The fibrillin-1 RGD motif posttranscriptionally regulates ERK1/2 signaling and fibroblast proliferation via miR-1208.

Fibrillin-1 is an extracellular matrix protein which contains one conserved RGD integrin-binding motif. It constitutes the backbone of microfibrils in many tissues, and mutations in fibrillin-1 cause various connective tissue disorders. Although it is well established that fibrillin-1 interacts with several RGD-dependent integrins, very little is known about the associated intracellular signaling pathways. Recent published evidence identified a subset of miRNAs regulated by fibrillin-1 RGD-cell adhesion, with miR-1208 among the most downregulated. The present study shows that the downregulated miR-1208 controls fibroblast proliferation. Inhibitor experiments revealed that fibrillin-1 RGD suppressed miR-1208 expression via c-Src kinase and the downstream JNK signaling. Bioinformatic prediction and experimental target sequence validation demonstrated four miR-1208 binding sites on the ERK2 mRNA and one on the MEK1 mRNA. ERK2 and MEK1 are critical proliferation-promoting kinases. Decreased miR-1208 levels elevated the total and phosphorylated ERK1/2 and MEK1/2 protein levels and the phosphorylated to total ERK1/2 ratio. Together, the data demonstrate a novel outside-in signaling mechanism explaining how fibrillin-1 RGD-cell binding regulates fibroblast proliferation.

pyHeart4Fish: Chamber-specific heart phenotype quantification of zebrafish in high-content screens.

Cardiovascular diseases (CVDs) are the leading cause of death. Of CVDs, congenital heart diseases are the most common congenital defects, with a prevalence of 1 in 100 live births. Despite the widespread knowledge that prenatal and postnatal drug exposure can lead to congenital abnormalities, the developmental toxicity of many FDA-approved drugs is rarely investigated. Therefore, to improve our understanding of drug side effects, we performed a high-content drug screen of 1,280 compounds using zebrafish as a model for cardiovascular analyses. Zebrafish are a well-established model for CVDs and developmental toxicity. However, flexible open-access tools to quantify cardiac phenotypes are lacking. Here, we provide pyHeart4Fish, a novel Python-based, platform-independent tool with a graphical user interface for automated quantification of cardiac chamber-specific parameters, such as heart rate (HR), contractility, arrhythmia score, and conduction score. In our study, about 10.5% of the tested drugs significantly affected HR at a concentration of 20 µM in zebrafish embryos at 2 days post-fertilization. Further, we provide insights into the effects of 13 compounds on the developing embryo, including the teratogenic effects of the steroid pregnenolone. In addition, analysis with pyHeart4Fish revealed multiple contractility defects induced by seven compounds. We also found implications for arrhythmias, such as atrioventricular block caused by chloropyramine HCl, as well as (R)-duloxetine HCl-induced atrial flutter. Taken together, our study presents a novel open-access tool for heart analysis and new data on potentially cardiotoxic compounds.