Vujic, A., et al., 2018. Exercise induces new cardiomyocyte generation in the adult mammalian heart. Nature Communications , 9 (1659). Publisher's VersionAbstract
Loss of cardiomyocytes is a major cause of heart failure, and while the adult heart has a limited capacity for cardiomyogenesis, little is known about what regulates this ability or whether it can be effectively harnessed. Here we show that 8 weeks of running exercise increase birth of new cardiomyocytes in adult mice (~4.6-fold). New cardiomyocytes are identified based on incorporation of 15N-thymidine by multi-isotope imaging mass spectrometry (MIMS) and on being mononucleate/diploid. Furthermore, we demonstrate that exercise after myocardial infarction induces a robust cardiomyogenic response in an extended border zone of the infarcted area. Inhibition of miR-222, a microRNA increased by exercise in both animal models and humans, completely blocks the cardiomyogenic exercise response. These findings demonstrate that cardiomyogenesis can be activated by exercise in the normal and injured adult mouse heart and suggest that stimulation of endogenous cardiomyocyte generation could contribute to the benefits of exercise.
Rodriguez-Muela, N., et al., 2018. Blocking p62/SQSTM1-dependent SMN degradation ameliorates Spinal Muscular Atrophy disease phenotypes. J Clin Invest.Abstract
Spinal muscular atrophy (SMA), a degenerative motor neuron (MN) disease caused by loss of functional SMN protein due to SMN1 gene mutations, is a leading cause of infant mortality. Increasing SMN levels ameliorates the disease phenotype and is unanimously accepted as a therapeutic approach for SMA patients. The ubiquitin/proteasome system is known to regulate SMN protein levels; however whether autophagy controls SMN levels remains poorly explored. Here we show that SMN protein is degraded by autophagy. Pharmacological and genetic inhibition of autophagy increase SMN levels, while induction of autophagy decreases SMN. SMN degradation occurs via its interaction with the autophagy adapter p62/SQSTM1. We also show that SMA neurons display reduced autophagosome clearance, increased p62/ubiquitinated protein levels, and hyperactivated mTORC1 signaling. Importantly, reducing p62 levels markedly increases SMN and its binding partner gemin2, promotes MN survival and extends lifespan in fly and mouse SMA models revealing p62 as a new potential therapeutic target to treat SMA.
Ordureau, A., et al., 2018. Dynamics of PARKIN-Dependent Mitochondrial Ubiquitylation in Induced Neurons and Model Systems Revealed by Digital Snapshot Proteomics. Mol Cell , 70 (2) , pp. 211-227.e8.Abstract
Flux through kinase and ubiquitin-driven signaling systems depends on the modification kinetics, stoichiometry, primary site specificity, and target abundance within the pathway, yet we rarely understand these parameters and their spatial organization within cells. Here we develop temporal digital snapshots of ubiquitin signaling on the mitochondrial outer membrane in embryonic stem cell-derived neurons, and we model HeLa cell systems upon activation of the PINK1 kinase and PARKIN ubiquitin ligase by proteomic counting of ubiquitylation and phosphorylation events. We define the kinetics and site specificity of PARKIN-dependent target ubiquitylation, and we demonstrate the power of this approach to quantify pathway modulators and to mechanistically define the role of PARKIN UBL phosphorylation in pathway activation in induced neurons. Finally, through modulation of pS65-Ub on mitochondria, we demonstrate that Ub hyper-phosphorylation is inhibitory to mitophagy receptor recruitment, indicating that pS65-Ub stoichiometry in vivo is optimized to coordinate PARKIN recruitment via pS65-Ub and mitophagy receptors via unphosphorylated chains.
Christiansen, E.M., et al., 2018. In Silico Labeling: Predicting Fluorescent Labels in Unlabeled Images. Cell , 173 (3) , pp. 792-803.e19.Abstract
Microscopy is a central method in life sciences. Many popular methods, such as antibody labeling, are used to add physical fluorescent labels to specific cellular constituents. However, these approaches have significant drawbacks, including inconsistency; limitations in the number of simultaneous labels because of spectral overlap; and necessary perturbations of the experiment, such as fixing the cells, to generate the measurement. Here, we show that a computational machine-learning approach, which we call "in silico labeling" (ISL), reliably predicts some fluorescent labels from transmitted-light images of unlabeled fixed or live biological samples. ISL predicts a range of labels, such as those for nuclei, cell type (e.g., neural), and cell state (e.g., cell death). Because prediction happens in silico, the method is consistent, is not limited by spectral overlap, and does not disturb the experiment. ISL generates biological measurements that would otherwise be problematic or impossible to acquire.
