Embryonic survival and severity of cardiac and craniofacial defects are affected by genetic background in fibroblast growth factor-16 null mice

Skeletal dysmorphology and mineralization defects in Fgf20 KO mice

Introduction

Fibroblast growth factor 20 (Fgf20), a member of the Fgf9 subfamily, was identified as an important regulator of bone differentiation and homeostasis processes. However, the role of Fgf20 in bone physiology has not been approached yet. Here we present a comprehensive bone phenotype analysis of mice with functional ablation of Fgf20.

Methods

The study conducts an extensive analysis of Fgf20 knockout mice compared to controls, incorporating microCT scanning, volumetric analysis, Fgf9 subfamily expression and stimulation experiment and histological evaluation.

Results

The bone phenotype could be detected especially in the area of​ the lumbar and caudal part of the spine and in fingers. Regarding the spine, Fgf20-/- mice exhibited adhesions of the transverse process of the sixth lumbar vertebra to the pelvis as well as malformations in the distal part of their tails. Preaxial polydactyly and polysyndactyly in varying degrees of severity were also detected. High resolution microCT analysis of distal femurs and the fourth lumbar vertebra showed significant differences in structure and mineralization in both cortical and trabecular bone. These findings were histologically validated and may be associated with the expression of Fgf20 in chondrocytes and their progenitors. Moreover, histological sections demonstrated increased bone tissue formation, disruption of Fgf20-/- femur cartilage, and cellular-level alterations, particularly in osteoclasts. We also observed molar dysmorphology, including root taurodontism, and described variations in mineralization and dentin thickness.

Discussion

Our analysis provides evidence that Fgf20, together with other members of the Fgf9 subfamily, plays a crucial regulatory role in skeletal development and bone homeostasis.

Patient-specific iPSC-derived cardiomyocytes reveal abnormal regulation of FGF16 in a familial atrial septal defect

AIMS

Congenital heart disease (CHD) frequently occurs in newborns due to abnormal formation of the heart or major blood vessels. Mutations in the GATA4 gene, which encodes GATA binding protein 4, are responsible for atrial septal defect (ASD), a common CHD. This study aims to gain insights into the molecular mechanisms of CHD using human-induced pluripotent stem cells (iPSCs) from a family cohort with ASD.

METHODS AND RESULTS

Patient-specific iPSCs possess the same genetic information as the donor and can differentiate into various cell types from all three germ layers in vitro, thus presenting a promising approach for disease modelling and molecular mechanism research. Here, we generated a patient-specific iPSC line (iPSC-G4T280M) from a family cohort carrying a hereditary ASD mutation in GATA4 gene (T280M), as well as a human embryonic stem cell line (ESC-G4T280M) carrying the isogenic T280M mutation using the CRISPR/Cas9 genome editing method. The GATA4-mutant iPSCs and ESCs were then differentiated into cardiomyocytes (CMs) to model GATA4 mutation-associated ASD. We observed an obvious defect in cell proliferation in cardiomyocytes derived from both GATA4T280M-mutant iPSCs (iPSC-G4T280M-CMs) and ESCs (ESC-G4T280M-CMs), while the impaired proliferation ability of iPSC-G4T280M-CMs could be restored by gene correction. Integrated analysis of RNA-Seq and ChIP-Seq data indicated that FGF16 is a direct target of wild-type GATA4. However, the T280M mutation obstructed GATA4 occupancy at the FGF16 promoter region, leading to impaired activation of FGF16 transcription. Overexpression of FGF16 in GATA4-mutant cardiomyocytes rescued the cell proliferation defect. The direct relationship between GATA4T280M and ASD was demonstrated in a human iPSC model for the first time.

CONCLUSIONS

In summary, our study revealed the molecular mechanism of the GATA4T280M mutation in ASD. Understanding the roles of the GATA4-FGF16 axis in iPSC-CMs will shed light on heart development and provide novel insights for the treatment of ASD and other CHD disorders.

