Synaptic Plasticity Dysfunctions in the Pathophysiology of 22q11 Deletion Syndrome: Is There a Role for Astrocytes?

The 22q11 deletion syndrome (DS) is the most common microdeletion syndrome in humans and gives a high probability of developing psychiatric disorders. Synaptic and neuronal malfunctions appear to be at the core of the symptoms presented by patients. In fact, it has long been suggested that the behavioural and cognitive impairments observed in 22q11DS are probably due to alterations in the mechanisms regulating synaptic function and plasticity. Often, synaptic changes are related to structural and functional changes observed in patients with cognitive dysfunctions, therefore suggesting that synaptic plasticity has a crucial role in the pathophysiology of the syndrome. Most interestingly, among the genes deleted in 22q11DS, six encode for mitochondrial proteins that, in mouse models, are highly expressed just after birth, when active synaptogenesis occurs, therefore indicating that mitochondrial processes are strictly related to synapse formation and maintenance of a correct synaptic signalling. Because correct synaptic functioning, not only requires correct neuronal function and metabolism, but also needs the active contribution of astrocytes, we summarize in this review recent studies showing the involvement of synaptic plasticity in the pathophysiology of 22q11DS and we discuss the relevance of mitochondria in these processes and the possible involvement of astrocytes.

Novel Combination of Surface Markers for the Reliable and Comprehensive Identification of Human Thymic Epithelial Cells by Flow Cytometry: Quantitation and Transcriptional Characterization of Thymic Stroma in a Pediatric Cohort.

Thymic epithelial cells (TECs) are essential in supporting the development of mature T cells from hematopoietic progenitor cells and facilitate their lineage-commitment, proliferation, T-cell receptor repertoire selection and maturation. While animal model systems have greatly aided in elucidating the contribution of stromal cells to these intricate processes, human tissue has been more difficult to study, partly due to a lack of suitable surface markers comprehensively defining human TECs. Here, we conducted a flow cytometry based surface marker screen to reliably identify and quantify human TECs and delineate medullary from cortical subsets. These findings were validated by transcriptomic and histologic means. The combination of EpCAM, podoplanin (pdpn), CD49f and CD200 comprehensively identified human TECs and not only allowed their reliable distinction in medullary and cortical subsets but also their detailed quantitation. Transcriptomic profiling of each subset in comparison to fibroblasts and endothelial cells confirmed the identity of the different stromal cell subsets sorted according to the proposed strategy. Our dataset not only demonstrated transcriptional similarities between TEC and cells of mesenchymal origin but furthermore revealed a subset-specific distribution of a specific set of extracellular matrix-related genes in TECs. This indicates that TECs significantly contribute to the distinct compartmentalization - and thus function - of the human thymus. We applied the strategy to quantify TEC subsets in 31 immunologically healthy children, which revealed sex-specific differences of TEC composition early in life. As the distribution of mature CD4- or CD8-single-positive thymocytes was correspondingly altered, the composition of the thymic epithelial compartment may directly impact on the CD4-CD8-lineage choice of thymocytes. We prove that the plain, reliable strategy proposed here to comprehensively identify human TEC subpopulations by flow cytometry based on surface marker expression is suitable to determine their frequency and phenotype in health and disease and allows sorting of live cells for downstream analysis. Its use reaches from a reliable diagnostic tool for thymic biopsies to improved phenotypic characterization of thymic grafts intended for therapeutic use.

Systems Analysis of the 22q11.2 Microdeletion Syndrome Converges on a Mitochondrial Interactome Necessary for Synapse Function and Behavior.

