Abstract: TH-PO636
Parathyroid Hormone Enhances Gluconeogenesis via the PKC/FoxO1 Pathway in Proximal Tubules
Session Information
- Health Maintenance, Nutrition, Metabolism - I
November 07, 2019 | Location: Exhibit Hall, Walter E. Washington Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Health Maintenance, Nutrition, and Metabolism
- 1300 Health Maintenance, Nutrition, and Metabolism
Authors
- Tsukada, Hiroyuki, The University of Tokyo, Tokyo, Japan
- Nakamura, Motonobu, The University of Tokyo, Tokyo, Japan
- Horita, Shoko, The University of Tokyo, Tokyo, Japan
- Fujii, Wataru, The University of Tokyo, Tokyo, Japan
- Mizuno, Tomohito, The University of Tokyo, Tokyo, Japan
- Satoh, Nobuhiko, The University of Tokyo, Tokyo, Japan
- Sato, Yusuke, The University of Tokyo, Tokyo, Japan
- Seki, George, Yaizu City Hospital, Yaizu, Japan
- Kume, Haruki, The University of Tokyo, Tokyo, Japan
- Nangaku, Masaomi, The University of Tokyo, Tokyo, Japan
- Suzuki, Masashi, Tokyo Gakugei University, Koganei, Japan
Background
Parathyroid hormone (PTH) has been reported to enhance gluconeogenesis in proximal tubules (PTs), which may be comparable to that in liver. PTH is known to activate both cAMP/PKA and PLC/calcium/PKC pathways. In this study, we tried to determine the detailed mechanism of stimulatory effect of PTH on PT gluconeogenesis.
Methods
Freshly isolated rat and human PTs were incubated overnight in DMEM with 0.2 mM dibutyryl-cAMP (cAMP) or 1 nM PTH, and subsequently incubated with 10 nM insulin for 4 hours. Total RNA was extracted from the PTs. The mRNA expression of gluconeogenic enzymes (phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6P)) was determined by quantitative PCR. To clarify the signaling pathway of PTH, PTs were also treated with protein kinase A (PKA) inhibitor H89, protein kinase C (PKC) inhibitor Gö6983, or siRNA against FoxO1. In addition, we performed western blotting in the kidney cortex tissue to analyze the Akt phosphorylation. To examine the effect of PTH on hepatic gluconeogenesis, similar experiments were performed using primary cultured rat hepatocytes.
Results
In rat and human PTs, cAMP and PTH increased the mRNA expression of PEPCK and G6P by 5 and 3 times, respectively. Insulin almost completely abolished the stimulatory effect of cAMP, but failed to attenuate that of PTH. H89 completely abolished the stimulatory effect of cAMP without affecting that of PTH. By contrast, Gö6983 completely abolished the stimulatory effect of PTH without affecting that of cAMP. siRNA against FoxO1 inhibited the stimulatory effects of both cAMP and PTH. Insulin-induced Akt phosphorylation was preserved after incubation with PTH in the kidney cortex. In rat hepatocytes, cAMP, but not PTH, increased the mRNA expression of PEPCK and G6P.
Conclusion
Our results, for the first time to our knowledge, revealed that PTH enhances gluconeogenesis in PTs via PKC/FoxO1 pathway. We also found that insulin was able to induce the Akt phosphorylation but failed to suppress gluconeogenesis in the presence of PTH. PTH-enhanced gluconeogenesis as well as insulin resistance in PTs may at least partially contribute to altered glucose homeostasis reported in patients with hyperparathyroidism and/or pseudohypoparathyroidism.
Funding
- Government Support - Non-U.S.