Systemic Analysis of Atg5-Null Mice Rescued from Neonatal Lethality by Transgenic ATG5 Expression in Neurons

TBC1D2B undergoes phase separation and mediates autophagy initiation

Small ubiquitin-like modifiers from the ATG8 family regulate autophagy initiation and progression in mammalian cells. Their interaction with LC3-interacting region (LIR) containing proteins promotes cargo sequestration, phagophore assembly, or even fusion between autophagosomes and lysosomes. Previously, we have shown that RabGAP proteins from the TBC family directly bind to LC3/GABARAP proteins. In the present study, we focus on the function of TBC1D2B. We show that TBC1D2B contains a functional canonical LIR motif and acts at an early stage of autophagy by binding to both LC3/GABARAP and ATG12 conjugation complexes. Subsequently, TBC1D2B is degraded by autophagy. TBC1D2B condensates into liquid droplets upon autophagy induction. Our study suggests that phase separation is an underlying mechanism of TBC1D2B-dependent autophagy induction.

Regulation and Functions of Autophagy During Animal Development

Autophagy is used to degrade cytoplasmic materials, and is critical to maintain cell and organismal health in diverse animals. Here we discuss the regulation, utilization and impact of autophagy on development, including roles in oogenesis, spermatogenesis and embryogenesis in animals. We also describe how autophagy influences postembryonic development in the context of neuronal and cardiac development, wound healing, and tissue regeneration. We describe recent studies of selective autophagy during development, including mitochondria-selective autophagy and endoplasmic reticulum (ER)-selective autophagy. Studies of developing model systems have also been used to discover novel regulators of autophagy, and we explain how studies of autophagy in these physiologically relevant systems are advancing our understanding of this important catabolic process.

YIPF3 and YIPF4 regulate autophagic turnover of the Golgi apparatus

The degradation of organelles by autophagy is essential for cellular homeostasis. The Golgi apparatus has recently been demonstrated to be degraded by autophagy, but little is known about how the Golgi is recognized by the forming autophagosome. Using quantitative proteomic analysis and two novel Golgiphagy reporter systems, we found that the five-pass transmembrane Golgi-resident proteins YIPF3 and YIPF4 constitute a Golgiphagy receptor. The interaction of this complex with LC3B, GABARAP, and GABARAPL1 is dependent on a LIR motif within YIPF3 and putative phosphorylation sites immediately upstream; the stability of the complex is governed by YIPF4. Expression of a YIPF3 protein containing a mutated LIR motif caused an elongated Golgi morphology, indicating the importance of Golgi turnover via selective autophagy. The reporter assays reported here may be readily adapted to different experimental contexts to help deepen our understanding of Golgiphagy.

NBR1-mediated selective autophagy of ARF7 modulates root branching

Auxin dictates root architecture via the Auxin Response Factor (ARF) family of transcription factors, which control lateral root (LR) formation. In Arabidopsis, ARF7 regulates the specification of prebranch sites (PBS) generating LRs through gene expression oscillations and plays a pivotal role during LR initiation. Despite the importance of ARF7 in this process, there is a surprising lack of knowledge about how ARF7 turnover is regulated and how this impacts root architecture. Here, we show that ARF7 accumulates in autophagy mutants and is degraded through NBR1-dependent selective autophagy. We demonstrate that the previously reported rhythmic changes to ARF7 abundance in roots are modulated via autophagy and might occur in other tissues. In addition, we show that the level of co-localization between ARF7 and autophagy markers oscillates and can be modulated by auxin to trigger ARF7 turnover. Furthermore, we observe that autophagy impairment prevents ARF7 oscillation and reduces both PBS establishment and LR formation. In conclusion, we report a novel role for autophagy during development, namely by enacting auxin-induced selective degradation of ARF7 to optimize periodic root branching.

Research progress on the role of autophagy in the development of varicocele

Varicocele (VC) is a common cause of infertility in men. Pathophysiological changes caused by VC, such as testicular hypoxia, high temperatures, oxidative stress, abnormal reproductive hormones, and Cd accumulation, can induce autophagy, thus affecting the reproductive function in patients with this condition. Autophagy regulators can be classified as activators or inhibitors. Autophagy activators upregulate autophagy, reduce the damage to the testis and epididymis, inhibit spermatogenic cell apoptosis, and protect fertility. In contrast, autophagy inhibitors block autophagy and aggravate the damage to the reproductive functions. Therefore, elucidating the role of autophagy in the occurrence, development, and regulation of VC may provide additional therapeutic options for men with infertility and VC. In this review, we briefly describe the progress made in autophagy research in the context of VC.

Functional role of autophagy in testicular and ovarian steroidogenesis

Autophagy is an evolutionarily conserved cellular recycling process that maintains cellular homeostasis. Despite extensive research in endocrine contexts, the role of autophagy in ovarian and testicular steroidogenesis remains elusive. The significant role of autophagy in testosterone production suggests potential treatments for conditions like oligospermia and azoospermia. Further, influence of autophagy in folliculogenesis, ovulation, and luteal development emphasizes its importance for improved fertility and reproductive health. Thus, investigating autophagy in gonadal cells is clinically significant. Understanding these processes could transform treatments for endocrine disorders, enhancing reproductive health and longevity. Herein, we provide the functional role of autophagy in testicular and ovarian steroidogenesis to date, highlighting its modulation in testicular steroidogenesis and its impact on hormone synthesis, follicle development, and fertility therapies.

Autophagy inhibition suppresses hormone production and cell growth in pituitary tumor cells: A potential approach to pituitary tumors

Pituitary tumors (PTs) represent about 10% of all intracranial tumors, and most are benign. However, some PTs exhibit continued growth despite multimodal therapies. Although temozolomide (TMZ), an alkylating chemotherapeutic agent, is a first-line medical treatment for aggressive PTs, some PTs are resistant to TMZ. Existing literature indicated the involvement of autophagy in cell growth in several types of tumors, including PTs, and autophagy inhibitors have anti-tumor effects. In this study, the expression of several autophagy-inducible genes, including Atg3, Beclin1, Map1lc3A, Map1lc3b, Ulk1, Wipi2, and Tfe3 in two PT cell lines, the mouse corticotroph AtT-20 cells and the rat mammosomatotroph GH4 cells were identified. Down regulation of Tfe3, a master switch of basal autophagy, using RNA interference, suppressed cell proliferation in AtT-20 cells, suggesting basal autophagy contributes to the maintenance of cellular functions in PT cells. Expectedly, treatment with bafilomycin A1, an autophagy inhibitor, suppressed cell proliferation, increased the cleavage of PARP1, and reduced ACTH production in AtT-20 cells. Treatment with two additional autophagy inhibitors, chloroquine (CQ) and monensin, demonstrated similar effects on cell proliferation, apoptosis, and ACTH production in AtT-20 cells. Also, treatment with CQ suppressed cell proliferation and growth hormone production in GH4 cells. Moreover, the combination of CQ and TMZ had an additive effect on the inhibition of cell proliferation in AtT-20 and GH4 cells. The additive effect of anti-cancer drugs such as CQ alone or in combination with TMZ may represent a novel therapeutic approach for PTs, in particular tumors with resistance to TMZ.

