Reversal of hyperglycemia by protein transduction of NeuroD in vivo

Aim: To test whether the neurogenic differentiation (NeuroD) protein could alleviate symptoms of diabetes mellitus by its transduction activity in vivo. Methods: Type 1 diabetes mellitus in mice was induced by ip (intraperitoneal) injection of streptozotocin (150 mg/kg). One group of diabetic mice were intravenously injected with the NeuroD-EGFP (Enhanced Green Fluorescent Protein) (5 mg/kg, n = 6) and the other group with EGFP (5 mg/kg, n = 5). After the transduction of NeuroD-EGFP, the distribution of the protein was examined by means of frozen section under fluorescent microscope observation. We conducted RT-PCR and Real-time quantitative PCR to measure the transcription levels of insulin mRNA. Immunohistochemistry was utilized to detect the insulin protein. Radioimmunoassay was conducted to determine the serum insulin levels. Blood glucose levels and body weights were regularly recorded after the protein administration. Results: The NeuroD protein can be transduced into cells in vivo with a high efficiency of nearly 100%. Insulin mRNA was highly expressed in NeuroD-treated diabetic mice, 38-fold higher than that of control group (P < 0.05). Immunohistochemistry revealed enteric insulin expression in the NeuroD-treated diabetic mice. The fasting serum insulin level of the NeuroD-EGFP group (n = 6) was 337 +/- 39 pg/mL, significantly higher than that of the control diabetic mice (n = 5) which was 84 +/- 23 pg/mL (P < 0.01, t-test). Records of blood glucose level also displayed alleviation of hyperglycemia after NeuroD administration (P < 0.01, t-test, n = 6). Conclusion: In vivo -transduced NeuroD in the small intestine remained functionally active and could ameliorate the non-fasting glucose levels of streptozotocin-induced, diabetic mice by inducing enteric insulin expression.