The Multifunctional Contribution of FGF Signaling to Cardiac Development, Homeostasis, Disease and Repair

The current focus on cardiovascular research reflects society’s concerns regarding the alarming incidence of cardiac-related diseases and mortality in the industrialized world and, notably, an urgent need to combat them by more efficient therapies. To pursue these therapeutic approaches, a comprehensive understanding of the mechanism of action for multifunctional fibroblast growth factor (FGF) signaling in the biology of the heart is a matter of high importance. The roles of FGFs in heart development range from outflow tract formation to the proliferation of cardiomyocytes and the formation of heart chambers. In the context of cardiac regeneration, FGFs 1, 2, 9, 16, 19, and 21 mediate adaptive responses including restoration of cardiac contracting rate after myocardial infarction and reduction of myocardial infarct size. However, cardiac complications in human diseases are correlated with pathogenic effects of FGF ligands and/or FGF signaling impairment. FGFs 2 and 23 are involved in maladaptive responses such as cardiac hypertrophic, fibrotic responses and heart failure. Among FGFs with known causative (FGFs 2, 21, and 23) or protective (FGFs 2, 15/19, 16, and 21) roles in cardiac diseases, FGFs 15/19, 21, and 23 display diagnostic potential. The effective role of FGFs on the induction of progenitor stem cells to cardiac cells during development has been employed to boost the limited capacity of postnatal cardiac repair. To renew or replenish damaged cardiomyocytes, FGFs 1, 2, 10, and 16 were tested in (induced-) pluripotent stem cell-based approaches and for stimulation of cell cycle re-entry in adult cardiomyocytes. This review will shed light on the wide range of beneficiary and detrimental actions mediated by FGF ligands and their receptors in the heart, which may open new therapeutic avenues for ameliorating cardiac complications.

Fibroblast growth factor 9 subfamily and the heart

The fibroblast growth factor (FGF) 9 subfamily is a member of the FGF family, including FGF9, 16, and 20, potentially sharing similar biochemical functions due to their high degree of sequence homology. Unlike other secreted proteins which have a cleavable N-terminal secreted signal peptide, FGF9/16/20 have non-cleaved N-terminal signal peptides. As an intercellular signaling molecule, they are involved in a variety of complex responses in animal development. Cardiogenesis is controlled by many members of the transcription factor family. Evidence suggests that FGF signaling, including the FGF9 subfamily, has a pretty close association with these cardiac-specific genes. In addition, recent studies have shown that the FGF9 subfamily maintains functional adaptation and survival after myocardial infarction in adult myocardium. Since FGF9/16/20 are secreted proteins, their function characterization in cardiac regeneration can promote their potential to be developed for the treatment of cardioprotection and revascularization. Here, we conclude that the FGF9 subfamily roles in cardiac development and maintenance of postnatal cardiac homeostasis, especially cardiac function maturation and functional maintenance of the heart after injury.

Roles of FGF Signals in Heart Development, Health, and Disease

The heart provides the body with oxygen and nutrients and assists in the removal of metabolic waste through the blood vessels of the circulatory system. It is the first organ to form during embryonic morphogenesis. FGFs with diverse functions in development, health, and disease are signaling proteins, mostly as paracrine growth factors or endocrine hormones. The human/mouse FGF family comprises 22 members. Findings obtained from mouse models and human diseases with FGF signaling disorders have indicated that several FGFs are involved in heart development, health, and disease. Paracrine FGFs including FGF8, FGF9, FGF10, and FGF16 act as paracrine signals in embryonic heart development. In addition, paracrine FGFs including FGF2, FGF9, FGF10, and FGF16 play roles as paracrine signals in postnatal heart pathophysiology. Although FGF15/19, FGF21, and FGF23 are typical endocrine FGFs, they mainly function as paracrine signals in heart development or pathophysiology. In heart diseases, serum FGF15/19 levels or FGF21 and FGF23 levels decrease or increase, respectively, indicating their possible roles in heart pathophysiology. FGF2 and FGF10 also stimulate the cardiac differentiation of cultured stem cells and cardiac reprogramming of cultured fibroblasts. These findings provide new insights into the roles of FGF signaling in the heart and potential therapeutic strategies for cardiac disorders.

