LMP2 Inhibitors as a Potential Treatment for Alzheimer’s Disease

Synthesis and Application of a Versatile Immunoproteasome Activity Probe

The immunoproteasome (iCP) has gained significant interest in recent years as it has been discovered to be significantly expressed under inflammatory conditions, as well as playing significant roles in several diseases, such as autoimmune disorders, viral infection, and cancer. Selective inhibitors have been generated as a method to overcome the off-target effects of current proteasome inhibitor therapeutics. However, selective probes that allow for monitoring this protein complex remain limited, hindering our understanding of the iCP. Current probes are non-selective, not commercially available, or require difficult synthesis. Here, we describe the modular synthesis and application of an iCP-selective probe. The modular nature of the synthetic strategy can enable the incorporation of different fluorophores and covalent warheads, demonstrating the versatility of this probe.

Targeting Microglial Immunoproteasome: A Novel Approach in Neuroinflammatory-Related Disorders

It is widely acknowledged that the aging process is linked to the accumulation of damaged and misfolded proteins. This phenomenon is accompanied by a decrease in proteasome (c20S) activity, concomitant with an increase in immunoproteasome (i20S) activity. These changes can be attributed, in part, to the chronic neuroinflammation that occurs in brain tissues. Neuroinflammation is a complex process characterized by the activation of immune cells in the central nervous system (CNS) in response to injury, infection, and other pathological stimuli. In certain cases, this immune response becomes chronic, contributing to the pathogenesis of various neurological disorders, including chronic pain, Alzheimer's disease, Parkinson's disease, brain traumatic injury, and others. Microglia, the resident immune cells in the brain, play a crucial role in the neuroinflammatory response. Recent research has highlighted the involvement of i20S in promoting neuroinflammation, increased activity of which may lead to the presentation of self-antigens, triggering an autoimmune response against the CNS, exacerbating inflammation, and contributing to neurodegeneration. Furthermore, since i20S plays a role in breaking down accumulated proteins during inflammation within the cell body, any disruption in its activity could lead to a prolonged state of inflammation and subsequent cell death. Given the pivotal role of i20S in neuroinflammation, targeting this proteasome subtype has emerged as a potential therapeutic approach for managing neuroinflammatory diseases. This review delves into the mechanisms of neuroinflammation and microglia activation, exploring the potential of i20S inhibitors as a promising therapeutic strategy for managing neuroinflammatory disorders.

Brain-Permeable Immunoproteasome-Targeting Macrocyclic Peptide Epoxyketones for Alzheimer's Disease

Previously, we demonstrated that linear peptide epoxyketones targeting the immunoproteasome (iP) could ameliorate cognitive deficits in mouse models of Alzheimer's disease (AD) independently of amyloid deposition. We also reported the first iP-targeting macrocyclic peptide epoxyketones, which exhibit improved metabolic stability compared with their linear counterparts. Here, we prepared additional macrocyclic peptide epoxyketones and compared them with existing macrocyclic iP inhibitors by assessing Caco2 cell-based permeability and microsomal stability, providing the four best macrocyclic iP inhibitors. We then evaluated the four compounds using the Ames test and the potency assays in BV2 cells, selecting compound 5 as our AD drug lead. When 5 was administered intravenously (40 mg/kg) or orally (150 mg/kg) into healthy BALB/c mice, we observed considerable iP inhibition in the mouse brain, indicating good blood-brain barrier permeability and target engagement. Combined results suggest that 5 is a promising AD drug lead that may need further investigation.

Inhibition of Immunoproteasome Attenuates NLRP3 Inflammasome Response by Regulating E3 Ubiquitin Ligase TRIM31

