Transcriptome-based molecular staging of human stem cell-derived retinal organoids uncovers accelerated photoreceptor differentiation by 9-cis retinal.

PURPOSE: Retinal organoids generated from human pluripotent stem cells exhibit considerable variability during differentiation. Our goals are to assess developmental maturity of the neural retina in vitro and design improved protocols based on objective criteria. METHODS: We performed transcriptome analyses of developing retinal organoids from human embryonic and induced pluripotent stem cell lines and utilized multiple bioinformatic tools for comparative analysis. Immunohistochemistry, immunoblotting and electron microscopy were employed for validation. RESULTS: We show that the developmental variability in organoids was reflected in gene expression profiles and could be evaluated by molecular staging with the human fetal and adult retinal transcriptome data. We also demonstrate that the addition of 9-cis retinal, instead of the widely used all-trans retinoic acid, accelerated rod photoreceptor differentiation in organoid cultures, with higher rhodopsin expression and more mature mitochondrial morphology evident by day 120. CONCLUSION: Our studies provide an objective transcriptome-based modality for determining the differentiation state of retinal organoids and for comparisons across different stem cell lines and platforms, which should facilitate disease modeling and evaluation of therapies in vitro.

Concise Review: Human Induced Pluripotent Stem Cell Models of Retinitis Pigmentosa.

Hereditary retinal dystrophies, specifically retinitis pigmentosa (RP) are clinically and genetically heterogeneous diseases affecting primarily retinal cells and retinal pigment epithelial cells with blindness as a final outcome. Understanding the pathogenicity behind these diseases has been largely precluded by the unavailability of affected tissue from patients, large genetic heterogeneity and animal models that do not faithfully represent some human diseases. A landmark discovery of human induced pluripotent stem cells (hiPSCs) permitted the derivation of patient-specific cells. These cells have unlimited self-renewing capacity and the ability to differentiate into RP-affected cell types, allowing the studies of disease mechanism, drug discovery, and cell replacement therapies, both as individual cell types and organoid cultures. Together with precise genome editing, the patient specific hiPSC technology offers novel strategies for targeting the pathogenic mutations and design therapies toward retinal dystrophies. This study summarizes current hiPSC-based RP models and highlights key achievements and challenges of these cellular models, as well as questions that still remain unanswered. Stem Cells 2018;36:474-481.

Concise review: reactive astrocytes and stem cells in spinal cord injury: good guys or bad guys?

Spinal cord injury (SCI) usually results in long lasting locomotor and sensory neuron degeneration below the injury. Astrocytes normally play a decisive role in mechanical and metabolic support of neurons, but in the spinal cord they cause injury, exerting well-known detrimental effects that contribute to glial scar formation and inhibition of axon outgrowth. Cell transplantation is considered a promising approach for replacing damaged cells and promoting neuroprotective and neuroregenerative repair, but the effects of the grafted cells on local tissue and the regenerative properties of endogenous neural stem cells in the injured spinal cord are largely unknown. During the last 2 decades cumulative evidence from diverse animal models has indicated that reactive astrocytes in synergy with transplanted cells could be beneficial for injury in multiple ways, including neuroprotection and axonal growth. In this review, we specifically focus on the dual opposing roles of reactive astrocytes in SCI and how they contribute to the creation of a permissive environment when combined with transplanted cells as the influential components for a local regenerative niche. Modulation of reactive astrocyte function might represent an extremely attractive new therapy to enhance the functional outcomes in patients.

Brief report: astrogliosis promotes functional recovery of completely transected spinal cord following transplantation of hESC-derived oligodendrocyte and motoneuron progenitors.

