Autophagy: Emerging roles in lipid homeostasis and metabolic control

Association of ultra-processed food consumption with muscle mass among young and middle-aged US adults

INTRODUCTION

Muscle mass is vital for physical activity and fundamental physiological processes supporting long-term health. While aging is inevitable, certain modifiable factors positively influence muscle preservation and overall well-being. However, the relationship between the consumption of ultra-processed foods (UPF) and muscle mass is not yet clear.

METHODS

This study included 7,173 men and nonpregnant women aged 20-59 years with valid 24-hour dietary recalls and accessible whole-body dual-energy x-ray absorptiometry (DXA) scans from NHANES 2011-2018. UPFs were identified through the NOVA classification system, and the percentage of energy derived from UPF consumption was evaluated in quintiles. Muscle mass measures were derived from DXA scans and quantified by the total and regional muscle mass index (MMI, kg/m²) and appendicular muscle mass index (AMMI, kg/m²). Multivariable-adjusted generalized linear regression models were applied to investigate the association between consumption of UPFs and muscle mass measures overall and by sociodemographic subgroups.

RESULTS

The multivariable-adjusted differences of total MMI from the lowest to highest quintile of UPF consumption were 0 (reference), -0.03 (95% CI, -0.13, 0.07), -0.13 (95%CI, -0.24, -0.04), -0.12 (95% CI, -0.23, -0.01), and - 0.17 (95% CI, -0.27, -0.08) (P for trend < 0.001). Subtotal MMI followed a similar magnitude of associational pattern as total MMI. For trunk MMI, corresponding values from the lowest to highest quintiles of UPF consumption were 0 (reference), -0.02 (95% CI, -0.07, 0.02), -0.05 (95%CI, -0.11, 0.00), -0.07 (95% CI, -0.13, -0.01), and - 0.07 (95% CI, -0.12, -0.01). For AMMI, corresponding values from the lowest to highest quintiles of UPF consumption were 0 (reference), -0.004 (95% CI, -0.07, 0.06), -0.08 (95%CI, -0.14, -0.02), -0.05 (95% CI, -0.11, 0.02), and - 0.10 (95% CI, -0.16, -0.04) (All P for trend < 0.001). While most subgroups maintained similar overall patterns, heterogeneous findings were also observed. For example, the multivariable-adjusted differences in total MMI between the lowest and highest quantile of UPF consumption were - 0.19 (95% CI, -0.32, -0.06) for non-Hispanic Whites, 0.18 (95% CI, 0.01, 0.36) for non-Hispanic Blacks, -0.25 (95%CI, -0.45, -0.04) for Hispanics, -0.25 (95% CI, -0.51, 0.05) for non-Hispanic Asians and - 0.32 (95% CI, -0.75, 0.12) for others (P for interaction < 0.001).

CONCLUSION

Higher consumption of UPFs was significantly associated with lower values of total and regional muscle mass. Specifically, comparing the highest quantile of UPF consumption to the lowest, total MMI decreased by 0.93%, trunk MMI decreased by 0.76%, and AMMI decreased by 1.25%. The differences in associational patterns between UPF consumption and muscle mass across sociodemographic subgroups require further investigation.

Role of Mitochondrial Reactive Oxygen Species-Mediated Chaperone-Mediated Autophagy and Lipophagy in Baicalin and N-Acetylcysteine Mitigation of Cadmium-Induced Lipid Accumulation in Liver

Cadmium (Cd) is a major health concern globally and can accumulate and cause damage in the liver for which there is no approved treatment. Baicalin and N-acetylcysteine (NAC) have been found to have protective effects against a variety of liver injuries, but it is not clear whether their combined use is effective in preventing and treating Cd-induced lipid accumulation. The study found that Cd increased the production of mitochondrial reactive oxygen species (mROS) and elevated the level of chaperone-mediated autophagy (CMA). Interestingly, mROS-mediated CMA exacerbates the Cd-induced inhibition of lipophagy. Baicalin and NAC counteracted inhibition of lipophagy by attenuating Cd-induced CMA, suggesting an interplay between CMA elevation, mitochondrial destruction, and mROS formation. Maintaining the stability of mitochondrial structure and function is essential for alleviating Cd-induced lipid accumulation in the liver. Choline is an essential component of the mitochondrial membrane and is responsible for maintaining its structure and function. Mitochondrial transcriptional factor A (TFAM) is involved in mitochondrial DNA transcriptional activation and replication. Our study revealed that the combination of baicalin and NAC can regulate choline metabolism through TFAM and thereby maintain mitochondrial structure and functionality. In summary, the combination of baicalin and NAC plays a more beneficial role in alleviating Cd-induced lipid accumulation than the drug alone, and the combination of baicalin and NAC can stabilize mitochondrial structure and function and inhibit mROS-mediated CMA through TFAM-choline, thereby promoting lipophagy to alleviate Cd-induced lipid accumulation.

Sub-Cellular Dynamic Analysis of BGC823 Cells after Treatment with the Multi-Component Drug CKI Using Raman Spectroscopy

Multi-component drugs (MCDs) can induce various cellular changes covering multiple levels, from molecular and subcellular structure to cell morphology. A "non-invasive" method for comprehensively detecting the dynamic changes of cellular fine structure and chemical components on the subcellular level is highly desirable for MCD studies. In this study, the subcellular dynamic processes of gastric cancer BGC823 cells after treatment with a multi-component drug, Compound Kushen Injection (CKI), were investigated using a homemade, high-resolution, confocal Raman spectroscopy (RS) device combined with bright-field imaging. The Raman spectra of the nucleus, cytoplasm and intracellular vesicles (0.4-1 μm) were collected simultaneously for each cell treated with CKI at different times and doses. The RS measurements showed that CKI decreased the DNA signatures, which the drug is known to inhibit. Meanwhile, the CKI-induced subcellular dynamic changes in the appearance of numerous intracellular vesicles and the deconstruction of cytoplasm components were observed and discussed. The results demonstrated that high-resolution subcellular micro-Raman spectroscopy has potential for detecting fine cellular dynamic variation induced by drugs and the screening of MCDs in cancer therapy.

Progressive transcriptional changes in metabolic genes and altered fatbody homeostasis in Drosophila model of Huntington's disease

Huntington's disease (HD) is an autosomal-dominant neurodegenerative disorder marked by progressive neuronal atrophy, particularly in striatum and cerebral cortex. Although predominant manifestations of the disease include loss in the triad of motor, cognitive and behavioral capabilities, metabolic dysfunction in patients and HD models are being increasingly recognized. Patients display progressive body weight loss, which aggravates the disease and leads to cachexia in the terminal stages. Using the Drosophila model of HD, we have earlier reported that diseased flies exhibit an atypical pattern of lipid gain and loss with progression along with exhibiting extensive mitochondrial dysfunction, impaired calcium homeostasis and heightened apoptosis in the fatbody. Here, we first monitored the structural changes that abdominal fatbody undergoes with disease progression. Further, we checked the transcriptional changes of key metabolic genes in whole fly as well as genes regulating mitochondrial function, apoptosis, autophagy and calcium homeostasis in the abdominal fatbody. We found extensive alterations in whole-body and fatbody-specific transcriptional profile of the diseased flies, which was in consort with their stage-specific physiological state. Additionally, we also assessed lysosome-mediated autophagy in the fatbody of diseased flies in order to ascertain the mechanisms contributing to fatbody atrophy at the terminal stage. Interestingly, we found elevated autophagy in fatbody of flies throughout disease progression. This study provides new insights into the effect on peripheral metabolism due to degeneration of neurons in the neurodegenerative disease, thereby discerns novel mechanisms leading to cachexia in diseased flies and advocates for the need of managing metabolic dysfunctions in HD.