Advances in the Molecular Genetics of Non-syndromic Syndactyly

Syndactyly, webbing of adjacent digits with or without bony fusion, is one of the most common hereditary limb malformations. It occurs either as an isolated abnormality or as a component of more than 300 syndromic anomalies. There are currently nine types of phenotypically diverse nonsyndromic syndactyly. Non-syndromic syndactyly is usually inherited as an autosomal dominant trait, although the more severe presenting types and subtypes may show autosomal recessive or X-linked pattern of inheritance. The phenotype appears to be not only caused by a main gene, but also dependant on genetic background and subsequent signaling pathways involved in limb formation. So far, the principal genes identified to be involved in congenital syndactyly are mainly involved in the zone of polarizing activity and sonic hedgehog pathway. This review summarizes the recent progress made in the molecular genetics, including known genes and loci responsible for non-syndromic syndactyly, and the signaling pathways those genetic factors involved in, as well as clinical features and animal models. We hope our review will contribute to the understanding of underlying pathogenesis of this complicated disorder and have implication on genetic counseling.

PON3 knockout mice are susceptible to obesity, gallstone formation, and atherosclerosis

We report the engineering and characterization of paraoxonase-3 knockout mice (Pon3KO). The mice were generally healthy but exhibited quantitative alterations in bile acid metabolism and a 37% increased body weight compared to the wild-type mice on a high fat diet. PON3 was enriched in the mitochondria-associated membrane fraction of hepatocytes. PON3 deficiency resulted in impaired mitochondrial respiration, increased mitochondrial superoxide levels, and increased hepatic expression of inflammatory genes. PON3 deficiency did not influence atherosclerosis development on an apolipoprotein E null hyperlipidemic background, but it did lead to a significant 60% increase in atherosclerotic lesion size in Pon3KO mice on the C57BL/6J background when fed a cholate-cholesterol diet. On the diet, the Pon3KO had significantly increased plasma intermediate-density lipoprotein/LDL cholesterol and bile acid levels. They also exhibited significantly elevated levels of hepatotoxicity markers in circulation, a 58% increase in gallstone weight, a 40% increase in hepatic cholesterol level, and increased mortality. Furthermore, Pon3KO mice exhibited decreased hepatic bile acid synthesis and decreased bile acid levels in the small intestine compared with wild-type mice. Our study suggests a role for PON3 in the metabolism of lipid and bile acid as well as protection against atherosclerosis, gallstone disease, and obesity.

Heart-specific expression of FGF-16 and a potential role in postnatal cardioprotection

Fibroblast growth factor 16 (FGF-16) was originally cloned from rat heart. Subsequent investigation of mouse FGF-16, including generation of null mice, revealed a specific pattern of expression in the endocardium and epicardium, and role for FGF-16 during embryonic heart development. FGF-16 is expressed mainly in brown adipose tissue during rat embryonic development, but is expressed mainly in the murine heart after birth. There is also an apparent switch from limited endocardial and epicardial expression in the embryo to the myocardium in the perinatal period. The FGF-16 gene and its location on the X chromosome are conserved between human and murine species, and no other member of the FGF family shows this pattern of spatial and temporal expression. The human and murine FGF-16 gene promoter regions also share an equivalent location for TATA sequences, as well as adjacent putative binding sites for transcription factors linked to cardiac expression and response to stress. Recent evidence has implicated nonsense mutation of FGF-16 with increased cardiovascular risk, and FGF-16 supplementation with cardioprotection. Here we review the important role of FGF-16 in embryonic heart development, its gene regulation, and evidence for FGF-16 as an endogenous and exogenous cardiac-specific and protective factor in the postnatal heart. Moreover, given the conservation of the FGF-16 gene and its chromosomal location between species, the question of support for a cardiac role in the human population is also considered.

