Functionally significant, novel variants of BMP4 are associated with isolated congenital heart disease

Bone morphogenetic proteins (BMPs) are multipotent cytokines of TGFβ super family, involved in wide range of biological processes including embryonic development, tissue differentiation, cell proliferation, migration and organogenesis. BMP signaling also plays a pivotal role during different phases of cardiogenesis. Although genetic variations in several components of BMP signaling have been linked to congenital heart disease (CHD), many of these findings lack thorough functional validation. To assess the role of BMPs in CHD, Sanger sequencing of BMP4 gene was conducted in 285 CHD cases along with 400 healthy controls. Four missense novel pathogenic variants were detected in four unrelated CHD probands with heterogeneous phenotypes. All the four variants (p.R113G, p.E151V, p.T197I and p.R226W) were located in BMP4 pro-peptide domain. Western blotting analysis revealed a significant increase in the phosphorylation of SMAD1/5 caused by all the four variants. Further, all the four variants enhance the transactivation of BMP-responsive promoters, Id1-luc and Id3-luc in luciferase reporter assay. Moreover, qRT-PCR analysis validating the enhanced endogenous expression of downstream targets namely Smad1 , Smad5 , Id1 , Id3 , and Irx4 which further confirm the augmented activity due to all the four variants. Besides, our computational modeling of RNA structures and its features, modifications in secondary and tertiary structures and various physiochemical properties are speculated to enhanced the binding of BMP4 muteins with its respective partner and thereby boosting the SMAD-dependent BMP signaling. Altogether, both in vitro and in silico observations unveiling the gain-of-function activity of mutants which potentially perturbing the normal BMP signaling/ dynamics, consequently inducing CHD.