Glucocorticoid protects rodent hearts from ischemia/reperfusion injury by activating lipocalin-type prostaglandin D synthase-derived PGD2 biosynthesis

The glucocorticoid receptor acts locally to protect dystrophic muscle and heart during disease

Absence of dystrophin results in muscular weakness, chronic inflammation and cardiomyopathy in Duchenne muscular dystrophy (DMD). Pharmacological corticosteroids are the DMD standard of care; however, they have harsh side effects and unclear molecular benefits. It is uncertain whether signaling by physiological corticosteroids and their receptors plays a modifying role in the natural etiology of DMD. Here, we knocked out the glucocorticoid receptor (GR, encoded by Nr3c1) specifically in myofibers and cardiomyocytes within wild-type and mdx52 mice to dissect its role in muscular dystrophy. Double-knockout mice showed significantly worse phenotypes than mdx52 littermate controls in measures of grip strength, hang time, inflammatory pathology and gene expression. In the heart, GR deletion acted additively with dystrophin loss to exacerbate cardiomyopathy, resulting in enlarged hearts, pathological gene expression and systolic dysfunction, consistent with imbalanced mineralocorticoid signaling. The results show that physiological GR functions provide a protective role during muscular dystrophy, directly contrasting its degenerative role in other disease states. These data provide new insights into corticosteroids in disease pathophysiology and establish a new model to investigate cell-autonomous roles of nuclear receptors and mechanisms of pharmacological corticosteroids.

Prostanoids in Cardiac and Vascular Remodeling

Prostanoids are biologically active lipids generated from arachidonic acid by the action of the COX (cyclooxygenase) isozymes. NSAIDs, which reduce the biosynthesis of prostanoids by inhibiting COX activity, are effective anti-inflammatory, antipyretic, and analgesic drugs. However, their use is limited by cardiovascular adverse effects, including myocardial infarction, stroke, hypertension, and heart failure. While it is well established that NSAIDs increase the risk of atherothrombotic events and hypertension by suppressing vasoprotective prostanoids, less is known about the link between NSAIDs and heart failure risk. Current evidence indicates that NSAIDs may increase the risk for heart failure by promoting adverse myocardial and vascular remodeling. Indeed, prostanoids play an important role in modulating structural and functional changes occurring in the myocardium and in the vasculature in response to physiological and pathological stimuli. This review will summarize current knowledge of the role of the different prostanoids in myocardial and vascular remodeling and explore how maladaptive remodeling can be counteracted by targeting specific prostanoids.

MRP1-Dependent Extracellular Release of Glutathione Induces Cardiomyocyte Ferroptosis After Ischemia-Reperfusion

BACKGROUND

The membrane components of cardiomyocytes are rich in polyunsaturated fatty acids, which are easily oxidized. Thus, an efficient glutathione-based lipid redox system is essential for maintaining cellular functions. However, the relationship between disruption of the redox system during ischemia-reperfusion (IR), oxidized lipid production, and consequent cell death (ferroptosis) remains unclear. We investigated the mechanisms underlying the disruption of the glutathione-mediated reduction system related to ferroptosis during IR and developed intervention strategies to suppress ferroptosis.

METHODS

In vivo fluctuations of both intra- and extracellular metabolite levels during IR were explored via microdialysis and tissue metabolome analysis. Oxidized phosphatidylcholines were assessed using liquid chromatography high-resolution mass spectrometry. The areas at risk following IR were assessed using triphenyl-tetrazolium chloride/Evans blue stain.

RESULTS

Metabolomic analysis combined with microdialysis revealed a significant release of glutathione from the ischemic region into extracellular spaces during ischemia and after reperfusion. The release of glutathione into extracellular spaces and a concomitant decrease in intracellular glutathione concentrations were also observed during anoxia-reperfusion in an in vitro cardiomyocyte model. This extracellular glutathione release was prevented by chemical inhibition or genetic suppression of glutathione transporters, mainly MRP1 (multidrug resistance protein 1). Treatment with MRP1 inhibitor reduced the intracellular reactive oxygen species levels and lipid peroxidation, thereby inhibiting cell death. Subsequent in vivo evaluation of endogenously oxidized phospholipids following IR demonstrated the involvement of ferroptosis, as levels of multiple oxidized phosphatidylcholines were significantly elevated in the ischemic region 12 hours after reperfusion. Inhibition of the MRP1 transporter also alleviated intracellular glutathione depletion in vivo and significantly reduced the generation of oxidized phosphatidylcholines. Administration of MRP1 inhibitors significantly attenuated infarct size after IR injury.

CONCLUSIONS

Glutathione was released continuously during IR, primarily in an MRP1-dependent manner, and induced ferroptosis. Suppression of glutathione release attenuated ferroptosis and reduced myocardial infarct size following IR.

Lipocalin family proteins and their diverse roles in cardiovascular disease

The lipocalin (LCN) family members, a group of small extracellular proteins with 160-180 amino acids in length, can be detected in all kingdoms of life from bacteria to human beings. They are characterized by low similarity of amino acid sequence but highly conserved tertiary structures with an eight-stranded antiparallel β-barrel which forms a cup-shaped ligand binding pocket. In addition to bind small hydrophobic ligands (i.e., fatty acids, odorants, retinoids, and steroids) and transport them to specific cells, lipocalins (LCNs) can interact with specific cell membrane receptors to activate their downstream signaling pathways, and with soluble macromolecules to form the complex. Consequently, LCNs exhibit great functional diversity. Accumulating evidence has demonstrated that LCN family proteins exert multiple layers of function in the regulation of many physiological processes and human diseases (i.e., cancers, immune disorders, metabolic disease, neurological/psychiatric disorders, and cardiovascular disease). In this review, we firstly introduce the structural and sequence properties of LCNs. Next, six LCNs including apolipoprotein D (ApoD), ApoM, lipocalin 2 (LCN2), LCN10, retinol-binding protein 4 (RBP4), and Lipocalin-type prostaglandin D synthase (L-PGDS) which have been characterized so far are highlighted for their diagnostic/prognostic values and their potential effects on coronary artery disease and myocardial infarction injury. The roles of these 6 LCNs in cardiac hypertrophy, heart failure, diabetes-induced cardiac disorder, and septic cardiomyopathy are also summarized. Finally, their therapeutic potential for cardiovascular disease is discussed in each section.

The Link between Prostanoids and Cardiovascular Diseases

Cardiovascular diseases are the leading cause of global deaths, and many risk factors contribute to their pathogenesis. In this context, prostanoids, which derive from arachidonic acid, have attracted attention for their involvement in cardiovascular homeostasis and inflammatory processes. Prostanoids are the target of several drugs, but it has been shown that some of them increase the risk of thrombosis. Overall, many studies have shown that prostanoids are tightly associated with cardiovascular diseases and that several polymorphisms in genes involved in their synthesis and function increase the risk of developing these pathologies. In this review, we focus on molecular mechanisms linking prostanoids to cardiovascular diseases and we provide an overview of genetic polymorphisms that increase the risk for cardiovascular disease.

Association between glucocorticoid use and all-cause mortality in critically ill patients with heart failure: A cohort study based on the MIMIC-III database

Background: Heart failure (HF) is the terminal stage of various heart diseases. Conventional treatments have poor efficacy, and diuretic resistance can present. Previous studies have found that the use of glucocorticoids can enhance the diuretic effect of patients with heart failure and reduce heart failure symptoms. However, the relationship between glucocorticoid use and mortality in patients with heart failure in intensive care units is unclear. Objectives: The aim of this study was to determine the association between glucocorticoid use and all-cause mortality in critically ill patients with heart failure. Methods: The information on patients with heart failure in this study was extracted from the MIMIC-III (Medical Information Mart for Intensive Care-III) database. Patients in the glucocorticoid and non-glucocorticoid groups were matched using propensity scores. The Kaplan-Meier method was used to explore the difference in survival probability between the two groups. A Cox proportional-hazards regression model was used to analyze the hazard ratios (HRs) for the two patient groups. Subgroup analyses were performed with prespecified stratification variables to demonstrate the robustness of the results. Results: The study included 9,482 patients: 2,099 in the glucocorticoid group and 7,383 in the non-glucocorticoid group. There were 2,055 patients in each group after propensity-score matching. The results indicated that the non-glucocorticoid group was not significantly associated with reduced mortality in patients with heart failure during the 14-day follow-up period [HRs = .901, 95% confidence interval (CI) = .767-1.059]. During the follow-up periods of 15-30 and 15-90 days, the mortality risk was significantly lower in the non-glucocorticoid group than in the glucocorticoid group (HRs = .497 and 95% CI = .370-.668, and HRs = .400 and 95% CI = .310-.517, respectively). Subgroup analyses indicated no interaction among each stratification variable and glucocorticoid use. Conclusion: Glucocorticoid use was associated with an increased mortality risk in critically ill patients with heart failure.

