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As terminally differentiated cells, cardiomyocytes stop proliferation soon after birth. However, it can re-enter into cell cycle as stimulated by some pathologic stimulation, then the synthesis of nucleic acid and protein in the cardiomyocytes will increase, which eventually result in hypertrophy. The tumor suppressor p53 is a transcription factor that regulates cell cycle, proliferation and apoptosis of cells. Accumulation of p53 results in the transactivation of several sets of target genes, such as p21WAF1/CIP1, which plays critical role in cell cycle as a negative regulator. However, the mechanism of p53 and p53-p21 signal pathway in cardiac hypertrophy remain unclear.
Neonatal rat ventricular myocytes (NRVM) were isolated and infected with p21-Ad or p53-Ad, or transfected with siRNA to block the expression of p21 or p53. The cell size was measured after staining with rhodamine-labeled phalloidine. NRVMs were subjected to immunofluorescence observed intracellular expression levels of p21. Twenty mice were randomly divided into four groups and received vehicle (control), isoproterenol (Iso, 40 mg/kg, s.c.), p53 inhibitor (pifithrin-α, 2 mg/kg, ip, qd) for 14 days or treated with 2×107 TU p53-Ad via femoral vein injection, respectively. The mRNA and protein expression levels of p21, p53, β-MHC and PCNA in NRVMs and left ventricle were detected by Real-time PCR and Western blot techniques. The pathological morphology changes were observed after lectin, HE and Masson’s trichrome staining.
The surface area of the NRVMs, mRNA and protein expression levels of p21, p53, β-MHC elevated significantly after angiotensin II stimulation. The heart weight index, myocardium injury, inflammatory cell infiltration, cross-sectional area, mRNA and protein expressions of p21, p53, β-MHC, PCNA in the ISO group were increased significantly by comparison to those in control group. p21 expression increased significantly and transfer from the cytoplasm to the nucleus after treated with p53-Ad transfection or AngII treatment, while it was down-regulated by p53 siRNA infection. Heart weight index increased obviously after treatment of p53 adenovirus. Meanwhile, p21 or p53 adenovirus transfection could aggravate the increase of cell size and expression elevation of p21, p53, and β-MHC induced by AngII stimulation. On the contrary, p21 or p53 siRNA could effectively attenuate the hypertrophic responses and abnormal gene expressions in NRVM.
p53-p21 signaling pathway activation is involved in the process of cardiac hypertrophy in vitro and in vivo, and inhibition of the activity of p53-p21 signal can effectively attenuate cardiac hypertrophy.