Identification of a candidate therapeutic autophagy-inducing peptide

The stress-responsive kinases MAPKAPK2/MAPKAPK3 activate starvation-induced autophagy through Beclin 1 phosphorylation

Autophagy is a fundamental adaptive response to amino acid starvation orchestrated by conserved gene products, the autophagy (ATG) proteins. However, the cellular cues that activate the function of ATG proteins during amino acid starvation are incompletely understood. Here we show that two related stress-responsive kinases, members of the p38 mitogen-activated protein kinase (MAPK) signaling pathway MAPKAPK2 (MK2) and MAPKAPK3 (MK3), positively regulate starvation-induced autophagy by phosphorylating an essential ATG protein, Beclin 1, at serine 90, and that this phosphorylation site is essential for the tumor suppressor function of Beclin 1. Moreover, MK2/MK3-dependent Beclin 1 phosphorylation (and starvation-induced autophagy) is blocked in vitro and in vivo by BCL2, a negative regulator of Beclin 1. Together, these findings reveal MK2/MK3 as crucial stress-responsive kinases that promote autophagy through Beclin 1 S90 phosphorylation, and identify the blockade of MK2/3-dependent Beclin 1 S90 phosphorylation as a mechanism by which BCL2 inhibits the autophagy function of Beclin 1.

DOI:http://dx.doi.org/10.7554/eLife.05289.001

Cells keep themselves healthy by breaking down unneeded or damaged internal structures via a process called autophagy. This process also helps a cell to survive if it is starved of nutrients. For example, if a cell does not receive enough amino acids, it cannot make new proteins. Autophagy can break down existing non-essential proteins so that their amino acids can be re-used to build other proteins that the cell needs to survive.

Autophagy is performed by a set of proteins that is found in many different species, ranging from yeast to humans and plants. How these proteins are activated when a cell is starved of amino acids is not fully understood. However, evidence suggests that activating one of these proteins, called Beclin 1, by adding phosphate groups to it controls the extent to which autophagy occurs. It is also known from previous work that less autophagy occurs when Beclin 1 binds to another protein called BCL2.

Wei, An et al. identified two enzymes that attach a phosphate group to a specific site on Beclin 1 to activate it, and revealed that autophagy is defective in cells that lack these enzymes. Furthermore, Wei, An et al. found the BCL2 protein prevents autophagy by binding to Beclin 1 in such a way that stops these two enzymes from activating Beclin 1.

Beclin 1 is also known to prevent the growth of malignant tumors. Wei, An et al. found that to do so, Beclin 1 must have a phosphate group added to the same site that activates the protein during autophagy. This suggests that drugs that enhance the addition of this phosphate group to Beclin 1 could help activate autophagy and have anti-cancer effects.

DOI:http://dx.doi.org/10.7554/eLife.05289.002

Metabolic control of autophagy

Macroautophagy (herein referred to as autophagy) is an evolutionarily conserved mechanism of adaptation to adverse microenvironmental conditions, including limited nutrient supplies. Several sensors interacting with the autophagic machinery have evolved to detect fluctuations in key metabolic parameters. The signal transduction cascades operating downstream of these sensors are highly interconnected to control a spatially and chronologically coordinated autophagic response that maintains the health and function of individual cells while preserving organismal homeostasis. Here, we discuss the physiological regulation of autophagy by metabolic circuitries, as well as alterations of such control in disease.

Autophagy in cancer

Autophagy is a catabolic degradation process in which cellular proteins and organelles are engulfed by double-membrane autophagosomes and degraded in lysosomes. Autophagy has emerged as a critical pathway in tumor development and cancer therapy, although its precise function remains a conundrum. The current consensus is that autophagy has a dual role in cancer. On the one hand, autophagy functions as a tumor suppressor mechanism by preventing the accumulation of damaged organelles and aggregated proteins. On the other hand, autophagy is a key cell survival mechanism for established tumors; therefore autophagy inhibition suppresses tumor progression. Here, we summarize recent progress on the role of autophagy in tumorigenesis and cancer therapy.

Amino acid substitutions in the non-structural proteins 4A or 4B modulate the induction of autophagy in West Nile virus infected cells independently of the activation of the unfolded protein response

West Nile virus (WNV) is a neurotropic mosquito-borne flavivirus responsible for outbreaks of meningitis and encephalitis. Whereas the activation of autophagy in cells infected with other flaviviruses is well known, the interaction of WNV with the autophagic pathway still remains unclear and there are reports describing opposite findings obtained even analyzing the same viral strain. To clarify this controversy, we first analyzed the induction of autophagic features in cells infected with a panel of WNV strains. WNV was determined to induce autophagy in a strain dependent manner. We observed that all WNV strains or isolates analyzed, except for the WNV NY99 used, upregulated the autophagic pathway in infected cells. Interestingly, a variant derived from this WNV NY99 isolated from a persistently infected mouse increased LC3 modification and aggregation. Genome sequencing of this variant revealed only two non-synonymous nucleotide substitutions when compared to parental NY99 strain. These nucleotide substitutions introduced one amino acid replacement in NS4A and other in NS4B. Using genetically engineered viruses we showed that introduction of only one of these replacements was sufficient to upregulate the autophagic pathway. Thus, in this work we have shown that naturally occurring point mutations in the viral non-structural proteins NS4A and NS4B confer WNV with the ability to induce the hallmarks of autophagy such as LC3 modification and aggregation. Even more, the differences on the induction of an autophagic response observed among WNV variants in infected cells did not correlate with alterations on the activation of the unfolded protein response (UPR), suggesting an uncoupling of UPR and autophagy during flavivirus infection. The findings here reported could help to improve the knowledge of the cellular processes involved on flavivirus–host cell interactions and contribute to the design of effective strategies to combat these pathogens.

