Deubiquitinating enzymes (DUBs): Regulation, homeostasis, and oxidative stress response

USP22 promotes angiotensin II-induced podocyte injury by deubiquitinating and stabilizing HMGB1

BACKGROUND

Chronic kidney disease (CKD) remains a significant global health burden, with hypertensive nephropathy (HN) as one of its primary causes. Podocyte injury is a key factor in the progression of CKD. However, the molecular mechanisms underlying angiotensin II-induced podocyte injury remain incompletely understood. Ubiquitin-specific protease 22 (USP22) has been reported to facilitate a range of cellular processes, including cell proliferation and apoptosis. However, the role of USP22 in HN pathogenesis is unclear.

METHODS

The expression of USP22 was assessed in kidney samples from hypertensive nephropathy patients, angiotensin II-induced hypertensive nephropathy mouse models, and cultured podocytes treated with angiotensin II. Podocyte-specific USP22 knockout mice were used to investigate the effects of USP22 deletion on podocyte injury and inflammation.

RESULTS

USP22 expression was significantly upregulated in kidneys of HN patients, angiotensin II-induced mouse models, and cultured podocytes. Podocyte-specific deletion of USP22 markedly reduced angiotensin II-induced podocyte injury and inflammatory responses. Furthermore, we identified high-mobility group box protein 1 (HMGB1) as a protein that interacts with USP22. USP22 deubiquitinated and stabilized HMGB1 through K48-linked ubiquitination. Downregulation of USP22 expression improved kidney function and pathological changes in HN by promoting HMGB1 degradation.

CONCLUSION

This study identifies USP22 as a key regulator of angiotensin II-induced podocyte injury and inflammation through its interaction with HMGB1. Our findings revealed that following glomerular injury, damage and shedding of tubular cells also occurred. Targeting the USP22-HMGB1 axis offers a promising therapeutic strategy for treating hypertensive nephropathy and other types of CKD.

Mechanisms and therapeutic strategies for NLRP3 degradation via post-translational modifications in ubiquitin-proteasome and autophagy lysosomal pathway

The NLRP3 inflammasome is crucial for immune responses. However, its overactivation can lead to severe inflammatory diseases, underscoring its importance as a target for therapeutic intervention. Although numerous inhibitors targeting NLRP3 exist, regulating its degradation offers an alternative and promising strategy to suppress its activation. The degradation of NLRP3 is primarily mediated by the proteasomal and autophagic pathways. The review not only elaborates on the traditional concepts of ubiquitination and NLRP3 degradation but also investigates the important roles of indirect regulatory modifications, such as phosphorylation, acetylation, ubiquitin-like modifications, and palmitoylation-key post-translational modifications (PTMs) that influence NLRP3 degradation. Additionally, we also discuss the potential targets that may affect NLRP3 degradation during the proteasomal and autophagic pathways. By unraveling these complex regulatory mechanisms, the review aims to enhance the understanding of NLRP3 regulation and its implications for developing therapeutic strategies to combat inflammatory diseases.

The Transfer of USP25 by Exosomes of Adipose Tissue-Derived Mesenchymal Stem Cells Ameliorates Diabetic Nephropathy Through Stabilizing SMAD7 Expression

Adipose tissue-derived mesenchymal stem cells (ADSCs) are identified to be potential therapeutic candidates for diabetic nephropathy (DN) through secreting exosomes (Exos). Ubiquitin-specific protease 25 (USP25) has been reported to be involved in DN-induced renal injury. Herein, this study aimed to investigate whether ADSCs affected DN progression by Exo transfer of USP25. High glucose (HG)-induced mouse podocytes were used to mimic DN-induced injury for in vitro viability, inflammation, and apoptosis analyses. The db/db mice of DN were established for renal injury and function analysis in vivo. The deubiquitination effect of USP25 was analyzed by cellular ubiquitination and immunoprecipitation assays. ADSCs reversed HG-induced apoptosis and inflammation in podocytes, and these effects were achieved by Exo-mediated transfer of USP25. Mechanistically, USP25 interacted with SMAD7 protein and elevated its expression in podocytes via inducing SMAD7 deubiquitination. USP25 transferred via ADSC-Exos abolished HG-induced apoptosis and inflammation in podocytes by elevating SMAD7 protein levels. In vivo assay also confirmed that ADSC-Exo attenuated Type 2 Diabetes Mellitus-induced kidney injury and podocyte apoptosis and inflammation by releasing USP25. ADSCs attenuated T2DM-induced kidney injury, podocyte apoptosis, and inflammation via elevating SMAD7 stabilization through exosome transfer of USP25.

Discovery of TNG-6132, a potent, selective, and orally bioavailable USP1 inhibitor

USP1 (ubiquitin-specific peptidase 1) is a deubiquitinating enzyme that has been identified as essential in BRCA1/2 mutant cells and implicated in the DNA damage response. Inhibition of USP1 by small molecule inhibitors disrupts DNA repair and replication and is being pursued as a potential anticancer therapeutic in BRCA1/2 mutant cancers. We report the discovery of an in vitro and in vivo USP1 inhibitor tool compound TNG-6132 (18), a reversible, allosteric inhibitor of USP1, which strongly inhibits USP1 enzymatic activity. This inhibitory effect translates into in vitro cellular viability defects in a BRCA1-mutant breast cancer cell line, as well as an in vivo pharmacodynamic (PD) response and tumor growth suppression in a mouse xenograft efficacy model. Additionally, we report an X-ray co-crystal structure of TNG-6132 (18) bound in the USP1-UAF1 complex, a result that furthered our understanding of the role played by key elements of the pharmacophore of this chemotype as well as its mechanism of inhibition of USP1.

USP14 promotes osteoarthritis progression by deubiquitinating FZD8 to activate the Wnt/β-catenin signaling pathway

BACKGROUND

Osteoarthritis (OA) is a chronic degenerative disease and associated with multiple pathogenic factors, such as old age, heredity, obesity, mechanical damage and inflammatory gene mutation. In this study, we aimed to explore the functions of ubiquitin specific peptidase 14 (USP14) in OA development.

METHODS

The in vitro model of OA was constructed by stimulating chondrocytes with IL-1β. qRT-PCR and western blot assays were used for gene expression. MTT assay and EdU assay were manipulated to evaluate cell proliferation. Flow cytometry analysis was conducted for cell apoptosis. ELISA kits were utilized to determine the concentrations of inflammatory cytokines. Co-immunoprecipitation (Co-IP) assay and GST pull-down assay were manipulated to estimate the interaction between USP14 and Frizzled 8 (FZD8). Ubiquitination assay was used to evaluate the deubiquitination of FZD8.

RESULTS

USP14 was highly expression in OA cartilage tissues and IL-1β-triggered chondrocytes. USP14 silencing aggravated the proliferation and repressed the apoptosis, inflammation and extracellular matrix (ECM) degradation of IL-1β-treated chondrocytes. USP14 could interact with FZD8 and regulate FZD8 expression through FZD8 deubiquitination. Moreover, FZD8 overexpression alleviated the effects of UPS14 silencing on IL-1β-treated chondrocyte proliferation, apoptosis, inflammation and ECM degradation. Additionally, USP14 knockdown inhibited Wnt/β-catenin signal pathway via the deubiquitination of FZD8.

CONCLUSION

USP14 repressed IL-1β-treated chondrocyte proliferation and promoted apoptosis, inflammation and ECM degradation by regulating FZD8 expression and Wnt/β-catenin signal pathway.

Targeting epigenetic and post-translational modifications of NRF2: key regulatory factors in disease treatment

Nuclear factor erythroid 2-related factor 2 (NRF2) is a key transcription factor involved in regulating cellular antioxidant defense and detoxification mechanisms. It mitigates oxidative stress and xenobiotic-induced damage by inducing the expression of cytoprotective enzymes, including HO-1 and NQO1. NRF2 also modulates inflammatory responses by inhibiting pro-inflammatory genes and mediates cell death pathways, including apoptosis and ferroptosis. Targeting NRF2 offers potential therapeutic avenues for treating various diseases. NRF2 is regulated through two principal mechanisms: post-translational modifications (PTMs) and epigenetic alterations. PTMs, including phosphorylation, ubiquitination, and acetylation, play a pivotal role in modulating NRF2's stability, activity, and subcellular localization, thereby precisely controlling its function in the antioxidant response. For instance, ubiquitination can lead to NRF2 degradation and reduced antioxidant activity, while deubiquitination enhances its stability and function. Epigenetic modifications, such as DNA methylation, histone modifications, and interactions with non-coding RNAs (e.g., MALAT1, PVT1, MIR4435-2HG, and TUG1), are essential for regulating NRF2 expression by modulating chromatin architecture and gene accessibility. This paper systematically summarizes the molecular mechanisms by which PTMs and epigenetic alterations regulate NRF2, and elucidates its critical role in cellular defense and disease. By analyzing the impact of PTMs, such as phosphorylation, ubiquitination, and acetylation, as well as DNA methylation, histone modifications, and non-coding RNA interactions on NRF2 stability, activity, and expression, the study reveals the complex cellular protection network mediated by NRF2. Furthermore, the paper explores how these regulatory mechanisms affect NRF2's roles in oxidative stress, inflammation, and cell death, identifying novel therapeutic targets and strategies. This provides new insights into the treatment of NRF2-related diseases, such as cancer, neurodegenerative disorders, and metabolic syndrome. This research deepens our understanding of NRF2's role in cellular homeostasis and lays the foundation for the development of NRF2-targeted therapies.

USP7 promotes PINK1/Parkin-dependent mitophagy to ameliorate cerebral ischemia-reperfusion injury by deubiquitinating and stabilizing SIRT1

BACKGROUND

Cerebral ischemia-reperfusion (CI/R) injury, a major complication of ischemic stroke, is characterized by mitochondrial dysfunction and neuronal apoptosis, and understanding its underlying molecular mechanisms is essential for the development of effective therapeutic strategies. This study aimed to investigate the role of ubiquitin-specific protease 7 (USP7) in CI/R injury and elucidate its regulatory mechanisms.

