RyR-mediated calcium release in hippocampal health and disease

Calcium-iron crosstalk in epileptogenesis: Unraveling mechanisms and therapeutic opportunities

Epilepsy, a chronic neurological disorder affecting millions globally, remains poorly understood in its etiology and therapeutic management. Emerging evidence highlights the intricate interplay between calcium (Ca2+) and iron (Fe2+/Fe3+) ions in modulating neuronal excitability, oxidative stress, and synaptic plasticity-key processes implicated in epileptogenesis. This review synthesizes current knowledge on the dual roles of Ca2+ and Fe2+/Fe3+ in epilepsy, emphasizing their bidirectional regulatory mechanisms and pathological synergism. Calcium dysregulation, mediated through voltage-gated channels (e.g., Cav1.2, Cav3.2), store-operated calcium entry (SOCE), and mitochondrial calcium uniporters (MCU), exacerbates neuronal hyperexcitability and seizure propagation. Concurrently, iron overload drives ferroptosis via lipid peroxidation and glutathione depletion, while iron deficiency impairs neurodevelopmental processes. Crucially, Ca2+-Fe2+ crosstalk intersects at multiple nodes: TRP channels (e.g., TRPC6, TRPML1) facilitate dual ion transport; mitochondrial dysfunction links Ca2+ overload with Fe2+-dependent ROS generation; and inflammatory cascades disrupt both ion homeostasis. Clinically, antiepileptic drugs targeting Ca2+ channels (e.g., ethosuximide, zonisamide) and emerging ferroptosis inhibitors (e.g., deferoxamine, RTA 408) underscore the therapeutic potential of modulating these pathways. However, drug resistance and incomplete seizure control necessitate novel strategies leveraging ion interaction networks. We propose that combinatorial approaches targeting Ca2+-Fe2+ signaling hubs-such as MCU-TRPML1 axes or redox-sensitive RyR channels-may offer synergistic benefits. Future research must prioritize cross-model validation, advanced neuroimaging biomarkers, and multidisciplinary frameworks to translate mechanistic insights into precision therapies. This comprehensive analysis positions Ca2+-Fe2+ crosstalk as a pivotal frontier in epilepsy research, bridging molecular pathophysiology with innovative treatment paradigms.

Rare Homozygous Variants in INSR and NFXL1 Are Associated with Severe Treatment-Resistant Psychosis

Psychosis constitutes a cardinal component of schizophrenia and affects nearly fifty percent of those with bipolar disorder. We sought to molecularly characterize psychosis segregating in consanguineous families. Participants from eight multiplex families were evaluated using standardized testing tools. DNA was subjected to exome sequencing followed by Sanger sequencing. Effects of variants were modeled using in-silico tools, while cDNA from a patient's blood sample was analyzed to evaluate the effect of a splice-site variant. Twelve patients in six families were diagnosed with schizophrenia, whereas four patients from two families had psychotic bipolar disorder. Two homozygous rare deleterious variants in INSR (c.2232-7T>G) and NFXL1 (c.1322G>A; p.Cys441Tyr) were identified, which segregated with severe treatment-resistant psychosis/schizophrenia in two families. There were none, or ambiguous findings in the other six families. The predicted deleterious missense variant affected a conserved amino acid, while the intronic variant was predicted to affect splicing. However, cDNA analysis from a patient's blood sample did not reveal an aberrant transcript. Our results indicate that INSR and NFXL1 variants may have a role in psychosis that requires to be investigated further. Lack of molecular diagnosis in some patients suggests the need for genome sequencing to pinpoint the genetic causes.

Estradiol Alleviates Elevated Temperature-Induced Damage in Yak Oviductal Epithelial Cells by Maintaining Endoplasmic Reticulum Calcium Homeostasis

BACKGROUND

The oviduct is an organ that participates in multiple critical reproductive processes and provides essential nutritional support while maintaining a specialized microenvironment. It is particularly vulnerable to damage following heat stress-induced hyperthermia. Therefore, mitigating heat-induced damage to oviduct epithelial cells while preserving their physiological integrity under hyperthermia represents a critical therapeutic goal.

OBJECTIVE

This study aims to simulate the cellular damage state in yak oviduct epithelial cells (YOECs) under thermal challenge by increasing the incubation temperature of cultured cells, while observing changes in cellular injury upon supplementation with 17β-estradiol (E2), in order to explore the underlying cellular regulatory mechanisms involved.

RESULTS

After 48 h of exposure to 41 °C, YOECs exhibited elevated HSP70 and HSP90 protein expression levels, reduced OVGP1 protein expression, and increased apoptotic cells. Compared to the 41 °C group, the E2 + 41 °C group displayed decreased HSP70 protein levels, increased OVGP1 protein expression, and reduced apoptotic cell numbers. Additionally, changes in endoplasmic reticulum calcium ion (ER-Ca2+) distribution and fluorescence intensity variations in ER-Ca2+ regulatory proteins SERCA and IP3R3 were analyzed in the 37 °C, 41 °C, and E2 + 41 °C groups. The ER-Ca2+ distribution pattern in the E2 + 41 °C group remained similar to that of the 37 °C group. However, the fluorescence intensity levels of SERCA and IP3R3 proteins in the E2 + 41 °C group did not recover to levels comparable to the 37 °C group.

