Deepening the understanding of CNVs on chromosome 15q11–13 by using hiPSCs: An overview

The human α7 neuronal nicotinic acetylcholine receptor gene (CHRNA7) is widely expressed in the central and peripheral nervous systems. This receptor is implicated in both brain development and adult neurogenesis thanks to its ability to mediate acetylcholine stimulus (Ach). Copy number variations (CNVs) of CHRNA7 gene have been identified in humans and are genetically linked to cognitive impairments associated with multiple disorders, including schizophrenia, bipolar disorder, epilepsy, Alzheimer’s disease, and others. Currently, α7 receptor analysis has been commonly performed in animal models due to the impossibility of direct investigation of the living human brain. But the use of model systems has shown that there are very large differences between humans and mice when researchers must study the CNVs and, in particular, the CNV of chromosome 15q13.3 where the CHRNA7 gene is present. In fact, human beings present genomic alterations as well as the presence of genes of recent origin that are not present in other model systems as well as they show a very heterogeneous symptomatology that is associated with both their genetic background and the environment where they live. To date, the induced pluripotent stem cells, obtained from patients carrying CNV in CHRNA7 gene, are a good in vitro model for studying the association of the α7 receptor to human diseases. In this review, we will outline the current state of hiPSCs technology applications in neurological diseases caused by CNVs in CHRNA7 gene. Furthermore, we will discuss some weaknesses that emerge from the overall analysis of the published articles

A Link between Genetic Disorders and Cellular Impairment, Using Human Induced Pluripotent Stem Cells to Reveal the Functional Consequences of Copy Number Variations in the Central Nervous System—A Close Look at Chromosome 15

Recent cutting-edge human genetics technology has allowed us to identify copy number variations (CNVs) and has provided new insights for understanding causative mechanisms of human diseases. A growing number of studies show that CNVs could be associated with physiological mechanisms linked to evolutionary trigger, as well as to the pathogenesis of various diseases, including cancer, autoimmune disease and mental disorders such as autism spectrum disorders, schizophrenia, intellectual disabilities or attention-deficit/hyperactivity disorder. Their incomplete penetrance and variable expressivity make diagnosis difficult and hinder comprehension of the mechanistic bases of these disorders. Additional elements such as co-presence of other CNVs, genomic background and environmental factors are involved in determining the final phenotype associated with a CNV. Genetically engineered animal models are helpful tools for understanding the behavioral consequences of CNVs. However, the genetic background and the biology of these animal model systems have sometimes led to confusing results. New cellular models obtained through somatic cellular reprogramming technology that produce induced pluripotent stem cells (iPSCs) from human subjects are being used to explore the mechanisms involved in the pathogenic consequences of CNVs. Considering the vast quantity of CNVs found in the human genome, we intend to focus on reviewing the current literature on the use of iPSCs carrying CNVs on chromosome 15, highlighting advantages and limits of this system with respect to mouse model systems

Functional outcomes of copy number variations of Chrna7 gene

The discovery of genomic rearrangements, known as copy number variations (CNVs), is relatively new; their contribution to genetic heterogeneity and their impact on human diseases is still largely unknown. CNVs within the human 15q13.3 region have been associated with neuropsychiatric and neurodevelopmental disorders such as schizophrenia, autism spectrum disorders (ASD), intellectual disability, and epilepsy. Several recent studies suggest that, within this chromosomic region, the gene CHRNA7, encoding for the human alfa7 subunit of the nicotinic acetylcholine receptor, plays a major role in the observed pathological phenotypes. Consistently, patients carrying deletions or duplications of CHRNA7 present symptoms comparable to patients with a larger 1.5 Mb deletion of the 15q13.3 region. The penetrance of CHRNA7 CNVs is variable, and the exact pathogenic mechanisms are currently being elucidated. In this chapter, we have critically reviewed all up-to-date studies regarding the functional outcomes of CNVs involving the alpha7-nicontinic receptor (a7nAChR), highlighting the advantages and disadvantages of the methodologies and models utilized. We have described the structure, functionality, and physiological role of the a7nAChR, analyzing the mechanisms that determine the occurrence of CNVs and the clinical features of patients carrying CNRNA7 CNVs. We have examined and compared the mice models used to study the role of these CNVs and the new human model of induced pluripotent stem cells, which is proving very useful in clarifying the clinical and phenotypic features pertaining specifically to humans

Cerebrospinal fluid and serum d-serine concentrations are unaltered across the whole clinical spectrum of Alzheimer's disease

The diagnosis of Alzheimer's disease (AD) relies on the presence of amyloidosis and tauopathy, as reflected in cerebrospinal fluid (CSF), independently from the clinical stage. Recently, CSF d-serine has been proposed as a possible new AD biomarker, reflecting dysfunctional activation of neuronal glutamatergic N-methyl-d-aspartate receptor (NMDAR). In this study, we measured blood serum and CSF concentration of two NMDAR modulators, such as d-serine and d-aspartate, in a cohort of drug-free subjects encompassing the whole AD clinical spectrum. In addition, we also analyzed d-serine levels in a cohort of post-mortem AD and control cortex samples. We reported unaltered serum and CSF concentrations of d-serine and d-aspartate in AD patients both during the AD progression and compared to non-demented controls. Accordingly, no correlation was detected between serum or CSF d-serine content and mini-mental state examination or Clinical Dementia Rating. Similarly, cortical d-serine levels were also unaltered in post-mortem samples of AD patients. Overall, our results failed to confirm previous findings indicating the CSF d-serine as a novel biomarker for AD

