Knockdown of STIM1 improves neuronal survival after traumatic neuronal injury through regulating mGluR1-dependent Ca(2+) signaling in mouse cortical neurons

Combined treatment targeting Ca2+ store mediated Ca2+ release and store-operated calcium entry reduces secondary axonal degeneration and improves functional outcome after SCI

Store-operated calcium entry (SOCE) is crucial for cellular processes, including cellular calcium homeostasis and signaling. However, uncontrolled activation of SOCE is implicated in neurological disorders and CNS trauma, but underlying mechanisms remain unclear. We hypothesized that inhibiting SOCE enhances neurological recovery following contusive spinal cord injury (SCI). To investigate key SOCE effectors, stromal interaction molecules (STIM) and Orai channels on neurological recovery following spinal cord injury (SCI), we utilized male and female conditional neuronal Stim1KO mice to investigate the role of neuronal STIM1 in SCI outcome following a mild (30 kdyn) contusion at T13. To investigate Ca2+ store mediated Ca2+ store depletion, and SOCE-mediated refilling in SCI outcome, we inhibited the IP3R with 2-APB, and uncoupled STIM/Orai activation with DPB162-AE, respectively. Intravital microscopy demonstrated that neuron specific Stim1KO increased axonal survival post-SCI. Likewise, pharmaceutical uncoupling of STIM1/Orai activation, alone or combined with IP3R inhibition, enhanced axon survival 24 h after T13 contusion in male and female Thy1YFP+ mice. Behavioral evaluation of female C57BL/6 J mice revealed that DPB162-AE, alone or combined with 2-APB, improved neurological recovery 4-6 weeks following a moderate (50 kdyn) T9 contusion. Immunohistochemical analysis showed that combined treatment improves axonal sparing, increases astrogliosis, and reduces microglia/macrophage density at the injury epicenter 6 weeks post-SCI. These findings reveal a novel role for neuronal STIM1 in "bystander" secondary axonal degeneration, and introduce STIM/Orai functional uncoupler DPB162-AE, combined with IP3R inhibitor 2-APB, as a novel therapeutic approach for improving neurological recovery following SCI.

STIM Proteins: The Gas and Brake of Calcium Entry in Neurons

Stromal interaction molecules (STIM)s are Ca2+ sensors in internal Ca2+ stores of the endoplasmic reticulum. They activate the store-operated Ca2+ channels, which are the main source of Ca2+ entry in non-excitable cells. Moreover, STIM proteins interact with other Ca2+ channel subunits and active transporters, making STIMs an important intermediate molecule in orchestrating a wide variety of Ca2+ influxes into excitable cells. Nevertheless, little is known about the role of STIM proteins in brain functioning. Being involved in many signaling pathways, STIMs replenish internal Ca2+ stores in neurons and mediate synaptic transmission and neuronal excitability. Ca2+ dyshomeostasis is a signature of many pathological conditions of the brain, including neurodegenerative diseases, injuries, stroke, and epilepsy. STIMs play a role in these disturbances not only by supporting abnormal store-operated Ca2+ entry but also by regulating Ca2+ influx through other channels. Here, we review the present knowledge of STIMs in neurons and their involvement in brain pathology.

STIM1 Mediates Methamphetamine-Induced Neuronal Autophagy and Apoptosis

Methamphetamine (METH) is a widely abused amphetamine-type psychoactive drug that causes serious health problems. Previous studies have demonstrated that METH can induce neuron autophagy and apoptosis in vivo and in vitro. However, the molecular mechanisms underlying METH-induced neuron autophagy and apoptosis remain poorly understood. Stromal interacting molecule 1 (STIM1) was hypothesized to be involved in METH-induced neuron autophagy and apoptosis. Therefore, the expression of STIM1 protein was measured and the effect of blocking STIM1 expression with siRNA was investigated in cultured neuronal cells, and the hippocampus and striatum of mice exposed to METH. Furthermore, intracellular calcium concentration and endoplasmic reticulum (ER) stress-related proteins were determined in vitro and in vivo in cells treated with METH. The results suggested that STIM1 mediates METH-induced neuron autophagy by activating the p-Akt/p-mTOR pathway. METH exposure also resulted in increased expression of Orai1, which was reversed after STIM1 silencing. Moreover, the disruption of intracellular calcium homeostasis induced ER stress and up-regulated the expression of pro-apoptotic protein CCAAT/enhancer-binding protein homologous protein (CHOP), resulting in classic mitochondria apoptosis. METH exposure can cause neuronal autophagy and apoptosis by increasing the expression of STIM1 protein; thus, STIM1 may be a potential gene target for therapeutics in METH-caused neurotoxicity.

