Disturbed Ca2+ signaling and apoptosis of medium spiny neurons in Huntington's disease

Multi-epitope immunocapture of huntingtin reveals striatum-selective molecular signatures

Huntington's disease (HD) is a debilitating neurodegenerative disorder affecting an individual's cognitive and motor abilities. HD is caused by a mutation in the huntingtin gene producing a toxic polyglutamine-expanded protein (mHTT) and leading to degeneration in the striatum and cortex. Yet, the molecular signatures that underlie tissue-specific vulnerabilities remain unclear. Here, we investigate this aspect by leveraging multi-epitope protein interaction assays, subcellular fractionation, thermal proteome profiling, and genetic modifier assays. The use of human cell, mouse, and fly models afforded capture of distinct subcellular pools of epitope-enriched and tissue-dependent interactions linked to dysregulated cellular pathways and disease relevance. We established an HTT association with nearly all subunits of the transcriptional regulatory Mediator complex (20/26), with preferential enrichment of MED15 in the tail domain. Using HD and KO models, we find HTT modulates the subcellular localization and assembly of the Mediator. We demonstrated striatal enriched and functional interactions with regulators of calcium homeostasis and chromatin remodeling, whose disease relevance was supported by HD fly genetic modifiers assays. Altogether, we offer insights into tissue- and localization-dependent (m)HTT functions and pathobiology.

Role of Thrombosis in Neurodegenerative Diseases: An Intricate Mechanism of Neurovascular Complications

Thrombosis, the formation of blood clots in arteries or veins, poses a significant health risk by disrupting the blood flow. It can potentially lead to major cardiovascular complications such as acute myocardial infarction or ischemic stroke (arterial thrombosis) and deep vein thrombosis or pulmonary embolism (venous thrombosis). Nevertheless, over the course of several decades, researchers have observed an association between different cardiovascular events and neurodegenerative diseases, which progressively harm and impair parts of the nervous system, particularly the brain. Furthermore, thrombotic complications have been identified in numerous clinical instances of neurodegenerative diseases, particularly Alzheimer's disease, Parkinson's disease, multiple sclerosis, and Huntington's disease. Substantial research indicates that endothelial dysfunction, vascular inflammation, coagulation abnormalities, and platelet hyperactivation are commonly observed in these conditions, collectively contributing to an increased risk of thrombosis. Thrombosis can, in turn, contribute to the onset, pathogenesis, and severity of these neurological disorders. Hence, this concise review comprehensively explores the correlation between cardiovascular diseases and neurodegenerative diseases, elucidating the cellular and molecular mechanisms of thrombosis in these neurodegenerative diseases. Additionally, a detailed discussion is provided on the commonly employed antithrombotic medications in the context of these neuronal diseases.

Unknown roles of tau pathology in neurological disorders. Challenges and new perspectives

Aging presents progressive changes that increase the susceptibility of the central nervous system (CNS) to suffer neurological disorders (NDs). Several studies have reported that an aged brain suffering from NDs shows the presence of pathological forms of tau protein, a microtubule accessory protein (MAP) critical for neuronal function. In this context, accumulative evidence has shown a pivotal contribution of pathological forms of tau to Alzheimer's disease (AD) and tauopathies. However, current investigations have implicated tau toxicity in other NDs that affect the central nervous system (CNS), including Parkinson's disease (PD), Huntington's disease (HD), Traumatic brain injury (TBI), Multiple sclerosis (MS), and Amyotrophic lateral sclerosis (ALS). These diseases are long-term acquired, affecting essential functions such as motor movement, cognition, hearing, and vision. Previous evidence indicated that toxic forms of tau do not have a critical contribution to the genesis or progression of these diseases. However, recent studies have shown that these tau forms contribute to neuronal dysfunction, inflammation, oxidative damage, and mitochondrial impairment events that contribute to the pathogenesis of these NDs. Recent studies have suggested that these neuropathologies could be associated with a prion-like behavior of tau, which induces a pathological dissemination of these toxic protein forms to different brain areas. Moreover, it has been suggested that this toxic propagation of tau from neurons into neighboring cells impairs the function of glial cells, oligodendrocytes, and endothelial cells by affecting metabolic function and mitochondrial health and inducing oxidative damage by tau pathology. Therefore, in this review, we will discuss current evidence demonstrating the critical role of toxic tau forms on NDs not related to AD and how its propagation and induced-bioenergetics failure may contribute to the pathogenic mechanism present in these NDs.

Calcium Ions in the Physiology and Pathology of the Central Nervous System

Calcium ions play a key role in the physiological processes of the central nervous system. The intracellular calcium signal, in nerve cells, is part of the neurotransmission mechanism. They are responsible for stabilizing membrane potential and controlling the excitability of neurons. Calcium ions are a universal second messenger that participates in depolarizing signal transduction and contributes to synaptic activity. These ions take an active part in the mechanisms related to memory and learning. As a result of depolarization of the plasma membrane or stimulation of receptors, there is an extracellular influx of calcium ions into the cytosol or mobilization of these cations inside the cell, which increases the concentration of these ions in neurons. The influx of calcium ions into neurons occurs via plasma membrane receptors and voltage-dependent ion channels. Calcium channels play a key role in the functioning of the nervous system, regulating, among others, neuronal depolarization and neurotransmitter release. Channelopathies are groups of diseases resulting from mutations in genes encoding ion channel subunits, observed including the pathophysiology of neurological diseases such as migraine. A disturbed ability of neurons to maintain an appropriate level of calcium ions is also observed in such neurodegenerative processes as Alzheimer's disease, Parkinson's disease, Huntington's disease, and epilepsy. This review focuses on the involvement of calcium ions in physiological and pathological processes of the central nervous system. We also consider the use of calcium ions as a target for pharmacotherapy in the future.

α-Tocotrienol Protects Neurons by Preventing Tau Hyperphosphorylation via Inhibiting Microtubule Affinity-Regulating Kinase Activation

In the pathological process of Alzheimer's disease, neuronal cell death is closely related to the accumulation of reactive oxygen species. Our previous studies have found that oxidative stress can activate microtubule affinity-regulating kinases, resulting in elevated phosphorylation levels of tau protein specifically at the Ser262 residue in N1E-115 cells that have been subjected to exposure to hydrogen peroxide. This process may be one of the pathogenic mechanisms of Alzheimer's disease. Vitamin E is a fat-soluble, naturally occurring antioxidant that plays a crucial role in biological systems. This study aimed to examine the probable processes that contribute to the inhibiting effect on the abnormal phosphorylation of tau protein and the neuroprotective activity of a particular type of vitamin E, α-tocotrienol. The experimental analysis revealed that α-tocotrienol showed significant neuroprotective effects in the N1E-115 cell line. Our data further suggest that one of the mechanisms underlying the neuroprotective effects of α-tocotrienol may be through the inhibition of microtubule affinity-regulated kinase activation, which significantly reduces the oxidative stress-induced aberrant elevation of p-Tau (Ser262) levels. These results indicate that α-tocotrienol may represent an intriguing strategy for treating or preventing Alzheimer's disease.

Altered mitochondrial Ca2+ uptake in presynaptic terminals of cultured striatal and cortical neurons from the zQ175 knock-in mouse model of Huntington's disease

Calcium (Ca2+) in mitochondria plays crucial roles in neurons including modulating metabolic processes. Moreover, excessive Ca2+ in mitochondria can lead to cell death. Thus, altered mitochondrial Ca2+ regulation has been implicated in several neurodegenerative diseases including Huntington's disease (HD). HD is a progressive hereditary neurodegenerative disorder that results from abnormally expanded cytosine-adenine-guanine trinucleotide repeats in the huntingtin gene. One neuropathological hallmark of HD is neuronal loss in the striatum and cortex. However, mechanisms underlying selective loss of striatal and cortical neurons in HD remain elusive. Here, we measured the basal Ca2+ levels and Ca2+ uptake in single presynaptic mitochondria during 100 external electrical stimuli using highly sensitive mitochondria-targeted Ca2+ indicators in cultured cortical and striatal neurons of a knock-in mouse model of HD (zQ175 mice). We observed elevated presynaptic mitochondrial Ca2+ uptake during 100 electrical stimuli in HD cortical neurons compared with wild-type (WT) cortical neurons. We also found the highly elevated presynaptic mitochondrial basal Ca2+ level and Ca2+ uptake during 100 stimuli in HD striatal neurons. The elevated presynaptic mitochondrial basal Ca2+ level in HD striatal neurons and Ca2+ uptake during stimulation in HD striatal and cortical neurons can disrupt neurotransmission and induce mitochondrial Ca2+ overload, eventually leading to neuronal death in the striatum and cortex of HD.

