p62/SQSTM1 - steering the cell through health and disease

p62 Binding to Protein Kinase C Regulates HIV-1 gp120 V3 Loop Induced Microglial Inflammation

The main pathogenic mechanism of HIV-associated neurocognitive disorders (HAND) is neuronal apoptosis induced by inflammatory mediators, in which microglial inflammation plays a crucial role. However, the exact pathogenic mechanism remains unclear. Previous studies have shown that the HIV-1 gp120 V3 loop can trigger inflammation in CHME-5 microglia. p62 is a post-translational modified multidomain protein that is involved in the regulation of autophagy and is closely related to neuroinflammation. In this study, we found that p62 knockout down-regulated the expression of MCP-1, IL-6 and COX-2, and improved the inflammation of HIV-1 gp120 V3 loop induced microglia, while overexpression of p62 up-regulated the expression of MCP-1, IL-6 and COX-2, and promoted the inflammation of microglia. In addition, protein kinase C (PKC) knockout down-regulated the expression of MCP-1, IL-6 and COX-2 and inhibited the activation of IKK/ NF-κ B pathway, while tumor necrosis factor receptor-associated factor 6 (TRAF6) knockout had no significant effect on the expression of MCP-1, IL-6 and COX-2. Co-immunoprecipitation showed that p62 was bound and interacted with PKC. Inhibition of IKK/ NF-κ B pathway can down-regulate the expression of MCP-1, IL-6 and COX-2, and improve the inflammatory response of microglia. Our research further found that inhibition of IKK/ NF-κ B can decrease the expression of Caspase-3 and reduce the apoptosis of neurons in the co-culture of CHME-5 microglia and primary mouse neurons. The results of this study suggest that HIV-1 gp120 V3 loop induced CHME-5 microglial inflammation may be activated by the direct binding of p62 and PKC through the IKK/ NF-κ B signaling pathway, and these findings provide an important reference for the prevention and treatment of HAND.

Berberine in rheumatoid arthritis: a comprehensive review and meta-analysis of its anti-inflammatory and immunomodulatory mechanisms in animal models

Berberine (BBR), an alkaloid derivative mostly found in Oregon grapes and barberry shoots, has several medical properties, including anti-microbial, anti-tumorigenic, and anti-inflammatory properties. As such, it is a superior alternative to presently recommended medications. From previous researches, which showed that BBR has anti-arthritic qualities by blocking a number of inflammatory signalling pathways. Furthermore, it has been demonstrated that BBR attenuates Beclin-1, which reduces autophagy-mediated survival of mature adipocytes. BBR has also been identified as an AhR inducer and a promoter of Treg differentiation. Berberine has been shown in earlier studies to be useful in treating rheumatoid arthritis (RA) in animal models. The pharmacological effects and possible action pathway of Berberine were evaluated in this study. We looked through three databases-PubMed, Web of Science, and Google Scholar-for pertinent research published from the time the databases were created and August 2024. This risk-of-bias measure was used to evaluate the methodological quality. Utilising RevMan 5.4, the statistical analysis was conducted. There were 12 studies in this research with 175 animals. The findings showed that Berberine lowers the levels of IL-1β, IL-17, IL-6, IL-10, and TNF-α), paw swelling, and histopathological scores. These connected to the anti-inflammatory, anti-oxidative stress, and osteoprotective qualities of berberine. Nonetheless, further superior animal research is required to evaluate berberine impact on rheumatoid arthritis (RA). Additionally, more research is needed to validate berberine safety. Considering the significance of the active component, further research is needed to determine the best dose and increase berberine bioavailability.

Rosmarinic acid-mediated downregulation of RIG-I and p62 in microglia confers resistance to Japanese encephalitis virus-induced inflammation

BACKGROUND

Japanese encephalitis virus (JEV) is a mosquito-borne zoonotic pathogen that causes encephalitis in humans and reproductive failure in pigs. The transmission of JEV between humans and animals poses a significant public health threat and results in substantial economic losses. Excessive inflammation in the central nervous system of JEV-infected patients is a major cause of mortality and disability. Rosmarinic acid (RA), a polyhydroxyphenolic compound isolated from medicinal herbs, has been preliminarily shown to possess anti-inflammatory properties and significantly inhibit JEV-induced neuroinflammation in mice.

RESULTS

This study investigated the antiviral capacity and potential mechanisms of RA in JEV-infected cells. The results demonstrated that RA could inhibit JEV replication in vitro. Furthermore, the expression levels of inflammatory cytokines (including IL-6, IL-1β, CCL-2, and TNF-α), membrane receptors (including RIG-I, TLR3, TLR4, TLR7, and TLR8), NF-κB complex and p62/SQSTM1 were assessed using qPCR, ELISA, and Western blot, respectively. The findings indicated that RA significantly suppressed the expression of IL-6, IL-1α, TNF-α, and CCL-2 in JEV-infected BV-2 cells in a dose-dependent manner. Additionally, RA treatment downregulated the expression levels of RIG-I and p62, while p62 silencing inhibited the upregulation of inflammatory cytokines in JEV-infected BV-2 cells.

CONCLUSION

Our present study highlights the important role of RA-mediated reduction of RIG-I and p62 in microglia, conferring resistance to Japanese encephalitis virus-induced inflammation.

Ceramide synthase 6 induces mitochondrial dysfunction and apoptosis in hemin-treated neurons by impairing mitophagy through interacting with sequestosome 1

Intracerebral hemorrhage (ICH) is a severe subtype of stroke linked to high morbidity and mortality rates. However, the underlying mechanisms of neuronal injury post-ICH remain poorly understood. In this study, we investigated sphingolipid metabolism alterations in neurons using lipidomics and explored the regulatory mechanisms involved. Western blot and live-cell imaging were applied to detect mitochondrial quality and mitophagy level. We found a significant upregulation of ceramide synthase 6 (CERS6)-related C16 ceramide biosynthesis after hemin treatment. Knockdown of CERS6 notably ameliorated mitochondrial dysfunction and reduced neuronal apoptosis. Additionally, impaired neuronal mitophagy was observed after hemin treatment, which was restored by CERS6 knockdown. Mechanistically, CERS6 impaired mitophagy by interacting with sequestosome 1, leading to mitochondrial dysfunction and neuronal apoptosis. Our study explored the relationship between ceramide metabolism and mitophagy in neurons, revealing the pro-apoptotic role of CERS6 while providing a potential therapeutic target for patients with ICH.

Harnessing luciferase chemistry in regulated cell death modalities and autophagy: overview and perspectives

Regulated cell death is a fate of cells in (patho)physiological conditions during which extrinsic or intrinsic signals or redox equilibrium pathways following infection, cellular stress or injury are coupled to cell death modalities like apoptosis, necroptosis, pyroptosis or ferroptosis. An immediate survival response to cellular stress is often induction of autophagy, a process that deals with removal of aggregated proteins and damaged organelles by a lysosomal recycling process. These cellular processes and their regulation are crucial in several human diseases. Exploiting high-throughput assays which discriminate distinct cell death modalities and autophagy are critical to identify potential therapeutic agents that modulate these cellular responses. In the past few years, luciferase-based assays have been widely developed for assessing regulated cell death and autophagy pathways due to their simplicity, sensitivity, known chemistry, different spectral properties and high-throughput potential. Here, we review basic principles of bioluminescent reactions from a mechanistic perspective, along with their implication in vitro and in vivo for probing cell death and autophagy pathways. These include applying luciferase-, luciferin-, and ATP-based biosensors for investigating regulated cell death modalities. We discuss multiplex bioluminescence platforms which simultaneously distinguish between the various cell death phenomena and cellular stress recovery processes such as autophagy. We also highlight the recent technological achievements of bioluminescent tools for the prediction of drug effectiveness in pathways associated with regulated cell death.

Establishment and characterization of the first immortalized vocal cord leukoplakia epithelial cell line

The importance of vocal cord leukoplakia (VCL) in the etiology and progression of laryngeal carcinoma has gained increasing recognition. However, research into the mechanisms of laryngeal precancerous lesions such as VCL, has been hampered by the small size of VCL epithelial cells and their limited culture lifespan. In this study, we enhanced the primary culture protocol for VCL epithelial cells and introduced simian virus 40 Large T to establish an immortalized cell line, designated hVCL-MSDEP01. We confirmed that hVCL-MSDEP01 expresses epithelial-specific genes and proteins; it also demonstrates distinct cell cycle dynamics and apoptosis rates compared with primary cells. In conclusion, hVCL-MSDEP01 serves as an ideal in vitro model for studying VCL. This cell line will substantially advance research into the etiology and progression of laryngeal carcinoma.

Ubiquitin-mediated endosomal stress: A novel organelle stress of early endosomes that initiates cellular signaling pathways: USP8 serves as a gatekeeper of ubiquitin-mediated endosomal stress to counteract the activation of cellular signaling pathways

Cells utilize diverse organelles to maintain homeostasis and to respond to extracellular stimuli. Recently, multifaceted aspects of organelle stress caused by various factors have been emerging. The endosome is an essential organelle, functioning as the central hub for membrane trafficking in cooperation with the ubiquitin system. However, knowledge regarding endosomal stress, which refers to organelle stress of the endosome, is currently limited. We recently revealed ubiquitin-mediated endosomal stress of early endosomes (EEs) and its responsive signaling pathways. These findings shed light on the relevance of ubiquitin-mediated endosomal stress to physiological and pathological processes. Here, we present a hypothesis that ubiquitin-mediated endosomal stress may have significant roles in biological contexts and that ubiquitin-specific protease 8 is a key regulator of ubiquitin clearance from EEs.