Effects of Simvastatin on Cartilage Homeostasis in Steroid-Induced Osteonecrosis of Femoral Head by Inhibiting Glucocorticoid Receptor

Steroid-induced osteonecrosis of femoral head (SONFH) is one of the most common bone disorders in humans. Statin treatment is beneficial in preventing the development of SONFH through anti-inflammation effects and inhibition of the glucocorticoid receptor (GR). However, potential mechanisms of statin action remain to be determined. In this study, pulse methylprednisolone (MP) treatment was used to induce SONFH in broilers, and then MP-treated birds were administrated with simvastatin simultaneously to investigate the changes in cartilage homeostasis. Meanwhile, chondrocytes were isolated, cultured, and treated with MP, simvastatin, or GR inhibitor in vitro. The changes in serum homeostasis factors, cell viability, and expression of GR were analyzed. The results showed that the morbidity of SONFH in the MP-treated group increased significantly compared with the simvastatin-treated and control group. Furthermore, MP treatment induced apoptosis and high-level catabolism and low-level anabolism in vitro and vivo, while simvastatin significantly decreased catabolism and slightly recovered anabolism via inhibiting GR and the hypoxia-inducible factor (HIF) pathway. The GR inhibitor or its siRNA mainly affected the catabolism of cartilage homeostasis in vitro. In conclusion, the occurrence of SONFH in broilers was related to the activation of GR and HIF pathway, and imbalance of cartilage homeostasis. Simvastatin and GR inhibitor maintained cartilage homeostasis via GR and the HIF pathway.

Identification of Hypothalamic Long Noncoding RNAs Associated with Hypertension and the Behavior/Neurological Phenotype of Hypertensive ISIAH Rats

Long noncoding RNAs (lncRNAs) play an important role in the control of many physiological and pathophysiological processes, including the development of hypertension and other cardiovascular diseases. Nonetheless, the understanding of the regulatory function of many lncRNAs is still incomplete. This work is a continuation of our earlier study on the sequencing of hypothalamic transcriptomes of hypertensive ISIAH rats and control normotensive WAG rats. It aims to identify lncRNAs that may be involved in the formation of the hypertensive state and the associated behavioral features of ISIAH rats. Interstrain differences in the expression of seven lncRNAs were validated by quantitative PCR. Differential hypothalamic expression of lncRNAs LOC100910237 and RGD1562890 between hypertensive and normotensive rats was shown for the first time. Expression of four lncRNAs (Snhg4, LOC100910237, RGD1562890, and Tnxa-ps1) correlated with transcription levels of many hypothalamic genes differentially expressed between ISIAH and WAG rats (DEGs), including genes associated with the behavior/neurological phenotype and hypertension. After functional annotation of these DEGs, it was concluded that lncRNAs Snhg4, LOC100910237, RGD1562890, and Tnxa-ps1 may be involved in the hypothalamic processes related to immune-system functioning and in the response to various exogenous and endogenous factors, including hormonal stimuli. Based on the functional enrichment analysis of the networks, an association of lncRNAs LOC100910237 and Tnxa-ps1 with retinol metabolism and an association of lncRNAs RGD1562890 and Tnxa-ps1 with type 1 diabetes mellitus are proposed for the first time. Based on a discussion, it is hypothesized that previously functionally uncharacterized lncRNA LOC100910237 is implicated in the regulation of hypothalamic processes associated with dopaminergic synaptic signaling, which may contribute to the formation of the behavioral/neurological phenotype and hypertensive state of ISIAH rats.

Qualitative and Quantitative Effects of Fatty Acids Involved in Heart Diseases

Fatty acids (FAs) have structural and functional diversity. FAs in the heart are closely associated with cardiac function, and their qualitative or quantitative abnormalities lead to the onset and progression of cardiac disease. FAs are important as an energy substrate for the heart, but when in excess, they exhibit cardio-lipotoxicity that causes cardiac dysfunction or heart failure with preserved ejection fraction. FAs also play a role as part of phospholipids that compose cell membranes, and the changes in mitochondrial phospholipid cardiolipin and the FA composition of plasma membrane phospholipids affect cardiomyocyte survival. In addition, FA metabolites exert a wide variety of bioactivities in the heart as lipid mediators. Recent advances in measurement using mass spectrometry have identified trace amounts of n-3 polyunsaturated fatty acids (PUFAs)-derived bioactive metabolites associated with heart disease. n-3 PUFAs have a variety of cardioprotective effects and have been shown in clinical trials to be effective in cardiovascular diseases, including heart failure. This review outlines the contributions of FAs to cardiac function and pathogenesis of heart diseases from the perspective of three major roles and proposes therapeutic applications and new medical perspectives of FAs represented by n-3 PUFAs.

Kidney in the net of acute and long-haul coronavirus disease 2019: a potential role for lipid mediators in causing renal injury and fibrosis

PURPOSE OF REVIEW

Severe COVID-19 disease is often complicated by acute kidney injury (AKI), which may transition to chronic kidney disease (CKD). Better understanding of underlying mechanisms is important in advancing therapeutic approaches.

RECENT FINDINGS

SARS-CoV-2-induced endothelial injury initiates platelet activation, platelet-neutrophil partnership and release of neutrophil extracellular traps. The resulting thromboinflammation causes ischemia-reperfusion (I/R) injury to end organs. Severe COVID-19 induces a lipid-mediator storm with massive increases in thromboxane A2 (TxA2) and PGD2, which promote thromboinflammation and apoptosis of renal tubular cells, respectively, and thereby enhance renal fibrosis. COVID-19-associated AKI improves rapidly in the majority. However, 15-30% have protracted renal injury, raising the specter of transition from AKI to CKD.

SUMMARY

In COVID-19, the lipid-mediator storm promotes thromboinflammation, ischemia-reperfusion injury and cytotoxicity. The thromboxane A2 and PGD2 signaling presents a therapeutic target with potential to mitigate AKI and transition to CKD. Ramatroban, the only dual antagonist of the thromboxane A2/TPr and PGD2/DPr2 signaling could potentially mitigate renal injury in acute and long-haul COVID. Urgent studies targeting the lipid-mediator storm are needed to potentially reduce the heavy burden of kidney disease emerging in the wake of the current pandemic.

Corticosteroid Receptors in Cardiac Health and Disease

Nuclear receptors play a central role in both energy metabolism and cardiomyocyte death and survival in the heart. Recent evidence suggests they may also influence cardiomyocyte endowment. Although several members of the nuclear receptor family play key roles in heart maturation (including thyroid hormone receptors) and cardiac metabolism, here, the focus will be on the corticosteroid receptors, the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR). The heart is an important target for the actions of corticosteroids, yet the homeostatic role of GR and MR in the healthy heart has been elusive. However, MR antagonists are important in the treatment of heart failure, a condition associated with mitochondrial dysfunction and energy failure in cardiomyocytes leading to mitochondria-initiated cardiomyocyte death (Ingwall and Weiss, Circ Res 95:135-145, 2014; Ingwall , Cardiovasc Res 81:412-419, 2009; Zhou and Tian , J Clin Invest 128:3716-3726, 2018). In contrast, animal studies suggest GR activation in cardiomyocytes has a cardioprotective role, including in heart failure.

Homeostatic Regulation of Glucocorticoid Receptor Activity by Hypoxia-Inducible Factor 1: From Physiology to Clinic

Glucocorticoids (GCs) represent a well-known class of lipophilic steroid hormones biosynthesised, with a circadian rhythm, by the adrenal glands in humans and by the inter-renal tissue in teleost fish (e.g., zebrafish). GCs play a key role in the regulation of numerous physiological processes, including inflammation, glucose, lipid, protein metabolism and stress response. This is achieved through binding to their cognate receptor, GR, which functions as a ligand-activated transcription factor. Due to their potent anti-inflammatory and immune-suppressive action, synthetic GCs are broadly used for treating pathological disorders that are very often linked to hypoxia (e.g., rheumatoid arthritis, inflammatory, allergic, infectious, and autoimmune diseases, among others) as well as to prevent graft rejections and against immune system malignancies. However, due to the presence of adverse effects and GC resistance their therapeutic benefits are limited in patients chronically treated with steroids. For this reason, understanding how to fine-tune GR activity is crucial in the search for novel therapeutic strategies aimed at reducing GC-related side effects and effectively restoring homeostasis. Recent research has uncovered novel mechanisms that inhibit GR function, thereby causing glucocorticoid resistance, and has produced some surprising new findings. In this review we analyse these mechanisms and focus on the crosstalk between GR and HIF signalling. Indeed, its comprehension may provide new routes to develop novel therapeutic targets for effectively treating immune and inflammatory response and to simultaneously facilitate the development of innovative GCs with a better benefits-risk ratio.

