Lysosomal calcium signalling regulates autophagy through calcineurin and ​TFEB

Autophagy-targeting modulation to promote peripheral nerve regeneration

Nerve regeneration following traumatic peripheral nerve injuries and neuropathies is a complex process modulated by diverse factors and intricate molecular mechanisms. Past studies have focused on factors that stimulate axonal outgrowth and myelin regeneration. However, recent studies have highlighted the pivotal role of autophagy in peripheral nerve regeneration, particularly in the context of traumatic injuries. Consequently, autophagy-targeting modulation has emerged as a promising therapeutic approach to enhancing peripheral nerve regeneration. Our current understanding suggests that activating autophagy facilitates the rapid clearance of damaged axons and myelin sheaths, thereby enhancing neuronal survival and mitigating injury-induced oxidative stress and inflammation. These actions collectively contribute to creating a favorable microenvironment for structural and functional nerve regeneration. A range of autophagy-inducing drugs and interventions have demonstrated beneficial effects in alleviating peripheral neuropathy and promoting nerve regeneration in preclinical models of traumatic peripheral nerve injuries. This review delves into the regulation of autophagy in cell types involved in peripheral nerve regeneration, summarizing the potential drugs and interventions that can be harnessed to promote this process. We hope that our review will offer novel insights and perspectives on the exploitation of autophagy pathways in the treatment of peripheral nerve injuries and neuropathies.

Restoring Autophagy by Exercise Ameliorates Insulin Resistance Partly via Calcineurin-Driven TFEB Nuclear Translocation

Exercise activates autophagy and lysosome system in skeletal muscle, which are known to play an important role in metabolic adaptation. However, the mechanism of exercise-activated autophagy and lysosome system in obese insulin resistance remains covert. In this study, we investigated the role of exercise-induced activation of autophagy and lysosome system in improving glucose metabolism of skeletal muscle. Male C57BL/6 mice were randomly divided into five groups: the chow diet (CD) group, the high-fat diet (HFD) group, the high-fat diet plus exercise (HFD-E) group and the HFD-E treated with calcineurin inhibitor FK506 (HFD-E-F) or saline (HFD-E-S) groups. The mice in exercise groups (HFD-E, HFD-E-F and HFD-E-S) were subjected to aerobic treadmill exercise (speed at 12 m/min for 1 h per session, 0° slope, 5 days per week for 12 weeks). Mice of HFD-E-F group were intraperitoneally administered FK506 (1 mg/kg), once each day for 2 weeks before the end of exercise. Expressions pTFEB, T-TFEB and autophagy-lysosome markers, including Beclin1, LC3, ULK1, SQSTM1, LAMP1, CTSD and CTSL proteins in gastrocnemius muscle were analysed. We demonstrated that HFD induced insulin resistance and decreased autophagy-lysosomal proteins and the exercise significantly increased transcription factor EB (TFEB) translocation from the cytoplasm to the nucleus, restored the impaired autophagy-lysosomal-related protein expressions, and improved glucose metabolism. The increase in TFEB nuclear translocation was partly blocked by the calcineurin inhibitor FK506. Our results suggest that exercise promotes autophagy and lysosome restoration by regulating calcineurin-mediated TFEB nuclear translocation, ultimately alleviating HFD-induced insulin resistance in mice skeletal muscle.

Pharmacological activation of TRPML1 enhances autophagy regulating hypertonicity and TGF-β-induced EMT in proximal tubular epithelial cells

Proximal tubular epithelial cells (PTECs) are central to maintaining kidney homeostasis. Under pathological conditions, such as ischemia or inflammation, PTECs promote profibrotic signals, including transforming growth factor (TGF)-β, and undergo epithelial-mesenchymal transition (EMT). EMT is characterized by decreased epithelial markers (e.g., E-cadherin) and increased mesenchymal markers (e.g., α-smooth muscle actin [α-SMA]), which promote myofibroblast activation and fibrosis progression. We previously demonstrated that hyperosmotic stress, characterized by elevated extracellular solute concentrations, induces EMT in PTECs. However, we observed that hyperosmotic stress simultaneously activates autophagy, a cellular process that has antagonistic effects on EMT, primarily mediated by transient receptor potential mucolipin 1 (TRPML1). However, the interplay between hyperosmotic stress-induced EMT and autophagy remains unclear. This study examined whether enhancing autophagy via TRPML1 activation could modulate EMT under hyperosmotic stress. Using the TRPML1 agonist ML-SA1, we observed a significantly increased autophagic flux, indicated by elevated LC3-II levels, without cytotoxic effects. Under hyperosmotic conditions, ML-SA1 further amplified autophagic flux in PTECs compared to hyperosmotic stress alone. Notably, this enhanced autophagy suppressed EMT by maintaining E-cadherin expression and reducing α-SMA levels. Furthermore, the ML-SA1-mediated autophagy enhancement attenuated EMT and profibrotic factor production in TGF-β-treated cells, suggesting a broader protective role beyond hyperosmotic stress. These findings reveal a novel interaction between hyperosmotic stress-induced autophagy and EMT, emphasizing TRPML1 activation's therapeutic potential to mitigate PTEC injury and fibrosis progression.

SMURF1 mediates damaged lysosomal homeostasis by ubiquitinating PPP3CB to promote the activation of TFEB

The calcium-activated phosphatase PPP3/calcineurin dephosphorylates TFEB (transcription factor EB) to trigger its nuclear translocation and the activation of macroautophagic/autophagic targets. However, the detailed molecular mechanism regulating TFEB activation remains poorly understood. Here, we highlighted the importance of SMURF1 (SMAD specific E3 ubiquitin protein ligase 1) in the activation of TFEB for lysosomal homeostasis. SMURF1 deficiency prevents the calcium-triggered ubiquitination of the catalytic subunit of PPP3/calcineurin in a manner consistent with defective autophagic degradation of damaged lysosomes. Mechanically, PPP3CB/CNA2 plays a bridging role in the recruitment of SMURF1 by LGALS3 (galectin 3) upon lysosome damage. Importantly, PPP3CB increases the dissociation of the N-terminal tail (NT) and C-terminal carbohydrate-recognition domain (CRD) of LGALS3, which may promote the formation of open conformers in a PPP3CB dephosphorylation activity-dependent manner. In addition, PPP3CB is ubiquitinated at lysine 146 by the recruited SMURF1 in response to intracellular calcium stimulation. The K63-linked ubiquitination of PPP3CB enhances the recruitment of TFEB. Moreover, TFEB directly interacts with both PPP3CB and the regulatory subunit PPP3R1 which facilitate the conformational correction of TFEB for its activation for the transcription of TFEB-targeted genes. Altogether, our results highlighted a critical mechanism for the regulation of PPP3/calcineurin activity via its ubiquitin ligase SMURF1 in response to lysosomal membrane damage, which may account for a potential target for the treatment of stress-related diseases.Abbreviation AID: autoinhibitory domain; ATG: autophagy related; CD: catalytic domain; CRD: carbohydrate-recognition domain; CsA: cyclosporin A; DMSO: dimethyl sulfoxide; ESCRT: endosomal sorting complexes required for transport; GSK3B: glycogen synthase kinase 3 beta; LAMP1: lysosomal associated membrane protein 1; LGALS3: galectin 3; LLOMe: L-leucyl-L-leucine methyl ester; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; ML-SA1: mucolipin synthetic agonist 1; MTORC1: mechanistic target of rapamycin kinase complex 1; NT: N-terminal tail; PPP3CB: protein phosphatase 3 catalytic subunit beta; PPP3R1: protein phosphatase 3 regulatory subunit B, alpha; SMURF1: SMAD specific E3 ubiquitin protein ligase 1; SQSTM1/p62: sequestosome 1; TFEB: transcription factor EB; VCP/p97: valosin containing protein; YWHA/14-3-3: tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein.

AAV-Mediated Gene Transfer of WDR45 Corrects Neurological Deficits in the Mouse Model of Beta-Propeller Protein-Associated Neurodegeneration

Beta-propeller protein-associated neurodegeneration (BPAN) is an ultra-rare, X-linked dominant, neurodevelopmental, and neurodegenerative disease caused by loss-of-function mutations in the WDR45 gene. It manifests in neurodevelopmental delay and seizures followed by secondary neurological decline with dystonia/parkinsonism and dementia in adolescence and early adulthood and is characterized by progressive accumulation of iron in the basal ganglia. WDR45 encodes β-propeller-shaped scaffold protein, or WD repeat domain phosphoinositide-interacting protein 4 (WIPI4), which plays an important role in autophagosome formation. While the mechanisms of how WIPI4 loss of function results in neurological decline and brain pathology have not yet been established, findings of lower autophagic activity provide a direct link between impaired autophagy and neurological disease in BPAN. Here we performed phenotypical characterization of a novel mouse model of BPAN, Wdr45_ex9+1g>a mouse. We identified hyperactive behavior and reduction of autophagy markers in brain tissue in Wdr45_ex9+1g>a hemizygous males as early as at 2 months of age. Given the early onset and spectrum of neurological symptoms such as hyper-arousal and attention deficits in human patients, this model presents a disease-relevant phenotype and can be used in preclinical studies. We used this mouse model for a proof-of-concept study to evaluate whether adeno-associated virus (AAV)-mediated central nervous system (CNS)-targeted gene transfer of WDR45 can provide therapeutic benefit and be considered a therapeutic paradigm for BPAN. We observed successful expression of human WDR45 transcripts and WIPI4 protein in the brain tissue, rescue of hyperactive behavior, and correction of autophagy markers. These data demonstrate that WDR45 gene transfer can be a promising therapeutic strategy for BPAN.

