiac myocyte injury and ischemia.

Moderate therapeutic hypothermia induces multimodal protective effects in oxygen-glucose deprivation/reperfusion injured cardiomyocytes

OBJECTIVE

Therapeutic hypothermia has been shown to attenuate myocardial cell death due to ischemia/reperfusion injury. However, cellular mechanisms of cooling remain to be elucidated. Especially during reperfusion, mitochondrial dysfunction contributes to cell death by releasing apoptosis inductors. The aim of the present study was to investigate the effects of moderate therapeutic hypothermia (33.5°C) on mitochondrial mediated apoptosis in ischemia/reperfusion-injured cardiomyocytes.

METHODS

Ischemic injury was simulated by oxygen-glucose deprivation for 6h in glucose/serum-free medium at 0.2% O₂ in mouse atrial HL-1 cardiomyocytes. Simulation of reperfusion was achieved by restoration of nutrients in complete supplemented medium and incubation at 21% O₂. Early application of therapeutic hypothermia, cooling during the oxygen-glucose deprivation phase, was initiated after 3h of oxygen-glucose deprivation and maintained for 24h. Mitochondrial membrane integrity was assessed by cytochrome c and AIF protein releases. Furthermore, mitochondria were stained with MitoTracker Red and intra-cellular cytochrome c localization was visualized by immunofluorescence staining. Moreover, anti-apoptotic Bcl-2 and Hsp70 as well as phagophore promoting LC3-II protein expressions were analyzed by Western-blot analysis.

RESULTS

Therapeutic hypothermia initiated during oxygen-glucose deprivation significantly reduced mitochondrial release of cytochrome c and AIF in cardiomyocytes during reperfusion. Secondly, anti-apoptotic Bcl-2/Bax ratio and Hsp70 protein expressions were significantly upregulated due to hypothermia, indicating an inhibition of both caspase-dependent and -independent apoptosis. Furthermore, cardiomyocytes treated with therapeutic hypothermia showed increased LC3-II protein levels associated with the mitochondria during the first 3h of reperfusion, indicating the initiation of phagophores formation and sequestration of presumably damaged mitochondrion.

CONCLUSION

Early application of therapeutic hypothermia effectively inhibited cardiomyocyte cell death due to oxygen-glucose deprivation/reperfusion-induced injury via multiple pathways. As hypothermia preserved mitochondrial membrane integrity, which resulted in reduced cytochrome c and AIF releases, induction of both caspase-dependent and -independent apoptosis was minimized. Secondly, cooling attenuated intrinsic apoptosis via Hsp70 upregulation and increasing anti-apoptotic Bcl-2/Bax ratio. Moreover, therapeutic hypothermia promoted mitochondrial associated LC3-II during the early phase of reperfusion, possibly leading to the sequestration and degradation of damaged mitochondrion to attenuate the activation of cell death.

Insulin-like growth factor 1 receptor-mediated cell survival in hypoxia depends on the promotion of autophagy via suppression of the PI3K/Akt/mTOR signaling pathway

Hypoxia is widely accepted as a fundamental biological phenomenon, which is strongly associated with tissue damage and cell viability under stress conditions. Insulin-like growth factor-1 (IGF-1) is known to protect tissues from multiple types of damage, and protect cells from apoptosis. Hypoxia is a regulatory factor of the IGF system, however the role of the IGF-1 receptor (IGF-1R) in hypoxia-induced apoptosis remains unclear. The present study investigated the potential mechanisms associated with IGF-1R-associated apoptosis under hypoxic conditions. Mouse embryonic fibroblasts exhibiting disruption or overexpression of IGF-1R (R- cells and R+ cells) were used to examine the level of apoptosis, autophagy, and production of reactive oxygen species (ROS). The autophagy inhibitor 3-methyladenine was used to assess the effect of autophagy on ROS production and apoptosis under hypoxic conditions. A potential downstream signaling pathway involving phosphatidylinositol 3-kinase (PI3K)/threonine protein kinase B (Akt)/mammalian target of rapamycin (mTOR) was identifiedby western blot analysis. The results demonstrated that hypoxia induced apoptosis, increased ROS production, and promoted autophagy in a time-dependent manner relative to that observed under normoxia. R+ cells exhibited a lower percentage of apoptotic cells, lower ROS production, and higher levels of autophagy when compared to that of R- cells. In addition, inhibition of autophagy led to increased ROS production and a higher percentage of apoptotic cells in the two cell types. Furthermore, IGF-1R is related with PI3K/Akt/mTOR signaling pathway and enhanced autophagy-associated protein expression, which was verified following treatment with the PI3K inhibitor LY294002. These results indicated that IGF-1R may increase cell viability under hypoxic conditions by promoting autophagy and scavenging ROS production, which is closed with PI3K/Akt/mTOR signaling pathway.

