Autophagosome-lysosomal Fusion Research Articles

AMPK-mediated autophagy pathway activation promotes ΔFosB degradation to improve levodopa-induced dyskinesia

BackgroundParkinson's disease patients on chronic levodopa often suffer from motor complications, which tend to reduce their quality of life. Levodopa-induced dyskinesia (LID) is one of the most prevalent motor complications, often characterized by abnormal involuntary movements, and the pathogenesis of LID is still unclear but recent studies have suggested the involvement of autophagy. MethodsThe onset of LID was mimicked by chronic levodopa treatment in a unilateral 6-hydroxydopamine (6-OHDA) -lesion rat model. Overexpression of ΔFosB in HEK293 cells to mimic the state of ΔFosB accumulation. The modulation of the AMP-activated protein kinase (AMPK)-mediated autophagy pathway using by metformin, AICAR (an AMPK activator), Compound C (an AMPK inhibitor) and chloroquine (an autophagy pathway inhibitor). The severity of LID was assessed by axial, limb, and orofacial (ALO) abnormal involuntary movements (AIMs) score and in vivo electrophysiology. The activity of AMPK pathway as well as autophagy markers and FosB-ΔFosB levels were detected by western blotting. RT-qPCR was performed to detect the transcription level of FosB-ΔFosB. The mechanism of autophagy dysfunction was further explored by immunofluorescence and transmission electron microscopy. ResultsIn vivo experiments demonstrated that chronic levodopa treatment reduced AMPK phosphorylation, impaired autophagosome-lysosomal fusion and caused FosB-ΔFosB accumulation in the striatum of PD rats. Long-term metformin intervention improved ALO AIMs scores as well as reduced the mean power of high gamma (hγ) oscillations and the proportion of striatal projection neurons unstable in response to dopamine for LID rats. Moreover, the intervention of metformin promoted AMPK phosphorylation, ameliorated the impairment of autophagosome-lysosomal fusion, thus, promoting FosB-ΔFosB degradation to attenuate its accumulation in the striatum of LID rats. However, the aforementioned roles of metformin were reversed by Compound C and chloroquine. The results of in vitro studies demonstrated the ability of metformin and AICAR to attenuate ΔFosB levels by promoting its degradation, while Compound C and chloroquine could block this effect. ConclusionsIn conclusion, our results suggest that long-term metformin treatment could promote ΔFosB degradation and thus attenuate the development of LID through activating the AMPK-mediated autophagy pathway. Overall, our results support the AMPK-mediated autophagy pathway as a novel therapeutic target for LID and also indicate that metformin is a promising therapeutic candidate for LID.

Recent advances of myotubularin-related (MTMR) protein family in cardiovascular diseases.

Belonging to a lipid phosphatase family containing 16 members, myotubularin-related proteins (MTMRs) are widely expressed in a variety of tissues and organs. MTMRs preferentially hydrolyzes phosphatidylinositol 3-monophosphate and phosphatidylinositol (3,5) bis-phosphate to generate phosphatidylinositol and phosphatidylinositol 5-monophosphate, respectively. These phosphoinositides (PIPs) promote membrane degradation during autophagosome-lysosomal fusion and are also involved in various regulatory signal transduction. Based on the ability of modulating the levels of these PIPs, MTMRs exert physiological functions such as vesicle trafficking, cell proliferation, differentiation, necrosis, cytoskeleton, and cell migration. It has recently been found that MTMRs are also involved in the occurrence and development of several cardiovascular diseases, including cardiomyocyte hypertrophy, proliferation of vascular smooth muscle cell, LQT1, aortic aneurysm, etc. This review summarizes the functions of MTMRs and highlights their pathophysiological roles in cardiovascular diseases.

Syringin alleviates hepatic fibrosis by enhancing autophagic flux and attenuating ER stress-TRIB3/SMAD3 in diabetic mice

Type 2 diabetes mellitus (T2DM) is a key risk factor for the developing of metabolic liver injury and easily evolving to advanced fibrosis. Syringin (SYR), isolated from Acanthopanax senticosus, has anti-inflammatory, anti-oxidant, and anti-apoptotic properties. However, its hepatoprotective effects and mechanisms in T2DM-induced liver fibrosis remain unclear. Here, we investigated whether syringin (SYR) could serve as a therapeutic agent for liver fibrosis and its mechanism in high-fat diet (HFD)/streptozotocin (STZ)-induced type 2 diabetic mice. C57BL/6 mice were induced with T2DM via HFD and STZ injection and treated with different doses of SYR. Serum lipid parameters and liver function indicators were measured, and hepatic histology and fibrosis were examined. The mechanism of SYR was explored through molecular analyses Results demonstrated SYR improved oral glucose tolerance, decreased the levels of ALT, AST, and AKP, and reduced hepatic lipid deposition in diabetic mice. Moreover, SYR ameliorated epithelial-to-mesenchymal transition to reverse hepatic fibrosis via suppressing TRIB3-SMAD3 interaction to restrain nuclear localization of SMAD3. Strikingly, SYR reversed hyperglycemia-induced deficiency in autophagic flux by regulation of Raptor/mTORC1, triggering nuclear translocation of TFEB to improve autophagosome-lysosomal fusion. In brief, SYR potentially ameliorates hepatic injury and fibrosis by enhancing autophagic flux and inhibing TRIB3 activation in diabetic mice.

