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Human calcium-sensing receptor (CaSR) is a G-protein-coupled receptor (GPCR) that maintains extracellular Ca2+ homeostasis through the regulation of parathyroid hormone secretion. It functions as a disulfide-tethered homodimer composed of three main domains, the Venus Flytrap module, cysteine-rich domain, and seven-helix transmembrane region. Here, we present the crystal structures of the entire extracellular domain of CaSR in the resting and active conformations. We provide direct evidence that L-amino acids are agonists of the receptor. In the active structure, L-Trp occupies the orthosteric agonist-binding site at the interdomain cleft and is primarily responsible for inducing extracellular domain closure to initiate receptor activation. Our structures reveal multiple binding sites for Ca2+ and PO43- ions. Both ions are crucial for structural integrity of the receptor. While Ca2+ ions stabilize the active state, PO43- ions reinforce the inactive conformation. The activation mechanism of CaSR involves the formation of a novel dimer interface between subunits. Calcium ions regulate many processes in the human body. The calcium-sensing receptor, called CaSR, is responsible for maintaining a stable level of calcium ions in the blood. This receptor can detect small changes in the concentration of calcium ions, and activates signalling events within the cell to restore the level of calcium ions back to normal. Abnormal activity of this receptor is associated with severe diseases in humans CaSR is found in the surface membrane of cells and belongs to a family of proteins called G-protein coupled receptors. Much of the protein extends out of the cell and interacts with calcium ions, phosphate ions and certain other molecules such as amino acids. However, it was not well understood how these small molecules bind to CaSR and how this activates the receptor. Geng et al. have now used a technique called X-ray crystallography to view the three-dimensional structure of the exterior domain of CaSR in its resting state and active state. These structures revealed that, contrary to expectations, calcium ions are not the main activator of the receptor. Instead, Geng et al. found that CaSR adopts an inactive state in the absence or presence of calcium ions, while the active state only forms when an amino acid is bound. Furthermore investigation showed that calcium ions are needed to stabilise the active form, while phosphate ions keep the inactive form stable. Geng et al. also identified the shape changes that must occur as CaSR transitions from its inactive to its active state. In particular, an amino acid binding to the exterior domain causes it to close like a venus flytrap, which is a crucial step in activating the receptor. Taken together, the findings show that the amino acids and calcium ions act jointly to fully activate CaSR. The next steps are to determine the structure of the entire receptor with and without its small molecule partners and to use these structures to design drugs that can alter CaSR’s activity in order to treat human diseases.

Calcium ions (Ca2+) are indispensable and versatile metal ions that play a pivotal role in regulating cell metabolism, encompassing cell survival, proliferation, migration, and gene expression. Aberrant Ca2+ levels are frequently linked to cell dysfunction and a variety of pathological conditions. Therefore, it is essential to maintain Ca2+ homeostasis to coordinate body function. Disrupting the balance of Ca2+ levels has emerged as a potential therapeutic strategy for various diseases, and there has been extensive research on integrating this approach into nanoplatforms. In this review, the current nanoplatforms that regulate Ca2+ homeostasis for cancer therapy are first discussed, including both direct and indirect approaches to manage Ca2+ overload or inhibit Ca2+ signalling. Then, the applications of these nanoplatforms in targeting different cells to regulate their Ca2+ homeostasis for achieving therapeutic effects in cancer treatment are systematically introduced, including tumour cells and immune cells. Finally, perspectives on the further development of nanoplatforms for regulating Ca2+ homeostasis, identifying scientific limitations and future directions for exploitation are offered. This review paper provides a comprehensive overview of nanoplatforms that manipulate calcium ions (Ca2+) homeostasis to enhance cancer therapy. It offers a detailed exploration of two Ca2+ regulation strategies employed by these nanoplatforms, including Ca2+ overload and inhibition, and discusses the applications of Ca2+‐related nanomaterials in various cell types, such as cancer cells and immune cells. The paper also presents perspectives on further advancing nanoplatforms for regulating Ca2+ homeostasis, identifying scientific limitations, and outlining future directions for exploration.

