Excessive Ca2+ influx through N-methyl-D-aspartate type glutamate receptors (NMDAR) is associated with excitotoxicity and neuronal death, but the inhibition of this receptor-channel causes severe adverse effects. Thus, a selective reduction of NMDA-mediated Ca2+ entry, leaving unaltered the Na+ current, could represent a valid neuroprotective strategy. We developed a new two-fluorophore approach to efficiently assess the Ca2+ permeability of ligand-gated ion channels, including NMDARs, in different conditions. This technique was able to discriminate differential Ca2+/Na+ permeation ratio through different receptor channels, and through the same channel in different conditions. With this method, we confirmed that EU1794-4, a negative allosteric modulator of NMDARs, decreased their Ca2+ permeability. Furthermore, we measured for the first time the fractional Ca2+ current (Pf, i.e. the percentage of the total current carried by Ca2+ ions) of human NMDARs in the presence of EU1794-4, exhibiting a 40% reduction in comparison to control conditions. EU1794-4 was also able to reduce NMDA-mediated Ca2+ entry in human neurons derived from induced pluripotent stem cells. This last effect was stronger in the absence of extracellular Mg2+, but still significant in its presence, supporting the hypothesis to use NMDA-selective allosteric modulators to lower Ca2+ influx in human neurons, to prevent Ca2+-dependent excitotoxicity and consequent neurodegeneration.

Cofilactin rod pathology, which can initiate synapse loss, has been extensively studied in rodent neurons, hippocampal slices, and in vivo mouse models of human neurodegenerative diseases such as Alzheimer\'s disease (AD). In these systems, rod formation induced by disease-associated factors, such as soluble oligomers of Amyloid-β (Aβ) in AD, utilizes a pathway requiring cellular prion protein (PrPC), NADPH oxidase (NOX), and cytokine/chemokine receptors (CCR5 and/or CXCR4). However, rod pathways have not been systematically assessed in a human neuronal model. Here, we characterize glutamatergic neurons differentiated from human-induced pluripotent stem cells (iPSCs) for the formation of rods in response to activators of the PrPC-dependent pathway. Optimization of substratum, cell density, and use of glial-conditioned medium yielded a robust system for studying the development of Aβ-induced rods in the absence of glia, suggesting a cell-autonomous pathway. Rod induction in younger neurons requires ectopic expression of PrPC, but this dependency disappears by Day 55. The quantification of proteins within the rod-inducing pathway suggests that increased PrPC and CXCR4 expression may be factors in the doubling of the rod response to Aβ between Days 35 and 55. FDA-approved antagonists to CXCR4 and CCR5 inhibit the rod response. Rods were predominantly observed in dendrites, although severe cytoskeletal disruptions prevented the assignment of over 40% of the rods to either an axon or dendrite. In the absence of glia, a condition in which rods are more readily observed, neurons mature and fire action potentials but do not form functional synapses. However, PSD95-containing dendritic spines associate with axonal regions of pre-synaptic vesicles containing the glutamate transporter, VGLUT1. Thus, our results identified stem cell-derived neurons as a robust model for studying cofilactin rod formation in a human cellular environment and for developing effective therapeutic strategies for the treatment of dementias arising from multiple proteinopathies with different rod initiators.

Toxoplasma gondii infects approximately one-third of the world\'s population resulting in a chronic infection with the parasite located in cysts in neurons in the brain. In most immunocompetent hosts the chronic infection is asymptomatic, but several studies have found correlations between Toxoplasma seropositivity and neuropsychiatric disorders, including Schizophrenia, and some other neurological disorders. Host-parasite interactions of bradyzoites in cysts in neurons is not well understood due in part to the lack of suitable in vitro human neuronal models. The advent of stem cell technologies in which human neurons can be derived in vitro from human induced pluripotent stem cells (hiPSCs) or direct conversion of somatic cells generating induced neurons (iNs), affords the opportunity to develop in vitro human neuronal culture systems to advance the understanding of T. gondii in human neurons. Human neurons derived from hiPSCs or iNs, generate pure human neuron monolayers that express differentiated neuronal characteristics. hiPSCs also generate 3D neuronal models that better recapitulate the cytoarchitecture of the human brain. In this review, an overview of iPSC-derived neurons and iN protocols leading to 2D human neuron cultures and hiPSC-derived 3D cerebral organoids will be given. The potential applications of these 2D and 3D human neuronal models to address questions about host-parasite interactions of T. gondii in neurons and the parasite in the CNS, will be discussed. These human neuronal in vitro models hold the promise to advance the understanding of T. gondii in human neurons and to improve the understanding of neuropathogenesis of chronic toxoplasmosis.

UNASSIGNED: Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly due in large part to age-dependent atrophy of retinal pigment epithelium (RPE) cells. RPE cells form a monolayer located between the choroid and the outer segments of photoreceptors, playing multifarious roles in maintenance of visual function. Allogeneically induced pluripotent stem cell-derived RPE (iPSC-RPE or iRPE) has become a potential approach for providing an abundant source of donors for clinical cell products. Transplantation of iRPE has been proven effective in rescuing impaired retinas in Royal College of Surgeons (RCS) rats after approximately 5 to 6 weeks. Here, we explore the long-term (19 weeks) safety and efficacy of human iRPE cell transplantation in pre-clinical animal models.
UNASSIGNED: The expression of human RPE-specific markers in iRPE cells was determined using immunofluorescence staining. For the proliferative test, Ki-67 expression was also verified by immunofluorescence and flow cytometric analysis. Then, iRPE cells were transplanted into the subretinal space of immune-deficient NOD/SCID/IL-2Rgcnull (NSG) mice to assess their safety. To evaluate whether the transplanted cells could survive and rescue visual function, we performed color fundus photography, focal electroretinogram and immunostaining after delivering iRPE cells into the subretinal space of RCS rats.
UNASSIGNED: Human iRPE cells expressed native RPE-specific markers, such as microphthalmia-associated transcription factor (MiTF), retinal pigment epithelium-specific 65-kDa protein (RPE65) and tight-junction associated structural protein (ZO-1), and their proliferative capacity (Ki-67 expression) was poor after 25 days of induction. A tumorigenicity test revealed no tumor formation or abnormal proliferation in the immunodeficient mice after subretinal injection of 5×105 iRPE cells. The transplanted iRPE cells survived for at least 19 weeks and maintained visual function for 15 weeks.
UNASSIGNED: In the present study, we provided further evidence for the use of human iRPE transplantation to treat retinal degenerative disease in pre-clinical animal models. Therefore, we consider human iRPE cells a promising source of cell replacement therapy for AMD.