Paik, E.J., et al., 2018. Using intracellular markers to identify a novel set of surface markers for live cell purification from a heterogeneous hIPSC culture. Sci Rep , 8 (1) , pp. 804.Abstract
Human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) can provide sources for midbrain dopaminergic (mDA) neural progenitors (NPCs) for cell therapy to treat Parkinson's disease (PD) patients. However, the well-known line-to-cell line variability in the differentiation capacity of individual cell lines needs to be improved for the success of this therapy. To address this issue, we sought to identify mDA NPC specific cell surface markers for fluorescence activated cell sorting (FACS). Through RNA isolation after sorting for NPCs based on staining for cell-specific transcription factors followed by microarray, we identified two positive cell surface markers (CORIN and CD166) and one negative cell surface marker (CXCR4) for mDA NPC sorting. These three markers can enrich floor plate NPCs to 90% purity, and the sorted NPCs more efficiently differentiate to mature dopaminergic neurons compared to unsorted or CORIN alone mDA NPCs. This surface marker identification strategy can be used broadly to facilitate isolation of cell subtypes of interest from heterogeneous cultures.
Natarajan, N., et al., 2018. Complement Receptor C5aR1 Plays an Evolutionarily Conserved Role in Successful Cardiac Regeneration. Circulation , 137 (5). Publisher's VersionAbstract

Background—Defining conserved molecular pathways in animal models of successful cardiac regeneration could yield insight into why adult mammals have inadequate cardiac regeneration after injury. Insight into the transcriptomic landscape of early cardiac regeneration from model organisms will shed light on evolutionarily conserved pathways in successful cardiac regeneration.

Methods—Here we describe a cross-species transcriptomic screen in three model organisms for cardiac regeneration -axolotl, neonatal mice and zebrafish. Apical resection to remove ~10 - 20% of ventricular mass was carried out in these model organisms. RNA-seq analysis was performed on the hearts harvested at three time points - 12, 24 and 48 hours post-resection. Sham surgery was used as internal control.

Results—Genes associated with inflammatory processes were found to be upregulated in a conserved manner. Complement receptors (activated by complement components, part of the innate immune system) were found to be highly upregulated in all three species. This approach revealed induction of gene expression for Complement 5a receptor1 (C5aR1) in the regenerating hearts of zebrafish, axolotls and mice. Inhibition of C5aR1 significantly attenuated the cardiomyocyte proliferative response to heart injury in all three species. Furthermore, following left ventricular apical resection, the cardiomyocyte proliferative response was abolished in mice with genetic deletion of C5aR1.

Conclusions—These data reveal that activation of C5aR1 mediates an evolutionarily conserved response that promotes cardiomyocyte proliferation following cardiac injury and identify complement pathway activation as a common pathway of successful heart regeneration.

d'Ydewalle, C., et al., 2017. The Antisense Transcript SMN-AS1 Regulates SMN Expression and Is a Novel Therapeutic Target for Spinal Muscular Atrophy. Neuron , 93 (1) , pp. 66-79.Abstract
The neuromuscular disorder spinal muscular atrophy (SMA), the most common inherited killer of infants, is caused by insufficient expression of survival motor neuron (SMN) protein. SMA therapeutics development efforts have focused on identifying strategies to increase SMN expression. We identified a long non-coding RNA (lncRNA) that arises from the antisense strand of SMN, SMN-AS1, which is enriched in neurons and transcriptionally represses SMN expression by recruiting the epigenetic Polycomb repressive complex-2. Targeted degradation of SMN-AS1 with antisense oligonucleotides (ASOs) increases SMN expression in patient-derived cells, cultured neurons, and the mouse central nervous system. SMN-AS1 ASOs delivered together with SMN2 splice-switching oligonucleotides additively increase SMN expression and improve survival of severe SMA mice. This study is the first proof of concept that targeting a lncRNA to transcriptionally activate SMN2 can be combined with SMN2 splicing modification to ameliorate SMA and demonstrates the promise of combinatorial ASOs for the treatment of neurogenetic disorders.
Feinberg, K., et al., 2017. A neuroprotective agent that inactivates prodegenerative TrkA and preserves mitochondria. J Cell Biol , 216 (11) , pp. 3655-3675.Abstract
Axon degeneration is an early event and pathological in neurodegenerative conditions and nerve injuries. To discover agents that suppress neuronal death and axonal degeneration, we performed drug screens on primary rodent neurons and identified the pan-kinase inhibitor foretinib, which potently rescued sympathetic, sensory, and motor wt and SOD1 mutant neurons from trophic factor withdrawal-induced degeneration. By using primary sympathetic neurons grown in mass cultures and Campenot chambers, we show that foretinib protected neurons by suppressing both known degenerative pathways and a new pathway involving unliganded TrkA and transcriptional regulation of the proapoptotic BH3 family members BimEL, Harakiri,and Puma, culminating in preservation of mitochondria in the degenerative setting. Foretinib delayed chemotherapy-induced and Wallerian axonal degeneration in culture by preventing axotomy-induced local energy deficit and preserving mitochondria, and peripheral Wallerian degeneration in vivo. These findings identify a new axon degeneration pathway and a potentially clinically useful therapeutic drug.
