Altered Calcium Permeability of AMPA Receptor Drives NMDA Receptor Inhibition in the Hippocampus of Murine Obesity Models

Evidence has accumulated that higher consumption of high-fat diets (HFDs) during the juvenile/adolescent period induces altered hippocampal function and morphology; however, the mechanism behind this phenomenon remains elusive. Using high-resolution structural imaging combined with molecular and functional interrogation, a murine model of obesity treated with HFDs for 12 weeks after weaning mice was shown to change in the glutamate-mediated intracellular calcium signaling and activity, including further selective reduction of gray matter volume in the hippocampus associated with memory recall disturbance. Dysregulation of intracellular calcium concentrations was restored by a non-competitive α-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) antagonist, followed by normalization of hippocampal volume and memory recall ability, indicating that AMPARs may serve as an attractive therapeutic target for obesity-associated cognitive decline.

Systematic Review of Calcium Channels and Intracellular Calcium Signaling: Relevance to Pesticide Neurotoxicity

Pesticides of different chemical classes exert their toxic effects on the nervous system by acting on the different regulatory mechanisms of calcium (Ca2+) homeostasis. Pesticides have been shown to alter Ca2+ homeostasis, mainly by increasing its intracellular concentration above physiological levels. The pesticide-induced Ca2+ overload occurs through two main mechanisms: the entry of Ca2+ from the extracellular medium through the different types of Ca2+ channels present in the plasma membrane or its release into the cytoplasm from intracellular stocks, mainly from the endoplasmic reticulum. It has also been observed that intracellular increases in the Ca2+ concentrations are maintained over time, because pesticides inhibit the enzymes involved in reducing its levels. Thus, the alteration of Ca2+ levels can lead to the activation of various signaling pathways that generate oxidative stress, neuroinflammation and, finally, neuronal death. In this review, we also discuss some proposed strategies to counteract the detrimental effects of pesticides on Ca2+ homeostasis.

The roles of distinct Ca2+ signaling mediated by Piezo and inositol triphosphate receptor (IP3R) in the remodeling of E-cadherin during cell dissemination

Given the role of E-cadherin (E-cad) in holding epithelial cells together, the inverse relationship between E-cad levels and cell invasion has been perceived as a principle underlying the invasiveness of tumor cells. In contrast, our study employing the Drosophila model of cell dissemination demonstrates that E-cad is necessary for the invasiveness of RasV12-transformed cells in vivo. Drosophila E-cad/β-catenin disassembles at adherens junctions and assembles at invasive protrusions—the actin- and cortactin-rich invadopodia-like protrusions associated with breach of the extracellular matrix (ECM)—during cell dissemination. Loss of E-cad attenuates dissemination of RasV12-transformed cells by impairing their ability to compromise the ECM. Strikingly, the remodeling of E-cad/β-catenin subcellular distribution is controlled by two discrete intracellular calcium signaling pathways: Ca2+ release from endoplasmic reticulum via the inositol triphosphate receptor (IP3R) disassembles E-cad at adherens junctions while Ca2+ entry via the mechanosensitive channel Piezo assembles E-cad at invasive protrusions. Thus, our study provides molecular insights into the unconventional role of E-cad in cell invasion during cell dissemination in vivo and describes the discrete roles of intracellular calcium signaling in the remodeling of E-cad/β-catenin subcellular localization.

Extracellular calcium alters calcium-sensing receptor network integrating intracellular calcium-signaling and related key pathway

G-protein-coupled receptors (GPCRs) are a target for over 34% of current drugs. The calcium-sensing receptor (CaSR), a family C GPCR, regulates systemic calcium (Ca2+) homeostasis that is critical for many physiological, calciotropical, and noncalciotropical outcomes in multiple organs. However, the mechanisms by which extracellular Ca2+ (Ca2+ex) and the CaSR mediate networks of intracellular Ca2+-signaling and players involved throughout the life cycle of CaSR are largely unknown. Here we report the first CaSR protein–protein interactome with 94 novel putative and 8 previously published interactors using proteomics. Ca2+ex promotes enrichment of 66% of the identified CaSR interactors, pertaining to Ca2+ dynamics, endocytosis, degradation, trafficking, and primarily to protein processing in the endoplasmic reticulum (ER). These enhanced ER-related processes are governed by Ca2+ex-activated CaSR which directly modulates ER-Ca2+ (Ca2+ER), as monitored by a novel ER targeted Ca2+-sensor. Moreover, we validated the Ca2+ex dependent colocalizations and interactions of CaSR with ER-protein processing chaperone, 78-kDa glucose regulated protein (GRP78), and with trafficking-related protein. Live cell imaging results indicated that CaSR and vesicle-associated membrane protein-associated A (VAPA) are inter-dependent during Ca2+ex induced enhancement of near-cell membrane expression. This study significantly extends the repertoire of the CaSR interactome and reveals likely novel players and pathways of CaSR participating in Ca2+ER dynamics, agonist mediated ER-protein processing and surface expression.