Lysosomal Quality Control

Healthy cells need functional lysosomes to degrade cargo delivered by autophagy and endocytosis. Defective lysosomes can lead to severe conditions such as lysosomal storage diseases (LSDs) and neurodegeneration. To maintain lysosome integrity and functionality, cells have evolved multiple quality control pathways corresponding to different types of stress and damage. These can be divided into five levels: regulation, reformation, repair, removal, and replacement. The different levels of lysosome quality control often work together to maintain the integrity of the lysosomal network. This review summarizes the different quality control pathways and discusses the less-studied area of lysosome membrane protein regulation and degradation, highlighting key unanswered questions in the field.

Buddleoside alleviates nonalcoholic steatohepatitis by targeting the AMPK-TFEB signaling pathway

Nonalcoholic steatohepatitis (NASH) is a combination of hepatic steatosis, inflammation, and fibrosis, and it often follows simple hepatic steatosis in nonalcoholic fatty liver disease (NAFLD). However, no pharmacological treatment is currently available for NASH. Given the important role of TFEB (transcription factor EB) in regulating the macroautophagy/autophagy-lysosomal pathway, TFEB is potentially a novel therapeutic target for treatment of NASH, which function can be regulated by AMP-activated protein kinase (AMPK) and MTOR (mechanistic target of rapamycin kinase) complex 1 (MTORC1). Buddleoside (Bud), a natural flavonoid compound, has recently emerged as a promising drug candidate for liver diseases. Here, we shown that Bud treatment alleviated hepatic steatosis, insulin resistance, inflammation, and fibrosis in mice fed a high-fat and high-cholesterol (HFHC) diet. Notably, Bud activated AMPK, inhibited MTORC1, and enhanced TFEB transcriptional activity as well as autophagic flux in vivo and in vitro. Inhibition of AMPK or knockout of hepatic Tfeb abrogated the alleviation effects of Bud on hepatic steatosis, insulin resistance, inflammation, and fibrosis. Mechanistic investigation revealed that Bud bound to the PRKAB1 subunit via Val81, Arg83, and Ser108 residues and activated AMPK, thereby eliciting phosphorylation of RPTOR (regulatory associated protein of MTOR complex 1) and inhibiting the kinase MTORC1, which activated the TFEB-mediated autophagy-lysosomal pathway and further ameliorated HFHC-induced NASH in mice. Altogether, our results indicate that Bud ameliorates NASH by activating hepatic the AMPK-TFEB axis, suggesting that Bud is a potential therapeutic strategy for NASH.

The cGAS-STING pathway activates transcription factor TFEB to stimulate lysosome biogenesis and pathogen clearance

Induction of autophagy is an ancient function of the cyclic GMP-AMP (cGAMP) synthase (cGAS)-stimulator of interferon genes (STING) pathway through which autophagic cargoes are delivered to lysosomes for degradation. However, whether lysosome function is also modulated by the cGAS-STING pathway remains unknown. Here, we discovered that the cGAS-STING pathway upregulated lysosomal activity by stimulating lysosome biogenesis independently of the downstream protein kinase TANK-binding kinase 1 (TBK1). STING activation enhanced lysosome biogenesis through inducing the nuclear translocation of transcription factor EB (TFEB) as well as its paralogs transcription factor E3 (TFE3) and microphthalmia-associated transcription factor (MITF). STING-induced lipidation of GABA type A receptor-associated protein (GABARAP), an autophagy-related protein, on STING vesicles was responsible for TFEB activation. Membrane-bound GABARAP sequestered the GTPase-activating protein folliculin (FLCN) and FLCN-interacting protein (FNIP) complex to block its function toward the Rag GTPases Ras-related GTP-binding C and D (RagC and RagD), abolishing mechanistic target of rapamycin (mTOR) complex 1 (mTORC1)-dependent phosphorylation and inactivation of TFEB. Functionally, STING-induced lysosome biogenesis within cells facilitated the clearance of cytoplasmic DNA and invading pathogens. Thus, our findings reveal that induction of lysosome biogenesis is another important function of the cGAS-STING pathway.

ZLDI-8 facilitates pexophagy by ROS-mediated activation of TFEB and ATM in HeLa cells

Autophagy-mediated organelle quality control is vital for cellular homeostasis. However, the mechanisms underlying selective autophagy of peroxisomes, known as pexophagy, are less well understood than those of other organelles, such as mitochondria. In this study, we screened a phosphatase inhibitor library using a cell-based system and identified several potent pexophagy inducers, including ZLDI-8, a known inhibitor of lymphoid-specific tyrosine phosphatase. Notably, treatment with ZLDI-8 selectively induces the loss of peroxisomes without affecting other organelles, such as mitochondria, the endoplasmic reticulum, or the Golgi apparatus. The peroxisome loss induced by ZLDI-8 was significantly blocked in ATG5-knockout HeLa cells, confirming its dependence on autophagy. We further found that ZLDI-8 treatment increases both cellular and peroxisomal reactive oxygen species (ROS), which were effectively scavenged by N-acetylcysteine (NAC). The increase in peroxisomal ROS leads to the activation of ATM kinase and the dephosphorylation of TFEB. Moreover, ROS scavenging prevents all of these processes. Taken together, these findings demonstrate that ZLDI-8 induces pexophagy through a mechanism involving peroxisomal ROS-mediated activation of TFEB and ATM. This study provides valuable insights into the molecular mechanisms regulating selective peroxisome degradation and potential therapeutic strategies for targeting pexophagy.

Calcium-mediated regulation of mitophagy: implications in neurodegenerative diseases

Calcium signaling plays a pivotal role in diverse cellular processes through precise spatiotemporal regulation and interaction with effector proteins across distinct subcellular compartments. Mitochondria, in particular, act as central hubs for calcium buffering, orchestrating energy production, redox balance and apoptotic signaling, among others. While controlled mitochondrial calcium uptake supports ATP synthesis and metabolic regulation, excessive accumulation can trigger oxidative stress, mitochondrial membrane permeabilization, and cell death. Emerging findings underscore the intricate interplay between calcium homeostasis and mitophagy, a selective type of autophagy for mitochondria elimination. Although the literature is still emerging, this review delves into the bidirectional relationship between calcium signaling and mitophagy pathways, providing compelling mechanistic insights. Furthermore, we discuss how disruptions in calcium homeostasis impair mitophagy, contributing to mitochondrial dysfunction and the pathogenesis of common neurodegenerative diseases.

Knockdown of regulator of Calcineurin 2 promotes transcription factor EB-mediated lipophagy to prevent non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a major cause of chronic liver disease. The present work aimed to explore the function of regulator of Calcineurin 2 (RCAN2) in NAFLD and its related mechanisms. Mice were fed with high-fat diet (HFD) to construct NAFLD model. Adeno-associated virus injection was performed to interference with RCAN2 in mice. RCAN2 knockdown meliorated HFD-induced NAFLD and impaired glucose metabolism. Abnormal lipid metabolism and inflammation in HFD-fed mice were relieved when RCAN2 was downregulated. Besides, hepatocyte Huh-7 cells, treated with free fatty acids (oleic acid and palmitic acid), were used as NAFLD models in vitro. We found that knockdown of RCAN2 inhibited the accumulation of lipid droplets and inflammation induced by free fatty acids. RCAN2 interference increased the activity of calcineurin (CaN), which enhanced the nuclear translocation of Transcription factor EB (TFEB). Autophagosome and lysosome biogenesis was augmented, and autophagy-dependent lipid degradation (lipophagy) was promoted. Collectively, we demonstrate that RCAN2 insufficiency protects against NAFLD by promoting TFEB-mediated lipophagy.

Hyperosmotic Stress Promotes the Nuclear Translocation of TFEB in Tubular Epithelial Cells Depending on Intracellular Ca2+ Signals via TRPML Channels

Purpose

We previously demonstrated that hyperosmotic stress, which acts as mechanical stress, induces autophagy of tubular epithelial cells. This study aims to elucidate the molecular mechanisms of hyperosmolarity-induced autophagy. The research question addresses how hyperosmotic stress activates autophagy through transcription factor EB (TFEB) and Ca2+ signaling pathways, contributing to understanding cellular responses to mechanical stress.

Methods

NRK-52E normal rat kidney cells were subjected to hyperosmotic stress using mannitol-containing medium. Fluorescence microscopy was utilized to observe TFEB nuclear translocation, a crucial event in autophagy regulation. An intracellular Ca2+ chelator, BAPTA-AM, and a calcineurin inhibitor were used to dissect the Ca2+ signaling pathway involved in TFEB translocation. The phosphorylation of p70S6K, a substrate of the mammalian target of rapamycin complex 1 kinase, was analyzed to explore its role in TFEB localization. Additionally, the function of transient receptor potential mucolipin 1 (TRPML1), an intracellular Ca2+ channel, was assessed using pharmacological inhibition to determine its impact on TFEB translocation and autophagy marker LC3-II levels.