Identification of three novel FGF16 mutations in X-linked recessive fusion of the fourth and fifth metacarpals and possible correlation with heart disease

Nonsense mutations in FGF16 have recently been linked to X-linked recessive hand malformations with fusion between the fourth and the fifth metacarpals and hypoplasia of the fifth digit (MF4; MIM#309630). The purpose of this study was to perform careful clinical phenotyping and to define molecular mechanisms behind X-linked recessive MF4 in three unrelated families. We performed whole-exome sequencing, and identified three novel mutations in FGF16. The functional impact of FGF16 loss was further studied using morpholino-based suppression of fgf16 in zebrafish. In addition, clinical investigations revealed reduced penetrance and variable expressivity of the MF4 phenotype. Cardiac disorders, including myocardial infarction and atrial fibrillation followed the X-linked FGF16 mutated trait in one large family. Our findings establish that a mutation in exon 1, 2 or 3 of FGF16 results in X-linked recessive MF4 and expand the phenotypic spectrum of FGF16 mutations to include a possible correlation with heart disease.

A novel method, the Variant Impact On Linkage Effect Test (VIOLET), leads to improved identification of causal variants in linkage regions

The Human Genome Project was expected to individualize medicine by rapidly advancing knowledge of common complex disease through discovery of disease-causing genetic variants. However, this has proved challenging. Although linkage analysis has identified replicated chromosomal regions, subsequent detection of causal variants for complex traits has been limited. One explanation for this difficulty is that utilization of association to follow up linkage is problematic given that linkage and association are not required to co-occur. Indeed, co-occurrence is likely to occur only in special circumstances, such as Mendelian inheritance, but cannot be universally expected. To overcome this problem, we propose a novel method, the Variant Impact On Linkage Effect Test (VIOLET), which differs from other quantitative methods in that it is designed to follow up linkage by identifying variants that influence the variance explained by a quantitative trait locus. VIOLET's performance was compared with measured genotype and combined linkage association in two data sets with quantitative traits. Using simulated data, VIOLET had high power to detect the causal variant and reduced false positives compared with standard methods. Using real data, VIOLET identified a single variant, which explained 24% of linkage; this variant exhibited only nominal association (P=0.04) using measured genotype and was not identified by combined linkage association. These results demonstrate that VIOLET is highly specific while retaining low false-negative results. In summary, VIOLET overcomes a barrier to gene discovery and thus may be broadly applicable to identify underlying genetic etiology for traits exhibiting linkage.

Angiotensin II-induced cardiac hypertrophy and fibrosis are promoted in mice lacking Fgf16

Fibroblast growth factors (Fgfs) are pleiotropic proteins involved in development, repair and metabolism. Fgf16 is predominantly expressed in the heart. However, as the heart function is essentially normal in Fgf16 knockout mice, its role has remained unclear. To elucidate the pathophysiological role of Fgf16 in the heart, we examined angiotensin II-induced cardiac hypertrophy and fibrosis in Fgf16 knockout mice. Angiotensin II-induced cardiac hypertrophy and fibrosis were significantly promoted by enhancing Tgf-β1 expression in Fgf16 knockout mice. Unexpectedly, the response to cardiac remodeling was apparently opposite to that in Fgf2 knockout mice. These results indicate that Fgf16 probably prevents cardiac remodeling, although Fgf2 promotes it. Cardiac Fgf16 expression was induced after the induction of Fgf2 expression by angiotensin II. In cultured cardiomyocytes, Fgf16 expression was promoted by Fgf2. In addition, Fgf16 antagonized Fgf2-induced Tgf-β1 expression in cultured cardiomyocytes and noncardiomyocytes. These results suggest a possible mechanism whereby Fgf16 prevents angiotensin II-induced cardiac hypertrophy and fibrosis by antagonizing Fgf2. The present findings should provide new insights into the roles of Fgf signaling in cardiac remodeling.

Dynamic regulation of the cerebral cavernous malformation pathway controls vascular stability and growth

Cardiovascular growth must balance stabilizing signals required to maintain endothelial connections and network integrity with destabilizing signals that enable individual endothelial cells to migrate and proliferate. The cerebral cavernous malformation (CCM) signaling pathway utilizes the adaptor protein CCM2 to strengthen endothelial cell junctions and stabilize vessels. Here we identify a CCM2 paralog, CCM2L, that is expressed selectively in endothelial cells during periods of active cardiovascular growth. CCM2L competitively blocks CCM2-mediated stabilizing signals biochemically, in cultured endothelial cells, and in developing mice. Loss of CCM2L reduces endocardial growth factor expression and impairs tumor growth and wound healing. Our studies identify CCM2L as a molecular mechanism by which endothelial cells coordinately regulate vessel stability and growth during cardiovascular development, as well as postnatal vessel growth.

