Autophagy during vertebrate development

Temperature- and chemical-induced neurotoxicity in zebrafish

Throughout their lives, humans encounter a plethora of substances capable of inducing neurotoxic effects, including drugs, heavy metals and pesticides. Neurotoxicity manifests when exposure to these chemicals disrupts the normal functioning of the nervous system, and some neurotoxic agents have been linked to neurodegenerative pathologies such as Parkinson's and Alzheimer's disease. The growing concern surrounding the neurotoxic impacts of both naturally occurring and man-made toxic substances necessitates the identification of animal models for rapid testing across a wide spectrum of substances and concentrations, and the utilization of tools capable of detecting nervous system alterations spanning from the molecular level up to the behavioural one. Zebrafish (Danio rerio) is gaining prominence in the field of neuroscience due to its versatility. The possibility of analysing all developmental stages (embryo, larva and adult), applying the most common "omics" approaches (transcriptomics, proteomics, lipidomics, etc.) and conducting a wide range of behavioural tests makes zebrafish an excellent model for neurotoxicity studies. This review delves into the main experimental approaches adopted and the main markers analysed in neurotoxicity studies in zebrafish, showing that neurotoxic phenomena can be triggered not only by exposure to chemical substances but also by fluctuations in temperature. The findings presented here serve as a valuable resource for the study of neurotoxicity in zebrafish and define new scenarios in ecotoxicology suggesting that alterations in temperature can synergistically compound the neurotoxic effects of chemical substances, intensifying their detrimental impact on fish populations.

Regulation of Developmental Cell Death in the Animal Kingdom: A Critical Analysis of Epigenetic versus Genetic Factors

The present paper proposes a new level of regulation of programmed cell death (PCD) in developing systems based on epigenetics. We argue against the traditional view of PCD as an altruistic “cell suicide” activated by specific gene-encoded signals with the function of favoring the development of their neighboring progenitors to properly form embryonic organs. In contrast, we propose that signals and local tissue interactions responsible for growth and differentiation of the embryonic tissues generate domains where cells retain an epigenetic profile sensitive to DNA damage that results in its subsequent elimination in a fashion reminiscent of what happens with scaffolding at the end of the construction of a building. Canonical death genes, including Bcl-2 family members, caspases, and lysosomal proteases, would reflect the downstream molecular machinery that executes the dying process rather than being master cell death regulatory signals.

c-FLIP regulates autophagy by interacting with Beclin-1 and influencing its stability

c-FLIP (cellular FLICE-like inhibitory protein) protein is mostly known as an apoptosis modulator. However, increasing data underline that c-FLIP plays multiple roles in cellular homoeostasis, influencing differently the same pathways depending on its expression level and isoform predominance. Few and controversial data are available regarding c-FLIP function in autophagy. Here we show that autophagic flux is less effective in c-FLIP−/− than in WT MEFs (mouse embryonic fibroblasts). Indeed, we show that the absence of c-FLIP compromises the expression levels of pivotal factors in the generation of autophagosomes. In line with the role of c-FLIP as a scaffold protein, we found that c-FLIP_L interacts with Beclin-1 (BECN1: coiled-coil, moesin-like BCL2-interacting protein), which is required for autophagosome nucleation. By a combination of bioinformatics tools and biochemistry assays, we demonstrate that c-FLIP_L interaction with Beclin-1 is important to prevent Beclin-1 ubiquitination and degradation through the proteasomal pathway. Taken together, our data describe a novel molecular mechanism through which c-FLIP_L positively regulates autophagy, by enhancing Beclin-1 protein stability.

Autophagy: A Novel Horizon for Hair Cell Protection

As a general sensory disorder, hearing loss was a major concern worldwide. Autophagy is a common cellular reaction to stress that degrades cytoplasmic waste through the lysosome pathway. Autophagy not only plays major roles in maintaining intracellular homeostasis but is also involved in the development and pathogenesis of many diseases. In the auditory system, several studies revealed the link between autophagy and hearing protection. In this review, we aimed to establish the correlation between autophagy and hair cells (HCs) from the aspects of ototoxic drugs, aging, and acoustic trauma and discussed whether autophagy could serve as a potential measure in the protection of HCs.

Otic Neurogenesis Is Regulated by TGFβ in a Senescence-Independent Manner

Cellular senescence has classically been associated with aging. Intriguingly, recent studies have also unraveled key roles for senescence in embryonic development, regeneration, and reprogramming. Developmental senescence has been reported during embryonic development in different organisms and structures, such as the endolymphatic duct during inner ear development of mammals and birds. However, there is no study addressing the possible role of senescence on otic neurogenesis. TGFβ/SMAD is the best-known pathway linked to the induction of developmentally programmed cell senescence. Here, we studied if TGFβ2 induces cellular senescence during acoustic-vestibular-ganglion (AVG) formation. Using organotypic cultures of AVG, and characterizing different stages of otic neurogenesis in the presence of TGFβ2 and a selective TGF-β receptor type-I inhibitor, we show that TGFβ2 exerts a powerful action in inner ear neurogenesis but, contrary to what we recently observed during endolymphatic duct development, these actions are independent of cellular senescence. We show that TGFβ2 reduces proliferation, and induces differentiation and neuritogenesis of neuroblasts, without altering cell death. Our studies highlight the roles of TGFβ2 and cellular senescence in the precise regulation of cell fate within the developing inner ear and its different cell types, being their mechanisms of action highly cell-type dependent.

microRNA-519d Induces Autophagy and Apoptosis of Human Hepatocellular Carcinoma Cells Through Activation of the AMPK Signaling Pathway via Rab10

Background and Aim

Hepatocellular carcinoma (HCC) is a type of cancer with high mortality rates. The overexpression of microRNA-519d (miR-519d) has been explored in different types of cancers, which could significantly help suppress cancer development. This study aimed to investigate the interaction of miR-519d with its target gene, Rab10, as well as its effects on cell proliferation and autophagy in HCC cells through modulation of the AMPK signaling pathway.

