The integrated stress response: From mechanism to disease

Neurotranscriptomic and behavioral effects of ISRIB, and its therapeutic effects in the traumatic brain injury model in zebrafish

Traumatic brain injury (TBI) is a global medical concern and has a lasting impact on brain activity with high risks of mortality. Current treatments are inadequate for repairing damaged brain cells or correcting cognitive and behavioral disabilities in TBI patients. Mounting evidence links TBI to the activation of the Integrated Stress Response (ISR) signaling in the brain. A novel small molecule, ISRIB, is an effective inhibitor of the ISR pathway, offering potential advantages for brain health. Here, we investigated how ISRIB affects brain transcriptome and behavior in zebrafish TBI model evoked by telencephalic brain injury. Overall, while TBI diminished memory and social behavior in zebrafish, administering ISRIB post-injury markedly reduced these behavioral deficits, and modulated brain gene expression, rescuing TBI-activated pathways related to inflammation and brain cell development. Collectively, this supports the role of brain ISR in TBI, and suggests potential utility of ISRIB for the treatment of TBI-related states.

Mitochondrial 'Birth-Death' coordinator: An intelligent hydrogen nanogenerator to enhance intervertebral disc regeneration

Currently, mitochondrial dysfunction caused by oxidative stress is a growing concern in degenerative diseases, notably intervertebral disc degeneration (IVDD). Dysregulation of the balance of mitochondrial quality control (MQC) has been considered the key contributor, while it's still challenging to effectively harmonize different MQC components in a simple and biologically safe way. Hydrogen gas (H2) is a promising mitochondrial therapeutic molecule due to its bio-reductivity and diffusibility across cellular membranes, yet its relationship with MQC regulation remains unknown. Herein, we propose a mitochondrial 'Birth-Death' coordinator achieved by an intelligent hydrogen nanogenerator (Fe@HP-OD), which can sustainably release H2 in response to the unique microenvironment in degenerated IVDs. Both in vitro and in vivo results prove alleviation of cellular oxidative stress and restoration of nucleus pulposus cells function, thereby facilitating successful IVD regeneration. Significantly, this study for the first time proposes the mitochondrial 'Birth-Death' coordination mechanism: 1) attenuation of overactivated mitochondrial 'Death' process (UPRmt and unselective mitophagy); and 2) activation of Adenosine 5'-monophosphate-activated protein kinase (AMPK) signaling pathway for mitochondrial 'Birth-Death' balance (mitochondrial biogenesis and controlled mitophagy). These pioneering findings can fill in the gaps in molecular mechanisms for H2 regulation on MQC homeostasis, and pave the way for future strategies towards restoring equilibrium of MQC system against degenerative diseases.

Selenoprotein K at the intersection of cellular pathways

Selenoprotein K (selenok) is linked to the integrated stress response, which helps cells combat stressors and regain normal function. The selenoprotein contains numerous protein interaction hubs and post-translational modification sites and is involved in protein palmitoylation, vesicle trafficking, and the resolution of ER stress. Anchored to the endoplasmic reticulum (ER) membrane, selenok interacts with protein partners to influence their stability, localization, and trafficking, impacting various cellular functions such as calcium homeostasis, cellular migration, phagocytosis, gene expression, and immune response. Consequently, selenok expression level is linked to cancer and neurodegenerative diseases. Because it contains the reactive amino acid selenocysteine, selenok is likely to function as an enzyme. However, highly unusual for enzymes, the protein segment containing the selenocysteine lacks a stable secondary or tertiary structure, yet it includes multiple interaction sites for protein partners and post-translational modifications. Currently, the reason(s) for the presence of the rare selenocysteine in selenok is not known. Furthermore, of selenok's numerous interaction sites, only some have been sufficiently characterized, leaving many of selenok's potential protein partners to be discovered. In this review, we explore selenok's role in various cellular pathways and its impact on human health, thereby highlighting the links between its diverse cellular functions.

Chronic CRYPTOCHROME deficiency enhances cell-intrinsic antiviral defences

The within-host environment changes over circadian time and influences the replication and severity of viruses. Genetic knockout of the circadian transcription factors CRYPTOCHROME 1 and CRYPTOCHROME 2 (CRY1-/-/CRY2-/-; CKO) leads to altered protein homeostasis and chronic activation of the integrated stress response (ISR). The adaptive ISR signalling pathways help restore cellular homeostasis by downregulating protein synthesis in response to endoplasmic reticulum overloading or viral infections. By quantitative mass spectrometry analysis, we reveal that many viral recognition proteins and type I interferon (IFN) effectors are significantly upregulated in lung fibroblast cells from CKO mice compared with wild-type (WT) mice. This basal 'antiviral state' restricts the growth of influenza A virus and is governed by the interaction between proteotoxic stress response pathways and constitutive type I IFN signalling. CKO proteome composition and type I IFN signature were partially phenocopied upon sustained depletion of CRYPTOCHROME (CRY) proteins using a small-molecule CRY degrader, with modest differential gene expression consistent with differences seen between CKO and WT cells. Our results highlight the crosstalk between circadian rhythms, cell-intrinsic antiviral defences and protein homeostasis, providing a tractable molecular model to investigate the interface of these key contributors to human health and disease.This article is part of the Theo Murphy meeting issue 'Circadian rhythms in infection and immunity'.

Spatial covariance reveals isothiocyanate natural products adjust redox stress to restore function in alpha-1-antitrypsin deficiency

Alpha-1 antitrypsin (AAT) deficiency (AATD) is a monogenic disease caused by misfolding of AAT variants resulting in gain-of-toxic aggregation in the liver and loss of monomer activity in the lung leading to chronic obstructive pulmonary disease (COPD). Using high-throughput screening, we discovered a bioactive natural product, phenethyl isothiocyanate (PEITC), highly enriched in cruciferous vegetables, including watercress and broccoli, which improves the level of monomer secretion and neutrophil elastase (NE) inhibitory activity of AAT-Z through the endoplasmic reticulum (ER) redox sensor protein disulfide isomerase (PDI) A4 (PDIA4). The intracellular polymer burden of AAT-Z can be managed by combination treatment of PEITC and an autophagy activator. Using Gaussian process (GP)-based spatial covariance (SCV) (GP-SCV) machine learning to map on a residue-by-residue basis at atomic resolution all variants in the worldwide AATD clinical population, we reveal a global rescue of monomer secretion and NE inhibitory activity for most variants triggering disease. We present a proof of concept that GP-SCV mapping of restoration of AAT variant function serves as a standard model to discover natural products such as the anti-oxidant PEITC that could potentially impact the redox/inflammatory environment of the ER to provide a nutraceutical approach to help minimize disease in AATD patients.

Tea Polyphenol-Derived Carbon Dots Alleviate Abdominal Aortic Aneurysm Progression by Mitigating Oxidative Stress and Ferroptosis

Abdominal aortic aneurysm (AAA) is a cardiovascular disease with potentially fatal consequences, yet effective therapies to prevent its progression remain unavailable. Oxidative stress is associated with AAA development. Carbon dots have reactive oxygen species-scavenging activity, while green tea extract exhibits robust antioxidant properties. However, the potential of green tea derived carbon dots in mitigating AAA progression has not been fully elucidated. In this study, tea polyphenol carbon dots (TP-CDs) were synthesized via hydrothermal methods and characterized for their antioxidant properties. The antioxidant effects of TP-CDs were evaluated, and TP-CDs' impact on phenotypic transformation, oxidative stress, apoptosis and ferroptosis was investigated comprehensively in an Ang II-induced AAA model, employing techniques such as Western blotting, flow cytometry, and immunohistochemistry. The results revealed that TP-CDs effectively alleviated oxidative stress induced by Ang II stimulation, thereby inhibiting phenotypic transformation, apoptosis, and ferroptosis in vivo. Furthermore, treatment with TP-CDs significantly attenuated AAA progression in a mouse AAA model. Overall, these findings demonstrate that TP-CDs reduced reactive oxygen species levels in the microenvironment and alleviated the progression of AAA, offering a promising therapeutic strategy for this condition.

