Relationship between Insulin Secretory Capacity and Mitochondrial Morphology in Pancreatic beta-Cell

Yang, Seung Won; Lee, Jae Hyuk; Park, Chang Soo; Chung, Min Young

Abstract

To investigate the relationship between insulin response and morphometric changes of the mitochondria of pancreatic beta-cell, this study was performed using hyperglycemia and streptozotocin as oxidative stresses. Adult and neonatal rats were used. Intravenous glucose tolerance test (IVGTT) and morphologic examination of pancreas using immunohistochemical stain, in situ end-labeling method and electron microscopic study were performed. Various mitochondrial parameters were measured by image analyzer. Immunohistochemical stain revealed a markedly reduced islet size and decreased number of beta-cells and the increased number of non-beta-cell in adult and neonatoal streptozotocin group, and the appearance of insulin positive cells throughout the exocrine parenchyma in neonatal streptozotocin group. Three days after injection of streptozotocin in adult streptozotocin group, TUNEL stain showed increased apoptotic cells in islets. Ultrastructurally, beta-cells in adult streptozotocin group showed increase in number and size of mitochondria, and disruption of mitochondrial structures. Hyperglycemic group and neonatal streptozotocin group showed preserved mitochondrial ultrastructure. Ultrastructural morphometric study revealed increase in size and number of mitochondria and decrease in mitochondrial contour index in adult streptozotocin-treated rats, which suggested mitochondrial degeneration. Hyperglycemic group showed mild increase in size of mitochondria. Increased number of mitochondria was also observed in neonatal streptozotocin group. IVGTT revealed marked decrease in insulin response in adult streptozotocin group, and non-insulin-dependent diabetes mellitus pattern in glucose and insulin response in neonatal streptozotocin group. Hyperglycemic group showed a glucose and insulin response similar to control group. The above results suggest that a severe oxidative injury may cause degeneration and disruption of mitochondria of pancreatic beta-cell, and may be associated with substantial apoptotic cell death. The changes in the morphology and the number of mitochondria may result from streptozotocin treatment within neonatal period and hyperglycemia treatment, which may be associated with changes in insulin response.