METHODS

A rat model of middle cerebral artery occlusion/reperfusion (MCAO/R) and an in vitro neuronal model subjected to oxygen-glucose deprivation/reperfusion (OGD/R) were used to mimic CI/R injury. USP7 was overexpressed or knocked down, with or without co-treatment, using the autophagy inhibitor 3-methyladenine (3-MA). Neurological function was evaluated using standardized scoring systems, and cerebral infarct volume was quantified by TTC staining. Histopathological changes in the cortex and hippocampus were assessed using hematoxylin-eosin (HE) and Nissl staining. Neuronal viability and apoptosis were measured by CCK-8 assay, TUNEL staining, and flow cytometry. To assess cellular metabolism and oxidative stress, ATP and LDH levels, along with antioxidant markers (including SOD, GSH, and GSH-Px), were analyzed using commercial biochemical kits. Mitochondrial morphology and autophagosome formation were visualized using transmission electron microscopy. Gene and protein expression levels were quantified by qRT-PCR and Western blotting, respectively. Immunofluorescence microscopy was performed to evaluate the subcellular localization of target proteins and co-localization with mitochondrial membrane markers. Lastly, protein-protein interactions and ubiquitination modification were analyzed by co-immunoprecipitation assays.

RESULTS

USP7 overexpression significantly alleviated neurological deficits, reduced infarct volume, attenuated histological damage, and decreased neuronal apoptosis in the MCAO/R model. Similarly, in the OGD/R model, USP7 overexpression markedly enhanced neuronal viability, suppressed apoptosis, restored ATP production, improved antioxidant capacity (as evidenced by increased levels of SOD, GSH, and GSH-Px), and reduced LDH release. Mechanistically, USP7 stabilized SIRT1 protein expression through deubiquitination, which in turn activated the PINK1/Parkin pathway and enhanced mitophagy. This activation was demonstrated by an increased LC3II/LC3I ratio, elevated ATG5 expression, enhanced co-localization of Tomm20 and Parkin, and increased autophagosome formation. Moreover, these protective effects were abolished when either 3-MA treatment was applied or SIRT1/PINK1 expression was knocked down.

CONCLUSION

USP7 mitigates CI/R injury by promoting PINK1/Parkin-dependent mitophagy through SIRT1 deubiquitination and stabilization, suggesting USP7 as a potential therapeutic target for ischemic stroke.

Deubiquitinating enzyme USP2 regulates brown adipose tissue thermogenesis via controlling EBF2 stabilization

OBJECTIVE

The activation of brown adipose tissue (BAT) promotes energy expenditure is recognized as a promising therapeutic strategy for combating obesity. The deubiquitinating enzyme family members are widely involved in the process of energy metabolism. However, the specific deubiquitinating enzyme member that affects the BAT thermogenesis remains largely unexplored.

METHODS

Adeno-associated virus, lentivirus and small molecule inhibitor were applied to generate USP2 gain- or loss-of-function both in vivo and in vitro. OxyMax comprehensive laboratory animal monitoring system, seahorse and transmission electron microscopy were used to determine the energy metabolism. Quantitative proteomics, immunofluorescence staining and co-immunoprecipitation were performed to reveal the potential substrates of USP2.

RESULTS

USP2 is upregulated upon thermogenic activation in adipose, and has a close correlation with UCP1 mRNA levels in human adipose tissue. BAT-specific Usp2 knockdown or systemic USP2 inhibition resulted in impaired thermogenic programs both in vivo and in vitro. Conversely, overexpression of Usp2 in BAT conferred protection against high-fat diet-induced obesity and associated metabolic disorders. Proteome-wide analysis identified EBF2 as the substrate of USP2 that mediates the thermogenic function of USP2 in BAT.

CONCLUSIONS

Our data demonstrated the vital role of USP2 in regulating BAT activation and systemic energy homeostasis. Activation of USP2-EBF2 interaction could be a potential therapeutic strategy against obesity.

N6-methyladenosine-mediated EIF3H promotes anaplastic thyroid cancer progression and ferroptosis resistance by stabilizing β-catenin

Anaplastic thyroid cancer (ATC) patients suffer from a poor prognosis with very limited treatment options. The accumulation of β-catenin and the activation of downstream signaling is one of the main events in ATC, while the role of JAMM family in ATC remains unknown. In this study, we aimed to identify a new deubiquitinating enzyme regulating β-catenin in ATC. We found that EIF3H was positively correlated with β-catenin, and the knockdown of EIF3H deactivated the Wnt/β-catenin signaling pathway in ATC. Further exploration revealed that EIF3H interacted with, deubiquitylated, and stabilized β-catenin by acting as a deubiquitinating enzyme. Mechanistically, EIF3H removed the K48-linked ubiquitin chain on β-catenin by binding the N tails of β-catenin. The knockdown of EIF3H could inhibit ATC cell proliferation, invasion, and ferroptosis resistance by regulating β-catenin. In addition, the dysregulation of EIF3H was associated with m6A modification in the 3'UTR and a m6A reader, IGF2BP2. In summary, the EIF3H/β-catenin axis promotes ATC progression and ferroptosis resistance by activating the Wnt/β-catenin signaling pathway. The EIF3H/β-catenin axis may serve as a potential diagnostic marker and a therapeutic target in ATC.

UVB radiation and amphibian resilience: Analyzing skin color, immune suppression and oxidative stress in Rana kukunoris from different elevations

Ultraviolet-B radiation (UVBR), intensified by ozone depletion and climate change, poses a growing ecological threat to amphibians, particularly in high-elevation regions such as the Qinghai-Tibet Plateau. Endemic to this region, Rana kukunoris spans a wide range of elevations, where distinct populations may have evolved unique strategies and regulatory mechanisms to cope with UVBR. However, specific adaptive responses in adult frogs remain underexplored. This study compared the physiological responses of high- and low-altitude Rana kukunoris populations to UVBR exposure, focusing on dorsal color, immune function, antioxidant capacity, and DNA repair gene expression. High-altitude populations exhibited stable, dark pigmentation-potentially reducing the need for rapid melanin synthesis-alongside a robust immune profile and enhanced antioxidant enzyme activity, collectively conferring resilience against oxidative and immune stress under chronic UVBR exposure. Conversely, low-altitude populations exhibited pronounced UVBR-induced responses, including significant skin darkening, heightened immune activation evidenced by increased white blood cell counts, and increased oxidative damage marked by higher malondialdehyde (MDA) levels, coupled with reduced superoxide dismutase (SOD) and catalase (CAT) activities. Furthermore, tissue-specific upregulation of DNA repair genes in high-altitude populations suggested a stable DNA repair capacity adapted to high-UVBR environments. These findings reveal distinct physiological strategies within the same species for coping with UVBR across altitudinal gradients. Amid global increases in UVBR, this study offers novel insights into amphibian resilience in high-UVBR habitats and informs conservation strategies for populations across varying elevations.

USP30 Aggravating the Malignant Progression of Breast Cancer and Its Resistance to Tamoxifen by Inhibiting the Ubiquitination of TOMM40

Breast cancer (BC) is the most common malignancy among women, with high incidence and mortality rates globally. Translocase of outer mitochondrial membrane 40 (TOMM40) has also been identified as an important prognostic biomarker for BC. Meanwhile, the ubiquitin-specific protease 30 (USP30) has also been shown to promote BC progression. However, the specific mechanisms underlying the role of USP30/TOMM40 in BC development remain unclear. Therefore, this study aims to delve into the potential mechanisms of USP30/TOMM40 in the progression of BC. The expression of TOMM40 and USP30 in BC tumors and cells was verified by bioinformatics analysis and western blot (WB). The effects of USP30/TOMM40 on BC cell proliferation, angiogenesis, glycolysis, and ferroptosis were determined by colony formation, tube formation assays and commercial kits. The co-immunoprecipitation (Co-IP) experiment was applied to verify the interaction between USP30 and TOMM40. The ubiquitination level of TOMM40 was detected by ubiquitinated antibodies. The effect of tamoxifen (TAM) on BC cell viability was measured by MTT assay. TOMM40 and USP30 were highly expressed in BC tumors and cells. Silencing TOMM40 blocked the proliferation, angiogenesis, glycolytic, and induced ferroptosis of BC cells. USP30 bound to TOMM40 and reduced its ubiquitination level. TOMM40 overexpressed abolished the tumor suppressive effect of USP30 knockdown and enhanced the resistance of BC to TAM. In conclusion, USP30 deubiquitinating TOMM40 promoted BC development and TAM resistance.

OTUD1 Deficiency Alleviates LPS-Induced Acute Lung Injury in Mice by Reducing Inflammatory Response

The ovarian tumor (OTU) family consists of deubiquitinating enzymes thought to play a crucial role in immunity. Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) pose substantial clinical challenges due to severe respiratory complications and high mortality resulting from uncontrolled inflammation. Despite this, no study has explored the potential link between the OTU family and ALI/ARDS. Using publicly available high-throughput data, 14 OTUs were screened in a simulating bacteria- or LPS-induced ALI model. Subsequently, gene knockout mice and transcriptome sequencing were employed to explore the roles and mechanisms of the selected OTUs in ALI. Our screen identified OTUD1 in the OTU family as a deubiquitinase highly related to ALI. In the LPS-induced ALI model, deficiency of OTUD1 significantly ameliorated pulmonary edema, reduced permeability damage, and decreased lung immunocyte infiltration. Furthermore, RNA-seq analysis revealed that OTUD1 deficiency inhibited key pathways, including the IFN-γ/STAT1 and TNF-α/NF-κB axes, ultimately mitigating the severity of immune responses in ALI. In summary, our study highlights OTUD1 as a critical immunomodulatory factor in acute inflammation. These findings suggest that targeting OTUD1 could hold promise for the development of novel treatments against ALI/ARDS.

