Abstract 17311: Molecular Memory and the Epigenetic Regulation of Cardiac Intracellular Matrix Metalloproteinase-2
Introduction: We have identified an intracellular isoform of MMP-2 generated by oxidative stress activation of a promoter in the first intron of the MMP-2 gene. This generates a N-terminal truncated isoform of MMP-2 (NTT-MMP-2) which is enzymatically active and found in mitochondria. NTT-MMP-2 triggers the mitochondrial permeability transition leading to myocyte regulated necrosis and inflammation. We hypothesized that transient oxidative stress induces durable epigenetic changes in the NTT-MMP-2 alternate promoter resulting in enhanced injury in subsequent episodes of stress (molecular memory).
Methods: The intronic promoter was mapped using a combination of PCR-based and intronic/luciferase constructs. In vivo studies used the hypomorphic ApoER61h/h SR-B1-/- murine model (HypoE mice) of diet-induced coronary atherogenesis and myocardial infarction. Chromatin immunopreciptation (ChIP) probed the RNA Pol II, H3K4Me1 and H3K27Me3 epigenetic marks. NTT-MMP-2 was measured by qPCR.
Results: NTT-MMP-2 transcription start sites were mapped to two stress-activated basal promoters along with a stress-activated NF-κB enhancer element. HypoE mice were fed a high fat diet (HFD) for 20 days, followed by gene repair of the hypomorphic ApoE alleles and returned to normal diet for 6-15 weeks. NTT-MMP-2 expression at 20 days of HFD was elevated two-three fold as compared to controls, remained elevated after 6 weeks of normal diet and returned to baseline at 15 weeks. ChIP of the intronic promoter revealed association of RNA Pol II at 6 weeks of normal diet and was not detectable at 15 weeks. In contrast, the pro-transcriptional mark H3K4Me1 remained elevated out to 15 weeks; the inhibitory H3K27Me3 mark returned to baseline at 15 weeks. A brief return to HFD (7 days) at 6 weeks increased NTT-MMP-2 expression resulting in myocyte inflammation and necrosis relative to controls exposed to only 7 days of HFD.
Conclusions: Transient periods of oxidative stress lead to durable epigenetic changes in the NTT-MMP-2 promoter that facilitate exaggerated responses to otherwise minor levels of oxidative stress. Our findings may provide an explanation for the enhanced injury susceptibility to relatively minor stresses of patients with pre-existing cardiac disease.
- N-terminal truncated matrix metalloproteinase-2
- oxidative stress
- myocyte necrosis
Author Disclosures: D.H. Lovett: None. S. Luk: None. L. Uttarwar: None. S. Joshi: None. R.L. RAffai: None.
- © 2015 by American Heart Association, Inc.