Autophagy protects against palmitate-induced apoptosis in hepatocytes

Targeting uric acid: a promising intervention against oxidative stress and neuroinflammation in neurodegenerative diseases

Oxidative stress and neuroinflammation are recognized as key factors in the development of neurodegenerative diseases, yet effective interventions and biomarkers to address oxidative stress and neuroinflammation in these conditions are limited. Uric acid (UA), traditionally associated with gout, is now gaining prominence as a potential target in neurodegenerative diseases. Soluble UA stands out as one of the most vital antioxidant compounds produced by the human body, accounting for up to 55% of the extracellular capacity to neutralize free radicals. While there is increasing evidence supporting the neuroprotective properties of UA in Parkinson's disease and Alzheimer's disease, gaps in knowledge still exist regarding the underlying mechanisms and how to effectively translate these benefits into clinical practice. Moreover, the current UA elevation therapy exhibits unstable antioxidant properties, individual variability, and even adverse effects, limiting its potential clinical applications. This review consolidates recent advancements in understanding how UA exerts neuroprotective effects on neurodegenerative diseases and emphasizes the dual roles of UA in managing oxidative stress and neuroinflammation. Additionally, the review elucidates the mechanisms through which UA confers neuroprotection. Based on this, the review underscores the significance of UA as a potential biomarker and aims to provide a comprehensive understanding of its potential as a therapeutic target, while also addressing possible challenges to clinical implementation.

The skin photoprotective effect of trilinolein: Induction of cellular autophagy via the AMPK-mTOR signaling pathway

Trilinolein (TL) is an active substance contained in traditional Chinese herbs; modern studies have shown that trilinolein has anti-inflammatory and antioxidant effects on the body. This study delves into the photoprotective effect of trilinolein on UVB-irradiated Human Skin Fibroblast (HSF) cells and the underlying mechanisms. Our findings reveal that trilinolein had a photoprotective effect on HSF cells: trilinolein enhanced cellular autophagy, restored UVB-inhibited cell proliferative viability, and curbing UVB-induced reactive oxygen species (ROS) and apoptosis. Intriguingly, after inhibition of TL-induced autophagy via wortmannin, diminished trilinolein's photoprotective effects. Meanwhile, trilinolein was shown to modulate the AMPK-mTOR signaling pathway, thus enhance cellular autophagy in HSF cells, and this tendency was suppressed after the administration of compound C (AMPK inhibitor). In a mouse model of skin photodamage, trilinolein significantly mitigated photodamage extent through morphological and histopathological analyses. This study illuminates trilinolein could inhibit the photodamaging effects of UVB irradiation by regulating cellular autophagy through the AMPK-mTOR signaling pathway, suggesting its promising application in combating UV-induced skin disorders.

Insulin Inhibits Autophagy by Inhibiting the Binding of FoXO1 to the Promoter Region of GABARAPL1

Hyperinsulinemia and insulin resistance in T2D have a potent suppressive effect on hepatic autophagy, however, the underlying mechanisms remain unclear. To explore the effect of insulin on hepatic autophagy and its possible signaling pathways, HL-7702 cells were treated with insulin with or without insulin signaling inhibitors. The interaction between insulin and the promoter region of GABARAPL1 was assessed through luciferase assay and EMSA. There were significant dose-dependent decreases in the number of intracellular autophagosomes and the protein levels of GABARAPL1 and beclin1 in insulin-treated HL-7702 cells. Insulin signaling inhibitors reversed the inhibitory effect of insulin on rapamycin-induced autophagy and autophagy-related gene upregulation. Insulin blocks the binding of FoxO1 to putative insulin response elements in GABARAPL1 gene promoter, leading to the repressed transcription of GABARAPL1 gene and the suppression of hepatic autophagy. Our study identified GABARAPL1 as a novel target of insulin in suppressing hepatic autophagy.

Pathogenesis of Hepatocellular Carcinoma: The Interplay of Apoptosis and Autophagy

The pathogenesis of hepatocellular carcinoma (HCC) is a multifactorial process that has not yet been fully investigated. Autophagy and apoptosis are two important cellular pathways that are critical for cell survival or death. The balance between apoptosis and autophagy regulates liver cell turnover and maintains intracellular homeostasis. However, the balance is often dysregulated in many cancers, including HCC. Autophagy and apoptosis pathways may be either independent or parallel or one may influence the other. Autophagy may either inhibit or promote apoptosis, thus regulating the fate of the liver cancer cells. In this review, a concise overview of the pathogenesis of HCC is presented, with emphasis on new developments, including the role of endoplasmic reticulum stress, the implication of microRNAs and the role of gut microbiota. The characteristics of HCC associated with a specific liver disease are also described and a brief description of autophagy and apoptosis is provided. The role of autophagy and apoptosis in the initiation, progress and metastatic potential is reviewed and the experimental evidence indicating an interplay between the two is extensively analyzed. The role of ferroptosis, a recently described specific pathway of regulated cell death, is presented. Finally, the potential therapeutic implications of autophagy and apoptosis in drug resistance are examined.

Inhibiting specificity protein 1 attenuated sevoflurane-induced mitochondrial stress and promoted autophagy in hippocampal neurons through PI3K/Akt/mTOR and α7-nAChR signaling

Sevoflurane, a commonly used anesthetic in surgery, is considered as an inducer of neurodegenerative diseases and postoperative complications including postoperative cognitive dysfunction. Evidence showed that specificity protein 1 (SP1) participated in the regulation of various cellular processes. Also, SP1 was found to modulate sevoflurane-induced hippocampal inflammatory injury both in vitro and in vivo. Our study aimed to illustrate the role of SP1 in mediating mitochondrial stress and autophagy in neurons under sevoflurane exposure. SiRNA for SP1 was transfected in to hippocampus neurons for the loss-of-function assay before sevoflurane stimulation. Meanwhile, recilisib was utilized for PI3K/Akt/mTOR signaling activation, GTS-21 and MLA (methylycaconitine citrate) were used to activate or inactivate alpha 7 nicotinic acetylcholine receptor (α7-nAChR), respectively. Sevoflurane induced SP1 upregulation and autophagy suppression. Interfering SP1 dramatically depressed the promoted oxidative stress and mitochondrial dysfunction induced by sevoflurane. Additionally, SP1 silence blocked sevoflurane-induced activation of PI3K/Akt/mTOR signaling and inhibition of α7-nAChR. Restoring PI3K/Akt/mTOR signaling or depressing CAP significantly reversed the repressive effects of SP1 knockdown on mitochondrial stress and autophagy imbalance in hippocampal cells. In conclusions, our research indicated that SP1 regulated sevoflurane-induced oxidative stress dysregulation, mitochondrial function and cell autophagy in hippocampus via mediating the PI3K/Akt/mTOR and α7-nAChR pathways. Therefore, it might provide a novel sight for sevoflurane-induced hippocampus injury and POCD therapy.

Current insights in molecular characterization of non-alcoholic fatty liver disease and treatment

There is a continuously rising incidence of non-alcoholic fatty liver disease (NAFLD) around the world, which parallels the increasing incidence of metabolic diseases. NAFLD is a range of liver conditions that contains simple non-alcoholic fatty liver and advanced non-alcoholic steatohepatitis. In serious cases, NAFLD may develop into cirrhosis or even liver cancer. NAFLD has an intense relationship with metabolic syndrome, type 2 diabetes mellitus. It is known that gut microbiota, and functional molecules such as adenosine monophosphate-activated protein kinase JNK, and peroxisome proliferator-activated receptors (PPARs) in progressing and treating NAFLD. Traditionally, the conventional and effective therapeutic strategy is lifestyle intervention. Nowadays, new medicines targeting specific molecules, such as farnesoid X receptor, PPARs, and GLP-1 receptor, have been discovered and shown beneficial effects on patients with NAFLD. In this article, we focus on the molecular mechanisms and therapeutic approaches to NAFLD.

Glycyrrhetinic acid regulates impaired macrophage autophagic flux in the treatment of non-alcoholic fatty liver disease

Macrophages are involved in hepatocyte steatosis and necroinflammation and play an important role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Impaired autophagy function (decreased autophagy or blocked autophagic flow) leads to cell damage and death and promotes NAFLD progression. The experimental and clinical research of glycyrrhetinic acid (GA) in the treatment of NAFLD has gradually attracted attention with clear pharmacological activities such as immune regulation, antiviral, antitumor, antioxidant, liver protection, and anti-inflammatory. However, the effects of GA on the STAT3-HIF-1α pathway and autophagy in macrophages are still unclear, and its mechanism of action in the treatment of NAFLD remains to be further elucidated. We constructed a NAFLD mouse model through a high-fat and high-sugar diet to investigate the therapeutic effects of GA. The results showed that GA reduced weight, improved the pathological changes and hepatic lipid deposition of liver, and abnormally elevated the levels of serum biochemical (AST, ALT, TG, T-CHO, LDL-C, and HDL-C) and inflammatory indexes (IL-1β, IL-4, IL-6, MCP-1, and TNF-α) in NAFLD mice. Further examination revealed that GA ameliorates excessive hepatic macrophage infiltration and hepatocyte apoptosis. The results of the cell experiments further elaborated that GA modulated the PA-induced macrophage STAT3-HIF-1α pathway and ameliorated impaired autophagic flux (blockade of autophagosome–lysosome fusion) and overactivation of inflammation. Excessive hepatocyte apoptosis caused by the uncontrolled release of inflammatory cytokines was also suppressed by GA.

