Extracellular Matrix Remodeling and Mechanical Stresses as Modulators of Adipose Tissue Metabolism and Inflammation - The Mechanobiology of Obesity and Related Diseases - page 109

adipogenesis, evident by up-regulation of adipose tissue gene (PPARgamma, LPL,
FABP4) and metabolic (GPDH and triglycerides) markers. Considering physio-
logical oxygen levels in normal adult AT ranges from 5.2 to 9.6 %, we also
performed these experiments in a 5 % oxygen environment to compare with those
at 20 % oxygen. Physiological oxygen levels significantly down-regulated adipose
tissue metabolic markers GPDH and triglycerides in the absence of cytoskeletal
inhibitors. However, cytoskeletal inhibitor treatment abrogated this effect and
up-regulated adipogenic gene expression and metabolic markers regardless of
oxygen levels.
Adding to these studies, others have focused on the combined effects of cell
morphology and matrix chemistry. The combined effects of single cell morphology
and adhesion ligand chemistry on mesenchymal stem cells were investigated by
culturing the cells on substrates that approximated the elastic modulus (\1 kPa) of
soft tissues [ 45 ]. Cells cultured on small islands to encourage circular morphology
had a greater adipogenic response when adherent to fibronectin or laminin, but not
when interacting with collagen type I, which instead promoted neurogenesis. In
contrast, allowing cells to take on spread morphology on substrates with any of the
three ECM molecules encouraged neurogenic differentiation. These findings
indicate ligand chemistry may couple or interfere with morphology-driven dif-
ferentiation pathways. The study also examined the effects of surface area on
adipogenic differentiation, finding that cells gradually decreased in adipogenic
tendency as circular surface area increased from 1,000 to 5,000 lm 2 , further
suggesting that cytoskeletal tension plays a significant role in adipose tissue
formation.
In these studies, cell mechanics has been controlled via cell shape. In other
works, the mechanical properties of the substrate have been altered to examine
another model of mechanical influence on adipogenic lineage commitment. In one
study, this was examined with mesenchymal stem cells cultured on hyaluronin-
based hydrogels that were controllably stiffened over time during culture by
increasing ultraviolet light-induced crosslinking density at specific time points
[ 46 ]. Gels that were maintained soft for an extended period of time promoted
adipogenesis, whereas stiffer gels and early stiffening both resulted in increased
cell spreading and osteogenesis. In another study, human adipose-derived adult
stem cells were cultured on polyacrylamide gels at varying stiffness (2, 20 and
40 kPa) [ 47 ]. Pulverized decellularized adipose ECM were mixed into the gels to
mimic the adipose tissue biochemical environment. Cells cultured on gels with
stiffness approaching that of native adipose tissue (2 kPa) maintained a rounded
morphology similar to adipocytes in vivo, exhibited upregulated adipogenic
markers, and accumulated lipids. Increasing substrate stiffness resulted in more
spread morphologies and failure to upregulate adipogenic markers.
These studies provide strong evidence that cell morphology and cytoskeletal
mechanics combined with various biochemical cues (e.g., ligand molecules and
oxygen tension) can significantly affect adipogenic differentiation. Interestingly,
cytoskeletal mechanics can be controlled via either cell shape or substrate
mechanical properties. It is anticipated that various modes of mechanoregulation