Increased innervation of forebrain targets by midbrain dopaminergic neurons in the absence of FGF-2.

Fibroblast growth factors (FGFs) regulate development and maintenance, and reduce vulnerability of neurons. FGF-2 is essential for survival of midbrain dopaminergic (DA) neurons and is responsible for their dysplasia and disease-related degeneration. We previously reported that FGF-2 is involved in adequate forebrain (FB) target innervation by these neurons in an organotypic co-culture model. It remains unclear, how this ex-vivo phenotype relates to the in vivo situation, and which FGF-related signaling pathway is involved in this process. Here, we demonstrate that lack of FGF-2 results in an increased volume of the striatal target area in mice. We further add evidence that the low molecular weight (LMW) FGF-2 isoform is responsible for this phenotype, as this isoform is predominantly expressed in the embryonic ventral midbrain (VM) as well as in postnatal striatum (STR) and known to act via canonical transmembrane FGF receptor (FGFR) activation. Additionally, we confirm that the phenotype with an enlarged FB-target area by DA neurons can be mimicked in an ex-vivo explant model by inhibiting the canonical FGFR signaling, which resulted in decreased extracellular signal-regulated kinase (ERK) activation, while AKT activation remained unchanged.

Transplantation of fetal ventral mesencephalic progenitor cells overexpressing high molecular weight fibroblast growth factor 2 isoforms in 6-hydroxydopamine lesioned rats.

Fibroblast growth factor-2 (FGF-2) is a potent neurotrophic factor promoting survival of dopaminergic (DA) neurons in vitro and in vivo. FGF-2 is expressed in different isoforms representing distinct translation products from a single mRNA. For this study, we focused on the high molecular weight (HMW) isoform, which, after non-viral plasmid-based overexpression in embryonic day 12 (E12) rat ventral mesencephalon (VM)-derived cells, revealed increased numbers of tyrosine hydroxylase-positive (TH(+)) cells in a 'colayer' cell culture model. To determine the therapeutic potential of VM cells producing FGF-2-HMW as their 'own' neurotrophic factor, we transplanted cell suspensions obtained from such in vitro modified and differentiated cell cultures into the 6-hydroxydopamine (6-OHDA) hemiparkinsonian rat model. Animals, having received either non-transfected cells, empty-control transfected, or FGF-2-HMW-plasmid transfected cells, were analyzed in two different transplantation paradigms each using 172,000 or 520,000 cells, respectively. The behavioral performances in the amphetamine- and apomorphine-induced rotational test as well as in the cylinder test were evaluated for up to thirteen weeks post transplantation (postTX). Finally, the integration of the grafted cells into the host striatum was analyzed by immunohistochemical measurements. Those analyses revealed improvements of behavioral deficits in all five groups receiving DA neuron grafts, except for amphetamine-induced rotation of the FGF-2-HMW small graft group. Altogether, genetic modification with the FGF-2-HMW-plasmid did not further improve functional recovery compared to the control groups and had no influence on either the number of surviving DA neurons or on the density of outgrowing TH(+) fibers.