GnRH neurons recruit astrocytes in infancy to facilitate network integration and sexual maturation

Neurons that produce gonadotropin-releasing hormone (GnRH), which control fertility, complete their nose-to-brain migration by birth. However, their function depends on integration within a complex neuroglial network during postnatal development. Here, we show that rodent GnRH neurons use a prostaglandin D₂ receptor DP1 signaling mechanism during infancy to recruit newborn astrocytes that 'escort' them into adulthood, and that the impairment of postnatal hypothalamic gliogenesis markedly alters sexual maturation by preventing this recruitment, a process mimicked by the endocrine disruptor bisphenol A. Inhibition of DP1 signaling in the infantile preoptic region, where GnRH cell bodies reside, disrupts the correct wiring and firing of GnRH neurons, alters minipuberty or the first activation of the hypothalamic-pituitary-gonadal axis during infancy, and delays the timely acquisition of reproductive capacity. These findings uncover a previously unknown neuron-to-neural-progenitor communication pathway and demonstrate that postnatal astrogenesis is a basic component of a complex set of mechanisms used by the neuroendocrine brain to control sexual maturation.

L-PGDS Attenuates Acute Lung Injury by Prostaglandin D2 in Both Dependent and Independent Ways

Lipocalin-type PG D synthase (L-PGDS) has two roles: it can be a PGD synthase, or it can be a carrier protein of hydrophobic small molecules. In this study, we investigated the dual roles of L-PGDS in acute lung injury by using L-PGDS-deficient and point-mutated mice, which lack PGD₂ producibility but maintain lipocalin ability. Hydrochloride (HCl) administration (0.1 M intratracheally for 6 h) caused hemorrhage and dysfunction in the wild-type (WT) mouse lung. These symptoms were accompanied by an increase in PGD₂ production. Both deficiency and point mutation of L-PGDS aggravated the HCl-induced hemorrhage and dysfunction. Although both the gene modifications decreased PGD₂ production, only L-PGDS-deficient mice, but not point mutation mice, lacked protein expressions of L-PGDS in the lungs. In the WT mice, HCl administration caused pulmonary edema, indexed as an increase in lung water content and protein leakage in bronchoalveolar lavage fluid. L-PGDS deficiency and point mutation similarly aggravated edema formation. HCl administration also stimulated mucin production and bronchoalveolar lavage fluid leukocyte infiltration in the WT mouse lungs. Of interest, L-PGDS deficiency, but not point mutation, exacerbated these manifestations. Consistently, only L-PGDS deficiency increased the mRNA expression of IL-33, which stimulates mucin production in the inflamed lung. These results show that L-PGDS attenuated HCl-induced acute lung injury progresses in two different ways: L-PGDS produced PGD₂, which inhibited pulmonary edema formation, whereas its lipocalin ability decreased mucin formation and inflammatory cell infiltration in the inflamed lung.

Biochemical and Structural Characteristics, Gene Regulation, Physiological, Pathological and Clinical Features of Lipocalin-Type Prostaglandin D2 Synthase as a Multifunctional Lipocalin

Lipocalin-type prostaglandin (PG) D₂ synthase (L-PGDS) catalyzes the isomerization of PGH₂, a common precursor of the two series of PGs, to produce PGD₂. PGD₂ stimulates three distinct types of G protein-coupled receptors: (1) D type of prostanoid (DP) receptors involved in the regulation of sleep, pain, food intake, and others; (2) chemoattractant receptor-homologous molecule expressed on T helper type 2 cells (CRTH2) receptors, in myelination of peripheral nervous system, adipocyte differentiation, inhibition of hair follicle neogenesis, and others; and (3) F type of prostanoid (FP) receptors, in dexamethasone-induced cardioprotection. L-PGDS is the same protein as β-trace, a major protein in human cerebrospinal fluid (CSF). L-PGDS exists in the central nervous system and male genital organs of various mammals, and human heart; and is secreted into the CSF, seminal plasma, and plasma, respectively. L-PGDS binds retinoic acids and retinal with high affinities (Kd < 100 nM) and diverse small lipophilic substances, such as thyroids, gangliosides, bilirubin and biliverdin, heme, NAD(P)H, and PGD₂, acting as an extracellular carrier of these substances. L-PGDS also binds amyloid β peptides, prevents their fibril formation, and disaggregates amyloid β fibrils, acting as a major amyloid β chaperone in human CSF. Here, I summarize the recent progress of the research on PGD₂ and L-PGDS, in terms of its “molecular properties,” “cell culture studies,” “animal experiments,” and “clinical studies,” all of which should help to understand the pathophysiological role of L-PGDS and inspire the future research of this multifunctional lipocalin.

The Impact of Glucocorticoid Therapy on Guideline-Directed Medical Treatment Titration in Patients Hospitalized for Heart Failure with Low Blood Pressure: A Retrospective Study

Background

Positive inotropic and renal protective actions of glucocorticoids have been observed clinically. Therefore, glucocorticoids may be used in patients with heart failure and low blood pressure (HF-LBP).

Methods

The medical records of 144 consecutive patients with HF-LBP who received glucocorticoids as an adjunctive treatment to facilitate the up-titration of β-blocker and angiotensin-converting enzyme inhibitor were reviewed.

Results

After four weeks of treatment, the metoprolol and captopril (or equivalent) dosages were progressively and consistently increased from 25 (interquartile range [IQR] = 12.5-75 mg/day) to 100 mg/day (IQR = 50-178.8 mg/day) and from 0 (IQR = 0-25 mg/day) to 12.5 mg/day (IQR = 0-50 mg/day), respectively. There was a remarkable beneficial hemodynamic response to the glucocorticoid treatment signified by an increase in blood pressure and decrease in heart rate. The average heart rate decreased by 6 beat per minute (bpm) (0.5-16 bpm), and the mean arterial blood pressure increased from 74.06 ± 7.81 to 78.85 ± 7.91 mmHg. We also observed an improvement in renal function and an increased diuretic response following glucocorticoid treatment. As a result, the left ventricular ejection fraction increased from 28.92 ± 8.06% to 33.86 ± 8.76%, and the diuretic response increased from 776.7 mL/40 mg furosemide (IQR = 133.8-2000 mL) to 4000 mL/40 mg furosemide on day 28 (IQR = 2200-5925 mL).

Conclusion

The use of glucocorticoid treatment to maintain hemodynamic and renal functional targets when titrating guideline-directed medical treatment in patients with HF-LBP may be safe, effective, and feasible.

New horizons in the roles and associations of COX-2 and novel natural inhibitors in cardiovascular diseases

Age-related cardiovascular disease is the leading cause of death in elderly populations. Coxibs, including celecoxib, valdecoxib, etoricoxib, parecoxib, lumiracoxib, and rofecoxib, are selective cyclooxygenase-2 (COX-2) inhibitors used to treat osteoarthritis and rheumatoid arthritis. However, many coxibs have been discontinued due to adverse cardiovascular events. COX-2 contains cyclooxygenase (COX) and peroxidase (POX) sites. COX-2 inhibitors block COX activity without affecting POX activity. Recently, quercetin-like flavonoid compounds with OH groups in their B-rings have been found to serve as activators of COX-2 by binding the POX site. Galangin-like flavonol compounds serve as inhibitors of COX-2. Interestingly, nabumetone, flurbiprofen axetil, piketoprofen-amide, and nepafenac are ester prodrugs that inhibit COX-2. The combination of galangin-like flavonol compounds with these prodrug metabolites may lead to the development of novel COX-2 inhibitors. This review focuses on the most compelling evidence regarding the role and mechanism of COX-2 in cardiovascular diseases and demonstrates that quercetin-like compounds exert potential cardioprotective effects by serving as cofactors of COX-2.