CIRBP Increases the synthesis and secretion of steroid hormones by in yak granulaso cells

As a regulatory protein that upregulates transcription in response to various stresses, cold-induced RNA-binding protein (CIRBP) is involved in a variety of physiological pathological processes in cells. However, little is known about the role of CIRBP in regulating autophagy and the synthesis and secretion of ovarian steroid hormones (estradiol E2 and progesterone P4). This study aimed to explore whether the synthetic secretion of ovarian steroid hormones is related to CIRBP-regulated autophagy. We detected the differential expression of CIRBP, LC3, E2 and P4 in YGCs cultured at mild low temperature (32 °C) for 6 and 12 h. CIRBP, LC3, E2 and P4 expression was increased in response to low temperature in YGCs. In order to illustrate that the changes in secretion of E2/P4 and autophagy might be caused by CIRBP induced by low temperature, we overexpressed CIRBP in YGCs cultured in vitro to detect its effects on autophagy and steroid hormone synthesis and secretion. We found that overexpression of CIRBP can induce autophagy of YGCs and enhance the synthesis and secretion of E2 and P4, suggesting that mild hypothermia may activate autophagy by inducing the expression of CIRBP and enhance the synthesis and secretion of E2 and P4. To further explore the relationship between CIRBP regulated autophagy and steroid hormone synthesis and secretion, we verified it by regulating autophagy. The results showed that Inhibition of autophagy significantly reversed CIRBP overexpression-enhanced autophagy and synthetic secretion of E2, P4 in YGCs, while activated autophagy showed similar results to overexpression of CIRBP. In conclusion, our data suggest that autophagy is involved in the synthesis and secretion of YGCs E2 and P4 and is associated with overexpression of CIRBP.

Combinatorial selective ER-phagy remodels the ER during neurogenesis

The endoplasmic reticulum (ER) employs a diverse proteome landscape to orchestrate many cellular functions, ranging from protein and lipid synthesis to calcium ion flux and inter-organelle communication. A case in point concerns the process of neurogenesis, where a refined tubular ER network is assembled via ER shaping proteins into the newly formed neuronal projections to create highly polarized dendrites and axons. Previous studies have suggested a role for autophagy in ER remodelling, as autophagy-deficient neurons in vivo display axonal ER accumulation within synaptic boutons, and the membrane-embedded ER-phagy receptor FAM134B has been genetically linked with human sensory and autonomic neuropathy. However, our understanding of the mechanisms underlying selective removal of the ER and the role of individual ER-phagy receptors is limited. Here we combine a genetically tractable induced neuron (iNeuron) system for monitoring ER remodelling during in vitro differentiation with proteomic and computational tools to create a quantitative landscape of ER proteome remodelling via selective autophagy. Through analysis of single and combinatorial ER-phagy receptor mutants, we delineate the extent to which each receptor contributes to both the magnitude and selectivity of ER protein clearance. We define specific subsets of ER membrane or lumenal proteins as preferred clients for distinct receptors. Using spatial sensors and flux reporters, we demonstrate receptor-specific autophagic capture of ER in axons, and directly visualize tubular ER membranes within autophagosomes in neuronal projections by cryo-electron tomography. This molecular inventory of ER proteome remodelling and versatile genetic toolkit provide a quantitative framework for understanding the contributions of individual ER-phagy receptors for reshaping ER during cell state transitions.

To squeeze or not: Regulation of cell size by mechanical forces in development and human diseases

Physical constraints, such as compression, shear stress, stretching and tension play major roles during development and tissue homeostasis. Mechanics directly impact physiology, and their alteration is also recognized as having an active role in driving human diseases. Recently, growing evidence has accumulated on how mechanical forces are translated into a wide panel of biological responses, including metabolism and changes in cell morphology. The aim of this review is to summarize and discuss our knowledge on the impact of mechanical forces on cell size regulation. Other biological consequences of mechanical forces will not be covered by this review. Moreover, wherever possible, we also discuss mechanosensors and molecular and cellular signaling pathways upstream of cell size regulation. We finally highlight the relevance of mechanical forces acting on cell size in physiology and human diseases.

Targeting the lipid kinase PIKfyve upregulates surface expression of MHC class I to augment cancer immunotherapy

Despite the remarkable clinical success of immunotherapies in a subset of cancer patients, many fail to respond to treatment and exhibit resistance. Here, we found that genetic or pharmacologic inhibition of the lipid kinase PIKfyve, a regulator of autophagic flux and lysosomal biogenesis, upregulated surface expression of major histocompatibility complex class I (MHC-I) in cancer cells via impairing autophagic flux, resulting in enhanced cancer cell killing mediated by CD8+ T cells. Genetic depletion or pharmacologic inhibition of PIKfyve elevated tumor-specific MHC-I surface expression, increased intratumoral functional CD8+ T cells, and slowed tumor progression in multiple syngeneic mouse models. Importantly, enhanced antitumor responses by Pikfyve-depletion were CD8+ T cell- and MHC-I-dependent, as CD8+ T cell depletion or B2m knockout rescued tumor growth. Furthermore, PIKfyve inhibition improved response to immune checkpoint blockade (ICB), adoptive cell therapy, and a therapeutic vaccine. High expression of PIKFYVE was also predictive of poor response to ICB and prognostic of poor survival in ICB-treated cohorts. Collectively, our findings show that targeting PIKfyve enhances immunotherapies by elevating surface expression of MHC-I in cancer cells, and PIKfyve inhibitors have potential as agents to increase immunotherapy response in cancer patients.

Nanosensor-based monitoring of autophagy-associated lysosomal acidification in vivo

Autophagy is a cellular process with important functions that drive neurodegenerative diseases and cancers. Lysosomal hyperacidification is a hallmark of autophagy. Lysosomal pH is currently measured by fluorescent probes in cell culture, but existing methods do not allow for quantitative, transient or in vivo measurements. In the present study, we developed near-infrared optical nanosensors using organic color centers (covalent sp3 defects on carbon nanotubes) to measure autophagy-mediated endolysosomal hyperacidification in live cells and in vivo. The nanosensors localize to the lysosomes, where the emission band shifts in response to local pH, enabling spatial, dynamic and quantitative mapping of subtle changes in lysosomal pH. Using the sensor, we observed cellular and intratumoral hyperacidification on administration of mTORC1 and V-ATPase modulators, revealing that lysosomal acidification mirrors the dynamics of S6K dephosphorylation and LC3B lipidation while diverging from p62 degradation. This sensor enables the transient and in vivo monitoring of the autophagy-lysosomal pathway.

LC3-independent autophagy is vital to prevent TNF cytotoxicity

The (macro)autophagy field is facing a paradigm shift after the recent discovery that cytosolic cargoes can still be selectively targeted to phagophores (the precursors to autophagosomes) even in the absence of LC3 or other Atg8-protein family members. Several in vitro studies have indeed reported on the existence of an unconventional selective autophagic pathway that involves the in-situ formation of an autophagosome around the cargo through the direct selective autophagy receptor-mediated recruitment of RB1CC1/FIP200, thereby bypassing the requirement of LC3. In an article recently published in Science, we demonstrate the physiological importance of this unconventional autophagic pathway in the context of TNF (tumor necrosis factor) signaling. We show that it promotes the degradation of the cytotoxic TNFRSF1A/TNFR1 (TNF receptor superfamily member 1A) complex II that assembles upon TNF sensing and thereby protects mice from TNFRSF1A-driven embryonic lethality and skin inflammation.Abbreviations: ATG: autophagy related; CASP: caspase; FIR: RB1CC1/FIP200-interacting region; LIR: LC3-interacting region; M1: linear; PAS: phagophore assembly site; PtdIns3K: phosphatidylinositol 3-kinase; TNF: tumor necrosis factor; TNFRSF1A: TNF receptor superfamily member 1A.