Mitochondrial Permeability Transition, Cell Death and Neurodegeneration

Neurodegenerative diseases are chronic conditions occurring when neurons die in specific brain regions that lead to loss of movement or cognitive functions. Despite the progress in understanding the mechanisms of this pathology, currently no cure exists to treat these types of diseases: for some of them the only help is alleviating the associated symptoms. Mitochondrial dysfunction has been shown to be involved in the pathogenesis of most the neurodegenerative disorders. The fast and transient permeability of mitochondria (the mitochondrial permeability transition, mPT) has been shown to be an initial step in the mechanism of apoptotic and necrotic cell death, which acts as a regulator of tissue regeneration for postmitotic neurons as it leads to the irreparable loss of cells and cell function. In this study, we review the role of the mitochondrial permeability transition in neuronal death in major neurodegenerative diseases, covering the inductors of mPTP opening in neurons, including the major ones-free radicals and calcium-and we discuss perspectives and difficulties in the development of a neuroprotective strategy based on the inhibition of mPTP in neurodegenerative disorders.

Desipramine induces eryptosis in human erythrocytes, an effect blunted by nitric oxide donor sodium nitroprusside and N-acetyl-L-cysteine but enhanced by Calcium depletion

Background: Desipramine a representative of tricyclic antidepressants (TCAs) promotes recovery of depressed patients by inhibition of reuptake of neurotransmitters serotonin (SER) and norepinephrine (NE) in the presynaptic membrane by directly blocking their respective transporters SERT and NET.Aims: To study the effect of desipramine on programmed erythrocyte death (eryptosis) and explore the underlying mechanisms.Methods: Phosphatidylserine (PS) exposure on the cell surface as marker of cell death was estimated from annexin-V-binding, cell volume from forward scatter in flow cytometry. Hemolysis was determined photometrically, and intracellular glutathione [GSH]i from high performance liquid chromatography.Results: Desipramine dose-dependently significantly enhanced the percentage of annexin-V-binding cells and didn´t impact glutathione (GSH) synthesis. Desipramine-induced eryptosis was significantly reversed by pre-treatment of erythrocytes with either nitric oxide (NO) donor sodium nitroprusside (SNP) or N-acetyl-L-cysteine (NAC). The highest inhibitory effect was obtained by using both inhibitors together. Calcium (Ca2+) depletion aggravated desipramine-induced eryptosis. Changing the order of treatment, i.e. desipramine first followed by inhibitors, could not influence the inhibitory effect of SNP or NAC.Conclusion: Antidepressants-caused intoxication can be treated by SNP and NAC, respectively. B) Patients with chronic hypocalcemia should not be treated with tricyclic anti-depressants or their dose should be noticeably reduced.

Dysfunction of cAMP-Protein Kinase A-Calcium Signaling Axis in Striatal Medium Spiny Neurons: A Role in Schizophrenia and Huntington's Disease Neuropathology

Background

Striatal medium spiny neurons (MSNs) are preferentially lost in Huntington's disease. Genomic studies also implicate a direct role for MSNs in schizophrenia, a psychiatric disorder known to involve cortical neuron dysfunction. It remains unknown whether the two diseases share similar MSN pathogenesis or if neuronal deficits can be attributed to cell type-dependent biological pathways. Transcription factor BCL11B, which is expressed by all MSNs and deep layer cortical neurons, was recently proposed to drive selective neurodegeneration in Huntington's disease and identified as a candidate risk gene in schizophrenia.

Methods

Using human stem cell-derived neurons lacking BCL11B as a model, we investigated cellular pathology in MSNs and cortical neurons in the context of these disorders. Integrative analyses between differentially expressed transcripts and published genome-wide association study datasets identified cell type-specific disease-related phenotypes.

Results

We uncover a role for BCL11B in calcium homeostasis in both neuronal types, while deficits in mitochondrial function and PKA (protein kinase A)-dependent calcium transients are detected only in MSNs. Moreover, BCL11B-deficient MSNs display abnormal responses to glutamate and fail to integrate dopaminergic and glutamatergic stimulation, a key feature of striatal neurons in vivo. Gene enrichment analysis reveals overrepresentation of disorder risk genes among BCL11B-regulated pathways, primarily relating to cAMP-PKA-calcium signaling axis and synaptic signaling.

Conclusions

Our study indicates that Huntington's disease and schizophrenia are likely to share neuronal pathophysiology where dysregulation of intracellular calcium homeostasis is found in both striatal and cortical neurons. In contrast, reduction in PKA signaling and abnormal dopamine/glutamate receptor signaling is largely specific to MSNs.

Genetic Ablation of Inositol 1,4,5-Trisphosphate Receptor Type 2 (IP3R2) Fails to Modify Disease Progression in a Mouse Model of Spinocerebellar Ataxia Type 3

Spinocerebellar ataxia type 3 (SCA3) is a rare neurodegenerative disease caused by an abnormal polyglutamine expansion within the ataxin-3 protein (ATXN3). This leads to neurodegeneration of specific brain and spinal cord regions, resulting in a progressive loss of motor function. Despite neuronal death, non-neuronal cells, including astrocytes, are also involved in SCA3 pathogenesis. Astrogliosis is a common pathological feature in SCA3 patients and animal models of the disease. However, the contribution of astrocytes to SCA3 is not clearly defined. Inositol 1,4,5-trisphosphate receptor type 2 (IP3R2) is the predominant IP3R in mediating astrocyte somatic calcium signals, and genetically ablation of IP3R2 has been widely used to study astrocyte function. Here, we aimed to investigate the relevance of IP3R2 in the onset and progression of SCA3. For this, we tested whether IP3R2 depletion and the consecutive suppression of global astrocytic calcium signalling would lead to marked changes in the behavioral phenotype of a SCA3 mouse model, the CMVMJD135 transgenic line. This was achieved by crossing IP3R2 null mice with the CMVMJD135 mouse model and performing a longitudinal behavioral characterization of these mice using well-established motor-related function tests. Our results demonstrate that IP3R2 deletion in astrocytes does not modify SCA3 progression.

NAADP-Evoked Ca2+ Signaling Leads to Mutant Huntingtin Aggregation and Autophagy Impairment in Murine Astrocytes

Huntington’s disease (HD) is a progressive neurodegenerative disease characterized by mutations in the huntingtin gene (mHtt), causing an unstable repeat of the CAG trinucleotide, leading to abnormal long repeats of polyglutamine (poly-Q) in the N-terminal region of the huntingtin, which form abnormal conformations and aggregates. Alterations in Ca2+ signaling are involved in HD models and the accumulation of mutated huntingtin interferes with Ca2+ homeostasis. Lysosomes are intracellular Ca2+ storages that participate in endocytic and lysosomal degradation processes, including autophagy. Nicotinic acid adenine dinucleotide phosphate (NAADP) is an intracellular second messenger that promotes Ca2+ release from the endo-lysosomal system via Two-Pore Channels (TPCs) activation. Herein, we show the impact of lysosomal Ca2+ signals on mHtt aggregation and autophagy blockade in murine astrocytes overexpressing mHtt-Q74. We observed that mHtt-Q74 overexpression causes an increase in NAADP-evoked Ca2+ signals and mHtt aggregation, which was inhibited in the presence of Ned-19, a TPC antagonist, or BAPTA-AM, a Ca2+ chelator. Additionally, TPC2 silencing revert the mHtt aggregation. Furthermore, mHtt has been shown co-localized with TPC2 which may contribute to its effects on lysosomal homeostasis. Moreover, NAADP-mediated autophagy was also blocked since its function is dependent on lysosomal functionality. Taken together, our data show that increased levels of cytosolic Ca2+ mediated by NAADP causes mHtt aggregation. Additionally, mHtt co-localizes with the lysosomes, where it possibly affects organelle functions and impairs autophagy.

