Taming the Promoter: Regulation of Tissue Inhibitor of Matrix Metalloprotease 4 in Heart Failure

Abstract

The remarkable property of tissue inhibitor of matrix metalloprotease 4 (TIMP4) to inhibit endogenous MMP9 potentiates its use in cardiac remodeling prior to heart failure. This concept stems from our previous discovery that TIMP4 goes down in heart failure and administration of TIMP4 intraperitonialy is cardio protective. This important finding instigated us to explore the differential regulation of TIMP4 during heart failure. We hypothesize that there are epigenetic changes in the promoter of TIMP4 pertaining to DNA methylation of CpG islands, acetylation of histone proteins and binding of microRNAs (mir122a) that lead to epigenetic silencing of TIMP4 and enhanced expression of MMP9 which consequently lead to heart failure. To test the hypothesis we created heart failure by aorta‐vena cava fistula (AVF) in 1) C57BL/6 mice 2) TIMP4‐Tg mice and examined the promoter methylation (methylation specific PCR, HRM and methylation sensitive restriction enzyme), histone modification (ChIP assay) and microRNAs (mir122a that binds to TIMP4). The cardiac function was assessed by echocardiography after 6 weeks. The data suggested that the promoter region of TIMP4 was methylated in the AVF failing heart, suggesting epigenetic silencing of TIMP4. To determine the contribution of epigenetic silencing by turning off the transcription machinery, we observed methylation of histone 3 at the lysine 9. We discovered that the CpG islands get methylated during heart failure with decreased acetylation of histone 3 at lysine 9 and 27. This is a novel finding suggesting that TIMP4 is epigenetically silenced in failing hearts and can be translated to regulate its expression prior to heart failure.