ERAD components Derlin-1 and Derlin-2 are essential for postnatal brain development and motor function

Mitochondria-associated endoplasmic reticulum membrane as a mediator of vanadium-induced endoplasmic reticulum quality control in duck brains

Vanadium (V) plays a crucial role in normal cells, but excess V causes multi-organ toxicity, including neurotoxicity. Mitochondria-associated endoplasmic reticulum membrane (MAM) is a dynamic structure between endoplasmic reticulum (ER) and mitochondria that mediates ER quality control (ERQC). To explore the effects of excess V on MAM and ERQC in the brain, 72 ducks were randomly divided into two groups: the control group (basal diet) and the V group (30 mg V/kg basal diet). On days 22 and 44, brain tissues were collected for histomorphological observation and determination of trace element contents. In addition, the mRNA and protein levels of MAM and ERQC-related factors in the brain were analyzed. Results show that excessive V causes the imbalance of trace elements, the integrity disruption of MAM, rupture of ER and autophagosomes formation. Moreover, it inhibits IP3R and VDAC1 co-localization, down-regulates the expression levels of MAM-related factors, but up-regulates the expression levels of ERQC and autophagy related factors. Together, results indicate that V exposure causes disruption of MAM and activates ERQC, which is further causing autophagy.

Hypomorphic human SEL1L and HRD1 variants uncouple multilayered ER-associated degradation machinery

The suppressor of lin-12-like-HMG-CoA reductase degradation 1 (SEL1L-HRD1) complex of the endoplasmic reticulum-associated degradation (ERAD) machinery is a key cellular proteostasis pathway. Although previous studies have shown ERAD as promoting the development and maintenance of many cell types in mice, its importance to human physiology remained undetermined. In two articles in this issue of the JCI, Qi and colleagues describe four biallelic hypomorphic SEL1L and HRD1 variants that were associated with neurodevelopment disorders, locomotor dysfunction, impaired immunity, and premature death in patients. These pathogenic SEL1L-HRD1 variants shine a light on the critical importance of ERAD in humans and pave the way for future studies dissecting ERAD mechanisms in specific cell types.

Changes in the liver of Tinca tinca under successive domestication using an integrated multi-omics approach

Domestication is the process of modifying the phenotype of a population through anthropic selection from human perspectives. Successive generations of domestication have influenced the physiological characteristics of tench Tinca tinca. In current study, we investigated gene and protein expression alterations in the liver of fifth-generation (F5). A total of 420 genes were found to be upregulated and 351 genes were downregulated, while 410 proteins were upregulated and 279 proteins were downregulated in domesticated T. tinca (DT). The integrated analysis of omics data revealed a total of 55 genes/proteins exhibiting consistent upregulation and 12 genes/proteins displaying consistent downregulation in DT. The upregulated genes/proteins in DT, such as SSR1, DERLIN2, OS9, DNAJB11, and HYOU1, exhibit enrichment in the protein processing in the endoplasmic reticulum pathway. Additionally, upregulated genes/proteins such as IL2RB, F13B, and IRF3 are associated with immune response. Conversely, downregulated genes/proteins in DT, including HSD11B1, CYP24A1, and COMT, play roles in hormone metabolism. These findings indicate that domestication can have a substantial impact on the physiological modifications related to protein processing, immune response, and hormone metabolism in DT. These adaptations potentially enhance their ability to thrive in artificial aquaculture environments, leading to improved growth and development. The exploration of genetic changes in DT will not only improve aquaculture practices but also provide significant insights into the broader process of domestication and its effects on physiological functions.

Genetic disruption of mammalian endoplasmic reticulum-associated protein degradation: Human phenotypes and animal and cellular disease models

Endoplasmic reticulum-associated protein degradation (ERAD) is a stringent quality control mechanism through which misfolded, unassembled and some native proteins are targeted for degradation to maintain appropriate cellular and organelle homeostasis. Several in vitro and in vivo ERAD-related studies have provided mechanistic insights into ERAD pathway activation and its consequent events; however, a majority of these have investigated the effect of ERAD substrates and their consequent diseases affecting the degradation process. In this review, we present all reported human single-gene disorders caused by genetic variation in genes that encode ERAD components rather than their substrates. Additionally, after extensive literature survey, we present various genetically manipulated higher cellular and mammalian animal models that lack specific components involved in various stages of the ERAD pathway.

The Role of the Rhomboid Superfamily in ER Protein Quality Control: From Mechanisms and Functions to Diseases

The endoplasmic reticulum (ER) is an essential organelle in eukaryotic cells and is a major site for protein folding, modification, and lipid synthesis. Perturbations within the ER, such as protein misfolding and high demand for protein folding, lead to dysregulation of the ER protein quality control network and ER stress. Recently, the rhomboid superfamily has emerged as a critical player in ER protein quality control because it has diverse cellular functions, including ER-associated degradation (ERAD), endosome Golgi-associated degradation (EGAD), and ER preemptive quality control (ERpQC). This breadth of function both illustrates the importance of the rhomboid superfamily in health and diseases and emphasizes the necessity of understanding their mechanisms of action. Because dysregulation of rhomboid proteins has been implicated in various diseases, such as neurological disorders and cancers, they represent promising potential therapeutic drug targets. This review provides a comprehensive account of the various roles of rhomboid proteins in the context of ER protein quality control and discusses their significance in health and disease.

