Beclin 1 deficiency causes hepatic cell apoptosis via endoplasmic reticulum stress in zebrafish larvae

Distinct roles of core autophagy-related genes in zebrafish definitive hematopoiesis

Despite the well-described discrepancy between ATG (macroautophagy/autophagy-related) genes in the regulation of hematopoiesis, varying essentiality of core ATG proteins in vertebrate definitive hematopoiesis remains largely unclear. Here, we employed zebrafish (Danio rerio) to compare the functions of six core atg genes, including atg13, becn1 (beclin1), atg9a, atg2a, atg5, and atg3, in vertebrate definitive hematopoiesis via clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 ribonucleoprotein and morpholino targeting. Zebrafish with various atg mutations showed autophagic deficiency and presented partially consistent hematopoietic abnormalities during early development. All six atg mutations led to a declined number of spi1b+ (Spi-1 proto-oncogene b) myeloid progenitor cells. However, only becn1 mutation resulted in the expansion of myb+ (v-myb avian myeloblastosis viral oncogene homolog) hematopoietic stem and progenitor cells (HSPCs) and transiently increased coro1a+ (coronin, actin binding protein, 1A) leukocytes, whereas atg3 mutation decreased the number of HSPCs and leukocytes. Proteomic analysis of caudal hematopoietic tissue identified sin3aa (SIN3 transcription regulator family member Aa) as a potential modulator of atg13- and becn1-regulated definitive hematopoiesis. Disruption of sin3aa rescued the expansion of HSPCs and leukocytes in becn1 mutants and exacerbated the decrease of HSPCs in atg13 mutants. Double mutations were also performed to examine alternative functions of various atg genes in definitive hematopoiesis. Notably, becn1 mutation failed to induce HSPCs expansion with one of the other five atg mutations. These findings demonstrated the distinct roles of atg genes and their interplays in zebrafish definitive hematopoiesis, thereby suggesting that the vertebrate definitive hematopoiesis is regulated in an atg gene-dependent manner.Abbreviations: AGM: aorta-gonad-mesonephros; AO: acridine orange; atg: autophagy related; becn1: beclin 1, autophagy related; CHT: caudal hematopoietic tissue; CKO: conditional knockout; coro1a: coronin, actin binding protein, 1A; CQ: chloroquine; CRISPR: clustered regularly interspaced short palindromic repeats; dpf: days post fertilization; FACS: fluorescence-activated cell sorting; hbae1.1: hemoglobin, alpha embryonic 1.1; HSCs: hematopoietic stem cells; HSPCs: hematopoietic stem and progenitor cells; KD: knockdown; KO: knockout; map1lc3/lc3: microtubule-associated protein 1 light chain 3; MO: morpholino; mpeg1.1: macrophage expressed 1, tandem duplicate 1; mpx: myeloid-specific peroxidase; myb: v-myb avian myeloblastosis viral oncogene homolog; PE: phosphatidylethanolamine; p-H3: phospho-H3 histone; PtdIns3K: class 3 phosphatidylinositol 3-kinase; rag1: recombination activating 1; rb1cc1/fip200: RB1-inducible coiled-coil 1; RFLP: restriction fragment length polymorphism; RNP: ribonucleoprotein; sin3aa: SIN3 transcription regulator family member Aa; spi1b: Spi-1 proto-oncogene b; ulk: unc-51 like autophagy activating kinase; vtg1: vitellogenin 1; WISH: whole-mount in situ hybridization.

