Cathepsin B Induced Cardiomyocyte Hypertrophy Requires Activation of The Na+/H+ Exchanger Isoform-1

Abstract

Multiple studies have demonstrated that proteases, specifically cathepsin B (Cat B) and matrix metalloproteinase-9 (MMP-9) contribute to the remodeling of the extracellular matrix (ECM), a hallmark of cardiac hypertrophy (CH). Cat B is activated under acidic conditions, a key stimuli of the Na+/H+ exchanger isoform-1 (NHE1). Enhanced NHE1 expression/activity have also been demonstrated to contribute to the progression of CH. Whether NHE1 contributes to the Cat B hypertrophic response remains unclear. NHE1 activity was stimulated in H9c2 cardiomyoblasts using 10 μM Angiotensin (Ang) II ±10 μM EMD, a NHE1 inhibitor or 10 μM CA-074Me, a Cat B inhibitor and characterized for changes in the cell surface area, protein content and atrial natriuretic peptide (ANP) mRNA, indices of cardiomyocyte hypertrophy. The localization of Cat B in lysosomes was measured using LysoTracker Red dye. The release of Cat B from the intracellular to the extracellular space was assessed by measuring Cat B protein expression in the media. MMP-9 was also measured in the extracellular space and assessed for its contribution to the CAT B hypertrophic response. NHE1 increased the Cat B protein (136.56 ± 9.4% Ang II vs. 100% control, 37 kDa and 169.84 ± 14.24% Ang II vs. 100% control, 25 kDa; P<0.05) and gene expression (288.11 ± 76.72% Ang II vs. 100% control; P<0.05) and induced cardiomyocyte hypertrophy. Furthermore, Cat B protein expression and MMP-9 activity were increased in the extracellular space. These effects was regressed upon inhibition of NHE1 or Cat B. Our study demonstrates for the first time that Cat B is involved in the NHE1 mediated cardiomyocyte hypertrophic response in cooperation with the activation of MMP-9.