Cardiac ubiquitin ligases: Their role in cardiac metabolism, autophagy, cardioprotection and therapeutic potential

Both the ubiquitin-proteasome system (UPS) and the lysosomal autophagy system have emerged as complementary key players responsible for the turnover of cellular proteins. The regulation of protein turnover is critical to cardiomyocytes as post-mitotic cells with very limited regenerative capacity. In this focused review, we describe the emerging interface between the UPS and autophagy, with E3's regulating autophagy at two critical points through multiple mechanisms. Moreover, we discuss recent insights in how both the UPS and autophagy can alter metabolism at various levels, to present new ways to think about therapeutically regulating autophagy in a focused manner to optimize disease-specific cardioprotection, without harming the overall homeostasis of protein quality control. This article is part of a Special Issue entitled: The role of post-translational protein modifications on heart and vascular metabolism edited by Jason R.B. Dyck & Jan F.C. Glatz.

Licochalcone A induces autophagy through PI3K/Akt/mTOR inactivation and autophagy suppression enhances Licochalcone A-induced apoptosis of human cervical cancer cells

The use of dietary bioactive compounds in chemoprevention can potentially reverse, suppress, or even prevent cancer progression. However, the effects of licochalcone A (LicA) on apoptosis and autophagy in cervical cancer cells have not yet been clearly elucidated. In this study, LicA treatment was found to significantly induce the apoptotic and autophagic capacities of cervical cancer cells in vitro and in vivo. MTT assay results showed dose- and time-dependent cytotoxicity in four cervical cancer cell lines treated with LicA. We found that LicA induced mitochondria-dependent apoptosis in SiHa cells, with decreasing Bcl-2 expression. LicA also induced autophagy effects were examined by identifying accumulation of Atg5, Atg7, Atg12 and microtubule-associated protein 1 light chain 3 (LC3)-II. Treatment with autophagy-specific inhibitors (3-methyladenine and bafilomycin A1) enhanced LicA-induced apoptosis. In addition, we suggested the inhibition of phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of mTOR pathway by LicA. Furthermore, the inhibition of PI3K/Akt by LY294002/si-Akt or of mTOR by rapamycin augmented LicA-induced apoptosis and autophagy. Finally, the in vivo mice bearing a SiHa xenograft, LicA dosed at 10 or 20 mg/kg significantly inhibited tumor growth. Our findings demonstrate the chemotherapeutic potential of LicA for treatment of human cervical cancer.

Regulation of cardiomyocyte autophagy by calcium

Calcium signaling plays a crucial role in a multitude of events within the cardiomyocyte, including cell cycle control, growth, apoptosis, and autophagy. With respect to calcium-dependent regulation of autophagy, ion channels and exchangers, receptors, and intracellular mediators play fundamental roles. In this review, we discuss calcium-dependent regulation of cardiomyocyte autophagy, a lysosomal mechanism that is often cytoprotective, serving to defend against disease-related stress and nutrient insufficiency. We also highlight the importance of the subcellular distribution of calcium and related proteins, interorganelle communication, and other key signaling events that govern cardiomyocyte autophagy.

Inside the biochemical pathways of thymidylate synthase perturbed by anticancer drugs: Novel strategies to overcome cancer chemoresistance

Our current understanding of the mechanisms of action of antitumor agents and the precise mechanisms underlying drug resistance is that these two processes are directly linked. Moreover, it is often possible to delineate chemoresistance mechanisms based on the specific mechanism of action of a given anticancer drug. A more holistic approach to the chemoresistance problem suggests that entire metabolic pathways, rather than single enzyme targets may better explain and educate us about the complexity of the cellular responses upon cytotoxic drug administration. Drugs, which target thymidylate synthase and folate-dependent enzymes, represent an important therapeutic arm in the treatment of various human malignancies. However, prolonged patient treatment often provokes drug resistance phenomena that render the chemotherapeutic treatment highly ineffective. Hence, strategies to overcome drug resistance are primarily designed to achieve either enhanced intracellular drug accumulation, to avoid the upregulation of folate-dependent enzymes, and to circumvent the impairment of DNA repair enzymes which are also responsible for cross-resistance to various anticancer drugs. The current clinical practice based on drug combination therapeutic regimens represents the most effective approach to counteract drug resistance. In the current paper, we review the molecular aspects of the activity of TS-targeting drugs and describe how such mechanisms are related to the emergence of clinical drug resistance. We also discuss the current possibilities to overcome drug resistance by using a molecular mechanistic approach based on medicinal chemistry methods focusing on rational structural modifications of novel antitumor agents. This paper also focuses on the importance of the modulation of metabolic pathways upon drug administration, their analysis and the assessment of their putative roles in the networks involved using a meta-analysis approach. The present review describes the main pathways that are modulated by TS-targeting anticancer drugs starting from the description of the normal functioning of the folate metabolic pathway, through the protein modulation occurring upon drug delivery to cultured tumor cells as well as cancer patients, finally describing how the pathways are modulated by drug resistance development. The data collected are then analyzed using network/netwire connecting methods in order to provide a wider view of the pathways involved and of the importance of such information in identifying additional proteins that could serve as novel druggable targets for efficacious cancer therapy.