Neurodevelopmental disorders offer insight into synaptic mechanisms. To unbiasedly uncover these mechanisms, we studied the 22q11.2 syndrome, a recurrent copy number variant, which is the highest schizophrenia genetic risk factor. We quantified the proteomes of 22q11.2 mutant human fibroblasts from both sexes and mouse brains carrying a 22q11.2-like defect, Df(16)A+/- Molecular ontologies defined mitochondrial compartments and pathways as some of top ranked categories. In particular, we identified perturbations in the SLC25A1-SLC25A4 mitochondrial transporter interactome as associated with the 22q11.2 genetic defect. Expression of SLC25A1-SLC25A4 interactome components was affected in neuronal cells from schizophrenia patients. Furthermore, hemideficiency of the Drosophila SLC25A1 or SLC25A4 orthologues, dSLC25A1-sea and dSLC25A4-sesB, affected synapse morphology, neurotransmission, plasticity, and sleep patterns. Our findings indicate that synapses are sensitive to partial loss of function of mitochondrial solute transporters. We propose that mitoproteomes regulate synapse development and function in normal and pathological conditions in a cell-specific manner.SIGNIFICANCE STATEMENT We address the central question of how to comprehensively define molecular mechanisms of the most prevalent and penetrant microdeletion associated with neurodevelopmental disorders, the 22q11.2 microdeletion syndrome. This complex mutation reduces gene dosage of ∼63 genes in humans. We describe a disruption of the mitoproteome in 22q11.2 patients and brains of a 22q11.2 mouse model. In particular, we identify a network of inner mitochondrial membrane transporters as a hub required for synapse function. Our findings suggest that mitochondrial composition and function modulate the risk of neurodevelopmental disorders, such as schizophrenia.

IQ and hemizygosity for the Val158 Met functional polymorphism of COMT in 22q11DS.

22q11.2 Deletion Syndrome (22q11DS) is a multisystem disorder caused by a hemizygous deletion within 22q11.2. Patients with the deletion display a wide range of cognitive deficits. The gene catechol-O-methyl-transferase (COMT) resides in the typically deleted region of 22q11.2 and is rendered hemizygous in individuals affected by the 22q11DS. COMT is a critical enzyme in the degradation of catecholamine neurotransmitters in the brain. A functional polymorphism, Val158 Met, has been associated with a variety of neurocognitive outcomes. In this study, 159 patients with 22q11DS were analyzed for a potential association between intelligence quotient (IQ) and COMT genotype. We performed a univariate analysis for overall influence and modified our analysis to focus on possible differences between average, borderline, and intellectually impaired patients. No correlation between COMT genotype and IQ performance was found. © 2016 Wiley Periodicals, Inc.

Dopamine dysfunction in 22q11 deletion syndrome: possible cause of motor symptoms.

22q11 Deletion syndrome (22q11DS) is a neurogenetic disorder, resulting from a hemizygous microdeletion on the long arm of chromosome 22. In 22q11DS, the phenotypic expression is highly variable. Approximately one-third of all individuals with 22q11DS develop schizophrenia-like psychotic disorder. Among the genes in the deleted region, catechol-O-methyltransferase (COMT) has a particular relevance for psychiatric disorders: lower COMT enzymatic activity decreases the clearance of dopamine (DA), yielding higher levels of catecholamines in the central nervous system. Deficits in myelinogenesis and dysfunctions in the DA system could justify the white matter abnormalities in motor/premotor circuits described in 22q11DS. The alterations in DA could determine the high incidence of psychiatric disorders and the presence of neurological soft signs in 22q11DS. Neurological soft signs are defined as non-normative performance on an examination of motor and sensory tasks without focal neurological deficits. COMT haploinsufficiency, DA dysfunction, and white matter abnormalities may contribute toward the presence of neurological soft signs in 22q11DS.

Deficits in microRNA-mediated Cxcr4/Cxcl12 signaling in neurodevelopmental deficits in a 22q11 deletion syndrome mouse model.