Phagocytes produce prostaglandin E2 in response to cytosolic Listeria monocytogenes

Listeria monocytogenes is an intracellular bacterium that elicits robust CD8+ T-cell responses. Despite the ongoing development of L. monocytogenes-based platforms as cancer vaccines, our understanding of how L. monocytogenes drives robust CD8+ T-cell responses remains incomplete. One overarching hypothesis is that activation of cytosolic innate pathways is critical for immunity, as strains of L. monocytogenes that are unable to access the cytosol fail to elicit robust CD8+ T-cell responses and in fact inhibit optimal T-cell priming. Counterintuitively, however, activation of known cytosolic pathways, such as the inflammasome and type I IFN, lead to impaired immunity. Conversely, production of prostaglandin E2 (PGE2) downstream of cyclooxygenase-2 (COX-2) is essential for optimal L. monocytogenes T-cell priming. Here, we demonstrate that vacuole-constrained L. monocytogenes elicit reduced PGE2 production compared to wild-type strains in macrophages and dendritic cells ex vivo. In vivo, infection with wild-type L. monocytogenes leads to 10-fold increases in PGE2 production early during infection whereas vacuole-constrained strains fail to induce PGE2 over mock-immunized controls. Mice deficient in COX-2 specifically in Lyz2+ or CD11c+ cells produce less PGE2, suggesting these cell subsets contribute to PGE2 levels in vivo, while depletion of phagocytes with clodronate abolishes PGE2 production completely. Taken together, this work demonstrates that optimal PGE2 production by phagocytes depends on L. monocytogenes access to the cytosol, suggesting that one reason cytosolic access is required to prime CD8+ T-cell responses may be to facilitate production of PGE2.

Dexamethasone Suppresses Radicular Pain Through Targeting the L-PGDS/PI3K/Akt Pathway in Rats With Lumbar Disc Herniation

PURPOSE

Lumbar disc herniation (LDH) is a frequently occurring disease with unknown etiology, which makes treatment a challenge. The aim of this study was to analyze the effects of dexamethasone on LDH and elucidate the underlying mechanisms.

GENERAL METHODS

An LDH rat model was established by nucleus pulposus implantation. The activity of the lipocalin type prostaglandin D synthase (L-PGDS)/phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) axis was evaluated by Western blotting. Paw withdrawal threshold and paw withdrawal latency were assessed by the Von Frey hairs method and the thermal dolorimeter of Hargreaves, respectively. The 21-point Basso-Beattie-Bresnahan scale was used to assess the locomotor function of rats. Pathological changes in the affected region were analyzed by hematoxylin-eosin staining. Immunofluorescence was used to measure the expression of microtubule-associated protein (MAP-2).

FINDINGS

Lumbar disc herniation markedly increased thermo-mechanical allodynia and induced dorsal root ganglion (DRG) degeneration by inactivating the L-PGS/PI3K/Akt pathway. Dexamethasone restored the L-PGDS/PI3K/Akt pathway and relieved LDH-induced thermo-mechanical allodynia. Furthermore, overexpression and knockdown of L-PGDS respectively attenuated and worsened LDH-triggered thermo-mechanical allodynia and tissue degeneration by modulating the PI3K/Akt pathway. Pretreatment with dexamethasone partially abrogated the effect of L-PGDS knockdown through PI3K/Akt activation.

CONCLUSIONS

Dexamethasone relieves LDH-mediated radicular pain by exerting anti-inflammatory effects and reducing the suppression of L-PGDS induced by LDH. Meanwhile, the activity of the PI3K/Akt pathway was decreased, possibly due to the attenuated inflammation induced by dexamethasone. Our results revealed the underlying mechanism of dexamethasone, which might be helpful in reducing the side effects of dexamethasone and provide more focused therapy in LDH.

Coronary Spastic Angina Induced by Adrenal Insufficiency

Adrenal insufficiency patients are treated with glucocorticoid replacement therapy. However, mimicking the in vivo circadian rhythm of cortisol levels is challenging, and suboptimal replacement increases the risk of mortality from cardiovascular disease. We herein report a case of coronary spastic angina (CSA) with simultaneous low early-morning serum cortisol levels in a patient undergoing corticosteroid replacement therapy for primary adrenal insufficiency. Steroid therapy is reportedly effective for refractory angina, but underlying adrenal deficiency has never been revealed. Our case intimates the probable risk of CSA as a complication of relative adrenal insufficiency and highlights the effectiveness of dexamethasone in these patients.

Cardiovascular Biology of Prostanoids and Drug Discovery

Prostanoids are a group of bioactive lipids that are synthesized de novo from membrane phospholipid-released arachidonic acid and have diverse functions in normal physiology and disease. NSAIDs (non-steroidal anti-inflammatory drugs), which are among the most commonly used medications, ameliorate pain, fever, and inflammation by inhibiting COX (cyclooxygenase), which is the rate-limiting enzyme in the biosynthetic cascade of prostanoids. The use of NSAIDs selective for COX-2 inhibition increases the risk of a thrombotic event (eg, myocardial infarction and stroke). All NSAIDs are associated with an increased risk of heart failure. Substantial variation in clinical responses to aspirin exists and is associated with cardiovascular risk. Limited clinical studies suggest the involvement of prostanoids in vascular restenosis in patients who received angioplasty intervention. mPGES (microsomal PG [prostaglandin] E synthase)-1, an alternative target downstream of COX, has the potential to be therapeutically targeted for inflammatory disease, with diminished thrombotic risk relative to selective COX-2 inhibitors. mPGES-1-derived PGE₂ critically regulates microcirculation via its receptor EP (receptor for prostanoid E) 4. This review summarizes the actions and associated mechanisms for modulating the biosynthesis of prostanoids in thrombosis, vascular remodeling, and ischemic heart disease as well as their therapeutic relevance.

Palmitate induces cardiomyocyte death via inositol requiring enzyme-1 (IRE1)-mediated signaling independent of X-box binding protein 1 (XBP1)

Overloading of the saturated fatty acid (SFA) palmitate induces cardiomyocyte death. The purpose of this study is to elucidate signaling pathways contributing to palmitate-induced cardiomyocyte death. Palmitate-induced cardiomyocyte death was induced in Toll-like receptor 2/4 double-knockdown cardiomyocytes to a similar extent as wild-type cardiomyocytes, while cardiomyocyte death was canceled out by triacsin C, a long-chain acyl-CoA synthetase inhibitor. These results indicated that palmitate induced cytotoxicity after entry and conversion into palmitoyl-CoA. Palmitoyl-CoA is not only degraded by mitochondrial oxidation but also taken up as a component of membrane phospholipids. Palmitate overloading causes cardiomyocyte membrane fatty acid (FA) saturation, which is associated with the activation of endoplasmic reticulum (ER) unfolded protein response (UPR) signaling. We focused on the ER UPR signaling as a possible mechanism of cell death. Palmitate loading activates the UPR signal via membrane FA saturation, but not via unfolded protein overload in the ER since the chemical chaperone 4-phenylbutyrate failed to suppress palmitate-induced ER UPR. The mammalian UPR relies on three ER stress sensors named inositol requiring enzyme-1 (IRE1), PKR-like endoplasmic reticulum kinase (PERK), and activating transcription factor 6 (ATF6). Palmitate loading activated only IRE1 and PERK. Knockdown of PERK did not affect palmitate-induced cardiomyocyte death, while knockdown of IRE1 suppressed palmitate-induced cardiomyocyte death. However, knockdown of X-box binding protein 1 (XBP1), the downstream effector of IRE1, did not affect palmitate-induced cardiomyocyte death. These results were validated by pharmacological inhibitor experiments. In conclusion, we identified that palmitate-induced cardiomyocyte death was triggered by IRE1-mediated signaling independent of XBP1.

Ischemia/Reperfusion Injury: Pathophysiology, Current Clinical Management, and Potential Preventive Approaches

Myocardial ischemia reperfusion syndrome is a complex entity where many inflammatory mediators play different roles, both to enhance myocardial infarction-derived damage and to heal injury. In such a setting, the establishment of an effective therapy to treat this condition has been elusive, perhaps because the experimental treatments have been conceived to block just one of the many pathogenic pathways of the disease, or because they thwart the tissue-repairing phase of the syndrome. Either way, we think that a discussion about the pathophysiology of the disease and the mechanisms of action of some drugs may shed some clarity on the topic.

DP1 Activation Reverses Age-Related Hypertension Via NEDD4L-Mediated T-Bet Degradation in T Cells

BACKGROUND

Blood pressure often rises with aging, but exact mechanisms are still not completely understood. With aging, the level of proinflammatory cytokines increases in T lymphocytes. Prostaglandin D₂, a proresolution mediator, suppresses Type 1 T helper (Th1) cytokines through D-prostanoid receptor 1 (DP1). In this study, we aimed to investigate the role of the prostaglandin D₂/DP1 axis in T cells on age-related hypertension.

METHODS

To clarify the physiological and pathophysiological roles of DP1 in T cells with aging, peripheral blood samples were collected from young and older male participants, and CD4⁺ T cells were sorted for gene expression, prostaglandin production, and Western blot assays. Mice blood pressure was quantified by invasive telemetric monitor.