Role of Macroautophagy in Mammalian Male Reproductive Physiology

Physiologically, autophagy is an evolutionarily conserved and self-degradative process in cells. Autophagy carries out normal physiological roles throughout mammalian life. Accumulating evidence shows autophagy as a mechanism for cellular growth, development, differentiation, survival, and homeostasis. In male reproductive systems, normal spermatogenesis and steroidogenesis need a balance between degradation and energy supply to preserve cellular metabolic homeostasis. The main process of autophagy includes the formation and maturation of the phagophore, autophagosome, and autolysosome. Autophagy is controlled by a group of autophagy-related genes that form the core machinery of autophagy. Three types of autophagy mechanisms have been discovered in mammalian cells: macroautophagy, microautophagy, and chaperone-mediated autophagy. Autophagy is classified as non-selective or selective. Non-selective macroautophagy randomly engulfs the cytoplasmic components in autophagosomes that are degraded by lysosomal enzymes. While selective macroautophagy precisely identifies and degrades a specific element, current findings have shown the novel functional roles of autophagy in male reproduction. It has been recognized that dysfunction in the autophagy process can be associated with male infertility. Overall, this review provides an overview of the cellular and molecular basics of autophagy and summarizes the latest findings on the key role of autophagy in mammalian male reproductive physiology.

CCPG1 recognizes endoplasmic reticulum luminal proteins for selective ER-phagy

The endoplasmic reticulum (ER) is a major cell compartment where protein synthesis, folding, and posttranslational modifications occur with assistance from a wide variety of chaperones and enzymes. Quality control systems selectively eliminate abnormal proteins that accumulate inside the ER due to cellular stresses. ER-phagy, that is, selective autophagy of the ER, is a mechanism that maintains or reestablishes cellular and ER-specific homeostasis through removal of abnormal proteins. However, how ER luminal proteins are recognized by the ER-phagy machinery remains unclear. Here, we applied the aggregation-prone protein, six-repeated islet amyloid polypeptide (6xIAPP), as a model ER-phagy substrate and found that cell cycle progression 1 (CCPG1), which is an ER-phagy receptor, efficiently mediates its degradation via ER-phagy. We also identified prolyl 3-hydroxylase family member 4 (P3H4) as an endogenous cargo of CCPG1-dependent ER-phagy. The ER luminal region of CCPG1 contains several highly conserved regions that we refer to as cargo-interacting regions (CIRs); these interact directly with specific luminal cargos for ER-phagy. Notably, 6xIAPP and P3H4 interact directly with different CIRs. These findings indicate that CCPG1 is a bispecific ER-phagy receptor for ER luminal proteins and the autophagosomal membrane that contributes to the efficient removal of aberrant ER-resident proteins through ER-phagy.

The Role of Autophagy in the Female Reproduction System: For Beginners to Experts in This Field

Autophagy is a fundamental process involved in regulating cellular homeostasis. Autophagy has been classically discovered as a cellular process that degrades cytoplasmic components non-selectively to produce energy. Over the past few decades, this process has been shown to work in energy production, as well as in the reduction of excessive proteins, damaged organelles, and membrane trafficking. It contributes to many human diseases, such as neurodegenerative diseases, carcinogenesis, diabetes mellitus, development, longevity, and reproduction. In this review, we provide important information for interpreting results related to autophagic experiments and present the role of autophagy in this field.

Autophagy genes in biology and disease

Macroautophagy and microautophagy are highly conserved eukaryotic cellular processes that degrade cytoplasmic material in lysosomes. Both pathways involve characteristic membrane dynamics regulated by autophagy-related proteins and other molecules, some of which are shared between the two pathways. Over the past few years, the application of new technologies, such as cryo-electron microscopy, coevolution-based structural prediction and in vitro reconstitution, has revealed the functions of individual autophagy gene products, especially in autophagy induction, membrane reorganization and cargo recognition. Concomitantly, mutations in autophagy genes have been linked to human disorders, particularly neurodegenerative diseases, emphasizing the potential pathogenic implications of autophagy defects. Accumulating genome data have also illuminated the evolution of autophagy genes within eukaryotes as well as their transition from possible ancestral elements in prokaryotes.

ATG9A prevents TNF cytotoxicity by an unconventional lysosomal targeting pathway

Cell death induced by tumor necrosis factor (TNF) can be beneficial during infection by helping to mount proper immune responses. However, TNF-induced death can also drive a variety of inflammatory pathologies. Protectives brakes, or cell-death checkpoints, normally repress TNF cytotoxicity to protect the organism from its potential detrimental consequences. Thus, although TNF can kill, this only occurs when one of the checkpoints is inactivated. Here, we describe a checkpoint that prevents apoptosis through the detoxification of the cytotoxic complex IIa that forms upon TNF sensing. We found that autophagy-related 9A (ATG9A) and 200kD FAK family kinase-interacting protein (FIP200) promote the degradation of this complex through a light chain 3 (LC3)-independent lysosomal targeting pathway. This detoxification mechanism was found to counteract TNF receptor 1 (TNFR1)-mediated embryonic lethality and inflammatory skin disease in mouse models.

Acute systemic knockdown of Atg7 is lethal and causes pancreatic destruction in shRNA transgenic mice

The notion that macroautophagy/autophagy is a potentially attractive therapeutic target for a variety of diseases, including cancer, largely stems from pre-clinical mouse studies. Most of these examine the effects of irreversible and organ confined autophagy deletion using site specific Cre-loxP recombination of the essential autophagy regulating genes Atg7 or Atg5. Model systems with the ability to impair autophagy systemically and reversibly at all disease stages would allow a more realistic approach to evaluate the consequences of authophagy inhibition as a therapeutic concept and its potential side effects. Here, we present shRNA transgenic mice that via doxycycline (DOX) regulable expression of a highly efficient miR30-E-based shRNA enabled knockdown of Atg7 simultaneously in the majority of organs, with the brain and spleen being noteable exceptions. Induced animals deteriorated rapidly and experienced profound destruction of the exocrine pancreas, severe hypoglycemia and depletion of hepatic glycogen storages. Cessation of DOX application restored apparent health, glucose homeostasis and pancreatic integrity. In a similar Atg5 knockdown model we neither observed loss of pancreatic integrity nor diminished survival after DOX treatment, but identified histological changes consistent with steatohepatitis and hepatic fibrosis in the recovery period after termination of DOX. Regulable Atg7-shRNA mice are valuable tools that will enable further studies on the role of autophagy impairment at various disease stages and thereby help to evaluate the consequences of acute autophagy inhibition as a therapeutic concept.Abbreviations: ACTB: actin, beta; AMY: amylase complex; ATG4B: autophagy related 4B, cysteine peptidase; ATG5: autophagy related 5; ATG7: autophagy related 7; Cag: CMV early enhancer/chicken ACTB promoter; Col1a1: collagen, type I, alpha 1; Cre: cre recombinase; DOX: doxycycline; GCG: glucagon; GFP: green fluorescent protein; INS: insulin; LC3: microtubule-associated protein 1 light chain 3; miR30-E: optimized microRNA backbone; NAFLD: non-alcoholic fatty liver disease; NASH: non-alcoholic steatohepatitis; PNLIP: pancreatic lipase; rtTA: reverse tetracycline transactivator protein; SQSTM1/p62: sequestome 1; TRE: tetracycline responsive element.

