Beyond the cell factory: Homeostatic regulation of and by the UPRER

Tubular ER structures shaped by ER-phagy receptors engage in stress-induced Golgi bypass

Cellular stresses, particularly endoplasmic reticulum (ER) stress induced by ER-to-Golgi transport blockade, trigger Golgi-independent secretion of cytosolic and transmembrane proteins. However, the molecular mechanisms underlying this unconventional protein secretion (UPS) remain largely elusive. Here, we report that an ER tubulovesicular structure (ER tubular body [ER-TB]), shaped by the tubular ER-phagy receptors ATL3 and RTN3L, plays an important role in stress-induced UPS of transmembrane proteins such as cystic fibrosis transmembrane conductance regulator (CFTR) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. Correlative light-electron microscopy analyses demonstrate the formation of ER-TB under UPS-inducing conditions in HEK293 and HeLa cells. Individual gene knockdowns of ATL3 and RTN3 inhibit ER-TB formation and the UPS of trafficking-deficient ΔF508-CFTR. Combined supplementation of ATL3 and RTN3L induces ER-TB formation and UPS. ATL3 also participates in the SARS-CoV-2-associated convoluted membrane formation and Golgi-independent trafficking of SARS-CoV-2 spike protein. These findings suggest that ER-TB serves a common function in mediating stress-induced UPS, which participates in various physiological and pathophysiological processes.

Dysfunctional RNA binding protein induced neurodegeneration is attenuated by inhibition of the integrated stress response

Dysfunction of the RNA binding protein heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) contributes to neurodegeneration, the primary cause of permanent disability in multiple sclerosis (MS). To better understand the role of hnRNP A1 dysfunction in the pathogenesis of neurodegeneration, we utilized optogenetics-driven hnRNP A1 clustering to model its dysfunction in neuron-like differentiated Neuro-2A cells. hnRNP A1 clustering activates the integrated stress response (ISR) and results in a neurodegenerative phenotype marked by decreased neuronal protein translation and neurite loss. Small molecule inhibition of the ISR with either PERKi (GSK2606414) or ISRIB (integrated stress response inhibitor) attenuated both the decrease in neuronal translation and neurite loss, without affecting hnRNP A1 clustering. We then confirmed a strong association between hnRNP A1 clustering and ISR activation in neurons from MS brains. These data illustrate that hnRNP A1 dysfunction promotes neurodegeneration by activation of the ISR in vitro and in vivo, thus revealing a novel therapeutic target to reduce neurodegeneration and subsequent disability in MS.

Regulation and function of endoplasmic reticulum autophagy in neurodegenerative diseases

The endoplasmic reticulum, a key cellular organelle, regulates a wide variety of cellular activities. Endoplasmic reticulum autophagy, one of the quality control systems of the endoplasmic reticulum, plays a pivotal role in maintaining endoplasmic reticulum homeostasis by controlling endoplasmic reticulum turnover, remodeling, and proteostasis. In this review, we briefly describe the endoplasmic reticulum quality control system, and subsequently focus on the role of endoplasmic reticulum autophagy, emphasizing the spatial and temporal mechanisms underlying the regulation of endoplasmic reticulum autophagy according to cellular requirements. We also summarize the evidence relating to how defective or abnormal endoplasmic reticulum autophagy contributes to the pathogenesis of neurodegenerative diseases. In summary, this review highlights the mechanisms associated with the regulation of endoplasmic reticulum autophagy and how they influence the pathophysiology of degenerative nerve disorders. This review would help researchers to understand the roles and regulatory mechanisms of endoplasmic reticulum-phagy in neurodegenerative disorders.

Endoplasmic reticulum stress regulates apoptosis and chemotherapeutic via enhancing TNFRSF10B recycling to the cell membrane in triple-negative breast cancer

BACKGROUND

Triple-negative breast cancer (TNBC) is the most common malignant tumor in China. The expression and cell surface levels of TNF receptor superfamily member 10B (TNFRSF10B) are associated with apoptosis and chemotherapy. However, the precise molecular mechanisms that govern the regulation of TNFRSF10B remain unclear.

MATERIALS AND METHODS

RNA-Seq data related to TNBC chemotherapy resistance were acquired from the GEO database. The mRNA and protein levels of TNFRSF10B were detected using RT-PCR and Western blotting, respectively. Cell Counting Kit-8 (CCK-8) and colony formation assays were used to detect cell proliferation. Annexin V/7-AAD staining was used to evaluate apoptosis. The cell membrane TNFRSF10B was analyzed by Western blotting and immunofluorescence. Inducers and inhibitors of endoplasmic reticulum stress (ERS) were used to assess the effect of ERS on TNFRSF10B localization.

RESULTS

TNFRSF10B expression was downregulated in TNBC and was associated with prognosis. TNFRSF10B overexpression inhibits the growth of TNBC both in vivo and in vitro and can partially counteract chemotherapy resistance. ERS activation in TNBC promotes the expression of TNFRSF10B, leading to its enrichment on the cell membrane surface, thereby activating the apoptotic pathways.

CONCLUSION

ERS regulates the expression and subcellular localization of TNFRSF10B in TNBC cells. They synergistically affect anti-apoptosis and chemotherapy resistance in TNBC cells.

The Kaposi sarcoma herpesvirus control of monocytes, macrophages, and the tumour microenvironment

Kaposi sarcoma herpesvirus (KSHV) is an oncogenic DNA virus associated with various malignancies, including tumours like Kaposi sarcoma and Primary effusion lymphoma. Recently, the importance of the tumour microenvironment in KSHV-associated tumours is being studied. New studies utilizing human primary cells, co-culture experiments with KSHV-infected cells, and modern techniques like time-resolved single cell analysis, have significantly advanced the understanding of KSHV interactions with monocytes and macrophages. These cells play key roles in shaping the tumour microenvironment. It has become clear that KSHV-infected endothelial cells regulate the growth and the differentiation of monocytes and macrophages. Monocytes and macrophages, in turn, can regulate KSHV-infected cells in tumorigenesis and cytokine secretion, leading to the pro-tumour microenvironment. Further investigations into the viral regulation of monocytes and macrophages thus have potential to lead to the discovery of novel antitumour therapeutics.

Melatonin Ameliorates Organellar Calcium Homeostasis, Improving Endoplasmic Reticulum Stress-Mediated Apoptosis in the Vastus Lateralis Muscle of Both Sexes of Obese Diabetic Rats

Endoplasmic reticulum (ER) stress is a crucial factor in the progression of obesity-related type 2 diabetes (diabesity), contributing to skeletal muscle (SKM) dysfunction, calcium imbalance, metabolic inflexibility, and muscle atrophy. The ER and mitochondria together regulate intracellular calcium levels, and melatonin, a natural compound with antioxidant properties, may alleviate these challenges. Our previous research showed that melatonin raises intracellular calcium and preserves muscle structure by enhancing mitochondrial function in obese diabetic rats. This study further explores melatonin's potential to reduce ER stress in the vastus lateralis (VL) muscle by modulating the unfolded protein response (UPR) and restoring calcium levels disrupted by diabesity. Five-week-old Zücker diabetic fatty (ZDF) rats and lean littermates of both sexes were divided into control and melatonin-treated groups (10 mg/kg/day for 12 weeks). Flame atomic absorption spectrometry results showed that melatonin restored VL intraorganellar calcium homeostasis, increasing calcium levels in mitochondria and reducing them in the ER by raising the activity and expression of calcium transporters in both sexes of ZDF rats. Melatonin also decreased ER stress markers (GRP78, ATF6, IRE1α, and PERK) and reduced pro-apoptosis markers (Bax, Bak, P-JNK, cleaved caspase 3 and 9) while increasing Bcl2 levels and melatonin receptor 2 (MT2) expression. These findings suggest that melatonin may protect against muscle atrophy in obese and diabetic conditions by mitigating ER stress and calcium imbalance, highlighting its therapeutic potential.

Endoplasmic reticulum stress induces renal fibrosis in high‑fat diet mice via the TGF‑β/SMAD pathway

The aim of the present study was to investigate the role and mechanism of endoplasmic reticulum stress (ERS) in kidney injury caused by high‑fat diet (HFD). An obese mouse model was established via HFD feeding and intervention was performed by intraperitoneal injection of the ERS inhibitor salubrinal (Sal). Changes in the body and kidney weight and serum biochemical indices of the mice were determined. Hematoxylin and eosin and Masson staining were used to observe the pathological changes of renal tissues. Reverse transcription‑quantitative PCR and western blotting were used to observe the expression of ERS‑related proteins and TGF‑β/SMAD pathway‑related proteins. Immunohistochemistry was employed to explore the distribution of these proteins. Compared with those in the control group, the weight gain, lipid metabolism disorders and deterioration of renal function in the model group were greater. Malondialdehyde was elevated and superoxide dismutase was decreased in renal tissues. The mRNA and protein levels of TGF‑β1, SMAD2/3, α‑smooth muscle actin, collagen I, glucose‑regulated protein 78 and C/EBP‑homologous protein were markedly elevated, whereas SMAD7 was markedly decreased. Sal markedly inhibited the aforementioned effects. This investigation revealed a link between ERS and renal injury caused by HFD. ERS in HFD‑fed mice triggers renal fibrosis through the TGF‑β/SMAD pathway.

