(772f) Utilizing Multiple Particle Tracking Microrheology and Traction Force Microscopy to Monitor Mechanical Progression of Differentiating Mesenchymal Stem Cells

Bone marrow derived mesenchymal stem cells (MSCs) are highly regenerative multipotent stem

cells that differentiate into a variety of non-hematopoietic cells, including adipocytes, osteoblasts,

chondrocytes, muscle cells and neurons. Recent studies have shown that mechanical properties have

a significant effect on stem cell fate [1]; however, the complex interaction between mechanical and

chemical cues has not been completely elucidated. In addition, traditional methods of determining if a

cell has differentiated typically are endpoint assays performed at late time points. We hypothesized that

changes in intracellular rheology and traction forces would correlate with early lineage commitment.

In this study, human MSCs (hMSCs) were cultured in mixed differentiation media on soft (10 kPa)

or intermediate (26kPa) polyacrylamide gels. The effect of mechanical and chemical cues on hMSC

fate was characterized by histological staining and quantitative real time PCR (qRT-PCR). In addition,

multiple particle tracking microrheology (MPT) and traction force microscopy (TFM) were used to

determine the intracellular rheology and traction forces associated with lineage commitment and stem

cell differentiation. Lineage commitment and cell differentiation were characterized with traditional

methods, including qRT-PCR and histological staining, after 21 and 35 days exposure to culture

conditions. Cells on soft substrates had an increased propensity to differentiate into fat, while cells on

hard substrates were more likely to differentiate along the osteogenic lineage. Differences in rheology

and traction forces were detected by day 7 in differentiation media. In addition, a correlation between

local rheology and local traction forces was developed. Changes in lineage commitment were associated

with changes in intracellular rheology and extracellular forces, suggesting these methods may be useful

for determining if a cell has differentiated at early time points without having to lyse or fix the cell,

which would result in cell death.

References:

1. Engler, A.J., et al., Matrix Elasticity Directs Stem Cell Lineage Specification. Cell, 2006. 126(4):
p. 677-689.