Spontaneous Calcium Transients in Human Neural Progenitor Cells Mediated by Transient Receptor Potential Channels

Calcium and Neural Stem Cell Proliferation

Intracellular calcium plays a pivotal role in central nervous system (CNS) development by regulating various processes such as cell proliferation, migration, differentiation, and maturation. However, understanding the involvement of calcium (Ca2+) in these processes during CNS development is challenging due to the dynamic nature of this cation and the evolving cell populations during development. While Ca2+ transient patterns have been observed in specific cell processes and molecules responsible for Ca2+ homeostasis have been identified in excitable and non-excitable cells, further research into Ca2+ dynamics and the underlying mechanisms in neural stem cells (NSCs) is required. This review focuses on molecules involved in Ca2+ entrance expressed in NSCs in vivo and in vitro, which are crucial for Ca2+ dynamics and signaling. It also discusses how these molecules might play a key role in balancing cell proliferation for self-renewal or promoting differentiation. These processes are finely regulated in a time-dependent manner throughout brain development, influenced by extrinsic and intrinsic factors that directly or indirectly modulate Ca2+ dynamics. Furthermore, this review addresses the potential implications of understanding Ca2+ dynamics in NSCs for treating neurological disorders. Despite significant progress in this field, unraveling the elements contributing to Ca2+ intracellular dynamics in cell proliferation remains a challenging puzzle that requires further investigation.

Modeling human brain rhabdoid tumor by inactivating tumor suppressor genes in induced pluripotent stem cells

Atypical teratoid/rhabdoid tumor (ATRT) is a rare childhood malignancy that originates in the central nervous system. Over ninety-five percent of ATRT patients have biallelic inactivation of the tumor suppressor gene SMARCB1. ATRT has no standard treatment, and a major limiting factor in therapeutic development is the lack of reliable ATRT models. We employed CRISPR/Cas9 gene-editing technology to knock out SMARCB1 and TP53 genes in human episomal induced pluripotent stem cells (Epi-iPSCs), followed by brief neural induction, to generate an ATRT-like model. The dual knockout Epi-iPSCs retained their stemness with the capacity to differentiate into three germ layers. High expression of OCT4 and NANOG in neurally induced knockout spheroids was comparable to that in two ATRT cell lines. Beta-catenin protein expression was higher in SMARCB1-deficient cells and spheroids than in normal Epi-iPSC-derived spheroids. Nucleophosmin, Osteopontin, and Ki-67 proteins were also expressed by the SMARCB1-deficient spheroids. In summary, the tumor model resembled embryonal features of ATRT and expressed ATRT biomarkers at mRNA and protein levels. Ribociclib, PTC-209, and the combination of clofilium tosylate and pazopanib decreased the viability of the ATRT-like cells. This disease modeling scheme may enable the establishment of individualized tumor models with patient-specific mutations and facilitate high-throughput drug testing.

New Insights into TRP Ion Channels in Stem Cells

Transient receptor potential (TRP) ion channels are cationic permeable proteins located on the plasma membrane. TRPs are cellular sensors for perceiving diverse physical and/or chemical stimuli; thus, serving various critical physiological functions, including chemo-sensation, hearing, homeostasis, mechano-sensation, pain, taste, thermoregulation, vision, and even carcinogenesis. Dysregulated TRPs are found to be linked to many human hereditary diseases. Recent studies indicate that TRP ion channels are not only involved in sensory functions but are also implicated in regulating the biological characteristics of stem cells. In the present review, we summarize the expressions and functions of TRP ion channels in stem cells, including cancer stem cells. It offers an overview of the current understanding of TRP ion channels in stem cells.

