A TRP Channel Senses Lysosome Neutralization by Pathogens to Trigger Their Expulsion

Extracellular Vesicles: Recent Insights Into the Interaction Between Host and Pathogenic Bacteria

Extracellular vesicles (EVs) are nanosized lipid particles released by virtually every living cell. EVs carry bioactive molecules, shuttle from cells to cells and transduce signals, regulating cell growth and metabolism. Pathogenic bacteria can cause serious infections via a wide range of strategies, and host immune systems also develop extremely complex adaptations to counteract bacterial infections. As notable carriers, EVs take part in the interaction between the host and bacteria in several approaches. For host cells, several strategies have been developed to resist bacteria via EVs, including expelling damaged membranes and bacteria, neutralizing toxins, triggering innate immune responses and provoking adaptive immune responses in nearly the whole body. For bacteria, EVs function as vehicles to deliver toxins and contribute to immune escape. Due to their crucial functions, EVs have great application potential in vaccines, diagnosis and treatments. In the present review, we highlight the most recent advances, application potential and remaining challenges in understanding EVs in the interaction between the host and bacteria.

Axonal transport of late endosomes and amphisomes is selectively modulated by local Ca2+ efflux and disrupted by PSEN1 loss of function

Dysfunction and mistrafficking of organelles in autophagy- and endosomal-lysosomal pathways are implicated in neurodegenerative diseases. Here, we reveal selective vulnerability of maturing degradative organelles (late endosomes/amphisomes) to disease-relevant local calcium dysregulation. These organelles undergo exclusive retrograde transport in axons, with occasional pauses triggered by regulated calcium efflux from agonist-evoked transient receptor potential cation channel mucolipin subfamily member 1 (TRPML1) channels-an effect greatly exaggerated by exogenous agonist mucolipin synthetic agonist 1 (ML-SA1). Deacidification of degradative organelles, as seen after Presenilin 1 (PSEN1) loss of function, induced pathological constitutive "inside-out" TRPML1 hyperactivation, slowing their transport comparably to ML-SA1 and causing accumulation in dystrophic axons. The mechanism involved calcium-mediated c-Jun N-terminal kinase (JNK) activation, which hyperphosphorylated dynein intermediate chain (DIC), reducing dynein activity. Blocking TRPML1 activation, JNK activity, or DIC1B serine-80 phosphorylation reversed transport deficits in PSEN1 knockout neurons. Our results, including features demonstrated in Alzheimer-mutant PSEN1 knockin mice, define a mechanism linking dysfunction and mistrafficking in lysosomal pathways to neuritic dystrophy under neurodegenerative conditions.

PITing it forward: A new link in the journey of uropathogenic E. coli in the urothelium

Urinary tract infections (UTIs) are a cause for alarm given the high rates of treatment failure. In a recent issue of Cell Reports, Pang et al. uncovered dueling molecular machinery at the host-pathogen interface in response to phosphate that points to new anti-infective strategies against UTIs.

Tissue Immunity in the Bladder

The bladder is a major component of the urinary tract, an organ system that expels metabolic waste and excess water, which necessitates proximity to the external environment and its pathogens. It also houses a commensal microbiome. Therefore, its tissue immunity must resist pathogen invasion while maintaining tolerance to commensals. Bacterial infection of the bladder is common, with half of women globally experiencing one or more episodes of cystitis in their lifetime. Despite this, our knowledge of bladder immunity, particularly in humans, is incomplete. Here we consider the current view of tissue immunity in the bladder, with a focus on defense against infection. The urothelium has robust immune functionality, and its defensive capabilities are supported by resident immune cells, including macrophages, dendritic cells, natural killer cells, and γδ T cells. We discuss each in turn and consider why adaptive immune responses are often ineffective in preventing recurrent infection, as well as areas of priority for future research.

Bladder epithelial cell phosphate transporter inhibition protects mice against uropathogenic Escherichia coli infection

Urinary tract infections are predominantly caused by uropathogenic Escherichia coli (UPEC). UPEC infects bladder epithelial cells (BECs) via fusiform vesicles, escapes into the cytosol to evade exocytosis, and establishes intracellular bacterial communities (IBCs) for the next round of infection. The UPEC vesicle escape mechanism remains unclear. Here we show that UPEC senses host immune responses and initiates escape by upregulating a key phospholipase. The UPEC phospholipase PldA disrupts the vesicle membrane, and pldA expression is activated by phosphate reduction in vesicles. The host phosphate transporter PIT1 is located on the fusiform vesicle membrane, transporting phosphate into the cytosol. UPEC infection upregulates PIT1 via nuclear factor κB (NF-κB), resulting in phosphate reduction. Silencing PIT1 blocks UPEC vesicle escape in BECs, inhibits IBC formation in mouse bladders, and protects mice from UPEC infection. Our results shed light on pathogenic bacteria responding to intracellular phosphate shortage and tackling host defense and provide insights for development of new therapeutic agents to treat UPEC infection.

Activation of TRPV4 Induces Exocytosis and Ferroptosis in Human Melanoma Cells

TRPV4 (transient receptor potential vanilloid 4), a calcium permeable TRP ion channel, is known to play a key role in endocytosis. However, whether it contributes to exocytosis remains unclear. Here, we report that activation of TRPV4 induced massive exocytosis in both melanoma A375 cell and heterologous expression systems. We show here that, upon application of TRPV4-specific agonists, prominent vesicle priming from endoplasmic reticulum (ER) was observed, followed by morphological changes of mitochondrial crista may lead to cell ferroptosis. We further identified interactions between TRPV4 and folding/vesicle trafficking proteins, which were triggered by calcium entry through activated TRPV4. This interplay, in turn, enhanced TRPV4-mediated activation of folding and vesicle trafficking proteins to promote exocytosis. Our study revealed a signaling mechanism underlying stimulus-triggered exocytosis in melanoma and highlighted the role of cellular sensor TRPV4 ion channel in mediating ferroptosis.

Endolysosomal cation channels point the way towards precision medicine of cancer and infectious diseases

Infectious diseases and cancer are among the key medical challenges that humankind is facing today. A growing amount of evidence suggests that ion channels in the endolysosomal system play a crucial role in the pathology of both groups of diseases. The development of advanced patch-clamp technologies has allowed us to directly characterize ion fluxes through endolysosomal ion channels in their native environments. Endolysosomes are essential organelles for intracellular transport, digestion and metabolism, and maintenance of homeostasis. The endolysosomal ion channels regulate the function of the endolysosomal system through four basic mechanisms: calcium release, control of membrane potential, pH change, and osmolarity regulation. In this review, we put particular emphasis on the endolysosomal cation channels, including TPC2 and TRPML2, which are particularly important in monocyte function. We discuss existing endogenous and synthetic ligands of these channels and summarize current knowledge of their impact on channel activity and function in different cell types. Moreover, we summarize recent findings on the importance of TPC2 and TRPML2 channels as potential drug targets for the prevention and treatment of the emerging infectious diseases and cancer.