Excessive secretion of pro-inflammatory cytokines leads to the disruption of intestinal barrier in inflammatory bowel disease (IBD). The inflammatory cytokine tumor necrosis factor alpha (TNFα) induces the assembly of the NLRP3 inflammasome, resulting in the augmented secretion of inflammatory cytokines implicated in the pathogenesis of inflammatory bowel disease (IBD). TNFα has also been known to induce the formation of immunoproteasome (IP), which incorporates immunosubunits LMP2, LMP7, and MECL-1. Inhibition of IP activity using the IP subunit LMP2-specific inhibitor YU102, a peptide epoxyketone, decreased the protein levels of NLRP3 and increased the K48-linked polyubiquitination levels of NLRP3 in TNFα-stimulated intestinal epithelial cells. We observed that inhibition of IP activity caused an increase in the protein level of the ubiquitin E3 ligase, tripartite motif-containing protein 31 (TRIM31). TRIM31 facilitated K48-linked polyubiquitination and proteasomal degradation of NLRP3 with an enhanced interaction between NLRP3 and TRIM31 in intestinal epithelial cells. In addition, IP inhibition using YU102 ameliorated the symptoms of colitis in the model mice inflicted with dextran sodium sulfate (DSS). Administration of YU102 in the DSS-treated colitis model mice caused suppression of the NLRP3 protein levels and accompanied inflammatory cytokine release in the intestinal epithelium. Taken together, we demonstrated that inhibiting IP under inflammatory conditions induces E3 ligase TRIM31-mediated NLRP3 degradation, leading to attenuation of the NLRP3 inflammatory response that triggers disruption of intestinal barrier.

Ubiquitin E3 ligases assisted technologies in protein degradation: Sharing pathways in neurodegenerative disorders and cancer

E3 ligases, essential components of the ubiquitin-proteasome-mediated protein degradation system, play a critical role in cellular regulation. By covalently attaching ubiquitin (Ub) molecules to target proteins, these ligases mark them for degradation, influencing various bioprocesses. With over 600 E3 ligases identified, there is a growing realization of their potential as therapeutic candidates for addressing proteinopathies in cancer and neurodegenerative disorders (NDDs). Recent research has highlighted the need to delve deeper into the intricate roles of E3 ligases as nexus points in the pathogenesis of both cancer and NDDs. Their dysregulation is emerging as a common thread linking these seemingly disparate diseases, necessitating a comprehensive understanding of their molecular intricacies. Herein, we have discussed (i) the fundamental mechanisms through which different types of E3 ligases actively participate in selective protein degradation in cancer and NDDs, followed by an examination of common E3 ligases playing pivotal roles in both situations, emphasising common players. Moving to, (ii) the functional domains and motifs of E3 ligases involved in ubiquitination, we have explored their interactions with specific substrates in NDDs and cancer. Additionally, (iii) we have explored techniques like PROTAC, molecular glues, and other state-of-the-art methods for hijacking neurotoxic and oncoproteins. Lastly, (iv) we have provided insights into ongoing clinical trials, offering a glimpse into the evolving landscape of E3-based therapeutics for cancer and NDDs. Unravelling the intricate network of E3 ligase-mediated regulation holds the key to unlocking targeted therapies that address the specific molecular signatures of individual patients, heralding a new era in personalized medicines.

Identification of differentially expressed exosome proteins in serum as potential biomarkers for cognitive impairments in cerebral small vessel disease

BACKGROUND

Cognitive impairment arising from cerebral small vessel disease (CSVD) represents a critical subtype of vascular cognitive impairments (VCI) and is the primary cause of vascular dementia. However, identifying reliable clinical and laboratory indicators for this disease remain elusive. We hypothesize that plasma exosome proteins hold the potential to serve as biomarkers for the onset of cognitive dysfunction associated with cerebrovascular diseases.

METHODS

We employed TMT-based proteomics to discern variations in serum exosome proteomes between individuals with cognitive impairments due to CSVD and healthy volunteers.

RESULTS

Each group comprised 18 subjects, and through differential expression analysis, we identified 22 down-regulated and 8 up-regulated proteins between the two groups. Our research revealed 30 differentially expressed plasma exosome proteins, including histone, proteasome, clusterin and coagulation factor XIII, in individuals with cognitive impairments caused by CSVD.

CONCLUSION

The 30 differentially expressed plasma exosome proteins identified in our study are promising as biomarkers for diagnosing cognitive impairments resulting from CSVD. These findings may help us better understand the underlying pathological mechanisms involved in the diseases.

Immunoproteasome Subunit Low Molecular Mass Peptide 2 (LMP2) Deficiency Ameliorates LPS/Aβ1-42-Induced Neuroinflammation

Low molecular mass peptide 2 (LMP2) is the β1i subunit of immunoproteasome (iP) which plays a key role in neuroinflammatory responses, and inhibition of iP exhibits a high neuroprotective action against neurodegenerative diseases. Since neuroinflammation has been shown to be involved in the development and progression of Alzheimer's disease (AD), the aim of this study was to evaluate the anti-inflammatory role of LMP2 deficiency in AD in vivo and in vitro. Here, we found that LMP2 was upregulated in the brains of 5 × FAD and APP/PS1 mice and increased with age in C57/BL6 mice. We showed that the lack of LMP2 significantly decreased NLRP3 expression and downstream cytokine release in microglia, resulting in partially blocking Aβ1-42- or LPS-induced inflammation in vivo and in vitro, which ameliorated cognitive deficits in aged rats and D-galactose + Aβ1-42-treated rats. These results suggest that LMP2 contributes to the regulation of LPS-or Aβ-driven innate immune responses by diminishing NLRP3 expression and clarify that inhibition of iP function may mediate the inflammatory-related cognitive phenotype.