The Frequency of Daily Consumption of Sugar-Sweetened Beverages Is Associated with Reduced Muscle Mass Index in Adolescents

The consumption of sugar-sweetened beverages (SSBs) has increased in recent years and has become a cause of concern because these beverages pose a risk to human health. Thus, we evaluated the association between SSBs consumption and muscle mass index (MMI) in adolescents. This cross-sectional study evaluated 2393 adolescents (18/19-years-old). Consumption of SSBs was analyzed based on the frequency of daily consumption and energy contribution categorized into tertiles. MMI was examined using the ratio of muscle mass (kilograms) to height (meters squared). The highest tertile of the frequency of daily SSB intake was associated with a reduced MMI in men (β = -0.31; 95%CI: -0.60, -0.01) and women (β = -0.24; 95%CI: -0.45, -0.02). However, these associations were not observed after adjusting for sugar contained in SSBs in men (β = -0.26; 95%CI: -0.69, 0.17) and for carbohydrate, lipid, and protein intake in women (β = -0.19; 95%CI: -0.42, 0.04). The highest energy contribution tertile of SSBs was associated with a reduced MMI in male adolescents (β = -0.34; 95%CI: -0.64, -0.04). This association was not observed after adjusting for intake of sugar in SSBs (β = -0.38; 95%CI: -0.75, 0.01). The frequency of daily consumption of SSBs was considered a risk factor for decreased MMI in both sexes, and the energy contribution of these drinks was a risk factor for MMI reduced only in male adolescents.

Chloroquine modulates the sulforaphane anti-obesity mechanisms in a high-fat diet model: Role of JAK-2/ STAT-3/ SOCS-3 pathway

The phytochemical sulforaphane (SFN) has been studied for its potential anti-obesity effect, but neither its molecular targets nor its interaction with the antimalarial drug chloroquine (CQ) has been fully delineated. Therefore, high-fat diet (HFD) obese rats were randomly allocated into one of five groups and were left untreated or gavaged orally with SFN (0.5 or 1 mg/kg), CQ (5 mg/kg), or their combination (0.5/5 mg/kg) for six successive weeks to assess their potential interaction and the enrolled mechanisms. SFN effectively reduced the HFD-induced weight gain, blood glucose, and serum leptin levels, and improved lipid profile. On the molecular level, SFN inhibited the lipogenesis-related enzymes, namely sterol regulatory element-binding protein (SREBP)-1c, fatty acid synthase (FAS), and acetyl-CoA carboxylase (ACC) in both liver and visceral white adipose tissue (vWAT) of HFD obese rats. SFN also turned off the inflammatory pathway conserved Janus kinase/signaling transducers and activators of transcription/suppressor of cytokine signaling (JAK-2/STAT-3/SOCS-3) in these tissues, as well as the inflammatory markers nuclear factor-kappa (NF-κ) B and interleukin (IL)-22 in serum. In contrast, SFN downregulated the gene expression of microRNA (miR-200a), while significantly increasing the autophagic parameters; viz., beclin-1, autophagy-related protein (ATG)-7, and microtubule-associated protein 2 light chain 3 (LC3-II) in both liver and vWAT. On most of the parameters mentioned above, treatment with CQ solely produced a satisfactory effect and intensified the low dose of SFN in the combination regimen. These findings demonstrated the beneficial effects of using CQ as an add-on anti-obesity medicine to SFN.

APOB CRISPR-Cas9 Engineering in Hypobetalipoproteinemia: A Promising Tool for Functional Studies of Novel Variants

Hypobetalipoproteinemia is characterized by LDL-cholesterol and apolipoprotein B (apoB) plasma levels below the fifth percentile for age and sex. Familial hypobetalipoproteinemia (FHBL) is mostly caused by premature termination codons in the APOB gene, a condition associated with fatty liver and steatohepatitis. Nevertheless, many families with a FHBL phenotype carry APOB missense variants of uncertain significance (VUS). We here aimed to develop a proof-of-principle experiment to assess the pathogenicity of VUS using the genome editing of human liver cells. We identified a novel heterozygous APOB-VUS (p.Leu351Arg), in a FHBL family. We generated APOB knock-out (KO) and APOB-p.Leu351Arg knock-in Huh7 cells using CRISPR-Cas9 technology and studied the APOB expression, synthesis and secretion by digital droplet PCR and ELISA quantification. The APOB expression was decreased by 70% in the heterozygous APOB-KO cells and almost abolished in the homozygous-KO cells, with a consistent decrease in apoB production and secretion. The APOB-p.Leu351Arg homozygous cells presented with a 40% decreased APOB expression and undetectable apoB levels in cellular extracts and supernatant. Thus, the p.Leu351Arg affected the apoB secretion, which led us to classify this new variant as likely pathogenic and to set up a hepatic follow-up in this family. Therefore, the functional assessment of APOB-missense variants, using gene-editing technologies, will lead to improvements in the molecular diagnosis of FHBL and the personalized follow-up of these patients.

Alterations in Lysosome Homeostasis in Lipid-Related Disorders: Impact on Metabolic Tissues and Immune Cells

Lipid-related disorders, which primarily affect metabolic tissues, including adipose tissue and the liver are associated with alterations in lysosome homeostasis. Obesity is one of the more prevalent diseases, which results in energy imbalance within metabolic tissues and lysosome dysfunction. Less frequent diseases include Niemann-Pick type C (NPC) and Gaucher diseases, both of which are known as Lysosomal Storage Diseases (LSDs), where lysosomal dysfunction within metabolic tissues remains to be fully characterized. Adipocytes and hepatocytes share common pathways involved in the lysosome-autophagic axis, which are regulated by the function of cathepsins and CD36, an immuno-metabolic receptor and display alterations in lipid diseases, and thereby impacting metabolic functions. In addition to intrinsic defects observed in metabolic tissues, cells of the immune system, such as B cells can infiltrate adipose and liver tissues, during metabolic imbalance favoring inflammation. Moreover, B cells rely on lysosomes to promote the processing and presentation of extracellular antigens and thus could also present lysosome dysfunction, consequently affecting such functions. On the other hand, growing evidence suggests that cells accumulating lipids display defective inter-organelle membrane contact sites (MCSs) established by lysosomes and other compartments, which contribute to metabolic dysfunctions at the cellular level. Overall, in this review we will discuss recent findings addressing common mechanisms that are involved in lysosome dysregulation in adipocytes and hepatocytes during obesity, NPC, and Gaucher diseases. We will discuss whether these mechanisms may modulate the function of B cells and how inter-organelle contacts, emerging as relevant cellular mechanisms in the control of lipid homeostasis, have an impact on these diseases.

DO-SRS imaging of metabolic dynamics in aging Drosophila

Emerging studies have shown that lipid metabolism plays an important role in aging. High resolution in situ imaging of lipid metabolic dynamics inside cells and tissues affords a novel and potent approach for understanding many biological processes such as aging. Here we established a new optical imaging platform that combines D2O-probed stimulated Raman scattering (DO-SRS) imaging microscopy and a Drosophila model to directly visualize metabolic activities in situ during aging. The sub-cellular spatial distribution of de novo lipogenesis in the fat body was quantitatively imaged and examined. We discovered a dramatic decrease in lipid turnover in 35-day-old flies. Decreases in protein turnover occurred earlier than lipids (25-day vs. 35-day), and there are many proteins localized on the cell and lipid droplet membrane. This suggests that protein metabolism may act as a prerequisite for lipid metabolism during aging. This alteration of maintenance of protein turnover indicates disrupted lipid metabolism. We further found a significantly higher lipid turnover rate in large LDs, indicating more active metabolism in large LDs, suggesting that large and small LDs play different roles in metabolism to maintain cellular homeostasis. This is the first study that directly visualizes spatiotemporal alterations of lipid (and protein) metabolism in Drosophila during the aging process. Our study not only demonstrates a new imaging platform for studying lipid metabolism, but also unravels the important interconnections between lipid metabolism and aging.

