TRPC1 Null Exacerbates Memory Deficit and Apoptosis Induced by Amyloid-β

TRPC1: The housekeeper of the hippocampus

The non-selective cation channel TRPC1 is highly expressed in the brain. Recent research shows that neuronal TRPC1 forms heteromeric complexes with TRPC4 and TRPC5, with a small portion existing as homotetramers, primarily in the ER. Given that most studies have focused on the role of heteromeric TRPC1/4/5 complexes, it is crucial to investigate the specific role of homomeric TRPC1 in maintaining brain homeostasis. This review highlights recent findings on TRPC1 in the brain, with a focus on the hippocampus, and compiles the latest data on modulators and their binding sites within the TRPC1/4/5 subfamily to stimulate new research on more selective TRPC1 ligands.

Ginsenosides Decrease β-Amyloid Production via Potentiating Capacitative Calcium Entry

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative disorder characterized by extracellular amyloid plaques composed of amyloid β-peptide (Aβ). Studies have indicated that Ca2+ dysregulation is involved in AD pathology. It is reported that decreased capacitative Ca2+ entry (CCE), a refilling mechanism of intracellular Ca2+, resulting in increased Aβ production. In contrast, constitutive activation of CCE could decrease Aβ production. Panax ginseng Meyer is known to enhance memory and cognitive functions in healthy human subjects. We have previously reported that some ginsenosides decrease Aβ levels in cultured primary neurons and AD mouse model brains. However, mechanisms involved in the Aβ-lowering effect of ginsenosides remain unclear. In this study, we investigated the relationship between CCE and Aβ production by examining the effects of various ginsenosides on CCE levels. Aβ-lowering ginsenosides such as Rk1, Rg5, and Rg3 potentiated CCE. In contrast, ginsenosides without Aβ-lowering effects (Re and Rb2) failed to potentiate CCE. The potentiating effect of ginsenosides on CCE was inhibited by the presence of 2-aminoethoxydipherryl borate (2APB), an inhibitor of CCE. 2APB alone increased Aβ42 production. Furthermore, the presence of 2APB prevented the effects of ginsenosides on Aβ42 production. Our results indicate that ginsenosides decrease Aβ production via potentiating CCE levels, confirming a close relationship between CCE levels and Aβ production. Since CCE levels are closely related to Aβ production, modulating CCE could be a novel target for AD therapeutics.

Amyloid-β mediates intestinal dysfunction and enteric neurons loss in Alzheimer's disease transgenic mouse

Alzheimer's disease (AD) is traditionally considered as a brain disorder featured by amyloid-β (Aβ) deposition. The current study on whether pathological changes of AD extend to the enteric nervous system (ENS) is still in its infancy. In this study, we found enteric Aβ deposition, intestinal dysfunction, and colonic inflammation in the young APP/PS1 mice. Moreover, these mice exhibited cholinergic and nitrergic signaling pathways damages and enteric neuronal loss. Our data show that Aβ42 treatment remarkably affected the gene expression of cultured myenteric neurons and the spontaneous contraction of intestinal smooth muscles. The intra-colon administration of Aβ42 induced ENS dysfunction, brain gliosis, and β-amyloidosis-like changes in the wild-type mice. Our results suggest that ENS mirrors the neuropathology observed in AD brains, and intestinal pathological changes may represent the prodromal events, which contribute to brain pathology in AD. In summary, our findings provide new opportunities for AD early diagnosis and prevention.

Restoration of metal homeostasis: a potential strategy against neurodegenerative diseases

Metal homeostasis is critical to normal neurophysiological activity. Metal ions are involved in the development, metabolism, redox and neurotransmitter transmission of the central nervous system (CNS). Thus, disturbance of homeostasis (such as metal deficiency or excess) can result in serious consequences, including neurooxidative stress, excitotoxicity, neuroinflammation, and nerve cell death. The uptake, transport and metabolism of metal ions are highly regulated by ion channels. There is growing evidence that metal ion disorders and/or the dysfunction of ion channels contribute to the progression of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). Therefore, metal homeostasis-related signaling pathways are emerging as promising therapeutic targets for diverse neurological diseases. This review summarizes recent advances in the studies regarding the physiological and pathophysiological functions of metal ions and their channels, as well as their role in neurodegenerative diseases. In addition, currently available metal ion modulators and in vivo quantitative metal ion imaging methods are also discussed. Current work provides certain recommendations based on literatures and in-depth reflections to improve neurodegenerative diseases. Future studies should turn to crosstalk and interactions between different metal ions and their channels. Concomitant pharmacological interventions for two or more metal signaling pathways may offer clinical advantages in treating the neurodegenerative diseases.

