Bulk ECM stiffness measurements are often used in research on cell mechanobiology. However, past studies by our group have shown that peri-cellular stiffness can span few orders of magnitude and diverges from the bulk properties. Us- ing optical tweezers active microrheology (AMR) we can de- scribe stiffness landscape around individual cells. In this study, we show how different cell lines cultured in 1.0 and 1.5 mg/ml type 1 collagen (T1C) create disparate patterns of peri-cellular stiffness. Dermal fibroblasts (DFs) increase peri-cellular stiffness, when embedded in 1.0 mg/ml T1C hy- drogels, but do not alter stiffness in 1.5 mg/ml T1C hydro- gels. In contrast, invasive human breast cancer MDA-MB- 231 cells (MDAs) do not significantly change the stiffness of T1C hydrogels, as compared to cell-free controls. Results indicate that while MDAs adapt to the bulk ECM stiffness, DFs regulate local stiffness to levels they intrinsically “fa- vor”. Further, cells were also subjected to treatments that were previously shown to regulate their migration, prolifera- tion and contractility. Following each treatment, cells estab- lished dissimilar stiffness patterns. Stiffness magnitude and extent of anisotropy varied with the cell line, T1C concen- tration and treatment. In summary, we demonstrate that AMR can reveal otherwise masked mechanical properties of the local ECM, which are known to affect cell behavior.
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Cells utilize strain hardening and crosslinking to establish their extracellular niche in fibrous tissue
Bulk measurements of ECM stiffness are commonly used in mechanobiology. However, peri-cellular stiffness can be quite heterogenous and divergent from the bulk properties. Here, we use optical tweezers active microrheology (AMR) to quantify how two different cell lines embedded in 1.0 and 1.5 mg/ml type 1 collagen (T1C) establish dissimilar patterns of peri-cellular stiffness. We found that dermal fibroblasts (DFs) increase local stiffness of 1.0 mg/ml T1C hydrogels, but surprisingly do not alter stiffness of 1.5 mg/ml T1C hydrogels. In contrast, MDA-MB-231 cells (MDAs) predominantly do not stiffen T1C hydrogels, as compared to cell-free controls. Results suggest that MDAs adapt to the bulk ECM stiffness, while DFs regulate local stiffness to levels they intrinsically “prefer”. Further, cells were subjected to treatments, that were previously shown to alter migration, proliferation and contractility of DFs and MDAs. Following treatment, both cell lines established different levels of stiffness magnitude and anisotropy, which were dependent on the cell line, T1C concentration and treatment. In summary, our findings demonstrate that AMR reveals otherwise masked mechanical properties such as spatial gradients and anisotropy, which are known to affect cell behavior at the macro-scale.
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- Award ID(s):
- 1953410
- NSF-PAR ID:
- 10321484
- Date Published:
- Journal Name:
- APS March Meeting 2021
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Cells are known to continuously remodel their local extracellular matrix (ECM) and in a reciprocal way, they can also respond to mechanical and biochemical properties of their fibrous environment. In this study, we measured how stiffness around dermal fibroblasts (DFs) and human fibrosarcoma HT1080 cells differs with concentration of rat tail type 1 collagen (T1C) and type of ECM. Peri-cellular stiffness was probed in four directions using multi-axes optical tweezers active microrheology (AMR). First, we found that neither cell type significantly altered local stiffness landscape at different concentrations of T1C. Next, rat tail T1C, bovine skin T1C and fibrin cell-free hydrogels were polymerized at concentrations formulated to match median stiffness value. Each of these hydrogels exhibited distinct fiber architecture. Stiffness landscape and fibronectin secretion, but not nuclear/cytoplasmic YAP ratio differed with ECM type. Further, cell response to Y27632 or BB94 treatments, inhibiting cell contractility and activity of matrix metalloproteinases, respectively, was also dependent on ECM type. Given differential effect of tested ECMs on peri-cellular stiffness landscape, treatment effect and cell properties, this study underscores the need for peri-cellular and not bulk stiffness measurements in studies on cellular mechanotransduction.more » « less
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