Conclusion

This study demonstrated that GA could regulate the STAT3-HIF-1α pathway of macrophages, ameliorate the impaired autophagy flux, and reduce the excessive production of inflammatory cytokines to improve the excessive apoptosis of liver cells, thus playing a therapeutic role on NAFLD.

Palmitate impairs the autophagic flux to induce p62-dependent apoptosis through the upregulation of CYLD in NRCMs

The most abundant saturated free fatty acid such as palmitate (PA), can accumulate in cardiomyocytes and induce lipotoxicity. CYLD is a known regulator in the development of cardiovascular disease and an important mediator of apoptosis. The role of CYLD in PA-induced cardiomyocyte apoptosis is not completely known. Here, we showed that PA treatment resulted in a concentration- and time-dependent effect on neonatal rat cardiomyocytes (NRCMs) apoptosis. PA impaired autophagy by significantly increasing the expression levels of LC3-II, Beclin 1, and also p62 in NRCMs. The autophagy flux was measured by detecting the fluorescence in the cells with Ad-mCherry-GFP-LC3B, a decrease in red puncta and a significant increase in yellow puncta in response to PA stimulation indicated that PA impairs the autophagic flux at the late stage of autophagosome-lysosome fusion. We further found knocked down of p62 by siRNA significantly decreased the expression level of cleaved caspase-3, decreased the apoptosis rate, also alleviated the loss of mitochondrial membrane potential, and decreased AIF and Cyt C releasing from mitochondria into the cytoplasm in the PA-treated NRCMs. From this, we considered that p62 accumulation was responsible for mitochondria-mediated apoptosis in PA-treated NRCMs. In addition, PA-induced a strong elevation of CYLD, siRNA-mediated knockdown of CYLD significantly antagonized PA-induced apoptosis and restored the autophagic flux in NRCMs. Knockdown of CYLD activation of the Wnt/β-catenin pathway to restore the autophagic flux and reduce the accumulation of p62 in PA- stimulated NRCMs, while an inhibitor of the Wnt/β-catenin pathway reversed this effect. Thus, our findings provide new insight into the molecular mechanism of PA toxicity in myocardial cells and suggest that CYLD may be a new therapeutic target for lipotoxic cardiomyopathy.

RIP1/RIP3/MLKL Mediates Myocardial Function Through Necroptosis in Experimental Autoimmune Myocarditis

Cardiomyopathy often leads to dilated cardiomyopathy (DCM) when caused by viral myocarditis. Apoptosis is long considered as the principal process of cell death in cardiomyocytes, but programmed necrosis or necroptosis is recently believed to play an important role in cardiomyocyte cell death. We investigated the role of necroptosis and its interdependency with other processes of cell death, autophagy, and apoptosis in a rat system of experimental autoimmune myocarditis (EAM). We successfully created a rat model system of EAM by injecting porcine cardiac myosin (PCM) and showed that in EAM, all three forms of cell death increase considerably, resulting in the deterioration of cardiac conditions with an increase in inflammatory infiltration in cardiomyocytes. To explore whether necroptosis occurs in EAM rats independent of autophagy, we treated EAM rats with a RIP1/RIP3/MLKL kinase-mediated necroptosis inhibitor, Necrostatin-1 (Nec-1). In Nec-1 treated rats, cell death proceeds through apoptosis but has no significant effect on autophagy. In contrast, autophagy inhibitor 3-Methyl Adenine (3-MA) increases necroptosis, implying that blockage of autophagy must be compensated through necroptosis. Caspase 8 inhibitor zVAD-fmk blocks apoptosis but increases both necroptosis and autophagy. However, all necroptosis, apoptosis, and autophagy inhibitors independently reduce inflammatory infiltration in cardiomyocytes and improve cardiac conditions. Since apoptosis or autophagy is involved in many important cellular aspects, instead of suppressing these two major cell death processes, Nec1 can be developed as a potential therapeutic target for inflammatory myocarditis.

γ-Linolenic Acid Prevents Lipid Metabolism Disorder in Palmitic Acid-Treated Alpha Mouse Liver-12 Cells by Balancing Autophagy and Apoptosis via the LKB1-AMPK-mTOR Pathway

Excessive fat deposition is the main character in nonalcoholic fatty liver disease (NAFLD), while γ-linolenic acid (GLA) is a polyunsaturated fatty acid that can reduce lipid deposition. This study investigated the effect and regulatory mechanism of GLA (100 μM) on lipid metabolism in alpha mouse liver 12 (AML-12) cells treated by 400 μM palmitic acid (PA). GLA reduced lipid content and increased fatty acid β oxidation, as indicated by decreasing triglyceride and cholesterol contents and increasing mRNA and protein expressions of CPT1α and PPARα. GLA relieved oxidative stress caused by PA, upregulated mRNA levels of superoxide dismutase and glutathione peroxidase, and decreased reactive oxygen species content. GLA reduced apoptosis, as indicated by decreases in the BAX/BCL2 expression level and apoptosis percentage. GLA activated autophagy, autophagosome-lysosome fusion, and LKB1-AMPK-mTOR signaling and upregulated mRNA and protein expressions of Beclin-1, autophagy-related 5, and liver kinase B1 (LKB1). These effects of GLA on lipid metabolism disorders of PA-treated hepatocytes were reversed by autophagy inhibitor 3MA and AMPK inhibitor compound C, confirming our conclusions. Overall, GLA can protect AML-12 cells from lipid metabolism disorder caused by PA via balancing autophagy and apoptosis mediated by the LKB1-AMPK-mTOR pathway. Consequently, GLA, as a dietary supplement, can help to prevent and treat NAFLD by regulating lipid metabolism and autophagy.

Lupin γ-conglutin protects against cell death induced by oxidative stress and lipotoxicity, but transiently inhibits in vitro insulin secretion by increasing KATP channel currents

Lupin γ-conglutin beneficially modulates glycemia, but whether it protects against oxidative and lipotoxic damage remains unknown. Here, we studied the effects of γ-conglutin on cell death provoked by hydrogen peroxide and palmitate in HepG2 hepatocytes and insulin-producing MIN6 cells, and if a modulation of mitochondrial potential and reactive oxygen species (ROS) levels was involved. We also investigated how γ-conglutin influences insulin secretion and electrical activity of β-cells. The increased apoptosis of HepG2 cells exposed to hydrogen peroxide was prevented by γ-conglutin, and the viability and ROS content in γ-conglutin-treated cells was similar to that of non-exposed cells. Additionally, γ-conglutin partially protected MIN6 cells against hydrogen peroxide-induced death. This was associated with a marked reduction in ROS. No significant changes were found in the mitochondrial potential of γ-conglutin-treated cells. Besides, we observed a partial protection against lipotoxicity only in hepatocytes. Unexpectedly, we found a transient inhibition of insulin secretion, plasma membrane hyperpolarization, and higher K_ATP channel currents in β-cells treated with γ-conglutin. Our data show that γ-conglutin protects against cell death induced by oxidative stress or lipotoxicity by decreasing ROS and might also indicate that γ-conglutin promotes a β-cell rest, which could be useful for preventing β-cell exhaustion in chronic hyperglycemia.

Restorative effect of adipose tissue-derived stem cells on impaired hepatocytes through Notch signaling in non-alcoholic steatohepatitis mice

Adipose tissue-derived stem cells (ADSCs) have been suggested as a novel treatment for non-alcoholic steatohepatitis (NASH); however, the mechanisms underlying their therapeutic effect remain poorly understood. In this study, we aimed to investigate the association of Notch signaling, which is crucial for cellular proliferation and differentiation in ADSC-mediated treatment of NASH. Flow cytometry analysis of ADSCs showed that they expressed the Notch ligands JAG1, DLL1, and DLL4. The expression of genes associated with the Notch signaling pathway was attenuated in hepatocytes of NASH model mice. We further observed ADSC-mediated activation of Notch signaling in these hepatocytes in addition to an increase in proliferating cell nuclear antigen⁺ cells and a decrease in TdT-mediated dUTP-biotin nick end labeling⁺ apoptotic cells. Co-culture of palmitic acid-induced steatotic hepatocytes and ADSCs resulted in the activation of Notch signaling and reduction of apoptosis of steatotic hepatocytes. Moreover, inhibition of Notch signaling by a γ-secretase inhibitor and knockdown of Notch ligands using siRNA attenuated the anti-apoptotic effect of co-cultured ADSCs in vitro. Our findings show that the Notch signaling pathway is involved in the inhibition of apoptosis and restoration of cellular proliferation of hepatocytes from NASH mice following ADSC treatment.

