Differential regulation of mRNA specific for beta 1- and beta 2-adrenergic receptors in human failing hearts. Evaluation of the absolute cardiac mRNA levels by two independent methods.
In human heart failure beta-adrenergic receptors are downregulated which contributes to the reduced responsiveness to positive inotropic beta-agonists in the diseased heart. The present study addressed the question whether the number of beta-adrenergic receptors in the failing human heart is regulated at the level of the mRNA and whether the absolute steady-state levels of subtype-specific mRNAs mirror the expression of receptor-subtype proteins in human heart. In a collaborative effort, two different and independent methods, performed in two independent laboratories, reverse transcription followed by polymerase chain reaction (RT-PCR) and RNase protection assays, were used to determine the absolute steady-state levels of beta 1- and beta 2-adrenergic receptor mRNAs in control (NF) and in failing human hearts. As determined by quantitative RT-PCR the beta 1-mRNA was significantly reduced from 0.98 +/- 0.12 (n = 10) to 0.49 +/- 0.11 pg/microgram total RNA in dilated cardiomyopathy (dCMP, n = 7) and to 0.40 +/- 0.11 pg/microgram total RNA in ischemic cardiomyopathy (iCMP, n = 8). The steady-state levels of mRNA specific for beta 2-adrenergic receptors also tended to be decreased but without reaching significance (NF: 0.16 +/- 0.05, dCMP: 0.11 +/- 0.03, iCMP: 0.13 +/- 0.04 pg/microgram total RNA). RNase protection assays revealed similar values. beta 1-mRNA was found to be significantly reduced from 1.22 +/- 0.22 in NF (n = 10) to 0.63 +/- 0.14 pg/microgram total RNA in dCMP (n = 5) and to 0.52 +/- 0.1 pg/microgram total RNA in iCMP (n = 8). The beta 2-mRNA also tended to be lower in dCMP and in iCMP as compared to NF but again without reaching significance (NF: 0.14 +/- 0.02, dCMP: 0.099 +/- 0.02, iCMP 0.107 +/- 0.02 pg/microgram total RNA). This is the first study to demonstrate in parallel by two different methods performed independently in two laboratories that the ratio of beta 1- and beta 2-adrenergic receptor densities in the left ventricle of the normal human heart of about 80/20 is closely related to the absolute steady state concentrations of their specific mRNA. In addition, the magnitude of the decrease in mRNA-levels of beta 1- and beta 2-adrenergic receptors in the failing human heart closely correlates with the decrease of the respective receptor proteins. These data suggest that the predominant regulation of beta-adrenergic receptors occurs at the mRNA level.
Ihl-Vahl
R
R
Department of Cardiology, University of Heidelberg, Germany.
Eschenhagen
T
T
Kübler
W
W
Marquetant
R
R
Nose
M
M
Schmitz
W
W
Scholz
H
H
Strasser
R H
RH
D000328:Adult; D015139:Blotting, Southern; D005786:Gene Expression Regulation; D006333:Heart Failure / Q000378:metabolism* / Q000601:surgery; D016027:Heart Transplantation; D006801:Humans; D008875:Middle Aged; D009206:Myocardium / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000302:isolation & purification / Q000378:metabolism*; D018342:Receptors, Adrenergic, beta-1 / Q000096:biosynthesis*; D018343:Receptors, Adrenergic, beta-2 / Q000096:biosynthesis*; D012016:Reference Values; D012260:Ribonucleases; D014158:Transcription, Genetic
D012333:RNA, Messenger; D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2; D012260:Ribonucleases