Differential reliance on autophagy for protection from HSV encephalitis between newborns and adults

Newborns are more susceptible to severe disease from infection than adults, with maturation of immune responses implicated as a major factor. The type I interferon response delays mortality and limits viral replication in adult mice in a model of herpes simplex virus (HSV) encephalitis. We found that intact type I interferon signaling did not control HSV disease in the neonatal brain. However, the multifunctional HSV protein γ34.5 involved in countering type I interferon responses was important for virulence in the brain in both age groups. To investigate this observation further, we studied a specific function of γ34.5 which contributes to HSV pathogenesis in the adult brain, inhibition of the cellular process of autophagy. Surprisingly, we found that the beclin binding domain of γ34.5 responsible for inhibiting autophagy was dispensable for HSV disease in the neonatal brain, as infection of newborns with the deletion mutant decreased time to mortality compared to the rescue virus. Additionally, a functional beclin binding domain in HSV γ34.5 did not effectively inhibit autophagy in the neonate, unlike in the adult. Type I IFN responses promote autophagy in adult, a finding we confirmed in the adult brain after HSV infection; however, in the newborn brain we observed that autophagy was activated through a type I IFN-independent mechanism. Furthermore, autophagy in the wild-type neonatal mouse was associated with increased apoptosis in infected regions of the brain. Observations in the mouse model were consistent with those in a human case of neonatal HSV encephalitis. Our findings reveal age-dependent differences in autophagy for protection from HSV encephalitis, indicating developmental differences in induction and regulation of this innate defense mechanism after HSV infection in the neonatal brain.

Disease after infection with a pathogen results from an intersection between the infectious agent and the host. Newborns are particularly susceptible to infectious illness compared to adults, and HSV infection commonly results in devastating encephalitis. We studied the interaction of HSV with the type I interferon pathway and found that a specific activity of the viral protein γ34.5, which counters host autophagy to promote encephalitis in adults, was not required to cause disease in newborns. Furthermore, autophagy was not inhibited by HSV in the neonate and was not activated by type I interferon signaling, unlike in the adult. Activated autophagy was associated with increased apoptosis, which may contribute to the increased pathology in newborns. Our findings reveal development-specific differences in the pathogenesis of HSV encephalitis, including a distinct role for autophagy in the neonatal brain.

Autophagy and neurodegeneration

Most neurodegenerative diseases that afflict humans are associated with the intracytoplasmic deposition of aggregate-prone proteins in neurons. Autophagy is a powerful process for removing such proteins. In this Review, we consider how certain neurodegenerative diseases may be associated with impaired autophagy and how this may affect pathology. We also discuss how autophagy induction may be a plausible therapeutic strategy for some conditions and review studies in various models that support this hypothesis. Finally, we briefly describe some of the signaling pathways that may be amenable to therapeutic targeting for these goals.

Pharmacologic agents targeting autophagy

Autophagy is an important intracellular catabolic mechanism critically involved in regulating tissue homeostasis. The implication of autophagy in human diseases and the need to understand its regulatory mechanisms in mammalian cells have stimulated research efforts that led to the development of high-throughput screening protocols and small-molecule modulators that can activate or inhibit autophagy. Herein we review the current landscape in the development of screening technology as well as the molecules and pharmacologic agents targeting the regulatory mechanisms of autophagy. We also evaluate the potential therapeutic application of these compounds in different human pathologies.

Autophagy in lung disease pathogenesis and therapeutics

Autophagy, a cellular pathway for the degradation of damaged organelles and proteins, has gained increasing importance in human pulmonary diseases, both as a modulator of pathogenesis and as a potential therapeutic target. In this pathway, cytosolic cargos are sequestered into autophagosomes, which are delivered to the lysosomes where they are enzymatically degraded and then recycled as metabolic precursors. Autophagy exerts an important effector function in the regulation of inflammation, and immune system functions. Selective pathways for autophagic degradation of cargoes may have variable significance in disease pathogenesis. Among these, the autophagic clearance of bacteria (xenophagy) may represent a crucial host defense mechanism in the pathogenesis of sepsis and inflammatory diseases. Our recent studies indicate that the autophagic clearance of mitochondria, a potentially protective program, may aggravate the pathogenesis of chronic obstructive pulmonary disease by activating cell death programs. We report similar findings with respect to the autophagic clearance of cilia components, which can contribute to airways dysfunction in chronic lung disease. In certain diseases such as pulmonary hypertension, autophagy may confer protection by modulating proliferation and cell death. In other disorders, such as idiopathic pulmonary fibrosis and cystic fibrosis, impaired autophagy may contribute to pathogenesis. In lung cancer, autophagy has multiple consequences by limiting carcinogenesis, modulating therapeutic effectiveness, and promoting tumor cell survival. In this review we highlight the multiple functions of autophagy and its selective autophagy subtypes that may be of significance to the pathogenesis of human disease, with an emphasis on lung disease and therapeutics.

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Autophagy may impact the pathogenesis of pulmonary diseases.

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Mitophagy may exert deleterious effects in the pathogenesis of COPD.

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Autophagy can exert pleiotropic effects in lung cancer.

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Targeting autophagy may represent a promising therapeutic strategy in human diseases.

Development of autophagy inducers in clinical medicine

Defects in autophagy have been linked to a wide range of medical illnesses, including cancer as well as infectious, neurodegenerative, inflammatory, and metabolic diseases. These observations have led to the hypothesis that autophagy inducers may prevent or treat certain clinical conditions. Lifestyle and nutritional factors, such as exercise and caloric restriction, may exert their known health benefits through the autophagy pathway. Several currently available FDA-approved drugs have been shown to enhance autophagy, and this autophagy-enhancing action may be repurposed for use in novel clinical indications. The development of new drugs that are designed to be more selective inducers of autophagy function in target organs is expected to maximize clinical benefits while minimizing toxicity. This Review summarizes the rationale and current approaches for developing autophagy inducers in medicine, the factors to be considered in defining disease targets for such therapy, and the potential benefits of such treatment for human health.

A novel leucine zipper motif-based hybrid peptide delivers a functional peptide cargo inside cells

We delivered a hybrid of an autophagy-inducing peptide and a cell-penetrating peptide via heterodimeric leucine zippers into the cell. By this method, the peptide successfully induced autophagy without significant cell death.