Loss of FIC-1-mediated AMPylation activates the UPR ER and upregulates cytosolic HSP70 chaperones to suppress polyglutamine toxicity

Targeted regulation of cellular proteostasis machinery represents a promising strategy for the attenuation of pathological protein aggregation. Recent work suggests that the unfolded protein response in the endoplasmic reticulum (UPR ER ) directly regulates the aggregation and toxicity of expanded polyglutamine (polyQ) proteins. However, the mechanisms underlying this phenomenon remain poorly understood. In this study, we report that perturbing ER homeostasis in Caenorhabditis elegans through the depletion of either BiP ortholog, hsp-3 or hsp-4, causes developmental arrest in worms expressing aggregation-prone polyQ proteins. This phenotype is rescued by the genetic deletion of the conserved UPR ER regulator, FIC-1. We demonstrate that the beneficial effects of fic-1 knock-out (KO) extend into adulthood, where the loss of FIC-1-mediated protein AMPylation in polyQ-expressing animals is sufficient to prevent declines in fitness and lifespan. We further show that loss of hsp-3 and hsp-4 leads to distinct, but complementary transcriptomic responses to ER stress involving all three UPR ER stress sensors (IRE-1, PEK-1, and ATF-6). We identify the cytosolic HSP70 family chaperone F44E5.4 , whose expression is increased in fic-1 -deficient animals upon ER dysregulation, as a key effector suppressing polyQ toxicity. Over-expression of F44E5.4 , but not other HSP70 family chaperones, is sufficient to rescue developmental arrest in polyQ-expressing embryos upon hsp-3 knock-down. Finally, we show that knock-down of ire-1 , pek-1 , or atf-6 blocks the upregulation of F44E5.4 in fic-1 -deficient worms. Taken together, our findings support a model in which the loss of FIC-1-mediated AMPylation engages UPR ER signaling to upregulate cytosolic chaperone activity in response to polyQ toxicity.

Endoplasmic reticulum stress triggers unfolded protein response as an antiviral strategy of teleost erythrocytes

Introduction

Fish nucleated red blood cells (RBCs), also known as erythrocytes, play a crucial role in maintaining immune system balance by modulating protein expression in response to various stimuli, including viral attack. This study explores the intriguing behavior of rainbow trout RBCs when faced with the viral hemorrhagic septicemia virus (VHSV), focusing on the endoplasmic reticulum (ER) stress and the unfolded protein response (UPR).

Methods

Rainbow trout RBCs were Ficoll-purified and exposed to ultraviolet (UV)-inactivated VHSV or live VHSV at different multiplicities of infection (MOIs). Using cryo-soft X-ray tomography (cryo-SXT), we uncovered structural and cellular modifications in RBCs exposed to UV-inactivated VHSV. Moreover, RBCs were treated with 4-phenylbutyric acid (4-PBA), an ER stress inhibitor, to investigate its effect on viral replication. Quantitative real-time PCR was also used to analyze the expression of genes related to the UPR and other related cellular pathways.

Results and discussion

Beyond their antiviral response, RBCs undergo notable intracellular changes to combat the virus. Cryo-SXT highlighted a significant increase in the ER volume. This increase is associated with ER stress and the activation of the UPR pathway. Interestingly, VHSV replication levels augmented in RBCs under ER-stress inhibition by 4-PBA treatment, suggesting that rainbow trout RBCs tune up ER stress to control viral replication. Therefore, our findings suggested the induction of ER stress and subsequent activation UPR signaling in the antiviral response of RBCs to VHSV. The results open a new line of investigation to uncover additional mechanisms that may become novel cellular targets for the development of RBC-targeted antiviral strategies.

Icariin alleviates cellular injury induced by cardiac ischemia-reperfusion injury by inhibiting IRE1/JNK-induced ferroptosis

BACKGROUND

Ischemia-induced cellular damage and stress responses significantly impact cellular viability and function. Icariin (ICA), known for its protective effects, has been studied to understand its role in mitigating oxygen-glucose deprivation/reperfusion (OGD/R)-induced endoplasmic reticulum (ER) stress and ferroptosis in H9C2 cardiomyoblast cells.

METHODS

We employed an in vitro OGD/R model using H9C2 cells. ICA's effects were analyzed across multiple concentrations. Key indicators of ER stress, autophagy, and ferroptosis-including markers like Bip, PERK, IRE1, ATF6, P62, FTH1, LC3II/LC3I, and NCOA4-were assessed using Western blotting, electron microscopy, and biochemical assays. Additionally, the role of the IRE1/JNK pathway in mitochondrial dynamics and its influence on mitochondrial dynamics protein was explored through specific inhibition and activation experiments.

RESULTS

ICA significantly reduced the activation of UPR pathways, decreased autophagic vacuole formation, and maintained cell viability in response to OGD/R and Erastin-induced ferroptosis. These protective effects were associated with modulated autophagic processes, reduced lipid peroxidation, and decreased ferrous ion accumulation. Inhibition of the IRE1/JNK pathway and subsequent Drp1 activity demonstrated reduced mitochondrial recruitment and mitophagy, correlating with decreased ferroptosis markers and improved cell survival.

CONCLUSION

Our findings highlight ICA's potential in modulating IRE1/JNK pathway, autophagy, providing a therapeutic avenue for mitigating ferroptosis in myocardial ischemia-reperfusion injury (MIRI).

Sirt1 Mitigates Hepatic Lipotoxic Injury Induced by High-Fat-Diet in Fish Through Ire1α Deacetylation

BACKGROUND

Silent information regulator protein 1 (Sirt1) is crucial in regulating lipid metabolism, but its specific role and mechanism in fish hepatic lipotoxic injury remain undefined.

OBJECTIVES

This study aimed to elucidate the regulatory role of Sirt1 and the underlying mechanisms in dietary lipid-induced hepatic lipotoxic injury in a marine teleost black seabream.

METHODS

Black seabream were fed a control diet (12% lipid level), high-fat diet (HFD) [18% lipid level, oleic acid (OA)-rich], or HFD supplemented with 0.25%, 0.50%, or 1.00% resveratrol (RSV) for 8 wk. The cultured hepatocytes were stimulated by OA (200 μM), OA supplemented with RSV (20 μM), or transfection with sirt1-small interfering RNA (sisirt1). Biochemical indices, gene expression (qPCR), histology, transmission electron microscope, immunofluorescence, Western blot, flow cytometry, and immunoprecipitation assays were conducted to evaluate hepatic lipid deposition, lipid metabolism, endoplasmic reticulum stress, inflammation and apoptosis, and determine protein interactions between Sirt1 and Ire1α.

RESULTS

In vivo, RSV supplementation increased mRNA and protein expression levels of sirt1 (236.2% ± 16.1% and 53.1% ± 14.3%) and downregulated the mRNA and phosphorylated protein expression levels of ire1α/Ire1α (46.0% ± 7.6% and 38.6% ± 7.0%), jnk/Jnk (57.6% ± 7.3% and 122.1%), and nuclear factor κ B (nf-κb/Nf-κb) p65 (41.7% ± 7.1% and 24.6% ± 0.8%) compared with the HFD group. Similar patterns were found in the in vitro experiments; however, after knockdown of sirt1, although the cells were incubated with RSV, the expression levels of ire1α/ Ire1α, jnk/Jnk, and nf-κb/Nf-κb p65 showed no significant differences compared with the OA treatment. Moreover, we found that mutation of K61 to arginine to mimic Ire1α deacetylation confers protection against Ire1α-mediated OA-rich HFD-induced inflammation and apoptosis.

CONCLUSIONS

The findings revealed that Sirt1 protects against OA-rich HFD-induced hepatic lipotoxic injury via the deacetylation of Ire1α on K61, hence reducing Ire1α autophosphorylation level, and suppressing Jnk and Nf-κb p65 activation. This mechanism is elucidated for the first time in fish.

The lipid side of unfolded protein response

Although our current knowledge of the molecular crosstalk between the ER stress, the unfolded protein response (UPR), and lipid homeostasis remains limited, there is increasing evidence that dysregulation of either protein or lipid homeostasis profoundly affects the other. Most research regarding UPR signaling in human diseases has focused on the causes and consequences of disrupted protein folding. The UPR itself consists of very complex pathways that function to not only maintain protein homeostasis, but just as importantly, modulate lipid biogenesis to allow the ER to adjust and promote cell survival. Lipid dysregulation is known to activate many aspects of the UPR, but the complexity of this crosstalk remains a major research barrier. ER lipid disequilibrium and lipotoxicity are known to be important contributors to numerous human pathologies, including insulin resistance, liver disease, cardiovascular diseases, neurodegenerative diseases, and cancer. Despite their medical significance and continuous research, however, the molecular mechanisms that modulate lipid synthesis during ER stress conditions, and their impact on cell fate decisions, remain poorly understood. Here we summarize the current view on crosstalk and connections between altered lipid metabolism, ER stress, and the UPR.

