Our overall objective is to elucidate how extracellular matrix (ECM) stimulates hormone production. Several estrogen-dependent pathological conditions including breast cancer, uterine fibroids, and endometriosis are associated with local overexpression of aromatase, a key enzyme in estrogen biosynthesis and important therapeutic target for postmenopausal ER+ breast cancer. In addition, excessive aromatase expression in adipose tissue at least partially accounts for obesity-associated breast cancer risk among postmenopausal women. While altered matrix homeostasis is associated with these aromatase- overexpressing tissues, little is known as to whether it can directly impact local steroidogenic gene expression and estrogen biosynthesis. A paucity of knowledge in this area is partly due to the lack of proper model systems that can recapitulate the mechanical properties of a cell's microenvironment. We hypothesize that ECM is a previously unappreciated critical determinant for local aromatase overexpression and estrogen production. In support of this hypothesis, our preliminary data indicate that matrix alone can significantly stimulate aromatase transcription in breast stromal cells (BSCs) via distinct signaling pathways. We have a repertoire of molecular and biophysical tools, in vitro and in vivo model systems, and cross-disciplinary expertise to further test the hypothesis. Specifically, we will first determine how ligand-receptor interactions rigidity, and three-dimensionality of a matrix affect aromatase expression; and how the matrix signals are sensed by cellular mechanosensory apparatus (Aim 1). We will then determine how the intracellular signaling cascades relay the matrix signals to the transcription machinery at the aromatase gene (Aim 2). Lastly, we will use in vitro co-culture systems, humanized animal models, and clinical samples to examine the functional consequences of matrix-induced stromal aromatase expression (Aim 3). The link between matrix homeostasis and hormone metabolism is a vastly under-explored topic. When successfully executed, the proposed work promises to fill a major gap of knowledge in this field. Findings from the study may also provide novel prognostic tools and markers, as well as new therapeutic targets for reducing local estrogen production, thus overcoming the side effects often associated with systemic inhibition of aromatase. In a broader sense, the conceptual and technical advances achieved in the current proposal may offer guidance to research on endocrine/paracrine dysfunction in a variety of tissues and organs.