Methods

Microarray analysis was used to analyze the differentially expressed genes in HCC, and the target genes of the screened-out miRNA were predicted and verified. The expression of miR-519d and Rab10, AMPK signaling pathway-related proteins, apoptosis- and autophagy-related proteins was determined by RT-qPCR and Western blot analysis in HCC tissues and cell lines. Lastly, the effects of miR-519d and Rab10 in HCC cell proliferation, apoptosis, and mouse tumour xenograft in vivo were examined through gain- and loss-of-function experiments.

Results

MiR-519d was down-regulated and Rab10 was upregulated in HCC tissues and cell lines. Overexpression of miR-519d decreased the expression of Rab10, mTOR, and Bcl-2, but increased the expression of Bax, Beclin1, Atg5, and p53. Upregulated miR-519d and downregulated Rab10 expression suppressed cell proliferation and induced cell apoptosis and autophagy in HCC cells. Finally, upregulation of miR-519d inhibited tumour growth in vivo.

Conclusion

The result obtained in this study indicates that up-regulation of miR-519d inhibits proliferation and promotes apoptosis and autophagy of HCC cells through activation of the AMPK signaling pathway via downregulating Rab10, which provides a potential target for the treatment of HCC.

Dissecting pharmacological effects of chloroquine in cancer treatment: interference with inflammatory signaling pathways

Chloroquines are 4-aminoquinoline-based drugs mainly used to treat malaria. At pharmacological concentrations, they have significant effects on tissue homeostasis, targeting diverse signaling pathways in mammalian cells. A key target pathway is autophagy, which regulates macromolecule turnover in the cell. In addition to affecting cellular metabolism and bioenergetic flow equilibrium, autophagy plays a pivotal role at the interface between inflammation and cancer progression. Chloroquines consequently have critical effects in tissue metabolic activity and importantly, in key functions of the immune system. In this article, we will review the work addressing the role of chloroquines in the homeostasis of mammalian tissue, and the potential strengths and weaknesses concerning their use in cancer therapy.

Autophagy is Required for Remodeling in Postnatal Developing Ribbon Synapses of Cochlear Inner Hair Cells

Cochlear ribbon synapses formed between inner hair cells (IHCs) and spiral ganglion neurons (SGNs) are immature at birth and they require dramatic morphological and functional developments to achieve auditory maturation in postnatal mice. However, the mechanism underlying this remodeling process of cochlear ribbon synapse remains elusive. Here, we report that autophagy is necessary for the development and maturation of cochlear ribbon synapses in mice. In this study, significantly high levels of LC3B (a widespread marker of autophagy) were found in the cochlea from postnatal day 1 (P1) to P15, which then decreased at P28 to P30. Treatment of mice at P7 with rapamycin or 3-methyladenine (activator and inhibitor of autophagy, respectively) for 7 days led to the significant elevations of hearing threshold across frequencies from P15 to P30. Moreover, abnormal morphology of cochlear ribbon synapses and reduced IHC exocytosis function were detected from P15 to P30, which were likely associated to hearing impairment. Thus, our study demonstrated that autophagy was required for remodeling of cochlear ribbon synapses and provided a new insight into autophagy-related hearing disorder during auditory development. Furthermore, we implicated a novel therapeutic target for sensorineural hearing loss.

SNARE proteins rescue impaired autophagic flux in Down syndrome

Down syndrome (DS) is a chromosomal disorder caused by trisomy of chromosome 21 (Ts21). Unbalanced karyotypes can lead to dysfunction of the proteostasis network (PN) and disrupted proteostasis is mechanistically associated with multiple DS comorbidities. Autophagy is a critical component of the PN that has not previously been investigated in DS. Based on our previous observations of PN disruption in DS, we investigated possible dysfunction of the autophagic machinery in human DS fibroblasts and other DS cell models. Following induction of autophagy by serum starvation, DS fibroblasts displayed impaired autophagic flux indicated by autophagolysosome accumulation and elevated p62, NBR1, and LC3-II abundance, compared to age- and sex-matched, euploid (CTL) fibroblasts. While lysosomal physiology was unaffected in both groups after serum starvation, we observed decreased basal abundance of the Soluble N-ethylmaleimide-sensitive-factor Attachment protein Receptor (SNARE) family members syntaxin 17 (STX17) and Vesicle Associated Membrane Protein 8 (VAMP8) indicating that decreased autophagic flux in DS is due at least in part to a possible impairment of autophagosome-lysosome fusion. This conclusion was further supported by the observation that over-expression of either STX17 or VAMP8 in DS fibroblasts restored autophagic degradation and reversed p62 accumulation. Collectively, our results indicate that impaired autophagic clearance is a characteristic of DS cells that can be reversed by enhancement of SNARE protein expression and provides further evidence that PN disruption represents a candidate mechanism for multiple aspects of pathogenesis in DS and a possible future target for therapeutic intervention.

