Glucocorticoid stimulation increases cardiac contractility by SGK1-dependent SOCE-activation in rat cardiac myocytes

STIM2 variants regulate Orai1/TRPC1/TRPC4-mediated store-operated Ca2+ entry and mitochondrial Ca2+ homeostasis in cardiomyocytes

The stromal interaction molecules (STIMs) are the sarcoplasmic reticulum (SR) Ca2+ sensors that trigger store-operated Ca2+ entry (SOCE) in a variety of cell types. While STIM1 isoform has been the focus of the research in cardiac pathophysiology, the function of the homolog STIM2 remains unknown. Using Ca2+ imaging and patch-clamp techniques, we showed that knockdown (KD) of STIM2 by siRNAs increased SOCE and the ISOC current in neonatal rat ventricular cardiomyocytes (NRVMs). Within this cardiomyocyte model, we identified the transcript expression of Stim2.1 and Stim2.2 splice variants, with predominance for Stim2.2. Using conventional and super-resolution confocal microscopy (STED), we found that exogenous STIM2.1 and STIM2.2 formed pre-clusters with a reticular organization at rest. Following SR Ca2+ store depletion, some STIM2.1 and STIM2.2 clusters were translocated to SR-plasma membrane (PM) junctions and co-localized with Orai1. The overexpression strategy revealed that STIM2.1 suppressed Orai1-mediated SOCE and the ISOC current while STIM2.2 enhanced SOCE. STIM2.2-enhanced SOCE was also dependent on TRPC1 and TRPC4. Even if STIM2 KD or splice variants overexpression did not affect cytosolic Ca2+ cycling, we observed, using Rhod-2/AM Ca2+ imaging, that Orai1 inhibition or STIM2.1 overexpression abolished the mitochondrial Ca2+ (mCa2+) uptake, as opposed to STIM2 KD. We also found that STIM2 was present in the mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) by interacting with the inositol trisphosphate receptors (IP3Rs), voltage-dependent anion channel (VDAC), mitochondrial Ca2+ uniporter (MCU), and mitofusin-2 (MNF2). Our results suggested that, in NRVMs, STIM2.1 constitutes the predominant functional variant that negatively regulates Orai1-generated SOCE. It participates in the control of mCa2+ uptake capacity possibly via the STIM2-IP3Rs-VDAC-MCU and MNF2 complex.

Dexamethasone upregulates macrophage PIEZO1 via SGK1, suppressing inflammation and increasing ROS and apoptosis

The side effects of high-dose dexamethasone in anti-infection include increased ROS production and immune cell apoptosis. Dexamethasone effectively activates serum/glucocorticoid-regulated kinase 1 (SGK1), which upregulates various ion channels by activating store-operated calcium entry (SOCE), leading to Ca2+ oscillations. PIEZO1 plays a crucial role in macrophages' immune activity and function, but whether dexamethasone can regulate PIEZO1 by enhancing SOCE via SGK1 activation remains unclear. The effects of dexamethasone were assessed in a mouse model of sepsis, and primary BMDMs and the RAW264.7 were treated with overexpression plasmids, siRNAs, or specific activators or inhibitors to examine the relationships between SGK1, SOCE, and PIEZO1. The functional and phenotypic changes of mouse and macrophage models were detected. The results indicate that high-dose dexamethasone upregulated SGK1 by activating the macrophage glucocorticoid receptor, which enhanced SOCE and subsequently activated PIEZO1. Activation of PIEZO1 resulted in Ca2+ influx and cytoskeletal remodelling. The increase in intracellular Ca2+ mediated by PIEZO1 further increased the activation of SGK1 and ORAI1/STIM1, leading to intracellular Ca2+ peaks. In the context of inflammation, activation of PIEZO1 suppressed the activation of TLR4/NFκB p65 in macrophages. In RAW264.7 cells, PIEZO1 continuous activation inhibited the change in mitochondrial membrane potential, accelerated ROS accumulation, and induced autophagic damage and cell apoptosis in the late stage. CaMK2α was identified as a downstream mediator of TLR4 and PIEZO1, facilitating high-dose dexamethasone-induced macrophage immunosuppression and apoptosis. PIEZO1 is a new glucocorticoid target to regulate macrophage function and activity. This study provides a theoretical basis for the rational use of dexamethasone.

