Tomoyuki Yuasa1,2, Kikuko Amo-Shiinoki3,4, Shuhei Ishikura3,5, Mitsuyoshi Takahara6,7, Takaaki Matsuoka6, Hideaki Kaneto6,8, Akio Kuroda9,10, Munehide Matsuhisa9,10, Seiichi Hashida11. 1. Division of Molecular Genetics, Institute for Enzyme Research, Tokushima University, Tokushima, Japan. yuasa.tomoyuki@tokushima-u.ac.jp. 2. Department of Community Medicine for Diabetes and Metabolic Disorders, Tokushima University Graduate School, 3-18-15 Kuramoto-cho, Tokushima-shi, Tokushima, 770-8503, Japan. yuasa.tomoyuki@tokushima-u.ac.jp. 3. Division of Molecular Genetics, Institute for Enzyme Research, Tokushima University, Tokushima, Japan. 4. Department of Diabetes Research, Yamaguchi University School of Medicine, Yamaguchi, Japan. 5. Department of Cell Biology, Faculty of Medicine, Fukuoka University, Fukuoka, Japan. 6. Department of Metabolic Medicine, Osaka University Graduate School of Medicine, Osaka, Japan. 7. Department of Diabetes Care Medicine, Osaka University Graduate School of Medicine, Osaka, Japan. 8. Department of Diabetes, Endocrinology and Metabolism, Kawasaki Medical School, Okayama, Japan. 9. Diabetes Clinical Research and Development Center, Tokushima University, Tokushima, Japan. 10. Diabetes Therapeutics and Research Center, Institute for Advanced Medical Sciences, Tokushima University, Tokushima, Japan. 11. Human Life Science, Tokushima Bunri University, Tokushima, Japan.
Abstract
AIMS/HYPOTHESIS: Soluble insulin receptor (sIR), the ectodomain of the insulin receptor (IR), has been detected in human plasma and its concentration paralleled that of blood glucose. We have previously developed an in vitro model using HepG2 liver-derived cells, which mimics changes in sIR levels in plasma from diabetic patients and shows that calcium-dependent proteases cleave IR extracellularly (a process known as shedding). The present study aimed to reveal the mechanisms of IR cleavage. METHODS: Using the in vitro model, we investigated the molecular mechanisms of IR cleavage, which is accelerated by high-glucose treatment. We also analysed the relationship between IR cleavage and cellular insulin resistance, and the correlation between plasma sIR levels and insulin sensitivity, which was assessed by the euglycaemic-hyperinsulinaemic clamp technique. RESULTS: Here, we determined that calpain 2, which is secreted into the extracellular space associated with exosomes, directly cleaved the ectodomain of the IRβ subunit (IRβ), which in turn promoted intramembrane cleavage of IRβ by γ-secretase. IR cleavage impaired insulin signalling and the inhibition of IR cleavage (by knockdown of calpain 2 and γ-secretase), restored IR substrate-1 and Akt, independent of IR. Furthermore, the glucose-lowering drug, metformin, prevented IR cleavage accompanied by inhibition of calpain 2 release in exosomes, and re-established insulin signalling. In patients with type 2 diabetes, plasma sIR levels inversely correlated with insulin sensitivity. CONCLUSIONS/ INTERPRETATION: Sequential cleavage of IR by calpain 2 and γ-secretase may contribute to insulin signalling in cells and its inhibition may be partly responsible for the glucose-lowering effects of metformin. Thus, IR cleavage may offer a new mechanism for the aetiology of insulin resistance.
AIMS/HYPOTHESIS: Soluble insulin receptor (sIR), the ectodomain of the insulin receptor (IR), has been detected in human plasma and its concentration paralleled that of blood glucose. We have previously developed an in vitro model using HepG2 liver-derived cells, which mimics changes in sIR levels in plasma from diabeticpatients and shows that calcium-dependent proteases cleave IR extracellularly (a process known as shedding). The present study aimed to reveal the mechanisms of IR cleavage. METHODS: Using the in vitro model, we investigated the molecular mechanisms of IR cleavage, which is accelerated by high-glucose treatment. We also analysed the relationship between IR cleavage and cellular insulin resistance, and the correlation between plasma sIR levels and insulin sensitivity, which was assessed by the euglycaemic-hyperinsulinaemic clamp technique. RESULTS: Here, we determined that calpain 2, which is secreted into the extracellular space associated with exosomes, directly cleaved the ectodomain of the IRβ subunit (IRβ), which in turn promoted intramembrane cleavage of IRβ by γ-secretase. IR cleavage impaired insulin signalling and the inhibition of IR cleavage (by knockdown of calpain 2 and γ-secretase), restored IR substrate-1 and Akt, independent of IR. Furthermore, the glucose-lowering drug, metformin, prevented IR cleavage accompanied by inhibition of calpain 2 release in exosomes, and re-established insulin signalling. In patients with type 2 diabetes, plasma sIR levels inversely correlated with insulin sensitivity. CONCLUSIONS/ INTERPRETATION: Sequential cleavage of IR by calpain 2 and γ-secretase may contribute to insulin signalling in cells and its inhibition may be partly responsible for the glucose-lowering effects of metformin. Thus, IR cleavage may offer a new mechanism for the aetiology of insulin resistance.
Authors: K Ueki; T Yamauchi; H Tamemoto; K Tobe; R Yamamoto-Honda; Y Kaburagi; Y Akanuma; Y Yazaki; S Aizawa; R Nagai; T Kadowaki Journal: J Clin Invest Date: 2000-05 Impact factor: 14.808
Authors: Emily M Heiston; Anna Ballantyne; Nathan R Stewart; Sabrina La Salvia; Luca Musante; Joanne Lanningan; Uta Erdbrügger; Steven K Malin Journal: Am J Physiol Endocrinol Metab Date: 2022-07-20 Impact factor: 5.900
Authors: Thaysa Ghiarone; Jorge A Castorena-Gonzalez; Christopher A Foote; Francisco I Ramirez-Perez; Larissa Ferreira-Santos; Francisco J Cabral-Amador; Roger de la Torre; Rama R Ganga; Andrew A Wheeler; Camila Manrique-Acevedo; Jaume Padilla; Luis A Martinez-Lemus Journal: Am J Physiol Heart Circ Physiol Date: 2022-08-26 Impact factor: 5.125