Results

Mannitol-induced hyperosmotic stress promoted the nuclear translocation of TFEB, which was completely abolished by treatment with BAPTA-AM. Inhibition of calcineurin suppressed TFEB nuclear translocation under hyperosmolarity, indicating that a signaling pathway governed by intracellular Ca2+ is involved in TFEB's nuclear translocation. In contrast, hyperosmotic stress did not significantly alter p70S6K phosphorylation. Pharmacological inhibition of TRPML1 attenuated both TFEB nuclear translocation and LC3-II upregulation in response to hyperosmotic stress.

Conclusions

Hyperosmotic stress promotes TFEB nuclear localization, and TRPML1-induced activation of calcineurin is involved in the mechanism of hyperosmolarity-induced autophagy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-024-00839-6.

Blockage of polycystin-2 alleviates myocardial ischemia/reperfusion injury by inhibiting autophagy through the Ca2+/Akt/Beclin 1 pathway

Autophagy is a well-conserved self-protection process that plays an important role in cardiovascular diseases. Excessive autophagy during myocardial ischemia/reperfusion injury (MIRI) induces calcium overload and the overactivation of an autophagic response, thereby aggravating cardiomyocyte damage. Polycystin-2 (PC2) is a Ca2+-permeable nonselective cation channel implicated in the regulation of autophagy. In the present study, autophagy was upregulated in myocardial ischemia/reperfusion in vivo and in vitro. PC2 knockdown using adeno-associated virus 9 particles containing Pkd2 short hairpin RNA infection markedly ameliorated MIRI, evidenced by reduced infarct size, diminished morphological changes, decreased cTnI levels, and improved cardiac function. Silencing PC2 reduced the autophagic flux in H9c2 cells. PC2 overexpression-mediated autophagic flux was inhibited by intracellular Ca2+ chelation with BAPTA-AM. Furthermore, PC2 ablation upregulated p-Akt (Ser473) and downregulated Beclin 1 in H/R. BAPTA-AM downregulated p-Akt(Ser473) and upregulated Beclin 1in PC2-overexpressing H9c2 cells. Moreover, the Akt inhibitor MK2206 abolished the BAPTA-AM-blunted PC2-dependent control of autophagy. Collectively, these results indicated that blockade of PC2 may be associated with the Ca2+/Akt/Beclin 1 signaling, thereby inhibiting excessive autophagy and serving as a potential strategy for mitigating MIRI.

How crosstalk between mitochondria, lysosomes, and other organelles can prevent or promote dry age-related macular degeneration

Organelles such as mitochondria, lysosomes, peroxisomes, and the endoplasmic reticulum form highly dynamic cellular networks and exchange information through sites of physical contact. While each organelle performs unique functions, this inter-organelle crosstalk helps maintain cell homeostasis. Age-related macular degeneration (AMD) is a devastating blinding disease strongly associated with mitochondrial dysfunction, oxidative stress, and decreased clearance of cellular debris in the retinal pigment epithelium (RPE). However, how these occur, and how they relate to organelle function both with the RPE and potentially the photoreceptors are fundamental, unresolved questions in AMD biology. Here, we report the discussions of the "Mitochondria, Lysosomes, and other Organelle Interactions" task group of the 2024 Ryan Initiative for Macular Research (RIMR). Our group focused on understanding the interplay between cellular organelles in maintaining homeostasis in the RPE and photoreceptors, how this could be derailed to promote AMD, and identifying where these pathways could potentially be targeted therapeutically.

Lysosomal cation channel TRPML1 suppression sensitizes acute myeloid leukemia cells to chemotherapeutics by inhibiting autophagy

Despite the implementation of novel therapeutic regimens and extensive research efforts, chemoresistance remains a formidable challenge in the treatment of acute myeloid leukemia (AML). Notably, the involvement of lysosomes in chemoresistance has sparked interest in developing lysosome-targeted therapies to sensitize tumor cells to currently approved chemotherapy or as innovative pharmacological approaches. Moreover, as ion channels on the lysosomal membrane are critical regulators of lysosomal function, they present potential as novel targets for enhancing chemosensitivity. Here, we discovered that the expression of a lysosomal cation channel, namely transient receptor potential mucolipin 1 (TRPML1), was elevated in AML cells. Inhibiting TRPML1 individually does not impact the proliferation and apoptosis of AML cells. Importantly, inhibition of TRPML1 demonstrated the potential to modulate the sensitivity of AML cells to chemotherapeutic agents. Exploration of the underlying mechanisms revealed that suppression of TRPML1 impaired autophagy while concurrently increasing the production of reactive oxygen species (ROS) and ROS-mediated lipid peroxidation (Lipid-ROS) in AML cells. Finally, the knockdown of TRPML1 significantly reduced OCI-AML3 tumor growth following chemotherapy in a mouse model of human leukemia. In summary, targeting TRPML1 represents a promising approach for combination therapy aimed at enhancing chemosensitivity in treating AML.

Recycle, repair, recover: the role of autophagy in modulating skeletal muscle repair and post-exercise recovery

Skeletal muscle is a highly plastic tissue that can adapt relatively rapidly to a range of stimuli. In response to novel mechanical loading, e.g. unaccustomed resistance exercise, myofibers are disrupted and undergo a period of ultrastructural remodeling to regain full physiological function, normally within 7 days. The mechanisms that underpin this remodeling are believed to be a combination of cellular processes including ubiquitin-proteasome/calpain-mediated degradation, immune cell infiltration, and satellite cell proliferation/differentiation. A relatively understudied system that has the potential to be a significant contributing mechanism to repair and recovery is the autophagolysosomal system, an intracellular process that degrades damaged and redundant cellular components to provide constituent metabolites for the resynthesis of new organelles and cellular structures. This review summarizes our current understanding of the autophagolysosomal system in the context of skeletal muscle repair and recovery. In addition, we also provide hypothetical models of how this system may interact with other processes involved in skeletal muscle remodeling and provide avenues for future research to improve our understanding of autophagy in human skeletal muscle.

Activation of lysophagy by a TBK1-SCFFBXO3-TMEM192-TAX1BP1 axis in response to lysosomal damage

Lysophagy eliminates damaged lysosomes and is crucial to cellular homeostasis; however, its underlying mechanisms are not entirely understood. We screen a ubiquitination-related compound library and determine that the substrate recognition component of the SCF-type E3 ubiquitin ligase complex, SCFFBXO3(FBXO3), which is a critical lysophagy regulator. Inhibition of FBXO3 reduces lysophagy and lysophagic flux in response to L-leucyl-L-leucine methyl ester (LLOMe). Furthermore, FBXO3 interacts with TMEM192, leading to its ubiquitination in LLOMe-treated cells. We also identify TAX1BP1 as a critical autophagic adaptor that recognizes ubiquitinated TMEM192 during lysophagy and find that TBK1 activation is crucial for lysophagy, as it phosphorylates FBXO3 in response to lysosomal damage. Knockout of FBXO3 significantly impairs lysophagy, and its reconstitution with a loss-of-function mutant (V221I) further confirms its essential role in lysophagy regulation. Collectively, our findings highlight the significance of the TBK1-FBXO3-TMEM192-TAX1BP1 axis in lysophagy and emphasize the critical role of FBXO3 in lysosomal integrity.

Phase-separated Condensates in Autophagosome Formation and Autophagy Regulation

Biomacromolecules partition into numerous types of biological condensates or membrane-less organelles via liquid-liquid phase separation (LLPS). Newly formed liquid-like condensates may further undergo phase transition to convert into other material states, such as gel or solid states. Different biological condensates possess distinct material properties to fulfil their physiological functions in diverse cellular pathways and processes. Phase separation and condensates are extensively involved in the autophagy pathway. The autophagosome formation sites in both yeast and multicellular organisms are assembled as phase-separated condensates. TORC1, one of the core regulators of the autophagy-lysosome pathway, is subject to nonconventional regulation by multiple biological condensates. TFEB, the master transcription factor of the autophagy-lysosome pathway, phase separates to assemble liquid-like condensates involved in transcription of autophagic and lysosomal genes. The behaviors and transcriptional activity of TFEB condensates are governed by their material properties, thus suggesting novel autophagy intervention strategies. The phase separation process and the resulting condensates are emerging therapeutic targets for autophagy-related diseases.