Lithium chloride promotes osteogenesis and suppresses apoptosis during orthodontic tooth movement in osteoporotic model via regulating autophagy

Osteoporosis is a widely distributed disease that may cause complications such as accelerated tooth movement, bone resorption, and tooth loss during orthodontic treatment. Promoting bone formation and reducing bone resorption are strategies for controlling these complications. For several decades, the autophagy inducer lithium chloride (LiCl) has been explored for bipolar . In this study, we investigated the autophagy-promoting effect of LiCl on bone remodeling under osteoporotic conditions during tooth movement. Ovariectomy was used to induce osteoporosis status in vivo. The results showed that LiCl rejuvenated autophagy, decreased apoptosis, and promoted bone formation, thus protecting tooth movement in osteoporotic mice. Furthermore, in vitro experiments showed that LiCl reversed the effects of ovariectomy on bone marrow-derived mesenchymal stem cells (BMSCs) extracted from ovariectomized mice, promoting osteogenesis and suppressing apoptosis by positively regulating autophagy. These findings suggest that LiCl can significantly decrease adverse effects of osteoporosis on bone remodeling, and that it has great potential significance in the field of bone formation during tooth movement in osteoporosis patients.

Inhibition of Notch1 signaling reduces hepatocyte injury in nonalcoholic fatty liver disease via autophagy

Nonalcoholic fatty liver disease (NAFLD) has become the most common cause of chronic liver disease worldwide and an urgent target for clinical intervention. Notch1 signaling pathway activity was found to be related to the severity of NAFLD, but the specific mechanism is not precise. Here, we investigated the potential mechanisms of Notch1 signaling in the development of NAFLD. Firstly, we found that Notch1 signaling is activated in free fatty acids-treated HepG2 cells accompanied by lipid accumulation, apoptosis, oxidative stress, and mitochondrial damage, which could be alleviated by Notch1 inhibitor N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT). In the meantime, we found that administration of DAPT activated the autophagy pathway in NAFLD. Furthermore, the use of autophagy inhibitor chloroquine reversed the DAPT-mediated protective effect in NAFLD. All our results uncover a vital role of Notch1 in hepatocyte injury and metabolism of NAFLD, giving rise to a new sight for NAFLD treatment by regulation of Notch signaling and autophagy pathway.

Propofol protects PC12 cells from cobalt chloride-induced injury by mediating miR-134

OBJECTIVE

Propofol (PRO) was reported to exert a neuroprotective effect by decreasing microRNA-134 (miR-134), a brain-specific miRNA, thus, the role of PRO against cobalt chloride (CoCl₂)-induced injury in rat pheochromocytoma cells (PC12) via mediating miR-134 was explored.

METHODS

CoCl₂-induced PC12 cells treated with PRO were transfected with or without miR-134 negative control (NC)/ inhibitor/mimic, and the following detections were then performed using cell counting kit-8 (CCK-8), Annexin V-fluorescein isothiocyanate/propidium iodide (Annexin V-FITC/PI) and Hoechst 33258 staining. Autophagy was observed by transmission electron microscope (TEM). Mitochondrial membrane potential (MMP) was detected by Rhodamine-123 (Rh123) staining, and reactive oxygen species (ROS) by dichloro-dihydro-fluorescein diacetate (DCFH-DA) staining. Protein and gene expressions were measured by Western blotting and quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), respectively.

RESULTS

PRO reversed the CoCl₂-induced decrease in the PC12 cell viability and increased miR-134 in a dose-dependent manner. CoCl₂ increased LC3II/I ratio and Beclin-1 expression, but decreased p62 expression, which was abolished by PRO. In addition, an increased cell apoptosis rates triggered by CoCl₂ were reduced by PRO with the down-regulations of Bax and Caspase-3 and the up-regulation of Bcl-2. Furthermore, PRO decreased methylenedioxyamphetamine (MDA), nitric oxide (NO) and ROS in CoCl₂-induced PC12 cells accompanying the increase in glutathione peroxidase (GSH-Px) and MMP. The effects of PRO on autophagy, apoptosis and oxidative stress in CoCl₂-induced PC12 cell were reversed by miR-134 mimic.

CONCLUSION

PRO may mitigate CoCl₂-induced autophagy in PC12 cells with decreased apoptosis and improved oxidative stress via mediating miR-134.

Punicalagin Attenuates Palmitate-Induced Lipid Droplet Content by Simultaneously Improving Autophagy in Hepatocytes

SCOPE

Several studies show that excessive lipid intake can cause hepatic steatosis. To investigate lipotoxicity on cellular level, palmitate (PA) is often used to highly increase lipid droplets (LDs). One way to remove LDs is autophagy, while it is controversially discussed if autophagy is also affected by PA. It is aimed to investigate whether PA-induced LD accumulation can impair autophagy and punicalagin, a natural autophagy inducer from pomegranate, can improve it.

METHODS AND RESULTS

To verify the role of autophagy in LD degradation, HepG2 cells are treated with PA and analyzed for LD and perilipin 2 content in presence of autophagy inducer Torin 1 and inhibitor 3-Methyladenine. PA alone seems to initially induce autophagy-related proteins but impairs autophagic-flux in a time-dependent manner, considering 6 and 24 h PA. To examine whether punicalagin can prevent autophagy impairment, cells are cotreated for 24 h with PA and punicalagin. Results show that punicalagin preserves expression of autophagy-related proteins and autophagic flux, while simultaneously decreasing LDs and perilipin 2.

CONCLUSION

Data provide new insights into the role of PA-induced excessive LD content on autophagy and suggest autophagy-inducing properties of punicalagin, indicating that punicalagin can be a health-beneficial compound for future research on lipotoxicity in liver.

Autophagy and Liver Diseases

Autophagy plays an important role in the physiology and pathology of the liver. It is involved in the development of many liver diseases such as α-1-antitrypsin deficiency, chronic hepatitis virus infection, alcoholic liver disease, nonalcoholic fatty liver disease, and liver cancer. Autophagy has thus become a new target for the treatment of liver diseases. How to treat liver diseases by regulating autophagy has been a hot topic.

Ursodeoxycholic acid alleviates nonalcoholic fatty liver disease by inhibiting apoptosis and improving autophagy via activating AMPK

Ursodeoxycholic acid (UDCA), first identified in bear bile, was widely used in cholestatic liver diseases. Our previous studies have suggested UDCA may exert favorable influence on hepatic steatosis. However, the molecular mechanism remains elusive. Given the role of autophagy and apoptosis dysregulation in the pathogenesis of nonalcoholic fatty liver disease (NAFLD) and pharmacological effects of UDCA on modulating autophagy, apoptosis. we sought to investigate whether UDCA had therapeutic effect on NAFLD and its mechanism of modulating autophagy, apoptosis. Our finding revealed that UDCA exerted obviously favorable influence on hepatic steatosis in NAFLD rats by activating AMP-activated protein kinase (AMPK). Mechanistic studies indicated UDCA inhibited apoptosis and improved autophagy by influencing Bcl-2/Beclin-1 and Bcl-2/Bax complex interaction. Importantly, above-mentioned influence of UDCA on autophagy, apoptosis and Bcl-2/Beclin-1, Bcl-2/Bax complex interaction in NAFLD were partly counteracted by AMPK inhibitor compound C(CC). In conclusion, UDCA exerts favorable influence on hepatic steatosis in NAFLD rats, which is attributable to apoptosis inhibition and autophagy induction by influencing Bcl-2/Beclin-1 complex and Bcl-2/Bax complex interaction via activating AMPK, indicating that UDCA may be a promising therapeutic target for NAFLD.

Corilagin Alleviates Nonalcoholic Fatty Liver Disease in High-Fat Diet-Induced C57BL/6 Mice by Ameliorating Oxidative Stress and Restoring Autophagic Flux

Corilagin (Cori) possesses multiple biological activities. To determine whether Cori can exert protective effects against nonalcoholic fatty liver disease (NAFLD) and its potential mechanisms. C57BL/6 mice were fed with high-fat diet (HFD) alone or in combination with Cori (20 mg/kg, i.p.) and AML12 cells were exposed to 200 μM PA/OA with or without Cori (10 μM or 20 μM). Phenotypes and key indicators relevant to NAFLD were examined both in vivo and in vitro. In this study, Cori significantly ameliorated hepatic steatosis, confirmed by improved serum lipid profiles, and hepatic TC, TG contents, and the gene expression related to lipid metabolism in livers of HFD mice. Moreover, Cori attenuated HFD-mediated autophagy (including mitophagy) blockage by restoring autophagic flux, evidenced by increased number of autophagic double vesicles containing mitochondria, elevated LC3II protein levels, decreased p62 protein levels, as well as enhanced colocalization of autophagy-related protein (LC3, Parkin) and mitochondria. In accordance with this, Cori also reduced the accumulation of ROS and MDA levels, and enhanced the activities of antioxidative enzymes including SOD, GSH-Px, and CAT. In addition, Cori treatment improved mitochondrial dysfunction, evidenced by increased mitochondrial membrane potential (ΔΨm). In parallel with this, Cori decreased mitochondrial DNA oxidative damage, while increased mitochondrial biogenesis related transcription factors expression, mitochondrial DNA content and oxygen consumption rate (OCR). In conclusion, these results demonstrate that Cori is a potential candidate for the treatment of NAFLD via diminishing oxidative stress, restoring autophagic flux, as well as improving mitochondrial functions.