Differential Cytotoxic Potential of Acridocarpus orientalis Leaf and Stem Extracts with the Ability to Induce Multiple Cell Death Pathways

This study systematically analyzed the anticancer potential of Acridocarpus orientalis (AO), a traditional medicinal plant of the Arabian Peninsula/East Africa known for its anti-inflammatory and pain relief properties. Tests of serial organic fractions from methanolic extracts of its leaves and stems revealed that only some fractions showed anti-proliferative potential with the dichloromethane fraction from leaves (AOD (L)) showing the most cytotoxic effect against both breast (MCF-7 and MDA-MB-231) and cervical (HeLa) cancer cell lines. The n-butanol fraction from the stems (AOB (S)), on the other hand, was more effective against cervical cancer cells and did not harm the normal cells. Further characterization of the mode of cell killing revealed that AOD (L) depended more on non-apoptotic pathways for its cytotoxicity in breast cancer cells, while it could activate some apoptosis and necroptosis in HeLa cells. The AOB (S) fraction could primarily activate apoptosis and some necroptosis in HeLa cells. Both fractions perturbed autophagy, but in a dissimilar manner. Thus, different parts of A. orientalis revealed variable potential to induce cell death in cancer cells via apoptotic and non-apoptotic pathways, making A. orientalis a valuable plant for the exploration of anticancer bioactive reagents, some of which may be protective for normal cells.

Identification of Cell Death Genes in Sea Urchin Paracentrotus lividus and Their Expression Patterns during Embryonic Development

Apoptosis and autophagy are fundamental mechanisms of programed cell death activated during protostome and deuterostome embryonic development, contributing to the creation and remodeling of different anatomical structures. Programed cell death has been investigated at morphological and biochemical levels, but there is a lack of information concerning gene expression of death factors during deuterostome embryonic development. In this study, we analyze the expression patterns of 13 genes involved in autophagy, extrinsic and intrinsic apoptosis during blastula, gastrula, and pluteus stages of the sea urchin Paracentrotus lividus embryonic development. Results suggested the occurrence of all death mechanisms investigated, highlighting the simultaneous involvement of apoptosis and autophagy during embryonic development. In particular, gastrula was the developmental stage where the majority of death genes were highly expressed. During gastrulation apoptotic processes are fundamental for tissue remodeling, such as cavity formation and removal of inner ectodermal cells. This is the first report that identifies a panel of cell death genes in the P. lividus genome and analyzes their expression variations during ontogenesis.

MiR-291a/b-5p inhibits autophagy by targeting Atg5 and Becn1 during mouse preimplantation embryo development

microRNA-290 (miR-290) clusters are highly expressed in mouse preimplantation embryos, but their specific role and regulatory mechanisms in the development of mouse preimplantation embryos remain unclear. Here, we found that miR-291a-5p and miR-291b-5p, as mature microRNA molecules of miR-290 clusters, were dynamically expressed in mouse preimplantation embryos. The expression of miR-291a-5p and miR-291b-5p in mouse embryos increased during the 2–4-cell stages and was accompanied by the decreasing expression of the autophagy-related genes Atg5 and Becn1 in mRNA. Immunofluorescence studies showed that the formation of autophagosomes and autophagic lysosomes increased in the 1-cell stage, decreased in the 2-cell stage, and rapidly decreased during the 4–8-cell stage. Transmission electron microscopy (TEM) also demonstrated that there were autophagosomes in the cytoplasm of fertilized eggs with a double-layer membrane structure, whereas this structure was not observed in the unfertilized oocyte cytoplasm. Moreover, miR-291a/b-5p inhibited the protein and mRNA expression of Atg5 and Becn1 in NIH/3T3 cells. A dual-luciferase reporter assay confirmed that miR-291a/b-5p directly targeted the Atg5 and Becn1 genes. MiR-291a/b-5p repressed rapamycin-induced autophagy-related LC3-I to LC3-II conversion, ultimately inhibiting the formation of autophagosomes. Furthermore, the microinjection of mouse zygote cytoplasm with miR-291a-5p inhibitors increased the mRNA expression of Atg5 and Becn1 in mouse embryos and facilitated the first cleavage of mouse embryos and blastocyst formation. Our results suggest the important role of miR-291a/b-5p during mouse preimplantation embryo development.

MiR-291a-5p and MiR-291b-5p, was dynamically expressed and inhibited autophagy by targeting Atg5 and Becn 1 during mouse preimplantation embryo development.

The Role of Primary Cilia in the Crosstalk between the Ubiquitin⁻Proteasome System and Autophagy

Protein degradation is a pivotal process for eukaryotic development and homeostasis. The majority of proteins are degraded by the ubiquitin⁻proteasome system and by autophagy. Recent studies describe a crosstalk between these two main eukaryotic degradation systems which allows for establishing a kind of safety mechanism. If one of these degradation systems is hampered, the other compensates for this defect. The mechanism behind this crosstalk is poorly understood. Novel studies suggest that primary cilia, little cellular protrusions, are involved in the regulation of the crosstalk between the two degradation systems. In this review article, we summarise the current knowledge about the association between cilia, the ubiquitin⁻proteasome system and autophagy.

