Search Results (95)

Rett syndrome (RTT) is a severe neurodevelopmental disorder caused primarily by mutations in the gene encoding the methyl-CpG-binding protein 2 (Mecp2). Mecp2 binds to methylated cytosines, playing a crucial role in chromatin organization and transcriptional regulation. At the neurobiological level, RTT is characterized by dendritic spine dysgenesis and altered excitation–inhibition balance, drawing attention to the mechanisms that scale from mutations in a nuclear protein to altered neuronal connectivity. Although Mecp2 dysfunction disrupts multiple neuronal processes, emerging evidence highlights altered calcium (Ca²⁺) signaling as a central contributor to RTT pathophysiology. This review explores the link between Mecp2 and Ca²⁺ regulation by highlighting how Mecp2 affects Ca²⁺-dependent transcriptional pathways, while Ca²⁺ modulates Mecp2 function by inducing post-translational modifications. We discuss this crosstalk in light of evidence from RTT models, with a particular focus on the brain-derived neurotrophic factor BDNF-miR132-Mecp2 axis and the dysregulation of ryanodine receptors (RyRs). Additionally, we examine how these perturbations contribute to the reduced structural plasticity and the altered activity-driven gene expression that characterizes RTT. Understanding the intersection between Mecp2 function and Ca²⁺ homeostasis will provide critical insights into RTT pathogenesis and potential therapeutic targets aimed at restoring neuronal connectivity. Full article

TRIC-A is an intracellular cation channel enriched in excitable tissues that is recently identified as a key modulator of sarcoplasmic reticulum (SR) Ca²⁺ homeostasis through direct interaction with type 2 ryanodine receptors (RyR₂). Given the intimate anatomical and functional coupling between the SR and mitochondria, we investigated whether TRIC-A contributes to SR–mitochondrial crosstalk under cardiac stress conditions. Using a transverse aortic constriction (TAC) model, we found that TRIC-A^−/− mice developed more severe cardiac hypertrophy, underwent maladaptive remodeling, and activated apoptotic pathways compared with wild-type littermates. At the cellular level, TRIC-A-deficient cardiomyocytes were more susceptible to H₂O₂-induced mitochondrial injury and displayed abnormal mitochondrial morphology. Live-cell imaging revealed exaggerated mitochondrial Ca²⁺ uptake during caffeine stimulation and increased propensity for store-overload-induced Ca²⁺ release (SOICR). Complementary studies in HEK293 cells expressing RyR₂ demonstrated that exogenous TRIC-A expression attenuates RyR₂-mediated mitochondrial Ca²⁺ overload, preserves respiratory function, and suppresses superoxide generation. Together, these findings identify TRIC-A as a critical regulator of SR–mitochondrial Ca²⁺ signaling. By constraining mitochondrial Ca²⁺ influx and limiting oxidative stress, TRIC-A safeguards cardiomyocytes against SOICR-driven injury and confers protection against pressure overload-induced cardiac dysfunction. Full article