Photochemical Desaturation and Epoxidation with Oxygen by Sequential Flavin Catalysis

Catalytic desaturations are important strategies for the functionalization of organic molecules. In nature, flavoenzymes mediate the formation of α,β-unsaturated carbonyl compounds by concomitant cofactor reduction. Contrary to many laboratory methods for these reactions, such as the Saegusa-Ito oxidation, no transition metal reagents or catalysts are required. However, a molecular flavin-mediated variant has not been reported so far. We disclose a photochemical approach for silyl enol ether oxidation, which leads to α,β-unsaturated ketones (13 examples) in very good yields. The flavin catalysts are stable throughout the desaturation reaction, and we successfully applied them in a subsequent aerobic epoxidation by simply changing the reaction conditions. This protocol allowed us to directly convert silyl enol ethers into α,β-epoxyketones in a one-pot fashion (12 examples). Sequential flavin catalysis is not limited to one specific reactivity combination and can, inter alia, couple the photochemical oxidation with radical additions. We anticipate that flavin-catalyzed desaturation will be applicable to other substrate classes and that its sequential catalytic activity will enable rapid substrate diversification.

[Alzheimer's disease, amyloid-b peptides and ubiquitin-proteasome system: Therapeutic perspectives]

The Alzheimer's disease - an age-related neurodegenerative disorder leading to a progressive cognitive impairment - is characterized by an intracerebral accumulation of soluble β-amyloid (Aβ) oligomers, followed by the appearance of abnormally ubiquitinylated neurofibrillary tangles - a process associated with a chronic inflammation. The systematic presence of ubiquitinylated inclusions reflects a decrease in the proteasome activity due to (and contributing to) the presence of Aβ oligomers - a central dysfunction in the etiology of the disease. The involvement of the ubiquitin-proteasome system opens new therapeutic perspectives for both prevention and treatment.

LMP2 deficiency causes abnormal metabolism, oxidative stress, neuroinflammation, myelin loss and neurobehavioral dysfunctions

BACKGROUND

Substantial evidence suggests that immunoproteasome is implicated in the various neurological diseases such as stroke, multiple sclerosis and neurodegenerative diseases. However, whether the immunoproteasome itself deficiency causes brain disease is still unclear. Therefore, the aim of this study was to explore the contribution of the immunoproteasome subunit low molecular weight protein 2 (LMP2) in neurobehavioral functions.

METHODS

Male LMP2 gene completed knockout (LMP2-KO) and littermate wild type (WT) Sprague-Dawley (SD) rats aged 12-month-old were used for neurobehavioral testing and detection of proteins expression by western blotting and immunofluorescence. A battery of neurobehavioral test tools including Morris water maze (MWM), open field maze, elevated plus maze were used to evaluate the neurobehavioral changes in rats. Evans blue (EB) assay, Luxol fast blue (LFB) and Dihydroethidium (DHE) staining were applied to explore the blood-brain barrier (BBB) integrity, brain myelin damage and brain intracellular reactive oxygen species (ROS) levels, respectively.

RESULTS

We firstly found that LMP2 gene deletion did not cause significantly difference in rats' daily feeding activity, growth and development as well as blood routine, but it led to metabolic abnormalities including higher levels of low-density lipoprotein cholesterol, uric acid and blood glucose in the LMP2-KO rats. Compared with the WT rats, LMP2-KO rats displayed obviously cognitive impairment and decreased exploratory activities, increased anxiety-like behavior and without strong effects on gross locomotor abilities. Furthermore, multiple myelin loss, increased BBB leakage, downregulation of tight junction proteins ZO-1, claudin-5 and occluding, and enhanced amyloid-β protein deposition were observed in brain regions of LMP2-KO rats. In addition, LMP2 deficiency significantly enhanced oxidative stress with elevated levels of ROS, caused the reactivation of astrocytes and microglials and markedly upregulated protein expression levels of interleukin (IL)-1 receptor-associated kinase 1 (IRAK1), IL-6 and tumor necrosis factor-α (TNF-α) compared to the WT rats, respectively.