RESULTS

The prostaglandin D₂/DP1 axis was downregulated in CD4⁺ T cells from older humans and aged mice. DP1 deletion in CD4⁺ T cells augmented age-related hypertension in aged male mice by enhancing Th1 cytokine secretion, vascular remodeling, CD4⁺ T cells infiltration, and superoxide production in vasculature and kidneys. Conversely, forced expression of exogenous DP1 in T cells retarded age-associated hypertension in mice by reducing Th1 cytokine secretion. Tumor necrosis factor α neutralization or interferon γ deletion ameliorated the age-related hypertension in DP1 deletion in CD4⁺ T cells mice. Mechanistically, DP1 inhibited Th1 activity via the PKA (protein kinase A)/p-Sp1 (phosphorylated specificity protein 1)/neural precursor cell expressed developmentally downregulated 4-like (NEDD4L) pathway-mediated T-box-expressed-in-T-cells (T-bet) ubiquitination. T-bet deletion or forced NEDD4L expression in CD4⁺ T cells attenuated age-related hypertension in CD4⁺ T cell-specific DP1-deficient mice. DP1 receptor activation by BW245C prevented age-associated blood pressure elevation and reduced vascular/renal superoxide production in male mice.

CONCLUSIONS

The prostaglandin D₂/DP1 axis suppresses age-related Th1 activation and subsequent hypertensive response in male mice through increase of NEDD4L-mediated T-bet degradation by ubiquitination. Therefore, the T cell DP1 receptor may be an attractive therapeutic target for age-related hypertension.

Hurdles to Cardioprotection in the Critically Ill

Cardiovascular disease is the largest contributor to worldwide mortality, and the deleterious impact of heart failure (HF) is projected to grow exponentially in the future. As heart transplantation (HTx) is the only effective treatment for end-stage HF, development of mechanical circulatory support (MCS) technology has unveiled additional therapeutic options for refractory cardiac disease. Unfortunately, despite both MCS and HTx being quintessential treatments for significant cardiac impairment, associated morbidity and mortality remain high. MCS technology continues to evolve, but is associated with numerous disturbances to cardiac function (e.g., oxidative damage, arrhythmias). Following MCS intervention, HTx is frequently the destination option for survival of critically ill cardiac patients. While effective, donor hearts are scarce, thus limiting HTx to few qualifying patients, and HTx remains correlated with substantial post-HTx complications. While MCS and HTx are vital to survival of critically ill cardiac patients, cardioprotective strategies to improve outcomes from these treatments are highly desirable. Accordingly, this review summarizes the current status of MCS and HTx in the clinic, and the associated cardiac complications inherent to these treatments. Furthermore, we detail current research being undertaken to improve cardiac outcomes following MCS/HTx, and important considerations for reducing the significant morbidity and mortality associated with these necessary treatment strategies.

A structure-function approach identifies L-PGDS as a mediator responsible for glucocorticoid-induced leptin expression in adipocytes

Leptin is an adipokine predominantly secreted by adipocytes and has many physiological roles, including in energy homeostasis. We identified that AM630, a cannabinoid receptor 2 (CB2) antagonist, down-regulated leptin expression in mature adipocytes differentiated from either stromal vascular fractions isolated from inguinal fat pads of C57BL/6J mice or 3T3-L1 preadipocytes. However, the leptin-suppressive effects of AM630 preserved in CB2-deficient adipocytes indicated the off-target activity of AM630 in leptin expression. Pharmacological and genetic studies, cheminformatics, and docking simulation were applied to identify the potential protein target of AM630 that modulates leptin expression in differentiated primary preadipocytes. Screening of the reported off-targets of AM630 identified a synthetic cannabinoid WIN55212-2 exerting the same function. Target deconvolution and docking simulation suggested that AM630 and WIN55212-2 were both inhibitors of lipocalin-type prostaglandin D2 synthase (L-PGDS). Further studies showed that L-PGDS positively regulates leptin expression. Although glucocorticoid and aldosterone were previously reported to induce expression of both L-PGDS and leptin, our data demonstrated that L-PGDS mediates only glucocorticoid-induced leptin expression in differentiated primary preadipocytes. No effect was observed after aldosterone treatment. This newly discovered glucocorticoid - L-PGDS - leptin pathway may provide insights into current clinical use of glucocorticoid and management of their undesired effects such as obesity.

Cardiomyocyte glucocorticoid and mineralocorticoid receptors directly and antagonistically regulate heart disease in mice

Stress is increasingly associated with heart dysfunction and is linked to higher mortality rates in patients with cardiometabolic disease. Glucocorticoids are primary stress hormones that regulate homeostasis through two nuclear receptors, the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR), both of which are present in cardiomyocytes. To examine the specific and coordinated roles that these receptors play in mediating the direct effects of stress on the heart, we generated mice with cardiomyocyte-specific deletion of GR (cardioGRKO), MR (cardioMRKO), or both GR and MR (cardioGRMRdKO). The cardioGRKO mice spontaneously developed cardiac hypertrophy and left ventricular systolic dysfunction and died prematurely from heart failure. In contrast, the cardioMRKO mice exhibited normal heart morphology and function. Despite the presence of myocardial stress, the cardioGRMRdKO mice were resistant to the cardiac remodeling, left ventricular dysfunction, and early death observed in the cardioGRKO mice. Gene expression analysis revealed the loss of gene changes associated with impaired Ca²⁺ handling, increased oxidative stress, and enhanced cell death and the presence of gene changes that limited the hypertrophic response and promoted cardiomyocyte survival in the double knockout hearts. Reexpression of MR in cardioGRMRdKO hearts reversed many of the cardioprotective gene changes and resulted in cardiac failure. These findings reveal a critical role for balanced cardiomyocyte GR and MR stress signaling in cardiovascular health. Therapies that shift stress signaling in the heart to favor more GR and less MR activity may provide an improved approach for treating heart disease.

Pressure overload inhibits glucocorticoid receptor transcriptional activity in cardiomyocytes and promotes pathological cardiac hypertrophy

Glucocorticoid receptor (GR) is abundantly expressed in cardiomyocytes. However, the role of GR in regulating cardiac hypertrophy and heart failure in response to pressure overload remains unclear. Cardiomyocyte-specific GR knockout (GRcKO) mice, mineralocorticoid receptor (MR) knockout (MRcKO), and GR and MR double KO (GRMRdcKO) mice were generated using the Cre-lox system. In response to pressure overload, GRcKO mice displayed worse cardiac remodeling compared to control (GR^f/f) mice, including a greater increase in heart weight to body weight ratio with a greater increase in cardiomyocytes size, a greater decline in left ventricular contractility, and higher reactivation of fetal genes. MRcKO mice showed a comparable degree of cardiac remodeling compared to control (MR^f/f) mice. The worse cardiac remodeling in pressure overloaded GRcKO mice is not due to compensatory activation of cardiomyocyte MR, since pressure overloaded GRMRdcKO mice displayed cardiac remodeling to the same extent as GRcKO mice. Pressure overload suppressed GR-target gene expression in the heart. Although plasma corticosterone levels and subcellular localization of GR (nuclear/cytoplasmic GR) were not changed, a chromatin immunoprecipitation assay revealed that GR recruitment onto the promoter of GR-target genes was significantly suppressed in response to pressure overload. Rescue of the expression of GR-target genes to the same extent as sham-operated hearts attenuated adverse cardiac remodeling in pressure-overloaded hearts. Thus, GR works as a repressor of adverse cardiac remodeling in response to pressure overload, but GR-mediated transcription is suppressed under pressure overload. Therapies that maintain GR-mediated transcription in cardiomyocytes under pressure overload can be a promising therapeutic strategy for heart failure.

CRTH2 promotes endoplasmic reticulum stress-induced cardiomyocyte apoptosis through m-calpain

Apoptotic death of cardiac myocytes is associated with ischemic heart disease and chemotherapy‐induced cardiomyopathy. Chemoattractant receptor‐homologous molecule expressed on T helper type 2 cells (CRTH2) is highly expressed in the heart. However, its specific role in ischemic cardiomyopathy is not fully understood. Here, we demonstrated that CRTH2 disruption markedly improved cardiac recovery in mice postmyocardial infarction and doxorubicin challenge by suppressing cardiomyocyte apoptosis. Mechanistically, CRTH2 activation specifically facilitated endoplasmic reticulum (ER) stress‐induced cardiomyocyte apoptosis via caspase‐12‐dependent pathway. Blockage of m‐calpain prevented CRTH2‐mediated cardiomyocyte apoptosis under ER stress by suppressing caspase‐12 activity. CRTH2 was coupled with G_αq to elicit intracellular Ca²⁺ flux and activated m‐calpain/caspase‐12 cascade in cardiomyocytes. Knockdown of caspase‐4, an alternative to caspase‐12 in humans, markedly alleviated CRHT2 activation‐induced apoptosis in human cardiomyocyte response to anoxia. Our findings revealed an unexpected role of CRTH2 in promoting ER stress‐induced cardiomyocyte apoptosis, suggesting that CRTH2 inhibition has therapeutic potential for ischemic cardiomyopathy.

