Transcriptional and functional effects of lithium in bipolar disorder iPSC-derived cortical spheroids.

Lithium (Li) is recommended for long-term treatment of bipolar disorder (BD). However, its mechanism of action is still poorly understood. Induced pluripotent stem cell (iPSC)-derived brain organoids have emerged as a powerful tool for modeling BD-related disease mechanisms. We studied the effects of 1 mM Li treatment for 1 month in iPSC-derived human cortical spheroids (hCS) from 10 healthy controls (CTRL) and 11 BD patients (6 Li-responders, Li-R, and 5 Li non-treated, Li-N). At day 180 of differentiation, BD hCS showed smaller size, reduced proportion of neurons, decreased neuronal excitability and reduced neural network activity compared to CTRL hCS. Li rescued excitability of BD hCS neurons by exerting an opposite effect in the two diagnostic groups, increasing excitability in BD hCS and decreasing it in CTRL hCS. We identified 132 Li-associated differentially expressed genes (DEGs), which were overrepresented in sodium ion homeostasis and kidney-related pathways. Moreover, Li regulated secretion of pro-inflammatory cytokines and increased mitochondrial reserve capacity in BD hCS. Through long-term Li treatment of a human 3D brain model, this study partly elucidates the functional and transcriptional mechanisms underlying the clinical effects of Li, such as rescue of neuronal excitability and neuroprotection. Our results also underscore the substantial influence of treatment duration in Li studies. Lastly, this study illustrates the potential of patient iPSC-derived 3D brain models for precision medicine in psychiatry.

Brain-on-a-chip: Recent advances in design and techniques for microfluidic models of the brain in health and disease.

Recent advances in biomaterials, microfabrication, microfluidics, and cell biology have led to the development of organ-on-a-chip devices that can reproduce key functions of various organs. Such platforms promise to provide novel insights into various physiological events, including mechanisms of disease, and evaluate the effects of external interventions, such as drug administration. The neuroscience field is expected to benefit greatly from these innovative tools. Conventional ex vivo studies of the nervous system have been limited by the inability of cell culture to adequately mimic in vivo physiology. While animal models can be used, their relevance to human physiology is uncertain and their use is laborious and associated with ethical issues. To date, organ-on-a-chip systems have been developed to model different tissue components of the brain, including brain regions with specific functions and the blood brain barrier, both in normal and pathophysiological conditions. While the field is still in its infancy, it is expected to have major impact on studies of neurophysiology, pathology and neuropharmacology in future. Here, we review advances made and limitations faced in an effort to stimulate development of the next generation of brain-on-a-chip devices.

N-acetylcysteine amide ameliorates mitochondrial dysfunction and reduces oxidative stress in hiPSC-derived dopaminergic neurons with POLG mutation.

The inability to reliably replicate mitochondrial DNA (mtDNA) by mitochondrial DNA polymerase gamma (POLG) leads to a subset of common mitochondrial diseases associated with neuronal death and depletion of neuronal mtDNA. Defining disease mechanisms in neurons remains difficult due to the limited access to human tissue. Using human induced pluripotent stem cells (hiPSCs), we generated functional dopaminergic (DA) neurons showing positive expression of dopaminergic markers TH and DAT, mature neuronal marker MAP2 and functional synaptic markers synaptophysin and PSD-95. These DA neurons were electrophysiologically characterized, and exhibited inward Na + currents, overshooting action potentials and spontaneous postsynaptic currents (sPSCs). POLG patient-specific DA neurons (POLG-DA neurons) manifested a phenotype that replicated the molecular and biochemical changes found in patient post-mortem brain samples namely loss of complex I and depletion of mtDNA. Compared to disease-free hiPSC-derived DA neurons, POLG-DA neurons exhibited loss of mitochondrial membrane potential, loss of complex I and loss of mtDNA and TFAM expression. POLG driven mitochondrial dysfunction also led to neuronal ROS overproduction and increased cellular senescence. This deficit was selectively rescued by treatment with N-acetylcysteine amide (NACA). In conclusion, our study illustrates the promise of hiPSC technology for assessing pathogenetic mechanisms associated with POLG disease, and that NACA can be a promising potential therapy for mitochondrial diseases such as those caused by POLG mutation.

