Calcium signalling and ER stress in insulin resistance and atherosclerosis

Omentin-1 ameliorates pulmonary arterial hypertension by inhibiting endoplasmic reticulum stress through AMPKα signaling

BACKGROUND

Endothelial dysfunction of the pulmonary artery contributes to hypoxia-induced pulmonary arterial hypertension (PAH). Omentin-1, as a novel adipocytokine, plays an important protective role against cardiovascular diseases. However, the effect and underlying mechanisms of omentin-1 against PAH remain unclear.

METHODS

PAH was induced in SD (Sprague & Dawley) rats via a low-oxygen chamber for 4 weeks. Hemodynamic evaluation was undertaken using a PowerLab data acquisition system, and histopathological analysis was stained with hematoxylin and eosin (H&E). Endothelial function of pulmonary artery was assessed using wire myography.

RESULTS

We found that omentin-1 significantly improved pulmonary endothelial function in rats exposed to hypoxia and attenuated PAH. Mechanistically, we found that omentin-1 increased phosphorylated 5'‑adenosine monophosphate‑activated protein kinase (p‑AMPK) level and reduced endoplasmic reticulum (ER) stress and increased NO production in pulmonary artery from rats exposed to hypoxia. However, the effect of omentin-1 was abolished by treatment with AMPK inhibitor (Compound C).

CONCLUSIONS

Our results reveal a protective effect of omentin-1 in PAH via inhibiting ER stress through AMPKα signaling and provide an agent with translational potential for the treatment of PAH.

Vitamin D and Atherosclerosis: Unraveling the Impact on Macrophage Function

Vitamin D plays a crucial role in preventing atherosclerosis and in the regulation of macrophage function. This review aims to provide a comprehensive summary of the clinical evidence regarding the impact of vitamin D on atherosclerotic cardiovascular disease, atherosclerotic cerebrovascular disease, peripheral arterial disease, and associated risk factors. Additionally, it explores the mechanistic studies investigating the influence of vitamin D on macrophage function in atherosclerosis. Numerous findings indicate that vitamin D inhibits monocyte or macrophage recruitment, macrophage cholesterol uptake, and esterification. Moreover, it induces autophagy of lipid droplets in macrophages, promotes cholesterol efflux from macrophages, and regulates macrophage polarization. This review particularly focuses on analyzing the molecular mechanisms and signaling pathways through which vitamin D modulates macrophage function in atherosclerosis. It claims that vitamin D has a direct inhibitory effect on the formation, adhesion, and migration of lipid-loaded monocytes, thus exerting anti-atherosclerotic effects. Therefore, this review emphasizes the crucial role of vitamin D in regulating macrophage function and preventing the development of atherosclerosis.

Endoplasmic reticulum stress-mediated cell death in cardiovascular disease

The endoplasmic reticulum (ER) plays a vital function in maintaining cellular homeostasis. Endoplasmic reticulum stress (ERS) can trigger various modes of cell death by activating the unfolded protein response (UPR) signaling pathway. Cell death plays a crucial role in the occurrence and development of diseases such as cancer, liver diseases, neurological diseases, and cardiovascular diseases. Several cardiovascular diseases including hypertension, atherosclerosis, and heart failure are associated with ER stress. ER stress-mediated cell death is of interest in cardiovascular disease. Moreover, an increasing body of evidence supports the potential of modulating ERS for treating cardiovascular disease. This paper provides a comprehensive review of the UPR signaling pathway, the mechanisms that induce cell death, and the modes of cell death in cardiovascular diseases. Additionally, we discuss the mechanisms of ERS and UPR in common cardiovascular diseases, along with potential therapeutic strategies.

Influence of Postharvest Natural Softening Conditions on the Nutritional Quality of Safou (Dacryodes edulis H.J.Lam) Flour: Rheological Properties of the Optimized Safou Flour

Safou (Dacryodes edulis H.J.Lam) is a seasonal fruit of great importance in the diet and economy of the populations of safou-producing countries. However, the valorization of this fruit is limited due to postharvest losses linked to the softening of the fruit, though this fruit is an essential source of macro- and micronutrients. Thus, this study is aimed at contributing to the valorization of softened safou by determining the optimum softening time, drying time, and temperature for good nutritional and rheological flour. The effects of the softening time, drying time, and drying temperature on the fat, protein, carbohydrate, dietary fibre, water, calcium, phosphorus, and potassium content were studied using the central composite design. The results showed that all the responses were affected by the factors. Also, the softening time of 4.75 days, drying time of 40.55 hours, and drying temperature of 41.83°C were the optimum conditions for producing safou flour with high nutritional value and good rheological properties. These optimum conditions resulted in safou flour with 58.95%, 12.40%, 22.40%, 4.38%, 4.91%, 2207.90 mg/1000 mg, 1898.30 mg/1000 mg, and 478.540 mg/1000 mg as lipid, protein, carbohydrates, fibre, moisture calcium, phosphorus, and potassium content, respectively. In addition, the pasting temperature, peak viscosity, breakdown, holding viscosity, final viscosity, setback, setback ratio, and stability ratio of the aforementioned flour were 50.42°C, 58 cp, 0.5 cp, 57.5 cp, 61.5 cp, 4 cp, 1.07, and 1, respectively. Based on its nutritional value and rheological properties, softened safou flour can be used in food formulation, thus contributing to the valorization of safou fruits.

Cigarette tar accelerates atherosclerosis progression via RIPK3-dependent necroptosis mediated by endoplasmic reticulum stress in vascular smooth muscle cells

BACKGROUND

Tar is the main toxic of cigarettes, and its effect on atherosclerosis progression and the underlying mechanisms remain largely unknown. Vascular smooth muscle cells (VSMCs) play a key role in atherogenesis and plaque vulnerability. The present study sought to investigate the mechanism of atherosclerosis progression through tar-induced VSMC necroptosis, a recently described form of necrosis.

METHODS

The effect of tar on atherosclerosis progression and VSMC necroptosis was examined in ApoE-/- mice and cultured VSMCs. The role of necroptosis in tar-induced plaque development was evaluated in RIPK3-deletion mice (ApoE-/-RIPK3-/-). The key proteins of necroptosis in carotid plaques of smokers and non-smokers were also examined. Quantitative proteomics of mice aortas was conducted to further investigate the underlying mechanism. Pharmacological approaches were then applied to modulate the expression of targets to verify the regulatory process of tar-induced necroptosis.

RESULTS

Tar administration led to increased atherosclerotic plaque area and reduced collagen and VSMCs in ApoE-/- mice. The expression of RIPK1、RIPK3、and MLKL in VSMCs of plaques were all increased in tar-exposed mice and smokers. RIPK3 deletion protected against VSMC loss and plaque progression stimulated by tar. In mechanistic studies, quantitative proteomics analysis of ApoE-/- mice aortas suggested that tar triggered endoplasmic reticulum (ER) stress. PERK-eIF2α-CHOP axis was activated in tar-treated VSMCs and atherosclerotic plaque. Inhibition of ER stress using 4PBA significantly reduced plaque progression and VSMC necroptosis. Further study revealed that ER stress resulted in calcium (Ca2+) release into mitochondria and cytoplasm. Elevated Ca2+ levels lead to mitochondrial dysfunction and excessive reactive oxygen species (ROS) production, which consequently promote RIPK3-dependent necroptosis. In addition, Ca2+/calmodulin-dependent protein kinase II (CaMKII) activated by cytosolic Ca2+ overload binds to RIPK3, accounting for necroptosis.