Identification of secreted proteins that reflect autophagy dynamics within tumor cells

Macroautophagy, a catabolic process of cellular self-digestion, is an important tumor cell survival mechanism and a potential target in antineoplastic therapies. Recent discoveries have implicated autophagy in the cellular secretory process, but potential roles of autophagy-mediated secretion in modifying the tumor microenvironment are poorly understood. Furthermore, efforts to inhibit autophagy in clinical trials have been hampered by suboptimal methods to quantitatively measure tumor autophagy levels. Here, we leveraged the autophagy-based involvement in cellular secretion to identify shed proteins associated with autophagy levels in melanoma. The secretome of low-autophagy WM793 melanoma cells was compared to its highly autophagic metastatic derivative, 1205Lu in physiological 3-dimensional cell culture using quantitative proteomics. These comparisons identified candidate autophagy biomarkers IL1B (interleukin 1, β), CXCL8 (chemokine (C-X-C motif) ligand 8), LIF (leukemia inhibitory factor), FAM3C (family with sequence similarity 3, member C), and DKK3 (dickkopf WNT signaling pathway inhibitor 3) with known roles in inflammation and tumorigenesis, and these proteins were subsequently shown to be elevated in supernatants of an independent panel of high-autophagy melanoma cell lines. Secretion levels of these proteins increased when low-autophagy melanoma cells were treated with the autophagy-inducing tat-BECN1 (Beclin 1) peptide and decreased when ATG7 (autophagy-related 7) was silenced in high-autophagy cells, thereby supporting a mechanistic link between these secreted proteins and autophagy. In addition, serum from metastatic melanoma patients with high tumor autophagy levels exhibited higher levels of these proteins than serum from patients with low-autophagy tumors. These results suggest that autophagy-related secretion affects the tumor microenvironment and measurement of autophagy-associated secreted proteins in plasma and possibly in tumors can serve as surrogates for intracellular autophagy dynamics in tumor cells.

Reinstating aberrant mTORC1 activity in Huntington's disease mice improves disease phenotypes

Huntington's disease (HD) is caused by a polyglutamine tract expansion in huntingtin (HTT). Despite HTTs ubiquitous expression, there is early and robust vulnerability in striatum, the cause of which is poorly understood. Here, we provide evidence that impaired striatal mTORC1 activity underlies varied metabolic and degenerative phenotypes in HD brain and show that introducing the constitutively active form of the mTORC1 regulator, Rheb, into HD mouse brain, alleviates mitochondrial dysfunction, aberrant cholesterol homeostasis, striatal atrophy, impaired dopamine signaling, and increases autophagy. We also find that the expression of Rhes, a striatum-enriched mTOR activator, is reduced in HD patient and mouse brain and that exogenous addition of Rhes alleviates motor deficits and improves brain pathology in HD mice. Our combined work indicates that impaired Rhes/mTORC1 activity in HD brain may underlie the notable striatal susceptibility and thus presents a promising therapeutic target for HD therapy.

Autophagy induction by histone deacetylase inhibitors inhibits HIV type 1

Histone deacetylase inhibitors (HDACi) are being evaluated in a "shock-and-kill" therapeutic approach to reverse human immunodeficiency virus type-1 (HIV) latency from CD4(+) T cells. Using this approach, HDACi have induced HIV RNA synthesis in latently infected cells from some patients. The hope is that the increase in viral production will lead to killing of the infected cell either by the virus itself or by the patient's immune system, a "sterilizing cure." Although administered within the context of combination antiretroviral therapy, the infection of bystander cells remains a concern. In this study, we investigated the effect of HDACi (belinostat, givinostat, panobinostat, romidepsin, and vorinostat) on the productive infection of macrophages. We demonstrate that the HDACi tested do not alter the initial susceptibility of macrophages to HIV infection. However, we demonstrate that HDACi decrease HIV release from macrophages in a dose-dependent manner (belinostat < givinostat < vorinostat < panobinostat < romidepsin) via degradation of intracellular HIV through the canonical autophagy pathway. This mechanism involves unc-51-like autophagy-activating kinase 1 (ULK1) and the inhibition of the mammalian target of rapamycin and requires the formation of autophagosomes and their maturation into autolysosomes in the absence of increased cell death. These data provide further evidence in support of a role for autophagy in the control of HIV infection and suggest that careful consideration of off-target effects will be essential if HDACi are to be a component of a multipronged approach to eliminate latently infected cells.

Autophagic flux without a block differentiates varicella-zoster virus infection from herpes simplex virus infection

Autophagy is a process by which misfolded and damaged proteins are sequestered into autophagosomes, before degradation in and recycling from lysosomes. We have extensively studied the role of autophagy in varicella-zoster virus (VZV) infection, and have observed that vesicular cells are filled with >100 autophagosomes that are easily detectable after immunolabeling for the LC3 protein. To confirm our hypothesis that increased autophagosome formation was not secondary to a block, we examined all conditions of VZV infection as well as carrying out two assessments of autophagic flux. We first investigated autophagy in human skin xenografts in the severe combined immunodeficiency (SCID) mouse model of VZV pathogenesis, and observed that autophagosomes were abundant in infected human skin tissues. We next investigated autophagy following infection with sonically prepared cell-free virus in cultured cells. Under these conditions, autophagy was detected in a majority of infected cells, but was much less than that seen after an infected-cell inoculum. In other words, inoculation with lower-titered cell-free virus did not reflect the level of stress to the VZV-infected cell that was seen after inoculation of human skin in the SCID mouse model or monolayers with higher-titered infected cells. Finally, we investigated VZV-induced autophagic flux by two different methods (radiolabeling proteins and a dual-colored LC3 plasmid); both showed no evidence of a block in autophagy. Overall, therefore, autophagy within a VZV-infected cell was remarkably different from autophagy within an HSV-infected cell, whose genome contains two modifiers of autophagy, ICP34.5 and US11, not present in VZV.

Role of NADPH oxidase in the regulation of autophagy in cardiomyocytes

In the past several years, it has been demonstrated that the reactive oxygen species (ROS) may act as intracellular signalling molecules to activate or inhibit specific signalling pathways and regulate physiological cellular functions. It is now well-established that ROS regulate autophagy, an intracellular degradation process. However, the signalling mechanisms through which ROS modulate autophagy in a regulated manner have only been minimally clarified. NADPH oxidase (Nox) enzymes are membrane-bound enzymatic complexes responsible for the dedicated generation of ROS. Different isoforms of Nox exist with different functions. Recent studies demonstrated that Nox-derived ROS can promote autophagy, with Nox2 and Nox4 representing the isoforms of Nox implicated thus far. Nox2- and Nox4-dependent autophagy plays an important role in the elimination of pathogens by phagocytes and in the regulation of vascular- and cancer-cell survival. Interestingly, we recently found that Nox is also important for autophagy regulation in cardiomyocytes. We found that Nox4, but not Nox2, promotes the activation of autophagy and survival in cardiomyocytes in response to nutrient deprivation and ischaemia through activation of the PERK (protein kinase RNA-like endoplasmic reticulum kinase) signalling pathway. In the present paper, we discuss the importance of Nox family proteins and ROS in the regulation of autophagy, with a particular focus on the role of Nox4 in the regulation of autophagy in the heart.