Ca2+-induced myelin pathology precedes axonal spheroid formation and is mediated in part by store-operated Ca2+ entry after spinal cord injury

The formation of axonal spheroid is a common feature following spinal cord injury. To further understand the source of Ca²⁺ that mediates axonal spheroid formation, we used our previously characterized ex vivo mouse spinal cord model that allows precise perturbation of extracellular Ca²⁺. We performed two-photon excitation imaging of spinal cords isolated from Thy1^YFP+ transgenic mice and applied the lipophilic dye, Nile red, to record dynamic changes in dorsal column axons and their myelin sheaths respectively. We selectively released Ca²⁺ from internal stores using the Ca²⁺ ionophore ionomycin in the presence or absence of external Ca²⁺. We reported that ionomycin dose-dependently induces pathological changes in myelin and pronounced axonal spheroid formation in the presence of normal 2 mM Ca²⁺ artificial cerebrospinal fluid. In contrast, removal of external Ca²⁺ significantly decreased ionomycin-induced myelin and axonal spheroid formation at 2 hours but not at 1 hour after treatment. Using mice that express a neuron-specific Ca²⁺ indicator in spinal cord axons, we confirmed that ionomycin induced significant increases in intra-axonal Ca²⁺, but not in the absence of external Ca²⁺. Periaxonal swelling and the resultant disruption in the axo-myelinic interface often precedes and is negatively correlated with axonal spheroid formation. Pretreatment with YM58483 (500 nM), a well-established blocker of store-operated Ca²⁺ entry, significantly decreased myelin injury and axonal spheroid formation. Collectively, these data reveal that ionomycin-induced depletion of internal Ca²⁺ stores and subsequent external Ca²⁺ entry through store-operated Ca²⁺ entry contributes to pathological changes in myelin and axonal spheroid formation, providing new targets to protect central myelinated fibers.

Too much of a good thing: The case of SOCE in cellular apoptosis

Intracellular calcium (Ca2+) is an essential second messenger in eukaryotic cells regulating numerous cellular functions such as contraction, secretion, immunity, growth, and metabolism. Ca2+ signaling is also a key signal transducer in the intrinsic apoptosis pathway. The store-operated Ca2+ entry pathway (SOCE) is ubiquitously expressed in eukaryotic cells, and is the primary Ca2+ influx pathway in non-excitable cells. SOCE is mediated by the endoplasmic reticulum Ca2+ sensing STIM proteins, and the plasma membrane Ca2+-selective Orai channels. A growing number of studies have implicated SOCE in regulating cell death primarily via the intrinsic apoptotic pathway in a variety of tissues and in response to physiological stressors such as traumatic brain injury, ischemia reperfusion injury, sepsis, and alcohol toxicity. Notably, the literature points to excessive cytosolic Ca2+ influx through SOCE in vulnerable cells as a key factor tipping the balance towards cellular apoptosis. While the literature primarily addresses the functions of STIM1 and Orai1, STIM2, Orai2 and Orai3 are also emerging as potential regulators of cell death. Here, we review the functions of STIM and Orai proteins in regulating cell death and the implications of this regulation to human pathologies.

Stromal Interaction Molecule 1-Mediated Store-Operated Calcium Entry Promotes Autophagy Through AKT/Mammalian Target of Rapamycin Pathway in Hippocampal Neurons After Ischemic Stroke