CONCLUSION

These findings highlight LMP2 gene global deletion causes significant neurobehavioral dysfunctions. All these factors including metabolic abnormalities, multiple myelin loss, elevated levels of ROS, increased BBB leakage and enhanced amyloid-β protein deposition maybe work together and eventually led to chronic oxidative stress and neuroinflammation response in the brain regions of LMP2-KO rats, which contributed to the initial and progress of cognitive impairment.

Targeting immunoproteasome in neurodegeneration: A glance to the future

The immunoproteasome is a specialized form of proteasome equipped with modified catalytic subunits that was initially discovered to play a pivotal role in MHC class I antigen processing and immune system modulation. However, over the last years, this proteolytic complex has been uncovered to serve additional functions unrelated to antigen presentation. Accordingly, it has been proposed that immunoproteasome synergizes with canonical proteasome in different cell types of the nervous system, regulating neurotransmission, metabolic pathways and adaptation of the cells to redox or inflammatory insults. Hence, studying the alterations of immunoproteasome expression and activity is gaining research interest to define the dynamics of neuroinflammation as well as the early and late molecular events that are likely involved in the pathogenesis of a variety of neurological disorders. Furthermore, these novel functions foster the perspective of immunoproteasome as a potential therapeutic target for neurodegeneration. In this review, we provide a brain and retina-wide overview, trying to correlate present knowledge on structure-function relationships of immunoproteasome with the variety of observed neuro-modulatory functions.

Inhibition of immunoproteasome attenuates NLRP3 inflammasome formation in tumor necrosis factor α-stimulated intestinal epithelial cell

Excessive release of inflammatory cytokines has been considered as a major cause of chronic inflammation, resulting in intestinal barrier disruption that leads to inflammatory bowel disease (IBD). Tumor necrosis factor α (TNFα) is one of the well-known inflammatory cytokines that activates formation of NLRP3 inflammasome, thus resulting in excessive secretion of inflammatory cytokines causing IBD. Although immunoproteasome inhibitors have been reported to inhibit inflammatory cytokine release, immunoproteasome inhibition has not yet been addressed for attenuation of NLRP3 inflammasome activity in intestinal epithelial cell. Here, we observed that NLRP3 inflammasome assembly was attenuated by peptide epoxyketone YU102, a LMP2 subunit immunoproteasome inhibitor, in intestinal epithelial cell. YU102 also inhibited maturation of active caspase-1 and secretion of IL-1β, which are subsequent inflammatory cascade after the formation of NLRP3 inflammasome. Progression of epithelial-mesenchymal transition and increase of cellular permeability, which were induced by TNFα, were also suppressed through inhibition of immunoproteasome. Furthermore, we found that YU102 does not inhibit degradation of IкBα and its following NF-кB activation that leads to transcription of NLRP3. These findings suggest that inhibition of immunoproteasome with YU102 offers a potential therapeutic premise for prevention of TNFα-induced chronic inflammation through attenuation of NLRP3 inflammasome assembly.

Site-Specific Proteasome Inhibitors

Proteasome is a multi-subunit protein degradation machine, which plays a key role in the maintenance of protein homeostasis and, through degradation of regulatory proteins, in the regulation of numerous cell functions. Proteasome inhibitors are essential tools for biomedical research. Three proteasome inhibitors, bortezomib, carfilzomib, and ixazomib are approved by the FDA for the treatment of multiple myeloma; another inhibitor, marizomib, is undergoing clinical trials. The proteolytic core of the proteasome has three pairs of active sites, β5, β2, and β1. All clinical inhibitors and inhibitors that are widely used as research tools (e.g., epoxomicin, MG-132) inhibit multiple active sites and have been extensively reviewed in the past. In the past decade, highly specific inhibitors of individual active sites and the distinct active sites of the lymphoid tissue-specific immunoproteasome have been developed. Here, we provide a comprehensive review of these site-specific inhibitors of mammalian proteasomes and describe their utilization in the studies of the biology of the active sites and their roles as drug targets for the treatment of different diseases.