The role of autophagic cell death in cardiac disease

Cardiomyocytes undergo various forms of cell death during heart disease such as myocardial infarction and heart failure. Understanding the mechanisms of cell death in cardiomyocytes is one of the most fundamental issues in the treatment of heart failure. Among the several kinds of cell death mechanisms, this review will focus on autophagy-related cardiomyocyte cell death. Although autophagy plays an essential role in mediating cellular quality control mechanisms for cell survival, dysregulation of autophagy can cause cell death, referred to as autophagy-dependent cell death or type II programmed cell death. The recent discovery of autosis as a modality of autophagy-dependent cell death with unique morphological and biochemical features has allowed us to broaden our understanding of the mechanistic role of autophagy in cell death. Here, we discuss autophagy-dependent cardiomyocyte cell death, including autosis, in pathophysiological conditions of the heart.

UTX deficiency in neural stem/progenitor cells results in impaired neural development, fetal ventriculomegaly, and postnatal death

Recent studies have demonstrated that epigenetic modifications are deeply involved in neurogenesis; however, the precise mechanisms remain largely unknown. To determine the role of UTX (also known as KDM6A), a demethylase of histone H3K27, in neural development, we generated Utx-deficient mice in neural stem/progenitor cells (NSPCs). Since Utx is an X chromosome-specific gene, the genotypes are sex-dependent; female mice lose both Utx alleles (Utx^Δ/Δ ), and male mice lose one Utx allele yet retain one Uty allele, the counterpart of Utx on the Y chromosome (Utx^Δ/Uty ). We found that Utx^Δ/Δ mice exhibited fetal ventriculomegaly and died soon after birth. Immunofluorescence staining and EdU labeling revealed a significant increase in NSPCs and a significant decrease in intermediate-progenitor and differentiated neural cells. Molecular analyses revealed the downregulation of pathways related to DNA replication and increased H3K27me3 levels around the transcription start sites in Utx^Δ/Δ NSPCs. These results indicate that UTX globally regulates the expression of genes required for proper neural development in NSPCs, and UTX deficiency leads to impaired cell cycle exit, reduced differentiation, and neonatal death. Interestingly, although Utx^Δ/Uty mice survived the postnatal period, most died of hydrocephalus, a clinical feature of Kabuki syndrome, a congenital anomaly involving UTX mutations. Our findings provide novel insights into the role of histone modifiers in neural development and suggest that Utx^Δ/Uty mice are a potential disease model for Kabuki syndrome.

Mitophagy in the aging nervous system

Aging is characterised by the progressive accumulation of cellular dysfunction, stress, and inflammation. A large body of evidence implicates mitochondrial dysfunction as a cause or consequence of age-related diseases including metabolic disorders, neuropathies, various forms of cancer and neurodegenerative diseases. Because neurons have high metabolic demands and cannot divide, they are especially vulnerable to mitochondrial dysfunction which promotes cell dysfunction and cytotoxicity. Mitophagy neutralises mitochondrial dysfunction, providing an adaptive quality control strategy that sustains metabolic homeostasis. Mitophagy has been extensively studied as an inducible stress response in cultured cells and short-lived model organisms. In contrast, our understanding of physiological mitophagy in mammalian aging remains extremely limited, particularly in the nervous system. The recent profiling of mitophagy reporter mice has revealed variegated vistas of steady-state mitochondrial destruction across different tissues. The discovery of patients with congenital autophagy deficiency provokes further intrigue into the mechanisms that underpin neural integrity. These dimensions have considerable implications for targeting mitophagy and other degradative pathways in age-related neurological disease.

Autophagy and pluripotency: self-eating your way to eternal youth

Pluripotent stem cells (PSCs) can self-renew indefinitely in culture while retaining the potential to differentiate into virtually all normal cell types in the adult animal. Due to these remarkable properties, PSCs not only provide a superb system to investigate mammalian development and model diseases, but also hold promise for regenerative therapies. Autophagy is a self-digestive process that targets proteins, organelles, and other cellular contents for lysosomal degradation. Here, we review recent literature on the mechanistic role of different types of autophagy in embryonic development, embryonic stem cells (ESCs), and induced PSCs (iPSCs), focusing on their remodeling functions on protein, metabolism, and epigenetics. We present a perspective on unsolved issues and propose that autophagy is a promising target to modulate acquisition, maintenance, and directed differentiation of PSCs.

Transcriptomic and epigenomic landscapes of Alzheimer's disease evidence mitochondrial-related pathways

Alzheimers disease (AD) is the main cause of dementia and it is defined by cognitive decline coupled to extracellular deposit of amyloid-beta protein and intracellular hyperphosphorylation of tau protein. Historically, efforts to target such hallmarks have failed in numerous clinical trials. In addition to these hallmark-targeted approaches, several clinical trials focus on other AD pathological processes, such as inflammation, mitochondrial dysfunction, and oxidative stress. Mitochondria and mitochondrial-related mechanisms have become an attractive target for disease-modifying strategies, as mitochondrial dysfunction prior to clinical onset has been widely described in AD patients and AD animal models. Mitochondrial function relies on both the nuclear and mitochondrial genome. Findings from omics technologies have shed light on AD pathophysiology at different levels (e.g., epigenome, transcriptome and proteome). Most of these studies have focused on the nuclear-encoded components. The first part of this review provides an updated overview of the mechanisms that regulate mitochondrial gene expression and function. The second part of this review focuses on evidence of mitochondrial dysfunction in AD. We have focused on published findings and datasets that study AD. We analyzed published data and provide examples for mitochondrial-related pathways. These pathways are strikingly dysregulated in AD neurons and glia in sex-, cell- and disease stage-specific manners. Analysis of mitochondrial omics data highlights the involvement of mitochondria in AD, providing a rationale for further disease modeling and drug targeting.

A unifying model for the role of the ATG8 system in autophagy

The formation of autophagosomes and their fusion with lysosomes are key events that underpin autophagic degradation of cargoes. The core ATG8 system, which consists of the ATG8 family of ubiquitin-like proteins and the machineries that conjugate them onto autophagosomal membranes, are among the most-studied autophagy components. Despite the research focus on the core ATG8 system, there are conflicting reports regarding its essential roles in autophagy. Here, we reconcile prior observations of the core ATG8 system into a unifying model of their function that aims to consider apparently conflicting discoveries. Bypass pathways of autophagy that function independently of the core ATG8 system are also discussed.