Lysosomes finely control macrophage inflammatory function via regulating the release of lysosomal Fe2+ through TRPML1 channel

Lysosomes are best known for their roles in inflammatory responses by engaging in autophagy to remove inflammasomes. Here, we describe an unrecognized role for the lysosome, showing that it finely controls macrophage inflammatory function by manipulating the lysosomal Fe2+-prolyl hydroxylase domain enzymes (PHDs)-NF-κB-interleukin 1 beta (IL1B) transcription pathway that directly links lysosomes with inflammatory responses. TRPML1, a lysosomal cationic channel, is activated secondarily to ROS elevation upon inflammatory stimuli, which in turn suppresses IL1B transcription, thus limiting the excessive production of IL-1β in macrophages. Mechanistically, the suppression of IL1B transcription caused by TRPML1 activation results from its modulation on the release of lysosomal Fe2+, which subsequently activates PHDs. The activated PHDs then represses transcriptional activity of NF-κB, ultimately resulting in suppressed IL1B transcription. More importantly, in vivo stimulation of TRPML1 ameliorates multiple clinical signs of Dextran sulfate sodium-induced colitis in mice, suggesting TRPML1 has potential in treating inflammatory bowel disease.

Lysosome Functions in Atherosclerosis: A Potential Therapeutic Target

Lysosomes in mammalian cells are recognized as key digestive organelles, containing a variety of hydrolytic enzymes that enable the processing of both endogenous and exogenous substrates. These organelles digest various macromolecules and recycle them through the autophagy-lysosomal system. Recent research has expanded our understanding of lysosomes, identifying them not only as centers of degradation but also as crucial regulators of nutrient sensing, immunity, secretion, and other vital cellular functions. The lysosomal pathway plays a significant role in vascular regulation and is implicated in diseases such as atherosclerosis. During atherosclerotic plaque formation, macrophages initially engulf large quantities of lipoproteins, triggering pathogenic responses that include lysosomal dysfunction, foam cell formation, and subsequent atherosclerosis development. Lysosomal dysfunction, along with the inefficient degradation of apoptotic cells and the accumulation of modified low-density lipoproteins, negatively impacts atherosclerotic lesion progression. Recent studies have highlighted that lysosomal dysfunction contributes critically to atherosclerosis in a cell- and stage-specific manner. In this review, we discuss the mechanisms of lysosomal biogenesis and its regulatory role in atherosclerotic lesions. Based on these lysosomal functions, we propose that targeting lysosomes could offer a novel therapeutic approach for atherosclerosis, shedding light on the connection between lysosomal dysfunction and disease progression while offering new insights into potential anti-atherosclerotic strategies.

Ferroptosis and pyroptosis are connected through autophagy: a new perspective of overcoming drug resistance

Drug resistance is a common challenge in clinical tumor treatment. A reduction in drug sensitivity of tumor cells is often accompanied by an increase in autophagy levels, leading to autophagy-related resistance. The effectiveness of combining chemotherapy drugs with autophagy inducers/inhibitors has been widely confirmed, but the mechanisms are still unclear. Ferroptosis and pyroptosis can be affected by various types of autophagy. Therefore, ferroptosis and pyroptosis have crosstalk via autophagy, potentially leading to a switch in cell death types under certain conditions. As two forms of inflammatory programmed cell death, ferroptosis and pyroptosis have different effects on inflammation, and the cGAS-STING signaling pathway is also involved. Therefore, it also plays an important role in the progression of some chronic inflammatory diseases. This review discusses the relationship between autophagy, ferroptosis and pyroptosis, and attempts to uncover the reasons behind the evasion of tumor cell death and the nature of drug resistance.

Skeletal and dental tissue mineralization: The potential role of the endoplasmic reticulum/Golgi complex and the endolysosomal and autophagic transport systems

This paper presents a review of the potential role of the endoplasmic reticulum/Golgi complex and intracellular vesicles in mediating events leading to or associated with vertebrate tissue mineralization. The possible importance of these organelles in this process is suggested by observations that calcium ions accumulate in the tubules and lacunae of the endoplasmic reticulum and Golgi. Similar levels of calcium ions (approaching millimolar) are present in vesicles derived from endosomes, lysosomes and autophagosomes. The cellular level of phosphate ions in these organelles is also high (millimolar). While the source of these ions for mineral formation has not been identified, there are sound reasons for considering that they may be liberated from mitochondria during the utilization of ATP for anabolic purposes, perhaps linked to matrix synthesis. Published studies indicate that calcium and phosphate ions or their clusters contained as cargo within the intracellular organelles noted above lead to formation of extracellular mineral. The mineral sequestered in mitochondria has been documented as an amorphous calcium phosphate. The ion-, ion cluster- or mineral-containing vesicles exit the cell in plasma membrane blebs, secretory lysosomes or possibly intraluminal vesicles. Such a cell-regulated process provides a means for the rapid transport of ions or mineral particles to the mineralization front of skeletal and dental tissues. Within the extracellular matrix, the ions or mineral may associate to form larger aggregates and potential mineral nuclei, and they may bind to collagen and other proteins. How cells of hard tissues perform their housekeeping and other biosynthetic functions while transporting the very large volumes of ions required for mineralization of the extracellular matrix is far from clear. Addressing this and related questions raised in this review suggests guidelines for further investigations of the intracellular processes promoting the mineralization of the skeletal and dental tissues.

Regulatory Mechanisms and Therapeutic Implications of Lysosomal Dysfunction in Alzheimer's Disease

Alzheimer's disease (AD) is characterized by the accumulation of amyloid-beta (Aβ) plaques, neurofibrillary tangles (NFTs) formed from hyperphosphorylated Tau, and widespread neuronal loss. The autophagy-lysosomal pathway plays a crucial role in maintaining cellular homeostasis by degrading and recycling of damaged organelles and aggregate amyloid proteins implicated in AD. Lysosomes are key effectors of autophagic process, responsible for the breakdown of a variety of damaged organelles and aggregate or dysfunctional proteins. This review examines the role of lysosomal dysfunction in AD pathophysiology, focusing on genetic factors, acidification abnormalities, and other contributing factors. We also explore the involvement of lysosomal dysfunction of microglia in AD pathology, and cover the role of lysosomal stress response (LSR) in cellular response to neuronal injury associated with AD. Furthermore, we discuss potential therapeutic strategies targeting lysosomal proteolysis pathway and addressing lysosomal dysfunction for AD treatment, including the pharmacologically activating lysosomal activity, regulating TFEB, and considering other emerging approaches.

Calcium signaling hypothesis: A non-negligible pathogenesis in Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) presents a significant challenge to global healthcare systems, with an exacerbation by an aging population. Although the plethora of hypotheses are proposed to elucidate the underlying mechanisms of AD, from amyloid-beta (Aβ) accumulation and Tau protein aggregation to neuroinflammation, a comprehensive understanding of its pathogenesis remains elusive. Recent research has highlighted the critical role of calcium (Ca2+) signaling pathway in the progression of AD, indicating a complex interplay between Ca2+ dysregulation and various pathological processes.

AIM OF REVIEW

This review aims to consolidate the current understanding of the role of Ca2+ signaling dysregulation in AD, thus emphasizing its central role amidst various pathological hypotheses. We aim to evaluate the potential of the Ca2+ signaling hypothesis to unify existing theories of AD pathogenesis and explore its implications for developing innovative therapeutic strategies through targeting Ca2+ dysregulation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

The review focuses on three principal concepts. First, the indispensable role of Ca2+ homeostasis in neuronal function and its disruption in AD. Second, the interaction between Ca2+ signaling dysfunction and established AD hypotheses posited that Ca2+ dysregulation is a unifying pathway. Third, the dual role of Ca2+ in neurodegeneration and neuroprotection, highlighting the nuanced effects of Ca2+ levels on AD pathology.

Fangchinoline eliminates intracellular Salmonella by enhancing lysosomal function via the AMPK-mTORC1-TFEB axis

INTRODUCTION

Salmonella, a foodborne zoonotic pathogen, is a significant cause of morbidity and mortality in animals and humans globally. With the prevalence of multidrug-resistant strains, Salmonellosis has become a formidable challenge. Host-directed therapy (HDT) has recently emerged as a promising anti-infective approach for treating intracellular bacterial infections.

OBJECTIVES

Plant-derived natural products, owing to their structural and functional diversity, are increasingly being explored and utilized as encouraging candidates for HDT compounds. This study aims to identify and screen natural compounds with potential as HDT for the treatment of intracellular Salmonella infections.

METHODS

A cell-based screening approach was deployed to identify natural compounds capable of mitigating the intracellular replication of S. enterica. Safety and efficacy of the candidate compounds were evaluated using multiple animal models. RNA sequencing, ELISA, and immunoblotting analyses were conducted to elucidate the underlying mechanisms of action.

RESULTS

Our results reveal that fangchinoline (FAN) effectively reduces S. enterica survival both in vitro and in vivo. Meanwhile, FAN also displays anti-infective activity against other intracellular pathogens, including multidrug-resistant isolates. A 14-day safety evaluation in mice showed no significant toxic or adverse effects from FAN administration. RNA sequencing analysis reveals an upregulation of lysosome pathways in S. enterica-infected cells treated with FAN. Mechanistic studies indicate that FAN increases acid lysosomal quantities and fosters autophagic response in Salmonella-infected cells via the AMPK-mTORC1-TFEB axis. In addition, FAN alleviates the inflammatory response in Salmonella-infected cells by inactivating the NF-κB pathway.

CONCLUSION

Our findings suggest that FAN represents a lead HDT compound for tackling recalcitrant infections caused by intracellular bacterial pathogens.