Proposed mechanisms of hypertension and risk of adverse cardiovascular outcomes in LGBT communities

Hypertension (HTN), a highly prevalent public issue affecting one in two adults in the United States, has recently been shown to differentially burden individuals belonging to marginalized communities, such as the lesbian, gay, bisexual, and transgender (LGBT) communities. The minority stress theory posits that a unique combination of marginalization-related psychosocial stressors and coping behaviors may underlie the increased burden of diseases like HTN in LGBT populations. Uncontrolled or poorly managed HTN often leads to the development of adverse cardiovascular outcomes, such as heart failure (HF). Despite our understanding of minority stress theory and demonstrated associations between LGBT identities and HTN, the mechanisms whereby psychosocial stress drives HTN in LGBT populations remain unclear. This mini-review discusses the physiological systems governing blood pressure and the epidemiology of HTN across different subgroups of LGBT people. In addition, we propose mechanisms demonstrated in the general population whereby psychological stress has been implicated in elevating blood pressure that may be occurring in LGBT populations. Finally, we discuss the limitations of current studies and methodological frameworks to make suggestions for study designs to better delineate the mechanisms of psychosocial stress-related HTN in LGBT communities.

Berberine attenuates sunitinib-induced cardiac dysfunction by normalizing calcium regulation disorder via SGK1 activation

Sunitinib (SNT)-induced cardiotoxicity is associated with abnormal calcium regulation caused by phosphoinositide 3 kinase inhibition in the heart. Berberine (BBR) is a natural compound that exhibits cardioprotective effects and regulates calcium homeostasis. We hypothesized that BBR ameliorates SNT-induced cardiotoxicity by normalizing the calcium regulation disorder via serum and glucocorticoid-regulated kinase 1 (SGK1) activation. Mice, neonatal rat cardiomyocytes (NRVMs), and human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were used to study the effects of BBR-mediated SGK1 activity on the calcium regulation disorder caused by SNT as well as the underlying mechanism. BBR offered prevention against SNT-induced cardiac systolic dysfunction, QT interval prolongation, and histopathological changes in mice. After the oral administration of SNT, the Ca²⁺ transient and contraction of cardiomyocytes was significantly inhibited, whereas BBR exhibited an antagonistic effect. In NRVMs, BBR was significantly preventive against the SNT-induced reduction of calcium transient amplitude, prolongation of calcium transient recovery, and decrease in SERCA2a protein expression; however, SGK1 inhibitors resisted the preventive effects of BBR. In hiPSC-CMs, BBR pretreatment significantly prevented SNT from inhibiting the contraction, whereas coincubation with SGK1 inhibitors antagonized the effects of BBR. These findings indicate that BBR attenuates SNT-induced cardiac dysfunction by normalizing the calcium regulation disorder via SGK1 activation.

Serum and glucocorticoid inducible kinase 1 modulates mitochondrial dysfunction and oxidative stress in doxorubicin-induced cardiomyocytes by regulating Hippo pathway via Neural precursor cell-expressed developmentally down-regulated 4 type 2

Doxorubicin (Dox) was reported to cause mitochondrial dysfunction and oxidative stress in cardiomyocytes, leading to cardiomyocyte apoptosis and ultimately heart failure. Serum and glucocorticoid inducible kinase 1 (SGK1) participates in the progression of various cardiovascular diseases. Thus, we aimed to explore the role and regulatory mechanism of SGK1 in Dox-induced cardiomyocyte injury. The expression of SGK1 was evaluated in blood samples of heart failure children, and in myocardial tissues and blood samples of Dox-induced rats. Subsequently, we treated cardiomyocytes with Dox in vitro. A gain-of-function assay was performed to assess the effects of SGK1 on mitochondrial dysfunction and oxidative stress in Dox-induced cardiomyocytes. Furthermore, the modulation of SGK1 on Neural precursor cell-expressed developmentally down-regulated 4 type 2 (NEDD4-2) expression and the subsequent Hippo pathway was validated. In our study, we found that SGK1 was downregulated in blood samples of heart failure children, as well as myocardial tissues and blood samples of Dox-induced rats. SGK1 overexpression alleviated the decreases of mitochondrial complex activity, mitochondrial membrane potential, adenosine triphosphate (ATP) content and ATP synthetase activity stimulated by Dox. Besides, SGK1 overexpression reversed the promoting effects of Dox on oxidative stress and apoptosis. Mechanistically, SGK1 overexpression inhibited the expression of NEDD4-2 and blocked the subsequent activation of Hippo pathway. NEDD4-2 overexpression or activation of Hippo reversed the protective effects of SGK1 overexpression on Dox-induced cardiomyocyte injury. In conclusion, our results revealed that SGK1 modulated mitochondrial dysfunction and oxidative stress in Dox-induced cardiomyocytes by regulating Hippo pathway via NEDD4-2.