Trifluoperazine reduces apoptosis and inflammatory responses in traumatic brain injury by preventing the accumulation of Aquaporin4 on the surface of brain cells

Currently, no specific and standard treatment for traumatic brain injury (TBI) has been developed. Therefore, studies on new therapeutic drugs for TBI treatment are urgently needed. Trifluoperazine (TFP) is a therapeutic agent for the treatment of psychiatric disorders that reduces edema of the central nervous system. However, the specific working mechanism of TFP is not fully understood in TBI. In this study, the immunofluorescence co-localization analysis revealed that the area and intensity covered by Aquaporin4 (AQP4) on the surface of brain cells (astrocyte endfeet) increased significantly after TBI. In contrast, TFP treatment reversed these phenomena. This finding showed that TFP inhibited AQP4 accumulation on the surface of brain cells (astrocyte endfeet). The tunel fluorescence intensity and fluorescence area were lower in the TBI+TFP group compared to the TBI group. Additionally, the brain edema, brain defect area, and modified neurological severity score (mNSS) were lower in the TBI+TFP. The RNA-seq was performed on the cortical tissues of rats in the Sham, TBI, and TBI+TFP groups. A total of 3774 genes differently expressed between the TBI and the Sham group were identified. Of these, 2940 genes were up-regulated and 834 genes were down-regulated. A total of 1845 differently expressed genes between the TBI+TFP and TBI group were also identified, in which 621 genes were up-regulated and 1224 genes were down-regulated. Analysis of the common differential genes in the three groups showed that TFP could reverse the expression of apoptosis and inflammation genes. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that the differentially expressed genes (DEGs) were highly enriched in the signaling pathways regulating inflammation. In conclusion, TFP alleviates brain edema after TBI by preventing the accumulation of AQP4 on the surface of brain cells. Generally, TFP alleviates apoptosis and inflammatory response induced by TBI, and promotes the recovery of nerve function in rats after TBI. Thus, TFP is a potential therapeutic agent for TBI treatment.

Mitochondrial Medicine: A Promising Therapeutic Option Against Various Neurodegenerative Disorders

Abnormal mitochondrial morphology and metabolic dysfunction have been observed in many neurodegenerative disorders (NDDs). Mitochondrial dysfunction can be caused by aberrant mitochondrial DNA, mutant nuclear proteins that interact with mitochondria directly or indirectly, or for unknown reasons. Since mitochondria play a significant role in neurodegeneration, mitochondriatargeted therapies represent a prosperous direction for the development of novel drug compounds that can be used to treat NDDs. This review gives a brief description of how mitochondrial abnormalities lead to various NDDs such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. We further explore the promising therapeutic effectiveness of mitochondria- directed antioxidants, MitoQ, MitoVitE, MitoPBN, and dimebon. We have also discussed the possibility of mitochondrial gene therapy as a therapeutic option for these NDDs.

Small-Molecule Disruptors of Mutant Huntingtin-Calmodulin Protein-Protein Interaction Attenuate Deleterious Effects of Mutant Huntingtin

Huntington's disease is a progressive and lethal neurodegenerative disease caused by an increased CAG repeat mutation in exon 1 of the huntingtin gene (mutant huntingtin). Current drug treatments provide only limited symptomatic relief without impacting disease progression. Previous studies in our lab and others identified the abnormal binding of mutant huntingtin protein with calmodulin, a key regulator of calcium signaling. Disrupting the abnormal binding of mutant huntingtin to calmodulin reduces perturbations caused by mutant huntingtin in cell and mouse models of Huntington's disease and importantly normalizes receptor-stimulated calcium release. Using a series of high-throughput in vitro and cell-based screening assays, we identified numerous small-molecule hits that disrupt the binding of mutant huntingtin to calmodulin and demonstrate protective effects. Iterative optimization of one hit resulted in nontoxic, selective compounds that are protective against mutant huntingtin cytotoxicity and normalized receptor-stimulated intracellular calcium release in PC12 cell models of Huntington's disease. Importantly, the compounds do not work by reducing the levels of mutant huntingtin, allowing this strategy to complement future molecular approaches to reduce mutant huntingtin expression. Our novel scaffold will serve as a prototype for further drug development in Huntington's disease. These studies indicate that the development of small-molecule compounds that disrupt the binding of mutant huntingtin to calmodulin is a promising approach for the advancement of therapeutics to treat Huntington's disease.

Huntington's disease iPSC models-using human patient cells to understand the pathology caused by expanded CAG repeats

A major advance in the study of Huntington's disease (HD) has been the development of human disease models employing induced pluripotent stem cells (iPSCs) derived from patients with HD. Because iPSCs provide an unlimited source of cells and can be obtained from large numbers of HD patients, they are a uniquely valuable tool for investigating disease mechanisms and for discovering potential disease-modifying therapeutics. Here, we summarize some of the important findings in HD pathophysiology that have emerged from studies of patient-derived iPSC lines. Because they retain the genome and actual disease mutations of the patient, they provide a cell source to investigate genetic contributions to the disease. iPSCs provide advantages over other disease models. While iPSC-based technology erases some epigenetic marks, newly developed transdifferentiation methods now let us investigate epigenetic factors that control expression of mutant huntingtin (mHTT). Human HD iPSC lines allow us to investigate how endogenous levels of mHTT affect cell health, in contrast to other models that often rely on overexpressing the protein. iPSCs can be differentiated into neurons and other disease-related cells such as astrocytes from different brain regions to study brain regional differences in the disease process, as well as the cell-cell dependencies involved in HD-associated neurodegeneration. They also serve as a tissue source to investigate factors that impact CAG repeat instability, which is involved in regional differences in neurodegeneration in the HD brain. Human iPSC models can serve as a powerful model system to identify genetic modifiers that may impact disease onset, progression, and symptomatology, providing novel molecular targets for drug discovery.

Human Pluripotent Stem Cell-Derived Medium Spiny Neuron-like Cells Exhibit Gene Desensitization

Gene desensitization in response to a repeated stimulus is a complex phenotype important across homeostatic and disease processes, including addiction, learning, and memory. These complex phenotypes are being characterized and connected to important physiologically relevant functions in rodent systems but are difficult to capture in human models where even acute responses to important neurotransmitters are understudied. Here through transcriptomic analysis, we map the dynamic responses of human stem cell-derived medium spiny neuron-like cells (hMSN-like cells) to dopamine. Furthermore, we show that these human neurons can reflect and capture cellular desensitization to chronic versus acute administration of dopamine. These human cells are further able to capture complex receptor crosstalk in response to the pharmacological perturbations of distinct dopamine receptor subtypes. This study demonstrates the potential utility and remaining challenges of using human stem cell-derived neurons to capture and study the complex dynamic mechanisms of the brain.

Inflammation and Nitro-oxidative Stress as Drivers of Endocannabinoid System Aberrations in Mood Disorders and Schizophrenia

The endocannabinoid system (ECS) is composed of the endocannabinoid ligands anandamide (AEA) and 2-arachidonoylgycerol (2-AG), their target cannabinoid receptors (CB₁ and CB₂) and the enzymes involved in their synthesis and metabolism (N-acyltransferase and fatty acid amide hydrolase (FAAH) in the case of AEA and diacylglycerol lipase (DAGL) and monoacylglycerol lipase (MAGL) in the case of 2-AG). The origins of ECS dysfunction in major neuropsychiatric disorders remain to be determined, and this paper explores the possibility that they may be associated with chronically increased nitro-oxidative stress and activated immune-inflammatory pathways, and it examines the mechanisms which might be involved. Inflammation and nitro-oxidative stress are associated with both increased CB₁ expression, via increased activity of the NADPH oxidases NOX4 and NOX1, and increased CNR1 expression and DNA methylation; and CB₂ upregulation via increased pro-inflammatory cytokine levels, binding of the transcription factor Nrf2 to an antioxidant response element in the CNR2 promoter region and the action of miR-139. CB₁ and CB₂ have antagonistic effects on redox signalling, which may result from a miRNA-enabled negative feedback loop. The effects of inflammation and oxidative stress are detailed in respect of AEA and 2-AG levels, via effects on calcium homeostasis and phospholipase A₂ activity; on FAAH activity, via nitrosylation/nitration of functional cysteine and/or tyrosine residues; and on 2-AG activity via effects on MGLL expression and MAGL. Finally, based on these detailed molecular neurobiological mechanisms, it is suggested that cannabidiol and dimethyl fumarate may have therapeutic potential for major depressive disorder, bipolar disorder and schizophrenia.