Dynamic networks connect the USP14 active site region with the proteasome interaction surface

Ubiquitin-specific protease 14 (USP14) is a member of the USP family responsible for the catalytic removal of ubiquitin (Ub) from proteins directed to the proteasome, implicated in the pathogenesis of neurodegeneration and cancer. Crystallography and cryo-EM analysis have identified loop regions crucial for the deubiquitinase activity of USP14, specifically those involved in Ub and proteasome binding. However, the structural changes in USP14 upon ligand binding to these regions are minimal, indicating significant yet uncharacterized dynamic contributions to its function. In this study, through structural and dynamical NMR experiments and functional evaluation, we demonstrate that small mutations designed to impact Ub binding and catalytic activity without disturbing the USP structure display both local and long-range effects. The affected residues connect the catalytic site and the Ub binding region with the proteasome interaction surface through a network of loops, which show varied dynamics on the ps-ms time scale. Collectively, our findings experimentally reveal different aspects of dynamic connections within USP14, suggesting the presence of allosteric networks that link enzyme activity with regulatory function. The identification of coupled clusters of possible allostery participants in the free USP domain provides new insights into the dynamic regulation of USP14, with potential implications for understanding its role in cellular processes.

Unraveling the role of deubiquitinating enzymes on cisplatin resistance in several cancers

The use of platinum-based drugs in cancer treatment is one of the most common methods in chemotherapy. Especially, cisplatin induces cell death by interrupting DNA synthesis by binding to the DNA bases, thereby leading to the apoptosis via multiple pathways. However, the major hurdle in chemotherapy is drug resistance. To overcome drug resistance, the ubiquitin-proteasome system (UPS) has emerged as a potential therapeutic target. The UPS is a pivotal signaling pathway that regulates the majority of cellular proteins by attaching ubiquitin to substrates, leading to proteasomal degradation. Conversely, deubiquitinating enzymes (DUBs) remove tagged ubiquitin from the substrate and inhibit degradation, thereby maintaining proteostasis. Recently, studies have been conducted to identify the substrates of DUBs and investigated the cellular mechanisms, and now the development of therapeutics using DUB inhibitors is in clinical trials. However, the mechanism of the DUB response to cisplatin remains still unclear. In this review, we summarize the research reported on the function of DUBs responding to cisplatin.

Exosome-transmitted HSPA9 facilitates bortezomib resistance by targeting TRIP13/USP1 signaling in multiple myeloma

BACKGROUND

Resistance to the proteasome inhibitor bortezomib (BTZ) poses a formidable therapeutic challenge in multiple myeloma (MM). Our study aims to analyze the mechanism by which exosomes heat shock 70 kDa protein 9 (HSPA9) secreted by BTZ-resistant MM cells disseminate resistance to BTZ-sensitive MM cells.

METHODS

The serum exosomes were identified by nanoparticle tracking analysis and transmission electron microscopy. Liquid chromatography-mass spectrometry and public databases were performed to screen exosomes HSPA9. Cell counting kit-8, western blotting and colony formation assay were used to detected the role of HSPA9 protein in vitro. Co-immunoprecipitation, immunofluorescence and protein truncation test experiments were used to determine the regulatory network of the HSPA9-USP1-TRIP13 complex. Optical imaging in vivo and xenograft mouse models were performed to investigate that exosomes HSPA9 promoted MM proliferation and BTZ resistance.

RESULTS

We demonstrated that HSPA9 was highly expressed in serum exosomes and BTZ-resistant MM patients. Knockdown of HSPA9 significantly suppressed tumorigenesis and reversed BTZ resistance in vitro. As a downstream molecular of HSPA9, thyroid hormone receptor-interacting protein 13 (TRIP13) was also highly expressed in BTZ-resistant MM patients. Mechanistically, the carboxyl-terminal peptide-binding domain of HSPA9, provides a platform for recruiting the deubiquitinating enzyme ubiquitin-specific peptidase 1 (USP1), which prevents TRIP13 protein degradation. The HSPA9-USP1-TRIP13 complex exhibits stability in the cytoplasm, and its inhibition remarkably enhances BTZ resistance in vito.

CONCLUSION

Our findings propose a pioneering molecular regulatory network in which MM-cell-derived exosomes HSPA9 transmitted BTZ resistance through the USP1/TRIP13 signaling pathway. This research highlights exosomes HSPA9 as a promising target to overcome MM BTZ resistance.

The Role of the Ubiquitin System in Eye Diseases

The ubiquitin-proteasome system (UPS) is a fundamental process that regulates various biological functions, including immune response, cell cycle, oxidative stress, migration, and cellular proliferation. This system is responsible for the degradation of proteins, while proteasomes play a significant role in mechanisms involved in health and human diseases. The participation of the UPS in immune response is particularly relevant, leading to the involvement of immunoproteasomes. This specialized proteasome is involved in the processing and presentation of antigenic peptides, making it crucial for proper immune function. Moreover, the impact of the UPS is considered essential in understanding several diseases, such as neurodegenerative disorders, infections, and vascular diseases. The dysregulation of the UPS may contribute to the pathogenesis of these conditions, highlighting its importance as a potential therapeutic target. Interestingly, the UPS is also related to ocular structures, playing a role in visual perception and ocular homeostasis. This involvement in the regulation of various ocular processes suggests its potential impact on both anterior and posterior eye pathologies. This review aims to discuss the general considerations of the UPS and provide information about its participation in anterior and posterior eye pathologies. By understanding its role in ocular health and disease, researchers and clinicians may explore novel therapeutic strategies targeting the UPS for the treatment of various eye conditions. In conclusion, the UPS is a crucial player in biological processes, with far-reaching implications in health and disease, including the anterior and posterior segments of the eye. Further research in this field may lead to the development of innovative therapies and a better understanding of the complex mechanisms underlying various eye disorders.

Serum-Based Proteomic Approach to Identify Clinical Biomarkers of Radiation Exposure

BACKGROUND

Ionizing radiation (IR) exposure poses a significant health risk due to its widespread use in medical diagnostics and therapeutic applications, necessitating rapid and effective biomarkers for assessment.

OBJECTIVE

The aim of this study is to identify the serum proteomic signature of IR exposure in patients undergoing radiotherapy (RT).

METHODS

Blood samples were obtained from eighteen patients with head and neck cancer (HNC) and five patients with rectal cancer before and immediately after they underwent curative intensity-modulated radiotherapy (IMRT). The comprehensive serum proteome was analyzed in individual samples using nanoHPLC-MS/MS.

RESULTS

Forty radiation-modulated proteins (RMPs), 24 upregulated and 16 downregulated, with a fold change ≥1.5 and p-value < 0.05 were identified. About 40% of the RMPs are involved in acute phase response, DNA repair, and inflammation; the key RMPs were ADCY1, HGF, MCEMP1, CHD4, RECQL5, MSH6, and ZNF224. Conclusions: This study identifies a panel of serum proteins that may reflect the radiation response, providing a valuable molecular fingerprint of IR exposure and paving the way for the development of sensitive and specific biomarkers for early detection and clinical management of IR-related injuries.

Small-molecule allosteric activator of ubiquitin-specific protease 7 (USP7)

Ubiquitin-specific protease 7 (USP7) is a deubiquitylase essential for cell homeostasis, DNA repair, and regulation of both tumor suppressors and oncogenes. Inactivating USP7 mutations have been associated with Hao-Fountain Syndrome (HAFOUS), a rare neurodevelopmental disorder. Although a range of USP7 inhibitors have been developed over the last decade, in the context of HAFOUS as well as oncogene regulation, USP7 activators may represent a more relevant approach. To address this challenge, we report the discovery and characterization of a small-molecule activator of USP7 called MS-8. We showed that MS-8 activates USP7 by engaging the allosteric C-terminal binding pocket of USP7, thus mimicking the allosteric autoactivation by the USP7 C-terminal tail. We observed that MS-8 engages and activates mutant USP7 in a cellular context, impacting downstream proteins. Taken together, our study provides validation of the USP7 activator that paves the way towards novel activation-driven USP7 pharmacology.

The roles of the ubiquitin-proteasome system in renal disease

The ubiquitin-proteasome system (UPS) is a major pathway of specific intracellular protein degradation through proteasome degradation of ubiquitin-labeled substrates. Numerous biological processes, including the cell cycle, transcription, translation, apoptosis, receptor activity, and intracellular signaling, are regulated by UPS. Alterations of the UPS, which render them more or less susceptible to degradation, are responsible for disorders of renal diseases. This review aims to summarize the mechanism of UPS in renal diseases. Besides, this review explores the relationship among UPS, autophagy, and deubiquitination in the development of renal disease. The specific molecular linkages among these systems and pathogenesis, on the other hand, are unknown and controversial. In addition, we briefly describe some anti-renal disease agents targeting UPS components. This review emphasizes UPS as a promising therapeutic modality for the treatment of kidney disease. Our work, though still basic and limited, could provide options to future potential therapeutic targets for renal diseases with a UPS underlying basis.

Tim-3 promotes viral infection by suppressing the USP25-TRAF3-IRF7 signaling pathway

Tim-3, an immune checkpoint inhibitor, plays key roles in maintaining immune homeostasis and is involved in viral evasion. However, the precise role of Tim-3 in viral infection remains to be determined. USP25 is a deubiquitinating enzyme that initiates antiviral immunity by deubiquitinating TRAF3 and triggering the antiviral signaling pathway. Here we found that Tim-3-specific knockout in myeloid cells leads to enhanced antiviral immunity in mice with vesicular stomatitis virus (VSV) encephalitis by increasing the type I interferon response. Mechanistically, Tim-3 inhibits the expression of USP25 via STAT1 and interacts with USP25 but does not regulate its posttranslational modification; as a result, Tim-3 inhibits USP25-mediated deubiquitination of TRAF3, promotes K48-linked ubiquitination and degradation of TRAF3, inhibits the phosphorylation of IRF7, and ultimately downregulates the interferon response. These findings provide new insights into the function of Tim-3 in antiviral immunity and its related clinical significance.