Effect of autophagy in cadmium chloride induced apoptosis of mouse spermatogenic cells

To study the effect of autophagy in cadmium chloride(CdCl_2)-induced apoptosis of mouse spermatocytes(GC-2 spd) cells and explore the underlying molecular mechanisms. The cells were treated with different concentrations of CdCl_2(0, 5 and 10 μmol/L) for 24 h. Hoechst33342 staining and monodansylcadaverine(MDC) were performed to explore the formation of autophagosomes and apoptotic bodies. The apoptosis of cadmium-treated cells was examined by TUNEL staining. Autophagy inhibitor 3-methyladenine(3-MA)(60 μmol/L), apoptotic inhibitorCaspase inhibitor Z-VAD-FMK( zVAD-FMK)(50 nmol/L), autophagy inducer rapamycin(RAPA)(50 nmol/L) and lysosomal inhibitor chloroquine(CQ)(10 μmol/L) were added to cell culture in the presence/absence of CdCl_2(10 μmol/L) to treat GC-2 spd cells for 24 h. The expression levels of autophagy-related proteins LC3, P62, and pro-apoptotic proteins cleaved Caspase-3 and cleaved Caspase-9 were examined by Western blot. Autophagosomes aggregated and the number of apoptotic cells increased after exposure to CdCl_2 for 24 h. Western blot result showed that in the 5 and 10 μmol/L CdCl_2 exposure groups, the protein expression levels of LC3II/LC3I increased to 9.23±0.81 and 12.15±0.80 compared with the control group(5.50±0.56)(P<0.05), LC3II protein expression level increased to 3.35±0.14 and 3.47±0.32 compared with the control group(2.35±0.34)(P<0.05), P62 protein expression level increased to 1.48±0.12 and 1.80±0.22 compared with the control group(0.83±0.09)(P<0.05). Compared with the CdCl_2-treated group, the protein expression levels of LC3II/LC3I, LC3II, P62, cleaved Caspase-9 and cleaved Caspase-3 after 3-MA treatment decreased to 0.90±0.07(CdCl_2 group: 1.47±0.06), 1.57±0.14(CdCl_2 group: 2.45±0.29), 0.82±0.05(CdCl_2 group: 1.44±0.18), 0.18±0.01(CdCl_2 group: 0.28±0.01) and 0.61±0.84(CdCl_2 group: 1.15±0.04)(P<0.05). Compared with the CdCl_2-treated group, the protein expression levels of cleaved Caspase-9 and cleaved Caspase-3 after zVAD-FMK treatment decreased to 0.12±0.01(CdCl_2 group: 0.28±0.01) and 0.34±0.01(CdCl_2 group: 1.15±0.04)(P<0.05), while those of LC3II/LC3I, LC3II and P62 had no significant change(P>0.05). Compared with the CdCl_2-treated group, RAPA enhanced cadmium-induced LC3II/LC3I, LC3II and P62 protein expressions to 2.22±0.21(CdCl_2 group: 1.56±0.06), 3.72±0.21(CdCl_2 group: 2.97±0.15) and 2.41±0.19(CdCl_2 group: 1.52±0.35)(P<0.05). Western blot result showed that compared with the CdCl_2 group, the protein expressions of LC3II/LC3I, LC3II, P62 and cleaved Caspase-3 in the CdCl_2 and CQ treatment groups increased to 3.21±0.31(CdCl_2 group: 2.09±0.25), 4.49±0.43(CdCl_2 group: 2.72±0.26), 2.59±0.19(CdCl_2 group: 1.84±0.19) and 2.43±0.23(CdCl_2 group: 1.50±0.27)(P<0.05). Cadmium chloride induces apoptosis of mouse spermatocyte cells by inhibiting autophagosome-lysosomal fusion and prompting abnormal aggregation of autophagosomes.

