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31p.-7 fig. 1 graph. abst., Frontotemporal dementia is the second most prevalent type of early-onset dementia and up to 40% of cases are familial forms. One of the genes mutated in patients is CHMP2B, which encodes a protein found in a complex important for maturation of late endosomes, an essential process for recycling membrane proteins through the endolysosomal system. Here, we have generated a CHMP2B-mutated human embryonic stem cell line using genome editing with the purpose to create a human in vitro Frontotemporal dementia disease model. To date, most studies have focused on neuronal alterations; however, we present a new co-culture system in which neurons and astrocytes are independently generated from human embryonic stem cells and combined in co-cultures. With this approach, we have identified alterations in the endolysosomal system of Frontotemporal dementia astrocytes, a higher capacity of astrocytes to uptake and respond to glutamate, and a neuronal network hyperactivity as well as excessive synchronization. Overall, our data indicates that astrocyte alterations precede neuronal impairments and could potentially trigger neuronal network changes, indicating the important and specific role of astrocytes in disease development., This study was supported by funding from the Swedish Society for Medical Research (SSMF, S20-0003), Kockska, Segerfalk and Hardebo foundations to IC; the Swedish Research Council (VR:2018-02695), Swedish Alzheimer and Åhlen foundations to HA; the Swedish Research Council (VR:2016-01789) to AH; and the Agencia Estatal de Investigación, Ministerio de Ciencia e Innovación (RTI2018-097624-BI00) and European Regional Development Fund to DPS.

Label-free chemical and structural imaging of complex living tissue and biological systems is the holy grail of biomedical research and clinical diagnostics. The current analysis techniques are time-consuming and/or require extensive sample preparation, often due to the presence of interfering molecules such as water, making them unsuitable for the analysis of such systems. Here, we demonstrate a proof-of-principle study using label-free optical photothermal mid-infrared microspectroscopy (O-PTIR) for fast, direct spatiotemporal chemical analysis of complex living biological systems at submicron resolution. While other analytical methods can provide only static snapshots of molecular structures, our O-PTIR approach enables time-resolved and in situ investigation of chemical and structural changes of diverse biomolecules in their native conditions. This comprises a technological breakthrough in infrared spectroscopy to analyze biomolecules under native conditions over time: in fresh unprocessed biopsies, living brain tissue, and vertebrates without compromising their viability.One-Sentence SummaryProof-of-principle application of non-destructive O-PTIR for high-resolution spatiotemporal chemical and structural analysis of unprocessed biopsies, living brain tissue, and vertebrates.

Peer reviewed: True, Funder: New York Stem Cell Foundation; Id: http://dx.doi.org/10.13039/100003194, Funder: Parkinsonfonden; Id: http://dx.doi.org/10.13039/100008444, Funder: Lund University; Id: http://dx.doi.org/10.13039/501100003252, Funder: HORIZON EUROPE Marie Sklodowska-Curie Actions, Significant efforts are ongoing to develop refined differentiation protocols to generate midbrain dopamine (DA) neurons from pluripotent stem cells for application in disease modeling, diagnostics, drug screening and cell-based therapies for Parkinson's disease. An increased understanding of the timing and molecular mechanisms that promote the generation of distinct subtypes of human midbrain DA during development will be essential for guiding future efforts to generate molecularly defined and subtype-specific DA neurons from pluripotent stem cells. Here, we use droplet-based single-cell RNA sequencing to transcriptionally profile the developing human ventral midbrain (VM) when the DA neurons are generated (6-11 weeks post-conception) and their subsequent differentiation into functional mature DA neurons in primary fetal 3D organoid-like cultures. This approach reveals that 3D cultures are superior to monolayer conditions for their ability to generate and maintain mature DA neurons; hence, they have the potential to be used for studying human VM development. These results provide a unique transcriptional profile of the developing human fetal VM and functionally mature human DA neurons that can be used to guide stem cell-based therapies and disease modeling approaches in Parkinson's disease.

