Caspase inhibition increases embryonic striatal graft survival

In transplants of embryonic striatal cells placed into the excitotoxically lesioned rat striatum (a model of Huntington's disease), as many as 60 to 90% of the grafted cells are believed to die. Caspase activation is part of a cascade of events that can lead to apoptosis. We investigated the effect of the caspase inhibitor acetyl-tyrosinyl-valyl-alanyl-aspartyl-chloromethylketone (Ac-YVAD-cmk) on grafted embryonic striatal cells in the excitotoxically lesioned or intact rat striatum. Female Sprague-Dawley rats were subjected to unilateral intrastriatal injection of quinolinic acid. After 10 days, rats received bilateral intrastriatal grafts from embryonic day 14 rat lateral ganglionic eminence. Rats were divided into the following groups: Ac-YVAD-cmk, pretreatment of the graft tissue with the caspase inhibitor (500 microM); and control, untreated control grafts. Rats were perfused 10 days or 5 weeks postgrafting. Brain sections were processed immunohistochemically using an antibody against the striatal neuron marker dopamine- and adenosine 3',5'-monophosphate-regulated phosphoprotein with a molecular weight of 32 kDa (DARPP-32). Adjacent sections were stained for acetylcholinesterase/cresyl violet cytochemistry and Fluoro-Jade cytochemistry, a marker for degenerating neurons. Total graft volume, P-zone volume, total number of neuron-like cells, and number of DARPP-32-positive cells were increased, compared to control, in the group receiving Ac-YVAD-cmk-treated graft tissue. Moreover, transplants injected into the intact striatum were found to be significantly smaller compared to transplants placed into the excitotoxically lesioned striatum. The Fluoro-Jade staining revealed ongoing cell death in transplants 10 days after intrastriatal implantation and that cell death was significantly reduced 5 weeks after grafting.