Strain-specific modifier genes governing craniofacial phenotypes

BACKGROUND

The presence of strain-specific modifier genes is known to modulate the phenotype and pathophysiology of mice harboring genetically engineered mutations. Thus, identification of genetic modifier genes is requisite to understanding control of phenotypic expression. c-Ski is a transcriptional regulator. Ski(-/-) mice on a C57BL6J (B6) background exhibit facial clefting, while Ski(-/-) mice on a 129P3 (129) background present with exencephaly.

METHODS

In the present study, oligonucleotide-based gene expression profiling was used to identify potential strain-specific modifier gene candidates present in wild type mice of B6 and 129 genetic backgrounds. Changes in gene expression were verified by TaqMan quantitative real-time PCR.

RESULTS

Steady-state levels of 89 genes demonstrated a significantly higher level of expression, and those of 68 genes demonstrated a significantly lower level of expression in the developing neural tubes from embryonic day (E) 8.5, B6 embryos when compared to expression levels in neural tubes derived from E 8.5, 129 embryos.

CONCLUSIONS

Based on the results from the current comparative microarray study, and taking into consideration a number of relevant published reports, several potential strain-specific gene candidates, likely to modify the craniofacial phenotypes in various knockout mouse models have been identified.

Role for p21-activated kinase PAK4 in development of the mammalian heart

The serine-threonine kinase PAK4 plays a pivotal role in cell proliferation, survival, and control of the cytoskeleton. Mice that lack Pak4 die in midgestation prior to embryonic day E11 from unidentified causes. Analysis of PAK4 protein levels demonstrated that it was highly expressed in the whole embryo and in the developing heart but became low in the hearts of adult mice. In this study we analyzed development of the heart in conventional and conditional Pak4 knockout mice and embryos. We found that in conventional Pak4 knockout mice cardiogenesis is strongly affected from early developmental stages and by E9.5, hearts of Pak4⁻/⁻ embryos developed multiple profound deficits. Conditional deletion of Pak4 in the progenitors of the secondary heart field led to abnormal development of the outflow tract, in which the pulmonary artery had a smaller diameter, and the aortal wall was thinner than in wildtype mice. The conditional knockout mice also displayed the characteristic enlargement of the right ventricles and right atria. Pak4⁻/⁻ embryos and cardiomyocytes in which PAK4 was depleted exhibited low levels of LIMK1, a protein that plays key roles in cytoskeletal organization. Knock down of PAK4 in cultured cardiomyocytes led to severely compromised sarcomeric structure and deficits in contraction. These results indicate that PAK4 functions, including control of actin dynamics, are necessary for normal development of the heart.

Fibroblast growth factors: from molecular evolution to roles in development, metabolism and disease

Fibroblast growth factors (FGFs) are a family of structurally related polypeptides that are essential for embryonic development and that function postnatally as homoeostatic factors, in the response to injury, in the regulation of electrical excitability of cells and as hormones that regulate metabolism. In humans, FGF signalling is involved in developmental, neoplastic, metabolic and neurological diseases. Fgfs have been identified in metazoans but not in unicellular organisms. In vertebrates, FGFs can be classified as having intracrine, paracrine and endocrine functions. Paracrine and endocrine FGFs act via cell-surface FGF receptors (FGFRs); while, intracrine FGFs act independent of FGFRs. The evolutionary history of the Fgf family indicates that an intracrine Fgf is the likely ancestor of the Fgf family. During metazoan evolution, the Fgf family expanded in two phases, after the separation of protostomes and deuterostomes and in the evolution of early vertebrates. These expansions enabled FGFs to acquire diverse actions and functions.