Functional Analysis of Rare Genetic Variants in the Negative Regulator of Intracellular Calcium Signaling RCAS/SLC10A7

The solute carrier family 10 member SLC10A7 is a negative regulator of intracellular calcium signaling (RCAS). In cell culture, SLC10A7 expression is negatively correlated with store-operated calcium entry (SOCE) via the plasma membrane. SLC10A7-deficient cells have significantly increased calcium influx after treatment with thapsigargin for depletion of ER calcium stores, whereas SLC10A7/RCAS overexpression limits calcium influx. Genetic variants in the human SLC10A7 gene are associated with skeletal dysplasia and amelogenesis imperfecta and reveal loss of function on cellular calcium influx. More recently, an additional disease-related genetic variant (P303L) as well as some novel genetic variants (V235F, T221M, I136M, L210F, P285L, and G146S) have been identified. In the present study, these variants were expressed in HEK293 cells to study their subcellular localization and their effect on cellular calcium influx. All variants were properly sorted to the ER compartment and closely co-localized with the STIM protein, a functional component of SOCE. The variants P303L and L210F showed significantly reduced effects on cellular calcium influx compared to the wild type but still maintained some degree of residual activity. This might explain the milder phenotype of patients bearing the P303L variant and might indicate disease potential for the newly identified L210F variant. In contrast, all other variants behaved like the wild type. In conclusion, the occurrence of variants in the SLC10A7 gene should be considered in patients with skeletal dysplasia and amelogenesis imperfecta. In addition to the already established variants, the present study identifies another potential disease-related SLC10A7/RCAS variant, namely, L210F, which seems to be most frequent in South Asian populations.

Ablation of Collagen VI leads to the release of platelets with altered function

Hemostatic abnormalities and impaired platelet function have been described in patients affected by connective tissue disorders. We observed a moderate bleeding tendency in patients affected by Collagen VI-related disorders and investigated the defects in platelet functionality whose mechanisms are unknown. We demonstrated that megakaryocytes express Collagen VI that is involved in the regulation of functional platelet production. By exploiting a Collagen VI null mouse model (Col6a1-/-), we found that Collagen VI null platelets display significantly increased susceptibility to activation and intracellular calcium signaling. Col6a1-/- megakaryocytes and platelets showed increased expression of STIM1 and ORAI1, the components of Store-Operated Calcium Entry (SOCE), and activation of the mTOR signaling pathway. In vivo mTOR inhibition by rapamycin reduced both STIM1 and ORAI1 expression and calcium flows, resulting in a normalization of platelet susceptibility to activation. These defects were cell-autonomous, as transplantation of lineage-negative bone marrow cells from Col6a1-/- mice into lethally irradiated wild-type animals showed the same alteration in SOCE and platelet activation as compared to Col6a1-/- mice. Peripheral blood platelets of patients affected by Collagen VI-related diseases, Bethlem myopathy and Ullrich congenital muscular dystrophy, displayed increased expression of STIM1 and ORAI1 and were more prone to activation. Altogether, these data demonstrate the importance of Collagen VI in the production of functional platelets by megakaryocytes in mouse models and in Collagen VI-related diseases.

Advances in Intracellular Calcium Signaling Reveal Untapped Targets for Cancer Therapy

Intracellular Ca2+ distribution is a tightly regulated process. Numerous Ca2+ chelating, storage, and transport mechanisms are required to maintain normal cellular physiology. Ca2+-binding proteins, mainly calmodulin and calbindins, sequester free intracellular Ca2+ ions and apportion or transport them to signaling hubs needing the cations. Ca2+ channels, ATP-driven pumps, and exchangers assist the binding proteins in transferring the ions to and from appropriate cellular compartments. Some, such as the endoplasmic reticulum, mitochondria, and lysosomes, act as Ca2+ repositories. Cellular Ca2+ homeostasis is inefficient without the active contribution of these organelles. Moreover, certain key cellular processes also rely on inter-organellar Ca2+ signaling. This review attempts to encapsulate the structure, function, and regulation of major intracellular Ca2+ buffers, sensors, channels, and signaling molecules before highlighting how cancer cells manipulate them to survive and thrive. The spotlight is then shifted to the slow pace of translating such research findings into anticancer therapeutics. We use the PubMed database to highlight current clinical studies that target intracellular Ca2+ signaling. Drug repurposing and improving the delivery of small molecule therapeutics are further discussed as promising strategies for speeding therapeutic development in this area.

Mechanical intercellular communication via matrix-borne cell force transmission during vascular network formation

Intercellular communication is critical to the development and homeostatic function of all tissues. Previous work has shown that cells can communicate mechanically via transmission of cell-generated forces through their surrounding extracellular matrix, but this process is not well understood. Here, we utilized synthetic, electrospun fibrous matrices in conjunction with a microfabrication-based cell patterning approach to examine mechanical intercellular communication (MIC) between endothelial cells (ECs) during the assembly of microvascular networks. We found that cell force-mediated matrix displacements in deformable fibrous matrices underly directional migration of neighboring ECs towards each other prior to the formation of stable cell-cell connections. We also identified a critical role for intracellular calcium signaling mediated by focal adhesion kinase and TRPV4 during MIC that extends to multicellular assembly of vessel-like networks in 3D fibrin hydrogels. The results presented here are critical to the design of biomaterials that support cellular self-assembly for tissue engineering applications.

Proteinase Activated Receptors Mediate the Trypsin-Induced Ca2 + Signaling in Human Uterine Epithelial Cells

Embryo implantation is a complex and tightly regulated process. In humans, uterine luminal epithelium functions as a biosensor gauging the embryo quality and transmitting this information to the underlying endometrial stromal cells. This quality control ensures that only high quality embryos are implanted, while aberrant ones are rejected. The mechanisms of the embryo-uterine mucosa crosstalk remain incompletely understood. Trypsin, a serine protease secreted by the blastocyst, has been implicated in the cross-signaling. Here we address the mechanisms by which trypsin triggers the intracellular calcium signaling in uterine epithelium. We found that protease-activated G-protein coupled receptors are the main mechanism mediating the effects of trypsin in human uterine epithelium. In addition, trypsin activates the epithelial sodium channels thus increasing the intracellular Na+ concentration and promoting Ca2+ entry on the reverse mode of the sodium/calcium exchanger.