USP32 Promotes Colorectal Carcinoma Progression Through Activating NF-κB Signalling Pathway

Ubiquitin-specific protease 32 (USP32) plays a key role in cancer progression. However, its functions in colorectal carcinoma (CRC) are still unexplored. In our study, we explored the expression and clinical significance of USP32 in CRC as well as its relationship with the tumour microenvironment (TME). As a result, we found that USP32 is overexpressed in CRC and it is associated with poor outcomes in CRC patients. In addition, the expression of USP32 is significantly related to the activation of the NF-κB signalling pathway and the immune infiltrates of the TME. Wet experiments also confirmed that USP32 is critical for the proliferation, survival, and migration of CRC cells and tumour growth, which may be due to the activation of the NF-κB signalling pathway. In conclusion, targeting the USP32-NF-κB axis may be a novel treatment strategy for CRC patients.

Ubiquitin-Proteasome System in Periodontitis: Mechanisms and Clinical Implications

The progression of periodontitis, a bacteria-driven inflammatory and bone-destructive disease, involves myriad cellular and molecular mechanisms. Protein regulation significantly influences the pathogenesis and management of periodontitis. However, research regarding its regulatory role in periodontitis remains relatively limited. The ubiquitin-proteasome system (UPS), which mainly involves ubiquitination by E3 ubiquitin ligases (E3s) and deubiquitination by deubiquitinating enzymes (DUBs), is the primary intracellular and non-lysosomal mechanism of protein degradation. Recent studies have provided compelling evidence to support the involvement of UPS in periodontitis progression. Increasing evidence indicated that E3s, such as CUL3, Nedd4-2, Synoviolin, FBXL19, PDLIM2, TRIMs and TRAFs, modulate inflammatory responses and bone resorption in periodontitis through multiple classical signalling pathways, including NLRP3, GSDMD, NF-κB, Wnt/β-catenin and Nrf2. Meanwhile, DUBs, including OTUD1, A20, CYLD, UCH-L1 and USPs, also broadly modulate periodontitis progression by regulating signalling pathways such as NF-κB, Wnt/β-catenin, NLRP3, and BMP2. Therefore, the modulation of E3s and DUBs has proven to be an effective therapy against periodontitis. This review provides a comprehensive overview of the regulatory role of ubiquitinating and deubiquitinating enzymes in periodontitis progression and the underlying mechanisms. Finally, we summarise several chemical and genetic methods that regulate UPS enzymes and pave the way for the development of targeted therapies for periodontitis.

Localized K63 Ubiquitin Signaling Is Regulated by VCP/p97 During Oxidative Stress

Under stress conditions, cells reprogram their molecular machineries to mitigate damage and promote survival. Ubiquitin signaling is globally increased during oxidative stress, controlling protein fate and supporting stress defenses at several subcellular compartments. However, the rules driving subcellular ubiquitin localization to promote concerted response mechanisms remain understudied. Here, we show that K63-linked polyubiquitin chains, known to promote proteasome-independent pathways, accumulate primarily in noncytosolic compartments during oxidative stress induced by sodium arsenite in mammalian cells. Our subcellular ubiquitin proteomic analyses of noncytosolic compartments expanded 2.5-fold the pool of proteins (2,494) and provided a comprehensive number of sites (10,157) known to be ubiquitinated during arsenite stress, suggesting their involvement in a myriad of cellular pathways. Moreover, subcellular proteome analyses revealed proteins that are recruited to noncytosolic compartments under stress, including a significant enrichment of helper ubiquitin-binding adaptors of the ATPase valosin-containing protein (VCP) that processes ubiquitinated substrates for downstream signaling. We further show that VCP recruitment to noncytosolic compartments under arsenite stress occurs in a ubiquitin-dependent manner mediated by its adaptor NPLOC4. Additionally, we show that VCP and NPLOC4 activities are critical to sustain low levels of noncytosolic K63-linked ubiquitin chains, supporting a cyclical model of ubiquitin conjugation and removal that is disrupted by reactive oxygen species. This work deepens our understanding of the role of localized ubiquitin and VCP signaling in the basic mechanisms of stress response and highlights new pathways and molecular players that are essential to reshape the composition and function of the human subcellular proteome under dynamic environments.

USP18 Confers Paclitaxel Resistance in Non-Small Cell Lung Cancer by Stabilizing SHANK1 Expression Via Deubiquitination

Ubiquitin-specific protease 18 (USP18) has been identified to promote lung cancer growth and metastasis by deubiquitinating protein substrates. Herein, the action and mechanism of USP18 on paclitaxel resistance in non-small cell lung cancer (NSCLC) were investigated in this study. The mRNA and protein levels of USP18 and SH3 and multiple ankyrin repeat domains protein 1 (SHANK1) were detected by qRT-PCR and western blot analysis analyses. PTX resistance in NSCLC cells was determined by analyzing cell proliferation, apoptosis, and IC50 values using colony formation assay, flow cytometry, and CCK-8 assay, respectively. The glycolysis was determined by detecting glucose consumption, lactate production and ATP levels. Protein interaction was validated using Co-IP assay. Cellular ubiquitination analyzed the deubiquitination effect of USP18 on SHANK1. Animal experiments was performed for in vivo analysis. USP18 was highly expressed in PTX-resistant NSCLC tissues and cells. Silencing of USP18 promoted PTX sensitivity by suppressing the proliferation and glycolysis and inducing apoptosis in PTX-resistant NSCLC cells. Mechanically, USP18 deubiquitinated SHANK1 and stabilized its expression. SHANK1 was highly expressed in PTX-resistant NSCLC tissues and cells, and the deficiency of SHANK1 promoted the sensitivity of PTX-resistant NSCLC cells to PTX. Moreover, the enhanced sensitivity of PTX-resistant NSCLC cells to PTX that was caused by USP18 silencing could be reversed by SHANK1 overexpression. In addition, USP18 silencing reinforced PTX-induced growth inhibition in NSCLC by regulating SHANK1. In conclusion, USP18 conferred paclitaxel resistance in NSCLC by stabilizing SHANK1 expression via deubiquitination.

The Deubiquitinating Enzyme USP4 Promotes Trophoblast Dysfunction by Stabilizing RYBP

Previous studies have suggested that impaired spiral artery remodeling, placental dysfunction, and insufficient trophoblast infiltration are the etiology and pathogenesis of Preeclampsia (PE). Ring 1 and YY1 binding protein (RYBP) has been reported to be associated with trophoblast dysfunction. However, the molecular mechanism of RYBP involved in trophoblasts in the pathogenesis of PE is poorly defined. RYBP and Ubiquitin-specific peptidase 4 (USP4) mRNA levels were determined using real-time quantitative polymerase chain reaction (RT-qPCR). RYBP, USP4, p-PI3K, PI3K, p-AKT, and AKT protein levels were measured using western blot assay. Cell viability, proliferation, apoptosis, invasion, and migration were assessed using 3-(4, 5-dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT), 5-ethynyl-2'-deoxyuridine (EdU), flow cytometry, transwell, and wound healing assays. After ubibrowser database analysis, the interaction between USP4 and RYBP was verified using Co-immunoprecipitation (CoIP) assay. RYBP and USP4 expression were upregulated in placental tissues from PE patients. By using JEG-3 and HTR-8/SVneo trophoblast cells, RYBP overexpression or USP4 upregulation could hinder cell viability, proliferation, invasion, migration, and promote apoptosis. Mechanistically, USP4 could trigger the deubiquitination of RYBP and prevent its degradation. In addition, USP4 repressed the PI3K/AKT signaling pathway by regulating RYBP. In total, Decreased USP4-mediated ubiquitination results in an adverse impact on trophoblast function by enhancing RYBP expression, providing a novel therapeutic target for PE.

Piceatannol upregulates USP14-mediated GPX4 deubiquitination to inhibit neuronal ferroptosis caused by cerebral ischemia-reperfusion in mice

Ischemic stroke is a very common brain disorder. This study aims to assess the neuroprotective effects of piceatannol (PCT) in preventing neuronal injury resulting from cerebral ischemia and reperfusion (I/R) in mice. Additionally, we investigated the underlying mechanisms through which PCT inhibits neuronal ferroptosis by modulating the USP14/GPX4 signaling axis. In vitro and in vivo experiments were conducted. In vitro, oxygen-glucose deprivation followed by reoxygenation (OGD/R) was used to simulate ischemic injury in neuronal cells. We utilized various techniques, including DCFH-DA staining, FeRhoNox-1 staining, MDA and GSH determination, immunofluorescence, Western blotting, co-immunoprecipitation, plasmid and siRNA transfection, to evaluate the therapeutic efficacy of PCT and elucidate its mechanism of action. For vivo studies, we established a mouse model of I/R by ligating the bilateral common carotid arteries. The efficacy of PCT in mitigating brain injury and cognitive dysfunction were assessed through behavioral tests, histological analysis, Western blotting, and immunohistochemistry. PCT treatment significantly enhanced cell viability under OGD/R and reduced lipid peroxidation by decreasing levels of ROS, MDA. Furthermore, PCT effectively inhibited neuronal ferroptosis by modulating the expression of key ferroptosis-related proteins, including GPX4, ACSL4, FPN1, and Ferritin. Mechanistically, PCT was found to prevent GPX4 degradation through USP14-mediated deubiquitination. Notably, silencing USP14 reversed the ferroptotic effects of PCT, whereas overexpressing of USP14 amplified these effects. In vivo, PCT significantly reduced pathological damage of brain tissue and improved cognitive dysfunction. Piceatannol exerts neuroprotective effects by regulating ferroptosis through the USP14/GPX4 axis, thereby preventing cerebral ischemia/reperfusion injury.

