Reverse engineering human neurodegenerative disease using pluripotent stem cell technology

Emerging Trends in the Field of Inflammation and Proteinopathy in ALS/FTD Spectrum Disorder

Proteinopathy and neuroinflammation are two main hallmarks of neurodegenerative diseases. They also represent rare common events in an exceptionally broad landscape of genetic, environmental, neuropathologic, and clinical heterogeneity present in patients. Here, we aim to recount the emerging trends in amyotrophic lateral sclerosis (ALS) and frontotemporal degeneration (FTD) spectrum disorder. Our review will predominantly focus on neuroinflammation and systemic immune imbalance in ALS and FTD, which have recently been highlighted as novel therapeutic targets. A common mechanism of most ALS and ~50% of FTD patients is dysregulation of TAR DNA-binding protein 43 (TDP-43), an RNA/DNA-binding protein, which becomes depleted from the nucleus and forms cytoplasmic aggregates in neurons and glia. This, in turn, via both gain and loss of function events, alters a variety of TDP-43-mediated cellular events. Experimental attempts to target TDP-43 aggregates or manipulate crosstalk in the context of inflammation will be discussed. Targeting inflammation, and the immune system in general, is of particular interest because of the high plasticity of immune cells compared to neurons.

Polyphenols and Stem Cells for Neuroregeneration in Parkinson's Disease and Amyotrophic Lateral Sclerosis

Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS) are neurological disorders, pathologically characterized by chronic degeneration of dopaminergic neurons and motor neurons respectively. There is still no cure or effective treatment against the disease progression and most of the treatments are symptomatic. The present review offers an overview of the different factors involved in the pathogenesis of these diseases. Subsequently, we focused on the recent advanced studies of dietary polyphenols and stem cell therapies, which have made it possible to slow down the progression of neurodegeneration. To date, stem cells and different polyphenols have been used for the directional induction of neural stem cells into dopaminergic neurons and motor neurons. We have also discussed their involvement in the modulation of different signal transduction pathways and growth factor levels in various in vivo and in vitro studies. Likewise stem cells, polyphenols also exhibit the potential of neuroprotection by their anti-apoptotic, anti-inflammatory, anti-oxidant properties regulating the growth factors levels and molecular signaling events. Overall this review provides a detailed insight into recent strategies that promise the use of polyphenol with stem cell therapy for the possible treatment of PD and ALS.

Human Induced Pluripotent Stem Cell-Derived TDP-43 Mutant Neurons Exhibit Consistent Functional Phenotypes Across Multiple Gene Edited Lines Despite Transcriptomic and Splicing Discrepancies

Gene editing technologies hold great potential to enhance our ability to model inheritable neurodegenerative diseases. Specifically, engineering multiple amyotrophic lateral sclerosis (ALS) mutations into isogenic cell populations facilitates determination of whether different causal mutations cause pathology via shared mechanisms, and provides the capacity to separate these mechanisms from genotype-specific effects. As gene-edited, cell-based models of human disease become more commonplace, there is an urgent need to verify that these models constitute consistent and accurate representations of native biology. Here, commercially sourced, induced pluripotent stem cell-derived motor neurons from Cellular Dynamics International, edited to express the ALS-relevant mutations TDP-43^M337V and TDP-43^Q331K were compared with in-house derived lines engineered to express the TDP-43^Q331K mutation within the WTC11 background. Our results highlight electrophysiological and mitochondrial deficits in these edited cells that correlate with patient-derived cells, suggesting a consistent cellular phenotype arising from TDP-43 mutation. However, significant differences in the transcriptomic profiles and splicing behavior of the edited cells underscores the need for careful comparison of multiple lines when attempting to use these cells as a means to better understand the onset and progression of ALS in humans.

