SRC-mediated and TKS5-enabled podosome formation is an inherent property of IPF fibroblasts, promoting ECM invasion and pulmonary fibrosis

The activation and accumulation of lung fibroblasts (LFs), resulting in aberrant deposition of collagens and other extracellular matrix (ECM) components, is a pathogenic hallmark of Idiopathic Pulmonary Fibrosis (IPF), a lethal and incurable disease. In this report, increased expression of TKS5, a scaffold protein essential for the formation of podosomes, was detected in the lung tissue of IPF patients and bleomycin (BLM)-treated mice, correlating with increased collagen type I alpha 1 chain (COL1A1) expression. The profibrotic milieu, TGF{beta}, as well as a stiff Col1a1-rich acellular fibrotic ECM, were found to induce TKS5 expression and the formation of prominent podosome rosettes in LFs, culminating in increased ECM invasion. Podosomes were retained ex vivo in the absence of any stimulation, indicating that the formation of TKS5-enabled podosomes is an inherent property of IPF LFs. Remarkably, haploinsufficient Tks5+/- mice were relatively resistant to BLM-induced pulmonary fibrosis. Disease protection was largely attributable to diminished podosome formation in LFs and decreased ECM invasion, thus indicating TKS5-enabled and podosome-mediated ECM invasion as a major pathogenic mechanism in pulmonary fibrosis. Expression profiling revealed an ECM-podosome cross talk, and pharmacologic connectivity map analysis suggested several inhibitors that could prevent podosome formation and thus pulmonary fibrosis. Among them, inhibition of src kinase was shown to potently attenuate podosome formation in LFs, ECM invasion, as well as pulmonary fibrosis in post BLM precision cut lung slices, suggesting that pharmacological targeting of TKS5-enabled podosome formation is a very promising therapeutic option in pulmonary fibrosis.