Human embryonic stem cell derived astrocytes mediate non-cell-autonomous neuroprotection through endogenous and drug-induced mechanisms.

The glial environment is an important determinant of neuronal health in experimental models of neurodegeneration. Specifically, astrocytes have been shown, dependent on context, to be both injurious and protective. Human pluripotent stem cells offer a powerful new system to improve our understanding of the mechanisms underlying astrocyte-mediated neuroprotection. Here, we describe a human embryonic stem cell (HESC)-based system to assess the scope and mechanism of human astrocyte-mediated neuroprotection. We first report the generation of enriched and functional HESC-derived astrocytes, by combining BMP-mediated Smad and LIF-mediated JAK-STAT signalling. These astrocytes promote the protection of HESC-derived neurons against oxidative insults. Moreover, their neuroprotective capacity can be greatly enhanced by treatment with the nuclear factor-erythroid 2-related factor 2 (Nrf2)-activating triterpenoid 1[2-Cyano-3,12-dioxool-eana-1,9(11)-dien-28-oyl] trifluoroethylamide (CDDO(TFEA)). Activation of the transcription factor Nrf2 in human astrocytes by CDDO(TFEA) treatment induced expression of the glutamate-cysteine ligase (GCL) catalytic subunit, leading to enhanced GCL activity and glutathione production, and strong neuroprotection against H(2)O(2). This enhanced neuroprotection was found to be dependent on astrocytic GCL activity, unlike the basal neuroprotection afforded by untreated astrocytes. Direct treatment of HESC-derived neurons with CDDO(TFEA) elicited no induction of Nrf2 target genes, nor any neuroprotection. Thus, human astrocytes can mediate neuroprotection through glutathione-dependent and glutathione-independent mechanisms, and represent a therapeutic target for human disorders associated with neuronal oxidative stress.

Retinoid-independent motor neurogenesis from human embryonic stem cells reveals a medial columnar ground state.

A major challenge in neurobiology is to understand mechanisms underlying human neuronal diversification. Motor neurons (MNs) represent a diverse collection of neuronal subtypes, displaying differential vulnerability in different human neurodegenerative diseases. The ability to manipulate cell subtype diversification is critical to establish accurate, clinically relevant in vitro disease models. Retinoid signalling contributes to caudal precursor specification and subsequent MN subtype diversification. Here we investigate the necessity for retinoic acid in motor neurogenesis from human embryonic stem cells. We show that activin/nodal signalling inhibition, followed by sonic hedgehog agonist treatment, is sufficient for MN precursor specification, which occurs even in the presence of retinoid pathway antagonists. Importantly, precursors mature into HB9/ChAT-expressing functional MNs. Furthermore, retinoid-independent motor neurogenesis results in a ground state biased to caudal, medial motor columnar identities from which a greater retinoid-dependent diversity of MNs, including those of lateral motor columns, can be selectively derived in vitro.

Stem cells as a resource for regenerative neurology.

Public and media interest in the potential applications of stem cells in regenerative neurology has led to growing hope and expectation. This interest is heightened by the current paucity of treatments available for neurodegenerative diseases and their generally poor prognosis. Patient discussions about stem cells are therefore a common occurrence in clinical practice, requiring neurologists to offer clear and accurate information. In the context of a complex and rapidly evolving field, this can be extremely challenging. Here we address issues around stem cell populations relevant to regenerative neurology, including the opportunities they offer for research and their potential application as direct therapies, concluding with a pragmatic assessment of the likely clinical benefits of stem cell research.

Abnormally phosphorylated tau is associated with neuronal and axonal loss in experimental autoimmune encephalomyelitis and multiple sclerosis.

The pathological correlate of clinical disability and progression in multiple sclerosis is neuronal and axonal loss; however, the underlying mechanisms are unknown. Abnormal phosphorylation of tau is a common feature of some neurodegenerative disorders, such as Alzheimer's disease. We investigated the presence of tau hyperphosphorylation and its relationship with neuronal and axonal loss in chronic experimental autoimmune encephalomyelitis (CEAE) and in brain samples from patients with secondary progressive multiple sclerosis. We report the novel finding of abnormal tau phosphorylation in CEAE. We further show that accumulation of insoluble tau is associated with both neuronal and axonal loss that correlates with progression from relapsing-remitting to chronic stages of EAE. Significantly, analysis of secondary progressive multiple sclerosis brain tissue also revealed abnormally phosphorylated tau and the formation of insoluble tau. Together, these observations provide the first evidence implicating abnormal tau in the neurodegenerative phase of tissue injury in experimental and human demyelinating disease.

Remyelination can be extensive in multiple sclerosis despite a long disease course.

Experimental studies using models of multiple sclerosis (MS) indicate that rapid and extensive remyelination of inflammatory demyelinated lesions is not only possible, but is the normal situation. The presence of completely remyelinated MS lesions has been noted in numerous studies and routine limited sampling of post mortem MS material suggests that remyelination may be extensive in the early stages but eventually fails. However, visual macroscopic guided sampling tends to be biased towards chronic demyelinated lesions. Here we have extensively sampled cerebral tissue from two MS cases to investigate the true extent of remyelination. Sections were cut from 185 cerebral tissue blocks and stained with haematoxylin and eosin (H&E), luxol fast blue and cresyl fast violet (LFB/CFV) and anti-myelin oligodendrocyte glycoprotein, human leucocyte antigen-DR (HLA-DR) and 200 kDa neurofilament protein antibodies. Demyelinated areas were identified in 141 blocks, comprising both white matter (WMLs) and/or grey matter lesions. In total, 168 WMLs were identified, 22% of which were shadow plaques, 73% were partially remyelinated and only 5% were completely demyelinated. The average extent of lesion remyelination for all WMLs investigated was 47%. Increased density of HLA-DR(+) macrophages and microglia at the lesion border correlated significantly with more extensive remyelination. Results from this study of two patients with long standing disease suggest that remyelination in MS may be more extensive than previously thought.