Complementary and distinct roles of autophagy, apoptosis and senescence during early inner ear development

The development of the inner ear complex cytoarchitecture and functional geometry requires the exquisite coordination of a variety of cellular processes in a temporal manner. At early stages of inner ear development several rounds of cell proliferation in the otocyst promote the growth of the structure. The apoptotic program is initiated in exceeding cells to adjust cell type numbers. Apoptotic cells are cleared by phagocytic cells that recognize the phosphatidylserine residues exposed in the cell membrane thanks to the energy supplied by autophagy. Specific molecular programs determine hair and supporting cell fate, these populations are responsible for the functions of the adult sensory organ: detection of sound, position and acceleration. The neurons that transmit auditory and balance information to the brain are also born at the otocyst by neurogenesis facilitated by autophagy. Cellular senescence participates in tissue repair, cancer and aging, situations in which cells enter a permanent cell cycle arrest and acquire a highly secretory phenotype that modulates their microenvironment. More recently, senescence has also been proposed to take place during vertebrate development in a limited number of transitory structures and organs; among the later, the endolymphatic duct in the inner ear. Here, we review these cellular processes during the early development of the inner ear, focusing on how the most recently described cellular senescence participates and cooperates with proliferation, apoptosis and autophagy to achieve otic morphogenesis and differentiation.

Autophagy inducers restore impaired autophagy, reduce apoptosis, and attenuate blunted alveolarization in hyperoxia-exposed newborn rats

AIM

Autophagy is a common process during development. Abnormal autophagy can impact cell apoptosis. Previous studies have shown that apoptosis is present during bronchopulmonary dysplasia (BPD). However, there is no consensus on the level of coexisting autophagy. This study was designed to investigate the role of autophagy and the effects of autophagy inducers in a BPD model.

METHOD

A total of 100 newborn Sprague-Dawley rats were randomly assigned to model and control groups. BPD models were established by hyperoxic induction(FiO₂ 0.80). Some of them were treated with autophagy-inducing agents.

RESULT

As compared to the control group, more autophagic bodies were found within Type II alveolar epithelial cells (AT-II cells) under transmission electron microscopy (TEM) in the model group at 3 d . These autophagic bodies were also accompanied by apoptotic bodies and expression of both bodies peaked at 7 d. As shown by TdT-mediated dUTP nick end labeling (TUNEL), there were more apoptotic cells in the model group than in the control group. Protein expression levels of LC3B-II, p62, Lamp1, and cleaved Caspase-3 increased with increased hyperoxic exposure time. No significant differences were observed in the mRNA expression levels of LC3B, p62, and Lamp1. After introducing an autophagy inducer, either rapamycin or lithium chloride, the radial alveolar count (RAC) value of BPD model group increased as compared with placebo group, the thickness of alveolar septum decreased, while apoptosis decreased.

CONCLUSION

Reduced autophagy resulting from blocked autophagy flow may be a key link in the pathogenesis of BPD. By enhancing repressed autophagy, apoptosis could be reduced and alveolar development improved.

Potential of Bacillus subtilis lipopeptides in anti-cancer I: induction of apoptosis and paraptosis and inhibition of autophagy in K562 cells

The lipopeptide iturin from Bacillus subtilis has been found to have a potential inhibitory effect on breast cancer, alveolar adenocarcinoma, renal carcinoma, and colon adenocarcinoma. In this study, the potential of B. subtilis lipopeptides (a mixture of iturin homologues, concentration of 42.75%) to inhibit chronic myelogenous leukemia was evaluated using K562 myelogenous leukemia cells. The results showed that the lipopeptides could completely inhibit the growth of K562 at 100 μM, with an IC50 value of 65.76 μM. The lipopeptides inhibited the profile of K562 via three pathways: (1) induction of paraptosis indicated by the occurrence of cytoplasmic vacuoles, and swelling of the mitochondria and endoplasmic reticulum (ER) without membrane blebbing in the presence of a caspase inhibitor; (2) inhibition of autophagy progress illustrated by the upregulated expression of LCII and P62; and (3) induction of apoptosis by causing ROS burst, and induction of the intrinsic pathway indicated by the upregulated expression of cytochrome c (Cyto-c), bax, and bad, together with downregulated expression of Bcl-2. The ROS-dependent apoptosis and caspase-independent paraptosis were verified using the ROS inhibitor and caspase inhibitor, respectively. The extrinsic apoptosis pathway was not involved in the lipopeptide’s effects on K562. Overall, the B. subtilis lipopeptides (consisting of a majority of iturin) exhibited promising potential in inhibiting chronic myelogenous leukemia in vitro via simultaneously causing paraptosis, apoptosis, and inhibition of autophagy.