CONCLUSION

These findings suggest that E2 may mitigate thermal challenge-induced cellular damage in YOECs by maintaining ER-Ca2+ homeostasis, thereby preserving cellular functionality under elevated temperatures.

Calcium release via IP3R/RyR channels contributes to the nuclear and mitochondrial Ca2+ signals elicited by neuronal stimulation

The brain constantly adapts to environmental changes by modifying the expression of genes that enable synaptic plasticity, learning and memory. The expression of several of these genes requires nuclear calcium (Ca2+) signals, which in turn requires that Ca2+ signals generated by neuronal activity at the synapses or the soma propagate to the nucleus. Since cytoplasmic Ca2+ diffusion is highly restricted, Ca2+ signal propagation to the nucleus requires the participation of other cellular mechanisms. The inositol trisphosphate receptor (IP3R) and the ryanodine receptor (RyR) channels, both of which reside in the endoplasmic reticulum (ER) membrane, play key roles in cellular Ca2+ signal generation. Yet, their roles in the generation of nuclear and mitochondrial Ca2+ signals induced by neuronal activity require further investigation. Here, the impact of IP3R1 or RyR2 knockdown on gabazine-induced nuclear and mitochondrial Ca2+ signals in neurons was evaluated. To this aim, recombinant adeno-associated viruses (rAAVs) were used to introduce small hairpin RNAs (shRNAs) to knockdown type-1 (IP3R1) and type-2 (RyR2) channel expression in cultured rat hippocampal neurons. Additionally, synaptic contact numbers were assessed through immunocytochemistry. Knockdown of IP3R1 or RyR2 channels significantly reduced their protein contents and the generation of gabazine-induced nuclear and mitochondrial Ca2+ signals, without altering synaptic contact numbers. Our results highlight the contribution of IP3R1 and RyR2 channels to the generation of nuclear and mitochondrial Ca2+ signal induced by neuronal activity, reinforcing the role that these Ca2+ release channels play in hippocampal synaptic plasticity and memory formation.

Aging Favors Calcium Activation of Ryanodine Receptor Channels from Brain Cortices and Hippocampi and Hinders Learning and Memory in Male Rats

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.

Voluntary running exercise promotes maturation differentiation and myelination of oligodendrocytes around Aβ plaques in the medial prefrontal cortex of APP/PS1 mice

BACKGROUND

Previous studies have reported that running exercise could improves myelinization in hippocampus. However, the effects of running exercise on the differentiation and maturation of oligodendrocytes, and myelination surrounding Aβ plaques in the medial prefrontal cortex (mPFC) of the Alzheimer's disease (AD) brain have not been reported.

METHODS

Forty 10-month-old male APP/PS1 AD mice were randomly divided into the AD group and the AD running (AD+RUN) group, while 20 age-matched wild-type littermate mice were included in the WT group. The running group received three-month voluntary running exercise in a running cage, while the AD and WT groups were untreated. After the exercise intervention, all mice were given behavioral tests. The total number of mature oligodendrocytes (CC1+) in the mPFC of mice was precisely quantified using unbiased stereology. Myelin basic protein (MBP) and Aβ plaque, as well as the fluorescence area of MBP surrounding Aβ plaques, and the density and morphology of PDGFα+ cells in the mPFC were analyzed using immunofluorescence.

RESULTS

The levels of working memory, cognitive memory, spatial learning and memory ability were decreased significantly in the AD group compared to the WT group, while these functions were significantly improved in the AD+RUN group compared to the AD group. The Aβ plaques in the mPFC were significantly reduced in the AD+RUN group compared to the AD group. The total number of CC1+ cells and the percentage of MBP fluorescence area surrounding Aβ plaques in the mPFC were significantly lower in the AD group compared to the WT group, but they were significantly higher in the AD+RUN group compared to the AD group. The density and branching complexity of PDGFα+ cells surrounding Aβ plaques in the mPFC were significantly higher in the AD group than in the WT group, while the AD+RUN group showed significantly lower density and branching complexity than the AD group. Changes in MBP expression around Aβ plaques, cell density and cell branching complexity of PDGFα+ cells around Aβ plaques were closely related to the number of Aβ plaques in mPFC, and they were also closely related to behavioral changes in mice.

CONCLUSIONS

Voluntary running exercise could reduce Aβ plaque deposition and promote the maturation and myelination capacity of oligodendrocytes surrounding Aβ plaques in the mPFC of AD mice, thereby improving the learning and memory abilities of APP/PS1 transgenic AD mice.

