Adipocyte extracellular matrix composition, dynamics and role in obesity

Abstract

The central role of the adipose tissue in lipid metabolism places specific demands on the cell structure of adipocytes. The protein composition and dynamics of the extracellular matrix (ECM) is of crucial importance for the functioning of those cells. Adipogenesis is a bi-phasic process in which the ECM develops from a fibrillar to a laminar structure as cells move from the commitment phase to the growth phase characterized by storage of vast amounts of triglycerides. Mature adipocytes appear to spend a lot of energy on the maintenance of the ECM. ECM remodeling is mediated by a balanced complement of constructive and destructive enzymes together with their enhancers and inhibitors. ECM remodeling is an energy costing process regulated by insulin, by the energy metabolism, and by mechanical forces. In the obese, overgrowth of adipocytes may lead to instability of the ECM, possibly mediated by hypoxia.

Fig. 1

Visualization of the ECM of 3T3-L1 preadipocyte (a) and adipocytes (b) by immunohistological staining of heparin sulfate proteoglycan: green heparin sulfate proteoglycans stained by antibody (10E4 epitope; Seikagaku, Tokyo, Japan); red nuclear stained with propidium iodide. The fat droplets are visible as dark vesicles in the cytosol

Fig. 2

Overview of some of the proteins involved in regulating the maintenance and turnover of the adipocyte ECM

Fig. 3

Summary of the factors that influence the activity of the prolyl hydroxylase/protein disulfide isomerase (PH/PDI) enzyme complex