Coronavirus M protein promotes mitophagy over virophagy by recruiting PDPK1 to phosphorylate SQSTM1 at T138

Autophagy plays a dual role in coronavirus infection, facilitating the elimination of either proviral components (virophagy) or antiviral factors such as mitochondria (mitophagy), leading to complex mechanisms of immune evasion. Understanding the mechanisms that govern the switch between the autophagic degradation of deleterious or beneficial substrates in coronavirus infection is crucial for developing precise drug targets to treat virus-induced diseases. However, this switch remains largely unknown. Using a dual split-fluorescence assay, we identify PDPK1 as a negative regulator of innate immunity, directing the transition from virophagy to mitophagy through the phosphorylation of SQSTM1 at T138. Remarkably, a PDPK1-targeting peptide inhibits the replication of various RNA viruses by restoring innate immunity through enhanced virophagy and suppressed mitophagy, thereby protecting female mice from lethal infections. These findings underscore the detrimental role of PDPK1 in innate immunity by orchestrating the shift from virophagy to mitophagy, positioning PDPK1 as a promising pharmacological target for effectively combating a broad spectrum of virus infections.

Muscle-derived IL-1β regulates EcSOD expression via the NBR1-p62-Nrf2 pathway in muscle during cancer cachexia

Oxidative stress contributes to the loss of skeletal muscle mass and function in cancer cachexia. However, this outcome may be mitigated by an improved endogenous antioxidant defence system. Here, using the well-established oxidative stress-inducing muscle atrophy model of Lewis lung carcinoma (LLC) in 13-week-old male C57BL/6J mice, we demonstrate that extracellular superoxide dismutase (EcSOD) levels increase in the cachexia-prone extensor digitorum longus muscle. LLC transplantation significantly increased interleukin-1β (IL-1β) expression and release from extensor digitorum longus muscle fibres. Moreover, IL-1β treatment of C2C12 myotubes increased NBR1, p62 phosphorylation at Ser351, Nrf2 nuclear translocation and EcSOD protein expression. Additional studies in vivo indicated that intramuscular IL-1β injection is sufficient to stimulate EcSOD expression, which is prevented by muscle-specific knockout of p62 and Nrf2 (i.e. in p62 skmKO and Nrf2 skmKO mice, respectively). Finally, since an increase in circulating IL-1β may lead to unwanted outcomes, we demonstrate that targeting this pathway at p62 is sufficient to drive muscle EcSOD expression in an Nrf2-dependent manner. In summary, cancer cachexia increases EcSOD expression in extensor digitorum longus muscle via muscle-derived IL-1β-induced upregulation of p62 phosphorylation and Nrf2 activation. These findings provide further mechanistic evidence for the therapeutic potential of p62 and Nrf2 to mitigate cancer cachexia-induced muscle atrophy. KEY POINTS: Oxidative stress plays an important role in muscle atrophy during cancer cachexia. EcSOD, which mitigates muscle loss during oxidative stress, is upregulated in 13-week-old male C57BL/6J mice of extensor digitorum longus muscles during cancer cachexia. Using mouse and cellular models, we demonstrate that cancer cachexia promotes muscle EcSOD protein expression via muscle-derived IL-1β-dependent stimulation of the NBR1-p62-Nrf2 signalling pathway. These results provide further evidence for the potential therapeutic targeting of the NBR1-p62-Nrf2 signalling pathway downstream of IL-1β to mitigate cancer cachexia-induced muscle atrophy.

SQSTM1 improves acute lung injury via inhibiting airway epithelium ferroptosis in a vitamin D receptor/autophagy-mediated manner

Emerging evidence has reported that acute lung injury (ALI), characterized by inflammation and oxidative stress in airway epithelium, is regulated by programmed cell death. Ferroptosis, a regulated form of cell death spurred by uncontrolled lipid peroxidation, has been proven to implicate various diseases. Inhibiting ferroptosis represents a feasible strategy for ALI through the suppression of lipid peroxidation, while the mechanism remains to be further elucidated. Here, we identified Sequestosome 1 (SQSTM1) as a negative regulator of airway epithelium ferroptosis during ALI. SQSTM1 knockdown cells manifested higher sensitivity to ferroptosis. Mechanistically, SQSTM1 was found to directly interact with vitamin D receptor (VDR) through its nuclear receptor (NR) box motif, facilitating its nuclear translocation and initiating autophagy at the transcriptional level. To further validate these findings, an in vivo preventive model utilizing spermidine, a proven inducer of SQSTM1 was established. The results consistently demonstrated that spermidine supplementation significantly induced SQSTM1 and ameliorated ALI by mitigating airway epithelial ferroptosis. Notably, these effects were abrogated in the absence of SQSTM1. Taken together, this study identified SQSTM1 as a negative regulator of airway epithelium ferroptosis in a VDR-mediated autophagy manner, making it a potential therapeutic target for the treatment of ALI.

Molecular Insights into Aggrephagy: Their Cellular Functions in the Context of Neurodegenerative Diseases

Protein homeostasis or proteostasis is an equilibrium of biosynthetic production, folding and transport of proteins, and their timely and efficient degradation. Proteostasis is guaranteed by a network of protein quality control systems aimed at maintaining the proteome function and avoiding accumulation of potentially cytotoxic proteins. Terminal unfolded and dysfunctional proteins can be directly turned over by the ubiquitin-proteasome system (UPS) or first amassed into aggregates prior to degradation. Aggregates can also be disposed into lysosomes by a selective type of autophagy known as aggrephagy, which relies on a set of so-called selective autophagy receptors (SARs) and adaptor proteins. Failure in eliminating aggregates, also due to defects in aggrephagy, can have devastating effects as underscored by several neurodegenerative diseases or proteinopathies, which are characterized by the accumulation of aggregates mostly formed by a specific disease-associated, aggregate-prone protein depending on the clinical pathology. Despite its medical relevance, however, the process of aggrephagy is far from being understood. Here we review the findings that have helped in assigning a possible function to specific SARs and adaptor proteins in aggrephagy in the context of proteinopathies, and also highlight the interplay between aggrephagy and the pathogenesis of proteinopathies.

Sex Differences Affect the NRF2 Signaling Pathway in the Early Phase of Liver Steatosis: A High-Fat-Diet-Fed Rat Model Supplemented with Liquid Fructose

Sex differences may play a role in the etiopathogenesis and severity of metabolic dysfunction-associated steatotic liver disease (MASLD), a disorder characterized by excessive fat accumulation associated with increased inflammation and oxidative stress. We previously observed the development of steatosis specifically in female rats fed a high-fat diet enriched with liquid fructose (HFHFr) for 12 weeks. The aim of this study was to better characterize the observed sex differences by focusing on the antioxidant and cytoprotective pathways related to the KEAP1/NRF2 axis. The KEAP1/NRF2 signaling pathway, autophagy process (LC3B and LAMP2), and endoplasmic reticulum stress response (XBP1) were analyzed in liver homogenates in male and female rats that were fed a 12-week HFHFr diet. In females, the HFHFr diet resulted in the initial activation of the KEAP1/NRF2 pathway, which was not followed by the modulation of downstream molecular targets; this was possibly due to the increase in KEAP1 levels preventing the nuclear translocation of NRF2 despite its cytosolic increase. Interestingly, while in both sexes the HFHFr diet resulted in an increase in the levels of LC3BII/LC3BI, a marker of autophagosome formation, only males showed a significant upregulation of LAMP2 and XBP1s; this did not occur in females, suggesting impaired autophagic flux in this sex. Overall, our results suggest that males are characterized by a greater ability to cope with an HFHFr metabolic stimulus mainly through an autophagic-mediated proteostatic process while in females, this is impaired. This might depend at least in part upon the fine modulation of the cytoprotective and antioxidant KEAP1/NRF2 pathway resulting in sex differences in the occurrence and severity of MASLD. These results should be considered to design effective therapeutics for MASLD.

Role of O-linked N-acetylglucosamine protein modification in oxidative stress-induced autophagy: a novel target for bone remodeling

O-linked N-acetylglucosamine protein modification (O-GlcNAcylation) is a dynamic post-translational modification (PTM) involving the covalent binding of serine and/or threonine residues, which regulates bone cell homeostasis. Reactive oxygen species (ROS) are increased due to oxidative stress in various pathological contexts related to bone remodeling, such as osteoporosis, arthritis, and bone fracture. Autophagy serves as a scavenger for ROS within bone marrow-derived mesenchymal stem cells, osteoclasts, and osteoblasts. However, oxidative stress-induced autophagy is affected by the metabolic status, leading to unfavorable clinical outcomes. O-GlcNAcylation can regulate the autophagy process both directly and indirectly through oxidative stress-related signaling pathways, ultimately improving bone remodeling. The present interventions for the bone remodeling process often focus on promoting osteogenesis or inhibiting osteoclast absorption, ignoring the effect of PTM on the overall process of bone remodeling. This review explores how O-GlcNAcylation synergizes with autophagy to exert multiple regulatory effects on bone remodeling under oxidative stress stimulation, indicating the application of O-GlcNAcylation as a new molecular target in the field of bone remodeling.