The ciliary protein RPGRIP1L governs autophagy independently of its proteasome-regulating function at the ciliary base in mouse embryonic fibroblasts

Previously, macroautophagy/autophagy was demonstrated to be regulated inter alia by the primary cilium. Mutations in RPGRIP1L cause ciliary dysfunctions resulting in severe human diseases summarized as ciliopathies. Recently, we showed that RPGRIP1L deficiency leads to a decreased proteasomal activity at the ciliary base in mice. Importantly, the drug-induced restoration of proteasomal activity does not rescue ciliary length alterations in the absence of RPGRIP1L indicating that RPGRIP1L affects ciliary function also via other mechanisms. Based on this knowledge, we analyzed autophagy in Rpgrip1l-negative mouse embryos. In these embryos, autophagic activity was decreased due to an increased activation of the MTOR complex 1 (MTORC1). Application of the MTORC1 inhibitor rapamycin rescued dysregulated MTORC1, autophagic activity and cilia length but not proteasomal activity in Rpgrip1l-deficient mouse embryonic fibroblasts demonstrating that RPGRIP1L seems to regulate autophagic and proteasomal activity independently from each other.

Altered Differentiation Potential of Gaucher's Disease iPSC Neuronal Progenitors due to Wnt/β-Catenin Downregulation

Gaucher’s disease (GD) is an autosomal recessive disorder caused by mutations in the GBA1 gene, which encodes acid β-glucocerebrosidase (GCase). Severe GBA1 mutations cause neuropathology that manifests soon after birth, suggesting that GCase deficiency interferes with neuronal development. We found that neuronopathic GD induced pluripotent stem cell (iPSC)-derived neuronal progenitor cells (NPCs) exhibit developmental defects due to downregulation of canonical Wnt/β-catenin signaling and that GD iPSCs’ ability to differentiate to dopaminergic (DA) neurons was strikingly reduced due to early loss of DA progenitors. Incubation of the mutant cells with the Wnt activator CHIR99021 (CHIR) or with recombinant GCase restored Wnt/β-catenin signaling and rescued DA differentiation. We also found that GD NPCs exhibit lysosomal dysfunction, which may be involved in Wnt downregulation by mutant GCase. We conclude that neuronopathic mutations in GCase lead to neurodevelopmental abnormalities due to a critical requirement of this enzyme for canonical Wnt/β-catenin signaling at early stages of neurogenesis.

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Neuronopathic GBA1 mutations attenuate canonical Wnt signaling in iPSC-derived NPCs

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GD NPC differentiation to DA neurons impaired due to early loss of DA progenitors

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GBA1-mediated lysosomal alterations may be involved in Wnt signal downregulation

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The Wnt pathway may be a potential new therapeutic target for neuronopathic GD

Cell proliferation and migration during early development of a symbiotic scleractinian coral

In scleractinian reef-building corals, patterns of cell self-renewal, migration and death remain virtually unknown, limiting our understanding of cellular mechanisms underlying initiation of calcification, and ontogenesis of the endosymbiotic dinoflagellate relationship. In this study, we pulse-labelled the coral Stylophora pistillata for 24 h with BrdU at four life stages (planula, early metamorphosis, primary polyp and adult colony) to investigate coral and endosymbiont cell proliferation during development, while simultaneously recording TUNEL-positive (i.e. apoptotic) nuclei. In the primary polyp, the fate of BrdU-labelled cells was tracked during a 3-day chase. The pharynx and gastrodermis were identified as the most proliferative tissues in the developing polyp, and BrdU-labelled cells accumulated in the surface pseudostratified epithelium and the skeletogenic calicodermis during the chase, revealing cell migration to these epithelia. Surprisingly, the lowest cell turnover was recorded in the calicodermis at all stages, despite active, ongoing skeletal deposition. In dinoflagellate symbionts, DNA synthesis was systematically higher than coral host gastrodermis, especially in planula and early metamorphosis. The symbiont to host cell ratio remained constant, however, indicating successive post-mitotic control mechanisms by the host of its dinoflagellate density in early life stages, increasingly shifting to apoptosis in the growing primary polyp.

Targeting autophagy to modulate cell survival: a comparative analysis in cancer, normal and embryonic cells

Autophagy is linked to multiple cancer-related signaling pathways, and represents a defense mechanism for cancer cells under therapeutic stress. The crosstalk between apoptosis and autophagy is essential for both tumorigenesis and embryonic development. We studied the influence of autophagy on cell survival in pro-apoptotic conditions induced by anticancer drugs in three model systems: human cancer cells (NCI-H460, COR-L23 and U87), human normal cells (HaCaT and MRC-5) and zebrafish embryos (Danio rerio). Autophagy induction with AZD2014 and tamoxifen antagonized the pro-apoptotic effect of chemotherapeutics doxorubicin and cisplatin in cell lines, while autophagy inhibition by wortmannin and chloroquine synergized the action of both anticancer agents. This effect was further verified by assessing cleaved caspase-3 and PARP-1 levels. Autophagy inhibitors significantly increased both apoptotic markers when applied in combination with doxorubicin while autophagy inducers had the opposite effect. In a similar manner, autophagy induction in zebrafish embryos prevented cisplatin-induced apoptosis in the tail region while autophagy inhibition increased cell death in the tail and retina of cisplatin-treated animals. Autophagy modulation with direct inhibitors of the PI3kinase/Akt/mTOR pathway (AZD2014 and wortmannin) triggered the cellular response to anticancer drugs more effectively in NCI-H460 and zebrafish embryonic models compared to HaCaT suggesting that these modulators are selective towards rapidly proliferating cells. Therefore, evaluating the autophagic properties of chemotherapeutics could help determine more accurately the fate of different cell types under treatment. Our study underlines the importance of testing autophagic activity of potential anticancer agents in a comparative approach to develop more rational anticancer therapeutic strategies.