22q11 deletion syndrome (22q11DS) frequently accompanies psychiatric conditions, some of which are classified as schizophrenia and bipolar disorder in the current diagnostic categorization. However, it remains elusive how the chromosomal microdeletion leads to the mental manifestation at the mechanistic level. Here we show that a 22q11DS mouse model with a deletion of 18 orthologous genes of human 22q11 (Df1/+ mice) has deficits in migration of cortical interneurons and hippocampal dentate precursor cells. Furthermore, Df1/+ mice show functional defects in Chemokine receptor 4/Chemokine ligand 12 (Cxcr4/Cxcl12; Sdf1) signaling, which reportedly underlie interneuron migration. Notably, the defects in interneuron progenitors are rescued by ectopic expression of Dgcr8, one of the genes in 22q11 microdeletion. Furthermore, heterozygous knockout mice for Dgcr8 show similar neurodevelopmental abnormalities as Df1/+ mice. Thus, Dgcr8-mediated regulation of microRNA is likely to underlie Cxcr4/Cxcl12 signaling and associated neurodevelopmental defects. Finally, we observe that expression of CXCL12 is decreased in olfactory neurons from sporadic cases with schizophrenia compared with normal controls. Given the increased risk of 22q11DS in schizophrenia that frequently shows interneuron abnormalities, the overall study suggests that CXCR4/CXCL12 signaling may represent a common downstream mediator in the pathophysiology of schizophrenia and related mental conditions.

The 22q11 deletion: DiGeorge and velocardiofacial syndromes and the role of TBX1.

Hemizygous deletion of 22q11 affects approximately 1:4000 live births and may give rise to many different malformations but classically results in a constellation of phenotypes that receive a diagnosis of DiGeorge syndrome or velocardiofacial syndrome. Particularly affected are the heart and great vessels, the endocrine glands of the neck, the face, the soft palate, and cognitive development. Although up to 50 genes may be deleted, it is haploinsufficiency of the transcription factor TBX1 that is thought to make the greatest contribution to the disorder. Mouse embryos are exquisitely sensitive to varying levels of Tbx1 mRNA, and Tbx1 is required in all three germ layers of the embryonic pharyngeal region for normal development. TBX1 controls cell proliferation and affects cellular differentiation in a cell autonomous fashion, but it also directs non-cell autonomous effects, most notably in the signaling between pharyngeal surface ectoderm and the rostral neural crest. TBX1 interacts with several signaling pathways, including fibroblast growth factor, retinoic acid, CTNNB1 (formerly known as ß-catenin), and bone morphogenetic protein (BMP), and may regulate pathways by both DNA-binding and non-binding activity. In addition to the structural abnormalities seen in 22q11 deletion syndrome (DS) and Tbx1 mutant mouse models, patients reaching adolescence and adulthood have a predisposition to psychiatric illness. Whether this has a developmental basis and, if so, which genes are involved is an ongoing strand of research. Thus, knowledge of the genetic and developmental mechanisms underlying 22q11DS has the potential to inform about common disease as well as developmental defect.

Delayed-onset hypoparathyroidism in an adolescent with chromosome 22Q11 deletion syndrome.

OBJECTIVE: To describe the first case of established chromosome 22q11 deletion syndrome with late onset presentation of hypocalcemia secondary to hypoparathyroidism. METHODS: We present the history, clinical and laboratory investigations, and management of a 17-year-old adolescent boy who presented with 3 separate seizures secondary to hypocalcemia. This patient had an established diagnosis of chromosome 22q11 deletion syndrome at the time of the seizure presentations, but had previously normal calcium levels. RESULTS: Hypocalcemia was noted during each seizure, with corrected calcium levels ranging from 6.64 to 7.76 mg/dL (reference range, 8.52 to 10.52 mg/dL). The hypocalcemia was secondary to hypoparathyroidism, with parathyroid hormone levels < 2.75 pg/mL (reference range, 22.9 to 68.75 pg/mL). He was treated with calcitriol, 0.5 µg daily, and calcium carbonate, 2,400 mg daily, leading to normalization of serum calcium and resolution of seizures. CONCLUSION: Chromosome 22q11 deletion syndrome is a relatively common genetic disorder with a wide variety of phenotypic manifestations including cardiac abnormalities, abnormal facies, thymic dysfunction, cleft palate, and hypocalcemia. This case shows that medical practitioners should be aware that hypocalcemia can present after an established diagnosis, which has implications for the management of this disorder.

Proton magnetic resonance spectroscopy in 22q11 deletion syndrome.

