PA28αβ overexpression enhances learning and memory of female mice without inducing 20S proteasome activity

Systematic evaluation of multifactorial causal associations for Alzheimer's disease and an interactive platform MRAD developed based on Mendelian randomization analysis

Alzheimer's disease (AD) is a complex degenerative disease of the central nervous system, and elucidating its pathogenesis remains challenging. In this study, we used the inverse-variance weighted (IVW) model as the major analysis method to perform hypothesis-free Mendelian randomization (MR) analysis on the data from MRC IEU OpenGWAS (18,097 exposure traits and 16 AD outcome traits), and conducted sensitivity analysis with six models, to assess the robustness of the IVW results, to identify various classes of risk or protective factors for AD, early-onset AD, and late-onset AD. We generated 400,274 data entries in total, among which the major analysis method of the IVW model consists of 73,129 records with 4840 exposure traits, which fall into 10 categories: Disease, Medical laboratory science, Imaging, Anthropometric, Treatment, Molecular trait, Gut microbiota, Past history, Family history, and Lifestyle trait. More importantly, a freely accessed online platform called MRAD (https://gwasmrad.com/mrad/) has been developed using the Shiny package with MR analysis results. Additionally, novel potential AD therapeutic targets (CD33, TBCA, VPS29, GNAI3, PSME1) are identified, among which CD33 was positively associated with the main outcome traits of AD, as well as with both EOAD and LOAD. TBCA and VPS29 were negatively associated with the main outcome traits of AD, as well as with both EOAD and LOAD. GNAI3 and PSME1 were negatively associated with the main outcome traits of AD, as well as with LOAD, but had no significant causal association with EOAD. The findings of our research advance our understanding of the etiology of AD.

Reduction in PA28αβ activation in HD mouse brain correlates to increased mHTT aggregation in cell models

Huntington's disease is an autosomal dominant heritable disorder caused by an expanded CAG trinucleotide repeat at the N-terminus of the Huntingtin (HTT) gene. Lowering the levels of soluble mutant HTT protein prior to aggregation through increased degradation by the proteasome would be a therapeutic strategy to prevent or delay the onset of disease. Native PAGE experiments in HdhQ150 mice and R6/2 mice showed that PA28αβ disassembles from the 20S proteasome during disease progression in the affected cortex, striatum and hippocampus but not in cerebellum and brainstem. Modulating PA28αβ activated proteasomes in various in vitro models showed that PA28αβ improved polyQ degradation, but decreased the turnover of mutant HTT. Silencing of PA28αβ in cells lead to an increase in mutant HTT aggregates, suggesting that PA28αβ is critical for overall proteostasis, but only indirectly affects mutant HTT aggregation.

Novel function of the C-Terminal region of the Hsp110 family member Osp94 in unfolded protein refolding

Osp94, a member of the Hsp110/Sse1 family of heat shock proteins, has a longer C-terminus than Hsc70/Hsp70, composed of the loop region with partial SBDβ (L), and SBDα and the C-terminal extension (H), but the functions of these domains are poorly understood. Osp94 suppressed heat-induced aggregation of luciferase (Luc). Osp94-bound heat-inactivated Luc was reactivated in the presence of rabbit reticulocyte lysate (RRL) and/or a combination of Hsc70 and Hsp40. Targeted deletion mutagenesis revealed that the SBDβ and H domains of Osp94 are critical for protein disaggregation and RRL-mediated refolding. Reactivation of Hsp90-bound heat-inactivated Luc was abolished in the absence of RRL but compensated by PA28α, a proteasome activator. Interestingly, the LH domain also reactivated heat-inactivated Luc, independent of PA28α. Biotin-tag cross-linking experiments indicated that the LH domain and PA28α interact with Luc bound by Hsp90 during refolding. A chimera protein in which the H domain was exchanged for PA28α also mediated disaggregation and reactivation of heat-inactivated Luc. These results indicate that Osp94 acts as a holdase and that the C-terminal region plays a PA28α-like role in the refolding of unfolded proteins.