Whole Endosome Recording of Vesicular Neurotransmitter Transporter Currents

The analysis of organellar membrane transporters presents many technical problems. In general, their activity depends on a H⁺ electrochemical driving force (Δμ_H+). However, transport itself influences the expression of Δμ_H+ in standard radiotracer flux assays, making it difficult to disentangle the role of the chemical component ΔpH and the membrane potential Δψ. Whole endosome recording in voltage clamp circumvents many of these problems, controlling ionic conditions as well as membrane potential inside and outside the organelle . This approach has been used primarily to study the properties of endolysosomal channels, which generate substantial currents (Saito et al., J Biol Chem 282(37):27327-27333, 2007; Cang et al., Nat Chem Biol 10(6):463-469, 2014; Cang et al., Cell 152(4):778-790, 2013; Chen et al., Nat Protoc 12(8):1639-1658, 2017; Samie et al., Dev Cell 26(5):511-524, 2013; Wang et al., Cell 151(2):372-383, 2012). Electrogenic transport produces much smaller currents, but we have recently reported the detection of transport currents and an uncoupled Cl^- conductance associated with the vesicular glutamate transporters (VGLUTs) that fill synaptic vesicles with glutamate (Chang et al., eLife 7:e34896, 2018). In this protocol, we will focus on the measurement of transport currents on enlarged endosomes of heterologous mammalian cells.

Cu-based nanoparticle toxicity to zebrafish cells regulated by cellular discharges

Cellular transport of metal nanoparticles (NPs) is critical in determining their potential toxicity, but the transformation of metal ions released from the internalized NPs is largely unknown. Cu-based NPs are the only metallic-based NPs that are reported to induce higher toxicity compared with their corresponding ions, likely due to their unique cellular turnover. In the present study, we developed a novel gold core to differentiate the particulate and ionic Cu in the Cu₂O microparticles (MPs), and the kinetics of bioaccumulation, exocytosis, and cytotoxicity of Au@Cu₂O MPs to zebrafish embryonic cells were subsequently studied. We demonstrated that the internalized MPs were rapidly dissolved to Cu ions, which then undergo lysosome-mediated exocytosis. The uptake rate of smaller MPs (130 nm) was lower than that of larger ones (200 nm), but smaller MPs were dissolved much quickly in cells and therefore activated the exocytosis more quickly. The rapid release of Cu ions resulted in an immediate toxic action of Cu₂O MPs, while the cell deaths mainly occurred by necrosis. During this process, the buffering ability of glutathione greatly alleviated the Cu toxicity. Therefore, although the turnover of intracellular Cu at a sublethal exposure level was hundred times faster than the basal values, labile Cu(I) concentration increased by only 2 times at most. Overall, this work provided new insights into the toxicity of copper NPs, suggesting that tolerance to Cu-based NPs depended on their ability to discharge the released Cu ions.

Structural biology of cation channels important for lysosomal calcium release

Calcium is one of the most important second messengers in cells. The uptake and release of calcium ions are conducted by channels and transporters. Inside a eukaryotic cell, calcium is stored in intracellular organelles including the endoplasmic reticulum (ER), mitochondrion, and lysosome. Lysosomes are acid membrane-bounded organelles serving as the crucial degradation and recycling center of the cell. Lysosomes involve in multiple important signaling events, including nutrient sensing, lipid metabolism, and trafficking. Hitherto, two lysosomal cation channel families have been suggested to function as calcium release channels, namely the Two-pore Channel (TPC) family, and the Transient Receptor Potential Channel Mucolipin (TRPML) family. Additionally, a few plasma membrane calcium channels have also been found in the lysosomal membrane under certain circumstances. In this review, we will discuss the structural mechanism of the cation channels that may be important for lysosomal calcium release, primarily focusing on the TPCs and TRPMLs.

Channels and Transporters of the Pulmonary Lamellar Body in Health and Disease

The lamellar body (LB) of the alveolar type II (ATII) cell is a lysosome-related organelle (LRO) that contains surfactant, a complex mix of mainly lipids and specific surfactant proteins. The major function of surfactant in the lung is the reduction of surface tension and stabilization of alveoli during respiration. Its lack or deficiency may cause various forms of respiratory distress syndrome (RDS). Surfactant is also part of the innate immune system in the lung, defending the organism against air-borne pathogens. The limiting (organelle) membrane that encloses the LB contains various transporters that are in part responsible for translocating lipids and other organic material into the LB. On the other hand, this membrane contains ion transporters and channels that maintain a specific internal ion composition including the acidic pH of about 5. Furthermore, P2X4 receptors, ligand gated ion channels of the danger signal ATP, are expressed in the limiting LB membrane. They play a role in boosting surfactant secretion and fluid clearance. In this review, we discuss the functions of these transporting pathways of the LB, including possible roles in disease and as therapeutic targets, including viral infections such as SARS-CoV-2.

ORF3a of SARS-CoV-2 promotes lysosomal exocytosis-mediated viral egress

Viral entry and egress are important determinants of virus infectivity and pathogenicity. β-coronaviruses, including the COVID-19 virus SARS-CoV-2 and mouse hepatitis virus (MHV), exploit the lysosomal exocytosis pathway for egress. Here, we show that SARS-CoV-2 ORF3a, but not SARS-CoV ORF3a, promotes lysosomal exocytosis. SARS-CoV-2 ORF3a facilitates lysosomal targeting of the BORC-ARL8b complex, which mediates trafficking of lysosomes to the vicinity of the plasma membrane, and exocytosis-related SNARE proteins. The Ca²⁺ channel TRPML3 is required for SARS-CoV-2 ORF3a-mediated lysosomal exocytosis. Expression of SARS-CoV-2 ORF3a greatly elevates extracellular viral release in cells infected with the coronavirus MHV-A59, which itself lacks ORF3a. In SARS-CoV-2 ORF3a, Ser171 and Trp193 are critical for promoting lysosomal exocytosis and blocking autophagy. When these residues are introduced into SARS-CoV ORF3a, it acquires the ability to promote lysosomal exocytosis and inhibit autophagy. Our results reveal a mechanism by which SARS-CoV-2 interacts with host factors to promote its extracellular egress.

Apoptosis, Pyroptosis, and Necroptosis-Oh My! The Many Ways a Cell Can Die

Cell death is an essential process in all living organisms and occurs through different mechanisms. The three main types of programmed cell death are apoptosis, pyroptosis, and necroptosis, and each of these pathways employs complex molecular and cellular mechanisms. Although there are mechanisms and outcomes specific to each pathway, they share common components and features. In this review, we discuss recent discoveries in these three best understood modes of cell death, highlighting their singularities, and examining the intriguing notion that common players shape different individual pathways in this highly interconnected and coordinated cell death system. Understanding the similarities and differences of these cell death processes is crucial to enable targeted strategies to manipulate these pathways for therapeutic benefit.