Targeting Ubiquitin-Proteasome system (UPS) in treating osteoarthritis

Despite osteoarthritis (OA) being recognised for over a century as a debilitating disease that affects millions, there are huge gaps in our understanding of the underlying pathophysiology that drives this disease. Present day studies that focussed on ubiquitination (Ub) and ubiquitylation-like (Ubl) modification related mechanisms have brought light into the possibility of attenuating OA development by targeting these specific proteins in chondrocytes. In the present review, we discuss recent advances in studies involving Ub ligases and deubiquitinating enzymes (DUBs) which are of importance in the development of OA, and may offer potential therapeutic strategies for OA. Such targets may involve attenuating proteases such as matrix metalloproteinases (MMP) 1, 8, 13, 4 and several A Disintegrin and Metalloproteinase with Thrombospondin Motifs (ADAMTS) that are well known for their roles in cartilage breakdown. Ligases such as ubiquitin-conjugating enzymes (E2) and ubiquitin-ligating enzymes (E3) that are involved in extracellular matrix (ECM) degradation in OA and of their pathogenesis would be discussed. In addition to catabolic and degenerative downstream effects of Ub and DUBs in OA, inflammatory mechanisms most notably involving nuclear factor-kappa B (NF-κB) signalling pathways regulated through Ub and using various targeting molecules would also be highlighted. Challenges, gaps and insights from clinical trials will provide valuable guidance for future investigations on targeting ubiquitin-proteosome system (UPS) as a therapeutic option for OA.

The Deubiquitinase OTUD1 Influences HIV-1 Release by Regulating the Host Restriction Factor BST-2

Bone marrow stromal cell antigen 2 (BST-2) is a restriction factor for human immunodeficiency virus type I (HIV-1) and plays an important role in regulating the release of viral particles. However, the antiviral efficacy of BST-2 is antagonized by the HIV-1-encoded accessory protein Vpu, which facilitates the degradation of BST-2 by recruiting E3 ubiquitin ligase β-TrCP. The involvement of deubiquitinases (DUBs) in counteracting BST-2 ubiquitination and influencing its stability during HIV-1 infection remains inadequately explored. In this study, we conducted a small interfering RNA (siRNA) screening of human DUBs and determined that OTUD1 interacts with BST-2, leading to a reduction in its K48- and K63-linked ubiquitination. This reduction increases BST-2 protein stability, and subsequently inhibits HIV-1 release. Our findings reveal a novel regulatory mechanism by which DUBs influence the stability of the HIV-1 restriction factor BST-2 to dampen viral release, providing a potential therapeutic target for HIV-1 antiviral intervention.

Ubiquitin-Specific Protease Inhibitors for Cancer Therapy: Recent Advances and Future Prospects

Cancer management has traditionally depended on chemotherapy as the mainstay of treatment; however, recent advancements in targeted therapies and immunotherapies have offered new options. Ubiquitin-specific proteases (USPs) have emerged as promising therapeutic targets in cancer treatment due to their crucial roles in regulating protein homeostasis and various essential cellular processes. This review covers the following: (1) the structural and functional characteristics of USPs, highlighting their involvement in key cancer-related pathways, and (2) the discovery, chemical structures, mechanisms of action, and potential clinical implications of USP inhibitors in cancer therapy. Particular attention is given to the role of USP inhibitors in enhancing cancer immunotherapy, e.g., modulation of the tumor microenvironment, effect on regulatory T cell function, and influence on immune checkpoint pathways. Furthermore, this review summarizes the current progress and challenges of clinical trials involving USP inhibitors as cancer therapy. We also discuss the complexities of achieving target selectivity, the ongoing efforts to develop more specific and potent USP inhibitors, and the potential of USP inhibitors to overcome drug resistance and synergize with existing cancer treatments. We finally provide a perspective on future directions in targeting USPs, including the potential for personalized medicine based on specific gene mutations, underscoring their significant potential for enhancing cancer treatment. By elucidating their mechanisms of action, clinical progress, and potential future applications, we hope that this review could serve as a useful resource for both basic scientists and clinicians in the field of cancer therapeutics.

Aspirin inhibits proteasomal degradation and promotes α-synuclein aggregate clearance through K63 ubiquitination

Aspirin is a potent lysine acetylation inducer, but its impact on lysine ubiquitination and ubiquitination-directed protein degradation is unclear. Herein, we develop the reversed-pulsed-SILAC strategy to systematically profile protein degradome in response to aspirin. By integrating degradome, acetylome, and ubiquitinome analyses, we show that aspirin impairs proteasome activity to inhibit proteasomal degradation, rather than directly suppressing lysine ubiquitination. Interestingly, aspirin increases lysosomal degradation-implicated K63-linked ubiquitination. Accordingly, using the major pathological protein of Parkinson's disease (PD), α-synuclein (α-syn), as an example of protein aggregates, we find that aspirin is able to reduce α-syn in cultured cells, neurons, and PD model mice with rescued locomotor ability. We further reveal that the α-syn aggregate clearance induced by aspirin is K63-ubiquitination dependent in both cells and PD mice. These findings suggest two complementary mechanisms by which aspirin regulates the degradation of soluble and insoluble proteins, providing insights into its diverse pharmacological effects that can aid in future drug development efforts.

USP34 regulates endothelial PAR1 mRNA transcript expression and cellular signaling

Signaling by G protein-coupled receptors (GPCRs) is regulated by temporally distinct processes including receptor desensitization, internalization, and lysosomal sorting, and are tightly controlled by posttranslational modifications. While the role of phosphorylation in regulating GPCR signaling is well studied and established, the mechanisms by which other posttranslational modifications, such as ubiquitination, regulate GPCR signaling are not clearly defined. We hypothesize that GPCR ubiquitination and deubiquitination is critical for proper signaling and cellular responses. In the present study, we show that the deubiquitinase ubiquitin-specific protease-34 (USP34) regulates thrombin-stimulated protease-activated receptor-1 (PAR1)-induced p38 autophosphorylation and activation. The PAR1-stimulated p38 signaling pathway is driven by ubiquitination. Interestingly, small interfering RNA-induced knockdown of USP34 expression markedly increased PAR1 cell surface abundance and protein expression without modulating PAR1 ubiquitination or the ubiquitination status of p38 signaling pathway components. In addition, increased PAR1 expression observed in USP34-depleted cells was not caused by altered PAR1 constitutive internalization, agonist-induced internalization, or receptor degradation. Rather, we report that loss of USP34 expression increased mRNA transcript expression of the PAR1-encoding gene, F2R. This study unexpectedly identified a critical role for USP34 in regulation of F2R mRNA transcript expression, which modulates PAR1 cell surface levels and thrombin-stimulated p38 mitogen-activated protein kinase signaling.

MLKL-USP7-UBA52 signaling is indispensable for autophagy in brain through maintaining ubiquitin homeostasis

Individuals with genetic elimination of MLKL (mixed lineage kinase domain like pseudokinase) exhibit an increased susceptibility to neurodegenerative diseases like Alzheimer disease (AD). However, the mechanism is not yet fully understood. Here, we observed significant compromise in macroautophagy/autophagy in the brains of mlkl knockout (KO) mice, as evidenced by the downregulation of BECN1/Beclin1 and ULK1 (unc-51 like autophagy activating kinase 1). We identified UBA52 (ubiquitin A-52 residue ribosomal protein fusion product 1) as the binding partner of MLKL under physiological conditions. Loss of Mlkl induced a decrease in ubiquitin levels by preventing UBA52 cleavage. Furthermore, we demonstrated that the deubiquitinase (DUB) USP7 (ubiquitin specific peptidase 7) mediates the processing of UBA52, which is regulated by MLKL. Moreover, our results indicated that the reduction of BECN1 and ULK1 upon Mlkl loss is attributed to a decrease in their lysine 63 (K63)-linked polyubiquitination. Additionally, single-nucleus RNA sequencing revealed that the loss of Mlkl resulted in the disruption of multiple neurodegenerative disease-related pathways, including those associated with AD. These results were consistent with the observation of cognitive impairment in mlkl KO mice and exacerbation of AD pathologies in an AD mouse model with mlkl deletion. Taken together, our findings demonstrate that MLKL-USP7-UBA52 signaling is required for autophagy in brain through maintaining ubiquitin homeostasis, and highlight the contribution of Mlkl loss-induced ubiquitin deficits to the development of neurodegeneration. Thus, the maintenance of adequate levels of ubiquitin may provide a novel perspective to protect individuals from multiple neurodegenerative diseases through regulating autophagy.Abbreviations: 4HB: four-helix bundle; AAV: adeno-associated virus; AD: Alzheimer disease; AIF1: allograft inflammatory factor 1; APOE: apolipoprotein E; APP: amyloid beta precursor protein; Aβ: amyloid β; BECN1: beclin 1; co-IP: co-immunoprecipitation; DEGs: differentially expressed genes; DLG4: discs large MAGUK scaffold protein 4; DUB: deubiquitinase; EBSS: Earle's balanced salt solution; GFAP: glial fibrillary acidic protein; HRP: horseradish peroxidase; IL1B: interleukin 1 beta; IL6: interleukin 6; IPed: immunoprecipitated; KEGG: Kyoto Encyclopedia of Genes and Genomes; KO: knockout; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MLKL: mixed lineage kinase domain like pseudokinase; NSA: necrosulfonamide; OPCs: oligodendrocyte precursor cells; PFA: paraformaldehyde; PsKD: pseudo-kinase domain; SYP: synaptophysin; UB: ubiquitin; UBA52: ubiquitin A-52 residue ribosomal protein fusion product 1; UCHL3: ubiquitin C-terminal hydrolase L3; ULK1: unc-51 like autophagy activating kinase 1; UMAP: uniform manifold approximation and projection; UPS: ubiquitin-proteasome system; USP7: ubiquitin specific peptidase 7; USP9X: ubiquitin specific peptidase 9 X-linked.