CONCLUSION

The findings revealed that cigarette tar promoted atherosclerosis progression by inducing RIPK3-dependent VSMC necroptosis and identified novel avenues of ER stress and Ca2+ overload.

Nutrition at the Intersection between Gut Microbiota Eubiosis and Effective Management of Type 2 Diabetes

Nutrition is one of the most influential environmental factors in both taxonomical shifts in gut microbiota as well as in the development of type 2 diabetes mellitus (T2DM). Emerging evidence has shown that the effects of nutrition on both these parameters is not mutually exclusive and that changes in gut microbiota and related metabolites such as short-chain fatty acids (SCFAs) and branched-chain amino acids (BCAAs) may influence systemic inflammation and signaling pathways that contribute to pathophysiological processes associated with T2DM. With this background, our review highlights the effects of macronutrients, carbohydrates, proteins, and lipids, as well as micronutrients, vitamins, and minerals, on T2DM, specifically through their alterations in gut microbiota and the metabolites they produce. Additionally, we describe the influences of common food groups, which incorporate varying combinations of these macronutrients and micronutrients, on both microbiota and metabolic parameters in the context of diabetes mellitus. Overall, nutrition is one of the first line modifiable therapies in the management of T2DM and a better understanding of the mechanisms by which gut microbiota influence its pathophysiology provides opportunities for optimizing dietary interventions.

Erigeron annuus Extract Alleviates Insulin Resistance via Regulating the Expression of Mitochondrial Damage and Endoplasmic Reticulum Stress-Related Genes

Diabetes is a prevalent and debilitating metabolic disorder affecting a large population worldwide. The condition is characterized by insulin resistance and impaired function of pancreatic β-cells, leading to elevated blood glucose levels. In this study, the antidiabetic effects of Erigeron annuus extract (EAE) on zebrafish with damaged pancreatic islets caused by insulin resistance were investigated. The study utilized the zebrafish model to monitor live pancreatic islets. RNA sequencing was also conducted to determine the mechanism by which EAE exerts its antidiabetic effect. The results showed that EAE was effective in recovering reduced islets in excess insulin-induced zebrafish. The effective concentration at 50% (EC₅₀) of EAE was determined to be 0.54 μg/mL, while the lethal concentration at 50% (LC₅₀) was calculated as 202.5 μg/mL. RNA sequencing indicated that the mode of action of EAE is related to its ability to induce mitochondrial damage and suppress endoplasmic reticulum stress. The findings of this study demonstrate the efficacy and therapeutic potential of EAE in treating insulin resistance in zebrafish. The results suggest that EAE may offer a promising approach for the management of diabetes by reducing mitochondrial damage and suppressing endoplasmic reticulum stress. Further research is required to establish the clinical application of EAE in diabetic patients.

Insulin Resistance Triggers Atherosclerosis: Caveolin 1 Cooperates with PKCzeta to Block Insulin Signaling in Vascular Endothelial Cells

OBJECTIVE

To date, therapies for endothelial dysfunction have primarily focused on ameliorating identified atherosclerosis (AS) risk factors rather than explicitly addressing endothelium-based mechanism. An in-depth exploration of the pathological mechanisms of endothelial injury was performed herein.

METHODS

Aortic caveolin 1 (Cav1) knockdown was achieved in mice using lentivirus, and AS was induced using a high-fat diet. Mouse body weight, blood glucose, insulin, lipid parameters, aortic plaque, endothelial injury, vascular nitric oxide synthase (eNOS), injury marker, and oxidative stress were examined. The effect of Cav1 knockdown on the content of PKCzeta and PI3K/Akt/eNOS pathway-related protein levels, as well as PKCzeta binding to Akt, was studied. ZIP, a PKCzeta inhibitor, was utilized to treat HUVECs in vitro, and the effect of ZIP on cell viability, inflammatory response, oxidative stress, and Akt activation was evaluated.

RESULTS

Cav1 knockdown had no significant effect on body weight or blood glucose in mice over an 8-week period, whereas drastically reduced insulin, lipid parameters, endothelial damage, E-selectin, and oxidative stress and elevated eNOS levels. Moreover, Cav1 knockdown triggered decreased PKCzeta enrichment and the activation of the PI3K/Akt/eNOS pathway. PKCzeta has a positive effect on cells without being coupled by Cav1, and ZIP had no marked influence on PKCzeta-Akt binding following Cav1/PKCzeta coupling.

CONCLUSION

Cav1/PKCzeta coupling antagonizes the activation of PI3K on Akt, leading to eNOS dysfunction, insulin resistance, and endothelial cell damage.

Capsaicin and Zinc Signalling Pathways as Promising Targets for Managing Insulin Resistance and Type 2 Diabetes

The global burden of type 2 diabetes (T2DM) has led to significant interest in finding novel and effective therapeutic targets for this chronic disorder. Bioactive food components have effectively improved abnormal glucose metabolism associated with this disease. Capsaicin and zinc are food components that have shown the potential to improve glucose metabolism by activating signalling events in the target cells. Capsaicin and zinc stimulate glucose uptake through the activation of distinct pathways (AMPK and AKT, respectively); however, calcium signal transduction seems to be the common pathway between the two. The investigation of molecular pathways that are activated by capsaicin and zinc has the potential to lead to the discovery of new therapeutic targets for T2DM. Therefore, this literature review aims to provide a summary of the main signalling pathways triggered by capsaicin and zinc in glucose metabolism.

Triglyceride-Glucose Index Linked to In-Hospital Mortality in Critically Ill Patients with Heart Disease

Background

As an alternative method to evaluate insulin resistance (IR), triglyceride-glucose index (TyG) was shown to be related to the severity and prognosis of cardiovascular diseases. The main aim of this study was to explore the association between TyG and in-hospital mortality in critically ill patients with heart disease.

Method

The calculation method of TyG has been confirmed in previous report: Ln [fasting TGs (mg/dL) × FBG (mg/dL)/2]. All patients were divided into four different categories according to TyG quartiles. Primary outcome was in-hospital mortality. Binary logistic regression analysis was performed to determine the independent effect of TyG.

Result

4839 critically ill patients with heart disease were involved. The overall mortality was 8.53 cases per 100 idviduals. In-hospital mortality increased as TyG quartiles increased (Quartile 4 vs Quartile 1: 12.1 vs 5.3, p < 0.001). Even after adjusting for confounding variables, TyG was still independently associated with the increased risk of in-hospital mortality in critically ill patients with heart disease (Quartile 4 vs Quartile 1: OR (95% CI): 1.83 (1.27, 2.64), p < 0.001, P for trend < 0.001). In the subgroup analysis, we failed to observe the association between increased TyG and the risk of mortality in patients complicated by diabetes. In addition, as TyG quartiles increased, the length of intensive care unit (ICU) stay was prolonged (Quartile 4 vs Quartile 1: 2.3 (1.3, 4.9) vs 2.1 (1.3, 3.8), p = 0.007). And the significant interactions were not found in most subgroups.

Conclusions

TyG was independently correlated with in-hospital mortality in critically ill patients with heart disease.

Substitution of the SERCA2 Cys674 reactive thiol accelerates atherosclerosis by inducing endoplasmic reticulum stress and inflammation

BACKGROUND AND PURPOSE

The cysteine⁶⁷⁴ (C674) thiol of sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2 is easily and irreversibly oxidized under atherosclerotic conditions. However, the contribution of the C674 thiol redox status in the development of atherosclerosis remains unclear. Our goal was to elucidate the possible mechanism involved.