NRF2 promotes urothelial cell response to bacterial infection by regulating reactive oxygen species and RAB27B expression

Uropathogenic Escherichia coli (UPEC) cause urinary tract infections (UTIs) by invading urothelial cells. In response, the host mounts an inflammatory response to expel bacteria. Here, we show that the NF-E2-related factor 2 (NRF2) pathway is activated in response to UPEC-triggered reactive oxygen species (ROS) production. We demonstrate the molecular sequence of events wherein NRF2 activation in urothelial cells reduces ROS production, inflammation, and cell death, promotes UPEC expulsion, and reduces the bacterial load. In contrast, loss of NRF2 leads to increased ROS production, bacterial burden, and inflammation, both in vitro and in vivo. NRF2 promotes UPEC expulsion by regulating transcription of the RAB-GTPase RAB27B. Finally, dimethyl fumarate, a US Food and Administration-approved NRF2 inducer, reduces the inflammatory response, increases RAB27B expression, and lowers bacterial burden in urothelial cells and in a mouse UTI model. Our findings elucidate mechanisms underlying the host response to UPEC and provide a potential strategy to combat UTIs.

Friends and foes: Extracellular vesicles in aging and rejuvenation

Extracellular vesicles (EVs) are released by many different cell types throughout the body and play a role in a diverse range of biological processes. EVs circulating in blood as well as in other body fluids undergo dramatic alterations over an organism's lifespan that are only beginning to be elucidated. The exact nature of these changes is an area of active and intense investigation, but lacks clear consensus due to the substantial heterogeneity in EV subpopulations and insufficiencies in current technologies. Nonetheless, emerging evidence suggests that EVs regulate systemic aging as well as the pathophysiology of age-related diseases. Here, we review the current literature investigating EVs and aging with an emphasis on consequences for the maintenance of human healthspan. Intriguingly, the biological utility of EVs both in vitro and in vivo and across contexts depends on the states of the source cells or tissues. As such, EVs secreted by cells in an aged or pathological state may impose detrimental consequences on recipient cells, while EVs secreted by youthful or healthy cells may promote functional improvement. Thus, it is critical to understand both functions of EVs and tip the balance toward their beneficial effects as an antiaging intervention.

Metformin strengthens uroepithelial immunity against E. coli infection

Urinary tract infection frequently caused by E. coli is one of the most common bacterial infections. Increasing antibiotic resistance jeopardizes successful treatment and alternative treatment strategies are therefore mandatory. Metformin, an oral antidiabetic drug, has been shown to activate macrophages in the protection against certain infecting microorganisms. Since epithelial cells often form the first line of defense, we here investigated the effect on uroepithelial cells during E. coli infection. Metformin upregulated the human antimicrobial peptides cathelicidin LL-37 and RNase7 via modulation of the TRPA1 channel and AMPK pathway. Interestingly, metformin stimulation enriched both LL-37 and TRPA1 in lysosomes. In addition, metformin specifically increased nitric oxide and mitochondrial, but not cytosolic ROS. Moreover, metformin also triggered mRNA expression of the proinflammatory cytokines IL1B, CXCL8 and growth factor GDF15 in human uroepithelial cells. The GDF15 peptide stimulated macrophages increased LL-37 expression, with increased bacterial killing. In conclusion, metformin stimulation strengthened the innate immunity of uroepithelial cells inducing enhanced extracellular and intracellular bacterial killing suggesting a favorable role of metformin in the host defense.

Porcine Hemagglutinating Encephalomyelitis Virus Triggers Neural Autophagy Independently of ULK1

Uncoordinated 51-like kinase 1 (ULK1) is a well-characterized initiator of canonical autophagy under basal or pathological conditions. Porcine hemagglutinating encephalomyelitis virus (PHEV), a neurotropic betacoronavirus (β-CoV), impairs ULK1 kinase but hijacks autophagy to facilitate viral proliferation. However, the machinery of PHEV-induced autophagy initiation upon ULK1 kinase deficiency remains unclear. Here, the time course of PHEV infection showed a significant accumulation of autophagosomes (APs) in nerve cells in vivo and in vitro. Utilizing ULK1-knockout neuroblastoma cells, we have identified that ULK1 is not essential for productive AP formation induced by PHEV. In vitro phosphorylation studies discovered that mTORC1-regulated ULK1 activation stalls during PHEV infection, whereas AP biogenesis was controlled by AMPK-driven BECN1 phosphorylation. A lack of BECN1 is sufficient to block LC3 lipidation and disrupt recruitment of the LC3-ATG14 complex. Moreover, BECN1 acts as a bona fide substrate for ULK1-independent neural autophagy, and ectopic expression of BECN1 somewhat enhances PHEV replication. These findings highlight a novel machinery of noncanonical autophagy independent of ULK1 that bypasses the conserved initiation circuit of AMPK-mTORC1-ULK1, providing new insights into the interplay between neurotropic β-CoV and the host. IMPORTANCE The ongoing coronavirus disease 2019 (COVID-19) pandemic alongside the outbreaks of severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) pose Betacoronavirus (β-CoV) as a global public health challenge. Coronaviruses subvert, hijack, or utilize autophagy to promote proliferation, and thus, exploring the cross talk between β-CoV and autophagy is of great significance in confronting future β-CoV outbreaks. Porcine hemagglutinating encephalomyelitis virus (PHEV) is a highly neurotropic β-CoV that invades the central nervous system (CNS) in pigs, but understanding of the pathogenesis for PHEV-induced neurological dysfunction is yet limited. Here, we discovered a novel regulatory principle of neural autophagy initiation during PHEV infection, where productive autophagosome (AP) biogenesis bypasses the multifaceted regulation of ULK1 kinase. The PHEV-triggered noncanonical autophagy underscores the complex interactions of virus and host and will help in the development of therapeutic strategies targeting noncanonical autophagy to treat β-CoV disease.

CNS-infecting pathogens Escherichia coli and Cryptococcus neoformans exploit the host Pdlim2 for intracellular traversal and exocytosis in the blood-brain barrier

Microbial penetration of the blood-brain barrier, a prerequisite for development of the central nervous system (CNS) infection, involves microbial invasion, intracellular traversal and exocytosis. Microbial invasion of the blood-brain barrier has been investigated, but the molecular basis for microbial traversal and exit from the blood-brain barrier remains unknown. We performed transcriptome analysis of the human brain microvascular endothelial cell (HBMEC) infected with Escherichia coli and Cryptococcus neoformans, representative bacterial and fungal pathogens common in CNS infection. Among the upregulated targets in response to E. coli and C. neoformans infection, PDLIM2 was knocked down by shRNA in HBMEC for further investigation. We demonstrated that Pdlim2 specifically regulated the microbial traversal and exit from HBMEC by assessing microbial invasion, transcytosis, intracellular multiplication and egression. Additionally, the defective exocytosis of internalized E. coli from the PDLIM2 shRNA knockdown cell was restored by treatment with a calcium ionophore (ionomycin). Moreover, we performed the proximity-dependent biotin labeling with the biotin ligase BioID2 and identified 210 potential Pdlim2-interactors. Among the nine enriched Pdlim2-interactors in response to both E. coli and C. neoformans infection, we selected MPRIP and showed that HBMEC with knockdown of MPRIP mimicked the phenotype of PDLIM2 knockdown cell. These results suggest that the CNS-infecting microbes hijack Pdlim2 and Mprip for intracellular traversal and exocytosis in the blood-brain barrier.