Autophagy in PDGFRα+ mesenchymal cells is essential for intestinal stem cell survival

Autophagy defects are a risk factor for inflammatory bowel diseases (IBDs) through unknown mechanisms. Whole-body conditional deletion of autophagy-related gene (Atg) Atg7 in adult mice (Atg7Δ/Δ) causes tissue damage and death within 3 mo due to neurodegeneration without substantial effect on intestine. In contrast, we report here that whole-body conditional deletion of other essential Atg genes Atg5 or Fip200/Atg17 in adult mice (Atg5Δ/Δ or Fip200Δ/Δ) caused death within 5 d due to rapid autophagy inhibition, elimination of ileum stem cells, and loss of barrier function. Atg5Δ/Δ mice lost PDGFRα+ mesenchymal cells (PMCs) and Wnt signaling essential for stem cell renewal, which were partially rescued by exogenous Wnt. Matrix-assisted laser desorption ionization coupled to mass spectrometry imaging (MALDI-MSI) of Atg5Δ/Δ ileum revealed depletion of aspartate and nucleotides, consistent with metabolic insufficiency underlying PMC loss. The difference in the autophagy gene knockout phenotypes is likely due to distinct kinetics of autophagy loss, as deletion of Atg5 more gradually extended lifespan phenocopying deletion of Atg7 or Atg12. Thus, autophagy is required for PMC metabolism and ileum stem cell and mammalian survival. Failure to maintain PMCs through autophagy may therefore contribute to IBD.

Negative Modulation of Macroautophagy by Stabilized HERPUD1 is Counteracted by an Increased ER-Lysosomal Network With Impact in Drug-Induced Stress Cell Survival

Macroautophagy and the ubiquitin proteasome system work as an interconnected network in the maintenance of cellular homeostasis. Indeed, efficient activation of macroautophagy upon nutritional deprivation is sustained by degradation of preexisting proteins by the proteasome. However, the specific substrates that are degraded by the proteasome in order to activate macroautophagy are currently unknown. By quantitative proteomic analysis we identified several proteins downregulated in response to starvation independently of ATG5 expression. Among them, the most significant was HERPUD1, an ER membrane protein with low expression and known to be degraded by the proteasome under normal conditions. Contrary, under ER stress, levels of HERPUD1 increased rapidly due to a blockage in its proteasomal degradation. Thus, we explored whether HERPUD1 stability could work as a negative regulator of autophagy. In this work, we expressed a version of HERPUD1 with its ubiquitin-like domain (UBL) deleted, which is known to be crucial for its proteasome degradation. In comparison to HERPUD1-WT, we found the UBL-deleted version caused a negative role on basal and induced macroautophagy. Unexpectedly, we found stabilized HERPUD1 promotes ER remodeling independent of unfolded protein response activation observing an increase in stacked-tubular structures resembling previously described tubular ER rearrangements. Importantly, a phosphomimetic S59D mutation within the UBL mimics the phenotype observed with the UBL-deleted version including an increase in HERPUD1 stability and ER remodeling together with a negative role on autophagy. Moreover, we found UBL-deleted version and HERPUD1-S59D trigger an increase in cellular size, whereas HERPUD1-S59D also causes an increased in nuclear size. Interestingly, ER remodeling by the deletion of the UBL and the phosphomimetic S59D version led to an increase in the number and function of lysosomes. In addition, the UBL-deleted version and phosphomimetic S59D version established a tight ER-lysosomal network with the presence of extended patches of ER-lysosomal membrane-contact sites condition that reveals an increase of cell survival under stress conditions. Altogether, we propose stabilized HERPUD1 downregulates macroautophagy favoring instead a closed interplay between the ER and lysosomes with consequences in drug-cell stress survival.

Autophagy: a multifaceted player in the fate of sperm

BACKGROUND

Autophagy is an intracellular catabolic process of degrading and recycling proteins and organelles to modulate various physiological and pathological events, including cell differentiation and development. Emerging data indicate that autophagy is closely associated with male reproduction, especially the biosynthetic and catabolic processes of sperm. Throughout the fate of sperm, a series of highly specialized cellular events occur, involving pre-testicular, testicular and post-testicular events. Nonetheless, the most fundamental question of whether autophagy plays a protective or harmful role in male reproduction, especially in sperm, remains unclear.

OBJECTIVE AND RATIONALE

We summarize the functional roles of autophagy in the pre-testicular (hypothalamic–pituitary–testis (HPG) axis), testicular (spermatocytogenesis, spermatidogenesis, spermiogenesis, spermiation) and post-testicular (sperm maturation and fertilization) processes according to the timeline of sperm fate. Additionally, critical mechanisms of the action and clinical impacts of autophagy on sperm are identified, laying the foundation for the treatment of male infertility.

SEARCH METHODS

In this narrative review, the PubMed database was used to search peer-reviewed publications for summarizing the functional roles of autophagy in the fate of sperm using the following terms: ‘autophagy’, ‘sperm’, ‘hypothalamic–pituitary–testis axis’, ‘spermatogenesis’, ‘spermatocytogenesis’, ‘spermatidogenesis’, ‘spermiogenesis’, ‘spermiation’, ‘sperm maturation’, ‘fertilization’, ‘capacitation’ and ‘acrosome’ in combination with autophagy-related proteins. We also performed a bibliographic search for the clinical impact of the autophagy process using the keywords of autophagy inhibitors such as ‘bafilomycin A1’, ‘chloroquine’, ‘hydroxychloroquine’, ‘3-Methyl Adenine (3-MA)’, ‘lucanthone’, ‘wortmannin’ and autophagy activators such as ‘rapamycin’, ‘perifosine’, ‘metformin’ in combination with ‘disease’, ‘treatment’, ‘therapy’, ‘male infertility’ and equivalent terms. In addition, reference lists of primary and review articles were reviewed for additional relevant publications. All relevant publications until August 2021 were critically evaluated and discussed on the basis of relevance, quality and timelines.

OUTCOMES

(i) In pre-testicular processes, autophagy-related genes are involved in the regulation of the HPG axis; and (ii) in testicular processes, mTORC1, the main gate to autophagy, is crucial for spermatogonia stem cell (SCCs) proliferation, differentiation, meiotic progression, inactivation of sex chromosomes and spermiogenesis. During spermatidogenesis, autophagy maintains haploid round spermatid chromatoid body homeostasis for differentiation. During spermiogenesis, autophagy participates in acrosome biogenesis, flagella assembly, head shaping and the removal of cytoplasm from elongating spermatid. After spermatogenesis, through PDLIM1, autophagy orchestrates apical ectoplasmic specialization and basal ectoplasmic specialization to handle cytoskeleton assembly, governing spermatid movement and release during spermiation. In post-testicular processes, there is no direct evidence that autophagy participates in the process of capacitation. However, autophagy modulates the acrosome reaction, paternal mitochondria elimination and clearance of membranous organelles during fertilization.

WIDER IMPLICATIONS

Deciphering the roles of autophagy in the entire fate of sperm will provide valuable insights into therapies for diseases, especially male infertility.

Emerging roles of ATG7 in human health and disease

The cardinal stages of macroautophagy are driven by core autophagy-related (ATG) proteins, whose ablation largely abolishes intracellular turnover. Disrupting ATG genes is paradigmatic of studying autophagy deficiency, yet emerging data suggest that ATG proteins have extensive biological importance beyond autophagic elimination. An important example is ATG7, an essential autophagy effector enzyme that in concert with other ATG proteins, also regulates immunity, cell death and protein secretion, and independently regulates the cell cycle and apoptosis. Recently, a direct association between ATG7 dysfunction and disease was established in patients with biallelic ATG7 variants and childhood-onset neuropathology. Moreover, a prodigious body of evidence supports a role for ATG7 in protecting against complex disease states in model organisms, although how dysfunctional ATG7 contributes to manifestation of these diseases, including cancer, neurodegeneration and infection, in humans remains unclear. Here, we systematically review the biological functions of ATG7, discussing the impact of its impairment on signalling pathways and human pathology. Future studies illuminating the molecular relationship between ATG7 dysfunction and disease will expedite therapies for disorders involving ATG7 deficiency and/or impaired autophagy.