Hypusinated and unhypusinated isoforms of the translation factor eIF5A exert distinct effects in models of pancreas development and function

Hypusination of eukaryotic translation initiation factor 5A (eIF5A) is essential for its role in translation elongation and termination. Although the function of hypusinated eIF5A (eIF5AHyp) in cellular proliferation is well-characterized, the role of its unhypusinated form (eIF5ALys) remains unclear. We hypothesized that eIF5ALys exerts independent, negative effects on cellular replication and metabolism, distinct from the loss of eIF5AHyp. To test this hypothesis, we utilized zebrafish and mouse models with inducible knockdowns of deoxyhypusine synthase (DHPS) and eIF5A to investigate their roles in cellular growth. Gene expression analysis via RNA sequencing and morphometric measurements of pancreas and β-cell mass were performed to assess phenotypic changes and identify affected biological pathways. Loss of DHPS in zebrafish resulted in significant defects in pancreatic growth, accompanied by changes in gene expression related to mRNA translation, neurogenesis, and stress pathways. By contrast, knockdown of eIF5A had minimal impact on pancreas development, suggesting that the effects of DHPS loss are not solely due to the lack of eIF5AHyp. In mice, β cell-specific deletion of DHPS impaired β cell mass expansion and glucose tolerance, while eIF5A deletion had no statistically significant effects. These findings provide evidence for an independent role for eIF5ALys in regulating developmental and functional responses in pancreas health and disease.

PHGDH Induction by MAPK Is Essential for Melanoma Formation and Creates an Actionable Metabolic Vulnerability

Overexpression of phosphoglycerate dehydrogenase (PHGDH), the rate-limiting enzyme in the serine synthesis pathway, promotes melanomagenesis, melanoma cell proliferation, and survival of metastases in serine-low environments such as the brain. Here, we found that PHGDH is universally increased in melanoma cells and required for melanomagenesis. Although PHGDH amplification explained PHGDH overexpression in a subset of melanomas, oncogenic BRAFV600E also promoted PHGDH transcription through mTORC1-mediated translation of ATF4. Importantly, depletion of PHGDH in genetic mouse melanoma models blocked tumor formation. In addition to BRAFV600E-mediated upregulation, PHGDH was further induced by exogenous serine restriction. Surprisingly, BRAFV600E inhibition diminished serine restriction-mediated PHGDH expression by preventing ATF4 induction. Consequently, melanoma cells could be specifically starved of serine by combining BRAFV600E inhibition with exogenous serine restriction, which promoted cell death in vitro and attenuated melanoma growth in vivo. In summary, this study identified that PHGDH is essential for melanomagenesis and regulated by BRAFV600E, revealing a targetable vulnerability in BRAFV600E-mutant melanoma. Significance: BRAFV600E promotes the expression of the serine synthesis enzyme PHGDH, which is required for melanoma formation, and can be targeted to sensitize melanoma to dietary serine restriction, providing a melanoma cell-specific treatment strategy.

Development and validation of a UHPLC-MS/MS method for the quantitative analysis of trans-ISRIB in human plasma

The integrated stress response (ISR) is a cellular defense mechanism activated under stress conditions. When the ISR is activated, it slows the production of proteins, the building blocks that cells need to function. Trans-integrated stress response inhibitor (trans-ISRIB) is a compound that can reverse the effects of ISR activation, showing promise for treating neurodegenerative diseases. The preclinical and clinical evaluation of trans-ISRIB necessitates a reliable analytical method. This study presents the development and validation of an ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for the quantitative analysis of trans-ISRIB in human plasma, conforming to the U.S. FDA's guidelines for bioanalytical method validation. The method developed utilizes a liquid-liquid extraction procedure to prepare plasma samples with a spiked internal standard (IS). The extracts containing trans-ISRIB and the IS were dried under nitrogen, reconstituted in the mobile phase, and separated on a Waters XSelect HSS T3 column under isocratic conditions with a mobile phase containing 0.1 % acetic acid in 70 % methanol aqueous solution at a flow rate of 0.500 mL/min. Detection and quantification were accomplished using a positive electrospray ionization tandem mass spectrometer (ESI+-MS/MS) operated in multiple-reaction-monitoring (MRM) mode. The method demonstrated a linear calibration range for trans-ISRIB concentrations from 0.500 to 1.00 x 103 nM, with high specificity, precision, accuracy, and recovery. This method addresses a significant analytical gap, offering a robust tool for quantifying trans-ISRIB in human plasma. Chemical compounds studied in this article: 2-(4-chlorophenoxy)-N-[4-[[2-(4-chlorophenoxy)acetyl]amino]cyclohexyl]acetamide (trans-ISRIB) (CAS # 1597403-47-8); 2-(4-chlorophenoxy)-N-(2-{[(4-chlorophenoxy)acetyl]amino}ethyl)acetamide (CAS # 327071-30-7).

Mitochondrial diseases: from molecular mechanisms to therapeutic advances

Mitochondria are essential for cellular function and viability, serving as central hubs of metabolism and signaling. They possess various metabolic and quality control mechanisms crucial for maintaining normal cellular activities. Mitochondrial genetic disorders can arise from a wide range of mutations in either mitochondrial or nuclear DNA, which encode mitochondrial proteins or other contents. These genetic defects can lead to a breakdown of mitochondrial function and metabolism, such as the collapse of oxidative phosphorylation, one of the mitochondria's most critical functions. Mitochondrial diseases, a common group of genetic disorders, are characterized by significant phenotypic and genetic heterogeneity. Clinical symptoms can manifest in various systems and organs throughout the body, with differing degrees and forms of severity. The complexity of the relationship between mitochondria and mitochondrial diseases results in an inadequate understanding of the genotype-phenotype correlation of these diseases, historically making diagnosis and treatment challenging and often leading to unsatisfactory clinical outcomes. However, recent advancements in research and technology have significantly improved our understanding and management of these conditions. Clinical translations of mitochondria-related therapies are actively progressing. This review focuses on the physiological mechanisms of mitochondria, the pathogenesis of mitochondrial diseases, and potential diagnostic and therapeutic applications. Additionally, this review discusses future perspectives on mitochondrial genetic diseases.

The integrated stress response drives MET oncogene overexpression in cancers

Cancer cells rely on invasive growth to survive in a hostile microenvironment; this growth is characterised by interconnected processes such as epithelial-to-mesenchymal transition and migration. A master regulator of these events is the MET oncogene, which is overexpressed in the majority of cancers; however, since mutations in the MET oncogene are seen only rarely in cancers and are relatively infrequent, the mechanisms that cause this widespread MET overexpression remain obscure. Here, we show that the 5' untranslated region (5'UTR) of MET mRNA harbours two functional stress-responsive elements, conferring translational regulation by the integrated stress response (ISR), regulated by phosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2α) at serine 52. ISR activation by serum starvation, leucine deprivation, hypoxia, irradiation, thapsigargin or gemcitabine is followed by MET protein overexpression. We mechanistically link MET translation to the ISR by (i) mutation of the two uORFs within the MET 5'UTR, (ii) CRISPR/Cas9-mediated mutation of eIF2α (S52A), or (iii) the application of ISR pathway inhibitors. All of these interventions reduce stress-induced MET overexpression. Finally, we show that blocking stress-induced MET translation blunts MET-dependent invasive growth. These findings indicate that upregulation of the MET oncogene is a functional requirement linking integrated stress response to cancer progression.