Recurrent Urinary Tract Infection: A Mystery in Search of Better Model Systems

Urinary tract infections (UTIs) are among the most common infectious diseases worldwide but are significantly understudied. Uropathogenic E. coli (UPEC) accounts for a significant proportion of UTI, but a large number of other species can infect the urinary tract, each of which will have unique host-pathogen interactions with the bladder environment. Given the substantial economic burden of UTI and its increasing antibiotic resistance, there is an urgent need to better understand UTI pathophysiology - especially its tendency to relapse and recur. Most models developed to date use murine infection; few human-relevant models exist. Of these, the majority of in vitro UTI models have utilized cells in static culture, but UTI needs to be studied in the context of the unique aspects of the bladder's biophysical environment (e.g., tissue architecture, urine, fluid flow, and stretch). In this review, we summarize the complexities of recurrent UTI, critically assess current infection models and discuss potential improvements. More advanced human cell-based in vitro models have the potential to enable a better understanding of the etiology of UTI disease and to provide a complementary platform alongside animals for drug screening and the search for better treatments.

Autophagy as a Target for Drug Development Of Skin Infection Caused by Mycobacteria

Pathogenic mycobacteria species may subvert the innate immune mechanisms and can modulate the activation of cells that cause disease in the skin. Cutaneous mycobacterial infection may present different clinical presentations and it is associated with stigma, deformity, and disability. The understanding of the immunopathogenic mechanisms related to mycobacterial infection in human skin is of pivotal importance to identify targets for new therapeutic strategies. The occurrence of reactional episodes and relapse in leprosy patients, the emergence of resistant mycobacteria strains, and the absence of effective drugs to treat mycobacterial cutaneous infection increased the interest in the development of therapies based on repurposed drugs against mycobacteria. The mechanism of action of many of these therapies evaluated is linked to the activation of autophagy. Autophagy is an evolutionary conserved lysosomal degradation pathway that has been associated with the control of the mycobacterial bacillary load. Here, we review the role of autophagy in the pathogenesis of cutaneous mycobacterial infection and discuss the perspectives of autophagy as a target for drug development and repurposing against cutaneous mycobacterial infection.

An infection-induced RhoB-Beclin 1-Hsp90 complex enhances clearance of uropathogenic Escherichia coli

Host cells use several anti-bacterial pathways to defend against pathogens. Here, using a uropathogenic Escherichia coli (UPEC) infection model, we demonstrate that bacterial infection upregulates RhoB, which subsequently promotes intracellular bacteria clearance by inducing LC3 lipidation and autophagosome formation. RhoB binds with Beclin 1 through its residues at 118 to 140 and the Beclin 1 CCD domain, with RhoB Arg133 being the key binding residue. Binding of RhoB to Beclin 1 enhances the Hsp90-Beclin 1 interaction, preventing Beclin 1 degradation. RhoB also directly interacts with Hsp90, maintaining RhoB levels. UPEC infections increase RhoB, Beclin 1 and LC3 levels in bladder epithelium in vivo, whereas Beclin 1 and LC3 levels as well as UPEC clearance are substantially reduced in RhoB^+/− and RhoB^−/− mice upon infection. We conclude that when stimulated by UPEC infections, host cells promote UPEC clearance through the RhoB-Beclin 1-HSP90 complex, indicating RhoB may be a useful target when developing UPEC treatment strategies.

Bacterial invasion can lead to multiple host cell responses. Here, the authors show that in a model of uropathogenic E. coli, RhoB is upregulated and induces autophagosome formation in a complex with Beclin1 and Hsp90, promoting bacterial clearance.

Necroptosis, pyroptosis and apoptosis: an intricate game of cell death

Cell death is a fundamental physiological process in all living organisms. Its roles extend from embryonic development, organ maintenance, and aging to the coordination of immune responses and autoimmunity. In recent years, our understanding of the mechanisms orchestrating cellular death and its consequences on immunity and homeostasis has increased substantially. Different modalities of what has become known as 'programmed cell death' have been described, and some key players in these processes have been identified. We have learned more about the intricacies that fine tune the activity of common players and ultimately shape the different types of cell death. These studies have highlighted the complex mechanisms tipping the balance between different cell fates. Here, we summarize the latest discoveries in the three most well understood modalities of cell death, namely, apoptosis, necroptosis, and pyroptosis, highlighting common and unique pathways and their effect on the surrounding cells and the organism as a whole.

Life in the lumen: The multivesicular endosome

The late endosomes/endo‐lysosomes of vertebrates contain an atypical phospholipid, lysobisphosphatidic acid (LBPA) (also termed bis[monoacylglycero]phosphate [BMP]), which is not detected elsewhere in the cell. LBPA is abundant in the membrane system present in the lumen of this compartment, including intralumenal vesicles (ILVs). In this review, the current knowledge on LBPA and LBPA‐containing membranes will be summarized, and their role in the control of endosomal cholesterol will be outlined. Some speculations will also be made on how this system may be overwhelmed in the cholesterol storage disorder Niemann‐Pick C. Then, the roles of intralumenal membranes in endo‐lysosomal dynamics and functions will be discussed in broader terms. Likewise, the mechanisms that drive the biogenesis of intralumenal membranes, including ESCRTs, will also be discussed, as well as their diverse composition and fate, including degradation in lysosomes and secretion as exosomes. This review will also discuss how intralumenal membranes are hijacked by pathogenic agents during intoxication and infection, and what is the biochemical composition and function of the intra‐endosomal lumenal milieu. Finally, this review will allude to the size limitations imposed on intralumenal vesicle functions and speculate on the possible role of LBPA as calcium chelator in the acidic calcium stores of endo‐lysosomes.

Choreographing endo-lysosomal Ca2+ throughout the life of a phagosome

The emergence of endo-lysosomes as ubiquitous Ca²⁺ stores with their unique cohort of channels has resulted in their being implicated in a growing number of processes in an ever-increasing number of cell types. The architectural and regulatory constraints of these acidic Ca²⁺ stores distinguishes them from other larger Ca²⁺ sources such as the ER and influx across the plasma membrane. In view of recent advances in the understanding of the modes of operation, we discuss phagocytosis as a template for how endo-lysosomal Ca²⁺ signals (generated via TPC and TRPML channels) can be integrated in multiple sophisticated ways into biological processes. Phagocytosis illustrates how different endo-lysosomal Ca²⁺ signals drive different phases of a process, and how these can be altered by disease or infection.

Extracellular vesicles in kidneys and their clinical potential in renal diseases

Extracellular vesicles (EVs), such as exosomes and microvesicles, are cell-derived lipid bilayer membrane particles, which deliver information from host cells to recipient cells. EVs are involved in various biological processes including the modulation of the immune response, cell-to-cell communications, thrombosis, and tissue regeneration. Different types of kidney cells are known to release EVs under physiologic as well as pathologic conditions, and recent studies have found that EVs have a pathophysiologic role in different renal diseases. Given the recent advancement in EV isolation and analysis techniques, many studies have shown the diagnostic and therapeutic potential of EVs in various renal diseases, such as acute kidney injury, polycystic kidney disease, chronic kidney disease, kidney transplantation, and renal cell carcinoma. This review updates recent clinical and experimental findings on the role of EVs in renal diseases and highlights the potential clinical applicability of EVs as novel diagnostics and therapeutics.

