RESUMO
Transforming Growth Factor ß (TGF-ß) is crucial for valve development and homeostasis. The long form of Latent TGF-ß binding protein 1 (LTBP1L) covalently binds all TGF-ß isoforms and regulates their bioavailability. Ltbp1L expression analysis during valvulogenesis revealed two patterns of Ltbp1L production: an early one (E9.5-11.5) associated with endothelial-to-mesenchymal transformation (EMT); and a late one (E12.5 to birth) contemporaneous with valve remodeling. Similarly, histological analysis of Ltbp1L(-/-) developing valves identified two different pathologies: generation of hypoplastic endocardial cushions in early valvulogenesis, followed by development of hyperplastic valves in late valvulogenesis. Ltbp1L promotes valve EMT, as Ltbp1L absence yields hypoplastic endocardial cushions in vivo and attenuated EMT in vitro. Ltbp1L(-/-) valve hyperplasia in late valvuogenesis represents a consequence of prolonged EMT. We demonstrate that Ltbp1L is a major regulator of Tgf-ß activity during valvulogenesis since its absence results in a perturbed Tgf-ß pathway that causes all Ltbp1L(-/-) valvular defects.
Assuntos
Valvas Cardíacas/embriologia , Proteínas de Ligação a TGF-beta Latente/fisiologia , Animais , Embrião de Mamíferos , Desenvolvimento Embrionário/genética , Regulação da Expressão Gênica no Desenvolvimento , Idade Gestacional , Cardiopatias Congênitas/genética , Valvas Cardíacas/anormalidades , Valvas Cardíacas/metabolismo , Hiperplasia , Proteínas de Ligação a TGF-beta Latente/química , Proteínas de Ligação a TGF-beta Latente/genética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Valva Mitral/anormalidades , Valva Mitral/embriologia , Valva Mitral/patologia , Isoformas de Proteínas/genética , Isoformas de Proteínas/fisiologia , Transdução de Sinais/genética , Transdução de Sinais/fisiologia , Fatores de Crescimento Transformadores/genética , Fatores de Crescimento Transformadores/metabolismoRESUMO
Latent TGF-beta binding protein 1 (LTBP1) is a member of the LTBP/fibrillin family of extracellular proteins. Due to the usage of different promoters, LTBP1 exists in two major forms, long (L) and short (S), each expressed in a temporally and spatially unique fashion. Both LTBP1 molecules covalently interact with latent TGF-beta and regulate its function, presumably via interaction with the extracellular matrix (ECM). To explore the in vivo role of Ltbp1 in mouse development, at the time when only the L isoform is expressed, we mutated the Ltbp1L locus by gene targeting. Ltbp1L-null animals die shortly after birth from defects in heart development, consisting of the improper septation of the cardiac outflow tract (OFT) and remodeling of the associated vessels. These cardiac anomalies present as persistent truncus arteriosus (PTA) and interrupted aortic arch (IAA), which are associated with the faulty function of cardiac neural crest cells (CNCCs). The lack of Ltbp1L in the ECM of the septating OFT and associated vessels results in altered gene expression and function of CNCCs and decreased Tgf-beta activity in the OFT. This phenotype reveals a crucial role for Ltbp1L and matrix as extracellular regulators of Tgf-beta activity in heart organogenesis.