Abstract 1593: Aging Affects Matrix Metalloproteinase Promoter Activity in Myocardial Fibroblasts
A structural milestone of the aging myocardium is abnormal extracellular matrix (ECM) accumulation, accompanied by abnormal (matrix metalloproteinase (MMP) expression, such as MMP-2 and MMP-9. Since LV myocardial fibroblasts (LVMFs) are primarily responsible for ECM homeostasis, unique MMP reporter constructs were used to examine whether abnormalities in MMP-2 or MMP-9 promoter activation occurred in aging LVMFs. MMP-2 or MMP-9 promoter sequences fused to the β-galactosidase (β-gal) reporter were inserted into the mouse genome (CD1 background). LVMFs were established from young (3 mos) and old (12–14 mos) MMP-2 or MMP-9 promoter mice (n=7; all groups). LVMFs (106 cells/well; in triplicate) were studied under steady-state conditions (serum free; 24 hrs), and following stimulation with either tumor necrosis factor (TNF;100 ng/mL), endothelin (ET-1;1 nM), or angiotensin II (ANG II; 1 nM). MMP promoter activity was computed as the change in β-gal mRNA expression by RT-PCR (FIGURE⇓). MMP-2 promoter activity was increased in young and old LVMFs with TNF stimulation, however MMP-9 promoter activity was blunted in old LVMFs. ET-1 and ANG II significantly increased MMP-2 and MMP-9 promoter activity in young, but not in old LVMFs. Transcription factor levels, such as c-Jun, were equivalent in young and old LVMFs, suggesting normal transcription factor synthesis. Selective reductions in MMP-2 and MMP-9 promoter activity, likely due to the emergence of specific repressors, were identified as a function of age. Thus, aging is likely associated with abnormalities in MMP transcriptional activity, which in turn, would promulgate fibrosis.