Local proliferation of macrophages in adipose tissue during obesity-induced inflammation
- 2.6k Downloads
Obesity is frequently associated with low-grade inflammation of adipose tissue (AT), and the increase in adipose tissue macrophages (ATMs) is linked to an increased risk of type 2 diabetes. Macrophages have been regarded as post-mitotic, but recent observations have challenged this view. In this study, we tested the hypothesis that macrophages proliferate within AT in diet-induced obesity in mice and humans.
We studied the expression of proliferation markers by immunofluorescence, PCR and flow cytometry in three different models of mouse obesity as well as in humans (n = 239). The cell fate of dividing macrophages was assessed by live imaging of AT explants.
We show that ATMs undergo mitosis within AT, predominantly within crown-like structures (CLS). We found a time-dependent increase in ATM proliferation when mice were fed a high-fat diet. Upregulation of CD206 and CD301 in proliferating ATMs indicated preferential M2 polarisation. Live imaging within AT explants from mice revealed that macrophages emigrate out of the CLS to become resident in the interstitium. In humans, we confirmed the increased expression of proliferation markers of CD68+ macrophages in CLS and demonstrated a higher mRNA expression of the proliferation marker Ki67 in AT from obese patients.
Local proliferation contributes to the increase in M2 macrophages in AT. Our data confirm CLS as the primary site of proliferation and a new source of ATMs and support a model of different recruitment mechanisms for classically activated (M1) and alternatively activated (M2) macrophages in obesity.
KeywordsAdipose tissue Crown-like structures Diabetes High-fat diet Inflammation Insulin resistance Macrophages Obesity Proliferation
Adipose tissue macrophages
C-C motif chemokine receptor 2
Colony-stimulating factor 1 receptor
Enhanced green fluorescent protein
Epididymal white adipose tissue
Monocyte chemoattractant protein 1
PBS with 0.3% Triton-X
Proliferating cell nuclear antigen
Subcutaneous white adipose tissue
We are grateful for the excellent technical assistance of C. Hobusch, A. Ehrlich and C. Merkwitz. We also thank M. Krüger for helpful discussions and K. Jäger and A. Lösche from the FACS core unit (all Leipzig University).
This work was in part supported by the Kompetenznetz Adipositas (Competence Network for Obesity) funded by the Federal Ministry of Education and Research (German Obesity Biomaterial Bank; FKZ 01GI1128 and FKZ 01EO1001), a grant from the Deutsche Forschungsgemeinschaft DFG-SFB 1052/1: ‘Obesity mechanisms’ (projects A04, B01, B04) and by the Helmholtz Alliance ‘Imaging and Curing Environmental Metabolic Disease’ through the Initiative and Networking Fund of the Helmholtz Association. MG received a start-up grant from the Medical Faculty of Leipzig University.
Duality of interest
The authors declare that there is no duality of interest associated with this manuscript.
JH planned and performed morphological analyses of murine and human AT samples. UW and JH analysed ATMs by flow cytometry. MG and JE designed, performed and evaluated live imaging experiments of AT explants. KI planned, established and analysed murine macrophage cultures. NK and MB analysed gene expression of human AT samples. IB and MG designed the study. JH and MG wrote the paper. All authors participated in drafting and revising this article. All authors approved the final version of the manuscript.
- 37.Handel-Fernandez ME, Lopez DM (2000) Isolation of macrophages from tissues, fluids, and immune response sites. In: Paulnock DM (ed) Macrophages. Oxford University Press, OxfordGoogle Scholar