Long way up: rethink diseases in light of phase separation and phase transition

Biomolecular condensation, driven by multivalency, serves as a fundamental mechanism within cells, facilitating the formation of distinct compartments, including membraneless organelles that play essential roles in various cellular processes. Perturbations in the delicate equilibrium of condensation, whether resulting in gain or loss of phase separation, have robustly been associated with cellular dysfunction and physiological disorders. As ongoing research endeavors wholeheartedly embrace this newly acknowledged principle, a transformative shift is occurring in our comprehension of disease. Consequently, significant strides have been made in unraveling the profound relevance and potential causal connections between abnormal phase separation and various diseases. This comprehensive review presents compelling recent evidence that highlight the intricate associations between aberrant phase separation and neurodegenerative diseases, cancers, and infectious diseases. Additionally, we provide a succinct summary of current efforts and propose innovative solutions for the development of potential therapeutics to combat the pathological consequences attributed to aberrant phase separation.

Sequestosome-1 (SQSTM1/p62) as a target in dopamine catabolite-mediated cellular dyshomeostasis

Alterations in the dopamine catabolic pathway are known to contribute to the degeneration of nigrostriatal neurons in Parkinson's disease (PD). The progressive cellular buildup of the highly reactive intermediate 3,4-dihydroxyphenylacetaldehye (DOPAL) generates protein cross-linking, oligomerization of the PD-linked αSynuclein (αSyn) and imbalance in protein quality control. In this scenario, the autophagic cargo sequestome-1 (SQSTM1/p62) emerges as a target of DOPAL-dependent oligomerization and accumulation in cytosolic clusters. Although DOPAL-induced oxidative stress and activation of the Nrf2 pathway promote p62 expression, p62 oligomerization rather seems to be a consequence of direct DOPAL modification. DOPAL-induced p62 clusters are positive for ubiquitin and accumulate within lysosomal-related structures, likely affecting the autophagy-lysosomal functionality. Finally, p62 oligomerization and clustering is synergistically augmented by DOPAL-induced αSyn buildup. Hence, the substantial impact on p62 proteostasis caused by DOPAL appears of relevance for dopaminergic neurodegeneration, in which the progressive failure of degradative pathways and the deposition of proteins like αSyn, ubiquitin and p62 in inclusion bodies represent a major trait of PD pathology.

Alginate Oligosaccharides Protect Gastric Epithelial Cells against Oxidative Stress Damage through Induction of the Nrf2 Pathway

Gastric diseases represent a significant global public health challenge, characterized by molecular dysregulation in redox homeostasis and heightened oxidative stress. Although prior preclinical studies have demonstrated the cytoprotective antioxidant effects of alginate oligosaccharides (AOSs) through the Nrf2 pathway, whether such mechanisms apply to gastric diseases remains unclear. In this study, we used the GES-1 gastric cell line exposed to hydrogen peroxide (H2O2) as a damage model to investigate the impact of AOS on cell viability and its associated mechanisms. Our results revealed that pre-incubation with AOS for either 4 h or 24 h significantly improved the viability of GES-1 cells exposed to H2O2. In addition, AOS reduced the intracellular ROS levels, activating the Nrf2 signaling pathway, with increased Nrf2 protein and mRNA expression and a significant upregulation of the target genes HO-1 and NQO1. The activation of Nrf2 was correlated with decreased Keap1 protein expression and an increased level of the autophagy protein p62/SQSTM1, suggesting the activation of Nrf2 through a noncanonical pathway. This study suggests that AOS is a potential treatment for protecting gastric epithelial cells from oxidative stress by activating the p62/SQSTM1-Keap1-Nrf2 axis and laying the foundation for future investigations about its specific therapeutic mechanisms.

Single-cell transcriptomics reveals the intra-tumoral heterogeneity and SQSTM1/P62 and Wnt/β-catenin mediated epithelial to mesenchymal transition and stemness of triple-negative breast cancer

Triple-negative breast cancer (TNBC) is characterized by the complex tumor microenvironment (TME) consisting of an abundance of mesenchymal stem cells (MSCs), which is known to facilitate epithelial-to-mesenchymal transition (EMT). The development of single-cell genomics is a powerful method for defining the intricate genetic landscapes of malignancies. In this study, we have employed single-cell RNA sequencing (scRNA-seq) to dissect the intra-tumoral heterogeneity and analyze the single-cell transcriptomic landscape to detect rare consequential cell subpopulations of significance. The scRNA-seq analysis of TNBC and Normal patient derived samples revealed that EMT markers and transcription factors were most upregulated in MSC population. Further, exploration of gene expression analysis among TNBC and Normal patient-derived MSCs ascertained the role of SQSTM1/P62 and Wnt/β-catenin in TNBC progression. Wnt/β-catenin and Wnt/PCP signaling pathways are prominent contributors of EMT, stemness, and cancer stem cell (CSC) properties of TNBC. SQSTM1/P62 cooperates with the components of the Wnt/PCP signaling pathway and is critically involved at the interface of autophagy and EMT. Moreover, siRNA targeting SQSTM1/P62 and inhibitor of Wnt/β-catenin (FH535) in conjunction was used to explore molecular modification of EMT and stemness markers. Although SQSTM1/P62 is not crucial for cell survival, cytotoxicity assay revealed synergistic interaction between the siRNA/inhibitor. Modulation of these important pathways helped in reduction of expression of genes and proteins contributing to CSC properties. Gene and protein expression analysis revealed the induction of EMT to MET. Moreover, co-treatment resulted in inactivation of non-canonical Wnt VANGL2-JNK signaling axis. The synergistic impact of inhibition of SQSTM1/P62 and Wnt/β-catenin signaling facilitates the development of a potential therapeutic regimen for TNBC.

Precision proteoform design for 4R tau isoform selective templated aggregation

Prion-like spread of disease-specific tau conformers is a hallmark of all tauopathies. A 19-residue probe peptide containing a P301L mutation and spanning the R2/R3 splice junction of tau folds and stacks into seeding-competent fibrils and induces aggregation of 4R, but not 3R tau. These tau peptide fibrils propagate aggregated intracellular tau over multiple generations, have a high β-sheet content, a colocalized lipid signal, and adopt a well-defined U-shaped fold found in 4R tauopathy brain-derived fibrils. Fully atomistic replica exchange molecular dynamics (MD) simulations were used to compute the free energy landscapes of the conformational ensemble of the peptide monomers. These identified an aggregation-prohibiting β-hairpin structure and an aggregation-competent U-fold unique to 4R tauopathy fibrils. Guided by MD simulations, we identified that the N-terminal-flanking residues to PHF6, which slightly vary between 4R and 3R isoforms, modulate seeding. Strikingly, when a single amino acid switch at position 305 replaced the serine of 4R tau with a lysine from the corresponding position in the first repeat of 3R tau, the seeding induced by the 19-residue peptide was markedly reduced. Conversely, a 4R tau mimic with three repeats, prepared by replacing those amino acids in the first repeat with those amino acids uniquely present in the second repeat, recovered aggregation when exposed to the 19-residue peptide. These peptide fibrils function as partial prions to recruit naive 4R tau-ten times the length of the peptide-and serve as a critical template for 4R tauopathy propagation. These results hint at opportunities for tau isoform-specific therapeutic interventions.

Effects of H2S-donor ascorbic acid derivative and ischemia/reperfusion-induced injury in isolated rat hearts

Hydrogen sulfide (H2S), a gasotransmitter, plays a crucial role in vasorelaxation, anti-inflammatory processes and mitigating myocardial ischemia/reperfusion-induced injury by regulating various signaling processes. We designed a water soluble H2S-releasing ascorbic acid derivative, BM-164, to combine the beneficial cardiovascular and anti-inflammatory effects of H2S with the excellent water solubility and antioxidant properties of ascorbic acid. DPPH antioxidant assay revealed that the antioxidant activity of BM-164 in the presence of a myocardial tissue homogenate (extract) increased continuously over the 120 min test interval due to the continuous release of H2S from BM-164. The cytotoxicity of BM-164 was tested by MTT assay on H9c2 cells, which resulted in no cytotoxic effect at concentrations of 10 to 30 μM. The possible beneficial effects of BM-164 (30 µM) was examined in isolated 'Langendorff' rat hearts. The incidence of ventricular fibrillation (VF) was significantly reduced from its control value of 79 % to 31 % in the BM-164 treated group, and the infarct size was also diminished from the control value of 28 % to 14 % in the BM-164 treated group. However, coronary flow (CF) and heart rate (HR) values in the BM-164 treated group did not show significantly different levels in comparison with the drug-free control, although a non-significant recovery in both CF and HR was observed at each time point. We attempted to reveal the mechanism of action of BM-164, focusing on the processes of autophagy and apoptosis. The expression of key autophagic and apoptotic markers in isolated rat hearts were detected by Western blot analysis. All the examined autophagy-related proteins showed increased expression levels in the BM-164 treated group in comparison to the drug-free control and/or ascorbic acid treated groups, while the changes in the expression of apoptotic markers were not obvious. In conclusion, the designed water soluble H2S releasing ascorbic acid derivative, BM-164, showed better cardiac protection against ischemia/reperfusion-induced injury compared to the untreated and ascorbic acid treated hearts, respectively.