Intracellular emetic signals involved in the cannabinoid CB₁ receptor inverse agonist/antagonist SR141716A were investigated. SR141716A (20 mg/kg, i.p.)-evoked vomiting occurred via both the central and peripheral mechanisms. This was accompanied by robust emesis-associated increases in the following: (i) c-fos- and phospho-glycogen synthase kinase-3α/β (p-GSK-3αβ)-expression in the shrew’s dorsal vagal complex (DVC), (ii) phospho-extracellular signal-regulated kinase1/2 (p-ERK_1/2) expression in both the DVC and jejunal enteric nervous system, and (iii) time-dependent upregulation of cAMP levels and phosphorylation of protein kinase A (PKA), protein kinase B (Akt), GSK-3α/β, ERK_1/2, and protein kinase C αβII (PKCαβII) in the brainstem. SR141716A-evoked emetic parameters were attenuated by diverse inhibitors of the following: PKA, ERK_1/2, GSK-3, phosphatidylinositol 3-kinase (PI3K)-Akt pathway, phospholipase C (PLC), PKC, Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), L-type Ca²⁺ channel (LTCC), store-operated Ca²⁺ entry (SOCE), inositol trisphosphate receptor (IP3R), ryanodine receptor (RyRs), both 5-HT₃-, and D_2/3-receptor antagonists, and the transient receptor potential vanilloid 1 receptor (TRPV1R) agonist. SR141716A appears to evoke vomiting via inverse agonist activity involving emesis-associated kinases, including cAMP/PKA, ERK_1/2, PI3K/Akt/GSK-3, PLC/PKCαβII, and CaMKII, which depend upon Ca²⁺ mobilization linking extracellular Ca²⁺ entry via plasma membrane Ca²⁺ channels (LTCC, SOCE, TRIPV1R) and intracellular Ca²⁺ release via IP3Rs and RyRs. The 5-HT₃, NK₁, and D_2/3 receptors also contribute to SR141716A-mediated vomiting. Full article

Dysferlin direct protein–protein interactions (PPI) previously have been elucidated with surface plasmon resonance (SPR) and predicted to underlie membrane repair in mechanotransducing myofibrils. In mechanotransducing inner ear hair cells, dysferlin is detected with Z-stack confocal immunofluorescence in the stereocilia and their inserts in the tectorial membrane (TM) co-localizing with FKBP8, consistent with the SPR determination of tight, positively Ca²⁺-dependent interaction. FKBP8, a direct binding partner of mechanotransducing TMC1, when overexpressed, evokes an elevation in anti-apoptotic BCL2, inhibition of ryanodine receptor (RYR) activity, and a consequent reduction in Ca²⁺ release. RYR3 has now been immunolocalized to the tip of the TM in close association with a third-row outer hair cell (OHC) stereociliary BCL2-positive insertion. Dysferlin, annexin A2, and Alzheimer’s proteins BACE1 and amyloid precursor protein (APP) are also accumulated in these stereociliary insertions. RYR2 and RYR1 have been immunolocalized to the TM core, in position to influence TM Ca²⁺. Dysferlin PPI pathways also intersect with AD protein pathways in the spiral ganglion (SG). Dysferlin segregates with FKBP8, BACE1, and RYR3 in the interiors of SG type I cell bodies. RYR1, RYR2, PSEN1, BCL2, and caspase 3 are primarily confined to plasma membrane sites. RYR3 pathways traverse the plasma membrane to the cell body interior. Western analysis of dysferlinopathy proteins links FKBP8 and BCL2 overexpression with RYR inhibition, indicative of dysferlin targets that are ameliorative in AD. Full article

This study aimed to investigate whether intracellular complement 3 (C3) activation regulates ATP production in yak rumen epithelial cells under inflammatory conditions and its potential mechanism. An in vitro inflammation model was established by stimulating yak rumen epithelial cells with lipopolysaccharide (LPS). Then, protease inhibitors targeting C3 activation enzymes were added. Additionally, to explore the downstream signaling pathway, exogenous C3a and the C3a receptor (C3aR) inhibitor C3aRY were applied to the inflammation model. After treatment with different concentrations of LPS, the gene expression levels and concentrations of pro-inflammatory cytokines, such as TNF-α, IL-1β, and IL-6 were significantly up-regulated (p < 0.05), while a significant reduction in cellular ATP levels was observed (p < 0.05), along with a significant reduction in mitochondrial membrane potential (p < 0.05). After treating the inflammation model with different protease inhibitors, the ATP content and gene expression of the ATP synthase subunit ATP5A were significantly increased (p < 0.05). Exogenous addition of the C3aR inhibitor C3aRY in the inflammation model exhibited a significant increase in ATP content and ATP5A gene expression (p < 0.05) when compared to the inflammation model. These results demonstrated that intracellular C3 activation inhibited ATP production in yak rumen epithelial cells under inflammatory conditions, likely through C3a–C3aR signaling and the cAMP/PKA pathway. Full article

