The effect of macrophage polarisation on adipose tissue fibrosis in the context of hyperinsulinaemia
Date: 10 February 2020
University of Exeter
MSc by Research Medical Studies
In obesity, adipose tissue (AT) must remodel to accommodate adipocyte expansion. This remodelling is achieved through degradation and synthesis of extracellular matrix (ECM) components. Obese AT fibrosis, where excess fibrous ECM proteins accumulate, is thought to limit lipid storage capacity, leading to AT dysfunction and pathogenic ...
In obesity, adipose tissue (AT) must remodel to accommodate adipocyte expansion. This remodelling is achieved through degradation and synthesis of extracellular matrix (ECM) components. Obese AT fibrosis, where excess fibrous ECM proteins accumulate, is thought to limit lipid storage capacity, leading to AT dysfunction and pathogenic ectopic lipid deposition. Dysfunctional AT is strongly associated with insulin resistance and characterised by low-level inflammation and increased macrophage infiltration. AT macrophages are classified as pro-inflammatory M1, or anti-inflammatory M2 (including M2a and M2c subtypes). M2 macrophage-secreted factors, as well as high levels of insulin, may induce AT fibrosis development thus increasing AT dysfunction. This study aimed to understand the role of polarised macrophage phenotypes and hyperinsulinaemia on the development of AT fibrosis. THP-1 monocytes were differentiated and resulting macrophage phenotypes analysed by protein secretion and macrophage marker mRNA quantification. Macrophages were co-cultured with human omental AT explants (age: 49.5±7.83, BMI: 27.98±6.12) with vehicle-only, 1nM, 10nM or 100nM insulin for 48h before AT expression of fibrosis-associated genes was measured using qRT-PCR. Macrophage characterisation suggested M (IFNγ+LPS) macrophages possessed a mixed M1/M2 phenotype, M (IL-4) macrophages were broadly M2-like, while M (IL-10) macrophages were considered not functionally differentiated. Co-culture with M (IFNγ+LPS) macrophages significantly upregulated FN1 (3.6±3.07 mean fold increase ±SD), and M (IL-4) macrophages upregulated molecular mediators of fibrosis LOX and SPARC (1.98±1.2 and 1.61±0.74) in AT. Under hyperinsulinaemic conditions (1nM or 10nM insulin) with M (IFNγ+LPS) macrophages, AT COL4A1, COL5A3, TGFB1 and FN1 were downregulated (0.78±0.13, 0.956±0.53, 1.00±0.34, 2.32±1.3 respectively) compared to the vehicle control. Results suggest that mixed M1/M2 phenotype and M2-like macrophages may contribute to AT fibrosis, and hyperinsulinaemic conditions may moderate this effect. However, poor experimental design and inadequate optimisation prevented scientifically sound conclusions being drawn from this study. Further comprehensive work is required to determine the role of macrophages and hyperinsulinaemia in AT fibrosis.
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