Nutrient-sensing nuclear receptors coordinate autophagy

Autophagy is an evolutionarily conserved catabolic process that recycles nutrients upon starvation and maintains cellular energy homeostasis. Its acute regulation by nutrient-sensing signalling pathways is well described, but its longer-term transcriptional regulation is not. The nuclear receptors peroxisome proliferator-activated receptor-α (PPARα) and farnesoid X receptor (FXR) are activated in the fasted and fed liver, respectively. Here we show that both PPARα and FXR regulate hepatic autophagy in mice. Pharmacological activation of PPARα reverses the normal suppression of autophagy in the fed state, inducing autophagic lipid degradation, or lipophagy. This response is lost in PPARα knockout (Ppara(-/-), also known as Nr1c1(-/-)) mice, which are partially defective in the induction of autophagy by fasting. Pharmacological activation of the bile acid receptor FXR strongly suppresses the induction of autophagy in the fasting state, and this response is absent in FXR knockout (Fxr(-/-), also known as Nr1h4(-/-)) mice, which show a partial defect in suppression of hepatic autophagy in the fed state. PPARα and FXR compete for binding to shared sites in autophagic gene promoters, with opposite transcriptional outputs. These results reveal complementary, interlocking mechanisms for regulation of autophagy by nutrient status.

The role of human dendritic cells in HIV-1 infection

Dendritic cells (DCs) and their subsets have multifaceted roles in the early stages of HIV-1 transmission and infection. DC studies have led to remarkable discoveries, including identification of restriction factors, cellular structures promoting viral transmission including the infectious synapse or the interplay of the C-type lectins, Langerin on Langerhans cells (LCs), and dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin on other DC subsets, limiting or facilitating HIV transmission to CD4(+) T cells, respectively. LCs/DCs are also exposed to encountering HIV-1 and other sexually transmitted infections (herpes simplex virus-2, bacteria, fungi), which reprogram HIV-1 interaction with these cells. This review will summarize advances in the role of DCs during HIV-1 infection and discuss their potential involvement in the development of preventive strategies against HIV-1 and other sexually transmitted infections.

Recent progress in research on molecular mechanisms of autophagy in the heart

Dysregulation of autophagy, an evolutionarily conserved process for degradation of long-lived proteins and organelles, has been implicated in the pathogenesis of human disease. Recent research has uncovered pathways that control autophagy in the heart and molecular mechanisms by which alterations in this process affect cardiac structure and function. Although initially thought to be a nonselective degradation process, autophagy, as it has become increasingly clear, can exhibit specificity in the degradation of molecules and organelles, such as mitochondria. Furthermore, it has been shown that autophagy is involved in a wide variety of previously unrecognized cellular functions, such as cell death and metabolism. A growing body of evidence suggests that deviation from appropriate levels of autophagy causes cellular dysfunction and death, which in turn leads to heart disease. Here, we review recent advances in understanding the role of autophagy in heart disease, highlight unsolved issues, and discuss the therapeutic potential of modulating autophagy in heart disease.

Mechanisms and biological functions of autophagy in diseased and ageing kidneys

Autophagy degrades pathogens, altered organelles and protein aggregates, and is characterized by the sequestration of cytoplasmic cargos within double-membrane-limited vesicles called autophagosomes. The process is regulated by inputs from the cellular microenvironment, and is activated in response to nutrient scarcity and immune triggers, which signal through a complex molecular network. Activation of autophagy leads to the formation of an isolation membrane, recognition of cytoplasmic cargos, expansion of the autophagosomal membrane, fusion with lysosomes and degradation of the autophagosome and its contents. Autophagy maintains cellular homeostasis during stressful conditions, dampens inflammation and shapes adaptive immunity. A growing body of evidence has implicated autophagy in kidney health, ageing and disease; it modulates tissue responses during acute kidney injuries, regulates podocyte homeostasis and protects against age-related renal disorders. The renoprotective functions of autophagy in epithelial renal cells and podocytes are mostly mediated by the clearance of altered mitochondria, which can activate inflammasomes and apoptosis, and the removal of protein aggregates, which might trigger inflammation and cell death. In translational terms, autophagy is undoubtedly an attractive target for developing new renoprotective treatments and identifying markers of kidney injury.

HIV life cycle, innate immunity and autophagy in the central nervous system

PURPOSE OF REVIEW

In this era of modern combination antiretroviral therapy (cART) HIV-associated neurocognitive disorders (HAND) continue to affect a large portion of the infected population. In this review, we highlight recent discoveries that help to define the interplay between HIV life cycle, the innate immune system and cellular autophagy in the context of the central nervous system (CNS).

RECENT FINDINGS

Investigators have recently elucidated themes in HAND, which place it in a unique framework. Cells of macrophage lineage and probably astrocytes play a role in disseminating virus through the CNS. Each of these cell types responds to a diverse population of constantly evolving virus existing in an inflammatory environment. This occurs though the failure of both host antiviral mechanisms, such as autophagy, and innate immunological signalling pathways to control viral replication.

SUMMARY

The newest findings detailed in this review help define why HIV CNS disease is a difficult target for therapeutics and create hope that these new mechanisms may be exploited to attenuate viral replication and eliminate disease.

Acinus integrates AKT1 and subapoptotic caspase activities to regulate basal autophagy

How cellular stresses up-regulate autophagy is not fully understood. One potential regulator is the Drosophila melanogaster protein Acinus (Acn), which is necessary for autophagy induction and triggers excess autophagy when overexpressed. We show that cell type-specific regulation of Acn depends on proteolysis by the caspase Dcp-1. Basal Dcp-1 activity in developing photoreceptors is sufficient for this cleavage without a need for apoptosis to elevate caspase activity. On the other hand, Acn was stabilized by loss of Dcp-1 function or by the presence of a mutation in Acn that eliminates its conserved caspase cleavage site. Acn stability also was regulated by AKT1-mediated phosphorylation. Flies that expressed stabilized forms of Acn, either the phosphomimetic Acn(S641,731D) or the caspase-resistant Acn(D527A), exhibited enhanced basal autophagy. Physiologically, these flies showed improvements in processes known to be autophagy dependent, including increased starvation resistance, reduced Huntingtin-induced neurodegeneration, and prolonged life span. These data indicate that AKT1 and caspase-dependent regulation of Acn stability adjusts basal autophagy levels.

