The 5-HT4 receptor -a foetal gene re-expressed in cardiomyocytes from failing hearts? : a real-time quantitative reverse transcriptase polymerase chain study

Abstract

Myocardial remodelling and failure are associated with alterations in gene expression characterised by the re-expression of a foetal gene pattern. This often involves a shift to foetal isoforms of contractile proteins such as e.g. MHC (myosin heavy chain). Little is known about whether or not serotonin receptors are part of this foetal gene program or about their expression in heart failure.

The aim of this study was to evaluate the expression level of 5-HT4(b), 5-HT2A and 5-HT2B receptors and the serotonin transporter (SERT, 5-HTT) in foetal, neonatal and adult rat hearts as well as in failing and Sham operated rat hearts (Sham).

To determine the localisation of the 5-HT receptors regulated in hypertrophic heart failure, 5-HT4(b), 5-HT2A and 5-HT2B expression in cardiomyocytes (CM) and non-cardiomyocytes (NCM) from Sham and aorta-banded animals were also studied.

Foetal and neonatal rat hearts were taken out at day 3 and 1 ahead of expected birth and 1, 3 and 5 days after birth, respectively. Hearts were also taken from adult rats at the age of 113 days. Systolic heart failure was induced in Wistar rats by coronary artery ligation. Sham operated rats were run in parallel. Real-time quantitative reverse transcriptase (RT) polymerase chain reaction (PCR) was run using TaqMan probes. The mRNA expression level of 5-HT4(b), 5-HT2A, 5-HT2B and SERT was determined and normalised to the expression of six normalisation genes by the use of geNorm software. The results were compared to adult hearts or Sham.

The CM and NCM fractions were isolated from Wistar rat hearts exposed to banding of the ascending aorta. By real-time quantitative RT-PCR the expression level of the 5-HT4(b), 5-HT2A and 5-HT2B receptor plus â1- and â2-adrenergic receptor (AR) of CM and NCM were analysed. The results were normalised to GAPDH and compared to Sham.

For the 5-HT4(b) receptor, the expression level in failing rat heart was modest compared to the foetal heart. However, it was comparable to the neonatal genotype, proposing 5-HT4(b) as a reactivated foetal gene. In the banded rat heart model, the 5-HT4(b) receptor mRNA expression level was six times higher in both the NCM and CM of ABHF rats, compared to Sham. At time of birth, associated with an acute increase in wall stress, the 5-HT2A and 5-HT2B receptor mRNA expression were increased. For the 5-HT2A receptor the expression level was elevated 2- and 3-fold in the NCM and CM, respectively, both in hypertrophied and failing heart. The 5-HT2B mRNA expression level was four times higher in NCM from heart failure rats but decreased by 50% in the CM heart failure group compared to Sham. The serotonin transporter is not regulated in heart failure.