Cadmium induces triglyceride levels via microsomal triglyceride transfer protein (MTTP) accumulation caused by lysosomal deacidification regulated by endoplasmic reticulum (ER) Ca2+ homeostasis

Cadmium (Cd) exposure induced lipid metabolic disorder with changes in lipid composition, as well as triglyceride (TG) levels. Liver is the main organ maintaining body TG level and previous studies suggested that Cd exposure might increase TG synthesis but reduce TG uptake in liver. However, the effects of Cd exposure on TG secretion from liver and underlying mechanism are still unclear. In the present study, the data revealed that Cd exposure increased TG levels in the HepG2 cells and the cultured medium by increasing the expression of microsomal triglyceride transfer protein (MTTP), which was abrogated by siRNA knockdown of MTTP. MTTP was synergistically accumulated after Cd exposure or treated with proteasome inhibitor MG132 and lysosome inhibitor chloroquine (CQ), which suggested the Cd increased MTTP protein stability by inhibiting both the proteasome and the lysosomal protein degradation pathways. In addition, our results demonstrated that Cd exposure inhibited the lysosomal acidic degradation pathway through disrupting endoplastic reticulum (ER) Ca2+ homeostasis. Cd-induced MTTP protein and TG levels were significantly reduced by pretreatments of BAPTA/AM chelation of intracellular Ca2+, 2-APB inhibition of ER Ca2+ release channel inositol 1,4,5-trisphosphate receptor (IP3R) and CDN1163 activation of ER Ca2+ reuptake pump sarcoplasmic reticulum Ca2+-ATPase (SERCA). These results suggest that Cd-induced ER Ca2+ release impaired the lysosomal acidity, which associated with MTTP protein accumulation and contributed to increased TG levels.

Dysregulation of autophagy acts as a pathogenic mechanism of non-alcoholic fatty liver disease (NAFLD) induced by common environmental pollutants

Non-alcoholic fatty liver disease (NAFLD) has been the most common chronic liver disease in the world, including the developing countries. NAFLD is metabolic disease with significant lipid deposition in the hepatocytes of the liver, which is usually associated with oxidative stress, inflammation and fibrogenesis, and insulin resistance. Progressive NAFLD can develop into non-alcoholic steatohepatitis (NASH) or hepatocellular carcinoma. The current evidence proposes that environmental pollutants promote development and progression of NAFLD, and autophagy plays a vital role but is multifactorial affected in NAFLD. In this review, we analyzed on the regulations of common environmental pollutants on autophagy in NAFLD. To clarify the involved roles of autophagy, we discussed the dysregulation of autophagy by environmental pollutants in adipose tissue and gut, and their interactions with liver, as well as epigenetic regulation on autophagy by environmental pollutants. Furthermore, protective roles of potential therapeutic treatments on the multiple-hits of autophagy in NAFLD were descripted.

Comparative Analysis of Metabolite Profiling of Momordica charantia Leaf and the Anti-Obesity Effect through Regulating Lipid Metabolism

This study investigated the effects of Momordica charantia (M. charantia) extract in obesity and abnormal lipid metabolism in mice fed high fat diet (HFD). Fruit, root, stem, and leaf extracts of M. charantia were obtained using distilled water, 70% ethanol and 95% hexane. M. charantia leaf distilled water extract (MCLW) showed the highest antioxidant activity in both 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity tests and reducing power. Metabolite profiles of M. charantia leaf extracts were analyzed for identification of bioactive compounds. HFD-fed mice were treated with MCLW (oral dose of 200 mg/kg/d) for 4 weeks. MCLW reduced lipid accumulation, body weight, organ weight, and adipose tissue volume and significantly improved glucose tolerance and insulin resistance in HFD mice. Furthermore, MCLW administration reduced serum total cholesterol and low-density lipoprotein cholesterol, and increased serum high-density lipoprotein cholesterol compared with HFD mice. Moreover, MCLW significantly reduced the levels of serum urea nitrogen, alanine aminotransferase, alkaline phosphatase, and aspartate aminotransferase; alleviated liver and kidney injury. MCLW decreases expression of genes that fatty acid synthesis; increase the expression of catabolic-related genes. These results indicate that MCLW has an inhibitory effect on obese induced by high fat diet intake, and the mechanism may be related to the regulation of abnormal lipid metabolism in liver and adipose tissue, suggesting that MCLW may be a suitable candidate for the treatment of obesity.

An Overview of the Perspective of Cellular Autophagy: Mechanism, Regulation, and the Role of Autophagy Dysregulation in the Pathogenesis of Diseases

Autophagy is a cellular process that eliminates unnecessary cytoplasmic materials, such as long-age proteins, destroyed organelles, and foreign microorganisms. Macroautophagy (MaA), chaperone-mediated autophagy, and microautophagy are the three main types of autophagy. It is regulated by the integration of signaling from the AMPK and mTOR-ULK1 pathways. Autophagy plays a physiological role in health, and its dysregulation could be a pathophysiologic mechanism in different disease conditions. In the current study, we reviewed papers of Google Scholar database, PubMed, PubMed Central, Cochrane Database of Systematic Reviews, MEDLINE, and MedlinePlus with no time limitation and a recent World Health Organization report. In the current review, it could be concluded that autophagy plays many physiological functions, including immune system modulation, and regulates different cellular processes such as metabolism, protein synthesis, and cellular transportation. Dysregulation of autophagy is implicated in tumorigenesis, aging, age-related neurodegeneration, and endothelial dysfunctions. Autophagy dysregulation is also implicated in the newly discovered CoV-COVID-19 pathogenesis.

The Transcriptomic and Phenotypic Response of the Melanized Yeast Exophiala dermatitidis to Ionizing Particle Exposure

Fungi can tolerate extremely high doses of ionizing radiation compared with most other eukaryotes, a phenomenon encompassing both the recovery from acute exposure and the growth of melanized fungi in chronically contaminated environments such as nuclear disaster sites. This observation has led to the use of fungi in radiobiology studies, with the goal of finding novel resistance mechanisms. However, it is still not entirely clear what underlies this phenomenon, as genetic studies have not pinpointed unique responses to ionizing radiation in the most resistant fungi. Additionally, little work has been done examining how fungi (other than budding yeast) respond to irradiation by ionizing particles (e.g., protons, α-particles), although particle irradiation may cause distinct cellular damage, and is more relevant for human risks. To address this paucity of data, in this study we have characterized the phenotypic and transcriptomic response of the highly radioresistant yeast Exophiala dermatitidis to irradiation by three separate ionizing radiation sources: protons, deuterons, and α-particles. The experiment was performed with both melanized and non-melanized strains of E. dermatitidis, to determine the effect of this pigment on the response. No significant difference in survival was observed between these strains under any condition, suggesting that melanin does not impart protection to acute irradiation to these particles. The transcriptomic response during recovery to particle exposure was similar to that observed after γ-irradiation, with DNA repair and replication genes upregulated, and genes involved in translation and ribosomal biogenesis being heavily repressed, indicating an attenuation of cell growth. However, a comparison of global gene expression showed clear clustering of particle and γ-radiation groups. The response elicited by particle irradiation was, in total, more complex. Compared to the γ-associated response, particle irradiation resulted in greater changes in gene expression, a more diverse set of differentially expressed genes, and a significant induction of gene categories such as autophagy and protein catabolism. Additionally, analysis of individual particle responses resulted in identification of the first unique expression signatures and individual genes for each particle type that could be used as radionuclide discrimination markers.

Lipophagy: A New Perspective of Natural Products in Type 2 Diabetes Mellitus Treatment

Autophagy has been reported to involve in the pathogenesis of type 2 diabetes mellitus (T2DM), which protects the insulin target tissues and pancreatic β-cells. However, autophagy is inhibited when the cells are lipid overload. That, in turn, increases the accumulation of fat. Lipotoxicity caused by excessive lipid accumulation contributes to pathogenesis of T2DM. Therefore, it is undeniable to break the vicious circles between lipid excess and autophagy deficiency. Lipophagy, a selective form of autophagy, is characterized by selective breakdown of lipid droplets (LDs). The nutritional status of cells contributes to the way of autophagy (selective or non-selective), while selective autophagy helps to accurately remove excess substances. It seems that lipophagy could be an effective means to decrease abnormal lipid accumulation that leads to insulin resistance and β-cell impairment by removing ectopic LDs. Based on this process, many natural compounds have been reported to decrease lipid accumulation in tissues through autophagy-lysosomal pathway, which gradually highlights the significance of lipophagy. In this review, we focus on the mechanisms that lipophagy improves T2DM and natural products that are applied to induce lipophagy. It is also suggested that natural herbs with rich contents of natural products inducing lipophagy would be potential candidates for alleviating T2DM.

