Sensitive detection of lysosomal membrane permeabilization by lysosomal galectin puncta assay

Hexamethylene amiloride synergizes with venetoclax to induce lysosome-dependent cell death in acute myeloid leukemia

Tumors maintain an alkaline intracellular environment to enable rapid growth. The proton exporter NHE1 participates in maintenance of this pH gradient. However, whether targeting NHE1 could inhibit the growth of tumor cells remains unknown. Here, we report that the NHE1 inhibitor Hexamethylene amiloride (HA) efficiently suppresses the growth of AML cell lines. Moreover, HA combined with venetoclax synergized to efficiently inhibit the growth of AML cells. Interestingly, lysosomes are the main contributors to the synergism of HA and venetoclax in inhibiting AML cells. Most importantly, the combination of HA and venetoclax also had prominent anti-leukemia effects in both xenograft models and bone marrow samples from AML patients. In summary, our results provide evidence that the NHE1 inhibitor HA or its combination with venetoclax efficiently inhibits the growth of AML in vitro and in vivo.

Hyaluronan nanogel co-loaded with chloroquine to enhance intracellular cisplatin delivery through lysosomal permeabilization and lysophagy inhibition

Hyaluronan (HA) has been widely used to construct nanocarriers for cancer-targeted drug delivery, due to its excellent biocompatibility and intrinsic affinity towards CD44 that is overexpressed in most cancer types. However, the HA-based nanocarriers are prone to trapping in lysosomes following the HA-mediated endocytosis, which limited the delivered drug to access its pharmacological action sites and subsequently compromised the therapeutic efficacy. To overcome this intracellular obstacle, here we demonstrated the co-loading of chloroquine (CQ) in HA nanogel could efficiently promote the intracellular delivery of cisplatin. The cisplatin coordination with HA generated the nanogel that could also co-encapsulate CQ (HA/Cis/CQ nanogel). Compared with cisplatin-loaded HA nanogel (HA/Cis), HA/Cis/CQ significantly promoted the lysosomal escape of cisplatin as well as enhanced tumor inhibition in the triple-negative breast cancer model. Mechanism studies suggested that co-delivery of CQ not only induced the lysosomal membrane permeabilization but also inhibited the lysophagy, which collectively contributed to the lysosomal instability and cisplatin escape. This HA/Cis/CQ nanogel elicited less toxicity compared with the combination of free Cis and CQ, thus suggesting a promising HA nanocarrier to boost the cisplatin delivery towards cancer-targeted therapy.

An in vitro-transcribed circular RNA targets the mitochondrial inner membrane cardiolipin to ablate EIF4G2+/PTBP1+ pan-adenocarcinoma

In vitro-transcribed (IVT) mRNA has arisen as a rapid method for the production of nucleic acid drugs. Here, we have constructed an oncolytic IVT mRNA that utilizes human rhinovirus type 2 (HRV2) internal ribosomal entry sites (IRESs) to selectively trigger translation in cancer cells with high expression of EIF4G2 and PTBP1. The oncolytic effect was provided by a long hGSDMDc .825 T>A/c.884 A>G-F1LCT mutant mRNA sequence with mitochondrial inner membrane cardiolipin targeting toxicity that triggers mitophagy. Utilizing the permuted intron-exon (PIE) splicing circularization strategy and lipid nanoparticle (LNP) encapsulation reduced immunogenicity of the mRNA and enabled delivery to eukaryotic cells in vivo. Engineered HRV2 IRESs-GSDMDp.D275E/E295G-F1LCT circRNA-LNPs (GSDMDENG circRNA) successfully inhibited EIF4G2+/PTBP1+ pan-adenocarcinoma xenografts growth. Importantly, in a spontaneous tumor model with abnormal EIF4G2 and PTBP1 caused by KRAS G12D mutation, GSDMDENG circRNA significantly prevented the occurrence of pancreatic, lung and colon adenocarcinoma, improved the survival rate and induced persistent KRAS G12D tumor antigen-specific cytotoxic T lymphocyte responses.

Microglia and Sleep Disorders

Sleep is a physiological state that is essential for maintaining physical and mental health. Sleep disorders and sleep deprivation therefore have many adverse effects, including an increased risk of metabolic diseases and a decline in cognitive function that may be implicated in the long-term development of neurodegenerative diseases. There is increasing evidence that microglia, the resident immune cells of the central nervous system (CNS), are involved in regulating the sleep-wake cycle and the CNS response to sleep alteration and deprivation. In this chapter, we will discuss the involvement of microglia in various sleep disorders, including sleep-disordered breathing, insomnia, narcolepsy, myalgic encephalomyelitis/chronic fatigue syndrome, and idiopathic rapid-eye-movement sleep behavior disorder. We will also explore the impact of acute and chronic sleep deprivation on microglial functions. Moreover, we will look into the potential involvement of microglia in sleep disorders as a comorbidity to Alzheimer's disease and Parkinson's disease.

Constitutive Endolysosomal Perforation in Neurons allows Induction of α-Synuclein Aggregation by Internalized Pre-Formed Fibrils

The endocytic pathway is both an essential route of molecular uptake in cells and a potential entry point for pathology-inducing cargo. The cell-to-cell spread of cytotoxic aggregates, such as those of α-synuclein (α-syn) in Parkinson's Disease (PD), exemplifies this duality. Here we used a human iPSC-derived induced neuronal model (iNs) prone to death mediated by aggregation in late endosomes and lysosomes of endogenous α-syn, seeded by internalized pre-formed fibrils of α-syn (PFFs). This PFF-mediated death was not observed with parental iPSCs or other non-neuronal cells. Using live-cell optical microscopy to visualize the read out of biosensors reporting endo-lysosome wounding, we discovered that up to about 10% of late endosomes and lysosomes in iNs exhibited spontaneous constitutive perforations, regardless of the presence of internalized PFFs. This wounding, absent in parental iPSCs and non-neuronal cells, corresponded to partial damage by nanopores in the limiting membranes of a subset of endolysosomes directly observed by volumetric focused ion beam scanning electron microscopy (FIB-SEM) in iNs and in CA1 pyramidal neurons from mouse brain, and not found in iPSCs or in other non-neuronal cells in culture or in mouse liver and skin. We suggest that the compromised limiting membranes in iNs and neurons in general are the primary conduit for cytosolic α-syn to access PFFs entrapped within endo-lysosomal lumens, initiating PFF-mediated α-syn aggregation. Significantly, eradicating the intrinsic endolysosomal perforations in iNs by inhibiting the endosomal Phosphatidylinositol-3-Phosphate/Phosphatidylinositol 5-Kinase (PIKfyve kinase) using Apilimod or Vacuolin-1 markedly reduced PFF-induced α-syn aggregation, despite PFFs continuing to enter the endolysosomal compartment. Crucially, this intervention also diminished iN death associated with PFF incubation. Our results reveal the surprising presence of intrinsically perforated endo-lysosomes in neurons, underscoring their crucial early involvement in the genesis of toxic α-syn aggregates induced by internalized PFFs. This discovery offers a basis for employing PIKfyve kinase inhibition as a potential therapeutic strategy to counteract synucleinopathies.

Inducin Triggers LC3-Lipidation and ESCRT-Mediated Lysosomal Membrane Repair

Lipidation of the LC3 protein has frequently been employed as a marker of autophagy. However, LC3-lipidation is also triggered by stimuli not related to canonical autophagy. Therefore, characterization of the driving parameters for LC3 lipidation is crucial to understanding the biological roles of LC3. We identified a pseudo-natural product, termed Inducin, that increases LC3 lipidation independently of canonical autophagy, impairs lysosomal function and rapidly recruits Galectin 3 to lysosomes. Inducin treatment promotes Endosomal Sorting Complex Required for Transport (ESCRT)-dependent membrane repair and transcription factor EB (TFEB)-dependent lysosome biogenesis ultimately leading to cell death.

