Targeting calcium homeostasis and impaired inter-organelle crosstalk as a potential therapeutic approach in Parkinson's disease

Effect of High-Dose Vitamin C on Tendon Cell Degeneration-An In Vitro Study

Tendinopathy is an aging-related disease, often caused by micro-scarring and degeneration due to overuse or trauma. Ascorbic acid (vitamin C) supplementation is reported to be a useful treatment for tendinopathy recovery. We compared the inhibitory effects of various ascorbic acid doses on tendon cell damage. H2O2 was added to human-derived tendon cells in vitro (Group H2O2, control), followed by incubation with 150 µM or 30 mM of ascorbic acid (Group C, Group HC). The oxidative injury degree was evaluated by determining reactive oxygen species levels. The cytoskeletal structure was examined via fluorescence immunostaining of actin filaments. Quantitative polymerase chain reaction (qPCR) was performed to analyze the expressions of mitochondria transcription factor A, adenosine triphosphate 5A, type I collagen, and p16. Cell death was reduced, and oxidative stress was inhibited in C and HC groups. The cytoskeleton was maintained in the HC group but not in the C group. qPCR analysis revealed that p16 expression was inhibited in both the C and HC groups compared to the H2O2 group; other markers had increased expression. The progression of cell death and cytoskeletal disruption was inhibited by the administration of high-dose vitamin C. Hence, high-dose vitamin C is a potential treatment for tendon cell degeneration.

ATF4 regulates mitochondrial dysfunction, mitophagy, and autophagy, contributing to corneal endothelial apoptosis under chronic ER stress in Fuchs' dystrophy

Purpose

Endoplasmic reticulum (ER) stress, mitochondrial dysfunction, mitophagy/autophagy are known to contribute independently to corneal endothelial (CE) apoptosis in Fuchs' endothelial corneal dystrophy (FECD). However, the role of a well-studied specific ER stress pathway (PERK-ATF4-CHOP) in regulating mitochondrial dysfunction, mitophagy/autophagy, and apoptosis is unknown. The purpose of this study is to explore the role of ATF4 in regulating mitochondrial dysfunction and mitophagy/autophagy, leading to CEnC apoptosis in FECD.

Methods

Human corneal endothelial cell line (HCEnC-21T), Fuchs' corneal endothelial cell line (F35T), and primary human corneal endothelial cells were treated with ER stressor tunicamycin (0.01, 0.1, 1, 10 μg/mL) for 24 and/or 48 hours. ATF4 siRNA was used to knock down ATF4 in 21T cell line and primary corneal endothelial cells. Cell viability was measured using an MTT assay (10 μg/mL tunicamycin for 24 hours). Mitochondrial bioenergetics was analyzed by measuring mitochondria membrane potential (MMP) loss using TMRE assay and ATP production using mitochondrial complex V assay kit at 48 hours post tunicamycin. Mitochondrial-mediated intrinsic apoptotic pathway proteins, mitophagy, and autophagy marker proteins were analyzed using Western blotting (10 μg/mL tunicamycin for 24 hours). ATF4 +/- and ATF4 +/+ mice were irradiated with UVA to assess pro-apoptotic ER stress and corneal endothelial cell death in vivo .

Results

F35T cell line had a significantly increased expression of ER stress pathway molecules (eIF2α, ATF4, CHOP) and mitochondrial-mediated intrinsic apoptotic molecules (cleaved PARP, caspase 9, caspase 3) along with mitochondrial fragmentation compared to 21T cells at the baseline, which further increased after treatment with tunicamycin. Mitochondrial membrane potential also significantly decreased in F35T compared to 21T after tunicamycin. ATF4 knockdown after tunicamycin significantly attenuated pro-apoptotic ER and mitochondrial stress molecules, rescued MMP loss, and reduced mitochondrial fragmentation in the 21T cell line and primary corneal endothelial cells. ATF4 knockdown post tunicamycin treatment also downregulated altered/excessive Parkin-mediated mitophagy and Akt/mTOR-mediated autophagy pathway with reduction of caspases, leading to increased cellular viability. ATF4+/-mice had significantly increased CE numbers with improved cellular morphology and decreased CHOP expression compared to ATF4+/+ post-UVA.

Conclusions

Pro-apoptotic ATF4 induction under tunicamycin-induced ER stress disrupts mitochondrial bioenergetics and dynamics, leading to activation of excessive autophagy/mitophagy. ATF4-induced activation of CHOP plays a key role in switching excessive autophagy to CEnC apoptosis. This study highlights the importance of ATF4 in ER-mitochondrial crosstalk and its contribution to CEnC apoptosis in FECD.

Selective Reduction of Ca2+ Entry Through the Human NMDA Receptor: a Quantitative Study by Simultaneous Ca2+ and Na+ Imaging

Excessive Ca2+ influx through N-methyl-D-aspartate type glutamate receptors (NMDAR) is associated with excitotoxicity and neuronal death, but the inhibition of this receptor-channel causes severe adverse effects. Thus, a selective reduction of NMDA-mediated Ca2+ entry, leaving unaltered the Na+ current, could represent a valid neuroprotective strategy. We developed a new two-fluorophore approach to efficiently assess the Ca2+ permeability of ligand-gated ion channels, including NMDARs, in different conditions. This technique was able to discriminate differential Ca2+/Na+ permeation ratio through different receptor channels, and through the same channel in different conditions. With this method, we confirmed that EU1794-4, a negative allosteric modulator of NMDARs, decreased their Ca2+ permeability. Furthermore, we measured for the first time the fractional Ca2+ current (Pf, i.e. the percentage of the total current carried by Ca2+ ions) of human NMDARs in the presence of EU1794-4, exhibiting a 40% reduction in comparison to control conditions. EU1794-4 was also able to reduce NMDA-mediated Ca2+ entry in human neurons derived from induced pluripotent stem cells. This last effect was stronger in the absence of extracellular Mg2+, but still significant in its presence, supporting the hypothesis to use NMDA-selective allosteric modulators to lower Ca2+ influx in human neurons, to prevent Ca2+-dependent excitotoxicity and consequent neurodegeneration.