Endoplasmic Reticulum Calcium Signaling in Hippocampal Neurons

The endoplasmic reticulum (ER) is a key organelle in cellular homeostasis, regulating calcium levels and coordinating protein synthesis and folding. In neurons, the ER forms interconnected sheets and tubules that facilitate the propagation of calcium-based signals. Calcium plays a central role in the modulation and regulation of numerous functions in excitable cells. It is a versatile signaling molecule that influences neurotransmitter release, muscle contraction, gene expression, and cell survival. This review focuses on the intricate dynamics of calcium signaling in hippocampal neurons, with particular emphasis on the activation of voltage-gated and ionotropic glutamate receptors in the plasma membrane and ryanodine and inositol 1,4,5-trisphosphate receptors in the ER. These channels and receptors are involved in the generation and transmission of electrical signals and the modulation of calcium concentrations within the neuronal network. By analyzing calcium fluctuations in neurons and the associated calcium handling mechanisms at the ER, mitochondria, endo-lysosome and cytosol, we can gain a deeper understanding of the mechanistic pathways underlying neuronal interactions and information transfer.

Impairment of Glucose Uptake Induced by Elevated Intracellular Ca2+ in Hippocampal Neurons of Malignant Hyperthermia-Susceptible Mice

Malignant hyperthermia (MH) is a genetic disorder triggered by depolarizing muscle relaxants or halogenated inhalational anesthetics in genetically predisposed individuals who have a chronic elevated intracellular Ca2+ concentration ([Ca2+]i) in their muscle cells. We have reported that the muscle dysregulation of [Ca2+]i impairs glucose uptake, leading to the development of insulin resistance in two rodent experimental models. In this study, we simultaneously measured the [Ca2+]i and glucose uptake in single enzymatically isolated hippocampal pyramidal neurons from wild-type (WT) and MH-R163C mice. The [Ca2+]i was recorded using a Ca2+-selective microelectrode, and the glucose uptake was assessed utilizing the fluorescent glucose analog 2-NBDG. The MH-R163C hippocampal neurons exhibited elevated [Ca2+]i and impaired insulin-dependent glucose uptake compared with the WT neurons. Additionally, exposure to isoflurane exacerbated these deficiencies in the MH-R163C neurons, while the WT neurons remained unaffected. Lowering [Ca2+]i using a Ca2+-free solution, SAR7334, or dantrolene increased the glucose uptake in the MH-R163C neurons without significantly affecting the WT neurons. However, further reduction of the [Ca2+]i below the physiological level using BAPTA decreased the insulin-dependent glucose uptake in both genotypes. Furthermore, the homogenates of the MH-R163C hippocampal neurons showed an altered protein expression of the PI3K/Akt signaling pathway and GLUT4 compared with the WT mice. Our study demonstrated that the chronic elevation of [Ca2+]i was sufficient to compromise the insulin-dependent glucose uptake in the MH-R163C hippocampal neurons. Moreover, reducing the [Ca2+]i within a specific range (100-130 nM) could reverse insulin resistance, a hallmark of type 2 diabetes mellitus (T2D).

Cryo-EM investigation of ryanodine receptor type 3

Ryanodine Receptor isoform 3 (RyR3) is a large ion channel found in the endoplasmic reticulum membrane of many different cell types. Within the hippocampal region of the brain, it is found in dendritic spines and regulates synaptic plasticity. It controls myogenic tone in arteries and is upregulated in skeletal muscle in early development. RyR3 has a unique functional profile with a very high sensitivity to activating ligands, enabling high gain in Ca2+-induced Ca2+ release. Here we solve high-resolution cryo-EM structures of RyR3 in non-activating and activating conditions, revealing structural transitions that occur during channel opening. Addition of activating ligands yields only open channels, indicating an intrinsically high open probability under these conditions. RyR3 has reduced binding affinity to the auxiliary protein FKBP12.6 due to several sequence variations in the binding interface. We map disease-associated sequence variants and binding sites for known pharmacological agents. The N-terminal region contains ligand binding sites for a putative chloride anion and ATP, both of which are targeted by sequence variants linked to epileptic encephalopathy.

Calcium channel signalling at neuronal endoplasmic reticulum-plasma membrane junctions

Neurons are highly specialised cells that need to relay information over long distances and integrate signals from thousands of synaptic inputs. The complexity of neuronal function is evident in the morphology of their plasma membrane (PM), by far the most intricate of all cell types. Yet, within the neuron lies an organelle whose architecture adds another level to this morphological sophistication - the endoplasmic reticulum (ER). Neuronal ER is abundant in the cell body and extends to distant axonal terminals and postsynaptic dendritic spines. It also adopts specialised structures like the spine apparatus in the postsynapse and the cisternal organelle in the axon initial segment. At membrane contact sites (MCSs) between the ER and the PM, the two membranes come in close proximity to create hubs of lipid exchange and Ca2+ signalling called ER-PM junctions. The development of electron and light microscopy techniques extended our knowledge on the physiological relevance of ER-PM MCSs. Equally important was the identification of ER and PM partners that interact in these junctions, most notably the STIM-ORAI and VAP-Kv2.1 pairs. The physiological functions of ER-PM junctions in neurons are being increasingly explored, but their molecular composition and the role in the dynamics of Ca2+ signalling are less clear. This review aims to outline the current state of research on the topic of neuronal ER-PM contacts. Specifically, we will summarise the involvement of different classes of Ca2+ channels in these junctions, discuss their role in neuronal development and neuropathology and propose directions for further research.