Direct reprogramming is an emerging research field where you can generate neurons from a somatic cell, such as a skin or glial cell by overexpressing neurogenic transcription factors. This technique allows fast generation of subtype-specific and functional neurons from both human and mouse cells. Despite the fact that neurons have been successfully generated both in vitro and in vivo, a more extensive analysis of the induced neurons including phenotypic functional identity or gradual maturity is still lacking. This is an important step for a further development of induced neurons towards cell therapy or disease modeling of neurological diseases. In this protocol, we describe a method for functional assessment of direct reprogrammed neuronal cells both in vitro and in vivo. Using a synapsin-driven reporter, our protocol allows for a direct identification of the reprogrammed neurons that permits functional assessment using patch-clamp electrophysiology. For in vitro reprogramming we further provide an optimized coating condition that allows a long-term maturation of human induced neurons in vitro.

The brain tissue has only a limited capacity for generating new neurons. Therefore, to treat neurological diseases, there is a need of other cell sources for brain repair. Different sources of cells have been subject of intense research over the years, including cells from primary tissue, stem cell-derived cells and reprogrammed cells. As an alternative, direct reprogramming of resident brain cells into neurons is a recent approach that could provide an attractive method for treating brain injuries or diseases as it uses the patient’s own cells for generating novel neurons inside the brain. In vivo reprogramming is still in its early stages but holds great promise as an option for cell therapy. To date, both inhibitory and excitatory neurons have been obtained via in vivo reprogramming, but the precise phenotype or functionality of these cells has not been analysed in detail in most of the studies. Recent data shows that in vivo reprogrammed neurons are able to functionally mature and integrate into the existing brain circuitry, and compose interneuron phenotypes that seem to correlate to their endogenous counterparts. Interneurons are of particular importance as they are essential in physiological brain function and when disturbed lead to several neurological disorders. In this review, we describe a comprehensive overview of the existing studies involving brain repair, including in vivo reprogramming, with a focus on interneurons, along with an overview on current efforts to generate interneurons for cell therapy for a number of neurological diseases.

Direct reprogramming is an emerging research field where you can generate neurons from a somatic cell, such as a skin or glial cell by overexpressing neurogenic transcription factors. This technique allows fast generation of subtype-specific and functional neurons from both human and mouse cells. Despite the fact that neurons have been successfully generated both in vitro and in vivo, a more extensive analysis of the induced neurons including phenotypic functional identity or gradual maturity is still lacking. This is an important step for a further development of induced neurons towards cell therapy or disease modeling of neurological diseases. In this protocol, we describe a method for functional assessment of direct reprogrammed neuronal cells both in vitro and in vivo. Using a synapsin-driven reporter, our protocol allows for a direct identification of the reprogrammed neurons that permits functional assessment using patch-clamp electrophysiology. For in vitro reprogramming we further provide an optimized coating condition that allows a long-term maturation of human induced neurons in vitro.

Background: Human induced pluripotent stem cells (hiPSCs) have been proposed as an alternative source for cell replacement therapy for Parkinson’s disease (PD) and they provide the option of using the patient’s own cells. A few studies have investigated transplantation of patient-derived dopaminergic (DA) neurons in preclinical models; however, little is known about the long-term integrity and function of grafts derived from patients with PD. Objective: To assess the viability and function of DA neuron grafts derived from a patient hiPSC line with an α-synuclein gene triplication (AST18), using a clinical grade human embryonic stem cell (hESC) line (RC17) as a reference control. Methods: Cells were differentiated into ventral mesencephalic (VM)-patterned DA progenitors using an established GMP protocol. The progenitors were then either terminally differentiated to mature DA neurons in vitro or transplanted into 6-hydroxydopamine (6-OHDA) lesioned rats and their survival, maturation, function, and propensity to develop α-synuclein related pathology, were assessed in vivo. Results: Both cell lines generated functional neurons with DA properties in vitro. AST18-derived VM progenitor cells survived transplantation and matured into neuron-rich grafts similar to the RC17 cells. After 24 weeks, both cell lines produced DA-rich grafts that mediated full functional recovery; however, pathological changes were only observed in grafts derived from the α-synuclein triplication patient line. Conclusion: This data shows proof-of-principle for survival and functional recovery with familial PD patient-derived cells in the 6-OHDA model of PD. However, signs of slowly developing pathology warrants further investigation before use of autologous grafts in patients.

