TL;DR
In insights on the research regarding therapeutic approaches of NDs which intend to target molecular components, a general understanding of proteostasis, ER stress, UPR signalling and how these cellular processes are related to neurodegeneration is provided.
Disrupted protein homeostasis is a shared characteristic in ageing, obesity-induced lipotoxicity and neurodegenerative diseases. The accumulation of misfolded or unfolded proteins within the cell triggers endoplasmic reticulum (ER) stress. In response, the unfolded protein response (UPR) and ER-associated degradation (ERAD) pathways are activated. A key mechanism to alleviate intracellular protein aggregation involves ubiquitination of substrates and their subsequent degradation by the proteasome. The ubiquitin-proteasome system (UPS) is indispensable for cellular protein quality control, and its dysfunction contributes to various proteopathies. However, the crosstalk between the proteasome subunit Rpt3 and the Ire1-Hac1 pathway appears to be rarely reported. In Saccharomyces cerevisiae, growth curve and spotting assay demonstrated that overexpression of Rpt3 reduced the sensitivity of ire1Δ or hac1Δ to ER stressors. The growth-promoting effect of Rpt3 is not a common feature of the BASE subunits, as overexpression of Rpt6 failed to rescue the growth inhibition. Deletion of hac1 resulted in stoichiometric imbalance among proteasomal subunits, which may be key for Rpt3-mediated rescue of hac1Δ growth, as deletion of the proteasome transcriptional factor Rpn4 impedes Rpt3 from restoring the growth of hac1Δ from ER stress. Overexpression of Rpt3 enhanced proteasome assembly and activity, reducing intracellular ubiquitin levels in hac1Δ. Moreover, Rpt3 increased the protein level of Hac1, and its alleviation of proteotoxic stress was dependent on the collaboration of ubiquitinating enzymes and chaperones. Western blot and proteasome activity assay in human cells confirmed the cross-species conservation of Rpt3 function. These results highlight a dual role for Rpt3 in proteostasis: beyond enhancing proteasomal activity, Rpt3 upregulates Hac1 protein abundance, thereby ensuring proteostasis maintenance.
Parkinson's disease (PD) is a common neurodegenerative disorder. It is characterized by the progressive loss of dopaminergic neurons in the midbrain substantia nigra and the abnormal aggregation of α-synuclein. In recent years, ERS and the triggered UPR have been identified as a central role connecting multiple pathogenic factors in PD. This review systematically elaborates on the key pathological roles and molecular mechanisms of ERS in PD. In PD, various factors including genetic mutations, environmental toxins, and oxidative stress can disrupt ER homeostasis. These disruptions activate the UPR, which is mediated by the PERK, IRE1α, and ATF6 signaling pathways. A moderate UPR aims to restore cellular homeostasis. However, persistent or severe ERS can switch irreversibly to pro-apoptotic pathways, leading to neuronal death. More importantly, ERS interacts extensively with other PD-related pathological processes. It forms complex positive feedback loops with other core pathological processes in PD. These processes include the abnormal aggregation and propagation of α-synuclein, mitochondrial dysfunction, neuroinflammation, and impaired autophagic flux. Together, they drive the progressive neurodegeneration. Given its central role, targeting ERS has become a potential therapeutic strategy. This article focuses on discussing various intervention approaches, their research progress, and associated challenges. These include: UPR pathway-specific modulators; chemical chaperones; enhancers of protein degradation systems; existing drugs and natural products with ERS-modulating effects; neurotrophic factors and gene therapy; and traditional Chinese medicine. Finally, we discuss future research directions, including developing central nervous system-selective drugs, utilizing precision medicine for personalized treatment, and exploring combination therapies. The aim is to provide new perspectives for disease-modifying treatments of PD.
This review summarizes the key receptors, regulatory mechanisms, and the latest research on ER-phagy in various inflammation-related diseases, aiming to draw academic attention to the important value of ER-phagy in inflammatory diseases.
Various cellular stressors inhibit translation initiation and promote ribosome disassembly, thereby transiently inducing stress granules (SGs), dynamic ribonucleoprotein condensates that contain mRNAs and RNA-binding proteins. Although SG assembly is usually reversible, dysregulated SG dynamics can trigger the formation of persistent ubiquitin-positive protein inclusions. There is increasing evidence that this conversion of SGs into insoluble aggregates represents a central pathogenic mechanism in neurodegenerative proteinopathies, such as amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD). TAR DNA-binding protein 43 (TDP-43) and Tau are causative factors in ALS and AD, respectively, and both localize to SGs under stress conditions. During disease progression, TDP-43 or Tau within SGs undergoes pathological changes that promote the formation of neurotoxic inclusions, which propagate neuronal dysfunction and death. This review summarizes recent advances in understanding the molecular factors that regulate SG assembly and disassembly, as well as the pathological processes that drive the conversion of SGs into aggregates associated with neurodegenerative diseases. Particular emphasis is placed on the role of the ubiquitin-specific protease 10 (USP10), which modulates SG dynamics and has been mechanistically implicated in both ALS and AD. Finally, we discuss the therapeutic potential of targeting these pathways to mitigate neurodegenerative disease progression.
