TIEG-null mice display an osteopenic gender-specific phenotype.

TGFbeta inducible early gene-1 (TIEG) was originally cloned from human osteoblasts (OB) and has been shown to play an important role in TGFbeta/Smad signaling, regulation of gene expression and OB growth and differentiation. To better understand the biological role of TIEG in the skeleton, we have generated congenic TIEG-null (TIEG(-/-)) mice in a pure C57BL/6 background. Through the use of DXA and pQCT analysis, we have demonstrated that the femurs and tibias of two-month-old female TIEG(-/-) mice display significant decreases in total bone mineral content, density, and area relative to wild-type (WT) littermates. However, no differences were observed for any of these bone parameters in male mice. Further characterization of the bone phenotype of female TIEG(-/-) mice involved mechanical 3-point bending tests, micro-CT, and histomorphometric analyses of bone. The 3-point bending tests revealed that the femurs of female TIEG(-/-) mice have reduced strength with increased flexibility compared to WT littermates. Micro-CT analysis of femurs of two-month-old female TIEG(-/-) mice revealed significant decreases in cortical bone parameters compared to WT littermates. Histomorphometric evaluation of the distal femur revealed that female TIEG(-/-) mice also display a 31% decrease in cancellous bone area, which is primarily due to a decrease in trabecular number. At the cellular level, female TIEG(-/-) mice exhibit a 42% reduction in bone formation rate which is almost entirely due to a reduction in double labeled perimeter. Differences in mineral apposition rate were not detected between WT and TIEG(-/-) mice. Taken together, these findings suggest that female TIEG(-/-) mice are osteopenic mainly due to a decrease in the total number of functional/mature OBs.

Estrogen-TGFbeta cross-talk in bone and other cell types: role of TIEG, Runx2, and other transcription factors.

It is well established that E(2) and TGFbeta have major biological effects in multiple tissues, including bone. The signaling pathways through which these two factors elicit their effects are well documented. However, the interaction between these two pathways and the potential consequences of cross-talk between E(2) and TGFbeta continue to be elucidated. In this prospectus, we present known and potential roles of TIEG, Runx2, and other transcription factors as important mediators of signaling between these two pathways.

Atorvastatin inhibits calcification and enhances nitric oxide synthase production in the hypercholesterolaemic aortic valve.

OBJECTIVE: To study in a rabbit model the expression of endothelial nitric oxide synthase (eNOS) in association with the development of calcification of the aortic valve, and to assess the effects of atorvastatin on eNOS expression, nitrite concentration, and aortic valve calcification. METHODS: Rabbits (n = 48) were treated for three months: 16, forming a control group, were fed a normal diet; 16 were fed a 0.5% (wt/wt) high cholesterol diet; and 16 were fed a 0.5% (wt/wt) cholesterol diet plus atorvastatin (2.5 mg/kg/day). The aortic valves were examined with eNOS immunostains and western blotting. Cholesterol and high sensitivity C reactive protein (hsCRP) concentrations were determined by standard assays. Serum nitrite concentrations were measured with a nitric oxide analyser. eNOS was localised by electron microscopy and immunogold labelling. Calcification in the aortic valve was evaluated by micro-computed tomography (CT). RESULTS: Cholesterol, hsCRP, and aortic valve calcification were increased in the cholesterol fed compared with control animals. Atorvastatin inhibited calcification in the aortic valve as assessed by micro-CT. eNOS protein concentrations were unchanged in the control and cholesterol groups but increased in the atorvastatin treated group. Serum nitrite concentrations were decreased in the hypercholesterolaemic animals and increased in the group treated with atorvastatin. CONCLUSION: These data provide evidence that chronic experimental hypercholesterolaemia produces bone mineralisation in the aortic valve, which is inhibited by atorvastatin.

Experimental hypercholesterolemia induces apoptosis in the aortic valve.

BACKGROUND AND AIM OF THE STUDY: Aortic valve disease is presently the number one indication for valve replacement in the United States, yet its molecular mechanisms remain unknown. As apoptosis (programmed cell death) occurs in degenerative disease states, it was postulated that experimental hypercholesterolemia is associated with apoptosis in rabbit aortic valves. METHODS: New Zealand White rabbits (n = 8) were fed a 1% cholesterol diet for 12 weeks; control rabbits (n = 8) were fed a normal diet. After sacrifice of the animals, the aortic valves were dissected. Apoptosis was identified in the valvular lesion by TdT-mediated dUTP-biotin nick end-labeling (TUNEL) technique, and confirmed with transmission electron microscopy. The number of apoptotic cells was measured by computed morphometry. RESULTS: Valves from hypercholesterolemic rabbits showed an increase in apoptosis. TUNEL staining was identified in the atherosclerotic layer of hypercholesterolemic valves (0.1% of cells), but not in the cells of controls (p <0.0001). CONCLUSION: Apoptosis is increased in rabbit aortic valves during experimental hypercholesterolemia. If fatal cellular degeneration occurs in hypercholesterolemic valve disease, these data suggest that apoptosis may play a role in the mechanism of valvular disease.

Cell proliferation in carcinoid valve disease: a mechanism for serotonin effects.

BACKGROUND AND AIM OF THE STUDY: Elevated serum serotonin is associated with carcinoid heart disease, the hallmark of which is valvular thickening. Yet, the mechanistic role of serotonin in carcinoid heart disease is poorly understood. We postulated that serotonin has a direct mitogenic effect on cardiac valvular subendocardial cells, and that this effect is mediated by serotonin receptors. METHODS: The dose-dependent proliferative effects of serotonin (10(-8) to 10(-4)M) on cultured porcine aortic valve cells via a [3H]thymidine assay were determined in vitro. Serotonin receptor antagonist studies in culture were also performed using methiotepin, a 5HT1b antagonist, and ketanserin, a 5HT2 receptor antagonist, to determine the mechanism of serotonin action. The ex-vivo proliferation level in human carcinoid (n = 26) and normal valves (n = 10) was compared using proliferating cell nuclear antigen (PCNA) staining, a marker for proliferation. Identification and localization of specific 5HT receptor was assessed by immunostaining for serotonin receptors in the valves. RESULTS: Serotonin increased valvular proliferation in vitro in a dose-dependent manner (10-fold increase) (p <0.001), and this mitogenic effect was inhibited by methiotepin but not ketanserin. In human carcinoid heart valves the level of proliferation was 35-fold higher than in normal human valves (p <0.001). 5HT1b receptors were found only in the carcinoid valves, and not in the normal valves. CONCLUSION: Serotonin is a powerful mitogen for valvular subendocardial cells. The mitogenic effect is at least partly mediated via 5HT1b receptors. Subendothelial cell proliferation is significantly elevated in human carcinoid valves in vivo. The data suggest a mechanism whereby serotonin may contribute to valvular proliferation in carcinoid heart disease.