Chloroquine and bafilomycin A mimic lysosomal storage disorders and impair mTORC1 signalling

Distinct regulation of Tau Monomer and aggregate uptake and intracellular accumulation in human neurons

BACKGROUND

The prion-like spreading of Tau pathology is the leading cause of disease progression in various tauopathies. A critical step in propagating pathologic Tau in the brain is the transport from the extracellular environment and accumulation inside naïve neurons. Current research indicates that human neurons internalize both the physiological extracellular Tau (eTau) monomers and the pathological eTau aggregates. However, similarities or differences in neuronal transport mechanisms between Tau species remain elusive.

METHOD

Monomers, oligomers, and fibrils of recombinant 2N4R Tau were produced and characterized by biochemical and biophysical methods. A neuronal eTau uptake and accumulation assay was developed for human induced pluripotent stem cell-derived neurons (iPSCNs) and Lund human mesencephalic cells (LUHMES)-derived neurons. Mechanisms of uptake and cellular accumulation of eTau species were studied by using small molecule inhibitors of endocytic mechanisms and siRNAs targeting Tau uptake mediators.

RESULTS

Extracellular Tau aggregates accumulated more than monomers in human neurons, mainly due to the higher efficiency of small fibrillar and soluble oligomeric aggregates in intraneuronal accumulation. A competition assay revealed a distinction in the neuronal accumulation between physiological eTau Monomers and pathology-relevant aggregates, suggesting differential transport mechanisms. Blocking heparan sulfate proteoglycans (HSPGs) with heparin only inhibited the accumulation of eTau aggregates, whereas monomers' uptake remained unaltered. At the molecular level, the downregulation of genes involved in HSPG synthesis exclusively blocked neuronal accumulation of eTau aggregates but not monomers, suggesting its role in the transport of pathologic Tau. Moreover, the knockdown of LRP1, as a receptor of Tau, mainly reduced the accumulation of monomeric form, confirming its involvement in Tau's physiological transport.

CONCLUSION

These data propose that despite the similarity in the cellular mechanism, the uptake and accumulation of eTau Monomers and aggregates in human neurons are regulated by different molecular mediators. Thus, they address the possibility of targeting the pathological spreading of Tau aggregates without disturbing the probable physiological or non-pathogenic transport of Tau Monomers.

Molecular Phenotypes Segregate Missense Mutations in SLC13A5 Epilepsy

The sodium-coupled citrate transporter (NaCT, SLC13A5) mediates citrate uptake across the plasma membrane via an inward Na+ gradient. Mutations in SLC13A5 cause early infantile epileptic encephalopathy type-25 (EIEE25, SLC13A5 Epilepsy) due to impaired citrate uptake in neurons and astrocytes. Despite clinical identification of disease-causing mutations, underlying mechanisms and cures remain elusive. Here we mechanistically classify six frequent SLC13A5 mutations by phenotyping their protein cell surface expression and citrate transport functions. Mutants C50R, T142M, and T227M exhibit impaired citrate transport despite normal expression at the cell surface. In contrast, mutations G219R, S427L, and L488P show low total protein expression levels, absence of mature, glycosylated proteins at the cell surface, retention of the proteins in the endoplasmic reticulum, and diminished transport activity. This mechanistic classification divides SLC13A5 mutants into two groups, Class I (C50R, T142M, and T227M) and Class II (G219R, S427L, and L488P). Importantly, mutants' mRNA levels resemble wildtype, suggesting post-translational defects. Class II mutations display immature core-glycosylation and shortened half-lives, indicating protein folding defects. Together, these experiments provide a comprehensive understanding of the disease-causing mutation's defects in SLC13A5 Epilepsy at the biochemical and molecular level and shed light into the trafficking pathway(s) of NaCT. The two classes of mutations will require fundamentally different approaches for treatment to either restore transport function of the mutant protein that is capable of reaching the cell surface (Class I), or therapies that enable the correction of protein folding defects to enable escape to the cell surface where it may restore transport function (Class II).

Protective effect of zinc against A2E-induced toxicity in ARPE-19 cells: Possible involvement of lysosomal acidification

A key pathogenic mechanism of dry age-related macular degeneration (AMD) is lysosomal dysfunction in retinal pigment epithelium (RPE) cells, which results in the accumulation of lipofuscins such as A2E (N-retinylidene-N-retinylethanolamine) that further compromises lysosomal function. This vicious cycle leads to cell death and poor visual acuity. Here, we established an in vitro model of AMD by treating a human RPE cell line (ARPE-19) with A2E and examined whether raising zinc levels confers protective effects against lysosomal dysfunction and cytotoxicity. MTT assay showed that A2E induced apoptosis in ARPE-19 cells. pHrodo™ Red fluorescence staining showed that lysosomal pH increased in A2E-treated ARPE-19 cells. Treatment with a zinc ionophore (clioquinol) reduced A2E accumulation, restored lysosomal pH to the acidic range, and reduced A2E-induced cell death, all of which were reversed by the addition of a zinc chelator (TPEN). Consistent with the in vitro results, subretinal injections of A2E in mouse eyes resulted in the death of RPE cells as well as lysosomal dysfunction, all of which were reversed by co-treatment with clioquinol. Our results suggest that restoring the levels of intracellular zinc, especially in lysosomes, would be helpful in mitigating A2E-induced cytotoxic changes including lysosomal dysfunction in RPE cells in the pathogenesis of AMD.

Angiogenesis is limited by LIC1-mediated lysosomal trafficking

Dynein cytoplasmic 1 light intermediate chain 1 (LIC1, DYNC1LI1) is a core subunit of the dynein motor complex. The LIC1 subunit also interacts with various cargo adaptors to regulate Rab-mediated endosomal recycling and lysosomal degradation. Defects in this gene are predicted to alter dynein motor function, Rab binding capabilities, and cytoplasmic cargo trafficking. Here, we have identified a dync1li1 zebrafish mutant, harboring a premature stop codon at the exon 12/13 splice acceptor site, that displays increased angiogenesis. In vitro, LIC1-deficient human endothelial cells display increases in cell surface levels of the pro-angiogenic receptor VEGFR2, SRC phosphorylation, and Rab11-mediated endosomal recycling. In vivo, endothelial-specific expression of constitutively active Rab11a leads to excessive angiogenesis, similar to the dync1li1 mutants. Increased angiogenesis is also evident in zebrafish harboring mutations in rilpl1/2, the adaptor proteins that promote Rab docking to Lic1 to mediate lysosomal targeting. These findings suggest that LIC1 and the Rab-adaptor proteins RILPL1 and 2 restrict angiogenesis by promoting degradation of VEGFR2-containing recycling endosomes. Disruption of LIC1- and RILPL1/2-mediated lysosomal targeting increases Rab11-mediated recycling endosome activity, promoting excessive SRC signaling and angiogenesis.

Pharmaceutical Agents for Targeting Autophagy and Their Applications in Clinics

Autophagy is the process by which damaged regions of the cytoplasm and intracellular pathogens are degraded. This mechanism often serves an adaptive role in cells, enhancing their survival. It plays a direct or indirect role in the development of various pathological conditions within the body. This phenomenon is common in various malignant diseases, where autophagy is associated with the resistance of transformed cells to chemotherapy. Conversely, abnormal activation of autophagy can trigger cell death, a process often seen in neurodegenerative conditions. Given that dysregulation of autophagy is associated with the progression of numerous pathological conditions, this is of significant interest to the developers of drugs that can effectively modulate autophagy for both basic research and clinical applications. Here, we provide a brief description of the mechanism of macroautophagy, the most prevalent form of autophagy identified in humans. We also discuss the clinical potential of drugs that can modulate autophagy, highlighting their use in combating diseases associated with direct or indirect dysregulation of this essential process.

A single bout of resistance exercise triggers mitophagy, potentially involving the ejection of mitochondria in human skeletal muscle

AIM

The present study aimed to investigate the effects of a single bout of resistance exercise on mitophagy in human skeletal muscle (SkM).

METHODS

Eight healthy men were recruited to complete an acute bout of one-leg resistance exercise. SkM biopsies were obtained one hour after exercise in the resting leg (Rest-leg) and the contracting leg (Ex-leg). Mitophagy was assessed using protein-related abundance, transmission electron microscopy (TEM), and fluorescence microscopy.

