Periostin Expression is Altered in Aortic Valves in Smad6 Mutant Mice

Identification of Gravida Serum Biomarkers for Noninvasive Prenatal Diagnosis Fetal Congenital Heart Disease

Congenital heart disease (CHD) is well established as the most common congenital defect worldwide. Given the lack of biomarkers available, we aimed to identify new biomarkers for the noninvasive prenatal diagnosis of fetal CHD. This study used data-independent acquisition (DIA) to explore potential protein biomarkers that co-expressed in gravida serum (GS) and fetal amniotic fluid (AF). Next, parallel reaction monitoring (PRM), enzyme-linked immunosorbent assay (ELISA), receiver operating characteristic curve (ROC) analysis, and the immunohistochemistry (IHC) were performed to validate the potential biomarkers. Based on DIA and PRM proteomics and bioinformatics results, we identified POSTN and PAPPA in GS as candidate biomarkers. Their differential expression during ELISA and IHC were generally consistent with our proteomics results. POSTN combined with PAPPA in GS yield a good diagnose fetal CHD with sensitivity of 83.9%, specificity of 73.9%, and an area under curve (AUC) of 0.842. This is the first study showing that POSTN in GS and AF is associated with fetal CHD. POSTN and PAPPA have huge prospects for application as potential biomarkers in the noninvasive prenatal diagnosis of fetal CHD. Congenital heart disease (CHD) is well-established as the most common congenital defect worldwide. Given the lack of biomarkers available, we aimed to identify new biomarkers for the noninvasive prenatal diagnosis of fetal CHD. We used data independent acquisition (DIA) to explore potential protein biomarkers that co-expressed in gravida serum (GS) and fetal amniotic fluid (AF). Next, parallel reaction monitoring (PRM), enzyme-linked immunosorbent assay (ELISA), receiver operating characteristic curve (ROC) analysis, and the immunohistochemistry (IHC) were performed to validate the potential biomarkers. Based on DIA and PRM proteomics and bioinformatics results, we identified POSTN and PAPPA in GS as candidate biomarkers. Their differential expression during ELISA and IHC were generally consistent with our proteomics results. POSTN combined with PAPPA in GS yield a good diagnose fetal CHD with sensitivity of 83.9 %, specificity of 73.9%, and an area under curve (AUC) of 0.842. This is the first study showing that POSTN in GS and AF is associated with fetal CHD. POSTN and PAPPA have huge prospects for application as potential biomarkers in the noninvasive prenatal diagnosis of fetal CHD.

Biomechanical Cues Direct Valvulogenesis

The vertebrate embryonic heart initially forms with two chambers, a ventricle and an atrium, separated by the atrioventricular junction. Localized genetic and biomechanical information guides the development of valves, which function to ensure unidirectional blood flow. If the valve development process goes awry, pathology associated with congenital valve defects can ensue. Congenital valve defects (CVD) are estimated to affect 1–2% of the population and can often require a lifetime of treatment. Despite significant clinical interest, molecular genetic mechanisms that direct valve development remain incompletely elucidated. Cells in the developing valve must contend with a dynamic hemodynamic environment. A growing body of research supports the idea that cells in the valve are highly sensitive to biomechanical forces, which cue changes in gene expression required for normal development or for maintenance of the adult valve. This review will focus on mechanotransductive pathways involved in valve development across model species. We highlight current knowledge regarding how cells sense physical forces associated with blood flow and pressure in the forming heart, and summarize how these changes are transduced into genetic and developmental responses. Lastly, we provide perspectives on how altered biomechanical cues may lead to CVD pathogenesis.

Role of Periostin in Cardiac Valve Development

Although periostin plays a significant role in adult cardiac remodeling diseases, the focus of this review is on periostin as a valvulogenic gene. Periostin is expressed throughout valvular development, initially being expressed in endocardial endothelial cells that have been activated to transform into prevalvular mesenchyme termed "cushion tissues" that sustain expression of periostin throughout their morphogenesis into mature (compacted) valve leaflets. The phenotype of periostin null indicates that periostin is not required for endocardial transformation nor the proliferation of its mesenchymal progeny but rather promotes cellular behaviors that promote migration, survival (anti-apoptotic), differentiation into fibroblastic lineages, collagen secretion and postnatal remodeling/maturation. These morphogenetic activities are promoted or coordinated by periostin signaling through integrin receptors activating downstream kinases in cushion cells that activate hyaluronan synthetase II (Akt/PI3K), collagen synthesis (Erk/MapK) and changes in cytoskeletal organization (Pak1) which regulate postnatal remodeling of cells and associated collagenous matrix into a trilaminar (zonal) histoarchitecture. Pak1 binding to filamin A is proposed as one mechanism by which periostin supports remodeling. The failure to properly remodel cushions sets up a trajectory of degenerative (myxomatous-like) changes that over time reduce biomechanical properties and increase chances for prolapse, regurgitation or calcification of the leaflets. Included in the review are considerations of lineage diversity and the role of periostin as a determinant of mesenchymal cell fate.