The pathophysiological process of neuronal injury due to cerebral ischemia is complex among which disturbance of calcium homeostasis and autophagy are two major pathogenesis. However, it remains ambiguous whether the two factors are independent. Stromal interaction molecule 1 (STIM1) is the most important Ca²⁺ sensor mediating the store-operated Ca²⁺ entry (SOCE) through interacting with Orai1 and has recently been proven to participate in autophagy in multiple cells. In this study, we aimed to investigate the potential role of STIM1-induced SOCE on autophagy and whether its regulator function contributes to neuronal injury under hypoxic conditions using in vivo transient middle cerebral artery occlusion (tMCAO) model and in vitro oxygen and glucose deprivation (OGD) primary cultured neuron model respectively. The present data indicated that STIM1 induces autophagic flux impairment in neurons through promoting SOCE and inhibiting AKT/mTOR signaling pathway. Pharmacological inhibition of SOCE or downregulation of STIM1 with siRNA suppressed the autophagic activity in neurons. Moreover, stim1 knockdown attenuated neurological deficits and brain damage after tMCAO, which could be reversed by AKT/mTOR pathway inhibitor AZD5363. Together, the modulation of STIM1 on autophagic activation indicated the potential link between Ca²⁺ homeostasis and autophagy which provided evidence that STIM1 could be a promising therapeutic target for ischemic stroke.

STIM and Orai Mediated Regulation of Calcium Signaling in Age-Related Diseases

Tight spatiotemporal regulation of intracellular Ca²⁺ plays a critical role in regulating diverse cellular functions including cell survival, metabolism, and transcription. As a result, eukaryotic cells have developed a wide variety of mechanisms for controlling Ca²⁺ influx and efflux across the plasma membrane as well as Ca²⁺ release and uptake from intracellular stores. The STIM and Orai protein families comprising of STIM1, STIM2, Orai1, Orai2, and Orai3, are evolutionarily highly conserved proteins that are core components of all mammalian Ca²⁺ signaling systems. STIM1 and Orai1 are considered key players in the regulation of Store Operated Calcium Entry (SOCE), where release of Ca²⁺ from intracellular stores such as the Endoplasmic/Sarcoplasmic reticulum (ER/SR) triggers Ca²⁺ influx across the plasma membrane. SOCE, which has been widely characterized in non-excitable cells, plays a central role in Ca²⁺-dependent transcriptional regulation. In addition to their role in Ca²⁺ signaling, STIM1 and Orai1 have been shown to contribute to the regulation of metabolism and mitochondrial function. STIM and Orai proteins are also subject to redox modifications, which influence their activities. Considering their ubiquitous expression, there has been increasing interest in the roles of STIM and Orai proteins in excitable cells such as neurons and myocytes. While controversy remains as to the importance of SOCE in excitable cells, STIM1 and Orai1 are essential for cellular homeostasis and their disruption is linked to various diseases associated with aging such as cardiovascular disease and neurodegeneration. The recent identification of splice variants for most STIM and Orai isoforms while complicating our understanding of their function, may also provide insight into some of the current contradictions on their roles. Therefore, the goal of this review is to describe our current understanding of the molecular regulation of STIM and Orai proteins and their roles in normal physiology and diseases of aging, with a particular focus on heart disease and neurodegeneration.

Calcium Ions Aggravate Alzheimer's Disease Through the Aberrant Activation of Neuronal Networks, Leading to Synaptic and Cognitive Deficits

Alzheimer’s disease (AD) is a neurodegenerative disease that is characterized by the production and deposition of β-amyloid protein (Aβ) and hyperphosphorylated tau, leading to the formation of β-amyloid plaques (APs) and neurofibrillary tangles (NFTs). Although calcium ions (Ca²⁺) promote the formation of APs and NFTs, no systematic review of the mechanisms by which Ca²⁺ affects the development and progression of AD has been published. Therefore, the current review aimed to fill the gaps between elevated Ca²⁺ levels and the pathogenesis of AD. Specifically, we mainly focus on the molecular mechanisms by which Ca²⁺ affects the neuronal networks of neuroinflammation, neuronal injury, neurogenesis, neurotoxicity, neuroprotection, and autophagy. Furthermore, the roles of Ca²⁺ transporters located in the cell membrane, endoplasmic reticulum (ER), mitochondria and lysosome in mediating the effects of Ca²⁺ on activating neuronal networks that ultimately contribute to the development and progression of AD are discussed. Finally, the drug candidates derived from herbs used as food or seasoning in Chinese daily life are summarized to provide a theoretical basis for improving the clinical treatment of AD.