Primary and Secondary Cone Cell Death Mechanisms in Inherited Retinal Diseases and Potential Treatment Options

Inherited retinal diseases (IRDs) are a leading cause of blindness. To date, 260 disease-causing genes have been identified, but there is currently a lack of available and effective treatment options. Cone photoreceptors are responsible for daylight vision but are highly susceptible to disease progression, the loss of cone-mediated vision having the highest impact on the quality of life of IRD patients. Cone degeneration can occur either directly via mutations in cone-specific genes (primary cone death), or indirectly via the primary degeneration of rods followed by subsequent degeneration of cones (secondary cone death). How cones degenerate as a result of pathological mutations remains unclear, hindering the development of effective therapies for IRDs. This review aims to highlight similarities and differences between primary and secondary cone cell death in inherited retinal diseases in order to better define cone death mechanisms and further identify potential treatment options.

Vitamin B12 Reduces TDP-43 Toxicity by Alleviating Oxidative Stress and Mitochondrial Dysfunction

TAR DNA-binding protein 43 (TDP-43) is a member of an evolutionarily conserved family of heterogeneous nuclear ribonucleoproteins that modulate multiple steps in RNA metabolic processes. Cytoplasmic aggregation of TDP-43 in affected neurons is a pathological hallmark of many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), Alzheimer’s disease (AD), and limbic predominant age-related TDP-43 encephalopathy (LATE). Mislocalized and accumulated TDP-43 in the cytoplasm induces mitochondrial dysfunction and reactive oxidative species (ROS) production. Here, we show that TDP-43- and rotenone-induced neurotoxicity in the human neuronal cell line SH-SY5Y were attenuated by hydroxocobalamin (Hb, vitamin B₁₂ analog) treatment. Although Hb did not affect the cytoplasmic accumulation of TDP-43, Hb attenuated TDP-43-induced toxicity by reducing oxidative stress and mitochondrial dysfunction. Moreover, a shortened lifespan and motility defects in TDP-43-expressing Drosophila were significantly mitigated by dietary treatment with hydroxocobalamin. Taken together, these findings suggest that oral intake of hydroxocobalamin may be a potential therapeutic intervention for TDP-43-associated proteinopathies.

Mitochondrial Abnormalities and Synaptic Damage in Huntington's Disease: a Focus on Defective Mitophagy and Mitochondria-Targeted Therapeutics

Huntington's disease (HD) is a fatal and pure genetic disease with a progressive loss of medium spiny neurons (MSN). HD is caused by expanded polyglutamine repeats in the exon 1 of HD gene. Clinically, HD is characterized by chorea, seizures, involuntary movements, dystonia, cognitive decline, intellectual impairment, and emotional disturbances. Several years of intense research revealed that multiple cellular changes, including defective axonal transport, protein-protein interactions, defective bioenergetics, calcium dyshomeostasis, NMDAR activation, synaptic damage, mitochondrial abnormalities, and selective loss of medium spiny neurons are implicated in HD. Recent research on mutant huntingtin (mHtt) and mitochondria has found that mHtt interacts with the mitochondrial division protein, dynamin-related protein 1 (DRP1), enhances GTPase DRP1 enzymatic activity, and causes excessive mitochondrial fragmentation and abnormal distribution, leading to defective axonal transport of mitochondria and selective synaptic degeneration. Recent research also revealed that failure to remove dead and/or dying mitochondria is an early event in the disease progression. Currently, efforts are being made to reduce abnormal protein interactions and enhance synaptic mitophagy as therapeutic strategies for HD. The purpose of this article is to discuss recent research in HD progression. This article also discusses recent developments of cell and mouse models, cellular changes, mitochondrial abnormalities, DNA damage, bioenergetics, oxidative stress, mitophagy, and therapeutics strategies in HD.

Non-Cell Autonomous and Epigenetic Mechanisms of Huntington's Disease

Huntington's disease (HD) is a rare neurodegenerative disorder caused by an expansion of CAG trinucleotide repeat located in the exon 1 of Huntingtin (HTT) gene in human chromosome 4. The HTT protein is ubiquitously expressed in the brain. Specifically, mutant HTT (mHTT) protein-mediated toxicity leads to a dramatic degeneration of the striatum among many regions of the brain. HD symptoms exhibit a major involuntary movement followed by cognitive and psychiatric dysfunctions. In this review, we address the conventional role of wild type HTT (wtHTT) and how mHTT protein disrupts the function of medium spiny neurons (MSNs). We also discuss how mHTT modulates epigenetic modifications and transcriptional pathways in MSNs. In addition, we define how non-cell autonomous pathways lead to damage and death of MSNs under HD pathological conditions. Lastly, we overview therapeutic approaches for HD. Together, understanding of precise neuropathological mechanisms of HD may improve therapeutic approaches to treat the onset and progression of HD.

CREB regulates the expression of type 1 inositol 1,4,5-trisphosphate receptors

Inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) play a central role in regulating intracellular Ca2+ signals in response to a variety of internal and external cues. Dysregulation of IP3R signaling is the underlying cause for numerous pathological conditions. It is well established that the activities of IP3Rs are governed by several post-translational modifications, including phosphorylation by protein kinase A (PKA). However, the long-term effects of PKA activation on expression of IP3R subtypes remains largely unexplored. In this report, we investigate the effects of chronic stimulation and tonic activity of PKA on the expression of IP3R subtypes. We demonstrate that expression of the type 1 IP3R (IP3R1) is augmented upon prolonged activation of PKA or upon ectopic overexpression of cyclic AMP-response element-binding protein (CREB) without altering IP3R2 and IP3R3 abundance. By contrast, inhibition of PKA or blocking CREB diminished IP3R1 expression. We also demonstrate that agonist-induced Ca2+-release mediated by IP3R1 is significantly attenuated upon blocking of CREB. Moreover, CREB - by regulating the expression of KRAS-induced actin-interacting protein (KRAP) - ensures correct localization and licensing of IP3R1. Overall, we report a crucial role for CREB in governing both the expression and correct localization of IP3R1. This article has an associated First Person interview with the first author of the paper.

Brain Region and Cell Compartment Dependent Regulation of Electron Transport System Components in Huntington's Disease Model Mice

Huntington’s disease (HD) is a rare hereditary neurodegenerative disorder characterized by multiple metabolic dysfunctions including defects in mitochondrial homeostasis and functions. Although we have recently reported age-related changes in the respiratory capacities in different brain areas in HD mice, the precise mechanisms of how mitochondria become compromised in HD are still poorly understood. In this study, we investigated mRNA and protein levels of selected subunits of electron transport system (ETS) complexes and ATP-synthase in the cortex and striatum of symptomatic R6/2 mice. Our findings reveal a brain-region-specific differential expression of both nuclear and mitochondrial-encoded ETS components, indicating defects of transcription, translation and/or mitochondrial import of mitochondrial ETS components in R6/2 mouse brains.

Transglutaminase 6 Is Colocalized and Interacts with Mutant Huntingtin in Huntington Disease Rodent Animal Models

Mammalian transglutaminases (TGs) catalyze calcium-dependent irreversible posttranslational modifications of proteins and their enzymatic activities contribute to the pathogenesis of several human neurodegenerative diseases. Although different transglutaminases are found in many different tissues, the TG6 isoform is mostly expressed in the CNS. The present study was embarked on/undertaken to investigate expression, distribution and activity of transglutaminases in Huntington disease transgenic rodent models, with a focus on analyzing the involvement of TG6 in the age- and genotype-specific pathological features relating to disease progression in HD transgenic mice and a tgHD transgenic rat model using biochemical, histological and functional assays. Our results demonstrate the physical interaction between TG6 and (mutant) huntingtin by co-immunoprecipitation analysis and the contribution of its enzymatic activity for the total aggregate load in SH-SY5Y cells. In addition, we identify that TG6 expression and activity are especially abundant in the olfactory tubercle and piriform cortex, the regions displaying the highest amount of mHTT aggregates in transgenic rodent models of HD. Furthermore, mHTT aggregates were colocalized within TG6-positive cells. These findings point towards a role of TG6 in disease pathogenesis via mHTT aggregate formation.

