Interleukin-18 knockout mice display maladaptive cardiac hypertrophy in response to pressure overload

Interleukin (IL)-18 is a cardiotropic proinflammatory cytokine chronically elevated in the serum of patients with cardiac hypertrophy (LVH). The purpose of this study was to examine the role of IL-18 in pressure-overload hypertrophy using wild type (WT) and IL-18 -/- (null) mice. Adult male C57Bl/6 mice underwent transaortic constriction (TAC) for 7days or sham surgery. Heart weight/body weight ratios showed blunted hypertrophy in IL-18 null TAC mice compared to WT TAC animals. Microarray analyses indicated differential expression of hypertrophy-related genes in WT versus IL-18 nulls. Northern, Western, and EMSA analyses showed Akt and GATA4 were increased in WT but unchanged in IL-18 null mice. Our results demonstrate blunted hypertrophy with reduced expression of contractile-, hypertrophy-, and remodeling-associated genes following pressure overload in IL-18 null mice, and suggest that IL-18 plays a critical role in the hypertrophic response.     

Sp1和Sp3介导的转录调控

基本转录因子Sp1和Sp3对转录调控区GC盒有很强的亲和力,参与几乎所有细胞功能,包括细胞增殖、凋亡、分化和新生物的转化.但在同一细胞中Sp1和Sp3对不同基因的作用并不相同,二者对基因特异性的转录调控是Sp1和Sp3研究领域的重要问题.近年来发现,Sp1和Sp3自身表达水平、结合的靶序列、磷酸化、糖基化等翻译后修饰,其他蛋白质的结合以及染色质结构与修饰等方面均可影响Sp1和Sp3的转录活性.本文从Sp1和Sp3蛋白参与转录调节的机制以及影响其基因特异性转录活性的诸方面因素这两大侧面,介绍了近年来的最新进展.     

Oxytocin receptor knockout mice display deficits in the expression of autism-related behaviors

A wealth of studies has implicated oxytocin (Oxt) and its receptors (Oxtr) in the mediation of social behaviors and social memory in rodents. It has been suggested that failures in this system contribute to deficits in social interaction that characterize autism spectrum disorders (ASD). In the current analyses, we investigated the expression of autism-related behaviors in mice that lack the ability to synthesize the oxytocin receptor itself, Oxtr knockout (KO) mice, as compared to their wild-type (WT) littermates. In the visible burrow system, Oxtr KO mice showed robust reductions in frontal approach, huddling, allo-grooming, and flight, with more time spent alone, and in self-grooming, as compared to WT. These results were corroborated in the three-chambered test: unlike WT, Oxtr KO mice failed to spend more time in the side of the test box containing an unfamiliar CD-1 mouse. In the social proximity test, Oxtr KO mice showed clear reductions in nose to nose and anogenital sniff behaviors oriented to an unfamiliar C57BL/6J (B6) mouse. In addition, our study revealed no differences between Oxtr WT and KO genotypes in the occurrence of motor and cognitive stereotyped behaviors. A significant genotype effect was found in the scent marking analysis, with Oxtr KO mice showing a decreased number of scent marks, as compared to WT. Overall, the present data indicate that the profile for Oxtr KO mice, including consistent social deficits, and reduced levels of communication, models multiple components of the ASD phenotype. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.     

Maternal toxicity--a possible factor in fetal malformations in mice

The assumption that major fetal malformations are indicative of a chemical's teratogenic potential was not supported by a literature review of teratology studies conducted in mice. In these studies, dose levels of test agents that manifested maternal toxicity as suggested by reduction in dam's body weight, clinical signs of toxicity, or deaths, also invariably caused reduction in fetal body weight, increased resorptions, and rarely fetal deaths. In several such studies, conducted with maternotoxic doses of structurally unrelated test agents, a consistent pattern of fetal defects was discovered. These defects included exencephaly, open eyes, hemivertebrae, fused arches or centra of lumbar or thoracic vertebrae, fused, missing or supernumerary ribs, and fused or scrambled sternebrae. These defects were absent at drug dosages that were distinctly nontoxic for the mother. In a few studies conducted at two or more maternally toxic doses, the degree and severity of maternal toxicity showed a positive correlation with the incidence and severity of above fetal defects. It is hypothesized that maternal toxicity, on its own, may have an etiologic role in these fetal defects.     