Reduced White Matter Damage and Lower Neuroinflammatory Potential of Microglia and Macrophages in Hri/Eif2ak1-/- Mice After Contusive Spinal Cord Injury

Cellular stressors inhibit general protein synthesis while upregulating stress response transcripts and/or proteins. Phosphorylation of the translation factor eIF2α by one of the several stress-activated kinases is a trigger for such signaling, known as the integrated stress response (ISR). The ISR regulates cell survival and function under stress. Here, germline knockout mice were used to determine contributions by three major ISR kinases, HRI/EIF2AK1, GCN2/EIF2AK4, and PKR//EIF2AK2, to pathogenesis of moderate contusive spinal cord injury (SCI) at the thoracic T9 level. One-day post-injury (dpi), reduced levels of peIF2α were found in Hri-/- and Gcn2-/-, but not in Pkr-/- mice. In addition, Hri-/- mice showed attenuated expression of the downstream ISR transcripts, Atf4 or Chop. Such differential effects of SCI-activated ISR correlated with a strong or moderate enhancement of locomotor recovery in Hri-/- or Gcn2-/- mice, respectively. Hri-/- mice also showed reduced white matter loss, increased content of oligodendrocytes (OL) and attenuated neuroinflammation, including decreased lipid accumulation in microglia/macrophages. Cultured neonatal Hri-/- OLs showed lower ISR cytotoxicity. Moreover, cell autonomous reduction in neuroinflammatory potential was observed in microglia and bone marrow-derived macrophages derived from Hri-/- mice. These data identify HRI as a major positive regulator of SCI-associated secondary injury. In addition, targeting HRI may enable multimodal neuroprotection to enhance functional recovery after SCI.

The interplay between gut microbiota and the unfolded protein response: Implications for intestinal homeostasis preservation and dysbiosis-related diseases

The unfolded protein response (UPR) is a complex intracellular signal transduction system that orchestrates the cellular response during Endoplasmic Reticulum (ER) stress conditions to reestablish cellular proteostasis. If, on one side, prolonged ER stress conditions can lead to programmed cell death and autophagy as a cytoprotective mechanism, on the other, unresolved ER stress and improper UPR activation represent a perilous condition able to trigger or exacerbate inflammatory responses. Notably, intestinal and immune cells experience ER stress physiologically due to their high protein secretory rate. Indeed, there is evidence of UPR's involvement in both physiological and pathological intestinal conditions, while less is known about its bidirectional interaction with gut microbiota. However, gut microbes and their metabolites can influence ER stress and UPR pathways, and, in turn, ER stress conditions can shape gut microbiota composition, with important implications for overall intestinal health. Thus, targeting UPR components is an intriguing strategy for treating ER stress-linked dysbiosis and diseases, particularly intestinal inflammation.

PIM2 inhibition promotes MCL1 dependency in plasma cells involving integrated stress response-driven NOXA expression

Our study explores the complex dynamics of the integrated stress response (ISR) axis, highlighting PIM2 kinase's critical role and its interaction with the BCL2 protein family, uncovering key mechanisms of cell survival and tumor progression. Elevated PIM2 expression, a marker of various cancers, often correlates with disease aggressiveness. Using a model of normal and malignant plasma cells, we show that inhibiting PIM2 kinase inhibits phosphorylated BAD production and activates ISR-mediated NOXA expression. This shift towards MCL1 dependence underscores the synergy achieved through combined PIM/MCL1 inhibition, driven largely by ISR-mediated NOXA expression. In mouse xenograft models, dual targeting of PIM2 and MCL1 effectively controls tumor growth-a response reversed by ISR-specific inhibition and upregulation of genes linked to tumor cell dissemination. This work elucidates the molecular intricacies of PIM2 inhibition and its implications for cancer therapy, especially in tumors with elevated PIM2 expression.

Sensory quiescence induces a cell-non-autonomous integrated stress response curbed by condensate formation of the ATF4 and XRP1 effectors

Sensory disabilities have been identified as significant risk factors for dementia but underlying molecular mechanisms are unknown. In different Drosophila models with loss of sensory input, we observe non-autonomous induction of the integrated stress response (ISR) deep in the brain, as indicated by eIF2αS50 phosphorylation-dependent elevated levels of the ISR effectors ATF4 and XRP1. Unlike during canonical ISR, however, the ATF4 and XRP1 transcription factors are enriched in cytosolic granules that are positive for RNA and the stress granule markers Caprin, FMR1, and p62, and are reversible upon restoration of vision for blind flies. Cytosolic restraint of the ATF4 and XRP1 transcription factors dampens expression of their downstream targets including genes of cell death pathways activated during chronic cellular stress and thus constitutes a chronic stress protective response (CSPR). Cytosolic granules containing both p62 and ATF4 are also evident in the thalamus and hippocampus of mouse models of congenital or degenerative blindness. These data indicate a conserved link between loss of sensory input and curbed stress responses critical for protein quality control in the brain.

Stress Granule Induction in Rat Retinas Damaged by Constant LED Light

Purpose

Stress granules (SGs) are cytoplasmic biocondensates formed in response to various cellular stressors, contributing to cell survival. Although implicated in diverse pathologies, their role in retinal degeneration (RD) remains unclear. We aimed to investigate SG formation in the retina and its induction by excessive LED light in an RD model.

Methods

Rat retinas were immunohistochemically analyzed for SG markers G3BP1 and eIF3, and SGs were also visualized by RNA fluorescence in situ hybridization. Additionally, SGs were induced in primary retinal cell and eyeball cultures using sodium arsenite. Light exposure experiments used LED lamps with a color temperature of 5500 K and 200 lux intensity for short-term or two- to eight-day exposures.

Results

SGs were predominantly detected in retinal ganglion cells (RGCs) and inner nuclear layer (INL) cells, with arsenite-induction verified in RGCs. SG abundance was higher in animals exposed to light for 2-8 days compared to light/dark cycle controls. RGCs consistently exhibited more SGs than INL cells, and INL cells more than outer nuclear layer (ONL) cells (Scheirer-Ray-Hare test: H = 13.2, P = 0.0103 for light condition, and H = 278.2, P < 0.00001 for retinal layer). These observations were consistent across four independent experiments, each with three animals per light condition.

Conclusions

This study characterizes SGs in the mammalian retina for the first time, with increased prevalence after excessive LED light exposure. RGCs and INL cells showed heightened SG formation, suggesting a potential protective mechanism against photodamage. Further investigations are warranted to elucidate the role of SGs in shielding against light stress and their implications in retinopathies.

When "loss-of-function" means proteostasis burden: Thinking again about coding DNA variants

Each human genome has approximately 5 million DNA variants. Even for complete loss-of-function variants causing inherited, monogenic diseases, current understanding based on gene-specific molecular function does not adequately predict variability observed between people with identical mutations or fluctuating disease trajectories. We present a parallel paradigm for loss-of-function variants based on broader consequences to the cell when aberrant polypeptide chains of amino acids are translated from mutant RNA to generate mutated proteins. Missense variants that modify primary amino acid sequence, and nonsense/frameshift variants that generate premature termination codons (PTCs), are placed in context alongside emergent themes of chaperone binding, protein quality control capacity, and cellular adaptation to stress. Relatively stable proteostasis burdens are contrasted with rapid changes after induction of gene expression, or stress responses that suppress nonsense mediated decay (NMD) leading to higher PTC transcript levels where mutant proteins can augment cellular stress. For known disease-causal mutations, an adjunctive variant categorization system enhances clinical predictive power and precision therapeutic opportunities. Additionally, with typically more than 100 nonsense and frameshift variants, and ∼10,000 missense variants per human DNA, the paradigm focuses attention on all protein-coding DNA variants, and their potential contributions to multimorbid states beyond classically designated inherited diseases. Experimental testing in clinically relevant systems is encouraged to augment current atlases of protein expression at single-cell resolution, and high-throughput experimental data and deep-learning models that predict which amino acid substitutions generate enhanced degradative burdens. Incorporating additional dimensions such as pan-proteome competition for chaperones, and age-related loss of proteostasis capacity, should further accelerate health impacts.