Gestational Hypoxia and Developmental Plasticity

Hypoxia is one of the most common and severe challenges to the maintenance of homeostasis. Oxygen sensing is a property of all tissues, and the response to hypoxia is multidimensional involving complicated intracellular networks concerned with the transduction of hypoxia-induced responses. Of all the stresses to which the fetus and newborn infant are subjected, perhaps the most important and clinically relevant is that of hypoxia. Hypoxia during gestation impacts both the mother and fetal development through interactions with an individual's genetic traits acquired over multiple generations by natural selection and changes in gene expression patterns by altering the epigenetic code. Changes in the epigenome determine "genomic plasticity," i.e., the ability of genes to be differentially expressed according to environmental cues. The genomic plasticity defined by epigenomic mechanisms including DNA methylation, histone modifications, and noncoding RNAs during development is the mechanistic substrate for phenotypic programming that determines physiological response and risk for healthy or deleterious outcomes. This review explores the impact of gestational hypoxia on maternal health and fetal development, and epigenetic mechanisms of developmental plasticity with emphasis on the uteroplacental circulation, heart development, cerebral circulation, pulmonary development, and the hypothalamic-pituitary-adrenal axis and adipose tissue. The complex molecular and epigenetic interactions that may impact an individual's physiology and developmental programming of health and disease later in life are discussed.

Nrf2 Deficiency Unmasks the Significance of Nitric Oxide Synthase Activity for Cardioprotection

The transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2) is a key master switch that controls the expression of antioxidant and cytoprotective enzymes, including enzymes catalyzing glutathione de novo synthesis. In this study, we aimed to analyze whether Nrf2 deficiency influences antioxidative capacity, redox state, NO metabolites, and outcome of myocardial ischemia reperfusion (I/R) injury. In Nrf2 knockout (Nrf2 KO) mice, we found elevated eNOS expression and preserved NO metabolite concentrations in the aorta and heart as compared to wild types (WT). Unexpectedly, Nrf2 KO mice have a smaller infarct size following myocardial ischemia/reperfusion injury than WT mice and show fully preserved left ventricular systolic function. Inhibition of NO synthesis at onset of ischemia and during early reperfusion increased myocardial damage and systolic dysfunction in Nrf2 KO mice, but not in WT mice. Consistent with this, infarct size and diastolic function were unaffected in eNOS knockout (eNOS KO) mice after ischemia/reperfusion. Taken together, these data suggest that eNOS upregulation under conditions of decreased antioxidant capacity might play an important role in cardioprotection against I/R. Due to the redundancy in cytoprotective mechanisms, this fundamental antioxidant property of eNOS is not evident upon acute NOS inhibition in WT mice or in eNOS KO mice until Nrf2-related signaling is abrogated.

Adenosine Production by Biomaterial-Supported Mesenchymal Stromal Cells Reduces the Innate Inflammatory Response in Myocardial Ischemia/Reperfusion Injury

BACKGROUND

During myocardial ischemia/reperfusion (MI/R) injury, there is extensive release of immunogenic metabolites that activate cells of the innate immune system. These include ATP and AMP, which upregulate chemotaxis, migration, and effector function of early infiltrating inflammatory cells. These cells subsequently drive further tissue devitalization. Mesenchymal stromal cells (MSCs) are a potential treatment modality for MI/R because of their powerful anti-inflammatory capabilities; however, the manner in which they regulate the acute inflammatory milieu requires further elucidation. CD73, an ecto-5'-nucleotidase, may be critical in regulating inflammation by converting pro-inflammatory AMP to anti-inflammatory adenosine. We hypothesized that MSC-mediated conversion of AMP into adenosine reduces inflammation in early MI/R, favoring a micro-environment that attenuates excessive innate immune cell activation and facilitates earlier cardiac recovery.

METHODS AND RESULTS

Adult rats were subjected to 30 minutes of MI/R injury. MSCs were encapsulated within a hydrogel vehicle and implanted onto the myocardium. A subset of MSCs were pretreated with the CD73 inhibitor, α,β-methylene adenosine diphosphate, before implantation. Using liquid chromatography/mass spectrometry, we found that MSCs increase myocardial adenosine availability following injury via CD73 activity. MSCs also reduce innate immune cell infiltration as measured by flow cytometry, and hydrogen peroxide formation as measured by Amplex Red assay. These effects were dependent on MSC-mediated CD73 activity. Finally, through echocardiography we found that CD73 activity on MSCs was critical to optimal protection of cardiac function following MI/R injury.

CONCLUSIONS

MSC-mediated conversion of AMP to adenosine by CD73 exerts a powerful anti-inflammatory effect critical for cardiac recovery following MI/R injury.

HIF-1α-l-PGDS-PPARγ regulates hypoxia-induced ANP secretion in beating rat atria

Lipocalin-type prostaglandin D synthase (L-PGDS) and peroxisome proliferator activated receptor γ (PPARγ) play important roles in cardiovascular diseases. Nevertheless, effects of hypoxia-inducible factor 1α (HIF-1α) on L-PGDS and PPARγ protein levels and its role in hypoxia-induced atrial natriuretic peptide (ANP) secretion are unclear. In perfused beating rat atria, we observed that hypoxia significantly increased HIF-1α protein levels and stimulated ANP secretion, while upregulating L-PGDS. Hypoxia-induced ANP secretion was clearly attenuated by HIF-1α antagonist 2-methoxyestradiol, downregulating both HIF-1α and L-PGDS protein levels. It was also attenuated by L-PGDS antagonists, AT-56 and HQL-49, downregulating L-PGDS protein levels. In addition, hypoxia-induced ANP secretion was accompanied by increased PPARγ protein levels and was strongly attenuated by PPARγ antagonist GW9662. Hypoxia-induced increase in atrial PPARγ protein levels were dramatically inhibited by both 2-methoxyestradiol and AT-56. These results indicated that hypoxia promotes ANP secretion, at least in part, by activating HIF-1α-l-PGDS-PPARγ signaling in beating rat atria.

Budesonide instillation immediately after reperfusion ameliorates ischemia/reperfusion-induced injury in the transplanted lung of rat

PURPOSE

Lung ischemia-reperfusion injury (LIRI) after lung transplantation can lead to primary graft dysfunction. Budesonide can improve endothelial function to reduce lung injury. This study was aimed to examine the effects of budesonide on LIRI and potential mechanisms.

METHODS

Wistar rats were randomized and transplanted with syngeneic left lung or received the sham surgery. The recipients were instilled with saline or budesonide immediately after reperfusion. The mean arterial pressure (MAP), blood gas, and lung histology were analyzed. The ratios of wet to dry lung weights, the levels of total proteins, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and IL-10, and neutrophil elastase in bronchoalveolar lavage fluid (BALF) were measured. The levels of malondialdehyde (MDA), myeloperoxidase (MPO), and xanthine oxidase (XO) in the lung, and the levels of plasma lymphocyte function-associated antigen (LFA)-1 and P-selectin were determined.

RESULTS

Compared with the saline group, treatment with budesonide significantly increased blood PaO₂, but reduced PaCO₂, and mitigated lung damages after reperfusion, the levels of BALF proteins, and the ratios of wet to dry lung weights in rats. Furthermore, treatment with budesonide significantly decreased the levels of MDA, MPO, and XO in the lung and the levels of TNF-α, IL-1β, IL-6, and neutrophil elastase, but increased IL-10 in the BALF, accompanied by significantly reduced levels of serum P-selectin and LFA-1 in rats.

CONCLUSIONS

Budesonide effectively mitigated LIRI and ameliorated the lung function by attenuating oxidative stress and inflammation following syngeneic lung transplantation.