While calcium (Ca²⁺) is a universal cellular messenger, the ionic properties of magnesium (Mg²⁺) make it less suited for rapid signaling and more for structural integrity. Still, besides being a passive player, Mg²⁺ is the only active Ca²⁺ antagonist, essential for tuning the efficacy of Ca²⁺-dependent cardiac excitation–contraction coupling (ECC) and for ensuring cardiac function robustness and stability. This review aims to provide a comprehensive framework to link the structural and molecular mechanisms of Mg²⁺/Ca²⁺ antagonistic binding across key proteins of the cardiac ECC machinery to their physiopathological relevance. The pervasive “dampening” effect of Mg²⁺ on ECC activity is exerted across various players and mechanisms, and lies in the ions’ physiological competition for multiple, flexible binding protein motifs across multiple compartments. Mg²⁺ profoundly modulates the cardiac action potential waveform by inhibiting the L-type Ca²⁺ channel Cav1.2, i.e., the key trigger of cardiac ryanodine receptor (RyR2) opening. Cytosolic Mg²⁺ favors RyR2 closed or inactive conformations not only through physical binding at specific sites, but also indirectly through modulation of RyR2 phosphorylation by Camk2d and PKA. RyR2 is also potently inhibited by luminal Mg²⁺, a vital mechanism in the cardiac setting for preventing excessive Ca²⁺ release during diastole. This mechanism, able to distinguish between Ca²⁺ and Mg²⁺, is mediated by luminal partners Calsequestrin 2 (CASQ2) and Triadin (TRDN). In addition, Mg²⁺ favors a rearrangement of the RyR2 cluster configuration that is associated with lower Ca²⁺ spark frequencies. Full article

The increasing global prevalence of hyperuricemia (HUA), particularly among younger populations, underscores the urgent need for safe and effective dietary interventions. Monascus fungi, long utilized in East Asian food culture, ferment rice to produce red yeast rice (RYR), a functional food rich in monacolin K and Monascus pigments. Among these, Monascus yellow pigments (MYPs)—natural azaphilone compounds used as food additives and colorants—have shown antioxidant, anti-inflammatory, and metabolic regulatory activities. However, their potential to alleviate hyperuricemia remains unexplored. This study investigates the urate-lowering and organ-protective effects of MYPs through a combination of in vitro, in vivo, and gut microbiota analyses. MYPs exhibited significant xanthine oxidase (XOD) inhibitory activity, and molecular docking confirmed that monascin (MS) and ankaflavin (AK) competitively bind to the XOD active site. In a murine HUA model, MYPs significantly reduced serum uric acid (SUA) levels without causing hepatic or renal toxicity. Mechanistically, MYPs downregulated renal UA reabsorption transporters (URAT1, GLUT9) and upregulated the excretory transporter ABCG2, enhancing uric acid (UA) excretion. These findings highlight MYPs as promising food-derived bioactives with dual XOD inhibition and uricosuric effects, offering a novel nutraceutical strategy for hyperuricemia prevention and management. Full article

Right heart failure (RHF) is a major cause of morbidity and mortality, often resulting from pulmonary arterial hypertension and characterized by impaired calcium (Ca²⁺) handling and maladaptive remodeling. Phosphodiesterase 9A (PDE9A), a cGMP-specific phosphodiesterase, has been proposed as a potential contributor to RHF pathogenesis by suppressing the cardioprotective cGMP–PKG signaling pathway—a conclusion largely extrapolated from left-sided heart failure models. This review examines existing evidence regarding PDE9A’s role in RHF, focusing on its effects on intracellular calcium cycling, fibrosis, hypertrophy, and contractile dysfunction. Data from preclinical models demonstrate that pathological stress upregulates PDE9A expression in cardiomyocytes, leading to diminished PKG activation, impaired SERCA2a function, RyR2 instability, and increased arrhythmogenic Ca²⁺ leak. Pharmacological or genetic inhibition of PDE9A restores cGMP signaling, improves calcium handling, attenuates hypertrophic and fibrotic remodeling, and enhances ventricular compliance. Early-phase clinical studies in heart failure populations suggest that PDE9A inhibitors are well tolerated and effectively augment cGMP levels, although dedicated trials in RHF are still needed. Overall, these findings indicate that targeting PDE9A may represent a promising therapeutic strategy to improve outcomes in RHF by directly addressing the molecular mechanisms underlying calcium mishandling and myocardial remodeling. Full article

