Background Knee osteoarthritis (KOA) is a degenerative joint disease characterized by progressive cartilage degradation, in which chondrocyte apoptosis plays a pivotal role. Acupuncture is widely used for KOA management, but its underlying molecular mechanisms remain poorly understood. Endoplasmic reticulum (ER) stress-induced apoptosis via the c-Jun N-terminal kinase (JNK) pathway is a critical driver of chondrocyte death in KOA. This study aimed to investigate whether acupuncture exerts its chondroprotective effects by modulating the ER stress-JNK signaling axis. Methods A rat model of KOA was established by joint immobilization. Fifty rats were randomly assigned to five groups: Normal, Model, Model+Acupuncture (Acu), Model+ Acu+Anisomycin(JNK activator), and Model+SP600125(JNK inhibitor). The therapeutic efficacy of a 4-week acupuncture regimen was evaluated through behavioral scores, radiographic imaging, and histological analysis. Unbiased RNA-sequencing was performed to identify key signaling pathways. The mechanism was further validated through TUNEL staining, Transmission electron microscopy (TEM), Western blot, RTqPCR, immunofluorescence, and ELISA. Results Unbiased transcriptomic analysis identified the ER stress and MAPK/JNK signaling pathways as key targets of acupuncture. Acupuncture significantly improved joint function, alleviated cartilage degradation, and preserved proteoglycan content in KOA rats. Mechanistically, acupuncture suppressed the expression of the ER stress marker IRE1α, inhibited the phosphorylation of JNK, and consequently downregulated the pro-apoptotic Bax/Bcl-2 ratio and Caspase-3 expression. This led to a marked decrease in chondrocyte apoptosis and restoration of ER homeostasis, as confirmed by TUNEL and TEM. Crucially, the anti-apoptotic effects of acupuncture were significantly counteracted by the JNK activator Anisomycin. In addition, acupuncture remodels the systemic inflammatory network by suppressing the production of proinflammatory cytokines IL-1β and TNF-α, which triggers a compensatory upregulation of the anti-inflammatory mediator IL-10. Conclusion Our findings demonstrate for the first time that acupuncture ameliorates knee osteoarthritis by inhibiting chondrocyte apoptosis via suppression of the ER stress-JNK signaling pathway. This study provides a novel and robust mechanistic rationale for the clinical application of acupuncture and highlights the ER stress-JNK axis as a promising therapeutic target for KOA.
In our previous report, PERK/NRF2/CX43/StAR/progesterone pathway activation in ovarian granulosa cells was shown to mediate cold-induced female reproductive disorders. However, how PERK is activated by low temperature remained unclear. In the present study, we found that the circadian protein E4BP4 was significantly upregulated in ovarian granulosa cells following exposure to cold or isoproterenol (ISO), a non-selective β-adrenergic receptor agonist that pharmacologically activates β-adrenergic signaling, a key component of the cold stress response. Mechanistically, E4BP4 interacted with PERK and was required for PERK activation and subsequent NRF2/CX43/StAR signaling, leading to increased progesterone secretion. Interestingly, NRF2 also acted as a transcriptional activator of E4BP4 under ISO treatment, and blocking PERK or NRF2 expression attenuated ISO-induced E4BP4 accumulation, suggesting a positive feedback loop involving PERK/NRF2/E4BP4. Collectively, these findings identify E4BP4 as a cold-responsive circadian protein that interacts with PERK and may contribute to cold-induced reproductive disorders via a bidirectional E4BP4-PERK feedback loop.
