ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

5. DISCUSSION
The results of our study provide preliminary evidence that it is feasible to quantitatively
map stiffness distribution within differentiating adipocytes, by the non-contact WFDI
technique, where no exogenous labeling or special sample preparations are involved.
Lipid areas in the adipocyte were found to be ~10 times stiffer than the surrounding
cytoplasm. Nevertheless, expanding the number of examined adipocytes as well as
measuring the exact characteristic refractive indexes of the adipocyte cytoplasm and its
lipid droplets are needed in order to improve the accuracy of the results.
Our findings are in agreement with results obtained previously for red blood cells, using
the same WFDI method (Shaked et el., 2011). Stiffness of adipocytes was measured in
only one reported study by means of AFM (Darling et al., 2008), but the measurements
were made before the adipocytes were allowed to adhere to their substrate, which makes
the results non-comparable. Nevertheless, the data provided in our study, can be used in
numerical models for the purpose of determining how effective stiffness of adipoctye is
influenced by the differentiation process (and the accumulation of the additional lipid
droplets). Given that the effective stiffness of adipocytes (and fat tissues) directly
influence on the applied deformation when adipose tissues are weight bearing, such
studies might clarify whether there exists a positive or negative feedback in the
structure-function-adaption loop for fat, that is, whether formation or growth of
intracytoplasmic lipid droplets leads to softening or stiffening of the cells and tissues. If
this process ultimately results in continuum-scale stiffening, the extent of tissue
deformations, in particular their tensional components would eventually plateau, hence
the mechanical driving force for the differentiation would also stabilize, which would
lead to a physiological equilibrium in the tissue. If on the other hand adipocytes (and
adipose tissues) soften as they mature – that would increase deformability at the tissue
scale, would deliver more stretching to pre-adipocytes and promote further
differentiation, in a positive feedback loop which could contribute to obesity or weight
gaining, and eventually to hyperlipidemia as well. These exciting ideas might open
completely new research paths for studying obesity, diabetes and related diseases from a
biomechanical point-of-view, involving the mechanotransduction and structurefunction-adaptation
concepts that are well known to exist for other tissues but were so
far very poorly studied in fat.
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