Increased expression of PSME2 is associated with clear cell renal cell carcinoma invasion by regulating BNIP3‑mediated autophagy

Previous studies have showed that proteasome activator complex subunit 2 (PSME2) may play a role in some types of cancer. However, the involvement of PSME2 in clear cell renal cell carcinoma (ccRCC) remains unknown. The aim of the present study was to assess the poorly understood function of PSME2 expression in renal carcinoma. Using bioinformatics analysis, PSME2 mRNA expression profiles were investigated, along with its potential prognostic value and its functional enrichment. Signaling pathways and putative hub genes associated with PSME2 in ccRCC were identified. Based on the bioinformatics analysis results, immunohistochemistry of human ccRCC samples and renal carcinoma cell lines (CAKI-1 and 786-O) transfected with short interfering RNA targeting PSME2 were analyzed using western blot analysis, reverse transcription-quantitative PCR, immunofluorescence, and Cell Counting Kit-8, Transwell and transmission electron microscope assays. The results showed that when PSME2 expression was knocked down, the invasive abilities of the tumor cell lines were reduced, while autophagy was enhanced. The present study demonstrated that PSME2 was associated with the invasion ability of ccRCC cell lines by inhibiting BNIP3-mediated autophagy. In summary, PSME2 could be used as a prognostic factor and a promising therapeutic target in ccRCC.

PA28α overexpressing female mice maintain exploratory behavior and capacity to prevent protein aggregation in hippocampus as they age

With age, protein damage accumulates and increases the risk of age-related diseases. The proteasome activator PA28αβ is involved in protein damage clearance during early embryogenesis and has demonstrated protective effects against proteinopathy. We have recently discovered that adult female mice overexpressing PA28α (PA28αOE) have enhanced learning and memory, and protein extracts from their hippocampi prevent aggregation more efficiently than wild type. In this study, we investigated the effect of overexpressing PA28α on aging using C57BL/6N×BALB/c F2 hybrid mice. We found that the hippocampal anti-aggregation effect was maintained in young adult (7 months) to middle-aged (15 months) and old (22 months) PA28αOE females. While the PA28αOE influence on learning and memory gradually decreased with aging, old PA28αOE females did not display the typical drop in explorative behavior-a behavioral hallmark of aging-but were as explorative as young mice. PA28αOE lowered PA28-dependent proteasome capacity in both heart and hippocampus, and there was no indication of lower protein damage load in PA28αOE. The life span of PA28αOE was also similar to wild type. In both wild type and PA28αOE, PA28-dependent proteasome capacity increased with aging in the heart, while 26S and 20S proteasome capacities were unchanged in the timepoints analyzed. Thus, PA28αOE females exhibit improved hippocampal ability to prevent aggregation throughout life and enhanced cognitive capabilities with different behavioral outcomes dependent on age; improved memory at early age and a youth-like exploration at old age. The cognitive effects of PA28αβ combined with its anti-aggregation molecular effect highlight the therapeutical potential of PA28αβ in combating proteinopathies.

An Integrative Pharmacology-Based Pattern to Uncover the Pharmacological Mechanism of Ginsenoside H Dripping Pills in the Treatment of Depression

Objectives: To evaluate the pharmacodynamical effects and pharmacological mechanism of Ginsenoside H dripping pills (GH) in chronic unpredictable mild stress (CUMS) model rats. Methods: First, the CUMS-induced rat model was established to assess the anti-depressant effects of GH (28, 56, and 112 mg/kg) by the changes of the behavioral indexes (sucrose preference, crossing score, rearing score) and biochemical indexes (serotonin, dopamine, norepinephrine) in Hippocampus. Then, the components of GH were identified by ultra-performance liquid chromatography-iron trap-time of flight-mass spectrometry (UPLC/IT-TOF MS). After network pharmacology analysis, the active ingredients of GH were further screened out based on OB and DL, and the PPI network of putative targets of active ingredients of GH and depression candidate targets was established based on STRING database. The PPI network was analyzed topologically to obtain key targets, so as to predict the potential pharmacological mechanism of GH acting on depression. Finally, some major target proteins involved in the predictive signaling pathway were validated experimentally. Results: The establishment of CUMS depression model was successful and GH has antidepressant effects, and the middle dose of GH (56 mg/kg) showed the best inhibitory effects on rats with depressant-like behavior induced by CUMS. Twenty-eight chemical components of GH were identified by UPLC/IT-TOF MS. Subsequently, 20(S)-ginsenoside Rh2 was selected as active ingredient and the PPI network of the 43 putative targets of 20(S)-ginsenoside Rh2 containing in GH and the 230 depression candidate targets, was established based on STRING database, and 47 major targets were extracted. Further network pharmacological analysis indicated that the cAMP signaling pathway may be potential pharmacological mechanism regulated by GH acting on depression. Among the cAMP signaling pathway, the major target proteins, namely, cAMP, PKA, CREB, p-CREB, BDNF, were used to verify in the CUMS model rats. The results showed that GH could activate the cAMP-PKA-CREB-BDNF signaling pathway to exert antidepressant effects. Conclusions: An integrative pharmacology-based pattern was used to uncover that GH could increase the contents of DA, NE and 5-HT, activate cAMP-PKA-CREB-BDNF signaling pathway exert antidepressant effects.