Background Epichaperomes are stable, stress-induced supramolecular assemblies formed through extensive integration of molecular chaperones, co-chaperones, signaling proteins, and client proteins. Although increasing evidence indicates that epichaperomes act as organizational hubs that coordinate proteostasis and signaling networks in cancer, neurodegenerative disorders, and chronic inflammatory diseases, their potential physical roles in cellular organization remain largely unexplored. Results Here, the Epichaperome Matrix Theory, a systems-level theoretical framework that conceptualizes the epichaperome as a dynamic, nonequilibrium biomolecular matrix possessing emergent transport-regulatory properties is proposed. In this model, epichaperome assemblies generate heterogeneous electrostatic landscapes through the collective distribution of charged amino acid residues, phosphorylation-dependent charge accumulation, ATP-driven conformational dynamics, and high-order network connectivity. By integrating principles from Poisson-Boltzmann electrostatics, Nernst-Planck transport theory, active matter physics, percolation theory, graph theory, biomolecular condensate thermodynamics, and porous hydrogel transport models, a mathematical description in which epichaperomes function as adaptive organizational scaffolds capable of influencing molecular flux, signaling efficiency, and spatial coordination within cells is developed. This framework is further extended through the Transcellular Epichaperome Continuum Hypothesis, proposing that intracellular epichaperomes may be functionally coupled to plasma membrane-associated and extracellular epichaperome assemblies, forming a multiscale organizational network spanning individual cells, tissues, and organ systems. In this extended model, membrane-bound epichaperomes act as coupling interfaces between intracellular and extracellular compartments, while secreted chaperones, extracellular vesicles, and extracellular protein assemblies contribute to intercellular connectivity. Mathematical analysis predicts the emergence of percolating transport networks, electrostatic coupling domains, synchronized conformational dynamics, and stress-responsive communication pathways when epichaperome connectivity exceeds critical thresholds. Conclusions The proposed framework suggests that epichaperomes may represent more than stress-associated protein interaction networks and could function as dynamic organizational matrices integrating molecular organization, signaling, and adaptive responses across multiple biological scales. Although the theory remains speculative and currently lacks direct experimental validation, it generates testable predictions regarding membrane-associated epichaperomes, extracellular epichaperome assemblies, electrostatic organization, and intercellular transport behaviors. By providing a unified theoretical foundation linking stress biology, chaperone networks, systems biology, and biophysics, this work expands the conceptual landscape of epichaperome research and identifies new directions for investigating the role of higher-order chaperome organization in health and disease.
The essential molecular chaperone CCT/TRiC, found in the cytosol of all eukaryotes, has long been established as the molecular chaperone required for folding the abundant cytoskeletal components actin and tubulin. Advances in single-molecule imaging, cryoelectron microscopy, and the availability of extensive omics data contribute to revealing the functional scope of this multi-subunit assembly. This review focuses on how the regulation of CCT assembly and degradation of subunits contributes to the complex interplay between CCT oligomer and monomeric subunit functions and the implications of this for cancer cell biology and during impaired proteostasis.
Mechanical ventilation is a key respiratory support measure for critically ill patients. During improper ventilation, continuous exposure of alveolar epithelial cells (AECs) to abnormal mechanical environment can lead to ventilator-induced lung injury (VILI). Heat shock transcription factor 1 (HSF1) is a stress-responsive transcriptional regulator that orchestrates cytoprotective heat shock protein (HSP) expression in response to diverse stresses, including thermal and oxidative stress, but its role in stretch-induced AEC injury remains unclear. In this study, A549 cells were subjected to biaxial cyclic stretch to model mechanical stress associated with VILI in vitro. Consistent with the established role of YAP as a mechanotransduction regulator activated by cyclic stretch, we observed YAP signaling activation in our biaxial stretch system. Transcriptomic analysis revealed that mechanical stretch markedly induced the expression of HSP genes, and subsequent validation confirmed that stretch activated HSF1 and increased HSF1-dependent HSP expression. Pharmacological inhibition of HSF1 with DTHIB or CRISPR-Cas9-mediated HSF1 knockout attenuated stretch-induced HSP expression, while exacerbating ROS accumulation, cell death, and IL-6 production. Moreover, oxidative-stress-associated HSF1 targets were significantly enriched among stretch-induced genes, antioxidant treatment partially suppressed stretch-induced HSF1 activation, and HSF1 knockout increased oxidative stress after stretch. These findings indicate that HSF1 functions as an endogenous cytoprotective feedback mechanism in mechanically stretched AECs by inducing HSP expression and limiting stretch-induced oxidative damage and inflammatory injury. Activation of the HSF1-HSP axis may therefore represent a potential strategy for mitigating epithelial injury during VILI.
