Mouse Keratinocytes Without Keratin Intermediate Filaments Demonstrate Substrate Stiffness Dependent Behaviors
Traditionally thought to serve active vs. passive mechanical functions, respectively, a growing body of evidence suggests that actin microfilament and keratin intermediate filament (IF) networks, together with their associated cell–cell and cell–matrix anchoring junctions, may have a large degree of functional interdependence. Therefore, we hypothesized that the loss of keratin IFs in a knockout mouse keratinocyte model would affect the kinematics of colony formation, i.e., the spatiotemporal process by which individual cells join to form colonies and eventually a nascent epithelial sheet.
Time-lapse imaging and deformation tracking microscopy was used to observe colony formation for both wild type (WT) and keratin-deficient knockout (KO) mouse keratinocytes over 24 h. Cells were cultured under high calcium conditions on collagen-coated substrates with nominal stiffnesses of ~ 1.2 kPa (soft) and 24 kPa (stiff). Immunofluorescent staining of actin and selected adhesion proteins was also performed.
The absence of keratin IFs markedly affected cell morphology, spread area, and cytoskeleton and adhesion protein organization on both soft and stiff substrates. Strikingly, an absence of keratin IFs also significantly reduced the ability of mouse keratinocytes to mechanically deform the soft substrate. Furthermore, KO cells formed colonies more efficiently on stiff vs. soft substrates, a behavior opposite to that observed for WT keratinocytes.
Collectively, these data are strongly supportive of the idea that an interdependence between actin microfilaments and keratin IFs does exist, while further suggesting that keratin IFs may represent an important and under-recognized component of keratinocyte mechanosensation and the force generation apparatus.
KeywordsMechanosensing Keratins Polyacrylamide gels Traction microscopy Intermediate filaments Force
Support of this work was provided by the National Science Foundation (National Science Foundation CAREER CMMI 1452728) and the Carver Charitable Trust #14-4384 and #18-5045. In addition, J.C.S. acknowledges the Dermatology Foundation for their support of this work through a career development award. Work in the Magin lab is supported by the DFG (German Research Council; MA1316-15, MA1316-17, MA1316-19, MA1316-21, INST 268/230-1).
Conflict of interest
Hoda Zarkoob, Sathivel Chinnathambi, Spencer A. Halberg, John C. Selby, Thomas M. Magin, and Edward A. Sander declare that they have no conflict of interest.
No human or animal studies or were carried out by the authors for this article.
- 8.Eckes, B., et al. Impaired mechanical stability, migration and contractile capacity in vimentin-deficient fibroblasts. J. Cell Sci. 111(13):1897–1907, 1998.Google Scholar
- 37.Selby, J.C., Mechanobiology of epidermal keratinocytes: desmosomes, hemidesmosomes, keratin intermediate filaments, and blistering skin diseases. In: Mechanobiology of Cell-Cell and Cell-Matrix Interactions. New York: Springer, pp. 169–210, 2011.Google Scholar
- 41.Tsuruta, D., et al. Hemidesmosomes and focal contact proteins: Functions and cross-talk in keratinocytes, bullous diseases and wound healing. J. Dermatol. Sci. 62(1):1–7, 2011.Google Scholar