Spinal cord injury results in neural loss and consequently motor and sensory impairment below the injury. Reactive astrocytes contribute to formation of glial scar, thus impeding axonal regeneration, through secretion of extracellular matrix molecules, chondroitin sulfate proteoglycans (CSPGs). In this study, we analyze lesion site tissue to reveal the possible mechanism underlying the functional recovery after cell transplantation of human embryonic stem cell (hESC)-derived oligodendrocyte progenitor cell (OPC) and motoneuron progenitors (MP) and propose that transplanted cells increase astrogliosis through the regenerative signaling pathways activated in the host tissue that may crucial for restoring locomotor ability. We show that the transplantation of hESC-derived OPC and MP promotes astrogliosis, through activation of Jagged1-dependent Notch and Jak/STAT signaling that support axonal survival. The transplanted cells in synergism with reactive astrocytes create permissive environment in which the expression of detrimental genes (Cspg, Tenascins, and genes involved in SLIT/ROBO signaling) was significantly decreased while expression of beneficial ones (Laminins and Fibronectin) was increased. According to our data, this mechanism is activated in all transplantation groups independently of the level of locomotor recovery. These results indicate that modifying the beneficial function of reactive astrocytes could be a feasible therapeutic strategy for spinal cord injury in future.

Hypoxia increases the yield of photoreceptors differentiating from mouse embryonic stem cells and improves the modeling of retinogenesis in vitro.

Retinitis pigmentosa (RP), a genetically heterogeneous group of diseases together with age-related macular degeneration (AMD), are the leading causes of permanent blindness and are characterized by the progressive dysfunction and death of the light sensing photoreceptors of the retina. Due to the limited regeneration capacity of the mammalian retina, the scientific community has invested significantly in trying to obtain retinal progenitor cells from embryonic stem cells (ESC). These represent an unlimited source of retinal cells, but it has not yet been possible to achieve specific populations, such as photoreceptors, efficiently enough to allow them to be used safely in the future as cell therapy of RP or AMD. In this study, we generated a high yield of photoreceptors from directed differentiation of mouse ESC (mESC) by recapitulating crucial phases of retinal development. We present a new protocol of differentiation, involving hypoxia and taking into account extrinsic and intrinsic cues. These include niche-specific conditions as well as the manipulation of the signaling pathways involved in retinal development. Our results show that hypoxia promotes and improves the differentiation of mESC toward photoreceptors. Different populations of retinal cells are increased in number under the hypoxic conditions applied, such as Crx-positive cells, S-Opsin-positive cells, and double positive cells for Rhodopsin and Recoverin, as shown by immunofluorescence analysis. For the first time, this manuscript reports the high efficiency of differentiation in vivo and the expression of mature rod photoreceptor markers in a large number of differentiated cells, transplanted in the subretinal space of wild-type mice.

Concise review: human pluripotent stem cells in the treatment of spinal cord injury.

Spinal cord injury (SCI) results in neural loss and consequently motor and sensory impairment below the injury. There are currently no effective therapies for the treatment of traumatic SCI in humans. Different kinds of cells including embryonic, fetal, and adult stem cells have been transplanted into animal models of SCI resulting in sensorimotor benefits. Transplantation of human embryonic stem cell (hESC)- or induced pluripotent stem cell (hiPSC)-derived neural cells is nowadays a promising therapy for SCI. This review updates the recent progress in preclinical studies and discusses the advantages and flaws of various neural cell types derived from hESCs and hiPSCs. Before introducing the stem cell replacement strategies in clinical practice, this complex field needs to advance significantly in understanding the lesion itself, the animal model adequacy, and improve cell replacement source. This knowledge will contribute to the successful translation from animals to humans and lead to established guidelines for rigorous safety screening in order to be implemented in clinical practice.

Interfacial behavior of recombinant forms of human pulmonary surfactant protein SP-C.

The behavior at air-liquid interfaces of two recombinant versions of human surfactant protein SP-C has been characterized in comparison with that of native palmitoylated SP-C purified from porcine lungs. Both native and recombinant proteins promoted interfacial adsorption of dipalmitoylphosphatidylcholine bilayers to a limited extent, but catalyzed very rapid formation of films from different lipid mixtures containing both zwitterionic and anionic phospholipids. Once at the interface, the recombinant variants exhibited compression-driven structural transitions, consistent with changes in the orientation of the deacylated N-terminal segment, which were not observed in the native protein. Compression isotherms of lipid/protein films suggest that the recombinant SP-C forms promote expulsion at high pressures of a higher number of lipid molecules per mole of protein than does native SP-C. A more dynamic conformation of the N-terminal segment in recombinant SP-C forms is likely also responsible for facilitating compression-driven condensation of domains in anionic phospholipid films as observed by epifluorescence microscopy. Finally, both native palmitoylated SP-C and the phenylalanine-containing recombinant versions facilitate similarly the repetitive compression-expansion dynamics of lipid/protein films, which were able to reach maximal surface pressures with practically no hysteresis along multiple quasi-static or dynamic cycles.

