Anne-Marie Koop

2 37 Association of regulatory mechanisms of cardiomyocyte relaxation, fibrosis, hypertrophy and capillary growth to RVF with clinical symptoms In PAB+CF, mRNA expression of the compliant isoform of titin, N2Ba, was significantly increased ( table 1 ), indicating an adaptive response to counter passive ventricular stiffness. However, activities of protein kinase A and G, phosphorylation status of phospholamban and expression of SERCA ATPase, which regulate active cardiomyocyte relaxationwere not significantly changed ( table 1 ). Diastolic dysfunction has also been associated with increased stiffness due to interstitial fibrosis and/or hypertrophy. However, fibrosis was lower in PAB+CF than in PAB- ( figure 4a,e ). Figure 4. Histology and gene expression. RV fibrosis (A, E: two top rows are representative images of Masson-Trichrome stained RVs, ruler is 500μm, black box with 1mm). RV hypertrophy (RV free wall weight normalized for tibia length, B) and RV cardiomyocyte cross-sectional area (C, E third row are representative images of RV sections stained with a membrane marker (wheat germ agglutinin, green), ruler is 75μm. RV capillary density, expressed as capillary-to-cardiomyocyte ratio (D, E bottom row are representative images of RV sections stained with capillary-marker lectin, ruler is 130μm). mRNA expression of genes related to hypertrophy, fetal gene program, oxidative stress and fibrogenesis (CON =1, relative to 36B4 reference gene expression). Mean±SEM. Arrows indicate p<0.05 between respective groups. CCSA= cardiomyocyte cross- sectional area, cap= capillary, MYH7/6= β /α -myosin heavy chain, RCAN1= regulator of calcineurin 1, NPPA/ B= natriuretic pro-peptides type A/B, ACTC= α -cardiac actin, ACTA= α -skeletal actin, HO-1= hemoxygenase-1, TGF β -1= transforming growth factor- β -1, OPN-1= osteopontin-1, COL1A2/3A1= collagen subunits 1A2 and 3A1. This was not accompanied by blunted signaling in the pro-fibrotic pathways or attenuated expression of collagen-isoforms ( figure 4f ). Fibrosis has been suggested to result from deficient hemoxigenase-1 (HO-1) activation; one of the protective