Centrosome amplification mediates small extracellular vesicle secretion via lysosome disruption

Bidirectional communication between cells and their surrounding environment is critical in both normal and pathological settings. Extracellular vesicles (EVs), which facilitate the horizontal transfer of molecules between cells, are recognized as an important constituent of cell-cell communication. In cancer, alterations in EV secretion contribute to the growth and metastasis of tumor cells. However, the mechanisms underlying these changes remain largely unknown. Here, we show that centrosome amplification is associated with and sufficient to promote small extracellular vesicle (SEV) secretion in pancreatic cancer cells. This is a direct result of lysosomal dysfunction, caused by increased reactive oxygen species (ROS) downstream of extra centrosomes. We propose that defects in lysosome function could promote multivesicular body fusion with the plasma membrane, thereby enhancing SEV secretion. Furthermore, we find that SEVs secreted in response to amplified centrosomes are functionally distinct and activate pancreatic stellate cells (PSCs). These activated PSCs promote the invasion of pancreatic cancer cells in heterotypic 3D cultures. We propose that SEVs secreted by cancer cells with amplified centrosomes influence the bidirectional communication between the tumor cells and the surrounding stroma to promote malignancy.

Anaplasmataceae: Dichotomous Autophagic Interplay for Infection

Autophagy is a vital conserved degradative process that maintains cellular homeostasis by recycling or eliminating dysfunctional cellular organelles and proteins. More recently, autophagy has become a well-recognized host defense mechanism against intracellular pathogens through a process known as xenophagy. On the host-microbe battlefield many intracellular bacterial pathogens have developed the ability to subvert xenophagy to establish infection. Obligately intracellular bacterial pathogens of the Anaplasmataceae family, including Ehrlichia chaffeensis, Anaplasma phaogocytophilium and Orientia tsutsugamushi have developed a dichotomous strategy to exploit the host autophagic pathway to obtain nutrients while escaping lysosomal destruction for intracellular survival within the host cell. In this review, the recent findings regarding how these master manipulators engage and inhibit autophagy for infection are explored. Future investigation to understand mechanisms used by Anaplasmataceae to exploit autophagy may advance novel antimicrobial therapies and provide new insights into how intracellular microbes exploit autophagy to survive.

Sex Differences in Population Dynamics during Formation of Kidney Bacterial Communities by Uropathogenic Escherichia coli

Uropathogenic Escherichia coli (UPEC), the primary etiologic agent of urinary tract infections (UTIs), encounters a restrictive population bottleneck within the female mammalian bladder. Its genetic diversity is restricted during establishment of cystitis because successful UPEC must invade superficial bladder epithelial cells prior to forming clonal intracellular bacterial communities (IBCs). In this study, we aimed to understand UPEC population dynamics during ascending pyelonephritis, namely, formation of kidney bacterial communities (KBCs) in the renal tubular lumen and nucleation of renal abscesses. We inoculated the bladders of both male and female C3H/HeN mice, a background which features vesicoureteral reflux; we have previously shown that in this model, males develop severe, high-titer pyelonephritis and renal abscesses much more frequently than females. Mice were infected with 40 isogenic, PCR-tagged ("barcoded") UPEC strains, and tags remaining in bladder and kidneys were ascertained at intervals following infection. In contrast to females, males maintained a majority of strains within both the bladder and kidneys throughout the course of infection, indicating only a modest host-imposed bottleneck on overall population diversity during successful renal infection. Moreover, the diverse population in the infected male kidneys obscured any restrictive bottleneck in the male bladder. Finally, using RNA in situ hybridization following mixed infections with isogenic UPEC bearing distinct markers, we found that despite their extracellular location (in the urinary space), KBCs are clonal in origin. This finding indicates that even with bulk reflux of infected bladder urine into the renal pelvis, successful ascension of UPEC to establish the tubular niche is an uncommon event.

Unstructural Biology of TRP Ion Channels: The Role of Intrinsically Disordered Regions in Channel Function and Regulation

The first genuine high-resolution single particle cryo-electron microscopy structure of a membrane protein determined was a transient receptor potential (TRP) ion channel, TRPV1, in 2013. This methodical breakthrough opened up a whole new world for structural biology and ion channel aficionados alike. TRP channels capture the imagination due to the sheer endless number of tasks they carry out in all aspects of animal physiology. To date, structures of at least one representative member of each of the six mammalian TRP channel subfamilies as well as of a few non-mammalian families have been determined. These structures were instrumental for a better understanding of TRP channel function and regulation. However, all of the TRP channel structures solved so far are incomplete since they miss important information about highly flexible regions found mostly in the channel N- and C-termini. These intrinsically disordered regions (IDRs) can represent between a quarter to almost half of the entire protein sequence and act as important recruitment hubs for lipids and regulatory proteins. Here, we analyze the currently available TRP channel structures with regard to the extent of these "missing" regions and compare these findings to disorder predictions. We discuss select examples of intra- and intermolecular crosstalk of TRP channel IDRs with proteins and lipids as well as the effect of splicing and post-translational modifications, to illuminate their importance for channel function and to complement the prevalently discussed structural biology of these versatile and fascinating proteins with their equally relevant 'unstructural' biology.

Autophagy in inflammation, infection, and immunometabolism

Autophagy is a quality-control, metabolic, and innate immunity process. Normative autophagy affects many cell types, including hematopoietic as well as non-hematopoietic, and promotes health in model organisms and humans. When autophagy is perturbed, this has repercussions on diseases with inflammatory components, including infections, autoimmunity and cancer, metabolic disorders, neurodegeneration, and cardiovascular and liver diseases. As a cytoplasmic degradative pathway, autophagy protects from exogenous hazards, including infection, and from endogenous sources of inflammation, including molecular aggregates and damaged organelles. The focus of this review is on the role of autophagy in inflammation, including type I interferon responses and inflammasome outputs, from molecules to immune cells. A special emphasis is given to the intersections of autophagy with innate immunity, immunometabolism, and functions of organelles such as mitochondria and lysosomes that act as innate immunity and immunometabolic signaling platforms.

Modes of Regulated Cell Death in Cancer

Cell suicide pathways, termed regulated cell death (RCD), play a critical role in organismal development, homeostasis, and pathogenesis. Here, we provide an overview of key RCD modalities, namely apoptosis, entosis, necroptosis, pyroptosis, and ferroptosis. We explore how various RCD modules serve as a defense mechanism against the emergence of cancer as well as the manner in which they can be exploited to drive oncogenesis. Furthermore, we outline current therapeutic agents that activate RCD and consider novel RCD-based strategies for tumor elimination. SIGNIFICANCE: A variety of antitumor therapeutics eliminate cancer cells by harnessing the devastating potential of cellular suicide pathways, emphasizing the critical importance of RCD in battling cancer. This review supplies a mechanistic perspective of distinct RCD modalities and explores the important role they play in tumorigenesis. We discuss how RCD modules serve as a double-edged sword as well as novel approaches aimed at selectively manipulating RCD for tumor eradication.