Activation of lysosomal Ca2+ channels mitigates mitochondrial damage and oxidative stress

Elevated levels of plasma-free fatty acids and oxidative stress have been identified as putative primary pathogenic factors in endothelial dysfunction etiology, though their roles are unclear. In human endothelial cells, we found that saturated fatty acids (SFAs)-including the plasma-predominant palmitic acid (PA)-cause mitochondrial fragmentation and elevation of intracellular reactive oxygen species (ROS) levels. TRPML1 is a lysosomal ROS-sensitive Ca2+ channel that regulates lysosomal trafficking and biogenesis. Small-molecule agonists of TRPML1 prevented PA-induced mitochondrial damage and ROS elevation through activation of transcriptional factor EB (TFEB), which boosts lysosome biogenesis and mitophagy. Whereas genetically silencing TRPML1 abolished the protective effects of TRPML1 agonism, TRPML1 overexpression conferred a full resistance to PA-induced oxidative damage. Pharmacologically activating the TRPML1-TFEB pathway was sufficient to restore mitochondrial and redox homeostasis in SFA-damaged endothelial cells. The present results suggest that lysosome activation represents a viable strategy for alleviating oxidative damage, a common pathogenic mechanism of metabolic and age-related diseases.

Tacrolimus regulates extracellular vesicle secretion from T cells via autophagy-lysosomal pathway

Extracellular vesicles (EVs) derived from T cells have been proposed to mediate intercellular communication and orchestrate immune responses. The immunosuppressive drug, tacrolimus (TAC), suppresses T cell activity; however, the impact of TAC on T cell-derived EVs remains primarily unexplored. In this study, human primary T cells purified from healthy donors were used to investigate TAC-mediated regulation of EV secretion by T cells. Using size exclusion chromatography (SEC) to isolate EVs released by T cells, we found that the number of released EVs was increased upon anti-CD3/CD28 bead-mediated activation. Furthermore, pre-treatment with TAC before activation had a potentiating effect on EV release, as evidenced by western blot analysis of EV markers and small particle flow cytometry. In addition, we showed that EVs isolated from the plasma of TAC-treated kidney transplant patients were increased compared to those observed with pre-transplant plasma. Upon examining the mechanism underlying the action of TAC, we found that TAC impaired autophagy-lysosome-mediated degradation by inhibiting the nuclear translocation of transcription factor EB, a master regulator of lysosomal biogenesis. Notably, the addition of trehalose, an autophagy inducer, abrogated the TAC-induced EV release, indicating that TAC regulated EV secretion via the autophagy-lysosomal pathway. At the functional level, we demonstrated that EVs from TAC-treated T cells carried a decreased amount of CD40L, a protein critical for the activation of the adaptive immune response. Collectively, these findings demonstrate that an overall increase in EV production and decreased CD40L levels in EVs are characteristic responses of T cells to TAC.

A role for lysosomal calcium channels in mitigating mitochondrial damage and oxidative stress

Elevated free fatty acids and oxidative stress may function as pathogenic factors in endothelial dysfunction that is associated with various cardiovascular complications. In recent work, Feng and colleagues report that activation of a lysosomal Ca2+ channel may be a viable option to alleviate oxidative damage by boosting lysosome biogenesis and mitophagy.

Cellular mechanisms of acute rhabdomyolysis in inherited metabolic diseases

Acute rhabdomyolysis (RM) constitutes a life-threatening emergency resulting from the (acute) breakdown of skeletal myofibers, characterized by a plasma creatine kinase (CK) level exceeding 1000 IU/L in response to a precipitating factor. Genetic predisposition, particularly inherited metabolic diseases, often underlie RM, contributing to recurrent episodes. Both sporadic and congenital forms of RM share common triggers. Considering the skeletal muscle's urgent need to rapidly adjust to environmental cues, sustaining sufficient energy levels and functional autophagy and mitophagy processes are vital for its preservation and response to stressors. Crucially, the composition of membrane lipids, along with lipid and calcium transport, and the availability of adenosine triphosphate (ATP), influence membrane biophysical properties, membrane curvature in skeletal muscle, calcium channel signaling regulation, and determine the characteristics of autophagic organelles. Consequently, a genetic defect involving ATP depletion, aberrant calcium release, abnormal lipid metabolism and/or lipid or calcium transport, and/or impaired anterograde trafficking may disrupt autophagy resulting in RM. The complex composition of lipid membranes also alters Toll-like receptor signaling and viral replication. In response, infections, recognized triggers of RM, stimulate increased levels of inflammatory cytokines, affecting skeletal muscle integrity, energy metabolism, and cellular trafficking, while elevated temperatures can reduce the activity of thermolabile enzymes. Overall, several mechanisms can account for RMs and may be associated in the same disease-causing RM.

Bisphosphonate-mineralized nano-IFNγ suppresses residual tumor growth caused by incomplete radiofrequency ablation through metabolically remodeling tumor-associated macrophages

Rationale: Radiofrequency ablation (RFA), as a minimally invasive surgery strategy based on local thermal-killing effect, is widely used in the clinical treatment of multiple solid tumors. Nevertheless, RFA cannot achieve the complete elimination of tumor lesions with larger burden or proximity to blood vessels. Incomplete RFA (iRFA) has even been validated to promote residual tumor growth due to the suppressive tumor immune microenvironment (TIME). Therefore, exploring strategies to remodel TIME is a key issue for the development of RFA therapy. Methods: The negative effect of iRFA on colorectal cancer therapy was firstly investigated. Then a zoledronate-mineralized nanoparticle loaded with IFNγ (Nano-IFNγ/Zole) was designed and its tumor suppressive efficacy was evaluated. Finally, the metabolic reprogramming mechanism of Nano-IFNγ/Zole on tumor-associated macrophages (TAMs) was studied in detail. Results: We found iRFA dynamically altered TIME and promoted TAM differentiation from M1 to M2. Nano-IFNγ/Zole was fabricated to metabolically remodel TAMs. IFNγ in Nano-IFNγ/Zole concentrated in the ablation site to play a long-term remodeling role. Acting on mevalonate pathway, Nano-IFNγ/Zole was discovered to reduce lysosomal acidification and activate transcription factor TFEB by inhibiting isoprene modification of the Rab protein family. These mechanisms, in conjunction with IFNγ-activated JAK/STAT1 signaling, accelerated the reprogramming of TAMs from M2 to M1, and suppressed tumor recurrence after iRFA. Conclusions: This study elaborates the synergistic mechanism of zoledronate and IFNγ in Nano-IFNγ/Zole to reshape suppressive TIME caused by iRFA by remodeling TAMs, and highlights the important value of metabolically induced cellular reprogramming. Since both zoledronate and IFNγ have already been approved in clinics, this integrative nano-drug delivery system establishes an effective strategy with great translational promise to overcome the poor prognosis after clinically incomplete RFA.

20-Deoxyingenol Activates Mitophagy Through TFEB and Promotes Functional Recovery After Spinal Cord Injury

Spinal cord injury (SCI) can lead to permanent paralysis and various motor, sensory and autonomic nervous system dysfunction. The complex pathophysiological processes limit the effectiveness of many clinical treatments. Mitochondria has been reported to play a key role in the pathogenesis of SCI; while mitophagy is a protective mechanism against mitochondrial dysfunction. However, there is recently little drugs that may targeted activate mitophagy to treat SCI. In this study, we evaluated the role of 20-Deoxyingenol (20-DOI) in SCI and explored its potential mechanisms. We used a SCI rat model and evaluated the functional outcomes after the injury. Western blotting and immunofluorescence techniques were used to analyze the levels of mitophagy, apoptosis, and TFEB-related signaling pathways. Our research results show that 20-DOI significantly improves the apoptosis of neural cells after TBHP stimulation and functional recovery after spinal cord injury. In addition, mitophagy, TFEB levels, and apoptosis are related to the mechanism of 20-DOI treatment for spinal cord injury. Specifically, our research results indicate that 20-DOI restored the autophagic flux after injury, thereby inducing mitophagy, eliminating the accumulation of Cyto C, and inhibiting apoptosis. Further mechanism research suggests that 20-DOI may regulate mitophagy by promoting TFEB nuclear translocation. These results indicate that 20-DOI can significantly promote recovery after spinal cord injury, which may be a promising treatment method for spinal cord injury.