Emerging Molecular-Genetic Families in Dystonia: Endosome-Autophagosome-Lysosome and Integrated Stress Response Pathways

Advances in genetic technologies and disease modeling have greatly accelerated the pace of introducing and validating molecular-genetic contributors to disease. In dystonia, there is a growing convergence across multiple distinct forms of the disease onto core biological processes. Here, we discuss two of these, the endosome-autophagosome-lysosome pathway and the integrated stress response, to highlight recent advances in the field. Using these two pathomechanisms as examples, we further discuss the opportunities that molecular-genetic grouping of dystonias present to transform dystonia care. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Wars1 downregulation in hepatocytes induces mitochondrial stress and disrupts metabolic homeostasis

Several laboratories, including ours, have employed the Slc25a47tm1c(EUCOMM)Hmgu mouse model to investigate the role of SLC25A47, a hepatocyte-specific mitochondrial carrier, in regulating hepatic metabolism and systemic physiology. In this study, we reveal that the hepatic and systemic phenotypes observed following recombination of the Slc25a47-Wars1 locus in hepatocytes are primarily driven by the unexpected downregulation of Wars1, the cytosolic tryptophan aminoacyl-tRNA synthetase located adjacent to Slc25a47. While the downregulation of Wars1 predictably affects cytosolic translation, we also observed a significant impairment in mitochondrial protein synthesis within hepatocytes. This disturbance in mitochondrial function leads to an activation of the mitochondrial unfolded protein response (UPRmt), a critical component of the mitochondrial stress response (MSR). Our findings clarify the distinct roles of Slc25a47 and Wars1 in maintaining both systemic and hepatic metabolic homeostasis. This study sheds new light on the broader implications of aminoacyl-tRNA synthetases in mitochondrial physiology and stress responses.

Heat shock protein HSPA8 impedes hemin-induced cellular-toxicity in liver

Accumulation of hemin in cells, tissues, and organs is one of the major pathological conditions linked to hemolytic diseases like malaria. Pro-oxidant hemin confers high toxicity following its accumulation. We tested the cellular toxicity of hemin on HepG2 cells by exploring modulation in various cellular characteristics. Hemin reduces the viability of HepG2 cells and brings about visible morphological changes. Hemin causes perforations on the surface of HepG2 cells observed through SEM. Hemin leads to the extracellular release of liver enzymes and reduces the wound-healing potential of HepG2 cells. Hemin leads to the fragmentation of HepG2 DNA, arrests the cell cycle progression in the S-phase and induces apoptosis in these cells. Western blot analysis revealed that hemin triggers both the extrinsic and intrinsic pathways of apoptosis in HepG2 cells. We have already shown that the cytoprotective protein HSPA8 can polymerize hemin and minimize its toxicity. Similar experiments with hemin in the presence and absence of HSPA8 showed that HSPA8 reverses all the tested toxic effects of hemin on HepG2 cells. The protection from hemin toxicity in HepG2 cells appeared to be due to the extracellular polymerization of hemin by HSPA8.

Astrocytic proteostasis in the tale of aging and neurodegeneration

Homeostasis of proteins (proteostasis), which governs protein processing, folding, quality control, and degradation, is a fundamental cellular process that plays a pivotal role in various neurodegenerative diseases and in the natural aging process of the mammalian brain. While the role of neuronal proteostasis in neuronal physiology is well characterized, the contribution of proteostasis of glial cells, particularly of astrocytes, has received fairly less attention in this context. Here, we summarize recent data highlighting proteostasis dysfunction in astrocytes and its putative implication to neurodegenerative diseases and aging. We discuss how distinct proteostasis nodes and pathways in astrocytes may specifically contribute to brain function and different age-associated pathologies. Finally, we argue that the understanding of astrocytic proteostasis role in neuronal physiology and functional decay may arise as a potential new avenue of intervention in neurodegenerative diseases and grant relevant data in the biology of aging.

ADAR1: from basic mechanisms to inhibitors

Adenosine deaminase acting on RNA 1 (ADAR1) converts adenosine to inosine in double-stranded RNA (dsRNA) molecules, a process known as A-to-I editing. ADAR1 deficiency in humans and mice results in profound inflammatory diseases characterised by the spontaneous induction of innate immunity. In cells lacking ADAR1, unedited RNAs activate RNA sensors. These include melanoma differentiation-associated gene 5 (MDA5) that induces the expression of cytokines, particularly type I interferons (IFNs), protein kinase R (PKR), oligoadenylate synthase (OAS), and Z-DNA/RNA binding protein 1 (ZBP1). Immunogenic RNAs 'defused' by ADAR1 may include transcripts from repetitive elements and other long duplex RNAs. Here, we review these recent fundamental discoveries and discuss implications for human diseases. Some tumours depend on ADAR1 to escape immune surveillance, opening the possibility of unleashing anticancer therapies with ADAR1 inhibitors.

Aminoacyl-tRNA synthetase defects in neurological diseases

Aminoacyl-tRNA synthetases (aaRSs) are essential enzymes to support protein synthesis in all organisms. Recent studies, empowered by advancements in genome sequencing, have uncovered an increasing number of disease-causing mutations in aaRSs. Monoallelic aaRS mutations typically lead to dominant peripheral neuropathies such as Charcot-Marie-Tooth (CMT) disease, whereas biallelic aaRS mutations often impair the central nervous system (CNS) and cause neurodevelopmental disorders. Here, we review recent progress in the disease onsets, molecular basis, and potential therapies for diseases caused by aaRS mutations, with a focus on biallelic mutations in cytoplasmic aaRSs.

The mitochondrial integrated stress response: A novel approach to anti-aging and pro-longevity

The ISR is a cellular signaling pathway that responds to various physiological changes and types of stimulation. The mitochondrial integrated stress response (ISRmt) is a stress response specific to mitochondria which is initiated by eIF2α phosphorylation and is responsive to mitochondrial stressors. The ISRmt triggers diverse metabolic responses reliant on activating transcription factor 4 (ATF4). The preliminary phases of ISRmt can provoke an adaptive stress response that antagonizes age-related diseases and promotes longevity. In this review, we provide an overview of the molecular mechanisms of the ISRmt, with a particular focus on its potential as a therapeutic target for age-related disease and the promotion of longevity.

GDF15 antagonism limits severe heart failure and prevents cardiac cachexia

AIMS

Heart failure and associated cachexia is an unresolved and important problem. This study aimed to determine the factors that contribute to cardiac cachexia in a new model of heart failure in mice that lack the integrated stress response (ISR) induced eIF2α phosphatase, PPP1R15A.

METHODS AND RESULTS

Mice were irradiated and reconstituted with bone marrow cells. Mice lacking functional PPP1R15A, exhibited dilated cardiomyopathy and severe weight loss following irradiation, whilst wild-type mice were unaffected. This was associated with increased expression of Gdf15 in the heart and increased levels of GDF15 in circulation. We provide evidence that the blockade of GDF15 activity prevents cachexia and slows the progression of heart failure. We also show the relevance of GDF15 to lean mass and protein intake in patients with heart failure.

CONCLUSION

Our data suggest that cardiac stress mediates a GDF15-dependent pathway that drives weight loss and worsens cardiac function. Blockade of GDF15 could constitute a novel therapeutic option to limit cardiac cachexia and improve clinical outcomes in patients with severe systolic heart failure.