The Classification and Basic Processes of Autophagy

Autophagy is a general term for the process of the lysosomal degradation of intracellular components, a process occurring exclusively in eukaryotic cells. Based on the way that intracellular substrates are transported to lysosomes, autophagy in mammalian cells can be divided into three main types: macroautophagy, microautophagy, and chaperone-mediated autophagy (CMA). Each type has its unique molecular machinery and is tightly regulated by various cellular signals, helping cells adapt to a changing environment. Autophagy can also be divided into two categories based on cargo selectivity: selective autophagy and nonselective autophagy. Nonselective autophagy refers to the bulk transport of organelles or other cytoplasmic components to lysosomes, while selective autophagy refers to the degradation of a specific substrate. Autophagy plays an essential role in maintaining cellular homeostasis, and dysregulation of it may participate in the pathological process of many human diseases.

Prion peptide-mediated calcium level alteration governs neuronal cell damage through AMPK-autophagy flux

BACKGROUND

The distinctive molecular structure of the prion protein, PrPsc, is established only in mammals with infectious prion diseases. Prion protein characterizes either the transmissible pathogen itself or a primary constituent of the disease. Our report suggested that prion protein-mediated neuronal cell death is triggered by the autophagy flux. However, the alteration of intracellular calcium levels, AMPK activity in prion models has not been described. This study is focused on the effect of the changes in intracellular calcium levels on AMPK/autophagy flux pathway and PrP (106-126)-induced neurotoxicity.

METHODS

Western blot and Immunocytochemistry was used to detect AMPK and autophagy-related protein expression. Flow cytometry and a TdT-mediated biotin-16-dUTP nick-end labeling (TUNEL) assay were used to detect the percentage of apoptotic cells. Calcium measurement was employed using fluo-4 by confocal microscope.

RESULTS

We examined the effect of calcium homeostasis alterations induced by human prion peptide on the autophagy flux in neuronal cells. Treatment with human prion peptide increased the intracellular calcium concentration and induced cell death in primary neurons as well as in a neuronal cell line. Using pharmacological inhibitors, we showed that the L-type calcium channel is involved in the cellular entry of calcium ions. Inhibition of calcium uptake prevented autophagic cell death and reduction in AMP-activated protein kinase (AMPK) activity induced by human prion peptide.

CONCLUSION

Our data demonstrated that prion peptide-mediated calcium inflow plays a pivotal role in prion peptide-induced autophagic cell death, and reduction in AMPK activity in neurons. Altogether, our results suggest that calcium influx might play a critical role in neurodegenerative diseases, including prion diseases. Video Abstract.

Exercise and dietary intervention ameliorate high-fat diet-induced NAFLD and liver aging by inducing lipophagy

Exercise and dietary intervention are currently available strategies to treat nonalcoholic fatty liver disease (NAFLD), while the underlying mechanism remains controversial. Emerging evidence shows that lipophagy is involved in the inhibition of the lipid droplets accumulation. However, it is still unclear if exercise and dietary intervention improve NAFLD through regulating lipophagy, and how exercise of skeletal muscle can modulate lipid metabolism in liver. Moreover, NAFLD is associated with aging, and little is known about the effect of lipid accumulation on aging process. Here in vivo and in vitro models, we found that exercise and dietary intervention reduced lipid droplets formation, decreased hepatic triglyceride in the liver induced by high-fat diet. Exercise and dietary intervention enhanced the lipophagy by activating AMPK/ULK1 and inhibiting Akt/mTOR/ULK1 pathways respectively. Furthermore, exercise stimulated FGF21 production in the muscle, followed by secretion to the circulation to promote the lipophagy in the liver via an AMPK-dependent pathway. Importantly, for the first time, we demonstrated that lipid accumulation exacerbated liver aging, which was ameliorated by exercise and dietary intervention through inducing lipophagy. Our findings suggested a new mechanism of exercise and dietary intervention to improve NAFLD through promoting lipophagy. The study also provided evidence to support that muscle exercise is beneficial to other metabolic organs such as liver. The FGF21-mediated AMPK dependent lipophagy might be a potential drug target for NAFLD and aging caused by lipid metabolic dysfunction.

Towards understanding leydigioma: do G protein-coupled estrogen receptor and peroxisome proliferator-activated receptor regulate lipid metabolism and steroidogenesis in Leydig cell tumors?

Leydig cell tumors (LCT) are the most common type of testicular stromal tumor. Herein, we investigate the G protein-coupled estrogen receptor (GPER) and peroxisome proliferator-activated receptor (PPAR) implication in regulation of lipid homeostasis including the expression of steroidogenesis-controlling molecules in clinical specimens of LCTs and tumor Leydig cells (MA-10). We showed the general structure and morphology of LCTs by scanning electron and light microscopy. In LCTs, mRNA and protein analyses revealed increased expression of GPER and decreased expression of PPARα, β, and γ. Concomitantly, changes in expression pattern of the lutropin receptor (LHR), protein kinase A (PKA), perilipin (PLIN), hormone sensitive lipase (HSL), steroidogenic acute regulatory protein (StAR), translocator protein (TSPO), HMG-CoA synthase, and reductase (HMGCS, HMGCR) were observed. Using MA-10 cells treated with GPER and PPAR antagonists (alone and in combination), we demonstrated GPER-PPAR-mediated control of estradiol secretion via GPER-PPARα and cyclic guanosine monophosphate (cGMP) concentration via GPER-PPARγ. It is assumed that GPER and PPAR can crosstalk, and this can be altered in LCT, resulting in a perturbed lipid balance and steroidogenesis. In LCTs, the phosphatidylinositol-3-kinase (PI3K)-Akt-mTOR pathway was disturbed. Thus, PI3K-Akt-mTOR with cGMP can play a role in LCT outcome and biology including lipid metabolism.

Bromelain Confers Protection against the Non-Alcoholic Fatty Liver Disease in Male C57bl/6 Mice

We aimed to investigate the effect of bromelain, the extract from stems of pineapples on the high-fat diet (HFD)-induced deregulation of hepatic lipid metabolism and non-alcoholic fatty liver disease (NAFLD), and its underlying mechanism in mice. Mice were daily administrated with HFD with or without bromelain (20 mg/kg) for 12 weeks, and we found that bromelain decreased the HFD-induced increase in body weight by ~30%, organ weight by ~20% in liver weight and ~40% in white adipose tissue weight. Additionally, bromelain attenuated HFD-induced hyperlipidemia by decreasing the serum level of total cholesterol by ~15% and triglycerides level by ~25% in mice. Moreover, hepatic lipid accumulation, particularly that of total cholesterol, free cholesterol, triglycerides, fatty acids, and glycerol, was decreased by 15–30% with bromelain treatment. Mechanistically, these beneficial effects of bromelain on HFD-induced hyperlipidemia and hepatic lipid accumulation may be attributed to the decreased fatty acid uptake and cholesteryl ester synthesis and the increased lipoprotein internalization, bile acid metabolism, cholesterol clearance, the assembly and secretion of very low-density lipoprotein, and the β-oxidation of fatty acids by regulating the protein expression involved in the above mentioned hepatic metabolic pathways. Collectively, these findings suggest that bromelain has therapeutic value for treating NAFLD and metabolic diseases.

Catalpol Attenuates Hepatic Steatosis by Regulating Lipid Metabolism via AMP-Activated Protein Kinase Activation

The increased prevalence of nonalcoholic fatty liver disease (NAFLD), which develops from hepatic steatosis, represents a public health challenge. Catalpol, a natural component extracted from the roots of Radix Rehmanniae, has several pharmacological activities. The present study is aimed at examining whether catalpol prevents hepatic steatosis in cell and animal experiments and elucidating the possible mechanisms. HepG2 cells were treated with 300 μM palmitate (PA) and/or catalpol for 24 h in vitro, and male C57BL/6J mice fed a high-fat diet (HFD) were administered catalpol for 18 weeks in vivo. The results revealed that catalpol significantly decreased lipid accumulation in PA-treated HepG2 cells. Moreover, catalpol drastically reduced body weight and lipid accumulation in the liver, whereas it ameliorated hepatocyte steatosis in HFD-fed mice. Notably, catalpol remarkably promoted the phosphorylation of AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase. Subsequently, catalpol repressed the expressions of lipogenesis-associated genes such as sterol regulatory element-binding protein 1c and fatty acid synthase but promoted the expressions of genes associated with fatty acid β-oxidation such as peroxisome proliferator-activated receptor α together with its target genes carnitine palmitoyltransferase 1 and acyl-CoA oxidase 1 (ACOX1). However, the preincubation of the HepG2 cells with compound C (10 μM), an AMPK inhibitor, prevented catalpol-mediated beneficial effects. These findings suggest that catalpol ameliorates hepatic steatosis by suppressing lipogenesis and enhancing fatty acid β-oxidation in an AMPK-dependent manner. Therefore, catalpol has potential as a novel agent in the treatment of NAFLD.

