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A2223 - A Role for Myocardin Related Transcription Factor A in Multi-Organ Fibrosis
Author Block: A. Rackow1, T. H. Thatcher2, C. F. Woeller3, E. M. Small3, R. P. Phipps4, P. J. Sime5; 1Environmental Medicine, University of Rochester Medical Center, Rochester, NY, United States, 2University of Rochester, Rochester, NY, United States, 3University of Rochester Medical Center, Rochester, NY, United States, 4Univ of Rochester, Rochester, NY, United States, 5Univ of Rochester Med Ctr, Rochester, NY, United States.
Rationale: Idiopathic pulmonary fibrosis (IPF) is a chronic interstitial lung disease characterized by excess deposition of extracellular matrix proteins. Our lab has previously demonstrated that one mechanism involved in the development and progression of fibrosis is the dysregulation of cellular metabolism. Lung tissue of patients with IPF has both increased expression of the glycolytic enzyme lactate dehydrogenase A (LDHA) and the byproduct lactate, which contributes to the activation of transforming growth factor beta (TGFβ) in a pro-fibrotic feed-forward loop. We have recently identified that Myocardin related transcription factor A (MRTF-A), originally identified as a pro-fibrotic transcription factor in cardiac fibrosis, also regulates cellular metabolism. We hypothesize that MRTF-A represents a novel pro-fibrotic pathway in the heart and lung by upregulating LDHA expression and activity in fibroblasts, leading to production of excess lactic acid which activates the key pro-fibrotic cytokine TGFβ to induce myofibroblast differentiation. Methods: To demonstrate MRTF-A regulates LDHA, NIH-3T3 cells were transfected with an LDHA luciferase reporter. MRTF-A was then overexpressed and luciferase activity was recorded. To explore the specific role of MRTF-A in metabolic activation, primary human lung and cardiac fibroblasts were treated with the LDH inhibitor gossypol following MRTF-A overexpression. Cells were harvested for gene and protein expression. Results: Using the LDHA luciferase reporter coupled with overexpression of MRTF-A, we identified a previously uncharacterized binding domain for MRTF-A in the promoter of LDHA. The LDHA promoter contains a binding site for MRTF-A, allowing for direct activation of LDHA and further contributing to metabolic dysregulation observed in IPF. Overexpression of MRTF-A induces protein expression of LDHA and drives myofibroblast differentiation as evidenced by an increase in alpha smooth muscle actin (αSMA) expression. Gossypol inhibited the MRTF-induced expression of LDHA and prevented myofibroblast differentiation in primary human lung fibroblasts. In cardiac fibroblasts, treatment with lactate induced expression of myofibroblast markers, promoting pro-fibrotic gene expression. Conclusions: MRTF-A drives the expression of LDHA in human lung fibroblasts. We present a novel mechanism whereby MRTF-A drives expression of LDHA, and directly contributes to the pathogenesis of fibrosis in the heart and lung. Furthermore, we demonstrate gossypol inhibits both LDHA expression and myofibroblast differentiation given MRTF-A overexpression. This evidence suggests a common mechanism of fibrosis in both the heart and lung, providing valuable insight into common pathways of fibrotic disease. The MRTF family represents a novel therapeutic target that can be applied across organ systems to develop novel treatments for multi-organ fibrosis.