Ryanodine receptors (RyRs) are large intracellular Ca²⁺ release channels primarily found in muscle and nerve cells and also present at low levels in pancreatic islet endocrine cells. This review examines the role of RyRs in islet cell function, focusing on calcium signaling and hormone secretion, while addressing the ongoing debate regarding their significance due to their limited expression. We explore conflicting experimental results and their potential causes, synthesizing current knowledge on RyR isoforms in islet cells, particularly in beta and delta cells. The review discusses how RyR-mediated calcium-induced calcium release enhances, rather than drives, glucose-stimulated insulin secretion. We examine the phosphorylation-dependent regulation of beta-cell RyRs, the concept of “leaky ryanodine receptors”, and the roles of RyRs in endoplasmic reticulum stress, apoptosis, store-operated calcium entry, and beta-cell electrical activity. The relationship between RyR dysfunction and the development of impaired insulin secretion in diabetes is assessed, noting their limited role in human diabetes pathogenesis given the disease’s polygenic nature. We highlight the established role of RyR-mediated CICR in the mechanism of action of common type 2 diabetes treatments, such as glucagon-like peptide-1, which enhances insulin secretion. By integrating findings from electrophysiological, molecular, and clinical studies, this review provides a balanced perspective on RyRs in islet cell physiology and pathology, emphasizing their significance in both normal insulin secretion and current diabetes therapies. Full article

The response of ryanodine receptor (RyR) channels to increases in free cytoplasmic calcium concentration ([Ca²⁺]) is tuned by several mechanisms, including redox signaling. Three different responses to [Ca²⁺] have been described in RyR channels, low, moderate and high activity responses, which depend on the RyR channel protein oxidation state. Thus, reduced RyR channels display the low activity response, whereas partially oxidized channels display the moderate response and more oxidized channels, the high activity response. As described here, RyR channels from rat brain cortices or hippocampi displayed aged-related marked changes in the distribution of these channel responses; RyR channels from aged rats displayed reduced fraction of low activity channels and increased fraction of high activity channels, which would favor Ca²⁺-induced Ca²⁺ release. In addition, compared with young rats, aged rats displayed learning and memory defects, with lower hit rates when tested in the Oasis maze, a dry version of the Morris water maze. Previous oral administration of N-acetylcysteine for 3 weeks prevented both the age-dependent effects on RyR channel activation by [Ca²⁺], and the learning and memory defects. Based on these results, it is proposed that redox-sensitive neuronal RyR channels partake in the mechanism underlying the learning and memory disruptions displayed by aged rats. Full article