Prospects of Directly Reprogrammed Adult Human Neurons for Neurodegenerative Disease Modeling and Drug Discovery: iN vs. iPSCs Models

A reliable disease model is critical to the study of specific disease mechanisms as well as for the discovery and development of new drugs. Despite providing crucial insights into the mechanisms of neurodegenerative diseases, translation of this information to develop therapeutics in clinical trials have been unsuccessful. Reprogramming technology to convert adult somatic cells to induced Pluripotent Stem Cells (iPSCs) or directly reprogramming adult somatic cells to induced Neurons (iN), has allowed for the creation of better models to understand the molecular mechanisms and design of new drugs. In recent times, iPSC technology has been commonly used for modeling neurodegenerative diseases and drug discovery. However, several technological challenges have limited the application of iN. As evidence suggests, iN for the modeling of neurodegenerative disorders is advantageous compared to those derived from iPSCs. In this review, we will compare iPSCs and iN models for neurodegenerative diseases and their potential applications in the future.

R534C mutation in hERG causes a trafficking defect in iPSC-derived cardiomyocytes from patients with type 2 long QT syndrome

Patient-specific cardiomyocytes obtained from induced pluripotent stem cells (CM-iPSC) offer unprecedented mechanistic insights in the study of inherited cardiac diseases. The objective of this work was to study a type 2 long QT syndrome (LQTS2)-associated mutation (c.1600C > T in KCNH2, p.R534C in hERG) in CM-iPSC. Peripheral blood mononuclear cells were isolated from two patients with the R534C mutation and iPSCs were generated. In addition, the same mutation was inserted in a control iPSC line by genome editing using CRISPR/Cas9. Cells expressed pluripotency markers and showed spontaneous differentiation into the three embryonic germ layers. Electrophysiology demonstrated that action potential duration (APD) of LQTS2 CM-iPSC was significantly longer than that of the control line, as well as the triangulation of the action potentials (AP), implying a longer duration of phase 3. Treatment with the I_Kr inhibitor E4031 only caused APD prolongation in the control line. Patch clamp showed a reduction of I_Kr on LQTS2 CM-iPSC compared to control, but channel activation was not significantly affected. Immunofluorescence for hERG demonstrated perinuclear staining in LQTS2 CM-iPSC. In conclusion, CM-iPSC recapitulated the LQTS2 phenotype and our findings suggest that the R534C mutation in KCNH2 leads to a channel trafficking defect to the plasma membrane.

Reporter Scaffolds for Clinically Relevant Cell Transplantation Studies

There are a number of cell therapies that are either in clinical trials or moving toward clinical trials, particularly for diseases of the retina. One of the challenges with cell therapies is tracking the status of cells over time. Genetic manipulation can facilitate this, but it can limit the clinical application of the cells. There are a host of fluorophores that have been developed to assess the status of cells, but these molecules tend to be cleared rapidly from cells. There are preclinical strategies that use degradable scaffolds, and we hypothesized that these scaffolds could be used to track the state of cells during preclinical studies. In this work, we explored whether fluorophores could be delivered from simple scaffolds fabricated under extremely harsh conditions, be active upon release, and report on the cells growing on the scaffolds over time. We encapsulated CellROX® Green Reagent, and pHrodo™ Red AM in poly(lactic-co-glycolic acid) (PLGA) scaffolds, showed that they could be delivered over weeks and were still active upon release and taken up by cells. These experiments provide the foundation for using scaffolds to deliver molecules to report on cells.

CRISPR/Cas9 facilitates genomic editing for large-scale functional studies in pluripotent stem cell cultures

Pluripotent stem cell (PSC) cultures form an integral part of biomedical and medical research due to their capacity to rapidly proliferate and differentiate into hundreds of highly specialized cell types. This makes them a highly useful tool in exploring human physiology and disease. Genomic editing of PSC cultures is an essential method of attaining answers to basic physiological functions, developing in vitro models of human disease, and exploring potential therapeutic strategies and the identification of drug targets. Achieving reliable and efficient genomic editing is an important aspect of using large-scale PSC cultures. The CRISPR/Cas9 genomic editing tool has facilitated highly efficient gene knockout, gene correction, or gene modifications through the design and use of single-guide RNAs which are delivered to the target DNA via Cas9. CRISPR/Cas9 modification of PSCs has furthered the understanding of basic physiology and has been utilized to develop in vitro disease models, to test therapeutic strategies, and to facilitate regenerative or tissue repair approaches. In this review, we discuss the benefits of the CRISPR/Cas9 system in large-scale PSC cultures.