EXPERIMENTAL APPROACH

Heterozygous SERCA2 C674S knock-in mice in which half of the C674 was substituted by serine⁶⁷⁴ (S674) were used to mimic the removal of the reactive C674 thiol which occurs under pathological conditions. Bone marrow-derived macrophages (BMDMs) and cardiac endothelial cells (ECs) were used for intracellular Ca²⁺ , macrophage adhesion, and protein expression analysis. The whole aorta and aortic root were isolated for histological analysis.

KEY RESULTS

Cell culture studies suggest the partial substitution of SERCA2 C674 increased intracellular Ca²⁺ levels and induced ER stress in both BMDMs and ECs. The release of pro-inflammatory factors and macrophage adhesion increased in SKI BMDMs. In ECs, the overexpression of S674 induced endothelial inflammation and promoted macrophage recruitment. SKI mice developed more severe atherosclerotic plaque and macrophage accumulation. Additionally, 4-phenyl butyric acid (PBA), an ER stress inhibitor, suppressed ER stress and inflammatory responses in BMDMs and ECs, and alleviate atherosclerosis in SKI mice.

CONCLUSIONS AND IMPLICATIONS

The substitution of SERCA2 C674 thiol accelerates the development of atherosclerosis by inducing ER stress and inflammation. Our findings highlight the importance of SERCA2 C674 redox state in the context of atherosclerosis and open up a novel therapeutic strategy to combat atherosclerosis.

The Mystery of Exosomes in Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) is one of the common pregnancy complications, which increases the risk of short-term and long-term adverse consequences in both the mother and offspring. However, the pathophysiological mechanism of GDM is still poorly understood. Inflammation, insulin resistance and oxidative stress are considered critical factors in the occurrence and development of GDM. Although the lifestyle intervention and insulin are the primary treatment, adverse pregnancy outcomes still cannot be ignored. Exosomes have a specific function of carrying biological information, which can transmit information to target cells and play an essential role in intercellular communication. Their possible roles in normal pregnancy and GDM have been widely concerned. The possibility of exosomal cargos as biomarkers of GDM is proposed. This paper reviews the literature in recent years and discusses the role of exosomes in GDM and their possible mechanisms to provide some reference for the prediction, prevention, and treatment of GDM and improve the outcome of pregnancy.

Triglyceride-glucose index as a marker in cardiovascular diseases: landscape and limitations

The triglyceride-glucose (TyG) index has been identified as a reliable alternative biomarker of insulin resistance (IR). Recently, a considerable number of studies have provided robust statistical evidence suggesting that the TyG index is associated with the development and prognosis of cardiovascular disease (CVD). Nevertheless, the application of the TyG index as a marker of CVD has not systemically been evaluated, and even less information exists regarding the underlying mechanisms associated with CVD. To this end, in this review, we summarize the history of the use of the TyG index as a surrogate marker for IR. We aimed to highlight the application value of the TyG index for a variety of CVD types and to explore the potential limitations of using this index as a predictor for cardiovascular events to improve its application value for CVD and provide more extensive and precise supporting evidence.

Serum Elemental Analysis of Type 2 Diabetes Patients Using SRXRF

A total of 158 serum samples of newly diagnosed type 2 diabetes patients and control subjects were analyzed using Synchrotron Radiation X-ray Fluorescence (SRXRF) technique. The microprobe XRF beam line-16 of Indus-2 synchrotron radiation facility at Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, India, was used to identify and quantify the elements K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Rb, Sr, and Pb. A significant decrease in the mean concentrations of K, Ca, Ti, Cr, Mn, Ni, Zn, and As and an increase in the concentrations of V, Fe, Co, Cu, Se, and Pb were observed in the serum samples of the patient group when compared to the control group. It is hypothesized that the observed alterations in the elemental concentrations might have led to ineffective uptake of insulin and have interfered with glucose homeostasis by either directly or indirectly causing oxidative stress.

Nature׳s gifts to medicine: The metabolic effects of extracts from cocoons of Larinus hedenborgi (Coleoptera: Curculionidae) and their host plant Echinops cephalotes (Asteraceae) in diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Trehala manna (TM), the edible cocoons of several weevil species, e.g. Larinus hedenborgi Boheman, 1845 (Coleoptera: Curculionidae) and their host plant, i.e. Echinops cephalotes DC. (EC) (Asteraceae), are traditionally used to treat pain, inflammation, infectious diseases, as well as respiratory, renal, reproductive and metabolic disorders.

AIM OF THE STUDY

This study investigated the metabolic effects of aqueous extracts from TM and EC on diabetic male Wistar albino rats.

MATERIALS AND METHODS

Animals were orally gavaged with the extracts (75, 150, and 300 mg/kg), normal saline, and glibenclamide (Glbn), for 28 days. The serum levels of glucose, insulin, lipid profile, and hepatic enzymes, plus the body weight of rats were measured at the beginning and the end of study. The proximate composition of the extracts was determined, additionally. The antioxidant and cytotoxic potency of the extracts were evaluated by radical scavenging/ferric reducing and viability assays, respectively.

RESULTS

Treatment of diabetic rats with the extracts significantly altered metabolic biomarkers compared with diabetic, control and Glbn-treated groups, but not in a dose-dependent manner. However, the antihyperglycemic effects of TM₇₅/EC₃₀₀, the antiobesity effects of EC₁₅₀, and the hepatoprotective effects of TM₁₅₀/EC₁₅₀ were even stronger than those of Glbn. TM/EC-treated groups represented normal cell architecture in the pancreatic and renal tissues. Nutrient analysis displayed that TM is rich in sugar and magnesium, whereas EC is abundant in protein, sodium, potassium, and calcium. The extracts showed no antioxidant and cytotoxic effects, as compared to the control groups.

CONCLUSIONS

The findings suggest that active ingredients in the extracts evaluated are responsible for the metabolic effects by lowering blood sugar and restoring the damaged islets of Langerhans. The close trophic relationship of the TM-producing beetle with the host thistle justifies the overlaps of the bioactivity of the TM and EC extracts.

Characteristics of the New Insulin-Resistant Zebrafish Model

Insulin resistance, which occurs when insulin levels are sufficiently high over a prolonged period, causing the cells to fail to respond normally to the hormone. As a system for insulin resistance and diabetes drug development, insulin-resistant rodent models have been clearly established, but there is a limitation to high-throughput drug screening. Recently, zebrafish have been identified as an excellent system for drug discovery and identification of therapeutic targets, but studies on insulin resistance models have not been extensively performed. Therefore, we aimed to make a rapid insulin-resistant zebrafish model that complements the existing rodent models. To establish this model, zebrafish were treated with 10 μM insulin for 48 h. This model showed characteristics of insulin-resistant disease such as damaged pancreatic islets. Then we confirmed the recovery of the pancreatic islets after pioglitazone treatment. In addition, it was found that insulin-resistant drugs have as significant an effect in zebrafish as in humans, and these results proved the value of the zebrafish insulin resistance model for drug selection. In addition, RNA sequencing was performed to elucidate the mechanism involved. KEGG pathway enrichment analysis of differentially expressed genes showed that insulin resistance altered gene expression due to the MAPK signaling and calcium signaling pathways. This model demonstrates the utility of the zebrafish model for drug testing and drug discovery in insulin resistance and diabetes.