Mutant PRPF8 Causes Widespread Splicing Changes in Spliceosome Components in Retinitis Pigmentosa Patient iPSC-Derived RPE Cells.

Retinitis pigmentosa (RP) is a rare, progressive disease that affects photoreceptors and retinal pigment epithelial (RPE) cells with blindness as a final outcome. Despite high medical and social impact, there is currently no therapeutic options to slow down the progression of or cure the disease. The development of effective therapies was largely hindered by high genetic heterogeneity, inaccessible disease tissue, and unfaithful model organisms. The fact that components of ubiquitously expressed splicing factors lead to the retina-specific disease is an additional intriguing question. Herein, we sought to correlate the retinal cell-type-specific disease phenotype with the splicing profile shown by a patient with autosomal recessive RP, caused by a mutation in pre-mRNA splicing factor 8 (PRPF8). In order to get insight into the role of PRPF8 in homeostasis and disease, we capitalize on the ability to generate patient-specific RPE cells and reveal differentially expressed genes unique to RPE cells. We found that spliceosomal complex and ribosomal functions are crucial in determining cell-type specificity through differential expression and alternative splicing (AS) and that PRPF8 mutation causes global changes in splice site selection and exon inclusion that particularly affect genes involved in these cellular functions. This finding corroborates the hypothesis that retinal tissue identity is conferred by a specific splicing program and identifies retinal AS events as a framework toward the design of novel therapeutic opportunities.

Unraveling the Developmental Roadmap toward Human Brown Adipose Tissue.

Increasing brown adipose tissue (BAT) mass and activation is a therapeutic strategy to treat obesity and complications. Obese and diabetic patients possess low amounts of BAT, so an efficient way to expand their mass is necessary. There is limited knowledge about how human BAT develops, differentiates, and is optimally activated. Accessing human BAT is challenging, given its low volume and anatomical dispersion. These constraints make detailed BAT-related developmental and functional mechanistic studies in humans virtually impossible. We have developed and characterized functionally and molecularly a new chemically defined protocol for the differentiation of human pluripotent stem cells (hPSCs) into brown adipocytes (BAs) that overcomes current limitations. This protocol recapitulates step by step the physiological developmental path of human BAT. The BAs obtained express BA and thermogenic markers, are insulin sensitive, and responsive to ß-adrenergic stimuli. This new protocol is scalable, enabling the study of human BAs at early stages of development.

Pluripotent stem cell regulation in Spain and the Spanish National Stem Cell Bank.

The Spanish National Stem Cell Bank (Banco Nacional de Líneas Celulares, BNLC) was established in 2006 thanks to a change in the legislative framework in Spain. The Law 14/2006 updated the previous Assisted Reproduction Techniques Law (Law 45/2003) allowing the use of the surplus frozen embryos following IVF for research. The BNLC has a network structure with 3 nodes: the Regenerative Medicine Program (IDIBELL), the Principe Felipe Research Center (CIPF) in Valencia and the Andalusian Public Health System Biobank (SSPA Biobank) in Granada. The aim of the BNLC is to guarantee throughout the national territory the availability of human stem cell lines for biomedical research. At present time, there are 40 human embryonic stem cell lines (hESC) and 171 human induced pluripotent stem cell lines (hiPSC) registered in the BNLC. These lines are fully characterized and available in the context of research projects approved by the Technical Committee of the BNLC.

Retinal Organoids derived from hiPSCs of an AIPL1-LCA Patient Maintain Cytoarchitecture despite Reduced levels of Mutant AIPL1.

Aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1) is a photoreceptor-specific chaperone that stabilizes the effector enzyme of phototransduction, cGMP phosphodiesterase 6 (PDE6). Mutations in the AIPL1 gene cause a severe inherited retinal dystrophy, Leber congenital amaurosis type 4 (LCA4), that manifests as the loss of vision during the first year of life. In this study, we generated three-dimensional (3D) retinal organoids (ROs) from human induced pluripotent stem cells (hiPSCs) derived from an LCA4 patient carrying a Cys89Arg mutation in AIPL1. This study aimed to (i) explore whether the patient hiPSC-derived ROs recapitulate LCA4 disease phenotype, and (ii) generate a clinically relevant resource to investigate the molecular mechanism of disease and safely test novel therapies for LCA4 in vitro. We demonstrate reduced levels of the mutant AIPL1 and PDE6 proteins in patient organoids, corroborating the findings in animal models; however, patient-derived organoids maintained retinal cell cytoarchitecture despite significantly reduced levels of AIPL1.

Generation of an iPSC line from a retinitis pigmentosa patient carrying a homozygous mutation in CERKL and a healthy sibling.

Dermal fibroblasts from an autosomal recessive retinitis pigmentosa (RP) patient, homozygous for the mutation c.769 C>T, p.Arg257Ter, in CERKL (Ceramide Kinase-Like) gene, and a healthy sibling were derived and reprogrammed by Sendai virus. The generated human induced pluripotent stem cell (hiPSC) lines RP3-FiPS4F1 and Ctrl3-FiPS4F1, were free of genomically integrated reprogramming genes, showed stable karyotypes, expressed pluripotency markers and could be differentiated towards the three germ layers in vitro. These hiPSC lines offer a useful resource to study RP pathomechanisms, drug testing and therapeutic opportunities.

Generation of gene-corrected human induced pluripotent stem cell lines derived from retinitis pigmentosa patient with Ser331Cysfs*5 mutation in MERTK.

The human induced pluripotent stem cell (hiPSC) line RP1-FiPS4F1 generated from the patient with autosomal recessive retinitis pigmentosa (arRP) caused by homozygous Ser331Cysfs*5 mutation in Mer tyrosine kinase receptor (MERTK) was genetically corrected using CRISPR/Cas9 system. Two isogenic hiPSCs lines, with heterozygous and homozygous correction of c.992_993delCA mutation in the MERTK gene were generated. These cell lines demonstrate normal karyotype, maintain a pluripotent state, and can differentiate toward three germ layers in vitro. These genetically corrected hiPSCs represent accurate controls to study the contribution of the specific genetic change to the disease, and potentially therapeutic material for cell-replacement therapy.

Synthetic pulmonary surfactant preparations: new developments and future trends.

Pulmonary surfactant is a lipid-protein complex that coats the interior of the alveoli and enables the lungs to function properly. Upon its synthesis, lung surfactant adsorbs at the interface between the air and the hypophase, a capillary aqueous layer covering the alveoli. By lowering and modulating surface tension during breathing, lung surfactant reduces respiratory work of expansion, and stabilises alveoli against collapse during expiration. Pulmonary surfactant deficiency, or dysfunction, contributes to several respiratory pathologies, such as infant respiratory distress syndrome (IRDS) in premature neonates, and acute respiratory distress syndrome (ARDS) in children and adults. The main clinical exogenous surfactants currently in use to treat some of these pathologies are essentially organic extracts obtained from animal lungs. Although very efficient, natural surfactants bear serious defects: i) they could vary in composition from batch to batch; ii) their production involves relatively high costs, and sources are limited; and iii) they carry a potential risk of transmission of animal infectious agents and the possibility of immunological reaction. All these caveats justify the necessity for a highly controlled synthetic material. In the present review the efforts aimed at new surfactant development, including the modification of existing exogenous surfactants by adding molecules that can enhance their activity, and the progress achieved in the production of completely new preparations, are discussed.

Generation of a human iPSC line by mRNA reprogramming.