Epigenetic regulation of global proteostasis dynamics by RBBP5 ensures mammalian organismal health

Proteostasis is vital for cellular health, with disruptions leading to pathologies including aging, neurodegeneration and metabolic disorders. Traditionally, proteotoxic stress responses were studied as acute reactions to various noxious factors; however, recent evidence reveals that many proteostasis stress-response genes exhibit ~12-hour ultradian rhythms under physiological conditions in mammals. These rhythms, driven by an XBP1s-dependent 12h oscillator, are crucial for managing proteostasis. By exploring the chromatin landscape of the murine 12h hepatic oscillator, we identified RBBP5, a key subunit of the COMPASS complex writing H3K4me3, as an essential epigenetic regulator of proteostasis. RBBP5 is indispensable for regulating both the hepatic 12h oscillator and transcriptional response to acute proteotoxic stress, acting as a co-activator for proteostasis transcription factor XBP1s. RBBP5 ablation leads to increased sensitivity to proteotoxic stress, chronic inflammation, and hepatic steatosis in mice, along with impaired autophagy and reduced cell survival in vitro. In humans, lower RBBP5 expression is associated with reduced adaptive stress-response gene expression and hepatic steatosis. Our findings establish RBBP5 as a central regulator of proteostasis, essential for maintaining mammalian organismal health.

Growth on stiffer substrates impacts animal health and longevity in C. elegans

Mechanical stress is a measure of internal resistance exhibited by a body or material when external forces, such as compression, tension, bending, etc. are applied. The study of mechanical stress on health and aging is a continuously growing field, as major changes to the extracellular matrix and cell-to-cell adhesions can result in dramatic changes to tissue stiffness during aging and diseased conditions. For example, during normal aging, many tissues including the ovaries, skin, blood vessels, and heart exhibit increased stiffness, which can result in a significant reduction in function of that organ. As such, numerous model systems have recently emerged to study the impact of mechanical and physical stress on cell and tissue health, including cell-culture conditions with matrigels and other surfaces that alter substrate stiffness and ex vivo tissue models that can apply stress directly to organs like muscle or tendons. Here, we sought to develop a novel method in an in vivo model organism setting to study the impact of altering substrate stiffness on aging by changing the stiffness of solid agar medium used for growth of C. elegans. We found that greater substrate stiffness had limited effects on cellular health, gene expression, organismal health, stress resilience, and longevity. Overall, our study reveals that altering substrate stiffness of growth medium for C. elegans has only mild impact on animal health and longevity; however, these impacts were not nominal and open up important considerations for C. elegans biologists in standardizing agar medium choice for experimental assays.

Endoplasmic reticulum stress as a target for retinoids in cancer treatment

Retinoids, natural and synthetic derivatives of vitamin A, have various regulatory activities including controlling cellular proliferation, differentiation, and death. Furthermore, they have been used to treat specific cancers with satisfying results. Nevertheless, retinoids have yet to be converted into effective systemic therapies for the majority of tumor types. Regulation of unfolded protein response signaling, and persistent activation of endoplasmic reticulum stress (ER-stress) are promising treatment methods for cancer. The present article reviews the current understanding of how vitamin A and its derivatives may aid to cause ER-stress-activated apoptosis, as well as therapeutic options for exploiting ER-stress for achieving beneficial goal. The therapeutic use of some retinoids discussed in this article was related to decreased disease recurrence and improved therapeutic outcomes via ER-stress activation and promotion, indicating that retinoids may play an important role in cancer treatment and prevention. More research is needed to expand the use of vitamin A derivatives in cancer therapy, either alone or in combination with unfolded protein response inducers.

ER-phagy drives age-onset remodeling of endoplasmic reticulum structure-function and lifespan

The endoplasmic reticulum (ER) comprises an array of structurally distinct subdomains, each with characteristic functions. While altered ER-associated processes are linked to age-onset pathogenesis, whether shifts in ER morphology underlie these functional changes is unclear. We report that ER remodeling is a conserved feature of the aging process in models ranging from yeast to C. elegans and mammals. Focusing on C. elegans as an exemplar of metazoan aging, we find that as animals age, ER mass declines in virtually all tissues and ER morphology shifts from rough sheets to tubular ER. The accompanying large-scale shifts in proteomic composition correspond to the ER turning from protein synthesis to lipid metabolism. To drive this substantial remodeling, ER-phagy is activated early in adulthood, promoting turnover of rough ER in response to rises in luminal protein-folding burden and reduced global protein synthesis. Surprisingly, ER remodeling is a pro-active and protective response during aging, as ER-phagy impairment limits lifespan in yeast and diverse lifespan-extending paradigms promote profound remodeling of ER morphology even in young animals. Altogether our results reveal ER-phagy and ER morphological dynamics as pronounced, underappreciated mechanisms of both normal aging and enhanced longevity.

Current potential pathogenic mechanisms of copper-zinc superoxide dismutase 1 (SOD1) in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rare neurodegenerative disease which damages upper and lower motor neurons (UMN and LMN) innervating the muscles of the trunk, extremities, head, neck and face in cerebrum, brain stem and spinal cord, which results in the progressive weakness, atrophy and fasciculation of muscle innervated by the related UMN and LMN, accompanying with the pathological signs leaded by the cortical spinal lateral tract lesion. The pathogenesis about ALS is not fully understood, and no specific drugs are available to cure and prevent the progression of this disease at present. In this review, we reviewed the structure and associated functions of copper-zinc superoxide dismutase 1 (SOD1), discuss why SOD1 is crucial to the pathogenesis of ALS, and outline the pathogenic mechanisms of SOD1 in ALS that have been identified at recent years, including glutamate-related excitotoxicity, mitochondrial dysfunction, endoplasmic reticulum stress, oxidative stress, axonal transport disruption, prion-like propagation, and the non-cytologic toxicity of glial cells. This review will help us to deeply understand the current progression in this field of SOD1 pathogenic mechanisms in ALS.

Sex-specific and cell-specific regulation of ER stress and neuroinflammation after traumatic brain injury in juvenile mice

Endoplasmic reticulum (ER) stress and neuroinflammation play an important role in secondary brain damage after traumatic brain injury (TBI). Due to the complex brain cytoarchitecture, multiple cell types are affected by TBI. However, cell type-specific and sex-specific responses to ER stress and neuroinflammation remain unclear. Here we investigated differential regulation of ER stress and neuroinflammatory pathways in neurons and microglia during the acute phase post-injury in a mouse model of impact acceleration TBI in both males and females. We found that TBI resulted in significant weight loss only in males, and sensorimotor impairment and depressive-like behaviors in both males and females at the acute phase post-injury. By concurrently isolating neurons and microglia from the same brain sample of the same animal, we were able to evaluate the simultaneous responses in neurons and microglia towards ER stress and neuroinflammation in both males and females. We discovered that the ER stress and anti-inflammatory responses were significantly stronger in microglia, especially in female microglia, compared with the male and female neurons. Whereas the degree of phosphorylated-tau (pTau) accumulation was significantly higher in neurons, compared with the microglia. In conclusion, TBI resulted in behavioral deficits and cell type-specific and sex-specific responses to ER stress and neuroinflammation, and abnormal protein accumulation at the acute phase after TBI in immature mice.

TXNDC5 Plays a Crucial Role in Regulating Endoplasmic Reticulum Activity through Different ER Stress Signaling Pathways in Hepatic Cells

The pathogenesis of non-alcoholic fatty liver disease (NAFLD) is influenced by a number of variables, including endoplasmic reticulum stress (ER). Thioredoxin domain-containing 5 (TXNDC5) is a member of the protein disulfide isomerase family and acts as an endoplasmic reticulum (ER) chaperone. Nevertheless, the function of TXNDC5 in hepatocytes under ER stress remains largely uncharacterized. In order to identify the role of TXNDC5 in hepatic wild-type (WT) and TXNDC5-deficient (KO) AML12 cell lines, tunicamycin, palmitic acid, and thapsigargin were employed as stressors. Cell viability, mRNA, protein levels, and mRNA splicing were then assayed. The protein expression results of prominent ER stress markers indicated that the ERN1 and EIF2AK3 proteins were downregulated, while the HSPA5 protein was upregulated. Furthermore, the ATF6 protein demonstrated no significant alterations in the absence of TXNDC5 at the protein level. The knockout of TXNDC5 has been demonstrated to increase cellular ROS production and its activity is required to maintain normal mitochondrial function during tunicamycin-induced ER stress. Tunicamycin has been observed to disrupt the protein levels of HSPA5, ERN1, and EIF2AK3 in TXNDC5-deficient cells. However, palmitic acid has been observed to disrupt the protein levels of ATF6, HSPA5, and EIF2AK3. In conclusion, TXNDC5 can selectively activate distinct ER stress pathways via HSPA5, contingent on the origin of ER stress. Conversely, the absence of TXNDC5 can disrupt the EIF2AK3 cascade.

