Cadherin-13 is a critical regulator of GABAergic modulation in human stem-cell-derived neuronal networks.

Activity in the healthy brain relies on a concerted interplay of excitation (E) and inhibition (I) via balanced synaptic communication between glutamatergic and GABAergic neurons. A growing number of studies imply that disruption of this E/I balance is a commonality in many brain disorders; however, obtaining mechanistic insight into these disruptions, with translational value for the patient, has typically been hampered by methodological limitations. Cadherin-13 (CDH13) has been associated with autism and attention-deficit/hyperactivity disorder. CDH13 localizes at inhibitory presynapses, specifically of parvalbumin (PV) and somatostatin (SST) expressing GABAergic neurons. However, the mechanism by which CDH13 regulates the function of inhibitory synapses in human neurons remains unknown. Starting from human-induced pluripotent stem cells, we established a robust method to generate a homogenous population of SST and MEF2C (PV-precursor marker protein) expressing GABAergic neurons (iGABA) in vitro, and co-cultured these with glutamatergic neurons at defined E/I ratios on micro-electrode arrays. We identified functional network parameters that are most reliably affected by GABAergic modulation as such, and through alterations of E/I balance by reduced expression of CDH13 in iGABAs. We found that CDH13 deficiency in iGABAs decreased E/I balance by means of increased inhibition. Moreover, CDH13 interacts with Integrin-ß1 and Integrin-ß3, which play opposite roles in the regulation of inhibitory synaptic strength via this interaction. Taken together, this model allows for standardized investigation of the E/I balance in a human neuronal background and can be deployed to dissect the cell-type-specific contribution of disease genes to the E/I balance.

Serotonin-specific neurons differentiated from human iPSCs form distinct subtypes with synaptic protein assembly.

Human induced pluripotent stem cells (hiPSCs) have revolutionized the generation of experimental disease models, but the development of protocols for the differentiation of functionally active neuronal subtypes with defined specification is still in its infancy. While dysfunction of the brain serotonin (5-HT) system has been implicated in the etiology of various neuropsychiatric disorders, investigation of functional human 5-HT specific neurons in vitro has been restricted by technical limitations. We describe an efficient generation of functionally active neurons from hiPSCs displaying 5-HT specification by modification of a previously reported protocol. Furthermore, 5-HT specific neurons were characterized using high-end fluorescence imaging including super-resolution microscopy in combination with electrophysiological techniques. Differentiated hiPSCs synthesize 5-HT, express specific markers, such as tryptophan hydroxylase 2 and 5-HT transporter, and exhibit an electrophysiological signature characteristic of serotonergic neurons, with spontaneous rhythmic activities, broad action potentials and large afterhyperpolarization potentials. 5-HT specific neurons form synapses reflected by the expression of pre- and postsynaptic proteins, such as Bassoon and Homer. The distribution pattern of Bassoon, a marker of the active zone along the soma and extensions of neurons, indicates functionality via volume transmission. Among the high percentage of 5-HT specific neurons (~ 42%), a subpopulation of CDH13 + cells presumably designates dorsal raphe neurons. hiPSC-derived 5-HT specific neuronal cell cultures reflect the heterogeneous nature of dorsal and median raphe nuclei and may facilitate examining the association of serotonergic neuron subpopulations with neuropsychiatric disorders.

Effects of DNA methyltransferase inhibition on pattern separation performance in mice.

Enhancement of synaptic plasticity through changes in neuronal gene expression is a prerequisite for improved cognitive performance. Moreover, several studies have shown that DNA methylation is able to affect the expression of (e.g. plasticity) genes that are important for several cognitive functions. In this study, the effect of the DNA methyltransferase (DNMT) inhibitor RG108 was assessed on object pattern separation (OPS) task in mice. In addition, its effect on the expression of target genes was monitored. Administration of RG108 before the test led to a short-lasting, dose-dependent increase in pattern separation memory that was not present anymore after 48 h. Furthermore, treatment with RG108 did not enhance long-term memory of the animals when tested after a 24 h inter-trial interval in the same task. At the transcriptomic level, acute treatment with RG108 was accompanied by increased expression of Bdnf1, while expression of Bdnf4, Bdnf9, Gria1 and Hdac2 was not altered within 1 h after treatment. Methylation analysis of 14 loci in the promoter region of Bdnf1 revealed a counterintuitive increase in the levels of DNA methylation at three CpG sites. Taken together, these results indicate that acute administration of RG108 has a short-lasting pro-cognitive effect on object pattern separation that could be explained by increased Bdnf1 expression. The observed increase in Bdnf1 methylation suggests a complex interplay between Bdnf methylation-demethylation that promotes Bdnf1 expression and associated cognitive performance. Considering that impaired pattern separation could constitute the underlying problem of a wide range of mental and cognitive disorders, pharmacological agents including DNA methylation inhibitors that improve pattern separation could be compelling targets for the treatment of these disorders. In that respect, future studies are needed in order to determine the effect of chronic administration of such agents.