Blunting ROS/TRPML1 pathway protects AFB1-induced porcine intestinal epithelial cells apoptosis by restoring impaired autophagic flux

Aflatoxin B1 (AFB1) is a stable mycotoxin that contaminates animal feed on a large scale and causes severe damage to intestinal cells, induces inflammation and stimulates autophagy. Transient receptor potential mucolipin subfamily 1 (TRPML1) is a regulatory factor of autophagy, but the underlying mechanisms of TRPML1-mediated autophagy in AFB1 intestine toxicity remain elucidated. In the present study, AFB1 (0, 5, 10 μg/mL) was shown to reduce cell viability, increase reactive oxygen species (ROS) accumulation and apoptosis rate. Additionally, AFB1 caused structural damage to mitochondria and lysosomes and increased autophagosomes numbers. Furthermore, AFB1 promoted Ca2+ release by activating the TRPML1 channel, stimulated the expression of autophagy-related proteins, and induced autophagic flux blockade. Moreover, pharmacological inhibition of autophagosome formation by 3-methyladenine attenuated AFB1-induced apoptosis by downregulating the levels of TRPML1 and ROS, whereas blockade of autophagosome-lysosomal fusion by chloroquine alleviated AFB1-induced apoptosis by upregulating TRPML1 expression and exacerbating ROS accumulation. Intriguingly, blocking AFB1-induced autophagic flux generated ROS- and TRPML1-dependent cell death, as shown by the decreased apoptosis in the presence the free radical scavenger N-Acetyl-L-cysteine and the TRPML1 inhibitor ML-SI1. Overall, these results showed that AFB1 promoted apoptosis of IPEC-J2 cells by disrupting autophagic flux through activation of the ROS/TRPML1 pathway.

Chinese herbal medicine Feiyanning cooperates with cisplatin to enhance cytotoxicity to non-small-cell lung cancer by inhibiting protective autophagy

Ethnopharmacological relevanceFeiyanning (FYN), the Chinese herbal medicine (CHM), has been used to manage non-small cell lung cancer (NSCLC) for the past 23 years. Chemotherapeutic drugs can induce autophagy in cancer cells to protect themselves from death. However, FYN can inhibit the protective autophagy in cancer cells. We investigated the biological mechanisms on the synergistic effects of FYN combined with chemotherapy in lung cancer cells. Materials and methodsWe analyzed the effective chemical components for the quality control of FYN using the UPLC-Q-TOF-MS.The cell proliferation ability was detected by the cell counting kit-8 (CCK-8) and colony formation. The cell apoptosis was determined with Flow cytometry. Expression of important differential proteins were detected by western blot. Autophagy structure was observed by TEM (Tansmission electron microscopy). Tandem mCherry-EGFP-LC3B immunofluorescence was used to measure autophagic flux. ResultsBoth FYN and cisplatin significantly induced apoptosis and inhibited cell proliferation in A549 cells. FYN reduced cell viability and increased apoptotic cell populations less effectively than cisplatin. FYN cooperated with cisplatin suppressed the cell viability, colony formation, as well as increased the cell apoptosis rate, and the expression of cleaved caspase-3 and PARP. FYN inhibited autophagy in A549 cells, which characterized by the decrease of autophagosome formation, lysosomal fusion, LC3B-II accumulation and SQSTM1 degradation, down-regulation of ATG5 and ATG7. Protective autophagy in A549 cells was induced by cisplatin. Suppression of the autophagic response using chloroquine (CQ) which is autophagy inhibitor improved the ability of cisplatin to kill cancer cells, as did FYN combined with cisplatin. ConclusionIn summary, we revealed that the synergistic mechanism of FYN and cisplatin is that FYN inhibited the protective autophagy induced by cisplatin in A549 cells.

IFN-γ-induced ER stress impairs autophagy and triggers apoptosis in lung cancer cells

ABSTRACT Interferon-gamma (IFN-γ) is a major effector molecule of immunity and a common feature of tumors responding to immunotherapy. Active IFN-γ signaling can directly trigger apoptosis and cell cycle arrest in human cancer cells. However, the mechanisms underlying these actions remain unclear. Here, we report that IFN-γ rapidly increases protein synthesis and causes the unfolded protein response (UPR), as evidenced by the increased expression of glucose-regulated protein 78, activating transcription factor-4, and c/EBP homologous protein (CHOP) in cells treated with IFN-γ. The JAK1/2-STAT1 and AKT-mTOR signaling pathways are required for IFN-γ-induced UPR. Endoplasmic reticulum (ER) stress promotes autophagy and restores homeostasis. Surprisingly, in IFN-γ-treated cells, autophagy was impaired at the step of autophagosome-lysosomal fusion and caused by a significant decline in the expression of lysosomal membrane protein-1 and −2 (LAMP-1/LAMP-2). The ER stress inhibitor 4-PBA restored LAMP expression in IFN-γ-treated cells. IFN-γ stimulation activated the protein kinase-like ER kinase (PERK)-eukaryotic initiation factor 2a subunit (eIF2α) axis and caused a reduction in global protein synthesis. The PERK inhibitor, GSK2606414, partially restored global protein synthesis and LAMP expression in cells treated with IFN-γ. We further investigated the functional consequences of IFN-γ-induced ER stress. We show that inhibition of ER stress significantly prevents IFN-γ-triggered apoptosis. CHOP knockdown abrogated IFN-γ-mediated apoptosis. Inhibition of ER stress also restored cyclin D1 expression in IFN-γ-treated cells. Thus, ER stress and the UPR caused by IFN-γ represent novel mechanisms underlying IFN-γ-mediated anticancer effects. This study expands our understanding of IFN-γ-mediated signaling and its cellular actions in tumor cells.