RESULTS

Our results show that acute resistance exercise increased pro-fission protein phosphorylation (DRP1Ser616) and decreased mitophagy markers such as PARKIN and BNIP3L/NIX protein abundance in the Ex-leg. Additionally, mitochondrial complex IV decreased in the Ex-leg when compared to the Rest-leg. In the Ex-leg, TEM and immunofluorescence images showed mitochondrial cristae abnormalities, a mitochondrial fission phenotype, and increased mitophagosome-like structures in both subsarcolemmal and intermyofibrillar mitochondria. We also observed increased mitophagosome-like structures on the subsarcolemmal cleft and mitochondria in the extracellular space of SkM in the Ex-leg. We stimulated human primary myotubes with CCCP, which mimics mitophagy induction in the Ex-leg, and found that BNIP3L/NIX protein abundance decreased independently of lysosomal degradation. Finally, in another human cohort, we found a negative association between BNIP3L/NIX protein abundance with both mitophagosome-like structures and mitochondrial cristae density in the SkM.

CONCLUSION

The findings suggest that a single bout of resistance exercise can initiate mitophagy, potentially involving mitochondrial ejection, in human skeletal muscle. BNIP3L/NIX is proposed as a sensitive marker for assessing mitophagy flux in SkM.

Increased burden of rare risk variants across gene expression networks predisposes to sporadic Parkinson's disease

Alpha-synuclein (αSyn) is an intrinsically disordered protein that accumulates in the brains of patients with Parkinson's disease and forms intraneuronal inclusions called Lewy Bodies. While the mechanism underlying the dysregulation of αSyn in Parkinson's disease is unclear, it is thought that prionoid cell-to-cell propagation of αSyn has an important role. Through a high throughput screen, we recently identified 38 genes whose knock down modulates αSyn propagation. Follow up experiments were undertaken for two of those genes, TAX1BP1 and ADAMTS19, to study the mechanism with which they regulate αSyn homeostasis. We used a recently developed M17D neuroblastoma cell line expressing triple mutant (E35K+E46K+E61K) "3K" αSyn under doxycycline induction. 3K αSyn spontaneously forms inclusions that show ultrastructural similarities to Lewy Bodies. Experiments using that cell line showed that TAX1BP1 and ADAMTS19 regulate how αSyn interacts with lipids and phase separates into inclusions, respectively, adding to the growing body of evidence implicating those processes in Parkinson's disease. Through RNA sequencing, we identified several genes that are differentially expressed after knock-down of TAX1BP1 or ADAMTS19. Burden analysis revealed that those differentially expressed genes (DEGs) carry an increased frequency of rare risk variants in Parkinson's disease patients versus healthy controls, an effect that was independently replicated across two separate cohorts (GP2 and AMP-PD). Weighted gene co-expression network analysis (WGCNA) showed that the DEGs cluster within modules in regions of the brain that develop high degrees of αSyn pathology (basal ganglia, cortex). We propose a novel model for the genetic architecture of sporadic Parkinson's disease: increased burden of risk variants across genetic networks dysregulates pathways underlying αSyn homeostasis, thereby leading to pathology and neurodegeneration.

Pharmacokinetics and antioxidant activity of dihydrocaffeic acid grafted chitosan nanomicelles loaded with chicoric acid in broilers

Chicoric acid (CA) is a natural nutrient found in plants, showcasing diverse biological activities, including anti-inflammatory and antioxidant properties. Despite its valuable properties, CA faces limitations in bioavailability and susceptibility to oxidative breakdown during utilization. Previous research introduced synthesized dihydrocaffeic acid grafted chitosan self-assembled nanomicelles (DA-g-CS), demonstrating its potential to enhance CA absorption. This study aims to investigate the pharmacokinetics, tissue distribution, and antioxidant activity of both CA and DA-g-CS loaded CA (DA-g-CS/CA) in broilers. An IPEC-J2 cell model was established and evaluated to delve deeper into the transport mechanism and antioxidant potential. The in vivo pharmacokinetic analysis in broilers highlighted a substantial difference: the maximum plasma concentration (Cmax) of DA-g-CS/CA exceeded CA by 2.6-fold, yielding a notable increased relative bioavailability to 214%. This evidence underscores the significant enhancement in CA's oral absorption, facilitated by DA-g-CS. The collective evaluation outcomes affirm the successful development of the cell model, indicating its suitability for drug transporter experiments. The findings from the intestinal transit analysis revealed that both CA and DA-g-CS/CA underwent passive entry into IPEC-J2 cells. Notably, the cellular uptake rate of DA-g-CS loaded with CA was significantly amplified, reaching 2.1 times higher than that of CA alone. Intracellular transport mechanisms involved microtubules, lysosomes, and the endoplasmic reticulum, with an additional pathway involving the endoplasmic reticulum observed specifically for DA-g-CS/CA, distinguishing it from CA. Moreover, the results from both in vivo and in vitro antioxidant assessments highlight the potent antioxidant activity of DA-g-CS/CA, showcasing its efficacy in preventing and treating cellular damage induced by oxidative stress. In summary, these findings underscore the significant enhancement of CA's efficacy facilitated by DA-g-CS, establishing a robust theoretical foundation for the prospective application of CA within livestock and poultry farming.

Upregulation of cholesterol synthesis by lysosomal defects requires a functional mitochondrial respiratory chain

Mitochondria and lysosomes are two organelles that carry out both signaling and metabolic roles in cells. Recent evidence has shown that mitochondria and lysosomes are dependent on one another, as primary defects in one cause secondary defects in the other. Although there are functional impairments in both cases, the signaling consequences of primary mitochondrial dysfunction and lysosomal defects are dissimilar. Here, we used RNA sequencing to obtain transcriptomes from cells with primary mitochondrial or lysosomal defects to identify the global cellular consequences associated with mitochondrial or lysosomal dysfunction. We used these data to determine the pathways affected by defects in both organelles, which revealed a prominent role for the cholesterol synthesis pathway. We observed a transcriptional upregulation of this pathway in cellular and murine models of lysosomal defects, while it is transcriptionally downregulated in cellular and murine models of mitochondrial defects. We identified a role for the posttranscriptional regulation of transcription factor SREBF1, a master regulator of cholesterol and lipid biosynthesis, in models of mitochondrial respiratory chain deficiency. Furthermore, we found that retention of Ca2+ in lysosomes of cells with mitochondrial respiratory chain defects contributes to the differential regulation of the cholesterol synthesis pathway in the mitochondrial and lysosomal defects tested. Finally, we verified in vivo, using a model of mitochondria-associated disease in Caenorhabditis elegans that normalization of lysosomal Ca2+ levels results in partial rescue of the developmental delay induced by the respiratory chain deficiency.

HSP70-mediated mitochondrial dynamics and autophagy represent a novel vulnerability in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC), the most prevalent type of pancreatic cancer, is one of the deadliest forms of cancer with limited therapy options. Overexpression of the heat shock protein 70 (HSP70) is a hallmark of cancer that is strongly associated with aggressive disease and worse clinical outcomes. However, the underlying mechanisms by which HSP70 allows tumor cells to thrive under conditions of continuous stress have not been fully described. Here, we report that PDAC has the highest expression of HSP70 relative to normal tissue across all cancers analyzed. Furthermore, HSP70 expression is associated with tumor grade and is further enhanced in metastatic PDAC. We show that genetic or therapeutic ablation of HSP70 alters mitochondrial subcellular localization, impairs mitochondrial dynamics, and promotes mitochondrial swelling to induce apoptosis. Mechanistically, we find that targeting HSP70 suppresses the PTEN-induced kinase 1 (PINK1) mediated phosphorylation of dynamin-related protein 1 (DRP1). Treatment with the HSP70 inhibitor AP-4-139B was efficacious as a single agent in primary and metastatic mouse models of PDAC. In addition, we demonstrate that HSP70 inhibition promotes the AMP-activated protein kinase (AMPK) mediated phosphorylation of Beclin-1, a key regulator of autophagic flux. Accordingly, we find that the autophagy inhibitor hydroxychloroquine (HCQ) enhances the ability of AP-4-139B to mediate anti-tumor activity in vivo. Collectively, our results suggest that HSP70 is a multi-functional driver of tumorigenesis that orchestrates mitochondrial dynamics and autophagy. Moreover, these findings support the rationale for concurrent inhibition of HSP70 and autophagy as a novel therapeutic approach for HSP70-driven PDAC.

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.