Calcium-Deficiency during Pregnancy Affects Insulin Resistance in Offspring

Prenatal malnutrition is known to affect the phenotype of the offspring through changes in epigenetic regulation. Growing evidence suggests that epigenetics is one of the mechanisms by which nutrients and minerals affect metabolic traits. Although the perinatal period is the time of highest phenotypic plasticity, which contributes largely to developmental programming, there is evidence of nutritional influence on epigenetic regulation during adulthood. Calcium (Ca) plays an important role in the pathogenesis of insulin resistance syndrome. Cortisol, the most important glucocorticoid, is considered to lead to insulin resistance and metabolic syndrome. 11β-hydroxysteroid dehydrogenase-1 is a key enzyme that catalyzes the intracellular conversion of cortisone to physiologically active cortisol. This brief review aims to identify the effects of Ca deficiency during pregnancy and/or lactation on insulin resistance in the offspring. Those findings demonstrate that maternal Ca deficiency during pregnancy may affect the epigenetic regulation of gene expression and thereby induce different metabolic phenotypes. We aim to address the need for Ca during pregnancy and propose the scaling-up of clinical and public health approaches that improved pregnancy outcomes.

Impaired Ca2+ signaling due to hepatic steatosis mediates hepatic insulin resistance in Alström syndrome mice that is reversed by GLP-1 analog treatment

Ca²⁺ signaling plays a critical role in the regulation of hepatic metabolism by hormones including insulin. Changes in cytoplasmic Ca²⁺ regulate synthesis and posttranslational modification of key signaling proteins in the insulin pathways. Emerging evidence suggests that hepatocyte intracellular Ca²⁺ signaling is altered in lipid-loaded liver cells isolated from obese rodent models. The mechanisms of altered Ca²⁺-insulin and insulin-Ca²⁺ signaling pathways in obesity remain poorly understood. Here, we show that the kinetics of insulin-initiated intracellular (initial) Ca²⁺ release from endoplasmic reticulum is significantly impaired in steatotic hepatocytes from obese Alström syndrome mice. Furthermore, exenatide, a glucagon-like peptide-1 (GLP-1) analog, reversed lipid-induced inhibition of intracellular Ca²⁺ release kinetics in steatotic hepatocytes, without affecting the total content of intracellular Ca²⁺ released. Exenatide reversed the lipid-induced inhibition of intracellular Ca²⁺ release, at least partially, via lipid reduction in hepatocytes, which then restored hormone-regulated cytoplasmic Ca²⁺ signaling and insulin sensitivity. This data provides additional evidence for the important role of Ca²⁺ signaling pathways in obesity-associated impaired hepatic lipid homeostasis and insulin signaling. It also highlights a potential advantage of GLP-1 analogs when used to treat type 2 diabetes associated with hepatic steatosis.

Association between rosacea and cardiovascular disease: A systematic review and meta-analysis

BACKGROUND

Rosacea and cardiovascular diseases (CVD) are chronic inflammatory disorders. While CVD is the leading cause of mortality globally, increasing evidence indicates that CVD prevalence could be higher among patients with rosacea.

AIMS

This review aimed to determine the association between the prevalence of CVD and rosacea.

PATIENTS/METHODS

A systematic review of observational studies with controls available in MEDLINE, EMBASE, PubMed, Cochrane, and Web of Science databases was conducted. We performed a pooled meta-analysis using random-effects weighting. Overall, 11 studies met the inclusion criteria, which indicated increased odds for at least one risk factor of CVD, including diabetes, high blood pressure, or dyslipidemia.

RESULTS

The pooled meta-analysis indicated an association of rosacea with higher odds of insulin resistance or diabetes (odds ratio [OR], 1.18; 95% confidence interval [CI], 0.97-1.45), high systolic blood pressure (OR, 1.96; 95% CI, 1.35-2.84), dyslipidemia (OR, 1.50; 95% CI, 1.19-1.88), and CVD (OR, 6.65; 95% CI, 2.80-15.76). No publication bias was detected. The effect of confounding factors due to overlapping symptoms and lack of individual-level data were limitations of this review.

CONCLUSION

Patients with rosacea have a high risk of CVD. However, further studies are warranted to confirm the association between rosacea and CVD.

Role of Endoplasmic Reticulum Stress in Atherosclerosis and Its Potential as a Therapeutic Target

Endoplasmic reticulum (ER) stress is closely associated with atherosclerosis and related cardiovascular diseases (CVDs). It occurs due to various pathological factors that interfere with ER homeostasis, resulting in the accumulation of unfolded or misfolded proteins in the ER lumen, thereby causing ER dysfunction. Here, we discuss the role of ER stress in different types of cells in atherosclerotic lesions. This discussion includes the activation of apoptotic and inflammatory pathways induced by prolonged ER stress, especially in advanced lesional macrophages and endothelial cells (ECs), as well as common atherosclerosis-related ER stressors in different lesional cells, which all contribute to the clinical progression of atherosclerosis. In view of the important role of ER stress and the unfolded protein response (UPR) signaling pathways in atherosclerosis and CVDs, targeting these processes to reduce ER stress may be a novel therapeutic strategy.

Natural Product Luteolin Rescues THAP-Induced Pancreatic β-Cell Dysfunction through HNF4α Pathway

Endoplasmic reticulum stress (ER stress) plays a main role in pancreatic [Formula: see text]-cell dysfunction and death because of intracellular Ca[Formula: see text] turbulence and inflammation activation. Although several drugs are targeting pancreatic [Formula: see text]-cell to improve [Formula: see text]-cell function, there still lacks agents to alleviate [Formula: see text]-cell ER stress conditions. Therefore we used thapsigargin (THAP) or high glucose (HG) to induce ER stress in [Formula: see text]-cell and aimed to screen natural molecules against ER stress-induced [Formula: see text]-cell dysfunction. Through screening the Traditional Chinese drug library ([Formula: see text] molecules), luteolin was finally discovered to improve [Formula: see text]-cell function. Cellular viability results indicated luteolin reduced the THAP or HG-induced [Formula: see text]-cell death and apoptosis through MTT and flow cytometry assay. Moreover, luteolin improved [Formula: see text]-cell insulin secretion ability under ER stress conditions. Also ER stress-induced intracellular Ca[Formula: see text] turbulence and inflammation activation were inhibited by luteolin treatment. Mechanically, luteolin inhibited HNF4[Formula: see text] signaling, which was induced by ER stress. Moreover, luteolin reduced the transcriptional level of HNF4[Formula: see text] downstream gene, such as Asnk4b and HNF1[Formula: see text]. Conversely HNF4[Formula: see text] knockdown abolished the effect of luteolin on [Formula: see text]-cell using siRNA. These results suggested the protective effect of luteolin on [Formula: see text]-cell was through HNF4[Formula: see text]/Asnk4b pathway. In conclusion, our study discovered that luteolin improved [Formula: see text]-cell function and disclosed the underlying mechanism of luteolin on [Formula: see text]-cell, suggesting luteolin is a promising agent against pancreatic dysfunction.