Sexually dimorphic ATF4 expression in the fat confers female stress tolerance in Drosophila melanogaster

Metabolic differences between males and females have been well documented across many species. However, the molecular basis of these differences and how they impact tolerance to nutrient deprivation is still under investigation. In this work, we use Drosophila melanogaster to demonstrate that sex-specific differences in fat tissue metabolism are driven, in part, by dimorphic expression of the Integrated Stress Response (ISR) transcription factor, ATF4. We found that female fat tissues have higher ATF4 activity than their male counter parts under homeostatic conditions. This dimorphism was partly due to a female bias in transcript abundance of specific ATF4 splice isoforms. We found that the canonical sex determinants transformer (tra) and doublesex (dsx) drive such dimorphic ATF4 transcript abundance. These differences persist in a genetic model of nutrient deprivation, where female animals showed greater resistance to lethality than males in an ATF4-dependent manner. These results suggest that higher ATF4 activity confers higher tolerance to stress in females. Together, our data describe a previously unknown facet of ISR signaling wherein sexual identity of adipose tissue confers differential stress tolerance in males and females. Since energy storage mechanisms are known to be dimorphic and have been linked to ATF4 regulation, our studies provide a mechanistic starting point for understanding how sexual identity influences metabolic disease outcomes.

SUCNR 1 promotes atherosclerosis by inducing endoplasmic reticulum stress mediated ER-mito crosstalk

Atherosclerosis is a progressive inflammatory disease within the large and medium arteries. SUCNR1(Succinate receptor 1) has been reported to regulate the inflammatory response in cardiovascular diseases, but how it works in atherosclerosis remains unclear. In this study, we observed that SUCNR1 is upregulated in endothelial cells within human atherosclerotic lesions. The deletion of SUCNR1 in vascular endothelial cells can mitigate the progression of atherosclerotic lesions in high-fat diet ApoE-/- mice. The overexpression or activation of SUCNR1 intensified endoplasmic reticulum stress and mitochondria-endoplasmic reticulum interactions. Moreover, SUCNR1 exacerbated mitochondrial injury, mtDNA leakage, and the activation of cGAS-STING signaling. Elevated mitochondrial damage, ER-mitochondrial interactions, and inflammation induced by SUCNR1 activation were blocked by the endoplasmic reticulum stress inhibitor. Collectively, these findings suggest that SUCNR1 promotes atherosclerosis through endoplasmic reticulum stress signaling mediated ER-mitochondrial crosstalk and its downstream cGAS-STING pathway. Our results provide new insights into the mechanism of SUCNR1 in atherosclerosis and inhibiting endoplasmic reticulum stress signaling may provide a promising strategy to prevent and treat atherosclerosis.

Mapping the Genetic Architecture of the Adaptive Integrated Stress Response in S. cerevisiae

The integrated stress response (ISR) is a conserved eukaryotic signaling pathway that responds to diverse stress stimuli to restore proteostasis. The strength and speed of ISR activation must be tuned properly to allow protein synthesis while maintaining proteostasis. Here, we describe how genetic perturbations change the dynamics of the ISR in budding yeast. We treated ISR dynamics, comprising timecourses of ISR activity across different levels of stress, as a holistic phenotype. We profiled changes in ISR dynamics across thousands of genetic perturbations in parallel using CRISPR interference with barcoded expression reporter sequencing (CiBER-seq). We treated cells with sulfometuron methyl, a titratable inhibitor of branched-amino acid synthesis, and measured expression of an ISR reporter. Perturbations to translation such as depletion of aminoacyl-tRNA synthetases or tRNA biogenesis factors reduced cell growth and caused a strikingly proportionate activation of the ISR activation. In contrast, impaired ribosome biogenesis reduced basal ISR activity and weakened ISR dynamics. Reduced ribosome capacity may lower the demand for amino acids and thereby explain these changes. Our work illustrates how CiBER-seq enables high-throughput measurements of complex and dynamic phenotypes that shed light on adaptive and homeostatic mechanisms.

Role of periodontal ligament fibroblasts in periodontitis: pathological mechanisms and therapeutic potential

Periodontal ligament fibroblasts (PDLFs) play a crucial role in the etiology of periodontitis and periodontal tissue regeneration. In healthy periodontal tissues, PDLFs maintain the homeostasis of periodontal soft and hard tissues as well as the local immune microenvironment. PDLFs also have the potential for multidirectional transdifferentiation and are involved in periodontal tissue regeneration. On the other hand, PDLFs can become dysfunctional and acquire an inflammatory phenotype to secret various inflammatory cytokines when affected by pathological factors. These cytokines further trigger immune and inflammatory events, and lead to destruction of periodontal soft and hard tissues as well as damage to the regenerative potential of PDLFs. This review summarizes the physiological functions of PDLFs. Meanwhile, this review also highlights recent insights into the pathological mechanisms driving the development of periodontitis through dysfunctional PDLFs and the negative impact on periodontal tissue regeneration. Additionally, this paper summarizes strategies for targeting PDLFs to treat periodontitis, involving blocking multiple stages of the inflammatory response induced by PDLFs and promoting the multidirectional transdifferentiation of PDLFs. Future research directions are proposed to address important questions that have not yet been answered in this field. This article provides a reference for understanding the important role of PDLFs in the pathological mechanisms of periodontitis and for developing new strategies for targeting PDLFs in periodontitis treatment.

Inhibition of the Integrated Stress Response Prevents Natural Forgetting and Corrects Accelerated Forgetting Associated with Epilepsy

The neural mechanisms underlying the natural and maladaptive forgetting of established memory remain largely unknown. Brain disease states might hijack the physiological forgetting mechanisms, resulting in maladaptive forgetting such as accelerated forgetting that contributes to cognitive decline in various neurologic conditions including epilepsy. Based on the key role of the integrated stress response (ISR) in memory storage and maintenance, we determined whether the ISR underpins natural and accelerated forgetting. Here, based on the object location recognition (OLR) and novel object recognition (NOR) paradigms in mice, we found that the ISR was activated while an established memory was naturally forgotten, which was denoted by increased levels of phosphorylated eukaryotic translation initiation factor 2α (eIF2α) and activating transcription factor 4 (ATF4), and reduced general protein synthesis. Multiple administrations of ISRIB, a small molecule ISR inhibitor, during the memory retention interval attenuated the ISR activation, and prevented the natural forgetting of established OLR and NOR memories. At the same time, a single injection of ISRIB has no effect on natural forgetting and memory retrieval. Moreover, administration of pentylenetetrazole (PTZ), an inducer of epileptic seizures, during the memory retention interval provoked the ISR activation and accelerated forgetting, which was corrected by ISRIB treatment. Together, our findings suggest that the ISR is critically involved in natural forgetting and accelerated forgetting associated with epilepsy, and pharmacological inhibition of the ISR may emerge as a novel intervention strategy for accelerated forgetting in patients with epilepsy.

IFRD1 is required for maintenance of bladder epithelial homeostasis

The maintenance of homeostasis and rapid regeneration of the urothelium following stress are critical for bladder function. Here, we identify a key role for IFRD1 in maintaining urothelial homeostasis in a mouse model. We demonstrate that the murine bladder expresses IFRD1 at homeostasis, particularly in the urothelium, and its loss alters the global transcriptome with significant accumulation of endolysosomes and dysregulated uroplakin expression pattern. We show that IFRD1 interacts with mRNA-translation-regulating factors in human urothelial cells. Loss of Ifrd1 leads to disrupted proteostasis, enhanced endoplasmic reticulum (ER stress) with activation of the PERK arm of the unfolded protein response pathway, and increased oxidative stress. Ifrd1-deficient bladders exhibit urothelial cell apoptosis/exfoliation, enhanced basal cell proliferation, reduced differentiation into superficial cells, increased urothelial permeability, and aberrant voiding behavior. These findings highlight a crucial role for IFRD1 in urothelial homeostasis, suggesting its potential as a therapeutic target for bladder dysfunction.