A non-coding GWAS variant impacts anthracycline-induced cardiotoxic phenotypes in human iPSC-derived cardiomyocytes

Anthracyclines, widely used to treat breast cancer, have the potential for cardiotoxicity. We have previously identified and validated a germline single nucleotide polymorphism, rs28714259, associated with an increased risk of anthracycline-induced heart failure. We now provide insights into the mechanism by which rs28714259 might confer increased risk of cardiac damage. Using hiPSC-derived cardiomyocyte cell lines with either intrinsic polymorphism or CRISPR-Cas9-mediated deletion of rs28714259 locus, we demonstrate that glucocorticoid receptor signaling activated by dexamethasone pretreatment prior to doxorubicin exposure preserves cardiomyocyte viability and contractility in cardiomyocytes containing the major allele. Homozygous loss of the rs28714259 major allele diminishes dexamethasone's protective effect. We further demonstrate that the risk allele of rs28714259 disrupts glucocorticoid receptor and rs28714259 binding affinity. Finally, we highlight the activation of genes and pathways involved in cardiac hypertrophy signaling that are blocked by the risk allele, suggesting a decreased adaptive survival response to doxorubicin-related stress.

Biomimetic cardiac tissue culture model (CTCM) to emulate cardiac physiology and pathophysiology ex vivo

There is need for a reliable in vitro system that can accurately replicate the cardiac physiological environment for drug testing. The limited availability of human heart tissue culture systems has led to inaccurate interpretations of cardiac-related drug effects. Here, we developed a cardiac tissue culture model (CTCM) that can electro-mechanically stimulate heart slices with physiological stretches in systole and diastole during the cardiac cycle. After 12 days in culture, this approach partially improved the viability of heart slices but did not completely maintain their structural integrity. Therefore, following small molecule screening, we found that the incorporation of 100 nM tri-iodothyronine (T3) and 1 μM dexamethasone (Dex) into our culture media preserved the microscopic structure of the slices for 12 days. When combined with T3/Dex treatment, the CTCM system maintained the transcriptional profile, viability, metabolic activity, and structural integrity for 12 days at the same levels as the fresh heart tissue. Furthermore, overstretching the cardiac tissue induced cardiac hypertrophic signaling in culture, which provides a proof of concept for the ability of the CTCM to emulate cardiac stretch-induced hypertrophic conditions. In conclusion, CTCM can emulate cardiac physiology and pathophysiology in culture for an extended time, thereby enabling reliable drug screening.

Intermittent glucocorticoid treatment enhances skeletal muscle performance through sexually dimorphic mechanisms

Glucocorticoid steroids are commonly prescribed for many inflammatory conditions, but chronic daily use produces adverse effects, including muscle wasting and weakness. In contrast, shorter glucocorticoid pulses may improve athletic performance, although the mechanisms remain unclear. Muscle is sexually dimorphic and comparatively little is known about how male and female muscles respond to glucocorticoids. We investigated the impact of once-weekly glucocorticoid exposure on skeletal muscle performance comparing male and female mice. One month of once-weekly glucocorticoid dosing improved muscle specific force in both males and females. Transcriptomic profiling of isolated myofibers identified a striking sexually dimorphic response to weekly glucocorticoids. Male myofibers had increased expression of genes in the IGF1/PI3K pathway and calcium handling, while female myofibers had profound upregulation of lipid metabolism genes. Muscles from weekly prednisone–treated males had improved calcium handling, while comparably treated female muscles had reduced intramuscular triglycerides. Consistent with altered lipid metabolism, weekly prednisone–treated female mice had greater endurance relative to controls. Using chromatin immunoprecipitation, we defined a sexually dimorphic chromatin landscape after weekly prednisone. These results demonstrate that weekly glucocorticoid exposure elicits distinct pathways in males versus females, resulting in enhanced performance.

Major surgery leads to a proinflammatory phenotype: Differential gene expression following a laparotomy

BACKGROUND

The trauma of surgery is a neglected area of research. Our aim was to examine the differential expression of genes of stress, metabolism and inflammation in the major organs of a rat following a laparotomy.

MATERIALS AND METHODS

Anaesthetised Sprague-Dawley rats were randomised into baseline, 6-hr and 3-day groups (n = 6 each), catheterised and laparotomy performed. Animals were sacrificed at each timepoint and tissues collected for gene and protein analysis. Blood stress hormones, cytokines, endothelial injury markers and coagulation were measured.

RESULTS

Stress hormone corticosterone significantly increased and was accompanied by significant increases in inflammatory cytokines, endothelial markers, increased neutrophils (6-hr), higher lactate (3-days), and coagulopathy. In brain, there were significant increases in M1 muscarinic (31-fold) and α-1A-adrenergic (39-fold) receptor expression. Cortical expression of metabolic genes increased ∼3-fold, and IL-1β by 6-fold at 3-days. Cardiac β-1-adrenergic receptor expression increased up to 8.4-fold, and M2 and M1 muscarinic receptors by 2 to 4-fold (6-hr). At 3-days, cardiac mitochondrial gene expression (Tfam, Mtco3) and inflammation (IL-1α, IL-4, IL-6, MIP-1α, MCP-1) were significantly elevated. Haemodynamics remained stable. In liver, there was a dramatic suppression of adrenergic and muscarinic receptor expression (up to 90%) and increased inflammation. Gut also underwent autonomic suppression with 140-fold increase in IL-1β expression (3-days).

