Aortic carboxypeptidase-like protein signaling on stiff collagen matrices and conditional deletion in mice
Phalen, Joseph Michael
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Idiopathic pulmonary fibrosis (IPF) is a disease in which the accumulation of excess extracellular matrix proteins including collagen causes thickening and scarring of the lung tissue leading to a decline in lung function. There are currently no effective treatments for this disease. In addition to collagen, IPF lungs contain α-smooth muscle actin (SMA) expressing myofibroblasts, which leads to increased tissue stiffness. Work in this laboratory lead to the discovery of aortic carboxypeptidase-like protein (ACLP), which is upregulated in the lungs of IPF patients. Previous work in this laboratory also demonstrated that ACLP induces SMA expression and collagen deposition. Additionally, ACLP knockout mice were protected against bleomycin-induced fibrosis. Matrix stiffening was also shown to increase the effect of ACLP and create a fibrotic feed forward mechanism through mechanical signaling. These findings led to the hypothesis that the presence of ACLP and collagen on a stiff matrix would increase expression of myofibroblast markers. The goal of this research was to further understand the relationship between ACLP, collagen, and mechanical signaling. An additional goal of this work was to generate a novel mouse system in which ACLP can be conditionally deleted through cre-mediated recombination. Using primary lung fibroblasts plated on a collagen and ACLP coated matrices, ACLP increased the expression of myofibroblast markers and potentiated the effects of exogenous transforming growth factor β (TGFβ). Experiments using this central collagen binding discoidin domain of ACLP did not detect changes in TGFβ signaling. To develop a conditional ACLP deletion mouse model, optimized genotyping procedures we developed to detect recombination in response to cre-mediated recombination. Taken together these studies identified a relationship between ACLP and mechanical signaling, which can be targeted for treatment of IPF. In addition, the new mouse model will enable future studies to better define the function of ACLP in fibrotic disease.