Emerging therapeutics in Huntington's disease

INTRODUCTION

Huntington's disease is a neurodegenerative disease that is characterized by motor dysfunction, behavioral/psychiatric symptoms, and cognitive impairment. Because of the lack of availability of curative or disease modifying treatments, much of clinical practice in HD care to date has focused on symptomatic treatment. Recent work has created optimism surrounding possible emerging disease modifying therapeutics. HD is a developing therapeutic field with diverse and promising emerging therapies.

AREAS COVERED

A PubMed literature review was completed to discover pertinent reviews and analyses. ClinicalTrials.gov was referenced to find updated information about ongoing and planned trials. Lastly, because of the rapidly evolving nature of HD treatments, drug manufacturer websites and press releases were reviewed to provide current information surrounding recently reported trial results.

EXPERT OPINION

Recent setbacks involving antisense oligonucleotide research should not diminish enthusiasm and hope for the many other novel therapies currently being pursued. We remain optimistic about the many promising emerging therapies for HD, and we expect that growing knowledge about the pathophysiology of the underlying disease and constant advances in biotechnology will lead to therapies that have a meaningful impact in the lives of patients, their families, and those who care for them.

Novel in vivo potential of trifluoperazine to ameliorate doxorubicin-induced cardiotoxicity involves suppression of NF-κB and apoptosis

AIMS

Cardiotoxicity of doxorubicin frequently complicates treatment outcome. Aberrantly activated calcium/calmodulin pathway can eventually trigger signaling cascades that mediate cardiotoxicity. Therefore, we tested the hypothesis that trifluoperazine, a strong calmodulin antagonist, may alleviate this morbidity.

MATERIALS AND METHODS

Heart failure and cardiotoxicity were assessed via echocardiography, PCR, immunohistochemistry, histopathology, Masson's trichrome staining and transmission electron microscopy. Whereas liver and kidney structural and functional alterations were evaluated histopathologically and biochemically.

KEY FINDINGS

Results revealed that combination treatment with trifluoperazine could overcome doxorubicin-induced heart failure with reduced ejection fraction. Moreover, heart weight/body weight ratio and histopathological examination showed that trifluoperazine mitigated doxorubicin-induced cardiac atrophy, inflammation and myofibril degeneration. Transmission electron microscopy further confirmed the marked restoration of the left ventricular ultrastructures by trifluoperazine pretreatment. In addition, Masson's trichrome staining revealed that trifluoperazine could significantly inhibit doxorubicin-induced left ventricular remodeling by fibrosis. Of note, doxorubicin induced the expression of myocardial nuclear NF-κB-p65 and caspase-3 which were markedly inhibited by trifluoperazine, suggesting that cardioprotection conferred by trifluoperazine involved, at least in part, suppression of NF-κB and apoptosis. Furthermore, biochemical and histopathological examinations showed that trifluoperazine improved doxorubicin-induced renal and hepatic impairments both functionally and structurally.

SIGNIFICANCE

In conclusion, the present in vivo study is the first to provide evidences underscoring the protective effects of trifluoperazine that may pave the way for repurposing this calmodulin antagonist in ameliorating organ toxicity by doxorubicin.

Blood-Brain Barrier and Neurodegenerative Diseases-Modeling with iPSC-Derived Brain Cells

The blood-brain barrier (BBB) regulates the delivery of oxygen and important nutrients to the brain through active and passive transport and prevents neurotoxins from entering the brain. It also has a clearance function and removes carbon dioxide and toxic metabolites from the central nervous system (CNS). Several drugs are unable to cross the BBB and enter the CNS, adding complexity to drug screens targeting brain disorders. A well-functioning BBB is essential for maintaining healthy brain tissue, and a malfunction of the BBB, linked to its permeability, results in toxins and immune cells entering the CNS. This impairment is associated with a variety of neurological diseases, including Alzheimer's disease and Parkinson's disease. Here, we summarize current knowledge about the BBB in neurodegenerative diseases. Furthermore, we focus on recent progress of using human-induced pluripotent stem cell (iPSC)-derived models to study the BBB. We review the potential of novel stem cell-based platforms in modeling the BBB and address advances and key challenges of using stem cell technology in modeling the human BBB. Finally, we highlight future directions in this area.

Pridopidine reduces mutant huntingtin-induced endoplasmic reticulum stress by modulation of the Sigma-1 receptor

The endoplasmic reticulum (ER)-localized Sigma-1 receptor (S1R) is neuroprotective in models of neurodegenerative diseases, among them Huntington disease (HD). Recent clinical trials in HD patients and preclinical studies in cellular and mouse HD models suggest a therapeutic potential for the high-affinity S1R agonist pridopidine. However, the molecular mechanisms of the cytoprotective effect are unclear. We have previously reported strong induction of ER stress by toxic mutant huntingtin (mHtt) oligomers, which is reduced upon sequestration of these mHtt oligomers into large aggregates. Here, we show that pridopidine significantly ameliorates mHtt-induced ER stress in cellular HD models, starting at low nanomolar concentrations. Pridopidine reduced the levels of markers of the three branches of the unfolded protein response (UPR), showing the strongest effects on the PKR-like endoplasmic reticulum kinase (PERK) branch. The effect is S1R-dependent, as it is abolished in cells expressing mHtt in which the S1R was deleted using CRISPR/Cas9 technology. mHtt increased the level of the detergent-insoluble fraction of S1R, suggesting a compensatory cellular mechanism that responds to increased ER stress. Pridopidine further enhanced the levels of insoluble S1R, suggesting the stabilization of activated S1R oligomers. These S1R oligomeric species appeared in ER-localized patches, and not in the mitochondria-associated membranes nor the ER-derived quality control compartment. The colocalization of S1R with the chaperone BiP was significantly reduced by mHtt, and pridopidine restored this colocalization to normal, unstressed levels. Pridopidine increased toxic oligomeric mHtt recruitment into less toxic large sodium dodecyl sulfate-insoluble aggregates, suggesting that this in turn reduces ER stress and cytotoxicity.

Selective Neuron Vulnerability in Common and Rare Diseases-Mitochondria in the Focus

Mitochondrial dysfunction is a central feature of neurodegeneration within the central and peripheral nervous system, highlighting a strong dependence on proper mitochondrial function of neurons with especially high energy consumptions. The fitness of mitochondria critically depends on preservation of distinct processes, including the maintenance of their own genome, mitochondrial dynamics, quality control, and Ca²⁺ handling. These processes appear to be differently affected in common neurodegenerative diseases, such as Alzheimer’s and Parkinson’s disease, as well as in rare neurological disorders, including Huntington’s disease, Amyotrophic Lateral Sclerosis and peripheral neuropathies. Strikingly, particular neuron populations of different morphology and function perish in these diseases, suggesting that cell-type specific factors contribute to the vulnerability to distinct mitochondrial defects. Here we review the disruption of mitochondrial processes in common as well as in rare neurological disorders and its impact on selective neurodegeneration. Understanding discrepancies and commonalities regarding mitochondrial dysfunction as well as individual neuronal demands will help to design new targets and to make use of already established treatments in order to improve treatment of these diseases.

Mitochondrial Ca2+ Signaling in Health, Disease and Therapy

The divalent cation calcium (Ca²⁺) is considered one of the main second messengers inside cells and acts as the most prominent signal in a plethora of biological processes. Its homeostasis is guaranteed by an intricate and complex system of channels, pumps, and exchangers. In this context, by regulating cellular Ca²⁺ levels, mitochondria control both the uptake and release of Ca²⁺. Therefore, at the mitochondrial level, Ca²⁺ plays a dual role, participating in both vital physiological processes (ATP production and regulation of mitochondrial metabolism) and pathophysiological processes (cell death, cancer progression and metastasis). Hence, it is not surprising that alterations in mitochondrial Ca²⁺ (mCa²⁺) pathways or mutations in Ca²⁺ transporters affect the activities and functions of the entire cell. Indeed, it is widely recognized that dysregulation of mCa²⁺ signaling leads to various pathological scenarios, including cancer, neurological defects and cardiovascular diseases (CVDs). This review summarizes the current knowledge on the regulation of mCa²⁺ homeostasis, the related mechanisms and the significance of this regulation in physiology and human diseases. We also highlight strategies aimed at remedying mCa²⁺ dysregulation as promising therapeutical approaches.

