Striatal pleiotrophin overexpression provides functional and morphological neuroprotection in the 6-hydroxydopamine model.

Neurotrophic factors are integrally involved in the development of the nigrostriatal system and in combination with gene therapy, possess great therapeutic potential for Parkinson's disease (PD). Pleiotrophin (PTN) is involved in the development, maintenance, and repair of the nigrostriatal dopamine (DA) system. The present study examined the ability of striatal PTN overexpression, delivered via psueudotyped recombinant adeno-associated virus type 2/1 (rAAV2/1), to provide neuroprotection and functional restoration from 6-hydroxydopamine (6-OHDA). Striatal PTN overexpression led to significant neuroprotection of tyrosine hydroxylase immunoreactive (THir) neurons in the substantia nigra pars compacta (SNpc) and THir neurite density in the striatum, with long-term PTN overexpression producing recovery from 6-OHDA-induced deficits in contralateral forelimb use. Transduced striatal PTN levels were increased threefold compared to adult striatal PTN expression and approximated peak endogenous developmental levels (P1). rAAV2/1 vector exclusively transduced neurons within the striatum and SNpc with approximately half the total striatal volume routinely transduced using our injection parameters. Our results indicate that striatal PTN overexpression can provide neuroprotection for the 6-OHDA lesioned nigrostriatal system based upon morphological and functional measures and that striatal PTN levels similar in magnitude to those expressed in the striatum during development are sufficient to provide neuroprotection from Parkinsonian insult.

3,4-Methylenedioxy-N-methamphetamine (ecstasy) promotes the survival of fetal dopamine neurons in culture.

The current study examined whether modest concentrations of MDMA could increase the survival and/or neurite outgrowth of fetal midbrain dopamine (DA) neurons in vitro since increased DA neurite outgrowth has been previously observed in vivo from prenatal exposure. MDMA concentrations in fetal brain were quantified to determine relevant in vivo concentrations to employ in vitro. A dose response study in vitro demonstrated that MDMA, at concentrations observed in vivo, resulted in increased, DA-specific, neuron survival. Higher doses resulted in non-specific neurotoxicity. MDMA application immediately after culture establishment resulted in greater survival than delayed application, however both were superior to control. MDMA significantly increased the expression of the slc6a3 gene (dopamine transporter; DAT) in culture. Co-application of the DAT reuptake inhibitor methylphenidate (MPH) with MDMA attenuated this effect. Progressive reductions in MPH concentrations restored the MDMA-induced survival effect. This suggests that MDMA's action at DAT mediates the survival effect. Neurite density per neuron was unaffected by MDMA in vitro suggesting that MDMA promotes DA neuron survival but not neurite outgrowth in culture. Finally, animals prenatally exposed to MDMA and examined on postnatal day 35 showed an increase in tyrosine hydroxylase-positive (TH+) neurons in the substantia nigra but not in the ventral tegmental area. These data suggest that during development, MDMA can increase the survival of DA neurons through its action at its transporter. Understanding how MDMA increases DA neuron survival may provide insight into normal DA neuron loss during development.

Increased cell suspension concentration augments the survival rate of grafted tyrosine hydroxylase immunoreactive neurons.

The poor survival rate (5-20%) of grafted embryonic dopamine (DA) neurons is one of the primary factors preventing cell replacement from becoming a viable treatment for Parkinson's disease. Previous studies have demonstrated that graft volume impacts grafted DA neuron survival, indicating that transplant parameters influence survival rates. However, the effects of mesencephalic cell concentration on grafted DA neuron survival have not been investigated. The current study compares the survival rates of DA neurons in grafts of varying concentrations. Mesencephalic cell suspensions derived from E14 Fisher 344 rat pups were concentrated to 25,000, 50,000, 100,000 and 200,000 cells/microl and transplanted into two 0.5 microl sites in the 6-OHDA-denervated rat striatum. Animals were sacrificed 10 days and 6 weeks post-transplantation for histochemical analysis of striatal grafts. The absolute number of DA neurons per graft increased proportionally to the total number of cells transplanted. However, our results show that the 200,000 cells/microl group exhibited significantly higher survival rates (5.48+/-0.83%) compared to the 25,000 cells/microl (2.81+/-0.39%) and 50,000 cells/microl (3.36+/-0.51%) groups (p=0.02 and 0.03, respectively). Soma size of grafted DA neurons in the 200,000 cells/microl group was significantly larger than that of the 25,000 cells/microl (p<0.0001) and 50,000 cells/microl groups (p=0.004). In conclusion, increasing the concentration of mesencephalic cells prior to transplantation, augments the survival and functionality of grafted DA neurons. These data have the potential to identify optimal transplantation parameters that can be applied to procedures utilizing stem cells, neural progenitors, and primary mesencephalic cells.

Failure of proteasome inhibitor administration to provide a model of Parkinson's disease in rats and monkeys.

McNaught and colleagues reported recently that systemic administration of proteasome inhibitors PSI (Z-Ileu-Glu(OtBu)-Ala-Leu-CHO) or epoxomicin recapitulated many of the degenerative changes seen in Parkinson's disease including loss of striatal dopamine and cell loss in the substantia nigra, locus ceruleus, dorsal motor nucleus of the X cranial nerve, and nucleus basalis of Meynert. Intracytoplasmic inclusions resembling Lewy bodies were also described. All experiments administering PSI to rats using identical procedures and multiple attempts failed to induce any of the previously described changes. Furthermore, administration of PSI or epoxomicin to monkeys in an attempt to extend the model to a primate species failed. Currently, systemic proteasome inhibition is not a reliable model for Parkinson's disease.