OBJECTIVE: People with velo-cardio-facial syndrome or 22q11 deletion syndrome (22q11DS) have behavioral, cognitive and psychiatric problems. Approximately 30% of affected individuals develop schizophrenia-like psychosis. Glutamate dysfunction is thought to play a crucial role in schizophrenia. However, it is unknown if and how the glutamate system is altered in 22q11DS. People with 22q11DS are vulnerable for haploinsufficiency of PRODH, a gene that codes for an enzyme converting proline into glutamate. Therefore, it can be hypothesized that glutamatergic abnormalities may be present in 22q11DS. METHOD: We employed proton magnetic resonance spectroscopy ((1)H-MRS) to quantify glutamate and other neurometabolites in the dorsolateral prefrontal cortex (DLPFC) and hippocampus of 22 adults with 22q11DS (22q11DS SCZ+) and without (22q11DS SCZ-) schizophrenia and 23 age-matched healthy controls. Also, plasma proline levels were determined in the 22q11DS group. RESULTS: We found significantly increased concentrations of glutamate and myo-inositol in the hippocampal region of 22q11DS SCZ+ compared to 22q11DS SCZ-. There were no significant differences in levels of plasma proline between 22q11DS SCZ+ and 22q11DS SCZ-. There was no relationship between plasma proline and cerebral glutamate in 22q11DS. CONCLUSION: This is the first in vivo(1)H-MRS study in 22q11DS. Our results suggest vulnerability of the hippocampus in the psychopathology of 22q11DS SCZ+. Altered hippocampal glutamate and myo-inositol metabolism may partially explain the psychotic symptoms and cognitive impairments seen in this group of patients.

Dysregulation of presynaptic calcium and synaptic plasticity in a mouse model of 22q11 deletion syndrome.

The 22q11 deletion syndrome (22q11DS) is characterized by cognitive decline and increased risk of psychiatric disorders, mainly schizophrenia. The molecular mechanisms of neuronal dysfunction in cognitive symptoms of 22q11DS are poorly understood. Here, we report that a mouse model of 22q11DS, the Df(16)1/+ mouse, exhibits substantially enhanced short- and long-term synaptic plasticity at hippocampal CA3-CA1 synapses, which coincides with deficits in hippocampus-dependent spatial memory. These changes are evident in mature but not young animals. Electrophysiological, two-photon imaging and glutamate uncaging, and electron microscopic assays in acute brain slices showed that enhanced neurotransmitter release but not altered postsynaptic function or structure caused these changes. Enhanced neurotransmitter release in Df(16)1/+ mice coincided with altered calcium kinetics in CA3 presynaptic terminals and upregulated sarco(endo)plasmic reticulum calcium-ATPase type 2 (SERCA2). SERCA inhibitors rescued synaptic phenotypes of Df(16)1/+ mice. Thus, presynaptic SERCA2 upregulation may be a pathogenic event contributing to the cognitive symptoms of 22q11DS.

Striatal D2 receptor binding in 22q11 deletion syndrome: an [¹²³I]IBZM SPECT study.

It has been hypothesised that in subjects with 22q11 deletion syndrome (22q11DS) disturbances of the dopamine (DA) system contribute to their increased risk for cognitive deficits and psychiatric problems. However, central DAergic neurotransmission in 22q11DS has not been investigated. We measured striatal D2 receptor binding potential (D2R BP(ND)) using (S)-(-)-3-iodo-2-hydroxy-6-methoxy-N-[(1-ethyl-2-pyrrolidinyl)methyl] benzamide-single photon emission computed tomography ([¹²³I]IBZM SPECT) in 12 adults with 22q11DS and 12 matched controls. Correlations between D2R BP(ND) and plasma prolactin (pPRL) levels were also determined. 22q11DS subjects and controls had similar D2R BP( ND). There was a positive correlation between D2R BP( ND) and pPRL values in controls, but no such relation was found in 22q11DS subjects. This study suggests that a 22q11 deletion does not affect striatal DAergic neurotransmission in the living human brain. However, the disturbed relationship between D2R BP(ND) and pPRL values suggests DAergic dysfunction at a different level. Further studies on DAergic function in extra-striatal brain regions and under challenged conditions are needed.