Cisplatin Nephrotoxicity Is Critically Mediated by the Availability of BECLIN1

Cisplatin nephrotoxicity is a critical limitation of solid cancer treatment. Until now, the complex interplay of various pathophysiological mechanisms leading to proximal tubular cell apoptosis after cisplatin exposure has not been fully understood. In our study, we assessed the role of the autophagy-related protein BECLIN1 (ATG6) in cisplatin-induced acute renal injury (AKI)-a candidate protein involved in autophagy and with putative impact on apoptosis by harboring a B-cell lymphoma 2 (BCL2) interaction site of unknown significance. By using mice with heterozygous deletion of Becn1, we demonstrate that reduced intracellular content of BECLIN1 does not impact renal function or autophagy within 12 months. However, these mice were significantly sensitized towards cisplatin-induced AKI, and by using Becn1+/-;Sglt2-Cre;Tomato/EGFP mice with subsequent primary cell analysis, we confirmed that nephrotoxicity depends on proximal tubular BECLIN1 content. Mechanistically, BECLIN1 did not impact autophagy or primarily the apoptotic pathway. In fact, a lack of BECLIN1 sensitized mice towards cisplatin-induced ER stress. Accordingly, the ER stress inhibitor tauroursodeoxycholic acid (TUDCA) blunted cisplatin-induced cell death in Becn1 heterozygosity. In conclusion, our data first highlight a novel role of BECLIN1 in protecting against cellular ER stress independent from autophagy. These novel findings open new therapeutic avenues to intervene in this important intracellular stress response pathway with a promising impact on future AKI management.

Effects of dietary chloroquine on fish growth, hepatic intermediary metabolism, antioxidant and inflammatory responses in turbot

Autophagy is a conserved cellular self-digestion process and is essential for individual growth, cellular metabolism and inflammatory responses. It was responsive to starvation, pathogens infection and environmental stress. However, the information on the regulation of autophagy in fish hepatic intermediary metabolism, antioxidant system, and immune responses were limited. In the present study, turbot with inhibited autophagy flux was built by dietary chloroquine. The hepatic metabolic response, antioxidant enzymes and immune responses were explored. Results showed that dietary chloroquine induced the expression of Beclin 1, SQSTM and LC-3II, and effectively inhibited autophagy flux. Autophagy dysfunction depressed fish growth and feed utilization, while it induced clusters of liver lipid droplets. The genes involved in lipolysis and fatty acid β-oxidation, as well as the lipogenesis-related genes in chloroquine group were depressed. The phosphorylation of AMPK was activated in chloroquine group, and the genes involved in glycolysis were induced. The hepatic content of malonyldialdehyde and the activities of SOD and CAT were induced when autophagy was inhibited. The content of Complement 3, Complement 4 and Immunoglobulin M, as well as the activity of lysozyme in plasma were depressed in chloroquine group. Dietary chloroquine induced the expression of toll-like receptors and stimulated the expression of myd88 and nf-κb p65, as well as the pro-inflammatory cytokines, such as tnf-α and il-1β. The expression of anti-inflammatory cytokine tgf-β was depressed in the chloroquine group. Our results would extend the knowledge on the role of autophagy in teleost and assist in improving fishery production.

Endoplasmic reticulum stress-mediated cell death in liver injury

The endoplasmic reticulum is an important intracellular organelle that plays an important role in maintaining cellular homeostasis. Endoplasmic reticulum stress (ERS) and unfolded protein response (UPR) are induced when the body is exposed to adverse external stimuli. It has been established that ERS can induce different cell death modes, including autophagy, apoptosis, ferroptosis, and pyroptosis, through three major transmembrane receptors on the ER membrane, including inositol requirement enzyme 1α, protein kinase-like endoplasmic reticulum kinase and activating transcription factor 6. These different modes of cell death play an important role in the occurrence and development of various diseases, such as neurodegenerative diseases, inflammation, metabolic diseases, and liver injury. As the largest metabolic organ, the liver is rich in enzymes, carries out different functions such as metabolism and secretion, and is the body's main site of protein synthesis. Accordingly, a well-developed endoplasmic reticulum system is present in hepatocytes to help the liver perform its physiological functions. Current evidence suggests that ERS is closely related to different stages of liver injury, and the death of hepatocytes caused by ERS may be key in liver injury. In addition, an increasing body of evidence suggests that modulating ERS has great potential for treating the liver injury. This article provided a comprehensive overview of the relationship between ERS and four types of cell death. Moreover, we discussed the mechanism of ERS and UPR in different liver injuries and their potential therapeutic strategies.