Triphenylphosphonium-Conjugated Palmitic Acid for Mitochondrial Targeting of Pancreatic Cancer Cells: Proteomic and Molecular Evidence

Pancreatic ductal adenocarcinoma (PDAC)'s resistance to therapies is mainly attributed to pancreatic cancer stem cells (PCSCs). Mitochondria-impairing agents can be used to hamper PCSC propagation and reduce PDAC progression. Therefore, to develop an efficient vector for delivering drugs to the mitochondria, we synthesized tris(3,5-dimethylphenyl)phosphonium-conjugated palmitic acid. Triphenylphosphonium (TPP) is a lipophilic cationic moiety that promotes the accumulation of conjugated agents in the mitochondrion. Palmitic acid (PA), the most common saturated fatty acid, has pro-apoptotic activity in different types of cancer cells. TPP-PA was prepared by the reaction of 16-bromopalmitic acid with TPP, and its structure was characterized by 1H and 13C NMR and HRMS. We compared the proteomes of TPP-PA-treated and untreated PDAC cells and PCSCs, identifying dysregulated proteins and pathways. Furthermore, assessments of mitochondrial membrane potential, intracellular ROS, cardiolipin content and lipid peroxidation, ER stress, and autophagy markers provided information on the mechanism of action of TPP-PA. The findings showed that TPP-PA reduces PDAC cell proliferation through mitochondrial disruption that leads to increased ROS, activation of ER stress, and autophagy. Hence, TPP-PA might offer a new approach for eliminating both the primary population of cancer cells and PCSCs, which highlights the promise of TPP-derived compounds as anticancer agents for PDAC.

Oxidative photocatalysis on membranes triggers non-canonical pyroptosis

Intracellular membranes composing organelles of eukaryotes include membrane proteins playing crucial roles in physiological functions. However, a comprehensive understanding of the cellular responses triggered by intracellular membrane-focused oxidative stress remains elusive. Herein, we report an amphiphilic photocatalyst localised in intracellular membranes to damage membrane proteins oxidatively, resulting in non-canonical pyroptosis. Our developed photocatalysis generates hydroxyl radicals and hydrogen peroxides via water oxidation, which is accelerated under hypoxia. Single-molecule magnetic tweezers reveal that photocatalysis-induced oxidation markedly destabilised membrane protein folding. In cell environment, label-free quantification reveals that oxidative damage occurs primarily in membrane proteins related to protein quality control, thereby aggravating mitochondrial and endoplasmic reticulum stress and inducing lytic cell death. Notably, the photocatalysis activates non-canonical inflammasome caspases, resulting in gasdermin D cleavage to its pore-forming fragment and subsequent pyroptosis. These findings suggest that the oxidation of intracellular membrane proteins triggers non-canonical pyroptosis.

Ceramides and mitochondrial homeostasis

Lipotoxicity arises from the accumulation of lipid intermediates in non-adipose tissue, precipitating cellular dysfunction and death. Ceramide, a toxic byproduct of excessive free fatty acids, has been widely recognized as a primary contributor to lipotoxicity, mediating various cellular processes such as apoptosis, differentiation, senescence, migration, and adhesion. As the hub of lipid metabolism, the excessive accumulation of ceramides inevitably imposes stress on the mitochondria, leading to the disruption of mitochondrial homeostasis, which is typified by adequate ATP production, regulated oxidative stress, an optimal quantity of mitochondria, and controlled mitochondrial quality. Consequently, this review aims to collate current knowledge and facts regarding the involvement of ceramides in mitochondrial energy metabolism and quality control, thereby providing insights for future research.

Thapsigargin and Tunicamycin Block SARS-CoV-2 Entry into Host Cells via Differential Modulation of Unfolded Protein Response (UPR), AKT Signaling, and Apoptosis

BACKGROUND

SARS-Co-V2 infection can induce ER stress-associated activation of unfolded protein response (UPR) in host cells, which may contribute to the pathogenesis of COVID-19. To understand the complex interplay between SARS-Co-V2 infection and UPR signaling, we examined the effects of acute pre-existing ER stress on SARS-Co-V2 infectivity.

METHODS

Huh-7 cells were treated with Tunicamycin (TUN) and Thapsigargin (THA) prior to SARS-CoV-2pp transduction (48 h p.i.) to induce ER stress. Pseudo-typed particles (SARS-CoV-2pp) entry into host cells was measured by Bright GloTM luciferase assay. Cell viability was assessed by cell titer Glo® luminescent assay. The mRNA and protein expression was evaluated by RT-qPCR and Western Blot.

RESULTS

TUN (5 µg/mL) and THA (1 µM) efficiently inhibited the entry of SARS-CoV-2pp into host cells without any cytotoxic effect. TUN and THA's attenuation of virus entry was associated with differential modulation of ACE2 expression. Both TUN and THA significantly reduced the expression of stress-inducible ER chaperone GRP78/BiP in transduced cells. In contrast, the IRE1-XBP1s and PERK-eIF2α-ATF4-CHOP signaling pathways were downregulated with THA treatment, but not TUN in transduced cells. Insulin-mediated glucose uptake and phosphorylation of Ser307 IRS-1 and downstream p-AKT were enhanced with THA in transduced cells. Furthermore, TUN and THA differentially affected lipid metabolism and apoptotic signaling pathways.

CONCLUSIONS

These findings suggest that short-term pre-existing ER stress prior to virus infection induces a specific UPR response in host cells capable of counteracting stress-inducible elements signaling, thereby depriving SARS-Co-V2 of essential components for entry and replication. Pharmacological manipulation of ER stress in host cells might provide new therapeutic strategies to alleviate SARS-CoV-2 infection.

How does the neuronal proteostasis network react to cellular cues?

Even though neurons are post-mitotic cells, they still engage in protein synthesis to uphold their cellular content balance, including for organelles, such as the endoplasmic reticulum or mitochondria. Additionally, they expend significant energy on tasks like neurotransmitter production and maintaining redox homeostasis. This cellular homeostasis is upheld through a delicate interplay between mRNA transcription-translation and protein degradative pathways, such as autophagy and proteasome degradation. When faced with cues such as nutrient stress, neurons must adapt by altering their proteome to survive. However, in many neurodegenerative disorders, such as Parkinson's disease, the pathway and processes for coping with cellular stress are impaired. This review explores neuronal proteome adaptation in response to cellular stress, such as nutrient stress, with a focus on proteins associated with autophagy, stress response pathways, and neurotransmitters.

Cell non-autonomous control of autophagy and metabolism by glial cells

Glia are the protectors of the nervous system, providing neurons with support and protection from cytotoxic insults. We previously discovered that four astrocyte-like glia can regulate organismal proteostasis and longevity in C. elegans. Expression of the UPRER transcription factor, XBP-1s, in these glia increases stress resistance, and longevity, and activates the UPRER in intestinal cells via neuropeptides. Autophagy, a key regulator of metabolism and aging, has been described as a cell autonomous process. Surprisingly, we find that glial XBP-1s enhances proteostasis and longevity by cell non-autonomously reprogramming organismal lipid metabolism and activating autophagy. Glial XBP-1s regulates the activation of another transcription factor, HLH-30/TFEB, in the intestine. HLH-30 activates intestinal autophagy, increases intestinal lipid catabolism, and upregulates a robust transcriptional program. Our study reveals a novel role for glia in regulating peripheral lipid metabolism, autophagy, and organellar health through peripheral activation of HLH-30 and autophagy.

Mechanical stress through growth on stiffer substrates impacts animal health and longevity in C. elegans

Mechanical stress is a measure of internal resistance exhibited by a body or material when external forces, such as compression, tension, bending, etc. are applied. The study of mechanical stress on health and aging is a continuously growing field, as major changes to the extracellular matrix and cell-to-cell adhesions can result in dramatic changes to tissue stiffness during aging and diseased conditions. For example, during normal aging, many tissues including the ovaries, skin, blood vessels, and heart exhibit increased stiffness, which can result in a significant reduction in function of that organ. As such, numerous model systems have recently emerged to study the impact of mechanical and physical stress on cell and tissue health, including cell-culture conditions with matrigels and other surfaces that alter substrate stiffness and ex vivo tissue models that can apply stress directly to organs like muscle or tendons. Here, we sought to develop a novel method in an in vivo, model organism setting to study the impact of mechanical stress on aging, by increasing substrate stiffness in solid agar medium of C. elegans. To our surprise, we found shockingly limited impact of growth of C. elegans on stiffer substrates, including limited effects on cellular health, gene expression, organismal health, stress resilience, and longevity. Overall, our studies reveal that altering substrate stiffness of growth medium for C. elegans have only mild impact on animal health and longevity; however, these impacts were not nominal and open up important considerations for C. elegans biologists in standardizing agar medium choice for experimental assays.