Targeting CAMKK2 and SOC Channels as a Novel Therapeutic Approach for Sensitizing Acute Promyelocytic Leukemia Cells to All-Trans Retinoic Acid

Calcium ions (Ca²⁺) play important and diverse roles in the regulation of autophagy, cell death and differentiation. Here, we investigated the impact of Ca²⁺ in regulating acute promyelocytic leukemia (APL) cell fate in response to the anti-cancer agent all-trans retinoic acid (ATRA). We observed that ATRA promotes calcium entry through store-operated calcium (SOC) channels into acute promyelocytic leukemia (APL) cells. This response is associated with changes in the expression profiles of ORAI1 and STIM1, two proteins involved in SOC channels activation, as well as with a significant upregulation of several key proteins associated to calcium signaling. Moreover, ATRA treatment of APL cells led to a significant activation of calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) and its downstream effector AMP-activated protein kinase (AMPK), linking Ca²⁺ signaling to autophagy. Pharmacological inhibition of SOC channels and CAMKK2 enhanced ATRA-induced cell differentiation and death. Altogether, our results unravel an ATRA-elicited signaling pathway that involves SOC channels/CAMKK2 activation, induction of autophagy, inhibition of cellular differentiation and suppression of cell death. We suggest that SOC channels and CAMKK2 may constitute novel drug targets for potentiating the anti-cancer effect of ATRA in APL patients.

Plasma Membrane and Organellar Targets of STIM1 for Intracellular Calcium Handling in Health and Neurodegenerative Diseases

Located at the level of the endoplasmic reticulum (ER) membrane, stromal interacting molecule 1 (STIM1) undergoes a complex conformational rearrangement after depletion of ER luminal Ca²⁺. Then, STIM1 translocates into discrete ER-plasma membrane (PM) junctions where it directly interacts with and activates plasma membrane Orai1 channels to refill ER with Ca²⁺. Furthermore, Ca²⁺ entry due to Orai1/STIM1 interaction may induce canonical transient receptor potential channel 1 (TRPC1) translocation to the plasma membrane, where it is activated by STIM1. All these events give rise to store-operated calcium entry (SOCE). Besides the main pathway underlying SOCE, which mainly involves Orai1 and TRPC1 activation, STIM1 modulates many other plasma membrane proteins in order to potentiate the influxof Ca²⁺. Furthermore, it is now clear that STIM1 may inhibit Ca²⁺ currents mediated by L-type Ca²⁺ channels. Interestingly, STIM1 also interacts with some intracellular channels and transporters, including nuclear and lysosomal ionic proteins, thus orchestrating organellar Ca²⁺ homeostasis. STIM1 and its partners/effectors are significantly modulated in diverse acute and chronic neurodegenerative conditions. This highlights the importance of further disclosing their cellular functions as they might represent promising molecular targets for neuroprotection.

A Novel Modulator of STIM2-Dependent Store-Operated Ca2+ Channel Activity

Store-operated Ca2+ entry is one of the main pathways of calcium influx into non-excitable cells, which entails the initiation of many intracellular processes. The endoplasmic reticulum Ca2+ sensors STIM1 and STIM2 are the key components of store-operated Ca2+ entry in mammalian cells. Under physiological conditions, STIM proteins are responsible for store-operated Ca2+ entry activation. The STIM1 and STIM2 proteins differ in their potency for activating different store-operated channels. At the moment, there are no selective modulators of the STIM protein activity. We screened a library of small molecules and found the 4-MPTC compound, which selectively inhibited STIM2-dependent store-operated Ca2+ entry (IC50 = 1 μM) and had almost no effect on the STIM1-dependent activation of store-operated channels.

Store-Operated Calcium Channels in Physiological and Pathological States of the Nervous System

Store-operated calcium channels (SOCs) are widely expressed in excitatory and non-excitatory cells where they mediate significant store-operated calcium entry (SOCE), an important pathway for calcium signaling throughout the body. While the activity of SOCs has been well studied in non-excitable cells, attention has turned to their role in neurons and glia in recent years. In particular, the role of SOCs in the nervous system has been extensively investigated, with links to their dysregulation found in a wide variety of neurological diseases from Alzheimer’s disease (AD) to pain. In this review, we provide an overview of their molecular components, expression, and physiological role in the nervous system and describe how the dysregulation of those roles could potentially lead to various neurological disorders. Although further studies are still needed to understand how SOCs are activated under physiological conditions and how they are linked to pathological states, growing evidence indicates that SOCs are important players in neurological disorders and could be potential new targets for therapies. While the role of SOCE in the nervous system continues to be multifaceted and controversial, the study of SOCs provides a potentially fruitful avenue into better understanding the nervous system and its pathologies.

