Cardiac Specific Expression Of Heat Shock Protein 27 Induced Cardiac Hypertrophy Depend On Its High Expression In Transgenic Mice Model

Background Heat shock protein 27 (Hsp27) is an important member of small heat shock proteins(sHsps). Many studies have demonstrated its protect role in different kind cell and animal model. We also found over expression Hsp27 could diminish H₂O₂ damage in cultured cell and conserve cardiac function when mice treated with Doxorubicin. But whether Hsp27 has other functions such as promote cell growth and hypertrophy is lack direct evidence.Objective Use transgenic mice model of cardiac specific expression Hsp27 to study whether Hsp27 could induce cardiac hypertrophy and the internal mechanism. Further more tested the cardiac structure and function of the hypertrophic heart.Methods Transgenic (TG) mice model of cardiac specific expressing Hsp27 was established by our lab previously. First, tested whether Hsp27 only expressed in heart and the protein level in different TG line by wetern blot. We explored the relationship between heart weight (HW)/body weight (BW), HW/tibia length (TL) and Hsp27 expression level. Second, in the hypertrophic line, further determine other index of cardiac hypertrophy, including the morphological difference, individual cell cross section area(WGA stain) and re-expression of foetal heart marker protein, ANP and BNP(reverse transcription PCR and semi-quantification of mRNA). Then analysised whether hypertrophy signal transduction pathways ERKs and Akt were activated (Western blot) and whether Akt pathway specific inhibitor Rapamycin could attenuate the hypertrophy phenomenon by continous action for 30 days when mice was one month old. Third, checkd the caridiac structure change (HE stain) and cardiomyocyte apoptosis (TUNEL), also the left ventricular function (LVF) on base condition and 6 and 24 hours after treated by lipopolysaccharide (LPS) (10 mg/kg).Results We got five TG lines and divided to high (HTG), moderate (MTG) and low TG (LTG) according to the expression level of Hsp27. Hsp27 didn't express in any tissue except the heart. Only the HTG line appeared hypertrophy profile. We took one HTG, TG10 for further investigation. HTG's HW/BW and HW/TL ratio were significant higher compared with wild type (WT) mice in 1, 2, 4, 8 month group, and the increase also exaggerated with aging. Morphological study revealed that raw hearts of 4 month-old HTG were larger than that of their WT littermates. The similar results exhibited in the transversal heart sections from both 4 month-and 8 month-old mice of THG and WT. The HTG individual cell corss section area increased by 57.70% (209.02±12.86 vs. 329.63±19.87, P＜0.01,) and 37.96% (250.44±20.46 vs. 345.50±21.85, P＜0.05) at the age of 4 month and 8 month compared with WT, respectively, mRNA expression of ANP in HTG increased by 107.90% (1.00±0.07 vs. 2.08±0.23, P＜0.05), 89.72% (1.26±0.09 vs. 2.39±0.23, P ＜0.05), 93.86% (1.13±0.10 vs. 2.43±0.34, P＜0.05) and 115.84% (1.31±0.23vs. 2.74±0.08, P＜0.05) in 1, 2, 4 and 8 month group, respectively. BNP was not significant different from WT at the age of 1 month (1.00±0.05 vs. 1.04±0.09, P＞0.05) but at 2, 4 and 8 month group, increased significantly by 63.44% (1.08±0.05 vs. 1.77±0.14, P＜0.05), 42.97% (1.33±0.09 vs. 1.90±0.06, P＜0.05) and 31.66% (1.69±0.0.06 vs. 2.23±0.06, P＜0.05), respectively, the content of p-ERKs in HTG increased by 287.20% (1.00±0.22 vs. 3.87±0.25, P＜0.001),116.66% (1.00±0.08 vs. 2.17±0.03, P＜0.001) and 112.39% (1.00±0.10 vs. 2.12±0.27, P＜0.01) in 2, 4, 8 month group, respectively. But the content of p-Akt remained unchanged. Continues m-TOR inhibitor, Rapamycin, administration had no influence on the hypertrophy in HTG. HE stain showed no disarray and cell loss in HTG and apoptosis displayed no difference compared with WT. The base LVF had no difference in 2 month group, but interestingly contaminated in 4 month compared with WT. FS% decreased by 22 % (30.79±1.98 vs. 39.43±2.70, P＜0.05) while EF% by 14% (63.55±2.71vs. 74.15±2.65, P＜0.05). 6 hours after LPS injection, LVF of both HTG and WT decreased significantly, FS% and EF% to 42.88% and 52.69% in WT (P＜0.01), while to 55.50% and 63.96% in HTG (P＜0.01). 24 after LPS administation, in comparison with the respective LVF of 6 hours after LPS injection, FS% and EF% restored significantly to 75.86% and 82.24% of baselines in WT (P＜0.01), whereas FS% and EF% of HTG maintained 54.91% and 62.94% of baselines and did not show significant restoration. Conclusion These findings indicated that Hsp27 induced cardiac hypertrophy in a high dose-dependent manner in mice. ERKs might participate in hypertrophy signal transduction pathway. Long-term high expression of Hsp27 minght be harmful.