Known Drugs Identified by Structure-Based Virtual Screening Are Able to Bind Sigma-1 Receptor and Increase Growth of Huntington Disease Patient-Derived Cells

Huntington disease (HD) is a devastating and presently untreatable neurodegenerative disease characterized by progressively disabling motor and mental manifestations. The sigma-1 receptor (σ1R) is a protein expressed in the central nervous system, whose 3D structure has been recently determined by X-ray crystallography and whose agonists have been shown to have neuroprotective activity in neurodegenerative diseases. To identify therapeutic agents against HD, we have implemented a drug repositioning strategy consisting of: (i) Prediction of the ability of the FDA-approved drugs publicly available through the ZINC database to interact with σ1R by virtual screening, followed by computational docking and visual examination of the 20 highest scoring drugs; and (ii) Assessment of the ability of the six drugs selected by computational analyses to directly bind purified σ1R in vitro by Surface Plasmon Resonance and improve the growth of fibroblasts obtained from HD patients, which is significantly impaired with respect to control cells. All six of the selected drugs proved able to directly bind purified σ1R in vitro and improve the growth of HD cells from both or one HD patient. These results support the validity of the drug repositioning procedure implemented herein for the identification of new therapeutic tools against HD

Known Drugs Identified by Structure-Based Virtual Screening Are Able to Bind Sigma-1 Receptor and Increase Growth of Huntington Disease Patient-Derived Cells

Huntington disease (HD) is a devastating and presently untreatable neurodegenerative disease characterized by progressively disabling motor and mental manifestations. The sigma-1 receptor (σ1R) is a protein expressed in the central nervous system, whose 3D structure has been recently determined by X-ray crystallography and whose agonists have been shown to have neuroprotective activity in neurodegenerative diseases. To identify therapeutic agents against HD, we have implemented a drug repositioning strategy consisting of: (i) Prediction of the ability of the FDA-approved drugs publicly available through the ZINC database to interact with σ1R by virtual screening, followed by computational docking and visual examination of the 20 highest scoring drugs; and (ii) Assessment of the ability of the six drugs selected by computational analyses to directly bind purified σ1R in vitro by Surface Plasmon Resonance and improve the growth of fibroblasts obtained from HD patients, which is significantly impaired with respect to control cells. All six of the selected drugs proved able to directly bind purified σ1R in vitro and improve the growth of HD cells from both or one HD patient. These results support the validity of the drug repositioning procedure implemented herein for the identification of new therapeutic tools against HD

Anti-GluA3 antibodies in frontotemporal dementia: effects on glutamatergic neurotransmission and synaptic failure

Despite the great effort of the scientific community in the field, the pathogenesis of frontotemporal dementia (FTD) remains elusive. Recently, a role for autoimmunity and altered glutamatergic neurotransmission in triggering disease onset has been put forward. We reported the presence of autoantibodies recognizing the GluA3 subunit of \u3b1-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors in about 25% of FTD cases. In this study, we evaluated the mechanisms involved in anti-GluA3 autoimmunity, through molecular/neurochemical analyses conducted on patients' brain specimens with frontotemporal lobar degeneration-tau neuropathology. We then corroborated these results in vivo in FTD patients with transcranial magnetic stimulation and glutamate, D-serine, and L-serine dosages in the cerebrospinal fluid and serum. We observed that GluA3 autoantibodies affect glutamatergic neurotransmission, decreasing glutamate release and altering GluA3-containing \u3b1-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor levels. These alterations were accompanied by changes of scaffolding proteins involved in receptor synaptic retention/internalization. The above results were confirmed by transcranial magnetic stimulation, suggesting a significant impairment of indirect measures of glutamatergic neurotransmission in FTD patients compared with controls, with further add-on harmful effect in those FTD patients with anti-GluA3 antibodies. Finally, FTD patients showed a significant increase of glutamate, D-serine, and L-serine levels in the cerebrospinal fluid

Cerebrospinal fluid levels of L-glutamate signal central inflammatory neurodegeneration in multiple sclerosis

Excessive extracellular concentrations of L-glutamate (L-Glu) can be neurotoxic and contribute to neurodegenerative processes in multiple sclerosis (MS). The association between cerebrospinal fluid (CSF) L-Glu levels, clinical features, and inflammatory biomarkers in patients with MS remains unclear. In 179 MS patients (relapsing remitting, RR, N = 157; secondary progressive/primary progressive, SP/PP, N = 22), CSF levels of L-Glu at diagnosis were determined and compared with those obtained in a group of 40 patients with non-inflammatory/non-degenerative disorders. Disability at the time of diagnosis, and after 1 year follow-up, was assessed using the Expanded Disability Status Scale (EDSS). CSF concentrations of lactate and of a large set of pro-inflammatory and anti-inflammatory molecules were explored. CSF levels of L-Glu were slightly reduced in MS patients compared to controls. In RR-MS patients, L-Glu levels correlated with EDSS after 1 year follow-up. Moreover, in MS patients, significant correlations were found between L-Glu and both CSF levels of lactate and the inflammatory molecules interleukin (IL)-2, IL-6, and IL-1 receptor antagonist. Altered expression of L-Glu is associated with disability progression, oxidative stress, and inflammation. These findings identify CSF L-Glu as a candidate neurochemical marker of inflammatory neurodegeneration in MS