TNFAIP8 regulates autophagy, cell steatosis, and promotes hepatocellular carcinoma cell proliferation

Tumor necrosis factor-α-induced protein 8 (TNFAIP8) expression has been linked to tumor progression in various cancer types, but the detailed mechanisms of TNFAIP8 are not fully elucidated. Here we define the role of TNFAIP8 in early events associated with development of hepatocellular carcinoma (HCC). Increased TNFAIP8 levels in HCC cells enhanced cell survival by blocking apoptosis, rendering HCC cells more resistant to the anticancer drugs, sorafenib and regorafenib. TNFAIP8 also induced autophagy and steatosis in liver cancer cells. Consistent with these observations, TNFAIP8 blocked AKT/mTOR signaling and showed direct interaction with ATG3-ATG7 proteins. TNFAIP8 also exhibited binding with fatty acids and modulated expression of lipid/fatty-acid metabolizing enzymes. Chronic feeding of mice with alcohol increased hepatic levels of TNFAIP8, autophagy, and steatosis but not in high-fat-fed obese mice. Similarly, higher TNFAIP8 expression was associated with steatotic livers of human patients with a history of alcohol use but not in steatotic patients with no history of alcohol use. Our data indicate a novel role of TNFAIP8 in modulation of drug resistance, autophagy, and hepatic steatosis, all key early events in HCC progression.

Worming into the Uncharacterized Human Proteome

Using neXtProt release 2019-01-11, we manually curated a list of 1837 functionally uncharacterized human proteins. Using OrthoList 2, we found that 270 of them have homologues in Caenorhabditis elegans, including 60 with a one-to-one orthology relationship. According to annotations extracted from WormBase, the vast majority of these 60 worm genes have RNAi experimental data or mutant alleles, but manual inspection shows that only 15% have phenotypes that could be interpreted in terms of a specific function. One third of the worm orthologs have protein-protein interaction data, and two of these interactions are conserved in humans. The combination of phenotypic, protein-protein interaction, and gene expression data provides functional hypotheses for 8 uncharacterized human proteins. Experimental validation in human or orthologs is necessary before they can be considered for annotation.

Apolipoproteins and cancer

The role of apolipoproteins in cardiovascular disease has been well investigated, but their participation in cancer has only been explored in a few published studies which showed a close link with certain kinds of cancer. In this review, we focused on the function of different kinds of apolipoproteins in cancers, autophagy, oxidative stress, and drug resistance. The potential application of apolipoproteins as biomarkers for cancer diagnosis and prognosis was highlighted, together with an investigation of their potential as drug targets for cancer treatment. Many important roles of apolipoproteins and their mechanisms in cancers were reviewed in detail and future perspectives of apolipoprotein research were discussed.

Ectopic localization of autophagosome in fatty liver is a key factor for liver regeneration

Autophagy has a critical role in liver regeneration. However, no studies have demonstrated autophagic flux in the regenerating fatty liver. The aim of this study was to clarify the dynamics of autophagy in the regeneration of the fatty liver. Following 70% partial hepatectomy (PH) in db/db fatty mice, which is a non-alcoholic fatty liver disease (NAFLD) model, we investigated the survival rate and recovery of liver volume. Histological examination of the regenerating liver was examined using electron microscopy. The 7-day survival rate after PH in db/db mice was 20%, which was significantly lower than that in control mice (P< .01). Liver regeneration within 48 h after PH was significantly impaired in db/db mice (P< .05). The number of proliferating cell nuclear antigen (PCNA) positive cells and the expression levels of cell-cycle markers cyclins D, E, and A were lower in db/db mice compared with controls. In the regenerating liver, LC3-II level was higher in db/db mice, but p62 expression was increased and cathepsin D expression, a marker of autophagolysosome proteolysis, was decreased compared with controls. Additionally, electronic microscopy revealed that autophagosomes during liver regeneration in db/db mice were mainly located in lipid droplets. Our findings indicate that the different localization of autophagosomes in db/db mice compared with controls led to impairment of liver regeneration in the fatty liver.

Linking Lipid Metabolism to Chromatin Regulation in Aging

The lifespan of an organism is strongly influenced by environmental factors (including diet) and by internal factors (notably reproductive status). Lipid metabolism is critical for adaptation to external conditions or reproduction. Interestingly, specific lipid profiles are associated with longevity, and increased uptake of certain lipids extends longevity in Caenorhabditis elegans and ameliorates disease phenotypes in humans. How lipids impact longevity, and how lipid metabolism is regulated during aging, is just beginning to be unraveled. This review describes recent advances in the regulation and role of lipids in longevity, focusing on the interaction between lipid metabolism and chromatin states in aging and age-related diseases.

Autophagy: An Essential Degradation Program for Cellular Homeostasis and Life

Autophagy is a lysosome-dependent cellular degradation program that responds to a variety of environmental and cellular stresses. It is an evolutionarily well-conserved and essential pathway to maintain cellular homeostasis, therefore, dysfunction of autophagy is closely associated with a wide spectrum of human pathophysiological conditions including cancers and neurodegenerative diseases. The discovery and characterization of the kingdom of autophagy proteins have uncovered the molecular basis of the autophagy process. In addition, recent advances on the various post-translational modifications of autophagy proteins have shed light on the multiple layers of autophagy regulatory mechanisms, and provide novel therapeutic targets for the treatment of the diseases.

Lipophagy in nonliver tissues and some related diseases: Pathogenic and therapeutic implications

Lipid autophagy (lipophagy) is defined as a selective autophagy process in which some intracellular lipid droplets are selectively degraded by autophagic lysosomes pathway. The occurrence of lipophagy was first discovered in liver tissues. Additionally, abundant evidence indicated that the occurrence of hepatic lipophagy has been implicated in many liver diseases including fatty liver diseases, nonalcoholic fatty liver diseases, liver fibrosis, and liver cirrhosis. However, recent studies suggested that hepatic lipophagy occurs not only in liver tissue but also in other nonliver tissues and cells. Furthermore, the occurrence of lipophagy plays a crucial role in nonliver tissues and some related diseases. For instance, lipophagy relieves insulin resistance in adipose tissue from obesity patient with type 2 diabetes. Additionally, lipophagy has the ability to remit neurodegenerative diseases by reducing activity-dependent neurodegeneration in nervous tissue. Lipophagy decreases muscle lipid accumulation and accordingly improves lipid storage myopathy in muscle tissue. Moreover, lipophagy alleviates the malignancy and metastasis of cancer in clear renal cell carcinoma tissue. Lipophagy is also involved in other processes, such as spermatogenesis, osteoblastogenesis, and mucosal ulceration. In conclusion, targeting lipophagy may be a critical regulator and a new therapeutic strategy for nonliver tissues and some related diseases.

Pathways and mechanisms linking dietary components to cardiometabolic disease: thinking beyond calories

Calories from any food have the potential to increase risk for obesity and cardiometabolic disease because all calories can directly contribute to positive energy balance and fat gain. However, various dietary components or patterns may promote obesity and cardiometabolic disease by additional mechanisms that are not mediated solely by caloric content. Researchers explored this topic at the 2017 CrossFit Foundation Academic Conference 'Diet and Cardiometabolic Health - Beyond Calories', and this paper summarizes the presentations and follow-up discussions. Regarding the health effects of dietary fat, sugar and non-nutritive sweeteners, it is concluded that food-specific saturated fatty acids and sugar-sweetened beverages promote cardiometabolic diseases by mechanisms that are additional to their contribution of calories to positive energy balance and that aspartame does not promote weight gain. The challenges involved in conducting and interpreting clinical nutritional research, which preclude more extensive conclusions, are detailed. Emerging research is presented exploring the possibility that responses to certain dietary components/patterns are influenced by the metabolic status, developmental period or genotype of the individual; by the responsiveness of brain regions associated with reward to food cues; or by the microbiome. More research regarding these potential 'beyond calories' mechanisms may lead to new strategies for attenuating the obesity crisis.