STING-Mediated Autophagy Is Protective against H2O2-Induced Cell Death.

Stimulator of interferon genes (STING)-mediated type-I interferon signaling is a well characterized instigator of the innate immune response following bacterial or viral infections in the periphery. Emerging evidence has recently linked STING to various neuropathological conditions, however, both protective and deleterious effects of the pathway have been reported. Elevated oxidative stress, such as neuroinflammation, is a feature of a number of neuropathologies, therefore, this study investigated the role of the STING pathway in cell death induced by elevated oxidative stress. Here, we report that the H2O2-induced activation of the STING pathway is protective against cell death in wildtype (WT) MEFSV40 cells as compared to STING−/− MEF SV40 cells. This protective effect of STING can be attributed, in part, to an increase in autophagy flux with an increased LC3II/I ratio identified in H2O2-treated WT cells as compared to STING−/− cells. STING−/− cells also exhibited impaired autophagic flux as indicated by p62, LC3-II and LAMP2 accumulation following H2O2 treatment, suggestive of an impairment at the autophagosome-lysosomal fusion step. This indicates a previously unrecognized role for STING in maintaining efficient autophagy flux and protecting against H2O2-induced cell death. This finding supports a multifaceted role for the STING pathway in the underlying cellular mechanisms contributing to the pathogenesis of neurological disorders.

Regulation of Autophagy Progress via Lysosomal Depletion by Fluvastatin Nanoparticle Treatment in Breast Cancer Cells.

Fluvastatin (FLV) is a statin family member that may play a role in modulating a variety of medical disorders such as atherosclerosis and breast cancer. The present study addresses the ability of FLV to modulate the cellular immune response and provides a new nanosized FLV formula (self-nanoemulsifying delivery system, SNED) potentially more effective for suppression of breast cancer development. We monitored autophagic machinery through the expression of microtubule-associated protein 1A/1B-light chain 3 (LC3I/II). Lysosomal activity upon treatment was evaluated by mRNA and protein expression of lysosomal-associated membrane protein 1 (LAMP-1). Mitogen-activated protein kinase (MAPK) signaling and its association with proinflammatory cytokine secretion were assessed in treated cells. Autophagosome formation was significantly increased in cells that were pretreated with FLV-SNED in comparison to FLV-treated cells. Activation of autophagy was accompanied with arrest of LAMP-1 expression, which correlates with lysosomal activity. Simultaneously, both FLV and FLV-SNED activated MAPK signaling and modified interleukin-6 and tumor necrosis factor-α levels in treated cells. These findings indicate that FLV reduces cell viability via depletion of lysosomal activities along with accumulation of autophagosomes leading to disturbance of autophagosome-lysosomal fusion in treated cells. Furthermore, our data reveal the effectiveness of both FLV agents in the modulation of proinflammatory cytokine secretion from treated cells via regulation of MAPK signaling cascades and indicate that FLV-SNED is more efficient than FLV. This study provides new insights into how FLV regulates breast cancer cell viability via modulation of AMPK-mTOR and ERK-mTOR signaling, and through autophagosome formation accompanied by lysosomal degradation.

Disruptions of Autophagy in the Rat Retina with Age During the Development of Age-Related-Macular-Degeneration-like Retinopathy.

Age-related macular degeneration (AMD) is one of the main causes of vision impairment in the elderly. Autophagy is the process of delivery of cytoplasmic components into lysosomes for cleavage; its age-related malfunction may contribute to AMD. Here we showed that the development of AMD-like retinopathy in OXYS rats is accompanied by retinal transcriptome changes affecting genes involved in autophagy. These genes are associated with kinase activity, immune processes, and FoxO, mTOR, PI3K-AKT, MAPK, AMPK, and neurotrophin pathways at preclinical and manifestation stages, as well as vesicle transport and processes in lysosomes at the progression stage. We demonstrated a reduced response to autophagy modulation (inhibition or induction) in the OXYS retina at age 16 months: expression of genes Atg5, Atg7, Becn1, Nbr1, Map1lc3b, p62, and Gabarapl1 differed between OXYS and Wistar (control) rats. The impaired reactivity of autophagy was confirmed by a decreased number of autophagosomes under the conditions of blocked autophagosome–lysosomal fusion according to immunohistochemical analysis and transmission electron microscopy. Thus, the development of AMD signs occurs against the background of changes in the expression of autophagy-related genes and a decrease in autophagy reactivity: the ability to enhance autophagic flux in response to stress.