Influence of partial and complete glutamine-and glucose deprivation of breast-and cervical tumorigenic cell lines

BACKGROUND

Due to their high proliferative requirements, tumorigenic cells possess altered metabolic systems whereby cells utilize higher quantities of glutamine and glucose. These altered metabolic requirements make it of interest to investigate the effects of physiological non-tumorigenic concentrations of glucose and glutamine on tumorigenic cells since deprivation of either results in a canonical amino acid response in mammalian cell.

METHODS

The influence of short-term exposure of tumorigenic cells to correlating decreasing glutamine- and glucose quantities were demonstrated in a highly glycolytic metastatic breast cell line and a cervical carcinoma cell line. Thereafter, cells were propagated in medium containing typical physiological concentrations of 1 mM glutamine and 6 mM glucose for 7 days. The effects on morphology were investigated by means of polarization-optical transmitted light differential interference contrast. Flow cytometry was used to demonstrate the effects of glutamine-and glucose starvation on cell cycle progression and apoptosis induction. Fluorometrics were also conducted to investigate the effects on intrinsic apoptosis induction (mitocapture), reactive oxygen species production (2,7-dichlorofluorescein diacetate) and acidic vesicle formation (acridine orange).

RESULTS

Morphological data suggests that glutamine-and glucose deprivation resulted in reduced cell density and rounded cells. Glutamine-and glucose starvation also resulted in an increase in the G2M phase and a sub-G1 peak. Complete starvation of glutamine and glucose resulted in the reduction of the mitochondrial membrane potential in both cell lines with MDA-MB-231 cells more prominently affected when compared to HeLa cells. Further, starved cells could not be rescued sufficiently by propagating since cells possessed an increase in reactive oxygen species, acidic compartments and vacuole formation.

CONCLUSION

Starvation from glutamine and glucose for short periods resulted in decreased cell density, rounded cells and apoptosis induction by means of reactive oxygen species generation and mitochondrial dysfunction. In addition, the metastatic cell line reacted more prominently to glutamine-and glucose starvation due to their highly glycolytic nature. Satisfactory cellular rescue was not possible as cells demonstrated oxidative stress and depolarized mitochondrial membrane potential. This study contributes to the knowledge regarding the in vitro effects and signal transduction of glucose and/or l-glutamine deprivation in tumorigenic cell lines.

Pharmacological modulation of autophagy to protect cardiomyocytes according to the time windows of ischaemia/reperfusion

BACKGROUND AND PURPOSE

Targeted modulation of autophagy induced by myocardial ischaemia/reperfusion has been the subject of intensive investigation, but it is debatable whether autophagy is beneficial or harmful. Hence, we evaluated the effects of pharmacological manipulation of autophagy on the survival of cardiomyocytes in different time windows of ischaemia/reperfusion.

EXPERIMENTAL APPROACH

We examined the autophagy and apoptosis in cardiomyocytes subjected to different durations of anoxia/re-oxygenation or ischaemia/reperfusion, and evaluated the effects of the autophagic enhancer rapamycin and inhibitor wortmannin on cell survival.

KEY RESULTS

In neonatal rat cardiomyocytes (NRCs) or murine hearts, autophagy was increased in response to anoxia/reoxygenation or ischaemia/reperfusion in a time-dependent manner. Rapamycin-enhanced autophagy in NRCs led to higher cell viability and less apoptosis when anoxia was sustained for ≦ 6 h. When anoxia was prolonged to 12 h, rapamycin did not increase cell viability, induced less apoptosis and more autophagic cell death. When anoxia was prolonged to 24 h, rapamycin increased autophagic cell death, while wortmannin reduced autophagic cell death and apoptosis. Similar results were obtained in mice subjected to ischaemia/reperfusion. Rapamycin inhibited the opening of mitochondrial transition pore in NRCs exposed to 6 h anoxia/4 h re-oxygenation but did not exert any effect when anoxia was extended to 24 h. Similarly, rapamycin reduced the myocardial expression of Bax in mice subjected to short-time ischaemia, but this effect disappeared when ischaemia was extended to 24 h.

CONCLUSIONS AND IMPLICATIONS

The cardioprotection of autophagy is context-dependent and therapies involving the modification of autophagy should be determined according to the duration of ischaemia/reperfusion.