The human iPSC cell line, derived from foreskin fibroblasts was generated by non-integrative, non-viral reprogramming technology using OCT4, SOX2, KLF4, LIN28, c-MYC mRNAs.

Generation of a human iPSC line from a patient with Leber congenital amaurosis caused by mutation in AIPL1.

The human induced pluripotent stem cell (hiPSC) line, derived from dermal fibroblasts from Leber congenital amaurosis patient with homozygous mutation c.265 T > C, p.Cys89Arg in aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1) was generated by Sendai virus reprogramming. The generated hiPSC line was free of Sendai virus genes, had stable karyotype, carried the homozygous mutation, was immunopositive to pluripotency markers and able to generate all three germ layers upon embryoid body formation. Resource table.

Generation of a human iPSC line from a patient with congenital glaucoma caused by mutation in CYP1B1 gene.

The human iPSC cell line, GLC-FiPS4F1 (ESi047-A), derived from dermal fibroblast from the patient with congenital glaucoma caused by the mutation of the gene CYP1B1, was generated by non-integrative reprogramming technology using OCT3/4, SOX2, CMYC and KLF4 reprogramming factors.

Production and characterisation of recombinant forms of human pulmonary surfactant protein C (SP-C): Structure and surface activity.

Surfactant protein C (SP-C) is an essential component for the surface tension-lowering activity of the pulmonary surfactant system. It contains a valine-rich alpha helix that spans the lipid bilayer, and is one of the most hydrophobic proteins known so far. SP-C is also an essential component of various surfactant preparations of animal origin currently used to treat neonatal respiratory distress syndrome (NRDS) in preterm infants. The limited supply of this material and the risk of transmission of infectious agents and immunological reactions have prompted the development of synthetic SP-C-derived peptides or recombinant humanized SP-C for inclusion in new preparations for therapeutic use. We describe herein the recombinant production in bacterial cultures of SP-C variants containing phenylalanines instead of the palmitoylated cysteines of the native protein, as fusions to the hydrophilic nuclease A (SN) from Staphylococcus aureus. The resulting chimerae were partially purified by affinity chromatography and subsequently subjected to protease digestion. The SP-C forms were recovered from the digestion mixtures by organic extraction and further purified by size exclusion chromatography. The two recombinant SP-C variants so obtained retained more than 50% alpha-helical content and showed surface activity comparable to the native protein, as measured by surface spreading of lipid/protein suspensions and from compression pi-A isotherms of lipid/protein films. Compared to the protein purified from porcine lungs, the recombinant SP-C forms improved movement of phospholipid molecules into the interface (during adsorption), or out from the interfacial film (during compression), suggesting new possibilities to develop improved therapeutic preparations.

Generation of a human iPSC line from a patient with retinitis pigmentosa caused by mutation in PRPF8 gene.

The human iPSC cell line, RP2-FiPS4F1 (RCPFi001-A), derived from dermal fibroblasts from the patient with retinitis pigmentosa caused by the mutation of the gene PRPF8, was generated by non-integrative reprogramming technology using OCT3/4, SOX2, CMYC and KLF4 reprogramming factors.

hiPSC Disease Modeling of Rare Hereditary Cerebellar Ataxias: Opportunities and Future Challenges.

Cerebellar ataxias are clinically and genetically heterogeneous diseases affecting primary cerebellar cells. The lack of availability of affected tissue from cerebellar ataxias patients is the main obstacle in investigating the pathogenicity of these diseases. The landmark discovery of human-induced pluripotent stem cells (hiPSC) has permitted the derivation of patient-specific cells with an unlimited self-renewing capacity. Additionally, their potential to differentiate into virtually any cell type of the human organism allows for large amounts of affected cells to be generated in culture, converting this hiPSC technology into a revolutionary tool in the study of the mechanisms of disease, drug discovery, and gene correction. In this review, we will summarize the current studies in which hiPSC were utilized to study cerebellar ataxias. Describing the currently available 2D and 3D hiPSC-based cellular models, and due to the fact that extracerebellar cells were used to model these diseases, we will discuss whether or not they represent a faithful cellular model and whether they have contributed to a better understanding of disease mechanisms.