PRRSV degrades MDA5 via dual autophagy receptors P62 and CCT2 to evade antiviral innate immunity

Porcine reproductive and respiratory syndrome virus (PRRSV) is a major economically devastating pathogen that has evolved various strategies to evade innate immunity. Downregulation of antiviral interferon largely promotes PRRSV immunoevasion by utilizing cytoplasmic melanoma differentiation-associated gene 5 (MDA5), a receptor that senses viral RNA. In this study, the downregulated transcription and expression levels of porcine MDA5 in PRRSV infection were observed, and the detailed mechanisms were explored. We found that the interaction between P62 and MDA5 is enhanced due to two factors: the phosphorylation modification of the autophagic receptor P62 by the upregulated kinase CK2α and the K63 ubiquitination of porcine MDA5 catalyzed by the E3 ubiquitinase TRIM21 in PRRSV-infected cells. As a result of these modifications, the classic P62-mediated autophagy is triggered. Additionally, porcine MDA5 interacts with the chaperonin containing TCP1 subunit 2 (CCT2), which is enhanced by PRRSV nsp3. This interaction promotes the aggregate formation and autophagic clearance of MDA5-CCT2-nsp3 independently of ubiquitination. In summary, enhanced MDA5 degradation occurs in PRRSV infection via two autophagic pathways: the binding of MDA5 with the autophagy receptor P62 and the aggrephagy receptor CCT2, leading to intense innate immune suppression. The research reveals a novel mechanism of immune evasion in PRRSV infection and provides fundamental insights for the development of new vaccines or therapeutic strategies.

Trichinella spiralis inhibits myoblast differentiation by targeting SQSTM1/p62 with a secreted E3 ubiquitin ligase

Trichinella spiralis infection is associated with the formation of cysts within host skeletal muscle cells, thereby enabling immune evasion and subsequent growth and development; however, the pathogenic factors involved in this process and their mechanisms remain elusive. Here, we found that Ts-RNF secreted by T. spiralis is required for its growth and development in host cells. Further study revealed that Ts-RNF functions as an E3 ubiquitin ligase that targets the UBA domain of SQSTM1/p62 by forming K63-type ubiquitin chains. This modification interferes with autophagic flux, leading to impaired mitochondrial clearance and abnormal myotube differentiation and fusion. Our results established that T. spiralis increases its escape by interfering with host autophagy via the secretion of an E3 ubiquitin ligase.

USP8 prevents aberrant NF-κB and Nrf2 activation by counteracting ubiquitin signals from endosomes

K63-linked ubiquitin chains attached to plasma membrane proteins serve as tags for endocytosis and endosome-to-lysosome sorting. USP8 is an essential deubiquitinase for the maintenance of endosomal functions. Prolonged depletion of USP8 leads to cell death, but the major effects on cellular signaling pathways are poorly understood. Here, we show that USP8 depletion causes aberrant accumulation of K63-linked ubiquitin chains on endosomes and induces immune and stress responses. Upon USP8 depletion, two different decoders for K63-linked ubiquitin chains, TAB2/3 and p62, were recruited to endosomes and activated the TAK1-NF-κB and Keap1-Nrf2 pathways, respectively. Oxidative stress, an environmental stimulus that potentially suppresses USP8 activity, induced accumulation of K63-linked ubiquitin chains on endosomes, recruitment of TAB2, and expression of the inflammatory cytokine. The results demonstrate that USP8 is a gatekeeper of misdirected ubiquitin signals and inhibits immune and stress response pathways by removing K63-linked ubiquitin chains from endosomes.

AMPKα is active in autophagy of endothelial cells in arsenic-induced vascular endothelial dysfunction by regulating mTORC1/p70S6K/ULK1

Cardiovascular disease (CVD) is the most common cause of death, environmental factors, such as arsenic, playing an important role in the progress of CVD. Vascular endothelial dysfunction (VED) is a crucial early feature for CVD, inorganic arsenic (iAs) can induce autophagy in various cells. However, the role of endothelial autophagy has rarely been studied in VED triggered by arsenic. Total of one hundred and twenty healthy male C57BL/6J mice weighing 18-22 g were randomly divided into an arsenic-exposure group and a control group for 3, 6, 9, and 12 weeks. The results showed that, independent of the exposure period, autophagy markers of p-ATG16L1 levels and Beclin 1 contents in the aortic arch endothelium increased significantly compared with those of the corresponding control group. And different exposure duration decreased NO contents in the serum significantly. Combined with the histological changes that endothelial injury aggravated gradually with the increasing exposure period, suggesting that under exposure to iAs over 9 weeks, VED was remarkably induced, and consistant high levels of endothelial autophagy may play an important role. Additionally, levels of p-AMPKα/AMPKα increased significantly and p-mTORC1/mTORC1 levels decreased remarkably in the aortic arch endothelium. Then, a NaAsO2-induced-VED in vitro model was used to explore the mechanism of arsenic-induced endothelial autophagy. Similarly, p-AMPKα/AMPKα level significantly increased, and p-mTORC1/mTORC1 level remarkably decreased induced by 30 μmol/L NaAsO2 in HUAECs. Further, an AMPK inhibitor (Compound C) pre-treatment prior to arsenic exposure reversed the increased autophagy level, and alleviated the endothelial dysfunction in HUVECs, as shown by the significant increase in the intracellular NO content and the cell vitality. Mechanistically, we revealed that AMPKα is active in autophagy of endothelial cells in arsenic-induced VED by regulating mTORC1/p70S6K/ULK1. The present study provide a new promising target for prevention and control arsenic-associated CVD.

NEMO reshapes the α-Synuclein aggregate interface and acts as an autophagy adapter by co-condensation with p62

NEMO is a ubiquitin-binding protein which regulates canonical NF-κB pathway activation in innate immune signaling, cell death regulation and host-pathogen interactions. Here we identify an NF-κB-independent function of NEMO in proteostasis regulation by promoting autophagosomal clearance of protein aggregates. NEMO-deficient cells accumulate misfolded proteins upon proteotoxic stress and are vulnerable to proteostasis challenges. Moreover, a patient with a mutation in the NEMO-encoding IKBKG gene resulting in defective binding of NEMO to linear ubiquitin chains, developed a widespread mixed brain proteinopathy, including α-synuclein, tau and TDP-43 pathology. NEMO amplifies linear ubiquitylation at α-synuclein aggregates and promotes the local concentration of p62 into foci. In vitro, NEMO lowers the threshold concentrations required for ubiquitin-dependent phase transition of p62. In summary, NEMO reshapes the aggregate surface for efficient autophagosomal clearance by providing a mobile phase at the aggregate interphase favoring co-condensation with p62.

HO-1-Mediated Autophagic Restoration Protects Lens Epithelial Cells Against Oxidative Stress and Cellular Senescence

Purpose

Oxidative stress and cellular senescence are risk factors for age-related cataract. Heme oxygenase 1 (HO-1) is a critical antioxidant enzyme and related to autophagy. Here, we investigate the crosstalk among HO-1, oxidative stress, and cellular senescence in mouse lens epithelial cells (LECs).

Methods

The gene expression of HO-1, p21, LC3, and p62 was measured in human samples. The protective properties of HO-1 were examined in hydrogen peroxide (H2O2)-damaged LECs. Autophagic flux was examined by Western blot and mRFP-GFP-LC3 assay. Western blotting and lysotracker staining were used to analyze lysosomal function. Flow cytometry was used to detect intracellular reactive oxygen species and analyze cell cycle. Senescence-associated β-galactosidase assay was used to determine cellular senescence. The crosstalk between HO-1 and transcription factor EB (TFEB) was further observed in TFEB-knockdown cells. The TFEB binding site in the promoter region of Hmox1 was predicted by the Jasper website and was confirmed by chromatin immunoprecipitation assay.

Results

HO-1 gene expression decreased in LECs of patients with age-related nuclear cataract, whereas mRNA expression levels of p21, LC3, and p62 increased. Upon H2O2-induced oxidative stress, LECs showed the characteristics of autophagic flux blockade, lysosomal dysfunction, and premature senescence. Interestingly, HO-1 significantly restored the impaired autophagic flux and lysosomal function and delayed cellular senescence. TFEB gene silencing greatly reduced the HO-1-mediated autophagic restoration, leading to a failure to prevent LECs from oxidative stress and premature senescence.

Conclusions

We demonstrated HO-1 effects on restoring autophagic flux and delaying cellular senescence under oxidative stress in LECs, which are dependent on TFEB.