Molecular phenotypes segregate missense mutations in SLC13A5 Epilepsy

The sodium-coupled citrate transporter (NaCT, SLC13A5) mediates citrate uptake across the plasma membrane via an inward Na + gradient. Mutations in SLC13A5 cause early infantile epileptic encephalopathy type-25 (EIEE25, SLC13A5 Epilepsy) due to impaired citrate uptake in neurons. Despite clinical identification of disease-causing mutations, underlying mechanisms and cures remain elusive. We mechanistically classify the molecular phenotypes of six mutations. C50R, T142M, and T227M exhibit impaired citrate transport despite normal expression at the cell surface. G219R, S427L, and L488P are hampered by low protein expression, ER retention, and reduced transport. Mutants' mRNA levels resemble wildtype, suggesting post-translational defects. Class II mutations display immature core-glycosylation and shortened half-lives, indicating protein folding defects. These experiments provide a comprehensive understanding of the mutation's defects in SLC13A5 Epilepsy at the biochemical and molecular level and shed light into the trafficking pathway(s) of NaCT. The two classes of mutations will require fundamentally different treatment approaches to either restore transport function, or enable correction of protein folding defects.

Summary

Loss-of-function mutations in the SLC13A5 causes SLC13A5-Epilepsy, a devastating disease characterized by neonatal epilepsy. Currently no cure is available. We clarify the molecular-level defects to guide future developments for phenotype-specific treatment of disease-causing mutations.

Collagen fibril formation at the plasma membrane occurs independently from collagen secretion

Collagen fibrils are the primary supporting scaffold of vertebrate tissues but how they are assembled is unclear. Here, using CRISPR-tagging of type I collagen and SILAC labelling, we elucidate the cellular mechanism for the spatiotemporal assembly of collagen fibrils, in cultured fibroblasts. Our findings reveal multifaceted trafficking of collagen, including constitutive secretion, intracellular pooling, and plasma membrane-directed fibrillogenesis. Notably, we differentiate the processes of collagen secretion and fibril assembly and identify the crucial involvement of endocytosis in regulating fibril formation. By employing Col1a1 knockout fibroblasts we demonstrate the incorporation of exogenous collagen into nucleation sites at the plasma membrane through these recycling mechanisms. Our study sheds light on the assembly process and its regulation in health and disease. Mass spectrometry data are available via ProteomeXchange with identifier PXD036794.

epHero - a tandem-fluorescent probe to track the fate of apoptotic cells during efferocytosis

The efficient removal of apoptotic cells via efferocytosis is critical for maintaining optimal tissue function. This involves the binding and engulfment of apoptotic cells by phagocytes and the subsequent maturation of the phagosome, culminating in lysosomal fusion and cargo destruction. However, current approaches to measure efferocytosis rely on labelling apoptotic targets with fluorescent dyes, which do not sufficiently distinguish between changes to the engulfment and acidification of apoptotic material. To address this limitation, we have developed a genetically coded ratiometric probe epHero which when expressed in the cytoplasm of target cells, bypasses the need for additional labelling steps. We demonstrate that epHero is a pH-sensitive reporter for efferocytosis and can be used to simultaneously track changes to apoptotic cell uptake and acidification, both in vitro and in mice. As proof-of-principle, we modify extracellular nutrition to show how epHero can distinguish between changes to cargo engulfment and acidification. Thus, tracking efferocytosis with epHero is a simple, cost-effective improvement on conventional techniques.

The Influence of Lysosomal Stress on Dental Pulp Stem Cell-Derived Schwann Cells

BACKGROUND

Dysregulation of the endo-lysosomal-autophagy pathway has been identified as a critical factor in the pathology of various demyelinating neurodegenerative diseases, including peripheral neuropathies. This pathway plays a crucial role in transporting newly synthesized myelin proteins to the plasma membrane in myelinating Schwann cells, making these cells susceptible to lysosome-related dysfunctions. Nevertheless, the specific impact of lysosomal dysfunction in Schwann cells and its contribution to neurodegeneration remain poorly understood.

METHODS

We aim to mimic lysosomal dysfunction in Schwann cells using chloroquine, a lysosomal dysfunction inducer, and to monitor lysosomal leakiness, Schwann cell viability, and apoptosis over time. Additionally, due to the ethical and experimental issues associated with cell isolation and the culturing of human Schwann cells, we use human dental pulp stem cell-derived Schwann cells (DPSC-SCs) as a model in our study.

RESULTS

Chloroquine incubation boosts lysosomal presence as demonstrated by an increased Lysotracker signal. Further in-depth lysosomal analysis demonstrated an increased lysosomal size and permeability as illustrated by a TEM analysis and GAL3-LAMP1 staining. Moreover, an Alamar blue assay and Caspase-3 staining demonstrates a reduced viability and increased apoptosis, respectively.

CONCLUSIONS

Our data indicate that prolonged lysosomal dysfunction leads to lysosomal permeability, reduced viability, and eventually apoptosis in human DPSC-SCs.

Impaired lysosomal acidity maintenance in acid lipase-deficient cells leads to defective autophagy

The lysosome is an acid organelle that contains a variety of hydrolytic enzymes and plays a significant role in intracellular degradation to maintain cellular homeostasis. Genetic variants in lysosome-related genes can lead to severe congenital diseases, such as lysosomal storage diseases. In the present study, we investigated the impact of depleting lysosomal acid lipase A (LIPA), a lysosomal esterase that metabolizes esterified cholesterol or triglyceride, on lysosomal function. Under nutrient-rich conditions, LIPA gene KO (LIPAKO) cells exhibited impaired autophagy, whereas, under starved conditions, they showed normal autophagy. The cause underlying the differential autophagic activity was increased sensitivity of LIPAKO cells to ammonia, which was produced from l-glutamine in the medium. Further investigation revealed that ammonia did not affect upstream signals involved in autophagy induction, autophagosome-lysosome fusion, and hydrolytic enzyme activities in LIPAKO cells. On the other hand, LIPAKO cells showed defective lysosomal acidity upon ammonia loading. Microscopic analyses revealed that lysosomes of LIPAKO cells enlarged, whereas the amount of lysosomal proton pump V-ATPase did not proportionally increase. Since the enlargement of lysosomes in LIPAKO cells was not normalized under starved conditions, this is the primary change that occurred in the LIPAKO cells, and autophagy was affected by impaired lysosomal function under the specific conditions. These findings expand our comprehension of the pathogenesis of Wolman's disease, which is caused by a defect in the LIPA gene, and suggest that conditions, such as hyperlipidemia, may easily disrupt lysosomal functions.

Impaired mitophagosome-lysosome fusion mediates olanzapine-induced aging

The lifespan of schizophrenia patients is significantly shorter than the general population. Olanzapine is one of the most commonly used antipsychotic drugs (APDs) for treating patients with psychosis, including schizophrenia and bipolar disorder. Despite their effectiveness in treating positive and negative symptoms, prolonged exposure to APDs may lead to accelerated aging and cognitive decline, among other side effects. Here we report that dysfunctional mitophagy is a fundamental mechanism underlying accelerated aging induced by olanzapine, using in vitro and in vivo (Caenorhabditis elegans) models. We showed that the aberrant mitophagy caused by olanzapine was via blocking mitophagosome-lysosome fusion. Furthermore, olanzapine can induce mitochondrial damage and hyperfragmentation of the mitochondrial network. The mitophagosome-lysosome fusion in olanzapine-induced aging models can be restored by a mitophagy inducer, urolithin A, which alleviates defective mitophagy, mitochondrial damage, and fragmentation of the mitochondrial network. Moreover, the mitophagy inducer ameliorated behavioral changes induced by olanzapine, including shortened lifespan, and impaired health span, learning, and memory. These data indicate that olanzapine impairs mitophagy, leading to the shortened lifespan, impaired health span, and cognitive deficits. Furthermore, this study suggests the potential application of mitophagy inducers as therapeutic strategies to reverse APD-induced adverse effects associated with accelerated aging.

Role of lysosomes in insulin signaling and glucose uptake in cultured rat podocytes

Podocytes are sensitive to insulin, which governs the functional and structural integrity of podocytes that are essential for proper function of the glomerular filtration barrier. Lysosomes are acidic organelles that are implicated in regulation of the insulin signaling pathway. Cathepsin D (CTPD) and lysosome-associated membrane protein 1 (LAMP1) are major lysosomal proteins that reflect the functional state of lysosomes. However, the effect of insulin on lysosome activity and role of lysosomes in the regulation of insulin-dependent glucose uptake in podocytes are unknown. Our studies showed that the short-term incubation of podocytes with insulin decreased LAMP1 and CTPD mRNA levels. Insulin and bafilomycin A1 reduced both the amounts of LAMP1 and CTPD proteins and activity of CTPD, which were associated with a decrease in the fluorescence intensity of lysosomes that were labeled with LysoTracker. Bafilomycin A1 inhibited insulin-dependent endocytosis of the insulin receptor and increased the amounts of the insulin receptor and glucose transporter 4 on the cell surface of podocytes. Bafilomycin A1 also inhibited insulin-dependent glucose uptake despite an increase in the amount of glucose transporter 4 in the plasma membrane of podocytes. These results suggest that lysosomes are signaling hubs that may be involved in the coupling of insulin signaling with the regulation of glucose uptake in podocytes. The dysregulation of this mechanism can lead to the dysfunction of podocytes and development of insulin resistance.