Microplastics (MPs) are ubiquitously detected in aquatic ecosystems and represent a growing environmental concern due to their persistence, accumulative toxicity, and ability to cross biological barriers, posing substantial risks to fish species. Although numerous studies have investigated the toxicity of MPs in fish, there is limited data on the potential toxic effects of MP exposure at the cellular level. In this study, we aimed to compare the cellular toxicity of polystyrene MPs of different shapes and sizes in fin and muscle cells derived from marine (red sea bream: PMF) and freshwater (fathead minnow: FHM) fish. Our results showed that exposure to MPs of various shapes and sizes did not cause significant changes in cell viability in either cell line. No significant differences were observed, although exposure to spherical MPs (1 μm) induced a decrease in cell viability at relatively high concentrations. The cellular uptake of MPs was observed following exposure to spherical MPs (0.2 and 1 μm), with internalization occurring at 6 h for 1 μm and 24 h for 0.2 μm of incubation. Internalization efficiency was higher for 1 μm MPs than for 0.2 μm MPs. Exposure to spherical MPs (0.2 and 1 μm) induced alterations in intracellular ROS levels and triggered the up-regulation of the NRF2 gene, a transcription factor involved in the stress response. The expression of pro-inflammatory cytokines, including TNF-α and IL1-β, was increased by exposure to spherical MPs (0.2 and 1 μm). In addition, this exposure changed the transcriptional responses of immune defense-related genes. Overall, our results suggest that acute exposure to spherical MPs (0.2 and 1 μm) may be related to the disruption of the immune defense system through continuous inflammation at the cellular level in fish, although it does not directly affect cell viability.
While the cardioprotective role of heat shock proteins (HSPs) in cardiovascular diseases is well established, the isoform-specific functions of HSP70 members in ischemia-reperfusion (I/R) injury remain unclear. This study investigates the role of Hspa1b, a stress-inducible HSP70 isoform, in cardiac I/R injury and elucidates its underlying mechanisms. In vivo, male C57BL/6 J mice were subjected to myocardial I/R surgery. In vitro, H9C2 cardiomyocytes were transfected with siRNA targeting Hspa1b or p53 and subjected to a hypoxia/reoxygenation (H/R) model. Cellular injury was quantified via lactate dehydrogenase (LDH) release, while viability was assessed using the CCK-8 assay. Apoptotic (Bax, Bcl2, and cleaved Caspase3) and ferroptotic (GPX4, XCT/SLC7A11) markers were analyzed by Western blotting. We found that I/R injury in mouse hearts upregulated Hspa1b and p53 protein levels, accompanied by increased infarct size and elevated plasma CK-MB levels. Similarly, H/R treatment in H9C2 cells increased Hspa1b and p53, which coincided with increased apoptosis and ferroptosis. Knockdown of Hspa1b exacerbated H/R-induced cellular injury, as evidenced by further increases in LDH release and reductions in cell viability, and amplified the changes in apoptotic and ferroptotic markers. Crucially, co-silencing Hspa1b and p53 partially rescued these effects, restoring cell viability and suppressing death pathways. Hspa1b confers cardioprotection against H/R injury by suppressing p53-mediated apoptosis and ferroptosis. These findings identify Hspa1b as a key protective regulator that mitigates I/R injury through dual regulation of cell death pathways.
Hsp90 inhibitors represent a decades-long experimental framework that has progressively uncovered how molecular chaperone systems are organized, regulated, and rewired in disease. Early natural products established that pharmacologic engagement of Hsp90 simultaneously destabilizes broad client networks and exposes a central layer of proteostasis control. Subsequent structural, biochemical, and translational studies revealed the mechanistic importance of nucleotide-driven conformational cycling, cochaperone exchange, paralog specialization, and subcellular compartmentalization, as well as the emergence of disease-specific chaperone assemblies such as the epichaperome. In parallel, adaptive responses to Hsp90 inhibition, including heat-shock factor 1 activation, unfolded-protein-response signaling, autophagy induction, and oncogenic network rewiring, illuminated the resilience built into proteostasis architecture and the conditions under which it can be overcome. Later inhibitor classes, encompassing C-terminal allosteric ligands, middle-domain modulators, isoform-selective agents, epichaperome-directed compounds, and targeted degraders, extended the field from pan-inhibition toward increasingly precise intervention in specific chaperone states. The first regulatory approval of an Hsp90 inhibitor, Pimitespib, for refractory gastrointestinal stromal tumor, marks a translational milestone that validates this framework clinically. Combination studies have further mapped where Hsp90 inhibition is most informative and most effective, demonstrating that benefit is strongest when deployment is guided by defined client dependency, proteostasis burden, immune context, or biomarker selection. Together, these advances position Hsp90 inhibitor research as a major source of mechanistic insight into molecular chaperones and as a foundation for biomarker-guided, context-aware targeting of proteostasis in oncology and beyond.