Transcriptome Analysis of Testis from HFD-Induced Obese Rats (Rattus norvigicus) Indicated Predisposition for Male Infertility

Obesity is a worldwide life-threatening metabolic disorder, associated with various chronic diseases, including male infertility. Obesity was induced by high fat diet (HFD), and testis RNA was used for the transcriptome analysis using RNAseq via Illumina NovaSeq 6000 System and NovaSeq 6000 Kit. Gene expression level was estimated as FPKM (Fragments Per Kilobase of transcript per Million mapped reads). Differential expressed genes (DEGs) were annotated against gene ontology (GO) and KEGG databases. More than 63.66 million reads per sample were performed with 100 bp cutoff and 6 Gb sequencing depth. Results of this study revealed that 267 GO terms (245 biological processes (BP), 14 cellular components (CC), eight molecular functions (MF)), and 89 KEGG pathways were significantly enriched. Moreover, total numbers of 136 genes were differentially expressed (107 upregulated, 29 downregulated) with |FC| ≥ 2 and bh adjusted <0.05. Interesting DEGs were detected, including obesity and lipid metabolism-related genes, immune response-related genes, cytochrome P450 genes, including aromatase were upregulated, whereas genes related to male fertility and fertilization, cell adhesion, and olfactory receptors were downregulated. The combined expression pattern of the DEGs in obese animals indicated an increase in cholesterol metabolism. Furthermore, high aromatase activity enhances the testosterone turnover into estradiol and lowers the testosterone/estradiol (T/E) ratio, which ultimately reduces fertility. In addition, downregulation of cadherens junction components genes leads to the pre-mature release of sperm from Sertoli cells resulting in the reduction of fertility. Moreover, the downregulation of olfactory receptor genes reduces the chemotaxis capacity of sperms in tracking the oocyte for fertilization, which reduces male fertility. Furthermore, various obesity molecular markers were detected in our transcriptome. The results of this study will enhance our understanding of the molecular network of obesity development, development of obesity novel molecular diagnosis markers, molecular bases of obesity-induced infertility, and the development of anti-obesity drugs.

Role of Minerals and Trace Elements in Diabetes and Insulin Resistance

Minerals and trace elements are micronutrients that are essential to the human body but present only in traceable amounts. Nonetheless, they exhibit well-defined biochemical functions. Deficiencies in these micronutrients are related to widespread human health problems. This review article is focused on some of these minerals and trace element deficiencies and their consequences in diabetes and insulin resistance. The levels of trace elements vary considerably among different populations, contingent on the composition of the diet. In several Asian countries, large proportions of the population are affected by a number of micronutrient deficiencies. Local differences in selenium, zinc, copper, iron, chromium and iodine in the diet occur in both developed and developing countries, largely due to malnutrition and dependence on indigenous nutrition. These overall deficiencies and, in a few cases, excess of essential trace elements may lead to imbalances in glucose homeostasis and insulin resistance. The most extensive problems affecting one billion people or more worldwide are associated with inadequate supply of a number of minerals and trace elements including iodine, selenium, zinc, calcium, chromium, cobalt, iron, boron and magnesium. This review comprises various randomized controlled trials, cohort and case-controlled studies, and observational and laboratory-based studies with substantial outcomes of micronutrient deficiencies on diabetes and insulin resistance in diverse racial inhabitants from parts of Asia, Africa, and North America. Changes in these micronutrient levels in the serum and urine of subjects may indicate the trajectory toward metabolic changes, oxidative stress and provide disease-relevant information.

Association of AMPK Pathway-Related Gene Polymorphisms with Symptomatic Intracranial Atherosclerotic Stenosis in a Chinese Han Population

Background and Objective: Recently, AMP-activated protein kinase (AMPK) signaling was confirmed to be intimately associated with atherosclerosis. Evidence indicates that genetic susceptibility plays an important role in the etiology of symptomatic intracranial atherosclerotic stenosis (sICAS), however few genes have been pinpointed being etiologically associated. This study investigated possible links between single nucleotide polymorphisms (SNPs) of AMPK-related genes and sICAS in Han Chinese subjects. Methods: Target gene sequencing was carried out in 400 sICAS Han Chinese patients and 1007 healthy controls for 11 AMPK pathway-related genes. Chi-squared testing and multiple logistic regression in dominant, recessive, and additive models were used to evaluate the association between SNPs and risk of sICAS. Bonferroni corrections were performed with a p < (0.05/44 = 0.0011) as statistically significant. Further subgroup data analyses was conducted using chi-squared or t-tests. Results: There were 44 common variants of 11 candidate genes distributed differently between sICAS patients and healthy controls, among which the INSR rs78312382 SNP remained significant even after a Bonferroni correction. Logistic regression analysis showed that rs78312382 was significantly associated with the risk of sICAS in both dominant and additive models (p_Bonferroni = 7.874e^-5 and 0.000506, respectively), with the A allele being much more prevalent in the sICAS group (p = 0.000404). Conclusions: Variants of the INSR rs7831282 locus may play an important role in the development of sICAS among the Han Chinese with the A allele being a risk factor and a potential biomarker for this illness.

CTCF inhibits endoplasmic reticulum stress and apoptosis in cardiomyocytes by upregulating RYR2 via inhibiting S100A1

AIMS

Pediatric heart failure is a common cardiovascular disease in clinical pediatrics. CCCTC-binding factor (CTCF), a novel transcriptional repressor, was reported to participate in the occurrence of various cardiovascular diseases. The present study focuses on exploring the effects of CTCF on tunicamycin (TM)-induced endoplasmic reticulum (ER) stress, and investigating the underlying mechanisms.

MATERIALS AND METHOD

Expression of CTCF in blood samples of heart failure children and TM-induced cardiomyocytes were evaluated by real-time quantitative PCR (RT-qPCR). Apoptotic rate of cardiomyocytes was detected by Annexin v assay. Western blotting and enzyme-linked immunosorbent assay (ELISA) were applied to examine the effect of CTCF on ER stress. Co-immunoprecipitation and western blotting were devoted to explore the mechanism by which CTCF contributes to ER stress.

KEY FINDINGS

We proved that CTCF was lowly expressed in blood samples of heart failure children and TM-induced cardiomyocytes, and overexpression of CTCF weaken the TM-induced ER stress. Using co-immunoprecipitation and protein blots, we demonstrated that CTCF upregulates RYR2 by inhibiting S100A1, thus mediating the PERK signaling pathway and regulating ER stress.

SIGNIFICANCE

Our data revealed that CTCF protects cardiomyocytes from ER stress through S100A1-RYR2 axis, and can be applied as a therapeutic target for the treatment of pediatric heart failure in future.

Calcium Signaling in ß-cell Physiology and Pathology: A Revisit

Pancreatic beta (β) cell dysfunction results in compromised insulin release and, thus, failed regulation of blood glucose levels. This forms the backbone of the development of diabetes mellitus (DM), a disease that affects a significant portion of the global adult population. Physiological calcium (Ca²⁺) signaling has been found to be vital for the proper insulin-releasing function of β-cells. Calcium dysregulation events can have a dramatic effect on the proper functioning of the pancreatic β-cells. The current review discusses the role of calcium signaling in health and disease in pancreatic β-cells and provides an in-depth look into the potential role of alterations in β-cell Ca²⁺ homeostasis and signaling in the development of diabetes and highlights recent work that introduced the current theories on the connection between calcium and the onset of diabetes.