Background: A comparative 12-week dietary intervention of red yeast rice (RYR, Beni-koji, Kobayashi, Japan) and Cuban policosanol (PCO, Raydel^®, Thornleigh, Australia) was assessed for dyslipidemia, antioxidant status, and vital organ functionality in hyperlipidemic zebrafish. Methods: Hyperlipidemic zebrafish were supplemented with a high-cholesterol diet (HC, final 4%, w/w) infused with either a powdered RYR tablet (final 1.0%, w/w), a PCO tablet (final 1.0%, w/w), or a combination of 0.5% (w/w) each of RYR and PCO powder for 12 weeks. Subsequently, blood and organs were collected and processed for biochemical and histological examination. Results: RYR and PCO consumption showed a substantial effect against HC-induced hyperlipidemia by reducing the total cholesterol (TC), triglyceride (TG), and low-density lipoprotein cholesterol (LDL-C). Exclusively, PCO supplementation revealed a significant elevation in the HC-diminished high-density lipoprotein cholesterol (HDL-C). In addition, PCO supplementation showed a significant elevation in plasma ferric ion-reducing ability (FRA) and sulfhydryl content, as well as alleviating the blood glucose level of hyperlipidemic zebrafish. The most noteworthy impact, with a significant two-fold (p < 0.001) augmentation of HC-diminished plasma paraoxonase (PON) activity, was observed in response to PCO. In contrast, the RYR supplementation failed to establish curative effects against HC-disturbed plasma antioxidant variables and blood glucose levels. The histological outcome revealed a severe toxicological impact of the RYR on the liver, reflected by fatty liver changes and three-fold heightened IL-6 production compared to HC control. Contrastingly, PCO exhibited significant hepatoprotection and effectively neutralized the hepatic toxicity triggered by HC and RYR. Also, RYR showed kidney atrophy, intense ROS generation, apoptosis, and senescence. Conversely, the PCO supplementation protected the kidney from HC- and RYR-induced toxicity. Likewise, PCO supplementation notably alleviated histological alterations and oxidative stress in the brain, ovary, and testis of hyperlipidemic zebrafish. Conclusions: This comparative study establishes PCO’s therapeutic effect against the challenges posed by HC, while RYR emerged with serious toxicological concerns towards the liver, kidney, and other organs of hyperlipidemic zebrafish. Full article

The association of the 12 KDa FK506 binding protein (FKBP12) with ryanodine receptor type 1 (RyR1) in skeletal muscle is thought to suppress RyR1 channel opening and contribute to healthy muscle function. The strongest evidence for this role is increased RyR1 channel activity following FKBP12 dissociation. However, the corollary that channel activity will decrease when FKBP12 is added back to FKBP12-depleted RyR1 is not well established, and when reported, the time- and concentration-dependence of inhibition vary over orders of magnitude. Here, we address this problem with an investigation of the molecular mechanisms of the FKBP12 regulation of RyR1. Muscle processing to obtain sarcoplasmic reticulum (SR) vesicle preparations enriched in RyR1 resulted in substantial FKBP12 dissociation from RyR1, indicating low-affinity binding. Conversely, high-affinity binding was indicated by some FKBP12 remaining bound to RyR1 after solubilization. We report, for the first time, an increase in the activity of FKBP12-depleted channels after the addition of exogenous FKBP12 (5 nM to 5 µM), followed by a reduction in activity consistent with inhibition after 20–30 min exposure to higher [FKBP12]s. Both the increase and later decline in activity were time- and concentration-dependent. The results suggest a high-affinity activation when FKBP12 binding sites on the RyR1 tetramer are partially occupied by FKBP12 and lower affinity inhibition as more RyR1 monomers become occupied. These novel results imply negative cooperativity in FKBP12 binding to RyR1 and a dynamic role for FKBP12/RyR1 interactions in intact muscle fibers. Full article

Nucleic acid (NA)-based drugs are promising therapeutics agents. Beyond efficacy, addressing safety concerns—particularly those specific to this class of drugs—is crucial. Here, we propose an in vitro approach to screen for potential adverse off-target effects of NA-based drugs. Human peripheral blood mononuclear cells (PBMCs), purified from buffy coats of healthy donors, were used to investigate the ability of NA-drugs to trigger toxicity pathways and inappropriate immune stimulation. PBMCs were selected for their ability to represent potential human responses, given their likelihood of interacting with administered drugs. As proof of concept, a small interfering RNA (siRNA) targeting Ryanodine Receptor mRNA (RyR2) identified by the Italian National Center for Gene Therapy and Drugs based on RNA Technology as a potential therapeutic target for dominant catecholaminergic polymorphic ventricular tachycardia, was selected. This compound and its scramble were formulated within a calcium phosphate nanoparticle-based delivery system. Positive controls for four toxicity pathways were identified through literature review, each associated with a specific type of cellular stress: oxidative stress (tert-butyl hydroperoxide), mitochondrial stress (rotenone), endoplasmic reticulum stress (thapsigargin), and autophagy (rapamycin). These controls were used to define specific mRNA signatures triggered in PBMCs, which were subsequently used as indicators of off-target effects. To assess immune activation, the release of pro-inflammatory cytokines (interleukin-6, interleukin-8, tumor necrosis factor-α, and interferon-γ) was measured 24 h after exposure. The proposed approach provides a rapid and effective screening method for identifying potential unintended effects in a relevant human model, which also allows to address gender effects and variability in responses. Full article