Sudden cardiac death due to malignant ventricular arrhythmias remains the major cause of mortality in the postindustrial world. Defective intracellular Ca2+ homeostasis has been well established as a key contributing factor to the enhanced propensity for arrhythmia in acquired cardiac disease, such as heart failure or diabetic cardiomyopathy. More recent advances provide a strong basis to the emerging view that hereditary cardiac arrhythmia syndromes are accompanied by maladaptive remodeling of Ca2+ homeostasis which substantially increases arrhythmic risk. This brief review will focus on functional changes in elements of Ca2+ handling machinery in cardiomyocytes that occur secondary to genetic mutations associated with catecholaminergic polymorphic ventricular tachycardia, and long QT syndrome.

The accumulation of amyloid-β₁₋₄₂ (Aβ₁₋₄₂) in the brain is a hallmark of Alzheimer’s disease (AD), contributing to intracellular calcium dysregulation and neuronal death. Ryanodine receptors (RyRs), located in the endoplasmic reticulum (ER), play a pivotal role in intracellular calcium release and homeostasis. In this study, we employed an in vitro model of AD using cultured rat hippocampal neurons treated with Aβ₁₋₄₂ to investigate the effects of dantrolene, a RyR antagonist, on calcium signaling and neuronal viability. Dantrolene significantly reduced basal cytosolic calcium levels and attenuated stimulus-induced calcium transients in response to depolarizing solution, electrical field stimulation, and caffeine application. These findings indicate that dantrolene stabilizes intracellular calcium signaling by limiting calcium release from ER stores. Furthermore, co-application of dantrolene with Aβ₁₋₄₂ increased neuronal survival from 26 to 76% and significantly reduced the proportions of apoptotic and necrotic cells. These results demonstrate that RyRs contribute to calcium overload and neurotoxicity under AD-like conditions and that dantrolene effectively counteracts Aβ₁₋₄₂-induced calcium dysregulation. Altogether, our findings support the calcium hypothesis of AD and highlight dantrolene as a potential disease-modifying agent targeting ER-mediated calcium homeostasis.

Targeting senescent pancreatic β‐cells represents a promising therapeutic avenue for age‐related diabetes; however, current anti‐senescence strategies often compromise β‐cell mass. In this study, human amniotic mesenchymal stem cell‐derived small extracellular vesicles (hAMSC‐sEVs) were identified as a novel intervention that can be used to effectively counteract cellular senescence and preserve β‐cell integrity. We aimed to systemically delineate the molecular mechanisms underlying hAMSC‐sEV‐mediated reversal of β‐cell senescence in age‐related diabetes. In oxidative stress‐induced and naturally aged β‐cell models, hAMSC‐sEVs mitigated senescence‐associated phenotypes, restored mitochondrial homeostasis, and enhanced insulin secretion capacity. In aged diabetic mice, administering these vesicles significantly ameliorated hyperglycemia, improved glucose tolerance, and reversed β‐cell functional decline by reducing senescent β‐cell populations, reinstating β‐cell identity markers, and suppressing senescence‐associated secretory phenotype (SASP) component production. Mechanistic investigations revealed that the miR‐21‐5p‐enriched hAMSC‐sEVs directly target the interleukin (IL)‐6 receptor α subunit (IL‐6RA), thereby inhibiting signal transducer and activator of transcription 3 (STAT3) phosphorylation at tyrosine 705 and its subsequent nuclear translocation. This epigenetic modulation alleviated STAT3‐mediated transcriptional repression of the mitochondrial calcium uniporter (MCU), rectifying age‐related mitochondrial calcium mishandling and insulin secretion defects. Genetic ablation of MCU clearly established the central role of the miR‐21‐5p/IL‐6RA/STAT3/MCU axis in this regulatory cascade. Our findings reveal hAMSC‐sEVs as a novel senotherapeutic strategy for age‐related diabetes, elucidating the pivotal role of miR‐21‐5p‐driven epigenetic–mitochondrial calcium homeostasis in reversing β‐cell dysfunction, establishing a framework for targeting cellular senescence in metabolic disorders. hAMSC‐sEVs rejuvenate β cells and improve glycaemic control via the miR‐21‐5p/IL‐6RA/STAT3/MCU axis, restoring mitochondrial Ca2+ homeostasis and insulin secretion in aged T2DM mice.

