Ras signaling in NGF reduction and TNF-α-related pancreatic β cell apoptosis in hyperglycemic rats.

Recent evidence suggested that tumor necrosis factor-alpha (TNF-α) and nerve growth factor (NGF) withdrawal activated a common apoptotic pathway. Here, we aimed to investigate the possible role of apoptotic Ras effectors RASSF1 and NORE1 in NGF reduction and TNF-α-related β cell apoptosis in streptozotocin (STZ)-induced hyperglycemic rats. Rats were divided into four groups: the first group was given saline and citrate buffer, the second group was injected 4-methylcatechol (4-MC), an inducer of NGF synthesis, the third group received STZ, and the fourth group was given both 4-MC and STZ. 4-MC (10 μg/kg) was administered by daily intraperitoneal injection for 10 days before the animals were rendered hyperglycemic by administration of single dose STZ (75 mg/kg). With 4-MC pretreatment to hyperglycemic rats the following results were noted: (i) Decrease in pancreatic NGF level was blocked, (ii) Increase in pancreatic TNF-α level and the number of TNF-α(+) beta cell in the islets were prevented, (iii) Increase in the number of β cell synthhesized apoptotic Ras effectors that RASSF1 and NORE1 was blocked, (iv) While pancreatic lipid peroxidation level decreased, antioxidant molecule glutathione and antioxidant enzymes glutathione peroxidase, catalase and superoxide dismutase activities increased, (v) Pancreatic caspase-3 activity and the number of cleaved caspase-3(+) β cells were decreased. These results strengthen the idea that TNF-α and reduction in NGF can activate a common apoptotic pathway. Moreover, these data display that new apoptotic Ras effector molecules RASSF1 and NORE1 play important role with oxidative stress in NGF reduction and TNF-α-related pancreatic β cell apoptosis in hyperglycemic rats. Furthermore, these findings suggest that 4-MC can prevent β cell apoptosis possibly through increasing NGF synthesis in hyperglycemic rats.

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