Characterization of the development of hypertrophy in hl5 murine cardiomyocyte

Cardiac hypertrophy and consequent heart failure derive from a complex sequence of events. Since, the molecular dissection of this process is hardly feasible in the intact organ, this prompted us to develop a cellular model of hypertrophy. We investigated the occurrence and the temporal sequence of events characterizing the hypertrophy program in HL-5 cells, a stable line that retains most of the electrophysiological and biochemical characteristics of cardiomyocytes. According to the original procedure, HL-5 cells are usually maintained in the presence of norepinephrine (NE). In order to reestablish the ability to respond to NE stimulation, a protocol was implemented whereby 50mM NE is added to the cell culture after a washout period of5 days. Under these conditions, a sequence of events, which reproduces the characteristic traits of the hypertrophic cardiomyocyte, is obtained. In particular, (i) during the first day, addition ofNE produced cytoplasmic Ca2+ oscillations, that were followed by the induction of the MAP kinase pathway. Indeed, 5 minutes after addition ofNE, Erk p42 phosphorylation increased 50.7fold returning to baseline levels within 10 minutes. Concomitantly, we observed the phosphorylation of Erk p44, which is completely de-phospho-rylated under control (ctrl) conditions; (ii) after two days of treatment, protein content was significantly increased by 125.5% due to a stimulation of protein synthesis, as documented by the 129% increase ofeH] leucine incorporation in cellular proteins; (iii) modifications in gene expression were evident after 3 days oftreatment with NE as shown by the increase in mRNA levels of two hypertrophy markers, namely ANF and TNFa (133% and 140% respectively vs. ctrl). In conclusion, we suggest that the development of hypertrophy can be reliably investigated m HL-5 cardiomyocytes.