Autosis and autophagic cell death: the dark side of autophagy

It is controversial whether cells truly die via autophagy or whether — in dying cells — autophagy is merely an innocent bystander or a well-intentioned ‘Good Samaritan' trying to prevent inevitable cellular demise. However, there is increasing evidence that the genetic machinery of autophagy may be essential for cell death in certain settings. We recently identified a novel form of autophagy gene-dependent cell death, termed autosis, which is mediated by the Na⁺,K⁺-ATPase pump and has unique morphological features. High levels of cellular autophagy, as occurs with treatment with autophagy-inducing peptides, starvation, or in vivo during certain types of ischemia, can trigger autosis. These findings provide insights into the mechanisms and strategies for prevention of cell death during extreme stress conditions.

Pharmacological regulators of autophagy and their link with modulators of lupus disease

Autophagy is a central regulator of cell survival. It displays both anti- and pro-death roles that are decisive in the maintenance of cell homeostasis. Initially described in several eukaryotic cellular models as being induced under nutrient stress favouring survival by energy supply, autophagy was found later to display other decisive physiological roles, especially in the immune system. Thus, it is involved in antigen presentation and lymphocyte differentiation as well as in the balance regulating survival/death and activation of lymphocytes. Autophagy therefore appears to be central in the regulation of inflammation. The observation that autophagy is deregulated in systemic lupus erythematosus is recent. This discovery revives the programme dealing with the design and development of pharmacological autophagy regulators in the therapeutic context of lupus, a debilitating autoimmune disease that affects several million people in the world. A large number of molecules that positively and negatively regulate autophagy have been described, most of them with therapeutic indications in cancer and infection. Only a few, however, are effectively potent activators or inhibitors endowed with experimentally demonstrated selective properties. In this review article, we highlight the most relevant ones and summarize what we know regarding their mechanism of action. We emphasize the link between pharmacological regulators of autophagy and inducers or inhibitors of lupus disease and discuss the fundamental and pharmacological/therapeutic interest of this functional interplay.

Spontaneous self-assembly of pathogenic huntingtin exon 1 protein into amyloid structures

PolyQ (polyglutamine) diseases such as HD (Huntington's disease) or SCA1 (spinocerebellar ataxia type 1) are neurodegenerative disorders caused by abnormally elongated polyQ tracts in human proteins. PolyQ expansions promote misfolding and aggregation of disease-causing proteins, leading to the appearance of nuclear and cytoplasmic inclusion bodies in patient neurons. Several lines of experimental evidence indicate that this process is critical for disease pathogenesis. However, the molecular mechanisms underlying spontaneous polyQ-containing aggregate formation and the perturbation of neuronal processes are still largely unclear. The present chapter reviews the current literature regarding misfolding and aggregation of polyQ-containing disease proteins. We specifically focus on studies that have investigated the amyloidogenesis of polyQ-containing HTTex1 (huntingtin exon 1) fragments. These protein fragments are disease-relevant and play a critical role in HD pathogenesis. We outline potential mechanisms behind mutant HTTex1 aggregation and toxicity, as well as proteins and small molecules that can modify HTTex1 amyloidogenesis in vitro and in vivo. The potential implications of such studies for the development of novel therapeutic strategies are discussed.

Targeting autophagy in breast cancer

Macroautophagy (referred to as autophagy here) is an intracellular degradation pathway enhanced in response to a variety of stresses and in response to nutrient deprivation. This process provides the cell with nutrients and energy by degrading aggregated and damaged proteins as well as compromised organelles. Since autophagy has been linked to diverse diseases including cancer, it has recently become a very interesting target in breast cancer treatment. Indeed, current clinical trials are trying to use chloroquine or hydroxychloroquine, alone or in combination with other drugs to inhibit autophagy during breast cancer therapy since chemotherapy and radiation, regimens that are used to treat breast cancer, are known to induce autophagy in cancer cells. Importantly, in breast cancer, autophagy has been involved in the development of resistance to chemotherapy and to anti-estrogens. Moreover, a close relationship has recently been described between autophagy and the HER2 receptor. Here, we discuss some of the recent findings relating autophagy and cancer with a particular focus on breast cancer therapy.

Autophagy in adipose tissue and the beta cell: implications for obesity and diabetes

Autophagy is a lysosomal degradation pathway recycling intracellular long-lived proteins and damaged organelles, thereby maintaining cellular homeostasis. In addition to inflammatory processes, autophagy has been implicated in the regulation of adipose tissue and beta cell functions. In obesity and type 2 diabetes autophagic activity is modulated in a tissue-dependent manner. In this review we discuss the regulation of autophagy in adipose tissue and beta cells, exemplifying tissue-specific dysregulation of autophagy and its implications for the pathophysiology of obesity and type 2 diabetes. We will highlight common themes and outstanding gaps in our understanding, which need to be addressed before autophagy could be envisioned as a therapeutic target for the treatment of obesity and diabetes.

Moxibustion Activates Macrophage Autophagy and Protects Experimental Mice against Bacterial Infection

Moxibustion is one of main therapies in traditional Chinese medicine and uses heat stimulation on the body surface from the burning of moxa to release pain or treat diseases. Emerging studies have shown that moxibustion can generate therapeutic effects by activating a series of signaling pathways and neuroendocrine-immune activities. Here we show moxibustion promoted profound macrophage autophagy in experimental Kunming mice, with reduced Akt phosphorylation and activated eIF2α phosphorylation. Consequently, moxibustion promoted bacterial clearance by macrophages and protected mice from mortality due to bacterial infection. These results indicate that moxibustion generates a protective response by activating autophagy against bacterial infections.

Autophagy-inducing peptides from mammalian VSV and fish VHSV rhabdoviral G glycoproteins (G) as models for the development of new therapeutic molecules

It has not been elucidated whether or not autophagy is induced by rhabdoviral G glycoproteins (G) in vertebrate organisms for which rhabdovirus infection is lethal. Our work provides the first evidence that both mammalian (vesicular stomatitis virus, VSV) and fish (viral hemorrhagic septicemia virus, VHSV, and spring viremia carp virus, SVCV) rhabdoviral Gs induce an autophagic antiviral program in vertebrate cell lines. The transcriptomic profiles obtained from zebrafish genetically immunized with either Gsvcv or Gvhsv suggest that autophagy is induced shortly after immunization and therefore, it may be an important component of the strong antiviral immune responses elicited by these viral proteins. Pepscan mapping of autophagy-inducing linear determinants of Gvhsv and Gvsv showed that peptides located in their fusion domains induce autophagy. Altogether these results suggest that strategies aimed at modulating autophagy could be used for the prevention and treatment of rhabdoviral infections such as rabies, which causes thousands of human deaths every year.