Metabolic degradation of polysaccharides from Lentinus edodes by Kupffer cells via the Dectin-1/Syk signaling pathway

It had been shown that lentinan (LNT) was mainly distributed in the liver after intravenous administration. The study aimed to investigate the integrated metabolic processes and mechanisms of LNT in the liver, as these have not been thoroughly explored. In current work, 5-([4,6-dichlorotriazin-2-yl] amino) fluorescein and cyanine 7 were used to label LNT for tracking its metabolic behavior and mechanisms. Near-infrared imaging demonstrated that LNT was captured mainly by the liver. Kupffer cell (KC) depletion reduced LNT liver localization and degradation in BALB/c mice. Moreover, experiments with Dectin-1 siRNA and Dectin-1/Syk signaling pathway inhibitors showed that LNT was mainly taken up by KCs via the Dectin-1/Syk pathway and promoted lysosomal maturation in KCs via this same pathway, which in turn promoted LNT degradation. These empirical findings offer novel insights into the metabolism of LNT in vivo and in vitro, which will facilitate the further application of LNT and other β-glucans.

Chlorpromazine affects autophagy in association with altered Rag GTPase-mTORC1-TFEB signaling

Autophagy is a critical protein and organelle quality control system, which regulates cellular homeostasis and survival. Growing pieces of evidence suggest that autophagic dysfunction is strongly associated with many human diseases, including neurological diseases and cancer. Among various autophagic regulators, microphthalmia (MiT)/TFE transcription factors, including transcription factor EB (TFEB), have been shown to act as the master regulators of autophagosome and lysosome biogenesis in both physiological and pathological conditions. According to the previous studies, chlorpromazine (CPZ), an FDA-approved antipsychotic drug, affects autophagy in diverse cell lines, but the underlying mechanism remains elusive. In our present study, we find that CPZ treatment induces TFEB nuclear translocation through Rag GTPases, the upstream regulators of mechanistic target of rapamycin complex 1 (mTORC1) signaling. Meanwhile, CPZ treatment also blocks autophagosome-lysosome fusion. Notably, we find a significant accumulation of immature autophagosome vesicles in CPZ-treated cells, which may impede cellular homeostasis due to the dysfunction of the autophagy-lysosome pathway. Interestingly and importantly, our data suggest that the expression of the active form of Rag GTPase heterodimers helps in reducing the accumulation of autophagosomes in CPZ-treated cells, further suggesting a major contribution of the Rag GTPase-mTORC1-TFEB signaling axis in CPZ-induced autophagic impairment.

Protective role of autophagy in triptolide-induced apoptosis of TM3 Leydig cells

Background and Objectives

Triptolide (TP) is known to impair testicular development and spermatogenesis in mammals, but the mechanism of the side effects still needs to be investigated. The aim of the research is to confirm whether TP can cause autophagy in TM3 Leydig cells and the potential molecular pathway in vitro.

Methods

TM3 Leydig cells are used to investigate the molecular pathway through Western blot, detection of apoptosis, transmission electron microscopy for autophagosomes and so on.

Results

The data show that TP treatment resulted in the decreasing of the viability of TM3 cells due to the increased apoptosis. Treated with TP, the formation of autophagosomes, the decrease in P62, and the increase in the conversion of LC3-I to LC3-II suggested the induction of autophagy. The induction of autophagy has accompanied the activation of the mTOR/P70S6K signal pathway. The viability of the TM3 cells was further inhibited when they were co-treated with autophagy inhibitor, chloroquine (CQ).

Conclusion

All these data suggest that autophagy plays a very important role in antagonizing TM3 cell apoptosis during the TP exposure.

The β6 Integrin Negatively Regulates TLR7-Mediated Epithelial Immunity via Autophagy During Influenza A Virus Infection

Integrins are essential surface receptors that sense extracellular changes to initiate various intracellular signaling cascades. The rapid activation of the epithelial-intrinsic β6 integrin during influenza A virus (IAV) infection has been linked to innate immune impairments. Yet, how β6 regulates epithelial immunity remains undefined. Here, we identify the role of β6 in mediating the Toll-like receptor 7 (TLR7) through the regulation of intracellular trafficking. We demonstrate that deletion of the β6 integrin in lung epithelial cells significantly enhances the TLR7-mediated activation of the type I interferon (IFN) response during homeostasis and respiratory infection. IAV-induced β6 facilitates TLR7 trafficking to lysosome-associated membrane protein (LAMP2a) components, leading to a reduction in endosomal compartments and associated TLR7 signaling. Our findings reveal an unappreciated role of β6-induced autophagy in influencing epithelial immune responses during influenza virus infection.

TMEM106B aggregation in neurodegenerative diseases: linking genetics to function

BACKGROUND

Mutations of the gene TMEM106B are risk factors for diverse neurodegenerative diseases. Previous understanding of the underlying mechanism focused on the impairment of lysosome biogenesis caused by TMEM106B loss-of-function. However, mutations in TMEM106B increase its expression level, thus the molecular process linking these mutations to the apparent disruption in TMEM106B function remains mysterious.

MAIN BODY

Recent new studies reported that TMEM106B proteins form intracellular amyloid filaments which universally exist in various neurodegenerative diseases, sometimes being the dominant form of protein aggregation. In light of these new findings, in this review we systematically examined previous efforts in understanding the function of TMEM106B in physiological and pathological conditions. We propose that TMEM106B aggregations could recruit normal TMEM106B proteins and interfere with their function.

CONCLUSIONS

TMEM106B mutations could lead to lysosome dysfunction by promoting the aggregation of TMEM106B and reducing these aggregations may restore lysosomal function, providing a potential therapeutic target for various neurodegenerative diseases.

Apolipoprotein E intersects with amyloid-β within neurons

Apolipoprotein E4 (ApoE4) is the most important genetic risk factor for Alzheimer's disease (AD). Among the earliest changes in AD is endosomal enlargement in neurons, which was reported as enhanced in ApoE4 carriers. ApoE is thought to be internalized into endosomes of neurons, whereas β-amyloid (Aβ) accumulates within neuronal endosomes early in AD. However, it remains unknown whether ApoE and Aβ intersect intracellularly. We show that internalized astrocytic ApoE localizes mostly to lysosomes in neuroblastoma cells and astrocytes, whereas in neurons, it preferentially localizes to endosomes-autophagosomes of neurites. In AD transgenic neurons, astrocyte-derived ApoE intersects intracellularly with amyloid precursor protein/Aβ. Moreover, ApoE4 increases the levels of endogenous and internalized Aβ42 in neurons. Taken together, we demonstrate differential localization of ApoE in neurons, astrocytes, and neuron-like cells, and show that internalized ApoE intersects with amyloid precursor protein/Aβ in neurons, which may be of considerable relevance to AD.

Title: The C-terminal amphipathic helix of Carboxypeptidase E mediates export from the ER and secretion via lysosomes

Carboxypeptidase E (CPE), an essential enzyme in the biosynthetic production line of most peptide hormones and neuropeptides, is predominantly expressed in endocrine tissues and in the nervous system. CPE is active in acidic environments where it cleaves the C'-terminal basic residues of peptide precursors to generate their bioactive form. Consequently, this highly conserved enzyme regulates numerous fundamental biological processes. Here, we combined live-cell microscopy and molecular analysis to examine the intracellular distribution and secretion dynamics of fluorescently tagged CPE. We show that, in non-endocrine cells, tagged-CPE is a soluble luminal protein that is efficiently exported from the ER via the Golgi apparatus to lysosomes. The C'-terminal conserved amphipathic helix serves as a lysosomal and secretory granule targeting and a secretion motif. Following secretion, CPE may be reinternalized into the lysosomes of neighboring cells.

