Organ culture as a tool to identify early mechanisms of serotonergic valve disease.

BACKGROUND AND AIM OF THE STUDY: Although the late effects of serotonergic valve disease are known, the early mechanisms of the characteristic plaque formation are poorly understood. METHODS: To model conditions leading to plaque formation on mitral valves, samples (n = 6-8 per treatment) cultured in a splashing bioreactor were exposed to serotonin (5HT) and norfenfluramine (NF). In order to assess the role of 5HT2B receptor activation, the effects of these drugs were also tested with a 5HT2B receptor antagonist. After two weeks, tissue samples were stained immunohistochemically to localize changes in multiple extracellular matrix (ECM) components and synthesis mediators. RESULTS: Decorin and versican expression tended to increase with 5HT treatment compared to NF or baseline controls, regardless of the presence of the receptor antagonist. Samples treated with 5HT or with the receptor antagonist tended to express less collagen (types I and III) and biglycan than NF or the baseline controls. Heat shock protein 47, prolyl-4-hydroxylase, matrix metalloproteinase 9 (MMP9) and MMP13 tended to be down-regulated with 5HT or NF exposure, although some samples treated with the antagonist displayed normal levels of these mediators. Superficial plaques grew on a subgroup of the NF-treated organ cultures, but on none of the 5HT and control valves. CONCLUSION: Although both serotonin agents lead to plaque formation in a clinical setting, the early effects of exposure to the different drugs were found to be quite different. Additionally, the different drug responses suggest that a mechanism other than 5HT2B receptor activation might contribute to plaque formation.

Differential expression of genes in the calcium-signaling pathway underlies lesion development in the LDb mouse model of atherosclerosis.

OBJECTIVE: Atherosclerosis is influenced by the interaction of environmental and genetic susceptibility risk factors. We used global microarray expression profiling to investigate differentially regulated genes in aorta during development of atherosclerosis in a susceptible genetically modified mouse model in response to the interaction between risk factors including hyperlipidemic genotype, shear stress, diet, and age. METHODS AND RESULTS: In this study we investigated transcriptional changes in lesion-prone and lesion-resistant regions of aortas in genetically modified mice lacking both genes of the LDL receptor and the apolipoprotein B mRNA editing enzyme (LDb; Ldlr(-/-)Apobec1(-/-)). Risk factors including hyperlipidemic genotype (LDb vs. C57BL/6 wildtype), shear stress (lesion-prone vs. lesion resistant aortic regions), diet (chow vs. Western high-fat), and age (2- vs. 8-months) were studied. We hybridized aortic RNA samples with microarray chips containing probes for 45,000 mouse genes and expressed sequence tags (ESTs). Overall, the differentially expressed genes were components of 20 metabolic and physiological pathways. Notably, calcium signaling is the major pathway identified with differential regulation of 30 genes within this pathway. We also found differential expression of calcium-signaling genes in cultured primary endothelial cells from lesion-prone and lesion-resistant arterial regions (LDb mice vs. C57BL/6 controls), providing further support for involvement of calcium signaling in the pathogenesis of atherosclerosis. Moreover, we demonstrated protein expression of genes in the calcium-signaling pathway using Western blot analysis and immunofluorescence. CONCLUSIONS: Our results suggest that calcium signaling may play an important role in regulation of genes expressed in aorta during development of atherosclerosis. Calcium signaling may act via mechanistic responses to genetic, mechanical, and environmental insults that trigger an imbalance of intracellular calcium homeostasis, resulting in altered biological processes leading to lesion development.