CONCLUSIONS

A single laparotomy led to a surgical-induced proinflammatory phenotype involving neuroendocrine stress, cortical excitability, immune activation, metabolic changes and coagulopathy. The pervasive nature of systemic and tissue inflammation was noteworthy. There is an urgent need for new therapies to prevent hyper-inflammation and restore homeostasis following major surgery.

Mechanisms and Clinical Applications of Glucocorticoid Steroids in Muscular Dystrophy

Glucocorticoid steroids are widely used as immunomodulatory agents in acute and chronic conditions. Glucocorticoid steroids such as prednisone and deflazacort are recommended for treating Duchenne Muscular Dystrophy where their use prolongs ambulation and life expectancy. Despite this benefit, glucocorticoid use in Duchenne Muscular Dystrophy is also associated with significant adverse consequences including adrenal suppression, growth impairment, poor bone health and metabolic syndrome. For other forms of muscular dystrophy like the limb girdle dystrophies, glucocorticoids are not typically used. Here we review the experimental evidence supporting multiple mechanisms of glucocorticoid action in dystrophic muscle including their role in dampening inflammation and myofiber injury. We also discuss alternative dosing strategies as well as novel steroid agents that are in development and testing, with the goal to reduce adverse consequences of prolonged glucocorticoid exposure while maximizing beneficial outcomes.

The mitochondrial K-ATP channel opener diazoxide upregulates STIM1 and Orai1 via ROS and the MAPK pathway in adult rat cardiomyocytes

Background

Openers of mitochondrial adenosine triphosphate-dependent potassium (mKATP) channels like diazoxide increase reactive oxygen species (ROS) production in cardiac cells and reduce Ca²⁺ elevations produced by ischemia–reperfusion, protecting the heart from damage. In this study we tested the hypothesis that opening mKATP channels regulates expression of the major components of store-operated Ca²⁺ entry (SOCE) STIM1 and Orai1.

Results

Quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) and western blot experiments showed that diazoxide increased expression of STIM1 and Orai1 at the mRNA and protein levels, respectively, in adult rat cardiomyocytes. Immunofluorescence analyses revealed that diazoxide also disrupted the striated distribution pattern of STIM1. These effects were prevented by the ROS scavenger N-acetyl cysteine (NAC), the mKATP channel antagonist 5-hydroxydecanoate (5-HD), or the protein synthesis inhibitor cycloheximide (CHX). Confocal microscopy revealed that diazoxide also led to nuclear translocation of the transcription factors c-Fos and NFκB, which was also blocked by NAC or 5-HD. Finally, the MAPK pathway inhibitor UO126 attenuated diazoxide-induced upregulation of STIM1 and Orai1 expression.

Conclusions

Our results suggest that opening mitochondrial potassium ATP channels with diazoxide upregulates the expression of STIM1 and Orai1 by de novo synthesis by a mechanism that involves NFkB, c-Fos, and ROS via MAPK/ERK signaling.

Specific Upregulation of TRPC1 and TRPC5 Channels by Mineralocorticoid Pathway in Adult Rat Ventricular Cardiomyocytes

Whereas cardiac TRPC (transient receptor potential canonical) channels and the associated store-operated Ca²⁺ entry (SOCE) are abnormally elevated during cardiac hypertrophy and heart failure, the mechanism of this upregulation is not fully elucidated but might be related to the activation of the mineralocorticoid pathway. Using a combination of biochemical, Ca²⁺ imaging, and electrophysiological techniques, we determined the effect of 24-h aldosterone treatment on the TRPCs/Orai-dependent SOCE in adult rat ventricular cardiomyocytes (ARVMs). The 24-h aldosterone treatment (from 100 nM to 1 µM) enhanced depletion-induced Ca²⁺ entry in ARVMs, as assessed by a faster reduction of Fura-2 fluorescence decay upon the addition of Mn²⁺ and increased Fluo-4/AM fluorescence following Ca²⁺ store depletion. These effects were prevented by co-treatment with a specific mineralocorticoid receptor (MR) antagonist, RU-28318, and they are associated with the enhanced depletion-induced N-[4-[3,5-Bis(trifluoromethyl)-1H-pyrazol-1-yl]phenyl]-4-methyl-1,2,3-thiadiazole-5-carboxamide (BTP2)-sensitive macroscopic current recorded by patch-clamp experiments. Molecular screening by qRT-PCR and Western blot showed a specific upregulation of TRPC1, TRPC5, and STIM1 expression at the messenger RNA (mRNA) and protein levels upon 24-h aldosterone treatment of ARVMs, corroborated by immunostaining. Our study provides evidence that the mineralocorticoid pathway specifically promotes TRPC1/TRPC5-mediated SOCE in adult rat cardiomyocytes.