Roles of β-Cell Hypoxia in the Progression of Type 2 Diabetes

Type 2 diabetes is a chronic disease marked by hyperglycemia; impaired insulin secretion by pancreatic β-cells is a hallmark of this disease. Recent studies have shown that hypoxia occurs in the β-cells of patients with type 2 diabetes and hypoxia, in turn, contributes to the insulin secretion defect and β-cell loss through various mechanisms, including the activation of hypoxia-inducible factors, induction of transcriptional repressors, and activation of AMP-activated protein kinase. This review focuses on advances in our understanding of the contribution of β-cell hypoxia to the development of β-cell dysfunction in type 2 diabetes. A better understanding of β-cell hypoxia might be useful in the development of new strategies for treating type 2 diabetes.

Uncloaking the viral glycocalyx: How do viruses exploit glycoimmune checkpoints?

The surfaces of cells and enveloped viruses alike are coated in carbohydrates that play multifarious roles in infection and immunity. Organisms across all kingdoms of life make use of a diverse set of monosaccharide subunits, glycosidic linkages, and branching patterns to encode information within glycans. Accordingly, sugar-patterning enzymes and glycan binding proteins play integral roles in cell and organismal biology, ranging from glycoprotein quality control within the endoplasmic reticulum to lymphocyte migration, coagulation, inflammation, and tissue homeostasis. Unsurprisingly, genes involved in generating and recognizing oligosaccharide patterns are playgrounds for evolutionary conflicts that abound in cross-species interactions, exemplified by the myriad plant lectins that function as toxins. In vertebrates, glycans bearing acidic nine-carbon sugars called sialic acids are key regulators of immune responses. Various bacterial and fungal pathogens adorn their cells in sialic acids that either mimic their hosts' or are stolen from them. Yet, how viruses commandeer host sugar-patterning enzymes to thwart immune responses remains poorly studied. Here, we review examples of viruses that interact with sialic acid-binding immunoglobulin-like lectins (Siglecs), a family of immune cell receptors that regulate toll-like receptor signaling and govern glycoimmune checkpoints, while highlighting knowledge gaps that merit investigation. Efforts to illuminate how viruses leverage glycan-dependent checkpoints may translate into new clinical treatments that uncloak viral antigens and infected cell surfaces by removing or masking immunosuppressive sialoglycans, or by inhibiting viral gene products that induce their biosynthesis. Such approaches may hold the potential to unleash the immune system to clear long intractable chronic viral infections.

Zinc attenuates arsenic overdose-induced brain damage via PERK/ATF6 and TLR/MyD88/NF-κB pathways

Exposure to arsenic (As), a widespread non-metallic toxicant in nature, often results in neurotoxicity, although the exact mechanism is unknown. Zinc (Zn) is a powerful nutrient often thought to be beneficial for growth, development and immunity. Whether Zn can rescue brain damage caused by As contamination remains to be demonstrated. Therefore, in this study, a 30-day model of As poisoning (2.83 mg/L) in carp was established and treated with Zn (1 mg/L) to investigate the detoxification mechanism involved. Histological observations showed that As induced the loosening of the molecular layer structure of the cerebellum and the dissolution or even disappearance of nuclei, accompanied by the occurrence of microthrombi in the granular layer, and the addition of Zn attenuated such As-induced damage. Further mechanistic studies indicated that Zn ameliorated As exposure-induced abnormalities in antioxidant capacity (decreased CAT and Cu/Zn-SOD), activation of the Nrf2/keap1 pathway and endoplasmic reticulum stress (ERs), which is a key factor in As-induced brain damage. ERs (high expression of PERK, ATF6, CHOP, eiF2α and GRP78) and inflammation (overexpression of TLR2, TLR4, MyD88, IKK, NF-κB, IL-1β and IL-6 and low expression of IκBα and IL-10). We suggest that Zn can alleviate excessive As-induced brain damage by attenuating As-induced oxidative stress, PERK/ATF6 and TLR/MyD88/NF-κB pathways. The present study fills in the preventive mechanism of As injury in fish and provides the possibility of prevention and control of As pollution-induced brain tissue injury by Zn rescue.

Heat Shock Proteins Function as Signaling Molecules to Mediate Neuron-Glia Communication During Aging

The nervous system is primarily composed of neurons and glia, and the communication between them plays profound roles in regulating the development and function of the brain. Neuron-glia signal transduction is known to be mediated by secreted or juxtacrine signals through ligand-receptor interactions on the cell membrane. Here, we report a novel mechanism for neuron-glia signal transduction, wherein neurons transmit proteins to glia through extracellular vesicles, activating glial signaling pathways. We find that in the amphid sensory organ of Caenorhabditis elegans, different sensory neurons exhibit varying aging rates. This discrepancy in aging is governed by the crosstalk between neurons and glia. We demonstrate that early-aged neurons can transmit heat shock proteins (HSP) to glia via extracellular vesicles. These neuronal HSPs activate the IRE1-XBP1 pathway, further increasing their expression in glia, forming a positive feedback loop. Ultimately, the activation of the IRE1-XBP-1 pathway leads to the transcriptional regulation of chondroitin synthases to protect glia-embedded neurons from aging-associated functional decline. Therefore, our studies unveil a novel mechanism for neuron-glia communication in the nervous system and provide new insights into our understanding of brain aging.

Endoplasmic reticulum stress participates in apoptosis of HeLa cells exposed to TPHP and OH-TPHP via the eIF2α-ATF4/ATF3-CHOP-DR5/P53 signaling pathway

Purpose

Triphenyl phosphate (TPHP) is a widely used organophosphate flame retardant, which can be transformed in vivo into diphenyl phosphate (DPHP) and 4-hydroxyphenyl phosphate (diphenyl) ester (OH-TPHP) through biotransformation process. Accumulation of TPHP and its derivatives in biological tissues makes it necessary to investigate their toxicity and molecular mechanism.

Methods

The present study evaluated the cellular effects of TPHP, DPHP, and OH-TPHP on cell survival, cell membrane damage, oxidative damage, and cell apoptosis using HeLa cells as in vitro model. RNA sequencing and bioinformatics analysis were conducted to monitor the differently expressed genes, and then RT-qPCR and Western bolt were used to identify potential molecular mechanisms and key hub genes.

Results

Results showed that OH-TPHP had the most significant cytotoxic effect in HeLa cells, followed by TPHP; and no significant cytotoxic effects were observed for DPHP exposure within the experimental concentrations. Biological function enrichment analysis suggested that TPHP and OH-TPHP exposure may induce endoplasmic reticulum stress (ERS) and cell apoptosis. The nodes filtering revealed that ERS and apoptosis related genes were involved in biological effects induced by TPHP and OH-TPHP, which may be mediated through the eukaryotic translation initiation factor 2α/activating transcription factor 4 (ATF4)/ATF3- CCAAT/ enhancer-binding protein homologous protein (CHOP) cascade pathway and death receptor 5 (DR5) /P53 signaling axis.

Conclusion

Above all, these findings indicated that ERS-mediated apoptosis might be one of potential mechanisms for cytotoxicity of TPHP and OH-TPHP.

The Dynamic Role of Endoplasmic Reticulum Stress in Chronic Liver Disease

Chronic liver disease (CLD) is a major worldwide public health threat, with an estimated prevalence of 1.5 billion individuals with CLD in 2020. Chronic activation of endoplasmic reticulum (ER) stress-related pathways is recognized as substantially contributing to the pathologic progression of CLD. The ER is an intracellular organelle that folds proteins into their correct three-dimensional shapes. ER-associated enzymes and chaperone proteins highly regulate this process. Perturbations in protein folding lead to misfolded or unfolded protein accumulation in the ER lumen, resulting in ER stress and concomitant activation of the unfolded protein response (UPR). The adaptive UPR is a set of signal transduction pathways evolved in mammalian cells that attempts to reestablish ER protein homeostasis by reducing protein load and increasing ER-associated degradation. However, maladaptive UPR responses in CLD occur due to prolonged UPR activation, leading to concomitant inflammation and cell death. This review assesses the current understanding of the cellular and molecular mechanisms that regulate ER stress and the UPR in the progression of various liver diseases and the potential pharmacologic and biological interventions that target the UPR.

Ajugol's upregulation of TFEB-mediated autophagy alleviates endoplasmic reticulum stress in chondrocytes and retards osteoarthritis progression in a mouse model

BACKGROUND

Osteoarthritis (OA), a degenerative disease with a high global prevalence, is characterized by the degradation of the extracellular matrix (ECM) and the apoptosis of chondrocytes. Ajugol, a extract derived from the herb Rehmannia glutinosa, has not yet been investigated for its potential in modulating the development of OA.