The Burden of the Serious and Difficult-to-Treat Infections and a New Antibiotic Available: Cefiderocol

Background: Infection is a disease that can occur due to the entrance of a virus, bacteria, and other infectious agents. Cefiderocol is innovative cephalosporin drug that belongs to a special class of antibiotics, sideromycins, which are taken up by bacterial cells through active transport. The unique cell entry and stability to β-lactamases allow cefiderocol to overcome the most common resistance mechanisms in Gram-negative bacteria. Objective: This article aims to highlight the therapeutic efficacy, safety and tolerability of cefiderocol, with a focus on the FDA label. Methods: The pharmacological properties of cefiderocol are also summarized. In this review, we conducted literature research on the PubMed database using the following keywords: "antimicrobial treatment", "new antibiotic", "cefiderocol", "siderophore cephalosporin"; "multidrug-resistant", "Gram-negative bacilli", "critically ill patients"; "severe bacterial infections". Results: There were identified the most relevant data about the pathophysiology of serious bacterial infections, antibacterial mechanism of action, microbiology, mechanisms of resistance, pharmacokinetic and pharmacodynamic properties of cefiderocol. Conclusion: The results highlighted there appeared to be clinical benefit from cefiderocol in the treatment of infections caused by Gram-negative aerobic microorganisms in adult patients with severe infections and limited treatment options.

Endolysosomal TRPMLs in Cancer

Lysosomes, the degradative endpoints and sophisticated cellular signaling hubs, are emerging as intracellular Ca²⁺ stores that govern multiple cellular processes. Dys-homeostasis of lysosomal Ca²⁺ is intimately associated with a variety of human diseases including cancer. Recent studies have suggested that the Ca²⁺-permeable channels Transient Receptor Potential (TRP) Mucolipins (TRPMLs, TRPML1-3) integrate multiple processes of cell growth, division and metabolism. Dysregulation of TRPMLs activity has been implicated in cancer development. In this review, we provide a summary of the latest development of TRPMLs in cancer. The expression of TRPMLs in cancer, TRPMLs in cancer cell nutrient sensing, TRPMLs-mediated lysosomal exocytosis in cancer development, TRPMLs in TFEB-mediated gene transcription of cancer cells, TRPMLs in bacteria-related cancer development and TRPMLs-regulated antitumor immunity are discussed. We hope to guide readers toward a more in-depth discussion of the importance of lysosomal TRPMLs in cancer progression and other human diseases.

Follow Your Nose: A Key Clue to Understanding and Treating COVID-19

This paper suggests that ATP release induced by the SARS-CoV-2 virus plays a key role in the genesis of the major symptoms and complications of COVID-19. Infection of specific cells which contain the Angiotensin-Converting Enzyme 2 (ACE2) receptor results in a loss of protection of the Mineralocorticoid Receptor (MR). Local activation by cortisol stimulates the release of ATP initially into the basolateral compartment and then by lysosomal exocytosis from the cell surface. This then acts on adjacent cells. In the nose ATP acts as a nociceptive stimulus which results in anosmia. It is suggested that a similar paracrine mechanism is responsible for the loss of taste. In the lung ATP release from type 2 alveolar cells produces the non-productive cough by acting on purinergic receptors on adjacent neuroepithelial cells and activating, via the vagus, the cough reflex. Infection of endothelial cells results in the exocytosis of WeibelPalade bodies. These contain the Von Willebrand Factor responsible for micro-clotting and angiopoietin-2 which increases vascular permeability and plays a key role in the Acute Respiratory Distress Syndrome. To test this hypothesis this paper reports proof of concept studies in which MR blockade using spironolactone and low dose dexamethasone (SpiDex) was given to PCR-confirmed COVID-19 patients. In 80 patients with moderate to severe respiratory failure 40 were given SpiDex and 40 conventional treatment with high dose dexamethasone (HiDex). There was 1 death in the HiDex group and none in the SpiDex. As judged by clinical, biochemical and radiological parameters there were clear statistically significant benefits of SpiDex in comparison to HiDex. A further 20 outpatients with COVID-19 were given SpiDex. There was no control group and the aim was to demonstrate safety. No adverse effects were noted and no patient became hyperkalaemic. 90% were asymptomatic at 10 days. The very positive results suggest that blockade of the MR can produce major benefit in COVID19 patients. Further larger controlled studies of inpatients and outpatients are required not only for SARS-CoV-2 infection per se but also to determine if this treatment affects the incidence of Long COVID.

Radiation-Induced Bystander Effect can be Transmitted Through Exosomes Using miRNAs as Effector Molecules

The radiation-induced bystander effect (RIBE) is a destructive reaction in nonirradiated cells and is one primary factor in determining the efficacy and success of radiation therapy in the field of cancer treatment. Previously reported studies have shown that the RIBE can be mediated by exosomes that carry miRNA components within. Exosomes, which are one type of cell-derived vesicle, exist in different biological conditions and serve as an important additional pathway for signal exchange between cells. In addition, exosome-derived miRNAs are confirmed to play an important role in RIBE, activating the bystander effect and genomic instability after radiotherapy. After investigating the field of RIBE, it is important to understand the mechanisms and consequences of biological effects as well as the role of exosomes and exosomal miRNAs therein, from different sources and under different circumstances, respectively. More discoveries could help to establish early interventions against RIBE while improving the efficacy of radiotherapy. Meanwhile, measures that would alleviate or even inhibit RIBE to some extent may exist in the near future.

Lysosomal Exocytosis: The Extracellular Role of an Intracellular Organelle

Lysosomes are acidic cell compartments containing a large set of hydrolytic enzymes. These lysosomal hydrolases degrade proteins, lipids, polysaccharides, and nucleic acids into their constituents. Materials to be degraded can reach lysosomes either from inside the cell, by autophagy, or from outside the cell, by different forms of endocytosis. In addition to their degradative functions, lysosomes are also able to extracellularly release their contents by lysosomal exocytosis. These organelles move from the perinuclear region along microtubules towards the proximity of the plasma membrane, then the lysosomal and plasma membrane fuse together via a Ca2+-dependent process. The fusion of the lysosomal membrane with plasma membrane plays an important role in plasma membrane repair, while the secretion of lysosomal content is relevant for the remodelling of extracellular matrix and release of functional substrates. Lysosomal storage disorders (LSDs) and age-related neurodegenerative disorders, such as Parkinson's and Alzheimer's diseases, share as a pathological feature the accumulation of undigested material within organelles of the endolysosomal system. Recent studies suggest that lysosomal exocytosis stimulation may have beneficial effects on the accumulation of these unprocessed aggregates, leading to their extracellular elimination. However, many details of the molecular machinery required for lysosomal exocytosis are only beginning to be unravelled. Here, we are going to review the current literature on molecular mechanisms and biological functions underlying lysosomal exocytosis, to shed light on the potential of lysosomal exocytosis stimulation as a therapeutic approach.

Regulation of Beclin 1-Mediated Autophagy by Oncogenic Tyrosine Kinases

Beclin 1 is a major regulator of autophagy, and it is a core component of the class III PI3K complexes. Beclin 1 is a highly conserved protein and its function is regulated in a number of ways, including post-translational modifications. Several studies indicate that receptor and non-receptor tyrosine kinases regulate autophagy activity in cancer, and some suggest the importance of Beclin 1 tyrosine phosphorylation in this process. Here we summarize the current knowledge of the mechanism whereby some oncogenic tyrosine kinases regulate autophagy through Beclin 1.