Identification of potentially relevant genes for myocardial infarction using RNA sequencing data analysis

Myocardial infarction (MI) is a heart disease with high morbidity and mortality rates, thus it is critical to identify genes that serve roles during its pathogenesis. The objective of the present study was to identify potentially relevant genes during the progression of the disease. Blood samples from patients with MI and normal controls (n=3/group) were obtained, the RNA was extracted and cDNA libraries were established. RNA sequencing (RNA-seq) was performed on a HiSeq 2500 platform and fragments per kilobase of exon per million fragments mapped was utilized to calculate the gene expression value following preprocessing of the RNA-seq data. Electronic validation of several identified differentially expressed genes (DEGs) was performed on a Gene Expression Omnibus (GEO) dataset GSE59867 (390 cases and 46 healthy controls). Functional enrichment and protein-protein interaction network analysis was conducted for DEGs. A total of 977 DEGs, including 817 upregulated and 160 downregulated genes were identified in patients with MI. These DEGs were significantly enriched for ‘positive regulation of the immune system process,’ ‘inflammatory response,’ ‘regulation of I-kappaB-kinase/NF-kappaB signaling’ and ‘TNF signaling pathway’. A protein-protein interaction network of the top 40 DEGs was used to identify high degree genes, including interferon induced protein with tetratricopeptide repeats 3 (IFIT3), MX dynamin like GTPase 1 (MX1), major histocompatibility complex, class II, DQ α1 (HLA-DQA1), RAR related orphan receptor A (RORA), prostaglandin D2 synthase (PTGDS), cysteine rich protein 2 (CRIP2), collagen type VI α 2 chain (COL6A2) and S100 calcium binding protein P (S100P). The results of validation in the GEO dataset were consistent with the sequencing analysis. A total of eight genes, including IFIT3, MX1, HLA-DQA1, RORA, PTGDS, CRIP2, COL6A2 and S100P may therefore be considered as potentially relevant genes in the pathology of MI.

Hypothalamic-Pituitary-Adrenal Axis Modulation of Glucocorticoids in the Cardiovascular System

The collective of endocrine organs acting in homeostatic regulation—known as the hypothalamic-pituitary-adrenal (HPA) axis—comprises an integration of the central nervous system as well as peripheral tissues. These organs respond to imminent or perceived threats that elicit a stress response, primarily culminating in the release of glucocorticoids into the systemic circulation by the adrenal glands. Although the secretion of glucocorticoids serves to protect and maintain homeostasis in the typical operation at baseline levels, inadequate regulation can lead to physiologic and psychologic pathologies. The cardiovascular system is especially susceptible to prolonged dysregulation of the HPA axis and glucocorticoid production. There is debate about whether cardiovascular health risks arise from the direct detrimental effects of stress axis activation or whether pathologies develop secondary to the accompanying metabolic strain of excess glucocorticoids. In this review, we will explore the emerging research that indicates stress does have direct effects on the cardiovascular system via the HPA axis activation, with emphasis on the latest research on the impact of glucocorticoids signaling in the vasculature and the heart.

Role of G3BP1 in glucocorticoid receptor-mediated microRNA-15b and microRNA-23a biogenesis in endothelial cells

MicroRNAs (miRNAs) are a family of non-coding RNAs that play crucial roles in regulating various normal cellular responses. Recent studies revealed that the canonical miRNA biogenesis pathway is subject to sophisticated regulation. Hormonal control of miRNA biogenesis by androgen and estrogen has been demonstrated, but the direct effects of the glucocorticoid receptor (GR) on miRNA biogenesis are unknown. This study revealed the role of GR in miRNA maturation. We showed that two GR agonists, dexamethasone and ginsenoside-Rg1 rapidly suppressed the expression of mature miR-15b, miR-23a, and miR-214 in human endothelial cells. RNA pulldown coupled with proteomic analysis identified GTPase-activating protein (SH3 domain) binding protein 1 (G3BP1) as one of the RNA-binding proteins mediating GR-regulated miRNA maturation. Activated GR induced phosphorylation of v-AKT Murine Thymoma Viral Oncogene Homologue (AKT) kinase, which in turn phosphorylated and promoted nuclear translocation of G3BP1. The nuclear G3BP1 bound to the G3BP1 consensus sequence located on primary miR-15b~16-2 and miR-23a~27a~24-2 to inhibit their maturation. The findings from this study have advanced our understanding of the non-genomic effects of GR in the vascular system.

Glucocorticoids promote Von Hippel Lindau degradation and Hif-1α stabilization

Glucocorticoid (GC) and hypoxic transcriptional responses play a central role in tissue homeostasis and regulate the cellular response to stress and inflammation, highlighting the potential for cross-talk between these two signaling pathways. We present results from an unbiased in vivo chemical screen in zebrafish that identifies GCs as activators of hypoxia-inducible factors (HIFs) in the liver. GCs activated consensus hypoxia response element (HRE) reporters in a glucocorticoid receptor (GR)-dependent manner. Importantly, GCs activated HIF transcriptional responses in a zebrafish mutant line harboring a point mutation in the GR DNA-binding domain, suggesting a nontranscriptional route for GR to activate HIF signaling. We noted that GCs increase the transcription of several key regulators of glucose metabolism that contain HREs, suggesting a role for GC/HIF cross-talk in regulating glucose homeostasis. Importantly, we show that GCs stabilize HIF protein in intact human liver tissue and isolated hepatocytes. We find that GCs limit the expression of Von Hippel Lindau protein (pVHL), a negative regulator of HIF, and that treatment with the c-src inhibitor PP2 rescued this effect, suggesting a role for GCs in promoting c-src-mediated proteosomal degradation of pVHL. Our data support a model for GCs to stabilize HIF through activation of c-src and subsequent destabilization of pVHL.

Non-linear actions of physiological agents: Finite disarrangements elicit fitness benefits

Finite disarrangements of important (vital) physiological agents and nutrients can induce plethora of beneficial effects, exceeding mere attenuation of the specific stress. Such response to disrupted homeostasis appears to be universally conserved among species. The underlying mechanism of improved fitness and longevity, when physiological agents act outside their normal range is similar to hormesis, a phenomenon whereby toxins elicit beneficial effects at low doses. Due to similarity with such non-linear response to toxins described with J-shaped curve, we have coined a new term “mirror J-shaped curves” for non-linear response to finite disarrangement of physiological agents. Examples from the clinical trials and basic research are provided, along with the unifying mechanisms that tie classical non-linear response to toxins with the non-linear response to physiological agents (glucose, oxygen, osmolarity, thermal energy, calcium, body mass, calorie intake and exercise). Reactive oxygen species and cytosolic calcium seem to be common triggers of signaling pathways that result in these beneficial effects. Awareness of such phenomena and exploring underlying mechanisms can help physicians in their everyday practice. It can also benefit researchers when designing studies and interpreting growing number of scientific data showing non-linear responses to physiological agents.

MicroRNA-210 suppresses glucocorticoid receptor expression in response to hypoxia in fetal rat cardiomyocytes

Hypoxia is a common intrauterine stressor, often resulting in intrauterine growth restriction and increased risk for cardiovascular disease later in life. The aim of this work was to test the hypothesis that microRNA-210 (miR-210) mediates the detrimental suppression of glucocorticoid receptor (GR) in response to hypoxia in fetal rat cardiomyocytes. Cardiomyocytes isolated from gestational day 21 Sprague Dawley fetal rats showed increased miR-210 levels and reduced GR abundance after exposure to ex vivo hypoxia (1% O2). In regard to mechanisms, the different contributions of hypoxia response elements (HREs) motifs in the regulation of miR-210 promoter activity and the miR-210-mediated repression of GR expression were determined in rat embryonic heart-derived myogenic cell line H9c2. Moreover, using a cell culture-based model of hypoxia-reoxygenation injury, we assessed the cytotoxic effects of GR suppression under hypoxic conditions. The results showed that hypoxia induced HIF-1α-dependent miR-210 production, as well as miR-210-mediated GR suppression, in cardiomyocytes. Furthermore, inhibition or knockdown of GR exacerbated cell death in response to hypoxia-reoxygenation injury. Altogether, the present study demonstrates that the HIF-1α-dependent miR-210-mediated suppression of GR in fetal rat cardiomyocytes increases cell death in response to hypoxia, providing novel evidence for a possible mechanistic link between fetal hypoxia and programming of ischemic-sensitive phenotype in the developing heart.

Niacin Promotes Cardiac Healing after Myocardial Infarction through Activation of the Myeloid Prostaglandin D2 Receptor Subtype 1

Niacin is a well established drug used to lower cholesterol and prevent cardiovascular disease events. However, niacin also causes cutaneous flushing side effects due to release of the proresolution mediator prostaglandin D₂ (PGD₂). Recent randomized clinical trials have demonstrated that addition of niacin with laropiprant [a PGD₂ receptor subtype 1 (DP1) blocker] to statin-based therapies does not significantly decrease the risk of cardiovascular disease events, but increases the risk of serious adverse events. Here, we tested whether, and how, niacin beneficial effects on myocardial ischemia require the activation of the PGD₂/DP1 axis. Myocardial infarction (MI) was reproduced by ligation of the left anterior descending branch of the coronary artery in mice. We found that niacin increased PGD₂ release in macrophages and shifted macrophages to M2 polarization both in vitro and in vivo by activation of DP1 and accelerated inflammation resolution in zymosan-induced peritonitis in mice. Moreover, niacin treatment facilitated wound healing and improved cardiac function after MI through DP1-mediated M2 bias and timely resolution of inflammation in infarcted hearts. In addition, we found that niacin intake also stimulated M2 polarization of peripheral monocytes in humans. Collectively, niacin promoted cardiac functional recovery after ischemic myocardial infarction through DP1-mediated M2 polarization and timely resolution of inflammation in hearts. These results indicated that DP1 inhibition may attenuate the cardiovascular benefits of niacin.