Circulating MicroRNA Profiles Differ between Qi-Stagnation and Qi-Deficiency in Coronary Heart Disease Patients with Blood Stasis Syndrome

We compared the circulating microRNA profiles of Qi-stagnation (QSB) and Qi-deficiency (QDB) in coronary heart disease (CHD) patients with blood stasis syndrome. Twenty-nine CHD patients were divided into QSB group and QDB group. The analysis was carried out through comparing their circulating microRNA profiles and the following bioinformatics analysis. The number of differential miRNAs in QDB group was much more than that in QSB group. Functional annotations of the differentially expressed miRNAs target genes in the QSB group and QDB group were, respectively, related to regulation of cellular component organization, regulation of glucose metabolic process, and so forth and protein kinase cascade, phosphate metabolic process, and so forth. KEGG pathway analysis showed that the process Qi-deficiency was associated with phagocytosis including endocytosis and mTOR signaling pathway. Specifically, pathway of cell adhesion molecules played the crucial role in the pathological process of Qi-stagnation, with a unique upregulation except for pathways associated with cancer signal. MicroRNA-gene-net analysis indicated that let-7c, miR-4487, miR-619, miR-8075, miR-6735, and miR-32-5p and miR-17-5p, miR-130a, and miR 320 family had the most important and extensive regulatory function for Qi-stagnation syndromes and Qi-deficiency syndromes, respectively. Differentially expressed miRNAs and concerned pathways suggest different molecular mechanisms that may mediate the pathological process of QSB and QDB syndromes.

Apoptins: selective anticancer agents

Therapies that selectively target cancer cells for death have been the center of intense research recently. One potential therapy may involve apoptin proteins, which are able to induce apoptosis in cancer cells leaving normal cells unharmed. Apoptin was originally discovered in the Chicken anemia virus (CAV); however, human gyroviruses (HGyV) have recently been found that also harbor apoptin-like proteins. Although the cancer cell specific activity of these apoptins appears to be well conserved, the precise functions and mechanisms of action are yet to be fully elucidated. Strategies for both delivering apoptin to treat tumors and disseminating the protein inside the tumor body are now being developed, and have shown promise in preclinical animal studies.

Differential effects of LY294002 and wortmannin on neurons and vascular endothelial cells in the rat retina

BACKGROUND

Neuronal damage leads to capillary degeneration in an N-methyl-D-aspartate (NMDA)-induced retinal degeneration model; however, the mechanisms underlying this phenomenon are not fully understood. The phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway has been recognized as an intracellular pro-survival signaling system. Therefore, we used the PI3K inhibitors LY294002 and wortmannin to investigate the role of this pathway in neuronal and blood vessel injury in the rat retina treated with NMDA.

METHODS

Male Sprague-Dawley rats weighing 220-240 g were used in this study. NMDA combined with LY294002, wortmannin, or vehicle was administered intravitreally, and histological evaluation was performed at 2 and 7 days after injection. The effects of LY294002 or wortmannin alone were also evaluated.

RESULTS

The number of cells in the ganglion cell layer (GCL) was significantly reduced at 2 and 7 days after intravitreal injection of NMDA, whereas enhanced capillary degeneration was observed at 7 days. Simultaneous injection of LY294002 with NMDA significantly attenuated NMDA-induced retinal cell loss and capillary degeneration at 7 days. However, simultaneous injection of wortmannin with NMDA did not affect cell loss, but enhanced capillary degeneration. Treatment with LY294002 alone showed no effect on neuronal or vascular cells, whereas wortmannin induced capillary degeneration without significantly affecting the cell number in the GCL.

CONCLUSIONS

Although both LY294002 and wortmannin are known as PI3K inhibitors, they exhibit differential effects on neurons and vascular endothelial cells in the rat retina. Therefore, the results obtained using these inhibitors should be carefully interpreted. However, our finding that LY294002 was protective against NMDA-induced retinal damage suggests that this compound may be an effective candidate for preventing the development of retinal diseases associated with glutamate-induced excitotoxicity.

Pemetrexed induces S-phase arrest and apoptosis via a deregulated activation of Akt signaling pathway

Pemetrexed is approved for first-line and maintenance treatment of patients with advanced or metastatic non-small-cell lung cancer (NSCLC). The protein kinase Akt/protein kinase B is a well-known regulator of cell survival which is activated by pemetrexed, but its role in pemetrexed-mediated cell death and its molecular mechanisms are unclear. This study showed that stimulation with pemetrexed induced S-phase arrest and cell apoptosis and a parallel increase in sustained Akt phosphorylation and nuclear accumulation in the NSCLC A549 cell line. Inhibition of Akt expression by Akt specific siRNA blocked S-phase arrest and protected cells from apoptosis, indicating an unexpected proapoptotic role of Akt in the pemetrexed-mediated toxicity. Treatment of A549 cells with pharmacological inhibitors of phosphatidylinositol 3-kinase (PI₃K), wortmannin and Ly294002, similarly inhibited pemetrexed-induced S-phase arrest and apoptosis and Akt phosphorylation, indicating that PI₃K is an upstream mediator of Akt and is involved in pemetrexed-mediated cell death. Previously, we identified cyclin A-associated cyclin-dependent kinase 2 (Cdk2) as the principal kinase that was required for pemetrexed-induced S-phase arrest and apoptosis. The current study showed that inhibition of Akt function and expression by pharmacological inhibitors as well as Akt siRNA drastically inhibited cyclin A/Cdk2 activation. These pemetrexed-mediated biological and molecular events were also observed in a H1299 cell line. Overall, our results indicate that, in contrast to its normal prosurvival role, the activated Akt plays a proapoptotic role in pemetrexed-mediated S-phase arrest and cell death through a mechanism that involves Cdk2/cyclin A activation.

