Many studies have shown that transplanted or endogenous neural progenitor cells will migrate toward damaged areas of the brain. However, the mechanism underlying this effect is not clear. Here we report that, using hippocampal slice cultures, grafted neural progenitor cells (NPs) migrate toward areas of neuroinflammation and that chemokines are a major regulator of this process. Migration of NPs was observed after injecting an inflammatory stimulus into the area of the fimbria and transplanting enhanced green fluorescent protein (EGFP)-labeled NPs into the dentate gyrus of cultured hippocampal slices. Three to 7 d after transplantation, EGFP-NPs in control slices showed little tendency to migrate and had differentiated into neurons and glia. In contrast, in slices injected with inflammatory stimuli, EGFP-NPs migrated toward the site of the injection. NPs in these slices also survived less well. The inflammatory stimuli used were a combination of the cytokines tumor necrosis factor-␣ and interferon-␥, the bacterial toxin lipopolysaccharide, the human immunodeficiency virus-1 coat protein glycoprotein 120, or a ␤-amyloid-expressing adenovirus. We showed that these inflammatory stimuli increased the synthesis of numerous chemokines and cytokines by hippocampal slices. When EGFP-NPs from CC chemokine receptor CCR 2 knock-out mice were transplanted into slices, they exhibited little migration toward sites of inflammation. Similarly, wild-type EGFP-NPs exhibited little migration toward inflammatory sites when transplanted into slices prepared from monocyte chemoattractant protein-1 (MCP-1) knock-out mice. These data indicate that factors secreted by sites of neuroinflammation are attractive to neural progenitors and suggest that chemokines such as MCP-1 play an important role in this process.

Chemokines and their receptors are essential for the development and organization of the hematopoietic/lymphopoietic system and have now been shown to be expressed by different types of cells in the nervous system. In mouse embryos, we observed expression of the chemokine (CXC motif) receptor 4 (CXCR4) by neural crest cells migrating from the dorsal neural tube and in the dorsal root ganglia (DRGs). Stromal cell-derived factor-1 (SDF-1), the unique agonist for CXCR4, was expressed along the path taken by crest cells to the DRGs, suggesting that SDF-1/CXCR4 signaling is needed for their migration. CXCR4 null mice exhibited small and malformed DRGs. Delayed migration to the DRGs was suggested by ectopic cells expressing tyrosine receptor kinase A (TrkA) and TrkC, neurotrophin receptors required by DRG sensory neuron development. In vitro, the CXCR4 chemokine receptor was upregulated by migratory progenitor cells just as they exited mouse neural tube explants, and SDF-1 acted as a chemoattractant for these cells. Most CXCR4-expressing progenitors differentiated to form sensory neurons with the properties of polymodal nociceptors. Furthermore, DRGs contained a population of progenitor cells that expressed CXCR4 receptors in vitro and differentiated into neurons with a similar phenotype. Our findings indicate an important role for SDF-1/CXCR4 signaling in directing the migration of sensory neuron progenitors to the DRG and potentially in other aspects of development once the DRGs have coalesced.

An early substantial loss of basal forebrain cholinergic neurons (BFCN) is a constant feature of Alzheimer's disease and is associated with deficits in spatial learning and memory. The ability to selectively control the differentiation of human embryonic stem cells (hESCs) into BFCN would be a significant step toward a cell replacement therapy. We demonstrate here a method for the derivation of a predominantly pure population of BFCN from hESC cells using diffusible ligands present in the forebrain at developmentally relevant time periods. Overexpression of two relevant human transcription factors in hESC-derived neural progenitors also generates BFCN. These neurons express only those markers characteristic of BFCN, generate action potentials, and form functional cholinergic synapses in murine hippocampal slice cultures. siRNA-mediated knockdown of the transcription factors blocks BFCN generation by the diffusible ligands, clearly demonstrating the factors both necessary and sufficient for the controlled derivation of this neuronal population. The ability to selectively control the differentiation of hESCs into BFCN is a significant step both for understanding mechanisms regulating BFCN lineage commitment and for the development of both cell transplant-mediated therapeutic interventions for Alzheimer's disease and high-throughput screening for agents that promote BFCN survival.

Painful diabetic neuropathy (PDN) is an intractable complication of diabetes that affects 25% of patients. PDN is characterized by neuropathic pain and small-fiber degeneration, accompanied by dorsal root ganglion (DRG) nociceptor hyperexcitability and loss of their axons within the skin. The molecular mechanisms underlying DRG nociceptor hyperexcitability and small-fiber degeneration in PDN are unknown. We hypothesize that chemokine CXCL12/CXCR4 signaling is central to this mechanism, as we have shown that CXCL12/CXCR4 signaling is necessary for the development of mechanical allodynia, a pain hypersensitivity behavior common in PDN. Focusing on DRG neurons expressing the sodium channel Nav1.8, we applied transgenic, electrophysiological, imaging, and chemogenetic techniques to test this hypothesis. In the high-fat diet mouse model of PDN, we were able to prevent and reverse mechanical allodynia and small-fiber degeneration by limiting CXCR4 signaling or neuronal excitability. This study reveals that excitatory CXCR4/CXCL12 signaling in Nav1.8-positive DRG neurons plays a critical role in the pathogenesis of mechanical allodynia and small-fiber degeneration in a mouse model of PDN. Hence, we propose that targeting CXCR4-mediated DRG nociceptor hyperexcitability is a promising therapeutic approach for disease-modifying treatments for this currently intractable and widespread affliction.

An early substantial loss of basal forebrain cholinergic neurons (BFCNs) is a constant feature of Alzheimer’s disease (AD) and is associated with deficits in spatial learning and memory. Induced pluripotent stem cells (iPSCs) derived from patients with AD as well as from normal controls could be efficiently differentiated into neurons with characteristics of BFCNs. We used BFCNs derived from iPSCs to model sporadic AD with a focus on patients with ApoE3/E4 genotypes (AD-E3/E4). BFCNs derived from AD-E3/E4 patients showed typical AD biochemical features evidenced by increased Aβ42/Aβ40 ratios. AD-E3/E4 neurons also exhibited altered responses to treatment with γ-secretase inhibitors compared to control BFCNs or neurons derived from patients with familial AD. BFCNs from patients with AD-E3/E4 also exhibited increased vulnerability to glutamate-mediated cell death which correlated with increased intracellular free calcium upon glutamate exposure. The ability to generate BFCNs with an AD phenotype is a significant step both for understanding disease mechanisms and for facilitating screening for agents that promote synaptic integrity and neuronal survival.