Sustained synchronized neuronal network activity in a human astrocyte co-culture system

Impaired neuronal network function is a hallmark of neurodevelopmental and neurodegenerative disorders such as autism, schizophrenia, and Alzheimer's disease and is typically studied using genetically modified cellular and animal models. Weak predictive capacity and poor translational value of these models urge for better human derived in vitro models. The implementation of human induced pluripotent stem cells (hiPSCs) allows studying pathologies in differentiated disease-relevant and patient-derived neuronal cells. However, the differentiation process and growth conditions of hiPSC-derived neurons are non-trivial. In order to study neuronal network formation and (mal) function in a fully humanized system, we have established an in vitro co-culture model of hiPSC-derived cortical neurons and human primary astrocytes that recapitulates neuronal network synchronization and connectivity within three to four weeks after final plating. Live cell calcium imaging, electrophysiology and high content image analyses revealed an increased maturation of network functionality and synchronicity over time for co-cultures compared to neuronal monocultures. The cells express GABAergic and glutamatergic markers and respond to inhibitors of both neurotransmitter pathways in a functional assay. The combination of this co-culture model with quantitative imaging of network morphofunction is amenable to high throughput screening for lead discovery and drug optimization for neurological diseases

In Vitro Pharmacological Characterization of RXFP3 Allosterism: An Example of Probe Dependency

Recent findings suggest that the relaxin-3 neural network may represent a new ascending arousal pathway able to modulate a range of neural circuits including those affecting circadian rhythm and sleep/wake states, spatial and emotional memory, motivation and reward, the response to stress, and feeding and metabolism. Therefore, the relaxin-3 receptor (RXFP3) is a potential therapeutic target for the treatment of various CNS diseases. Here we describe a novel selective RXFP3 receptor positive allosteric modulator (PAM), 3-[3,5-Bis(trifluoromethyl)phenyl]-1-(3,4-dichlorobenzyl)-1-[2-(5-methoxy-1H-indol-3-yl)ethyl]urea (135PAM1). Calcium mobilization and cAMP accumulation assays in cell lines expressing the cloned human RXFP3 receptor show the compound does not directly activate RXFP3 receptor but increases functional responses to amidated relaxin-3 or R3/I5, a chimera of the INSL5 A chain and the Relaxin-3 B chain. 135PAM1 increases calcium mobilization in the presence of relaxin-3NH2 and R3/I5NH2 with pEC50 values of 6.54 (6.46 to 6.64) and 6.07 (5.94 to 6.20), respectively. In the cAMP accumulation assay, 135PAM1 inhibits the CRE response to forskolin with a pIC50 of 6.12 (5.98 to 6.27) in the presence of a probe (10 nM) concentration of relaxin-3NH2. 135PAM1 does not compete for binding with the orthosteric radioligand, [125I] R3I5 (amide), in membranes prepared from cells expressing the cloned human RXFP3 receptor. 135PAM1 is selective for RXFP3 over RXFP4, which also responds to relaxin-3. However, when using the free acid (native) form of relaxin-3 or R3/I5, 135PAM1 doesn't activate RXFP3 indicating that the compound's effect is probe dependent. Thus one can exchange the entire A-chain of the probe peptide while retaining PAM activity, but the state of the probe's c-terminus is crucial to allosteric activity of the PAM. These data demonstrate the existence of an allosteric site for modulation of this GPCR as well as the subtlety of changes in probe molecules that can affect allosteric modulation of RXFP3

Molecular characterisation of the N-methyl-D-aspartate receptor expressed in mammalian cells