Hepatic PLIN5 signals via SIRT1 to promote autophagy and prevent inflammation during fasting

Lipid droplets (LDs) are energy-storage organelles that are coated with hundreds of proteins, including members of the perilipin (PLIN) family. PLIN5 is highly expressed in oxidative tissues, including the liver, and is thought to play a key role in uncoupling LD accumulation from lipotoxicity; however, the mechanisms behind this action are incompletely defined. We investigated the role of hepatic PLIN5 in inflammation and lipotoxicity in a murine model under both fasting and refeeding conditions and in hepatocyte cultures. PLIN5 ablation with antisense oligonucleotides triggered a pro-inflammatory response in livers from mice only under fasting conditions. Similarly, PLIN5 mitigated lipopolysaccharide- or palmitic acid-induced inflammatory responses in hepatocytes. During fasting, PLIN5 was also required for the induction of autophagy, which contributed to its anti-inflammatory effects. The ability of PLIN5 to promote autophagy and prevent inflammation were dependent upon signaling through sirtuin 1 (SIRT1), which is known to be activated in response to nuclear PLIN5 under fasting conditions. Taken together, these data show that PLIN5 signals via SIRT1 to promote autophagy and prevent FA-induced inflammation as a means to maintain hepatocyte homeostasis during periods of fasting and FA mobilization.

Abnormal expression of liver autophagy and apoptosis-related mRNA in fatty liver haemorrhagic syndrome and improvement function of resveratrol in laying hens

Fatty liver haemorrhagic syndrome (FLHS) is characterized by hepatic rupture and haemorrhage leading to sudden death in laying hens. Resveratrol (Res) is a natural polyphenol with antioxidant and anti-inflammatory effects that can ameliorate chronic liver disease. The aim of this study was to investigate the improved effect of Res on the altered expression of autophagy and apoptosis-related genes in laying hens with FLHS. A total of 144 healthy 150-day-old laying hens were randomly divided into four groups: control group (standard diet), HELP group (high-energy-low-protein (HELP) diet), HELP + Res group (HELP diet with 400 mg/kg Res) and Res group (standard diet with 400 mg/kg Res). Histopathological lesions of the liver and the mRNA levels of Beclin-1, Atg5, Atg7, p62, Bcl-2, Bax and Caspase-3 on days 40, 80, and 120 were measured. The results showed that lipid accumulation and hepatocyte damage in the HELP group were more serious than those in the HELP + Res group. The mRNA levels of Beclin-1, Atg5, Atg7, and Bcl-2 in the HELP and HELP + Res groups were strikingly declined (P < 0.01) compared to the control group, and their mRNA levels were markedly higher in HELP group than those in the HELP + Res group (P < 0.05). Additionally, the mRNA levels of p62, Bax and Caspase-3 were significantly increased in the HELP and HELP + Res groups (P < 0.01 or P < 0.05), but their mRNA levels in the HELP group were higher than those in the HELP + Res group (P < 0.05). Collectively, FLHS could induce severe lipid accumulation, abnormal mRNA levels of liver autophagy and apoptosis-related genes. Res as a dietary supplement could attenuate these abnormal changes.

Induction of Chemerin on Autophagy and Apoptosis in Dairy Cow Mammary Epithelial Cells

Involution of the mammary gland is a complex process controlled by various endocrine hormones and cytokine. As a novel adipocytokine, Chemerin not only plays a pivotal role in physiological and pathological processes such as immune response and lipid metabolism, but is also involved in the regulation of programmed cell death, including autophagy and apoptosis. The purpose of the present study was to elucidate whether autophagy and apoptosis of bovine mammary epithelial cells (BMECs) was triggered by Chemerin. BMECs were cultured and treated with Chemerin in vitro. The expression of autophagosome-forming marker, microtubule-associated protein 1 light chain 3 II (LC3-II) and sequestosome-1 (SQSTM 1, best known as p62), a substrate of autophagosome degradation were detected. The result showed that Chemerin significantly decreased the expression of p62 and markedly induced the conversion of LC3-I to LC3-II. The ratio of Bcl2-associated X and B-cell lymphoma-2 (Bax/Bcl-2) and the activity of caspase-3 were up-regulated after being treated by Chemerin, and the apoptotic rate was also significantly increased. These results suggested that Chemerin promoted the occurrence of autophagy and apoptosis in BMECs. Chloroquine (CQ), which is an inhibitor of autophagy. To explore effects of Chemerin on apoptosis, we prevented Chemerin-induced autophagy by pre-adding CQ in BMECs. Interestingly, this part of the experiment helped us find that all effects of Chemerin on apoptosis of BMECs could be enhanced with the inhibition of autophagy. Our study demonstrates that Chemerin-induced autophagy and apoptosis are mutually regulated in BMECs, but the specific mechanism remains to be further researched.

Denatonium Benzoate-Induces Oxidative Stress in the Heart and Kidney of Chinese Fast Yellow Chickens by Regulating Apoptosis, Autophagy, Antioxidative Activities and Bitter Taste Receptor Gene Expressions

Simple Summary

Denatonium benzoate is a strong bitter taste receptor agonist, extensively used for its activation of different cell pathways. Taste signals have been associated to food recognition and avoidance, and bitter taste provokes an aversive reaction and is assumed to protect chickens from consuming poisons and harmful toxic substances. The results of the study revealed that dietary supplementation with medium and high doses of denatonium benzoate damaged the epithelial cells of the heart and kidneys by inducing apoptosis and autophagy and reduced the growth of chickens, respectively. However, mRNA expressions of bitter taste receptors, downstream signaling effector genes, apoptosis-, autophagy- and antioxidant-related genes were higher on day 7, while these expressions were subsequently decreased on day-28 in the heart and kidney of Chinese Fast Yellow chickens in a dose-response manner.

Abstract

The sense of taste which tells us which prospective foods are nutritious, poisonous and harmful is essential for the life of the organisms. Denatonium benzoate (DB) is a bitter taste agonist known for its activation of bitter taste receptors in different cells. The aim of the current study was to investigate the mRNA expressions of bitter taste, downstream signaling effectors, apoptosis-, autophagy- and antioxidant-related genes and effector signaling pathways in the heart/kidney of chickens after DB dietary exposure. We randomly assigned 240, 1-day-old Chinese Fast Yellow chicks into four groups with five replicates of 12 chicks and studied them for 28 consecutive days. The dietary treatments consisted of basal diet and feed containing DB (5, 20 and 100 mg/kg). The results revealed that dietary DB impaired (p < 0.05) the growth performance of the chickens. Haemotoxylin and eosin staining and TUNEL assays confirmed that medium and high doses of DB damaged the epithelial cells of heart/kidney and induced apoptosis and autophagy. Remarkably, the results of RT-PCR and qRT-PCR indicated that different doses of DB gradually increased (p < 0.05) mRNA expressions of bitter taste, signaling effectors, apoptosis-, autophagy- and antioxidant- related genes on day 7 in a dose-response manner, while, these expressions were decreased (p < 0.05) subsequently by day-28 but exceptional higher (P < 0.05) expressions were observed in the high-dose DB groups of chickens. In conclusion, DB exerts adverse effects on the heart/kidney of chickens in a dose-response manner via damaging the epithelium of the heart/kidney by inducing apoptosis, autophagy associated with bitter taste and effector gene expressions. Correlation analyses for apoptosis/autophagy showed agonistic relationships. Our data provide a novel perspective for understanding the interaction of bitter taste, apoptosis, autophagy and antioxidative genes with bitter taste strong activators in the heart/kidney of chicken. These insights might help the feed industries and pave the way toward innovative directions in chicken husbandry.

Interplay between oxidative stress and autophagy function and its role in inflammatory cytokine expression induced by palmitate in skeletal muscle cells

Autophagy is a cellular process activated in response to various stresses such as starvation, hypoxia, and oxidative stress. Autophagy was reported to modulate the inflammatory pathways. However, whether autophagy is involved in regulation of palmitate-induced inflammation of skeletal muscle C2C12 cells is still unknown. The present study aimed to investigate the autophagic pathway in C2C12 cells treated with 0.5 mM palmitate. The results showed that the protein levels of LC3BII and P62 were increased in C2C12 cells after 12 h palmitate treatment. Besides, inhibition of autophagy by chloroquine or 3-methyladenin and its activation by rapamycin were associated with elevated mRNA and protein levels of IL-6 and TNF-α inflammatory cytokines in C2C12 cells. To study the mechanism by which autophagy impairment leads to activation of inflammatory responses, reactive oxygen species (ROS) levels in palmitate-treated cells were measured. The results showed that while palmitate stimulates ROS production, pretreatment of the cells with N-acetyl cysteine (NAC), a ROS scavenger, reduced inflammatory responses and also improved LC3-BII and P62 protein in the C2C12 cells exposed to palmitate. These findings suggest that palmitate-induced defect of autophagic flux leads to elevated inflammatory cytokine expression in the skeletal muscle cells by regulating the oxidative stress process.