Ca2+ Flux: Searching for a Role in Efferocytosis of Apoptotic Cells in Atherosclerosis

In atherosclerosis, macrophages in the arterial wall ingest plasma lipoprotein-derived lipids and become lipid-filled foam cells with a limited lifespan. Thus, efficient removal of apoptotic foam cells by efferocytic macrophages is vital to preventing the dying foam cells from forming a large necrotic lipid core, which, otherwise, would render the atherosclerotic plaque vulnerable to rupture and would cause clinical complications. Ca²⁺ plays a role in macrophage migration, survival, and foam cell generation. Importantly, in efferocytic macrophages, Ca²⁺ induces actin polymerization, thereby promoting the formation of a phagocytic cup necessary for efferocytosis. Moreover, in the efferocytic macrophages, Ca²⁺ enhances the secretion of anti-inflammatory cytokines. Various Ca²⁺ antagonists have been seminal for the demonstration of the role of Ca²⁺ in the multiple steps of efferocytosis by macrophages. Moreover, in vitro and in vivo experiments and clinical investigations have revealed the capability of Ca²⁺ antagonists in attenuating the development of atherosclerotic plaques by interfering with the deposition of lipids in macrophages and by reducing plaque calcification. However, the regulation of cellular Ca²⁺ fluxes in the processes of efferocytic clearance of apoptotic foam cells and in the extracellular calcification in atherosclerosis remains unknown. Here, we attempted to unravel the molecular links between Ca²⁺ and efferocytosis in atherosclerosis and to evaluate cellular Ca²⁺ fluxes as potential treatment targets in atherosclerotic cardiovascular diseases.

ER Stress Activates the NLRP3 Inflammasome: A Novel Mechanism of Atherosclerosis

The endoplasmic reticulum (ER) is an important organelle that regulates several fundamental cellular processes, and ER dysfunction has implications for many intracellular events. The nucleotide-binding oligomerization domain-like receptor family, pyrin domain-containing 3 (NLRP3) inflammasome is an intracellularly produced macromolecular complex that can trigger pyroptosis and inflammation, and its activation is induced by a variety of signals. ER stress has been found to affect NLRP3 inflammasome activation through multiple effects including the unfolded protein response (UPR), calcium or lipid metabolism, and reactive oxygen species (ROS) generation. Intriguingly, the role of ER stress in inflammasome activation has not attracted a great deal of attention. In addition, increasing evidence highlights that both ER stress and NLRP3 inflammasome activation contribute to atherosclerosis (AS). AS is a common cardiovascular disease with complex pathogenesis, and the precise mechanisms behind its pathogenesis remain to be determined. Both ER stress and the NLRP3 inflammasome have emerged as critical individual contributors of AS, and owing to the multiple associations between these two events, we speculate that they contribute to the mechanisms of pathogenesis in AS. In this review, we aim to summarize the molecular mechanisms of ER stress, NLRP3 inflammasome activation, and the cross talk between these two pathways in AS in the hopes of providing new pharmacological targets for AS treatment.

Deranged hepatocyte intracellular Ca2+ homeostasis and the progression of non-alcoholic fatty liver disease to hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths in men, and the sixth in women. Non-alcoholic fatty liver disease (NAFLD) is now one of the major risk factors for HCC. NAFLD, which involves the accumulation of excess lipid in cytoplasmic lipid droplets in hepatocytes, can progress to non-alcoholic steatosis, fibrosis, and HCC. Changes in intracellular Ca²⁺ constitute important signaling pathways for the regulation of lipid and carbohydrate metabolism in normal hepatocytes. Recent studies of steatotic hepatocytes have identified lipid-induced changes in intracellular Ca²⁺, and have provided evidence that altered Ca²⁺ signaling exacerbates lipid accumulation and may promote HCC. The aims of this review are to summarise current knowledge of the lipid-induced changes in hepatocyte Ca²⁺ homeostasis, to comment on the mechanisms involved, and discuss the pathways leading from altered Ca²⁺ homeostasis to enhanced lipid accumulation and the potential promotion of HCC. In steatotic hepatocytes, lipid inhibits store-operated Ca²⁺ entry and SERCA2b, and activates Ca²⁺ efflux from the endoplasmic reticulum (ER) and its transfer to mitochondria. These changes are associated with changes in Ca²⁺ concentrations in the ER (decreased), cytoplasmic space (increased) and mitochondria (likely increased). They lead to: inhibition of lipolysis, lipid autophagy, lipid oxidation, and lipid secretion; activation of lipogenesis; increased lipid; ER stress, generation of reactive oxygen species (ROS), activation of Ca²⁺/calmodulin-dependent kinases and activation of transcription factor Nrf2. These all can potentially mediate the transition of NAFLD to HCC. It is concluded that lipid-induced changes in hepatocyte Ca²⁺ homeostasis are important in the initiation and progression of HCC. Further research is desirable to better understand the cause and effect relationships, the time courses and mechanisms involved, and the potential of Ca²⁺ transporters, channels, and binding proteins as targets for pharmacological intervention.

C/EBPβ mediates palmitate-induced musclin expression via the regulation of PERK/ATF4 pathways in myotubes

Musclin is a muscle-secreted cytokine that disrupts glucose uptake and glycogen synthesis in type 2 diabetes. The purpose of this study was to investigate the mechanisms responsible for the regulation of musclin gene expression in response to treatment with palmitate. RNA sequencing results showed that biological processes activated by palmitate are mainly enriched in endoplasmic reticulum (ER) stress. The protein kinase RNA-like ER kinase (PERK) signaling pathway is involved in the regulation of musclin expression induced by palmitate. Chromatin immunoprecipitation data showed that activating transcription factor 4 (ATF4)-downstream of PERK-bound to the promoter of the C/EBPβ gene. Notably, C/EBPβ also contains a binding site in the region -94~-52 of the musclin gene promoter. Knockdown or knockout of PERK and ATF4 using short hairpin RNA or CRISPR-Cas9 decreased the expression of C/EBPβ and musclin induced by palmitate. Furthermore, knockdown and knockout of C/EBPβ alleviated the high expression of musclin in response to treatment with palmitate. Moreover, CRISPR-Cas9 knockout of the region -94~-52 in which C/EBPβ binds to the promoter of musclin abrogated the induction of high musclin expression caused by palmitate. Collectively, these findings suggest that treatment with palmitate activates the PERK/ATF4 signaling pathway, which in turn increases the expression of C/EBPβ. C/EBPβ binds directly to the promoter of the musclin gene and upregulates its expression.

"Sex hormone independent associations between insulin resistance and thyroid status -a gender based biochemical study on clinically euthyroid non-obese, overweight and obese type 2 diabetics''

AIM

Studies indicate that type 2 diabetes mellitus (T2DM) might contribute to the development of thyroid disorders (TD). However, few gender based reports are available describing therelationship between T2DM and TD in clinically euthyroid, anthropometry specified groups of type 2 diabetics. The aim of this study was to relategender based biochemical changes in anthropometry specified, clinically euthyroid type 2 diabetics.

METHODOLOGY

The study was carried out on clinically euthyroid type 2 diabetics (male n = 269; female n = 301) at a tertiary health care unit in Pondicherry, South India. Three groups were segregatedbased on Body mass Index: 153 non-obese type 2 diabetics (BMI = 18.5-24.99), 291 overweight type 2 diabetics (BMI = 25-29.99) and 126 obese type 2 diabetics (BMI ≥ 30). Biochemical parameters included glycated hemoglobin, insulin resistance, Cortisol and Thyroid profile.

RESULTS

The study had included clinically euthyroid type 2 diabetics (52.8% females and 47.2% males). Statistically significant associationsweredifferently observed between insulin resistance (dependent variable) andother independent variables, irrespective of sex hormone status. Total protein was negatively related in non -obese male type 2 diabetics (R = 0.780); Triiodothyronine was inversely associated in overweight males, whereas cortisol and the divalent cations (Zinc and Magnesium) depicted positive association (R = 0.555) in the same group (overweight), butcortisol in non -obese female type 2 diabeticswas negative (R = 0.742); Glycated hemoglobin and calcium exhibited positive relationshipin obese type 2 female diabetics (R = 0.771)..

