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Background: O-linked N-acyl-glycosylation may regulate protein function by competing with phosphorylation of serine residues. Availability of substrate for this process is regulated, in part, by N-Acyl-D-glucosamine 2-epimerase (NAGE), which interconverts N-acetyl-glucosamine (GlcNAc) and N-acetylmannosamine (ManNAc). NAGE is also a putative renin-binding protein. This study tested the hypothesis that NAGE is present in the human heart and that NAGE expression is increased in the failing human heart. Methods and Results: Ribonuclease protection assays (RPAs) demonstrated increased NAGE gene expression in failing hearts from subjects with idiopathic dilated and ischemic cardiomyopathies compared with nonfailing hearts. In situ reverse transcriptase–polymerase chain reaction, using primers designed to localize NAGE mRNA, demonstrated that, in nonfailing hearts, NAGE gene expression was restricted to endothelial cells and not detectable in cardiac myocytes. However, in failing human hearts NAGE gene expression was selectively activated in cardiac myocytes, but not endothelial cells. Immunohistochemistry confirmed that the pattern of NAGE protein expression corresponded to the pattern of gene expression. Conclusions: NAGE gene and protein expression were selectively activated in left ventricular myocytes from end-stage failing human hearts.

Background —The regulation and interaction of ACE and the angiotensin II (Ang II) type I (AT 1 ) receptor in the failing human heart are not understood. Methods and Results —Radioligand binding with 3 H-ramiprilat was used to measure ACE protein in membrane preparations of hearts obtained from 36 subjects with idiopathic dilated cardiomyopathy (IDC), 8 subjects with primary pulmonary hypertension (PPH), and 32 organ donors with normal cardiac function (NF hearts). 125 I-Ang II formation was measured in a subset of hearts. Saralasin ( 125 I-{Sar 1 ,Ile 8 }-Ang II) was used to measure total Ang II receptor density. AT 1 and AT 2 receptor binding were determined with the AT 1 receptor antagonist losartan. Maximal ACE binding ( B max ) was 578±47 fmol/mg in IDC left ventricle (LV), 713±97 fmol/mg in PPH LV, and 325±27 fmol/mg in NF LV ( P B max was 737±78, 638±137, and 422±49 fmol/mg, respectively ( P =0.02, IDC versus NF; P =0.08, PPH versus NF). 125 I-Ang II formation correlated with ACE binding sites ( r =0.60, P =0.00005). There was selective downregulation of the AT 1 receptor subtype in failing PPH ventricles: 6.41±1.23 fmol/mg in PPH LV, 2.37±0.50 fmol/mg in PPH RV, 5.38±0.53 fmol/mg in NF LV, and 7.30±1.10 fmol/mg in NF RV ( P =0.01, PPH RV versus PPH LV; P =0.0006, PPH RV versus NF RV). Conclusions —ACE binding sites are increased in both failing IDC and nonfailing PPH ventricles. In PPH hearts, the AT 1 receptor is downregulated only in the failing RV.