Human coronaviruses: activation and antagonism of innate immune responses

SUMMARYHuman coronaviruses cause a range of respiratory diseases, from the common cold (HCoV-229E, HCoV-NL63, HCoV-OC43, and SARS-CoV-2) to lethal pneumonia (SARS-CoV, SARS-CoV-2, and MERS-CoV). Coronavirus interactions with host innate immune antiviral responses are an important determinant of disease outcome. This review compares the host's innate response to different human coronaviruses. Host antiviral defenses discussed in this review include frontline defenses against respiratory viruses in the nasal epithelium, early sensing of viral infection by innate immune effectors, double-stranded RNA and stress-induced antiviral pathways, and viral antagonism of innate immune responses conferred by conserved coronavirus nonstructural proteins and genus-specific accessory proteins. The common cold coronaviruses HCoV-229E and -NL63 induce robust interferon signaling and related innate immune pathways, SARS-CoV and SARS-CoV-2 induce intermediate levels of activation, and MERS-CoV shuts down these pathways almost completely.

Triple coding in human SRD5A1 mRNA

Background

Nucleotide sequence can be translated in three reading frames from 5' to 3' producing distinct protein products. Many examples of RNA translation in two reading frames (dual coding) have been identified so far.

Results

We report simultaneous translation of mRNA transcripts derived from SRD5A1 locus in all three reading frames that result in the synthesis of long proteins. This occurs due to initiation at three nearby AUG codons occurring in all three-reading frame. Only one of the three proteoforms contains the conserved catalytical domain of SDRD5A1 produced either from the second or the third AUG codon depending on the transcript. Paradoxically, ribosome profiling data and expression reporters indicate that the most efficient translation produces catalytically inactive proteoforms. While phylogenetic analysis suggests that the long triple decoding region is specific to primates, occurrence of nearby AUGs in all three reading frames is ancestral to placental mammals. This suggests that their evolutionary significance belongs to regulation of translation rather than biological role of their products. By analysing multiple publicly available ribosome profiling data and with gene expression assays carried out in different cellular environments, we show that relative expression of these proteoforms is mutually dependent and vary across environments supporting this conjecture. A remarkable feature of triple decoding is its resistance to indel mutations with apparent implications to clinical interpretation of genomic variants.

Conclusion

We argue for the importance of identification, characterisation and annotation of productive RNA translation irrespective of the presumed biological roles of the products of this translation.

A neurodegenerative cellular stress response linked to dark microglia and toxic lipid secretion

The brain's primary immune cells, microglia, are a leading causal cell type in Alzheimer's disease (AD). Yet, the mechanisms by which microglia can drive neurodegeneration remain unresolved. Here, we discover that a conserved stress signaling pathway, the integrated stress response (ISR), characterizes a microglia subset with neurodegenerative outcomes. Autonomous activation of ISR in microglia is sufficient to induce early features of the ultrastructurally distinct "dark microglia" linked to pathological synapse loss. In AD models, microglial ISR activation exacerbates neurodegenerative pathologies and synapse loss while its inhibition ameliorates them. Mechanistically, we present evidence that ISR activation promotes the secretion of toxic lipids by microglia, impairing neuron homeostasis and survival in vitro. Accordingly, pharmacological inhibition of ISR or lipid synthesis mitigates synapse loss in AD models. Our results demonstrate that microglial ISR activation represents a neurodegenerative phenotype, which may be sustained, at least in part, by the secretion of toxic lipids.

Integrating Time-Resolved nrf2 Gene-Expression Data into a Full GUTS Model as a Proxy for Toxicodynamic Damage in Zebrafish Embryo

The immense production of the chemical industry requires an improved predictive risk assessment that can handle constantly evolving challenges while reducing the dependency of risk assessment on animal testing. Integrating omics data into mechanistic models offers a promising solution by linking cellular processes triggered after chemical exposure with observed effects in the organism. With the emerging availability of time-resolved RNA data, the goal of integrating gene expression data into mechanistic models can be approached. We propose a biologically anchored TKTD model, which describes key processes that link the gene expression level of the stress regulator nrf2 to detoxification and lethality by associating toxicodynamic damage with nrf2 expression. Fitting such a model to complex data sets consisting of multiple endpoints required the combination of methods from molecular biology, mechanistic dynamic systems modeling, and Bayesian inference. In this study, we successfully integrate time-resolved gene expression data into TKTD models and thus provide a method for assessing the influence of molecular markers on survival. This novel method was used to test whether nrf2 can be applied to predict lethality in zebrafish embryos. With the presented approach, we outline a method to successfully approach the goal of a predictive risk assessment based on molecular data.

A New Insight into the Mechanism of Atrazine-Induced Neurotoxicity: Triggering Neural Stem Cell Senescence by Activating the Integrated Stress Response Pathway

Atrazine (AT), a widely utilized chemical herbicide, causes widespread contamination of agricultural water bodies. Recently, exposure to AT has been linked to the development of age-related neurodegenerative diseases (NDs), suggesting its neurotoxicity potential. As an endocrine disruptor, AT targets the hypothalamus, a crucial part of the neuroendocrine system. However, the toxicological mechanism of AT exposure to the hypothalamus and its correlation with ND development remain unexplored. Our results indicated that AT exposure caused significant morphological and structural damage to the hypothalamus, leading to the loss of mature and intact neurons and microglial activation. Furthermore, hypothalamic neural stem cells (HtNSCs) were recruited to areas of neuronal damage caused by AT. Through in vivo and in vitro experiments, we clarified the outcomes of AT-induced HtNSC recruitment alongside the loss of mature/intact neurons. Mechanistically, AT induces senescence in these recruited HtNSCs by activating integrated stress response signaling. This consequently hinders the repair of damaged neurons by inhibiting HtNSC proliferation and differentiation. Overall, our findings underscore the pivotal role of the integrated stress response pathway in AT-induced HtNSC senescence and hypothalamic damage. Additionally, the present study offers novel perspectives to understand the mechanisms of AT-induced neurotoxicity and provides preliminary evidence linking AT contamination to the development of NDs.

Circadian Control of Protein Synthesis

Daily rhythms in the rate and specificity of protein synthesis occur in most mammalian cells through an interaction between cell-autonomous circadian regulation and daily cycles of systemic cues. However, the overall protein content of a typical cell changes little over 24 h. For most proteins, translation appears to be coordinated with protein degradation, producing phases of proteomic renewal that maximize energy efficiency while broadly maintaining proteostasis across the solar cycle. We propose that a major function of this temporal compartmentalization-and of circadian rhythmicity in general-is to optimize the energy efficiency of protein synthesis and associated processes such as complex assembly. We further propose that much of this temporal compartmentalization is achieved at the level of translational initiation, such that the translational machinery alternates between distinct translational mechanisms, each using a distinct toolkit of phosphoproteins to preferentially recognize and translate different classes of mRNA.

Single-cell transcriptomic and neuropathologic analysis reveals dysregulation of the integrated stress response in progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is a sporadic neurodegenerative tauopathy variably affecting brainstem and cortical structures, and characterized by tau inclusions in neurons and glia. The precise mechanism whereby these protein aggregates lead to cell death remains unclear. To investigate the contribution of these different cellular abnormalities to PSP pathogenesis, we performed single-nucleus RNA sequencing (snRNA-seq) and analyzed 50,708 high quality nuclei targeting the diencephalon, including the subthalamic nucleus and adjacent structures, from human post-mortem PSP brains with varying degrees of pathology compared to controls. Cell-type-specific differential expression and pathway analysis identified both common and discrete changes in numerous pathways previously implicated in PSP and other neurodegenerative disorders. This included EIF2 signaling, an adaptive pathway activated in response to diverse stressors, which was activated in multiple vulnerable cell types and validated in independent snRNA-seq and bulk RNA-seq datasets. Using immunohistochemistry, we found that activated eIF2α was positively correlated with tau pathology burden in vulnerable brain regions. Multiplex immunofluorescence localized activated eIF2α positivity to hyperphosphorylated tau (p-tau) positive neurons and ALDH1L1-positive astrocytes, supporting the increased transcriptomic EIF2 activation observed in these vulnerable cell types. In conclusion, these data provide insights into cell-type-specific pathological changes in PSP and support the hypothesis that failure of adaptive stress pathways play a mechanistic role in the pathogenesis and progression of PSP.