The Mechanisms and Management of Age-Related Oxidative Stress in Male Hypogonadism Associated with Non-communicable Chronic Disease

Androgens have diverse functions in muscle physiology, lean body mass, the regulation of adipose tissue, bone density, neurocognitive regulation, and spermatogenesis, the male reproductive and sexual function. Male hypogonadism, characterized by reduced testosterone, is commonly seen in ageing males, and has a complex relationship as a risk factor and a comorbidity in age-related noncommunicable chronic diseases (NCDs), such as obesity, metabolic syndrome, type 2 diabetes, and malignancy. Oxidative stress, as a significant contributor to the ageing process, is a common feature between ageing and NCDs, and the related comorbidities, including hypertension, dyslipidemia, hyperglycemia, hyperinsulinemia, and chronic inflammation. Oxidative stress may also be a mediator of hypogonadism in males. Consequently, the management of oxidative stress may represent a novel therapeutic approach in this context. Therefore, this narrative review aims to discuss the mechanisms of age-related oxidative stress in male hypogonadism associated with NCDs and discusses current and potential approaches for the clinical management of these patients, which may include conventional hormone replacement therapy, nutrition and lifestyle changes, adherence to the optimal body mass index, and dietary antioxidant supplementation and/or phytomedicines.

Cathepsin B Regulates Mice Granulosa Cells' Apoptosis and Proliferation In Vitro

Cathepsin B (CTSB), a lysosomal cysteine protease’s high expression and activity, has been reported to cause poor-quality embryos in porcine and bovine. Nevertheless, CTSB functions in mice granulosa cells remain to explore. To discuss the CTSB functional role in follicular dynamics, we studied apoptosis, proliferation, cell cycle progression, and related signaling pathways in primary mouse granulosa cells transfected with small interference RNA specific to CTSB (siCTSB) for 48 h. Further, mRNA and protein expression of cell proliferation regulators (Myc and cyclin D2), apoptosis regulators (caspase 3, caspase 8, TNF-α, and Bcl2), steroidogenesis-related genes (FSHR and CYP11A1), and autophagy markers (LC3-I and ATG5) were investigated. In addition, the effect of CTSB on steroidogenesis and autophagy was also examined. Flow cytometry analysis assay displayed that silencing of CTSB decreased the early and total apoptosis rate by downregulating TNF-α, caspase 8, and caspase 3, and upregulating Bcl2. By regulating Myc and cyclin D2 expression and activating the p-Akt and p-ERK pathways, CTSB knockdown increased GC proliferation and number. A significant decline in estradiol and progesterone concentrations was observed parallel to a significant decrease in autophagy-related markers LC3-I and ATG5 compared to the control group. Herein, we demonstrated that CTSB serves as a proapoptotic agent and plays a critical role in folliculogenesis in female mice by mediating apoptosis, autophagy, proliferation, and steroidogenesis. Hence, CTSB could be a potential prognostic agent for female infertility.

Autophagy in major human diseases

Autophagy is a core molecular pathway for the preservation of cellular and organismal homeostasis. Pharmacological and genetic interventions impairing autophagy responses promote or aggravate disease in a plethora of experimental models. Consistently, mutations in autophagy-related processes cause severe human pathologies. Here, we review and discuss preclinical data linking autophagy dysfunction to the pathogenesis of major human disorders including cancer as well as cardiovascular, neurodegenerative, metabolic, pulmonary, renal, infectious, musculoskeletal, and ocular disorders.

Metabolome Characteristics of Liver Autophagy Deficiency under Starvation Conditions in Infancy

The liver function is essential for metabolism, detoxification, and bile synthesis, even in the neonatal period. Autophagy plays significance roles in THE adult liver, whereas the role of liver autophagy in the early neonatal period largely remains unclear. To clarify the importance of liver autophagy in the neonatal starvation period, we generated liver-specific autophagy-deficient (Atg5^flox/flox; Albumin-Cre) mice and investigated under starvation conditions comparing with control (Atg5^flox/+; Albumin-Cre) mice, focusing on serum metabolites and liver histopathology. As a result, autophagy in the liver was found to unessential for the survival under postnatal starvation. A metabolomics analysis of serum metabolites by gas chromatography-tandem mass spectrometry showed a significant difference between the groups, especially after 12-h starvation, suggesting the synergistical adaption of metabolic pathways, such as the “malate-aspartate shuttle”, “aspartate metabolism”, “urea cycle”, and “glycine and serine metabolism”. Liver-specific autophagy-deficiency under postnatal starvation conditions can cause a characteristic metabolic alteration suggesting a change of the mitochondrial function. Neonates seemed to maintain ketone production under starvation conditions, even in the autophagy-deficient liver, through a change in the mitochondrial function, which may be an adaptive mechanism for avoiding fatal starvation.

Calcium Signaling Regulates Autophagy and Apoptosis

Calcium (Ca²⁺) functions as a second messenger that is critical in regulating fundamental physiological functions such as cell growth/development, cell survival, neuronal development and/or the maintenance of cellular functions. The coordination among various proteins/pumps/Ca²⁺ channels and Ca²⁺ storage in various organelles is critical in maintaining cytosolic Ca²⁺ levels that provide the spatial resolution needed for cellular homeostasis. An important regulatory aspect of Ca²⁺ homeostasis is a store operated Ca²⁺ entry (SOCE) mechanism that is activated by the depletion of Ca²⁺ from internal ER stores and has gained much attention for influencing functions in both excitable and non-excitable cells. Ca²⁺ has been shown to regulate opposing functions such as autophagy, that promote cell survival; on the other hand, Ca²⁺ also regulates programmed cell death processes such as apoptosis. The functional significance of the TRP/Orai channels has been elaborately studied; however, information on how they can modulate opposing functions and modulate function in excitable and non-excitable cells is limited. Importantly, perturbations in SOCE have been implicated in a spectrum of pathological neurodegenerative conditions. The critical role of autophagy machinery in the pathogenesis of neurodegenerative diseases such as Alzheimer’s, Parkinson’s, and Huntington’s diseases, would presumably unveil avenues for plausible therapeutic interventions for these diseases. We thus review the role of SOCE-regulated Ca²⁺ signaling in modulating these diverse functions in stem cell, immune regulation and neuromodulation.