Lipofuscin, Its Origin, Properties, and Contribution to Retinal Fluorescence as a Potential Biomarker of Oxidative Damage to the Retina

Lipofuscin accumulates with age as intracellular fluorescent granules originating from incomplete lysosomal digestion of phagocytosed and autophagocytosed material. The purpose of this review is to provide an update on the current understanding of the role of oxidative stress and/or lysosomal dysfunction in lipofuscin accumulation and its consequences, particularly for retinal pigment epithelium (RPE). Next, the fluorescence of lipofuscin, spectral changes induced by oxidation, and its contribution to retinal fluorescence are discussed. This is followed by reviewing recent developments in fluorescence imaging of the retina and the current evidence on the prognostic value of retinal fluorescence for the progression of age-related macular degeneration (AMD), the major blinding disease affecting elderly people in developed countries. The evidence of lipofuscin oxidation in vivo and the evidence of increased oxidative damage in AMD retina ex vivo lead to the conclusion that imaging of spectral characteristics of lipofuscin fluorescence may serve as a useful biomarker of oxidative damage, which can be helpful in assessing the efficacy of potential antioxidant therapies in retinal degenerations associated with accumulation of lipofuscin and increased oxidative stress. Finally, amendments to currently used fluorescence imaging instruments are suggested to be more sensitive and specific for imaging spectral characteristics of lipofuscin fluorescence.

Imipramine Treatment Alters Sphingomyelin, Cholesterol, and Glycerophospholipid Metabolism in Isolated Macrophage Lysosomes

Lysosomes are degradative organelles that facilitate the removal and recycling of potentially cytotoxic materials and mediate a variety of other cellular processes, such as nutrient sensing, intracellular signaling, and lipid metabolism. Due to these central roles, lysosome dysfunction can lead to deleterious outcomes, including the accumulation of cytotoxic material, inflammation, and cell death. We previously reported that cationic amphiphilic drugs, such as imipramine, alter pH and lipid metabolism within macrophage lysosomes. Therefore, the ability for imipramine to induce changes to the lipid content of isolated macrophage lysosomes was investigated, focusing on sphingomyelin, cholesterol, and glycerophospholipid metabolism as these lipid classes have important roles in inflammation and disease. The lysosomes were isolated from control and imipramine-treated macrophages using density gradient ultracentrifugation, and mass spectrometry was used to measure the changes in their lipid composition. An unsupervised hierarchical cluster analysis revealed a clear differentiation between the imipramine-treated and control lysosomes. There was a significant overall increase in the abundance of specific lipids mostly composed of cholesterol esters, sphingomyelins, and phosphatidylcholines, while lysophosphatidylcholines and ceramides were overall decreased. These results support the conclusion that imipramine's ability to change the lysosomal pH inhibits multiple pH-sensitive enzymes in macrophage lysosomes.

Periplocin suppresses the growth of colorectal cancer cells by triggering LGALS3 (galectin 3)-mediated lysophagy

Colorectal cancer (CRC) is one of the most common malignancies worldwide and remains a major clinical challenge. Periplocin, a major bioactive component of the traditional Chinese herb Cortex periplocae, has recently been reported to be a potential anticancer drug. However, the mechanism of action is poorly understood. Here, we show that periplocin exhibits promising anticancer activity against CRC both in vitro and in vivo. Mechanistically, periplocin promotes lysosomal damage and induces apoptosis in CRC cells. Notably, periplocin upregulates LGALS3 (galectin 3) by binding and preventing LGALS3 from Lys210 ubiquitination-mediated proteasomal degradation, leading to the induction of excessive lysophagy and resultant exacerbation of lysosomal damage. Inhibition of LGALS3-mediated lysophagy attenuates periplocin-induced lysosomal damage and growth inhibition in CRC cells, suggesting a critical role of lysophagy in the anticancer effects of periplocin. Taken together, our results reveal a novel link between periplocin and the lysophagy machinery, and indicate periplocin as a potential therapeutic option for the treatment of CRC.Abbreviations: 3-MA: 3-methyladenine; ACACA/ACC1: acetyl-CoA carboxylase alpha; AMPK: adenosine monophosphate-activated protein kinase; AO: Acridine orange; ATG5: autophagy related 5; ATG7: autophagy related 7; CALM: calmodulin; CHX: cycloheximide; CRC: colorectal cancer; CQ: chloroquine; CTSB: cathepsin B; CTSD: cathepsin D; ESCRT: endosomal sorting complex required for transport; LAMP1: lysosomal associated membrane protein 1; LMP: lysosomal membrane permeabilization; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MCOLN1/TRPML1: mucolipin TRP cation channel 1; MKI67/Ki-67: marker of proliferation Ki-67; MTOR: mechanistic target of rapamycin kinase; P2RX4/P2X4: purinergic receptor P2X 4; PARP1/PARP: poly(ADP-ribose) polymerase 1; PRKAA/AMPKα: protein kinase AMP-activated catalytic subunit alpha; SQSTM1/p62: sequestosome 1; TFEB: transcription factor EB; TRIM16: tripartite motif containing 16.

Senescent and disease-associated microglia are modifiable features of aged brain white matter

Brain white matter tracts undergo structural and functional changes linked to late-life cognitive decline, but the cellular and molecular contributions to their selective vulnerability are not well defined. In naturally aged mice, we demonstrate that senescent and disease-associated microglia (DAM) phenotypes converge in hippocampus-adjacent white matter. Through gold-standard gene expression and immunolabeling combined with high-dimensional spatial mapping, we identified microglial cell fates in aged white matter characterized by aberrant morphology, microenvironment reorganization, and expression of senescence and DAM markers, including galectin 3 (GAL3/Lgals3), B-cell lymphoma 2 (Bcl2), and cyclin dependent kinase inhibitors, including Cdkn2a/p16ink4a. Pharmacogenetic or pharmacological targeting of p16ink4a or BCL2 reduced white matter GAL3+ DAM abundance and rejuvenated microglial fimbria organization. Our results demonstrate dynamic changes in microglial identity in aged white matter that can be reverted by senotherapeutic intervention to promote homeostatic maintenance in the aged brain.

Fungal mechanisms of intracellular survival: what can we learn from bacterial pathogens?

Fungal infections represent a major, albeit neglected, public health threat with serious medical and economic burdens globally. With unacceptably high mortality rates, invasive fungal pathogens are responsible for millions of deaths each year, with a steadily increasing incidence primarily in immunocompromised individuals. The poor therapeutic options and rise of antifungal drug resistance pose further challenges in controlling these infections. These fungal pathogens have adapted to survive within mammalian hosts and can establish intracellular niches to promote survival within host immune cells. To do that, they have developed diverse methods to circumvent the innate immune system attack. This includes strategies such as altering their morphology, counteracting macrophage antimicrobial action, and metabolic adaptation. This is reminiscent of how bacterial pathogens have adapted to survive within host cells and cause disease. However, relative to the great deal of information available concerning intracellular bacterial pathogenesis, less is known about the mechanisms fungal pathogens employ. Therefore, here we review our current knowledge and recent advances in our understanding of how fungi can evade and persist within host immune cells. This review will focus on the major fungal pathogens, including Cryptococcus neoformans, Candida albicans, and Aspergillus fumigatus, among others. As we discover and understand the strategies used by these fungi, similarities with their bacterial counterparts are becoming apparent, hence we can use the abundant information from bacteria to guide our studies in fungi. By understanding these strategies, new lines of research will open that can improve the treatments of these devastating fungal diseases.

Lysosome-Associated Membrane Protein 3 Induces Lysosome-Dependent Cell Death by Impairing Autophagic Caspase 8 Degradation in the Salivary Glands of Individuals With Sjögren's Disease

OBJECTIVE

Lysosome-associated membrane protein 3 (LAMP3) overexpression is implicated in the development and progression of Sjögren's disease (SjD) by inducing lysosomal membrane permeabilization (LMP) and apoptotic cell death in salivary gland epithelium. The aim of this study was to clarify the molecular details of LAMP3-induced lysosome-dependent cell death and to test lysosomal biogenesis as a therapeutic intervention.

METHODS

Human labial minor salivary gland biopsies were analyzed using immunofluorescence staining for LAMP3 expression levels and galectin-3 puncta formation, a marker of LMP. Expression level of caspase 8, an initiator of LMP, was determined by Western blotting in cell culture. Galectin-3 puncta formation and apoptosis were evaluated in cell cultures and a mouse model treated with glucagon-like peptide 1 receptor (GLP-1R) agonists, a known promoter of lysosomal biogenesis.

RESULTS

Galectin-3 puncta formation was more frequent in the salivary glands of SjD patients compared to control glands. The proportion of galectin-3 puncta-positive cells was positively correlated with LAMP3 expression levels in the glands. LAMP3 overexpression increased caspase 8 expression, and knockdown of caspase 8 decreased galectin-3 puncta formation and apoptosis in LAMP3-overexpressing cells. Inhibition of autophagy increased caspase 8 expression, while restoration of lysosomal function using GLP-1R agonists decreased caspase 8 expression, which reduced galectin-3 puncta formation and apoptosis in both LAMP3-overexpressing cells and mice.

