Salubrinal promotes phospho-eIF2α-dependent activation of UPR leading to autophagy-mediated attenuation of iron-induced insulin resistance

Potential therapeutic targets of eukaryotic translation initiation factors in tumor therapy

Translation initiation is the first and rate-limiting step in protein synthesis, and its dysregulation is frequently observed in various malignancies. Cap-dependent translation, the predominant form of translation initiation, relies on the coordinated action of eukaryotic translation initiation factors (eIFs), including eIF1, eIF2, eIF4, and others. These factors play critical roles in regulating the efficiency and fidelity of protein synthesis, and their overexpression has been linked to tumor progression, proliferation, and metastasis. Notably, certain eIFs have emerged as potential prognostic markers due to their elevated expression in tumors. Targeting eIFs represents a promising strategy, particularly for cancers characterized by aberrant eIF activity. In this review, we summarize the roles of individual eIFs in cap-dependent translation and discuss their potential as therapeutic targets in cancer treatment. We also highlight recent advances in drug discovery efforts aimed at modulating eIF activity, providing insights into the development of novel anticancer therapies.

Pharmacological landscape of endoplasmic reticulum stress: Uncovering therapeutic avenues for metabolic diseases

The endoplasmic reticulum (ER) plays a fundamental role in maintaining cellular homeostasis by ensuring proper protein folding, lipid metabolism, and calcium regulation. However, disruptions to ER function, known as ER stress, activate the unfolded protein response (UPR) to restore balance. Chronic or unresolved ER stress contributes to metabolic dysfunctions, including insulin resistance, non-alcoholic fatty liver disease (NAFLD), and neurodegenerative disorders such as Parkinson's disease and Alzheimer's disease. Recent studies have also highlighted the importance of mitochondria-ER contact sites (MERCs) and ER-associated inflammation in disease progression. This review explores the current pharmacological landscape targeting ER stress, focusing on therapeutic strategies for rare metabolic and neurodegenerative diseases. It examines small molecules such as tauroursodeoxycholic acid (TUDCA) and 4-phenylbutyric acid (4-PBA), repurposed drugs like 17-AAG (17-N-allylamino-17demethoxygeldanamycin (tanespimycin)) and berberine, and phytochemicals such as resveratrol and hesperidin. Additionally, it discusses emerging therapeutic areas, including soluble epoxide hydrolase (sEH) inhibitors for metabolic disorders and MERCs modulation for neurological diseases. The review emphasizes challenges in translating these therapies to clinical applications, such as toxicity, off-target effects, limited bioavailability, and the lack of large-scale randomized controlled trials (RCTs). It also highlights the potential of personalized medicine approaches and pharmacogenomics in optimizing ER stress-targeting therapies.

Hydrogen Sulfide (H2S) Metabolism, Iron Overload, and Apoptosis-Autophagy Equilibrium in Vascular Smooth Muscle Cells

Iron overload contributes to proliferative vascular diseases, yet its interplay with hydrogen sulfide (H2S) in vascular smooth muscle cell (VSMC) proliferation remains poorly understood. This study elucidates H2S's role in mitigating iron-overload-induced oxidative stress and cellular damage. Using aortic VSMCs from wildtype (WT) and cystathionine γ-lyase-knockout (CSE-KO) mice treated with ferric ammonium citrate (FAC) at concentrations equivalent to serum levels of iron and citrate, we demonstrate that FAC triggers the integrated stress response (ISR) in WT cells, upregulating CSE to enhance H2S production. The ISR mediator ATF4 activates caspases but simultaneously induces CSE, which inhibits caspase activity and promotes autophagy via AMPK signaling. In CSE-KO cells, iron overload leads to diminished Ferritin upregulation, unchecked Caspase activation, and impaired autophagy compared to WT cells. Exogenous H2S restored iron homeostasis by enhancing Ferritin expression, activating NRF2 antioxidant pathways, and restoring apoptosis-autophagy equilibrium in both WT and KO cells. These findings establish H2S as a critical regulator of iron-induced VSMC dysfunction, highlighting its therapeutic potential in managing vascular pathologies linked to iron dysregulation.