METHODS

We employed techniques such as western blotting, immunofluorescence, immunohistochemistry, X-ray imaging, HE staining, and SO staining to provide biological evidence supporting the role of Ajugol as a potential therapeutic agent for modulating OA. Furthermore, in an in vivo experiment, intra-peritoneal injection of 50 mg/kg Ajugol effectively mitigated the progression of OA following destabilization of the medial meniscus (DMM) surgery.

RESULTS

Our findings revealed that treatment with 50 μM Ajugol activated TFEB-mediated autophagy, alleviating ER stress-induced chondrocyte apoptosis and ECM degradation caused by TBHP. Furthermore, in an in vivo experiment, intra-peritoneal injection of 50 mg/kg Ajugol effectively mitigated the progression of OA following destabilization of the medial meniscus (DMM) surgery.

CONCLUSION

These results provide compelling biological evidence supporting the role of Ajugol as a potential therapeutic agent for modulating OA by activating autophagy and attenuating ER stress-induced cell death and ECM degradation. The promising in vivo results further suggest the potential of Ajugol as a treatment strategy for OA progression.

Harnessing Oncolytic Extracellular Vesicles for Tumor Cell-Preferential Cytoplasmic Delivery of Misfolded Proteins for Cancer Immunotherapy

In this study, extracellular vesicles (EVs) are reimagined as more than just a cellular waste disposal system and are repurposed for cancer immunotherapy. Potent oncolytic EVs (bRSVF-EVs) loaded with misfolded proteins (MPs) are engineered, which are typically considered cellular debris. By impairing lysosomal function using bafilomycin A1 and expressing the respiratory syncytial virus F protein, a viral fusogen, MPs are successfully loaded into the EVs expressing RSVF. bRSVF-EVs preferentially transplant a xenogeneic antigen onto cancer cell membranes in a nucleolin-dependent manner, triggering an innate immune response. Furthermore, bRSVF-EV-mediated direct delivery of MPs into the cancer cell cytoplasm initiates endoplasmic reticulum stress and immunogenic cell death (ICD). This mechanism of action leads to substantial antitumor immune responses in murine tumor models. Importantly, when combined with PD-1 blockade, bRSVF-EV treatment elicits robust antitumor immunity, resulting in prolonged survival and complete remission in some cases. Overall, the findings demonstrate that utilizing tumor-targeting oncolytic EVs for direct cytoplasmic delivery of MPs to induce ICD in cancer cells represents a promising approach for enhancing durable antitumor immunity.

A novel endoplasmic reticulum adaptation is critical for the long-lived Caenorhabditis elegans rpn-10 proteasomal mutant

The loss of proteostasis due to reduced efficiency of protein degradation pathways plays a key role in multiple age-related diseases and is a hallmark of the aging process. Paradoxically, we have previously reported that the Caenorhabditis elegans rpn-10(ok1865) mutant, which lacks the RPN-10/RPN10/PSMD4 subunit of the 19S regulatory particle of the 26S proteasome, exhibits enhanced cytosolic proteostasis, elevated stress resistance and extended lifespan, despite possessing reduced proteasome function. However, the response of this mutant against threats to endoplasmic reticulum (ER) homeostasis and proteostasis was unknown. Here, we find that the rpn-10 mutant is highly ER stress resistant compared to the wildtype. Under unstressed conditions, the ER unfolded protein response (UPR) is activated in the rpn-10 mutant as signified by increased xbp-1 splicing. This primed response appears to alter ER homeostasis through the upregulated expression of genes involved in ER protein quality control (ERQC), including those in the ER-associated protein degradation (ERAD) pathway. Pertinently, we find that ERQC is critical for the rpn-10 mutant longevity. These changes also alter ER proteostasis, as studied using the C. elegans alpha-1 antitrypsin (AAT) deficiency model, which comprises an intestinal ER-localised transgenic reporter of an aggregation-prone form of AAT called ATZ. The rpn-10 mutant shows a significant reduction in the accumulation of the ATZ reporter, thus indicating that its ER proteostasis is augmented. Via a genetic screen for suppressors of decreased ATZ aggregation in the rpn-10 mutant, we then identified ecps-2/H04D03.3, a novel ortholog of the proteasome-associated adaptor and scaffold protein ECM29/ECPAS. We further show that ecps-2 is required for improved ER proteostasis as well as lifespan extension of the rpn-10 mutant. Thus, we propose that ECPS-2-proteasome functional interactions, alongside additional putative molecular processes, contribute to a novel ERQC adaptation which underlies the superior proteostasis and longevity of the rpn-10 mutant.

The unfolded protein response links ER stress to cancer-associated thrombosis

Thrombosis is a common complication of advanced cancer, yet the cellular mechanisms linking malignancy to thrombosis are poorly understood. The unfolded protein response (UPR) is an ER stress response associated with advanced cancers. A proteomic evaluation of plasma from patients with gastric and non-small cell lung cancer who were monitored prospectively for venous thromboembolism demonstrated increased levels of UPR-related markers in plasma of patients who developed clots compared with those who did not. Release of procoagulant activity into supernatants of gastric, lung, and pancreatic cancer cells was enhanced by UPR induction and blocked by antagonists of the UPR receptors inositol-requiring enzyme 1α (IRE1α) and protein kinase RNA-like endoplasmic reticulum kinase (PERK). Release of extracellular vesicles bearing tissue factor (EVTFs) from pancreatic cancer cells was inhibited by siRNA-mediated knockdown of IRE1α/XBP1 or PERK pathways. Induction of UPR did not increase tissue factor (TF) synthesis, but rather stimulated localization of TF to the cell surface. UPR-induced TF delivery to EVTFs was inhibited by ADP-ribosylation factor 1 knockdown or GBF1 antagonism, verifying the role of vesicular trafficking. Our findings show that UPR activation resulted in increased vesicular trafficking leading to release of prothrombotic EVTFs, thus providing a mechanistic link between ER stress and cancer-associated thrombosis.

High-Dose Deltamethrin Induces Developmental Toxicity in Caenorhabditis elegans via IRE-1

Deltamethrin (DM), a Type II pyrethroid, is widely used worldwide in agriculture, household applications, and medicine. Recent studies have shown that DM exerts a variety of toxic effects on organs such as the kidney, heart muscle, and nerves in animals. However, little is known about the effects of high-dose DM on growth and development, and the mechanism of toxicity remains unclear. Using the Caenorhabditis elegans model, we found that high-dose DM caused a delay in nematode development. Our results showed that high-dose DM reduced the activation of the endoplasmic reticulum unfolded protein response (UPRER). Further studies revealed that high-dose DM-induced developmental toxicity and reduced capacity for UPRER activation were associated with the IRE-1/XBP-1 pathway. Our results provide new evidence for the developmental toxicity of DM and new insights into the mechanism of DM toxicity.

Lipid homeostasis is essential for a maximal ER stress response

Changes in lipid metabolism are associated with aging and age-related diseases, including proteopathies. The endoplasmic reticulum (ER) is uniquely a major hub for protein and lipid synthesis, making its function essential for both protein and lipid homeostasis. However, it is less clear how lipid metabolism and protein quality may impact each other. Here, we identified let-767, a putative hydroxysteroid dehydrogenase in Caenorhabditis elegans, as an essential gene for both lipid and ER protein homeostasis. Knockdown of let-767 reduces lipid stores, alters ER morphology in a lipid-dependent manner, and blocks induction of the Unfolded Protein Response of the ER (UPRER). Interestingly, a global reduction in lipogenic pathways restores UPRER induction in animals with reduced let-767. Specifically, we find that supplementation of 3-oxoacyl, the predicted metabolite directly upstream of let-767, is sufficient to block induction of the UPRER. This study highlights a novel interaction through which changes in lipid metabolism can alter a cell's response to protein-induced stress.

Multitranscript analysis reveals an effect of 2-deoxy-d-glucose on gene expression linked to unfolded protein response and integrated stress response in primary human monocytes and monocyte-derived macrophages

BACKGROUND

Glycolytic inhibitor 2-deoxy-d-glucose (2-DG) binds to hexokinase in a non-competitive manner and phosphoglucose isomerase in a competitive manner, blocking the initial steps of the glycolytic pathway. Although 2-DG stimulates endoplasmic reticulum (ER) stress, activating the unfolded protein response to restore protein homeostasis, it is unclear which ER stress-related genes are modulated in response to 2-DG treatment in human primary cells. Here, we aimed to determine whether the treatment of monocytes and monocyte-derived macrophages (MDMs) with 2-DG leads to a transcriptional profile specific to ER stress.

METHODS

We performed bioinformatics analysis to identify differentially expressed genes (DEGs) in previously reported RNA-seq datasets of 2-DG treated cells. RT-qPCR was performed to verify the sequencing data on cultured MDMs.

RESULTS

A total of 95 common DEGs were found by transcriptional analysis of monocytes and MDMs treated with 2-DG. Among these, 74 were up-regulated and 21 were down-regulated. Multitranscript analysis showed that DEGs are linked to integrated stress response (GRP78/BiP, PERK, ATF4, CHOP, GADD34, IRE1α, XBP1, SESN2, ASNS, PHGDH), hexosamine biosynthetic pathway (GFAT1, GNA1, PGM3, UAP1), and mannose metabolism (GMPPA and GMPPB).