BackgroundSignet ring cell carcinoma (SRCC) is a particular histologic variant of gastric cancer (GC). However, the critical factor related to the aggressive characteristics of SRCC has not been determined.MethodsWe collected surgically resected tissues from 360 GC patients in the Kumamoto University cohort and generated survival curves via the Kaplan–Meier method. In vitro, we identified the specific transcript variant of MUC20 in SRCC cells by direct sequencing and investigated the role of MUC20 in GC progression using GC cells with MUC20 silencing and forced expression. In vivo, we examined chemoresistance using MUC20 variant 2 (MUC20v2)-overexpressing non-SRCC cells to construct a xenograft mouse model.ResultsWe analyzed a comprehensive GC cell line database to identify the specifically expressed genes in gastric SRCC. We focused on MUC20 and investigated its role in GC progression. Survival analysis revealed that GC patients with high MUC20 expression exhibited a poor prognosis and that MUC20 expression was significantly correlated with SRCC histological type. Moreover, we found that gastric SRCC cells specifically expressed MUC20v2, which was dominantly expressed in the cytoplasm. Silencing MUC20v2 caused cell death with characteristic morphological changes in gastric SRCC cells. To further determine the types of cell death, we examined apoptosis, pyroptosis and ferroptosis by detecting cleaved PARP, gasdermin E-N-terminal (GSDME-N), and lipid reactive oxygen species (ROS) levels, respectively. We found that apoptosis and pyroptosis occurred in MUC20-silenced gastric SRCC cells. In addition, MUC20v2-overexpressing GC cells exhibited chemoresistance to cisplatin (CDDP) and paclitaxel (PTX). RNA sequencing revealed that the pathways involved in intracellular calcium regulation were significantly upregulated in MUC20v2-overexpressing GC cells. Notably, forced expression of MUC20v2 in the cytoplasm of GC cells led to the maintenance of mitochondrial calcium homeostasis and mitochondrial membrane potential (MMP), which promoted cell survival and chemoresistance by suppressing apoptosis and pyroptosis. Finally, we investigated the significance of MUC20v2 in a xenograft model treated with CDDP and showed that MUC20v2 overexpression caused chemoresistance by inhibiting cell death.ConclusionThese findings highlight the novel functions of MUC20v2, which may confer cell survival and drug resistance in GC cells.SignificanceMUC20v2 protects GC cells from apoptosis and pyroptosis by maintaining mitochondrial calcium levels and mitochondrial membrane potential and subsequently induces drug resistance.

Background: To better understand the Ca2+ overload mechanism of SDT killing gliomas, we examined the hypothesis that the early application of the mechanosensitive Ca2+ channel Piezo1 antagonist (GsMTx4) could have a better anti-tumor effect. Methods: The in vitro effect of low-energy SDT combined with GsMTx4 or agonist Yoda 1 on both the ROS-induced distribution of Ca2+ as well as on the opening of Piezo1 and the dissociation and polymerization of the Ca2+ lipid complex were assessed. The same groups were also studied to determine their effects on both tumor-bearing BALB/c-nude and C57BL/6 intracranial tumors, and their effects on the tumor-infiltrating macrophages were studied as well. Results: It was determined that ultrasound-activated Piezo1 contributes to the course of intracellular Ca2+ overload, which mediates macrophages (M1 and M2) infiltrating under the oxidative stress caused by SDT. Moreover, we explored the effects of SDT based on the dissociation of the Ca2+ lipid complex by inhibiting the expression of fatty acid binding protein 4 (FABP4). The Piezo1 channel was blocked early and combined with SDT treatment, recruited macrophages in the orthotopic transplantation glioma model. Conclusions: SDT regulates intracellular Ca2+ signals by upregulating Piezo1 leading to the inhibition of the energy supply from lipid and recruitment of macrophages. Therefore, intervening with the function of the Ca2+ channel on the glioma cell membrane in advance is likely to be the key factor to obtain a better effect combined with SDT treatment.