GA binding protein augments autophagy via transcriptional activation of BECN1-PIK3C3 complex genes

Macroautophagy is a vesicular catabolic trafficking pathway that is thought to protect cells from diverse stressors and to promote longevity. Recent studies have revealed that transcription factors play important roles in the regulation of autophagy. In this study, we have identified GA binding protein (GABP) as a transcriptional regulator of the combinatorial expression of BECN1-PIK3C3 complex genes involved in autophagosome initiation. We performed bioinformatics analyses that demonstrated highly conserved putative GABP sites in genes that encode BECN1/Beclin 1, several BECN1 interacting proteins, and downstream autophagy proteins including the ATG12-ATG5-ATG16L1 complex. We demonstrate that GABP binds to the promoter regions of BECN1-PIK3C3 complex genes and activates their transcriptional activities. Knockdown of GABP reduced BECN1-PIK3C3 complex transcripts, BECN1-PIK3C3 complex protein levels and autophagy in cultured cells. Conversely, overexpression of GABP increased autophagy. Nutrient starvation increased GABP-dependent transcriptional activity of BECN1-PIK3C3 complex gene promoters and increased the recruitment of GABP to the BECN1 promoter. Our data reveal a novel function of GABP in the regulation of autophagy via transcriptional activation of the BECN1-PIK3C3 complex.

Genetic causes of Parkinson's disease and their links to autophagy regulation

Genetic studies over the past 15 years have revolutionized our understanding towards the etiology of Parkinson's disease (PD). These studies have discovered many disease-linked genetic loci (PARK 1 to 18), which are now being interrogated for cellular pathways contributing to PD. Various pathogenic pathways were proposed but validation of each pathway awaits rigorous experimental testing. Here we review recent progress in understanding the influence of disease risk genes on cellular functions, specifically, autophagy pathways. Autophagy is a cell self-eating, lysosomal degradation system that plays an important role in cell homeostasis and survival. Neurons are post-mitotic cells and particularly vulnerable to the impairment of autophagic degradation due to their inability to redistribute damaged proteins and organelles to daughter cells. Emerging evidence has implicated dysfunctional autophagy in a growing number of neurodegenerative diseases including PD. We will also discuss the prospect of intervening autophagy pathways as a potential strategy to treat PD.

Rapamycin improves peripheral nerve myelination while it fails to benefit neuromuscular performance in neuropathic mice

Charcot--Marie-Tooth disease type 1A (CMT1A) is a hereditary peripheral neuropathy characterized by progressive demyelination and distal muscle weakness. Abnormal expression of peripheral myelin protein 22 (PMP22) has been linked to CMT1A and is modeled by Trembler J (TrJ) mice, which carry the same leucine to proline substitution in PMP22 as affected pedigrees. Pharmacologic modulation of autophagy by rapamycin in neuron-Schwann cell explant cultures from neuropathic mice reduced PMP22 aggregate formation and improved myelination. Here we asked whether rapamycin administration by food supplementation, or intraperitoneal injection, could alleviate the neuropathic phenotype of affected mice and improve neuromuscular performance. Cohorts of male and female wild type (Wt) and TrJ mice were assigned to placebo or rapamycin treatment starting at 2 or 4months of age and tested monthly on the rotarod. While neither long-term feeding (8 or 10months) on rapamycin-enriched diet, or short-term injection (2months) of rapamycin improved locomotor performance of the neuropathic mice, both regimen benefited peripheral nerve myelination. Together, these results indicate that while treatment with rapamycin benefits the myelination capacity of neuropathic Schwann cells, this intervention does not improve neuromuscular function. The observed outcome might be the result of the differential response of nerve and skeletal muscle tissue to rapamycin.

Biological activities of novel pyrazolyl hydroxamic acid derivatives against human lung cancer cell line A549

We synthesized a series of novel pyrazolyl hydroxamic acid derivatives (4a-4l) and investigated their biological activities against human lung cancer cell line A549 in vitro to determine their mechanism of action. The results showed that the majority of derivatives had inhibitory effects on the growth of A549 cancer cells in dose and time-dependent manners, in which the compounds 4b, 4f, 4h and 4j (10 μM) exerted more effective anti-proliferation activity. However, it should be noted that 4j may result in necrosis at 10 μM. Furthermore, the three compounds 4b, 4f and 4h induced cell cycle arrest at G1 phase and triggered autophagy, but could not obviously induce apoptosis and necrosis under the stimulatory condition. Therefore, the pyrazolyl hydroxamic acid derivatives 4b, 4f and 4h can be used to investigate the regulatory mechanism of autophagy and offer new approaches to the prevention of lung cancer.

A single pathway targets several health challenges of the elderly

New avenues to modulate the autophagy-lysosomal route of protein clearance have the potential to help treat several disease states to which the elderly are particularly vulnerable. Two recent papers identified distinct ways to tap into the lysosomal degradation pathway of autophagy to reduce age-related protein accumulation events. Shoji-Kawata et al. (Nature 2013;494:201-206) describe a new autophagy-inducing peptide, Tat-Beclin 1, that enhances the clearance of polyglutamine aggregates related to Huntington's disease and, interestingly, suppresses viral and bacterial infections. Savolainen et al. (Neurobiol Dis 2014;68:1-15) describe a prolyl oligopeptidase inhibitor that reduces α-synuclein species related to Parkinson's disease and other α-synucleinopathies, and this inhibitor caused a concomitant increase in autophagic activation markers. Previous studies have also linked the autophagy-lysosomal pathway to the protective clearing of the Aβ peptides of Alzheimer's disease and tau species of tauopathies. Enhancing autophagy-lysosomal efficiency may provide a therapeutic avenue for diverse types of proteinopathies, including the most common neurodegenerative disorders of the elderly.

Rapamycin relieves lentiviral vector transduction resistance in human and mouse hematopoietic stem cells

Transplantation of genetically modified hematopoietic stem cells (HSCs) is a promising therapeutic strategy for genetic diseases, HIV, and cancer. However, a barrier for clinical HSC gene therapy is the limited efficiency of gene delivery via lentiviral vectors (LVs) into HSCs. We show here that rapamycin, an allosteric inhibitor of the mammalian target of rapamycin complexes, facilitates highly efficient lentiviral transduction of mouse and human HSCs and dramatically enhances marking frequency in long-term engrafting cells in mice. Mechanistically, rapamycin enhanced postbinding endocytic events, leading to increased levels of LV cytoplasmic entry, reverse transcription, and genomic integration. Despite increasing LV copy number, rapamycin did not significantly alter LV integration site profile or chromosomal distribution in mouse HSCs. Rapamycin also enhanced in situ transduction of mouse HSCs via direct intraosseous infusion. Collectively, rapamycin strongly augments LV transduction of HSCs in vitro and in vivo and may prove useful for therapeutic gene delivery.

