Determining the Roles of Inositol Trisphosphate Receptors in Neurodegeneration: Interdisciplinary Perspectives on a Complex Topic

Steady-state regulation of COPII-dependent secretory cargo sorting by inositol trisphosphate receptors, calcium, and penta EF hand proteins

Recently, we demonstrated that agonist-stimulated Ca2+ signaling involving IP3 receptors modulates ER export rates through activation of the penta-EF Hand proteins apoptosis-linked gene-2 (ALG-2) and peflin. It is unknown, however, whether IP3Rs and penta-EF proteins regulate ER export rates at steady state. Here we tested this idea in normal rat kidney epithelial cells by manipulation of IP3R isoform expression. Under standard growth conditions, spontaneous cytosolic Ca2+ oscillations occurred simultaneously in successive groups of contiguous cells, generating intercellular Ca2+ waves that moved across the monolayer periodically. Depletion of IP3R-3, typically the least promiscuous IP3R isoform, caused increased cell participation in intercellular Ca2+ waves in unstimulated cells. The increased spontaneous signaling was sufficient to cause increased ALG-2 and COPII coat subunit Sec31A and decreased peflin localization at ER exit sites, resulting in increased ER-to-Golgi transport of the COPII client cargo VSV-G. The elevated ER-to-Golgi transport caused greater concentration of VSV-G at ER exit sites and had reciprocal effects on transport of VSV-G and a bulk-flow cargo, though both cargos equally required Sec31A. Inactivation of client cargo sorting using 4-phenylbutyrate had opposing reciprocal effects on client and bulk-flow cargo and neutralized any effect of ALG-2 activation on transport. This work extends our knowledge of ALG-2 mechanisms and indicates that in normal rat kidney cells, IP3R isoforms regulate homeostatic Ca2+ signaling that helps determine the basal secretion rate and stringency of COPII-dependent cargo sorting.

Cyclitols: From Basic Understanding to Their Association with Neurodegeneration

One of the most common cyclitols found in eukaryotic cells-Myo-inositol (MI) and its derivatives play a key role in many cellular processes such as ion channel physiology, signal transduction, phosphate storage, cell wall formation, membrane biogenesis and osmoregulation. The aim of this paper is to characterize the possibility of neurodegenerative disorders treatment using MI and the research of other therapeutic methods linked to MI's derivatives. Based on the reviewed literature the researchers focus on the most common neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease and Spinocerebellar ataxias, but there are also works describing other seldom encountered diseases. The use of MI, d-pinitol and other methods altering MI's metabolism, although research on this topic has been conducted for years, still needs much closer examination. The dietary supplementation of MI shows a promising effect on the treatment of neurodegenerative disorders and can be of great help in alleviating the accompanying depressive symptoms.

Paranodal Axoglial Junctions, an Essential Component in Axonal Homeostasis

In vertebrates, a high density of voltage-gated Na⁺ channel at nodes of Ranvier and of voltage-gated K⁺ channel at juxtaparanodes is necessary for rapid propagation of action potential, that is, for saltatory conduction in myelinated axons. Myelin loops attach to the axonal membrane and form paranodal axoglial junctions (PNJs) at paranodes adjacent to nodes of Ranvier. There is growing evidence that the PNJs contribute to axonal homeostasis in addition to their roles as lateral fences that restrict the location of nodal axolemmal proteins for effective saltatory conduction. Perturbations of PNJs, as in specific PNJ protein knockouts as well as in myelin lipid deficient mice, result in internodal axonal alterations, even if their internodal myelin is preserved. Here we review studies showing that PNJs play crucial roles in the myelinated axonal homeostasis. The present evidence points to two functions in particular: 1) PNJs facilitate axonal transport of membranous organelles as well as cytoskeletal proteins; and 2) they regulate the axonal distribution of type 1 inositol 1,4,5-trisphosphate receptor (IP₃R1) in cerebellar Purkinje axons. Myelinated axonal homeostasis depends among others on the state of PNJs, and consequently, a better understanding of this dependency may contribute to the clarification of CNS disease mechanisms and the development of novel therapies.