Emerging Role of the Nucleolar Stress Response in Autophagy.

Autophagy represents a conserved self-digestion program, which allows regulated degradation of cellular material. Autophagy is activated by cellular stress, serum starvation and nutrient deprivation. Several autophagic pathways have been uncovered, which either non-selectively or selectively target the cellular cargo for lysosomal degradation. Autophagy engages the coordinated action of various key regulators involved in the steps of autophagosome formation, cargo targeting and lysosomal fusion. While non-selective (macro)autophagy is required for removal of bulk material or recycling of nutrients, selective autophagy mediates specific targeting of damaged organelles or protein aggregates. By proper action of the autophagic machinery, cellular homeostasis is maintained. In contrast, failure of this fundamental process is accompanied by severe pathophysiological conditions. Hallmarks of neuropathological disorders are for instance accumulated, mis-folded protein aggregates and damaged mitochondria. The nucleolus has been recognized as central hub in the cellular stress response. It represents a sub-nuclear organelle essential for ribosome biogenesis and also functions as stress sensor by mediating cell cycle arrest or apoptosis. Thus, proper nucleolar function is mandatory for cell growth and survival. Here, I highlight the emerging role of nucleolar factors in the regulation of autophagy. Moreover, I discuss the nucleolar stress response as a novel signaling pathway in the context of autophagy, health and disease.

FoxO1 inhibits autophagosome-lysosome fusion leading to endothelial autophagic-apoptosis in diabetes.

Inadequate autophagy contributed to endothelial dysfunction in diabetic patients. We aimed to investigate the relationship between inadequate autophagy and endothelial cells (ECs) apoptosis in diabetes and its underlying mechanism. Aortic intima and ECs were isolated from diabetic patients. Cultured human aortic endothelial cells (HAECs) were stimulated with advanced glycation end products (AGEs). The expression of autophagy and apoptosis-related proteins were determined by western blotting. Autophagosomes were observed by electron microscopy. The fusion of autophagosome and lysosomes was detected by immunofluorescence. Compared with non-diabetic subjects, the levels of LC3-II, p62, FoxO1, and Ac-FoxO1 were increased in ECs from diabetic patients, accompanied by the decreased expressions of Atg14, STX17, and co-localization of LC3-II/LAMP2 and Atg14/STX17. Long-term stimulation with AGEs up-regulated LC3-II and p62 expression and the number of autophagosomes with decreased level of Atg14, STX17, Ras-related protein 7 (Rab7), and co-localization of LC3-II/LAMP2 and Atg14/STX17 in HAECs. The apoptosis rates were increased with elevated cleaved-caspase-3 and declined Bcl-2 expression. Inhibition of autophagy with 3-methyladenine could reduce long-term AGEs-induced apoptosis. Higher levels of FoxO1, Ac-FoxO1, and Ac-FoxO1 binding to Atg7 were detected in AGEs-treated HAECs. AGEs-induced FoxO1 enhanced Akt activity, decreased SIRT1-deacetylase activity by phosphorylation and elevated Ac-FoxO1. Knockout of FoxO1 reduced AGEs-induced autophagy and promoted the expression of Atg14 and the co-localization of LC3-II/LAMP 2 and Atg14/STX17. Inadequate autophagy with impaired autophagosome-lysosomal fusion exists in aortic intima and ECs from diabetic patients. FoxO1 mediates AGEs-induced ECs autophagic apoptosis through impairing autophagosome-lysosomes fusion by inhibiting Atg14 expression.

Sasanquasaponin ΙΙΙ from Schima crenata Korth induces autophagy through Akt/mTOR/p70S6K pathway and promotes apoptosis in human melanoma A375 cells