Background Impaired Ca 2+ handling is involved in diabetic cardiomyopathy (DCM) progression. The activation of acid sphingomyelinase (ASMase) stimulated cardiomyocytes apoptosis and caused DCM. Here, we aimed to investigate whether ASMase regulates mitochondrial Ca 2+ homeostasis by acting on mitochondrial calcium uptake 1 (MICU1) and mitochondria-associated endoplasmic reticulum membranes (MAMs) formation to induce apoptosis during DCM. Methods and results We established a type 2 diabetes model by combining high-fat diet (HFD) with streptozotocin (STZ) injection in wild-type and cardiomyocyte-specific ASMase deletion (ASMase Myh6KO ) mice. ASMase deletion restored HFD/STZ-induced cardiac dysfunction, remodeling, myocardial lipid accumulation and apoptosis. Single cell sequencing and Gene ontology (GO) enrichment analysis pointed to “cardiac muscle contraction” and “positive regulation of mitochondrial calcium ion concentration”, which were confirmed by high glucose (HG, 30 mM) and palmitic acid (PA, 200 μM) induced mitochondrial Ca 2+ overload in H9c2 cell lines at time dependence, accompanied by the upregulation of ASMase and MICU1 protein expressions. The similar effects were noted in ASMase overexpressed cardiomyocytes. Interestingly, endoplasmic reticulum (ER) Ca 2+ level was decreased at the corresponding time, suggesting that increased mitochondrial Ca 2+ level may be derived from ER. Notably, enhanced MAMs formation was found in HG + PA treated H9c2 cells, accompanied by blocked autophagy, similar results were obtained in ASMase overexpressing cells or HFD/STZ hearts. Loss of ASMase prevented HFD/STZ or HG + PA incubation induced cardiac hypertrophy, mitochondrialCa 2+ overload, ROS production, autophagy blockage and MICU1 upregulation. Conclusions HFD/STZ-induced ASMase upregulation enhances MAMs formation, promoting mitochondrial Ca 2+ overload through MICU1 activation, leading to ROS generation, autophagy blockage and apoptosis in DCM. Therefore, targeting ASMase-MICU1 pathway emerges as a potential therapeutic approach for managing DCM. Graphical Abstract

Heart failure (HF) with preserved ejection fraction (HFpEF) causes a progressive limitation of functional capacity, poor quality of life (QoL) and increased mortality, yet unlike HF with reduced ejection fraction (HFrEF) there are no effective device-based therapies. Both HFrEF and HFpEF are associated with dysregulations in myocardial cellular calcium homeostasis and modifications in calcium-handling proteins, leading to abnormal myocardial contractility and pathological remodelling. Cardiac contractility modulation (CCM) therapy, based on a pacemaker-like implanted device, applies extracellular electrical stimulation to myocytes during the absolute refractory period of the action potential, which leads to an increase in cytosolic peak calcium concentrations and thereby the force of isometric contraction promoting positive inotropism. Subgroup analysis of CCM trials in HFrEF has demonstrated particular benefits in patients with LVEF between 35% and 45%, suggesting its potential effectiveness also in patients with higher LVEF values. Available evidence on CCM in HFpEF is still preliminary, but improvements in terms of symptoms and QoL have been observed. Future large, dedicated, prospective studies are needed to evaluate the safety and efficacy of this therapy in patients with HFpEF.

Darier′s disease (DD) is a rare, autosomal dominant genodermatosis caused by pathogenic variants in the ATP2A2 gene, which encodes the SERCA2 protein, an endoplasmic reticulum ATPase Ca2+ transporter. These mutations impair the intracellular calcium homeostasis leading to increased protein misfolding, endoplasmic reticulum (ER) stress response, and the activation of the unfolded protein response (UPR), culminating in keratinocyte apoptosis and anomalies in interfollicular epidermal stratification. Clinically, the disease is characterized by the presence of skin lesions with hyperkeratotic papules and an increased susceptibility to inflammatory reactions, bacterial and viral infections. The histological hallmarks include acantholysis, dyskeratosis, and increased apoptotic keratinocytes, referred to as “corp ronds”. The SERCA2b isoform is expressed not only in the epidermis but it is present ubiquitously in all tissues, suggesting that its alteration may have multi-organ effects. The review aims to provide a broad overview of the pathology, from intracellular dysfunction to the clinical manifestations, elucidating the molecular effects of SERCA2 variants found in DD patients and exploring the potential cell signaling pathways that may contribute to disease progression. Beginning with an examination of the cellular alterations, our work then shifts to exploring their impact in an organ-specific context, providing insights into new potential therapeutic strategies tailored to clinical manifestations.