Reciprocal regulation of autophagy and dNTP pools in human cancer cells

Ribonucleotide reductase (RNR) plays a critical role in catalyzing the biosynthesis and maintaining the intracellular concentration of 4 deoxyribonucleoside triphosphates (dNTPs). Unbalanced or deficient dNTP pools cause serious genotoxic consequences. Autophagy is the process by which cytoplasmic constituents are degraded in lysosomes to maintain cellular homeostasis and bioenergetics. However, the role of autophagy in regulating dNTP pools is not well understood. Herein, we reported that starvation- or rapamycin-induced autophagy was accompanied by a decrease in RNR activity and dNTP pools in human cancer cells. Furthermore, downregulation of the small subunit of RNR (RRM2) by siRNA or treatment with the RNR inhibitor hydroxyurea substantially induced autophagy. Conversely, cancer cells with abundant endogenous intracellular dNTPs or treated with dNTP precursors were less responsive to autophagy induction by rapamycin, suggesting that autophagy and dNTP pool levels are regulated through a negative feedback loop. Lastly, treatment with si-RRM2 caused an increase in MAP1LC3B, ATG5, BECN1, and ATG12 transcript abundance in xenografted Tu212 tumors in vivo. Together, our results revealed a previously unrecognized reciprocal regulation between dNTP pools and autophagy in cancer cells.

Akt and mTOR mediate programmed necrosis in neurons

Necroptosis is a newly described form of regulated necrosis that contributes to neuronal death in experimental models of stroke and brain trauma. Although much work has been done elucidating initiating mechanisms, signaling events governing necroptosis remain largely unexplored. Akt is known to inhibit apoptotic neuronal cell death. Mechanistic target of rapamycin (mTOR) is a downstream effector of Akt that controls protein synthesis. We previously reported that dual inhibition of Akt and mTOR reduced acute cell death and improved long term cognitive deficits after controlled-cortical impact in mice. These findings raised the possibility that Akt/mTOR might regulate necroptosis. To test this hypothesis, we induced necroptosis in the hippocampal neuronal cell line HT22 using concomitant treatment with tumor necrosis factor α (TNFα) and the pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone. TNFα/zVAD treatment induced cell death within 4 h. Cell death was preceded by RIPK1–RIPK3–pAkt assembly, and phosphorylation of Thr-308 and Thr473 of AKT and its direct substrate glycogen synthase kinase-3β, as well as mTOR and its direct substrate S6 ribosomal protein (S6), suggesting activation of Akt/mTOR pathways. Pretreatment with Akt inhibitor viii and rapamycin inhibited Akt and S6 phosphorylation events, mitochondrial reactive oxygen species production, and necroptosis by over 50% without affecting RIPK1–RIPK3 complex assembly. These data were confirmed using small inhibitory ribonucleic acid-mediated knockdown of AKT1/2 and mTOR. All of the aforementioned biochemical events were inhibited by necrostatin-1, including Akt and mTOR phosphorylation, generation of oxidative stress, and RIPK1–RIPK3–pAkt complex assembly. The data suggest a novel, heretofore unexpected role for Akt and mTOR downstream of RIPK1 activation in neuronal cell death.

Inhibition of 6-phosphofructo-2-kinase (PFKFB3) induces autophagy as a survival mechanism

Background

Unlike glycolytic enzymes that directly catabolize glucose to pyruvate, the family of 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatases (PFKFBs) control the conversion of fructose-6-phosphate to and from fructose-2,6-bisphosphate, a key regulator of the glycolytic enzyme phosphofructokinase-1 (PFK-1). One family member, PFKFB3, has been shown to be highly expressed and activated in human cancer cells, and derivatives of a PFKFB3 inhibitor, 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO), are currently being developed in clinical trials. However, the effectiveness of drugs such as 3PO that target energetic pathways is limited by survival pathways that can be activated by reduced ATP and nutrient uptake. One such pathway is the process of cellular self-catabolism termed autophagy. We hypothesized that the functional glucose starvation induced by inhibition of PFKFB3 in tumor cells would induce autophagy as a pro-survival mechanism and that inhibitors of autophagy could increase the anti-tumor effects of PFKFB3 inhibitors.

