Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Physiology and Pharmacology

Supervisor

Andrew Leask

Abstract

Fibrosis, a phenotype associated with mortality for a multitude of diseases, has no disease-modifying treatment. We examine if Verteporfin (VP), an inhibitor of the YAP-TEAD complex, currently in wide clinical use for macular degeneration, can inhibit pro-fibrotic gene expression in human dermal fibroblasts. Also, an in vivo approach was taken using a Pten-deficient mouse of progressive skin fibrosis for examining effects on melanoma metastasis. We found that treatment with VP reduced basal expression of a variety of profibrotic genes and prevented a myofibroblast-like phenotype in response to TGFβ1. Indeed, genome-wide expression analysis suggested that VP inhibited a cluster of profibrotic genes with and without added TGFβ1. Preliminary analysis of metastasis to the lung of melanoma tumors in Pten-deficient mice showed a trend towards increased metastasis the absence of Pten expression by fibroblasts; i.e., in a fibrotic microenvironment. My findings support targeting YAP as a potential treatment for fibrotic diseases.

Summary for Lay Audience

Pathological fibrosis is the progressive stiffening of skin or other organs, ultimately interfering with organ function and resulting in death. Pathological fibrosis is involved with 45% of mortalities in the developed world and has no available treatment. Progressive stiffening of the tissue is characterized by the progressive differentiation of local cells known as fibroblasts into stiff cells known as myofibroblasts. These cells exert mechanical tension onto themselves and the scaffolding around cells known as the extracellular matrix. This effect is involved in normal processes such as wound repair, however in fibrotic disease, it becomes dysregulated. The progressive increase of tension in the tissue also changes gene expression of proteins in the cell. The most well-known protein that is produced in cases of fibrotic disease is CCN2. This protein is known to bind to the cell surface and is thought to prevent the resolution of cellular stiffness. In fact, CCN2 also functions to transition more cells into myofibroblasts and increase tissue stiffness, creating a positive-feedback loop. Increased stiffness seen in fibrotic disease highly reflects the tumor microenvironment, the scaffolding around cancerous cells, and is thought to aid the migration of tumor cells to other locations in the body. Recent research has pointed towards YAP as a central mediator of fibrotic gene expression, including CCN2. Here, we repurposed Verteporfin, a drug currently on the market for macular degeneration, as an inhibitor of YAP. Administering Verteporfin to fibroblasts prevented differentiation into myofibroblasts normally induced by TGFβ1. A mass analysis of gene expression revealed that inhibiting YAP with Verteporfin reduced expression of many known fibrosis-related genes, including CCN2. These findings support YAP as a central mediator of fibrosis, and repurposing Verteporfin to inhibit YAP could be a viable therapeutic strategy with relatively little financial investment. To test the ability of a fibrotic microenvironment to enhance cancer metastasis, we used a mouse model with silenced Pten, a cellular signaling protein upstream from Yap in the cellular signaling pathway, to induce spontaneous fibrosis. However, the induced fibrotic phenotype was not as stiff as expected, and the results were inconclusive.

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