VDAC1 regulates neuronal cell loss after retinal trauma injury by a mitochondria-independent pathway

The voltage-dependent anion channel 1 (VDAC1) was first described as a mitochondrial porin that mediates the flux of metabolites and ions, thereby integrating both cell survival and death signals. In the nervous system, the functional roles of VDAC1 remain poorly understood. Herein, the rat retina was employed to study VDAC1. First, it was observed that even subtle changes in VDAC1 levels affect neuronal survival, inducing severe alterations in the retinal morphology. We next examined the regulation of VDAC1 after traumatic retinal injury. After mechanical trauma, SOD1 translocates towards the nucleus, which is insufficient to contain the consequences of oxidative stress, as determined by the evaluation of protein carbonylation. Using in vitro models of oxidative stress and mechanical injury in primary retinal cell cultures, it was possible to determine that inhibition of VDAC1 oligomerization by 4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS) rescues cell viability, impacting microglial cell activation. We next focused on the regulation of VDAC1 after retinal mechanical injury. VDAC1 was promptly upregulated 2 h after lesion in the plasma membrane and endoplasmic reticulum rather than in the mitochondria, and multimers of VDAC1 were assembled after lesion. DIDS intraocular application decreased apoptosis and prevented microglial polarization, which confirmed in vitro observations. Considering the role of microglia in neuroinflammation, multiplex evaluation of cytokines showed that DIDS application disorganized the inflammatory response 2 h after the lesion, matching the fast regulation of VDAC1. Taken together, data disclosed that fine regulation of VDAC1 influences neuronal survival, and pharmacological inhibition after trauma injury has neuroprotective effects. This protection may be attributed to the effects on VDAC1 abnormal accumulation in the plasma membrane, thereby controlling the activation of microglial cells. We concluded that VDAC1 is a putative therapeutic target in neuronal disorders since it integrates both death and survival cellular signaling.

Analysis and Identification Genetic Effect of SARS-CoV-2 Infections to Alzheimer's Disease Patients by Integrated Bioinformatics

BACKGROUND

COVID-19 pandemic is a global crisis which results in millions of deaths and causes long-term neurological sequelae, such as Alzheimer's disease (AD).

OBJECTIVE

We aimed to explore the interaction between COVID-19 and AD by integrating bioinformatics to find the biomarkers which lead to AD occurrence and development with COVID-19 and provide early intervention.

METHODS

The differential expressed genes (DEGs) were found by GSE147507 and GSE132903, respectively. The common genes between COVID-19 and AD were identified. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and protein-protein interactions (PPI) network analysis were carried out. Hub genes were found by cytoscape. A multivariate logistic regression model was constructed. NetworkAnalyst was used for the analysis of TF-gene interactions, TF-miRNA coregulatory network, and Protein-chemical Interactions.

RESULTS

Forty common DEGs for AD and COVID-19 were found. GO and KEGG analysis indicated that the DEGs were enriched in the calcium signal pathway and other pathways. A PPI network was constructed, and 5 hub genes were identified (ITPR1, ITPR3, ITPKB, RAPGEF3, MFGE8). Four hub genes (ITPR1, ITPR3, ITPKB, RAPGEF3) which were considered as important factors in the development of AD that were affected by COVID-19 were shown by nomogram. Utilizing NetworkAnalyst, the interaction network of 4 hub genes and TF, miRNA, common AD risk genes, and known compounds is displayed, respectively.

CONCLUSION

COVID-19 patients are at high risk of developing AD. Vaccination is required. Four hub genes can be considered as biomarkers for prediction and treatment of AD development caused by COVID-19. Compounds with neuroprotective effects can be used as adjuvant therapy for COVID-19 patients.