Cholesterol-dependent molecular mechanisms contribute to cationic amphiphilic drugs' prevention of silica-induced inflammation

Silicosis is considered an irreversible chronic inflammatory disease caused by the inhalation of crystalline silica (cSiO2). The cycle of inflammation that drives silicosis and other particle-caused respiratory diseases is mediated by NLRP3 inflammasome activity in macrophages resulting in the release of IL-1β. Lysosomal membrane permeability (LMP) initiated by inhaled particles is the key regulatory step in leading to NLRP3 activity. In addition to its role in LMP, the lysosome is crucial to cellular cholesterol trafficking. Lysosomal cholesterol has been demonstrated to regulate LMP while cationic amphiphilic drugs (CADs) reduce cholesterol trafficking from lysosomes and promote endolysosomal cholesterol accumulation as seen in Niemann Pick disease. Using a bone marrow derived macrophage (BMdM) model, four CADs were examined for their potential to reduce cSiO2-induced inflammation. Here we found that FDA-approved CAD drugs imipramine, hydroxychloroquine, fluvoxamine, and fluoxetine contributed to reduced LMP and IL-1β release in cSiO2 treated BMdM. These drugs inhibited lysosomal enzymatic activity of acid sphingomyelinase, decreased lysosomal proteolytic function, and increased lysosomal pH. CADs also demonstrated a significant increase in lysosomal-associated free cholesterol. Increased lysosomal cholesterol was associated with a significant reduction in cSiO2 induced LMP and IL-1β release. In contrast, reduced lysosomal cholesterol significantly exacerbated cSiO2-induced IL-1β release and reduced the protective effect of CADs on IL-1β release following cSiO2 exposure. Taken together, these results suggest that CAD modification of lysosomal cholesterol may be used to reduce LMP and cSiO2-induced inflammation and could prove an effective therapeutic for silicosis and other particle-caused respiratory diseases.

A Turn-On Fluorescent Amino Acid Sensor Reveals Chloroquine's Effect on Cellular Amino Acids via Inhibiting Cathepsin L

Maintaining homeostasis of metabolites such as amino acids is critical for cell survival. Dysfunction of nutrient balance can result in human diseases such as diabetes. Much remains to be discovered about how cells transport, store, and utilize amino acids due to limited research tools. Here we developed a novel, pan-amino acid fluorescent turn-on sensor, NS560. It detects 18 of the 20 proteogenic amino acids and can be visualized in mammalian cells. Using NS560, we identified amino acids pools in lysosomes, late endosomes, and surrounding the rough endoplasmic reticulum. Interestingly, we observed amino acid accumulation in large cellular foci after treatment with chloroquine, but not with other autophagy inhibitors. Using a biotinylated photo-cross-linking chloroquine analog and chemical proteomics, we identified Cathepsin L (CTSL) as the chloroquine target leading to the amino acid accumulation phenotype. This study establishes NS560 as a useful tool to study amino acid regulation, identifies new mechanisms of action of chloroquine, and demonstrates the importance of CTSL regulation of lysosomes.

Role of UPRmt and mitochondrial dynamics in host immunity: it takes two to tango

The immune system of a host contains a group of heterogeneous cells with the prime aim of restraining pathogenic infection and maintaining homeostasis. Recent reports have proved that the various subtypes of immune cells exploit distinct metabolic programs for their functioning. Mitochondria are central signaling organelles regulating a range of cellular activities including metabolic reprogramming and immune homeostasis which eventually decree the immunological fate of the host under pathogenic stress. Emerging evidence suggests that following bacterial infection, innate immune cells undergo profound metabolic switching to restrain and countervail the bacterial pathogens, promote inflammation and restore tissue homeostasis. On the other hand, bacterial pathogens affect mitochondrial structure and functions to evade host immunity and influence their intracellular survival. Mitochondria employ several mechanisms to overcome bacterial stress of which mitochondrial UPR (UPR^mt) and mitochondrial dynamics are critical. This review discusses the latest advances in our understanding of the immune functions of mitochondria against bacterial infection, particularly the mechanisms of mitochondrial UPR^mt and mitochondrial dynamics and their involvement in host immunity.

HCMV-encoded viral protein US12 promotes autophagy by inducing autophagy flux

The human cytomegalovirus (HCMV)-encoded US12 gene family is a group of ten predicted seven-transmembrane domain proteins that are structurally similar to G-protein-coupled receptors or transmembrane Bax inhibitor-1 motif-containing proteins; however, the roles of US12 family proteins in virus-host interactions remain to be discovered. Here, we suggest a new function of the US12 protein in regulating cellular autophagy. US12 is predominantly located to the lysosome and interacts with the lysosomal membrane protein 2 (LAMP2). A liquid chromatography-mass spectrometry (MS)/MS-based targeted proteomics analysis shows that US12 is tightly correlated with autophagy. US12 induces autophagy via upregulating ULK1 phosphorylation and subsequent LC3-II conversion, thereby accelerating autophagic flux. Moreover, HeLa cells overexpressing US12 displays intense LC3-specific staining and autolysosome formation even under nutrient-sufficient conditions. Furthermore, the physical interaction of p62/SQSTM1 with US12 is involved in the resistance to the degradation of p62/SQSTM1 by autophagy, despite the induction of both autolysosome formation and autophagic flux. Although the effect of US12 expression in HCMV infection on autophagy remains undetermined, these findings provide new insights into the viral drivers of host autophagy during HCMV evolution and pathogenesis.

HTT (huntingtin) and RAB7 co-migrate retrogradely on a signaling LAMP1-containing late endosome during axonal injury

ABBREVIATIONS

Atg5: Autophagy-related 5; Atg8a: Autophagy-related 8a; AL: autolysosome; AP: autophagosome; BAF1: bafilomycin A1; BDNF: brain derived neurotrophic factor; BMP: bone morphogenetic protein; Cyt-c-p: Cytochrome c proximal; CQ: chloroquine; DCTN1: dynactin 1; Dhc: dynein heavy chain; EE: early endosome; DYNC1I1: dynein cytoplasmic 1 intermediate chain 1; HD: Huntington disease; HIP1/Hip1: huntingtin interacting protein 1; HTT/htt: huntingtin; iNeuron: iPSC-derived human neurons; IP: immunoprecipitation; Khc: kinesin heavy chain; KIF5C: kinesin family member 5C; LAMP1/Lamp1: lysosomal associated membrane protein 1; LE: late endosome; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAP3K12/DLK: mitogen-activated protein kinase kinase kinase 12; MAPK8/JNK/bsk: mitogen-activated protein kinase 8/basket; MAPK8IP3/JIP3: mitogen-activated protein kinase 8 interacting protein 3; NGF: nerve growth factor; NMJ: neuromuscular junction; NTRK1/TRKA: neurotrophic receptor tyrosine kinase 1; NRTK2/TRKB: neurotrophic receptor tyrosine kinase 2; nuf: nuclear fallout; PG: phagophore; PtdIns3P: phosphatidylinositol-3-phosphate; puc: puckered; ref(2)P: refractory to sigma P; Rilpl: Rab interacting lysosomal protein like; Rip11: Rab11 interacting protein; RTN1: reticulon 1; syd: sunday driver; SYP: synaptophysin; SYT1/Syt1: synaptotagmin 1; STX17/Syx17: syntaxin 17; tkv: thickveins; VF: vesicle fraction; wit: wishful thinking; wnd: wallenda.

Impaired Autophagy in Krabbe Disease: The Role of BCL2 and Beclin-1 Phosphorylation

Autophagic impairment was identified in many lysosomal storage diseases and adult neurodegenerative diseases. It seems that this defect could be directly related to the appearance of a neurodegenerative phenotype and could contribute to worsen metabolite accumulation and lysosomal distress. Thus, autophagy is becoming a promising target for supportive therapies. Autophagy alterations were recently identified also in Krabbe disease. Krabbe disease is characterized by extensive demyelination and dysmyelination and it is due to the genetic loss of function of the lysosomal enzyme galactocerebrosidase (GALC). This enzyme leads to the accumulation of galactosylceramide, psychosine, and secondary substrates such as lactosylceramide. In this paper, we induced autophagy through starvation and examined the cellular response occurring in fibroblasts isolated from patients. We demonstrated that the inhibitory AKT-mediated phosphorylation of beclin-1 and the BCL2-beclin-1 complex concur to reduce autophagosomes formation in response to starvation. These events were not dependent on the accumulation of psychosine, which was previously identified as a possible player in autophagic impairment in Krabbe disease. We believe that these data could better elucidate the capability of response to autophagic stimuli in Krabbe disease, in order to identify possible molecules able to stimulate the process.