Magnetic Nanobubble Mechanical Stress Induces the Piezo1-Ca2+ -BMP2/Smad Pathway to Modulate Neural Stem Cell Fate and MRI/Ultrasound Dual Imaging Surveillance for Ischemic Stroke

Neural stem cells (NSCs) are used to treat various nervous system diseases because of their self-renewal ability and multidirectional differentiation potential. However, an insufficient ability to track their migration in vivo and poor control over their survival and differentiation efficiency are two major critical challenges for clinical application. Here, it is shown that when magnetic nanobubbles (MNBs), which are assembled from magnetic nanoparticles, are internalized by NSCs, intramembrane volumetric oscillation of the MNBs induces an increase in intracellular hydrostatic pressure and cytoskeleton force, resulting in the activation of the Piezo1-Ca²⁺ mechanosensory channel. This subsequently triggers the BMP2/Smad biochemical signaling pathway, leading to differentiation of NSCs into the neuronal phenotype. Signaling through the Piezo1-Ca²⁺ -BMP2/Smad pathway can be further accelerated by application of an external shear stress force using low-intensity pulsed ultrasound. More importantly, magnetic resonance imaging and ultrasound imaging surveillance of NSCs based on MNB labeling can be leveraged to provide NSC therapeutic outcomes. Both the in vitro and in vivo findings demonstrate that a bubble nanostructure-induced physical force can modulate and control the mechanical signaling pathway regulating stem cell development.

Thermosensitive receptors in neural stem cells link stress-induced hyperthermia to impaired neurogenesis via microglial engulfment

Social stress impairs hippocampal neurogenesis and causes psychiatric disorders such as depression. Recent studies have highlighted the significance of increased body temperature in stress responses; however, whether and how social stress–induced hyperthermia affects hippocampal neurogenesis remains unknown. Here, using transgenic mice in which the thermosensitive transient receptor potential vanilloid 4 (TRPV4) is conditionally knocked out in Nestin-expressing neural stem cells (NSCs), we found that social defeat stress (SDS)–induced hyperthermia activates TRPV4 in NSCs in the dentate gyrus and thereby impairs hippocampal neurogenesis. Specifically, SDS activated TRPV4 in NSCs and induced the externalization of phosphatidylserine in NSCs, which was recognized by the brain-resident macrophage, microglia, and promoted the microglial engulfment of NSCs. SDS-induced impairment of hippocampal neurogenesis was ameliorated by NSC-specific knockout of TRPV4 or pharmacological removal of microglia. Thus, this study reveals a previously unknown role of thermosensitive receptors expressed by NSCs in stress responses.

The Systemic Administration of the Histamine H1 Receptor Antagonist/Inverse Agonist Chlorpheniramine to Pregnant Rats Impairs the Development of Nigro-Striatal Dopaminergic Neurons

The dopaminergic and histaminergic systems are the first to appear during the development of the nervous system. Through the activation of H₁ receptors (H₁Rs), histamine increases neurogenesis of the cortical deep layers, while reducing the dopaminergic phenotype (cells immunoreactive to tyrosine hydroxylase, TH⁺) in embryo ventral mesencephalon. Although the function of histamine in neuronal differentiation has been studied, the role of H₁Rs in neurogenesis has not been addressed. For this purpose, the H₁R antagonist/inverse agonist chlorpheniramine was systemically administered (5 mg/kg, i.p.) to pregnant Wistar rats (gestational days 12-14, E12-14), and control and experimental embryos (E14 and E16) and pups (21-day-old) were evaluated for changes in nigro-striatal development. Western blot and immunohistochemistry determinations showed a significant increase in the dopaminergic markers' TH and PITX3 in embryos from chlorpheniramine-treated rats at E16. Unexpectedly, 21-day-old pups from the chlorpheniramine-treated group, showed a significant reduction in TH immunoreactivity in the substantia nigra pars compacta and dorsal striatum. Furthermore, striatal dopamine content, evoked [³H]-dopamine release and methamphetamine-stimulated motor activity were significantly lower compared to the control group. These results indicate that H₁R blockade at E14-E16 favors the differentiation of dopaminergic neurons, but hampers their migration, leading to a decrease in dopaminergic innervation of the striatum in post-natal life.