Macrophage-Specific Hypoxia-Inducible Factor-1α Contributes to Impaired Autophagic Flux in Nonalcoholic Steatohepatitis

Inflammatory cell activation drives diverse cellular programming during hepatic diseases. Hypoxia-inducible factors (HIFs) have recently been identified as important regulators of immunity and inflammation. In nonalcoholic steatohepatitis (NASH), HIF-1α is upregulated in hepatocytes, where it induces steatosis; however, the role of HIF-1α in macrophages under metabolic stress has not been explored. In this study, we found increased HIF-1α levels in hepatic macrophages in methionine-choline-deficient (MCD) diet-fed mice and in macrophages of patients with NASH compared with controls. The HIF-1α increase was concomitant with elevated levels of autophagy markers BNIP3, Beclin-1, LC3-II, and p62 in both mouse and human macrophages. LysM^Cre HIF^dPA fl/fl mice, which have HIF-1α levels stabilized in macrophages, showed higher steatosis and liver inflammation compared with HIF^dPA fl/fl mice on MCD diet. In vitro and ex vivo experiments reveal that saturated fatty acid, palmitic acid (PA), both induces HIF-1α and impairs autophagic flux in macrophages. Using small interfering RNA-mediated knock-down and overexpression of HIF-1α in macrophages, we demonstrated that PA impairs autophagy via HIF-1α. We found that HIF-1α mediates NF-κB activation and MCP-1 production and that HIF-1α-mediated impairment of macrophage autophagy increases IL-1β production, contributing to MCD diet-induced NASH. Conclusion: Palmitic acid impairs autophagy via HIF-1α activation in macrophages. HIF-1α and impaired autophagy are present in NASH in vivo in mouse macrophages and in human blood monocytes. We identified that HIF-1α activation and decreased autophagic flux stimulate inflammation in macrophages through upregulation of NF-κB activation. These results suggest that macrophage activation in NASH involves a complex interplay between HIF-1α and autophagy as these pathways promote proinflammatory overactivation in MCD diet-induced NASH.

Protective effects of tanshinone IIA on SH-SY5Y cells against oAβ1-42-induced apoptosis due to prevention of endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress caused by β-amyloid protein (Aβ) may play an important role in the pathogenesis of Alzheimer disease (AD). Our previous data have indicated that tanshinone IIA (tan IIA) protected primary neurons from Aβ induced neurotoxicity. To further explore the neuroprotection of tan IIA, here we study the effects of tan IIA on the ER stress response in oligomeric Aβ_1-42 (oAβ_1-42)-induced SH-SY5Y cell injury. Our data showed that tan IIA pretreatment could increase cell viability and inhibit apoptosis caused by oAβ_1-42. Furthermore, tan IIA markedly suppressed ER dilation and prevented oAβ_1-42-induced abnormal expression of glucose regulated protein 78 (GRP78), initiation factor 2α (eIF2α), activating transcription factor 6 (ATF6), as well as inhibited the activation of C/EBP homologous protein (CHOP) and c-Jun N-terminal kinase (JNK) pathways. Moreover, tan IIA ameliorated oAβ_1-42-induced Bcl-2/Bax ratio reduction, prevented cytochrome c translocation into cytosol from mitochondria, reduced oAβ_1-42-induced cleavage of caspase-9 and caspase-3, suppressed caspase-3/7 activity, and increased mitochondrial membrane potential (MMP) and ATP content. Meanwhile, oAβ_1-42-induced cell apoptosis and activation of ER stress can also be attenuated by the inhibitor of ER stress 4-phenylbutyric acid (4-PBA). Taken together, these data indicated that tan IIA protects SH-SY5Y cells against oAβ_1-42-induced apoptosis through attenuating ER stress, modulating CHOP and JNK pathways, decreasing the expression of cytochrome c, cleaved caspase-9 and cleaved caspase-3, as well as increasing the ratio of Bcl-2/Bax, MMP and ATP content. Our results strongly suggested that tan IIA may be effective in treating AD associated with ER stress.

The functional role of Bax/Bak in palmitate-induced lipoapoptosis

Induction of programmed cell death, mainly apoptosis (lipoapoptosis) is a major cellular consequence of the lipotoxicity, a harmful effect resulting from the overload of lipids. Both Endoplasmic reticulum (ER) stress and autophagy have been suggested to play important role in the regulation of lipoapoptosis. However, the exact mechanisms underlying lipoapoptosis remain unclear. In the present study, we aimed to investigate the functional role of Bax/Bak in lipoapoptosis using mouse embryonic fibroblasts (MEFs) cell culture model. Results showed that palmitate induced caspase-dependent apoptosis in wild-type Bax/Bak MEF cells, whereas a caspase-independent cell death was induced by palmitate in Bax/Bak knockout MEF cells, suggesting requirement of Bax/Bak in palmitate-induced caspase activation. More importantly, we found that the status of Bax/Bak is a determinant that governs the decision between the pro-survival or pro-death function of autophagy in response to palmitate exposure, and Bax/Bak is required for palmitate-induced activation of endoplasmic reticulum (ER) stress and subsequently ER stress-mediated apoptosis. The findings of the present study provided novel insights into understanding the mechanisms involved in the regulation of palmitate-induced lipoapoptosis.

Deciphering the ionic homeostasis, oxidative stress, apoptosis, and autophagy in chicken intestine under copper(II) stress

As cofactors of several enzymatic, copper (Cu) participates in many essential metabolic processes. Also, as a heavy metal, it exhibits highly toxic to the organism if excessive. This study endeavored to detect the pathophysiological changes in the jejunum of chickens, which were insulted by CuSO₄ (300 mg/kg diet) for 90 days. Results showed metabolic disorders of trace elements evidenced by their significant downregulations (Na, Al, Li, B, Cr, Ni, Sn, Sb, Ba) and upregulations (Cu, Si, As, Cd, Se, and Tl) in 90 days. Simultaneously, increased TdT-mediated dUTP nick end labeling (TUNEL)-positive nuclei and distinct ultrastructural apoptotic features were observed. Meanwhile, in 30, 60, and 90 days, indicators of oxidative stress, apoptosis, autophagy, and mitochondrial dynamic were detected to uncover the molecular mechanism behind these pathological changes. The results showed that suppressed antioxidant ability was companied by increased mRNA and protein levels of proapoptosis and mitochondrial fission activating genes in the Cu group compared with chickens in the control group (P < 0.05). Moreover, the markers of autophagy long-chain 3 (LC3-II/LC3-I), Bcl-2-interacting protein (beclin-1), and autophagy-related gene (ATG4B and ATG5) displayed a time-dependent increase during 30, 60, and 90 days. We conjectured that subchronic copper poisoning, under the background of redistribution of trace elements, induced oxidative stress and cascaded apoptosis, autophagy, and mitochondrial disorder, which contributed to jejunotoxicity in chicken. Collectively, our study provides a basic assessment of subchronic Cu exposure on poultry, voicing concerns about copper pollution by anthropogenic activities.

Copper (II) and/or arsenite-induced oxidative stress cascades apoptosis and autophagy in the skeletal muscles of chicken

Arsenic (As) is a ubiquitous environmental toxin and robust inducer of oxidative stress (OxS). Copper (Cu) is an essential microelement, which participates in OxS as a cofactor for certain enzymes, with narrow optimal range between essential and toxic concentrations. However, their effects are rarely studied in chicken skeletal muscles, which have soaring per capita consumption andare susceptible to oxidative damage. In the present study, we demonstrated that the administration of copper sulfate (300 mg kg^-1) or arsenite (30 mg kg^-1) individually or their co-administration leads to varying degrees of OxS in the skeletal muscles of chickens. Corresponding to the protein expression pattern, the mRNA levels of caspase, B-cell lymphoma-2 (Bcl-2) families, and autophagy-related genes were also compromised in the experimental groups, indicating the involvement of both apoptotic and autophagic cell death. Additionally, rampant mitochondrial fission caused the vicious cycle between imbalanced mitochondrial dynamics and OxS, thus tethering intracellular homeostasis. The abovementioned muscle damage and index anomalies were time dependent, and more deteriorated effects were observed in Cu²⁺ and arsenite co-administered groups than those in groups administered Cu²⁺ and arsenite alone. Intriguingly, in the studied skeletal muscles, namely wing biceps brachii and leg gastrocnemius, there were conspicuous differences in oxidative toxicity susceptibility, which needs further study. The present study showed that Cu and/or As induce oxidative damage in chicken skeletal muscles and discussed its mechanism in terms of apoptosis, autophagy, and mitochondrial dynamics, thus voicing concerns about poultry breeding areas cross-contaminated with Cu²⁺ and arsenite.