An autophagic deficit in the uterine vessel microenvironment provokes hyperpermeability through deregulated VEGFA, NOS1, and CTNNB1

The uterus undergoes vascular changes during the reproductive cycle and pregnancy. Steroid hormone deprivation induces macroautophagy/autophagy in major uterine cell types. Herein, we explored the functions of uterine autophagy using the Amhr2-Cre-driven atg7 deletion model. Deletion of Atg7 was confirmed by functional deficit of autophagy in uterine stromal, myometrial, and vascular smooth muscle cells, but not in endothelial cells. atg7d/d uteri exhibited enhanced stromal edema accompanied by dilation of blood vessels. Ovariectomized atg7d/d uteri showed decreased expression of endothelial junction-related proteins, such as CTNNB1/beta-catenin, with increased vascular permeability, and increased expression of VEGFA and NOS1. Nitric oxide (NO) was shown to mediate VEGFA-induced vascular permeability by targeting CTNNB1. NO involvement in maintaining endothelial junctional stability in atg7d/d uteri was confirmed by the reduction in extravasation following treatment with a NOS inhibitor. We also showed that atg7d/d uterine phenotype improved the fetal weight:placental weight ratio, which is one of the indicators of assessing the status of preeclampsia. We showed that autophagic deficit in the uterine vessel microenvironment provokes hyperpermeability through the deregulation of VEGFA, NOS1, and CTNNB1.Abbreviations: ACTA2: actin, alpha 2, smooth muscle, aortic; Amhr2: anti-Mullerian hormone type 2 receptor; ANGPT1: angiopoietin 1; ATG: autophagy-related; CDH5: cadherin 5; CLDN5: claudin 5; COL1A1: collagen, type I, alpha 1; CSPG4/NG2: chondroitin sulfate proteoglycan 4; CTNNB1: catenin (cadherin associated protein), beta 1; DES: desmin; EDN1: endothelin 1; EDNRB: endothelin receptor type B; F3: coagulation factor III; KDR/FLK1/VEGFR2: kinase insert domain protein receptor; LYVE1: lymphatic vessel endothelial hyaluronan receptor 1; MAP1LC3B: microtubule-associated protein 1 light chain 3 beta; MCAM/CD146: melanoma cell adhesion molecule; MYL2: myosin, light polypeptide 2, regulatory, cardiac, slow; MYLK: myosin, light polypeptide kinase; NOS1/nNOS: nitric oxide synthase 1, neuronal; NOS2/iNOS: nitric oxide synthase 2, inducible; NOS3/eNOS: nitric oxide synthase 3, endothelial cell; OVX: ovariectomy; PECAM1/CD31: platelet/endothelial cell adhesion molecule 1; POSTN: periostin, osteoblast specific factor; SQSTM1: sequestosome 1; TEK/Tie2: TEK receptor tyrosine kinase; TJP1/ZO-1: tight junction protein 1; TUBB1, tubulin, beta 1 class VI; USC: uterine stromal cell; VEGFA: vascular endothelial growth factor A; VSMC: vascular smooth muscle cell.

Developmental Consequences of Defective ATG7-Mediated Autophagy in Humans

BACKGROUND

Autophagy is the major intracellular degradation route in mammalian cells. Systemic ablation of core autophagy-related (ATG) genes in mice leads to embryonic or perinatal lethality, and conditional models show neurodegeneration. Impaired autophagy has been associated with a range of complex human diseases, yet congenital autophagy disorders are rare.

METHODS

We performed a genetic, clinical, and neuroimaging analysis involving five families. Mechanistic investigations were conducted with the use of patient-derived fibroblasts, skeletal muscle-biopsy specimens, mouse embryonic fibroblasts, and yeast.

RESULTS

We found deleterious, recessive variants in human ATG7, a core autophagy-related gene encoding a protein that is indispensable to classical degradative autophagy. Twelve patients from five families with distinct ATG7 variants had complex neurodevelopmental disorders with brain, muscle, and endocrine involvement. Patients had abnormalities of the cerebellum and corpus callosum and various degrees of facial dysmorphism. These patients have survived with impaired autophagic flux arising from a diminishment or absence of ATG7 protein. Although autophagic sequestration was markedly reduced, evidence of basal autophagy was readily identified in fibroblasts and skeletal muscle with loss of ATG7. Complementation of different model systems by deleterious ATG7 variants resulted in poor or absent autophagic function as compared with the reintroduction of wild-type ATG7.

CONCLUSIONS

We identified several patients with a neurodevelopmental disorder who have survived with a severe loss or complete absence of ATG7, an essential effector enzyme for autophagy without a known functional paralogue. (Funded by the Wellcome Centre for Mitochondrial Research and others.).

NEK9 regulates primary cilia formation by acting as a selective autophagy adaptor for MYH9/myosin IIA

Autophagy regulates primary cilia formation, but the underlying mechanism is not fully understood. In this study, we identify NIMA-related kinase 9 (NEK9) as a GABARAPs-interacting protein and find that NEK9 and its LC3-interacting region (LIR) are required for primary cilia formation. Mutation in the LIR of NEK9 in mice also impairs in vivo cilia formation in the kidneys. Mechanistically, NEK9 interacts with MYH9 (also known as myosin IIA), which has been implicated in inhibiting ciliogenesis through stabilization of the actin network. MYH9 accumulates in NEK9 LIR mutant cells and mice, and depletion of MYH9 restores ciliogenesis in NEK9 LIR mutant cells. These results suggest that NEK9 regulates ciliogenesis by acting as an autophagy adaptor for MYH9. Given that the LIR in NEK9 is conserved only in land vertebrates, the acquisition of the autophagic regulation of the NEK9–MYH9 axis in ciliogenesis may have possible adaptive implications for terrestrial life.

Ciliogenesis is a tightly regulated process, although the role of selective autophagy is unclear. Here, the authors show NIMA-related kinase 9 controls actin network stabilization and subsequently ciliogenesis by targeting myosin MYH9 for autophagic degradation via GABARAP interaction.

Inflammation, Nitro-Oxidative Stress, Impaired Autophagy, and Insulin Resistance as a Mechanistic Convergence Between Arterial Stiffness and Alzheimer's Disease

The average age of the world's elderly population is steadily increasing. This unprecedented rise in the aged world population will increase the prevalence of age-related disorders such as cardiovascular disease (CVD) and neurodegeneration. In recent years, there has been an increased interest in the potential interplay between CVDs and neurodegenerative syndromes, as several vascular risk factors have been associated with Alzheimer's disease (AD). Along these lines, arterial stiffness is an independent risk factor for both CVD and AD. In this review, we discuss several inflammaging-related disease mechanisms including acute tissue-specific inflammation, nitro-oxidative stress, impaired autophagy, and insulin resistance which may contribute to the proposed synergism between arterial stiffness and AD.

Autophagy and senescence, converging roles in pathophysiology as seen through mouse models

Both senescence and autophagy have been strongly linked to aging and also cancer development. Numerous molecular, cellular, and physiological changes are known to correlate with an increasing age, yet our understanding of what underlies these changes or how they combine to give rise to the various pathologies associated with aging is still unclear. Levels of autophagy activity are known to decrease with advancing age, in a variety of organisms including mammals. Whereas senescent cells are known to accumulate in our bodies with age. Herein we review evidence from some elegant genetic mouse models linking senescence and also autophagy to aging and cancer. It is especially interesting to note the convergence in the pathological phenotypes of these two processes, senescence and autophagy, in these mouse models.