On the Role of the Immunoproteasome in Protein Homeostasis

Numerous cellular processes are controlled by the proteasome, a multicatalytic protease in the cytosol and nucleus of all eukaryotic cells, through regulated protein degradation. The immunoproteasome is a special type of proteasome which is inducible under inflammatory conditions and constitutively expressed in hematopoietic cells. MECL-1 (β2i), LMP2 (β1i), and LMP7 (β5i) are the proteolytically active subunits of the immunoproteasome (IP), which is known to shape the antigenic repertoire presented on major histocompatibility complex (MHC) class I molecules. Furthermore, the immunoproteasome is involved in T cell expansion and inflammatory diseases. In recent years, targeting the immunoproteasome in cancer, autoimmune diseases, and transplantation proved to be therapeutically effective in preclinical animal models. However, the prime function of standard proteasomes and immunoproteasomes is the control of protein homeostasis in cells. To maintain protein homeostasis in cells, proteasomes remove proteins which are not properly folded, which are damaged by stress conditions such as reactive oxygen species formation, or which have to be degraded on the basis of regular protein turnover. In this review we summarize the latest insights on how the immunoproteasome influences protein homeostasis.

A Cell-Based Platform for the Investigation of Immunoproteasome Subunit β5i Expression and Biology of β5i-Containing Proteasomes

The degradation of most intracellular proteins is a dynamic and tightly regulated process performed by proteasomes. To date, different forms of proteasomes have been identified. Currently the role of non-constitutive proteasomes (immunoproteasomes (iPs) and intermediate proteasomes (intPs)) has attracted special attention. Here, using a CRISPR-Cas9 nickase technology, four cell lines: histiocytic lymphoma, colorectal adenocarcinoma, cervix adenocarcinoma, and hepatocarcinoma were modified to express proteasomes with mCherry-tagged β5i subunit, which is a catalytic subunit of iPs and intPs. Importantly, the expression of the chimeric gene in modified cells is under the control of endogenous regulatory mechanisms and is increased following IFN-γ and/or TNF-α stimulation. Fluorescent proteasomes retain catalytic activity and are distributed within the nucleus and cytoplasm. RNAseq reveals marginal differences in gene expression profiles between the modified and wild-type cell lines. Predominant metabolic pathways and patterns of expressed receptors were identified for each cell line. Using established cell lines, we demonstrated that anti-cancer drugs Ruxolitinib, Vincristine and Gefitinib stimulated the expression of β5i-containing proteasomes, which might affect disease prognosis. Taken together, obtained cell lines can be used as a platform for real-time studies of immunoproteasome gene expression, localization of iPs and intPs, interaction of non-constitutive proteasomes with other proteins, proteasome trafficking and many other aspects of proteasome biology in living cells. Moreover, the established platform might be especially useful for fast and large-scale experiments intended to evaluate the effects of different conditions including treatment with various drugs and compounds on the proteasome pool.

Macrocyclic Immunoproteasome Inhibitors as a Potential Therapy for Alzheimer's Disease

Previously, we reported that immunoproteasome (iP)-targeting linear peptide epoxyketones improve cognitive function in mouse models of Alzheimer's disease (AD) in a manner independent of amyloid β. However, these compounds' clinical prospect for AD is limited due to potential issues, such as poor brain penetration and metabolic instability. Here, we report the development of iP-selective macrocyclic peptide epoxyketones prepared by a ring-closing metathesis reaction between two terminal alkenes attached at the P2 and P3/P4 positions of linear counterparts. We show that a lead macrocyclic compound DB-60 (20) effectively inhibits the catalytic activity of iP in ABCB1-overexpressing cells (IC50: 105 nM) and has metabolic stability superior to its linear counterpart. DB-60 (20) also lowered the serum levels of IL-1α and ameliorated cognitive deficits in Tg2576 mice. The results collectively suggest that macrocyclic peptide epoxyketones have improved CNS drug properties than their linear counterparts and offer promising potential as an AD drug candidate.

A Nut for Every Bolt: Subunit-Selective Inhibitors of the Immunoproteasome and Their Therapeutic Potential

At the heart of the ubiquitin-proteasome system, the 20S proteasome core particle (CP) breaks down the majority of intracellular proteins tagged for destruction. Thereby, the CP controls many cellular processes including cell cycle progression and cell signalling. Inhibitors of the CP can suppress these essential biological pathways, resulting in cytotoxicity, an effect that is beneficial for the treatment of certain blood cancer patients. During the last decade, several preclinical studies demonstrated that selective inhibition of the immunoproteasome (iCP), one of several CP variants in mammals, suppresses autoimmune diseases without inducing toxic side effects. These promising findings led to the identification of natural and synthetic iCP inhibitors with distinct chemical structures, varying potency and subunit selectivity. This review presents the most prominent iCP inhibitors with respect to possible scientific and medicinal applications, and discloses recent trends towards pan-immunoproteasome reactive inhibitors that cumulated in phase II clinical trials of the lead compound KZR-616 for chronic inflammations.

