Effect of inflamed macrophage-induced extracellular matrix remodeling on adipocyte function

Abstract

Over the last 40 years obesity rates around the world have significantly increased Recent studies suggest that obesity is accompanied by adipose tissue fibrosis An increase of extracellular matrix (ECM) crosslinking has been shown to cause tissue fibrosis followed by increasing tissue stiffness Lysyl oxidase (LOX) is an enzyme crucial for collagen crosslinking that causes ECM stiffening LOX is synthesized as a pro-LOX originally and processed by proteases such as BMP1 MMP2 TLL1 and TLL2 Our previous results suggest that LOX is increased by macrophages upon the inflammatory stimulation We therefore hypothesize that inflamed macrophages play a pivotal role in the ECM remodeling and adipocyte dysfunction We first found that LOX is present in the macrophage-enriched region in the adipose tissue of obese ob/ob mice Peritoneal macrophages from ob/ob mice showed increased LOX production and secretion In vitro cytokine treatment on Raw 264 7 cells induced the production and secretion of pro-LOX LOX BMP-1 and MMP-2 We then applied an in vitro collagen gel system to test whether inflamed macrophages reset the ECM microenvironment Raw 264 7 cells were firstly cultivated on the FITC-conjugated collagen gel and then treated cytokines as an inflammatory stimulation followed by a decellularization procedure Immunofluorescence microscopy revealed that cytokine treatment increased collagen fiber thickness near residual macrophages We further cultured fibroblasts on this macrophage-processed gel to test their physical property We found that cytokine treatment increased collagen gel contraction and the alignment and thickness of collagen fiber in macrophage-processed gel Thus inflamed macrophages are able to remodel the ECM via matrix contraction and increasing collagen fiber alignment and thickness Interestingly differentiated 3T3-L1 cells cultivated on the macrophage-processed collagen gel showed downregulation in adipocyte functional marker genes Our study provides a novel crosstalk between adipocyte and ECM particularly remodeled by inflamed macrophages

Date of Award	2020
Original language	English
Supervisor	Yau-Sheng Tsai (Supervisor)