Apoptosis and non-alcoholic fatty liver diseases

The number of patients with nonalcoholic fatty liver diseases (NAFLD) including nonalcoholic steatohepatitis (NASH), has been increasing. NASH causes cirrhosis and hepatocellular carcinoma (HCC) and is one of the most serious health problems in the world. The mechanism through which NASH progresses is still largely unknown. Activation of caspases, Bcl-2 family proteins, and c-Jun N-terminal kinase-induced hepatocyte apoptosis plays a role in the activation of NAFLD/NASH. Apoptotic hepatocytes stimulate immune cells and hepatic stellate cells toward the progression of fibrosis in the liver through the production of inflammasomes and cytokines. Abnormalities in glucose and lipid metabolism as well as microbiota accelerate these processes. The production of reactive oxygen species, oxidative stress, and endoplasmic reticulum stress is also involved. Cell death, including apoptosis, seems very important in the progression of NAFLD and NASH. Recently, inhibitors of apoptosis have been developed as drugs for the treatment of NASH and may prevent cirrhosis and HCC. Increased hepatocyte apoptosis may distinguish NASH from NAFLD, and the improvement of apoptosis could play a role in controlling the development of NASH. In this review, the association between apoptosis and NAFLD/NASH are discussed. This review could provide their knowledge, which plays a role in seeing the patients with NAFLD/NASH in daily clinical practice.

Autophagy: The Last Defense against Cellular Nutritional Stress

Homeostasis of nutrient metabolism is critical for maintenance of the normal physiologic status of the cell and the integral health of humans and mammals. In vivo, there is a highly efficient and precise process involved in nutrient recycling and organelle cleaning. This process is named autophagy, and it can be induced in response to the dynamic change of nutrients. When cells face nutritional stress, such as stress caused by nutrient deficiency or nutrient excess, the autophagy pathway will be activated. Generally, when nutrients are withdrawn, cells will sense the signs of starvation and respond. AMP-activated protein kinase and the mammalian target of rapamycin, two of the major metabolic kinases, are responsible for monitoring cellular energy and the concentration of amino acids, respectively. Nutrient excess also induces autophagy, mainly via the reactive oxygen species and endoplasmic reticulum stress pathway. When nutritional stress activates the autophagy pathway, the nutrients or damaged organelles will be recycled for cell survival. However, if autophagy is overwhelmingly induced, autophagic cell death will possibly occur. The balance of the autophagy induction is the crucial factor for cell survival or death. Herein, we summarize the current knowledge on the induction of autophagy, the autophagy response under nutritional stresses, and autophagic cell death and related diseases, which will highlight the process of nutritional stress-induced autophagy and its important physiologic and/or pathologic roles in cell metabolism and diseases, and shed light on the research into the mechanism and clinical applications of autophagy induced by nutritional stresses.

Interplay between elemental imbalance-related PI3K/Akt/mTOR-regulated apoptosis and autophagy in arsenic (III)-induced jejunum toxicity of chicken

Arsenic trioxide (As₂O₃), the most toxic form of arsenic found in foodstuffs, is considered a carcinogen for human and animal. But many of the events that occur during its passage through the gastrointestinal tract are uncharted in birds. This study assesses the toxic effect on the jejunum of chicken which subchronically exposed to diets that contain As₂O₃ (0, 0.625, 1.25, 2.5 mg/kg body weight) for 90 days. Electron microscopy, TdT-mediated dUTP nick-end labeling (TUNEL), qPCR, and Western blot were performed. The results showed that mitochondrial fusion and apoptosis inhibiting genes had degressive trends, whereas mitochondrial fission and apoptosis activating genes presented heightened expressions in the treatment group compared with the control (P < 0.05). Subsequently, significant inhibition in PI3K/AKT/mTOR signaling was observed. Moreover, the expression of autophagy markers (LC3-II/LC3-I, Beclin-1) increased time and dose-dependently. Additionally, metabolic disorders of trace elements were detected evidenced by their significant decreases (aluminum, silicon, calcium, manganese, strontium, titanium, lithium, boron, cobalt, mercury, chromium) and increases (arsenic, cadmium, selenium, lead, nickel) on 90 days using inductively coupled plasma mass spectrometer (ICP-MS). It is possible that the changes of trace elements have a hand in the come on and development of arsenism. Taken together, we conjectured that, in chicken jejunum, arsenic led to redistribution of trace elements, promoting apoptosis via regulating mitochondrial dynamics, leading to autophagy through PI3K/AKT/mTOR signal pathways.

Saturated fatty acid palmitate negatively regulates autophagy by promoting ATG5 protein degradation in meniscus cells

Obesity and associated metabolic factors are major risk factors for the development of osteoarthritis. Previously, we have shown that the free fatty acid palmitate induces endoplasmic reticulum (ER) stress and induces apoptosis in meniscus cells. However, the molecular mechanisms involved in these effects are not clearly understood. In our current study, we found that palmitate inhibits autophagy by modulating the protein levels of autophagy-related genes-5 (ATG5) that is associated with decreased lipidation of LC3 and increased activation of cleaved caspase 3. Pretreatment of meniscus cells with 4-phenyl butyric acid, a small molecule chemical chaperone that alleviates ER stress, or with MG-132, a proteasome inhibitor, restored normal levels of ATG5 and autophagosome formation, and decreased expression of cleaved caspase 3. Thus, our data suggest that palmitate downregulates autophagy in meniscus cells by degrading ATG5 protein via ER-associated protein degradation, and thus promotes apoptosis. This is the first study to demonstrate that palmitate-induced endoplasmic reticulum stress negatively regulates autophagy.

Autophagy protects bone marrow mesenchymal stem cells from palmitate‑induced apoptosis through the ROS‑JNK/p38 MAPK signaling pathways

In recent years, the association between saturated fatty acids (FA) and bone cells has received a high level of attention. Previous studies have shown that palmitate (PA), a common saturated FA, can cause apoptosis in bone marrow mesenchymal stem cells (BMSCs). However, whether PA can induce autophagy, an important intracellular protection mechanism that is closely associated with apoptosis, in BMSCs is still unknown; the association between autophagy and apoptosis is also unclear. The aim of the present study was to determine whether PA can induce autophagy in BMSCs. When BMSCs were treated with PA for >18 h, p62 began to accumulate, indicating that autophagic flux was impaired by prolonged exposure to PA. In addition, the proportion of apoptotic cells was increased when autophagy was inhibited by the autophagy inhibitor 3‑methyladenine. Furthermore, inducing autophagy by pretreating cells with rapamycin, a known inducer of autophagy, markedly reduced PA‑induced apoptosis, suggesting that autophagy may serve a protective role in PA‑induced apoptosis in BMSCs. PA also increased intracellular reactive oxygen species (ROS) production, which was decreased by the antioxidant N‑Acetyl‑cysteine, and promoted the activation of c‑Jun N‑terminal kinases (JNKs) and p38 mitogen‑activated protein kinase (MAPK). The addition of JNK and p38 MAPK inhibitors substantially reduced autophagy. Therefore, the results indicated that PA can induce autophagy in BMSCs and protect cells from PA‑induced apoptosis through the ROS‑JNK/p38 MAPK signaling pathways. These results may improve the general understanding of the mechanisms through which BMSCs adapt to PA‑induced apoptosis. The present study also provides a novel approach for the prevention and treatment of PA‑induced lipotoxicity.

Increased expression of sterol regulatory element binding protein‑2 alleviates autophagic dysfunction in NAFLD

Sterol regulatory element binding protein-2 (SREBP-2) is an important transcription factor in lipid homeostasis. A previous study showed that SREBP-2 also activated autophagic genes during cell-sterol depletion. Alterations in autophagy are reported to be involved in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). However, whether the regulation of SREBP-2 restores dysfunctional autophagy in hepatocytes during NAFLD remains to be elucidated. In the present study, a steatosis model was established with palmitic acid (PA) treatment at the indicated times and concentrations. Autophagosomes in hepatocytes were visualized by confocal microscopy after transfection with a tandem GFP-mCherry-LC3 construct. Autophagy-associated protein levels were analyzed by western blot analysis. Loss- and gain-of-function studies were performed to examine the role of SREBP-2 in the regulation of hepatocyte autophagy. It was demonstrated that PA induced autophagy and enhanced autophagic flux at the early stage, whereas prolonged treatment with PA resulted in dysfunction of autophagy in the PA-induced steatotic hepatocytes. In addition, different cellular models presented with differing dysfunctional autophagy in response to fatty acid overload. It was also confirmed that SREBP-2 regulated autophagy-related gene expression in hepatocytes, and it was shown that the overexpression of SREBP-2 increased the expression of autophagy-related genes, but did not affect the inhibition of the autophagic flux in lipid-overloaded HL-7702 cells. By contrast, increased SREBP-2 partly restored the inhibited autophagic activity in lipid-overloaded hepatoma HepG2 cells. Taken together, the present study demonstrated that autophagic function was impaired in lipid-overloaded human hepatocytes, and the differential effect of PA on autophagy was associated with the duration of PA and the cell type. Under these conditions, the overexpression of SREBP-2 alleviated the inhibited autophagic activity rather than the inhibition of autophagic flux. Consequently, the results indicated that restoration of autophagy dysfunction via the regulation of SREBP-2 may be a potential therapeutic target for the treatment of NAFLD.