PACSIN2 as a modulator of autophagy and mercaptopurine cytotoxicity: mechanisms in lymphoid and intestinal cells

PACSIN2 variants are associated with gastrointestinal effects of thiopurines and thiopurine methyltransferase activity through an uncharacterized mechanism that is postulated to involve autophagy. This study aims to clarify the role of PACSIN2 in autophagy and in thiopurine cytotoxicity in leukemic and intestinal models. Higher autophagy and lower PACSIN2 levels were observed in inflamed compared with non-inflamed colon biopsies of inflammatory bowel disease pediatric patients at diagnosis. PACSIN2 was identified as an inhibitor of autophagy, putatively through inhibition of autophagosome formation by a protein-protein interaction with LC3-II, mediated by a LIR motif. Moreover, PACSIN2 resulted a modulator of mercaptopurine-induced cytotoxicity in intestinal cells, suggesting that PACSIN2-regulated autophagy levels might influence thiopurine sensitivity. However, PACSIN2 modulates cellular thiopurine methyltransferase activity via mechanisms distinct from its modulation of autophagy.

Neutrophil CEACAM1 determines susceptibility to NETosis by regulating the S1PR2/S1PR3 axis in liver transplantation

Neutrophils, the largest innate immune cell population in humans, are the primary proinflammatory sentinel in the ischemia-reperfusion injury (IRI) mechanism in orthotopic liver transplantation (OLT). Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1, CC1, or CD66a) is essential in neutrophil activation and serves as a checkpoint regulator of innate immune-driven IRI cascade in OLT. Although CC1 alternative splicing generates two functionally distinct short and long cytoplasmic isoforms, their role in neutrophil activation remains unknown. Here, we undertook molecular and functional studies to interrogate the significance of neutrophil CC1 signaling in mouse and human OLT recipients. In the experimental arm, we employed a mouse OLT model to document that ablation of recipient-derived neutrophil CC1-long (CC1-L) isotype aggravated hepatic IRI by promoting neutrophil extracellular traps (NETs). Notably, by regulating the S1P-S1PR2/S1PR3 axis, neutrophil CC1-L determined susceptibility to NET formation via autophagy signaling. In the clinical arm, liver grafts from 55 transplant patients selectively enriched for neutrophil CC1-L showed relative resistance to ischemia-reperfusion (IR) stress/tissue damage, improved hepatocellular function, and clinical outcomes. In conclusion, despite neutrophils being considered a principal villain in peritransplant tissue injury, their CC1-L isoform may serve as a regulator of IR stress resistance/NETosis in human and mouse OLT recipients.

V-ATPase/TORC1-mediated ATFS-1 translation directs mitochondrial UPR activation in C. elegans

To adapt mitochondrial function to the ever-changing intra- and extracellular environment, multiple mitochondrial stress response (MSR) pathways, including the mitochondrial unfolded protein response (UPRmt), have evolved. However, how the mitochondrial stress signal is sensed and relayed to UPRmt transcription factors, such as ATFS-1 in Caenorhabditis elegans, remains largely unknown. Here, we show that a panel of vacuolar H+-ATPase (v-ATPase) subunits and the target of rapamycin complex 1 (TORC1) activity are essential for the cytosolic relay of mitochondrial stress to ATFS-1 and for the induction of the UPRmt. Mechanistically, mitochondrial stress stimulates v-ATPase/Rheb-dependent TORC1 activation, subsequently promoting ATFS-1 translation. Increased translation of ATFS-1 upon mitochondrial stress furthermore relies on a set of ribosomal components but is independent of GCN-2/PEK-1 signaling. Finally, the v-ATPase and ribosomal subunits are required for mitochondrial surveillance and mitochondrial stress-induced longevity. These results reveal a v-ATPase-TORC1-ATFS-1 signaling pathway that links mitochondrial stress to the UPRmt through intimate crosstalks between multiple organelles.

Targeting of phagolysosomes containing conidia of the fungus Aspergillus fumigatus with polymeric particles

Conidia of the airborne human-pathogenic fungus Aspergillus fumigatus are inhaled by humans. In the lung, they are phagocytosed by alveolar macrophages and intracellularly processed. In macrophages, however, conidia can interfere with the maturation of phagolysosomes to avoid their elimination. To investigate whether polymeric particles (PPs) can reach this intracellular pathogen in macrophages, we formulated dye-labeled PPs with a size allowing for their phagocytosis. PPs were efficiently taken up by RAW 264.7 macrophages and were found in phagolysosomes. When macrophages were infected with conidia prior to the addition of PPs, we found that they co-localized in the same phagolysosomes. Mechanistically, the fusion of phagolysosomes containing PPs with phagolysosomes containing conidia was observed. Increasing concentrations of PPs increased fusion events, resulting in 14% of phagolysosomes containing both conidia and PPs. We demonstrate that PPs can reach conidia-containing phagolysosomes, making these particles a promising carrier system for antimicrobial drugs to target intracellular pathogens. KEY POINTS: • Polymer particles of a size larger than 500 nm are internalized by macrophages and localized in phagolysosomes. • These particles can be delivered to Aspergillus fumigatus conidia-containing phagolysosomes of macrophages. • Enhanced phagolysosome fusion by the use of vacuolin1 can increase particle delivery.

AP2S1 regulates APP degradation through late endosome-lysosome fusion in cells and APP/PS1 mice

AP2S1 is the sigma 2 subunit of adaptor protein 2 (AP2) that is essential for endocytosis. In this study, we investigated the potential role of AP2S1 in intracellular processing of amyloid precursor protein (APP), which contributes to the pathogenesis of Alzheimer disease (AD) by generating the toxic β-amyloid peptide (Aβ). We found that knockdown or overexpression of AP2S1 decreased or increased the protein levels of APP and Aβ in cells stably expressing human full-length APP695, respectively. This effect was unrelated to endocytosis but involved lysosomal degradation. Morphological studies revealed that silencing of AP2S1 promoted the translocalization of APP from RAB9-positive late endosomes (LE) to LAMP1-positive lysosomes, which was paralleled by the enhanced LE-lysosome fusion. In support, silencing of vacuolar protein sorting-associated protein 41 (VPS41) that is implicated in LE-lyso fusion prevented AP2S1-mediated regulation of APP degradation and translocalization. In APP/PS1 mice, an animal model of AD, AAV-mediated delivery of AP2S1 shRNA in the hippocampus significantly reduced the protein levels of APP and Aβ, with the concomitant APP translocalization, LE-lyso fusion and the improved cognitive functions. Taken together, these data uncover a LE-lyso fusion mechanism in APP degradation and suggest a novel role for AP2S1 in the pathophysiology of AD.

Mucopolysaccharidoses: Cellular Consequences of Glycosaminoglycans Accumulation and Potential Targets

Mucopolysaccharidoses (MPSs) constitute a heterogeneous group of lysosomal storage disorders characterized by the lysosomal accumulation of glycosaminoglycans (GAGs). Although lysosomal dysfunction is mainly affected, several cellular organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus, and their related process are also impaired, leading to the activation of pathophysiological cascades. While supplying missing enzymes is the mainstream for the treatment of MPS, including enzyme replacement therapy (ERT), hematopoietic stem cell transplantation (HSCT), or gene therapy (GT), the use of modulators available to restore affected organelles for recovering cell homeostasis may be a simultaneous approach. This review summarizes the current knowledge about the cellular consequences of the lysosomal GAGs accumulation and discusses the use of potential modulators that can reestablish normal cell function beyond ERT-, HSCT-, or GT-based alternatives.

Extracellular Vesicles as an Endocrine Mechanism Connecting Distant Cells

The field of extracellular vesicles (EVs) has expanded tremendously over the last decade. The role of cell-to-cell communication in neighboring or distant cells has been increasingly ascribed to EVs generated by various cells. Initially, EVs were thought to a means of cellular debris or disposal system of unwanted cellular materials that provided an alternative to autolysis in lysosomes. Intercellular exchange of information has been considered to be achieved by well-known systems such as hormones, cytokines, and nervous networks. However, most research in this field has searched for and found evidence to support paracrine or endocrine roles of EV, which inevitably leads to a new concept that EVs are synthesized to achieve their paracrine or endocrine purposes. Here, we attempted to verify the endocrine role of EV production and their contents, such as RNAs and bioactive proteins, from the regulation of biogenesis, secretion, and action mechanisms while discussing the current technical limitations. It will also be important to discuss how blood EV concentrations are regulated as if EVs are humoral endocrine machinery.