Stress responses in flavivirus-infected cells: activation of unfolded protein response and autophagy

The Flavivirus is a genus of RNA viruses that includes multiple long known human, animal, and zoonotic pathogens such as Dengue virus, yellow fever virus, West Nile virus, or Japanese encephalitis virus, as well as other less known viruses that represent potential threats for human and animal health such as Usutu or Zika viruses. Flavivirus replication is based on endoplasmic reticulum-derived structures. Membrane remodeling and accumulation of viral factors induce endoplasmic reticulum stress that results in activation of a cellular signaling response termed unfolded protein response (UPR), which can be modulated by the viruses for their own benefit. Concomitant with the activation of the UPR, an upregulation of the autophagic pathway in cells infected with different flaviviruses has also been described. This review addresses the current knowledge of the relationship between endoplasmic reticulum stress, UPR, and autophagy in flavivirus-infected cells and the growing evidences for an involvement of these cellular pathways in the replication and pathogenesis of these viruses.

Capitalizing on the autophagic response for treatment of liver disease caused by alpha-1-antitrypsin deficiency and other genetic diseases

Alpha-1-antitrypsin deficiency (ATD) is one of the most common genetic causes of liver disease and is a prototype of liver diseases caused by the pathologic accumulation of aggregated mutant alpha-1-antitrypsin Z (ATZ) within liver cells. In the case of ATD-associated liver disease, the resulting “gain-of-function” toxicity can lead to serious clinical manifestations, including cirrhosis and hepatocellular carcinoma. Currently, the only definitive therapy for ATD-associated liver disease is liver transplantation, but recent efforts have demonstrated the exciting potential for novel therapies that target disposal of the mutant protein aggregates by harnessing a cellular homeostasis mechanism called autophagy. In this review, we will summarize research advances on autophagy and genetic liver diseases. We will discuss autophagy enhancer strategies for liver disease due to ATD and another genetic liver disease, inherited hypofibrinogenemia, caused by the proteotoxic effects of a misfolded protein. On the basis of recent evidence that autophagy plays a role in cellular lipid degradation, we also speculate about autophagy enhancer strategies for treatment of hepatic lipid storage diseases such as cholesterol ester storage disease.

Golgi-Associated plant Pathogenesis Related protein 1 (GAPR-1) forms amyloid-like fibrils by interaction with acidic phospholipids and inhibits Aβ aggregation

Golgi-Associated plant Pathogenesis Related protein 1 (GAPR-1) is a mammalian protein that is a member of the Cysteine-rich secretory proteins, Antigen 5 and Pathogenesis related proteins group 1 (CAP) superfamily of proteins. A role for the common CAP domain in the function of the diverse superfamily members has not been described so far. Here, we show by a combination of independent techniques including electron microscopy, Thioflavin T fluorescence, and circular dichroism that GAPR-1 has the capability to form amyloid-like fibrils in the presence of liposomes containing negatively charged lipids. Surprisingly, GAPR-1 was also shown to bind the amyloid-oligomer specific antibody A11 in the absence of lipids, indicating that GAPR-1 has an intrinsic tendency to form oligomers. This behavior is characteristic for proteins that interfere with Aβ aggregation and indeed we found that GAPR-1 effectively inhibited aggregation of Aβ(1-40) peptide. Immuno-dot blot analysis revealed that GAPR-1 binds to prefibrillar oligomeric Aβ structures during the early stages of fibril formation. Another CAP domain-containing protein, CRISP2, was also capable of forming fibrils, indicating that oligomerization and fibril formation is a shared characteristic between CAP family members. We suggest that the CAP domain may regulate protein oligomerization in a large variety of proteins that define the CAP superfamily.

Autophagy--a key player in cellular and body metabolism

Knowledge gained over the past 10 years about the mechanisms that underpin autophagy has provided a universal framework for studies of diverse physiological and pathological processes. Of particular interest is the emerging role of autophagy in the maintenance of energy homeostasis, both at the cellular level and within the organism as a whole. Dysregulation of autophagy might contribute to the development of metabolic disorders, including insulin resistance, diabetes mellitus, obesity, atherosclerosis and osteoporosis. The authors of this Review highlight research findings on the regulation of cellular autophagy by nutrients. They also describe the role of autophagy in various tissues in the regulation of energy metabolism and the development of diseases related to altered metabolism. Finally, the potential of pharmacological modulation of autophagy as a treatment for human metabolic disorders is discussed.

Prediction and redesign of protein-protein interactions

Understanding the molecular basis of protein function remains a central goal of biology, with the hope to elucidate the role of human genes in health and in disease, and to rationally design therapies through targeted molecular perturbations. We review here some of the computational techniques and resources available for characterizing a critical aspect of protein function - those mediated by protein-protein interactions (PPI). We describe several applications and recent successes of the Evolutionary Trace (ET) in identifying molecular events and shapes that underlie protein function and specificity in both eukaryotes and prokaryotes. ET is a part of analytical approaches based on the successes and failures of evolution that enable the rational control of PPI.

Intracellular fibril formation, calcification, and enrichment of chaperones, cytoskeletal, and intermediate filament proteins in the adult hippocampus CA1 following neonatal exposure to the nonprotein amino acid BMAA

The environmental neurotoxin β-N-methylamino-l-alanine (BMAA) has been implicated in the etiology of neurodegenerative disease, and recent studies indicate that BMAA can be misincorporated into proteins. BMAA is a developmental neurotoxicant that can induce long-term learning and memory deficits, as well as regionally restricted neuronal degeneration and mineralization in the hippocampal CA1. The aim of the study was to characterize long-term changes (2 weeks to 6 months) further in the brain of adult rats treated neonatally (postnatal days 9–10) with BMAA (460 mg/kg) using immunohistochemistry (IHC), transmission electron microscopy, and laser capture microdissection followed by LC-MS/MS for proteomic analysis. The histological examination demonstrated progressive neurodegenerative changes, astrogliosis, microglial activation, and calcification in the hippocampal CA1 3–6 months after exposure. The IHC showed an increased staining for α-synuclein and ubiquitin in the area. The ultrastructural examination revealed intracellular deposition of abundant bundles of closely packed parallel fibrils in neurons, axons, and astrocytes of the CA1. Proteomic analysis of the affected site demonstrated an enrichment of chaperones (e.g., clusterin, GRP-78), cytoskeletal and intermediate filament proteins, and proteins involved in the antioxidant defense system. Several of the most enriched proteins (plectin, glial fibrillar acidic protein, vimentin, Hsp 27, and ubiquitin) are known to form complex astrocytic inclusions, so-called Rosenthal fibers, in the neurodegenerative disorder Alexander disease. In addition, TDP-43 and the negative regulator of autophagy, GLIPR-2, were exclusively detected. The present study demonstrates that neonatal exposure to BMAA may offer a novel model for the study of hippocampal fibril formation in vivo.