Tripathi, P., et al., 2017. Reactive Astrocytes Promote ALS-like Degeneration and Intracellular Protein Aggregation in Human Motor Neurons by Disrupting Autophagy through TGF-β1. Stem Cell Reports , 9 (2) , pp. 667-680.Abstract
Amyotrophic lateral sclerosis (ALS) is a fatal and rapidly progressing motor neuron disease. Astrocytic factors are known to contribute to motor neuron degeneration and death in ALS. However, the role of astrocyte in promoting motor neuron protein aggregation, a disease hallmark of ALS, remains largely unclear. Here, using culture models of human motor neurons and primary astrocytes of different genotypes (wild-type or SOD1 mutant) and reactive states (non-reactive or reactive), we show that reactive astrocytes, regardless of their genotypes, reduce motor neuron health and lead to moderate neuronal loss. After prolonged co-cultures of up to 2 months, motor neurons show increased axonal and cytoplasmic protein inclusions characteristic of ALS. Reactive astrocytes induce protein aggregation in part by releasing transforming growth factor β1 (TGF-β1), which disrupts motor neuron autophagy through the mTOR pathway. These results reveal the important contribution of reactive astrocytes in promoting aspects of ALS pathology independent of genetic influences.
Ahfeldt, T., Litterman, N.K. & Rubin, L.L., 2017. Studying human disease using human neurons. Brain Res , 1656 , pp. 40-48.Abstract
Utilizing patient derived cells has enormous promise for discovering new drugs for diseases of the nervous system, a goal that has been historically quite challenging. In this review, we will outline the potential of human stem cell derived neuron models for assessing therapeutics and high-throughput screening and compare to more traditional drug discovery strategies. We summarize recent successes of the approach and discuss special considerations for developing human stem cell based assays. New technologies, such as genome editing, offer improvements to help overcome the challenges that remain. Finally, human neurons derived from patient cells have advantages for translational research beyond drug screening as they can also be used to identify individual efficacy and safety prior to clinical testing and for dissecting disease mechanisms. This article is part of a Special Issue entitled SI: Exploiting human neurons.
Palomo, V., et al., 2017. Subtly Modulating Glycogen Synthase Kinase 3 β: Allosteric Inhibitor Development and Their Potential for the Treatment of Chronic Diseases. J Med Chem , 60 (12) , pp. 4983-5001.Abstract
Glycogen synthase kinase 3 β (GSK-3β) is a central target in several unmet diseases. To increase the specificity of GSK-3β inhibitors in chronic treatments, we developed small molecules allowing subtle modulation of GSK-3β activity. Design synthesis, structure-activity relationships, and binding mode of quinoline-3-carbohydrazide derivatives as allosteric modulators of GSK-3β are presented here. Furthermore, we show how allosteric binders may overcome the β-catenin side effects associated with strong GSK-3β inhibition. The therapeutic potential of some of these modulators has been tested in human samples from patients with congenital myotonic dystrophy type 1 (CDM1) and spinal muscular atrophy (SMA) patients. We found that compound 53 improves delayed myogenesis in CDM1 myoblasts, while compounds 1 and 53 have neuroprotective properties in SMA-derived cells. These findings suggest that the allosteric modulators of GSK-3β may be used for future development of drugs for DM1, SMA, and other chronic diseases where GSK-3β inhibition exhibits therapeutic effects.
Quadrato, G., et al., 2017. Cell diversity and network dynamics in photosensitive human brain organoids. Nature , 545 (7652) , pp. 48-53.Abstract
In vitro models of the developing brain such as three-dimensional brain organoids offer an unprecedented opportunity to study aspects of human brain development and disease. However, the cells generated within organoids and the extent to which they recapitulate the regional complexity, cellular diversity and circuit functionality of the brain remain undefined. Here we analyse gene expression in over 80,000 individual cells isolated from 31 human brain organoids. We find that organoids can generate a broad diversity of cells, which are related to endogenous classes, including cells from the cerebral cortex and the retina. Organoids could be developed over extended periods (more than 9 months), allowing for the establishment of relatively mature features, including the formation of dendritic spines and spontaneously active neuronal networks. Finally, neuronal activity within organoids could be controlled using light stimulation of photosensitive cells, which may offer a way to probe the functionality of human neuronal circuits using physiological sensory stimuli.
