Vigneshwaran Pitchaimani1, Somasundaram Arumugam1, Rajarajan Amirthalingam Thandavarayan2, Vengadeshprabhu Karuppagounder1, Mst Rejina Afrin1, Remya Sreedhar1, Meilei Harima1, Hiroshi Suzuki1, Shizuka Miyashita1, Kenji Suzuki3, Masahiko Nakamura4, Kazuyuki Ueno5, Kenichi Watanabe6. 1. Department of Clinical Pharmacology, Faculty of Pharmaceutical Sciences, Niigata University of Pharmacy and Applied Life Sciences, Niigata 956-8603, Japan. 2. Department of Cardiovascular Sciences, Houston Methodist Research Institute, Houston, TX 77030, USA. 3. Department of Gastroenterology, Niigata University of Graduate School of Medicine and Dental Sciences, Niigata City 951-8510, Japan. 4. Department of Cardiology, Yamanashi Prefectural Central Hospital, Kofu, Yamanashi 400-8506, Japan. 5. Department of Pharmaceutical Sciences, Niigata University of Pharmacy and Applied Life Sciences, Niigata 956-8603, Japan. 6. Department of Clinical Pharmacology, Faculty of Pharmaceutical Sciences, Niigata University of Pharmacy and Applied Life Sciences, Niigata 956-8603, Japan. Electronic address: watanabe@nupals.ac.jp.
Abstract
AIMS: Sustained glucagon infusion increases hepatic glucose production, but this effect is transient due to hypothalamic glucagon signaling. In hypoglycemia, glucagon acts as a major defense to sustain the blood glucose level and this raises the question regarding glucagon signaling associated glucose production in prolonged fasting hypoglycemia. In this study, we investigated the proteins associated with hypothalamic glucagon signaling and liver gluconeogenesis during fasting hypoglycemia. MAIN METHODS: 8-9week old, male C57BL6/J mice were fasted for 4, 8, 12, 18, 24, 30, 36 or 42h. In the hypothalamus, we investigated glucagon signaling by analyzing the glucagon receptor and its downstream protein, peroxisome proliferator-activated receptor-gamma coactivator 1 (PGC-1) expression. In the liver, we investigated gluconeogenesis by analyzing p-protein kinase A (PKA)(Ser/Thr) substrate and phosphoenolpyruvate carboxykinase - cytosolic (PEPCK-C) expression using the western blotting technique. KEY FINDINGS: The elevated or trended higher hypothalamic glucagon receptor and PGC-1 expressions at 18 and 42h were correlated with the attenuated liver p-PKA(Ser/Thr) substrate expression. The attenuated hypothalamic glucagon receptor and PGC-1 expressions at 12, 24, 30 and 36h were correlated with the elevated or trended higher liver p-PKA(Ser/Thr) substrate expression. SIGNIFICANCE: The hypothalamic glucagon signaling during fasting hypoglycemia might have been modulated by circadian rhythm and this possibly attenuates the liver p-PKA(Ser/Thr) substrate to modify the gluconeogenesis pathway. This mechanism will help to understand the hyperglucagonemia associated complications in diabetes.
AIMS: Sustained glucagon infusion increases hepatic glucose production, but this effect is transient due to hypothalamic glucagon signaling. In hypoglycemia, glucagon acts as a major defense to sustain the blood glucose level and this raises the question regarding glucagon signaling associated glucose production in prolonged fasting hypoglycemia. In this study, we investigated the proteins associated with hypothalamic glucagon signaling and liver gluconeogenesis during fasting hypoglycemia. MAIN METHODS: 8-9week old, male C57BL6/J mice were fasted for 4, 8, 12, 18, 24, 30, 36 or 42h. In the hypothalamus, we investigated glucagon signaling by analyzing the glucagon receptor and its downstream protein, peroxisome proliferator-activated receptor-gamma coactivator 1 (PGC-1) expression. In the liver, we investigated gluconeogenesis by analyzing p-protein kinase A (PKA)(Ser/Thr) substrate and phosphoenolpyruvate carboxykinase - cytosolic (PEPCK-C) expression using the western blotting technique. KEY FINDINGS: The elevated or trended higher hypothalamic glucagon receptor and PGC-1 expressions at 18 and 42h were correlated with the attenuated liver p-PKA(Ser/Thr) substrate expression. The attenuated hypothalamic glucagon receptor and PGC-1 expressions at 12, 24, 30 and 36h were correlated with the elevated or trended higher liver p-PKA(Ser/Thr) substrate expression. SIGNIFICANCE: The hypothalamic glucagon signaling during fasting hypoglycemia might have been modulated by circadian rhythm and this possibly attenuates the liver p-PKA(Ser/Thr) substrate to modify the gluconeogenesis pathway. This mechanism will help to understand the hyperglucagonemia associated complications in diabetes.