Loss of Tiparp Results in Aberrant Layering of the Cerebral Cortex.

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible poly-ADP-ribose polymerase (TIPARP) is an enzyme that adds a single ADP-ribose moiety to itself or other proteins. Tiparp is highly expressed in the brain; however, its function in this organ is unknown. Here, we used Tiparp-/- mice to determine Tiparp's role in the development of the prefrontal cortex. Loss of Tiparp resulted in an aberrant organization of the mouse cortex, where the upper layers presented increased cell density in the knock-out mice compared with wild type. Tiparp loss predominantly affected the correct distribution and number of GABAergic neurons. Furthermore, neural progenitor cell proliferation was significantly reduced. Neural stem cells (NSCs) derived from Tiparp-/- mice showed a slower rate of migration. Cytoskeletal components, such as α-tubulin are key regulators of neuronal differentiation and cortical development. α-tubulin mono-ADP ribosylation (MAR) levels were reduced in Tiparp-/- cells, suggesting that Tiparp plays a role in the MAR of α-tubulin. Despite the mild phenotype presented by Tiparp-/- mice, our findings reveal an important function for Tiparp and MAR in the correct development of the cortex. Unravelling Tiparp's role in the cortex, could pave the way to a better understanding of a wide spectrum of neurological diseases which are known to have increased expression of TIPARP.

Locomotor central pattern generator excitability states and serotonin sensitivity after spontaneous recovery from a neonatal lumbar spinal cord injury.

The spinal locomotor central pattern generator (CPG) in neonatal mice exhibits diverse output patterns, ranging from sub-rhythmic to multi-rhythmic to fictive locomotion, depending on its general level of excitation and neuromodulatory status. We have recently reported that the locomotor CPG in neonatal mice rapidly recovers the ability to produce neurochemically induced fictive locomotion following an upper lumbar spinal cord compression injury. Here we address the question of recovery of multi-rhythmic activity and the serotonin-sensitivity of the CPG. In isolated spinal cords from control and 3 days post-injury mice, application of dopamine and NMDA elicited multi-rhythmic activity with slow and fast components. The slow component comprised 10-20 s episodes of activity that were synchronous in ipsilateral or all lumbar ventral roots, and the fast components involved bursts within these episodes that displayed coordinated patterns of alternation between ipsilateral roots. Rhythm strength was the same in control and injured spinal cords. However, power spectral analysis of signal within episodes showed a reduced peak frequency after recovery. In control spinal cords, serotonin triggered fictive locomotion only when applied at high concentration (30 µM, constant NMDA). By contrast, in about 50% of injured preparations fictive locomotion was evoked by 2-3 times lower serotonin concentrations (10-15 µM). This increased serotonin sensitivity was correlated with post-injury changes in the expression of specific serotonin receptor transcripts, but not of dopamine receptor transcripts.

Novel Potent Orthosteric Antagonist of ASIC1a Prevents NMDAR-Dependent LTP Induction.

Acid sensing ion channels 1a (ASIC1a) are of crucial importance in numerous physiological and pathological processes in the brain. Here we demonstrate that novel 2-oxo-2H-chromene-3-carboxamidine derivative 5b, designed with molecular modeling approach, inhibits ASIC1a currents with an apparent IC50 of 27 nM when measured at pH 6.7. Acidification to 5.0 decreases the inhibition efficacy by up to 3 orders of magnitude. The 5b molecule not only shifts pH dependence of ASIC1a activation but also inhibits its maximal evoked response. These findings suggest that compound 5b binds to pH sensor of ASIC1a acting as orthosteric noncompetitive antagonist. At 100 nM, compound 5b completely inhibits induction of long-term potentiation (LTP) in CA3-CA1 but not in MF-CA3 synapses. These findings support the knockout data indicating the crucial modulatory role of ASIC1a channels in the NMDAR-dependent LTP and introduce a novel type of ASIC1a antagonists.