L-Glutamate is the major excitatory neurotransmitter in the vertebrate central nervous system, mediating its effects via interaction with glutamate receptors. Several pharmacological subclasses of the glutamate receptor have been identified, including the N-methyl-D-aspartate (NMDA) receptor. Molecular cloning has recently identified five genes encoding the NMDA receptor subunits, NMDAR1 and NMDAR2A-D. In this thesis, work is described in which conditions for the optimal transient expression of homo- and heteromeric NMDA receptors in mammalian cells were established, thus providing a model system for structure-function studies of this important brain protein. Thus, the cDNAs encoding the NMDAR1-1a and NMDAR2A subunits were subcloned into the mammalian expression vector, pCIS. The resultant constructs were transfected alone or in combination in human embryonic kidney (HEK) 293 cells by the calcium phosphate method. Co-transfection studies resulted in cell death, which was prevented by inclusion of NMDA receptor antagonists in the cell culture medium post-transfection. A study was made of the efficacy for the prevention against cell death for a series of different NMDA receptor antagonists, which included DL-2-amino-5 phosphonovalerate (AP5), 5,7-dichlorokynurenic acid (DKA) and Mg2+. The percentage cell death was quantified by either Trypan Blue exclusion or the CytoTox 96TM assay system. The combination of AP5 and DKA gave optimal protection with no significant difference between cotransfected and control samples. Site-directed in vitro mutagenesis was used to generate point mutations of the NMDAR1-1a subunit. Co-transfection studies with the wild-type and mutant NMDA receptor cDNAs were carried out and the effect of the mutations on cell viability quantified. Most notably, it was found that the mutation (N598Q), previously shown to reduce the Ca2+ permeability of cloned receptors, significantly reduced cell toxicity, thus providing evidence for the role of Ca2+ in NMDA-receptor mediated cytotoxic mechanisms

Shifting of amidated RXFP3 agonist concentration response curves by 135PAM1 in cells lacking chimeric G proteins.

<p>SK-N-MC cells coexpressing RXFP3 and a reporter construct linking CRE activity to β-galactosidase were incubated with fixed concentrations of 135PAM1 (0, 0.2, 2 and 20 µM) and increasing concentrations of Relaxin-3_NH2 (A) or R3I5_NH2 (B).</p

135PAM1 increases the intracellular Ca²⁺ response to amidated, but not free acid RXFP3 agonists in cells coexpressing RXFP3 and G_qI5.

<p>Intracellular Ca²⁺ responses by HEK-293 cells coexpressing RXFP3 and G_qI5 were measured in response to escalating concentrations of 135PAM1 using probe (EC₂₀) concentrations of Relaxin-3_NH2 (A), Relaxin-3_OH (B), R3/I5_NH2 (C), or R3/I5_OH (D).</p

135PAM1 shifts the concentration response curves of Relaxin-3_NH2 and R3/I5_NH2.

<p>HEK-293 cells coexpressing RXFP3 and G_qI5 were incubated with fixed concentrations of 135PAM1 (0, 0.2, 2 and 20 µM) 10 min before the addition of increasing concentrations of Relaxin-3_NH2 (A), R3I5_NH2 (B), Relaxin-3_OH (C) or R3I5_OH (D).</p

135PAM1 lacks affinity at the orthosteric binding site of RXFP3 receptor.

<p>135PAM1 did not displace [125I] R3/I5_NH2 at concentrations of up to 20 µM, but instead increased total binding. R3/I5_NH2 displaced the tracer with a pIC₅₀ of 8.76 (8.91 to 8.61).</p

Structure of 135PAM1 (3-[3,5-Bis(trifluoromethyl)phenyl]-1-(3,4-dichlorobenzyl)-1-[2-(5-methoxy-1H-indol-3-yl)ethyl]urea).

<p>Structure of 135PAM1 (3-[3,5-Bis(trifluoromethyl)phenyl]-1-(3,4-dichlorobenzyl)-1-[2-(5-methoxy-1H-indol-3-yl)ethyl]urea).</p

Using Human iPSC-Derived Neurons to Model TAU Aggregation

<div><p>Alzheimer’s disease and frontotemporal dementia are amongst the most common forms of dementia characterized by the formation and deposition of abnormal TAU in the brain. In order to develop a translational human TAU aggregation model suitable for screening, we transduced TAU harboring the pro-aggregating P301L mutation into control hiPSC-derived neural progenitor cells followed by differentiation into cortical neurons. TAU aggregation and phosphorylation was quantified using AlphaLISA technology. Although no spontaneous aggregation was observed upon expressing TAU-P301L in neurons, seeding with preformed aggregates consisting of the TAU-microtubule binding repeat domain triggered robust TAU aggregation and hyperphosphorylation already after 2 weeks, without affecting general cell health. To validate our model, activity of two autophagy inducers was tested. Both rapamycin and trehalose significantly reduced TAU aggregation levels suggesting that iPSC-derived neurons allow for the generation of a biologically relevant human Tauopathy model, highly suitable to screen for compounds that modulate TAU aggregation.</p></div