Reducing Glypican-4 in ES Cells Improves Recovery in a Rat Model of Parkinson's Disease by Increasing the Production of Dopaminergic Neurons and Decreasing Teratoma Formation

The heparan sulfate proteoglycan Glypican 4 (Gpc4) is strongly expressed in mouse embryonic stem (ES) cells where it controls the maintenance of self-renewal by modulating Wnt/beta-catenin signaling activities. Here we show that mouse ES cells carrying a hypomorphic Gpc4 allele, in a single-step neuronal differentiation protocol, show increased differentiation into dopaminergic neurons expressing tyrosine hydroxylase (TH) and nuclear receptor related-1 protein (Nurr1) 1. In contrast to wild-type cells, these differentiating Gpc4-mutant cells expressed high levels of DOPA decarboxylase and the dopamine transporter, two markers expressed by fully mature dopaminergic neurons. Intrastriatal transplantation of Gpc4 hypomorphic cells into a 6-OHDA rat model for Parkinson's disease improved motor behavior in the cylinder test and amphetamine-induced rotations at a higher level than transplanted wild-type cells. Importantly, Gpc4 hypomorphic cell grafts, in contrast to wild-type cells, did not generate teratomas in the host brains, leading to strongly enhanced animal survival. Therefore, control of Gpc4 activity level represents a new potential strategy to reduce ES cell tumorigenic features while at the same time increasing neuronal differentiation and integration.