High-throughput screening for broad-spectrum chemical inhibitors of RNA viruses

RNA viruses are responsible for major human diseases such as flu, bronchitis, dengue, Hepatitis C or measles. They also represent an emerging threat because of increased worldwide exchanges and human populations penetrating more and more natural ecosystems. A good example of such an emerging situation is chikungunya virus epidemics of 2005-2006 in the Indian Ocean. Recent progresses in our understanding of cellular pathways controlling viral replication suggest that compounds targeting host cell functions, rather than the virus itself, could inhibit a large panel of RNA viruses. Some broad-spectrum antiviral compounds have been identified with host target-oriented assays. However, measuring the inhibition of viral replication in cell cultures using reduction of cytopathic effects as a readout still represents a paramount screening strategy. Such functional screens have been greatly improved by the development of recombinant viruses expressing reporter enzymes capable of bioluminescence such as luciferase. In the present report, we detail a high-throughput screening pipeline, which combines recombinant measles and chikungunya viruses with cellular viability assays, to identify compounds with a broad-spectrum antiviral profile.

Self-eating in the plaque: what macrophage autophagy reveals about atherosclerosis

Autophagy (or 'self-eating') is the process by which cellular contents are recycled to support downstream metabolism. An explosion in research in the past decade has implicated its role in both health and disease and established the importance of the autophagic response during periods of stress and nutrient deprivation. Atherosclerosis is a state where chronic exposure to cellular stressors promotes disease progression, and alterations in autophagy are predicted to be consequential. Recent reports linking macrophage autophagy to lipid metabolism, blunted inflammatory signaling, and an overall suppression of proatherogenic processes support this notion. We review these data and provide a framework for understanding the role of macrophage autophagy in the pathogenesis of atherosclerosis, one of the most formidable diseases of our time.

Rotavirus increases levels of lipidated LC3 supporting accumulation of infectious progeny virus without inducing autophagosome formation

Replication of many RNA viruses benefits from subversion of the autophagic pathway through many different mechanisms. Rotavirus, the main etiologic agent of pediatric gastroenteritis worldwide, has been recently described to induce accumulation of autophagosomes as a mean for targeting viral proteins to the sites of viral replication. Here we show that the viral-induced increase of the lipidated form of LC3 does not correlate with an augmented formation of autophagosomes, as detected by immunofluorescence and electron microscopy. The LC3-II accumulation was found to be dependent on active rotavirus replication through the use of antigenically intact inactivated viral particles and of siRNAs targeting viral genes that are essential for viral replication. Silencing expression of LC3 or of Atg7, a protein involved in LC3 lipidation, resulted in a significant impairment of viral titers, indicating that these elements of the autophagic pathway are required at late stages of the viral cycle.

Regulation of autophagy by mTOR-dependent and mTOR-independent pathways: autophagy dysfunction in neurodegenerative diseases and therapeutic application of autophagy enhancers

Autophagy is an intracellular degradation pathway essential for cellular and energy homoeostasis. It functions in the clearance of misfolded proteins and damaged organelles, as well as recycling of cytosolic components during starvation to compensate for nutrient deprivation. This process is regulated by mTOR (mammalian target of rapamycin)-dependent and mTOR-independent pathways that are amenable to chemical perturbations. Several small molecules modulating autophagy have been identified that have potential therapeutic application in diverse human diseases, including neurodegeneration. Neurodegeneration-associated aggregation-prone proteins are predominantly degraded by autophagy and therefore stimulating this process with chemical inducers is beneficial in a wide range of transgenic disease models. Emerging evidence indicates that compromised autophagy contributes to the aetiology of various neurodegenerative diseases related to protein conformational disorders by causing the accumulation of mutant proteins and cellular toxicity. Combining the knowledge of autophagy dysfunction and the mechanism of drug action may thus be rational for designing targeted therapy. The present review describes the cellular signalling pathways regulating mammalian autophagy and highlights the potential therapeutic application of autophagy inducers in neurodegenerative disorders.

Autophagy: regulation and role in development

Autophagy is an evolutionarily conserved cellular process through which long-lived proteins and damaged organelles are recycled to maintain energy homeostasis. These proteins and organelles are sequestered into a double-membrane structure, or autophagosome, which subsequently fuses with a lysosome in order to degrade the cargo. Although originally classified as a type of programmed cell death, autophagy is more widely viewed as a basic cell survival mechanism to combat environmental stressors. Autophagy genes were initially identified in yeast and were found to be necessary to circumvent nutrient stress and starvation. Subsequent elucidation of mammalian gene counterparts has highlighted the importance of this process to normal development. This review provides an overview of autophagy, the types of autophagy, its regulation and its known impact on development gleaned primarily from murine models.

Caffeine stimulates hepatic lipid metabolism by the autophagy-lysosomal pathway in mice

Caffeine is one of the world's most consumed drugs. Recently, several studies showed that its consumption is associated with lower risk for nonalcoholic fatty liver disease (NAFLD), an obesity-related condition that recently has become the major cause of liver disease worldwide. Although caffeine is known to stimulate hepatic fat oxidation, its mechanism of action on lipid metabolism is still not clear. Here, we show that caffeine surprisingly is a potent stimulator of hepatic autophagic flux. Using genetic, pharmacological, and metabolomic approaches, we demonstrate that caffeine reduces intrahepatic lipid content and stimulates β-oxidation in hepatic cells and liver by an autophagy-lysosomal pathway. Furthermore, caffeine-induced autophagy involved down-regulation of mammalian target of rapamycin signaling and alteration in hepatic amino acids and sphingolipid levels. In mice fed a high-fat diet, caffeine markedly reduces hepatosteatosis and concomitantly increases autophagy and lipid uptake in lysosomes.

CONCLUSION

These results provide novel insight into caffeine's lipolytic actions through autophagy in mammalian liver and its potential beneficial effects in NAFLD.