Trans-Ferulic Acid-4-β-Glucoside Alleviates Cold-Induced Oxidative Stress and Promotes Cold Tolerance

Trans-ferulic acid-4-β-glucoside (C₁₆H₂₀O₉, TFA-4β-G) is a monomer extracted from the Chinese medicine called radix aconiti carmichaeli (Fuzi). To date, research on this substance is lacking. Here, we found that trans-ferulic acid-4-β-glucoside effectively promoted cold acclimatization in mice via increased heat production and alleviation of oxidative stress in a cold environment. Thus, our work indicates that ferulic acid-4-β-glucoside is a potential therapeutic candidate for prevention and treatment of cold stress injury.

Lipid Droplets in Cancer: Guardians of Fat in a Stressful World

Cancer cells possess remarkable abilities to adapt to adverse environmental conditions. Their survival during severe nutrient and oxidative stress depends on their capacity to acquire extracellular lipids and the plasticity of their mechanisms for intracellular lipid synthesis, mobilisation, and recycling. Lipid droplets, cytosolic fat storage organelles present in most cells from yeast to men, are emerging as major regulators of lipid metabolism, trafficking, and signalling in various cells and tissues exposed to stress. Their biogenesis is induced by nutrient and oxidative stress and they accumulate in various cancers. Lipid droplets act as switches that coordinate lipid trafficking and consumption for different purposes in the cell, such as energy production, protection against oxidative stress or membrane biogenesis during rapid cell growth. They sequester toxic lipids, such as fatty acids, cholesterol and ceramides, thereby preventing lipotoxic cell damage and engage in a complex relationship with autophagy. Here, we focus on the emerging mechanisms of stress-induced lipid droplet biogenesis; their roles during nutrient, lipotoxic, and oxidative stress; and the relationship between lipid droplets and autophagy. The recently discovered principles of lipid droplet biology can improve our understanding of the mechanisms that govern cancer cell adaptability and resilience to stress.

Cannabis use is associated with reduced prevalence of progressive stages of alcoholic liver disease

BACKGROUND

Abusive alcohol use has well-established health risks including causing liver disease (ALD) characterized by alcoholic steatosis (AS), steatohepatitis (AH), fibrosis, cirrhosis (AC) and hepatocellular carcinoma (HCC). Strikingly, a significant number of individuals who abuse alcohol also use Cannabis, which has seen increased legalization globally. While cannabis has demonstrated anti-inflammatory properties, its combined use with alcohol and the development of liver disease remain unclear.

AIM

The aim of this study was to determine the effects of cannabis use on the incidence of liver disease in individuals who abuse alcohol.

METHODS

We analysed the 2014 Healthcare Cost and Utilization Project-Nationwide Inpatient Sample (NIS) discharge records of patients 18 years and older, who had a past or current history of abusive alcohol use (n = 319 514). Using the International Classification of Disease, Ninth Edition codes, we studied the four distinct phases of progressive ALD with respect to three cannabis exposure groups: non-cannabis users (90.39%), non-dependent cannabis users (8.26%) and dependent cannabis users (1.36%). We accounted for the complex survey sampling methodology and estimated the adjusted odds ratio (AOR) for developing AS, AH, AC and HCC with respect to cannabis use (SAS 9.4).

RESULTS

Our study revealed that among alcohol users, individuals who additionally use cannabis (dependent and non-dependent cannabis use) showed significantly lower odds of developing AS, AH, AC and HCC (AOR: 0.55 [0.48-0.64], 0.57 [0.53-0.61], 0.45 [0.43-0.48] and 0.62 [0.51-0.76]). Furthermore, dependent users had significantly lower odds than non-dependent users for developing liver disease.

CONCLUSIONS

Our findings suggest that cannabis use is associated with a reduced incidence of liver disease in alcoholics.

Autophagic Regulation of Lipid Homeostasis in Cardiometabolic Syndrome

As an important protein quality control process, autophagy is essential for the degradation and removal of long-lived or injured cellular components and organelles. Autophagy is known to participate in a number of pathophysiological processes including cardiometabolic syndrome. Recent findings have shown compelling evidence for the intricate interplay between autophagy and lipid metabolism. Autophagy serves as a major regulator of lipid homeostasis while lipid can also influence autophagosome formation and autophagic signaling. Lipophagy is a unique form of selective autophagy and functions as a fundamental mechanism for clearance of lipid excess in atherosclerotic plaques. Ample of evidence has denoted a novel therapeutic potential for autophagy in deranged lipid metabolism and management of cardiometabolic diseases such as atherosclerosis and diabetic cardiomyopathy. Here we will review the interplays between cardiac autophagy and lipid metabolism in an effort to seek new therapeutic options for cardiometabolic diseases.

Vanadium(IV)-chlorodipicolinate alleviates hepatic lipid accumulation by inducing autophagy via the LKB1/AMPK signaling pathway in vitro and in vivo

Numerous studies have demonstrated that vanadium compounds are able to improve lipemia and triglyceridemia in both humans and animals. However, the molecular mechanism remains elusive. The present study was conducted to investigate the anti-hyperlipidemic effect of vanadium(IV) complex with 4-chlorodipicolinic acid (VOdipic-Cl)-induced autophagy on hepatic lipid accumulation. To explore the possible underlying mechanisms, primary rat hepatocytes, human hepatoma cell line HepG2, and liver tissue from C57BL/6 mice fed a high-fat diet (HFD) were used. In vitro, cultured primary rat hepatocytes were treated with palmitate (0.25, 0.5 and 0.75 mM) prior to VOdipic-Cl (50, 100, and 200 μM) for 24 h, respectively. In vivo, C57BL/6 mice were fed with high-fat diet for 16 weeks. VOdipic-Cl (10 mg V/kg body weight) was given by daily gavage for 4 weeks. In vitro results showed that VOdipic-Cl significantly inhibited lipid droplet formation by increasing the level of conversion and punctuation of microtubule-associated proteins light chain 3 (LC3) in a dose-dependent manner, and activated liver kinase B-1 (LKB1) and adenosine monophosphate-activated protein kinase (AMPK) phosphorylation. Confocal microscopy images also showed that VOdipic-Cl induced sequestration of lipid droplets (LDs) by autophagy. In vivo, VOdipic-Cl attenuated the increase in serum and liver triglyceride levels in the mice fed with high-fat diet, while significantly increased autophagy induction and activated LKB1 and AMPK phosphorylation in the liver. Taken together, these results suggest that VOdipic-Cl reduces hepatic lipid accumulation by inducing autophagy via the activation of LKB1/AMPK-dependent signaling pathway.

Autophagy activation by Jiang Zhi Granule protects against metabolic stress-induced hepatocyte injury

AIM

To elucidate the potential role of autophagy and the protective effects of Jiang Zhi Granule (JZG) in metabolic stress-induced hepatocyte injury.

METHODS

An in vitro and in vivo approach was used in this study. HepG2 cells were incubated in culture medium containing palmitate (PA; 0, 0.1, 0.2, 0.3, 0.4 or 0.5 mmol/L) and treated with or without JZG (100 μg/mL) for 24 h or 48 h, and the progression of autophagy was visualized by stable fluorescence-expressing cell lines LC3 and p62. Western blot analyses were performed to examine the expression of LC3-II/LC3-I, p62, mTOR and PI3K, while mitochondrial integrity and oxidative stress were observed by fluorescence staining of JC-1 and reactive oxygen species. C57BL/6 mice were divided into three groups: control group (n = 10), high fat (HF) group (n = 13) and JZG group (n = 13); and, histological staining was carried out to detect inflammation and lipid content in the liver.

