The role of growth/differentiation factor 5 (GDF5) in the induction and survival of midbrain dopaminergic neurones: relevance to Parkinson's disease treatment

Abstract

Growth/differentiation factor-5 (GDF5) is a member of the transforming growth factor-beta superfamily which has potent effects on dopaminergic neurones in vitro and in vivo. GDF5 is under investigation as a potential therapeutic agent for Parkinson's disease (PD), which is caused by the progressive degeneration of dopaminergic neurones projecting from the substantia nigra (SN) to the striatum. In the rat ventral mesencephalon (VM; the developing SN), GDF5 expression peaks at embryonic day 14, the time at which dopaminergic neurones undergo terminal differentiation. Addition of GDF5 protein to cultures of embryonic rat VM increases the survival and improves the morphology of dopaminergic neurones in these cultures. GDF5 treatment also increases the number of cells which adopt a dopaminergic phenotype in cultures of VM progenitor cells. Intracerebral administration of GDF5 has potent neuroprotective and restorative effects on the nigrostriatal pathway in animal models of PD. Furthermore, addition of GDF5 protein to embryonic rat dopaminergic neuronal transplants improves their survival and function in a rat model of PD. Thus, GDF5 has potential applications to PD therapy as a dopaminergic neuroprotective agent and as a factor that may induce a dopaminergic neuronal fate in unrestricted progenitor cells.

Fig. 1

(A) Alignment of known protein sequences of human BMP and GDFs beginning at the first conserved cysteine residue in the mature C-terminal protein. Alignment shows the classical seven conserved cysteine (C) residues that form the structure known as the ‘cysteine-knot motif’. Protein sequences were obtained from www.ncbi.nih.gov and the alignment was performed using a web-based version of Clustal W™ from EMBL (http://www.ebi.ac.uk/clustalw/). (B) Phylogeny tree showing evolutionary relationship between human BMPs and GDFs, generated from data obtained from Clustal W alignment of protein sequences in (A). Line lengths represent evolutionary distance. Numbers in parenthese represent percentage similiarity of the sequence to the GDF5 sequence. GDF5, GDF6 and GDF7 have a high sequence similarity with GDF5 and are grouped into their own subfamily.

Fig. 2

Photomicrographs showing representative (A) control and (B) GDF5-treated (10ngmL⁻¹ at time of plating) cultures of E14 rat VM, immunocytochemically stained for TH for 6DIV. Scale bar = 100µm. Photomicrographs showing representative (C) control and (D) GDF5-treated (10ngmL⁻¹ for 2h at 24h after plating) cultures of E14 rat VM immunocytochemically stained for β-III tubulin (red; a neuronal marker) and phosphorylated Smad-1/-5/-8 (green) at 1 DIV. There was no Smad activation in (C) control cultures, whereas in (D) GDF5-treated cultures, nuclear accumulation of phosphorylated Smad protein was present in a subset of neurones. Scale bar=25µm.