Inhibition of methionine aminopeptidase in C2C12 myoblasts disrupts cell integrity via increasing endoplasmic reticulum stress

Proteasome-dependent protein degradation and the digestion of peptides by aminopeptidases are essential for myogenesis. Methionine aminopeptidases (MetAPs) are uniquely involved in, both, the proteasomal degradation of proteins and in the regulation of translation (via involvement in post-translational modification). Suppressing MetAP1 and MetAP2 expression inhibits the myogenic differentiation of C2C12 myoblasts. However, the molecular mechanism by which inhibiting MetAPs impairs cellular function remains to be elucidated. Here, we provide evidence for our hypothesis that MetAPs regulate proteostasis and that their inhibition increases ER stress by disrupting the post-translational modification, and thereby compromises cell integrity. Thus, using C2C12 myoblasts, we investigate the effect of inhibiting MetAPs on cell proliferation and the molecular mechanisms underpinning its effects. We found that exposure to bengamide B (a MetAP inhibitor) caused C2C12 myoblasts to lose their proliferative abilities via cell cycle arrest. The underlying mechanism involved the accumulation of abnormal proteins (due to the decrease in the N-terminal methionine removal function) which led to increased endoplasmic reticulum stress, decreased protein synthesis, and a protective activation of the autophagy pathway. To identify the MetAP involved in these effects, we use siRNAs to specifically knockdown MetAP1 and MetAP2 expressions. We found that only MetAP2 knockdown mimicked the effects seen with bengamide B treatment. Thus, we suggest that MetAP2, rather than MetAP1, is involved in maintaining the integrity of C2C12 myoblasts. Our results are useful in understanding muscle regeneration, obesity, and overeating disorders. It will help guide new treatment strategies for these disorders.

Targeting endoplasmic reticulum stress as a potential therapeutic strategy for diabetic cardiomyopathy

Endoplasmic reticulum (ER) is an essential organelle involved in vesicular transport, calcium handling, protein synthesis and folding, and lipid biosynthesis and metabolism. ER stress occurs when ER homeostasis is disrupted by the accumulation of unfolded and/or misfolded proteins in the ER lumen. Adaptive pathways of the unfolded protein response (UPR) are activated to maintain ER homeostasis. In obesity and type 2 diabetes mellitus (T2DM), accumulating data indicate that persistent ER stress due to maladaptive UPR interacts with insulin/leptin signaling, which may be the potential and central mechanistic link between obesity-/T2DM-induced metabolic dysregulation (chronic hyperglycemia, dyslipidemia and lipotoxicity in cardiomyocytes), insulin/leptin resistance and the development of diabetic cardiomyopathy (DiabCM). Meanwhile, these pathological conditions further exacerbate ER stress. However, their interrelationships and the underlying molecular mechanisms are not fully understood. A deeper understanding of ER stress-mediated pathways in DiabCM is needed to develop novel therapeutic strategies. The aim of this review is to discuss the crosstalk between ER stress and leptin/insulin signaling and their involvement in the development of DiabCM focusing on mitochondria-associated ER membranes and chronic inflammation. We also present the current direction of drug development and important considerations for translational research into targeting ER stress for the treatment of DiabCM.

Physical Activity Reduces Metabolic Risk via Iron Metabolism: Cross-National Evidence Using the Triglyceride-Glucose Index