Neural differentiation of mouse induced pluripotent stem cells using cadherin gene-engineered PA6 feeder cells

Investigating neural differentiation of pluripotent stem cells, including induced pluripotent stem (iPS) cells, is of importance for studying early neural development and providing a potential source of cells for nerve regeneration. Stromal cell-derived inducing activity (SDIA) using PA6 stromal cells promotes neural differentiation of iPS cells. Thus, we hypothesized that cadherin gene-engineered PA6 feeder cells will enhance the performance of SDIA by facilitating cell-cell interactions. Consequently, we created cadherin gene-engineered PA6 cells. Efficiency of neural differentiation from mouse iPS cells on PA6 feeder cells overexpressing E-cadherin gene (46%) or N-cadherin gene (27%) was significantly higher compared with parental PA6 feeder cells (19%). In addition, efficiency of motor neuron differentiation from mouse iPS cells on cadherin-gene engineered feeder cells (E-cadherin, 7.4%; N-cadherin, 11%) was significantly higher compared with parental PA6 feeder cells (4.1%). Altogether, these results indicate that cadherin gene-engineered feeder cells are a potent tool for promoting neural differentiation of pluripotent stem cells.

Materials for Neural Differentiation, Trans-Differentiation, and Modeling of Neurological Disease

Neuron regeneration from pluripotent stem cells (PSCs) differentiation or somatic cells trans-differentiation is a promising approach for cell replacement in neurodegenerative diseases and provides a powerful tool for investigating neural development, modeling neurological diseases, and uncovering the mechanisms that underlie diseases. Advancing the materials that are applied in neural differentiation and trans-differentiation promotes the safety, efficiency, and efficacy of neuron regeneration. In the neural differentiation process, matrix materials, either natural or synthetic, not only provide a structural and biochemical support for the monolayer or three-dimensional (3D) cultured cells but also assist in cell adhesion and cell-to-cell communication. They play important roles in directing the differentiation of PSCs into neural cells and modeling neurological diseases. For the trans-differentiation of neural cells, several materials have been used to make the conversion feasible for future therapy. Here, the most current applications of materials for neural differentiation for PSCs, neuronal trans-differentiation, and neurological disease modeling is summarized and discussed.

Generation of kisspeptin-responsive GnRH neurons from human pluripotent stem cells

GnRH neurons are fundamental for reproduction in all vertebrates, integrating all reproductive inputs. The inaccessibility of human GnRH-neurons has been a major impediment to studying the central control of reproduction and its disorders. Here, we report the efficient generation of kisspeptin responsive GnRH-secreting neurons by directed differentiation of human Embryonic Stem Cells and induced-Pluripotent Stem Cells derived from a Kallman Syndrome patient and a healthy family member. The protocol involves the generation of intermediate Neural Progenitor Cells (NPCs) through long-term Bone morphogenetic protein 4 inhibition, followed by terminal specification of these NPCs in media containing Fibroblast Growth Factor 8 and a NOTCH inhibitor. The resulting GnRH-expressing and -secreting neurons display a neuroendocrine gene expression pattern and present spontaneous calcium transients that can be stimulated by kisspeptin. These in vitro generated GnRH expressing cells provide a new resource for studying the molecular mechanisms underlying the development and function of GnRH neurons.

C-X-C motif chemokine ligand 8 promotes endothelial cell homing via the Akt-signal transducer and activator of transcription pathway to accelerate healing of ischemic and hypoxic skin ulcers