Two-pore and TRPML cation channels: Regulators of phagocytosis, autophagy and lysosomal exocytosis

The old Greek saying "Panta Rhei" ("everything flows") is true for all life and all living things in general. It also becomes nicely evident when looking closely into cells. There, material from the extracellular space is taken up by endocytic processes and transported to endosomes where it is sorted either for recycling or degradation. Cargo is also packaged for export through exocytosis involving the Golgi network, lysosomes and other organelles. Everything in this system is in constant motion and many proteins are necessary to coordinate transport along the different intracellular pathways to avoid chaos. Among these proteins are ion channels., in particular TRPML channels (mucolipins) and two-pore channels (TPCs) which reside on endosomal and lysosomal membranes to speed up movement between organelles, e.g. by regulating fusion and fission; they help readjust pH and osmolarity changes due to such processes, or they promote exocytosis of export material. Pathophysiologically, these channels are involved in neurodegenerative, metabolic, retinal and infectious diseases, cancer, pigmentation defects, and immune cell function, and thus have been proposed as novel pharmacological targets, e.g. for the treatment of lysosomal storage disorders, Duchenne muscular dystrophy, or different types of cancer. Here, we discuss the similarities but also differences of TPCs and TRPMLs in regulating phagocytosis, autophagy and lysosomal exocytosis, and we address the contradictions and open questions in the field relating to the roles TPCs and TRPMLs play in these different processes.

A non-enveloped arbovirus released in lysosome-derived extracellular vesicles induces super-infection exclusion

Recent developments on extracellular vesicles (EVs) containing multiple virus particles challenge the rigid definition of non-enveloped viruses. However, how non-enveloped viruses hijack cell machinery to promote non-lytic release in EVs, and their functional roles, remain to be clarified. Here we used Bluetongue virus (BTV) as a model of a non-enveloped arthropod-borne virus and discovered that the majority of viruses are released in EVs. Based on the cellular proteins detected in these EVs, and use of inhibitors targeting the cellular degradation process, we demonstrated that these extracellular vesicles are derived from secretory lysosomes, in which the acidic pH is neutralized upon the infection. Moreover, we report that secreted EVs are more efficient than free-viruses for initiating infections, but that they trigger super-infection exclusion that only free-viruses can overcome.

Small extracellular vesicles (sEVs): discovery, functions, applications, detection methods and various engineered forms

INTRODUCTION

Extracellular vesicles (EVs) are cell-created delivery systems of proteins, lipids, or nucleic acids, and means of extracellular communication. Though sEVs were initially considered to be the waste disposal mechanism, today they are at the forefront of research with different biological and pathological functions. Such EVs play a key role in the immunoregulation, CNS development, nervous system physiology, mammary gland development, induction of immunosuppression in pregnancy, the developmental signaling pathways, regeneration of different tissues, inflammation, angiogenesis, coagulation, apoptosis, stem cell differentiation, and extracellular matrix turnover.

AREAS COVERED

SEVs contribute to the pathogenesis of different cancers and the progression of various neurodegenerative diseases, infections, as well as metabolic and cardiovascular diseases. Expert Opinion: There is no exact classification for EVs; however, according to size, density, morphological features, content, and biogenesis, they can be categorized into three major classes: microvesicles (ectosomes or microparticles), apoptotic bodies, and sEVs. SEVs, as an important class of EVs, have a crucial role in distinct biological functions. Moreover, shedding light on different structural and molecular aspects of sEV has led to their application in various therapeutic, diagnostic, and drug delivery fields. In this review, we have endeavored to elaborate on different aspects of EVs, especially sEVs.

Bluetongue virus assembly and exit pathways

Bluetongue virus (BTV) is an insect-vectored emerging pathogen of wild ruminants and livestock in many parts of the world. The virion particle is a complex structure of consecutive layers of protein surrounding a genome of 10 double-stranded (ds) RNA segments. BTV has been studied extensively as a model system for large, nonenveloped dsRNA viruses. A combination of recombinant proteins and particles together with reverse genetics, high-resolution structural analysis by X-ray crystallography and cryo-electron microscopy techniques have been utilized to provide an order for the assembly of the capsid shell and the protein sequestration required for it. Further, a reconstituted in vitro assembly system and RNA-RNA interaction assay, have defined the individual steps required for the assembly and packaging of the 10-segmented RNA genome. In addition, various microscopic techniques have been utilized to illuminate the stages of virus maturation and its egress via multiple pathways. These findings have not only given an overall understanding of BTV assembly and morphogenesis but also indicated that similar assembly and egress pathways are likely to be used by related viruses and provided an informed starting point for intervention or prevention.

Janus sword actions of chloroquine and hydroxychloroquine against COVID-19

Chloroquine (CQ) and its analogue hydroxychloroquine (HCQ) have been thrust into our everyday vernacular because some believe, based on very limited basic and clinical data, that they might be helpful in preventing and/or lessening the severity of the pandemic coronavirus disease 2019 (COVID-19). However, lacking is a temperance in enthusiasm for their possible use as well as sufficient perspective on their effects and side-effects. CQ and HCQ have well-known properties of being diprotic weak bases that preferentially accumulate in acidic organelles (endolysosomes and Golgi apparatus) and neutralize luminal pH of acidic organelles. These primary actions of CQ and HCQ are responsible for their anti-malarial effects; malaria parasites rely on acidic digestive vacuoles for survival. Similarly, de-acidification of endolysosomes and Golgi by CQ and HCQ may block severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) integration into host cells because SARS-CoV-2 may require an acidic environment for its entry and for its ability to bud and infect bystander cells. Further, de-acidification of endolysosomes and Golgi may underly the immunosuppressive effects of these two drugs. However, modern cell biology studies have shown clearly that de-acidification results in profound changes in the structure, function and cellular positioning of endolysosomes and Golgi, in signaling between these organelles and other subcellular organelles, and in fundamental cellular functions. Thus, studying the possible therapeutic effects of CQ and HCQ against COVID-19 must occur concurrent with studies of the extent to which these drugs affect organellar and cell biology. When comprehensively examined, a better understanding of the Janus sword actions of these and other drugs might yield better decisions and better outcomes.

Altered level of plasma exosomes in patients with Gaucher disease

Mutations in the glucocerebrosidase gene (GBA) cause Gaucher disease (GD), the lysosomal storage disorder (LSD), and are the most common genetic risk factor of Parkinson's disease (PD). Lysosome functionality plays a critical role for secretion of extracellular vesicles (EVs) and their content. Here we compared EVs from the blood plasma of 8 GD patients and 8 controls in terms of amounts, size distribution, and composition of their protein cargo. EVs were isolated via sequential centrifugation and characterized by сryo-electron microscopy (cryo-EM), nanoparticle tracking analysis (NTA), and dynamic light scattering (DLS). The presence of exosomal markers HSP70 and tetrasponins were analyzed by Western blot and flow cytometry. Protein profiling was performed by mass-spectrometry (shotgun analysis). Here, for the first time we reported an increased size and altered morphology in exosomes derived from blood plasma of GD patients. An increased size of plasma exosomes from GD patients compared to controls was demonstrated by cryo-EM and DLS (р<0.0001, p < 0.001, respectively) and confirmed by mode size detected by NTA (p < 0.02). Cryo-EM demonstrated an increased number of double and multilayer vesicles in plasma EVs from GD patients. We found that the EVs were enriched with the surface exosomal markers (CD9, СD63, CD81) and an exosome-associated protein HSP70 in case of the patients with the disease. Proteomic profiling of exosomal proteins did not reveal any proteins associated with PD pathogenesis. Thus, we showed that lysosomal dysfunction in GD patients lead to a striking alteration of plasma exosomes in size and morphology.