CONCLUSION

Our study has revealed distinctive relationship between T2DM and TD in the anthropometry specified, clinically euthyroid and gender based type 2 diabetics, independent of the sex hormones.

Role of elastin peptides and elastin receptor complex in metabolic and cardiovascular diseases

The Cardiovascular Continuum describes a sequence of events from cardiovascular risk factors to end-stage heart disease. It includes conventional pathologies affecting cardiovascular functions such as hypertension, atherosclerosis or thrombosis and was traditionally considered from the metabolic point of view. This Cardiovascular Continuum, originally described by Dzau and Braunwald, was extended by O'Rourke to consider also the crucial role played by degradation of elastic fibers, occurring during aging, in the appearance of vascular stiffness, another deleterious risk factor of the continuum. However, the involvement of the elastin degradation products, named elastin-derived peptides, to the Cardiovascular Continuum progression has not been considered before. Data from our laboratory and others clearly showed that these bioactive peptides are central regulators of this continuum, thereby amplifying appearance and evolution of cardiovascular risk factors such as diabetes or hypertension, of vascular alterations such as atherothrombosis and calcification, but also nonalcoholic fatty liver disease and nonalcoholic steatohepatitis. The Elastin Receptor Complex has been shown to be a crucial actor in these processes. We propose here the participation of these elastin-derived peptides and of the Elastin Receptor Complex in these events, and introduce a revisited Cardiovascular Continuum based on their involvement, for which elastin-based pharmacological strategies could have a strong impact in the future.

Calcium Signaling As a Therapeutic Target for Liver Steatosis

Hepatic steatosis, the first step in nonalcoholic fatty liver disease (NAFLD), can arise from various pathophysiological conditions. While lipid metabolism in the liver is normally balanced such that there is no excessive lipid accumulation, when this homeostasis is disrupted lipid droplets (LDs) accumulate in hepatocytes resulting in cellular toxicity. The mechanisms underlying this accumulation and the subsequent hepatocellular damage are multifactorial and poorly understood, with the result that there are no currently approved treatments for NAFLD. Impaired calcium signaling has recently been identified as a cause of increased endoplasmic reticulum (ER) stress contributing to hepatic lipid accumulation. This review highlights new findings on the role of impaired Ca²⁺ signaling in the development of steatosis and discusses potential new approaches to NAFLD treatment based on these new insights.

Nonlinear relationship between ER Ca2+ depletion versus induction of the unfolded protein response, autophagy inhibition, and cell death

Endoplasmic reticulum (ER) Ca²⁺ depletion activates the unfolded protein response (UPR), inhibits bulk autophagy and eventually induces cell death in mammalian cells. However, the extent and duration of ER Ca²⁺ depletion required is unknown. We instigated a detailed study in two different cell lines, using sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) inhibitors to gradually reduce ER Ca²⁺ levels in a controlled manner. Remarkably, UPR induction (as assessed by expression analyses of UPR-regulated proteins) and autophagy inhibition (as assessed by analyses of effects on starvation-induced bulk autophagy) required substantially higher drug concentrations than those needed to strongly decrease total ER Ca²⁺ levels. In fact, even when ER Ca²⁺ levels were so low that we could hardly detect any release of Ca²⁺ upon challenge with ER Ca²⁺ purging agents, UPR was not induced, and starvation-induced bulk autophagy was still fully supported. Moreover, although we observed reduced cell proliferation at this very low level of ER Ca²⁺, cells could tolerate prolonged periods (days) without succumbing to cell death. Addition of increasing concentrations of extracellular EGTA also gradually depleted the ER of Ca²⁺, and, as with the SERCA inhibitors, EGTA-induced activation of UPR and cell death required higher EGTA concentrations than those needed to strongly reduce ER Ca²⁺ levels. We conclude that ER Ca²⁺ depletion-induced effects on UPR, autophagy and cell death require either an extreme general depletion of ER Ca²⁺ levels, or Ca²⁺ depletion in areas of the ER that have a higher resistance to Ca²⁺ drainage than the bulk of the ER.

Crosstalk Between the Unfolded Protein Response, MicroRNAs, and Insulin Signaling Pathways: In Search of Biomarkers for the Diagnosis and Treatment of Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) is a metabolic disorder that is characterized by functional defects in glucose metabolism and insulin secretion. Its complex etiology and multifaceted nature have made it difficult to design effective therapies for early diagnosis and treatment. Several lines of evidence indicate that aberrant activation of the unfolded protein response (UPR) in response to endoplasmic reticulum (ER) stress impairs the β cell's ability to respond to glucose and promotes apoptosis. Elucidating the molecular mechanisms that govern β cell dysfunction and cell death can help investigators design therapies to halt or prevent the development of T2DM. Early diagnosis of T2DM, however, warrants additionally the identification of potential biomarkers. MicroRNAs (miRNAs) are key regulators of transcriptional processes that modulate various features of insulin signaling, such as insulin sensitivity, glucose tolerance, and insulin secretion. A deeper understanding of how changes in patterns of expression of miRNAs correlate with altered glucose metabolism can enable investigators to develop methods for the early diagnosis and treatment of T2DM. The first part of this review examines how altered expression of specific UPR pathway proteins disrupts ER function and causes β cell dysfunction, while the second part discusses the potential role of miRNAs in the diagnostic and treatment of T2DM.

Defective STIM-mediated store operated Ca2+ entry in hepatocytes leads to metabolic dysfunction in obesity

Defective Ca²⁺ handling is a key mechanism underlying hepatic endoplasmic reticulum (ER) dysfunction in obesity. ER Ca²⁺ level is in part monitored by the store-operated Ca²⁺ entry (SOCE) system, an adaptive mechanism that senses ER luminal Ca²⁺ concentrations through the STIM proteins and facilitates import of the ion from the extracellular space. Here, we show that hepatocytes from obese mice displayed significantly diminished SOCE as a result of impaired STIM1 translocation, which was associated with aberrant STIM1 O-GlycNAcylation. Primary hepatocytes deficient in STIM1 exhibited elevated cellular stress as well as impaired insulin action, increased glucose production and lipid droplet accumulation. Additionally, mice with acute liver deletion of STIM1 displayed systemic glucose intolerance. Conversely, over-expression of STIM1 in obese mice led to increased SOCE, which was sufficient to improve systemic glucose tolerance. These findings demonstrate that SOCE is an important mechanism for healthy hepatic Ca²⁺ balance and systemic metabolic control.

Obesity is a chronic metabolic disorder. Some people’s genetics make them more vulnerable to the condition, and it is generally caused by eating too much and moving too little. The resulting surplus of nutrients affects the cells and organs of the body in several adverse ways. For example, excessive nutrients impair a compartment within cells called the endoplasmic reticulum. This compartment is where many proteins and fats are made and transported. It is also the site for a lot of metabolic processes, and the main place in the cell where calcium ions are stored. Many proteins need calcium ions to work properly, including metabolic enzymes. In obesity, the endoplasmic reticulum becomes less able to store calcium ions.

A protein called STIM1 senses and regulates the levels of calcium ions in the endoplasmic reticulum. When calcium levels drop, STIM1 moves along the endoplasmic reticulum membrane towards the part that is next to the cell surface. Here, STIM1 joins up with a calcium channel called Orai1. The STIM1-Orai1 complex allows calcium ions to enter the cell and replenish its levels in the endoplasmic reticulum.