SUMMARYTransplantation of midbrain dopamine (DA) neurons for the treatment of Parkinson’s disease (PD) is a strategy that has being extensively explored and clinical trials using fetal and stem cell-derived DA neurons are ongoing. An increased understanding of the mechanisms promoting the generation of distinct subtypes of midbrain DA during normal development will be essential for guiding future efforts to precisely generate molecularly defined and subtype specific DA neurons from pluripotent stem cells. In this study, we used droplet-based scRNA-seq to transcriptionally profile a large number of fetal cells from human embryos at different stages of ventral midbrain (VM) development (6, 8, and 11 weeks post conception). This revealed that the emergence of transcriptionally distinct cellular populations was evident already at these early timepoints. To study late events of human DA differentiation and functional maturation, we established a primary fetal 3D culture system that recapitulates key molecular aspects of late human DA neurogenesis and sustains differentiation and functional maturation of DA neurons in a physiologically relevant cellular context. This approach allowed us to define the molecular identities of distinct human DA progenitors and neurons at single cell resolution and construct developmental trajectories of cell types in the developing fetal VM.Overall these findings provide a unique transcriptional profile of developing fetal VM and functionally mature human DA neurons, which can be used to quality control stem cell-derived DA neurons and guide stem cell-based therapies and disease modeling approaches in PD.

Summary Human glial progenitor cells (hGPCs) are promising cellular substrates to explore for the in situ production of new neurons for brain repair. Proof of concept for direct neuronal reprogramming of glial progenitors has been obtained in mouse models in vivo, but conversion using human cells has not yet been demonstrated. Such studies have been difficult to perform since hGPCs are born late during human fetal development, with limited accessibility for in vitro culture. In this study, we show proof of concept of hGPC conversion using fetal cells and also establish a renewable and reproducible stem cell-based hGPC system for direct neural conversion in vitro. Using this system, we have identified optimal combinations of fate determinants for the efficient dopaminergic (DA) conversion of hGPCs, thereby yielding a therapeutically relevant cell type that selectively degenerates in Parkinson's disease. The induced DA neurons show a progressive, subtype-specific phenotypic maturation and acquire functional electrophysiological properties indicative of DA phenotype., Graphical Abstract, Highlights • Human glial progenitors (hGPCs) can be directly converted into functional neurons • Specific transcription factor combinations result in dopaminergic conversion • Reprogrammed neurons show subtype-specific and functional maturation over time, In this article, Parmar and colleagues show proof of concept that human glial progenitors (hGPCs) sourced from fetal brains can be converted into functional neurons. To allow for large-scale studies, a stem cell-based model system that mimics the fetal cell conversion was established and used to identify optimal combinations of fate determinants for the efficient dopaminergic conversion of hGPCs.

The intricate balance between dopaminergic and cholinergic neurotransmission in the striatum has been thoroughly difficult to characterize. It was initially described as a seesaw with a competing function of dopamine versus acetylcholine. Recent technical advances however, have brought this view into question suggesting that the two systems work rather in concert with the cholinergic interneurons (ChIs) driving dopamine release. In this study, we have utilized two transgenic Cre-driver rat lines, a choline acetyl transferase ChAT-Cre transgenic rat and a novel double-transgenic tyrosine hydroxylase TH-Cre/ChAT-Cre rat to further elucidate the role of striatal ChIs in normal motor function and in Parkinson's disease. Here we show that selective and reversible activation of ChIs using chemogenetic (DREADD) receptors increases locomotor function in intact rats and potentiate the therapeutic effect of L-DOPA in the rats with lesions of the nigral dopamine system. However, the potentiation of the L-DOPA effect is accompanied by an aggravation of L-DOPA induced dyskinesias (LIDs). These LIDs appear to be driven primarily through the indirect striato-pallidal pathway since the same effect can be induced by the D2 agonist Quinpirole. Taken together, the results highlight the intricate regulation of balance between the two output pathways from the striatum orchestrated by the ChIs.

