Background: The beneficial metabolic effects of the PPARγ agonist rosiglitazone (Rosi) are associated with anti-inflammatory changes in adipose tissue macrophages (ATMs) . One study aim was to characterize the in vivo Rosi-induced phenotypic switch of ATMs using a variety of macrophage markers, including the lipid-associated macrophage markers CD9 and Trem2. As a second aim, since ATM-derived exosomes can exert insulin-sensitizing or desensitizing effects dependent on ATM cell context, we assessed the effects of ATM exosomes from Rosi-treated obese mice on in vitro insulin actions.
Research Design and Method: ATMs were isolated from 4 months HFD/obese mice treated for the last month with Rosi (60 mg/kg HFD) compared to HFD or chow-fed controls. Among CD11b+F4/80+ or CD64+ macrophages, we identified pro-inflammatory (“M1-like” CD11c+ and/or CD9+) , anti-inflammatory (“M2-like” CD11c-CD206+) and lipid-associated (CD9+ and/or Trem2+) ATMs by flow cytometry. Bone marrow-derived macrophages (BMDMs) were treated in vitro with µM Rosi for 24h. 3T3-L1 adipocytes, L6 myotubes, and primary hepatocytes were cultured 24h with exosomes isolated from ATMs of Rosi treated obese mice or in vitro Rosi treated BMDMs and then assessed for insulin sensitivity.
Results: Rosi treatment reduced adipose tissue inflammation, as seen by reduced numbers of pro-inflammatory (“M1-like”) ATMs and increased the Trem2signature in “M2-like” ATMs. Importantly, Rosi directly induced Trem2 expression in vitro in BMDMs. Additionally, exosomes isolated from Rosi-treated obese mice or M1 BMDMs increased glucose uptake and insulin signalling (pAKT) in adipocytes and myotubes and reduced glucose production in hepatocytes compared to control exosomes.
Conclusion: Our data indicate that Trem2 is a PPARγ target gene. Since exosomes from Rosi treated ATMs or BMDMs enhance cellular insulin action, this could provide a new explanation for the well-known insulin-sensitizing effects of PPARγ agonists.
T.V.Rohm: None. F.C.G.Reis: None. R.Isaac: None. M.Paszek: None. G.Bandyopadhyay: None. J.M.Olefsky: None.
Swiss National Science Foundation (SNF) Early Postdoc.Mobility grant (to T.R.) .