CONCLUSIONS

Results reveal that 2-DG triggers a gene expression program that might be involved in restoring protein homeostasis in primary cells.

GENERAL SIGNIFICANCE

2-DG is known to inhibit glycolysis and induce ER stress; however, its effect on gene expression in primary cells is not well understood. This work shows that 2-DG is a stress inducer shifting the metabolic state of monocytes and macrophages.

Atherosclerosis and Inflammation: Insights from the Theory of General Pathological Processes

Recent advances have greatly improved our understanding of the molecular mechanisms behind atherosclerosis pathogenesis. However, there is still a need to systematize this data from a general pathology perspective, particularly with regard to atherogenesis patterns in the context of both canonical and non-classical inflammation types. In this review, we analyze various typical phenomena and outcomes of cellular pro-inflammatory stress in atherosclerosis, as well as the role of endothelial dysfunction in local and systemic manifestations of low-grade inflammation. We also present the features of immune mechanisms in the development of productive inflammation in stable and unstable plaques, along with their similarities and differences compared to canonical inflammation. There are numerous factors that act as inducers of the inflammatory process in atherosclerosis, including vascular endothelium aging, metabolic dysfunctions, autoimmune, and in some cases, infectious damage factors. Life-critical complications of atherosclerosis, such as cardiogenic shock and severe strokes, are associated with the development of acute systemic hyperinflammation. Additionally, critical atherosclerotic ischemia of the lower extremities induces paracoagulation and the development of chronic systemic inflammation. Conversely, sepsis, other critical conditions, and severe systemic chronic diseases contribute to atherogenesis. In summary, atherosclerosis can be characterized as an independent form of inflammation, sharing similarities but also having fundamental differences from low-grade inflammation and various variants of canonical inflammation (classic vasculitis).

Endoplasmic reticulum stress regulates autophagic response that is involved in Saikosaponin a-induced liver cell damage

Saikosaponin a (Ssa) is an active ingredient of the Chinese herbal plant Radix Bupleuri (RB) and has severe hepatotoxicity. However, biomolecular mechanisms involved in Ssa-induced hepatotoxicity are not yet entirely clear. Previous studies reported that Ssd (an isomer of Ssa) as a sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) inhibitor can induce autophagy in apoptotic defective cells, leading to autophagy-dependent cell death. Therefore, we speculate that endoplasmic reticulum (ER) stress and autophagy may also play an important role in Ssa-induced hepatocyte death. This study aimed to explore the connection between ER stress and autophagy and Ssa-induced hepatotoxicity. Experiments in vitro showed that the cell viability of L-02 cells in the Ssa treatment group decreased, the level of autophagy marker LC3-II/LC3-I and Beclin1 increased, the level of p62 decreased, the colocalization of autophagosome and lysosome increased, and the cell viability was significantly increased after the application of autophagy inhibitors 3-MA. In addition, SSa can induce ER stress in L-02 cells in vitro. Further studies demonstrated that SSa activated the PERK/eIF2α/ATF4/CHOP pathway, IRE1-TRAF2 pathway, ATF6 pathway, and AMPK/mTOR pathway associated with ER stress. Application of ER stress inhibitors 4-PBA can significantly down-regulate the level of autophagy and improve cell viability. Results of in vivo experiments showed that treatment with 150 and 300 mg/kg Ssa significantly elevated the liver/body weight ratio and caused histological injury in mice liver. Furthermore, Ssa treatment induced significantly downregulated p62 expression but upregulated LC3-II, CHOP, and GRP78 expression in mice livers. Taken together, our results showed that SSa can activate endoplasmic reticulum stress, promote toxic autophagy, and then induce cell death. We revealed an alternative mechanism involving autophagy and ERs, by which Ssa induced hepatotoxicity.

Insights into the Molecular Mechanisms of NRF2 in Kidney Injury and Diseases

Redox is a constant phenomenon in organisms. From the signaling pathway transduction to the oxidative stress during the inflammation and disease process, all are related to reduction-oxidation (redox). Nuclear factor erythroid 2-related factor 2 (NRF2) is a transcription factor targeting many antioxidant genes. In non-stressed conditions, NRF2 maintains the hemostasis of redox with housekeeping work. It expresses constitutively with basal activity, maintained by Kelch-like-ECH-associated protein 1 (KEAP1)-associated ubiquitination and degradation. When encountering stress, it can be up-regulated by several mechanisms to exert its anti-oxidative ability in diseases or inflammatory processes to protect tissues and organs from further damage. From acute kidney injury to chronic kidney diseases, such as diabetic nephropathy or glomerular disease, many results of studies have suggested that, as a master of regulating redox, NRF2 is a therapeutic option. It was not until the early termination of the clinical phase 3 trial of diabetic nephropathy due to heart failure as an unexpected side effect that we renewed our understanding of NRF2. NRF2 is not just a simple antioxidant capacity but has pleiotropic activities, harmful or helpful, depending on the conditions and backgrounds.

Effects of Spatial Expression of Activating Transcription Factor 4 on the Pathogenicity of Two Phenotypes of Bovine Viral Diarrhea Virus by Regulating the Endoplasmic Reticulum-Mediated Autophagy Process

The endoplasmic reticulum (ER) stress response is a highly conserved stress-defense mechanism and activates the adaptive unfolded protein response (UPR) to mitigate imbalance. The ER stress-activated signaling pathways can also trigger autophagy to facilitate cellular repair. Bovine viral diarrhea virus (BVDV) utilizes the host cellular ER as the primary site of the life cycle. However, the interplay between cellular ER stress and BVDV replication remains unclear. This report reveals that cytopathic (cp) and noncytopathic (ncp) BVDV have distinct strategies to regulate UPR mechanisms and ER stress-mediated autophagy for their own benefit. Immunoblot analysis revealed that cp and ncp BVDV differentially regulated the abundance of ER chaperone GRP78 for viral replication, while the protein kinase RNA-like ER kinase (PERK)-eukaryotic translation initiation factor 2 subunit α (eIF2α)-activating transcription factor 4 (ATF4) pathway of the UPR was switched on at different stages of infection. Pretreatment with ER stress inducer promoted virion replication, but RNA interference (RNAi) knockdown of ATF4 in BVDV-infected cells significantly attenuated BVDV infectivity titers. More importantly, the effector ATF4 activated by cp BVDV infection translocated into the nucleus to mediate autophagy, but ATF4 was retained in the cytoplasm during ncp BVDV infection. In addition, we found that cp BVDV core protein was localized in the ER to induce ER stress-mediated autophagy. Overall, the potential therapeutic target ATF4 may contribute to the global eradication campaign of BVDV. IMPORTANCE The ER-tropic viruses hijack the host cellular ER as the replication platform of the life cycle, which can lead to strong ER stress. The UPR and related transcriptional cascades triggered by ER stress play a crucial role in viral replication and pathogenesis, but little is known about these underlying mechanisms. Here, we report that cytopathic and noncytopathic BVDV use different strategies to reprogram the cellular UPR and ER stress-mediated autophagy for their own advantage. The cytopathic BVDV unconventionally downregulated the expression level of GRP78, creating perfect conditions for self-replication via the UPR, and the noncytopathic BVDV retained ATF4 in the cytoplasm to provide an advantage for its persistent infection. Our findings provide new insights into exploring how BVDV and other ER-tropic viruses reprogram the UPR signaling pathway in the host cells for replication and reveal the attractive host target ATF4 for new antiviral agents.

Sustained overexpression of spliced X-box-binding protein-1 in neurons leads to spontaneous seizures and sudden death in mice

The underlying etiologies of seizures are highly heterogeneous and remain incompletely understood. While studying the unfolded protein response (UPR) pathways in the brain, we unexpectedly discovered that transgenic mice (XBP1s-TG) expressing spliced X-box-binding protein-1 (Xbp1s), a key effector of UPR signaling, in forebrain excitatory neurons, rapidly develop neurologic deficits, most notably recurrent spontaneous seizures. This seizure phenotype begins around 8 days after Xbp1s transgene expression is induced in XBP1s-TG mice, and by approximately 14 days post induction, the seizures evolve into status epilepticus with nearly continuous seizure activity followed by sudden death. Animal death is likely due to severe seizures because the anticonvulsant valproic acid could significantly prolong the lives of XBP1s-TG mice. Mechanistically, our gene profiling analysis indicates that compared to control mice, XBP1s-TG mice exhibit 591 differentially regulated genes (mostly upregulated) in the brain, including several GABAA receptor genes that are notably downregulated. Finally, whole-cell patch clamp analysis reveals a significant reduction in both spontaneous and tonic GABAergic inhibitory responses in Xbp1s-expressing neurons. Taken together, our findings unravel a link between XBP1s signaling and seizure occurrence.