ATG5 in microglia does not contribute vitally to autoimmune neuroinflammation in mice

Microglia, resident myeloid immune cells of the central nervous system (CNS), actively shape the circuitry of the brain, maintain CNS homeostasis during the steady state and orchestrate immune responses upon CNS injury. Both canonical and non-canonical functions of the macroautophagy/autophagy-related protein ATG5 regulate myeloid cell survival and immune responses. Here, we report that loss of ATG5 in postnatal microglia does not perturb CNS tissue integrity, microglial cell survival, or immune activation. Learning task performances were unchanged in mutant mice. Furthermore, lack of ATG5 expression in microglia had no impact on the development of experimental autoimmune encephalomyelitis. These data indicate that, basal autophagy, identified to be essential for the survival and function of neuronal cells, is not required to maintain CNS homeostasis if absent in adult microglia and ATG5 expression is dispensable for the development of autoimmune neuroinflammation.Abbreviations Ag, antigen; APC, antigen presenting cell; ATG/Atg, autophagy-related; CD, cluster of differentiation; CNS, central nervous system; DC, dendritic cell; EAE, experimental autoimmune encephalomyelitis; fl, floxed; LAP, LC3-associated phagocytosis; LC3, microtubule-associated protein 1 light chain 3; MFI, median fluorescence intensity; MHCII, major histocompatibility complex class II; MOG, myelin oligodendrocyte glycoprotein; MS, multiple sclerosis.

Essential role of autophagy in protecting neonatal haematopoietic stem cells from oxidative stress in a p62-independent manner

Autophagy is a cellular degradation system contributing to homeostasis of tissue stem cells including haematopoietic stem cells (HSCs). It plays pleiotropic roles in HSC characteristics throughout life, but its stage-specific roles in HSC self-renewal are unclear. To investigate the effects of Atg5 deletion on stage-specific HSC functions, we compared the repopulating capacity of HSCs in Atg5^f/f;Vavi-cre mice from postnatal day (P) 0-7 weeks of age. Interestingly, Atg5 deficiency led to no remarkable abnormality in the HSC self-renewal capacity at P0, but significant defects at P7, followed by severe defects. Induction of Atg5 deletion at P5 by tamoxifen administration to Atg5^f/f;Rosa26-Cre-ER^T2 mice resulted in normal haematopoiesis, including the HSC population, until around 1 year, suggesting that Atg5 in the early neonatal period was critical for haematopoiesis in adults. Mitochondrial oxidative stress was increased by Atg5 loss in neonatal HSC/progenitor cells. Although p62 had accumulated in immature bone marrow cells of Atg5^f/f;Vavi-cre mice, p62 deletion did not restore defective HSC functions, indicating that Atg5-dependent haematopoietic regulation in the developmental period was independent of p62. This study proposes a critical role of autophagy in HSC protection against harsh environments in the early neonatal stage, which is essential for healthy long-term haematopoiesis.

Spatiotemporal analysis of soluble aggregates and autophagy markers in the R6/2 mouse model

Maintenance of cellular proteostasis is vital for post-mitotic cells like neurons to sustain normal physiological function and homeostasis, defects in which are established hallmarks of several age-related conditions like AD, PD, HD, and ALS. The Spatio-temporal accumulation of aggregated proteins in the form of inclusion bodies/plaques is one of the major characteristics of many neurodegenerative diseases, including Huntington's disease (HD). Toxic accumulation of HUNTINGTIN (HTT) aggregates in neurons bring about the aberrant phenotypes of HD, including severe motor dysfunction, dementia, and cognitive impairment at the organismal level, in an age-dependent manner. In several cellular and animal models, aggrephagy induction has been shown to clear aggregate-prone proteins like HTT and ameliorate disease pathology by conferring neuroprotection. In this study, we used the mouse model of HD, R6/2, to understand the pathogenicity of mHTT aggregates, primarily focusing on autophagy dysfunction. We report that basal autophagy is not altered in R6/2 mice, whilst being functional at a steady-state level in neurons. Moreover, we tested the efficacy of a known autophagy modulator, Nilotinib (Tasigna™), presently in clinical trials for PD, and HD, in curbing mHTT aggregate growth and their potential clearance, which was ineffective in both inducing autophagy and rescuing the pathological phenotypes in R6/2 mice.

Autophagy as a therapeutic target in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is characterised by early metastasis and resistance to anti-cancer therapy, leading to an overall poor prognosis. Despite continued research efforts, no targeted therapy has yet shown meaningful efficacy in PDAC; mutations in the oncogene KRAS and the tumour suppressor TP53, which are the most common genomic alterations in PDAC, have so far shown poor clinical actionability. Autophagy, a conserved process allowing cells to recycle altered or unused organelles and cellular components, has been shown to be upregulated in PDAC and is implicated in resistance to both cytotoxic chemotherapy and targeted therapy. Autophagy is thus regarded as a potential therapeutic target in PDAC and other cancers. Although the molecular mechanisms of autophagy activation in PDAC are only beginning to emerge, several groups have reported interesting results when combining inhibitors of the extracellular-signal-regulated kinase/mitogen-activated protein kinase pathway and inhibitors of autophagy in models of PDAC and other KRAS-driven cancers. In this article, we review the existing preclinical data regarding the role of autophagy in PDAC, as well as results of relevant clinical trials with agents that modulate autophagy in this cancer.

A DNM2 Centronuclear Myopathy Mutation Reveals a Link between Recycling Endosome Scission and Autophagy

Autophagy involves engulfment of cytoplasmic contents by double-membraned autophagosomes, which ultimately fuse with lysosomes to enable degradation of their substrates. We recently proposed that the tubular-vesicular recycling endosome membranes were a core platform on which the critical early events of autophagosome formation occurred, including LC3-membrane conjugation to autophagic precursors. Here, we report that the release of autophagosome precursors from recycling endosomes is mediated by DNM2-dependent scission of these tubules. This process is regulated by DNM2 binding to LC3 and is increased by autophagy-inducing stimuli. This scission is defective in cells expressing a centronuclear-myopathy-causing DNM2 mutant. This mutant has an unusual mechanism as it depletes normal-functioning DNM2 from autophagosome formation sites on recycling endosomes by causing increased binding to an alternative plasma membrane partner, ITSN1. This "scission" step is, thus, critical for autophagosome formation, is defective in a human disease, and influences the way we consider how autophagosomes are formed.

Autophagy in the Regulation of Tissue Differentiation and Homeostasis

Autophagy is a constitutive pathway that allows the lysosomal degradation of damaged components. This conserved process is essential for metabolic plasticity and tissue homeostasis and is crucial for mammalian post-mitotic cells. Autophagy also controls stem cell fate and defective autophagy is involved in many pathophysiological processes. In this review, we focus on established and recent breakthroughs aimed at elucidating the impact of autophagy in differentiation and homeostasis maintenance of endothelium, muscle, immune system, and brain providing a suitable framework of the emerging results and highlighting the pivotal role of autophagic response in tissue functions, stem cell dynamics and differentiation rates.

Placental autophagy failure: A risk factor for preeclampsia

Hypertensive disorders of pregnancy, including preeclampsia, directly affect maternal and perinatal morbidity and mortality. As the pathophysiology of preeclampsia is multi-factorial and has been studied using different approaches, we have demonstrated that impaired autophagy is an intertwined risk factor for preeclampsia. This concept has been verified in both in vitro and in vivo experiments. Autophagy is primarily involved in maintaining cellular homeostasis, and in immune regulation, longevity, cytokines secretion and a variety of other biological functions. Here, we review the role of autophagy in normal embryogenesis and placentation. Once placental autophagy is impaired by metabolic stress such as hypoxia, endoplasmic reticulum stress or starvation, placental development could be disrupted, resulting in functional maladaptations at the maternal-fetal interface. These malfunctions may result in fetal growth restriction or preeclampsia.