STIM Proteins and Glutamate Receptors in Neurons: Role in Neuronal Physiology and Neurodegenerative Diseases

Neuronal calcium (Ca²⁺) influx has long been ascribed mainly to voltage-gated Ca²⁺ channels and glutamate receptor channels. Recent research has shown that it is also complemented by stromal interaction molecule (STIM) protein-mediated store-operated Ca²⁺ entry (SOCE). SOCE is described as Ca²⁺ flow into cells in response to the depletion of endoplasmic reticulum Ca²⁺ stores. The present review summarizes recent studies that indicate a relationship between neuronal SOCE that is mediated by STIM1 and STIM2 proteins and glutamate receptors under both physiological and pathological conditions, such as neurodegenerative disorders. We present evidence that the dysregulation of neuronal SOCE and glutamate receptor activity are hallmarks of acute neurodegenerative diseases (e.g., traumatic brain injury and cerebral ischemia) and chronic neurodegenerative diseases (e.g., Alzheimer's disease and Huntington's disease). Emerging evidence indicates a role for STIM proteins and glutamate receptors in neuronal physiology and pathology, making them potential therapeutic targets.

Calcium Deregulation and Mitochondrial Bioenergetics in GDAP1-Related CMT Disease

The pathology of Charcot-Marie-Tooth (CMT), a disease arising from mutations in different genes, has been associated with an impairment of mitochondrial dynamics and axonal biology of mitochondria. Mutations in ganglioside-induced differentiation-associated protein 1 (GDAP1) cause several forms of CMT neuropathy, but the pathogenic mechanisms involved remain unclear. GDAP1 is an outer mitochondrial membrane protein highly expressed in neurons. It has been proposed to play a role in different aspects of mitochondrial physiology, including mitochondrial dynamics, oxidative stress processes, and mitochondrial transport along the axons. Disruption of the mitochondrial network in a neuroblastoma model of GDAP1-related CMT has been shown to decrease Ca²⁺ entry through the store-operated calcium entry (SOCE), which caused a failure in stimulation of mitochondrial respiration. In this review, we summarize the different functions proposed for GDAP1 and focus on the consequences for Ca²⁺ homeostasis and mitochondrial energy production linked to CMT disease caused by different GDAP1 mutations.

Microglial Calcium Release-Activated Calcium Channel Inhibition Improves Outcome from Experimental Traumatic Brain Injury and Microglia-Induced Neuronal Death

Store-operated Ca²⁺ entry (SOCE) mediated by calcium release-activated calcium (CRAC) channels contributes to calcium signaling. The resulting intracellular calcium increases activate calcineurin, which in turn activates immune transcription factor nuclear factor of activated T cells (NFAT). Microglia contain CRAC channels, but little is known whether these channels play a role in acute brain insults. We studied a novel CRAC channel inhibitor to explore the therapeutic potential of this compound in microglia-mediated injury. Cultured microglial BV2 cells were activated by Toll-like receptor agonists or IFNγ. Some cultures were treated with a novel CRAC channel inhibitor (CM-EX-137). Western blots revealed the presence of CRAC channel proteins STIM1 and Orai1 in BV2 cells. CM-EX-137 decreased nitric oxide (NO) release and inducible nitric oxide synthase (iNOS) expression in activated microglia and reduced agonist-induced intracellular calcium accumulation in microglia, while suppressing inflammatory transcription factors nuclear factor kappa B (NF-κB) and nuclear factor of activated T cells (NFAT). Male C57/BL6 mice exposed to experimental brain trauma and treated with CM-EX-137 had decreased lesion size, brain hemorrhage, and improved neurological deficits with decreased microglial activation, iNOS and Orai1 and STIM1 levels. We suggest a novel anti-inflammatory approach for managing acute brain injury. Our observations also shed light on new calcium signaling pathways not described previously in brain injury models.