Canagliflozin differentially modulates carfilzomib-induced endoplasmic reticulum stress in multiple myeloma and endothelial cells

Carfilzomib (CFZ), a second-generation proteasome inhibitor, is a key treatment for multiple myeloma (MM), but its use is associated with significant cardiovascular adverse events (CVAEs), including heart failure and hypertension. Endothelial dysfunction is believed to contribute to these CVAEs. Building on our previous findings that CFZ induces endothelial toxicity and that canagliflozin protects against CFZ-induced endothelial apoptosis, this study aimed to evaluate CFZ-induced endoplasmic reticulum (ER) stress and autophagy in endothelial and MM cells, as well as the impact of canagliflozin on these processes and its impact on the anticancer effects of CFZ in MM cells. Endothelial cells (HUVECs and EA.hy926) and multiple myeloma cells (RPMI8226) were treated with 0.5 µM CFZ, either alone or in combination with canagliflozin (5-20 µM), to assess the effects on ER stress and autophagy in both cell types. CFZ induced ER stress in endothelial and MM cells. In endothelial cells, canagliflozin mitigated CFZ-induced markers of ER stress, while unexpectedly upregulating CFZ-induced CHOP. Whereas, in MM cells, canagliflozin did not alter CFZ-induced ER stress, but instead further upregulated CFZ-induced ATF-4. In addition, CFZ induced autophagy in endothelial cells while inhibiting it in MM cells. Canagliflozin abrogated CFZ-induced autophagy in endothelial cells. In striking contrast to its effects in endothelial cells, canagliflozin enhanced the cytotoxic effects of CFZ in MM cells. Intriguingly, in an innovative co-culture system, canagliflozin enhanced CFZ-induced apoptosis in MM cells while protecting endothelial cells. These findings underscore the dual role of canagliflozin in reducing CFZ-induced endothelial toxicity, while enhancing its cytotoxic effect in MM.

Icariin alleviates the injury of Sertoli cell junction function by upregulating PKR pathway via ERα/c-fos signaling in aged mice

ETHNOPHARMACOLOGICAL RELEVENACE

Sertoli cells are vital to maintain spermatogenesis and their function decline during aging. Epimedium has the effects of tonifying kidney-yang, strengthening bones and muscles, and expelling wind and dampness, and is commonly used in the treatment of kidney-yang deficiency, impotence and spermatorrhea. Icariin is the main active ingredients from Epimedium exhibiting delaying aging effects and improving male reproductive dysfunction. Whereas, it remains poorly understood how icariin alleviates age-associated decline in testicular function by protecting against the damage of junction function of Sertoli cells.

AIM OF THE STUDY

This study aimed to evaluate the improvement effect of icariin on Sertoli cell junction function damage and explore the underlying mechanisms.

MATERIALS AND METHODS

Male C57BL/6 mice and mouse Sertoli cell line TM4 cells were utilized to assess the improvement effect of icariin on aging-associated Sertoli cell junction function injury. H&E staining, transmission electron microscopy, qPCR, Western blot, molecular docking, siRNA transfection, and immunofluorescence were performed in this study.

RESULTS

Dietary administration of icariin remarkly attenuated age-associated deterioration in spermatogenic function as evidenced by elevated testicular weight and index, sperm concentration and sperm viability. In addition, icariin protected Sertoli cell junction function from age-associated damage as proven by increased Sertoli cell numbers, improved tight junction ultrastructure, and upregulated junction-related proteins (ZO-1, Occludin and β-Catenin). Moreover, icariin significantly upregulated ERα/c-fos signaling and PKR pathway in testicular Sertoli cells. Similarly, in vitro studies revealed that deletion of ERα, c-fos or PKR abolished the improvement effects of icariin on Sertoli cell junction function damage.

CONCLUSIONS

Icariin effectively mitigates age-associated decline in testicular function by diminished Sertoli cell junction function damage through upregulating PKR pathway via ERα/c-fos signaling. Therefore, attenuating Sertoli cell junction function injury by the upregulation of PKR pathway via ERα/c-fos signaling probably indicates an effective target for the prevention and treatment of testicular spermatogenic function with aging.

Regulated resource reallocation is transcriptionally hard wired into the yeast stress response

Many organisms maintain generalized stress responses activated by adverse conditions. Although details vary, a common theme is the redirection of transcriptional and translational capacity away from growth-promoting genes and toward defense genes. Yet the precise roles of these coupled programs are difficult to dissect. Here we investigated Saccharomyces cerevisiae responding to salt as a model stressor. We used molecular, genomic, and single-cell microfluidic methods to examine the interplay between transcription factors Msn2 and Msn4 that induce stress-defense genes and Dot6 and Tod6 that transiently repress growth-promoting genes during stress. Surprisingly, loss of Dot6/Tod6 led to slower acclimation to salt, whereas loss of Msn2/4 produced faster growth during stress. This supports a model where transient repression of growth-promoting genes accelerates the Msn2/4 response, which is essential for acquisition of subsequent peroxide tolerance. Remarkably, we find that Msn2/4 regulate DOT6 mRNA production, influence Dot6 activation dynamics, and are required for full repression of growth-promoting genes. Thus, Msn2/4 directly regulate resource reallocation needed to mount their own response. We discuss broader implications for common stress responses across organisms.

Lethal COVID-19 associates with RAAS-induced inflammation for multiple organ damage including mediastinal lymph nodes

Lethal COVID-19 outcomes are attributed to classic cytokine storm. We revisit this using RNA sequencing of nasopharyngeal and 40 autopsy samples from patients dying of SARS-CoV-2. Subsets of the 100 top-upregulated genes in nasal swabs are upregulated in the heart, lung, kidney, and liver, but not mediastinal lymph nodes. Twenty-two of these are "noncanonical" immune genes, which we link to components of the renin-angiotensin-activation-system that manifest as increased fibrin deposition, leaky vessels, thrombotic tendency, PANoptosis, and mitochondrial dysfunction. Immunohistochemistry of mediastinal lymph nodes reveals altered architecture, excess collagen deposition, and pathogenic fibroblast infiltration. Many of the above findings are paralleled in animal models of SARS-CoV-2 infection and human peripheral blood mononuclear and whole blood samples from individuals with early and later SARS-CoV-2 variants. We then redefine cytokine storm in lethal COVID-19 as driven by upstream immune gene and mitochondrial signaling producing downstream RAAS (renin-angiotensin-aldosterone system) overactivation and organ damage, including compromised mediastinal lymph node function.

Targeting autophagy in HCC treatment: exploiting the CD147 internalization pathway

BACKGROUND/AIMS

Chemotherapy resistance in liver cancer is a major clinical issue, with CD147 playing a vital role in this process. However, the specific mechanisms underlying these processes remain largely unknown. This study investigates how CD147 internalization leads to cytoprotective autophagy, contributing to chemotherapy resistance in hepatocellular carcinoma (HCC).

METHODS

Utilizing bioinformatics methods for KEGG pathways enrichment and screening key molecules associated with chemotherapy resistance through analyses of GEO and TCGA databases. An overexpression/knockdown system was used to study how CD147 internalization leads to autophagy in vitro and in vivo. The process was observed using microscopes, and molecular interactions and autophagy flux were analyzed. Analyzing the internalization of CD147 intracellular domains and the interaction with G3BP1 in clinical chemotherapy recurrence HCC tissues by immunohistochemistry, tissue immunofluorescence, and mass spectrometry. A tumor xenograft mice model was used to study cytoprotective autophagy induced by CD147 and test the effectiveness of combining cisplatin with an autophagy inhibitor in nude mice models.