Purpose: Studies suggest that the triglyceride-glucose index (TyG) is a novel and comprehensive marker of metabolic health. While most research indicates that increased physical activity (PA) is linked to improved metabolic health, some studies argue that the previous markers may not fully capture this relationship. This study uses TyG as a marker of metabolic health to examine the association between PA and TyG. Methods: Data are from cross-sectional surveys in three large population studies in China and the United States: CHARLS, CHNS, and NHANES. Regression models were applied to analyze the relationship between PA and TyG, with covariates adjusted in a stepwise manner. Stratified analysis was used to explore this relationship among different population groups, and, since it has been suggested that iron metabolism plays an important role in metabolic health, it was used as a mediating variable to construct a mediation model for analysis and discussion. Results: Higher PA was significantly associated with lower TyG levels across all three databases (p < 0.001), and this relationship remained robust after full adjustment for covariates. This negative association was more pronounced in older males (over 45 years). Iron metabolism also mediated this relationship, with mediation proportions ranging from 10% to 12.5%. Conclusions: There is a significant inverse association between PA and TyG, suggesting a link between increased PA and metabolic health, with iron metabolism moderating this relationship, especially among older males.

Iron Overload Induces Hepatic Ferroptosis and Insulin Resistance by Inhibiting the Jak2/stat3/slc7a11 Signaling Pathway

Recent studies showed that patients with iron overload had increased risk of insulin resistance or diabetes. Ferroptosis is a new type of cell death mainly caused by iron-dependent oxidative damage. In the present study, we investigated potential mechanisms of iron overload induced hepatic ferroptosis and insulin resistance through in vivo and in vitro experiments. In vivo, the mice models of iron overload were established by intraperitoneal injection of iron dextran. The changes of body weight, serum ferritin and blood glucose were measured. Hematoxylin-eosin (HE) and Perl's stainings were used to observe the pathological changes and iron deposition in the liver of mice. In vitro, HepG2 cells were treated with ferric ammonium citrate (FAC, 9 mmol/L, 24 h) to establish the cell models of iron overload. The labile iron pool, cell viability, glucose consumption and glycogen contents were measured. The ultrastructure of mitochondria was observed by transmission electron microscope (TEM). The malondialdehyde (MDA) and glutathione (GSH) kits were used to detect lipid peroxidation in liver tissues of mice and HepG2 cells. RT-PCR and Western blot were used to detect the mRNA and protein expression levels of ferroptosis factors and JAK2/STAT3 signaling pathway. In this study, we used the iron chelator deferasirox in mice and HepG2 cells. Iron overload caused weight loss, elevated serum ferritin, fasting blood glucose, fasting insulin, HOMA-IR, impaired glucose tolerance, and decreased insulin sensitivity in mice. HE staining and Perls staining showed clumps of iron deposition in the liver of iron overload mice. Iron overload could reduce the glucose consumption, increase MDA contents of HepG2 cells, while reduce glycogen and GSH contents in liver tissues of mice and HepG2 cells. TEM showed deletion of mitochondrial ridge and rupture of outer membrane in HepG2 cells with iron overload. Iron chelator deferasirox could significantly improve the above indicators, which might be related to the activation of JAK2/STAT3/SLC7A11 signaling pathway and hepatic ferroptosis. Iron overload could induce hepatic ferroptosis and insulin resistance by inhibiting the JAK2/STAT3/SLC7A11 signaling pathway, and the iron chelator deferasirox might improve hepatic insulin resistance induced by iron overload.

Navigating the landscape of the unfolded protein response in CD8+ T cells

Endoplasmic reticulum stress occurs due to large amounts of misfolded proteins, hypoxia, nutrient deprivation, and more. The unfolded protein is a complex intracellular signaling network designed to operate under this stress. Composed of three individual arms, inositol-requiring enzyme 1, protein kinase RNA-like ER kinase, and activating transcription factor-6, the unfolded protein response looks to resolve stress and return to proteostasis. The CD8+ T cell is a critical cell type for the adaptive immune system. The unfolded protein response has been shown to have a wide-ranging spectrum of effects on CD8+ T cells. CD8+ T cells undergo cellular stress during activation and due to environmental insults. However, the magnitude of the effects this response has on CD8+ T cells is still understudied. Thus, studying these pathways is important to unraveling the inner machinations of these powerful cells. In this review, we will highlight the recent literature in this field, summarize the three pathways of the unfolded protein response, and discuss their roles in CD8+ T cell biology and functionality.