Scott J. Pollack

Growth factors regulate the survival and fate of cells derived from human neurospheres

Cells isolated from the embryonic, neonatal, and adult rodent central nervous system divide in response to epidermal growth factor (EGF) and fibroblast growth factor 2 (FGF-2), while retaining the ability to differentiate into neurons and glia. These cultures can be grown in aggregates termed neurospheres, which contain a heterogeneous mix of both multipotent stem cells and more restricted progenitor populations. Neurospheres can also be generated from the embryonic human brain and in some cases have been expanded for extended periods of time in culture. However, the mechanisms controlling the number of neurons generated from human neurospheres are poorly understood. Here we show that maintaining cell–cell contact during the differentiation stage, in combination with growth factor administration, can increase the number of neurons generated under serum-free conditions from 8% to >60%. Neurotrophic factors 3 and 4 (NT3, NT4) and platelet-derived growth factor (PDGF) were the most potent, and acted by increasing neuronal survival rather than inducing neuronal phenotype. Following differentiation, the neurons could survive dissociation and either replating or transplantation into the adult rat brain. This experimental system provides a practically limitless supply of enriched, non-genetically transformed neurons. These should be useful for both neuroactive drug screening in vitro and possibly cell therapy for neurodegenerative diseases.

Composition of perineuronal nets in the adult rat cerebellum and the cellular origin of their components

The decrease in plasticity that occurs in the central nervous system during postnatal development is accompanied by the appearance of perineuronal nets (PNNs) around the cell body and dendrites of many classes of neuron. These structures are composed of extracellular matrix molecules, such as chondroitin sulfate proteoglycans (CSPGs), hyaluronan (HA), tenascin‐R, and link proteins. To elucidate the role played by neurons and glial cells in constructing PNNs, we studied the expression of PNN components in the adult rat cerebellum by immunohistochemistry and in situ hybridization. In the deep cerebellar nuclei, only large excitatory neurons were surrounded by nets, which contained the CSPGs aggrecan, neurocan, brevican, versican, and phosphacan, along with tenascin‐R and HA. Whereas both net‐bearing neurons and glial cells were the sources of CSPGs and tenascin‐R, only the neurons expressed the mRNA for HA synthases (HASs), cartilage link protein, and link protein Bral2. In the cerebellar cortex, Golgi neurons possessed PNNs and also synthesized HASs, cartilage link protein, and Bral2 mRNAs. To see whether HA might link PNNs to the neuronal cell surface by binding to a receptor, we investigated the expression of the HA receptors CD44, RHAMM, and LYVE‐1. No immunolabelling for HA receptors on the membrane of net‐bearing neurons was found. We therefore propose that HASs, which can retain HA on the cell surface, may act as a link between PNNs and neurons. Thus, HAS and link proteins might be key molecules for PNN formation and stability. J. Comp. Neurol. 494:559–577, 2006.

Sulfated glycosaminoglycans and dyes attenuate the neurotoxic effects of β-amyloid in rat PC12 cells

Glycosaminoglycan (GAG)-containing proteoglycans are associated with the neuritic plaques and cerebrovascular beta-amyloid deposits of Alzheimers disease as well as with the amyloid deposits of prion and other disorders. GAGs and other sulfate-containing compounds have previously been shown to bind beta-amyloid peptide in vitro, suggesting possible effects of beta-amyloid deposition and/or toxicity in vivo. Using reduction of the redox dye 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) to measure beta-amyloid neurotoxicity in rat pheochromocytoma PC12 cells, several polysulfated GAGs and synthetic sulfate-containing compounds were found to attenuate the neurotoxic effects of beta-amyloid fragments beta 25-35 and beta 1-40. These results suggest that by binding beta-amyloid these compounds may prevent toxic interactions of the peptide with cells.

Inositol monophosphatase — a putative target for Li+ in the treatment of bipolar disorder

Attenuation of the phosphatidylinositol (PI) signal transduction pathway as a consequence of inhibition of inositol monophosphatase (IMPase) has been proposed as the mechanism for the efficacy of Li+ in the treatment of bipolar disorder. Nevertheless, Li+ also affects other aspects of PI signal transduction, and it is therefore not clear whether modulation of PI responses by Li+ can be attributed solely to inhibition of IMPase. However, inhibitors of IMPase mimic the effects of Li+ on some aspects of PI cell signalling, thus highlighting the potential of IMPase as a target for the treatment of bipolar disorder. The recent description of the three-dimensional structure of IMPase in conjunction with site-directed mutagenesis and kinetic studies has led to the elucidation of the enzyme mechanism. These structural and mechanistic data should prove useful in the development of novel inhibitors of IMPase that might ultimately prove useful clinically.

