Auts2 enhances neurogenesis and promotes expansion of the cerebral cortex.

INTRODUCTION: The AUTS2 gene is associated with various neurodevelopmental and psychiatric disorders and has been suggested to play a role in acquiring human-specific traits. Functional analyses of Auts2 knockout mice have focused on postmitotic neurons, and the reported phenotypes do not faithfully recapitulate the whole spectrum of AUTS2-related human diseases. OBJECTIVE: The objective of the study is to assess the role of AUTS2 in the biology of neural progenitor cells, cortical neurogenesis and expansion; and understand how its deregulation leads to neurological disorders. METHODS: We screened the literature and conducted a time point analysis of AUTS2 expression during cortical development. We used in utero electroporation to acutely modulate the expression level of AUTS2 in the developing cerebral cortex in vivo, and thoroughly characterized cortical neurogenesis and morphogenesis using immunofluorescence, cell tracing and sorting, transcriptomic profiling, and gene ontology enrichment analyses. RESULTS: In addition to its expression in postmitotic neurons, we showed that AUTS2 is also expressed in neural progenitor cells at the peak of neurogenesis. Upregulation of AUTS2 dramatically altered the differentiation program and fate determination of cortical progenitors. Notably, it increased the number of basal progenitors and neurons and changed the expression of hundreds of genes, among which 444 have not been implicated in mouse brain development or function. CONCLUSION: The study provides evidence that AUTS2 is expressed in germinal zones and plays a key role in fate decision of neural progenitor cells with impact on corticogenesis. It also presents comprehensive lists of AUTS2 target genes thus advancing the molecular mechanisms underlying AUTS2-associated diseases and the evolutionary expansion of the cerebral cortex.

Brief report: self-organizing neuroepithelium from human pluripotent stem cells facilitates derivation of photoreceptors.

Retinitis pigmentosa, other inherited retinal diseases, and age-related macular degeneration lead to untreatable blindness because of the loss of photoreceptors. We have recently shown that transplantation of mouse photoreceptors can result in improved vision. It is therefore timely to develop protocols for efficient derivation of photoreceptors from human pluripotent stem (hPS) cells. Current methods for photoreceptor derivation from hPS cells require long periods of culture and are rather inefficient. Here, we report that formation of a transient self-organized neuroepithelium from human embryonic stem cells cultured together with extracellular matrix is sufficient to induce a rapid conversion into retinal progenitors in 5 days. These retinal progenitors have the ability to differentiate very efficiently into Crx(+) photoreceptor precursors after only 10 days and subsequently acquire rod photoreceptor identity within 4 weeks. Directed differentiation into photoreceptors using this protocol is also possible with human-induced pluripotent stem (hiPS) cells, facilitating the use of patient-specific hiPS cell lines for regenerative medicine and disease modeling.

Induced pluripotent stem cell technology for generating photoreceptors.

The discovery of methods to produce pluripotent stem cells from human skin cells and other adult tissues has created a new era in stem cell research. In this article, we discuss the generation and use of pluripotent stem cells for the study of retinal disorders and the development of cell-based therapies. We describe advances in protocols for differentiating pluripotent cells into photoreceptor precursors that might be suitable for transplantation and discuss the use of human induced pluripotent stem cell-derived photoreceptors for disease modeling and drug screening.

Chimerization of astroglial population in the lumbar spinal cord after mesenchymal stem cell transplantation prolongs survival in a rat model of amyotrophic lateral sclerosis.

Adult mesenchymal stem cells (MSCs) exhibit neuroprotective properties when introduced into the degenerating central nervous system through different putative mechanisms including secretion of growth factors and transdifferentiation. In the present study, we injected MSCs into the cerebrospinal fluid of symptomatic hSOD1(G93A) rats, a transgenic animal model of familial amyotrophic lateral sclerosis (ALS) expressing a mutated form of the human superoxide dismutase. MSCs were found to infiltrate the nervous parenchyma and migrate substantially into the ventral gray matter, where motor neurons degenerate. Even though overall astrogliosis was not modified, MSCs differentiated massively into astrocytes at the site of degeneration. The intrathecal delivery of MSCs and the subsequent generation of healthy astrocytes at symptomatic stage decreased motor neuron loss in the lumbar spinal cord, preserving motor functions and extending the survival of hSOD1(G93A) rats. This neuroprotection was correlated with decreased inflammation, as shown by the lower proliferation of microglial cells and the reduced expressiontion of COX-2 and NOX-2. Together, these data highlight the protective capacity of adult MSC-derived astrocytes when grafted into the central nervous system and illustrate an attractive strategy to target excessive inflammation in ALS.

