Insulin receptor substrate-2-dependent interleukin-4 signaling in macrophages is impaired in two models of type 2 diabetes mellitus.
We have shown previously that hyperinsulinemia inhibits interferon-alpha-dependent activation of phosphatidylinositol 3-kinase (PI3-kinase) through mammalian target of rapamycin (mTOR)-induced serine phosphorylation of insulin receptor substrate (IRS)-1. Here we report that chronic insulin and high glucose synergistically inhibit interleukin (IL)-4-dependent activation of PI3-kinase in macrophages via the mTOR pathway. Resident peritoneal macrophages (PerMPhis) from diabetic (db/db) mice showed a 44% reduction in IRS-2-associated PI3-kinase activity stimulated by IL-4 compared with PerMPhis from heterozygote (db/+) control mice. IRS-2 from db/db mouse PerMPhis also showed a 78% increase in Ser/Thr-Pro motif phosphorylation without a difference in IRS-2 mass. To investigate the mechanism of this PI3-kinase inhibition, 12-O-tetradecanoylphorbol-13-acetate-matured U937 cells were treated chronically with insulin (1 nm, 18 h) and high glucose (4.5 g/liter, 48 h). In these cells, IL-4-stimulated IRS-2-associated PI3-kinase activity was reduced by 37.5%. Importantly, chronic insulin or high glucose alone did not impact IL-4-activated IRS-2-associated PI3-kinase. Chronic insulin + high glucose did reduce IL-4-dependent IRS-2 tyrosine phosphorylation and p85 association by 54 and 37%, respectively, but did not effect IL-4-activated JAK/STAT signaling. When IRS-2 Ser/Thr-Pro motif phosphorylation was examined, chronic insulin + high glucose resulted in a 92% increase in IRS-2 Ser/Thr-Pro motif phosphorylation without a change in IRS-2 mass. Pretreatment of matured U937 cells with rapamycin blocked chronic insulin + high glucose-dependent IRS-2 Ser/Thr-Pro motif phosphorylation and restored IL-4-dependent IRS-2-associated PI3-kinase activity. Taken together these results indicate that IRS-2-dependent IL-4 signaling in macrophages is impaired in models of type 2 diabetes mellitus through a mechanism that relies on insulin/glucose-dependent Ser/Thr-Pro motif serine phosphorylation mediated by the mTOR pathway.
Hartman
Matthew E
ME
Department of Animal Sciences, University of Illinois at Urbana-Champaign, 506 South Mathews, Urbana, IL 61801, USA.
O'Connor
Jason C
JC
Godbout
Jonathan P
JP
Minor
Kyle D
KD
Mazzocco
Valerie R
VR
Freund
Gregory G
GG
D020816:Amino Acid Motifs; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D015153:Blotting, Western; D002460:Cell Line; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006579:Heterozygote; D006801:Humans; D007328:Insulin / Q000097:blood / Q000378:metabolism; D055504:Insulin Receptor Substrate Proteins; D015847:Interleukin-4 / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D008264:Macrophages / Q000378:metabolism*; D017737:Macrophages, Peritoneal / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate; D013997:Time Factors; D014443:Tyrosine / Q000378:metabolism; D020298:U937 Cells
D001786:Blood Glucose; C526297:IRS2 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; C526298:Irs2 protein, mouse; D010750:Phosphoproteins; D015847:Interleukin-4; D014443:Tyrosine; D012694:Serine; D019869:Phosphatidylinositol 3-Kinases; D005947:Glucose; D013755:Tetradecanoylphorbol Acetate; D020123:Sirolimus