Longitudinal dysregulation of long non-coding RNAs in Parkinson's disease.

Long non-coding RNAs (lncRNAs) have been suggested as potential biomarkers for Parkinson's disease (PD). This study aimed to identify blood-based lncRNA transcripts that are dysregulated in PD over time and could serve as peripheral biomarkers. Using RNA-sequencing data from the Parkinson's Progression Markers Initiative, differential expression between case and control groups at five different time points was detected, and pathway analysis was conducted. Seven transcripts, not previously linked to PD, were consistently dysregulated across all time points, while PD-linked lncRNAs were dysregulated at some but not all time points. Pathway analysis highlighted pathways, known to be affected in PD. This suggested that dysregulated lncRNA transcripts could play a role in PD pathogenesis by affecting well-known PD pathways and highlighted their potential as longitudinal biomarkers for PD. Further studies are needed to validate these findings and explore the potential use of identified lncRNAs as diagnostic and therapeutic targets.

Proteomics analysis of the p.G849D variant in neurexin 2 alpha may reveal insight into Parkinson's disease pathobiology.

Parkinson's disease (PD), the fastest-growing neurological disorder globally, has a complex etiology. A previous study by our group identified the p.G849D variant in neurexin 2 (NRXN2), encoding the synaptic protein, NRXN2α, as a possible causal variant of PD. Therefore, we aimed to perform functional studies using proteomics in an attempt to understand the biological pathways affected by the variant. We hypothesized that this may reveal insight into the pathobiology of PD. Wild-type and mutant NRXN2α plasmids were transfected into SH-SY5Y cells. Thereafter, total protein was extracted and prepared for mass spectrometry using a Thermo Scientific Fusion mass spectrometer equipped with a Nanospray Flex ionization source. The data were then interrogated against the UniProt H. sapiens database and afterward, pathway and enrichment analyses were performed using in silico tools. Overexpression of the wild-type protein led to the enrichment of proteins involved in neurodegenerative diseases, while overexpression of the mutant protein led to the decline of proteins involved in ribosomal functioning. Thus, we concluded that the wild-type NRXN2α may be involved in pathways related to the development of neurodegenerative disorders, and that biological processes related to the ribosome, transcription, and tRNA, specifically at the synapse, could be an important mechanism in PD. Future studies targeting translation at the synapse in PD could therefore provide further information on the pathobiology of the disease.

Neurexin 2 p.G849D variant, implicated in Parkinson's disease, increases reactive oxygen species, and reduces cell viability and mitochondrial membrane potential in SH-SY5Y cells.

Parkinson's disease (PD) is a neurodegenerative movement disorder, affecting 1-2% of the human population over 65. A previous study by our group identified a p.G849D variant in neurexin 2α (NRXN2) co-segregating with PD, prompting validation of its role using experimental methods. This novel variant had been found in a South African family with autosomal dominant PD. NRXN2α is an essential synaptic maintenance protein with multiple functional roles at the synaptic cleft. The aim of the present study was to investigate the potential role of the translated protein NRXN2α and the observed mutant in PD by performing functional studies in an in vitro model. Wild-type and mutant NRXN2α plasmids were transfected into SH-SY5Y cells to assess the effect of the mutant on cell viability and apoptosis [(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) Assay; ApoTox-Glo™ Triplex Assay)], mitochondrial membrane potential (MMP; MitoProbe™ JC-1 Assay), mitochondrial network analysis (MitoTracker®) and reactive oxygen species (ROS; ROS-Glo™ H2O2 Assay). Cells transfected with the mutant NRXN2α plasmid showed decreased cell viability and MMP. They also exhibited increased ROS production. However, these cells showed no changes in mitochondrial fragmentation. Our findings led us to speculate that the p.G849D variant may be involved in a toxic feedback loop leading to neuronal death in PD. Mitochondrial dysfunction and synaptic dysfunction have been linked to PD. Therefore, findings from this exploratory study are in line with previous studies connecting these two processes and warrants further investigation into the role of this variant in other cellular and animal models.

Emerging evidence implicating a role for neurexins in neurodegenerative and neuropsychiatric disorders.

Synaptopathies are brain disorders characterized by dysfunctional synapses, which are specialized junctions between neurons that are essential for the transmission of information. Synaptic dysfunction can occur due to mutations that alter the structure and function of synaptic components or abnormal expression levels of a synaptic protein. One class of synaptic proteins that are essential to their biology are cell adhesion proteins that connect the pre- and post-synaptic compartments. Neurexins are one type of synaptic cell adhesion molecule that have, recently, gained more pathological interest. Variants in both neurexins and their common binding partners, neuroligins, have been associated with several neuropsychiatric disorders. In this review, we summarize some of the key physiological functions of the neurexin protein family and the protein networks they are involved in. Furthermore, examination of published literature has implicated neurexins in both neuropsychiatric and neurodegenerative disorders. There is a clear link between neurexins and neuropsychiatric disorders, such as autism spectrum disorder and schizophrenia. However, multiple expression studies have also shown changes in neurexin expression in several neurodegenerative disorders, including Alzheimer's disease and Parkinson's disease. Therefore, this review highlights the potential importance of neurexins in brain disorders and the importance of doing more targeted studies on these genes and proteins.