Adult stem cell therapies for neurological disorders: benefits beyond neuronal replacement?

The modest capacity of endogenous repair processes in the central nervous system (CNS) justifies the broad interest in the development of effective stem cell based therapies for neurodegenerative disorders and other acute or chronic lesions. Motivated by the ambitious expectation to achieve functional neuronal replacement, several studies have already evidenced a potential benefit of stem cell grafts in animal models of human disorders. Nevertheless, growing evidence suggests that the effects orchestrated by stem cells, in most experimental cases, are not necessarily associated with the generation of new neurons. This hypothesis correlates with the versatile properties of adult and embryonic stem cells. When introduced into the lesioned CNS, nondifferentiated stem cells can have a positive influence through intrinsic neuroprotective capacities related to the production of neurotrophic factors, stimulation of endogenous neurogenesis, and modulation of neuroinflammation. Stem cells are also endowed with a multipotent differentiation profile, suggesting that a positive outcome could result from the replacement of nonneuronal cell types, in particular astrocytes and oligodendrocytes. Focusing on adult stem cells, this Review aims at summarizing experimental observations supporting the concept that, in cell-based therapies, stem cells operate not through a unidirectional mechanism (e.g., generating neurons) but rather as cellular mediators of a multitude of biological activities that could provide a favorable outcome for diverse nervous disorders.

In vitro evidence for impaired neuroprotective capacities of adult mesenchymal stem cells derived from a rat model of familial amyotrophic lateral sclerosis (hSOD1(G93A)).

Protection of neurons by stem cells is an attractive challenge in the development of efficient therapies of neurodegenerative diseases. When giving preference to autologous grafts, the bone marrow constitutes a valuable source of adult stem cells. Therefore, we herein studied the acquisition of neuroprotective functions by cultured mesenchymal stem cells (MSCs) exposed to growth factors known to promote the differentiation of neural stem cells into astrocytes. In these conditions, MSCs showed increased transcription and expression of the high-affinity glutamate transporter GLT-1 and functional studies revealed increased aspartate uptake activity. In addition, differentiation was shown to endow the cells with the capacity to respond to riluzole which triggers a robust up-regulation of the GDNF production. In parallel, MSCs derived from the bone marrow of a transgenic rat model of familial ALS (hSOD1(G93A)) were also characterised. Unexpectedly, cells from this rat strain submitted to the differentiation protocol showed modest capacity to take up aspartate and did not respond to the riluzole treatments. These data highlight the neuroprotective potential attributable to MSCs, supporting their use as valuable tools for the treatment of neurodegenerative disorders. However, the cells from the transgenic animal model of ALS appeared deficient in their capacity to gain the neuroprotective properties, raising questions regarding the suitability of autologous stem cell grafts in future therapies against familial forms of this disease.

Unilateral induction of progenitors in the spinal cord of hSOD1(G93A) transgenic rats correlates with an asymmetrical hind limb paralysis.

Transgenic rats expressing a mutated form of the human Cu/Zn superoxide dismutase (hSOD1(G93A)) develop an amyotrophic lateral sclerosis (ALS)-like phenotype, including motor neurone degeneration and reactive gliosis in the spinal cord. This study aimed at examining the presence of endogenous neural progenitors in the lumbar spinal cord of these rats at the end-stage of the disease. Immunohistochemical data clearly demonstrated the induced expression of the stem cell factor reported as a chemoattractant and survival factor for neural stem cells as well as nestin (neuro-epithelial stem cell intermediate filament) in the spinal cord sections. While the stem cell factor immunolabelling appeared diffuse throughout the gray matter, nestin labelling was restricted to clusters within the ventral horn. Interestingly, as paralysis regularly develops asymmetrically, induction of nestin was only detected on the ipsilateral side of the predominant symptoms. Finally, immunohistochemical detection of the stem cell factor receptor (c-Kit) revealed its specific induction which coincided with nestin immunolabelling. Together, these results are indicative of endogenous recruitment of neural progenitors within lesioned tissues and could support the development of treatments involving endogenous or exogenous stem cells.