Directly reprogrammed Huntington's disease neural precursor cells generate striatal neurons exhibiting aggregates and impaired neuronal maturation

GelMA hydrogel as a scaffold to enhance the survival and differentiation of human induced lateral ganglionic eminence precursor cells

Cell reprogramming holds enormous potential to revolutionize our understanding of neurological and neurodevelopmental disorders, as well as enhance drug discovery and regenerative medicine. We have developed a direct cell reprogramming technology that allows us to generate lineage-specific neural cells. To extend our technology, we have investigated the incorporation of directly reprogrammed human lateral ganglionic eminence precursor cells (hiLGEPs) in a 3-dimensional (3D) matrix. Hydrogels are one of the most promising bio-scaffolds for 3D cell culture, providing cells with a supportive environment to adhere, proliferate, and differentiate. In particular, gelatin methacryloyl (GelMA) hydrogels have been used for a variety of 3D biomedical applications due to their biocompatibility, enzymatic cleavage, cell adhesion and tunable physical characteristics. This study therefore investigated the effect of GelMA hydrogel encapsulation on the survival and differentiation of hiLGEPs, both in vitro and following ex vivo transplantation into a quinolinic acid (QA) lesion rat organotypic slice culture model. We demonstrate, for the first time, that the encapsulation of hiLGEPs in GelMA hydrogel significantly enhances the survival and generation of DARPP32+ striatal neurons both in vitro and following ex vivo transplant. Furthermore, GelMA-encapsulated hiLGEPs were predominantly located away from the reactive astrocyte network that forms following QA lesioning, suggesting GelMA provides a protective barrier for cells in regions of inflammatory activation. Overall, these results indicate that GelMA hydrogel has the potential to act as a 3D bio-scaffold to augment the viability and differentiation of hiLGEPs for research and translation of pharmaceutical development and regenerative medicine.

Direct Reprogramming of Somatic Skin Cells from a Patient with Huntington's Disease into Striatal Neurons to Create Models of Pathology

A new in vitro model of Huntington's disease (HD) was developed via a direct reprogramming of dermal fibroblasts from HD patients into striatal neurons. A reprogramming into induced pluripotent stem (iPS) cells is obviated in the case of direct reprogramming, which thus yields neurons that preserve the epigenetic information inherent in cells of a particular donor and, consequently, the age-associated disease phenotype. A main histopathological feature of HD was reproduced in the new model; i.e., aggregates of mutant huntingtin accumulated in striatal neurons derived from a patient's fibroblasts. Experiments with cultured neurons obtained via direct reprogramming make it possible to individually assess the progression of neuropathology and to implement a personalized approach to choosing the treatment strategy and drugs for therapy. The in vitro model of HD can be used in preclinical drug studies.

Brain-Derived Neurotrophic Factor Dysregulation as an Essential Pathological Feature in Huntington's Disease: Mechanisms and Potential Therapeutics

Brain-derived neurotrophic factor (BDNF) is a major neurotrophin whose loss or interruption is well established to have numerous intersections with the pathogenesis of progressive neurological disorders. There is perhaps no greater example of disease pathogenesis resulting from the dysregulation of BDNF signaling than Huntington's disease (HD)-an inherited neurodegenerative disorder characterized by motor, psychiatric, and cognitive impairments associated with basal ganglia dysfunction and the ultimate death of striatal projection neurons. Investigation of the collection of mechanisms leading to BDNF loss in HD highlights this neurotrophin's importance to neuronal viability and calls attention to opportunities for therapeutic interventions. Using electronic database searches of existing and forthcoming research, we constructed a literature review with the overarching goal of exploring the diverse set of molecular events that trigger BDNF dysregulation within HD. We highlighted research that investigated these major mechanisms in preclinical models of HD and connected these studies to those evaluating similar endpoints in human HD subjects. We also included a special focus on the growing body of literature detailing key transcriptomic and epigenetic alterations that affect BDNF abundance in HD. Finally, we offer critical evaluation of proposed neurotrophin-directed therapies and assessed clinical trials seeking to correct BDNF expression in HD individuals.