H2O2-induced cataract as a model of age-related cataract: Lessons learned from overexpressing the proteasome activator PA28αβ in mouse eye lens

Cataract, the world-leading cause of blindness, is formed when crystallin aggregates cloud the eye lens. We overexpressed PA28αβ, a proteasome activator with properties protective against aggregation and oxidative stress, and examined whether they are less prone to develop cataract arisen from aging and/or hydrogen peroxide (H₂O₂) treatment. Another objective of this work was to compare the H₂O₂-induced cataracts of mouse lenses ex vivo to cataracts formed upon aging in mice. As part of an aging study of F2 hybrid C57BL/6NxBALB/c mice, ocular lenses of mature adult (7 months), middle-aged (15 months), and old (22 months of age) PA28αOE mice and their wildtype littermates (n = 22-44 lenses per group) were dissected and evaluated with regard to their cataractous state. In parallel, ocular lenses from 3 to 4 months old PA28αOE and wildtype C57BL/6 N littermates were treated with 100 μM H₂O₂ every 24 h for 7 days, with progression of cataract and physical appearance monitored daily. Lenses from both studies were also subjected to analysis of oxidative protein damage (carbonylation) and protein solubility. We found that overexpression of PA28αβ had no effect on neither age-related nor H₂O₂-induced cataract and conclude that overexpression of PA28αβ does not protect mice from developing cataract. The inefficiency of PA28αβ against cataract could be due to its anti-aggregation activity being already excessively present in the eye lens, exerted by crystallins. Crystallins are likely also constituting the 20-25 kDa proteins that were the dominant carbonyl targets in the eye lens irrespective of cataractous state. Assessment of H₂O₂-induced cataract in relation to age-related cataract demonstrated that high molecular weight protein carbonylation correlates to cataract both in vivo and ex vivo, while reduced protein solubility is more pronounced in age-related cataract. Furthermore, this work highlights vast dissimilarities in the physical manifestations of cataract upon aging and H₂O₂ ex vivo treatment. Age-related cataract initiation can take various forms, as a vague general blurriness or as a barely visible demarcated opacity, while H₂O₂-induced cataractogenesis seems to follow a specific scheme. In mice, this scheme begins with relatively opaque peripheral areas emerging that clear up later on as the lenses start to display a hat-like appearance. This transformation takes place synchronous to swelling of the eye lens, and is likely a result of osmotic disturbances causing a phase separation between the viscous lens cortex and the more solid fibers of the lens nucleus.

Exploring the proteasome system: A novel concept of proteasome inhibition and regulation