Direct neuronal reprogramming can be achieved using different approaches: by expressing neuronal transcription factors or microRNAs; and by knocking down neuronal repressive elements. However, there still exists a high variability in terms of the quality and maturity of the induced neurons obtained, depending on the reprogramming strategy employed. Here, we evaluate different long-term culture conditions and study the effect of expressing the neuronal-specific microRNAs, miR124 and miR9/9*, while reprogramming with forced expression of the transcription factors Ascl1, Brn2, and knockdown of the neuronal repressor REST. We show that the addition of microRNAs supports neuronal maturation in terms of gene and protein expression, as well as in terms of electrophysiological properties.

Converting resident glia in the brain into functional and subtype-specific neurons in vivo provides a step forward towards the development of alternative cell replacement therapies while also creating tools to study cell fate in situ. To date, it has been possible to obtain neurons via in vivo reprogramming, but the precise phenotype of these neurons or how they mature has not been analyzed in detail. In this protocol, we describe a more efficient conversion and cell-specific identification of the in vivo reprogrammed neurons, using an AAV-based viral vector system. We also provide a protocol for functional assessment of the reprogrammed cells' neuronal maturation. By injecting flip-excision (FLEX) vectors, containing the reprogramming and synapsin-driven reporter genes to specific cell types in the brain that serve as the target for cell reprogramming. This technique allows for the easy identification of newly reprogrammed neurons. Results show that the obtained reprogrammed neurons functionally mature over time, receive synaptic contacts and show electrophysiological properties of different types of interneurons. Using the transcription factors Ascl1, Lmx1a and Nurr1, the majority of the reprogrammed cells have properties of fast-spiking, parvalbumin-containing interneurons.

Summary The possibility of directly converting non-neuronal cells into neurons in situ in the brain would open therapeutic avenues aimed at repairing the brain after injury or degenerative disease. We have developed an adeno-associated virus (AAV)-based reporter system that allows selective GFP labeling of reprogrammed neurons. In this system, GFP is turned on only in reprogrammed neurons where it is stable and maintained for long time periods, allowing for histological and functional characterization of mature neurons. When combined with a modified rabies virus-based trans-synaptic tracing methodology, the system allows mapping of 3D circuitry integration into local and distal brain regions and shows that the newly reprogrammed neurons are integrated into host brain., Graphical Abstract, Highlights • Ascl1, Lmx1a, and Nurr1 convert striatal NG2 glia into functional neurons • Cre-inducible AAV conversion vectors result in efficient neural conversion in vivo • A neuron-specific reporter allows for long-term phenotypic and functional analysis • Rabies-based tracing show that converted neurons integrate into local circuitry, Torper et al. have developed an AAV-based system for in vivo neural conversion with neuron-specific reporters allowing for long-term histological and functional characterization. The in-vivo-converted neurons are shown to be functional and integrate into host neural circuits, as assessed with rabies-virus-based tracing.

Summary: Many neurodegenerative diseases are characterized by the presence of intracellular protein aggregates, resulting in alterations in autophagy. However, the consequences of impaired autophagy for neuronal function remain poorly understood. In this study, we used cell culture and mouse models of huntingtin protein aggregation as well as post-mortem material from patients with Huntington’s disease to demonstrate that Argonaute-2 (AGO2) accumulates in the presence of neuronal protein aggregates and that this is due to impaired autophagy. Accumulation of AGO2, a key factor of the RNA-induced silencing complex that executes microRNA functions, results in global alterations of microRNA levels and activity. Together, these results demonstrate that impaired autophagy found in neurodegenerative diseases not only influences protein aggregation but also directly contributes to global alterations of intracellular post-transcriptional networks. : Pircs et al. report that aggregation of the mutant huntingtin protein, a hallmark of Huntington’s disease proteinopathy, impairs macroautophagy, leading to Argonaute-2 accumulation and global dysregulation of microRNAs. These results indicate that autophagy not only influences protein aggregation but also directly contributes to the global alterations of post-transcriptional networks in Huntington’s disease. Keywords: Huntington’s disease, autophagy, microRNA, Argonaute-2, protein aggregation