CONCLUSION

LAMP3 overexpression induced lysosomal dysfunction, resulting in lysosome-dependent cell death via impaired autophagic caspase 8 degradation, and restoring lysosomal function using GLP-1R agonists could prevent this. These findings suggested that LAMP3-induced lysosomal dysfunction is central to disease development and is a target for therapeutic intervention in SjD.

Lysosomal Function and Intracellular Position Determine the Malignant Phenotype in Malignant Melanoma

Lysosomes are central in cell homeostasis and participate in macromolecular degradation, plasma membrane repair, exosome release, cell adhesion/migration, and apoptosis. In cancer, alterations in lysosomal function and spatial distribution may facilitate disease progression. In this study, we show enhanced lysosomal activity in malignant melanoma cells compared with that in normal human melanocytes. Most lysosomes show perinuclear location in melanocytes, while they are more dispersed in melanoma, with retained proteolytic activity and low pH also in the peripheral population. Rab7a expression is lower in melanoma cells than in melanocytes, and by increasing Rab7a, lysosomes are relocated to the perinuclear region in melanoma. Exposure to the lysosome-destabilizing drug L-leucyl-L-leucine methyl ester causes higher damage in the perinuclear subset of lysosomes in melanomas, whereas differences in subpopulation susceptibility cannot be found in melanocytes. Interestingly, melanoma cells recruit the endosomal sorting complex required for transport-III core protein CHMP4B, involved in lysosomal membrane repair, rather than initiate lysophagy. However, when the perinuclear lysosomal position is promoted by Rab7a overexpression or kinesore treatment, lysophagy is increased. In addition, Rab7a overexpression is accompanied by reduced migration capacity. Taken together, the study emphasizes that alterations in lysosomal properties facilitate the malignant phenotype and declares the targeting of lysosomal function as a future therapeutic approach.

Real-Time Monitoring of Lysosomal Membrane Permeabilization Using Acridine Orange

Loss of lysosomal membrane integrity results in leakage of lysosomal hydrolases to the cytosol which might harm cell function and induce cell death. Destabilization of lysosomes often precede apoptotic or necrotic cell death and occur during both physiological and pathological conditions. The weak base acridine orange readily enters cells and accumulates in the acidic environment of lysosomes. Vital staining with acridine orange is a well-proven technique to observe lysosomal destabilization using fluorescence microscopy and flow cytometry. These analyses are, however, time consuming and only adapted for discrete time points, which make them unsuitable for large-scale approaches. Therefore, we have developed a time-saving, high-throughput microplate reader-based method to follow destabilization of the lysosomal membrane in real-time using acridine orange. This protocol can easily be adopted for patient samples since the number of cells per sample is low and the time for analysis is short.

Induction of lysosomal exocytosis and biogenesis via TRPML1 activation for the treatment of uranium-induced nephrotoxicity

Uranium (U) is a well-known nephrotoxicant which forms precipitates in the lysosomes of renal proximal tubular epithelial cells (PTECs) after U-exposure at a cytotoxic dose. However, the roles of lysosomes in U decorporation and detoxification remain to be elucidated. Mucolipin transient receptor potential channel 1 (TRPML1) is a major lysosomal Ca2+ channel regulating lysosomal exocytosis. We herein demonstrate that the delayed administration of the specific TRPML1 agonist ML-SA1 significantly decreases U accumulation in the kidney, mitigates renal proximal tubular injury, increases apical exocytosis of lysosomes and reduces lysosomal membrane permeabilization (LMP) in renal PTECs of male mice with single-dose U poisoning or multiple-dose U exposure. Mechanistic studies reveal that ML-SA1 stimulates intracellular U removal and reduces U-induced LMP and cell death through activating the positive TRPML1-TFEB feedback loop and consequent lysosomal exocytosis and biogenesis in U-loaded PTECs in vitro. Together, our studies demonstrate that TRPML1 activation is an attractive therapeutic strategy for the treatment of U-induced nephrotoxicity.

Oxidative stress induces lysosomal membrane permeabilization and ceramide accumulation in retinal pigment epithelial cells

Oxidative stress has been implicated in the pathogenesis of age-related macular degeneration, the leading cause of blindness in older adults, with retinal pigment epithelium (RPE) cells playing a key role. To better understand the cytotoxic mechanisms underlying oxidative stress, we used cell culture and mouse models of iron overload, as iron can catalyze reactive oxygen species formation in the RPE. Iron-loading of cultured induced pluripotent stem cell-derived RPE cells increased lysosomal abundance, impaired proteolysis and reduced the activity of a subset of lysosomal enzymes, including lysosomal acid lipase (LIPA) and acid sphingomyelinase (SMPD1). In a liver-specific Hepc (Hamp) knockout murine model of systemic iron overload, RPE cells accumulated lipid peroxidation adducts and lysosomes, developed progressive hypertrophy and underwent cell death. Proteomic and lipidomic analyses revealed accumulation of lysosomal proteins, ceramide biosynthetic enzymes and ceramides. The proteolytic enzyme cathepsin D (CTSD) had impaired maturation. A large proportion of lysosomes were galectin-3 (Lgals3) positive, suggesting cytotoxic lysosomal membrane permeabilization. Collectively, these results demonstrate that iron overload induces lysosomal accumulation and impairs lysosomal function, likely due to iron-induced lipid peroxides that can inhibit lysosomal enzymes.

Antiretroviral treatment reveals a novel role for lysosomes in oligodendrocyte maturation

White matter deficits are a common neuropathologic finding in neurologic disorders, including HIV-associated neurocognitive disorders (HAND). In HAND, the persistence of white matter alterations despite suppressive antiretroviral (ARV) therapy suggests that ARVs may be directly contributing to these impairments. Here, we report that a frontline ARV, bictegravir (BIC), significantly attenuates remyelination following cuprizone-mediated demyelination, a model that recapitulates acute demyelination, but has no impact on already formed mature myelin. Mechanistic studies utilizing primary rat oligodendrocyte precursor cells (OPCs) revealed that treatment with BIC leads to significant decrease in mature oligodendrocytes accompanied by lysosomal deacidification and impairment of lysosomal degradative capacity with no alterations in lysosomal membrane permeability or total lysosome number. Activation of the endolysosomal cation channel TRPML1 prevents both lysosomal deacidification and impairment of oligodendrocyte differentiation by BIC. Lastly, we show that deacidification of lysosomes by compounds that raise lysosomal pH is sufficient to prevent maturation of oligodendrocytes. Overall, this study has uncovered a critical role for lysosomal acidification in modulating oligodendrocyte function and has implications for neurologic diseases characterized by lysosomal dysfunction and white matter abnormalities.

The interrelation of galectins and autophagy

Autophagy is a vital physiological process that maintains intracellular homeostasis by removing damaged organelles and senescent or misfolded molecules. However, excessive autophagy results in cell death and apoptosis, which will lead to a variety of diseases. Galectins are a type of animal lectin that binds to β-galactosides and can bind to the cell surface or extracellular matrix glycans, affecting a variety of immune processes in vivo and being linked to the development of many diseases. In many cases, galectins and autophagy both play important regulatory roles in the cellular life course, yet our understanding of the relationship between them is still incomplete. Galectins and autophagy may share common etiological cofactors for some diseases. Hence, we summarize the relationship between galectins and autophagy, aiming to draw attention to the existence of multiple associations between galectins and autophagy in a variety of physiological and pathological processes, which provide new ideas for etiological diagnosis, drug development, and therapeutic targets for related diseases.

ATG5 provides host protection acting as a switch in the atg8ylation cascade between autophagy and secretion

ATG5 is a part of the E3 ligase directing lipidation of ATG8 proteins, a process central to membrane atg8ylation and canonical autophagy. Loss of Atg5 in myeloid cells causes early mortality in murine models of tuberculosis. This in vivo phenotype is specific to ATG5. Here, we show using human cell lines that absence of ATG5, but not of other ATGs directing canonical autophagy, promotes lysosomal exocytosis and secretion of extracellular vesicles and, in murine Atg5fl/fl LysM-Cre neutrophils, their excessive degranulation. This is due to lysosomal disrepair in ATG5 knockout cells and the sequestration by an alternative conjugation complex, ATG12-ATG3, of ESCRT protein ALIX, which acts in membrane repair and exosome secretion. These findings reveal a previously undescribed function of ATG5 in its host-protective role in murine experimental models of tuberculosis and emphasize the significance of the branching aspects of the atg8ylation conjugation cascade beyond the canonical autophagy.