COVID-19-induced neurological symptoms: focus on the role of metal ions

Neurological symptoms are prevalent in both the acute and post-acute phases of coronavirus disease 2019 (COVID-19), and they are becoming a major concern for the prognosis of COVID-19 patients. Accumulation evidence has suggested that metal ion disorders occur in the central nervous system (CNS) of COVID-19 patients. Metal ions participate in the development, metabolism, redox and neurotransmitter transmission in the CNS and are tightly regulated by metal ion channels. COVID-19 infection causes neurological metal disorders and metal ion channels abnormal switching, subsequently resulting in neuroinflammation, oxidative stress, excitotoxicity, neuronal cell death, and eventually eliciting a series of COVID-19-induced neurological symptoms. Therefore, metal homeostasis-related signaling pathways are emerging as promising therapeutic targets for mitigating COVID-19-induced neurological symptoms. This review provides a summary for the latest advances in research related to the physiological and pathophysiological functions of metal ions and metal ion channels, as well as their role in COVID-19-induced neurological symptoms. In addition, currently available modulators of metal ions and their channels are also discussed. Collectively, the current work offers a few recommendations according to published reports and in-depth reflections to ameliorate COVID-19-induced neurological symptoms. Further studies need to focus on the crosstalk and interactions between different metal ions and their channels. Simultaneous pharmacological intervention of two or more metal signaling pathway disorders may provide clinical advantages in treating COVID-19-induced neurological symptoms.

Potential neuroprotection by Dendrobium nobile Lindl alkaloid in Alzheimer's disease models

At present, treatments for Alzheimer's disease can temporarily relieve symptoms but cannot prevent the decline of cognitive ability and other neurodegenerative changes. Dendrobium nobile Lindl alkaloid is the main active component of Dendrobium nobile Lindl. Dendrobium nobile Lindl alkaloid has been shown to resist aging, prolong life span, and exhibit immunomodulatory effects in animals. This review summarizes the mechanisms behind the neuroprotective effects reported in Alzheimer's disease animal models. The neuroprotective effects of Dendrobium nobile Lindl alkaloid have not been studied in patients. The mechanisms by which Dendrobium nobile Lindl alkaloid has been reported to improve cognitive dysfunction in Alzheimer's disease animal models may be associated with extracellular amyloid plaque production, regulation of tau protein hyperphosphorylation, inhibition of neuroinflammation and neuronal apoptosis, activation of autophagy, and enhanced synaptic connections.

Contribution of TRPC Channels in Neuronal Excitotoxicity Associated With Neurodegenerative Disease and Ischemic Stroke

The seven canonical members of transient receptor potential (TRPC) proteins form cation channels that evoke membrane depolarization and intracellular calcium concentration ([Ca²⁺] _i ) rise, which are not only important for regulating cell function but their deregulation can also lead to cell damage. Recent studies have implicated complex roles of TRPC channels in neurodegenerative diseases including ischemic stroke. Brain ischemia reduces oxygen and glucose supply to neurons, i.e., Oxygen and Glucose Deprivation (OGD), resulting in [Ca²⁺] _i elevation, ion dyshomeostasis, and excitotoxicity, which are also common in many forms of neurodegenerative diseases. Although ionotropic glutamate receptors, e.g., N-methyl-D-aspartate receptors, are well established to play roles in excitotoxicity, the contribution of metabotropic glutamate receptors and their downstream effectors, i.e., TRPC channels, should not be neglected. Here, we summarize the current findings about contributions of TRPC channels in neurodegenerative diseases, with a focus on OGD-induced neuronal death and rodent models of cerebral ischemia/reperfusion. TRPC channels play both detrimental and protective roles to neurodegeneration depending on the TRPC subtype and specific pathological conditions involved. When illustrated the mechanisms by which TRPC channels are involved in neuronal survival or death seem differ greatly, implicating diverse and complex regulation. We provide our own data showing that TRPC1/C4/C5, especially TRPC4, may be generally detrimental in OGD and cerebral ischemia/reperfusion. We propose that although TRPC channels significantly contribute to ischemic neuronal death, detailed mechanisms and specific roles of TRPC subtypes in brain injury at different stages of ischemia/reperfusion and in different brain regions need to be carefully and systematically investigated.