The Transient Receptor Potential Vanilloid Type-2(TRPV2) Ion Channels in Neurogenesis andGliomagenesis: Cross-Talk between TranscriptionFactors and Signaling Molecules

Recently, the finding of cancer stem cells in brain tumors has increased the possibilities for advancing new therapeutic approaches with the aim to overcome the limits of current available treatments. In addition, a role for ion channels, particularly of TRP channels, in developing neurons as well as in brain cancer development and progression have been demonstrated. Herein, we focus on the latest advancements in understanding the role of TRPV2, a Ca²⁺ permeable channel belonging to the TRPV subfamily in neurogenesis and gliomagenesis. TRPV2 has been found to be expressed in both neural progenitor cells and glioblastoma stem/progenitor-like cells (GSCs). In developing neurons, post-translational modifications of TRPV2 (e.g., phosphorylation by ERK2) are required to stimulate Ca²⁺ signaling and nerve growth factor-mediated neurite outgrowth. TRPV2 overexpression also promotes GSC differentiation and reduces gliomagenesis in vitro and in vivo. In glioblastoma, TRPV2 inhibits survival and proliferation, and induces Fas/CD95-dependent apoptosis. Furthermore, by proteomic analysis, the identification of a TRPV2 interactome-based signature and its relation to glioblastoma progression/recurrence, high or low overall survival and drug resistance strongly suggest an important role of the TRPV2 channel as a potential biomarker in glioblastoma prognosis and therapy.

Synergistic Effect of Transient Receptor Potential Antagonist and Amiloride against Maitotoxin Induced Calcium Increase and Cytotoxicity in Human Neuronal Stem Cells

Maitotoxins (MTX) are among the most potent marine toxins identified to date causing cell death trough massive calcium influx. However, the exact mechanism for the MTX-induced calcium entry and cytotoxicity is still unknown. In this work, the effect of MTX-1 on the cytosolic free calcium concentration and cellular viability of human neuronal stem cells was evaluated. MTX elicited a concentration-dependent decrease in cell viability which was already evident after 1 h of treatment with 0.25 nM MTX; however, at a concentration of 0.1 nM, the toxin did not cause cell death even after 14 days of exposure. Moreover, the toxin caused a concentration dependent rise in the cytosolic calcium concentration which was maximal at toxin concentrations of 1 nM and dependent on the presence of extracellular calcium on the bathing solution. Several pharmacological approaches were employed to evaluate the role of canonical transient potential receptor channels (TRPC) on the MTX effects. The results presented here lead to the identification of the TRPC4 channels as contributors to the MTX effects in human neuronal cells. Both, the calcium increase and the cytotoxicity of MTX were either fully (for the calcium increase) or partially (in the case of cytotoxicity) reverted by the blockade of canonical TRPC4 receptors with the selective antagonist ML204. Furthermore, the sodium proton exchanger blocker amiloride also partially inhibited the calcium rise and the cell death elicited by MTX while the combination of amiloride and ML204 fully prevented both the cytotoxicity and the calcium rise elicited by the toxin.

Identification of Ca2+ signaling components in neural stem/progenitor cells during differentiation into neurons and glia in intact and dissociated zebrafish neurospheres

The development of the CNS in vertebrate embryos involves the generation of different sub-types of neurons and glia in a complex but highly-ordered spatio-temporal manner. Zebrafish are commonly used for exploring the development, plasticity and regeneration of the CNS, and the recent development of reliable protocols for isolating and culturing neural stem/progenitor cells (NSCs/NPCs) from the brain of adult fish now enables the exploration of mechanisms underlying the induction/specification/differentiation of these cells. Here, we refined a protocol to generate proliferating and differentiating neurospheres from the entire brain of adult zebrafish. We demonstrated via RT-qPCR that some isoforms of ip3r, ryr and stim are upregulated/downregulated significantly in differentiating neurospheres, and via immunolabelling that 1,4,5-inositol trisphosphate receptor (IP₃R) type-1 and ryanodine receptor (RyR) type-2 are differentially expressed in cells with neuron- or radial glial-like properties. Furthermore, ATP but not caffeine (IP₃R and RyR agonists, respectively), induced the generation of Ca²⁺ transients in cells exhibiting neuron- or glial-like morphology. These results indicate the differential expression of components of the Ca²⁺-signaling toolkit in proliferating and differentiating cells. Thus, given the complexity of the intact vertebrate brain, neurospheres might be a useful system for exploring neurodegenerative disease diagnosis protocols and drug development using Ca²⁺ signaling as a read-out.