USP9X PROMOTES LPS-INDUCED FIBROBLAST CELL APOPTOSIS, INFLAMMATION, AND OXIDATIVE STRESS BY REGULATION OF TBL1XR1 DEUBIQUITINATION

ABSTRACT

Background: Ubiquitination and deubiquitination are involved in the progression of human diseases, including acute pneumonia. In this study, we aimed to explore the functions of ubiquitin-specific peptidase 9X-linked (USP9X) in lipopolysaccharide (LPS)-treated WI-38 cells. Methods: WI-38 cells were treated with LPS to induce the cellular damage and inflammation. 3-(4, 5-Dimethyl-2-thiazolyl)-2, 5-diphenyl-2-H-tetrazolium bromide (MTT) assay, and 5-ethynyl-2'-deoxyuridine (EdU) assay were performed to examine the proliferation of LPS-treated WI-38 cells. Flow cytometry analysis was conducted to detect LPS-treated WI-38 cell apoptosis. ELISA kits were utilized to determine the concentrations of inflammatory factors (IL-1β and TNF-α). Superoxide dismutase activity and reactive oxygen species level were examined with related kits. Ubibrowser (http://ubibrowser.bio-it.cn/ubibrowser/), ubiquitination assay, and co-immunoprecipitation assay demonstrated the interaction between USP9X and transducin β-like 1X related protein 1 (TBL1XR1). qRT-PCR assay and western blot assay were manipulated to determine the expression of USP9X and TBL1XR1. TBL1XR1 and USP9X knockdown experiments were conducted to explore their functions on LPS-induced WI-38 cell injury and inflammation. Results: TBL1XR1 expression was upregulated in LPS-treated WI-38 cells. TBL1XR1 knockdown promoted cell proliferation and repressed apoptosis, inflammation, and oxidative stress in LPS-treated WI-38 cells. Moreover, USP9X deubiquitinated TBL1XR1 to regulate TBL1XR1 expression. USP9X knockdown restored the effects of LPS on WI-38 cell proliferation, apoptosis, inflammation, and oxidative stress, but these effects of USP9X knockdown were further abolished by TBL1XR1 overexpression. In addition, USP9X promoted the NF-κB signaling pathway by the deubiquitination of TBL1XR1. Conclusion: USP9X promoted the apoptosis, inflammation, and oxidative stress of LPS-stimulated WI-38 cells through the deubiquitination of TBL1XR1.

The impact of chronic intermittent hypoxia on enzymatic activity in memory-associated brain regions of male and female rats

BACKGROUND

Obstructive sleep apnea (OSA) is an intermittent hypoxia disorder associated with cognitive dysfunction, including learning and memory impairments. There is evidence that alterations in protease activity and neuronal activation are associated with cognitive dysfunction, are dependent on sex, and may be brain region-specific. However, the mechanisms mediating OSA-induced cognitive impairments are unclear. Therefore, we used a rat model of OSA, chronic intermittent hypoxia (CIH) to investigate protease activity (e.g., calpain and caspase-3) on spectrin, a cytoskeletal protein associated with neurotransmitter release, and neuronal activation (early growth response protein 1, EGR-1) in brain regions associated with learning and memory.

METHODS

Male and female Sprague Dawley rats were exposed to CIH or room air (normoxic) for 14 days. We quantified protease activity and cleaved spectrin products, along with EGR-1 protein expression in hippocampal subregions (CA1, CA3), cortical regions [entorhinal cortex (ETC), retrosplenial cortex (RSC), cerebellar cortex (CC)], and subcortical regions [raphe nucleus (RN), locus coeruleus (LC)] associated with learning and memory. Within each group, Pearson correlations of calpain activity, caspase-3 activity, and EGR-1 expression were performed between brain regions. Sex differences within normoxic and CIH correlations were examined.

RESULTS

CIH dysregulated calpain activity in male ETC, and female CA1 and RSC. CIH dysregulated caspase-3 activity in male RN, and female CA1 and RSC. CIH decreased calpain and caspase-3 cleavage products in male ETC. CIH decreased calpain-cleaved spectrin in male RSC but increased these products in female RSC. EGR-1 expression was decreased in male and female RN. Correlational analysis revealed CIH increased excitatory connections in males and increased inhibitory connections in females. EGR-1 expression in males shifted from negative to positive correlations.

CONCLUSIONS

Overall, these data indicate CIH dysregulates protease activity and impairs neuronal function in a brain region- and sex-dependent manner. This indicates that males and females exhibit sex-specific vulnerabilities to mild OSA. These findings concur with our previous behavioral studies that demonstrated memory impairment in CIH-exposed rats.

Activation and Reactivity of the Deubiquitinylase OTU Cezanne-2 from MD Simulations and QM/MM Calculations

Cezanne-2 (Cez2) is a deubiquitinylating (DUB) enzyme involved in the regulation of ubiquitin-driven cellular signaling and selectively targets Lys11-linked polyubiquitin chains. As a representative member of the ovarian tumor (OTU) subfamily DUBs, it performs cysteine proteolytic isopeptide bond cleavage; however, its exact catalytic mechanism is not yet resolved. In this work, we used different computational approaches to get molecular insights into the Cezanne-2 catalytic mechanism. Extensive molecular dynamics (MD) simulations were performed for 12 μs to model free Cez2 and the diubiquitin (diUb) substrate-bound protein-protein complex in two different charge states of Cez2, each corresponding to a distinct reactive state in its catalytic cycle. The simulations were analyzed in terms of the relevant structural parameters for productive enzymatic catalysis. Reactive diUb-Cez2 complex configurations were identified, which lead to isopeptide bond cleavage and stabilization of the tetrahedral oxyanion intermediate. The reliability of these complexes was further assessed by quantum mechanics/molecular mechanics (QM/MM) optimizations. The results show that Cez2 follows a modified cysteine protease mechanism involving a catalytic Cys210/His367 dyad, with the oxyanion hole to be a part of the "C-loop," and polarization of His367 by the formation of a strictly conserved water bridge with Glu173. The third residue has a dual role in catalysis as it mediates substrate binding and polarization of the catalytic dyad. A similar mechanism was identified for Cezanne-1, the paralogue of Cez2. In general, our simulations provide valuable molecular information that may help in the rational design of selective inhibitors of Cez2 and closely related enzymes.

Analysis of Structures of SARS-CoV-2 Papain-like Protease Bound with Ligands Unveils Structural Features for Inhibiting the Enzyme

The COVID-19 pandemic, driven by the novel coronavirus SARS-CoV-2, has drastically reshaped global health and socioeconomic landscapes. The papain-like protease (PLpro) plays a critical role in viral polyprotein cleavage and immune evasion, making it a prime target for therapeutic intervention. Numerous compounds have been identified as inhibitors of SARS-CoV-2 PLpro, with many characterized through crystallographic studies. To date, over 70 three-dimensional (3D) structures of PLpro complexed ligands have been deposited in the Protein Data Bank, offering valuable insight into ligand-binding features that could aid the discovery and development of effective COVID-19 treatments targeting PLpro. In this study, we reviewed and analyzed these 3D structures, focusing on the key residues involved in ligand interactions. Our analysis revealed that most inhibitors bind to PLpro's substrate recognition sites S3/S4 and SUb2. While these sites are highly attractive and have been extensively explored, other potential binding regions, such as SUb1 and the Zn(II) domain, are less explored and may hold untapped potential for future COVID-19 drug discovery and development. Our structural analysis provides insights into the molecular features of PLpro that could accelerate the development of novel therapeutics targeting this essential viral enzyme.

Chemical tools to define and manipulate interferon-inducible Ubl protease USP18

Ubiquitin-specific protease 18 (USP18) is a multifunctional cysteine protease primarily responsible for deconjugating the interferon-inducible ubiquitin-like modifier ISG15 from protein substrates. Here, we report the design and synthesis of activity-based probes (ABPs) that incorporate unnatural amino acids into the C-terminal tail of ISG15, enabling the selective detection of USP18 activity over other ISG15 cross-reactive deubiquitinases (DUBs) such as USP5 and USP14. Combined with a ubiquitin-based DUB ABP, the USP18 ABP is employed in a chemoproteomics screening platform to identify and assess inhibitors of DUBs including USP18. We further demonstrate that USP18 ABPs can be utilized to profile differential activities of USP18 in lung cancer cell lines, providing a strategy that will help define the activity-related landscape of USP18 in different disease states and unravel important (de)ISGylation-dependent biological processes.

Exploring Ubiquitination in Spinal Cord Injury Therapy: Multifaceted Targets and Promising Strategies

Spinal cord injury (SCI) is a severely debilitating neurological condition that often results in significant functional impairment and is associated with poor long-term prognosis. Edema, oxidative stress, inflammatory responses, and cell death are the primary factors contributing to secondary injury following spinal cord damage. Ubiquitination is a crucial intracellular mechanism for protein regulation that has garnered significant attention as a therapeutic target in a variety of diseases. Numerous studies have shown that ubiquitination plays a key role in modulating processes such as inflammatory responses, apoptosis, and nerve regeneration following SCI, thereby influencing injury repair. Accordingly, targeting ubiquitination has the potential for mitigating harmful inflammatory responses, inhibiting dysregulated programmed cell death, and protecting the integrity of the blood-spinal cord barrier, thereby providing a novel therapeutic strategy for SCI. In this review, we discuss the role of ubiquitination and its potential as a therapeutic target in SCI, aiming to offer a foundation for developing ubiquitination-targeted therapies for this condition.