C4b-binding protein inhibits particulate- and crystalline-induced NLRP3 inflammasome activation

Dysregulated NLRP3 inflammasome activation drives a wide variety of diseases, while endogenous inhibition of this pathway is poorly characterised. The serum protein C4b-binding protein (C4BP) is a well-established inhibitor of complement with emerging functions as an endogenously expressed inhibitor of the NLRP3 inflammasome signalling pathway. Here, we identified that C4BP purified from human plasma is an inhibitor of crystalline- (monosodium urate, MSU) and particulate-induced (silica) NLRP3 inflammasome activation. Using a C4BP mutant panel, we identified that C4BP bound these particles via specific protein domains located on the C4BP α-chain. Plasma-purified C4BP was internalised into MSU- or silica-stimulated human primary macrophages, and inhibited MSU- or silica-induced inflammasome complex assembly and IL-1β cytokine secretion. While internalised C4BP in MSU or silica-stimulated human macrophages was in close proximity to the inflammasome adaptor protein ASC, C4BP had no direct effect on ASC polymerisation in in vitro assays. C4BP was also protective against MSU- and silica-induced lysosomal membrane damage. We further provide evidence for an anti-inflammatory function for C4BP in vivo, as C4bp^-/- mice showed an elevated pro-inflammatory state following intraperitoneal delivery of MSU. Therefore, internalised C4BP is an inhibitor of crystal- or particle-induced inflammasome responses in human primary macrophages, while murine C4BP protects against an enhanced inflammatory state in vivo. Our data suggests C4BP has important functions in retaining tissue homeostasis in both human and mice as an endogenous serum inhibitor of particulate-stimulated inflammasome activation.

Galectin-3 shapes toxic alpha-synuclein strains in Parkinson's disease

Parkinson's Disease (PD) is a neurodegenerative and progressive disorder characterised by intracytoplasmic inclusions called Lewy bodies (LB) and degeneration of dopaminergic neurons in the substantia nigra (SN). Aggregated α-synuclein (αSYN) is known to be the main component of the LB. It has also been reported to interact with several proteins and organelles. Galectin-3 (GAL3) is known to have a detrimental function in neurodegenerative diseases. It is a galactose-binding protein without known catalytic activity and is expressed mainly by activated microglial cells in the central nervous system (CNS). GAL3 has been previously found in the outer layer of the LB in post-mortem brains. However, the role of GAL3 in PD is yet to be elucidated. In post-mortem samples, we identified an association between GAL3 and LB in all the PD subjects studied. GAL3 was linked to less αSYN in the LB outer layer and other αSYN deposits, including pale bodies. GAL3 was also associated with disrupted lysosomes. In vitro studies demonstrate that exogenous recombinant Gal3 is internalised by neuronal cell lines and primary neurons where it interacts with endogenous αSyn fibrils. In addition, aggregation experiments show that Gal3 affects spatial propagation and the stability of pre-formed αSyn fibrils resulting in short, amorphous toxic strains. To further investigate these observations in vivo, we take advantage of WT and Gal3KO mice subjected to intranigral injection of adenovirus overexpressing human αSyn as a PD model. In line with our in vitro studies, under these conditions, genetic deletion of GAL3 leads to increased intracellular αSyn accumulation within dopaminergic neurons and remarkably preserved dopaminergic integrity and motor function. Overall, our data suggest a prominent role for GAL3 in the aggregation process of αSYN and LB formation, leading to the production of short species to the detriment of larger strains which triggers neuronal degeneration in a mouse model of PD.

Unresolved Excess Accumulation of Myelin-Derived Cholesterol Contributes to Scar Formation after Spinal Cord Injury

Spinal cord injury triggers complex pathological cascades, resulting in destructive tissue damage and incomplete tissue repair. Scar formation is generally considered a barrier for regeneration in the central nervous system. However, the intrinsic mechanism of scar formation after spinal cord injury has not been fully elucidated. Here, we report that excess cholesterol accumulates in phagocytes and is inefficiently removed from spinal cord lesions in young adult mice. Interestingly, we observed that excessive cholesterol also accumulates in injured peripheral nerves but is subsequently removed by reverse cholesterol transport. Meanwhile, preventing reverse cholesterol transport leads to macrophage accumulation and fibrosis in injured peripheral nerves. Furthermore, the neonatal mouse spinal cord lesions are devoid of myelin-derived lipids and can heal without excess cholesterol accumulation. We found that transplantation of myelin into neonatal lesions disrupts healing with excessive cholesterol accumulation, persistent macrophage activation, and fibrosis. Myelin internalization suppresses macrophage apoptosis mediated by CD5L expression, indicating that myelin-derived cholesterol plays a critical role in impaired wound healing. Taken together, our data suggest that the central nervous system lacks an efficient approach for cholesterol clearance, resulting in excessive accumulation of myelin-derived cholesterol, thereby inducing scar formation after injury.

Nanoplastics Shape Adaptive Anticancer Immunity in the Colon in Mice

The impact of nanoplastics (NPs) on human health is still not well understood, and more research is needed to better understand the risks associated with these particles. In this study, we found that oral administration of polyethylene (PE) NPs in a mice model significantly disrupted the intestinal microenvironment, which shapes adaptive immune response and favors the established in situ colorectal tumor growth. Using single-cell RNA sequencing technology, we show that NPs triggered colon IL-1β-producing macrophages by inducing lysosome damage, leading to colonic Treg and Th17 differentiation associated with T cell exhaustion, which creates a colon environment that favors the tumor initiation and progress. A similar effect is also observed in polystyrene NPs. Our result provides insight into the potential link between NPs ingestion and colon tumorigenesis, and the urgency of addressing plastic pollution worldwide.

Oral feeding of nanoplastics affects brain function of mice by inducing macrophage IL-1 signal in the intestine

Nanoplastics (NPs) as contaminants in food and water have drawn increasing public attention. However, little is known about how NPs shape the gut immune landscape after injection. In this study, we fabricate NPs (∼500 nm) and microplastics (MPs) (∼2 μm) and evaluate their in vivo effects by feeding them to mice. The results suggest that NPs show a better ability to induce gut macrophage activation than MPs. In addition, NPs trigger gut interleukin-1 (IL-1)-producing macrophage reprogramming via inducing lysosomal damage. More importantly, IL-1 signaling from the intestine can affect brain immunity, leading to microglial activation and Th17 differentiation, all of which correlates with a decline in cognitive and short-term memory in NP-fed mice. Thus, this study provides insight into the mechanism of action of the gut-brain axis, delineates the way NPs reduce brain function, and highlights the importance of fixing the plastic pollution problem worldwide.

Proteostasis and lysosomal quality control deficits in Alzheimer's disease neurons

The role of proteostasis and organelle homeostasis dysfunction in human aging and Alzheimer's disease (AD) remains unclear. Analyzing proteome-wide changes in human donor fibroblasts and their corresponding transdifferentiated neurons (tNeurons), we find aging and AD synergistically impair multiple proteostasis pathways, most notably lysosomal quality control (LQC). In particular, we show that ESCRT-mediated lysosomal repair defects are associated with both sporadic and PSEN1 familial AD. Aging- and AD-linked defects are detected in fibroblasts but highly exacerbated in tNeurons, leading to enhanced neuronal vulnerability, unrepaired lysosomal damage, inflammatory factor secretion and cytotoxicity. Surprisingly, tNeurons from aged and AD donors spontaneously develop amyloid-β inclusions co-localizing with LQC markers, LAMP1/2-positive lysosomes and proteostasis factors; we observe similar inclusions in brain tissue from AD patients and APP-transgenic mice. Importantly, compounds enhancing lysosomal function broadly ameliorate these AD-associated pathologies. Our findings establish cell-autonomous LQC dysfunction in neurons as a central vulnerability in aging and AD pathogenesis.