Antigen Presentation and Autophagy in Teleost Adaptive Immunity

Infectious diseases are a burden for aquaculture. Antigen processing and presentation (APP) to the immune effector cells that fight pathogens is key in the adaptive immune response. At the core of the adaptive immunity that appeared in lower vertebrates during evolution are the variable genes encoding the major histocompatibility complex (MHC). MHC class I molecules mainly present peptides processed in the cytosol by the proteasome and transported to the cell surface of all cells through secretory compartments. Professional antigen-presenting cells (pAPC) also express MHC class II molecules, which normally present peptides processed from exogenous antigens through lysosomal pathways. Autophagy is an intracellular self-degradation process that is conserved in all eukaryotes and is induced by starvation to contribute to cellular homeostasis. Self-digestion during autophagy mainly occurs by the fusion of autophagosomes, which engulf portions of cytosol and fuse with lysosomes (macroautophagy) or assisted by chaperones (chaperone-mediated autophagy, CMA) that deliver proteins to lysosomes. Thus, during self-degradation, antigens can be processed to be presented by the MHC to immune effector cells, thus, linking autophagy to APP. This review is focused on the essential components of the APP that are conserved in teleost fish and the increasing evidence related to the modulation of APP and autophagy during pathogen infection.

2-Amino-3-Methylimidazo[4,5-f]quinoline Triggering Liver Damage by Inhibiting Autophagy and Inducing Endoplasmic Reticulum Stress in Zebrafish (Danio rerio)

It is important to note that 2-Amino-3-methylimidazole[4,5-f]quinoline (IQ) is one of the most common heterocyclic amines (HCAs), which is a class of mutagenic/carcinogenic harmful compounds mainly found in high-protein thermal processed foods and contaminated environments. However, the pre-carcinogenic toxicity of IQ to the liver and its mechanism are poorly understood, further research is needed. In light of this, we exposed zebrafish to IQ (0, 8, 80, and 800 ng/mL) for 35 days, followed by comprehensive experimental studies. Histopathological and ultrastructural analysis showed that hepatocytes were damaged. TUNEL results showed that IQ induced apoptosis of liver cells, the expression of apoptosis factor gene was significantly increased, and the expression of Bcl-2 protein was significantly decreased. In addition, upregulated expression of the 78-kDa glucose-regulated protein (GRP78) and C/EBP homologous protein (CHOP) and endoplasmic reticulum stress (ERS)-related factors transcription levels were elevated obviously, suggesting that IQ induced ERS. Decreased protein expression of autophagy-related 5 (Atg5)-Atg12, Beclin1, and LC3-II, increased protein expression of p62, and autophagy-related factors transcription levels were significantly decreased, suggesting that IQ inhibited autophagy. Overall, our research showed that the potential harm of IQ to the liver before the occurrence of liver cancer was related to ERS and its mediated autophagy and apoptosis pathways.

Autophagy alleviates hypoxia-induced blood-brain barrier injury via regulation of CLDN5 (claudin 5)

Blood-brain barrier (BBB) disruption is a key event in triggering secondary damage to the central nervous system (CNS) under stroke, and is frequently associated with abnormal macroautophagy/autophagy in brain microvascular endothelial cells (BMECs). However, the underlying mechanism of autophagy in maintaining BBB integrity remains unclear. Here we report that in BMECs of patients suffering stroke, CLDN5 (claudin 5) abnormally aggregates in the cytosol accompanied by autophagy activation. In vivo zebrafish and in vitro cell studies reveal that BBB breakdown is partially caused by CAV1 (caveolin 1)-mediated redistribution of membranous CLDN5 into the cytosol under hypoxia. Meanwhile, autophagy is activated and contributes mainly to the degradation of CAV1 and aggregated CLDN5 in the cytosol of BMECs, therefore alleviating BBB breakdown. Blockage of autophagy by genetic methods or chemicals aggravates cytosolic aggregation of CLDN5, resulting in severer BBB impairment. These data demonstrate that autophagy functions in the protection of BBB integrity by regulating CLDN5 redistribution and provide a potential therapeutic strategy for BBB disorder-related cerebrovascular disease.Abbreviations: BBB: blood-brain barrier; BECN1: beclin 1; BMEC: brain microvascular endothelial cell; CAV1: caveolin 1; CCA: common carotid artery; CLDN5: claudin 5; CNS: central nervous system; CQ: chloroquine; HIF1A: hypoxia inducible factor 1 subunit alpha; MCAO: middle cerebral artery occlusion-reperfusion; OCLN: occludin; ROS: reactive oxygen species; STED: stimulated emission depletion; TEER: trans-endothelial electrical resistance; TEM: transmission electron microscopy; TJ: tight junction; TJP1: tight junction protein 1; UPS: ubiquitin-proteasome system.