Entosis Acts as a Novel Way within Sertoli Cells to Eliminate Spermatozoa in Seminiferous Tubule

The present study was designed to investigate the hypothesis that in vivo entosis is a novel pathway for eliminating spermatozoa in the seminiferous tubules (ST) during hibernation of the Chinese soft-shelled turtle. Western blot analysis revealed that the expression of LAMP1 in the testis was significantly higher during hibernation than that during non-hibernation. Immunohistochemistry reaction showed that LAMP1-positive substance was distributed within the Sertoli cells of the testis. Further examination by transmission electron microscopy (TEM), many degraded spermatozoa being enwrapped within large entotic vacuoles in Sertoli cells. The nucleus and the flagellum of the spermatozoa were shown to be decomposed and digested inside entotic vacuoles within Sertoli cells. More than two spermatozoa heads were always observed in each internalized vacuoles. Deserving note is that, a number of different autophagosomes, including initial autophagic vesicles and degradative autophagic vesicles were found inside the entotic vacuoles of the Sertoli cells during hibernation. At the end of hibernation, entotic vacuoles and their autophagosomes disappeared, and numerous large lipid droplets (LDs) appeared within the Sertoli cells. Adherens junctions were apparent between Sertoli cells and developing germ cells, which is the ultrastructural basis of entosis. Taken together, the results presented here show that in the turtle: (1) entosis with internal autophagosomes can take place within normal body cells during hibernation; (2) spermatozoa, as a highly differentiated cell can be internalized and degraded within Sertoli cell by entosis in vivo, which is in favor of the next reproductive cycle in the turtle.

Autophagy in the Vertebrate Inner Ear

Autophagy is a conserved catabolic process that results in the lysosomal degradation of cell components. During development, autophagy is associated with tissue and organ remodeling, and under physiological conditions it is tightly regulated as it plays a housekeeping role in removing misfolded proteins and damaged organelles. The vertebrate inner ear is a complex sensory organ responsible for the perception of sound and for balance. Cell survival, death and proliferation, as well as cell fate specification and differentiation, are processes that are strictly coordinated during the development of the inner ear in order to generate the more than a dozen specialized cell types that constitute this structure. Here, we review the existing evidence that implicates autophagy in the generation of the vertebrate inner ear. At early stages of chicken otic development, inhibiting autophagy impairs neurogenesis and causes aberrant otocyst morphogenesis. Autophagy provides energy for the clearing of dying cells and it favors neuronal differentiation. Moreover, autophagy is required for proper vestibular development in the mouse inner ear. The autophagy-related genes Becn1, Atg4g, Atg5, and Atg9, are expressed in the inner ear from late developmental stages to adulthood, and Atg4b mutants show impaired vestibular behavior associated to defects in otoconial biogenesis that are also common to Atg5 mutants. Autophagic flux appears to be age-regulated, augmenting from perinatal stages to young adulthood in mice. This up-regulation is concomitant with the functional maturation of the hearing receptor. Hence, autophagy can be considered an intracellular pathway fundamental for in vertebrate inner ear development and maturation.

Ca2+ signaling, apoptosis and autophagy in the developing cochlea: Milestones to hearing acquisition

In mammals, the sense of hearing arises through a complex sequence of morphogenetic events that drive the sculpting of the auditory sensory epithelium into its terminally functional three-dimensional shape. While the majority of the underlying mechanisms remain unknown, it has become increasingly clear that Ca²⁺ signaling is at center stage and plays numerous fundamental roles both in the sensory hair cells and in the matrix of non-sensory, epithelial and supporting cells, which embed them and are tightly interconnected by a dense network of gap junctions formed by connexin 26 (Cx26) and connexin 30 (Cx30) protein subunits. In this review, we discuss the intricate interplay between Ca²⁺ signaling, connexin expression and function, apoptosis and autophagy in the crucial steps that lead to hearing acquisition.

Atg7 Regulates Brain Angiogenesis via NF-κB-Dependent IL-6 Production

The formation of brain vasculature is an essential step during central nervous system development. The molecular mechanism underlying brain angiogenesis remains incompletely understood. The role of Atg7, an autophagy-related protein, in brain angiogenesis was investigated in this study. We found that the microvessel density in mice brains with endothelial-specific knockout of Atg7 (Atg7 EKO) was significantly decreased compared to wild-type control. Consistently, in vitro angiogenesis assays showed that Atg7 knockdown impaired angiogenesis in brain microvascular endothelial cells. Further results indicated that knockdown of Atg7 reduced interleukin-6 (IL-6) expression in brain microvascular endothelial cells, which is mediated by NF-κB-dependent transcriptional control. Interestingly, exogenous IL-6 restored the impaired angiogenesis and reduced cell motility caused by Atg7 knockdown. These results demonstrated that Atg7 has proangiogenic activity in brain angiogenesis which is mediated by IL-6 production in a NF-κB-dependent manner.

