Insulin-secreting pituitary GH3 cells: A potential beta-cell surrogate fordiabetes cell therapy

In a companion article, we describe the engineering and characterization of pituitary GH3 cell clones stably transfected with a furin-cleavable human insulin cDNA (InsGH3 cells). This article describes the performance of InsG H3 (clones 1 and 7) cell grafts into streptozotocin (STZ)-induced diabetic nude mice. Subcutaneous implantation of 2 x 10(6) InsGH3 cells resulted in the progressive reversal of hyperglycemia and diabetic symptoms, even thoug h the progressive growth of the transplanted cells (clone 7) eventually led to glycemic levels below the normal mouse range. Proinsulin transgene expr ession was maintained in harvested InsGH3 grafts that, conversely, lose the expression of the prolactin (PRL) gene. Elevated concentrations of circula ting mature human insulin were detected in graft recipients, demonstrating that proinsulin processing by InsGH3 cells did occur in vivo. Histologic an alysis showed that transplanted InsGH3 grew in forms of encapsulated tumors composed of cells with small cytoplasms weakly stained for the presence of insulin. Conversely, intense insulin immunoreactivity was detected in graf t-draining venules. Compared to pancreatic beta TC3 cells, InsGH3 cells sho wed in vitro a higher rate of replication, an elevate resistance to apoptos is induced by serum deprivation and proinflammatory cytokines, and signific antly higher antiapoptotic Bcl-2 protein levels. Moreover, InsGH3 cells wer e resistant to the streptozotocin toxicity that, in contrast, reduced beta TC3 cell viability to 50-60% of controls. In conclusion, proinsulin gene ex pression and mature insulin secretion persisted in transplanted InsGH3 cell s that reversed hyperglycemia in vivo. InsGH3 cells might represent a poten tial beta -cell surrogate because they are more resistant than pancreatic b eta cells to different apoptotic insults and might therefore he particularl y suitable for encapsulation.