Kim, J., et al., 2017. Changes in the Excitability of Neocortical Neurons in a Mouse Model of Amyotrophic Lateral Sclerosis Are Not Specific to Corticospinal Neurons and Are Modulated by Advancing Disease. J Neurosci , 37 (37) , pp. 9037-9053.Abstract
Cell type-specific changes in neuronal excitability have been proposed to contribute to the selective degeneration of corticospinal neurons in amyotrophic lateral sclerosis (ALS) and to neocortical hyperexcitability, a prominent feature of both inherited and sporadic variants of the disease, but the mechanisms underlying selective loss of specific cell types in ALS are not known. We analyzed the physiological properties of distinct classes of cortical neurons in the motor cortex of hSOD1G93A mice of both sexes and found that they all exhibit increases in intrinsic excitability that depend on disease stage. Targeted recordings and in vivo calcium imaging further revealed that neurons adapt their functional properties to normalize cortical excitability as the disease progresses. Although different neuron classes all exhibited increases in intrinsic excitability, transcriptional profiling indicated that the molecular mechanisms underlying these changes are cell type specific. The increases in excitability in both excitatory and inhibitory cortical neurons show that selective dysfunction of neuronal cell types cannot account for the specific vulnerability of corticospinal motor neurons in ALS. Furthermore, the stage-dependent alterations in neuronal function highlight the ability of cortical circuits to adapt as disease progresses. These findings show that both disease stage and cell type must be considered when developing therapeutic strategies for treating ALS.SIGNIFICANCE STATEMENT It is not known why certain classes of neurons preferentially die in different neurodegenerative diseases. It has been proposed that the enhanced excitability of affected neurons is a major contributor to their selective loss. We show using a mouse model of amyotrophic lateral sclerosis (ALS), a disease in which corticospinal neurons exhibit selective vulnerability, that changes in excitability are not restricted to this neuronal class and that excitability does not increase monotonically with disease progression. Moreover, although all neuronal cell types tested exhibited abnormal functional properties, analysis of their gene expression demonstrated cell type-specific responses to the ALS-causing mutation. These findings suggest that therapies for ALS may need to be tailored for different cell types and stages of disease.
Arlotta, P. & Vanderhaeghen, P., 2017. Editorial overview: Developmental neuroscience 2017. Curr Opin Neurobiol , 42 , pp. A1-A4.
Quadrato, G. & Arlotta, P., 2017. Present and future of modeling human brain development in 3D organoids. Curr Opin Cell Biol , 49 , pp. 47-52.Abstract
Three-dimensional (3D) brain organoids derived from human pluripotent stem cells hold great potential to investigate complex human genetic states and to model aspects of human brain development and pathology. However, the field of brain organoids is still in its infancy, and their use has been limited by their variability and their inability to differentiate into 3D structures with reproducible anatomical organization. Here, starting from a review of basic principles of in vitro 'brain organogenesis', we discuss which aspects of human brain development and disease can be faithfully modeled with current brain organoid protocols, and discuss improvements that would allow them to become reliable tools to investigate complex features of human brain development and disease.
Chen, Z., et al., 2017. Proposed association between the hexanucleotide repeat of C9orf72 and opposability index of the thumb. Amyotroph Lateral Scler Frontotemporal Degener , 18 (3-4) , pp. 175-181.Abstract
OBJECTIVE: Amyotrophic lateral sclerosis (ALS) is a fatal disease caused by motor neuron and sub-cerebral projection neuron degeneration. We sought to explore the particular susceptibility of humans to neurodegeneration and whether any characteristic human features might predispose to selective vulnerability of the critical motor circuitry in ALS. The pathophysiology of the C9orf72 repeat is not yet understood, despite its role as a common cause of ALS and frontotemporal dementia. METHODS: We examined the development of the monosynaptic cortico-motoneuronal system, key to skilled hand movements, measured by the thumb opposability index, and its relationship to the C9orf72 hexanucleotide repeat expansion, a strong predisposing factor for neurodegeneration, using the genomic tool BLAST. RESULTS: We found a statistically significant linear relationship between the C9orf72 hexanucleotide bit score, a measure of genomic conservation of the aligned region across different species, and the thumb opposability index (Pearson's correlation coefficient of 0.78, p value 0.023). The C9orf72 hexanucleotide repeat was only found in humans, chimpanzees and gorillas, species with higher opposability indices. CONCLUSIONS: This may support a role of the hexanucleotide repeat in the same developmental pathways in species with higher prehensility, which may be associated with the selective vulnerability of cortico-motoneuronal cells in humans, manifested most obviously as the 'split hand' syndrome in ALS.