Induced pluripotent stem cell-derived and directly reprogrammed neurons to study neurodegenerative diseases: The impact of aging signatures

Many diseases of the central nervous system are age-associated and do not directly result from genetic mutations. These include late-onset neurodegenerative diseases (NDDs), which represent a challenge for biomedical research and drug development due to the impossibility to access to viable human brain specimens. Advancements in reprogramming technologies have allowed to obtain neurons from induced pluripotent stem cells (iPSCs) or directly from somatic cells (iNs), leading to the generation of better models to understand the molecular mechanisms and design of new drugs. Nevertheless, iPSC technology faces some limitations due to reprogramming-associated cellular rejuvenation which resets the aging hallmarks of donor cells. Given the prominent role of aging for the development and manifestation of late-onset NDDs, this suggests that this approach is not the most suitable to accurately model age-related diseases. Direct neuronal reprogramming, by which a neuron is formed via direct conversion from a somatic cell without going through a pluripotent intermediate stage, allows the possibility to generate patient-derived neurons that maintain aging and epigenetic signatures of the donor. This aspect may be advantageous for investigating the role of aging in neurodegeneration and for finely dissecting underlying pathological mechanisms. Here, we will compare iPSC and iN models as regards the aging status and explore how this difference is reported to affect the phenotype of NDD in vitro models.

Molecular Pathophysiological Mechanisms in Huntington's Disease

Huntington’s disease is an inherited neurodegenerative disease described 150 years ago by George Huntington. The genetic defect was identified in 1993 to be an expanded CAG repeat on exon 1 of the huntingtin gene located on chromosome 4. In the following almost 30 years, a considerable amount of research, using mainly animal models or in vitro experiments, has tried to unravel the complex molecular cascades through which the transcription of the mutant protein leads to neuronal loss, especially in the medium spiny neurons of the striatum, and identified excitotoxicity, transcriptional dysregulation, mitochondrial dysfunction, oxidative stress, impaired proteostasis, altered axonal trafficking and reduced availability of trophic factors to be crucial contributors. This review discusses the pathogenic cascades described in the literature through which mutant huntingtin leads to neuronal demise. However, due to the ubiquitous presence of huntingtin, astrocytes are also dysfunctional, and neuroinflammation may additionally contribute to Huntington’s disease pathology. The quest for therapies to delay the onset and reduce the rate of Huntington’s disease progression is ongoing, but is based on findings from basic research.

Cell Reprogramming to Model Huntington's Disease: A Comprehensive Review

Huntington’s disease (HD) is a neurodegenerative disorder characterized by the progressive decline of motor, cognitive, and psychiatric functions. HD results from an autosomal dominant mutation that causes a trinucleotide CAG repeat expansion and the production of mutant Huntingtin protein (mHTT). This results in the initial selective and progressive loss of medium spiny neurons (MSNs) in the striatum before progressing to involve the whole brain. There are currently no effective treatments to prevent or delay the progression of HD as knowledge into the mechanisms driving the selective degeneration of MSNs has been hindered by a lack of access to live neurons from individuals with HD. The invention of cell reprogramming provides a revolutionary technique for the study, and potential treatment, of neurological conditions. Cell reprogramming technologies allow for the generation of live disease-affected neurons from patients with neurological conditions, becoming a primary technique for modelling these conditions in vitro. The ability to generate HD-affected neurons has widespread applications for investigating the pathogenesis of HD, the identification of new therapeutic targets, and for high-throughput drug screening. Cell reprogramming also offers a potential autologous source of cells for HD cell replacement therapy. This review provides a comprehensive analysis of the use of cell reprogramming to model HD and a discussion on recent advancements in cell reprogramming technologies that will benefit the HD field.

Directly reprogrammed Huntington's disease neural precursor cells generate striatal neurons exhibiting aggregates and impaired neuronal maturation

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterized by the progressive loss of striatal medium spiny neurons. Using a highly efficient protocol for direct reprogramming of adult human fibroblasts with chemically modified mRNA, we report the first generation of HD induced neural precursor cells (iNPs) expressing striatal lineage markers that differentiated into DARPP32+ neurons from individuals with adult-onset HD (41-57 CAG). While no transcriptional differences between normal and HD reprogrammed neurons were detected by NanoString nCounter analysis, a subpopulation of HD reprogrammed neurons contained ubiquitinated polyglutamine aggregates. Importantly, reprogrammed HD neurons exhibited impaired neuronal maturation, displaying altered neurite morphology and more depolarized resting membrane potentials. Reduced BDNF protein expression in reprogrammed HD neurons correlated with increased CAG repeat lengths and earlier symptom onset. This model represents a platform for investigating impaired neuronal maturation and screening for neuronal maturation modifiers to treat HD.