Deficiency of Perry syndrome-associated p150Glued in midbrain dopaminergic neurons leads to progressive neurodegeneration and endoplasmic reticulum abnormalities

Multiple missense mutations in p150Glued are linked to Perry syndrome (PS), a rare neurodegenerative disease pathologically characterized by loss of nigral dopaminergic (DAergic) neurons. Here we generated p150Glued conditional knockout (cKO) mice by deleting p150Glued in midbrain DAergic neurons. The young cKO mice displayed impaired motor coordination, dystrophic DAergic dendrites, swollen axon terminals, reduced striatal dopamine transporter (DAT), and dysregulated dopamine transmission. The aged cKO mice showed loss of DAergic neurons and axons, somatic accumulation of α-synuclein, and astrogliosis. Further mechanistic studies revealed that p150Glued deficiency in DAergic neurons led to the reorganization of endoplasmic reticulum (ER) in dystrophic dendrites, upregulation of ER tubule-shaping protein reticulon 3, accumulation of DAT in reorganized ERs, dysfunction of COPII-mediated ER export, activation of unfolded protein response, and exacerbation of ER stress-induced cell death. Our findings demonstrate the importance of p150Glued in controlling the structure and function of ER, which is critical for the survival and function of midbrain DAergic neurons in PS.

SIRT1 activation synergizes with FXR agonism in hepatoprotection via governing nucleocytoplasmic shuttling and degradation of FXR

Farnesoid X receptor (FXR) is widely accepted as a promising target for various liver diseases; however, panels of ligands in drug development show limited clinical benefits, without a clear mechanism. Here, we reveal that acetylation initiates and orchestrates FXR nucleocytoplasmic shuttling and then enhances degradation by the cytosolic E3 ligase CHIP under conditions of liver injury, which represents the major culprit that limits the clinical benefits of FXR agonists against liver diseases. Upon inflammatory and apoptotic stimulation, enhanced FXR acetylation at K217, closed to the nuclear location signal, blocks its recognition by importin KPNA3, thereby preventing its nuclear import. Concomitantly, reduced phosphorylation at T442 within the nuclear export signals promotes its recognition by exportin CRM1, and thereby facilitating FXR export to the cytosol. Acetylation governs nucleocytoplasmic shuttling of FXR, resulting in enhanced cytosolic retention of FXR that is amenable to degradation by CHIP. SIRT1 activators reduce FXR acetylation and prevent its cytosolic degradation. More importantly, SIRT1 activators synergize with FXR agonists in combating acute and chronic liver injuries. In conclusion, these findings innovate a promising strategy to develop therapeutics against liver diseases by combining SIRT1 activators and FXR agonists.

IRAK2 Downregulation in Triple-Negative Breast Cancer Cells Decreases Cellular Growth In Vitro and Delays Tumour Progression in Murine Models

Breast cancer stem cells (BCSCs) are responsible for tumour recurrence and therapy resistance. We have established primary BCSC cultures from human tumours of triple-negative breast cancer (TNBC), a subgroup of breast cancer likely driven by BCSCs. Primary BCSCs produce xenografts that phenocopy the tumours of origin, making them an ideal model for studying breast cancer treatment options. In the TNBC cell line MDA-MB-468, we previously screened kinases whose depletion elicited a differentiation response, among which IRAK2 was identified. Because primary BCSCs are enriched in IRAK2, we wondered whether IRAK2 downregulation might affect cellular growth. IRAK2 was downregulated in primary BCSCs and MDA-MB-468 by lentiviral delivery of shRNA, causing a decrease in cellular proliferation and sphere-forming capacity. When orthotopically transplanted into immunocompromised mice, IRAK2 knockdown cells produced smaller xenografts than control cells. At the molecular level, IRAK2 downregulation reduced NF-κB and ERK phosphorylation, IL-6 and cyclin D1 expression, ERN1 signalling and autophagy in a cell line-dependent way. Overall, IRAK2 downregulation decreased cellular aggressive growth and pathways often exploited by cancer cells to endure stress; therefore, IRAK2 may be considered an interesting target to compromise TNBC progression.

Integration of ER protein quality control mechanisms defines β cell function and ER architecture

Three principal ER quality-control mechanisms, namely, the unfolded protein response, ER-associated degradation (ERAD), and ER-phagy are each important for the maintenance of ER homeostasis, yet how they are integrated to regulate ER homeostasis and organellar architecture in vivo is largely unclear. Here we report intricate crosstalk among the 3 pathways, centered around the SEL1L-HRD1 protein complex of ERAD, in the regulation of organellar organization in β cells. SEL1L-HRD1 ERAD deficiency in β cells triggers activation of autophagy, at least in part, via IRE1α (an endogenous ERAD substrate). In the absence of functional SEL1L-HRD1 ERAD, proinsulin is retained in the ER as high molecular weight conformers, which are subsequently cleared via ER-phagy. A combined loss of both SEL1L and autophagy in β cells leads to diabetes in mice shortly after weaning, with premature death by approximately 11 weeks of age, associated with marked ER retention of proinsulin and β cell loss. Using focused ion beam scanning electron microscopy powered by deep-learning automated image segmentation and 3D reconstruction, our data demonstrate a profound organellar restructuring with a massive expansion of ER volume and network in β cells lacking both SEL1L and autophagy. These data reveal at an unprecedented detail the intimate crosstalk among the 3 ER quality-control mechanisms in the dynamic regulation of organellar architecture and β cell function.

GRP75 Modulates Endoplasmic Reticulum-Mitochondria Coupling and Accelerates Ca2+-Dependent Endothelial Cell Apoptosis in Diabetic Retinopathy

Endoplasmic reticulum (ER) and mitochondrial dysfunction play fundamental roles in the pathogenesis of diabetic retinopathy (DR). However, the interrelationship between the ER and mitochondria are poorly understood in DR. Here, we established high glucose (HG) or advanced glycosylation end products (AGE)-induced human retinal vascular endothelial cell (RMEC) models in vitro, as well as a streptozotocin (STZ)-induced DR rat model in vivo. Our data demonstrated that there was increased ER-mitochondria coupling in the RMECs, which was accompanied by elevated mitochondrial calcium ions (Ca²⁺) and mitochondrial dysfunction under HG or AGE incubation. Mechanistically, ER-mitochondria coupling was increased through activation of the IP3R1-GRP75-VDAC1 axis, which transferred Ca²⁺ from the ER to the mitochondria. Elevated mitochondrial Ca²⁺ led to an increase in mitochondrial ROS and a decline in mitochondrial membrane potential. These events resulted in the elevation of mitochondrial permeability and induced the release of cytochrome c from the mitochondria into the cytoplasm, which further activated caspase-3 and promoted apoptosis. The above phenomenon was also observed in tunicamycin (TUN, ER stress inducer)-treated cells. Meanwhile, BAPTA-AM (calcium chelator) rescued mitochondrial dysfunction and apoptosis in DR, which further confirmed of our suspicions. In addition, 4-phenylbutyric acid (4-PBA), an ER stress inhibitor, was shown to reverse retinal dysfunction in STZ-induced DR rats in vivo. Taken together, our findings demonstrated that DR fueled the formation of ER-mitochondria coupling via the IP3R1-GRP75-VDAC1 axis and accelerated Ca²⁺-dependent cell apoptosis. Our results demonstrated that inhibition of ER-mitochondrial coupling, including inhibition of GRP75 or Ca²⁺ overload, may be a potential therapeutic target in DR.

The envelope proteins from SARS-CoV-2 and SARS-CoV potently reduce the infectivity of human immunodeficiency virus type 1 (HIV-1)

BACKGROUND

Viroporins are virally encoded ion channels involved in virus assembly and release. Human immunodeficiency virus type 1 (HIV-1) and influenza A virus encode for viroporins. The human coronavirus SARS-CoV-2 encodes for at least two viroporins, a small 75 amino acid transmembrane protein known as the envelope (E) protein and a larger 275 amino acid protein known as Orf3a. Here, we compared the replication of HIV-1 in the presence of four different β-coronavirus E proteins.

RESULTS

We observed that the SARS-CoV-2 and SARS-CoV E proteins reduced the release of infectious HIV-1 yields by approximately 100-fold while MERS-CoV or HCoV-OC43 E proteins restricted HIV-1 infectivity to a lesser extent. Mechanistically, neither reverse transcription nor mRNA synthesis was involved in the restriction. We also show that all four E proteins caused phosphorylation of eIF2-α at similar levels and that lipidation of LC3-I could not account for the differences in restriction. However, the level of caspase 3 activity in transfected cells correlated with HIV-1 restriction in cells. Finally, we show that unlike the Vpu protein of HIV-1, the four E proteins did not significantly down-regulate bone marrow stromal cell antigen 2 (BST-2).

CONCLUSIONS

The results of this study indicate that while viroporins from homologous viruses can enhance virus release, we show that a viroporin from a heterologous virus can suppress HIV-1 protein synthesis and release of infectious virus.