The R2TP chaperone complex comprises two AAA+ proteins, RUVBL1 and RUVBL2, along with RPAP3 and PIH1D1. R2TP functions in concert with other chaperones, such as HSP90 and HSP70, to facilitate the assembly of macromolecular complexes integral to the regulation of cell growth and proliferation. Moreover, several adaptors interact with R2TP to impart substrate specificity. Nevertheless, the precise mechanism underlying R2TP-mediated complex assembly remains unknown. This review summarizes the current knowledge regarding R2TP’s involvement in the assembly, stabilization, and activity of multiple protein complexes, including box C/D and H/ACA small nucleolar ribonucleoproteins (snoRNPs), spliceosome small nuclear ribonucleoproteins (snRNPs), the tuberous sclerosis complex (TSC) , axonemal dynein arms, RNA polymerases, phosphatidylinositol 3-kinase-related kinases (PIKK), and the MRE11-RAD50-NBS1 (MRN) complex. Additionally, the role of R2TP in ciliogenesis, circadian rhythm regulation, and transcriptional condensate formation is discussed. Finally, the latest structural studies pertaining to R2TP and its related complexes are examined.
Originally J-domain proteins (JDPs) were viewed as accessory co-chaperones of 70 kDa heat shock proteins (Hsp70s), the actual chaperones, stimulating ATPase activity of Hsp70s when a protein substrate is bound. This view apparently underestimates the role of JDPs, as most of the decisions within the Hsp70 network seems to be taken at the level of JDPs. The JDPs are the brain, so to speak, and the Hsp70s are the muscles of this chaperone network.
The Hsp90 molecular chaperone is a key component of the protein homeostasis (proteostasis) system. Hsp90 likely serves as a gatekeeper in a cell's protein quality control decision tree since this chaperone is linked to nascent polypeptide folding, client maturation, metastable protein maintenance, and polypeptide degradation. Interestingly, how a client protein is directed through the decision process is unclear. Minimally, modifications to the amino-terminal ATP-binding domain of Hsp90 can favor client degradation. As this includes a common class of Hsp90 inhibitors that trigger the breakdown of clinically relevant factors, a better understanding of Hsp90's role in quality control is merited. Here, we explore how Hsp90 links to both polypeptide biogenesis and triage, the events that regulate the decision route, and how Hsp90's connections to proteolysis pathways are being exploited for the development of new therapeutics.
The 9th Birt-Hogg-Dubé (BHD) International Symposium convened virtually in March 2026. The meeting attracted more than 100 participants internationally and highlighted recent findings in a variety of areas, including genetic insight and molecular understanding of BHD syndrome, also known as the Hornstein-Knickenberg syndrome, structure and function of the tumor suppressor Folliculin (FLCN), therapeutic and clinical advances, as well as patient experiences living with this disease.
BACKGROUND & HYPOTHESIS:The 70 kDa heat shock protein family (HSP70) preserves the three-dimensional integrity of intracellular proteins, preventing the formation of cytotoxic aggregates that activate inflammatory pathways. Both constitutive and stress-inducible HSP70 isoforms uphold proteostasis during the heat shock response (HSR), an evolutionarily conserved, anti-inflammatory mechanism that restores cellular homeostasis following proteotoxic stress and metabolic disruption. Under conditions threatening homeostasis-such as heat shock (HS) and physical exertion, in which the sympathetic nervous system is strongly activated-HSP70 may be secreted into the extracellular space, where it functions as an immunomodulator and pro-inflammatory danger signal. Chronic inflammatory conditions, including obesity and type 2 diabetes, are characterized by persistently elevated levels of extracellular HSP70 in the bloodstream, which correlate with insulin resistance and β-cell dysfunction. Notably, glucose ingestion blocks exercise-induced HSP70 secretion, suggesting a previously unrecognized role of extracellular HSP70 in modulating glycaemia via insulin binding. RESULTS:Here we show a novel counterregulatory mechanism in which plasma HSP70 binds insulin with high affinity (Kd ∼3 pM), impairing glucose uptake in insulin-dependent tissues without affecting receptor signaling. In fasted rats subjected to HS, elevated plasma HSP70 raises glycaemia by ∼3 mM during glucose tolerance tests (at 30 min), enhancing glucose availability for non-insulin-dependent tissues. HS-induced glucose intolerance peaks 12 h post-HS in an HSP70-interacting protein (HIP)-dependent manner. However, HS enhances the insulinogenic index (IGI) and insulin sensitivity, peaking at 24 h. CONCLUSION:This observation challenges the paradigm that HSP70 functions to chaperone proteins solely intracellularly, revealing its role in extracellular glycaemic regulation by HIP-assisted protein-protein interactions in blood plasma, thus offering a novel clinical viewpoint in glycaemic management. TRANSLATIONAL PERSPECTIVES:These findings suggest that humanized anti-HSP70 monoclonal antibodies could mitigate insulin sequestration and offer a novel therapeutic strategy to restore insulin sensitivity, thereby improving metabolic outcomes in conditions with elevated plasma HSP70, such as type 2 diabetes, obesity, non-alcoholic fatty liver disease, and cardiovascular disease.
