(E-174) A finite element analysis of lipid-loaded adipocytes

Introduction:: Mechanobiology has been well-studied in many cell types, but less so in adipocytes. Until recently, adipocytes were considered inert bodies with little function aside from excess lipid storage, but in fact, they are highly active cells that respond to mechanical stimuli. Lipid droplets found in adipocytes and fatty hepatocytes have been observed to deform the nucleus, a mechanosensor that responds to deformation with gene expression changes. Yet, the effect of lipid droplet size on nuclear deformation and stress has not been fully elucidated. The two aims of this study are to evaluate 1) adipocyte mechanosensing and 2) the effect of lipid droplet size on cell stiffness and nuclear stress using atomic force microscopy (AFM) and computational modeling. We hypothesize that adipocytes are mechanosensing, and cell stiffness and nuclear stress increase with lipid droplet size.


Materials and Methods:: Differentiated 3T3-LI adipocytes were seeded at low confluency onto 100 (normal adipose) and 500 Pa (diseased adipose) polyacrylamide gels and glass, all coated with collagen and fibronectin. After treatment with 400 μM oleate fatty acid or BSA (control) for 48 hours, cells were fixed, stained for actin and nuclei, and imaged for cell morphology data. Adipocytes seeded onto glass were subjected to cell stiffness measurements using an MFP-3D Origin AFM fitted with a tip-less cantilever under aqueous conditions. Each cell was indented at a rate of 5.95 microns/sec three to five times at its periphery. Apparent effective stiffness was calculated from force versus displacement curves. Finite element models (FEMs) were developed to recapitulate the AFM response using material properties of cellular structures from literature and Abaqus FEA software.


Results, Conclusions, and Discussions:: Adipocyte area significantly increases with increasing stiffness (p < 0.001, Figure 1), demonstrating that adipocytes are mechanosensitive. Oleate treatment has no effect on the ability of the cell to sense its underlying substrate stiffness. Furthermore, cell stiffness as measured by AFM increases significantly with large lipid droplets (oleate treatment) compared to small lipid droplets (p < 0.001, Figure 2). FEM shows that nuclear stress (Figures 3 and 4) and cell stiffness (Figure 5) decrease with increasing lipid droplet size when load is applied directly centered above the lipid droplet, but increase when the load is applied directly centered above the nucleus.

Our experimental results demonstrate adipocyte mechanosensing and that large lipid droplets increase cell stiffness. Although FEM did not entirely recapitulate the complex mechanical behavior of adipocytes, they provide a foundation to simulate and better understand the mechanical behavior of adipocytes.


Acknowledgements (Optional): :

References (Optional): :