Presenilins as hub proteins controlling the endocytic and autophagic pathways and small extracellular vesicle secretion

Emerging evidence indicates that autophagy is tightly connected to the endocytic pathway. Here, we questioned the role of presenilins (PSENs 1 and 2), previously shown to be involved in autophagy regulation, in the secretion of small endocytic-originating extracellular vesicles known as exosomes. Indeed, while wild-type cells responded to stimuli promoting both multivesicular endosome (MVE) formation and secretion of small extracellular vesicles (sEVs) enriched in canonical exosomal proteins, PSEN-deficient cells were almost unaffected to these stimuli. Moreover, in PSEN-deficient cells, the re-expression of either PSEN1 or the functional active PSEN1delta9 mutant led to a rescue of most sEV secretion, while the deletion of PSEN1 alone almost fully phenocopied total PSEN invalidation. We found that the lack of sEV secretion in PSEN-deficient cells was also due to overactivated autophagy promoting MVEs to degradation rather than to plasma membrane fusion. Hence, in these cells, the autophagic blocker bafilomycin A1 (BafA1) not only increased the intracellular levels of the MVE protein CD63, but also turned on sEV secretion by stimulating autophagy-dependent unconventional secretion. In that case, sEVs arised from amphisomes and were enriched in both canonical exosomal proteins and lysosomal-autophagy-associated cargo. Altogether, we here demonstrate that PSENs, and particularly PSEN1, act as hub proteins controlling the balance between endosomal/autophagic degradation and secretion. More generally, our findings strengthen the view of a strong interconnection between the endocytic and autophagic pathways and their complementary roles in sEV secretion.

Tubulin-Binding Region Modulates Cholesterol-Triggered Aggregation of Tau Proteins

A hallmark of Alzheimer disease (AD) and tauopathies, severe neurodegenerative diseases, is the progressive aggregation of Tau, also known as microtubule-associated Tau protein. Full-length Tau1-441, also known as 2N4R, contains two N-terminal inserts that bind to tubulin. This facilitates the self-assembly of tubulin simultaneously enhancing stability of cell microtubules. Other Tau isoforms have one (1N4R) or zero (0N4R) N-terminal inserts, which makes 2N4R Tau more and 0N4R less effective in promoting microtubule self-assembly. A growing body of evidence indicates that lipids can alter the aggregation rate of Tau isoforms. However, the role of N-terminal inserts in Tau-lipid interactions remains unclear. In this study, we utilized a set of biophysical methods to determine the extent to which N-terminal inserts alter interactions of Tau isoforms with cholesterol, one of the most important lipids in plasma membranes. Our results showed that 2 N insert prevents amyloid-driven aggregation of Tau at the physiological concentration of cholesterol, while the absence of this N-terminal repeat (1N4R and 0N4R Tau) resulted in the self-assembly of Tau into toxic amyloid fibrils. We also found that the presence of cholesterol in the lipid bilayers caused a significant increase in the cytotoxicity of 1N4R and 0N4R Tau to neurons. This effect was not observed for 2N4R Tau fibrils formed in the presence of lipid membranes with low, physiological, and elevated concentrations of cholesterol. Using molecular assays, we found that Tau aggregates primarily exert cytotoxicity by damaging cell endosomes, endoplasmic reticulum, and mitochondria.

Hypoxia-induced TPC2 transcription and glycosylation aggravates pulmonary arterial hypertension by blocking autophagy flux

Pulmonary arterial hypertension (PAH) is a serious medical condition that causes a failure in the right heart. Two-pore channel 2 (TPC2) is upregulated in PAH, but its roles in PAH remain largely unknown. Our investigation aims at the mechanisms by which TPC2 regulates PAH development. We established an experimental PAH rat model via monocrotaline administration. Human and rat pulmonary arterial smooth muscle cells (PASMCs) were treated hypoxia as in vitro cell PAH models. The thickness of pulmonary arterial wall and obstructive arteriopathy in rats were examined. Autophagy was detected through TEM, and Ca2+ measurement and mRFP-GFP-LC3 transfection. The expression of α-SMA, LC3, p62, TPC2, HIF1α and STT3B were analyzed by qRT-PCR, western blot or IHC staining. The binding of HIF1α to TPC2 promoter was determined by ChIP-qPCR and EMSA assays. TPC2 glycosylation was evaluated by western blot. Transwell assay was applied to analyze cell migration. TPC2 expression was promoted and autophagy was inhibited in PAH rats and hypoxia-treated PASMCs. HIF1α directly bound to the promoter of TPC2, thus transcriptionally activating its expression in PAH rats and hypoxic PASMCs. Knockdown of TPC2 facilitated autophagic flux and repressed PASMC migration. STT3B enhanced TPC2 glycosylation in hypoxic PASMCs. Furthermore, Overexpression of TPC2 suppressed autophagic flux and promoted PASMC migration, but these effects were abrogated by STT3B knockdown or PNGase F, an eraser of N-linked glycans. Suppression of TPC2 enhanced autophagy and alleviated PAH in vivo. HIF1α-induced TPC2 transcription and subsequent STT3B-dependent TPC2 glycosylation inhibit autophagic flux and aggravate PAH. Our study suggests TCP2 as a potential therapeutic target for PAH.

Novel Role of Pin1-Cis P-Tau-ApoE Axis in the Pathogenesis of Preeclampsia and Its Connection with Dementia

Preeclampsia (preE) is a severe multisystem hypertensive syndrome of pregnancy associated with ischemia/hypoxia, angiogenic imbalance, apolipoprotein E (ApoE)-mediated dyslipidemia, placental insufficiency, and inflammation at the maternal-fetal interface. Our recent data further suggest that preE is associated with impaired autophagy, vascular dysfunction, and proteinopathy/tauopathy disorder, similar to neurodegenerative diseases such as Alzheimer's disease (AD), including the presence of the cis stereo-isoform of phosphorylated tau (cis P-tau), amyloid-β, and transthyretin in the placenta and circulation. This review provides an overview of the factors that may lead to the induction and accumulation of cis P-tau-like proteins by focusing on the inactivation of peptidyl-prolyl cis-trans isomerase (Pin1) that catalyzes the cis to trans isomerization of P-tau. We also highlighted the novel role of the Pin1-cis P-tau-ApoE axis in the development of preE, and propagation of cis P-tau-mediated abnormal protein aggregation (tauopathy) from the placenta to cerebral tissues later in life, leading to neurodegenerative conditions. In the case of preE, proteinopathy/tauopathy may interrupt trophoblast differentiation and induce cell death, similar to the events occurring in neurons. These events may eventually damage the endothelium and cause systemic features of disorders such as preE. Despite impressive research and therapeutic advances in both fields of preE and neurodegenerative diseases, further investigation of Pin1-cis P-tau and ApoE-related mechanistic underpinnings may unravel novel therapeutic options, and new transcriptional and proteomic markers. This review will also cover genetic polymorphisms in the ApoE alleles leading to dyslipidemia induction that may regulate the pathways causing preE or dementia-like features in the reproductive age or later in life, respectively.

The Impact of Calcium Overload on Cellular Processes: Exploring Calcicoptosis and Its Therapeutic Potential in Cancer

The key role of calcium in various physiological and pathological processes includes its involvement in various forms of regulated cell death (RCD). The concept of 'calcicoptosis' has been introduced as a calcium-induced phenomenon associated with oxidative stress and cellular damage. However, its definition remains controversial within the research community, with some considering it a general form of calcium overload stress, while others view it as a tumor-specific calcium-induced cell death. This review examines 'calcicoptosis' in the context of established RCD mechanisms such as apoptosis, necroptosis, ferroptosis, and others. It further analyzes the intricate relationship between calcium dysregulation and oxidative stress, emphasizing that while calcium overload often triggers cell death, it may not represent an entirely new type of RCD but rather an extension of known pathways. The purpose of this paper is to discuss the implications of this perspective for cancer therapy focusing on calcium-based nanoparticles. By investigating the connections between calcium dynamics and cell death pathways, this review contributes to the advancement of our understanding of calcicoptosis and its possible therapeutic uses.

TPC2: From Blond Hair to Melanoma?

Two-pore channel 2 (TPC2) is expressed in endolysosomes throughout the human body, as well as in melanosomes of melanocytes. Melanocytes produce pigment, i.e., melanin, which determines hair and skin color but also protects from UV light. Extensive exposure to UV light is one of the major risk factors for the development of melanoma, which develops from pigment-producing cells, i.e., melanocytes. In recent years, several human TPC2 single nucleotide polymorphisms have been identified to increase the likelihood of carriers presenting with blond hair and hypopigmentation. These variants were all characterized as gain-of-function versions of TPC2. Vice versa, the loss of function of TPC2 increases melanin production and reduces cancer hallmarks such as proliferation, migration, invasion, tumor growth, and metastasis formation. The activity of TPC2 is controlled in a complex manner, with several endogenous ligands as well as a number of interacting proteins being involved. We will discuss here the role of TPC2 in pigmentation and its potential to impact melanoma development and progression and highlight recent findings on Rab7a as an enhancer of TPC2 activity.