Hsp90 is a dimeric molecular chaperone essential for the maturation, activation, stabilization and folding of numerous clients required for cellular functions. Hsp90 progresses through a dynamic ATP-driven conformational cycle that is precisely regulated by accessory proteins known as co-chaperones. Here, we show that the isolated N-domain of Aha1 (Aha1N156) binds the apo state of Hsp90 but fails to associate with the closed, nucleotide-bound state. In contrast, the full-length Aha1 binds Hsp90 in both conformational states, suggesting a key role for the Aha1 C domain in binding to the nucleotide-bound, closed state of Hsp90. Surprisingly, the Aha1 paralogue Hch1, which corresponds to the Aha1 N domain, was capable of binding to Hsp90 in both the apo and nucleotide-bound states. Interestingly, the addition of a 14 amino acid residues section of the linker to the Aha1 N domain restores closed-state binding, indicating an unexpected role for the linker in stabilizing nucleotide-dependent interactions. Analysis of yeast-human Aha1 chimeras further demonstrates that the C-terminal domain of Aha-type co-chaperones serves as an evolutionarily conserved anchoring module, enabling stable engagement of the ATP-bound state despite significant sequence divergence. This work allows us to propose a model in which the Aha1 C domain allows for the repositioning of the Aha1 N domain that occurs during the transition from the apo to the ATP-bound state of Hsp90.
Pre-mRNA splicing produces intron lariats that must be cleaved at their internal 2-5' phosphodiester bond by the debranching endonuclease DBR1. While human DBR1 (hDBR1) is established as the lariat debranching enzyme, how it interfaces with broader RNA metabolic pathways is less clear. Using chemical inhibition of splicing, we show that DBR1 expression correlates with splicing activity. We then mapped the hDBR1 interactome by immunopurification coupled to mass spectrometry using complementary gel-based and on-bead workflows. hDBR1 associates with the spliceosome and intron-turnover factors, and with RNA quality-control proteins, including UPF1, XRN2, and the RNA helicase DHX29. RNase A treatment identifies an RNA-dependent subnetwork enriched for stress-granule proteins and hnRNPs, linking hDBR1 to RNA surveillance during stress. Comparison with BioGRID indicates that most detected associations were not previously reported. Finally, phosphoproteomic profiling reveals multiple hDBR1 phosphorylation sites, including four residues preferentially detected after RNase treatment, suggesting regulatory modifications that may tune hDBR1 interactions or activity. Together, these data expand the functional landscape of hDBR1 across splicing, intron turnover, and RNA quality control.
Maintenance of protein homeostasis, also known as proteostasis, is essential for cellular survival under both basal and stress conditions. Proteostasis relies on a coordinated action between molecular chaperones, such as heat shock proteins (HSPs), and stress-responsive transcription factors. HSP90 is an abundant and functionally central ATP-dependent chaperone that supports the stability and function of a great variety of client proteins, while specific members of the heat shock factor (HSF) family orchestrate transcriptional programs in cells exposed to proteotoxic stress. According to the established chaperone titration model, HSP90, together with other chaperones, represses the master regulator HSF1 by maintaining it in an inactive monomeric state. Emerging evidence, however, indicates that also other HSFs, especially HSF2, can form a complex with HSP90 and contribute to constitutive and stress-inducible HSP gene regulation, thereby expanding the HSF1-centric view of the chaperone titration model. This review discusses the current understanding of the HSP90-HSF interplay and highlights the recent advances in targeting HSP90 for therapeutic purposes. Together, these insights underscore the HSP90-HSF axis as a regulatory hub of proteostasis in health and disease.