BackgroundMelanoma is a high fatality skin cancer which lacks effective drugs. Sasanquasaponin, an important sort of constituents in theaceae, has been demonstrated to have potent anti-tumor effect in breast cancer and hepatocellular carcinoma. As a sasanquasaponin, we speculate that Sasanquasaponin III (SQS III) isolated from Schima crenata Korth may also have anti-tumor activity. PurposeThis study aims to investigate whether SQS III has anti-melanoma activity and examine the underlying mechanisms of SQS III against melanoma. Methods/Study designsThe anti-proliferative effect of SQS III was assessed by cells viability assay. Annexin V-FITC/PI double staining assay was utilized for detection of apoptosis. Mitochondrial membrane potential and reactive oxygen species (ROS) production were detected using JC-1 and DCFH-DA assay, respectively. Autophagy was monitored using transmission electron microscopy (TEM) and GFP-LC3 transfection fluorescence analysis. Autophagosome-lysosome fusion and lysosomal degradation were determined using a GFP-LC3 & LAMP1 co-localization assay and DQ-BSA staining. Proteins related to apoptosis and autophagy were analyzed by Western blotting. ResultsOur results demonstrated that the SQS III exhibited potent anti-cancer activity in A375 cells by inducing both apoptosis and autophagy. In melanoma cells treated with SQS III, caspases were activated and PARP was cleaved, proving the occurrence of apoptosis. Mechanistic studies indicated that the pro-apoptosis activity of SQS III was mediated by death receptor pathway and mitochondrial dysfunction which was induced by ROS accumulation and reversed by the ROS inhibitor N-acetyl-cysteine (NAC). In addition to triggering apoptosis, SQS III may also cause autophagy in melanoma cells. Our results demonstrated that SQS III induced up-regulated expression of GFP-LC3, autophagosome-lysosomal fusion and lysosomal degradation. Additionally, the ROS accumulation was also involved in the activation of autophagy. Meanwhile, it was also found that after SQS III treatment, the expression of LC3-II was up-regulated and the AKT/mTOR signaling pathway was inhibited. The autophagy inhibitor 3-MA converted cytotoxicity and apoptosis of SQS III in A375 cells, which indicated that autophagy promoted the SQS III-induced apoptosis. ConclusionSQS III showed potent anti-cancer activity by inducing apoptosis and autophagy, which provides insights into its possible use as a therapy for melanoma.

AMPK contributes to autophagosome maturation and lysosomal fusion

AMP-activated protein kinase (AMPK) regulates autophagy initiation when intracellular ATP level decreases. However, the role of AMPK during autophagosome maturation is not fully understood. Here, we report that AMPK contributes to efficient autophagosome maturation and lysosomal fusion. Using CRISPR-Cas9 gene editing, we generated AMPK α1 knockout HEK293T cell lines, in which starvation-induced autophagy is impaired. Compound C, an AMPK-independent autophagy inducer, and trehalose, an mTOR-independent autophagy inducer were used to examine the role of AMPK in autophagosome maturation and lysosomal fusion. While the treatment of control cells with either compound C or trehalose induces activation of autophagosomes as well as autolysosomes, the treatment of AMPK α1 knockout cells with compound C or trehalose induces mainly activation of autophagosomes, but not autolysosomes. We demonstrate that this effect is due to interference with the fusion of autophagosomes with lysosomes in AMPK α1 knockout cells. The transient expression of AMPK α1 can rescue autophagosome maturation. These results indicate that AMPK α1 is required for efficient autophagosome maturation and lysosomal fusion.

Abstract 1456: Integrin beta4-induced mitophagy promotes the lactate production of cancer-associated fibroblasts in breast cancer

Abstract Integrin beta4 neoexpression is induced in cancer-associated fibroblasts (CAFs) by some triple negative breast cancer cells (MDA-MB-231 and BT-20) through a contact-dependent manner. Integrin beta4 expression is well known to contribute to the migration and survival of cancer cells. However, there is very little known about the role of integrin beta4 expression in CAFs, especially in the aspect of tumor progression. In our study, we found that the exogenous expression of integrin beta4 increased the lactate production of CAFs. The observation made us to hypothesize that integrin beta4 neoexpression is associated with the mitophagy, a cause for aerobic glycolysis, in CAFs. To confirm the assumption, the expression alteration of mitophagy-related genes was first screened in the CAF transfected with integrin beta4 overexpression plasmid. BCL2 interacting protein 3 like (BNIP3L) and microtubule associated protein 1 light chain 3 alpha-II (LC3-II) were significantly upregulated in the integrin beta4 overexpressing CAFs, which was reversed both in the knockdown of integrin beta4 expression and the treatment with an integrin beta4 inhibitor. Autophagosome maturation and lysosomal fusion were also increased in the integrin beta4 overexpressing CAFs compared to the control. Phosphorylation level of c-Jun was upregulated by integrin beta4 overexpression in CAFs and was able to bind to the putative promoter regions of BNIP3L and LC3-II. Taken together, these results demonstrate that integrin beta4 neoexpression induces upregulation of BNIP3L and LC3-II ultimately leading to mitophagy in CAFs, contributing to cancer metabolism via mitophagy-induced lactate production, namely reverse Warburg effect. Citation Format: Jin Sol Sung, Suki Kang, Joo Hyun Lee, Seong Gyeong Mun, Baek Gil Kim, Nam Hoon Cho. Integrin beta4-induced mitophagy promotes the lactate production of cancer-associated fibroblasts in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1456.