Pre-treatment or post-treatment with hydroxychloroquine demonstrates neuroprotective effects in cerebral ischemia/reperfusion

Stroke is a serious life-threatening medical condition and is one of the principal reasons for death and disabilities worldwide. The aim of the present study was to determine the neuroprotective effects of hydroxychloroquine (HCQ) and the timing of its administration in cerebral ischemia/reperfusion (I/R) in rats. A global I/R model was used, and HCQ was administered in either pre- or post-treatment doses of 25 and 50 mg/kg. Effects of HCQ on infarct size, histological changes, oxidative stress, and learning and memory were evaluated. Phospho-AMPK and SQSTM1/p62 protein levels were also measured to elucidate the possible mechanisms involved. HCQ in both pre- (at doses of 25 and 50 mg/kg) or post-treatment (at a dose of 50 mg/kg) protocols reduces brain infarct size and histopathological changes and improves learning and memory after cerebral I/R. Pre-treatment with HCQ reduced AMPK activity with no significant effect on SQSTM1/p62 increment. Post-treatment with HCQ increased AMPK activity and SQSTM1/p62 protein levels. Our results show the neuroprotective effects of HCQ on cerebral I/R through the reduction in infarct size, histopathological changes, and improvement in memory and learning functions. Moreover, AMPK and autophagy may play a role in this protective effect.

Salmonella Promotes Its Own Survival in B Cells by Inhibiting Autophagy

Salmonella is a Gram-negative bacterium known to be the major cause of gastrointestinal diseases and systemic infections. During infection of murine B cells, Salmonella activates the PI3K/Akt pathway through its effector, SopB. This signaling pathway induces the downregulation of NLRC4 transcription, resulting in reduced secretion of IL-1β. Thus, Salmonella-infected B cells do not progress to pyroptosis; consequently, the bacteria can survive inside these cells. However, the mechanism by which Salmonella evades the control of B cells has not yet been elucidated. In this study, we found that SopB activates mTORC1, which is necessary for bacterial survival, since B cells cultured with the mTORC1 inhibitor rapamycin and B cells lacking raptor can control Salmonella infection. A similar result was observed in B cells when they were infected with the Salmonella SopB mutant (Δsopb). Salmonella also promoted the phosphorylation of the ULK1 complex at serine 757 (Ser757) by mTORC1, resulting in decreased levels of LC3-II in infected B cells. In this study, we did not observe these results when B cells were infected with Δsopb Salmonella. Our results demonstrated that Salmonella survival within B cells depends on the inhibition of autophagy by mTORC1 activation.

Blocking autophagy with chloroquine aggravates lipid accumulation and reduces intracellular energy synthesis in hepatocellular carcinoma cells, both contributing to its anti-proliferative effect

PURPOSE

The autophagy inhibitor chloroquine enhances the effect of targeted therapy using tyrosine kinase inhibitor in liver cancer. We would like to further understand the specific mechanism by which chloroquine inhibits the proliferation of tumor cells.

METHODS

We used a human hepatocarcinoma cell line (HepG2) as cell culture model. In contrast to the control groups (treated only with complete medium), cells in experimental groups were treated either with complete medium + 40 ng/ml Hepatocyte growth factor (HGF), or with complete medium + 60 μM chloroquine or with complete medium + 40 ng/ml HGF + 60 μM chloroquine for 24 h. Cell number and ATP content were investigated using spectrophotometric assays. Cell proliferation and apoptosis were detected by immunohistochemistry. Cell morphological alterations were examined by Giemsa and H&E staining. Cellular lipid content was determined by Oil Red O staining and Triglyceride quantification assay. Autophagy-related proteins (LC3B and p62) and hepatocyte proliferation-related protein (S6K1) were examined using western blot. The autophagic flux of cells was assessed by mRFP-EGFP-LC3 transfection assay.

RESULTS

We found that chloroquine inhibited the proliferation of HepG2 cells, as evidenced by a decrease in cellular ATP content, Ki-67 and S6K1 protein expression and a reduction in cell number. This finding was associated with an increase in lipid content. As expected, chloroquine inhibited autophagy of HepG2 cells, as evidenced by the accumulation of LC3B-II and the significant upregulation of p62. mRFP-EGFP-LC3 transfection assay showed that indeed chloroquine blocked the autophagic flux in HepG2 cells.

CONCLUSION

Chloroquine impaired proliferation of HepG2 cells might be due to intracellular accumulation of lipids and inhibition of energy synthesis.

Dynamics of Endocytosis and Degradation of Antibody-Drug Conjugate T-DM1 in HER2 Positive Cancer Cells

Purpose

T-DM1 is an antibody–drug conjugate (ADC) consisting of trastuzumab and DM1 linked together. T-DM1 binds to human epidermal growth factor receptor-2 (HER2) in tumors and then triggers the endocytosis of T-DM1 and release of payload. Therefore, endocytosis efficacy is considered as a critical step for the initiation of T-DM1 therapy; however, the endocytosis mechanism of T-DM1 remains poorly understood. Meanwhile, HER2 is regarded as an internalization-resistant receptor, which hinders the endocytosis and effectiveness of T-DM1. The present study is to explore the T-DM1 endocytosis pathway, which may provide insights into the internalization mechanism of ADCs and help to improve efficacy.

Methods

Confocal microscopy and flow cytometry were used to analyse T-DM1 intracellular trafficking and endocytosis efficiency, while Western blot assay was performed to detect T-DM1 degradation.

Results

We found that intracellular T-DM1 was increased to 50% within 12 h. T-DM1 was colocalized with cholera toxin B (CTxB), a lipid raft marker, within 2 h and then degraded in lysosome. Upon overexpression of caveolin-1 (CAV-1) and utilization of caveolae/lipid-raft disruptors, we found that temporal CAV-1 upregulation significantly facilitated T-DM1 endocytosis and degradation, whereas nystatin and lovastatin disrupted caveolae/lipid-raft structure and inhibited T-DM1 degradation. We demonstrate that T-DM1 internalizes through the lipid raft-mediated endocytosis in a CAV-1 dependent manner, rather than through the clathrin-mediated endocytosis in HER2-positive cancer cells.

Conclusion

Our findings suggest that modulation of the caveolae/lipid-raft mediated endocytosis may be a possible option for improving the clinical therapeutic effect of T-DM1 because it plays a key role in regulating T-DM1 internalization.

Regulation of basal autophagy by calmodulin availability

Macroautophagy (hereafter autophagy) is a process that degrades cellular components to maintain homeostasis. The Ca²⁺ sensor calmodulin (CaM) regulates numerous cell functions but is a limiting factor due to its insufficient availability for all target proteins. However, evidence that CaM availability regulates basal autophagy is lacking. Here, we have tested this hypothesis. CaM antagonists W-7, trifluoperazine and CGS9343b cause autophagosome accumulation and inhibit basal autophagic flux in the same manner as does chloroquine. These reagents promote the activity of AMP-activated protein kinase (AMPK) but not that of the mechanistic target of rapamycin (mTOR). Competitive binding assays using CaM sensors with different Ca²⁺ dependencies showed that chloroquine directly binds CaM in a Ca²⁺ -dependent fashion. The CaM antagonists have disparate effects on cytoplasmic Ca²⁺ , triggering from none to robust signals, indicating that their consistent inhibition of autophagy is due to inhibition of CaM and not Ca²⁺ . Chelating intracellular Ca²⁺ reduces the effect of the CaM antagonists to accumulate LC3-II, indicating that they do so by inhibiting CaM-dependent activities at basal Ca²⁺ level. The CaM antagonists cause lysosomal alkalinisation. Consistently, buffering CaM with a high-affinity CaM-binding protein that binds CaM at resting Ca²⁺ level increases lysosomal pH. Enhanced CaM buffering using a chimeric protein that contains two high-affinity CaM-binding sites that can collectively bind CaM at a large range of Ca²⁺ further increases lysosomal pH and increases LC3-II accumulation and AMPK activity, but not that of mTOR. These data demonstrate that CaM availability is required for basal autophagy.

The p97 Inhibitor UPCDC-30245 Blocks Endo-Lysosomal Degradation

The diverse modes of action of small molecule inhibitors provide versatile tools to investigate basic biology and develop therapeutics. However, it remains a challenging task to evaluate their exact mechanisms of action. We identified two classes of inhibitors for the p97 ATPase: ATP competitive and allosteric. We showed that the allosteric p97 inhibitor, UPCDC-30245, does not affect two well-known cellular functions of p97, endoplasmic-reticulum-associated protein degradation and the unfolded protein response pathway; instead, it strongly increases the lipidated form of microtubule-associated proteins 1A/1B light chain 3B (LC3-II), suggesting an alteration of autophagic pathways. To evaluate the molecular mechanism, we performed proteomic analysis of UPCDC-30245 treated cells. Our results revealed that UPCDC-30245 blocks endo-lysosomal degradation by inhibiting the formation of early endosome and reducing the acidity of the lysosome, an effect not observed with the potent p97 inhibitor CB-5083. This unique effect allows us to demonstrate UPCDC-30245 exhibits antiviral effects against coronavirus by blocking viral entry.

