The Effect Of Toll Like Receptor4Agonist On Cardiac Remodeling In Rats

Background:Pressure load, capacity load, neuroendocrine factors and other factors can activate several single pathways in the myocardial cells, including toll-like receptor4(TLR4) and mitogen original activated protein kinases (MAPKs) single systems, which interact, cause protein deposition out of cells and gene expression of ANP and beta myosin heavy chain ((3-MHC) etc, promote myocardial hypertrophy. Although these compensatory responses enhance pump function of the heart to a certain extent, yet long-term stimulations induce myocardial cell inflammation, cell death, myocardial cell outer fibrosis, which finally produce cardiac decompensation, and further heart failure and malignant arrhythmia. So, how to effectively curb this bad compensation and decompensation, has become an urgent need to solve clinical problem.TLR4is one of the important receptors across cell membrane in the innate immune system. It can not only identify cell ingredients of pathogenic microorganisms such as endotoxin, flagella and so on, but also be acted by the materials released by damaged cells. The activated TLR4induce immune reactions and release various inflammatory factors, which participate in a variety of diseases. The recent studies showed that TLR4signaling system may be involved in development of myocardial remodeling, but the specific mechanism is still unclear.Endotoxin or lipopolysaccharide (LPS) is the important component of the outer membrane of cell walls of gram-negative bacillus, which combine with CD14acting TLR4, mediating inflammation. It is the main activation of TLR4. Interestingly, small dose of LPS can induce endotoxin tolerance that the body performs low reactivity or no reactivity to endotoxin or LPS. Objective and methods:In this research, abdominal aortic constriction (AAC) rat model were used to discuss the effect of pressure overload on myocardial hypertrophy and proteins expression related to TLR4signaling system in myocardial cells, and the influence of the small dose of LPS on myocardial hypertrophy and TLR4signaling system. Age-matched male Wistar rats were randomly divided to4groups:(1) sham-operated (Sham) rats (n=10, each group),(2)four-week pressure-overloaded rats without LPS (AAC-4w),(3)eight-weck pressure-overloaded rats without LPS (AAC-8w), and (4) eight-week pressure-overloaded rats with LPS pretreatment (LPS+AAC-4w). Rats from L group were preconditioned with LPS by an intraperitoneal injection of10μg/kg (body weight) every two days for three times before challenge with AAC. Four or eight months after AAC, the form and function of heart were determined by color doppler ultrasonic diagnostic instrument and cardiac tissue; Body weight and left ventricular (LV) mass were measured, and LV mass were corrected for body weight (left ventricular mass index, LVMI); Fixed LV were stained by HE or Masson’s trichrome blue to determine the size of cardiomyocyte and collagen fractions; serum and spleen underwent mRNA or protein quantification by RT-PCR, Western blot, and ELISA.Results:1. LVMI, Left ventricular ejection fraction(LVEF), posterior wall (PW) thickness of left ventricular, the size of the myocardial cells and fibrosis area in our-week pressure-overloaded rats without LPS (AAC-4w) were significantly higher than those in the sham group (S), P<0.05.2. LVEF, LVMI, PW thickness, the size of the myocardial cells and fibrosis area in eight-week pressure-overloaded rats without LPS (AAC-8w) was significantly decreased compared toM2,P<0.05.3. There were no differences in the expression level of ANP TLR4TNF-amRNA and protein, and NF-kB in nuclear protein of Left ventricular between AAC-4w and AAC-8w group P>().05, while those in both groups were increasd compared with S group,P<0.05. 4. The level of TNF-ain serum of M2group was increased by comparison to Sham and AAC-4w groups.5. LPS downregulated LVEF, LVMI, PW thickness, the size of the myocardial cells and fibrosis area,and inhibited the expression of ANP、TLR4n TNF-amRNA and protein, and NF-kB in nuclear protein P<0.05。Conclusion:1. Pressure overload induced compensatory myocardial hypertrophy and decompensatory heart failure, and the activation of TLR4signaling system in myocardial tissue.2. The degree of myocardial tissue TLR4activation system in myocardial hypertrophy and heart failure had no difference. The TLR4activation system in the nonmyocytes played an important roal in the development of heart failure.3. Low dose of LPS pretreatment can adjust TLR4signaling system, inhibit inflammatory reaction, and inhibit myocardial hypertrophy.