Precision Proteoform Design for 4R Tau Isoform Selective Templated Aggregation

Prion-like spread of disease-specific tau conformers is a hallmark of all tauopathies. A 19-residue probe peptide containing a P301L mutation and spanning the R2/R3 splice junction of tau, folds and stacks into seeding-competent fibrils and induces aggregation of 4R, but not 3R tau. These tau peptide fibrils propagate aggregated intracellular tau over multiple generations, have a high β-sheet content, a colocalized lipid signal, and adopt a well-defined U-shaped fold found in 4R tauopathy brain-derived fibrils. Fully atomistic replica exchange molecular dynamics (MD) simulations were used to compute the free energy landscapes of the conformational ensemble of the peptide monomers. These identified an aggregation-prohibiting β-hairpin structure and an aggregation-competent U-fold unique to 4R tauopathy fibrils. Guided by MD simulations, we identified that the N-terminal-flanking residues to PHF6, which slightly vary between 4R and 3R isoforms, modulate seeding. Strikingly, when a single amino acid switch at position 305 replaced the serine of 4R tau with a lysine from the corresponding position in the first repeat of 3R tau, the seeding induced by the 19-residue peptide was markedly reduced. Conversely, a 4R tau mimic with three repeats, prepared by replacing those amino acids in the first repeat with those amino acids uniquely present in the second repeat, recovered aggregation when exposed to the 19-residue peptide. These peptide fibrils function as partial prions to recruit naïve 4R tau-ten times the length of the peptide-and serve as a critical template for 4R tauopathy propagation. These results hint at opportunities for tau isoform-specific therapeutic interventions.

lncRNA HOXC-AS2 promotes the progression of hypopharyngeal cancer by binding to the P62 protein mediating the autophagy process

Hypopharyngeal carcinoma is the most malignant type of head and neck squamous cell carcinoma, and lncRNAs play an important role in its formation and progression. However, the related specific mechanisms are rarely studied. lncRNAs closely associated with hypopharyngeal cancer were examined by lncRNA sequencing for in-depth exploration of the relationship between HOXC-AS2 and hypopharyngeal cancer pathogenesis. The mRNA expression of HOXC-AS2 and related genes was measured by qRT-PCR, and the biological function of HOXC-AS2 in hypopharyngeal carcinoma was demonstrated by gain- and loss-of-function experiments. RNA pulldown, RNA immunoprecipitation (RIP) and gene body truncation experiments and transcriptome sequencing were used to investigate the potential mechanism of HOXC-AS2 and its downstream genes, including P62, NF-KB and HMOX1. Finally, the biological function of HOXC-AS2 was confirmed in animal experiments. HOXC-AS2 and P62 expression was significantly upregulated in hypopharyngeal cancer tissues compared with normal hypopharyngeal tissues, while HMOX1 expression was decreased. Functionally, HOXC-AS2 overexpression can promote the viability, proliferation, migration and invasion of hypopharyngeal cancer cells and facilitate hypopharyngeal cancer progression. It was confirmed that HOXC-AS2 can bind to the P62 protein and activate the NF-KB signaling pathway, thereby affecting HMOX1 expression and regulating autophagy in hypopharyngeal cancer cells, ultimately regulating the formation and progression of hypopharyngeal cancer. In conclusion, our findings suggest that HOXC-AS2 regulates the progression of hypopharyngeal cancer by regulating autophagy and is abnormally highly expressed in hypopharyngeal cancer tissues. HOXC-AS2 may become a new target for the diagnosis and treatment of hypopharyngeal cancer.

USP13 deubiquitinates p62/SQSTM1 to induce autophagy and Nrf2 release for activating antioxidant response genes

SQSTM1/p62 (sequestosome 1) is a multifunctional protein that serves as a receptor for selective autophagy and scaffold. In selective autophagy, p62 functions as a bridge between polyubiquitinated proteins and autophagosomes. Further, p62 acts as a signaling hub for many cellular pathways including mTORC1, NF-κB, and Keap1-Nrf2. Post-translational modifications of p62, such as ubiquitination and phosphorylation, are known to determine its binding partners and regulate their intracellular functions. However, the mechanism of p62 deubiquitination remains unclear. In this study, we found that ubiquitin-specific protease 13 (USP13), a member of the USP family, directly binds p62 and removes ubiquitin at Lys7 (K7) of the PB1 domain. USP13-mediated p62 deubiquitination enhances p62 protein stability and facilitates p62 oligomerization, resulting in increased autophagy and degradation of Keap1, which is a negative regulator of the antioxidant response that promotes Nrf2 activation. Thus, USP13 can be considered a therapeutic target as a deubiquitination enzyme of p62 in autophagy-related diseases.

Tethering ATG16L1 or LC3 induces targeted autophagic degradation of protein aggregates and mitochondria

Proteolysis-targeting chimeras (PROTACs) based on the ubiquitin-proteasome system have made great progress in the field of drug discovery. There is mounting evidence that the accumulation of aggregation-prone proteins or malfunctioning organelles is associated with the occurrence of various age-related neurodegenerative disorders and cancers. However, PROTACs are inefficient for the degradation of such large targets due to the narrow entrance channel of the proteasome. Macroautophagy (hereafter referred to as autophagy) is known as a self-degradative process involved in the degradation of bulk cytoplasmic components or specific cargoes that are sequestered into autophagosomes. In the present study, we report the development of a generalizable strategy for the targeted degradation of large targets. Our results suggested that tethering large target models to phagophore-associated ATG16L1 or LC3 induced targeted autophagic degradation of the large target models. Furthermore, we successfully applied this autophagy-targeting degradation strategy to the targeted degradation of HTT65Q aggregates and mitochondria. Specifically, chimeras consisting of polyQ-binding peptide 1 (QBP) and ATG16L1-binding peptide (ABP) or LC3-interacting region (LIR) induced targeted autophagic degradation of pathogenic HTT65Q aggregates; and the chimeras consisting of mitochondria-targeting sequence (MTS) and ABP or LIR promoted targeted autophagic degradation of dysfunctional mitochondria, hence ameliorating mitochondrial dysfunction in a Parkinson disease cell model and protecting cells from apoptosis induced by the mitochondrial stress agent FCCP. Therefore, this study provides a new strategy for the selective proteolysis of large targets and enrich the toolkit for autophagy-targeting degradation.Abbreviations: ABP: ATG16L1-binding peptide; ATG16L1: autophagy related 16 like 1; ATTEC: autophagy-tethering compound; AUTAC: autophagy-targeting chimera; AUTOTAC: autophagy-targeting chimera; Baf A1: bafilomycin A1; BCL2: BCL2 apoptosis regulator; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CASP3: caspase 3; CPP: cell-penetrating peptide; CQ: chloroquine phosphate; DAPI: 4',6-diamidino-2-phenylindole; DCM: dichloromethane; DMF: N,N-dimethylformamide; DMSO: dimethyl sulfoxide; EBSS: Earle's balanced salt solution; FCCP: carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone; FITC: fluorescein-5-isothiocyanate; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFP: green fluorescent protein; HEK293: human embryonic kidney 293; HEK293T: human embryonic kidney 293T; HPLC: high-performance liquid chromatography; HRP: horseradish peroxidase; HTT: huntingtin; LIR: LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MFF: mitochondrial fission factor; MTS: mitochondria-targeting sequence; NBR1: NBR1 autophagy cargo receptor; NLRX1: NLR family member X1; OPTN: optineurin; P2A: self-cleaving 2A peptide; PB1: Phox and Bem1p; PBS: phosphate-buffered saline; PE: phosphatidylethanolamine; PINK1: PTEN induced kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; PROTACs: proteolysis-targeting chimeras; QBP: polyQ-binding peptide 1; SBP: streptavidin-binding peptide; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SPATA33: spermatogenesis associated 33; TIMM23: translocase of inner mitochondrial membrane 23; TMEM59: transmembrane protein 59; TOMM20: translocase of outer mitochondrial membrane 20; UBA: ubiquitin-associated; WT: wild type.

Inhibition of SQSTM1 S403 phosphorylation facilitates the aggresome formation of ubiquitinated proteins during proteasome dysfunction

BACKGROUND

Ubiquitin-proteasome-system-mediated clearance of misfolded proteins is essential for cells to maintain proteostasis and reduce the proteotoxicity caused by these aberrant proteins. When proteasome activity is inadequate, ubiquitinated proteins are sorted into perinuclear aggresomes, which is a significant defense mechanism employed by cells to combat insufficient proteasome activity, hence mitigating the proteotoxic crisis. It has been demonstrated that phosphorylation of SQSTM1 is crucial in regulating misfolded protein aggregation and autophagic degradation. Although SQSTM1 S403 phosphorylation is essential for the autophagic degradation of ubiquitinated proteins, its significance in proteasome inhibition-induced aggresome formation is yet unknown. Herein, we investigated the influence of SQSTM1 S403 phosphorylation on the aggresome production of ubiquitinated proteins during proteasome suppression.

METHODS

We examined the phosphorylation levels of SQSTM1 S403 or T269/S272 in cells after treated with proteasome inhibitors or/and autophagy inhibitors, by western blot and immunofluorescence. We detected the accumulation and aggresome formation of ubiquitinated misfolded proteins in cells treated with proteasome inhibition by western blot and immunofluorescence. Furthermore, we used SQSTM1 phosphorylation-associated kinase inhibitors and mutant constructs to confirm the regulation of different SQSTM1 phosphorylation in aggresome formation. We examined the cell viability using CCK-8 assay.

RESULTS

Herein, we ascertained that phosphorylation of SQSTM1 S403 did not enhance the autophagic degradation of ubiquitinated proteins during proteasome inhibition. Proteasome inhibition suppresses the phosphorylation of SQSTM1 S403, which facilitated the aggresome production of polyubiquitinated proteins. Interestingly, we found proteasome inhibition-induced SQSTM1 T269/S272 phosphorylation inhibits the S403 phosphorylation. Suppressing S403 phosphorylation rescues the defective aggresome formation and protects cells from cell death caused by unphosphorylated SQSTM1 (T269/S272).

CONCLUSIONS

This study shows that inhibition of SQSTM1 S403 phosphorylation facilitates the aggresome formation of ubiquitinated proteins during proteasome dysfunction. SQSTM1 T269/S272 phosphorylation inhibits the S403 phosphorylation, boosting the aggresome formation of ubiquitinated protein and shielding cells from proteotoxic crisis.