Therapeutic Strategies to Target Calcium Dysregulation in Alzheimer's Disease

Alzheimer’s disease (AD) is the most common form of dementia, affecting millions of people worldwide. Unfortunately, none of the current treatments are effective at improving cognitive function in AD patients and, therefore, there is an urgent need for the development of new therapies that target the early cause(s) of AD. Intracellular calcium (Ca²⁺) regulation is critical for proper cellular and neuronal function. It has been suggested that Ca²⁺ dyshomeostasis is an upstream factor of many neurodegenerative diseases, including AD. For this reason, chemical agents or small molecules aimed at targeting or correcting this Ca²⁺ dysregulation might serve as therapeutic strategies to prevent the development of AD. Moreover, neurons are not alone in exhibiting Ca²⁺ dyshomeostasis, since Ca²⁺ disruption is observed in other cell types in the brain in AD. In this review, we examine the distinct Ca²⁺ channels and compartments involved in the disease mechanisms that could be potential targets in AD.

Transient Receptor Potential Canonical (TRPC) Channels: Then and Now

Twenty-five years ago, the first mammalian Transient Receptor Potential Canonical (TRPC) channel was cloned, opening the vast horizon of the TRPC field. Today, we know that there are seven TRPC channels (TRPC1-7). TRPCs exhibit the highest protein sequence similarity to the Drosophila melanogaster TRP channels. Similar to Drosophila TRPs, TRPCs are localized to the plasma membrane and are activated in a G-protein-coupled receptor-phospholipase C-dependent manner. TRPCs may also be stimulated in a store-operated manner, via receptor tyrosine kinases, or by lysophospholipids, hypoosmotic solutions, and mechanical stimuli. Activated TRPCs allow the influx of Ca2+ and monovalent alkali cations into the cytosol of cells, leading to cell depolarization and rising intracellular Ca2+ concentration. TRPCs are involved in the continually growing number of cell functions. Furthermore, mutations in the TRPC6 gene are associated with hereditary diseases, such as focal segmental glomerulosclerosis. The most important recent breakthrough in TRPC research was the solving of cryo-EM structures of TRPC3, TRPC4, TRPC5, and TRPC6. These structural data shed light on the molecular mechanisms underlying TRPCs' functional properties and propelled the development of new modulators of the channels. This review provides a historical overview of the major advances in the TRPC field focusing on the role of gene knockouts and pharmacological tools.

How TRPC Channels Modulate Hippocampal Function

Transient receptor potential canonical (TRPC) proteins constitute a group of receptor-operated calcium-permeable nonselective cationic membrane channels of the TRP superfamily. They are largely expressed in the hippocampus and are able to modulate neuronal functions. Accordingly, they have been involved in different hippocampal functions such as learning processes and different types of memories, as well as hippocampal dysfunctions such as seizures. This review covers the mechanisms of activation of these channels, how these channels can modulate neuronal excitability, in particular the after-burst hyperpolarization, and in the persistent activity, how they control synaptic plasticity including pre- and postsynaptic processes and how they can interfere with cell survival and neurogenesis.