L-PGDS Mediates Vagus Nerve Stimulation-Induced Neuroprotection in a Rat Model of Ischemic Stroke by Suppressing the Apoptotic Response

The role of lipocalin prostaglandin D2 synthase (L-PGDS) in brain ischemia has not been fully clarified to date. Vagus nerve stimulation (VNS) protects against cerebral ischemia/reperfusion (I/R) injury, but the mechanisms involved need further exploration. This study investigated the role of L-PGDS in cerebral I/R and whether this process was involved in the mechanism of VNS-mediated neuroprotection. Male Sprague-Dawley rats were pretreated with a lentiviral vector (LV) through intracerebroventricular injection, followed by middle cerebral artery occlusion (MCAO) and VNS treatment. The expression of L-PGDS in the peri-infarct cortex was examined. The localization of L-PGDS was determined using double immunofluorescence staining. Neurologic scores, infarct volume and neuronal apoptosis were evaluated at 24 h after reperfusion. The expression of apoptosis-related molecules was measured by western blot analysis. The expression of L-PGDS in the peri-infarct cortex increased at 12 h, reached a peak at 24 h after reperfusion, and lasted up to 3 days. VNS treatment further enhanced the expression of L-PGDS following ischemic stroke. L-PGDS was mainly expressed in neurons in the peri-infarct cortex. I/R rats treated with VNS showed better neurological deficit scores, reduced infarct volume, and decreased neuronal apoptosis as indicated by the decreased levels of Bax and cleaved caspase-3 as well as increased levels of Bcl-2. Strikingly, the beneficial effects of VNS were weakened after L-PGDS down-regulation. In general, our results suggest that L-PGDS is a potential mediator of VNS-induced neuroprotection against I/R injury.

Investigations of Glucocorticoid Action in GN

For several decades, glucocorticoids have been used empirically to treat rapid progressive GN. It is commonly assumed that glucocorticoids act primarily by dampening the immune response, but the mechanisms remain incompletely understood. In this study, we inactivated the glucocorticoid receptor (GR) specifically in kidney epithelial cells using Pax8-Cre/GR^fl/fl mice. Pax8-Cre/GR^fl/fl mice did not exhibit an overt spontaneous phenotype. In mice treated with nephrotoxic serum to induce crescentic nephritis (rapidly progressive GN), this genetic inactivation of the GR in kidney epithelial cells exerted renal benefits, including inhibition of albuminuria and cellular crescent formation, similar to the renal benefits observed with high-dose prednisolone in control mice. However, genetic inactivation of the GR in kidney epithelial cells did not induce the immunosuppressive effects observed with prednisolone. In vitro, prednisolone and the pharmacologic GR antagonist mifepristone each acted directly on primary cultures of parietal epithelial cells, inhibiting cellular outgrowth and proliferation. In wild-type mice, pharmacologic treatment with the GR antagonist mifepristone also attenuated disease as effectively as high-dose prednisolone without the systemic immunosuppressive effects. Collectively, these data show that glucocorticoids act directly on activated glomerular parietal epithelial cells in crescentic nephritis. Furthermore, we identified a novel therapeutic approach in crescentic nephritis, that of glucocorticoid antagonism, which was at least as effective as high-dose prednisolone with potentially fewer adverse effects.

Krüppel-like Factor 13 Is a Major Mediator of Glucocorticoid Receptor Signaling in Cardiomyocytes and Protects These Cells from DNA Damage and Death

Glucocorticoid receptor (GR) signaling has recently been shown to play a direct role in the regulation of cardiomyocyte function. In this study, we investigated the potential role of KLF13 as a downstream effector of GR action utilizing both in vivo and in vitro approaches. Our data show that KLF13 mRNA and protein levels are significantly diminished in the hearts of mice lacking GR in cardiomyocytes. Glucocorticoid administration up-regulated Klf13 mRNA in the mouse heart, in isolated primary cardiomyocytes, and in immortal cardiomyocyte cell lines. Glucocorticoid Klf13 gene expression was abolished by treatment with a GR antagonist (RU486) or by knockdown of GR in cardiomyocytes. Moreover, glucocorticoid induction of Klf13 mRNA was resistant to de novo protein synthesis inhibition, demonstrating that Klf13 is a direct glucocorticoid receptor gene target. A glucocorticoid responsive element (GRE) was identified in the Klf13 gene and its function was verified by chromatin immunoprecipitation in HL-1 cells and mouse hearts. Functional studies showed that GR regulation of Klf13 is critical to protect cardiomyocytes from DNA damage and cell death induced by cobalt(II) chloride hexahydrate (CoCl2·6H2O) and the antineoplastic drug doxorubicin. These results established a novel role for GR and KLF13 signaling in adult cardiomyocytes with potential clinical implications for the prevention of cardiotoxicity induced heart failure.

Antenatal hypoxia induces epigenetic repression of glucocorticoid receptor and promotes ischemic-sensitive phenotype in the developing heart

Large studies in humans and animals have demonstrated a clear association of an adverse intrauterine environment with an increased risk of cardiovascular disease later in life. Yet mechanisms remain largely elusive. The present study tested the hypothesis that gestational hypoxia leads to promoter hypermethylation and epigenetic repression of the glucocorticoid receptor (GR) gene in the developing heart, resulting in increased heart susceptibility to ischemia and reperfusion injury in offspring. Hypoxic treatment of pregnant rats from day 15 to 21 of gestation resulted in a significant decrease of GR exon 14, 15, 16, and 17 transcripts, leading to down-regulation of GR mRNA and protein in the fetal heart. Functional cAMP-response elements (CREs) at -4408 and -3896 and Sp1 binding sites at -3425 and -3034 were identified at GR untranslated exon 1 promoters. Hypoxia significantly increased CpG methylation at the CREs and Sp1 binding sites and decreased transcription factor binding to GR exon 1 promoter, accounting for the repression of the GR gene in the developing heart. Of importance, treatment of newborn pups with 5-aza-2'-deoxycytidine reversed hypoxia-induced promoter methylation, restored GR expression and prevented hypoxia-mediated increase in ischemia and reperfusion injury of the heart in offspring. The findings demonstrate a novel mechanism of epigenetic repression of the GR gene in fetal stress-mediated programming of ischemic-sensitive phenotype in the heart.

Close teamwork between Nrf2 and peroxiredoxins 1 and 6 for the regulation of prostaglandin D2 and E2 production in macrophages in acute inflammation

Inflammation is a complex biological self-defense reaction triggered by tissue damage or infection by pathogens. Acute inflammation is regulated by the time- and cell type-dependent production of cytokines and small signaling molecules including reactive oxygen species and prostaglandins. Recent studies have unveiled the important role of the transcription factor Nrf2 in the regulation of prostaglandin production through transcriptional regulation of peroxiredoxins 1 and 6 (Prx1 and Prx6) and lipocalin-type prostaglandin D synthase (L-PGDS). Prx1 and Prx6 are multifunctional proteins important for cell protection against oxidative stress, but also work together to facilitate production of prostaglandins E2 and D2 (PGE2 and PGD2). Prx1 secreted from cells under mild oxidative stress binds Toll-like receptor 4 and induces NF-κB activation, important for the expression of cyclooxygenase-2 and microsomal PGE synthase-1 (mPGES-1) expression. The activated MAPKs p38 and ERK phosphorylate Prx6, leading to NADPH oxidase-2 activation, which contributes to production of PGD2 by hematopoietic prostaglandin D synthase (H-PGDS). PGD2 and its end product 15-deoxy-∆(12,14)-prostaglandin J2 (15d-PGJ2) activate Nrf2 thereby forming a positive feedback loop for further production of PGD2 by L-PGDS. Maintenance of cellular glutathione levels is an important role of Nrf2 not only for cell protection but also for the synthesis of prostaglandins, as mPGES-1 and H-PGDS require glutathione for their activities. This review is aimed at describing the functions of Prx1 and Prx6 in the regulation of PGD2 and PGE2 production in acute inflammation in macrophages and the importance of 15d-PGJ2 as an intrinsic Nrf2 activator.