Abstract P241: Autophagic Flux is Diminished in Mesenteric Resistance Arteries of Spontaneously Hypertensive Rats

Autophagy is the constitutively active catabolic process regulating protein quality control and energy homeostasis. However, dysregulation of this process can have detrimental effects on cellular function. In particular, insufficient autophagy has been proposed as a mechanism of cellular aging, as this leads to the accumulation of damaged macromolecules and organelles. Hypertension is a condition of vascular aging. In fact, many factors that contribute to the deterioration of vascular function as we age are exacerbated in clinical and experimental hypertension. Nonetheless, whether high blood pressure per se is the cause or effect of diminished autophagy remains to be clarified. We hypothesized that mesenteric resistance arteries (MRA) from spontaneously hypertensive rats (SHR) would have decreased autophagic flux as measured by conversion of microtubule-associated protein light chain 3 (LC3-I to LC3-II) compared to normotensive Wistar Kyoto rats (WKY). We observed that MRA from male 12-15 week old SHR have decreased basal expression both cytosolic LC3 (LC3-I) and phosphatidylethanolamine conjugated LC3 (LC3-II), and expression of these proteins are similarly decreased in SHR chronically treated with hydrochlorothiazide and reserpine (SHR+HCTZ/Res) [Arbitrary units (AU), LC3-1: WKY: 1.4±0.1, SHR: 1.1±0.1*, and SHR+HCTZ/Res: 0.7±0.1*; LC3-II: WKY: 1.4±0.1, SHR: 1.1±0.1*, and SHR+HCTZ/Res: 0.7±0.1*, *p<0.05 vs. WKY]. To understand autophagic flux, some MRA were incubated with lysosomal inhibitor chloroquine (CQ; 30 μM) for 2 hours. CQ incubation significantly increased LC3-II expression to a similar magnitude in WKY, SHR, and SHR+HCTZ/Res MRA (all *p<0.05 vs. basal). However, the percent increase in LC3-II expression after CQ incubation was significantly less in SHR compared to WKY, and SHR+HCTZ/Res was not different from either WKY or SHR (% increase from basal LC3-II, WKY: 546±187, SHR: 156±38*, and SHR+HCTZ/Res: 273±106, *p<0.05 vs. WKY). Overall, these data suggest that SHR have impaired autophagosome-lysosomal fusion, and this is not solely attributable to high blood pressure. Therefore, reconstituting autophagic activity could be a novel prophylactic or therapeutic measure against vascular aging in hypertension.

Stress fibers, autophagy and necrosis by persistent exposure to PM2.5 from biomass combustion.

Fine particulate matter (PM2.5) can adversely affect human health. Emissions from residential energy sources have the largest impact on premature mortality globally, but their pathological and molecular implications on cellular physiology are still elusive. In the present study potential molecular consequences were investigated during long-term exposure of human bronchial epithelial BEAS-2B cells to PM2.5, collected from a biomass power plant. Initially, we observed that PM2.5 did not affect cellular survival or proliferation. However, it triggered an activation of the stress response p38 MAPK which, along with RhoA GTPase and HSP27, mediated morphological changes in BEAS-2B cells, including actin cytoskeletal rearrangements and paracellular gap formation. The p38 inhibitor SB203580 prevented phosphorylation of HSP27 and ameliorated morphological changes. During an intermediate phase of long-term exposure, PM2.5 triggered proliferative regression and activation of an adaptive stress response necessary to maintain energy homeostasis, including AMPK, repression of translational elongation, and autophagy. Finally, accumulation of intracellular PM2.5 promoted lysosomal destabilization and cell death, which was dependent on lysosomal hydrolases and p38 MAPK, but not on the inflammasome and pyroptosis. TEM images revealed formation of protrusions and cellular internalization of PM2.5, induction of autophagosomes, amphisomes, autophagosome-lysosomal fusion, multiple compartmental fusion, lysosomal burst, swollen mitochondria and finally necrosis. In consequence, persistent exposure to PM2.5 may impair epithelial barriers and reduce regenerative capacity. Hence, our results contribute to a better understanding of PM-associated lung and systemic diseases on the basis of molecular events.