Cationic amphiphilic antihistamines inhibit STAT3 via Ca2+-dependent lysosomal H+ efflux

Commonly used antihistamines and other cationic amphiphilic drugs (CADs) are emerging as putative cancer drugs. Their unique chemical structure enables CADs to accumulate rapidly inside lysosomes, where they increase lysosomal pH, alter lysosomal lipid metabolism, and eventually cause lysosomal membrane permeabilization. Here, we show that CAD-induced rapid elevation in lysosomal pH is caused by a lysosomal H+ efflux that requires P2RX4-mediated lysosomal Ca2+ release and precedes the lysosomal membrane permeabilization. The subsequent cytosolic acidification triggers the dephosphorylation, lysosomal translocation, and inactivation of the oncogenic signal transducer and activator of transcription 3 (STAT3) transcription factor. Moreover, CAD-induced lysosomal H+ efflux sensitizes cancer cells to apoptosis induced by STAT3 inhibition and acts synergistically with STAT3 inhibition in restricting the tumor growth of A549 non-small cell lung carcinoma xenografts. These findings identify lysosomal H+ efflux and STAT3 inhibition as anticancer mechanisms of CADs and reinforce the repurposing of safe and inexpensive CADs as cancer drugs with a drug combination strategy.

The selective autophagy adaptor p62/SQSTM1 forms phase condensates regulated by HSP27 that facilitate the clearance of damaged lysosomes via lysophagy

In response to lysosomal damage, cells engage several quality-control mechanisms, including the selective isolation and degradation of damaged lysosomes by lysophagy. Here, we report that the selective autophagy adaptor SQSTM1/p62 is recruited to damaged lysosomes in both HeLa cells and neurons and is required for lysophagic flux. The Phox and Bem1p (PB1) domain of p62 mediates oligomerization and is specifically required for lysophagy. Consistent with this observation, we find that p62 forms condensates on damaged lysosomes. These condensates are precisely tuned by the small heat shock protein HSP27, which is phosphorylated in response to lysosomal injury and maintains the liquidity of p62 condensates, facilitating autophagosome formation. Mutations in p62 have been identified in patients with amyotrophic lateral sclerosis (ALS); ALS-associated mutations in p62 impair lysophagy, suggesting that deficits in this pathway may contribute to neurodegeneration. Thus, p62 condensates regulated by HSP27 promote lysophagy by forming platforms for autophagosome biogenesis at damaged lysosomes.

TFEB-mediated lysosomal exocytosis alleviates high-fat diet-induced lipotoxicity in the kidney

Obesity is a major risk factor for end-stage kidney disease. We previously found that lysosomal dysfunction and impaired autophagic flux contribute to lipotoxicity in obesity-related kidney disease, in both humans and experimental animal models. However, the regulatory factors involved in countering renal lipotoxicity are largely unknown. Here, we found that palmitic acid strongly promoted dephosphorylation and nuclear translocation of transcription factor EB (TFEB) by inhibiting the mechanistic target of rapamycin kinase complex 1 pathway in a Rag GTPase-dependent manner, though these effects gradually diminished after extended treatment. We then investigated the role of TFEB in the pathogenesis of obesity-related kidney disease. Proximal tubular epithelial cell-specific (PTEC-specific) Tfeb-deficient mice fed a high-fat diet (HFD) exhibited greater phospholipid accumulation in enlarged lysosomes, which manifested as multilamellar bodies (MLBs). Activated TFEB mediated lysosomal exocytosis of phospholipids, which helped reduce MLB accumulation in PTECs. Furthermore, HFD-fed, PTEC-specific Tfeb-deficient mice showed autophagic stagnation and exacerbated injury upon renal ischemia/reperfusion. Finally, higher body mass index was associated with increased vacuolation and decreased nuclear TFEB in the proximal tubules of patients with chronic kidney disease. These results indicate a critical role of TFEB-mediated lysosomal exocytosis in counteracting renal lipotoxicity.

Serine hydroxymethyltransferase 2 knockdown induces apoptosis in ccRCC by causing lysosomal membrane permeabilization via metabolic reprogramming

Serine hydroxymethyltransferase 2 (SHMT2) plays an important role in converting serine to glycine and supplying carbon to one-carbon metabolism to sustain cancer cell proliferation. However, the expression, function, and underlying mechanisms of SHMT2 in clear cell renal cell carcinoma (ccRCC) remain largely unknown. In this study, we demonstrated that SHMT2 was upregulated in ccRCC tissues compared with controls and associated with patient survival. SHMT2 knockdown inhibited proliferation, migration, and invasion in ccRCC cells. Overexpression of SHMT2 promoted tumor progression. Mechanistically, SHMT2 depletion disrupted one-carbon metabolism, increased reactive oxygen species (ROS) levels, and decreased ATP levels via metabolic reprogramming, which destroyed cell homeostasis. The SHMT2 knockdown-induced stress activated autophagy. A mass of autophagosomes fused with lysosomes, resulting in lysosomal membrane permeabilization (LMP) and leakage of lysosomal contents into the cytoplasm, which eventually led to apoptosis. Our work reveals that SHMT2 functions as an oncogenic gene to promote ccRCC progression. SHMT2 depletion induces apoptosis by causing LMP through excessive activation of the autophagy-lysosome pathway via metabolic reprogramming.

Novel Erlotinib-Chalcone Hybrids Diminish Resistance in Head and Neck Cancer by Inducing Multiple Cell Death Mechanisms

In a search for novel therapeutic options for head and neck squamous cell carcinomas (HNSCCs) generally treated with limited therapeutic success, we synthesized a series of novel erlotinib-chalcone molecular hybrids with 1,2,3-triazole and alkyne linkers and evaluated them for their anticancer activity on Fadu, Detroit 562 and SCC-25 HNSCC cell lines. Time- and dose-dependent cell viability measurements disclosed a significantly increased efficiency of the hybrids compared to the 1:1 combination of erlotinib and a reference chalcone. The clonogenic assay demonstrated that hybrids eradicate HNSCC cells in low micromolar concentrations. Experiments focusing on potential molecular targets indicate that the hybrids trigger the anticancer effect by a complementary mechanism of action that is independent of the canonical targets of their molecular fragments. Confocal microscopic imaging and real-time apoptosis/necrosis detection assay pointed to slightly different cell death mechanisms induced by the most prominent triazole- and alkyne-tethered hybrids (6a and 13, respectively). While 6a featured the lowest IC₅₀ values on each of the three HNSCC cell lines, in Detroit 562 cells, this hybrid induced necrosis more markedly compared to 13. The therapeutic potential indicated by the observed anticancer efficacy of our selected hybrid molecules validates the concept of development and justifies further investigation to reveal the underlying mechanism of action.

Targeting UGCG Overcomes Resistance to Lysosomal Autophagy Inhibition

Lysosomal autophagy inhibition (LAI) with hydroxychloroquine or DC661 can enhance cancer therapy, but tumor regrowth is common. To elucidate LAI resistance, proteomics and immunoblotting demonstrated that LAI induced lipid metabolism enzymes in multiple cancer cell lines. Lipidomics showed that LAI increased cholesterol, sphingolipids, and glycosphingolipids. These changes were associated with striking levels of GM1+ membrane microdomains (GMM) in plasma membranes and lysosomes. Inhibition of cholesterol/sphingolipid metabolism proteins enhanced LAI cytotoxicity. Targeting UDP-glucose ceramide glucosyltransferase (UGCG) synergistically augmented LAI cytotoxicity. Although UGCG inhibition decreased LAI-induced GMM and augmented cell death, UGCG overexpression led to LAI resistance. Melanoma patients with high UGCG expression had significantly shorter disease-specific survival. The FDA-approved UGCG inhibitor eliglustat combined with LAI significantly inhibited tumor growth and improved survival in syngeneic tumors and a therapy-resistant patient-derived xenograft. These findings nominate UGCG as a new cancer target, and clinical trials testing UGCG inhibition in combination with LAI are warranted.

SIGNIFICANCE

We discovered UGCG-dependent lipid remodeling drives resistance to LAI. Targeting UGCG with a drug approved for a lysosomal storage disorder enhanced LAI antitumor activity without toxicity. LAI and UGCG inhibition could be tested clinically in multiple cancers. This article is highlighted in the In This Issue feature, p. 247.