Results

We found that selective inhibition of PFKFB3 with either siRNA transfection or 3PO in HCT-116 colon adenocarcinoma cells caused a marked decrease in glucose uptake simultaneously with an increase in autophagy based on LC3-II and p62 protein expression, acridine orange fluorescence of acidic vacuoles and electron microscopic detection of autophagosomes. The induction of autophagy caused by PFKFB3 inhibition required an increase in reactive oxygen species since N-acetyl-cysteine blocked both the conversion of LC3-I to LC3-II and the increase in acridine orange fluorescence in acidic vesicles after exposure of HCT-116 cells to 3PO. We speculated that the induction of autophagy might protect cells from the pro-apoptotic effects of 3PO and found that agents that disrupt autophagy, including chloroquine, increased 3PO-induced apoptosis as measured by double staining with Annexin V and propidium iodide in both HCT-116 cells and Lewis lung carcinoma (LLC) cells. Chloroquine also increased the anti-growth effect of 3PO against LLCs in vivo and resulted in an increase in apoptotic cells within the tumors.

Conclusions

We conclude that PFKFB3 inhibitors suppress glucose uptake, which in turn causes an increase in autophagy. The addition of selective inhibitors of autophagy to 3PO and its more potent derivatives may prove useful as rational combinations for the treatment of cancer.

Activation of autophagy in ischemic postconditioning contributes to cardioprotective effects against ischemia/reperfusion injury in rat hearts

We tested the hypothesis that ischemic postconditioning (IPost) induces autophagy and the activation of autophagy contributes to the cardioprotective effects against ischemia/reperfusion injury in rat hearts. Rats were subjected to IPost established by 3 cycles of 10-second reperfusion followed by 10-second ischemia at the end of 30-minute ischemia. The activation of autophagy was assessed by the morphological and biochemical examinations after 120-minute reperfusion in ventricular tissue. To investigate the contribution of autophagy to IPost, the rats were pretreated with the autophagy inhibitor 3-methyl-adenine (3-MA). We found that IPost increased the formation of autophagic vacuoles, the autophagic-related protein levels of LC3-II, Beclin1, lysosome-associated membrane protein 2, and cathepsin D, and the mRNA level of LC3 and Beclin1 in the risk zone of the postconditioned hearts. Furthermore, 3-MA treatment significantly reversed the reduction effect of IPost on infarct volume, and in the meantime, inhibited the induction of LC3 and Beclin1. In addition, 3-MA treatment inhibited the antiapoptotic-related protein levels of Bcl-2 and increased the apoptotic-related protein levels of Bad. Taken together, these results indicate that the protective effects of IPost are associated with the activation of autophagy in rat hearts.

Insulin receptor substrate signaling suppresses neonatal autophagy in the heart

The induction of autophagy in the mammalian heart during the perinatal period is an essential adaptation required to survive early neonatal starvation; however, the mechanisms that mediate autophagy suppression once feeding is established are not known. Insulin signaling in the heart is transduced via insulin and IGF-1 receptors (IGF-1Rs). We disrupted insulin and IGF-1R signaling by generating mice with combined cardiomyocyte-specific deletion of Irs1 and Irs2. Here we show that loss of IRS signaling prevented the physiological suppression of autophagy that normally parallels the postnatal increase in circulating insulin. This resulted in unrestrained autophagy in cardiomyocytes, which contributed to myocyte loss, heart failure, and premature death. This process was ameliorated either by activation of mTOR with aa supplementation or by genetic suppression of autophagic activation. Loss of IRS1 and IRS2 signaling also increased apoptosis and precipitated mitochondrial dysfunction, which were not reduced when autophagic flux was normalized. Together, these data indicate that in addition to prosurvival signaling, insulin action in early life mediates the physiological postnatal suppression of autophagy, thereby linking nutrient sensing to postnatal cardiac development.

Glucose-starved cells do not engage in prosurvival autophagy

In response to nutrient shortage or organelle damage, cells undergo macroautophagy. Starvation of glucose, an essential nutrient, is thought to promote autophagy in mammalian cells. We thus aimed to determine the role of autophagy in cell death induced by glucose deprivation. Glucose withdrawal induces cell death that can occur by apoptosis (in Bax, Bak-deficient mouse embryonic fibroblasts or HeLa cells) or by necrosis (in Rh4 rhabdomyosarcoma cells). Inhibition of autophagy by chemical or genetic means by using 3-methyladenine, chloroquine, a dominant negative form of ATG4B or silencing Beclin-1, Atg7, or p62 indicated that macroautophagy does not protect cells undergoing necrosis or apoptosis upon glucose deprivation. Moreover, glucose deprivation did not induce autophagic flux in any of the four cell lines analyzed, even though mTOR was inhibited. Indeed, glucose deprivation inhibited basal autophagic flux. In contrast, the glycolytic inhibitor 2-deoxyglucose induced prosurvival autophagy. Further analyses indicated that in the absence of glucose, autophagic flux induced by other stimuli is inhibited. These data suggest that the role of autophagy in response to nutrient starvation should be reconsidered.