Identification of potential genomic biomarkers for Parkinson's disease using data pooling of gene expression microarrays

Aim: In this study, we aimed to identify potential diagnostic biomarkers Parkinson's disease (PD) by exploring microarray gene expression data of PD patients. Materials & methods: Differentially expressed genes associated with PD were screened from the GSE99039 dataset using weighted gene co-expression network analysis, followed by gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses, gene-gene interaction network analysis and receiver operator characteristics analysis. Results: We identified two PD-associated modules, in which genes from the chemokine signaling pathway were primarily enriched. In particular, CS, PRKCD, RHOG and VAMP2 directly interacted with known PD-associated genes and showed higher expression in the PD samples, and may thus be potential biomarkers in PD diagnosis. Conclusion: A DFG-analysis identified a four-gene panel (CS, PRKCD, RHOG, VAMP2) as a potential diagnostic predictor to diagnose PD.

Platelet biomarkers for a descending cognitive function: A proteomic approach

Memory loss is the most common clinical sign in Alzheimer's disease (AD); thus, searching for peripheral biomarkers to predict cognitive decline is promising for early diagnosis of AD. As platelets share similarities to neuron biology, it may serve as a peripheral matrix for biomarkers of neurological disorders. Here, we conducted a comprehensive and in-depth platelet proteomic analysis using TMT-LC-MS/MS in the populations with mild cognitive impairment (MCI, MMSE = 18-23), severe cognitive impairments (AD, MMSE = 2-17), and the age-/sex-matched normal cognition controls (MMSE = 29-30). A total of 360 differential proteins were detected in MCI and AD patients compared with the controls. These differential proteins were involved in multiple KEGG pathways, including AD, AMP-activated protein kinase (AMPK) pathway, telomerase RNA localization, platelet activation, and complement activation. By correlation analysis with MMSE score, three positively correlated pathways and two negatively correlated pathways were identified to be closely related to cognitive decline in MCI and AD patients. Partial least squares discriminant analysis (PLS-DA) showed that changes of nine proteins, including PHB, UQCRH, CD63, GP1BA, FINC, RAP1A, ITPR1/2, and ADAM10 could effectively distinguish the cognitively impaired patients from the controls. Further machine learning analysis revealed that a combination of four decreased platelet proteins, that is, PHB, UQCRH, GP1BA, and FINC, was most promising for predicting cognitive decline in MCI and AD patients. Taken together, our data provide a set of platelet biomarkers for predicting cognitive decline which may be applied for the early screening of AD.

Purkinje cell (PC) antibody positivity in a patient with autoimmune glial fibrillary acidic protein (GFAP) astrocytopathy

PURPOSE

This case report is the first to describe the detection of antibodies against inositol 1,4,5-trisphosphate receptor 1 (ITPR1, I3PR) in a patient diagnosed with autoimmune glial fibrillary acidic protein (GFAP) astrocytopathy. ITPR1 is known as one of the Purkinje cell antibodies present in autoimmune cerebellar ataxia (ACA). Here, we described the association between autoimmune GFAP astrocytopathy and autoimmune cerebellar disease (ACD).

MATERIALS AND METHODS

Demographic features, clinical characteristics, cerebrospinal fluid (CSF) parameters and neuroimaging findings were collected from this patient. Specifically, antibodies against GFAP and other proteins associated with neurological disorders were measured by immunofluorescence staining in both serum and CSF samples.

RESULTS

A 52-year-old woman was diagnosed with autoimmune inflammatory meningoencephalitis. She presented with cognitive dysfunction, psychiatric/behavioral abnormalities and serious insomnia with subacute onset. Brain magnetic resonance imaging (MRI) showed bilateral hyperintensity in the semioval centers on axial images and perivascular linear enhancement oriented radially to the ventricles on sagittal images. GFAP-IgG, oligoclonal bands (OBs), N-methyl-D-aspartate receptor (NMDAR)-IgG and ITPR1-IgG co-existed in her CSF. She responded well to immunoglobulin and steroid treatments.

CONCLUSION

Here, we describe the case of a patient with autoimmune GFAP astrocytopathy whose CSF was positive for ITPR1-IgG; however, she did not show typical ataxia manifestations or cerebellar lesions on her MRI scan. This suggests that ITPR1-IgG is not pathogenic, and the positivity of this antibody in CSF is probably associated with the presence of autoimmune inflammation.