Comparative Analysis of Spontaneous and Stimulus-Evoked Calcium Transients in Proliferating and Differentiating Human Midbrain-Derived Stem Cells

Spontaneous cytosolic calcium transients and oscillations have been reported in various tissues of nonhuman and human origin but not in human midbrain-derived stem cells. Using confocal microfluorimetry, we studied spontaneous calcium transients and calcium-regulating mechanisms in a human ventral mesencephalic stem cell line undergoing proliferation and neuronal differentiation. Spontaneous calcium transients were detected in a large fraction of both proliferating (>50%) and differentiating (>55%) cells. We provide evidence for the existence of intracellular calcium stores that respond to muscarinic activation of the cells, having sensitivity for ryanodine and thapsigargin possibly reflecting IP₃ receptor activity and the presence of ryanodine receptors and calcium ATPase pumps. The observed calcium transient activity potentially supports the existence of a sodium-calcium antiporter and the existence of calcium influx induced by depletion of calcium stores. We conclude that the cells have developed the most important mechanisms governing cytosolic calcium homeostasis. This is the first comparative report of spontaneous calcium transients in proliferating and differentiating human midbrain-derived stem cells that provides evidence for the mechanisms that are likely to be involved. We propose that the observed spontaneous calcium transients may contribute to mechanisms involved in cell proliferation, phenotypic differentiation, and general cell maturation.

Activation of TRPV3 Regulates Inflammatory Actions of Human Epidermal Keratinocytes

Transient receptor potential (TRP) ion channels were first characterized on neurons, where they are classically implicated in sensory functions; however, research in recent decades has shown that many of these channels are also expressed on nonneuronal cell types. Emerging findings have highlighted the role of TRP channels in the skin, where they have been shown to be important in numerous cutaneous functions. Of particular interest is TRPV3, which was first described on keratinocytes. Its functional importance was supported when its gain-of-function mutation was linked to Olmsted syndrome, which is characterized by palmoplantar keratoderma, periorifacial hyperkeratosis, diffuse hypotrichosis and alopecia, and itch. Despite these exciting results, we have no information about the role and functionality of TRPV3 on keratinocytes at the cellular level. In this study, we identified TRPV3 expression both on human skin and cultured epidermal keratinocytes. TRPV3 stimulation was found to function as a Ca²⁺-permeable ion channel that suppresses proliferation of epidermal keratinocytes and induces cell death. Stimulation of the channel also triggers a strong proinflammatory response via the NF-κB pathway. Collectively, our data show that TRPV3 is functionally expressed on human epidermal keratinocytes and that it plays a role in cutaneous inflammatory processes.

Critical role of TRPC1 in thyroid hormone-dependent dopaminergic neuron development

Thyroid hormones play a crucial role in midbrain dopaminergic (DA) neuron development. However, the underlying molecular mechanisms remain largely unknown. In this study, we revealed that thyroid hormone treatment evokes significant calcium entry through canonical transient receptor potential (TRPC) channels in ventral midbrain neural stem cells and this calcium signaling is essential for thyroid hormone-dependent DA neuronal differentiation. We also found that TRPC1 is the dominant TRPC channel expressed in ventral midbrain neural stem cells which responds to thyroid hormone. In addition, thyroid hormone increases TRPC1 expression through its receptor alpha 1 during DA neuron differentiation, and, importantly, produces calcium signals by activating TRPC1 channels. In vivo and in vitro gene silencing experiments indicate that TRPC1-mediated calcium signaling is required for thyroid hormone-dependent DA neuronal differentiation. Finally, we confirmed that the activation of OTX2, a determinant of DA neuron development and the expression of which is induced by thyroid hormone, is dependent on TRPC1-mediated calcium signaling. These data revealed the molecular mechanisms of how thyroid hormone regulates DA neuron development from ventral midbrain neural stem cells, particularly endowing a novel physiological relevance to TRPC1 channels.

