TAZ Activation Drives Fibroproliferation in Spheroid Culture

The transcriptional co‐activator TAZ plays a critical role in lung alveolarization (Mitani et al. Am J Respir Crit Care Med. 2009). We recently observed enhanced TAZ expression in the nuclei of fibroblasts present in lung tissue from patients with idiopathic pulmonary fibrosis, suggesting that TAZ is reactivated during fibrosis. To test the role of TAZ in driving a fibroproliferative response, we developed scaffold‐free cultures in which fibroblasts were grown in 3D hanging drop spheroids. This spheroid model removes the influence of the artificial 2D cell culture environment on cell growth. NIH3T3 fibroblasts were stably transduced with doxycycline (dox)‐inducible constructs expressing nuclear‐localizing mutant TAZ4SA or empty vector (courtesy of X. Varelas, Boston University). Spheroids were initiated by seeding 500 cells in hanging drops, and were subsequently fed growth media supplemented with 0, 1, 10, or 100 ng/mL dox every other day up to 15 days. Spheroid growth was tracked by measuring 2D projected area under light microscopy. Control NIH3T3 fibroblast spheroids remained stable in culture, but neither increased nor decreased in size significantly. In contrast, TAZ4SA‐transduced spheroids grew over time, and by day 15 spheroids treated with 100 ng/ml dox had a 2D projected area ~2.2‐fold larger than those grown in the absence of dox (p=0.0054). Intermediate growth levels were observed in 1 and 10 ng/ml doxycycline treated spheroids. Our results demonstrate the utility of the spheroid culture model for studying fibroproliferation, and document a prominent role for TAZ in promoting fibroblast spheroid growth. *Supported by NIH grants RO1 HL092961 and NIH R21 HL113796.