ZccE, a P-type ATPase contributing to biofilm formation and competitiveness in Streptococcus mutans.

Most living organisms require zinc for survival; however, excessive amounts of this trace element can be toxic. Therefore, the frequent fluctuations of salivary zinc, caused by the low physiological level and the frequent introduction of exogenous zinc ions, present a serious challenge for bacteria colonizing the oral cavity. Streptococcus mutans is considered one of the main bacterial pathobiont in dental caries. Here, we verified the role of a P-type ATPase ZccE as the main zinc-exporting transporter in S. mutans and delineated the effects of zinc toxification caused by zccE deletion in the physiology of this bacterium. The deletion of the gene zccE severely impaired the ability of S. mutans to grow under high zinc stress conditions. Intracellular metal quantification using inductively coupled plasma optical emission spectrometer revealed that the zccE mutant exhibited approximately two times higher zinc accumulation than the wild type when grown in the presence of a subinhibitory zinc concentration. Biofilm formation analysis revealed less single-strain biofilm formation and competitive weakness in the dual-species biofilm formed with Streptococcus sanguinis for zccE mutant under high zinc stress. The quantitive reverse transcription polymerase chain reaction test revealed decreased expressions of gtfB, gtfC, and nlmC in the mutant strain under excessive zinc treatment. Collectively, these findings suggest that ZccE plays an important role in the zinc detoxification of S. mutans and that zinc is a growth-limiting factor for S. mutans within the dental biofilm.

Loss of TRADD attenuates pressure overload-induced cardiac hypertrophy through regulating TAK1/P38 MAPK signalling in mice.

We investigated the role of tumour necrosis factor receptor (TNFR)-associated death domain (TRADD) on pressure overload-induced cardiac hypertrophy and the underlying molecular mechanisms by using a TRADD deficiency mice model. 6-8 weeks wild-type and TRADD knockout mice were performed to transverse aorta constriction (TAC) or sham operation (6-8 mice for each group). 14 days after TAC, cardiac function was measured by echocardiography, as well as by pathological and molecular analyses of heart samples. The expressions of cardiac hypertrophic and fibrotic markers were detected by qPCR. Phosphorylated and total TAK1, Akt, and p38 MAPK levels were examined by Western blotting. The ratios of lung or heart/body weight, wall thickness/chamber diameter of left ventricular and cross area of cardiomyocyte were significantly reduced in TRADD knockout (KO) mice than those of wild-type mice after TAC. Moreover, cardiac hypertrophic and fibrotic markers were downregulated in TRADD knockout mice than those of wild-type mice following TAC. Protein expression analysis showed phosphorylated TAK1, p38 MAPK and AKT were upregulated after TAC in both wild-type and TRADD KO mice, phosphorylation of TAK1 and p38 MAPK was reduced more remarkably after TRADD deficiency, while phosphorylated AKT expression was similar between TRADD KO and wild-type mice following TAC. Our data suggest that TRADD KO blunts pressure overload-induced cardiac hypertrophy through mediating TAK1/p38 MAPK but not AKT phosphorylation in mice.

Olmesartan ameliorates pressure overload-induced cardiac remodeling through inhibition of TAK1/p38 signaling in mice.

AIMS: Many studies have demonstrated the potent effects of ARB administration on heart failure. However, the mechanism of the potent effects of ARB on cardiac remodeling is less well understood. We investigated the role of Olmesartan on the fibrosis and hypertrophy in mouse heart. MATERIALS AND METHODS: We employed TAC surgery, a mouse model of chronic cardiac failure. All the mice were separated into three groups: the sham group, TAC group and TAC plus Olmesartan group (given Olmesartan treatment after TAC). We analyzed left ventricle remodeling, and function by echocardiography or pathology. We further detected the level of marker genes involved in fibrosis and hypertrophy and in cultured neonatal rat cardiac fibroblasts and myocytes infected by constitutively active TAK1 and p38MAPK. After TAC, all the mice developed hypertrophy, worse cardiac function and malignant remodeling in left ventricle. KEY FINDINGS: Olmesartan improved heart remodeling and function without changing pressure of blood. Moreover, Olmesartan reduced the level of transforming growth factor ß activated kinase-1 (TAK1) and phospho-p38MAPK. In neonatal rat cardiac fibroblast cells and cardiomyocytes, Olmesartan also decreased TAK1 and p38MAPK activation triggered by TGFß1 or AngII. The inhibitory effect of Olmesartan was abrogated by overexpression of constitutively active TAK1 and p38MAPK by adenovirus system. SIGNIFICANCE: Our results suggest Olmesartan improves heart remodeling and function induced by pressure overload. P38MAPK inactivation attenuated by olmesartan via inhibition of TAK1 pathway plays an important role in the process.

Increased cardiac remodeling in cardiac-specific Flt-1 receptor knockout mice with pressure overload.

Vascular endothelial growth factor (VEGF) inhibition has previously been shown to have damaging effects on the heart. Because the role of Flt-1 (a phosphotyrosine kinase receptor for VEGF) in cardiac function and hypertrophy is unclear, we generated mice lacking Flt-1 only in their cardiomyocytes (Flt-1 KO). The hearts from 8- to 10-week-old mice were measured by using echocardiography and histology. No significant differences were seen in fraction shortening, cross-sectional area of cardiomyocytes, and interstitial collagen fraction between littermate controls and KO mice at baseline. To test the hypothesis that Flt-1 is involved in cardiac remodeling, we performed transverse aorta constriction (TAC) by ligating the transverse ascending aorta. Four weeks after TAC, echocardiography of the mice was performed, and the hearts were excised for pathological analysis and Western blotting. No difference in mortality was found between Flt-1 KO mice and controls; however, KO mice showed a greater cardiomyocyte cross-sectional area and interstitial collagen fraction than controls. Western blotting indicated that AKT was activated less in Flt-1 KO hearts after TAC compared with that in control hearts. Thus, Flt-1 deletion in cardiomyocytes increased hypertrophy, fibrosis, and regression of AKT phosphorylation. Our study suggests that Flt-1 plays a critical role in cardiac hypertrophy induced by pressure overload via the activation of AKT, which seems to be cardioprotective.