Gene expression and β-adrenergic signaling are altered in hypoplastic left heart syndrome

Background The purpose of the current study was to define the myocellular changes and adaptation of the β-adrenergic receptor (β-AR) system that occur in the systemic right ventricle (RV) of children with hypoplastic left heart syndrome (HLHS). Methods Explanted hearts from children with HLHS and non-failing controls were used for this study. HLHS patients were divided into 2 groups: "compensated" (C-HLHS), infants listed for primary transplant with normal RV function and absence of heart failure symptoms, and "decompensated" (D-HLHS), patients listed for transplant after failed surgical palliation with RV failure and/or refractory protein-losing enteropathy or plastic bronchitis. Results Compared with non-failing control RVs, the HLHS RV demonstrated decreased sarcoplasmic reticulum calcium-adenosine triphosphatase 2a and α-myosin heavy chain (MHC) gene expression, decreased total β-AR due to down-regulation of β 1 -AR, preserved cyclic adenosine monophosphate levels, and increased calcium/calmodulin-dependent protein kinase II (CaMKII) activity. There was increased atrial natriuretic peptide expression only in the C-HLHS group. Unique to those in the D-HLHS group was increased β-MHC and decreased α-MHC protein expression (MHC isoform switching), increased adenylyl cyclase 5 expression, and increased phosphorylation of the CaMK target site on phospholamban, threonine 17. Conclusions The HLHS RV has an abnormal myocardial gene expression pattern, downregulation of β 1 -AR, preserved cyclic adenosine monophosphate levels, and increased CaMKII activity compared with the non-failing control RV. There is MHC isoform switching, increased adenylyl cyclase 5, and increased phosphorylation of phospholamban threonine 17 only in the D-HLHS group. Although abnormal gene expression and changes in the β-AR system precede clinically evident ventricular failure in HLHS, additional unique adaptations occur in those with HLHS and failed surgical palliation.