Utilizing endosomal capture for tumor therapy via membrane-lytic mechanism-based Pickering emulsion

Nanocarriers are easily captured by endosomes, where the abundant hydrolases inevitably destroy the nanocarriers and the drugs they carry, ultimately resulting in a compromised or lost therapeutic efficacy. Herein, we report a membrane-lytic mechanism-based Pickering emulsion that can in turn utilize this seemingly unfavorable endosomal capture behavior for tumor therapy. This Pickering emulsion is constructed as an oil-in-water (O/W) emulsion stabilized by the hybrid nanoparticles (HNPs) composed of two molecules with opposite charges, cetyl trimethylamine bromide (CTAB) and linoleic acid (LA), through electrostatic interaction (defined as HNPs@PE). After HNPs@PE enters the lysosomes through macropinocytosis-mediated endocytosis, LA can be protonated in response to the acidic stimulus, and causing the swelling or disintegration of HNPs due to the disrupted electrostatic interaction. The released CTAB holds strong membrane-lytic activity and can directly damage the lysosomal membranes. Under the acidic condition and the participation of excessive iron ions (II) in lysosomes, LA induces lipid peroxidation and the resulting lipid peroxides (LPO) will oxidize the lysosomal membranes, collectively causing the leakage of lysosome membranes and the release of contents into cytoplasm. Subsequently, the diffused CTAB and LPO will continue to attack the mitochondrial membranes and cell membranes, resulting in the death of different types of tumor cells both in vitro and in vivo due to membrane damage. This Pickering emulsion with membrane-lytic ability represents a potential self-anticancer nanocarrier.

The role of galectins in immunity and infection

The galectin family consists of carbohydrate (glycan) binding proteins that are expressed by a wide variety of cells and bind to galactose-containing glycans. Galectins can be located in the nucleus or the cytoplasm, or can be secreted into the extracellular space. They can modulate innate and adaptive immune cells by binding to glycans on the surface of immune cells or intracellularly via carbohydrate-dependent or carbohydrate-independent interactions. Galectins expressed by immune cells can also participate in host responses to infection by directly binding to microorganisms or by modulating antimicrobial functions such as autophagy. Here we explore the diverse ways in which galectins have been shown to impact immunity and discuss the opportunities and challenges in the field.

Monitoring Lysosome Function in Ferroptosis

Ferroptosis is a type of regulated cell death that occurs due to iron-induced membrane lipid peroxidation. Lysosomes, which are acidic, membrane-bound organelles containing various hydrolases, play a vital role in ferroptosis. They not only aid in the degradation of autophagic substrates, but also serve as signaling hubs in cell death. Specifically, lysosomes are involved in the induction and execution of ferroptosis through autophagy-mediated degradation of anti-ferroptotic proteins, lysosomal membrane permeability-mediated release of cathepsins, and iron-induced lysosomal membrane lipid peroxidation. Therefore, it is essential to have reliable methods for monitoring lysosomal functions, including lysosomal activity, pH, and membrane integrity, as well as iron accumulation and lipid peroxidation, to understand ferroptosis. This chapter introduces several protocols, such as western blotting, immunofluorescence, lysosomal probes, and lipid peroxidation assay kits, for monitoring the process of lysosome-related ferroptosis.

Boosting ROS-Mediated Lysosomal Membrane Permeabilization for Cancer Ferroptosis Therapy

Due to the deficient catalase, abundant reduced iron and low acidic environment in lysosomes, inducing lysosomal membrane permeabilization (LMP) through Fenton reaction-based reactive oxygen species (ROS) generation recently attracts increasing attention in cancer therapy. However, the lysosomal membranes are protected by highly glycosylated membrane proteins and several endolysosomal damage-response mechanisms can rapidly repair the injured lysosomes. To produce sufficient ROS and cause complete lysosomal membranes rupture, a lysosome-targeted ROS inducer, N-(3-Aminopropyl) morpholine grafted cross-linked lipoic acid vesicles with vitamin C-loading (VC@^N3AM cLAVs), is developed. VC@^N3AM cLAVs efficiently accumulate in lysosomes and convert into two redox couples LA/DHLA (dihydrolipoic acid, reduced form of LA) and VC/DHA (dehydroascorbic acid, oxidized form of VC) by the lysosomal glutathione, which can not only produce a large amount of H₂ O₂ by pro-oxidant action but also accelerate iron transformation through the cyclic redox reactions between each other and cause the efficient conversion of the generated H₂ O₂ into highly toxic •OH. Both in vitro and in vivo experiments demonstrate that VC@^N3AM cLAVs can effectively enhance ROS production and boost LMP, finally initiation irreversible death of tumor cells via ferroptosis pathway, thus representing a potential anticancer drug for cancer therapy.

Sleep-Disturbance-Induced Microglial Activation Involves CRH-Mediated Galectin 3 and Autophagy Dysregulation

Chronic sleep disturbances (CSDs) including insomnia, insufficient sleep time, and poor sleep quality are major public health concerns around the world, especially in developed countries. CSDs are major health risk factors linked to multiple neurodegenerative and neuropsychological diseases. It has been suggested that CSDs could activate microglia (Mg) leading to increased neuroinflammation levels, which ultimately lead to neuronal dysfunction. However, the detailed mechanisms underlying CSD-mediated microglial activation remain mostly unexplored. In this study, we used mice with three-weeks of sleep fragmentation (SF) to explore the underlying pathways responsible for Mg activation. Our results revealed that SF activates Mg in the hippocampus (HP) but not in the striatum and prefrontal cortex (PFc). SF increased the levels of corticotropin-releasing hormone (CRH) in the HP. In vitro mechanism studies revealed that CRH activation of Mg involves galectin 3 (Gal3) upregulation and autophagy dysregulation. CRH could disrupt lysosome membrane integrity resulting in lysosomal cathepsins leakage. CRHR2 blockage mitigated CRH-mediated effects on microglia in vitro. SF mice also show increased Gal3 levels and autophagy dysregulation in the HP compared to controls. Taken together, our results show that SF-mediated hippocampal Mg activation involves CRH mediated galectin 3 and autophagy dysregulation. These findings suggest that targeting the hippocampal CRH system might be a novel therapeutic approach to ameliorate CSD-mediated neuroinflammation and neurodegenerative diseases.

Ursolic Acid Impairs Cellular Lipid Homeostasis and Lysosomal Membrane Integrity in Breast Carcinoma Cells

Cancer is one of the leading causes of death worldwide, thus the search for new cancer therapies is of utmost importance. Ursolic acid is a naturally occurring pentacyclic triterpene with a wide range of pharmacological activities including anti-inflammatory and anti-neoplastic effects. The latter has been assigned to its ability to promote apoptosis and inhibit cancer cell proliferation by poorly defined mechanisms. In this report, we identify lysosomes as the essential targets of the anti-cancer activity of ursolic acid. The treatment of MCF7 breast cancer cells with ursolic acid elevates lysosomal pH, alters the cellular lipid profile, and causes lysosomal membrane permeabilization and leakage of lysosomal enzymes into the cytosol. Lysosomal membrane permeabilization precedes the essential hallmarks of apoptosis placing it as an initial event in the cascade of effects induced by ursolic acid. The disruption of the lysosomal function impairs the autophagic pathway and likely partakes in the mechanism by which ursolic acid kills cancer cells. Furthermore, we find that combining treatment with ursolic acid and cationic amphiphilic drugs can significantly enhance the degree of lysosomal membrane permeabilization and cell death in breast cancer cells.

Repurposing a tricyclic antidepressant in tumor and metabolism disease treatment through fatty acid uptake inhibition

Fatty acid uptake is essential for cell physiological function, but detailed mechanisms remain unclear. Here, we generated an acetyl-CoA carboxylases (ACC1/2) double-knockout cell line, which lacked fatty acid biosynthesis and survived on serum fatty acids and was used to screen for fatty acid uptake inhibitors. We identified a Food and Drug Administration-approved tricyclic antidepressant, nortriptyline, that potently blocked fatty acid uptake both in vitro and in vivo. We also characterized underlying mechanisms whereby nortriptyline provoked lysosomes to release protons and induce cell acidification to suppress macropinocytosis, which accounted for fatty acid endocytosis. Furthermore, nortriptyline alone or in combination with ND-646, a selective ACC1/2 inhibitor, significantly repressed tumor growth, lipogenesis, and hepatic steatosis in mice. Therefore, we show that cells actively take up fatty acids through macropinocytosis, and we provide a potential strategy suppressing tumor growth, lipogenesis, and hepatic steatosis through controlling the cellular level of fatty acids.