IP3R-mediated intra-axonal Ca2+ release contributes to secondary axonal degeneration following contusive spinal cord injury

Secondary axonal loss contributes to the persistent functional disability following trauma. Consequently, preserving axons following spinal cord injury (SCI) is a major therapeutic goal to improve neurological outcome; however, the complex molecular mechanisms that mediate secondary axonal degeneration remain unclear. We previously showed that IP₃R-mediated Ca²⁺ release contributes to axonal dieback and axonal loss following an ex vivo laser-induced SCI. Nevertheless, targeting IP₃R in a clinically relevant in vivo model of SCI and determining its contribution to secondary axonal degeneration has yet to be explored. Here we used intravital two-photon excitation microscopy to assess the role of IP₃R in secondary axonal degeneration in real-time after a contusive-SCI in vivo. To visualize Ca²⁺ changes specifically in spinal axons over time, adult 6-8 week-old triple transgenic Avil-Cre:Ai9:Ai95 (sensory neuron-specific expression of tdTomato and the genetic calcium indicator GCaMP6f) mice were subjected to a mild (30 kdyn) T12 contusive-SCI and received delayed treatment with the IP₃R blocker 2-APB (100 μM, intrathecal delivery at 3, and 24 h following injury) or vehicle control. To determine the IP₃R subtype involved, we knocked-down IP₃R3 using capped phosphodiester oligonucleotides. Delayed treatment with 2-APB significantly reduced axonal spheroids, increased axonal survival, and reduced intra-axonal Ca²⁺ accumulation within dorsal column axons at 24 h following SCI in vivo. Additionally, knockdown of IP₃R3 yielded increased axon survival 24 h post-SCI. These results suggest that IP₃R-mediated Ca²⁺ release contributes to secondary axonal degeneration in vivo following SCI.

Neural stem cell differentiation into mature neurons: Mechanisms of regulation and biotechnological applications

The abilities of stem cells to self-renew and form different mature cells expand the possibilities of applications in cell-based therapies such as tissue recomposition in regenerative medicine, drug screening, and treatment of neurodegenerative diseases. In addition to stem cells found in the embryo, various adult organs and tissues have niches of stem cells in an undifferentiated state. In the central nervous system of adult mammals, neurogenesis occurs in two regions: the subventricular zone and the dentate gyrus in the hippocampus. The generation of the different neural lines originates in adult neural stem cells that can self-renew or differentiate into astrocytes, oligodendrocytes, or neurons in response to specific stimuli. The regulation of the fate of neural stem cells is a finely controlled process relying on a complex regulatory network that extends from the epigenetic to the translational level and involves extracellular matrix components. Thus, a better understanding of the mechanisms underlying how the process of neurogenesis is induced, regulated, and maintained will provide elues for development of novel for strategies for neurodegenerative therapies. In this review, we focus on describing the mechanisms underlying the regulation of the neuronal differentiation process by transcription factors, microRNAs, and extracellular matrix components.

Lysosomal Calcium in Neurodegeneration

Lysosomes are the central organelles responsible for macromolecule recycling in the cell. Lysosomal dysfunction is the primary cause of lysosomal storage diseases (LSDs), and contributes significantly to the pathogenesis of common neurodegenerative diseases. The lysosomes are also intracellular stores for calcium ions, one of the most common second messenger in the cell. Lysosomal Ca2+ is required for diverse cellular processes including signal transduction, vesicular trafficking, autophagy, nutrient sensing, exocytosis, and membrane repair. In this review, we first summarize some recent progresses in the studies of lysosome Ca2+ regulation, with a focus on the newly discovered lysosomal Ca2+ channels and the mechanisms of lysosomal Ca2+ store refilling. We then discuss how defects in lysosomal Ca2+ release and store maintenance cause lysosomal dysfunction and neurodegeneration.