Melatonin and Autophagy in Aging-Related Neurodegenerative Diseases

With aging, the nervous system gradually undergoes degeneration. Increased oxidative stress, endoplasmic reticulum stress, mitochondrial dysfunction, and cell death are considered to be common pathophysiological mechanisms of various neurodegenerative diseases (NDDs) such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), organophosphate-induced delayed neuropathy (OPIDN), and amyotrophic lateral sclerosis (ALS). Autophagy is a cellular basic metabolic process that degrades the aggregated or misfolded proteins and abnormal organelles in cells. The abnormal regulation of neuronal autophagy is accompanied by the accumulation and deposition of irregular proteins, leading to changes in neuron homeostasis and neurodegeneration. Autophagy exhibits both a protective mechanism and a damage pathway related to programmed cell death. Because of its "double-edged sword", autophagy plays an important role in neurological damage and NDDs including AD, PD, HD, OPIDN, and ALS. Melatonin is a neuroendocrine hormone mainly synthesized in the pineal gland and exhibits a wide range of biological functions, such as sleep control, regulating circadian rhythm, immune enhancement, metabolism regulation, antioxidant, anti-aging, and anti-tumor effects. It can prevent cell death, reduce inflammation, block calcium channels, etc. In this review, we briefly discuss the neuroprotective role of melatonin against various NDDs via regulating autophagy, which could be a new field for future translational research and clinical studies to discover preventive or therapeutic agents for many NDDs.

Zebrafish as a model to study autophagy and its role in skeletal development and disease

In the last twenty years, research using zebrafish as a model organism has increased immensely. With the many advantages that zebrafish offer such as high fecundity, optical transparency, ex vivo development, and genetic tractability, they are well suited to studying developmental processes and the effect of genetic mutations. More recently, zebrafish models have been used to study autophagy. This important protein degradation pathway is needed for cell and tissue homeostasis in a variety of contexts. Correspondingly, its dysregulation has been implicated in multiple diseases including skeletal disorders. In this review, we explore how zebrafish are being used to study autophagy in the context of skeletal development and disease, and the ways these areas are intersecting to help identify potential therapeutic targets for skeletal disorders.

The Combination of Fasting, Acute Resistance Exercise, and Protein Ingestion Led to Different Responses of Autophagy Markers in Gastrocnemius and Liver Samples

The present study verified the responses of proteins related to the autophagy pathway after 10 h of fast with resistance exercise and protein ingestion in skeletal muscle and liver samples. The rats were distributed into five experimental groups: control (CT; sedentary and without gavage after fast), exercise immediately (EXE-imm; after fast, rats were submitted to the resistance protocol and received water by gavage immediately after exercise), exercise after 1 h (EXE-1h; after fast, rats were submitted to the resistance protocol and received water by gavage 1 h after exercise), exercise and supplementation immediately after exercise (EXE/Suppl-imm; after fast, rats were submitted to the resistance protocol and received a mix of casein: whey protein 1:1 (w/w) by gavage immediately after exercise), exercise and supplementation 1 h after exercise (EXE/Suppl-1h; after fast, rats were submitted to the resistance protocol and received a mix of casein: whey protein 1:1 (w/w) by gavage 1 h after exercise). In summary, the current findings show that the combination of fasting, acute resistance exercise, and protein blend ingestion (immediately or 1 h after the exercise stimulus) increased the serum levels of leucine, insulin, and glucose, as well as the autophagy protein contents in skeletal muscle, but decreased other proteins related to the autophagic pathway in the liver. These results deserve further mechanistic investigations since athletes are combining fasting with physical exercise to enhance health and performance outcomes.