IGF signaling directs ventricular cardiomyocyte proliferation during embryonic heart development

Abstract

SUMMARYSecreted factors from the epicardium are believed to be important in directing heart ventricular cardiomyocyte proliferation and morphogenesis, although the specific factors involved have not been identified or characterized adequately. We found that IGF2 is the most prominent mitogen made by primary mouse embryonic epicardial cells and by a newly derived immortalized mouse embryonic epicardial cell line called MEC1. In vivo, Igf2 is expressed in the embryonic mouse epicardium during midgestation heart development. Using a whole embryo culture assay in the presence of inhibitors, we confirmed that IGF signaling is required to activate the ERK proliferation pathway in the developing heart, and that the epicardium is required for this response. Global disruption of the Igf2 gene, or conditional disruption of the two IGF receptor genes Igf1r and Insr together in the myocardium, each resulted in a significant decrease in ventricular wall proliferation and in ventricular wall hypoplasia. Ventricular cardiomyocyte proliferation in mutant embryos was restored to normal at E14.5, concurrent with the establishment of coronary circulation. Our results define IGF2 as a previously unexplored epicardial mitogen that is required for normal ventricular chamber development.

Hydrogen peroxide primes heart regeneration with a derepression mechanism

“…New transgenic lines, such as Tg(tcf21:catalase) without autofluorescence or heat-inducible Tg(hsp70:catalase) without leaky transgene expression are needed for determining the levels of Dusp6 and pErk by immunostaining Based on the data from others and ours, we propose that the working model for cardiac regenerative signaling comprises two main branches: the forward pro-regenerative MAPK signaling triggered by FGF and other growth factors, as recently elucidated [20,21]; and the derepression mechanism through the Duox/Nox2-H 2 O 2 -Dusp6 pathway that converges on Erk1/2 MAPK signaling primarily in the epicardium, which then activate putative soluble factors to promote myocardial regeneration (Figure 8). Such epicardial soluble factors might include Wnt1 and IGF2 that were previously shown to play an essential function in the epicardium/cardiac fibroblasts and myocardium [46][47][48][49]. During heart regeneration, the growth factor-MAPK signaling (pErk) is gradually enhanced in injured hearts from 3 to 14 dpa with the peak around 14 dpa, which induces dusp6 expression (positive induction) that in turn dephosphorylates pErk (negative feedback) (Figures 3 and 4).…”

Insulin-Like Growth Factor Signaling Regulates the Timing of Sensory Cell Differentiation in the Mouse Cochlea

“…As discussed, expression of Igf2 in the cochlea overlaps with Igf1, suggesting possible functional compensation in Igf1 Ϫ/Ϫ mutants, or alternatively, unique roles for IGF2. Existing data have demonstrated specific roles for IGF2, in particular in regulation of cellular proliferation during placental growth and development of the heart (Constância et al, 2002;Li et al, 2011). …”

Adipogenesis and epicardial adipose tissue: A novel fate of the epicardium induced by mesenchymal transformation and PPARγ activation

“…MEC1 is a stably immortalized mouse embryonic ventricular epicardial cell line (31). Derivation and isolation of primary mouse epicardial cells were described previously (15, 31); briefly, mouse embryonic day E13.5 ventricular heart tissue was minced coarsely into pieces and allowed to settle on gelatin-coated dishes, from which epicardial cells migrate and expand.…”