The transcription factor NRF1 (NFE2L1) activates aggrephagy by inducing p62 and GABARAPL1 after proteasome inhibition to maintain proteostasis

The ubiquitin‒proteasome system (UPS) and autophagy are the two primary cellular pathways of misfolded or damaged protein degradation that maintain cellular proteostasis. When the proteasome is dysfunctional, cells compensate for impaired protein clearance by activating aggrephagy, a type of selective autophagy, to eliminate ubiquitinated protein aggregates; however, the molecular mechanisms by which impaired proteasome function activates aggrephagy remain poorly understood. Here, we demonstrate that activation of aggrephagy is transcriptionally induced by the transcription factor NRF1 (NFE2L1) in response to proteasome dysfunction. Although NRF1 has been previously shown to induce the expression of proteasome genes after proteasome inhibition (i.e., the proteasome bounce-back response), our genome-wide transcriptome analyses identified autophagy-related p62/SQSTM1 and GABARAPL1 as genes directly targeted by NRF1. Intriguingly, NRF1 was also found to be indispensable for the formation of p62-positive puncta and their colocalization with ULK1 and TBK1, which play roles in p62 activation via phosphorylation. Consistently, NRF1 knockdown substantially reduced the phosphorylation rate of Ser403 in p62. Finally, NRF1 selectively upregulated the expression of GABARAPL1, an ATG8 family gene, to induce the clearance of ubiquitinated proteins. Our findings highlight the discovery of an activation mechanism underlying NRF1-mediated aggrephagy through gene regulation when proteasome activity is impaired.

Mefenamic Acid-Upregulated Nrf2/SQSTM1 Protects Hepatocytes against Oxidative Stress-Induced Cell Damage

Mefenamic acid (MFA) is a commonly prescribed non-steroidal anti-inflammatory drug (NSAID) with anti-inflammatory and analgesic properties. MFA is known to have potent antioxidant properties and a neuroprotective effect against oxidative stress. However, its impact on the liver is unclear. This study aimed to elucidate the antioxidative effects of MFA and their underlying mechanisms. We observed that MFA treatment upregulated the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway. Treatment with various anthranilic acid derivative-class NSAIDs, including MFA, increased the expression of sequestosome 1 (SQSTM1) in HepG2 cells. MFA disrupted the interaction between Kelch-like ECH-associated protein 1 (Keap1) and Nrf2, activating the Nrf2 signaling pathway. SQTM1 knockdown experiments revealed that the effect of MFA on the Nrf2 pathway was masked in the absence of SQSTM1. To assess the cytoprotective effect of MFA, we employed tert-Butyl hydroperoxide (tBHP) as a ROS inducer. Notably, MFA exhibited a protective effect against tBHP-induced cytotoxicity in HepG2 cells. This cytoprotective effect was abolished when SQSTM1 was knocked down, suggesting the involvement of SQSTM1 in mediating the protective effect of MFA against tBHP-induced toxicity. In conclusion, this study demonstrated that MFA exhibits cytoprotective effects by upregulating SQSTM1 and activating the Nrf2 pathway. These findings improve our understanding of the pharmacological actions of MFA and highlight its potential as a therapeutic agent for oxidative stress-related conditions.

An update on the bridging factors connecting autophagy and Nrf2 antioxidant pathway

Macroautophagy/autophagy is a lysosome-dependent catabolic pathway for the degradation of intracellular proteins and organelles. Autophagy dysfunction is related to many diseases, including lysosomal storage diseases, cancer, neurodegenerative diseases, cardiomyopathy, and chronic metabolic diseases, in which increased reactive oxygen species (ROS) levels are also observed. ROS can randomly oxidize proteins, lipids, and DNA, causing oxidative stress and damage. Cells have developed various antioxidant pathways to reduce excessive ROS and maintain redox homeostasis. Treatment targeting only one aspect of diseases with autophagy dysfunction and oxidative stress shows very limited effects. Herein, identifying the bridging factors that can regulate both autophagy and antioxidant pathways is beneficial for dual-target therapies. This review intends to provide insights into the current identified bridging factors that connect autophagy and Nrf2 antioxidant pathway, as well as their tight interconnection with each other. These factors could be potential dual-purpose targets for the treatment of diseases implicated in both autophagy dysfunction and oxidative stress.

Slingshot homolog-1-mediated Nrf2 sequestration tips the balance from neuroprotection to neurodegeneration in Alzheimer's disease

Oxidative damage in the brain is one of the earliest drivers of pathology in Alzheimer's disease (AD) and related dementias, both preceding and exacerbating clinical symptoms. In response to oxidative stress, nuclear factor erythroid 2-related factor 2 (Nrf2) is normally activated to protect the brain from oxidative damage. However, Nrf2-mediated defense against oxidative stress declines in AD, rendering the brain increasingly vulnerable to oxidative damage. Although this phenomenon has long been recognized, its mechanistic basis has been a mystery. Here, we demonstrate through in vitro and in vivo models, as well as human AD brain tissue, that Slingshot homolog-1 (SSH1) drives this effect by acting as a counterweight to neuroprotective Nrf2 in response to oxidative stress and disease. Specifically, oxidative stress-activated SSH1 suppresses nuclear Nrf2 signaling by sequestering Nrf2 complexes on actin filaments and augmenting Kelch-like ECH-associated protein 1 (Keap1)-Nrf2 interaction, independently of SSH1 phosphatase activity. We also show that Ssh1 elimination in AD models increases Nrf2 activation, which mitigates tau and amyloid-β accumulation and protects against oxidative injury, neuroinflammation, and neurodegeneration. Furthermore, loss of Ssh1 preserves normal synaptic function and transcriptomic patterns in tauP301S mice. Importantly, we also show that human AD brains exhibit highly elevated interactions of Nrf2 with both SSH1 and Keap1. Thus, we demonstrate here a unique mode of Nrf2 blockade that occurs through SSH1, which drives oxidative damage and ensuing pathogenesis in AD. Strategies to inhibit SSH1-mediated Nrf2 suppression while preserving normal SSH1 catalytic function may provide new neuroprotective therapies for AD and related dementias.

Gene identification and RNAi-silencing of p62/SQSTM1 in the vector Rhodnius prolixus reveals a high degree of sequence conservation but no apparent deficiency-related phenotypes in vitellogenic females

Autophagy and the ubiquitin-proteasome system (UPS) are important cellular mechanisms that coordinate protein degradation essential for proteostasis. P62/SQSTM1 is a receptor cargo protein able to deliver ubiquitinated targets to the proteasome proteolytic complex and/or to the autophagosome. In the insect vector of Chagas disease, Rhodnius prolixus, previous works have shown that the knockdown of different autophagy-related genes (ATGs) and ubiquitin-conjugating enzymes resulted in abnormal oogenesis phenotypes and embryo lethality. Here, we investigate the role of the autophagy/UPS adaptor protein p62 during the oogenesis and reproduction of this vector. We found that R. prolixus presents one isoform of p62 encoded by a non-annotated gene. The predicted protein presents the domain architecture anticipated for p62: PB1 (N-term), ZZ-finger, and UBA (C-term) domains, and phylogenetic analysis showed that this pattern is highly conserved within insects. Using parental RNAi, we found that although p62 is expressed in the ovary, midgut, and fat body of adult females, systemic silencing of this gene did not result in any apparent phenotypes under in-house conditions. The insects' overall levels of blood meal digestion, lifespan, yolk protein production, oviposition, and embryo viability were not altered when compared to controls. Because it is known that autophagy and UPS can undergo compensatory mechanisms, we asked whether the silencing of p62 was triggering adaptative changes in the expression of genes of the autophagy, UPS, and the unfolded protein response (UPR) and found that only ATG1 was slightly up regulated in the ovaries of silenced females. In addition, experiments to further investigate the role of p62 in insects previously silenced for the E1-conjugating enzyme (a condition known to trigger the upregulation of p62), also did not result in any apparent phenotypes in vitellogenic females.

Autophagy in Crohn's Disease: Converging on Dysfunctional Innate Immunity

Crohn's disease (CD) is a chronic inflammatory bowel disease marked by relapsing, transmural intestinal inflammation driven by innate and adaptive immune responses. Autophagy is a multi-step process that plays a critical role in maintaining cellular homeostasis by degrading intracellular components, such as damaged organelles and invading bacteria. Dysregulation of autophagy in CD is revealed by the identification of several susceptibility genes, including ATG16L1, IRGM, NOD2, LRRK2, ULK1, ATG4, and TCF4, that are involved in autophagy. In this review, the role of altered autophagy in the mucosal innate immune response in the context of CD is discussed, with a specific focus on dendritic cells, macrophages, Paneth cells, and goblet cells. Selective autophagy, such as xenophagy, ERphagy, and mitophagy, that play crucial roles in maintaining intestinal homeostasis in these innate immune cells, are discussed. As our understanding of autophagy in CD pathogenesis evolves, the development of autophagy-targeted therapeutics may benefit subsets of patients harboring impaired autophagy.

