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Secreted Frizzled-related proteins (sFRPs) have emerged as key regulators of a wide range of developmental and disease processes. Most of the known functions of mammalian sFRPs have been attributed to their ability to antagonize Wnt signalling. Recently however, Xenopus laevis and zebrafish sFRP, Sizzled, was shown to function as an antagonist of Chordin processing by Tolloid-like metalloproteinases. This has led to the proposal that sFRPs may function as evolutionarily conserved antagonists of chordinase activities of this class of proteinases. In contrast to this proposal, we show here that the mammalian sFRP, sFRP2, does not affect Chordin processing, but instead, can serve as a direct enhancer of procollagen C proteinase activity of Tolloid-like metalloproteinases. We also show that the level of fibrosis, in which procollagen processing by Tolloid-like proteinases has a rate-limiting role, is markedly reduced in Sfrp2-null mice subjected to myocardial infarction. Importantly, this reduced level of fibrosis is accompanied by significantly improved cardiac function. This study thus uncovers a function for sFRP2 and a potential therapeutic application for sFRP2 antagonism in controlling fibrosis in the infarcted heart. [ABSTRACT FROM AUTHOR]

Carney complex is a genetic condition in which affected individuals develop benign tumours in various tissues, including the heart. Most individuals with Carney complex have a mutation in the PRKAR1A gene, which encodes the regulatory R1α subunit of protein kinase A — a significant component of the cyclic-AMP signalling pathway. Genetically engineered mutant Prkar1a mouse models show an increased propensity to develop tumours, and have established a role for R1α in initiating tumour formation and, potentially, in maintaining cell proliferation. Ongoing investigations are exploring the intersection of R1α-dependent cell signalling with other gene products such as perinatal myosin, mutation of which can also cause cardiac myxomas. [ABSTRACT FROM AUTHOR]

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is associated with fibrofatty replacement of cardiac myocytes, ventricular tachyarrhythmias and sudden cardiac death. In 32 of 120 unrelated individuals with ARVC, we identified heterozygous mutations in PKP2, which encodes plakophilin-2, an essential armadillo-repeat protein of the cardiac desmosome. In two kindreds with ARVC, disease was incompletely penetrant in most carriers of PKP2 mutations. [ABSTRACT FROM AUTHOR]

Reports on the results of a study of a mouse model of Holt-Oram syndrome, which has been associated with mutations in the T-box transcription factor TBX5. Its function; How mutations in it can cause disease; Results of previous studies; Effects of experimental changes in TBX5 expression on heart and limb development in various species; Influence of genetic background on disease manifestations; Importance of considering species-specific gene expression patterns; Conclusions.