The proteasome is a well-identified therapeutic target for cancer treatment. It acts as the main protein degradation system in the cell and degrades key mediators of cell growth, survival and function. The term "proteasome" embraces a whole family of distinct complexes, which share a common proteolytic core, the 20S proteasome, but differ by their attached proteasome activators. Each of these proteasome complexes plays specific roles in the control of cellular function. In addition, distinct proteasome interacting proteins regulate proteasome activity in subcellular compartments and in response to cellular signals. Proteasome activators and regulators may thus serve as building blocks to fine-tune proteasome function in the cell according to cellular needs. Inhibitors of the proteasome, e.g. the FDA approved drugs Velcade™, Kyprolis™, Ninlaro™, inactivate the catalytic 20S core and effectively block protein degradation of all proteasome complexes in the cell resulting in inhibition of cell growth and induction of apoptosis. Efficacy of these inhibitors, however, is hampered by their pronounced cytotoxic side-effects as well as by the emerging development of resistance to catalytic proteasome inhibitors. Targeted inhibition of distinct buiding blocks of the proteasome system, i.e. proteasome activators or regulators, represents an alternative strategy to overcome these limitations. In this review, we stress the importance of the diversity of the proteasome complexes constituting an entire proteasome system. Our building block concept provides a rationale for the defined targeting of distinct proteasome super-complexes in disease. We thereby aim to stimulate the development of innovative therapeutic approaches beyond broad catalytic proteasome inhibition.

Effect of olive oil consumption on aging in a senescence-accelerated mice-prone 8 (SAMP8) model

Background : Mediterranean diets have been linked to a reduced risk of cancer, vascular illnesses, Parkinson's and Alzheimer's disease. Olive oil is the primary fat source in the Mediterranean diet ; however, only a few studies have investigated the effect of olive oil on aging. In the present study, we aimed to determine whether consumption of olive oil significantly influences aging and memory in senescence-accelerated mouse-prone 8 (SAMP8). Methods : SAMP8 and senescence-accelerated mouse resistant 1 (SAMR1) mice were fed either 7% soy oil or 1% olive oil and 6% soy oil during a six-month study period. Reduction in memory in passive avoidance learning was examined after two months from the initiation of the experiment. Results : The weight of organs including the liver, kidney, spleen, and fat tissue changed significantly and memory performance was reduced in SAMP8 than in SAMR1 mice. There were no significant differences in SAMP8 and SAMR1 mice; however, blood triglyceride level decreased significantly in SAMP8 mice fed on olive oil. Conclusions : These results suggest that consuming olive oil may not have a protective role in aging and memory recall, but beneficial effects may be related to improvement in lipid metabolism. J. Med. Invest. 66 : 241-247, August, 2019.

Conclusions from a behavioral aging study on male and female F2 hybrid mice on age-related behavior, buoyancy in water-based tests, and an ethical method to assess lifespan

Due to strain-specific behavioral idiosyncrasies, inbred mouse strains are suboptimal research models for behavioral aging studies. The aim of this study is to determine age-related behavioral changes of F2 hybrid C57BL/6NxBALB/c male and female mice. Lifespan was followed (n_males=48, n_females=51) and cohorts of mature adult (7 months), middle-aged (15 months), and old mice (22 months of age; n=7-12 per group) were assessed regarding open-field activity, exploration, passive avoidance learning/memory, and depressive-like behavior. We found that both males and females demonstrated decreased exploratory behavior with age, while memory and depressive-like behavior were maintained. Females exhibited enhanced depressive-like behavior compared to males; however, a correlation between fat mass and swimming activity in the test directly accounted for 30-46% of this behavioral sex difference. In addition, we suggest a method to qualitatively estimate natural lifespan from survival analyses in which animals with signs of pain or severe disease are euthanized. This is, to our knowledge, the first behavioral study to consider both sex and aging in hybrid mice. We here define decreased exploratory behavior as a conserved hallmark of aging independent of sex, highlight the effect of buoyancy in water tests, and provide a method to assay lifespan with reduced animal suffering.

Regulation of Proteasome Activity by (Post-)transcriptional Mechanisms

Intracellular protein synthesis, folding, and degradation are tightly controlled processes to ensure proper protein homeostasis. The proteasome is responsible for the degradation of the majority of intracellular proteins, which are often targeted for degradation via polyubiquitination. However, the degradation rate of proteins is also affected by the capacity of proteasomes to recognize and degrade these substrate proteins. This capacity is regulated by a variety of proteasome modulations including (1) changes in complex composition, (2) post-translational modifications, and (3) altered transcription of proteasomal subunits and activators. Various diseases are linked to proteasome modulation and altered proteasome function. A better understanding of these modulations may offer new perspectives for therapeutic intervention. Here we present an overview of these three proteasome modulating mechanisms to give better insight into the diversity of proteasomes.