Intracellular galectin-3 is a lipopolysaccharide sensor that promotes glycolysis through mTORC1 activation

How the carbohydrate binding protein galectin-3 might act as a diabetogenic and tumorogenic factor remains to be investigated. Here we report that intracellular galectin-3 interacts with Rag GTPases and Ragulator on lysosomes. We show that galectin-3 senses lipopolysaccharide (LPS) to facilitate the interaction of Rag GTPases and Ragulator, leading to the activation of mTORC1. We find that the lipopolysaccharide/galectin-3-Rag GTPases/Ragulator-mTORC1 axis regulates a cohort of genes including GLUT1, and HK2, and PKM2 that are critically involved in glucose uptake and glycolysis. Indeed, galectin-3 deficiency severely compromises LPS-promoted glycolysis. Importantly, the expression of HK2 is significantly reduced in diabetes patients. In multiple types of cancer including hepatocellular carcinoma (HCC), galectin-3 is highly expressed, and its level of expression is positively correlated with that of HK2 and PKM2 and negatively correlated with the prognosis of HCC patients. Our study unravels that galectin-3 is a sensor of LPS, an important modulator of the mTORC1 signaling, and a critical regulator of glucose metabolism.

Catalase-deficient mice induce aging faster through lysosomal dysfunction

BACKGROUND

Lysosomes are a central hub for cellular metabolism and are involved in the regulation of cell homeostasis through the degradation or recycling of unwanted or dysfunctional organelles through the autophagy pathway. Catalase, a peroxisomal enzyme, plays an important role in cellular antioxidant defense by decomposing hydrogen peroxide into water and oxygen. In accordance with pleiotropic significance, both impaired lysosomes and catalase have been linked to many age-related pathologies with a decline in lifespan. Aging is characterized by progressive accumulation of macromolecular damage and the production of high levels of reactive oxygen species. Although lysosomes degrade the most long-lived proteins and organelles via the autophagic pathway, the role of lysosomes and their effect on catalase during aging is not known. The present study investigated the role of catalase and lysosomal function in catalase-knockout (KO) mice.

METHODS

We performed experiments on WT and catalase KO younger (9 weeks) and mature adult (53 weeks) male mice and Mouse embryonic fibroblasts isolated from WT and KO mice from E13.5 embryos as in vivo and in ex-vivo respectively. Mouse phenotyping studies were performed with controls, and a minimum of two independent experiments were performed with more than five mice in each group.

RESULTS

We found that at the age of 53 weeks (mature adult), catalase-KO mice exhibited an aging phenotype faster than wild-type (WT) mice. We also found that mature adult catalase-KO mice induced leaky lysosome by progressive accumulation of lysosomal content, such as cathespin D, into the cytosol. Leaky lysosomes inhibited autophagosome formation and triggered impaired autophagy. The dysregulation of autophagy triggered mTORC1 (mechanistic target of rapamycin complex 1) activation. However, the antioxidant N-acetyl-L-cysteine and mTORC1 inhibitor rapamycin rescued leaky lysosomes and aging phenotypes in catalase-deficient mature adult mice.

CONCLUSIONS

This study unveils the new role of catalase and its role in lysosomal function during aging. Video abstract.

Microscopy-based phenotypic profiling of infection by Staphylococcus aureus clinical isolates reveals intracellular lifestyle as a prevalent feature

Staphylococcus aureus is increasingly recognized as a facultative intracellular pathogen, although the significance and pervasiveness of its intracellular lifestyle remain controversial. Here, we applied fluorescence microscopy-based infection assays and automated image analysis to profile the interaction of 191 S. aureus isolates from patients with bone/joint infections, bacteremia, and infective endocarditis, with four host cell types, at five times post-infection. This multiparametric analysis revealed that almost all isolates are internalized and that a large fraction replicate and persist within host cells, presenting distinct infection profiles in non-professional vs. professional phagocytes. Phenotypic clustering highlighted interesting sub-groups, including one comprising isolates exhibiting high intracellular replication and inducing delayed host death in vitro and in vivo. These isolates are deficient for the cysteine protease staphopain A. This study establishes S. aureus intracellular lifestyle as a prevalent feature of infection, with potential implications for the effective treatment of staphylococcal infections.

Galactosyl- and glucosylsphingosine induce lysosomal membrane permeabilization and cell death in cancer cells

Isomeric lysosphingolipids, galactosylsphingosine (GalSph) and glucosylsphingosine (GlcSph), are present in only minute levels in healthy cells. Due to defects in their lysosomal hydrolysis, they accumulate at high levels and cause cytotoxicity in patients with Krabbe and Gaucher diseases, respectively. Here, we show that GalSph and GlcSph induce lysosomal membrane permeabilization, a hallmark of lysosome-dependent cell death, in human breast cancer cells (MCF7) and primary fibroblasts. Supporting lysosomal leakage as a causative event in lysosphingolipid-induced cytotoxicity, treatment of MCF7 cells with lysosome-stabilizing cholesterol prevented GalSph- and GlcSph-induced cell death almost completely. In line with this, fibroblasts from a patient with Niemann-Pick type C disease, which is caused by defective lysosomal cholesterol efflux, were significantly less sensitive to lysosphingolipid-induced lysosomal leakage and cell death. Prompted by the data showing that MCF7 cells with acquired resistance to lysosome-destabilizing cationic amphiphilic drugs (CADs) were partially resistant to the cell death induced by GalSph and GlcSph, we compared these cell death pathways with each other. Like CADs, GalSph and GlcSph activated the cyclic AMP (cAMP) signalling pathway, and cAMP-inducing forskolin sensitized cells to cell death induced by low concentrations of lysosphingolipids. Contrary to CADs, lysosphingolipid-induced cell death was independent of lysosomal Ca2+ efflux through P2X purinerigic receptor 4. These data reveal GalSph and GlcSph as lysosome-destabilizing lipids, whose putative use in cancer therapy should be further investigated. Furthermore, the data supports the development of lysosome stabilizing drugs for the treatment of Krabbe and Gaucher diseases and possibly other sphingolipidoses.

Galectin-1 and Galectin-3 in B-Cell Precursor Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemias arising from the malignant transformation of B-cell precursors (BCP-ALLs) are protected against chemotherapy by both intrinsic factors as well as by interactions with bone marrow stromal cells. Galectin-1 and Galectin-3 are lectins with overlapping specificity for binding polyLacNAc glycans. Both are expressed by bone marrow stromal cells and by hematopoietic cells but show different patterns of expression, with Galectin-3 dynamically regulated by extrinsic factors such as chemotherapy. In a comparison of Galectin-1 x Galectin-3 double null mutant to wild-type murine BCP-ALL cells, we found reduced migration, inhibition of proliferation, and increased sensitivity to drug treatment in the double knockout cells. Plant-derived carbohydrates GM-CT-01 and GR-MD-02 were used to inhibit extracellular Galectin-1/-3 binding to BCP-ALL cells in co-culture with stromal cells. Treatment with these compounds attenuated migration of the BCP-ALL cells to stromal cells and sensitized human BCP-ALL cells to vincristine and the targeted tyrosine kinase inhibitor nilotinib. Because N-glycan sialylation catalyzed by the enzyme ST6Gal1 can regulate Galectin cell-surface binding, we also compared the ability of BCP-ALL wild-type and ST6Gal1 knockdown cells to resist vincristine treatment when they were co-cultured with Galectin-1 or Galectin-3 knockout stromal cells. Consistent with previous results, stromal Galectin-3 was important for maintaining BCP-ALL fitness during chemotherapy exposure. In contrast, stromal Galectin-1 did not significantly contribute to drug resistance, and there was no clear effect of ST6Gal1-catalysed N-glycan sialylation. Taken together, our results indicate a complicated joint contribution of Galectin-1 and Galectin-3 to BCP-ALL survival, with different roles for endogenous and stromal produced Galectins. These data indicate it will be important to efficiently block both extracellular and intracellular Galectin-1 and Galectin-3 with the goal of reducing BCP-ALL persistence in the protective bone marrow niche during chemotherapy.

Stress granules and mTOR are regulated by membrane atg8ylation during lysosomal damage

We report that lysosomal damage is a hitherto unknown inducer of stress granule (SG) formation and that the process termed membrane atg8ylation coordinates SG formation with mTOR inactivation during lysosomal stress. SGs were induced by lysosome-damaging agents including SARS-CoV-2ORF3a, Mycobacterium tuberculosis, and proteopathic tau. During damage, mammalian ATG8s directly interacted with the core SG proteins NUFIP2 and G3BP1. Atg8ylation was needed for their recruitment to damaged lysosomes independently of SG condensates whereupon NUFIP2 contributed to mTOR inactivation via the Ragulator-RagA/B complex. Thus, cells employ membrane atg8ylation to control and coordinate SG and mTOR responses to lysosomal damage.