The role of Nrf2 in the pathogenesis and treatment of ulcerative colitis

Ulcerative colitis (UC) is a chronic inflammatory bowel disease involving mainly the colorectal mucosa and submucosa, the incidence of which has been on the rise in recent years. Nuclear factor erythroid 2-related factor 2 (Nrf2), known for its key function as a transcription factor, is pivotal in inducing antioxidant stress and regulating inflammatory responses. Numerous investigations have demonstrated the involvement of the Nrf2 pathway in maintaining the development and normal function of the intestine, the development of UC, and UC-related intestinal fibrosis and carcinogenesis; meanwhile, therapeutic agents targeting the Nrf2 pathway have been widely investigated. This paper reviews the research progress of the Nrf2 signaling pathway in UC.

The global landscape and research trend of phase separation in cancer: a bibliometric analysis and visualization

Background

Cancer as a deathly disease with high prevalence has impelled researchers to investigate its causative mechanisms in the search for effective therapeutics. Recently, the concept of phase separation has been introduced to biological science and extended to cancer research, which helps reveal various pathogenic processes that have not been identified before. As a process of soluble biomolecules condensed into solid-like and membraneless structures, phase separation is associated with multiple oncogenic processes. However, there are no bibliometric characteristics for these results. To provide future trends and identify new frontiers in this field, a bibliometric analysis was conducted in this study.

Methods

The Web of Science Core Collection (WoSCC) was used to search for literature on phase separation in cancer from 1/1/2009 to 31/12/2022. After screening the literature, statistical analysis and visualization were carried out by the VOSviewer software (version 1.6.18) and Citespace software (Version 6.1.R6).

Results

A total of 264 publications, covering 413 organizations and 32 countries, were published in 137 journals, with an increasing trend in publication and citation numbers per year. The USA and China were the two countries with the largest number of publications, and the University of Chinese Academy of Sciences was the most active institution based on the number of articles and cooperations. Molecular Cell was the most frequent publisher with high citations and H-index. The most productive authors were Fox AH, De Oliveira GAP, and Tompa P. Overlay, whilst few authors had a strong collaboration with each other. The combined analysis of concurrent and burst keywords revealed that the future research hotspots of phase separation in cancer were related to tumor microenvironments, immunotherapy, prognosis, p53, and cell death.

Conclusion

Phase separation-related cancer research remained in the hot streak period and exhibited a promising outlook. Although inter-agency collaboration existed, cooperation among research groups was rare, and no author dominated this field at the current stage. Investigating the interfaced effects between phase separation and tumor microenvironments on carcinoma behaviors, and constructing relevant prognoses and therapeutics such as immune infiltration-based prognosis and immunotherapy might be the next research trend in the study of phase separation and cancer.

Impairment of autophagy promotes human conjunctival fibrosis and pterygium occurrence via enhancing the SQSTM1-NF-κB signaling pathway

Pterygium is a common ocular disease with a high recurrence rate, characterized by hyperplasia of subconjunctival fibrovascular tissue. Autophagy, an important process to maintain cellular homeostasis, participates in the pathogenic fibrosis of different organs. However, the exact role of autophagy in pterygium pathogenesis remains unknown. Here, we found that autophagic activity was decreased in human pterygium tissues compared with adjacent normal conjunctival tissues. The in vitro model of fibrosis was successfully established using human primary conjunctival fibroblasts (ConFB) treated with transforming growth factor-β1 (TGF-β1), evidenced by increased fibrotic level and strong proliferative and invasive capabilities. The autophagic activity was suppressed during TGF-β1- or ultraviolet-induced fibrosis of ConFB. Activating autophagy dramatically retarded the fibrotic progress of ConFB, while blocking autophagy exacerbated this process. Furthermore, SQSTM1, the main cargo receptor of selective autophagy, was found to significantly promote the fibrosis of ConFB through activating the PKCι-NF-κB signaling pathway. Knockdown of SQSTM1, PKCι, or p65 in ConFB delayed TGF-β1-induced fibrosis. Overexpression of SQSTM1 drastically abrogated the inhibitory effect of rapamycin or serum starvation on TGF-β1-induced fibrosis. Collectively, our data suggested that autophagy impairment of human ConFB facilitates fibrosis via activating the SQSTM1-PKCι-NF-κB signaling cascades. This work was contributory to elucidating the mechanism of autophagy underlying pterygium occurrence.

Aggrephagy at a glance

Cells keep their proteome functional by the action of the proteostasis network, composed of the chaperones, the ubiquitin-proteasome system and autophagy. The decline of this network results in the accumulation of protein aggregates and is associated with aging and disease. In this Cell Science at a Glance and accompanying poster, we provide an overview of the molecular mechanisms of the removal of protein aggregates by a selective autophagy pathway, termed aggrephagy. We outline how aggrephagy is regulated by post-translational modifications and via auxiliary proteins. We further describe alternative aggrephagy pathways in physiology and their disruption in pathology. In particular, we discuss aggrephagy pathways in neurons and accumulation of protein aggregates in a wide range of diseases. Finally, we highlight strategies to reprogram aggrephagy to treat protein aggregation diseases.

Slingshot homolog-1 amplifies mitochondrial abnormalities by distinctly impairing health and clearance of mitochondria

Accumulating toxic protein assemblies, including Aβ and tau, and dysfunctional mitochondria are associated with synaptic and neuronal loss in Alzheimer's disease (AD). Such accumulations are thought to be owing to clearance defects in the autophagy-lysosome pathway. Mitochondrial dysfunction is evident in AD brains and animal models at multiple levels, such as mitochondrial genomic mutations, disrupted bioenergetics, deregulated mitochondrial dynamics and impaired clearance of damaged mitochondria (mitophagy). Slingshot homolog-1 (SSH1) is a phosphatase activated by oxidative stress, high intracellular levels of Ca2+ and Aβ42 oligomers (Aβ42O), known for its function to dephosphorylate/activate cofilin through the N-terminal region. SSH1-mediated cofilin dephosphorylation results in Ab42O-induced severing of F-actin and translocation of cofilin to mitochondria, which promotes mitochondria-mediated apoptosis, synaptic loss and synaptic deficits. On the other hand, SSH1-mediated dephosphorylation/deactivation of the autophagy-cargo receptor p62 (SQSTM1), through its C-terminal region, inhibits p62 autophagy flux. However, the interplay between these two different activities of SSH1 in Aβ42O-induced mitochondrial toxicity remains unclear. In this study, we assessed the role of endogenous SSH1 and different regions of SSH1 in regulating mitochondrial health, mitochondrial respiration, clearance of damaged mitochondria and synaptic integrity in vitro and in vivo. Our results indicate that SSH1 suppresses mitochondrial health and respiration through the cofilin-binding N-terminal region, whereas SSH1 impairs mitophagy through a newly identified ~ 100 residue p62-binding domain in the C-terminal region. These results indicate that both N-terminal and C-terminal regions negatively impact mitochondria by distinct and independent modalities to amplify mitochondrial abnormalities, making SSH1 an excellent target to mitigate AD pathogenesis.

Immortalized Alzheimer's Disease Astrocytes: Characterization of Their Proteolytic Systems

Alzheimer's disease (AD) is a progressive neurodegeneration with dysfunctions in both the ubiquitin-proteasome system (UPS) and autophagy. Astroglia participation in AD is an attractive topic of research, but molecular patterns are partially defined and available in vitro models have technical limitations. Immortalized astrocytes from the hippocampus of 3xTg-AD and wild-type mice (3Tg-iAstro and WT-iAstro, respectively) have been obtained as an attempt to overcome primary cell line limitations and this study aims at characterizing their proteolytic systems, focusing on UPS and autophagy. Both 26S and 20S proteasomal activities were downregulated in 3Tg-iAstro, in which a shift in catalytic subunits from constitutive 20S proteasome to immunoproteasome occurred, with consequences on immune functions. In fact, immunoproteasome is the specific complex in charge of clearing damaged proteins under inflammatory conditions. Parallelly, augmented expression and activity of the lysosomal cathepsin B, enhanced levels of lysosomal-associated membrane protein 1, beclin1, and LC3-II, together with an increased uptake of monodansylcadaverine in autophagic vacuoles, suggested autophagy activation in 3Tg-iAstro. The two proteolytic pathways were linked by p62 that accumulated in 3Tg-iAstro due to both increased synthesis and decreased degradation in the UPS defective astrocytes. Treatment with 4-phenylbutyric acid, a neuroprotective small chemical chaperone, partially restored proteasome and autophagy-mediated proteolysis in 3Tg-iAstro. Our data shed light on the impaired proteostasis in 3Tg-iAstro with proteasome inhibition and autophagic compensatory activation, providing additional validation of this AD in vitro model, and propose a new mechanism of action of 4-phenylbutyric acid in neurodegenerative disorders.

Autophagic Degradation Is Involved in Cell Protection against Ricin Toxin

Autophagy is a complex and highly regulated degradative process, which acts as a survival pathway in response to cellular stress, starvation and pathogen infection. Ricin toxin is a plant toxin produced by the castor bean and classified as a category B biothreat agent. Ricin toxin inhibits cellular protein synthesis by catalytically inactivating ribosomes, leading to cell death. Currently, there is no licensed treatment for patients exposed to ricin. Ricin-induced apoptosis has been extensively studied; however, whether its intoxication via protein synthesis inhibition affects autophagy is not yet resolved. In this work, we demonstrated that ricin intoxication is accompanied by its own autophagic degradation in mammalian cells. Autophagy deficiency, by knocking down ATG5, attenuates ricin degradation, thus aggravating ricin-induced cytotoxicity. Additionally, the autophagy inducer SMER28 (Small Molecule Enhancer 28) partially protects cells against ricin cytotoxicity, an effect not observed in autophagy-deficient cells. These results demonstrate that autophagic degradation acts as a survival response of cells against ricin intoxication. This suggests that stimulation of autophagic degradation may be a strategy to counteract ricin intoxication.