Exosomal cargos modulate autophagy in recipient cells via different signaling pathways

Vesicular system of mammalian cells is composed of two intracellular and extracellular vesicles systems, which contributes to the intra/intercellular communication and cellular homeostasis. These systems mediate transferring of biological molecules like proteins, nucleic acids, and lipids inside the cytoplasm, and between the cells. By the present study, authors describe molecular crosslink between exosome biogenesis and autophagy and take a certain focus on the autophagic cargos of exosomes and signaling pathways involved in exosome-induced autophagy in target cells and vice versa. Autophagy the generation of double-phospholipid vesicles, is a process that engulfs damaged proteins and organelles, share molecular similarity and function synergy with exosomes biogenesis for degradation or exocytosis of certain cargo. Exosomes, the smallest subtype of extracellular vesicles, originating from the membrane of the multivesicular body located inside cells demonstrate key roles in the intracellular and intercellular communication. Growing evidence demonstrates the interaction between exosome biogenesis and autophagy both at intertwined molecular pathways and crossbred vesicles known as amphisomes. Crosstalk between exosome biogenesis and autophagy contributes to maintain cellular homeostasis under external and internal stresses. Moreover, these processes can modulate each other via different signaling pathways. Exosomes contain autophagic cargos that induce autophagy via the cascade of molecular events in target cells, which called here exosome-induced autophagy. Taken together, crosstalk between exosome biogenesis and autophagy plays pivotal roles in cell homeostasis. Shedding light on the interaction between endomembrane systems may promote our knowledge about the relation between exosome and autophagy pathways in lysosome-related disorders against treatments; proposing a theoretical approach for therapy.

Early evidence of delayed oligodendrocyte maturation in the mouse model of mucolipidosis type IV

Mucolipidosis type IV (MLIV) is a lysosomal disease caused by mutations in the MCOLN1 gene that encodes the endolysosomal transient receptor potential channel mucolipin-1, or TRPML1. MLIV results in developmental delay, motor and cognitive impairments, and vision loss. Brain abnormalities include thinning and malformation of the corpus callosum, white-matter abnormalities, accumulation of undegraded intracellular 'storage' material and cerebellar atrophy in older patients. Identification of the early events in the MLIV course is key to understanding the disease and deploying therapies. The Mcoln1-/- mouse model reproduces all major aspects of the human disease. We have previously reported hypomyelination in the MLIV mouse brain. Here, we investigated the onset of hypomyelination and compared oligodendrocyte maturation between the cortex/forebrain and cerebellum. We found significant delays in expression of mature oligodendrocyte markers Mag, Mbp and Mobp in the Mcoln1-/- cortex, manifesting as early as 10 days after birth and persisting later in life. Such delays were less pronounced in the cerebellum. Despite our previous finding of diminished accumulation of the ferritin-bound iron in the Mcoln1-/- brain, we report no significant changes in expression of the cytosolic iron reporters, suggesting that iron-handling deficits in MLIV occur in the lysosomes and do not involve broad iron deficiency. These data demonstrate very early deficits of oligodendrocyte maturation and critical regional differences in myelination between the forebrain and cerebellum in the mouse model of MLIV. Furthermore, they establish quantitative readouts of the MLIV impact on early brain development, useful to gauge efficacy in pre-clinical trials.

Dendritic cells release exosomes together with phagocytosed pathogen; potential implications for the role of exosomes in antigen presentation

Dendritic cells (DC) have the unique capacity to activate naïve T cells by presenting T cell receptor specific peptides from exogenously acquired antigens bound to Major Histocompatibility Complex (MHC) molecules. MHC molecules are displayed on the DC plasma membrane as well as on extracellular vesicles (EV) that are released by DC, and both have antigen-presenting capacities. However, the physiological role of antigen presentation by EV is still unclear. We here demonstrate that the release of small EV by activated DC is strongly stimulated by phagocytic events. We show that, concomitant with the enhanced release of EV, a significant proportion of phagocytosed bacteria was expulsed back into the medium. High-resolution fluorescence microscopic images revealed that bacteria in phagosomes were surrounded by EV marker-proteins. Moreover, expulsed bacteria were often found associated with clustered HLA II and CD63. Together, these observations suggest that exosomes may be formed by the inward budding into phagosomes, whereupon they are secreted together with the phagosomal content. These findings may have important implications for selective loading of peptides derived from phagocytosed pathogens onto exosome associated HLA molecules, and have important implications for vaccine design.

The immune response to infection in the bladder

The bladder is continuously protected by passive defences such as a mucus layer, antimicrobial peptides and secretory immunoglobulins; however, these defences are occasionally overcome by invading bacteria that can induce a strong host inflammatory response in the bladder. The urothelium and resident immune cells produce additional defence molecules, cytokines and chemokines, which recruit inflammatory cells to the infected tissue. Resident and recruited immune cells act together to eradicate bacteria from the bladder and to develop lasting immune memory against infection. However, urinary tract infection (UTI) is commonly recurrent, suggesting that the induction of a memory response in the bladder is inadequate to prevent reinfection. Additionally, infection seems to induce long-lasting changes in the urothelium, which can render the tissue more susceptible to future infection. The innate immune response is well-studied in the field of UTI, but considerably less is known about how adaptive immunity develops and how repair mechanisms restore bladder homeostasis following infection. Furthermore, data demonstrate that sex-based differences in immunity affect resolution and infection can lead to tissue remodelling in the bladder following resolution of UTI. To combat the rise in antimicrobial resistance, innovative therapeutic approaches to bladder infection are currently in development. Improving our understanding of how the bladder responds to infection will support the development of improved treatments for UTI, particularly for those at risk of recurrent infection.

Multiple Routes of Bluetongue Virus Egress

Bluetongue virus (BTV) is an arthropod-borne virus infecting livestock. Its frequent emergence in Europe and North America had caused significant agricultural and economic loss. BTV is also of scientific interest as a model to understand the mechanisms underlying non-enveloped virus release from mammalian and insect cells. The BTV particle, which is formed of a complex double-layered capsid, was first considered as a lytic virus that needs to lyse the infected cells for cell to cell transmission. In the last decade, however, a more in-depth focus on the role of the non-structural proteins has led to several examples where BTV particles are also released through different budding mechanisms at the plasma membrane. It is now clear that the non-structural protein NS3 is the main driver of BTV release, via different interactions with both viral and cellular proteins of the cell sorting and exocytosis pathway. In this review, we discuss the most recent advances in the molecular biology of BTV egress and compare the mechanisms that lead to lytic or non-lytic BTV release.