Differential modulation of Sonic-hedgehog-induced cerebellar granule cell precursor proliferation by the IGF signaling network.

The molecular mechanisms regulating organ growth and size remain unclear. Sonic hedgehog (SHH) signaling is a major player in the regulation of cerebellar development: SHH is secreted by Purkinje neurons and acts on the proliferation of granule cell precursors (GCPs) in the external germinal layer. These then become postmitotic and form the internal granular layer but do so in the presence of SHH ligand, begging the question of how the proliferative response to SHH signaling is downregulated in differentiating GCPs. Here, we have determined the precise cellular localization of the expression of insulin-like growth factor (IGF) network components in the developing mouse cerebellum and show that this network modulates the proliferative effects of SHH signaling on GCPs. IGF1 and IGF2 are potent mitogens for GCPs and both synergize with SHH in inducing GCP proliferation. Whereas the proliferative activity of IGF1 or IGF2 on GCPs does not require intact SHH signaling, aspects of SHH activity on GCP proliferation require signaling through the IGF receptor 1. Moreover, we find that 3 of the IGF-binding proteins, IGFBP2, IGFBP3 and IGFBP5, inhibit IGF1/2-induced cell proliferation, whereas IGFBP5 also inhibits SHH-induced GCPs proliferation. This novel function of IGFBP5 that we have uncovered demonstrates the exquisite regulation of SHH signaling by different components of the IGF network.

ZNF238 is expressed in postmitotic brain cells and inhibits brain tumor growth.

Brain tumors such as medulloblastoma (MB) and glioblastoma multiforme (GBM) can derive from neural precursors. For instance, many MBs are thought to arise from the uncontrolled proliferation of cerebellar granule neuron precursors (GNP). GNPs normally proliferate in early postnatal stages in mice but then they become postmitotic and differentiate into granule neurons. The proliferation of neural precursors, GNPs, as well as at least subsets of GBM and MB depends on Hedgehog signaling. However, the gene functions that are lost or suppressed in brain tumors and that normally promote the proliferation arrest and differentiation of precursors remain unclear. Here we have identified a member of the BTB-POZ and zinc finger family, ZNF238, as a factor highly expressed in postmitotic GNPs and differentiated neurons. In contrast, proliferating GNPs as well as MB and GBM express low or no ZNF238. Functionally, inhibition of ZNF238 expression in mouse GNPs decreases the expression of the neuronal differentiation markers MAP2 and NeuN and downregulates the expression of the cell cycle arrest protein p27, a regulator of GNP differentiation. Conversely, reinstating ZNF238 expression in MB and GBM cells drastically decreases their proliferation and promotes cell death. It also downregulates cyclin D1 while increasing MAP2 and p27 protein levels. Importantly, ZNF238 antagonizes MB and GBM tumor growth in vivo in xenografts. We propose that the antiproliferative functions of ZNF238 in normal GNPs and possibly other neural precursors counteract brain tumor formation. ZNF238 is thus a novel brain tumor suppressor and its reactivation in tumors could open a novel anticancer strategy.

Design and synthesis of inhibitors of Hedgehog signaling based on the alkaloid cyclopamine.

The synthesis and biological evaluation of structurally simplified, metabolically stable cyclopamine-like Sonic Hedgehog (SHH) signaling inhibitors, i.e., 5, is described in four chemical steps from commercially available steroidal precursors. Biological evaluation of this cyclopamine analogue in two different systems establishes the high potency of 5 as a SHH signaling inhibitor. This approach provides important new lead structures for the development of new cancer chemotherapeutic agents based on the inhibition on SHH signaling.

Pharmacologically active microcarriers releasing glial cell line - derived neurotrophic factor: Survival and differentiation of embryonic dopaminergic neurons after grafting in hemiparkinsonian rats.

To improve the outcome of foetal dopaminergic cell transplantation for the treatment of Parkinson's disease, pharmacologically active microcarriers (PAM) were developed. PAM are able to convey cells on their surface and release a growth factor to improve cell survival, differentiation and integration after brain implantation. Lysozyme-releasing PAM were first produced and characterized. They served as a model system for the development of glial cell line-derived neurotrophic factor (GDNF)-releasing PAM conveying foetal ventral mesencephalic (FVM) cells. The effects of the intrastriatal implantation of this system were studied in hemiparkinsonian rats during a 6-week period. This study reports on the degradation of coated and non-coated PAM and the release of lysozyme and of biologically active GDNF for 42 days. Unloaded and GDNF-loaded PAM conveying FVM cells allowed a high improvement of the grafted cell survival and of fibre outgrowth, when compared to the cells transplanted alone. The animals receiving the PAM showed an earlier improvement in amphetamine-induced rotational behaviour compared to animals receiving FVM cells only; behaviour that appears to be more regular and stable with the GDNF-releasing PAM. The use of PAM to convey foetal cells is thus an efficient strategy for cell therapy in neurodegenerative diseases, as it allows improvement of cell survival and fibre outgrowth inducing a rapid recovery of behaviour using only low amounts of cells.

Neurotrophin-directed differentiation of human adult marrow stromal cells to dopaminergic-like neurons.

Marrow-isolated adult multilineage inducible (MIAMI) cells were differentiated in vitro to neuronal cells in a neurotrophin-dependent fashion. After induction, the cells revealed electrophysiological features similar to those observed in mature neurons. Primary early passage human MIAMI cells without any type of co-cultures with other cell types were used. The developmental program involved a multi-step process requiring the concerted action of brain-derived neurotrophic factor, nerve growth factor and depended on neurotrophin-3, after basic fibroblast growth factor withdrawal. MIAMI-derived neuron-like cells sequentially expressed the neuronal markers, developed a complex neurite outgrowth and arborization, and acquired electrophysiological characteristics similar to those observed in mature neurons. The young and old MIAMI-derived neuronal cells developed both inward and outward currents upon depolarization, similar to those observed in normal neurons. These results represent the earliest evidence that neurotrophin-3 can direct the differentiation of non-neural stem cells from human adult bone marrow stroma to neuron-like cells in vitro. Supplementing the aforementioned multi-step process with sonic hedgehog, fibroblast growth factor 8, and retinoic acid increased the expression of molecules involved in dopaminergic differentiation and of tyrosine hydroxylase, the rate limiting enzyme of dopamine synthesis. MIAMI cells from young and old individuals represent autologous human cell populations for the treatment of disorders of the skeletal and nervous systems and for applications in cell therapy and reparative medicine approaches.