The Parkinson's disease-associated gene ITPKB protects against α-synuclein aggregation by regulating ER-to-mitochondria calcium release

Parkinson’s disease (PD) is the second most prevalent neurodegenerative disease of aging, affecting approximately 10 million patients worldwide with no approved therapies to modify progression of disease. Further understanding of the cellular mechanisms contributing to the development of PD is necessary to discover therapies. Here, we characterize the role of a recently identified GWAS hit for sporadic PD, ITPKB, in the aggregation of α-synuclein, the primary pathological feature of disease. These results identify inhibition of inositol-1,4,5,-triphosphate (IP₃)-mediated ER-to-mitochondria calcium release as a potential therapeutic approach for reducing neuropathology in PD.

Inositol-1,4,5-triphosphate (IP₃) kinase B (ITPKB) is a ubiquitously expressed lipid kinase that inactivates IP₃, a secondary messenger that stimulates calcium release from the endoplasmic reticulum (ER). Genome-wide association studies have identified common variants in the ITPKB gene locus associated with reduced risk of sporadic Parkinson’s disease (PD). Here, we investigate whether ITPKB activity or expression level impacts PD phenotypes in cellular and animal models. In primary neurons, knockdown or pharmacological inhibition of ITPKB increased levels of phosphorylated, insoluble α-synuclein pathology following treatment with α-synuclein preformed fibrils (PFFs). Conversely, ITPKB overexpression reduced PFF-induced α-synuclein aggregation. We also demonstrate that ITPKB inhibition or knockdown increases intracellular calcium levels in neurons, leading to an accumulation of calcium in mitochondria that increases respiration and inhibits the initiation of autophagy, suggesting that ITPKB regulates α-synuclein pathology by inhibiting ER-to-mitochondria calcium transport. Furthermore, the effects of ITPKB on mitochondrial calcium and respiration were prevented by pretreatment with pharmacological inhibitors of the mitochondrial calcium uniporter complex, which was also sufficient to reduce α-synuclein pathology in PFF-treated neurons. Taken together, these results identify ITPKB as a negative regulator of α-synuclein aggregation and highlight modulation of ER-to-mitochondria calcium flux as a therapeutic strategy for the treatment of sporadic PD.

Normalization of Calcium Balance in Striatal Neurons in Huntington's Disease: Sigma 1 Receptor as a Potential Target for Therapy

Huntington's disease (HD) is a neurodegenerative, dominantly inherited genetic disease caused by expansion of the polyglutamine tract in the huntingtin gene. At the cellular level, HD is characterized by the accumulation of mutant huntingtin protein in brain cells, resulting in the development of the HD phenotype, which includes mental disorders, decreased cognitive abilities, and progressive motor impairments in the form of chorea. Despite numerous studies, no unambigous connection between the accumulation of mutant protein and selective death of striatal neurons has yet been established. Recent studies have shown impairments in the calcium homeostasis in striatal neurons in HD. These cells are extremely sensitive to changes in the cytoplasmic concentration of calcium and its excessive increase leads to their death. One of the possible ways to normalize the balance of calcium in striatal neurons is through the sigma 1 receptor (S1R), which act as a calcium sensor that also exhibits modulating chaperone activity upon the cell stress observed during the development of many neurodegenerative diseases. The fact that S1R is a ligand-operated protein makes it a new promising molecular target for the development of drug therapy of HD based on the agonists of this receptor.

The difficulty to model Huntington's disease in vitro using striatal medium spiny neurons differentiated from human induced pluripotent stem cells

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by an expanded polyglutamine repeat in the huntingtin gene. The neuropathology of HD is characterized by the decline of a specific neuronal population within the brain, the striatal medium spiny neurons (MSNs). The origins of this extreme vulnerability remain unknown. Human induced pluripotent stem cell (hiPS cell)-derived MSNs represent a powerful tool to study this genetic disease. However, the differentiation protocols published so far show a high heterogeneity of neuronal populations in vitro. Here, we compared two previously published protocols to obtain hiPS cell-derived striatal neurons from both healthy donors and HD patients. Patch-clamp experiments, immunostaining and RT-qPCR were performed to characterize the neurons in culture. While the neurons were mature enough to fire action potentials, a majority failed to express markers typical for MSNs. Voltage-clamp experiments on voltage-gated sodium (Nav) channels revealed a large variability between the two differentiation protocols. Action potential analysis did not reveal changes induced by the HD mutation. This study attempts to demonstrate the current challenges in reproducing data of previously published differentiation protocols and in generating hiPS cell-derived striatal MSNs to model a genetic neurodegenerative disorder in vitro.

Huntington's Disease: New Frontiers in Therapeutics

PURPOSE OF REVIEW

This article describes and discusses new potential disease-modifying therapies for Huntington's disease that are currently in human clinical trials as well as promising new therapies in preclinical development.

RECENT FINDINGS

Multiple potential disease-modifying therapeutics for HD are in active development, including direct DNA/gene therapies, RNA modulation, and therapies targeted at aberrant downstream pathways. The etiology of Huntington's disease (HD) is well-known as an abnormally expanded trinucleotide repeat within the huntingtin gene. However, the pathogenesis downstream of the mutant huntingtin gene is complex, involving multiple toxic pathways, including abnormal protein fragmentation and neuroinflammation. The current treatment of HD focuses largely on symptomatic management. This article discusses new, potential disease-modifying therapies that are currently in human clinical trials and preclinical development.

STIM2 Mediates Excessive Store-Operated Calcium Entry in Patient-Specific iPSC-Derived Neurons Modeling a Juvenile Form of Huntington's Disease

Huntington's disease (HD) is a severe autosomal-dominant neurodegenerative disorder caused by a mutation within a gene, encoding huntingtin protein. Here we have used the induced pluripotent stem cell technology to produce patient-specific terminally differentiated GABA-ergic medium spiny neurons modeling a juvenile form of HD (HD76). We have shown that calcium signaling is dramatically disturbed in HD76 neurons, specifically demonstrating higher levels of store-operated and voltage-gated calcium uptakes. However, comparing the HD76 neurons with the previously described low-repeat HD models, we have demonstrated that the severity of calcium signaling alterations does not depend on the length of the polyglutamine tract of the mutant huntingtin. Here we have also observed greater expression of huntingtin and an activator of store-operated calcium channels STIM2 in HD76 neurons. Since shRNA-mediated suppression of STIM2 decreased store-operated calcium uptake, we have speculated that high expression of STIM2 underlies the excessive entry through store-operated calcium channels in HD pathology. Moreover, a previously described potential anti-HD drug EVP4593 has been found to attenuate high levels of both huntingtin and STIM2 that may contribute to its neuroprotective effect. Our results are fully supportive in favor of the crucial role of calcium signaling deregulation in the HD pathogenesis and indicate that the cornerstone of excessive calcium uptake in HD-specific neurons is a calcium sensor and store-operated calcium channels activator STIM2, which should become a molecular target for medical treatment and novel neuroprotective drug development.

Therapeutic roles of natural remedies in combating hereditary ataxia: A systematic review

Background

Hereditary ataxia (HA) represents a group of genetically heterogeneous neurodegenerative diseases caused by dysfunction of the cerebellum or disruption of the connection between the cerebellum and other areas of the central nervous system. Phenotypic manifestation of HA includes unsteadiness of stance and gait, dysarthria, nystagmus, dysmetria and complaints of clumsiness. There are no specific treatments for HA. Management strategies provide supportive treatment to reduce symptoms.

Objectives

This systematic review aimed to identify, evaluate and summarise the published literature on the therapeutic roles of natural remedies in the treatment of HA to provide evidence for clinical practice.

Methods

A systematic literature search was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Web of Science, PubMed and Science Direct Scopus were thoroughly searched for relevant published articles from June 2007 to July 2020.

Results

Ten pre-clinical and two clinical studies were eligible for inclusion in this systematic review. We identified the therapeutic roles of medicinal plants Brassica napus, Gardenia jasminoides, Gastrodia elata, Ginkgo biloba, Glycyrrhiza inflata, Paeonia lactiflora, Pueraria lobata and Rehmannia glutinosa; herbal formulations Shaoyao Gancao Tang and Zhengan Xifeng Tang; and medicinal mushroom Hericium erinaceus in the treatment of HA. In this review, we evaluated the mode of actions contributing to their therapeutic effects, including activation of the ubiquitin–proteasome system, activation of antioxidant pathways, maintenance of intracellular calcium homeostasis and regulation of chaperones. We also briefly highlighted the integral cellular signalling pathways responsible for orchestrating the mode of actions.