Oleate ameliorates palmitate-induced reduction of NAMPT activity and NAD levels in primary human hepatocytes and hepatocarcinoma cells

BACKGROUND

Nicotinamide phosphoribosyltransferase (NAMPT) and nicotinamide adenine dinucleotide (NAD) levels are crucial for liver function. The saturated fatty acid palmitate and the unsaturated fatty acid oleate are the main free fatty acids in adipose tissue and human diet. We asked how these fatty acids affect cell survival, NAMPT and NAD levels in HepG2 cells and primary human hepatocytes.

METHODS

HepG2 cells were stimulated with palmitate (0.5mM), oleate (1mM) or a combination of both (0.5mM/1mM) as well as nicotinamide mononucleotide (NMN) (0.5 mM) or the specific NAMPT inhibitor FK866 (10nM). Cell survival was measured by WST-1 assay and Annexin V/propidium iodide staining. NAD levels were determined by NAD/NADH Assay or HPLC. Protein and mRNA levels were analysed by Western blot analyses and qPCR, respectively. NAMPT enzyme activity was measured using radiolabelled 14C-nicotinamide. Lipids were stained by Oil red O staining.

RESULTS

Palmitate significantly reduced cell survival and induced apoptosis at physiological doses. NAMPT activity and NAD levels significantly declined after 48h of palmitate. In addition, NAMPT mRNA expression was enhanced which was associated with increased NAMPT release into the supernatant, while intracellular NAMPT protein levels remained stable. Oleate alone did not influence cell viability and NAMPT activity but ameliorated the negative impact of palmitate on cell survival, NAMPT activity and NAD levels, as well as the increased NAMPT mRNA expression and secretion. NMN was able to normalize intracellular NAD levels but did not ameliorate cell viability after co-stimulation with palmitate. FK866, a specific NAMPT inhibitor did not influence lipid accumulation after oleate-treatment.

CONCLUSIONS

Palmitate targets NAMPT activity with a consequent cellular depletion of NAD. Oleate protects from palmitate-induced apoptosis and variation of NAMPT and NAD levels. Palmitate-induced cell stress leads to an increase of NAMPT mRNA and accumulation in the supernatant. However, the proapoptotic action of palmitate seems not to be mediated by decreased NAD levels.

Autophagy in the placenta

Autophagy is an evolutionarily conserved catalytic process by which cytoplasmic components including damaged macromolecules and organelles are degraded. The role of autophagy includes adaptive responses to nutrition deprivation or intracellular stimuli. Although autophagosomes were first observed in early 1960s, it was 1990s that autophagy-related genes in yeast were identified and studied. Nowadays, the molecular machinery of autophagy and signaling pathway to various stimuli are almost outlined. Dysregulation of autophagic activity has been implicated in many human diseases including neurodegenerative diseases, infection and inflammation, and malignancies. However, since current understanding of autophagy in placenta is just at the beginning, this paper aims to provide general information on autophagy (part I) and to summarize articles on autophagy in human placenta (part II). This review article will serve as a basis for further researches on autophagy in relation to human pregnancy and its complications.

Re-evaluation of fatty acids (E 570) as a food additive

The EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) provides a scientific opinion re-evaluating the safety of fatty acids (E 570) when used as a food additive. The food additive includes caprylic- (C8), capric- (C10), lauric- (C12), myristic- (C14), palmitic- (C16), stearic- (C18) and oleic acid (C18:1), present alone or in combination. In 1991, the Scientific Committee on Food (SCF) established a group acceptable daily intake (ADI) 'not specified' for the fatty acids (myristic, stearic, palmitic and oleic acid). The fatty acids (E 570) are absorbed in the same way as the free fatty acids from the regular diet. They show low acute toxicity. The available studies on subchronic toxicity were limited but there was no evidence for toxic effects at doses up to 10% in the diet (equivalent to 9,000 mg lauric acid/kg body weight (bw) per day). The Panel considered that the fatty acids (E 570) did not raise a concern for genotoxicity. Data on chronic toxicity, reproductive toxicity and developmental toxicity were too limited to reach a conclusion on these endpoints. The Panel noted that the contribution of fatty acids (E 570) represented on average only 1% of the overall exposure to saturated fatty acids from all dietary sources (food additive and regular diet). Based on the approach described in the conceptual framework for the risk assessment of certain food additives re-evaluated under Commission Regulation (EU) No 257/2010 and taking into account the considerations mentioned above, the Panel concluded that the food additive fatty acids (E 570) was of no safety concern at the reported uses and use levels.

Qingchangligan formula attenuates the inflammatory response to protect the liver from acute failure induced by d-galactosamine/lipopolysaccharide in mice

ETHNOPHARMACOLOGICAL RELEVANCE

The Qingchangligan formula, a traditional Chinese medicine comprising five herbs, is useful for treatment of patients with liver failure; however, its protective and regulatory mechanisms remain elusive.

AIM OF THE STUDY

To test the hypothesis that the Qingchangligan formula protects mice against acute liver failure by inhibiting liver inflammation.

MATERIALS AND METHODS

Acute liver failure (ALF) was induced by intraperitoneal injection of D-GalN (700mg/kg) plus LPS (10μg/kg). The Qingchangligan formula was administered to mice in three doses of 50mg/kg (on day 1, day 2, and day 3) prior to D-GalN/LPS injection by intragastric administration. The mice in different groups were sacrificed at 6h after D-GalN/LPS injection, and liver samples and blood were collected for analysis.

RESULTS

Administration of the Qingchangligan formula not only ameliorated liver injury, as evidenced by reduced transaminase levels and well-preserved liver architecture, but also decreased the lethality in ALF mice. Moreover, in the ALF model, pretreatment with the Qingchangligan formula alleviated liver inflammation and decreased hepatocyte apoptosis. Further demonstrating the protective effects of the Qingchangligan formula, we found that pretreatment with the Qingchangligan formula reduced the expression of inflammatory cytokines by decreasing the expression of components of the mitogen-activated protein kinase (MAPK) pathway and promoting autophagy in vitro and in vivo.

CONCLUSIONS

Our findings demonstrated that the Qingchangligan formula exerts a protective effect against the pathophysiology of ALF, especially in regulating liver inflammation, and provide a rationale for using the Qingchangligan formula as a potential therapeutic strategy to ameliorate ALF.

Traditional Chinese herbal extracts inducing autophagy as a novel approach in therapy of nonalcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is one of the leading causes of chronic liver diseases around the world due to the modern sedentary and food-abundant lifestyle, which is characterized by excessive fat accumulation in the liver related with causes other than alcohol abuse. It is widely acknowledged that insulin resistance, dysfunctional lipid metabolism, endoplasmic reticulum stress, oxidative stress, inflammation, and apoptosis/necrosis may all contribute to NAFLD. Autophagy is a protective self-digestion of intracellular organelles, including lipid droplets (lipophagy), in response to stress to maintain homeostasis. Lipophagy is another pathway for lipid degradation besides lipolysis. It is reported that impaired autophagy also contributes to NAFLD. Some studies have suggested that the histological characteristics of NAFLD (steatosis, lobular inflammation, and peri-sinusoid fibrosis) might be improved by treatment with traditional Chinese herbal extracts, while autophagy may be induced. This review will provide insights into the characteristics of autophagy in NAFLD and the related role/mechanisms of autophagy induced by traditional Chinese herbal extracts such as resveratrol, Lycium barbarum polysaccharides, dioscin, bergamot polyphenol fraction, capsaicin, and garlic-derived S-allylmercaptocysteine, which may inhibit the progression of NAFLD. Regulation of autophagy/lipophagy with traditional Chinese herbal extracts may be a novel approach for treating NAFLD, and the molecular mechanisms should be elucidated further in the near future.

Augmenter of liver regeneration protects against carbon tetrachloride-induced liver injury by promoting autophagy in mice

BACKGROUND

Augmenter of liver regeneration (ALR) exerts strong hepatoprotective properties in various animal models of liver injury, but its protective mechanisms have not yet been explored. Autophagy is a recently recognized rudimentary cellular response to inflammation and injury. The aim of this study was to test the hypothesis that ALR may protect against acute liver injury through the autophagic pathway.

METHODS

The level and role of ALR in liver injury were studied in a mouse model of acute liver injury induced by carbon tetrachloride (CCl4). The effect of ALR on autophagy was analyzed in vitro and in vivo. After autophagy was inhibited by 3-methyladenine (3-MA), apoptosis and proliferation were detected in the mouse model with acute liver injury. The ALR and autophagic levels were measured in patients with liver cirrhosis (LC) and acute liver failure (ALF), respectively.