Chemical chaperones ameliorate neurodegenerative disorders in Derlin-1-deficient mice via improvement of cholesterol biosynthesis

There are no available therapies targeting the underlying molecular mechanisms of neurodegenerative diseases. Although chaperone therapies that alleviate endoplasmic reticulum (ER) stress recently showed promise in the treatment of neurodegenerative diseases, the detailed mechanisms remain unclear. We previously reported that mice with central nervous system-specific deletion of Derlin-1, which encodes an essential component for ER quality control, are useful as models of neurodegenerative diseases such as spinocerebellar degeneration. Cholesterol biosynthesis is essential for brain development, and its disruption inhibits neurite outgrowth, causing brain atrophy. In this study, we report a novel mechanism by which chemical chaperones ameliorate brain atrophy and motor dysfunction. ER stress was induced in the cerebella of Derlin-1 deficiency mice, whereas the administration of a chemical chaperone did not alleviate ER stress. However, chemical chaperone treatment ameliorated cholesterol biosynthesis impairment through SREBP-2 activation and simultaneously relieved brain atrophy and motor dysfunction. Altogether, these findings demonstrate that ER stress may not be the target of action of chaperone therapies and that chemical chaperone-mediated improvement of brain cholesterol biosynthesis is a promising novel therapeutic strategy for neurodegenerative diseases.

Regulation of Derlin-1-mediated degradation of NADPH oxidase partner p22phox by thiol modification

The transmembrane protein p22^phox heterodimerizes with NADPH oxidase (Nox) 1–4 and is essential for the reactive oxygen species-producing capacity of oxidases. Missense mutations in the p22^phox gene prevent the formation of phagocytic Nox2-based oxidase, which contributes to host defense. This results in chronic granulomatous disease (CGD), a severe primary immunodeficiency syndrome. In this study, we characterized missense mutations in p22^phox (L51Q, L52P, E53V, and P55R) in the A22° type (wherein the p22^phox protein is undetectable) of CGD. We demonstrated that these substitutions enhanced the degradation of the p22^phox protein in the endoplasmic reticulum (ER) and the binding of p22^phox to Derlin-1, a key component of ER-associated degradation (ERAD). Therefore, the L⁵¹-L⁵²-E⁵³-P⁵⁵ sequence is responsible for protein stability in the ER. We observed that the oxidation of the thiol group of Cys-50, which is adjacent to the L⁵¹-L⁵²-E⁵³-P⁵⁵ sequence, suppressed p22^phox degradation. However, the suppression effect was markedly attenuated by the serine substitution of Cys-50. Blocking the free thiol of Cys-50 by alkylation or C50S substitution promoted the association of p22^phox with Derlin-1. Derlin-1 depletion partially suppressed the degradation of p22^phox mutant proteins. Furthermore, heterodimerization with p22^phox (C50S) induced rapid degradation of not only Nox2 but also nonphagocytic Nox4 protein, which is responsible for redox signaling. Thus, the redox-sensitive Cys-50 appears to determine whether p22^phox becomes a target for degradation by the ERAD system through its interaction with Derlin-1.

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Missense mutations in exon 3 of p22^phox enhance the binding of p22^phox to Derlin-1.

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Oxidation of the thiol group of p22^phox Cys50 suppresses p22^phox degradation.

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Serine substitution of Cys-50 increases the affinity of p22^phox for Derlin-1.

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Stability of the p22^phox protein is regulated by redox-sensitive Cys-50.

GPHR-mediated acidification of the Golgi lumen is essential for cholesterol biosynthesis in the brain

The Golgi pH regulator (GPHR) is essential for maintaining the function and morphology of the Golgi apparatus through the regulation of luminal acidic pH. Abnormal morphology of the Golgi apparatus is associated with neurodegenerative diseases. Here, we found that knockout of GPHR in the mouse brain led to morphological changes in the Golgi apparatus and neurodegeneration, which included brain atrophy, neuronal cell death, and gliosis. Furthermore, in the GPHR knockout mouse brain, transcriptional activity of sterol regulatory element-binding protein 2 (SREBP2) decreased, resulting in a reduction in cholesterol levels. GPHR-deficient cells exhibited suppressed neurite outgrowth, which was recovered by exogenous expression of the active form of SREBP2. Our results show that GPHR-mediated luminal acidification of the Golgi apparatus maintains proper cholesterol levels and, thereby, neuronal morphology.

miRNA Expression Is Increased in Serum from Patients with Semantic Variant Primary Progressive Aphasia

Primary progressive aphasia (PPA) damages the parts of the brain that control speech and language. There are three clinical PPA variants: nonfluent/agrammatic (nfvPPA), logopenic (lvPPA) and semantic (svPPA). The pathophysiology underlying PPA variants is not fully understood, including the role of micro (mi)RNAs which were previously shown to play a role in several neurodegenerative diseases. Using a two-step analysis (array and validation through real-time PCR), we investigated the miRNA expression pattern in serum from 54 PPA patients and 18 controls. In the svPPA cohort, we observed a generalized upregulation of miRNAs with miR-106b-5p and miR-133a-3p reaching statistical significance (miR-106b-5p: 2.69 ± 0.89 mean ± SD vs. 1.18 ± 0.28, p < 0.0001; miR-133a-3p: 2.09 ± 0.10 vs. 0.74 ± 0.11 mean ± SD, p = 0.0002). Conversely, in lvPPA, the majority of miRNAs were downregulated. GO enrichment and KEGG pathway analyses revealed that target genes of both miRNAs are involved in pathways potentially relevant for the pathogenesis of neurodegenerative diseases. This is the first study that investigates the expression profile of circulating miRNAs in PPA variant patients. We identified a specific miRNA expression profile in svPPA that could differentiate this pathological condition from other PPA variants. Nevertheless, these preliminary results need to be confirmed in a larger independent cohort.