Discovery of selective fragment-sized immunoproteasome inhibitors

Proteasomes contribute to maintaining protein homeostasis and their inhibition is beneficial in certain types of cancer and in autoimmune diseases. However, the inhibition of the proteasomes in healthy cells leads to unwanted side-effects and significant effort has been made to identify inhibitors specific for the immunoproteasome, especially to treat diseases which manifest increased levels and activity of this proteasome isoform. Here, we report our efforts to discover fragment-sized inhibitors of the human immunoproteasome. The screening of an in-house library of structurally diverse fragments resulted in the identification of benzo[d]oxazole-2(3H)-thiones, benzo[d]thiazole-2(3H)-thiones, benzo[d]imidazole-2(3H)-thiones, and 1-methylbenzo[d]imidazole-2(3H)-thiones (with a general term benzoXazole-2(3H)-thiones) as inhibitors of the chymotrypsin-like (β5i) subunit of the immunoproteasome. A subsequent structure-activity relationship study provided us with an insight regarding growing vectors. Binding to the β5i subunit was shown and selectivity against the β5 subunit of the constitutive proteasome was determined. Thorough characterization of these compounds suggested that they inhibit the immunoproteasome by forming a disulfide bond with the Cys48 available specifically in the β5i active site. To obtain fragments with biologically more tractable covalent interactions, we performed a warhead scan, which yielded benzoXazole-2-carbonitriles as promising starting points for the development of selective immunoproteasome inhibitors with non-peptidic scaffolds.

Role of immunoproteasomes and thymoproteasomes in health and disease

The proteasome is a multisubunit protease that degrades intracellular proteins into small peptides. Besides playing a pivotal role in many cellular processes indispensable for survival, it is involved in the production of peptides presented by major histocompatibility complex class I molecules. In addition to the standard proteasome shared in all eukaryotes, jawed vertebrates have two specialized forms of proteasome known as immunoproteasomes and thymoproteasomes. The immunoproteasome, which contains cytokine-inducible catalytic subunits with distinct cleavage specificities, produces peptides presented by class I molecules more efficiently than the standard proteasome. The thymoproteasome, which contains a unique catalytic subunit β5t, is a tissue-specific proteasome expressed exclusively in cortical thymic epithelial cells. It plays a critical role in CD8⁺ cytotoxic T cell development via positive selection. This review provides a brief overview on the structure and function of these specialized forms of proteasome and their involvement in human disease.

Recent insights how combined inhibition of immuno/proteasome subunits enables therapeutic efficacy

The proteasome is a multicatalytic protease in the cytosol and nucleus of all eukaryotic cells that controls numerous cellular processes through regulated protein degradation. Proteasome inhibitors have significantly improved the survival of multiple myeloma patients. However, clinically approved proteasome inhibitors have failed to show efficacy against solid tumors, neither alone nor in combination with other therapies. Targeting the immunoproteasome with selective inhibitors has been therapeutically effective in preclinical models for several autoimmune diseases and colon cancer. Moreover, immunoproteasome inhibitors prevented the chronic rejection of allogeneic organ transplants. In recent years, it has become apparent that inhibition of one single active center of the proteasome is insufficient to achieve therapeutic benefits. In this review we summarize the latest insights how targeting multiple catalytically active proteasome subunits can interfere with disease progression in autoimmunity, growth of solid tumors, and allograft rejection.

Immunoproteasome in IgA Nephropathy: State-of-Art and Future Perspectives

IgA nephropathy (IgAN) is a leading cause of chronic kidney disease and renal failure. The exact pathogenesis of IgAN is not well defined, but some genetic studies have led to a novel discovery that the immunoproteasome probably plays an important role in IgAN. The immunoproteasome is a proteasome variant that is expressed when cells are stressed or receive inflammatory signals. While immunoproteasome is suggested to be mainly involved in major histocompatibility complex-I (MHC-I) antigen presentation, recent studies indicate that it may assert broad functions in trafficking events that activate both innate and adaptive immunity. In this review, we first summarize new insights into its functions in immunity, and discuss how it underlies its associations with IgAN. We also highlight its potential as a therapeutic target for the future.