The Expression Of Cardiac Hypertrophy Correlated Factors In Heart Of UT-B Gene Knock Out Mice

Urea transporters are a membrane channel proteins that facilitate urea movement across biological membranes along concentration gradient. UT-B is abundantly expressed in the endothelium of the arterial vasa recta throughout the renal medulla, where it contributes to the urinary concentrating. UT-B was also found to be expressed in several other organs, such as marrow, heart, spleen, brain, testis etc. little has been known about their physiological function in no-renal tissue. Yang Baoxue generated UT-B knock-out mice, representing the first model of a urea transporter deletion. We had screen out a UT-Bnull family with progressive familial heart block. So, in present study, we using UT-B knock-out mice to explore the mechanism of progresive inherited heart block induced by Urea Transporter B knock-out by molecular biology and electrophysiology techniques. Here, we examined the morphology, The expression of cardiac hypertrophy correlated factors of hearts from UT-B knockout mice at age of 16-weeks and 52-weeks to address the role of UT-B in the cardiovascular function.The results and discussion showed as following:1. The mRNA and protein of UT-B expresses in heart tissue of mice.We extracted the RNA and protein from mice heart tissue for RT-PCR and Western blot, embeded the heart tissue for immunofluorescencein staining. results showed that UT-B expressed in heart of wild type mice. No UT-B transcript and protein was found in UT-B-/- mice.2. UT-B knock-out leading to urea accumulation in mice serum and heart.As expected, urea in the cardiac tissue was significantly accumulated in both 16-weeks-old and 52-weeks-old UT-B knockout mice.Moreover, in 52-weeks-old wild-type mice, the urea levels in serum and heart were significantly increased by 40% and 56% respectively as compared with the urea levels in 16-weeks-old wild-type mice, indicating a age-associated elevation in urea levels of serum and heart tissue in wild-type mice. However, the urea levels in serum and heart of 52-weeks-old UT-B knockout mice were much more increased by 80% and 108% versus the urea levels in 16-weeks-old UT-B knockout mice. This observation demonstrated that deletion of UT-B gene deteriorated age-associated urea accumulation both in the serum and heart tissue.3. UT-B deletion associated with age-dependent cardiac hypertrophyThe UT-B knockout mice had normal cardiac structure at young ages. There was no significant difference in heart size and morphology between UT-B mice and wild-type mice at age of 16 weeksHowever, hearts from the 52-weeks-old UT-B knockout mice were larger than those of their littermates of age-matched wild-type mice. Histological morphological analysis revealed a dramatic increase in left ventricular wall and intraventricular septal wall thickness in UT-B knockout at the age of 52 weeks by hematoxylin/eosin staining. The UT-B knockout mice had significantly higher heart weight/body weight (HW/BW) ratios.4. UT-B deletioncause cardiac hypertrophy markers enhancedMoreover, the mRNA levels of the cardiac hypertrophy markers ANP, BNP, SERCA2 andα-actin were also examined in the heart of these mice using real time PCR. The results indicate that expression of ANP, SERCA2 andα-actin in the heart were significant elevated in 52-weeks-old UT-B knockout mice, as compared with their 16-weeks-old liter mates and the age-matched wild-type mice. UT-B knockout mice exhibited enhancedα-actin expression at age of 16 weeks and this defect deteriorated with aging. The level of NO in heart of 16 weeks UT-B knockout mice were lower than wild type mice, and the mRNA and proteine levels also lower than wild type mice, suggested that decreased NO may play a role in the mechanism of cardiac hypertrophy.Conclusions: UT-B Knockout could change the electrophysiological characters in mouse myocytes, such as decreasing of APA and Vmax, prolonging of action potential duration, and sodium current and potassium current mechanism is involved in the change. The mechanism of the effects probably due to the UT-B knockout directly increases the blood urea concentration. Long-term stimulation of high level of urea, and unnormal electrophysiology of cell enflunce the gene and protein level of cardiac cell, finally causes accumulation of urea in heart tissue, cardiac hypertrophy and progressive cardiac dysfunction in mice, which suggests that UT-B play an important role in cardiac function and blood pressure control.