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a highly arrhythmogenic syndrome triggered by stress, primarily linked to gain-of-function point mutations in the cardiac ryanodine receptor (RyR2). Flecainide, as an effective therapy for CPVT, is a known blocker of the surface-membrane Na⁺ channel, also affecting the intracellular RyR2 channel. The therapeutic relevance of the flecainide-RyR2 interaction remains controversial, as flecainide blocks only the RyR2 current flowing in the opposite direction to the physiological Ca²⁺ release from the sarcoplasmic reticulum (SR). However, it has been proposed that charge-compensating countercurrent from the cytosol to SR lumen plays a critical role, and its reduction may indeed suppress excessive diastolic SR Ca²⁺ release through RyR2 channels in CPVT. Monitoring single-channel properties, we examined whether flecainide can target intracellular pathways for charge-balancing currents carried by RyR2 and SR Cl⁻ channels under cell-like conditions. Particularly, the Tris⁺ countercurrent flowed through the RyR2 channel simultaneously with a dominant reverse Ca²⁺/Ba²⁺ current. We demonstrate that flecainide blocked the RyR2-mediated countercurrent without affecting channel activity. In contrast, the SR Cl⁻ channel was completely resistant to flecainide. Based on these findings, it is reasonable to propose that the primary intracellular target of flecainide in vivo is the RyR2-mediated countercurrent. Full article

Head and neck cancers (HNCs) are the sixth most commonly diagnosed cancer and the eighth leading cause of cancer-related mortality worldwide, with squamous cell carcinoma being the most prevalent type. The global incidence of HNCs is steadily increasing, projected to rise by approximately 30% per year by 2030, a trend observed in both developed and undeveloped countries. This study involved serum proteomic profiling to identify predictive clinical biomarkers in cancer patients undergoing chemoradiotherapy (CRT). Fifteen HNC patients at Tikur Anbessa Specialized Hospital, Radiotherapy (RT) center in Addis Ababa were enrolled. Serum samples were collected before and after RT, and patients were classified as responders (R) or non-responders (NR). Protein concentrations in the serum were determined using the Bradford assay, followed by nano-HPLC–MS/MS for protein profiling. Progenesis QI for proteomics identified 55 differentially expressed proteins (DEPs) between R and NR, with a significance of p < 0.05 and a fold-change (FC) ≥ 1.5. The top five-up-regulated proteins included MAD1L1, PSMC2, TRIM29, C5, and SERPING1, while the top five-down-regulated proteins were RYR1, HEY2, HIF1A, TF, and CNN3. Notably, about 16.4% of the DEPs were involved in cellular responses to DNA damage from cancer treatments, encompassing proteins related to deoxyribonucleic acid (DNA) damage sensing, checkpoint activation, DNA repair, and apoptosis/cell cycle regulation. The analysis of the relative abundance of ten proteins with high confidence scores identified three DEPs: ADIPOQ, HEY2, and FUT10 as potential predictive biomarkers for treatment response. This study highlighted the identification of three potential predictive biomarkers—ADIPOQ, HEY2, and FUT10—through serum proteomic profiling in HNC patients undergoing RT, emphasizing their significance in predicting treatment response. Full article