Sulfonated dyes attenuate the toxic effects of β-amyloid in a structure-specific fashion

We recently reported that several sulfate-containing glycosaminoglycans, a class of compounds associated with the beta-amyloid plaques of Alzheimers disease, attenuate the toxic effects of beta-amyloid fragments beta 25-35 and beta 1-40. The amyloid-binding sulfonated dye Congo Red was shown to have a similar effect. Using two clonal cell lines, we now demonstrate that several sulfonated dyes attenuate beta-amyloid toxicity and that the protective effect appears specific for compounds whose sulfonate groups can interact with the beta-pleated structure of aggregated amyloid. These results suggest that by binding beta-amyloid these compounds may prevent toxic interactions of the peptide with cells.

STRUCTURE AND MECHANISM OF INOSITOL MONOPHOSPHATASE

Since lithium inhibits IMPase and modulates phosphatidylinositol (PtdIns) cell signalling at therapeutically relevant concentrations (0.5–1.0 mM), IMPase has attracted attention as a putative molecular target for lithium in the treatment of manic depression. IMPase is a homodimer, with each subunit organised in an αβαβα arrangement of α‐helices and β‐sheets, and this type of structure seems crucial to the two‐metal catalysed mechanism in which an activated water molecule serves as a nucleophile. Lithium appears to inhibit the enzyme following substrate hydrolysis by occupying the second metal binding site before the phosphate group can dissociate from its interaction with the site 1 metal. The understanding of IMPase structure and the mechanism of substrate hydrolysis and lithium inhibition should be useful in the development of novel inhibitors which may prove clinically useful in the treatment of manic depression.

Small molecule Trk receptor agonists and other neurotrophic factor mimetics.

Nerve growth factor belongs to a small family of proteins whose binding at the Trk and p75(NTR) transmembrane receptors triggers a cascade of signaling events that give rise to neurotrophic responses in neuronal cells and in vivo. Following their robust effects in animal models of neurodegeneration, neurotrophins have been evaluated for therapy for several human neurodegenerative diseases. However, due mainly to the poor pharmacokinetic behavior of these proteins, they have largely met without success in the clinic, making it desirable to develop small molecule neurotrophin mimetics. A range of compounds is described that achieves some of the neurotrophic and neuroprotective effects attributed to neurotrophins through a variety of mechanisms. These small molecules are divided into the following functional categories: (1). compounds that activate Trk receptors directly; (2). compounds that potentiate the actions of neurotrophins on Trk receptors; (3). compounds that activate Trk indirectly; (4). compounds that influence neurotrophin expression or secretion; and (5). a broad class of compounds that act downstream of, or independently of, Trk receptors. Unfortunately, most of the compounds that have been reported suffer from either lack of specificity for the desired mechanism/effect(s) or lack of efficacy of the compounds in appropriate in vivo models, or both. This second limitation has been particularly severe for compounds designed to mimic the neurotrophins in their interaction with Trk receptors, an ongoing and formidable challenge. Nevertheless, a small subset of the compounds, acting on intracellular signaling pathways downstream of Trk receptors, shows promise for the future treatment of neurodegenerative diseases.

Sulphated compounds attenuate β-amyloid toxicity by inhibiting its association with cells

Agents that interfere with the toxic effects of β-amyloid protein may be therapeutically useful against Alzheimers disease. We reported recently that several sulphated glycosaminoglycans and sulphonated dyes attenuate the toxic effects of β-amyloid fragments β25-35 and β1-40 in two clonal cell lines. We now demonstrate that this protective effect is due to interference with β-amyloid cell association rather than effects on β-amyloid structure. Using an enzyme-linked immunoabsorbance assay to detect cell-associated β1-40, we found in a range of compounds a strong correlation between inhibition of HeLa cell association of β1-40 and attenuation of cellular toxicity as measured by inhibition of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) reduction. In contrast, effects on peptide structure, as measured by Congo red binding, were generally inconsistent with the attenuating effects of the compounds on cellular toxicity. These results suggest that by binding β-amyloid these agents prevent its interaction with cells.

Asymmetric, biocatalytic labeled compound synthesis using transaminases

The use of transaminases for the incorporation of deuterium and tritium in chiral amines starting from prochiral ketone precursors has been demonstrated. Efficient labeling was demonstrated using a variety of ketone substrates. Amplification of the labeled product was observed, with tritium incorporation enriched up to 2.8X the statistically expected levels of labeling.

Potent, Selective, and CNS-Penetrant Tetrasubstituted Cyclopropane Class IIa Histone Deacetylase (HDAC) Inhibitors.

Potent and selective class IIa HDAC tetrasubstituted cyclopropane hydroxamic acid inhibitors were identified with high oral bioavailability that exhibited good brain and muscle exposure. Compound 14 displayed suitable properties for assessment of the impact of class IIa HDAC catalytic site inhibition in preclinical disease models.