Novel Targets for Stroke Therapy: Special Focus on TRPC Channels and TRPC6

Stroke remains a leading cause of death, disability, and medical care burden worldwide. However, transformation from laboratory findings toward effective pharmacological interventions for clinical stroke has been unsatisfactory. Novel evidence has been gained on the underlying mechanisms and therapeutic potential related to the transient receptor potential (TRP) channels in several disorders. The TRP superfamily consists of a diverse group of Ca²⁺ permeable non-selective cation channels. In particular, the members of TRP subfamilies, TRP canonical (TRPC) channels and TRPC6, have been found in different cell types in the whole body and have high levels of expression in the central nervous system (CNS). Notably, the TRPCs and TRPC6 channel have been implicated in neurite outgrowth and neuronal survival during normal development and in a range of CNS pathological conditions. Recent studies have shown that suppression of TRPC6 channel degradation prevents ischemic neuronal cell death in experimental stroke. Accumulating evidence supports the important functions of TRPC6 in brain ischemia. We have highlighted some crucial advancement that points toward an important involvement of TRPCs and TRPC6 in ischemic stroke. This review will make an overview of the TRP and TRPC channels due to their roles as targets for clinical trials and CNS disorders. Besides, the primary goal is to discuss and update the critical role of TRPC6 channels in stroke and provide a promising target for stroke prevention and therapy.

Inhibitory effect of INT-777 on lipopolysaccharide-induced cognitive impairment, neuroinflammation, apoptosis, and synaptic dysfunction in mice

Neuroinflammation plays an important role in the pathophysiology of Alzheimer's disease (AD) and memory impairment. Herein, we evaluated the neuroprotective effects of 6-ethyl-23(S)-methyl-cholic acid (INT-777), a specific G-protein coupled bile acid receptor 1 (TGR5) agonist, in the LPS-treated mouse model of acute neurotoxicity. Single intracerebroventricular (i.c.v.) injection of LPS remarkably induced mouse behavioral impairments in Morris water maze, novel object recognition, and Y-maze avoidance tests, which were ameliorated by INT-777 (1.5 or 3.0 μg/mouse, i.c.v.) treatment. Importantly, INT-777 treatment reversed LPS-induced TGR5 down-regulation, suppressed the increase of nuclear NF-κB p65, and mitigated neuroinflammation, evidenced by lower proinflammatory cytokines, less activation of microglia, and increased the ratio of p-CREB/CREB or mBDNF/proBDNF in the hippocampus and frontal cortex. In addition, INT-777 treatment also suppressed neuronal apoptosis, as indicated by the reduction of TUNEL-positive cells, decreased activation of caspase-3, increased the ratio of Bcl-2/Bax, and ameliorated synaptic dysfunction as evidenced by the upregulation of PSD95 and synaptophysin in the hippocampus and frontal cortex. Taken together, this study showed the potential neuroprotective effects of INT-777 against LPS-induced cognitive impairment, neuroinflammation, apoptosis, and synaptic dysfunction in mice.

Activation of TRPC1 Channel by Metabotropic Glutamate Receptor mGluR5 Modulates Synaptic Plasticity and Spatial Working Memory

Group I metabotropic glutamate receptors, in particular mGluR5, have been implicated in various forms of synaptic plasticity that are believed to underlie declarative memory. We observed that mGluR5 specifically activated a channel containing TRPC1, an isoform of the canonical family of transient receptor potential (TRPC) channels highly expressed in CA1-3 regions of the hippocampus. TRPC1 is able to form tetrameric complexes with TRPC4 and/or TRPC5 isoforms. TRPC1/4/5 complexes have recently been involved in the efficiency of synaptic transmission in the hippocampus. We therefore used a mouse model devoid of TRPC1 expression to investigate the involvement of mGluR5-TRPC1 pathway in synaptic plasticity and memory formation. Trpc1^-/- mice showed alterations in spatial working memory and fear conditioning. Activation of mGluR increased synaptic excitability in neurons from WT but not from Trpc1^-/- mice. LTP triggered by a theta burst could not maintain over time in brain slices from Trpc1^-/- mice. mGluR-induced LTD was also impaired in these mice. Finally, acute inhibition of TRPC1 by Pico145 on isolated neurons or on brain slices mimicked the genetic depletion of Trpc1 and inhibited mGluR-induced entry of cations and subsequent effects on synaptic plasticity, excluding developmental or compensatory mechanisms in Trpc1^-/- mice. In summary, our results indicate that TRPC1 plays a role in synaptic plasticity and spatial working memory processes.