Conclusion

We reviewed the therapeutic roles of natural remedies in improving or halting the progression of HA, which warrant further study for applications into clinical practice.

Cell Replacement Therapy for Huntington's Disease

Huntington's disease (HD) is an inherited neurodegenerative disorder which is characterised by a triad of highly debilitating motor, cognitive, and psychiatric symptoms. While cell death occurs in many brain regions, GABAergic medium spiny neurons (MSNs) in the striatum experience preferential and extensive degeneration. Unlike most neurodegenerative disorders, HD is caused by a single genetic mutation resulting in a CAG repeat expansion and the production of a mutant Huntingtin protein (mHTT). Despite identifying the mutation causative of HD in 1993, there are currently no disease-modifying treatments for HD. One potential strategy for the treatment of HD is the development of cell-based therapies. Cell-based therapies aim to restore neuronal circuitry and function by replacing lost neurons, as well as providing neurotropic support to prevent further degeneration. In order to successfully restore basal ganglia functioning in HD, cell-based therapies would need to reconstitute the complex signalling network disrupted by extensive MSN degeneration. This chapter will discuss the potential use of foetal tissue grafts, pluripotent stem cells, neural stem cells, and somatic cell reprogramming to develop cell-based therapies for treating HD.

Targeting microglia L-type voltage-dependent calcium channels for the treatment of central nervous system disorders

Calcium (Ca2+ ) is a ubiquitous mediator of a multitude of cellular functions in the central nervous system (CNS). Intracellular Ca2+ is tightly regulated by cells, including entry via plasma membrane Ca2+ permeable channels. Of specific interest for this review are L-type voltage-dependent Ca2+ channels (L-VDCCs), due to their pleiotropic role in several CNS disorders. Currently, there are numerous approved drugs that target L-VDCCs, including dihydropyridines. These drugs are safe and effective for the treatment of humans with cardiovascular disease and may also confer neuroprotection. Here, we review the potential of L-VDCCs as a target for the treatment of CNS disorders with a focus on microglia L-VDCCs. Microglia, the resident immune cells of the brain, have attracted recent attention for their emerging inflammatory role in several CNS diseases. Intracellular Ca2+ regulates microglia transition from a resting quiescent state to an "activated" immune-effector state and is thus a valuable target for manipulation of microglia phenotype. We will review the literature on L-VDCC expression and function in the CNS and on microglia in vitro and in vivo and explore the therapeutic landscape of L-VDCC-targeting agents at present and future challenges in the context of Alzheimer's disease, Parkinson's disease, Huntington's disease, neuropsychiatric diseases, and other CNS disorders.

Human mini-brain models

Engineered human mini-brains, made possible by knowledge from the convergence of precision microengineering and cell biology, permit systematic studies of complex neurological processes and of pathogenesis beyond what can be done with animal models. By culturing human brain cells with physiological microenvironmental cues, human mini-brain models reconstitute the arrangement of structural tissues and some of the complex biological functions of the human brain. In this Review, we highlight the most significant developments that have led to microphysiological human mini-brain models. We introduce the history of mini-brain development, review methods for creating mini-brain models in static conditions, and discuss relevant state-of-the-art dynamic cell-culture systems. We also review human mini-brain models that reconstruct aspects of major neurological disorders under static or dynamic conditions. Engineered human mini-brains will contribute to advancing the study of the physiology and aetiology of neurological disorders, and to the development of personalized medicines for them.

Dysregulation of Neuronal Calcium Signaling via Store-Operated Channels in Huntington's Disease

Huntington's disease (HD) is a progressive neurodegenerative disorder that is characterized by motor, cognitive, and psychiatric problems. It is caused by a polyglutamine expansion in the huntingtin protein that leads to striatal degeneration via the transcriptional dysregulation of several genes, including genes that are involved in the calcium (Ca²⁺) signalosome. Recent research has shown that one of the major Ca²⁺ signaling pathways, store-operated Ca²⁺ entry (SOCE), is significantly elevated in HD. SOCE refers to Ca²⁺ flow into cells in response to the depletion of endoplasmic reticulum Ca²⁺ stores. The dysregulation of Ca²⁺ homeostasis is postulated to be a cause of HD progression because the SOCE pathway is indirectly and abnormally activated by mutant huntingtin (HTT) in γ-aminobutyric acid (GABA)ergic medium spiny neurons (MSNs) from the striatum in HD models before the first symptoms of the disease appear. The present review summarizes recent studies that revealed a relationship between HD pathology and elevations of SOCE in different models of HD, including YAC128 mice (a transgenic model of HD), cellular HD models, and induced pluripotent stem cell (iPSC)-based GABAergic medium spiny neurons (MSNs) that are obtained from adult HD patient fibroblasts. SOCE in MSNs was shown to be mediated by currents through at least two different channel groups, Ca²⁺ release-activated Ca²⁺ current (I_CRAC) and store-operated Ca²⁺ current (I_SOC), which are composed of stromal interaction molecule (STIM) proteins and Orai or transient receptor potential channel (TRPC) channels. Their role under physiological and pathological conditions in HD are discussed. The role of Huntingtin-associated protein 1 isoform A in elevations of SOCE in HD MSNs and potential compounds that may stabilize elevations of SOCE in HD are also summarized. Evidence is presented that shows that the dysregulation of molecular components of SOCE or pathways upstream of SOCE in HD MSN neurons is a hallmark of HD, and these changes could lead to HD pathology, making them potential therapeutic targets.

Dysfunction of Mitochondrial Ca2+ Regulatory Machineries in Brain Aging and Neurodegenerative Diseases

Calcium ions (Ca²⁺) play critical roles in neuronal processes, such as signaling pathway activation, transcriptional regulation, and synaptic transmission initiation. Therefore, the regulation of Ca²⁺ homeostasis is one of the most important processes underlying the basic cellular viability and function of the neuron. Multiple components, including intracellular organelles and plasma membrane Ca²⁺-ATPase, are involved in neuronal Ca²⁺ control, and recent studies have focused on investigating the roles of mitochondria in synaptic function. Numerous mitochondrial Ca²⁺ regulatory proteins have been identified in the past decade, with studies demonstrating the tissue- or cell-type-specific function of each component. The mitochondrial calcium uniporter and its binding subunits are major inner mitochondrial membrane proteins contributing to mitochondrial Ca²⁺ uptake, whereas the mitochondrial Na⁺/Ca²⁺ exchanger (NCLX) and mitochondrial permeability transition pore (mPTP) are well-studied proteins involved in Ca²⁺ extrusion. The level of cytosolic Ca²⁺ and the resulting characteristics of synaptic vesicle release properties are controlled via mitochondrial Ca²⁺ uptake and release at presynaptic sites, while in dendrites, mitochondrial Ca²⁺ regulation affects synaptic plasticity. During brain aging and the progress of neurodegenerative disease, mitochondrial Ca²⁺ mishandling has been observed using various techniques, including live imaging of Ca²⁺ dynamics. Furthermore, Ca²⁺ dysregulation not only disrupts synaptic transmission but also causes neuronal cell death. Therefore, understanding the detailed pathophysiological mechanisms affecting the recently discovered mitochondrial Ca²⁺ regulatory machineries will help to identify novel therapeutic targets. Here, we discuss current research into mitochondrial Ca²⁺ regulatory machineries and how mitochondrial Ca²⁺ dysregulation contributes to brain aging and neurodegenerative disease.

Purinergic Receptors in Basal Ganglia Diseases: Shared Molecular Mechanisms between Huntington's and Parkinson's Disease

Huntington's (HD) and Parkinson's diseases (PD) are neurodegenerative disorders caused by the death of GABAergic and dopaminergic neurons in the basal ganglia leading to hyperkinetic and hypokinetic symptoms, respectively. We review here the participation of purinergic receptors through intracellular Ca2+ signaling in these neurodegenerative diseases. The adenosine A2A receptor stimulates striatopallidal GABAergic neurons, resulting in inhibitory actions on GABAergic neurons of the globus pallidus. A2A and dopamine D2 receptors form functional heteromeric complexes inducing allosteric inhibition, and A2A receptor activation results in motor inhibition. Furthermore, the A2A receptor physically and functionally interacts with glutamate receptors, mainly with the mGlu5 receptor subtype. This interaction facilitates glutamate release, resulting in NMDA glutamate receptor activation and an increase of Ca2+ influx. P2X7 receptor activation also promotes glutamate release and neuronal damage. Thus, modulation of purinergic receptor activity, such as A2A and P2X7 receptors, and subsequent aberrant Ca2+ signaling, might present interesting therapeutic potential for HD and PD.