Nanoparticles encapsulating phosphatidylinositol derivatives promote neuroprotection and functional improvement in preclinical models of ALS via a long-lasting activation of TRPML1 lysosomal channel

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease currently incurable, in which motor neuron degeneration leads to voluntary skeletal muscle atrophy. Molecularly, ALS is characterized by protein aggregation, synaptic and organellar dysfunction, and Ca2+ dyshomeostasis. Of interest, autophagy dysfunction is emerging as one of the main putative targets of ALS therapy. A tune regulation of this cleansing process is affordable by a proper stimulation of TRPML1, one of the main lysosomal channels. However, TRPML1 activation by PI(3,5)P2 has low open probability to remain in an active conformation. To overcome this drawback we developed a lipid-based formulation of PI(3,5)P2 whose putative therapeutic potential has been tested in in vitro and in vivo ALS models. Pharmacodynamic properties of PI(3,5)P2 lipid-based formulations (F1 and F2) on TRPML1 activity have been characterized by means of patch-clamp electrophysiology and Fura-2AM video-imaging in motor neuronal cells. Once selected for the ability to stabilize TRPML1 activity, the most effective preparation F1 was studied in vivo to measure neuromuscular function and survival of SOD1G93A ALS mice, thereby establishing its therapeutic profile. F1, but not PI(3,5)P2 alone, stabilized the open state of the lysosomal channel TRPML1 and increased the persistence of intracellular calcium concentration ([Ca2+]i). Then, F1 was effective in delaying motor neuron loss, improving innervated endplants and muscle performance in SOD1G93A mice, extending overall lifespan by an average of 10 days. Of note F1 prevented gliosis and autophagy dysfunction in ALS mice by restoring PI(3,5)P2 level. Our novel self-assembling lipidic formulation for PI(3,5)P2 delivery exerts a neuroprotective effect in preclinical models of ALS mainly regulating dysfunctional autophagy through TRPML1 activity stabilization.

Integrated stress response plasticity governs normal cell adaptation to chronic stress via the PP2A-TFE3-ATF4 pathway

The integrated stress response (ISR) regulates cell fate during conditions of stress by leveraging the cell's capacity to endure sustainable and efficient adaptive stress responses. Protein phosphatase 2A (PP2A) activity modulation has been shown to be successful in achieving both therapeutic efficacy and safety across various cancer models. However, the molecular mechanisms driving its selective antitumor effects remain unclear. Here, we show for the first time that ISR plasticity relies on PP2A activation to regulate drug response and dictate cellular survival under conditions of chronic stress. We demonstrate that genetic and chemical modulation of the PP2A leads to chronic proteolytic stress and triggers an ISR to dictate whether the cell lives or dies. More specifically, we uncovered that the PP2A-TFE3-ATF4 pathway governs ISR cell plasticity during endoplasmic reticular and cellular stress independent of the unfolded protein response. We further show that normal cells reprogram their genetic signatures to undergo ISR-mediated adaptation and homeostatic recovery thereby avoiding toxicity following PP2A-mediated stress. Conversely, oncogenic specific cytotoxicity induced by chemical modulation of PP2A is achieved by activating chronic and irreversible ISR in cancer cells. Our findings propose that a differential response to chemical modulation of PP2A is determined by intrinsic ISR plasticity, providing a novel biological vulnerability to selectively induce cancer cell death and improve targeted therapeutic efficacy.

TRPML1 agonist ML-SA5 mitigates uranium-induced nephrotoxicity via promoting lysosomal exocytosis

Uranium (U) released from U mining and spent nuclear fuel reprocessing in the nuclear industry, nuclear accidents and military activities as a primary environmental pollutant (e.g., drinking water pollution) is a threat to human health. Kidney is one of the main target organs for U accumulation, leading to nephrotoxicity mainly associated with the injuries in proximal tubular epithelial cells (PTECs). Transient receptor potential mucolipin 1 (TRPML1) is a novel therapeutic target for nephrotoxicity caused by acute or chronic U poisoning. We herein investigate the therapeutic efficacy of ML-SA5, a small molecule agonist of TRPML1, in U-induced nephrotoxicity in acute U intoxicated mice. We demonstrate that delayed treatment with ML-SA5 enhances U clearance from the kidneys via urine excretion by activating lysosomal exocytosis, and thereby attenuates U-induced kidney dysfunction and cell death/apoptosis of renal PTECs in acute U intoxicated mice. In addition, ML-SA5 promotes the nuclear translocation of transcription factor EB (TFEB) in renal PTECs in acute U intoxicated mice. Mechanistically, ML-SA5 triggers the TRPML1-mediated lysosomal calcium release and consequently induces TFEB activation in U-loaded renal PTECs-derived HK-2 cells. Moreover, knockdown of TRPML1 or TFEB abolishes the effects of ML-SA5 on the removal of intracellular U and reduction of the cellular injury/death in U-loaded HK-2 cells. Our findings indicate that pharmacological activation of TRPML1 is a promising therapeutic approach for the delayed treatment of U-induced nephrotoxicity via the activation of the positive feedback loop of TRPML1 and TFEB and consequent the induction of lysosomal exocytosis.

Ubiquitin regulatory X (UBX) domain-containing protein 6 is essential for autophagy induction and inflammation control in macrophages

Ubiquitin regulatory X (UBX) domain-containing protein 6 (UBXN6) is an essential cofactor for the activity of the valosin-containing protein p97, an adenosine triphosphatase associated with diverse cellular activities. Nonetheless, its role in cells of the innate immune system remains largely unexplored. In this study, we report that UBXN6 is upregulated in humans with sepsis and may serve as a pivotal regulator of inflammatory responses via the activation of autophagy. Notably, the upregulation of UBXN6 in sepsis patients was negatively correlated with inflammatory gene profiles but positively correlated with the expression of Forkhead box O3, an autophagy-driving transcription factor. Compared with those of control mice, the macrophages of mice subjected to myeloid cell-specific UBXN6 depletion exhibited exacerbated inflammation, increased mitochondrial oxidative stress, and greater impairment of autophagy and endoplasmic reticulum-associated degradation pathways. UBXN6-deficient macrophages also exhibited immunometabolic remodeling, characterized by a shift to aerobic glycolysis and elevated levels of branched-chain amino acids. These metabolic shifts amplify mammalian target of rapamycin pathway signaling, in turn reducing the nuclear translocation of the transcription factor EB and impairing lysosomal biogenesis. Together, these data reveal that UBXN6 serves as an activator of autophagy and regulates inflammation to maintain immune system suppression during human sepsis.

TRPML1 ameliorates seizures-related neuronal injury by regulating autophagy and lysosomal biogenesis via Ca2+/TFEB signaling pathway

Alterations in autophagy have been observed in epilepsy, although their exact etiopathogenesis remains elusive. Transient Receptor Potential Mucolipin Protein 1 (TRPML1) is an ion channel protein that regulates autophagy and lysosome biogenesis. To explore the role of TRPML1 in seizures-induced neuronal injury and the potential mechanisms involved, an hyperexcitable neuronal model induced by Mg2+-free solution was used for the study. Our results revealed that TRPML1 expression was upregulated after seizures, which was accompanied by intracellular ROS accumulation, mitochondrial damage, and neuronal apoptosis. Activation of TRPML1 by ML-SA1 diminished intracellular ROS, restored mitochondrial function, and subsequently alleviated neuronal apoptosis. Conversely, inhibition of TRPML1 had the opposite effect. Further examination revealed that the accumulation of ROS and damaged mitochondria was associated with interrupted mitophagy flux and enlarged defective lysosomes, which were attenuated by TRPML1 activation. Mechanistically, TRPML1 activation allows more Ca2+ to permeate from the lysosome into the cytoplasm, resulting in the dephosphorylation of TFEB and its nuclear translocation. This process further enhances autophagy initiation and lysosomal biogenesis. Additionally, the expression of TRPML1 is positively regulated by WTAP-mediated m6A modification. Our findings highlighted crucial roles of TRPML1 and autophagy in seizures-induced neuronal injury, which provides a new target for epilepsy treatment.

EGCG suppressed activation of hepatic stellate cells by regulating the PLCE1/IP3/Ca2+ pathway

(-)-Epigallocatechin-3-O-gallate (EGCG), one of the green tea catechins, exhibits significant antioxidant properties that play an essential role in various diseases. However, the functional role and underlying mechanism of EGCG in stimulating of hepatic stellate cells (HSCs) remain unexplored in transcriptomics sequencing studies. The present study suggests that oral administration of EGCG at a dosage of 200 mg/kg/day for a duration of four weeks exhibits significant therapeutic potential in a murine model of liver fibrosis induced by CCl4. The activation of HSCs in vitro was dose-dependently inhibited by EGCG. The sequencing analysis data reveled that EGCG exerted a regulatory effect on the calcium signal in mouse HSCs, resulting in a decrease in calcium ion concentration. Further analysis revealed that EGCG inhibited the expression of phospholipase C epsilon-1 (PLCE1) and inositol 1, 4, 5-trisphosphate (IP3) in activated mouse HSCs. Additionally, EGCG contributes to the reduction the concentration of calcium ions by regulating PLCE1. After the knockdown of PLCE1, free calcium ion concentrations decreased, resulting in the inhibition of both cell proliferation and migration. Interestingly, the expression of PLCE1 and cytosolic calcium levels were regulated by reactive oxygen species(ROS). Furthermore, our findings suggest that ROS might inhibit the expression of PLCE1 by inhibiting TFEB, a transcription activator involved in the nuclear translocation process. Our study provided novel evidence regarding the regulatory effects of EGCG on activated HSCs (aHSCs) in mice by the calcium signaling pathway, emphasizing the crucial role of PLCE1 within the calcium signaling network of HSCs. The proposition was also made that PLCE1 holds promise as a novel therapeutic target for murine liver fibrosis.