TLR3-/4-Priming Differentially Promotes Ca(2+) Signaling and Cytokine Expression and Ca(2+)-Dependently Augments Cytokine Release in hMSCs

In human mesenchymal stem cells (hMSCs), toll-like receptor 3 (TLR3) and TLR4 act as key players in the tissue repair process by recognizing their ligands and stimulating downstream processes including cytokine release. The mechanisms of TLR3- and TLR4-mediated cytokine releases from hMSCs remain uncertain. Here, we show that exposure to the TLR3 agonist polyinosinic-polycytidylic acid (poly(I:C)) or incubation with the TLR4 agonist lipopolysaccharide (LPS) increased the mRNA expression levels of TLR3, TLR4 and cytokines in hMSCs. Poly(I:C) exposure rather than LPS incubation not only elevated inositol 1,4,5-triphosphate receptor (IP3R) expression and IP3R-mediated Ca(2+) release, but also promoted Orai and STIM expression as well as store-operated Ca(2+) entry into hMSCs. In addition, we also observed that 21 Ca(2+) signaling genes were significantly up-regulated in response to TLR3 priming of hMSCs by RNA sequencing analysis. Both poly(I:C) and LPS exposure enhanced cytokine release from hMSCs. The enhanced cytokine release vanished upon siRNA knockdown and chelation of intracellular Ca(2+). These data demonstrate that TLR3- and TLR4-priming differentially enhance Ca(2+) signaling and cytokine expression, and Ca(2+) -dependently potentiates cytokine release in hMSCs.

Regulation of neurogenesis by calcium signaling

Calcium (Ca(2+)) signaling has essential roles in the development of the nervous system from neural induction to the proliferation, migration, and differentiation of neural cells. Ca(2+) signaling pathways are shaped by interactions among metabotropic signaling cascades, intracellular Ca(2+) stores, ion channels, and a multitude of downstream effector proteins that activate specific genetic programs. The temporal and spatial dynamics of Ca(2+) signals are widely presumed to control the highly diverse yet specific genetic programs that establish the complex structures of the adult nervous system. Progress in the last two decades has led to significant advances in our understanding of the functional architecture of Ca(2+) signaling networks involved in neurogenesis. In this review, we assess the literature on the molecular and functional organization of Ca(2+) signaling networks in the developing nervous system and its impact on neural induction, gene expression, proliferation, migration, and differentiation. Particular emphasis is placed on the growing evidence for the involvement of store-operated Ca(2+) release-activated Ca(2+) (CRAC) channels in these processes.

The role of Ca(2+) signaling on the self-renewal and neural differentiation of embryonic stem cells (ESCs)

Embryonic stem cells (ESCs) are promising resources for both scientific research and clinical regenerative medicine. With regards to the latter, ESCs are especially useful for treating several neurodegenerative disorders. Two significant characteristics of ESCs, which make them so valuable, are their capacity for self-renewal and their pluripotency, both of which are regulated by the integration of various signaling pathways. Intracellular Ca(2+) signaling is involved in several of these pathways. It is known to be precisely controlled by different Ca(2+) channels and pumps, which play an important role in a variety of cellular activities, including proliferation, differentiation and apoptosis. Here, we provide a review of the recent work conducted to investigate the function of Ca(2+) signaling in the self-renewal and the neural differentiation of ESCs. Specifically, we describe the role of intracellular Ca(2+) mobilization mediated by RyRs (ryanodine receptors); by cADPR (cyclic adenosine 5'-diphosphate ribose) and CD38 (cluster of differentiation 38/cADPR hydrolase); and by NAADP (nicotinic acid adenine dinucleotide phosphate) and TPC2 (two pore channel 2). We also discuss the Ca(2+) influx mediated by SOCs (store-operated Ca(2+) channels), TRPCs (transient receptor potential cation channels) and LTCC (L-type Ca(2+) channels) in the pluripotent ESCs as well as in neural differentiation of ESCs. Moreover, we describe the integration of Ca(2+) signaling in the other signaling pathways that are known to regulate the fate of ESCs.