Cell death and cell proliferation in human spina bifida

BACKGROUND

Spina bifida is a multifactorial congenital malformation of the central nervous system. The aim of this study was to ascertain the relevance of cell death/proliferation balance in human spina bifida and to assess autophagy distribution and levels during embryo-fetal development in neural tissue.

METHODS

Five human cases with myelomeningocoele were compared with 10 healthy human controls and LC3 protein expression was also analyzed in mouse embryos. Cell death was evaluated using TUNEL (terminal deoxynucleotidyl transferase-mediated deoxyuridinetriphosphate nick end-labeling) assay; cell proliferation was studied by counting Ki67-positive cells, and autophagy was assessed by observing the presence of LC3 punctuate dots.

RESULTS

Comparing human cases and controls (13 to 21 weeks of gestation), we observed a significant increase in TUNEL-positive cells in human spina bifida associated with a significantly decreased proliferation rate, indicating an alteration of the physiological cell rate homeostasis. LC3 distribution was found to be spatiotemporally regulated in both human and murine embryo-fetuses: in early pregnancy a diffuse and ubiquitous LC3 signal was detected. After neural tube closure, an intense LC3-positive signal, normally associated to extra energy requirement, was confined to the Lissauer's tract, the dorsolateral spinal zone containing centrally projecting axons from dorsal root ganglia, at any medullar levels. LC3 signal disappeared from 12 weeks of gestation.

CONCLUSION

In conclusion, this study confirms the fundamental role of cell death/proliferation balance during central nervous system development and reports the changing expression of LC3 protein in mouse and human neural tube. Birth Defects Research (Part A) 106:104-113, 2016. © 2015 Wiley Periodicals, Inc.

Recent advances in autophagy-based neuroprotection

Macroautophagy is a highly regulated intracellular process that, under certain circumstances, delivers cytoplasmic components to the lysosomes for degradation. It consists of several sequential steps including initiation and nucleation, double membrane formation and elongation, formation and maturation of autophagosomes and finally autophagosomes/lysosomes fusion and degradation of intra-autophagosomal contents by lysosomal enzymes. After decades of considering autophagy as a cell death pathway, it has recently been shown to have a survival function through clearing of protein aggregates and damaged cytoplasmic organelles in response to a variety of stress conditions. Most recently, there is increasing evidence from literature revealing that autophagy induction may combat neurodegeneration. In the light of this, our current review tried to address the recent advances in the role of induced autophagy in neuroprotection with a particular focus on its contribution in the most common neurodegenerative disorders like Alzheimer's disease, Parkinson's disease and Huntington's disease.

Amino acid starvation induced by protease inhibition produces differential alterations in redox status and the thiol proteome in organogenesis-stage rat embryos and visceral yolk sacs

The process of embryonic nutrition in rodent conceptuses during organogenesis has been shown to involve a dominant histiotrophic mechanism where essential developmental substrates and micronutrients are supplied as whole maternal proteins or cargoes associated with proteins. The histiotrophic nutrition pathways (HNP) responsible for uptake and initial processing of proteins across maternal-conceptal interfaces involve uptake via receptor mediated endocytosis and protein degradation via lysosomal proteolysis. Chemical inhibition of either process can lead to growth deficits and malformation in the embryo (EMB), but selective inhibition of either HNP component will elicit a different subset of developmental perturbations. In vitro, whole embryo culture exposure of GD10 or GD11 rat conceptuses to the natural protease inhibitor, leupeptin, leads to significant reductions in all measured embryonic growth parameters as well as a myriad of other effects. Leupeptin doses of 10 μM or 20 μM over a 26-h period (GD10-GD11) and 50 μM over a 3 h pulse period produced significant decreases in the clearance of FITC-albumin from culture media. The near complete loss of acid soluble fluorescence and increased total visceral yolk sac (VYS) protein content confirmed the selective inhibition of proteolysis. Inhibition of lysosomal proteolysis thus deprives the developing EMB of essential nutrient amino acids producing conditions akin to amino acid starvation, but may also cause direct effects on pathways critical for normal growth and differentiation. Following leupeptin exposure for 26 or 6 h, total glutathione (GSH) concentrations dropped significantly in the VYS, but only slightly in yolk sac (YSF) and amniotic (AF) fluids. Cys concentrations increased in VYS and EMB, but dropped in YSF and AF fluids. Redox potentials (Eh) for the glutathione disulfide (GSSG)/glutathione (GSH) redox couple trended significantly toward the positive, confirming the net oxidation of conceptual tissues following leupeptin treatment. Analysis of the thiol proteome showed few alterations to specific pathways mapped to the Kyoto Encyclopedia of Genes and Genomes Pathway database, but did reveal significant increases in concentrations of proteins associated with glycolysis/gluconeogenesis in the VYS and decreased concentrations proteins associated with ribosome biogenesis and function in the EMB. A subset of proteins elevated by >2-23-fold in the VYS were identified as serum (blood) proteins and represent the maternal-side proteins captured by the VYS and which are not degraded in the lysosomes as a result of leupeptin's inhibitory action. The observed constellation of proteins decreased in the EMB by leupeptin represent proteins from several adaptive pathways that are commonly altered in responses to amino acid starvation. These studies show clear differential responses to protease inhibition in VYS and EMB during organogenesis and suggest the possibility for additional roles of redox regulation, cellular adaptations and metabolic insufficiency caused by protease inhibition.

