DNA damage and expression of checkpoint genes p21^WAF1/CIP1 and 14-3-3 σ in taurine-deficient cardiomyocytes

Objective: Taurine depletion is associated with development of cardiomyopathy. Further, oxidative stress is advanced as a critical factor mediating the effect of taurine deficiency on target organs. However, the molecular mechanism(s) linking taurine deficiency with the development of cardiomyopathy remains elusive. Since transition between apoptotic degeneration and cell proliferation in stress conditions is regulated at cell cycle checkpoints, we determined the expression of two such genes, namely p21^WAF1/CIP1 and 14-3-3 σ as well as p53 that are responsible for oxidative stress and DNA damage. We also carried out quantitative determination of DNA damage. Methods: Cardiomyocytes from β-alanine-induced taurine-depleted (TD) rats were used for this investigation. Single- and double-stranded DNA damage was quantified using comet assay analysis. Western blot and two-dimensional polyacrylamide gel electrophoresis with immunoblotting analysis were applied for protein analysis. Results: Comet assay analysis indicated that the extent of double-stranded DNA damage was greater in TD than in control cardiomyocytes. Whereas only traces of both p53 and p21^WAF1/CIP1 and no detectable expression of 14-3-3 σ were found in cardiomyocytes of control animals, the TD cardiomyocytes expressed all three genes. Conclusions: DNA damage and the consequent up-regulation of checkpoint proteins observed in TD cardiomyocytes indicate the involvement of cell cycle control mechanisms in the effect of taurine deficiency on cardiomyocytes. Single- and double-stranded DNA damage and the consequent arrest of cell proliferation in both G₁ and G₂ phases of the cell cycle induced by checkpoint proteins may trigger the cardiomyopathy that is associated with taurine deficiency.