RESULTS

In our study, we identified the tumor-associated membrane protein CD147, which implicated in chemoresistance lysosome pathways, by evaluating its protein degree value and betweenness centrality using Cytoscape. Our findings revealed that CD147 undergoes internalization and interacts with G3BP1 following treatment with cisplatin and methyl-β-cyclodextrin, forming a complex that is transported to lysosomes via Rab7A. Notably, higher doses of cisplatin enhanced CD147-mediated lysosomal transport while concurrently inhibiting SG assembly. The CD147-G3BP1 complex additionally inhibits mTOR activity, promoting autophagy and augmenting chemoresistance in hepatoma cells. In vivo studies investigations and analyses of clinical samples revealed that elevated internalization of CD147 is associated with chemotherapy recurrence in liver cancer and the maintenance of stem cells. Mice experiments found that the combined administration of cisplatin and hydroxychloroquine enhanced the efficacy of treatment.

CONCLUSIONS

This study reveals that CD147 internalization and CD147-G3BP1 complex translocation to lysosomes induce cytoprotective autophagy, reducing chemotherapy sensitivity by suppressing mTOR activity. It is also shown that chemotherapy drugs combined with autophagy inhibitors can improve the therapeutic effect of cancer, providing new insights into potential targeted therapeutic approaches in treating HCC.

Programmed cell death: molecular mechanisms, biological functions, diseases, and therapeutic targets

Programmed cell death represents a precisely regulated and active cellular demise, governed by a complex network of specific genes and proteins. The identification of multiple forms of programmed cell death has significantly advanced the understanding of its intricate mechanisms, as demonstrated in recent studies. A thorough grasp of these processes is essential across various biological disciplines and in the study of diseases. Nonetheless, despite notable progress, the exploration of the relationship between programmed cell death and disease, as well as its clinical application, are still in a nascent stage. Therefore, further exploration of programmed cell death and the development of corresponding therapeutic methods and strategies holds substantial potential. Our review provides a detailed examination of the primary mechanisms behind apoptosis, autophagy, necroptosis, pyroptosis, and ferroptosis. Following this, the discussion delves into biological functions and diseases associated dysregulated programmed cell death. Finally, we highlight existing and potential therapeutic targets and strategies focused on cancers and neurodegenerative diseases. This review aims to summarize the latest insights on programmed cell death from mechanisms to diseases and provides a more reliable approach for clinical transformation.

Cryo-EM structure of histidyl-tRNA synthetase-like domain reveals activating crossed helices at the core of GCN2

GCN2 is a conserved receptor kinase activating the integrated stress response (ISR) in eukaryotic cells. The ISR kinases detect accumulation of stress molecules and reprogram translation from basal tasks to preferred production of cytoprotective proteins. GCN2 stands out evolutionarily among all protein kinases due to the presence of a histidyl-tRNA synthetase-like (HRSL) domain, which arises only in GCN2 and is located next to the kinase domain (KD). How HRSL contributes to GCN2 signaling remains unknown. Here, we report a 3.2 Å cryo-EM structure of HRSL from thermotolerant yeast Kluyveromyces marxianus. This structure shows a constitutive symmetrical homodimer featuring a compact helical-bundle structure at the junction between HRSL and KDs, in the core of the receptor. Mutagenesis demonstrates that this junction structure activates GCN2 and indicates that our cryo-EM structure captures the active signaling state of HRSL. Based on these results, we put forward a GCN2 regulation mechanism, where HRSL drives the formation of activated kinase dimers. The remaining domains of GCN2 have the opposite role and in the absence of stress they help keep GCN2 basally inactive. This auto-inhibitory activity is relieved upon stress ligand binding. We propose that the opposing action of HRSL and additional GCN2 domains thus yields a regulated ISR receptor.

Translation regulation in response to stress

Cell stresses occur in a wide variety of settings: in disease, during industrial processes, and as part of normal day-to-day rhythms. Adaptation to these stresses requires cells to alter their proteome. Cells modify the proteins they synthesize to aid proteome adaptation. Changes in both mRNA transcription and translation contribute to altered protein synthesis. Here, we discuss the changes in translational mechanisms that occur following the onset of stress, and the impact these have on stress adaptation.

Integrated stress response mediates HSP70 to inhibit testosterone synthesis in aging testicular Leydig cells

The integrated stress response (ISR) is implicated in age-related diseases, while the molecular chaperone heat shock protein 70 (HSP70) can facilitate proper protein folding. However, the regulatory mechanism of ISR in insufficient testosterone synthesis of aging Leydig cells (LCs) remains unclear. This study aims to elucidate the regulatory role of ISR in inadequate testosterone synthesis of aging LCs. We observed a positive correlation between testosterone and HSP70 levels, which were found to be decreased in elderly men. ISR was detected in testicular tissue from old mice. The expression of testosterone synthesis related protein and the content of testosterone decreased in testicular tissue of old mice. Conversely, inhibition of the integrated stress response in testicular tissue led to an increase in steroid synthase expression among old mice. Furthermore, inhibiting ISR specifically within aging LCs resulted in enhanced protein translation efficiency and increased expression levels of new HSP70 and steroidogenic acute regulatory protein (StAR). These findings suggest that ISR occurrence within aging LCs affects StAR protein expression through regulation of HSP70-mediated translation, consequently impairing testosterone synthesis.

Cutting through the stress: RNA decay pathways at the endoplasmic reticulum

The endoplasmic reticulum (ER) is central to the processing of luminal, transmembrane, and secretory proteins, and maintaining a functional ER is essential for organismal physiology and health. Increased protein-folding load on the ER causes ER stress, which activates quality control mechanisms to restore ER function and protein homeostasis. Beyond protein quality control, mRNA decay pathways have emerged as potent ER fidelity regulators, but their mechanistic roles in ER quality control and their interrelationships remain incompletely understood. Herein, we review ER-associated RNA decay pathways - including regulated inositol-requiring enzyme 1α (IRE1α)-dependent mRNA decay (RIDD), nonsense-mediated mRNA decay (NMD), and Argonaute-dependent RNA silencing - in ER homeostasis, and highlight the intricate coordination of ER-targeted RNA and protein decay mechanisms and their association with antiviral defense.

Calcium signaling from damaged lysosomes induces cytoprotective stress granules

Lysosomal damage induces stress granule (SG) formation. However, the importance of SGs in determining cell fate and the precise mechanisms that mediate SG formation in response to lysosomal damage remain unclear. Here, we describe a novel calcium-dependent pathway controlling SG formation, which promotes cell survival during lysosomal damage. Mechanistically, the calcium-activated protein ALIX transduces lysosomal damage signals to SG formation by controlling eIF2α phosphorylation after sensing calcium leakage. ALIX enhances eIF2α phosphorylation by promoting the association between PKR and its activator PACT, with galectin-3 inhibiting this interaction; these regulatory events occur on damaged lysosomes. We further find that SG formation plays a crucial role in promoting cell survival upon lysosomal damage caused by factors such as SARS-CoV-2ORF3a, adenovirus, malarial pigment, proteopathic tau, or environmental hazards. Collectively, these data provide insights into the mechanism of SG formation upon lysosomal damage and implicate it in diseases associated with damaged lysosomes and SGs.

The UPRising connection between endoplasmic reticulum stress and the tumor microenvironment

The tumor microenvironment (TME) represents a dynamic network of cancer cells, stromal cells, immune mediators, and extracellular matrix components, crucial for cancer progression. Stress conditions such as oncogene activation, nutrient deprivation, and hypoxia disrupt the endoplasmic reticulum (ER), activating the unfolded protein response (UPR), the main adaptive mechanism to restore ER function. The UPR regulates cancer progression by engaging cell-autonomous and cell-non-autonomous mechanisms, reprogramming the stroma and promoting immune evasion, angiogenesis, and invasion. This review explores the role of UPR beyond cancer cells, focusing on how ER stress signaling reshapes the TME, supporting tumor growth. The therapeutic potential of targeting the UPR is also discussed.