Generation of a ST3GAL3 null mutant induced pluripotent stem cell (iPSC) line (UKWMPi002-A-3) by CRISPR/Cas9 genome editing.

Fibroblasts isolated from a skin biopsy of a healthy individual were infected with Sendai virus containing the Yamanaka factors to produce transgene-free human induced pluripotent stem cells (iPSCs). CRISPR/Cas9 was used to generate an isogenic cell line carrying an inactivation of ST3GAL3, a risk gene associated with neurodevelopmental and psychiatric disorders. This ST3GAL3 null mutant (ST3GAL3-/-) iPSC line, which displays the expression of pluripotency-associated markers, the ability to differentiate into cells of the three germ layers in vitro, and a normal karyotype, is a powerful tool to investigate the impact of deficient sialylation of glycoproteins in neural development and plasticity.

Generation of induced pluripotent stem cell (iPSC) lines carrying a heterozygous (UKWMPi002-A-1) and null mutant knockout (UKWMPi002-A-2) of Cadherin 13 associated with neurodevelopmental disorders using CRISPR/Cas9.

Fibroblasts isolated from a skin biopsy of a healthy 46-year-old female were infected with Sendai virus containing the Yamanaka factors to produce transgene-free human induced pluripotent stem cells (iPSCs). CRISPR/Cas9 was used to generate isogenic cell lines with a gene dose-dependent deficiency of CDH13, a risk gene associated with neurodevelopmental and psychiatric disorders. Thereby, a heterozygous CDH13 knockout (CDH13+/-) and a CDH13 null mutant (CDH13-/-) iPSC line was obtained. All three lines showed expression of pluripotency-associated markers, the ability to differentiate into cells of the three germ layers in vitro, and a normal female karyotype.

A Common CDH13 Variant Is Associated with Low Agreeableness and Neural Responses to Working Memory Tasks in ADHD.

The cell-cell signaling gene CDH13 is associated with a wide spectrum of neuropsychiatric disorders, including attention-deficit/hyperactivity disorder (ADHD), autism, and major depression. CDH13 regulates axonal outgrowth and synapse formation, substantiating its relevance for neurodevelopmental processes. Several studies support the influence of CDH13 on personality traits, behavior, and executive functions. However, evidence for functional effects of common gene variation in the CDH13 gene in humans is sparse. Therefore, we tested for association of a functional intronic CDH13 SNP rs2199430 with ADHD in a sample of 998 adult patients and 884 healthy controls. The Big Five personality traits were assessed by the NEO-PI-R questionnaire. Assuming that altered neural correlates of working memory and cognitive response inhibition show genotype-dependent alterations, task performance and electroencephalographic event-related potentials were measured by n-back and continuous performance (Go/NoGo) tasks. The rs2199430 genotype was not associated with adult ADHD on the categorical diagnosis level. However, rs2199430 was significantly associated with agreeableness, with minor G allele homozygotes scoring lower than A allele carriers. Whereas task performance was not affected by genotype, a significant heterosis effect limited to the ADHD group was identified for the n-back task. Heterozygotes (AG) exhibited significantly higher N200 amplitudes during both the 1-back and 2-back condition in the central electrode position Cz. Consequently, the common genetic variation of CDH13 is associated with personality traits and impacts neural processing during working memory tasks. Thus, CDH13 might contribute to symptomatic core dysfunctions of social and cognitive impairment in ADHD.