Human stem cell-derived spinal cord astrocytes with defined mature or reactive phenotypes. Cell Rep. 2013;4:1035-1048. [PMID: 23994478 DOI: 10.1016/j.celrep.2013.06.021]

Induced pluripotent stem cells from ALS patients for disease modeling

The ability to reprogram adult somatic cells into pluripotent stem cells that can differentiate into all three germ layers of the developing human has fundamentally changed the landscape of biomedical research. For a neurodegenerative disease like Amyotrophic Lateral Sclerosis (ALS), which does not manifest itself until adulthood and is a heterogeneous disease with few animal models, this technology may be particularly important. Induced pluripotent stem cells (iPSC) have been created from patients with several familial forms of ALS as well as some sporadic forms of ALS. These cells have been differentiated into ALS-relevant cell subtypes including motor neurons and astrocytes, among others. ALS-relevant pathologies have also been identified in motor neurons from these cells and may provide a window into understanding disease mechanisms in vitro. Given that this is a relatively new field of research, numerous challenges remain before iPSC methodologies can fulfill their potential as tools for modeling ALS as well as providing a platform for the investigation of ALS therapeutics. This article is part of a Special Issue entitled ALS complex pathogenesis.

S100β as an early biomarker of excitotoxic damage in spinal cord organotypic cultures

S100β is a cytoplasmic calcium-binding protein mainly expressed by glia and considered to be a useful biomarker for brain or spinal cord injury. Indeed, clinical studies suggest that the S100β concentration in serum or cerebrospinal fluid may predict lesion outcome and prognosis. The relation of S100β levels to damage severity and its timecourse remains, however, unclear. This study used a validated in vitro model of spinal cord injury induced by kainate-mediated excitotoxicity to investigate these issues. After 22 days in vitro, rat organotypic spinal cord slices were subjected to one transient application (1 h) of 1 or 100 μM kainate followed by washout. While the lower kainate concentration did not evoke neuronal loss or S100β increase, the larger concentration elicited 40% neuronal death, no change in glial number and a delayed, significant rise in extracellular S100β that peaked at 24 h. This increase was associated with a stronger expression of the S100β protein as indicated by western blotting and immunohistochemistry. Application of the microtubule disrupting agent colchicine did not change the rise in S100β induced by kainate, an effect blocked by the glutamate receptor antagonists CNQX and APV. Our data suggest that excitotoxicity was followed by release of S100β perhaps from a readily releasable pool through a mechanism independent of microtubule assembly. The raised extracellular level of S100β appeared to reflect glial reactivity to the kainate-evoked lesion in accordance with the view that this protein may be involved in tissue protection and repair after acute injury. Excitotoxicity is a major mechanism responsible for neuronal death following acute spinal cord injury. The calcium-binding protein S100β is released by astrocytes into the extracellular compartment during the first 24 h after the initial insult and represents a useful biomarker of lesion progression as its level is related to the occurrence and severity of neuronal loss.

Gene profiling of human induced pluripotent stem cell-derived astrocyte progenitors following spinal cord engraftment

The generation of human induced pluripotent stem cells (hiPSCs) represents an exciting advancement with promise for stem cell transplantation therapies as well as for neurological disease modeling. Based on the emerging roles for astrocytes in neurological disorders, we investigated whether hiPSC-derived astrocyte progenitors could be engrafted to the rodent spinal cord and how the characteristics of these cells changed between in vitro culture and after transplantation to the in vivo spinal cord environment. Our results show that human embryonic stem cell- and hiPSC-derived astrocyte progenitors survive long-term after spinal cord engraftment and differentiate to astrocytes in vivo with few cells from other lineages present. Gene profiling of the transplanted cells demonstrates the astrocyte progenitors continue to mature in vivo and upregulate a variety of astrocyte-specific genes. Given this mature astrocyte gene profile, this work highlights hiPSCs as a tool to investigate disease-related astrocyte biology using in vivo disease modeling with significant implications for human neurological diseases currently lacking animal models.

Advances in cellular models to explore the pathophysiology of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS), the most common adult-onset motor neuron disorder, is fatal for most patients less than 3 years from when the first symptoms appear. The aetiologies for sporadic and most familial forms of ALS are unknown, but genetic factors are increasingly recognized as causal in a subset of patients. Studies of disease physiology suggest roles for oxidative stress, glutamate-mediated excitotoxicity or protein aggregation; how these pathways interact in the complex pathophysiology of ALS awaits elucidation. Cellular models are being used to examine disease mechanisms. Recent advances include the availability of expanded cell types, from neuronal or glial cell culture to motoneuron-astrocyte co-culture genetically or environmentally modified. Cell culture experiments confirmed the central role of glial cells in ALS. The recent adaptation of induced pluripotent stem cells (iPSC) for ALS modeling could allow a broader perspective and is expected to generate new hypotheses, related particularly to mechanisms underlying genetic factors. Cellular models have provided meaningful advances in the understanding of ALS, but, to date, complete characterization of in vitro models is only partially described. Consensus on methodological approaches, strategies for validation and techniques that allow rapid adaptation to new genetic or environmental influences is needed. In this article, we review the principal cellular models being employed in ALS and highlight their contribution to the understanding of disease mechanisms. We conclude with recommendations on means to enhance the robustness and generalizability of the different concepts for experimental ALS.