RESULTS

The cell trauma induced by PA was aggravated in a dose- and time-dependent manner, and hepatic function was improved by JZG. PA had dual effects on autophagy by activating autophagy induction and blocking autophagic flux. The PI3K-AKT-mTOR signaling pathway and the fusion of isolated hepatic autophagosomes and lysosomes were critically involved in this process. JZG activated autophagy progression by either induction of autophagosomes or co-localization of autophagosomes and lysosomes as well as degradation of autolysosomes to protect against PA-induced hepatocyte injury, and protected mitochondrial integrity against oxidative stress in PA-induced mitochondrial dysfunction. In addition, JZG ameliorated lipid droplets and inflammation induced by HF diet in vivo, leading to improved metabolic disorder and associated liver injury in a mouse model of non-alcoholic fatty liver disease (NAFLD).

CONCLUSION

Metabolic stress-induced hepatocyte injury exhibited dual effects on autophagy and JZG activated the entire process, resulting in beneficial effects in NAFLD.

Sidt2 regulates hepatocellular lipid metabolism through autophagy

SID1 transmembrane family member 2 (Sidt2) is an integral lysosomal membrane protein. To investigate its explicit function, we generated a global Sidt2 knockout mouse model (Sidt2^-/-). Compared with the littermate controls, Sidt2^-/- mice exhibited a remarkable accumulation of lipid droplets in liver. First, it was observed that food consumption, hepatocyte fatty acid uptake and de novo lipogenesis, hepatocyte lipolysis, and TG secretion in the form of very low density lipoprotein were comparable between Sidt2^-/- and WT mice. However, the hepatic β-oxidation of fatty acids decreased significantly as revealed by a low level of serum β-hydroxybutyrate in the Sidt2^-/- mice along with normal mRNA expression of genes involved in fatty acid oxidation. In addition, the classical autophagy pathway marker proteins, p62 and LC3-II, increased in liver, along with compromised autophagic flux in primary hepatocytes, indicating a block of autophagosome maturation due to Sidt2 deficiency, which was also supported by electron microscopy image analysis both in livers and in primary hepatocytes from Sidt2^-/- mice. It was concluded that Sidt2 plays an important role in mouse hepatic lipid homeostasis by regulating autophagy at the terminal stage.

Chronic Alcohol Consumption Inhibits Autophagy and Promotes Apoptosis in the Liver

Background: Chronic alcohol consumption is a major cause of liver injury. However, the molecular mechanisms by which alcohol impairs hepatocellular function and induces cell death remain unclear. Macroautophagy (hereafter called 'autophagy') is a degradation pathway involved in the survival or death of cells during conditions of cellular stress. This study examines the effect of chronic alcohol consumption on hepatocellular autophagy in an animal model. Methods: During a 12-week period male Wistar rats were fed a Lieber-DeCarli diet containing 5% alcohol (EtOH group; n=10), or an isocaloric diet (control group; n=10). Hepatic expression of key regulatory autophagy proteins (e.g. Beclin-1, ATG-3, ATG-5, p62/SQSTM1 and LC3) were detected by real-time polymerase chain reaction and Western blot analysis. Markers of cellular stress and apoptotic cell death (e.g. HO-1, caspase-3, PARP-1 and Bcl-2) were determined, and levels of reduced and oxidized glutathione were measured. Results: Chronic alcohol consumption caused cellular and oxidative stress in the liver. Transcriptional and translational expression of Beclin-1 and ATG-5 was significantly impaired. The protein expression of LC3-I and LC3-II was significantly increased, while the ratio of LC3I/II remained unchanged in the EtOH group compared with controls. Hepatocellular expression of p62/SQSTM1 and markers of apoptotic cell death (such as cleaved caspase-3 and cleaved PARP-1) were significantly increased in the EtOH group indicating a disrupted autophagic flux and increased rate of apoptosis in the liver. Conclusions: In this model, chronic alcohol consumption impaired hepatocellular autophagy and induced apoptotic cell death. It appears that changes in autophagy might contribute to alcohol-induced structural and functional hepatocellular injury.

Aerobic endurance training improves nonalcoholic fatty liver disease (NAFLD) features via miR-33 dependent autophagy induction in high fat diet fed mice

Due to changes in life style, obesity and obesity related complication such as insulin resistance, type 2 diabetes and non-alcoholic fatty liver disease caused worldwide health problems. Regular exercise has been frequently prescribed to combat metabolic complication of obesity but its molecular mechanism has not been fully illustrated. We investigated molecular mechanism of lipid lowering effect of exercise training in high fat diet fed mice by focusing on miR-33 expression and autophagy pathway. 24 mice were assigned to normal chow (NC) (n=8), high-fat diet (HFD) (n=16) group and subjected to NC and HFD for 13-weeks. HFD groups were divided to sedentary (HFD n=8) or continuous endurance training (HFD+CET, n=8) subgroups. The HFD+CET mice were subjected to treadmill running for 10-weeks in 23-week HFD course. HFD increased body weight, fasting blood sugar, triglyceride, cholesterol, aspartate aminotransferase (AST), alanine aminotransferase (ALT), liver lipogenic genes expression and reduced miR-33 mRNA expression and autopahgy pathway while training program reversed them. Exogenous miR-33 mimic sequence induced autophagy and reduced lipogenesis in HepG2 cells. Autophagy induction by rapamycin reduced lipogenesis and autophagy inhibition by chloroquine, enhanced lipogenesis in HepG2 cells. These findings suggest that aerobic exercise training as a non-pharmacological therapy exerts its lipid lowering effects by miR-33 dependent autophagy induction.

Role of autophagy in hepatic ischemia-reperfusion injury

Hepatic ischemia-reperfusion injury (IRI) is a crucial cause of liver damage occurring in some surgical procedures including hepatic resection and liver transplantation, and it remains the key potential cause of hepatic failure after liver transplantation. The mechanism of hepatic IRI is diverse and complicated, and involves various stages. Autophagy, an evolutionarily conserved process responsible for the degradation of damaged and dysfunctional cytoplasmic contents such as mitochondrion and lipids, regulates cellular homeostasis and survival during hepatic IRI. This review summarizes the molecular mechanisms underlying hepatic IRI, epitomizes the functions of autophagy, and describes the prospects of using autophagy as a therapeutic target for hepatic IRI.

Relevance of autophagy to fatty liver diseases and potential therapeutic applications

Autophagy is an evolutionarily conserved lysosome-mediated cellular degradation program. Accumulating evidence shows that autophagy is important to the maintenance of liver homeostasis. Autophagy involves recycling of cellular nutrients recycling as well as quality control of subcellular organelles. Autophagy deficiency in the liver causes various liver pathologies. Fatty liver disease (FLD) is characterized by the accumulation of lipids in hepatocytes and the dysfunction in energy metabolism. Autophagy is negatively affected by the pathogenesis of FLD and the activation of autophagy could ameliorate steatosis, which suggests a potential therapeutic approach to FLD. In this review, we will discuss autophagy and its relevance to liver diseases, especially FLD. In addition, we will discuss recent findings on potential therapeutic applications of autophagy modulators for FLD.

Identification of autophagy related genes LC3 and ATG4 from yellow catfish Pelteobagrus fulvidraco and their transcriptional responses to waterborne and dietborne zinc exposure

Autophagy mediates the regulation of lipid metabolism. Moreover, our recent study indicated that waterborne and dietborne zinc (Zn) exposure differentially influenced lipid metabolism in a fish species of significance for aquaculture, yellow catfish Pelteobagrus fulvidraco, but further mechanism remained unknown. The hypothesis of the present study is that autophagy mediated the Zn-induced changes of lipid metabolism of yellow catfish subjected to different exposure pathways. To this end, we cloned key genes involved in autophagy in yellow catfish, explored their mRNA expressions in responses to different Zn exposure pathways. Full-length cDNA sequences of two LC3 subtypes and six ATG4 isoforms were isolated from yellow catfish. More ATG4 members were firstly identified in fish that might have arisen by teleost-specific whole genome duplication events. All of these members shared similar domain structure to their orthologous genes of vertebrates. Their mRNAs were widely expressed in various tissues, but at variable levels. Extra Zn addition in water or diets induced (P < 0.05) mRNA expression of ATG4Da, ATG4Db and LC3B. Considering their important roles of these genes in lipid metabolism, ATG4Da, ATG4Db and LC3B may mediate the changes of Zn-induced hepatic lipid metabolism of yellow catfish under different Zn exposure pathways. For the first time, we characterized the full-length cDNA sequences of six ATG4 isoforms and two LC3 subtypes, determined their tissue expression profiles and transcriptional responses to different Zn exposure pathways, which would contribute to our understanding of the molecular basis of autophagy, and also provide new insights into physiological responses to different Zn exposure pathways.