Age-regulated function of autophagy in the mouse inner ear

Autophagy is a highly conserved catabolic process essential for embryonic development and adult homeostasis. The autophagic machinery supplies energy by recycling intracellular components and facilitates the removal of apoptotic cells. In the inner ear, autophagy has been reported to play roles during early development in the chicken embryo and in the response to otic injury in the adult mouse. However, there are no studies on the expression of the autophagy machinery in the postnatal and adult inner ear. Insulin-like growth factor 1 (IGF-1) is one of the factors that regulate both otic development and cochlear postnatal maturation and function. Here, we hypothesised that autophagy could be one of the processes involved in the cochlear development and functional maturation. We report that autophagy-related genes (ATG) Becn1, Atg4g and Atg5 are expressed in the mouse cochlea, vestibular system and brainstem cochlear nuclei from late developmental stages to adulthood. Atg9 was studied in the mouse cochlea and showed a similar pattern. The presence of autophagic flux was confirmed by decreased sequestosome 1 (SQSTM1/p62) and increased relative levels of microtubule-associated protein light chain 3-II (LC3-II). Inner ear autophagy flux is developmentally regulated and is lower at perinatal stages than in the adult mouse, where an expression plateau is reached at the age of two-months, coinciding with the age at which full functional activity is reached. Expression is maintained in adult mice and declines after the age of twelve months. LC3B labelling showed that autophagy was primarily associated with spiral ganglion neurons. Over time, Igf1 wild type mice showed lower expression of genes coding for IGF-1 high affinity receptor and the family factor IGF-2 than null mice. Parallel analysis of autophagy machinery gene expression showed no significant differences between the genotypes over the lifespan of the null mice. Taken together, these results show that the autophagy machinery expression in the inner ear is regulated with age but is not compromised by the chronic absence of IGF-1. Our data also strongly support that the up-regulation of autophagy machinery genes is concomitant with the functional maturation of the inner ear.

Ethanol Attenuates Histiotrophic Nutrition Pathways and Alters the Intracellular Redox Environment and Thiol Proteome during Rat Organogenesis

Ethanol (EtOH) is a reactive oxygen-generating teratogen involved in the etiology of structural and functional developmental defects. Embryonic nutrition, redox environment, and changes in the thiol proteome following EtOH exposures (1.56.0 mg/ml) were studied in rat whole embryo culture. Glutathione (GSH) and cysteine (Cys) concentrations with their respective intracellular redox potentials (Eh) were determined using high-performance liquid chromatography. EtOH reduced GSH and Cys concentrations in embryo (EMB) and visceral yolk sac (VYS) tissues, and also in yolk sac and amniotic fluids. These changes produced greater oxidation as indicated by increasingly positive Eh values. EtOH reduced histiotrophic nutrition pathway activities as measured by the clearance of fluorescin isothiocyanate (FITC)-albumin from culture media. A significant decrease in total FITC clearance was observed at all concentrations, reaching approximately 50% at the highest dose. EtOH-induced changes to the thiol proteome were measured in EMBs and VYSs using isotope-coded affinity tags. Decreased concentrations for specific proteins from cytoskeletal dynamics and endocytosis pathways (α-actinin, α-tubulin, cubilin, and actin-related protein 2); nuclear translocation (Ran and RanBP1); and maintenance of receptor-mediated endocytosis (cubilin) were observed. Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis also identified a decrease in ribosomal proteins in both EMB and VYS. Results show that EtOH interferes with nutrient uptake to reduce availability of amino acids and micronutrients required by the conceptus. Intracellular antioxidants such as GSH and Cys are depleted following EtOH and Eh values increase. Thiol proteome analysis in the EMB and VYS show selectively altered actin/cytoskeleton, endocytosis, ribosome biogenesis and function, nuclear transport, and stress-related responses.

Early otic development depends on autophagy for apoptotic cell clearance and neural differentiation

Autophagy is a highly regulated program of self-degradation of the cytosolic constituents that has key roles during early development and in adult cell growth and homeostasis. To investigate the role of autophagy in otic neurogenesis, we studied the expression of autophagy genes in early stages of chicken (Gallus gallus) inner ear development and the consequences of inhibiting the autophagic pathway in organotypic cultures of explanted chicken otic vesicles (OVs). Here we show the expression of autophagy-related genes (Atg) Beclin-1 (Atg6), Atg5 and LC3B (Atg8) in the otocyst and the presence of autophagic vesicles by using transmission electron microscopy in the otic neurogenic zone. The inhibition of the transcription of LC3B by using antisense morpholinos and of class III phosphatidylinositol 3-kinase with 3-methyladenine causes an aberrant morphology of the OV with accumulation of apoptotic cells. Moreover, inhibition of autophagy provokes the misregulation of the cell cycle in the otic epithelium, impaired neurogenesis and poor axonal outgrowth. Finally, our results indicate that autophagy provides the energy required for the clearing of neuroepithelial dying cells and suggest that it is required for the migration of otic neuronal precursors. Taken together, our results show for the first time that autophagy is an active and essential process during early inner ear development.