Sustained over-expression of calpain-2 induces age-dependent dilated cardiomyopathy in mice through aberrant autophagy

Calpains have been implicated in heart diseases. While calpain-1 has been detrimental to the heart, the role of calpain-2 in cardiac pathology remains controversial. In this study we investigated whether sustained over-expression of calpain-2 had any adverse effects on the heart and the underlying mechanisms. Double transgenic mice (Tg-Capn2/tTA) were generated, which express human CAPN2 restricted to cardiomyocytes. The mice were subjected to echocardiography at age 3, 6, 8 and 12 months, and their heart tissues and sera were collected for analyses. We showed that transgenic mice over-expressing calpain-2 restricted to cardiomyocytes had normal heart function with no evidence of cardiac pathological remodeling at age 3 months. However, they exhibited features of dilated cardiomyopathy including increased heart size, enlarged heart chambers and heart dysfunction from age 8 months; histological analysis revealed loss of cardiomyocytes replaced by myocardial fibrosis and cardiomyocyte hypertrophy in transgenic mice from age 8 months. These cardiac alterations closely correlated with aberrant autophagy evidenced by significantly increased LC3BII and p62 protein levels and accumulation of autophagosomes in the hearts of transgenic mice. Notably, injection of 3-methyladenine, a well-established inhibitor of autophagy (30 mg/kg, i.p. once every 3 days starting from age 6 months for 2 months) prevented aberrant autophagy, attenuated myocardial injury and improved heart function in the transgenic mice. In cultured cardiomyocytes, over-expression of calpain-2 blocked autophagic flux by impairing lysosomal function. Furthermore, over-expression of calpain-2 resulted in lower levels of junctophilin-2 protein in the heart of transgenic mice and in cultured cardiomyocytes, which was attenuated by 3-methyladenine. In addition, blockade of autophagic flux by bafilomycin A (100 nM) induced a reduction of junctophilin-2 protein in cardiomyocytes. In summary, transgenic over-expression of calpain-2 induces age-dependent dilated cardiomyopathy in mice, which may be mediated through aberrant autophagy and a reduction of junctophilin-2. Thus, a sustained increase in calpain-2 may be detrimental to the heart.

LRRK2 recruitment, activity, and function in organelles

Protein coding mutations in leucine-rich repeat kinase 2 (LRRK2) cause familial Parkinson's disease (PD), and noncoding variations around the gene increase the risk of developing sporadic PD. It is generally accepted that pathogenic LRRK2 mutations increase LRRK2 kinase activity, resulting in a toxic hyperactive protein that is inferred to lead to the PD phenotype. LRRK2 has long been linked to different membrane trafficking events, but the specific role of LRRK2 in these events has been difficult to resolve. Recently, several papers have reported the activation and translocation of LRRK2 to cellular organelles under specific conditions, which suggests that LRRK2 may influence intracellular membrane trafficking. Here, we review what is known about the role of LRRK2 at various organelle compartments.

Exosomal and vesicle-free tau seeds-propagation and convergence in endolysosomal permeabilization

In Alzheimer's disease (AD), β-amyloid peptides aggregate to form amyloid plaques, and the microtubule-associated protein tau forms neurofibrillary tangles. However, severity and duration of AD correlate with the stereotypical emergence of tau tangles throughout the brain, suggestive of a gradual region-to-region spreading of pathological tau. The current notion in the field is that misfolded tau seeds propagate transsynaptically and corrupt the proper folding of soluble tau in recipient neurons. This is supported by accumulating evidence showing that in AD, functional connectivity and not proximity predicts the spreading of tau pathology. Tau seeds can be found in two flavors, vesicle-free, that is, naked as in oligomers and fibrils, or encapsulated by membranes of secreted vesicles known as exosomes. Both types of seeds have been shown to propagate between interconnected neurons. Here, we describe potential ways of how their propagation can be controlled in several subcellular compartments by manipulating mechanisms affecting production, neuron-to-neuron transmission, internalization, endosomal escape, and autophagy. We emphasize that although vesicle-free tau seeds and exosomes differ, they share the ability to trigger endolysosomal permeabilization. Such a mechanistic convergence in endolysosomal permeabilization presents itself as a unique opportunity to target both types of tau seeding. We discuss the cellular response to endolysosomal damage that might be key to control permeabilization, and the significant overlap in the seeding mechanism of proteopathic agents other than tau, which suggests that targeting the endolysosomal pathway could pave the way toward developing broad-spectrum treatments for neurodegenerative diseases.

Mesenchymal stem cells exosomal let-7a-5p improve autophagic flux and alleviate liver injury in acute-on-chronic liver failure by promoting nuclear expression of TFEB

Acute-on-chronic liver failure is a distinct clinical syndrome characterized by a dysregulated immune response and extensive hepatocyte death without satisfactory therapies. As a cytoplasmic degradative and quality-control process, autophagy was implicated in maintaining intracellular homeostasis, and decreased hepatic autophagy was found in many liver diseases and contributes to disease pathogenesis. Previously, we identified the therapeutic potential of mesenchymal stem cells (MSCs) in ACLF patients; however, the intrinsic mechanisms are incompletely understood. Herein, we showed that MSCs restored the impaired autophagic flux and alleviated liver injuries in ACLF mice, but these effects were abolished when autophago-lysosomal maturation was inhibited by leupeptin (leu), suggesting that MSCs exerted their hepatoprotective function in a pro-autophagic dependent manner. Moreover, we described a connection between transcription factor EB (TFEB) and autophagic activity in this context, as evidenced by increased nuclei translocation of TFEB elicited by MSCs were capable of promoting liver autophagy. Mechanistically, we confirmed that let-7a-5p enriched in MSCs derived exosomes (MSC-Exo) could activate autophagy by targeting MAP4K3 to reduce TFEB phosphorylation, and MAP4K3 knockdown partially attenuates the effect of anti-let-7a-5p oligonucleotide via decreasing the inflammatory response, in addition, inducing autophagy. Altogether, these findings revealed that the hepatoprotective effect of MSCs may partially profit from its exosomal let-7a-5p mediating autophagy repairment, which may provide new insights for the therapeutic target of ACLF treatment.

Lysosomal lipid alterations caused by glucocerebrosidase deficiency promote lysosomal dysfunction, chaperone-mediated-autophagy deficiency, and alpha-synuclein pathology

Mutations in the GBA gene that encodes the lysosomal enzyme β-glucocerebrosidase (GCase) are a major genetic risk factor for Parkinson’s disease (PD). In this study, we generated a set of differentiated and stable human dopaminergic cell lines that express the two most prevalent GBA mutations as well as GBA knockout cell lines as a in vitro disease modeling system to study the relationship between mutant GBA and the abnormal accumulation of α-synuclein. We performed a deep analysis of the consequences triggered by the presence of mutant GBA protein and the loss of GCase activity in different cellular compartments, focusing primarily on the lysosomal compartment, and analyzed in detail the lysosomal activity, composition, and integrity. The loss of GCase activity generates extensive lysosomal dysfunction, promoting the loss of activity of other lysosomal enzymes, affecting lysosomal membrane stability, promoting intralysosomal pH changes, and favoring the intralysosomal accumulation of sphingolipids and cholesterol. These local events, occurring only at a subcellular level, lead to an impairment of autophagy pathways, particularly chaperone-mediated autophagy, the main α-synuclein degradative pathway. The findings of this study highlighted the role of lysosomal function and lipid metabolism in PD and allowed us to describe a molecular mechanism to understand how mutations in GBA can contribute to an abnormal accumulation of different α-synuclein neurotoxic species in PD pathology.

Mechanisms Controlling Selective Elimination of Damaged Lysosomes

Lysosomes are subjected to physiological and patho-physiological insults over the course of their life cycle and are accordingly repaired or recycled. Lysophagy, the selective degradation of lysosomes via autophagy, occurs upon unrepairable lysosomal membrane rupture; galectins bind to glycosylated macromolecules in the lysosome lumen, orchestrating a series of cellular responses to promote autophagic recycling of damaged lysosomes and transcriptional upregulation of lysosomal genes. Damaged lysosomes are ubiquitylated, resulting in the recruitment of ubiquitin-binding autophagy receptors, which promote assembly of an autophagosome around damaged lysosomes for delivery to healthy lysosomes for degradation. Here, we review the current state of our understanding of mechanisms used to mark and eliminate damaged lysosomes, and discuss the complexities of galectin function and ubiquitin-chain linkage types. Finally, we discuss the limitations of available data and challenges with the goal of understanding the mechanistic basis of key steps in lysophagic flux.