title: Endogenous retinoic acid regulates cardiac progenitor differentiation.
abstract: Retinoic acid (RA) has several established functions during cardiac development, including actions in the fetal epicardium required for myocardial growth. An open question is if retinoid effects are limited to growth factor stimulation pathway(s) or if additional actions on uncommitted progenitor/stem populations might drive cardiac differentiation. Here we report the dual effects of RA deficiency on cardiac growth factor signaling and progenitor/stem biology using the mouse retinaldehyde dehydrogenase 2 (Raldh2) knockout model. Although early heart defects in Raldh2(-/-) embryos result from second-heart-field abnormalities, it is unclear whether this role is transient or whether RA has sustained effects on cardiac progenitors. To address this, we used transient maternal RA supplementation to overcome early Raldh2(-/-) lethality. By embryonic day 11.5-14.5, Raldh2(-/-) hearts exhibited reduced venticular compact layer outgrowth and altered coronary vessel development. Although reductions in Fgf2 and target pERK levels occurred, no alterations in Wnt/beta-catenin expression were observed. Cell proliferation is increased in compact zone myocardium, whereas cardiomyocyte differentiation is reduced, alterations that suggest progenitor defects. We report that the fetal heart contains a reservoir of stem/progenitor cells, which can be isolated by their ability to efflux a fluorescent dye and that retinoid signaling acts on this fetal cardiac side population (SP). Raldh2(-/-) hearts display increased SP cell numbers, with selective increases in expression of cardiac progenitor cell markers and reduced differentiation marker levels. Hence, although lack of RA signaling increases cardiac SP numbers, simultaneous reductions in Fgf signaling reduce cardiomyocyte differentiation, possibly accounting for long-term defects in myocardial growth.
authors.affiliation: Departments of Medicine and Molecular and Cellular Biology, Center for Cardiovascular Development, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: Song-Chang
authors.initials: SC
authors.lastname: Lin
authors.forename: Pascal
authors.initials: P
authors.lastname: Dollé
authors.forename: Lucile
authors.initials: L
authors.lastname: Ryckebüsch
authors.forename: Michela
authors.initials: M
authors.lastname: Noseda
authors.forename: Stéphane
authors.initials: S
authors.lastname: Zaffran
authors.forename: Michael D
authors.initials: MD
authors.lastname: Schneider
authors.forename: Karen
authors.initials: K
authors.lastname: Niederreither
mesh_terms: D000445:Aldehyde Oxidoreductases / Q000235:genetics; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects* / Q000502:physiology; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism; D005434:Flow Cytometry; D006321:Heart / Q000196:embryology*; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D013234:Stem Cells / Q000187:drug effects* / Q000502:physiology; D014212:Tretinoin / Q000494:pharmacology*; D051153:Wnt Proteins / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D051153:Wnt Proteins; D051176:beta Catenin; D016222:Fibroblast Growth Factor 2; D014212:Tretinoin; D000445:Aldehyde Oxidoreductases; C470579:RALDH2 protein, mouse