Direct conversion of human fibroblasts into mature and functional neurons, termed induced neurons (iNs), was achieved for the first time 6 years ago. This technology offers a promising shortcut for obtaining patient‐ and disease‐specific neurons for disease modeling, drug screening, and other biomedical applications. However, fibroblasts from adult donors do not reprogram as easily as fetal donors, and no current reprogramming approach is sufficiently efficient to allow the use of this technology using patient‐derived material for large‐scale applications. Here, we investigate the difference in reprogramming requirements between fetal and adult human fibroblasts and identify REST as a major reprogramming barrier in adult fibroblasts. Via functional experiments where we overexpress and knockdown the REST‐controlled neuron‐specific microRNAs miR‐9 and miR‐124, we show that the effect of REST inhibition is only partially mediated via microRNA up‐regulation. Transcriptional analysis confirmed that REST knockdown activates an overlapping subset of neuronal genes as microRNA overexpression and also a distinct set of neuronal genes that are not activated via microRNA overexpression. Based on this, we developed an optimized one‐step method to efficiently reprogram dermal fibroblasts from elderly individuals using a single‐vector system and demonstrate that it is possible to obtain iNs of high yield and purity from aged individuals with a range of familial and sporadic neurodegenerative disorders including Parkinson9s, Huntington9s, as well as Alzheimer9s disease.

Summary: Recent findings show that human fibroblasts can be directly programmed into functional neurons without passing via a proliferative stem cell intermediate. These findings open up the possibility of generating subtype-specific neurons of human origin for therapeutic use from fetal cell, from patients themselves, or from matched donors. In this study, we present an improved system for direct neural conversion of human fibroblasts. The neural reprogramming genes are regulated by the neuron-specific microRNA, miR-124, such that each cell turns off expression of the reprogramming genes once the cell has reached a stable neuronal fate. The regulated system can be combined with integrase-deficient vectors, providing a nonintegrative and self-regulated conversion system that rids problems associated with the integration of viral transgenes into the host genome. These modifications make the system suitable for clinical use and therefore represent a major step forward in the development of induced neurons for cell therapy. : Lau et al. now use miRNA targeting to build a self-regulating neural conversion system. Combined with nonintegrating vectors, this system can efficiently drive conversion of human fibroblasts into functional induced neurons (iNs) suitable for clinical applications.

Induced neurons (iNs) are reprogrammed somatic cells that are forced to change their fate without passing through a pluripotent state, shortening the process of neuronal generation compared to the use of human pluripotent stem cells. The scientific interest in these cells is explained by their suitable use for disease modelling, drug screening and cell therapy for diseases such as Parkinson Disease (PD). Recently, we have developed an all-in-one vector that delivers two factors, Brn2a and Ascl1, together with a REST (RE1-silencing transcription factor) inhibition to successfully generate neurons from both PD patient and control fibroblasts at high efficiencies. An important characteristic of the reprogrammed cells that has to be taken into account to confirm their neuronal identities is their electrophysiological profile. Here, we aim at studying the electrical activity of iNs using the whole cell patch-clamp technique. We first evaluate different culture conditions by testing different coatings to promote an optimal long-term maturation of the iNs, neccessary for electrophysiological maturity. More specifically, we compare Gelatin, Matrigel, laminin 111 and different polyornithine, laminin and fibronectin triple coatings, and found that the later condition provides better plating and long-term survival (>80 days). We further compare our best coating condition with the co-culturing of iNs with either primary rodent astrocytes or neurons. These experiments will allow further assessment of the long-term adult iNs electrical activity, which constitutes an important step towards using iNs for disease modelling of patient-derived cells.

