Reversal of streptozotocin-induced diabetes in mice by cellular transduction with recombinant pancreatic transcription factor pancreatic duodenal homeobox-1 - A novel protein transduction domain-based therapy

OBJECTIVE-The key pancreatic transcription factor pancreatic duodenal homeobox-1 (Pdx1), known to control development and maintenance of pancreatic P-cells, possesses a protein transduction domain (PTD) that facilitates its entry into cells. We therefore sought to evaluate the capacity of in vivo-administered recombinant Pdxl (rPdx1) to ameliorate hyperglycemia, in mice with streptozotocin-induced diabetes. RESEARCH DESIGN AND METHODS-Cell entry and transcriptional regulatory properties of rPdx1 protein and its PTD-deletion mutant rPdx1 Delta protein, as well as a PTD-green fluorescent protein, were evaluated in vitro. After intraperitoneal rPdx1 injction into mice with streptozotocin-induced diabetes, we assessed its action on blood glucose levels, insulin content, intraperitoneal glucose tolerance test (IPGTT), Pdx1 distribution, pancreatic gene expression, islet cell proliferation, and organ histology. RESULTS-Restoration of euglycemia in Pdx1-treated diabetic mice was evident by improved IPGTT and glucose-stimulated insulin release. Insulin, glucagon, and Ki67 immunostaining revealed increased islet cell number and proliferation in pancreata of rPdx1-treated mice. Real-time PCR of pancreas and liver demonstrated upregulation of INS and PDX1 genes and other genes relevant to pancreas regeneration. While the time course of P-cell gene expression and serum/tissue insulin levels indicated that both liver- and pancreas-derived insulin contributed to restoration of normoglycemia, near-total pancreatectomy resulted in hyperglycemia, suggesting that P-cell regeneration played the primary role in rPdx1-induced glucose homeostasis. CONCLUSIONS-rPdx1 treatment of mice with streptozotocin-induced diabetes promotes P-cell regeneration and liver cell reprogramming, leading to restoration of normoglycemia. This novel PTD-based protein therapy offers a promising way to treat patients with diabetes while avoiding potential side effects associated with the use of viral vectors.