Ryanodine Receptors: A Potential Treatment Target in Various Neurodegenerative Disease

Progressive neuronal demise is a key contributor to the key pathogenic event implicated in many different neurodegenerative disorders (NDDs). There are several therapeutic strategies available; however, none of them are particularly effective. Targeted neuroprotective therapy is one such therapy, which seems a compelling option, yet remains challenging due to the internal heterogeneity of the mechanisms underlying various NDDs. An alternative method to treat NDDs is to exploit common modalities involving molecularly distinct subtypes and thus develop specialized drugs with broad-spectrum characteristics. There is mounting evidence which supports for the theory that dysfunctional ryanodine receptors (RyRs) disrupt intracellular Ca²⁺ homeostasis, contributing to NDDs significantly. This review aims to provide direct and indirect evidence on the intersection of NDDs and RyRs malfunction, and to shed light on novel strategies to treat RyRs-mediated disease, modifying pharmacological therapies such as the potential therapeutic role of dantrolene, a RyRs antagonist.

Mitochondrial Dysfunction, Neurogenesis, and Epigenetics: Putative Implications for Amyotrophic Lateral Sclerosis Neurodegeneration and Treatment

Amyotrophic lateral sclerosis (ALS) is a progressive and devastating multifactorial neurodegenerative disorder. Although the pathogenesis of ALS is still not completely understood, numerous studies suggest that mitochondrial deregulation may be implicated in its onset and progression. Interestingly, mitochondrial deregulation has also been associated with changes in neural stem cells (NSC) proliferation, differentiation, and migration. In this review, we highlight the importance of mitochondrial function for neurogenesis, and how both processes are correlated and may contribute to the pathogenesis of ALS; we have focused primarily on preclinical data from animal models of ALS, since to date no studies have evaluated this link using human samples. As there is currently no cure and no effective therapy to counteract ALS, we have also discussed how improving neurogenic function by epigenetic modulation could benefit ALS. In support of this hypothesis, changes in histone deacetylation can alter mitochondrial function, which in turn might ameliorate cellular proliferation as well as neuronal differentiation and migration. We propose that modulation of epigenetics, mitochondrial function, and neurogenesis might provide new hope for ALS patients, and studies exploring these new territories are warranted in the near future.

Calcium-Handling Defects and Neurodegenerative Disease

Calcium signaling is critical to neuronal function and regulates highly diverse processes such as gene transcription, energy production, protein handling, and synaptic structure and function. Because there are many common underlying calcium-mediated pathological features observed across several neurological conditions, it has been proposed that neurodegenerative diseases have an upstream underlying calcium basis in their pathogenesis. With certain diseases such as Alzheimer's, Parkinson's, and Huntington's, specific sources of calcium dysregulation originating from distinct neuronal compartments or channels have been shown to have defined roles in initiating or sustaining disease mechanisms. Herein, we will review the major hallmarks of these diseases, and how they relate to calcium dysregulation. We will then discuss neuronal calcium handling throughout the neuron, with special emphasis on channels involved in neurodegeneration.

Promising Molecular Targets for Pharmacological Therapy of Neurodegenerative Pathologies

Drug development for the treatment of neurodegenerative diseases has to confront numerous problems occurring, in particular, because of attempts to address only one of the causes of the pathogenesis of neurological disorders. Recent advances in multitarget therapy research are gaining momentum by utilizing pharmacophores that simultaneously affect different pathological pathways in the neurodegeneration process. The application of such a therapeutic strategy not only involves the treatment of symptoms, but also mainly addresses prevention of the fundamental pathological processes of neurodegenerative diseases and the reduction of cognitive abilities. Neuroinflammation and oxidative stress, mitochondrial dysfunction, dysregulation of the expression of histone deacetylases, and aggregation of pathogenic forms of proteins are among the most common and significant pathological features of neurodegenerative diseases. In this review, we focus on the molecular mechanisms and highlight the main aspects, including reactive oxygen species, the cell endogenous antioxidant system, neuroinflammation triggers, metalloproteinases, α-synuclein, tau proteins, neuromelanin, histone deacetylases, presenilins, etc. The processes and molecular targets discussed in this review could serve as a starting point for screening leader compounds that could help prevent or slow down the development of neurodegenerative diseases.

Regulation of microglia by glutamate and its signal pathway in neurodegenerative diseases

Microglia are an essential component of the central nervous system (CNS) and are involved in the primary response to microorganisms, neuroinflammation, homeostasis, and tissue regeneration, as well as contributing to the pathogenesis of neurodegenerative diseases. Research has shown that microglial diversity, multifunctionality, and their relationship with glutamate are crucial to determining their roles in these diseases. In this review, we focus on recent progress in determining microglial characteristics and the role of glutamate and its receptors in microglia regulation, which could be a novel therapeutic strategy for neurodegenerative diseases.

Ninety-Day Nephrotoxicity Evaluation of 3-MCPD 1-Monooleate and 1-Monostearate Exposures in Male Sprague Dawley Rats Using Proteomic Analysis

Fatty acid esters of 3-monochloropropane 1,2-diol (3-MCPD esters) are processing-induced food toxicants, with the kidney as their major target organ. For the first time, this study treated Sprague Dawley (SD) rats with 3-MCPD 1-monooleate at 10 and 100 mg/kg BW/day and 1-monostearate at 15 and 150 mg/kg BW/day for 90 days and examined for their potential semi-long-term nephrotoxicity and the associated molecular mechanisms. No bodyweight difference was observed between groups during the study. Both 3-MCPD 1-monooleate and 1-monostearate resulted in a dose-dependent increase of serum urea creatinine, uric acid and urea nitrogen levels, and histological renal impairment. The proteomic analysis of the kidney samples showed that the 3-MCPD esters deregulated proteins involved in the pathways for ion transportation, apoptosis, the metabolism of xenobiotics, and enzymes related to endogenous biological metabolisms of carbohydrates, amino acids, nitrogen, lipids, fatty acids, and the tricarboxylic acid (TCA) cycle, providing partial explanation for the nephrotoxicity of 3-MCPD esters.

Axonal Endoplasmic Reticulum Dynamics and Its Roles in Neurodegeneration

The physical continuity of axons over long cellular distances poses challenges for their maintenance. One organelle that faces this challenge is endoplasmic reticulum (ER); unlike other intracellular organelles, this forms a physically continuous network throughout the cell, with a single membrane and a single lumen. In axons, ER is mainly smooth, forming a tubular network with occasional sheets or cisternae and low amounts of rough ER. It has many potential roles: lipid biosynthesis, glucose homeostasis, a Ca2+ store, protein export, and contacting and regulating other organelles. This tubular network structure is determined by ER-shaping proteins, mutations in some of which are causative for neurodegenerative disorders such as hereditary spastic paraplegia (HSP). While axonal ER shares many features with the tubular ER network in other contexts, these features must be adapted to the long and narrow dimensions of axons. ER appears to be physically continuous throughout axons, over distances that are enormous on a subcellular scale. It is therefore a potential channel for long-distance or regional communication within neurons, independent of action potentials or physical transport of cargos, but involving its physiological roles such as Ca2+ or organelle homeostasis. Despite its apparent stability, axonal ER is highly dynamic, showing features like anterograde and retrograde transport, potentially reflecting continuous fusion and breakage of the network. Here we discuss the transport processes that must contribute to this dynamic behavior of ER. We also discuss the model that these processes underpin a homeostatic process that ensures both enough ER to maintain continuity of the network and repair breaks in it, but not too much ER that might disrupt local cellular physiology. Finally, we discuss how failure of ER organization in axons could lead to axon degenerative diseases, and how a requirement for ER continuity could make distal axons most susceptible to degeneration in conditions that disrupt ER continuity.