Polymodal Transient Receptor Potential Vanilloid (TRPV) Ion Channels in Chondrogenic Cells

Mature and developing chondrocytes exist in a microenvironment where mechanical load, changes of temperature, osmolarity and acidic pH may influence cellular metabolism. Polymodal Transient Receptor Potential Vanilloid (TRPV) receptors are environmental sensors mediating responses through activation of linked intracellular signalling pathways. In chondrogenic high density cultures established from limb buds of chicken and mouse embryos, we identified TRPV1, TRPV2, TRPV3, TRPV4 and TRPV6 mRNA expression with RT-PCR. In both cultures, a switch in the expression pattern of TRPVs was observed during cartilage formation. The inhibition of TRPVs with the non-selective calcium channel blocker ruthenium red diminished chondrogenesis and caused significant inhibition of proliferation. Incubating cell cultures at 41 °C elevated the expression of TRPV1, and increased cartilage matrix production. When chondrogenic cells were exposed to mechanical load at the time of their differentiation into matrix producing chondrocytes, we detected increased mRNA levels of TRPV3. Our results demonstrate that developing chondrocytes express a full palette of TRPV channels and the switch in the expression pattern suggests differentiation stage-dependent roles of TRPVs during cartilage formation. As TRPV1 and TRPV3 expression was altered by thermal and mechanical stimuli, respectively, these are candidate channels that contribute to the transduction of environmental stimuli in chondrogenic cells.

HES5 is a key mediator of Wnt-3a-induced neuronal differentiation

Human neural stem/progenitor cell (hNPC)-derived neuronal progeny has been suggested as a promising cell source in a variety of neurodegenerative diseases. Understanding the underlying mechanisms that regulate neuronal differentiation is essential for efficient cell-based therapies. Wnt and Notch signaling has been shown to be crucial in this process. However, their interactions in the process of neuronal differentiation remain elusive. By using human fetal (ReNcell VM) and iPS-derived hNPCs we demonstrate that Wnt-3a immediately induced a transient HES1 upregulation and a sustained HES5 repression that was accompanied by upregulation of the proneural gene MASH1. Conversely, overexpression of HES5 resulted in reduced MASH1 expression. Remarkably, HES5 overexpression efficiently blocked Wnt-3a as well as γ-secretase inhibitor N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT)-induced neuronal differentiation that was accompanied by a strong MASH1 downregulation thus directly linking HES5 repression/MASH1 induction to the proneurogenic effect of Wnt-3a. Stabilized β-catenin or treatment with the specific glycogen synthase kinase 3 beta (GSK3β) inhibitor SB-216763 failed to or only partially mimicked these effects, suggesting a GSK3β- and β-catenin-independent mechanism. Further, inhibition of Wnt-3a-LDL-receptor-related protein 5/6 (LRP5/6) interactions using Dickkopf-1 (Dkk-1) failed to inhibit the modulatory effect of Wnt-3a on HES1/5 and neuronal differentiation. Taken together, these data identify HES5 as a key mediator of the Wnt-3a proneurogenic effect occurring independently of the classical Wnt/β-catenin signaling cascade thus further deciphering crosstalk mechanisms of Wnt and Notch signaling pathways regulating cell fate of hNPCs.

Ion channels in regulation of neuronal regenerative activities

The regeneration of the nervous system is achieved by the regrowth of damaged neuronal axons, the restoration of damaged nerve cells, and the generation of new neurons to replace those that have been lost. In the central nervous system, the regenerative ability is limited by various factors including damaged oligodendrocytes that are essential for neuronal axon myelination, an emerging glial scar, and secondary injury in the surrounding areas. Stem cell transplantation therapy has been shown to be a promising approach to treat neurodegenerative diseases because of the regenerative capability of the stem cells that secrete neurotrophic factors and give rise to differentiated progeny. However, some issues of stem cell transplantation, such as survival, homing, and efficiency of neural differentiation after transplantation, still need to be improved. Ion channels allow for the exchange of ions between the intra- and extracellular spaces or between the cytoplasm and organelles. These ion channels maintain the ion homeostasis in the brain and play a key role in regulating the physiological function of the nervous system and allowing the processing of neuronal signals. In seeking a potential strategy to enhance the efficacy of stem cell therapy in neurological and neurodegenerative diseases, this review briefly summarizes the roles of ion channels in cell proliferation, differentiation, migration, chemotropic axon guidance of growth cones, and axon outgrowth after injury.