Impairment of autophagic flux promotes glucose reperfusion-induced neuro2A cell death after glucose deprivation

Hypoglycemia-induced brain injury is a common and serious complication of intensive insulin therapy experienced by Type 1 diabetic patients. We previously reported that hypoglycemic neuronal death is triggered by glucose reperfusion after hypoglycemia rather than as a simple result of glucose deprivation. However, the precise mechanism of neuronal death initiated by glucose reperfusion is still unclear. Autophagy is a self-degradation process that acts through a lysosome-mediated trafficking pathway to degrade and recycle intracellular components, thereby regulating metabolism and energy production. Recent studies suggest that autophagic and lysosomal dysfunction leads to abnormal protein degradation and deposition that may contribute to neuronal death. Here, we focused on the relationship between autophagy and lysosomal dysfunction in hypoglycemia-induced neuronal death. In neuronal cells, glucose reperfusion after glucose deprivation resulted in inhibition of autophagy, which may promote cell death. This cell death was accompanied with activation of caspase3 and the lysosomal proteases cathepsin B and D, which indicated impairment of autophagic flux. Taken together, these results suggest that interplay of autophagy, caspase3 activation and lysosomal proteases serve as a basis for neuronal death after hypoglycemia. Thus, we provide the molecular mechanism of neuronal death by glucose reperfusion and suggest some clues for therapeutic strategies to prevent hypoglycemia-induced neuronal death.

Heme oxygenase-1 prevents cardiac dysfunction in streptozotocin-diabetic mice by reducing inflammation, oxidative stress, apoptosis and enhancing autophagy

Heme oxygenase-1 (HO-1) has been implicated in cardiac dysfunction, oxidative stress, inflammation, apoptosis and autophagy associated with heart failure, and atherosclerosis, in addition to its recognized role in metabolic syndrome and diabetes. Numerous studies have presented contradictory findings about the role of HO-1 in diabetic cardiomyopathy (DCM). In this study, we explored the role of HO-1 in myocardial dysfunction, myofibril structure, oxidative stress, inflammation, apoptosis and autophagy using a streptozotocin (STZ)-induced diabetes model in mice systemically overexpressing HO-1 (Tg-HO-1) or mutant HO-1 (Tg-mutHO-1). The diabetic mouse model was induced by multiple peritoneal injections of STZ. Two months after injection, left ventricular (LV) function was measured by echocardiography. In addition, molecular biomarkers related to oxidative stress, inflammation, apoptosis and autophagy were evaluated using classical molecular biological/biochemical techniques. Mice with DCM exhibited severe LV dysfunction, myofibril structure disarray, aberrant cardiac oxidative stress, inflammation, apoptosis, autophagy and increased levels of HO-1. In addition, we determined that systemic overexpression of HO-1 ameliorated left ventricular dysfunction, myofibril structure disarray, oxidative stress, inflammation, apoptosis and autophagy in DCM mice. Furthermore, serine/threonine-specific protein kinase (Akt) and AMP-activated protein kinase (AMPK) phosphorylation is normally inhibited in DCM, but overexpression of the HO-1 gene restored the phosphorylation of these kinases to normal levels. In contrast, the functions of HO-1 in DCM were significantly reversed by overexpression of mutant HO-1. This study underlines the unique roles of HO-1, including the inhibition of oxidative stress, inflammation and apoptosis and the enhancement of autophagy, in the pathogenesis of DCM.

Transplanted induced pluripotent stem cells mitigate oxidative stress and improve cardiac function through the Akt cell survival pathway in diabetic cardiomyopathy

Recent evidence suggests transplanted stem cells improve left ventricular function in diabetic induced cardiomyopathy (DICM). However, little is known about the mechanisms by which induced pluripotent stem (iPS) cells or factors released from these cells inhibit adverse cardiac remodeling in DICM. The present study was designed to determine molecular mediators and pathways regulated by transplanted iPS cells and their conditioned media (CM) in DICM. Animals were divided into four experimental groups such as control, streptozotocin (STZ), STZ+iPS-CM, and STZ+iPS cells. Experimental diabetes was induced in C57BL/6 mice by intraperitoneal STZ injections (100 mg/kg body weight for 2 consecutive days). Following STZ injections, iPS cells or CM was given intravenously for 3 consecutive days. Animals were humanely killed, and hearts were harvested at D14. Animals transplanted with iPS cells or CM demonstrated a significant reduction in apoptosis, mediated by Akt upregulation and ERK1/2 downregulation, and inhibition of interstitial fibrosis via MMP-9 suppression compared with the STZ group. Oxidative stress was significantly hindered in iPS cell and CM groups as evidenced by diminished pro-oxidant expression and enhanced antioxidant (catalase and MnSOD) concentration. Echocardiography data suggest a significant improvement in cardiac function in cells and CM groups in comparison to STZ. In conclusion, our data strongly suggest that iPS cells and CM attenuate oxidative stress and associated apoptosis and fibrosis. Moreover, we also suggest that increased antioxidant levels, decreased adverse cardiac remodeling, and improved cardiac function is mediated by iPS CM and cells in DICM through multiple autocrine and paracrine mechanisms.

