During embryonic heart development, the transcription factors Tcf21, Wt1, and Tbx18 regulate activation and differentiation of epicardium-derived cells, including fibroblast lineages. Expression of these epicardial progenitor factors and localization of cardiac fibrosis were examined in mouse models of cardiovascular disease and in human diseased hearts. Following ischemic injury in mice, epicardial fibrosis is apparent in the thickened layer of subepicardial cells that express Wt1, Tbx18, and Tcf21. Perivascular fibrosis with predominant expression of Tcf21, but not Wt1 or Tbx18, occurs in mouse models of pressure overload or hypertensive heart disease, but not following ischemic injury. Areas of interstitial fibrosis in ischemic and hypertensive hearts actively express Tcf21, Wt1, and Tbx18. In all areas of fibrosis, cells that express epicardial progenitor factors are distinct from CD45-positive immune cells. In human diseased hearts, differential expression of Tcf21, Wt1, and Tbx18 also is detected with epicardial, perivascular, and interstitial fibrosis, indicating conservation of reactivated developmental mechanisms in cardiac fibrosis in mice and humans. Together, these data provide evidence for distinct fibrogenic mechanisms that include Tcf21, separate from Wt1 and Tbx18, in different fibroblast populations in response to specific types of cardiac injury.

Peters plus syndrome is a rare recessive autosomal disorder comprising ocular anterior segment dysgenesis, short stature, hand abnormalities and distinctive facial features. It was related only to mutations in the B3GALTL gene in the 13q12.3 region. In this study, we undertook the first functional analysis of a novel c.597-2 A>G splicing mutation within the B3GALTL gene using an ex-vivo approach. The results showed a complete skipping of exon 8 in the B3GALTL cDNA, which altered the open reading frame of the mutant transcript and generated a PTC within exon 9. This finding potentially elicits the nonsense mRNA to degradation by NMD (nonsense-mediated mRNA decay). The theoretical consequences of splice site mutations, predicted with the bioinformatics tool Human Splice Finder, were investigated and evaluated in relation to ex-vivo results. The findings confirmed the key role played by the B3GALTL gene in typical Peters-plus syndromes and the utility of mRNA analysis to understand the primary impacts of this mutation and the phenotype of the disease.