DCAF13-mediated K63-linked ubiquitination of RNA polymerase I promotes uncontrolled proliferation in Breast Cancer

Hyperactivation of ribosome biogenesis (RiBi) drives cancer progression, yet the role of RiBi-associated proteins (RiBPs) in breast cancer (BC) is underexplored. In this study, we perform a comprehensive multi-omics analysis and reveal that assembly and maturation factors (AMFs), a subclass of RiBPs, are upregulated at both RNA and protein levels in BC, correlating with poor patient outcomes. In contrast, ribosomal proteins (RPs) do not show systematic upregulation across various cancers, including BC. We further demonstrate that the oncogenic activation of a top AMF candidate in BC, DCAF13, enhances Pol I transcription and promotes proliferation in BC cells both in vitro and in vivo. Mechanistically, DCAF13 promotes Pol I transcription activity by facilitating the K63-linked ubiquitination of RPA194. This process stimulates global protein synthesis and cell growth. Our findings uncover a modification of RPA194 that regulates Pol I activity; this modification is dysregulated in BC, contributing to cancer progression.

Next-generation cancer therapeutics: PROTACs and the role of heterocyclic warheads in targeting resistance

One of the major obstacles to sustained cancer treatment effectiveness is the development of medication resistance. Current therapies that block proteins associated with cancer progression often lose their efficacy due to acquired drug resistance, which is frequently driven by mutated or overexpressed protein targets. Proteolysis-targeting chimeras (PROTACs) offer an alternative therapeutic strategy by hijacking the cell's ubiquitin-proteasome system to degrade disease-causing proteins, presenting several potential advantages. Over the past few years, PROTACs have been developed to target various cancer-related proteins, offering new treatment options for patients with previously untreatable malignancies and serving as a foundation for next-generation therapeutics. One of the notable benefits of PROTACs is their ability to overcome certain resistance mechanisms that limit the effectiveness of conventional targeted therapies, as shown in several recent studies. Additionally, research teams are investigating how PROTACs can selectively degrade mutant proteins responsible for resistance to first-line cancer therapies. In the pursuit of novel and effective treatments, this review highlights recent advancements in the development of PROTACs aimed at overcoming cancer resistance. When it comes to drug design, heterocyclic scaffolds often serve as a foundational framework, offering opportunities for modification and optimization of novel molecules. Researchers are similarly exploring various heterocyclic derivatives as "warheads" in the design of PROTACs has been instrumental in pushing the boundaries of targeted protein degradation. As warheads, these heterocyclic compounds are responsible for recognizing and binding to the target protein, which ultimately leads to its degradation via the ubiquitin-proteasome system. This study aims to provide a comprehensive overview of cutting-edge strategies in PROTAC design, offering detailed insights into key concepts and methodologies for creating effective PROTACs. Special emphasis is placed on structure-based rational design, the development of novel warheads, and their critical in influencing biological activity.

Deletion of BRCC3 ameliorates airway inflammation in asthma by inhibiting the activation of NLRP3 inflammasome

BRCA1/BRCA2-containing complex subunit 3 (BRCC3) serves as a deubiquitinating enzyme contributing to multiple inflammation-related disorders. However, the role of BRCC3 in modulating airway inflammation in asthma has not been investigated. This study aimed to examine the role of BRCC3 in airway inflammation using a mouse model of asthma induced by ovalbumin (OVA). BRCC3 levels were found to be elevated in mice with asthma. BRCC3 knockout (KO) mice demonstrated a notable improvement in pathological changes, accompanied by reduced levels of inflammatory cell infiltration and inflammatory cytokines, compared to wild-type (WT) mice following OVA challenge. The NLRP3 inflammasome was high activated in asthmatic mice, which was restrained by BRCC3 KO, as companied by a decrease in NLRP3, ASC, cleaved Caspase-1, cleaved Gasdermin D (GSDMD), IL-1β, and IL-18. In vitro studies demonstrated BRCC3 levels increased in airway epithelial cells in response to house dust mite (HDM) stimulation, depending on the dose and duration of exposure. Silencing BRCC3 in airway epithelial cells protected against HDM-induced cell injury and inflammation, along with inhibiting the NLRP3 inflammasome and pyroptosis. Conversely, the overexpression of BRCC3 in airway epithelial cells worsened DM-induced cell injury and inflammation while also enhancing the NLRP3 inflammasome and pyroptosis. Further investigations revealed that silencing BRCC3 increased the ubiquitination of NLRP3, whereas overexpressing BRCC3 decreased it. Pharmacological inhibition of the NLRP3 inflammasome diminished the effects of BRCC3 overexpression on the inflammation and pyroptosis induced by HDM in airway epithelial cells. Overall, these findings underscore the importance of BRCC3 in the pathogenesis of asthma. Deletion of BRCC3 alleviates airway inflammation in asthma by impeding the activation of the NLRP3 inflammasome, thus indicating that BRCC3 could serve as a potential target for asthma therapy.

USP5 inhibits anti-RNA viral innate immunity by deconjugating K48-linked unanchored and K63-linked anchored ubiquitin on IRF3

Interferon regulatory factor 3 (IRF3) is a central hub transcription factor that controls host antiviral innate immunity. The expression and function of IRF3 are tightly regulated by the post-translational modifications. However, it is unknown whether unanchored ubiquitination and deubiquitination of IRF3 involve modulating antiviral innate immunity against RNA viruses. Here, we find that USP5, a deubiquitinase (DUB) regulating unanchored polyubiquitin, is downregulated during host anti-RNA viral innate immunity in a type I interferon (IFN-I) receptor (IFNAR)-dependent manner. USP5 is further identified to inhibit IRF3-triggered antiviral immune responses through its DUB enzyme activity. K48-linked unanchored ubiquitin promotes IRF3-driven transcription of IFN-β and induction of IFN-stimulated genes (ISGs) in a dose-dependent manner. USP5 simultaneously removes both K48-linked unanchored and K63-linked anchored polyubiquitin chains on IRF3. Our study not only provides evidence that unanchored ubiquitin regulates anti-RNA viral innate immunity but also proposes a novel mechanism for DUB-controlled IRF3 activation, suggesting that USP5 is a potential target for the treatment of RNA viral infectious diseases.

Deubiquitinase USP47 Ameliorates Cardiac Hypertrophy Through Reducing Protein O-GlcNAcylation

ABSTRACT

Cardiac hypertrophy is a crucial risk factor for heart failure when the heart is confronted with physiologic or pathologic stimuli. The ubiquitin-proteasome system plays a critical role in the pathogenesis of cardiac hypertrophy. However, as a key component of the ubiquitin-proteasome system, the role of deubiquitinating enzymes in cardiac hypertrophy is not well understood. In this study, we observed that the expression level of deubiquitinase USP47 was increased in hypertrophic hearts and angiotensin II (Ang II)-stimulated neonatal rat cardiomyocytes. Adenovirus-mediated gain- and loss-of-function approaches indicated that USP47 overexpression significantly attenuated Ang II-induced cardiac hypertrophy in vitro and in vivo, whereas endogenous USP47 deficiency promoted the prohypertrophic effect of Ang II. Further investigation demonstrated that USP47 inhibited O-GlcNAcylation in cardiomyocytes by controlling the expression of O-GlcNAcase. Mechanistically, USP47 bound, deubiquitinated, and stabilized protein arginine methyltransferase 5 (PRMT5), thus upregulating O-GlcNAcase expression. We found that the restoration of PRMT5 abolished the prohypertrophic effects of USP47 silence in vitro. Therefore, our results provide the first evidence of the involvement of USP47 in cardiac hypertrophy and identify USP47 as a potential target for hypertrophic therapy.

Harnessing the ubiquitin proteasome system as a key player in stem cell biology

Intracellular proteins take part in almost every body function; thus, protein homeostasis is of utmost importance. The ubiquitin proteasome system (UPS) has a fundamental role in protein homeostasis. Its main role is to selectively eradicate impaired or misfolded proteins, thus halting any damage that could arise from the accumulation of these malfunctioning proteins. Proteasomes have a critical role in controlling protein homeostasis in all cell types, including stem cells. We will discuss the role of UPS enzymes as well as the 26S proteasome complex in stem cell biology from several angles. First, we shall overview common trends of proteasomal activity and gene expression of different proteasomal subunits and UPS enzymes upon passaging and differentiation of stem cells toward various cell lineages. Second, we shall explore the effect of modulating proteasomal activity in stem cells and navigate through the interrelation between proteasomes' activity and various proteasome-related transcription factors. Third, we will shed light on curated microRNAs and long non-coding RNAs using various bioinformatics tools that might have a possible role in regulating UPS in stem cells and possibly, upon manipulation, can enhance the differentiation process into different lineages and/or delay senescence upon cell passaging. This will help to decipher the role played by individual UPS enzymes and subunits as well as various interrelated molecular mediators in stem cells' maintenance and/or differentiation and open new avenues in stem cell research. This can ultimately provide a leap toward developing novel therapeutic interventions related to proteasome dysregulation.