Tetraspanin 6: a pivotal protein of the multiple vesicular body determining exosome release and lysosomal degradation of amyloid precursor protein fragments

BackgroundThe mechanisms behind Aβ-peptide accumulation in non-familial Alzheimer’s disease (AD) remain elusive. Proteins of the tetraspanin family modulate Aβ production by interacting to γ-secretase.MethodsWe searched for tetraspanins with altered expression in AD brains. The function of the selected tetraspanin was studied in vitro and the physiological relevance of our findings was confirmed in vivo.ResultsTetraspanin-6 (TSPAN6) is increased in AD brains and overexpression in cells exerts paradoxical effects on Amyloid Precursor Protein (APP) metabolism, increasing APP-C-terminal fragments (APP-CTF) and Aβ levels at the same time. TSPAN6 affects autophagosome-lysosomal fusion slowing down the degradation of APP-CTF. TSPAN6 recruits also the cytosolic, exosome-forming adaptor syntenin which increases secretion of exosomes that contain APP-CTF.ConclusionsTSPAN6 is a key player in the bifurcation between lysosomal-dependent degradation and exosome mediated secretion of APP-CTF. This corroborates the central role of the autophagosomal/lysosomal pathway in APP metabolism and shows that TSPAN6 is a crucial player in APP-CTF turnover.

A Drosophila Model of Neuronopathic Gaucher Disease Demonstrates Lysosomal-Autophagic Defects and Altered mTOR Signalling and Is Functionally Rescued by Rapamycin.

Glucocerebrosidase (GBA1) mutations are associated with Gaucher disease (GD), an autosomal recessive disorder caused by functional deficiency of glucocerebrosidase (GBA), a lysosomal enzyme that hydrolyzes glucosylceramide to ceramide and glucose. Neuronopathic forms of GD can be associated with rapid neurological decline (Type II) or manifest as a chronic form (Type III) with a wide spectrum of neurological signs. Furthermore, there is now a well-established link between GBA1 mutations and Parkinson's disease (PD), with heterozygote mutations in GBA1 considered the commonest genetic defect in PD. Here we describe a novel Drosophila model of GD that lacks the two fly GBA1 orthologs. This knock-out model recapitulates the main features of GD at the cellular level with severe lysosomal defects and accumulation of glucosylceramide in the fly brain. We also demonstrate a block in autophagy flux in association with reduced lifespan, age-dependent locomotor deficits and accumulation of autophagy substrates in dGBA-deficient fly brains. Furthermore, mechanistic target of rapamycin (mTOR) signaling is downregulated in dGBA knock-out flies, with a concomitant upregulation of Mitf gene expression, the fly ortholog of mammalian TFEB, likely as a compensatory response to the autophagy block. Moreover, the mTOR inhibitor rapamycin is able to partially ameliorate the lifespan, locomotor, and oxidative stress phenotypes. Together, our results demonstrate that this dGBA1-deficient fly model is a useful platform for the further study of the role of lysosomal-autophagic impairment and the potential therapeutic benefits of rapamycin in neuronopathic GD. These results also have important implications for the role of autophagy and mTOR signaling in GBA1-associated PD SIGNIFICANCE STATEMENT: We developed a Drosophila model of neuronopathic GD by knocking-out the fly orthologs of the GBA1 gene, demonstrating abnormal lysosomal pathology in the fly brain. Functioning lysosomes are required for autophagosome-lysosomal fusion in the autophagy pathway. We show in vivo that autophagy is impaired in dGBA-deficient fly brains. In response, mechanistic target of rapamycin (mTOR) activity is downregulated in dGBA-deficient flies and rapamycin ameliorates the lifespan, locomotor, and oxidative stress phenotypes. dGBA knock-out flies also display an upregulation of the Drosophila ortholog of mammalian TFEB, Mitf, a response that is unable to overcome the autophagy block. Together, our results suggest that rapamycin may have potential benefits in the treatment of GD, as well as PD linked to GBA1 mutations.

IRF8 directs stress-induced autophagy in macrophages and promotes clearance of Listeria monocytogenes.

Autophagy, activated by many stresses, plays a critical role in innate immune responses. Here we show that Interferon Regulatory Factor 8 (IRF8) is required for expression of autophagy-related genes in dendritic cells. Furthermore in macrophages, IRF8 is induced by multiple autophagy-inducing stresses, including IFNγ and toll like receptor stimulation, bacterial infection, starvation and by macrophage colony-stimulating factor. IRF8 directly activates many genes involved in various steps of autophagy, promoting autophagosome formation and lysosomal fusion. Consequently, Irf8-/- macrophages are deficient in autophagic activity, and excessively accumulate SQSTM1 and ubiquitin-bound proteins. We show that clearance of Listeria monocytogenes in macrophages requires IRF8-dependent activation of autophagy genes and subsequent autophagic capturing and degradation of Listeria antigens. These processes are defective in Irf8-/- macrophages where uninhibited bacterial growth ensues. Together, these data suggest that IRF8 is a major autophagy regulator in macrophages, essential for macrophage maturation, survival and innate immune responses.