BMP2 expression in the endocardial lineage is required for AV endocardial cushion maturation and remodeling

Distal outgrowth, maturation and remodeling of the endocardial cushion mesenchyme in the atrioventricular (AV) canal are the essential morphogenetic events during four-chambered heart formation. Mesenchymalized AV endocardial cushions give rise to the AV valves and the membranous ventricular septum (VS). Failure of these processes results in several human congenital heart defects. Despite this clinical relevance, the mechanisms governing how mesenchymalized AV endocardial cushions mature and remodel into the membranous VS and AV valves have only begun to be elucidated. The role of BMP signaling in the myocardial and secondary heart forming lineage has been well studied; however, little is known about the role of BMP2 expression in the endocardial lineage. To fill this knowledge gap, we generated Bmp2 endocardial lineage-specific conditional knockouts (referred to as Bmp2 cKO^Endo) by crossing conditionally-targeted Bmp2^flox/flox mice with a Cre-driver line, Nfatc1^Cre, wherein Cre-mediated recombination was restricted to the endocardial cells and their mesenchymal progeny. Bmp2 cKO^Endo mouse embryos did not exhibit failure or delay in the initial AV endocardial cushion formation at embryonic day (ED) 9.5-11.5; however, significant reductions in AV cushion size were detected in Bmp2 cKO^Endo mouse embryos when compared to control embryos at ED13.5 and ED16.5. Moreover, deletion of Bmp2 from the endocardial lineage consistently resulted in membranous ventricular septal defects (VSDs), and mitral valve deficiencies, as evidenced by the absence of stratification of mitral valves at birth. Muscular VSDs were not found in Bmp2 cKO^Endo mouse hearts. To understand the underlying morphogenetic mechanisms leading to a decrease in cushion size, cell proliferation and cell death were examined for AV endocardial cushions. Phospho-histone H3 analyses for cell proliferation and TUNEL assays for apoptotic cell death did not reveal significant differences between control and Bmp2 cKO^Endo in AV endocardial cushions. However, mRNA expression of the extracellular matrix components, versican, Has2, collagen 9a1, and periostin was significantly reduced in Bmp2 cKO^Endo AV cushions. Expression of transcription factors implicated in the cardiac valvulogenesis, Snail2, Twist1 and Sox9, was also significantly reduced in Bmp2 cKO^Endo AV cushions. These data provide evidence that BMP2 expression in the endocardial lineage is essential for the distal outgrowth, maturation and remodeling of AV endocardial cushions into the normal membranous VS and the stratified AV valves.

BMP-2 induces versican and hyaluronan that contribute to post-EMT AV cushion cell migration

Distal outgrowth and maturation of mesenchymalized endocardial cushions are critical morphogenetic events during post-EMT atrioventricular (AV) valvuloseptal morphogenesis. We explored the role of BMP-2 in the regulation of valvulogenic extracellular matrix (ECM) components, versican and hyaluronan (HA), and cell migration during post-EMT AV cushion distal outgrowth/expansion. We observed intense staining of versican and HA in AV cushion mesenchyme from the early cushion expansion stage, Hamburger and Hamilton (HH) stage-17 to the cushion maturation stage, HH stage-29 in the chick. Based on this expression pattern we examined the role of BMP-2 in regulating versican and HA using 3D AV cushion mesenchymal cell (CMC) aggregate cultures on hydrated collagen gels. BMP-2 induced versican expression and HA deposition as well as mRNA expression of versican and Has2 by CMCs in a dose dependent manner. Noggin, an antagonist of BMP, abolished BMP-2-induced versican and HA as well as mRNA expression of versican and Has2. We further examined whether BMP-2-promoted cell migration was associated with expression of versican and HA. BMP-2- promoted cell migration was significantly impaired by treatments with versican siRNA and HA oligomer. In conclusion, we provide evidence that BMP-2 induces expression of versican and HA by AV CMCs and that these ECM components contribute to BMP-2-induced CMC migration, indicating critical roles for BMP-2 in distal outgrowth/expansion of mesenchymalized AV cushions.