Danger signal extracellular calcium initiates differentiation of monocytes into SPP1/osteopontin-producing macrophages

The danger signal extracellular calcium is pathophysiologically increased in the synovial fluid of patients with rheumatoid arthritis (RA). Calcium activates the NLRP3-inflammasome via the calcium-sensing receptor in monocytes/macrophages primed by lipopolysaccharide, and this effect is mediated by the uptake of calciprotein particles (CPPs) formed out of calcium, phosphate, and fetuin-A. Aim of the study was to unravel the influence of calcium on monocytes when the priming signal is not present. Monocytes were isolated from the blood of healthy controls and RA patients. Macrophages were characterized using scRNA-seq, DNA microarray, and proteomics. Imaging flow cytometry was utilized to study intracellular events. Here we show that extracellular calcium and CPPs lead to the differentiation of monocytes into calcium-macrophages when the priming signal is absent. Additional growth factors are not needed, and differentiation is triggered by calcium-dependent CPP-uptake, lysosomal alkalization due to CPP overload, and TFEB- and STAT3-dependent increased transcription of the lysosomal gene network. Calcium-macrophages have a needle-like shape, are characterized by excessive, constitutive SPP1/osteopontin production and a strong pro-inflammatory cytokine response. Calcium-macrophages differentiated out of RA monocytes show a stronger manifestation of this phenotype, suggesting the differentiation process might lead to the pro-inflammatory macrophage response seen in the RA synovial membrane.

Robust LC3B lipidation analysis by precisely adjusting autophagic flux

Autophagic flux can be quantified based on the accumulation of lipidated LC3B in the presence of late-stage autophagy inhibitors. This method has been widely applied to identify novel compounds that activate autophagy. Here we scrutinize this approach and show that bafilomycin A1 (BafA) but not chloroquine is suitable for flux quantification due to the stimulating effect of chloroquine on non-canonical LC3B-lipidation. Significant autophagic flux increase by rapamycin could only be observed when combining it with BafA concentrations not affecting basal flux, a condition which created a bottleneck, rather than fully blocking autophagosome-lysosome fusion, concomitant with autophagy stimulation. When rapamycin was combined with saturating concentrations of BafA, no significant further increase of LC3B lipidation could be detected over the levels induced by the late-stage inhibitor. The large assay window obtained by this approach enables an effective discrimination of autophagy activators based on their cellular potency. To demonstrate the validity of this approach, we show that a novel inhibitor of the acetyltransferase EP300 activates autophagy in a mTORC1-dependent manner. We propose that the creation of a sensitized background rather than a full block of autophagosome progression is required to quantitatively capture changes in autophagic flux.

Proteomic Analysis of Trichomonas vaginalis Phagolysosome, Lysosomal Targeting, and Unconventional Secretion of Cysteine Peptidases

The lysosome represents a central degradative compartment of eukaryote cells, yet little is known about the biogenesis and function of this organelle in parasitic protists. Whereas the mannose 6-phosphate (M6P)-dependent system is dominant for lysosomal targeting in metazoans, oligosaccharide-independent sorting has been reported in other eukaryotes. In this study, we investigated the phagolysosomal proteome of the human parasite Trichomonas vaginalis, its protein targeting and the involvement of lysosomes in hydrolase secretion. The organelles were purified using Percoll and OptiPrep gradient centrifugation and a novel purification protocol based on the phagocytosis of lactoferrin-covered magnetic nanoparticles. The analysis resulted in a lysosomal proteome of 462 proteins, which were sorted into 21 classes. Hydrolases represented the largest functional class and included proteases, lipases, phosphatases, and glycosidases. Identification of a large set of proteins involved in vesicular trafficking (80) and turnover of actin cytoskeleton rearrangement (29) indicate a dynamic phagolysosomal compartment. Several cysteine proteases such as TvCP2 were previously shown to be secreted. Our experiments showed that secretion of TvCP2 was strongly inhibited by chloroquine, which increases intralysosomal pH, thus indicating that TvCP2 secretion occurs through lysosomes rather than the classical secretory pathway. Unexpectedly, we identified divergent homologues of the M6P receptor TvMPR in the phagolysosomal proteome, although T. vaginalis lacks enzymes for M6P formation. To test whether oligosaccharides are involved in lysosomal targeting, we selected the lysosome-resident cysteine protease CLCP, which possesses two glycosylation sites. Mutation of any of the sites redirected CLCP to the secretory pathway. Similarly, the introduction of glycosylation sites to secreted β-amylase redirected this protein to lysosomes. Thus, unlike other parasitic protists, T. vaginalis seems to utilize glycosylation as a recognition marker for lysosomal hydrolases. Our findings provide the first insight into the complexity of T. vaginalis phagolysosomes, their biogenesis, and role in the unconventional secretion of cysteine peptidases.

Drosophila D-idua Reduction Mimics Mucopolysaccharidosis Type I Disease-Related Phenotypes

Deficit of the IDUA (α-L-iduronidase) enzyme causes the lysosomal storage disorder mucopolysaccharidosis type I (MPS I), a rare pediatric neurometabolic disease, due to pathological variants in the IDUA gene and is characterized by the accumulation of the undegraded mucopolysaccharides heparan sulfate and dermatan sulfate into lysosomes, with secondary cellular consequences that are still mostly unclarified. Here, we report a new fruit fly RNAi-mediated knockdown model of a IDUA homolog (D-idua) displaying a phenotype mimicking some typical molecular features of Lysosomal Storage Disorders (LSD). In this study, we showed that D-idua is a vital gene in Drosophila and that ubiquitous reduction of its expression leads to lethality during the pupal stage, when the precise degradation/synthesis of macromolecules, together with a functional autophagic pathway, are indispensable for the correct development to the adult stage. Tissue-specific analysis of the D-idua model showed an increase in the number and size of lysosomes in the brain and muscle. Moreover, the incorrect acidification of lysosomes led to dysfunctional lysosome-autophagosome fusion and the consequent block of autophagy flux. A concomitant metabolic drift of glycolysis and lipogenesis pathways was observed. After starvation, D-idua larvae showed a quite complete rescue of both autophagy/lysosome phenotypes and metabolic alterations. Metabolism and autophagy are strictly interconnected vital processes that contribute to maintain homeostatic control of energy balance, and little is known about this regulation in LSDs. Our results provide new starting points for future investigations on the disease’s pathogenic mechanisms and possible pharmacological manipulations.

Catch me if you can - the crosstalk of ZIKV and the restriction factor Tetherin

Zika virus (ZIKV) is a flavivirus that is mainly transmitted by Aedes mosquitos and normally causes mild symptoms. During the outbreak in the Americas in 2015, it was associated with more severe implications, like microcephaly in new-borns and the Gullain-Barré syndrome. The lack of specific vaccines and cures strengthen the need for a deeper understanding of the virus life cycle and virus-host interactions. The restriction factor tetherin (THN) is an interferon-inducible cellular protein with broad antiviral properties. It is known to inhibit the release of various enveloped viruses by tethering them to each other and to the cell membrane, thereby preventing their further spread. On the other hand, different viruses have developed various escape strategies against THN. Analysis of the crosstalk between ZIKV and THN revealed that in spite of a strong induction of THN mRNA expression in ZIKV-infected cells, this is not reflected by an elevated protein level of THN. Contrariwise, the THN protein level is decreased due to a reduced half-life. The increased degradation of THN in ZIKV infected cells involves the endo-lysosomal system, but does not depend on the early steps of autophagy. Enrichment of THN by depletion of the ESCRT-0 protein HRS diminishes ZIKV release and spread, which points out the capacity of THN to restrict ZIKV and explains the enhanced THN degradation in infected cells as an effective viral escape strategy. Importance Although tetherin expression is strongly induced by ZIKV infection there is a reduction in the amount of tetherin protein. This is due to an enhanced lysosomal degradation. However, if tetherin level is rescued release of ZIKV is impaired. This shows that tetherin is a restriction factor for ZIKV and the induction of an efficient degradation represents a viral escape strategy. To our knowledge this is the first study that describes and characterizes tetherin as an restriction factor for ZIKV life cycle.