RESULTS

During the progression of acute liver injury, the ALR levels increased slightly in early stage and significantly decreased in late stage in mice. Treatment with an ALR plasmid via tail vein injection protected mice against acute liver injury. The protective effect of ALR relied on the induction of autophagy, which was supported by the following evidence: (1) ALR overexpression directly induced autophagy flux in vitro and in vivo; and (2) ALR treatment suppressed apoptosis and promoted proliferation in mice exposed to CCl4, but the inhibition of autophagy reversed these effects. More importantly, the ALR levels decreased in patients with LC and ALF compared with normal controls.

CONCLUSION

We demonstrated that ALR ameliorated liver injury via an autophagic mechanism, which indicates a potential therapeutic application for liver injury.

Moderate physical activity promotes basal hepatic autophagy in diet-induced obese mice

Obesity is a known risk factor for the development of hepatic disease; obesity-induced fatty liver can lead to inflammation, steatosis, and cirrhosis and is associated with degeneration of the mitochondria. Lifestyle interventions such as physical activity may ameliorate this condition. The purpose of this study was to investigate regulation of mitochondrial and autophagy quality control in liver following Western diet-induced obesity and voluntary physical activity. Eight-week-old C57BL/6J mice were fed a Western diet (WD) or normal chow (NC, control) for 4 weeks; afterwards, groups were divided into voluntary wheel running (VWR) or sedentary (SED) conditions for an additional 4 weeks. WD-SED animals had a median histology score of 2, whereas WD-VWR was not different from NC groups (median score 1). There was no difference in mRNA of inflammatory markers Il6 and Tnfa in WD animals. WD animals had 50% lower mitochondrial content (COX IV and Cytochrome C proteins), 50% lower Pgc1a mRNA content, and reduced content of mitochondrial fusion and fission markers. Markers of autophagy were increased in VWR animals, regardless of obesity, as measured by 50% greater LC3-II/I ratio and 40% lower p62 protein content. BNIP3 protein content was 30% less in WD animals compared with NC animals, regardless of physical activity. Diet-induced obesity results in derangements in mitochondrial quality control that appear to occur prior to the onset of hepatic inflammation. Moderate physical activity appears to enhance basal autophagy in the liver; increased autophagy may provide protection from hepatic fat accumulation.

Effect of acute and chronic autophagy deficiency on skeletal muscle apoptotic signaling, morphology, and function

Autophagy is a catabolic process that targets and degrades cytoplasmic materials. In skeletal muscle, autophagy is required for the control of mass under catabolic conditions, but is also basally active in the maintenance of myofiber homeostasis. In this study, we found that some specific autophagic markers (LC3-I, LC3-II, SQSTM1) were basally lower in glycolytic muscle compared to oxidative muscle of autophagy competent mice. In contrast, basal autophagic flux was higher in glycolytic muscle. In addition, we used several skeletal muscle-specific Atg7 transgenic mouse models to investigate the effect of acute (iAtg7^-/-) and chronic (cAtg7^-/-) autophagy deficiency on skeletal muscle morphology, contractility, and apoptotic signaling. While acute autophagy ablation (iAtg7^-/-) resulted in increased centralized nuclei in glycolytic muscle, it did not alter contractile properties or measures of apoptosis and proteolysis. In contrast, with chronic autophagy deficiency (cAtg7^-/-) there was an increased proportion of centralized nuclei, as well as reduced force and altered twitch kinetics in glycolytic muscle. Glycolytic muscle of cAtg7^-/- mice also displayed an increased level of the pro-apoptotic protein BAX, as well as calpain and proteasomal enzymatic activity. Collectively, our data demonstrate cumulative damage from chronic skeletal muscle-specific autophagy deficiency with associated apoptotic and proteasomal upregulation. These findings point towards the importance of investigating different muscle/fiber types when studying skeletal muscle autophagy, and the critical role of autophagy in the maintenance of myofiber function, integrity, and cellular health.

A Molecular Probe for the Detection of Polar Lipids in Live Cells

Lipids have an important role in many aspects of cell biology, including membrane architecture/compartment formation, intracellular traffic, signalling, hormone regulation, inflammation, energy storage and metabolism. Lipid biology is therefore integrally involved in major human diseases, including metabolic disorders, neurodegenerative diseases, obesity, heart disease, immune disorders and cancers, which commonly display altered lipid transport and metabolism. However, the investigation of these important cellular processes has been limited by the availability of specific tools to visualise lipids in live cells. Here we describe the potential for ReZolve-L1^™ to localise to intracellular compartments containing polar lipids, such as for example sphingomyelin and phosphatidylethanolamine. In live Drosophila fat body tissue from third instar larvae, ReZolve-L1^™ interacted mainly with lipid droplets, including the core region of these organelles. The presence of polar lipids in the core of these lipid droplets was confirmed by Raman mapping and while this was consistent with the distribution of ReZolve-L1^™ it did not exclude that the molecular probe might be detecting other lipid species. In response to complete starvation conditions, ReZolve-L1^™ was detected mainly in Atg8-GFP autophagic compartments, and showed reduced staining in the lipid droplets of fat body cells. The induction of autophagy by Tor inhibition also increased ReZolve-L1^™ detection in autophagic compartments, whereas Atg9 knock down impaired autophagosome formation and altered the distribution of ReZolve-L1^™. Finally, during Drosophila metamorphosis fat body tissues showed increased ReZolve-L1^™ staining in autophagic compartments at two hours post puparium formation, when compared to earlier developmental time points. We concluded that ReZolve-L1^™ is a new live cell imaging tool, which can be used as an imaging reagent for the detection of polar lipids in different intracellular compartments.

LRP1 Protein Deficiency Exacerbates Palmitate-induced Steatosis and Toxicity in Hepatocytes

LRP1 (LDL receptor-related protein-1) is a ubiquitous receptor with both cell signaling and ligand endocytosis properties. In the liver, LRP1 serves as a chylomicron remnant receptor and also participates in the transport of extracellular cathepsin D to the lysosome for prosaposin activation. The current study showed that in comparison with wild type mice, hepatocyte-specific LRP1 knock-out (hLrp1(-/-)) mice were more susceptible to fasting-induced lipid accumulation in the liver. Primary hepatocytes isolated from hLrp1(-/-) mice also accumulated more intracellular lipids and experienced higher levels of endoplasmic reticulum (ER) stress after palmitate treatment compared with similarly treated hLrp1(+/+) hepatocytes. Palmitate-treated hLrp1(-/-) hepatocytes displayed similar LC3-II levels, but the levels of p62 were elevated in comparison with palmitate-treated hLrp1(+/+) hepatocytes, suggesting that the elevated lipid accumulation in LRP1-defective hepatocytes was not due to defects in autophagosome formation but was due to impairment of lipophagic lipid hydrolysis in the lysosome. Additional studies showed increased palmitate-induced oxidative stress, mitochondrial and lysosomal permeability, and cell death in hLrp1(-/-) hepatocytes. Importantly, the elevated cell death and ER stress observed in hLrp1(-/-) hepatocytes were abrogated by E64D treatment, whereas inhibiting ER stress diminished cell death but not lysosomal permeabilization. Taken together, these results documented that LRP1 deficiency in hepatocytes promotes lipid accumulation and lipotoxicity through lysosomal-mitochondrial permeabilization and ER stress that ultimately result in cell death. Hence, LRP1 dysfunction may be a major risk factor in fatty liver disease progression.

Autophagy Is Involved in the Sevoflurane Anesthesia-Induced Cognitive Dysfunction of Aged Rats

Autophagy is associated with regulation of both the survival and death of neurons, and has been linked to many neurodegenerative diseases. Postoperative cognitive dysfunction is commonly observed in elderly patients following anesthesia, but the pathophysiological mechanisms are largely unexplored. Similar effects have been found in aged rats under sevoflurane anesthesia; however, the role of autophagy in sevoflurane anesthesia-induced hippocampal neuron apoptosis of older rats remains elusive. The present study was designed to investigate the effects of autophagy on the sevoflurane-induced cognitive dysfunction in aged rats, and to identify the role of autophagy in sevoflurane-induced neuron apoptosis. We used 20-month-old rats under sevoflurane anesthesia to study memory performance, neuron apoptosis, and autophagy. The results demonstrated that sevoflurane anesthesia significantly impaired memory performance and induced hippocampal neuron apoptosis. Interestingly, treatment of rapamycin, an autophagy inducer, improved the cognitive deficit observed in the aged rats under sevoflurane anesthesia by improving autophagic flux. Rapamycin treatment led to the rapid accumulation of autophagic bodies and autophagy lysosomes, decreased p62 protein levels, and increased the ratio of microtubule-associated protein light chain 3 II (LC3-II) to LC3-I in hippocampal neurons through the mTOR signaling pathway. However, administration of an autophagy inhibitor (chloroquine) attenuated the autophagic flux and increased the severity of sevoflurane anesthesia-induced neuronal apoptosis and memory impairment. These findings suggest that impaired autophagy in the hippocampal neurons of aged rats after sevoflurane anesthesia may contribute to cognitive impairment. Therefore, our findings represent a potential novel target for pro-autophagy treatments in patients with sevoflurane anesthesia-induced neurodegeneration.