Rodriguez-Muela, N., et al., 2017. Single-Cell Analysis of SMN Reveals Its Broader Role in Neuromuscular Disease. Cell Rep , 18 (6) , pp. 1484-1498. PubMedAbstract
The mechanism underlying selective motor neuron (MN) death remains an essential question in the MN disease field. The MN disease spinal muscular atrophy (SMA) is attributable to reduced levels of the ubiquitous protein SMN. Here, we report that SMN levels are widely variable in MNs within a single genetic background and that this heterogeneity is seen not only in SMA MNs but also in MNs derived from controls and amyotrophic lateral sclerosis (ALS) patients. Furthermore, cells with low SMN are more susceptible to cell death. These findings raise the important clinical implication that some SMN-elevating therapeutics might be effective in MN diseases besides SMA. Supporting this, we found that increasing SMN across all MN populations using an Nedd8-activating enzyme inhibitor promotes survival in both SMA and ALS-derived MNs. Altogether, our work demonstrates that examination of human neurons at the single-cell level can reveal alternative strategies to be explored in the treatment of degenerative diseases.
Itoh, Y., Poulopoulos, A. & Macklis, J.D., 2017. Unfolding the Folding Problem of the Cerebral Cortex: Movin' and Groovin'. Dev Cell , 41 (4) , pp. 332-334. PubMedAbstract
The development of reproducible folding in the gyrencephalic cerebral cortex is a topic of great interest to neuroscientists. In a recent paper in Cell, del Toro et al. (2017) show that changing the adhesive properties of neurons in the normally lissencephalic mouse cortex leads to the formation of stereotyped folding.
Walker, R.G., et al., 2017. Structural basis for potency differences between GDF8 and GDF11. BMC Biol , 15 (1) , pp. 19.Abstract

BACKGROUND: Growth/differentiation factor 8 (GDF8) and GDF11 are two highly similar members of the transforming growth factor β (TGFβ) family. While GDF8 has been recognized as a negative regulator of muscle growth and differentiation, there are conflicting studies on the function of GDF11 and whether GDF11 has beneficial effects on age-related dysfunction. To address whether GDF8 and GDF11 are functionally identical, we compared their signaling and structural properties. RESULTS: Here we show that, despite their high similarity, GDF11 is a more potent activator of SMAD2/3 and signals more effectively through the type I activin-like receptor kinase receptors ALK4/5/7 than GDF8. Resolution of the GDF11:FS288 complex, apo-GDF8, and apo-GDF11 crystal structures reveals unique properties of both ligands, specifically in the type I receptor binding site. Lastly, substitution of GDF11 residues into GDF8 confers enhanced activity to GDF8. CONCLUSIONS: These studies identify distinctive structural features of GDF11 that enhance its potency, relative to GDF8; however, the biological consequences of these differences remain to be determined.

Fame, R.M., et al., 2017. Subtype-Specific Genes that Characterize Subpopulations of Callosal Projection Neurons in Mouse Identify Molecularly Homologous Populations in Macaque Cortex. Cereb Cortex , 27 (3) , pp. 1817-1830. PubMedAbstract
Callosal projection neurons (CPN) interconnect the neocortical hemispheres via the corpus callosum and are implicated in associative integration of multimodal information. CPN have undergone differential evolutionary elaboration, leading to increased diversity of cortical neurons-and more extensive and varied connections in neocortical gray and white matter-in primates compared with rodents. In mouse, distinct sets of genes are enriched in discrete subpopulations of CPN, indicating the molecular diversity of rodent CPN. Elements of rodent CPN functional and organizational diversity might thus be present in the further elaborated primate cortex. We address the hypothesis that genes controlling mouse CPN subtype diversity might reflect molecular patterns shared among mammals that arose prior to the divergence of rodents and primates. We find that, while early expression of the examined CPN-enriched genes, and postmigratory expression of these CPN-enriched genes in deep layers are highly conserved (e.g., Ptn, Nnmt, Cited2, Dkk3), in contrast, the examined genes expressed by superficial layer CPN show more variable levels of conservation (e.g., EphA3, Chn2). These results suggest that there has been evolutionarily differential retraction and elaboration of superficial layer CPN subpopulations between mouse and macaque, with independent derivation of novel populations in primates. Together, these data inform future studies regarding CPN subpopulations that are unique to primates and rodents, and indicate putative evolutionary relationships.