Role of STIM1 in neurodegeneration

STIM1 is an endoplasmic reticulum (ER) protein with a key role in Ca2+ mobilization. Due to its ability to act as an ER-intraluminal Ca2+ sensor, it regulates store-operated Ca2+ entry (SOCE), which is a Ca2+ influx pathway involved in a wide variety of signalling pathways in eukaryotic cells. Despite its important role in Ca2+ transport, current knowledge about the role of STIM1 in neurons is much more limited. Growing evidence supports a role for STIM1 and SOCE in the preservation of dendritic spines required for long-term potentiation and the formation of memory. In this regard, recent studies have demonstrated that the loss of STIM1, which impairs Ca2+ mobilization in neurons, risks cell viability and could be the cause of neurodegenerative diseases. The role of STIM1 in neurodegeneration and the molecular basis of cell death triggered by low levels of STIM1 are discussed in this review.

Knockdown of RTN1-C attenuates traumatic neuronal injury through regulating intracellular Ca2+ homeostasis

Reticulons (RTNs) are a family of membrane-bound proteins that are dominantly localized to the endoplasmic reticulum (ER) membrane. RTN1-C is one member of RTNs abundantly expressed in the brain and has been shown to mediate neuronal injury in cerebral ischemia models. In the present study, we investigated the role of RTN1-C in an in vitro brain trauma model mimicked by traumatic neuronal injury (TNI) in primary cultured cortical neurons. TNI increased the expression of RTN1-C in cortical neurons but had no effect on RTN1-A and RTN1-B. Knockdown of RTN1-C with specific siRNA (Si-RTN1-C) significantly decreased cytotoxicity and apoptosis after TNI. The results of Ca²⁺ imaging showed that intracellular Ca²⁺ overload induced by TNI was attenuated by RTN1-C knockdown. Furthermore, the activation of metabotropic glutamate receptor 1 (mGluR1)-induced Ca²⁺ response was partially prevented by Si-RTN1-C transfection. We also evaluated the role of RTN1-C in store-operated Ca²⁺ entry (SOCE) in cortical neurons using the ER Ca²⁺ inducer thapsigargin (Tg). The results showed that knockdown of RTN1-C alleviated the SOCE-mediated Ca²⁺ influx and decreased the expression of stromal interactive molecule 1 (STIM1). In summary, the present study found that knockdown of RTN1-C protected neurons against TNI via preservation of intracellular Ca²⁺ homeostasis, which was associated with the inhibition of mGluR1-mediated ER Ca²⁺ release and suppression of STIM1-related SOCE. Thus, RTN1-C might represent a therapeutic target for traumatic brain injury (TBI) research.

Store-Operated Calcium Entry Is Required for mGluR-Dependent Long Term Depression in Cortical Neurons

Store-operated calcium entry (SOCE) is a Calcium (Ca²⁺) influx pathway activated by depletion of intracellular stores that occurs in eukaryotic cells. In neurons, the presence and functions of SOCE are still in question. Here, we show evidences for the existence of SOCE in primary mouse cortical neurons. Endoplasmic reticulum (ER)-Ca²⁺ depletion using thapsigargin (Tg) triggered a maintained cytosolic Ca²⁺ increase, which rapidly returned to basal level in the presence of the SOCE blockers 2-Aminoethoxydiphenyl borate (2-APB) and YM-58483. Neural SOCE is also engaged by activation of metabotropic glutamate receptors (mGluRs) with (S)-3,5-dihydroxyphenylglycine (DHPG) (agonist of group I mGluRs), being an essential mechanism to maintain the mGluR-driven Ca²⁺ signal. Activation of group I of mGluRs triggers long-term depression (LTD) in many brain regions, but the underlying mechanism and, specifically, the necessity of Ca²⁺ increase in the postsynaptic neuron is controversial. In primary cortical neurons, we now show that the inhibition of Ca²⁺ influx through SOCE impaired DHPG-LTD, pointing out a key function of calcium and SOCE in synaptic plasticity.

Membrane ion Channels and Receptors in Animal lifespan Modulation

Acting in the interfaces between environment and membrane compartments, membrane ion channels, and receptors transduce various physical and chemical cues into downstream signaling events. Not surprisingly, these membrane proteins play essential roles in a wide range of cellular processes such as sensory perception, synaptic transmission, cellular growth and development, fate determination, and apoptosis. However, except insulin and insulin-like growth factor receptors, the functions of membrane receptors in animal lifespan modulation have not been well appreciated. On the other hand, although ion channels are popular therapeutic targets for many age-related diseases, their potential roles in aging itself are largely neglected. In this review, we will discuss our current understanding of the conserved functions and mechanisms of membrane ion channels and receptors in the modulation of lifespan across multiple species including Caenorhabditis elegans, Drosophila, mouse, and human.