Autophagy and hepatic lipid metabolism

Autophagy is initially thought to be a non-selective process in which intracellular proteins or damaged organelles are degraded. It is activated when cells lack nutrients and energy. Autophagy degrades cytoplasmic components within lysosomes and reuses the energy of amino acids to promote cell survival and maintain the cytoplasmic content. Current evidence implicates autophagy in the regulation of lipid stores within the two main organs involved in maintaining lipid homeostasis, the liver and adipose tissue. Upregulation of autophagy may lead to conversion of white adipose tissue into brown adipose tissue, thus regulating energy expenditure and obesity. Discovering new therapeutic interventions to treat lipid and lipoprotein disorders is of great interest and the discovery of autophagy as a regulator of lipid metabolism has opened up a new avenue for this area. In the liver, autophagy can play a role in some common metabolic disorders, which needs further research.

Complex role of autophagy in regulation of hepatic lipid and lipoprotein metabolism

Discovering new therapeutic interventions to treat lipid and lipoprotein disorders is of great interest and the discovery of autophagy as a regulator of lipid metabolism has opened up new avenues for targeting modulators of this pathway. Autophagy is a degradative process that targets cellular components to the lysosome and recent studies have indicated a role for autophagy in regulating hepatic lipid metabolism (known as lipophagy) as well as lipoprotein assembly. Autophagy directly targets apolipoprotein B-100 (apoB100), the structural protein component of very low-density lipoproteins (VLDLs), and further targets lipid droplets (LDs), the cellular storage for neutral lipids. Autophagy thus plays a complex and dual role in VLDL particle assembly by regulating apoB100 degradation as well as aiding the maturation of VLDL particles by hydrolyzing lipid from LDs. The purpose of this article is to review our current understanding of molecular and cellular mechanisms mediating authophagic control of hepatic lipid biogenesis and VLDL production as well as dysregulation in insulin resistance and dyslipidemia.

Role of autophagy in bone and muscle biology

Autophagy in eukaryotic cells is a constitutive process and functions as a homeostatic mechanism; it is upregulated in response to specific stress stimuli such as starvation, hypoxia and as oxidative stress. In addition to playing a crucial role in adaptive responses to different stimuli, autophagy is also required for intracellular quality control. This second aspect is important to prevent the activation of pathological processes. Autophagy also plays a central role in cellular development and differentiation because it is involved in the regulation of energetic balance. This final aspect is critical for maintaining proper bone and muscle function as well as to prevent any pathological changes. Therefore, identifying new molecular targets involved in autophagy is critical to assure a good quality of life.

Inhibition of JNK suppresses autophagy and attenuates insulin resistance in a rat model of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a common chronic liver disease, the pathological process of which is complex. Activation of the c‑Jun N‑terminal kinase (JNK) signaling pathway is associated with the mechanism underlying obesity-induced insulin resistance. Furthermore, the JNK signaling pathway and dysfunctional autophagy serve important roles in hepatic lipid metabolism. However, the exact role of JNK in autophagy and obesity‑induced insulin resistance is not fully understood. Therefore, the present study aimed to investigate the underlying mechanisms by which the JNK signaling pathway regulates autophagy and insulin resistance in fatty liver. A rat model of NAFLD was established using a high‑fat diet (HFD), and insulin resistance in the livers of HFD rats was determined by peritoneal glucose tolerance testing. The results indicated that a HFD induced impaired glucose tolerance, liver function injury, insulin resistance and increased autophagy in rats. Treatment with SP600125, an inhibitor of JNK, relieved NAFLD in rats. Furthermore, SP600125 decreased the expression levels of autophagy-associated genes, including Beclin-1, microtubule-associated protein 1A/1B light chain 3, autophagy related gene (Atg)3 and Atg5, and the phosphorylation of insulin receptor (IR) β-subunit, IR substrate-1 and protein kinase B in vivo. In conclusion, JNK inhibition may suppress autophagy and attenuate insulin resistance. Therefore, JNK inhibition may provide a novel therapeutic strategy for the treatment of NAFLD.

Altered expression of lysosomal hydrolase, acid α-glucosidase, gene in coronary artery disease

BACKGROUND

Coronary artery disease (CAD) is a common complex disease caused by atherosclerosis. Autophagy is a cellular degradation process that delivers long-lived macromolecules and dysfunctional organelles into lysosomes for digestion. Autophagy regulates lipid and cholesterol metabolism. We have previously shown that expression of autophagic and lysosomal genes is altered in CAD patients. In this study, we investigated gene expression of a lysosomal hydrolase, acid α-glucosidase (GAA), in CAD patients and controls.

METHODS

GAA gene expression was examined in large cohorts of CAD patients (n=248) and ethnically matched controls (n=208). GAA enzymatic activity, protein levels, and transcript levels were determined and compared between CAD patients and controls.

RESULTS

GAA activities in CAD patients were significantly elevated (P<0.05) compared with controls. Consistently, GAA transcription levels were also significantly increased in CAD patients (P<0.01). Multivariate logistic regression analyses (GAA transcript level, hypertension, diabetes, and smoking) revealed that GAA transcript levels were strongly associated with CAD (odds ratio 5.93, 95% confidence interval 2.98-11.78, P=3.89×10(-7)). GAA protein levels were insignificantly increased in CAD patients (P>0.05), likely due to assay insensitivity.

CONCLUSION

Compared with controls, GAA gene expression levels in CAD patients were significantly increased, suggesting that GAA may be involved in the CAD development.

Lanthanide co-doped paramagnetic spindle-like mesocrystals for imaging and autophagy induction

We synthesized two novel lanthanide doped spindle-like mesocrystals, YF3:Ce,Eu,Gd and YF3:Ce,Tb,Gd (abbreviated as YEG and YTG mesospindles, respectively). Both of them possess paramagnetic and fluorescent properties, and their excellent cyto-compatibility and low haemolysis are further confirmed. Therefore, they could act as dual mode contrast agents for magnetic resonance imaging (MRI) and fluorescence imaging. Furthermore, YEG and YTG mesospindles induce dose and time dependent autophagy by activating the PI3K signaling pathway. The autophagy induced by YEG and YTG mesocrystals is confirmed by enhanced autophagosome formation, normal cargo degradation, and no disruption of lysosomal function. This work is important to illustrate how rare-earth mesocrystals affect the autophagic pathway, indicating the potential of the YEG and YTG mesospindles in diagnosis and therapy.

Deletion of autophagy inducer RB1CC1 results in degeneration of the retinal pigment epithelium

Autophagy regulates cellular homeostasis and response to environmental stress. Within the retinal pigment epithelium (RPE) of the eye, the level of autophagy can change with both age and disease. The purpose of this study is to determine the relationship between reduced autophagy and age-related degeneration of the RPE. The gene encoding RB1CC1/FIP200 (RB1-inducible coiled-coil 1), a protein essential for induction of autophagy, was selectively knocked out in the RPE by crossing Best1-Cre mice with mice in which the Rb1cc1 gene was flanked with Lox-P sites (Rb1cc1(flox/flox)). Ex vivo and in vivo analyses, including western blot, immunohistochemistry, transmission electron microscopy, fundus photography, optical coherence tomography, fluorescein angiography, and electroretinography were performed to assess the structure and function of the retina as a function of age. Deletion of Rb1cc1 resulted in multiple autophagy defects within the RPE including decreased conversion of LC3-I to LC3-II, accumulation of autophagy-targeted precursors, and increased numbers of mitochondria. Age-dependent degeneration of the RPE occurred, with formation of atrophic patches, subretinal migration of activated microglial cells, subRPE deposition of inflammatory and oxidatively damaged proteins, subretinal drusenoid deposits, and occasional foci of choroidal neovascularization. There was secondary loss of photoreceptors overlying the degenerated RPE and reduction in the electroretinogram. These observations are consistent with a critical role of autophagy in the maintenance of normal homeostasis in the aging RPE, and indicate that disruption of autophagy leads to retinal phenotypes associated with age-related degeneration.