ER-organelle contacts: A signaling hub for neurological diseases

Neuronal health is closely linked to the homeostasis of intracellular organelles, and organelle dysfunction affects the pathological progression of neurological diseases. In contrast to isolated cellular compartments, a growing number of studies have found that organelles are largely interdependent structures capable of communicating through membrane contact sites (MCSs). MCSs have been identified as key pathways mediating inter-organelle communication crosstalk in neurons, and their alterations have been linked to neurological disease pathology. The endoplasmic reticulum (ER) is a membrane-bound organelle capable of forming an extensive network of pools and tubules with important physiological functions within neurons. There are multiple MCSs between the ER and other organelles and the plasma membrane (PM), which regulate a variety of cellular processes. In this review, we focus on ER-organelle MCSs and their role in a variety of neurological diseases. We compared the biological effects between different tethering proteins and the effects of their respective disease counterparts. We also discuss how altered ER-organelle contacts may affect disease pathogenesis. Therefore, understanding the molecular mechanisms of ER-organelle MCSs in neuronal homeostasis will lay the foundation for the development of new therapies targeting ER-organelle contacts.

Unique Interactions of the Small Translocases of the Mitochondrial Inner Membrane (Tims) in Trypanosoma brucei

The infectious agent for African trypanosomiasis, Trypanosoma brucei, possesses a unique and essential translocase of the mitochondrial inner membrane, known as the TbTIM17 complex. TbTim17 associates with six small TbTims (TbTim9, TbTim10, TbTim11, TbTim12, TbTim13, and TbTim8/13). However, the interaction patterns of these smaller TbTims with each other and TbTim17 are not clear. Through yeast two-hybrid (Y2H) and co-immunoprecipitation analyses, we demonstrate that all six small TbTims interact with each other. Stronger interactions were found among TbTim8/13, TbTim9, and TbTim10. However, TbTim10 shows weaker associations with TbTim13, which has a stronger connection with TbTim17. Each of the small TbTims also interacts strongly with the C-terminal region of TbTim17. RNAi studies indicated that among all small TbTims, TbTim13 is most crucial for maintaining the steady-state levels of the TbTIM17 complex. Further analysis of the small TbTim complexes by size exclusion chromatography revealed that each small TbTim, except for TbTim13, is present in ~70 kDa complexes, possibly existing in heterohexameric forms. In contrast, TbTim13 is primarily present in the larger complex (>800 kDa) and co-fractionates with TbTim17. Altogether, our results demonstrate that, relative to other eukaryotes, the architecture and function of the small TbTim complexes are specific to T. brucei.

Advancements in Genetic and Biochemical Insights: Unraveling the Etiopathogenesis of Neurodegeneration in Parkinson's Disease

Parkinson's disease (PD) is the second most prevalent neurodegenerative movement disorder worldwide, which is primarily characterized by motor impairments. Even though multiple hypotheses have been proposed over the decades that explain the pathogenesis of PD, presently, there are no cures or promising preventive therapies for PD. This could be attributed to the intricate pathophysiology of PD and the poorly understood molecular mechanism. To address these challenges comprehensively, a thorough disease model is imperative for a nuanced understanding of PD's underlying pathogenic mechanisms. This review offers a detailed analysis of the current state of knowledge regarding the molecular mechanisms underlying the pathogenesis of PD, with a particular emphasis on the roles played by gene-based factors in the disease's development and progression. This study includes an extensive discussion of the proteins and mutations of primary genes that are linked to PD, including α-synuclein, GBA1, LRRK2, VPS35, PINK1, DJ-1, and Parkin. Further, this review explores plausible mechanisms for DAergic neural loss, non-motor and non-dopaminergic pathologies, and the risk factors associated with PD. The present study will encourage the related research fields to understand better and analyze the current status of the biochemical mechanisms of PD, which might contribute to the design and development of efficacious and safe treatment strategies for PD in future endeavors.

Calcium channelopathies in neurodegenerative disorder: an untold story of RyR and SERCA

INTRODUCTION

Recent neuroscience breakthroughs have shed light on the sophisticated relationship between calcium channelopathies and movement disorders, exposing a previously undiscovered tale focusing on the Ryanodine Receptor (RyR) and the Sarco/Endoplasmic Reticulum Calcium ATPase (SERCA). Calcium signaling mainly orchestrates neural communication, which regulates synaptic transmission and total network activity. It has been determined that RyR play a significant role in managing neuronal functions, most notably in releasing intracellular calcium from the endoplasmic reticulum.

AREAS COVERED

It highlights the involvement of calcium channels such as RyR and SERCA in physiological and pathophysiological conditions.

EXPERT OPINION

Links between RyR and SERCA activity dysregulation, aberrant calcium levels, motor and cognitive dysfunction have brought attention to the importance of RyR and SERCA modulation in neurodegenerative disorders. Understanding the obscure function of these proteins will open up new therapeutic possibilities to address the underlying causes of neurodegenerative diseases. The unreported RyR and SERCA narrative broadens the understanding of calcium channelopathies in movement disorders and calls for more research into cutting-edge therapeutic approaches.