Mice lacking connexin45 conditionally in cardiac myocytes display embryonic lethality similar to that of germline knockout mice without endocardial cushion defect

The gap junction protein connexin45-deficient (Cx45-KO) mice die shortly after the hearts begin to beat. In addition to the heart defect, they also show defective vascular development which may be closely related with the cardiac phenotype. Therefore, we created mice whose floxed-Cx45 locus could be removed conditionally. We utilized cardiac alpha-actin-Cre transgenic mice to investigate the specific cardiac muscular function of Cx45 in vivo. The resultant conditional mutants were lethal, showing conduction block similar to that of the Cx45-KO mice. Unlike Cx45-KO, development of the endocardial cushion was not disrupted in the conditional mutants. X-gal staining was detected in the embryonic cardiac myocytes as a hallmark of Cre-loxP mediated floxed-Cx45 deletion. These results reconfirm the requirement of Cx45 for developing cardiac myocytes. These also indicate that establishing the first contractions is a crucial task for the early hearts.     

Role of phosphodiesterase type 3A and 3B in regulating platelet and cardiac function using subtype-selective knockout mice

Phosphodiesterase type 3 (PDE3) is an important regulator of cAMP-mediated responses within the cardiovascular system. PDE3 exists as two subtypes: PDE3A and PDE3B, with distinct cellular and subcellular locations. Due to the lack of subtype-specific pharmacological tools, the definitive role of each subtype in regulating cardiovascular function has not been determined. In this study, we investigated platelet and cardiac function, using PDE3A and PDE3B gene knockout (KO) mice. Platelet-rich-plasma was prepared from the blood of KO and age-matched wild-type (WT) mice. PGE1 (1 microg/mL) almost completely inhibited aggregation of platelets from WT, PDE3A KO and PDE3B KO mice. In platelets from WT mice, cilostamide (100 microM), a selective PDE3 inhibitor, blocked collagen- and ADP-induced aggregation. In contrast, cilostamide had no effect on aggregation of platelets from PDE3A KO mice. In PDE3B KO mice, inhibition of collagen- and ADP-induced platelet aggregation was similar to that in WT mice. The resting intra-platelet cAMP concentration in platelets from PDE3A KO mice was twice that in the WT platelets. After PGE1 (0.1 microg/mL) stimulation, intra-cellular cAMP concentration was increased significantly more in platelets from PDE3A KO mice compared to WT mice. In vivo, PDE3A KO mice were protected against collagen/epinephrine-induced pulmonary thrombosis and death, while no such protection was observed in PDE3B KO mice. The heart rate of PDE3A KO mice was significantly higher, compared with age-matched WT mice, while that of PDE3B KO mice was similar to WT. There was no difference in cardiac contractility between PDE3A or PDE3B KO mice. Heart rate and contractility were increased in a similar dose-dependent fashion by isoproterenol in both types of KO mice. Cilostamide increased heart rate and contractility in WT and PDE3B KO but not in PDE3A KO mice. Compared to WT and PDE3B KO mice, cyclic AMP-PDE activity in membrane fractions prepared from the hearts of PDE3A KO mice was lower and not inhibited by cilostamide. The data suggest that PDE3A is the main subtype of PDE3 expressed in platelets and cardiac ventricular myocytes, and is responsible for the functional changes caused by PDE3 inhibition.     

Generation and characterization of Rac3 knockout mice

Rac proteins are members of the Rho family of GTPases involved in the regulation of actin dynamics. The three highly homologous Rac proteins in mammals are the ubiquitous Rac1, the hematopoiesis-specific Rac2, and the least-characterized Rac3. We show here that Rac3 mRNA is widely and specifically expressed in the developing nervous system, with highest concentration at embryonic day 13 in the dorsal root ganglia and ventral spinal cord. At postnatal day 7 Rac3 appears particularly abundant in populations of projection neurons in several regions of the brain, including the fifth layer of the cortex and the CA1-CA3 region of the hippocampus. We generated mice deleted for the Rac3 gene with the aim of analyzing the function of this GTPase in vivo. Rac3 knockout animals survive embryogenesis and show no obvious developmental defects. Interestingly, specific behavioral differences were detected in the Rac3-deficient animals, since motor coordination and motor learning on the rotarod was superior to that of their wild-type littermates. No obvious histological or immunohistological differences were observed at major sites of Rac3 expression. Our results indicate that, in vivo, Rac3 activity is not strictly required for normal development in utero but may be relevant to later events in the development of a functional nervous system.