Formation and structure of transplantable tissue constructs generated in simulated microgravity from Sertoli cells and neuron precursors.

Cell transplantation therapy for Parkinson's disease (PD) has received much attention as a potential treatment protocol for this neurodegenerative condition. Although there have been promising successes with this approach, it remains problematic, especially regarding the inability to provide immediate trophic support to the newly grafted cells and the inability to prevent acute and/or long-term graft rejection by the host. To address these issues of cell graftability, we have created a novel tissue construct from isolated rat Sertoli cells (SC) and the NTerra-2 immortalized human neuron precursor cell line (NT2) utilizing NASA-developed simulated microgravity technology. The two cell types were cocultured at a 1:4 (SC/NT2) ratio in the High Aspect Rotating Vessel (HARV) biochamber for 3 days, after which a disc-shaped aggregate (1-4 mm diameter) was formed. Sertoli neuron aggregated cells (SNAC) were collected by gravity sedimentation and processed either for light and electron microscopy or for fluorescent immunocytochemistry. Intra-SNAC clusters of SC and NT2 cells were identified by anti-human mitochondrial protein (huMT--specific for NT2 cells) and cholera toxin subunit B (CTb--specific for SC). There was little evidence of cell death throughout the aggregate and the absence of central necrosis, as might be expected in such a large aggregate in vitro. Ultrastructurally, SC did not express junctional modifications with NT2 cells nor with adjacent SC as is typical of SC in vivo and, in some protocols, in vitro. NT2 cells, however, showed distinct intercellular junction-like densities with adjacent NT2 cells, often defining canaliculi-like channels between the microvillus borders of the cells. The results show that the use of simulated microgravity coculture provides a culture environment suitable for the formation of a unique and viable Sertoli-NT2 (i.e., SNAC) tissue construct displaying intra-aggregate cellular organization. The structural integration of SC with NT2 cells provides a novel transplantable tissue source, which can be tested to determine if SC will suppress rejection of the grafted NT2 cells and provide for their short- and long-term trophic support in situ in the treatment of experimental PD.