USP9X deubiquitinates TRRAP to promote glioblastoma cell proliferation and migration and M2 macrophage polarization

Glioblastoma (GBM) is the most aggressive form of brain cancer, characterized by rapid growth and invasion into surrounding brain tissue. Ubiquitin-specific protease 9X (USP9X) has emerged as a key regulator in various cancers, but its role in GBM pathogenesis remains unclear. Understanding the molecular mechanisms underlying USP9X modulation of GBM progression could unveil potential therapeutic targets for this deadly disease. The mRNA and protein levels were determined in GBM tissues and/or cells using quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting assays, respectively. Cell migration was evaluated through wound-healing assay, while cell proliferation was measured using colony formation and CCK-8 assays. Flow cytometry analysis was performed to quantify the CD206-positive macrophages to assess M2 polarization. Co-immunoprecipitation (Co-IP) assays were conducted to elucidate the association between USP9X and transformation/transcription domain-associated protein (TRRAP). Cycloheximide (CHX) treatment was used to determine the impact of USP9X on TRRAP protein stabilization. Furthermore, the effect of USP9X depletion on GBM cell malignancy was validated using a xenograft mouse model. We found that USP9X expression was elevated in GBM tissues and cells. Depletion of USP9X suppressed GBM cell migration, proliferation, and M2 macrophage polarization. Mechanistically, USP9X stabilized TRRAP through the deubiquitination pathway in GBM cells, and TRRAP mitigated the effects of USP9X silencing on GBM cell malignant phenotypes and M2 macrophage polarization. Moreover, silencing of USP9X inhibited tumor formation in vivo. Together, USP9X deubiquitinated TRRAP, thereby promoting glioblastoma cell proliferation, migration, and M2 macrophage polarization. These results highlight the potential of targeting the USP9X-TRRAP axis as a therapeutic strategy for GBM.

Ubiquitin-specific protease 7 maintains c-Myc stability to support pancreatic cancer glycolysis and tumor growth

BACKGROUND

The typical pathological feature of pancreatic ductal adenocarcinoma (PDAC) is a significant increase in stromal reaction, leading to a hypoxic and poorly vascularized tumor microenvironment. Tumor cells undergo metabolic reprogramming, such as the Warburg effect, yet the underlying mechanisms are not fully understood.

METHODS

Interference and overexpression experiments were conducted to analyze the in vivo and in vitro effects of USP7 on the growth and glycolysis of tumor cells. Small-molecule inhibitors of USP7 and transgenic mouse models of PDAC were employed to assess the consequences of targeting USP7 in PDAC. The molecular mechanism underlying USP7-induced c-Myc stabilization was determined by RNA sequencing, co-IP and western blot analyses.

RESULTS

USP7 is abnormally overexpressed in PDAC and predicts a poor prognosis. Hypoxia and extracellular matrix stiffness can induce USP7 expression in PDAC cells. Genetic silencing of USP7 inhibits the glycolytic phenotypes in PDAC cells, while its overexpression has the opposite effect, as demonstrated by glucose uptake, lactate production, and extracellular acidification rate. Importantly, USP7 promotes PDAC tumor growth in a glycolysis-dependent manner. The small-molecule inhibitor P5091 targeting USP7 effectively suppresses the Warburg effect and cell growth in PDAC. In a transgenic mouse model of PDAC, named KPC, P5091 effectively blocks tumor progression. Mechanistically, USP7 interacts with c-Myc, enhancing its stability and expression, which in turn upregulates expression of glycolysis-related genes.

CONCLUSIONS

This study sheds light on the molecular mechanisms underlying the Warburg effect in PDAC and unveils USP7 as a potential therapeutic target for improving PDAC treatment.

USP21-EGFR signaling axis is functionally implicated in metastatic colorectal cancer

The emerging role of ubiquitin-specific peptidase 21 (USP21) in stabilizing Fra-1 (FOSL1) highlights its involvement in promoting colorectal cancer (CRC) metastasis. Additionally, a reciprocal link between EGFR signaling and Fra-1 activation has been identified, mediated through matrix metalloproteinases (MMPs). However, the functional implications of the USP21-EGFR signaling axis in metastatic CRC (mCRC) are not fully understood. To investigate the clinical correlation between USP21 and EGFR expression, RNA-Seq data from tumor tissues (n = 27) and matched normal tissues (n = 27) of 27 mCRC patients were analyzed. Functional studies were performed, including the use of CRISPR/Cas9 to generate USP21-knockout (USP21-KO) CRC cells, in vitro assays for cancer progression and tumor formation, in vivo xenograft assays in NSG mice. Additionally, the therapeutic effect of the USP21 inhibitor, BAY-805, was evaluated. We found that elevated levels of USP21 and EGFR expression in mCRC patients were associated with poorer survival outcomes. Mechanistically, USP21 was found to enhance EGFR stability by deubiquitinating EGFR, leading to reduced EGFR degradation. USP21-KO colon cancer cells exhibited significantly reduced proliferation, migration, colony formation, and 3D tumor spheroid formation in response to EGF. Furthermore, the tumorigenic activity in vivo was markedly diminished in NSG mice xenografted with USP21-KO colon cancer cells. Importantly, BAY-805 demonstrated a notable inhibitory effect on the formation of 3D tumor spheroids in colorectal cancer cells stimulated with EGF. These findings suggest that USP21 could be a valuable therapeutic target and predictive biomarker for managing mCRC driven by EGF.

Recent pharmacological insights on abating toxic protein species burden in neurological disorders: Emphasis on 26S proteasome activation

Protein homeostasis (proteostasis) refers to the plethora of mechanisms that safeguard the proper folding of the newly synthesized proteins. It entails various intricately regulated cues that demolish the toxic protein species to prevent their aggregation. The ubiquitin-proteasome system (UPS) is recognized as a salient protein degradation system, with a substantial role in maintaining proteostasis. However, under certain circumstances the protein degradation capacity of the UPS is overwhelmed, leading to the accumulation of misfolded proteins. Several neurodegenerative disorders, such as Alzheimer's disease, Parkinson's disease, Huntington disease, and amyotrophic lateral sclerosis are characterized with the presence of protein aggregates and proteinopathy. Accordingly, enhancing the 26S proteasome degradation activity might delineate a pioneering approach in targeting various proteotoxic disorders. Regrettably, the exact molecular approaches that enhance the proteasomal activity are still not fully understood. Therefore, this review aimed to underscore several signaling cascades that might restore the degradation capacity of this molecular machine. In this review, we discuss the different molecular components of the UPS and how 26S proteasomes are deleteriously affected in many neurodegenerative diseases. Moreover, we summarize different signaling pathways that can be utilized to renovate the 26S proteasome functional capacity, alongside currently known druggable targets in this circuit and various classes of proteasome activators.

The impact of chronic intermittent hypoxia on enzymatic activity in memory-associated brain regions of male and female rats

Background

Obstructive sleep apnea (OSA) is an intermittent hypoxia disorder associated with cognitive dysfunction, including learning and memory impairments. There is evidence that alterations in protease activity and neuronal activation as associated with cognitive dysfunction, are dependent on sex, and may be brain region-specific. However, the mechanisms mediating OSA-induced cognitive impairments are unclear. Therefore, we used a rat model of OSA, chronic intermittent hypoxia (CIH), to investigate protease activity (e.g., calpain and caspase-3) and neuronal activation (early growth response protein 1, EGR-1) in brain regions associated with learning and memory. We used a rat model of OSA known as chronic intermittent hypoxia (CIH) to investigate protease activity (calpain and caspase-3) and neuronal activation (early growth response protein 1, EGR-1) in brain regions associated with learning and memory.

Methods

Male and female Sprague Dawley rats were exposed to CIH or room air (normoxic) for 14 days. We quantified protease activity and cleaved spectrin products, along with EGR-1 protein expression in hippocampal subregions (CA1, CA3), cortical regions [entorhinal cortex (ETC), retrosplenial cortex (RSC), cerebellar cortex (CC)], and subcortical regions [raphe nucleus (RN), locus coeruleus (LC)] associated with learning and memory. Within each group, Pearson correlations of calpain activity, caspase-3 activity, and EGR-1 expression were performed between brain regions. Sex differences within normoxic and CIH correlations were examined.

Results

CIH dysregulated calpain activity in male ETC and female CA1 and RSC. CIH dysregulated caspase-3 activity in male RN and female CA1 and RSC. CIH decreased calpain and caspase-3 cleavage products in male ETC. CIH decreased calpain-cleaved spectrin in male RSC but increased these products in female RSC. EGR-1 expression was decreased in male and female RN. Correlational analysis revealed CIH increased excitatory connections in males and increased inhibitory connections in females. EGR-1 expression in males shifted from negative to positive correlations.

Conclusions

Overall, these data show that CIH dysregulates protease activity and impairs neuronal function in a brain region- and sex-dependent manner. This indicates that males and females exhibit sex-specific vulnerabilities to mild OSA. These findings concur with our previous behavioral studies that demonstrated memory impairment in CIH-exposed rats.

Quercetin prevents the USP22-Snail1 signaling pathway to ameliorate diabetic tubulointerstitial fibrosis

Our previous studies have demonstrated that ubiquitin-specific peptidase 22 (USP22) has the capacity to accelerate renal epithelial-to-mesenchymal transition (EMT) and promote the pathological progression of diabetic tubulointerstitial fibrosis (TIF) by regulating the ubiquitination of Snail1, an EMT transcription factor. Quercetin is a type of flavonol compound widely found in fruits and vegetables that has anti-inflammatory, antioxidant and anti-fibrosis effects. However, whether quercetin promotes the degradation of Snail1 and regulates the pathological progression of TIF by inhibiting USP22 requires further investigation. In this study, we found that quercetin significantly inhibited the expression of USP22 and Snail1 in high glucose (HG)-induced renal tubular epithelial cells (TECs), and reversed the expression of EMT-related proteins and inhibited the overproduction of fibronectin (FN) and Collage Type IV (Collagen IV) induced by high glucose. Additionally, quercetin blocked the deubiquitination of Snail1 mediated by USP22. Further study found that quercetin inhibited the interaction between USP22 and Snail1, thereby reducing the stability of Snail1. Furthermore, quercetin also reduced the protein levels of USP22 and Snail1 in the kidney tissue of diabetic mice and ameliorated renal function, delayed EMT and TIF. In conclusion, quercetin regulates the USP22-Snail1 signal pathway to inhibit the occurrence of EMT both in vitro and in vivo, and ultimately ameliorate the pathological progress of TIF.