A mutation in the ZNF687 gene that is responsible for the severe form of Paget's disease of bone causes severely altered bone remodeling and promotes hepatocellular carcinoma onset in a knock-in mouse model

Paget's disease (PDB) is a late-onset bone remodeling disorder with a broad spectrum of symptoms and complications. One of the most aggressive forms is caused by the P937R mutation in the ZNF687 gene. Although the genetic involvement of ZNF687 in PDB has been extensively studied, the molecular mechanisms underlying this association remain unclear. Here, we describe the first Zfp687 knock-in mouse model and demonstrate that the mutation recapitulates the PDB phenotype, resulting in severely altered bone remodeling. Through microcomputed tomography analysis, we observed that 8-month-old mutant mice showed a mainly osteolytic phase, with a significant decrease in the trabecular bone volume affecting the femurs and the vertebrae. Conversely, osteoblast activity was deregulated, producing disorganized bone. Notably, this phenotype became pervasive in 16-month-old mice, where osteoblast function overtook bone resorption, as highlighted by the presence of woven bone in histological analyses, consistent with the PDB phenotype. Furthermore, we detected osteophytes and intervertebral disc degeneration, outlining for the first time the link between osteoarthritis and PDB in a PDB mouse model. RNA sequencing of wild-type and Zfp687 knockout RAW264.7 cells identified a set of genes involved in osteoclastogenesis potentially regulated by Zfp687, e.g., Tspan7, Cpe, Vegfc, and Ggt1, confirming its role in this process. Strikingly, in this mouse model, the mutation was also associated with a high penetrance of hepatocellular carcinomas. Thus, this study established an essential role of Zfp687 in the regulation of bone remodeling, offering the potential to therapeutically treat PDB, and underlines the oncogenic potential of ZNF687.

Frameshift mutation in SQSTM1 causes proximal myopathy with rimmed vacuoles: A case report

p62/Sequestosome-1 (SQSTM1) is a stress-inducible scaffold protein involved in multiple cellular processes, including apoptosis, inflammation, cell survival, and selective autophagy. SQSTM1 mutations are associated with a spectrum of multisystem proteinopathy, including Paget disease of the bone, amyotrophic lateral sclerosis, frontotemporal dementia, and distal myopathy with rimmed vacuoles (MRV). Herein, we report a new phenotype of SQSTM1-associated proteinopathy, a novel frameshift mutation in SQSTM1 causing proximal MRV. A 44-year-old Chinese patient presented with progressive limb–girdle weakness. She had asymmetric proximal limb weakness and myopathic features on electromyography. The magnetic resonance images showed fatty infiltration into muscles, predominantly in the thighs and medial gastrocnemius, sparing the tibialis anterior. Muscle histopathology revealed abnormal protein deposition, p62/SQSTM1-positive inclusions, and rimmed vacuoles. Next-generation sequencing showed a novel pathogenic SQSTM1 frameshift mutation, c.542_549delACAGCCGC (p. H181Lfs*66). We expanded the pathogenic genotype of SQSTM1 to include a new, related phenotype: proximal MRV. We suggest that SQSTM1 variations should be screened in cases of proximal MRV.

A Novel Phenazine Analog, CPUL1, Suppresses Autophagic Flux and Proliferation in Hepatocellular Carcinoma: Insight from Integrated Transcriptomic and Metabolomic Analysis

BACKGROUND

CPUL1, a phenazine analog, has demonstrated potent antitumor properties against hepatocellular carcinoma (HCC) and indicates a promising prospect in pharmaceutical development. However, the underlying mechanisms remain largely obscure.

METHODS

Multiple HCC cell lines were used to investigate the in vitro effects of CPUL1. The antineoplastic properties of CPUL1 were assessed in vivo by establishing a xenograft nude mice model. After that, metabolomics, transcriptomics, and bioinformatics were integrated to elucidate the mechanisms underlying the therapeutic efficacy of CPUL1, highlighting an unanticipated involvement of autophagy dysregulation.

RESULTS

CPUL1 suppressed HCC cell proliferation in vitro and in vivo, thereby endorsing the potential as a leading agent for HCC therapy. Integrative omics characterized a deteriorating scenario of metabolic debilitation with CPUL1, presenting an issue in the autophagy contribution of autophagy. Subsequent observations indicated that CPUL1 treatment could impede autophagic flow by suppressing autophagosome degradation rather than its formation, which supposedly exacerbated cellular damage triggered by metabolic impairment. Moreover, the observed late autophagosome degradation may be attributed to lysosome dysfunction, which is essential for the final stage of autophagy and cargo disposal.

CONCLUSIONS

Our study comprehensively profiled the anti-hepatoma characteristics and molecular mechanisms of CPUL1, highlighting the implications of progressive metabolic failure. This could partially be ascribed to autophagy blockage, which supposedly conveyed nutritional deprivation and intensified cellular vulnerability to stress.

Measles virus-imposed remodeling of the autophagy machinery determines the outcome of bacterial coinfection

Although it is admitted that secondary infection can complicate viral diseases, the consequences of viral infection on cell susceptibility to other infections remain underexplored at the cellular level. We though to examine whether the sustained macroautophagy/autophagy associated with measles virus (MeV) infection could help cells oppose invasion by Salmonella Typhimurium, a bacterium sensitive to autophagic restriction. We report here the unexpected finding that Salmonella markedly replicated in MeV-infected cultures due to selective growth within multinucleated cells. Hyper-replicating Salmonella localized outside of LAMP1-positive compartments to an extent that equaled that of the predominantly cytosolic sifA mutant Salmonella. Bacteria were subjected to effective ubiquitination but failed to be targeted by LC3 despite an ongoing productive autophagy. Such a phenotype could not be further aggravated upon silencing of the selective autophagy regulator TBK1 or core autophagy factors ATG5 or ATG7. MeV infection also conditioned primary human epithelial cells for augmented Salmonella replication. The analysis of selective autophagy receptors able to target Salmonella revealed that a lowered expression level of SQSTM1/p62 and TAX1BP1/T6BP autophagy receptors prevented effective anti-Salmonella autophagy in MeV-induced syncytia. Conversely, as SQSTM1/p62 is promoting the cytosolic growth of Shigella flexneri, MeV infection led to reduced Shigella replication. The results indicate that the rarefaction of dedicated autophagy receptors associated with MeV infection differentially affects the outcome of bacterial coinfection depending on the nature of the functional relationship between bacteria and such receptors. Thus, virus-imposed reconfiguration of the autophagy machinery can be instrumental in determining the fate of bacterial coinfection.Abbreviations: ACTB/β-ACTIN: actin beta; ATG: autophagy related; BAFA1: bafilomycin A1; CFU: colony-forming units; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; FIP: fusion inhibitory peptide; GFP: green fluorescent protein; LAMP1: lysosomal associated membrane protein 1; LIR: MAP1LC3/LC3-interacting region; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MeV: measles virus; MOI: multiplicity of infection; OPTN: optineurin; PHH: primary human hepatocyte; SCV: Salmonella-containing vacuoles; SQSTM1/p62: sequestosome 1; S. flexneri: Shigella flexneri; S. Typhimurium: Salmonella enterica serovar Typhimurium; TAX1BP1/T6BP: Tax1 binding protein 1; TBK1: TANK binding kinase 1.

Suppression of small nucleolar RNA host gene 8 (SNHG8) inhibits the progression of colorectal cancer cells

Colorectal cancer (CRC) is one of the most common gastrointestinal malignancies around the world with high mortality. Accumulating evidences demonstrate that long non-coding RNAs (lncRNAs) play critical roles in CRC tumorigenesis by regulating different pathways of carcinogenesis. SNHG8 (small nucleolar RNA host gene 8), a lncRNA, is highly expressed in several cancers and acts as an oncogene that promotes cancer progression. However, the oncogenic role of SNHG8 in CRC carcinogenesis and the underlying molecular mechanisms remain unknown. In this study, we explored the role of SNHG8 in CRC cell lines by performing a series of functional experiments. Similar to the data reported in the Encyclopedia of RNA Interactome, our RT-qPCR results showed that SNHG8 expression was significantly upregulated in CRC cell lines (DLD-1, HT-29, HCT-116, and SW480) compared to the normal colon cell line (CCD-112CoN). We performed dicer-substrate siRNA transfection to knockdown the expression of SNHG8 in HCT-116 and SW480 cell lines which were expressing high levels of SNHG8. SNHG8 knockdown significantly reduced CRC cell growth and proliferation by inducing autophagy and apoptosis pathways through the AKT/AMPK/mTOR axis. We performed wound healing migration assay and demonstrated that SNHG8 knockdown significantly increased migration index in both cell lines, indicating reduced migration abilities of cells. Further investigation showed that SNHG8 knockdown suppresses epithelial to mesenchymal transition and reduces cellular migratory properties of CRC cells. Taken together, our study suggests that SNHG8 acts as an oncogene in CRC through the mTOR-dependent autophagy, apoptosis, and EMT pathways. Our study provides a better understanding the role of SNHG8 in CRC at molecular level and SNHG8 might be used as novel therapeutic target for CRC management.