Role of SOCE architects STIM and Orai proteins in Cell Death

Calcium (Ca²⁺) signaling plays a critical role in regulating plethora of cellular functions including cell survival, proliferation and migration. The perturbations in cellular Ca²⁺ homeostasis can lead to cell death either by activating autophagic pathways or through induction of apoptosis. Endoplasmic reticulum (ER) is the major storehouse of Ca²⁺ within cells and a number of physiological agonists mediate ER Ca²⁺ release by activating IP₃ receptors (IP₃R). This decrease in ER Ca²⁺ levels is sensed by STIM, which physically interacts and activates plasma membrane Ca²⁺ selective Orai channels. Emerging literature implicates a key role for STIM1, STIM2, Orai1 and Orai3 in regulating both cell survival and death pathways. In this review, we will retrospect the work highlighting the role of STIM and Orai homologs in regulating cell death signaling. We will further discuss the rationales that could explain the dual role of STIM and Orai proteins in regulating cell fate decisions.

Emerging pathways driving early synaptic pathology in Alzheimer's disease

The current state of the AD research field is highly dynamic is some respects, while seemingly stagnant in others. Regarding the former, our current lack of understanding of initiating disease mechanisms, the absence of effective treatment options, and the looming escalation of AD patients is energizing new research directions including a much-needed re-focusing on early pathogenic mechanisms, validating novel targets, and investigating relevant biomarkers, among other exciting new efforts to curb disease progression and foremost, preserve memory function. With regard to the latter, the recent disappointing series of failed Phase III clinical trials targeting Aβ and APP processing, in concert with poor association between brain Aβ levels and cognitive function, have led many to call for a re-evaluation of the primacy of the amyloid cascade hypothesis. In this review, we integrate new insights into one of the earliest described signaling abnormalities in AD pathogenesis, namely intracellular Ca²⁺ signaling disruptions, and focus on its role in driving synaptic deficits - which is the feature that does correlate with AD-associated memory loss. Excess Ca²⁺release from intracellular stores such as the endoplasmic reticulum (ER) has been well-described in cellular and animal models of AD, as well as human patients, and here we expand upon recent developments in ER-localized release channels such as the IP₃R and RyR, and the recent emphasis on RyR2. Consistent with ER Ca²⁺ mishandling in AD are recent findings implicating aspects of SOCE, such as STIM2 function, and TRPC3 and TRPC6 levels. Other Ca²⁺-regulated organelles important in signaling and protein handling are brought into the discussion, with new perspectives on lysosomal regulation. These early signaling abnormalities are discussed in the context of synaptic pathophysiology and disruptions in synaptic plasticity with a particular emphasis on short-term plasticity deficits. Overall, we aim to update and expand the list of early neuronal signaling abnormalities implicated in AD pathogenesis, identify specific channels and organelles involved, and link these to proximal synaptic impairments driving the memory loss in AD. This is all within the broader goal of identifying novel therapeutic targets to preserve cognitive function in AD.

Diffuse axonal injury in brain trauma: insights from alterations in neurofilaments

Traumatic brain injury (TBI) from penetrating or closed forces to the cranium can result in a range of forms of neural damage, which culminate in mortality or impart mild to significant neurological disability. In this regard, diffuse axonal injury (DAI) is a major neuronal pathophenotype of TBI and is associated with a complex set of cytoskeletal changes. The neurofilament triplet proteins are key structural cytoskeletal elements, which may also be important contributors to the tensile strength of axons. This has significant implications with respect to how axons may respond to TBI. It is not known, however, whether neurofilament compaction and the cytoskeletal changes that evolve following axonal injury represent a component of a protective mechanism following damage, or whether they serve to augment degeneration and progression to secondary axotomy. Here we review the structure and role of neurofilament proteins in normal neuronal function. We also discuss the processes that characterize DAI and the resultant alterations in neurofilaments, highlighting potential clues to a possible protective or degenerative influence of specific neurofilament alterations within injured neurons. The potential utility of neurofilament assays as biomarkers for axonal injury is also discussed. Insights into the complex alterations in neurofilaments will contribute to future efforts in developing therapeutic strategies to prevent, ameliorate or reverse neuronal degeneration in the central nervous system (CNS) following traumatic injury.