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Intracellular actin as a marker for myofibroblasts in vitro
I T Foo1, I L Naylor, M J Timmons
1Plastic Surgery and Burns Research Unit, Postgraduate School of Pharmacology, University of Bradford, United Kingdom.
Background:
Myofibroblasts are found in a wide variety of normal tissues and pathological conditions. It is suggested that myofibroblasts are derived from normal fibroblasts and share with smooth muscle cells the expression of actin microfilament bundles. The aim of this study was to establish if the myofibroblast phenotype from tissue expander capsules and Dupuytren's nodules could be distinguished from normal dermal fibroblasts by quantitation of intracellular actin and the ratio of polymerized (filamentous) actin to nonpolymerized (globular) actin.
Experimental Design:
Cell lines were established from six patients from each group. In addition to quantitation of intracellular actin, the cells were characterized by criteria of light microscopy, ultrastructure, actin immunofluorescence, and growth rates.
Results:
Dermal fibroblasts were the smallest and the most spindle-shaped but grew rapidly and had few actin microfilament bundles. By contrast, myofibroblasts from expander capsules were larger and more stellate, proliferated slowly, and had the most prominent microfilament arrays. Cells from Dupuytren's nodules were intermediate in phenotype. Substantial and significant differences in intracellular actin contents were found, ranging from 0.69 +/- 0.05 micrograms/10(4) cells in fibroblasts and 0.77 +/- 0.15 micrograms/10(4) cells for Dupuytren's nodule cells to 1.46 +/- 0.44 micrograms/10(4) cells in expander capsule myofibroblasts (p < 0.05). Similar findings were found with respect to ratios of fibroblast to globular actins, being 0.22 for fibroblasts and 0.38 for Dupuytren's nodule cells compared with 0.70 for expander capsule myofibroblasts (p < 0.01).
Conclusions:
Measurement of intracellular actin contents and fibroblast:globular actin ratios offers a rapid, sensitive, and reliable technique for establishment of the myofibroblast phenotype and has considerable advantages over traditional ultrastructural approaches for the study of myofibroblast differentiation/regression and in vitro responses to experimental manipulation.