Calcium signaling from damaged lysosomes induces cytoprotective stress granules

Lysosomal damage induces stress granule (SG) formation. However, the importance of SGs in determining cell fate and the precise mechanisms that mediate SG formation in response to lysosomal damage remain unclear. Here, we describe a novel calcium-dependent pathway controlling SG formation, which promotes cell survival during lysosomal damage. Mechanistically, the calcium-activated protein ALIX transduces lysosomal damage signals to SG formation by controlling eIF2α phosphorylation after sensing calcium leakage. ALIX enhances eIF2α phosphorylation by promoting the association between PKR and its activator PACT, with galectin-3 inhibiting this interaction; these regulatory events occur on damaged lysosomes. We further find that SG formation plays a crucial role in promoting cell survival upon lysosomal damage caused by factors such as SARS-CoV-2ORF3a, adenovirus, malarial pigment, proteopathic tau, or environmental hazards. Collectively, these data provide insights into the mechanism of SG formation upon lysosomal damage and implicate it in diseases associated with damaged lysosomes and SGs.

An artificial peptide inhibits autophagy through calcineurin-TFEB pathway

We previously reported that a bioactive peptide (pep3) can potently inhibit the enzyme activity of purified calcineurin (CN). In this paper, we further demonstrate that transfected pep3 can strongly inhibit CN enzyme activity in HEK293 cells. Transcription factor EB (TFEB) plays an important role in the autophagy-lysosome pathway (ALP) as one of the substrates of CN, so we study the effect of pep3 on the CN-TFEB-ALP pathway. Pep3 can significantly inhibit the mRNA levels of the TFEB downstream genes and the expression of the autophagy-associated proteins, and autophagy flux in HEK293 cells. We also validated the inhibitory effect of pep3 on autophagy in mice. These findings may provide a new idea for discovering more CN inhibitors and autophagy inhibitory drugs.

Tumor cell membrane-based vaccines: A potential boost for cancer immunotherapy

Because therapeutic cancer vaccines can, in theory, eliminate tumor cells specifically with relatively low toxicity, they have long been considered for application in repressing cancer progression. Traditional cancer vaccines containing a single or a few discrete tumor epitopes have failed in the clinic, possibly due to challenges in epitope selection, target downregulation, cancer cell heterogeneity, tumor microenvironment immunosuppression, or a lack of vaccine immunogenicity. Whole cancer cell or cancer membrane vaccines, which provide a rich source of antigens, are emerging as viable alternatives. Autologous and allogenic cellular cancer vaccines have been evaluated as clinical treatments. Tumor cell membranes (TCMs) are an intriguing antigen source, as they provide membrane-accessible targets and, at the same time, serve as integrated carriers of vaccine adjuvants and other therapeutic agents. This review provides a summary of the properties and technologies for TCM cancer vaccines. Characteristics, categories, mechanisms, and preparation methods are discussed, as are the demonstrable additional benefits derived from combining TCM vaccines with chemotherapy, sonodynamic therapy, phototherapy, and oncolytic viruses. Further research in chemistry, biomedicine, cancer immunology, and bioinformatics to address current drawbacks could facilitate the clinical adoption of TCM vaccines.

Mechanisms and cross-talk of regulated cell death and their epigenetic modifications in tumor progression

Cell death is a fundamental part of life for metazoans. To maintain the balance between cell proliferation and metabolism of human bodies, a certain number of cells need to be removed regularly. Hence, the mechanisms of cell death have been preserved during the evolution of multicellular organisms. Tumorigenesis is closely related with exceptional inhibition of cell death. Mutations or defects in cell death-related genes block the elimination of abnormal cells and enhance the resistance of malignant cells to chemotherapy. Therefore, the investigation of cell death mechanisms enables the development of drugs that directly induce tumor cell death. In the guidelines updated by the Cell Death Nomenclature Committee (NCCD) in 2018, cell death was classified into 12 types according to morphological, biochemical and functional classification, including intrinsic apoptosis, extrinsic apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, PARP-1 parthanatos, entotic cell death, NETotic cell death, lysosome-dependent cell death, autophagy-dependent cell death, immunogenic cell death, cellular senescence and mitotic catastrophe. The mechanistic relationships between epigenetic controls and cell death in cancer progression were previously unclear. In this review, we will summarize the mechanisms of cell death pathways and corresponding epigenetic regulations. Also, we will explore the extensive interactions between these pathways and discuss the mechanisms of cell death in epigenetics which bring benefits to tumor therapy.

LAMTOR1 regulates dendritic lysosomal positioning in hippocampal neurons through TRPML1 inhibition

Intracellular lysosomal trafficking and positioning are fundamental cellular processes critical for proper neuronal function. Among the diverse array of proteins involved in regulating lysosomal positioning, the Transient Receptor Potential Mucolipin 1 (TRPML1) and the Ragulator complex have emerged as central players. TRPML1, a lysosomal cation channel, has been implicated in lysosomal biogenesis, endosomal/lysosomal trafficking including in neuronal dendrites, and autophagy. LAMTOR1, a subunit of the Ragulator complex, also participates in the regulation of lysosomal trafficking. Here we report that LAMTOR1 regulates lysosomal positioning in dendrites of hippocampal neurons by interacting with TRPML1. LAMTOR1 knockdown (KD) increased lysosomal accumulation in proximal dendrites of cultured hippocampal neurons, an effect reversed by TRPML1 KD or inhibition. On the other hand, TRPML1 activation with ML-SA1 or prevention of TRPML1 interaction with LAMTOR1 using a TAT-decoy peptide induced dendritic lysosomal accumulation. LAMTOR1 KD-induced proximal dendritic lysosomal accumulation was blocked by the dynein inhibitor, ciliobrevin D, suggesting the involvement of a dynein-mediated transport. These results indicate that LAMTOR1-mediated inhibition of TRPML1 is critical for normal dendritic lysosomal distribution and that release of this inhibition or direct activation of TRPML1 results in abnormal dendritic lysosomal accumulation. The roles of LAMTOR1-TRPML1 interactions in lysosomal trafficking and positioning could have broad implications for understanding cognitive disorders associated with lysosomal pathology and calcium dysregulation.

Regulation of lysosomes in skeletal muscle during exercise, disuse and aging

Lysosomes play a critical role as a terminal organelle in autophagy flux and in regulating protein degradation, but their function and adaptability in skeletal muscle is understudied. Lysosome functions include both housekeeping and signaling functions essential for cellular homeostasis. This review focuses on the regulation of lysosomes in skeletal muscle during exercise, disuse, and aging, with a consideration of sex differences as well as the role of lysosomes in mediating the degradation of mitochondria, termed mitophagy. Exercise enhances mitophagy during elevated mitochondrial stress and energy demand. A critical response to this deviation from homeostasis is the activation of transcription factors TFEB and TFE3, which drive the expression of lysosomal and autophagic genes. Conversely, during muscle disuse, the suppression of lysosomal activity contributes to the accumulation of defective mitochondria and other cellular debris, impairing muscle function. Aging further exacerbates these effects by diminishing lysosomal efficacy, leading to the accumulation of damaged cellular components. mTORC1, a key nutrient sensor, modulates lysosomal activity by inhibiting TFEB/TFE3 translocation to the nucleus under nutrient-rich conditions, thereby suppressing autophagy. During nutrient deprivation or exercise, AMPK activation inhibits mTORC1, facilitating TFEB/TFE3 nuclear translocation and promoting lysosomal biogenesis and autophagy. TRPML1 activation by mitochondrial ROS enhances lysosomal calcium release, which is essential for autophagy and maintaining mitochondrial quality. Overall, the intricate regulation of lysosomal functions and signaling pathways in skeletal muscle is crucial for adaptation to physiological demands, and disruptions in these processes during disuse and aging underscore the ubiquitous power of exercise-induced adaptations, and also highlight the potential for targeted therapeutic interventions to preserve muscle health.

(S)-ML-SA1 Activates Autophagy via TRPML1-TFEB Pathway

Autophagic flux plays a crucial role in various diseases. Recently, the lysosomal ion channel TRPML1 has emerged as a promising target in lysosomal storage diseases, such as mucolipidosis. The discovery of mucolipin synthetic agonist-1 (ML-SA1) has expanded our understanding of TRPML1's function and its potential therapeutic uses. However, ML-SA1 is a racemate with limited cellular potency and poor water solubility. In this study, we synthetized rac-ML-SA1, separated the enantiomers by chiral liquid chromatography and determined their absolute configuration by vibrational circular dichroism (VCD). In addition, we focused on investigating the impact of each enantiomer of ML-SA1 on the TRPML1-TFEB axis. Our findings revealed that (S)-ML-SA1 acts as an agonist for TRPML1 at the lysosomal membrane. This activation prompts transcription factor EB (TFEB) to translocate from the cytosol to the nucleus in a dose-dependent manner within live cells. Consequently, this signaling pathway enhances the expression of coordinated lysosomal expression and regulation (CLEAR) genes and activates autophagic flux. Our study presents evidence for the potential use of (S)-ML-SA1 in the development of new therapies for lysosomal storage diseases that target TRPML1.