Regulation of cardiac autophagy by insulin-like growth factor 1

Insulin-like growth factor-1 (IGF-1) signaling is a key pathway in the control of cell growth and survival. Three critical nodes in the IGF-1 signaling pathway have been described in cardiomyocytes: protein kinase Akt/mammalian target of rapamycin (mTOR), Ras/Raf/extracellular signal-regulated kinase (ERK), and phospholipase C (PLC)/inositol 1,4,5-triphosphate (InsP3 )/Ca(2+) . The Akt/mTOR and Ras/Raf/ERK signaling arms govern survival in the settings of cardiac stress and hypertrophic growth. By contrast, PLC/InsP3 /Ca(2+) functions to regulate metabolic adaptability and gene transcription. Autophagy is a catabolic process involved in protein degradation, organelle turnover, and nonselective breakdown of cytoplasmic components during nutrient starvation or stress. In the heart, autophagy is observed in a variety of human pathologies, where it can be either adaptive or maladaptive, depending on the context. We proposed the hypothesis that IGF-1 protects the heart by rescuing the mitochondrial metabolism and the energetics state, reducing cell death and controls the potentially exacerbate autophagic response to nutritional stress. In light of the importance of IGF-1 and autophagy in the heart, we review here IGF-1 signaling and autophagy regulation in the context of cardiomyocyte nutritional stress.

The role of SIRT1/AKT/ERK pathway in ultraviolet B induced damage on human retinal pigment epithelial cells

Ultraviolet (UV)-induced damage plays a major role in ocular diseases, such as cataracts and retinal degeneration. UVB may also cause retinal phototoxicity and photic retinopathy. In this study, we explored the effects of UVB on the cell cycle and the role of silent mating type information regulation 2 homolog 1 (SIRT1) in the UVB-induced damage. UVB dose-dependently suppressed the growth of retinal pigment epithelial (RPE) cells by activating the phosphatidylinositol 3-kinase (PI3K) pathway and triggering cell cycle arrest at the S phase. SIRT1, an NAD-dependent histone deacetylase, is involved in multiple biological processes, such as the stress response and the regulation of the cell cycle. However, its role in the effects of UVB on RPE cells is unclear. We showed that UVB down-regulates SIRT1 expression in a dose-dependent manner. Resveratrol, an SIRT1 activator, prevented the UVB-induced damage by inhibiting AKT and ERK phosphorylation. A specific PI3K inhibitor attenuated the UVB-induced ERK1/2 and p53 phosphorylation. Finally, UVB activated the PI3K/AKT/ERK pathway by reducing the expression of SIRT1 in ARPE-19 cells. Our study, therefore, illustrated the molecular mechanisms of UVB-induced phototoxicity and damage of RPE cells. SIRT1 and resveratrol may be significant regulators, protecting against UVB-induced injury.

The protective roles of autophagy in ischemic preconditioning

Autophagy, a process for the degradation of protein aggregates and dysfunctional organelles, is required for cellular homeostasis and cell survival in response to stress and is implicated in endogenous protection. Ischemic preconditioning is a brief and nonlethal episode of ischemia, confers protection against subsequent ischemia-reperfusion through the up-regulation of endogenous protective mechanisms. Emerging evidence shows that autophagy is associated with the protective effect of ischemic preconditioning. This review summarizes recent progress in research on the functions and regulations of the autophagy pathway in preconditioning-induced protection and cellular survival.

The miRNA-212/132 family regulates both cardiac hypertrophy and cardiomyocyte autophagy

Pathological growth of cardiomyocytes (hypertrophy) is a major determinant for the development of heart failure, one of the leading medical causes of mortality worldwide. Here we show that the microRNA (miRNA)-212/132 family regulates cardiac hypertrophy and autophagy in cardiomyocytes. Hypertrophic stimuli upregulate cardiomyocyte expression of miR-212 and miR-132, which are both necessary and sufficient to drive the hypertrophic growth of cardiomyocytes. MiR-212/132 null mice are protected from pressure-overload-induced heart failure, whereas cardiomyocyte-specific overexpression of the miR-212/132 family leads to pathological cardiac hypertrophy, heart failure and death in mice. Both miR-212 and miR-132 directly target the anti-hypertrophic and pro-autophagic FoxO3 transcription factor and overexpression of these miRNAs leads to hyperactivation of pro-hypertrophic calcineurin/NFAT signalling and an impaired autophagic response upon starvation. Pharmacological inhibition of miR-132 by antagomir injection rescues cardiac hypertrophy and heart failure in mice, offering a possible therapeutic approach for cardiac failure.

Heart failure is often a consequence of pathological growth of cardiomyocytes or cardiac hypertrophy. Here Ucar and colleagues report that the microRNAs miR-132 and miR-212 promote cardiac hypertrophy and inhibit autophagy in cardiomyocytes by downregulating the transcription factor FoxO3.