Arruda, Pers et al. have now asked if STIM1 is altered in obesity and, if so, whether it contributes to the endoplasmic reticulum’s inability to maintain proper calcium levels. High-resolution microscopy and biochemical techniques confirmed that STIM1 is indeed compromised in liver cells from obese mice. In these cells, STIM1 was found in unusual small clusters. It also could not move along the endoplasmic reticulum membrane when calcium levels dropped. As a result of these navigational errors, STIM1 failed to couple with Orai1, meaning less calcium could enter the cell. Further work identified that a small sugar molecule that is added onto STIM1 in obesity is behind its reduced ability to move accurately.

Arruda, Pers et al. next created mice that lacked STIM1 in their liver. These mice showed signs of metabolic abnormalities. Notably, when STIM1 levels were experimentally increased in obese mice, it restored calcium levels in the endoplasmic reticulum closer to normal, and improved metabolism too.

Thus, regulating calcium levels in the endoplasmic reticulum via proteins such as STIM1 is essential for maintaining a healthy metabolism. Interventions to correct calcium levels may have therapeutic promise to combat metabolic diseases.

Mechanism by which arylamine N-acetyltransferase 1 ablation causes insulin resistance in mice

Insulin resistance in liver and skeletal muscle are major factors in the pathogenesis of type 2 diabetes; however, the molecular mechanism or mechanisms responsible for this phenomenon have not been established. Recently, an association of a single-nucleotide polymorphism in the human N-acetyltransferase 2 (Nat2) gene with insulin resistance in humans was found. Here, we show that the murine ortholog Nat1 knockout (KO) mice manifested whole-body insulin resistance associated with marked increases in liver and muscle lipid content. Nat1 KO mice also displayed reduced whole-body energy expenditure and reduced mitochondrial activity. Taken together, these studies demonstrate that Nat1 deletion promotes reduced mitochondrial activity and is associated with ectopic lipid-induced liver and muscle insulin resistance.

A single-nucleotide polymorphism in the human arylamine N-acetyltransferase 2 (Nat2) gene has recently been identified as associated with insulin resistance in humans. To understand the cellular and molecular mechanisms by which alterations in Nat2 activity might cause insulin resistance, we examined murine ortholog Nat1 knockout (KO) mice. Nat1 KO mice manifested whole-body insulin resistance, which could be attributed to reduced muscle, liver, and adipose tissue insulin sensitivity. Hepatic and muscle insulin resistance were associated with marked increases in both liver and muscle triglyceride (TAG) and diacylglycerol (DAG) content, which was associated with increased PKCε activation in liver and increased PKCθ activation in skeletal muscle. Nat1 KO mice also displayed reduced whole-body energy expenditure and reduced mitochondrial oxygen consumption in white adipose tissue, brown adipose tissue, and hepatocytes. Taken together, these studies demonstrate that Nat1 deletion promotes reduced mitochondrial activity and is associated with ectopic lipid-induced insulin resistance. These results provide a potential genetic link among mitochondrial dysfunction with increased ectopic lipid deposition, insulin resistance, and type 2 diabetes.

Activation of the Integrated Stress Response and Metabolic Dysfunction in a Murine Model of Sleep Apnea

Intermittent hypoxia (IH) induces activation of the integrated stress response (ISR), but its role in IH-induced visceral white adipose tissue (vWAT) insulin resistance is unknown. CHOP is activated by chronic ISR, whereas GADD34 dephosphorylates the subunit of translation initiation factor 2 (eIF2α), leading to termination of the ISR. We hypothesized that CHOP/Gadd34 null mice would not manifest evidence of insulin resistance after IH exposures. Eight-week-old CHOP/GADD34^-/- (double mutant [DM]) and wild-type (WT) littermates were randomly assigned to IH or room air (RA) exposures for 6 weeks. Glucose and insulin tolerance tests were performed, and regulatory T cells (Tregs) and macrophages in vWAT were assessed. Phosphorylated eIF2α:total eIF2α, ATF4, XBP1 expression, and insulin-induced pAKT/AKT expression changes were examined in vWATs. Single GADD34^-/- and PERK^+/- mice were also evaluated. Body weight and vWAT mass were reduced in DM and WT mice after IH. M1/M2 macrophages and inflammatory macrophages (Ly-6c^high) were significantly increased in WT vWAT but remained unchanged in DM mice. Tregs were significantly decreased in WT vWAT but not in DM mice. Systemic insulin and glucose tolerance tests revealed insulin resistance in IH-WT but not in IH-DM mice. Similarly, decreased pAKT/AKT responses to exogenous insulin emerged in IH-WT compared with RA-WT mice, whereas no significant differences emerged in IH-DM compared with DM-RA. Chronic ISR activation appears to contribute to the insulin resistance and vWAT inflammation that characteristically emerge after long-term IH exposures in a murine model of obstructive sleep apnea.

Inhibition of endoplasmic reticulum stress alleviates cigarette smoke-induced airway inflammation and emphysema

Chronic bronchitis and emphysema are pathologic features of chronic obstructive pulmonary disease (COPD). Cigarette smoke (CS)-induced endoplasmic reticulum (ER) stress has been implicated in the COPD development, but the molecular mechanism by which it contributes to COPD etiology and the specific role it plays in COPD pathogenesis remain poorly understood. Here, we aimed to determine the role of ER stress in the pathogenesis of CS-induced airway inflammation and emphysema. Exposure to CS significantly increased the expression of ER stress markers in Beas-2B cells and in mouse lungs, possibly through the production of oxidative stress. Further, inhibition of ER stress by 4-phenylbutyric acid (4-PBA) reduced CS extract-induced inflammation in Beas-2B cells through the modulation of NF-κB signaling. 4-PBA also protected against CS-induced airway inflammation and the development of emphysema in mice, which was associated with a reduction in NF-κB activation and alveolar cell apoptosis in the lungs. Taken together, our results suggest that ER stress is crucial for CS-induced inflammation and emphysema, and that targeting ER stress may represent a novel approach to the treatment of COPD.

SERCA control of cell death and survival

Intracellular calcium (Ca²⁺⁾ is a critical coordinator of various aspects of cellular physiology. It is increasingly apparent that changes in cellular Ca²⁺ dynamics contribute to the regulation of normal and pathological signal transduction that controls cell growth and survival. Aberrant perturbations in Ca²⁺ homeostasis have been implicated in a range of pathological conditions, such as cardiovascular diseases, diabetes, tumorigenesis and steatosis hepatitis. Intracellular Ca²⁺ concentrations are therefore tightly regulated by a number of Ca²⁺ handling enzymes, proteins, channels and transporters located in the plasma membrane and in Ca²⁺ storage organelles, which work in concert to fine tune a temporally and spatially precise Ca²⁺ signal. Chief amongst them is the sarco/endoplasmic reticulum (SR/ER) Ca²⁺ ATPase pump (SERCA) which actively re-accumulates released Ca²⁺ back into the SR/ER, therefore maintaining Ca²⁺ homeostasis. There are at least 14 different SERCA isoforms encoded by three ATP2A1-3 genes whose expressions are species- and tissue-specific. Altered SERCA expression and activity results in cellular malignancy and induction of ER stress and ER stress-associated apoptosis. The role of SERCA misregulation in the control of apoptosis in various cell types and disease setting with prospective therapeutic implications is the focus of this review. Ca²⁺ is a double edge sword for both life as well as death, and current experimental evidence supports a model in which Ca²⁺ homeostasis and SERCA activity represent a nodal point that controls cell survival. Pharmacological or genetic targeting of this axis constitutes an incredible therapeutic potential to treat different diseases sharing similar biological disorders.