Abstract 18353: FOXO3a and Cardiac Remodeling - Modulation of MMP13 Expression

Objective: Structural alterations of cardiac extracellular matrix occur as a result of pathological processes in the heart, e.g. dilated cardiomyopathy or myocardial infarction. Matrix metalloproteinases (MMPs) are proteolytic enzymes which play a pivotal role in stress induced matrix remodeling. FOXO transcription factors are important stress-activated regulators of cell cycle and size. Therefore, we hypothesized that FOXO3a, a member of the FOXO family known to be expressed in myocardium, modulates the expression of MMPs. Methods: Cardiac myocytes and fibroblasts were transduced with adenoviral vectors encoding either wild-type FOXO3a (WT-FOXO3a), constitutive-active FOXO3a (TM-FOXO3a) or GFP as control. Effects on potential target genes were assessed by QRT-PCR, Western blot/IHC, specific Collagenase assay, CHIP or luciferase promoter assay. Effects of viral myocarditis were studied in WT and FOXO3a-/- mice. Results: Cardiac myocytes and fibroblasts transduced with FOXO3a did not show differences in MMP1, -2, -3, -9 as well as TIMP 1,-2,-4 gene or protein expression when compared with control vector. However, WT-FOXO3a or TM-FOXO3a gene transfer dose-dependently upregulated MMP13 mRNA expression (3.5 ± 1.2 and 22.0 ± 11.0 fold; p < 0.001, WT and TM-FOXO3a vs. GFP, respectively). Furthermore, MMP13 protein levels were also significantly upregulated under these conditions (p < 0.01). Moreover, FOXO3a transduction led to significantly increased Collagenase activity (p < 0.01). Accordingly, FOXO3a-/- mice showed diminished MMP13 mRNA and protein expression. CHIP and luciferase promoter assays revealed binding of FOXO3a to the MMP13 promoter and its transcriptional activation. Finally, viral myocarditis led to FOXO3a activation associated with increased MMP13 mRNA expression that was significantly diminished in FOXO3a-/- mice which demonstrated increased Collagen 1 and 3 protein expression in IHC (p < 0.05). Conclusion: In conclusion our results implicate FOXO3a directly in the regulation of MMP13 expression. FOXO3a might play an important role in controlling extracellular matrix remodeling processes under cardiovascular stress and injury such as inflammation. Thus, targeting FOXO3a might have therapeutic potential.