One of the major symptoms of the neurodegenerative condition Parkinson’s disease is a slowness or loss of voluntary movement, yet frustratingly therapeutic strategies designed to restore movement can result in the development of excessive abnormal movements known as dyskinesia. These dyskinesias commonly develop as a result of pharmacotherapy in the form of L-DOPA administration, but have also been identified following deep brain stimulation and intrastriatal cell transplantation. In the case of L-DOPA these movements can be treatment limiting, and whilst they are not long lasting or troubling following deep brain stimulation, recognition of their development had a near devastating effect on the field of cell transplantation for Parkinson’s disease. Understanding the relationship between these therapeutic approaches and the development of dyskinesia may improve our ability to restore function without disabling side effects. Interestingly, despite the fact that dopaminergic cell transplantation repairs many of the changes induced by the disease process and through L-DOPA treatment, there appears to be a relationship between the two. In rodent models of the disease, the severity of dyskinesia induced by L-DOPA prior to the transplantation procedure correlated with post-transplantation, graft induced dyskinesia. A review of clinical data also suggested that the worse preoperational dyskinesia causes worsened graft-induced dyskinesia. Understanding how these aberrant behaviours come about has been of keen interest to open up these therapeutic options more widely and one major underlying theory is the effects of these approaches on the plasticity of synapses within the basal ganglia. This review uniquely brings together developments in understanding the role of striatal synaptic plasticity in both L-DOPA and graft-induced dyskinesia to guide and stimulate further investigations on the important striatal plasticity.

Reprogramming of cellular identity using exogenous expression of transcription factors (TFs) is a powerful and exciting tool for tissue engineering, disease modeling, and regenerative medicine. However, generation of desired cell types using this approach is often plagued by inefficiency, slow conversion, and an inability to produce mature functional cells. Here, we show that expression of constitutively active SMAD2/3 significantly improves the efficiency of induced pluripotent stem cell (iPSC) generation by the Yamanaka factors. Mechanistically, SMAD3 interacts with reprogramming factors and co-activators and co-occupies OCT4 target loci during reprogramming. Unexpectedly, active SMAD2/3 also markedly enhances three other TF-mediated direct reprogramming conversions, from B cells to macrophages, myoblasts to adipocytes, and human fibroblasts to neurons, highlighting broad and general roles for SMAD2/3 as cell-reprogramming potentiators. Our results suggest that co-expression of active SMAD2/3 could enhance multiple types of TF-based cell identity conversion and therefore be a powerful tool for cellular engineering.

Summary Converting resident glia into functional and subtype-specific neurons in vivo by delivering reprogramming genes directly to the brain provides a step forward toward the possibility of treating brain injuries or diseases. To date, it has been possible to obtain GABAergic and glutamatergic neurons via in vivo conversion, but the precise phenotype of these cells has not yet been analyzed in detail. Here, we show that neurons reprogrammed using Ascl1, Lmx1a, and Nurr1 functionally mature and integrate into existing brain circuitry and that the majority of the reprogrammed neurons have properties of fast-spiking, parvalbumin-containing interneurons. When testing different combinations of genes for neural conversion with a focus on pro-neural genes and dopamine fate determinants, we found that functional neurons can be generated using different gene combinations and in different brain regions and that most of the reprogrammed neurons become interneurons, independently of the combination of reprogramming factors used., Highlights • Reprogramed striatal NG2 glia yield neurons similar to fast-spiking interneurons • Reprogrammed neurons reach functional maturation after 12 weeks • Dopamine (DA) denervation leads to TH expression but no reprogramming into DA neurons • Variation in pro-neural genes or fate specifiers does not affect neuronal phenotype, In this study, Parmar, Ottosson, and colleagues show how endogenous NG2 glia can be reprogrammed into GABAergic interneurons of different subtypes, the majority of them with properties of fast-spiking parvalbumin-containing interneurons. This neuronal subtype has been implicated in several neurological diseases, and the findings can open up new therapeutic options.