C-X-C motif chemokine ligand 8 (CXCL-8) promotes cell homing and angiogenesis. However, under hypoxic conditions, the role of CXCL-8 in the homing of human umbilical vein endothelial cells (HUVECs), and its effect on the healing of skin ulcers caused by ischemia and hypoxia remain unknown. In the current study, assays measuring cell proliferation, in vitro angiogenesis and cell migration were performed to evaluate alterations in the proliferation, angiogenic capacity and chemotaxis of HUVECs treated with CXCL-8 protein and/or an Akt inhibitor (AZD5363 group) under hypoxic conditions. Changes in the levels of Akt, signal transducer and activator of transcription 3 (STAT3), vascular endothelial growth factor (VEGF), malondialdehyde (MDA) and total-superoxide dismutase (total-SOD) were also detected by western blotting and ELISA. In addition, in vivo experiments were performed using a skin ulcer model in mice. Ischemic and hypoxic skin ulcers were created on the thighs of C57BL/6J mice, and the effects of CXCL-8 and HUVEC transplantation on the healing capacity of skin ulcers was determined by injecting mice with HUVECs and/or CXCL-8 recombinant protein (CXCL-8, HUVEC and HUVEC + CXCL-8 groups). Vascular endothelial cell homing, changes in vascular density and the expression of VEGF, SOD, EGF and MDA within the ulcer tissue were subsequently measured. In vitro experiments demonstrated that HUVEC proliferation, migration and tube forming capacity were significantly increased by CXCL-8 under hypoxic conditions. Additionally, levels of VEGF, MDA and SOD were significantly higher in the CXCL-8 group, though were significantly decreased by the Akt and STAT3 inhibitors. In vivo experiments demonstrated that the expression of VEGF, total-SOD and EGF proteins were higher in the skin ulcer tissue of mice treated with CXCL-8 + HUVEC, relative to mice treated with HUVECs alone. Furthermore, vascular endothelial cell homing and vascular density were significantly increased in the CXCL-8 + HUVEC group, indicating that combined use of HUVECs and CXCL-8 may promote the healing of ischemic skin ulcers. The present results demonstrate that CXCL-8 may stimulate vascular endothelial cells to secrete VEGF, SOD and other cytokines via the Akt-STAT3 pathway, which in turn serves a key regulatory role in the recruitment of vascular endothelial cells, reduction of hypoxia-related injury and promotion of tissue repair following hypoxic/ischemic injury.

Human neural progenitors derived from integration-free iPSCs for SCI therapy

As a potentially unlimited autologous cell source, patient induced pluripotent stem cells (iPSCs) provide great capability for tissue regeneration, particularly in spinal cord injury (SCI). However, despite significant progress made in translation of iPSC-derived neural progenitor cells (NPCs) to clinical settings, a few hurdles remain. Among them, non-invasive approach to obtain source cells in a timely manner, safer integration-free delivery of reprogramming factors, and purification of NPCs before transplantation are top priorities to overcome. In this study, we developed a safe and cost-effective pipeline to generate clinically relevant NPCs. We first isolated cells from patients' urine and reprogrammed them into iPSCs by non-integrating Sendai viral vectors, and carried out experiments on neural differentiation. NPCs were purified by A2B5, an antibody specifically recognizing a glycoganglioside on the cell surface of neural lineage cells, via fluorescence activated cell sorting. Upon further in vitro induction, NPCs were able to give rise to neurons, oligodendrocytes and astrocytes. To test the functionality of the A2B5+ NPCs, we grafted them into the contused mouse thoracic spinal cord. Eight weeks after transplantation, the grafted cells survived, integrated into the injured spinal cord, and differentiated into neurons and glia. Our specific focus on cell source, reprogramming, differentiation and purification method purposely addresses timing and safety issues of transplantation to SCI models. It is our belief that this work takes one step closer on using human iPSC derivatives to SCI clinical settings.

CNS Target Identification and Validation: Avoiding the Valley of Death or Naive Optimism?

There are many challenges along the path to the approval of new drugs to treat CNS disorders, one of the greatest areas of unmet medical need with a large societal burden and health-care impact. Unfortunately, over the past two decades, few CNS drug approvals have succeeded, leading many pharmaceutical companies to deprioritize this therapeutic area. The reasons for the failures in CNS drug discovery are likely to be multifactorial. However, selecting the most biologically plausible molecular targets that are relevant to the disorder is a critical first step to improve the probability of success. In this review, we outline previous methods for identifying and validating novel targets for CNS drug discovery, and, cognizant of previous failures, we discuss potential new strategies that may improve the probability of success of developing novel treatments for CNS disorders.