Prioritization of candidate genes for a South African family with Parkinson's disease using in-silico tools.

Parkinson's disease (PD) is a neurodegenerative disorder exhibiting Mendelian inheritance in some families. Next-generation sequencing approaches, including whole exome sequencing (WES), have revolutionized the field of Mendelian disorders and have identified a number of PD genes. We recruited a South African family with autosomal dominant PD and used WES to identify a possible pathogenic mutation. After filtration and prioritization, we found five potential causative variants in CFAP65, RTF1, NRXN2, TEP1 and CCNF. The variant in NRXN2 was selected for further analysis based on consistent prediction of deleteriousness across computational tools, not being present in unaffected family members, ethnic-matched controls or public databases, and its expression in the substantia nigra. A protein model for NRNX2 was created which provided a three-dimensional (3D) structure that satisfied qualitative mean and global model quality assessment scores. Trajectory analysis showed destabilizing effects of the variant on protein structure, indicated by high flexibility of the LNS-6 domain adopting an extended conformation. We also found that the known substrate N-acetyl-D-glucosamine (NAG) contributed to restoration of the structural stability of mutant NRXN2. If NRXN2 is indeed found to be the causal gene, this could reveal a new mechanism for the pathobiology of PD.

LRP::FLAG Reduces Phosphorylated Tau Levels in Alzheimer's Disease Cell Culture Models.

BACKGROUND: Alzheimer's disease (AD) is characterized by amyloid-ß (Aß) plaque and neurofibrillary tangle formation, respectively. Neurofibrillary tangles form as a result of the intracellular accumulation of hyperphosphorylated tau. Telomerase activity and levels of the human reverse transcriptase (hTERT) subunit of telomerase are significantly decreased in AD. Recently, it has been demonstrated that the 37 kDa/67 kDa laminin receptor (LRP/LR) interacts with telomerase and is implicated in Aß pathology. Since both LRP/LR and telomerase are known to play a role in the Aß facet of AD, we hypothesized that they might also play a role in tauopathy. OBJECTIVE: This study aimed to determine if LRP/LR has a relationship with tau and whether overexpression of LRP::FLAG has an effect on tauopathy-related proteins. METHODS: We employed confocal microscopy and FRET to determine whether LRP/LR and tau co-localize and interact. LRP::FLAG overexpression in HEK-293 and SH-SY5Y cells as well as analysis of tauopathy-related proteins was assessed by western blotting. RESULTS: We demonstrate that LRP/LR co-localizes with tau in the perinuclear cell compartment and confirmed a direct interaction between LRP/LR and tau in HEK-293 cells. Overexpression of LRP::FLAG in HEK-293 and SH-SY5Y cells decreased total and phosphorylated tau levels with a concomitant decrease in PrPc levels, a tauopathy-related protein. LRP::FLAG overexpression also resulted in increased hTERT levels. CONCLUSION: This data suggest that LRP/LR extends its role in AD through a direct interaction with tau, and recommend LRP::FLAG as a possible alternative AD therapeutic via decreasing phosphorylated tau levels.

LRP::FLAG Rescues Cells from Amyloid-ß-Mediated Cytotoxicity Through Increased TERT Levels and Telomerase Activity.

Alzheimer's disease (AD) represents the most common form of neurodegenerative disorders with only palliative treatments currently available. Amyloid plaque formation caused by amyloid-ß (Aß) aggregation and neurofibrillary tangle formation caused by hyperphosphorylated tau are hallmarks for the development of AD. The 37 kDa/67 kDa laminin receptor (LRP/LR) has been implicated in AD and tools blocking or downregulating LRP/LR impede amyloid plaque formation in vitro and in vivo. We have recently shown that LRP::FLAG enhances telomerase activity with a concomitant reduction of senescent markers. Here, we overexpressed LRP::FLAG in HEK293 and SH-SY5Y cells, which resulted in an increase in hTERT levels as well as increased telomerase activity and increased cell viability in the presence of cytotoxic levels of exogenous Aß. LRP::FLAG overexpression decreased Aß shedding and intracellular Aß levels in HEK293 cells. This suggests that LRP::FLAG rescues cells from Aß-induced cytotoxicity through increased telomerase activity. This study recommends LRP::FLAG as a novel alternative therapeutic for AD treatment through activation of telomerase activity.