Sequential cleavage of insulin receptor by calpain 2 and γ-secretase impairs insulin signalling

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...

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Bibliographic Details
Published in:Diabetologia 2016-12, Vol.59 (12), p.2711-2721
Main Authors: Yuasa, Tomoyuki, Amo-Shiinoki, Kikuko, Ishikura, Shuhei, Takahara, Mitsuyoshi, Matsuoka, Takaaki, Kaneto, Hideaki, Kuroda, Akio, Matsuhisa, Munehide, Hashida, Seiichi
Format: Article
Language:English
Subjects:
Amyloid Precursor Protein Secretases - genetics
Amyloid Precursor Protein Secretases - metabolism
Blotting, Western
Calpain - genetics
Calpain - metabolism
Diabetes Mellitus, Type 2 - genetics
Diabetes Mellitus, Type 2 - metabolism
Enzyme-Linked Immunosorbent Assay
Exosomes - metabolism
Hep G2 Cells
Human Physiology
Humans
Immunoprecipitation
Insulin Resistance - genetics
Insulin Resistance - physiology
Internal Medicine
Medicine
Medicine & Public Health
Metabolic Diseases
Receptor, Insulin - genetics
Receptor, Insulin - metabolism
RNA, Small Interfering
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Summary: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.
ISSN:0012-186X
1432-0428
DOI:10.1007/s00125-016-4102-5