In Vitro Investigation of Insulin-Like Growth Factor-I and Mechano-Growth Factor on Proliferation of Neural Stem Cells in High Glucose Environment

Abstract

Objective: High glucose levels cause metabolic and vascular complications by affecting the nervous system with an increased risk of stroke and seizures. There are still no effective treatment modalities for the high morbidity and mortality rates detected in such situations. Neural stem cells (NSCs) provide neurogenesis in the nervous system, but high glucose is detrimental to NSCs. This study investigates the intrinsic and extrinsic effects of the growth factors insulin-like growth factor-I (IGF-I) and mechano-growth factor (MGF) on NSCs when exposed to high glucose levels. Thus, the possibility of new treatment options for diabetes patients is explored. Materials and Methods: Rat NSCs grown in cell culture conditions were exposed to a control glucose concentration of 17.5 mM and high concentrations of 27.75, 41.75, and 83.75 mM for 24 h. The high glucose concentrations were designed to recapitulate the in vivo conditions of diabetes mellitus, diabetic ketoacidosis, and hyperglycemia hyperosmolar status. Then, 0.2 μg/ml IGF-I and MGF growth factors were separately added and their expressions in the NCSs investigated by real-time reverse transcription-polymerase chain reaction. The effects of exogenous IGF-I and MGF administration on NSC proliferation under high glucose conditions were measured by BrdU incorporation assay using flow cytometry analysis. Results: A significant increase was detected in the relative gene expression fold changes of IGF-I and MGF in the NSCs. The MGF relative fold change was greater than the IGF-I for each high glucose condition. NSCs exposed to 27.75 mM glucose revealed a 17-fold and 40-fold increase in the IGF-I and MGF gene expressions, respectively; the 41.75 mM glucose similarly revealed 68-and 161-fold increases and the 83.75 mM glucose 75-and 137-fold increases. Exogenous IGF-I administration increased its expression profile, while the administration of MGF lowered its expression. The NSC was in the growth (G0/G1) phase of the cell cycle during the 24 h culture time. The percentage of proliferated NSC decreased to 89% (17.5 mM), 85% (27.75 mM), 50.30% (41.75 mM), and 28.97% (83.75 mM). Surprisingly, the increase in both IGF-I and MGF saved the NSCs from cell death. Conclusion: Exogenous IGF-I and MGF administrations via high glucose environments increased NSC proliferation at the time of injury and protected the NSCs from cell death. The neuroprotective effect of MGF was greater than that of IGF-I. Thus, due to their neurogenesis potential, exogenous IGF-I and MGF could be applied in the treatment of diabetes patients to relieve neural damage.