Insulin detemir enhances proglucagon gene expression in the intestinal L cells via stimulating β-catenin and CREB activities.
Insulin therapy using insulin detemir (d-INS) has demonstrated weight-sparing effects compared with other insulin formulations. Mechanisms underlying these effects, however, remain largely unknown. Here we postulate that the intestinal tissues' selective preference allows d-INS to exert enhanced action on proglucagon (Gcg) expression and the production of glucagon-like peptide (GLP)-1, an incretin hormone possessing both glycemia-lowering and weight loss effects. To test this hypothesis, we used obese type 2 diabetic db/db mice and conducted a 14-day intervention with daily injection of a therapeutic dose of d-INS or human insulin (h-INS) in these mice. The body weight of the mice after 14-day daily injection of d-INS (5 IU/kg) was decreased significantly compared with those injected with the same dose of h-INS or saline. The weight-sparing effect of d-INS was associated with significantly elevated circulating levels of total GLP-1 and reduced food intake. Histochemistry analysis demonstrated that d-INS induced rapid phosphorylation of protein kinase B (Akt) in the gut L cells of normal mice. Western blotting showed that d-INS stimulated Akt activation in a more rapid and enhanced fashion in the mouse distal ileum compared with those by h-INS. In vitro investigation in primary fetal rat intestinal cell (FRIC) cultures showed that d-INS increased Gcg mRNA expression as determined by Northern blotting and real-time RT-PCR. Consistent with these in vivo investigations, d-INS significantly increased GLP-1 secretion in FRIC cultures. Consistently, d-INS was also shown to induce rapid phosphorylation of Akt in the clonal gut cell line GLUTag. Furthermore, d-INS increased β-catenin phosphorylation, its nuclear translocation, and enhanced cAMP response element-binding protein (CREB) phosphorylation in a phosphatidylinositol 3-kinase and/or mitogen-activated protein kinase kinase/extracellular signal-regulated kinase-sensitive manner. We suggest that the weight-sparing benefit of d-INS in mice is related to its intestinal tissues preference that leads to profound stimulation of Gcg expression and enhanced GLP-1 secretion in intestinal L cells, potentially involving the activation of insulin/β-catenin/CREB signaling pathways.
Division of Endocrinology and Metabolism, the Keenan Research Centre in the Li Ka Shing Knowledge Institute, St. Michael’s Hospital, Toronto, Ontario, Canada.
Shenghao
S
Liu
Rui
R
Liu
Yu-Ting
YT
Chiang
Lifang
L
Song
Xiaoming
X
Li
Tianru
T
Jin
Qinghua
Q
Wang
D000818:Animals; D002478:Cells, Cultured; D017362:Cyclic AMP Response Element-Binding Protein / Q000819:agonists / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000150:complications / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D005333:Fetus / Q000166:cytology; D005786:Gene Expression Regulation / Q000187:drug effects; D052216:Glucagon-Like Peptide 1 / Q000097:blood / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology / Q000627:therapeutic use*; D000069057:Insulin Detemir; D049528:Insulin, Long-Acting / Q000494:pharmacology / Q000627:therapeutic use*; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D007739:L Cells; D051379:Mice; D008817:Mice, Mutant Strains; D009765:Obesity / Q000150:complications / Q000517:prevention & control; D009928:Organ Specificity; D010766:Phosphorylation / Q000187:drug effects; D052336:Proglucagon / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D051176:beta Catenin / Q000819:agonists / Q000378:metabolism*
D017362:Cyclic AMP Response Element-Binding Protein; D007004:Hypoglycemic Agents; D049528:Insulin, Long-Acting; D012333:RNA, Messenger; D051176:beta Catenin; D000069057:Insulin Detemir; D052336:Proglucagon; D052216:Glucagon-Like Peptide 1