Of mice and Marfan: genetic linkage analyses of the fibrillin genes, Fbn1 and Fbn2, in the mouse genome

FBN2 pathogenic variants in congenital contractural arachnodactyly with severe cardiovascular manifestations

PURPOSE

Congenital contractural arachnodactyly (CCA) is an extremely rare autosomal dominant connective tissue genetic disorder caused by pathogenic variants in FBN2. CCA is characterized by arachnodactyly, camptodactyly, contracture of major joints, scoliosis, pectus deformities, and crumpled ears, but rarely with lethal cardiovascular manifestations as in Marfan syndrome. It is imperative to conduct a comprehensive analysis and review of the pathogenesis of CCA resulting from pathogenic variants in FBN2 gene.

MATERIALS AND METHODS

Using whole-exome sequencing and Sanger sequencing, we identified a novel pathogenic splice-altering variant (c.4472-3C>A) in intron 34 of FBN2 gene in a CCA pedigree. The transcriptional result of the splicing-altering variant was analyzed by RNA sequencing. We systematically analyzed the clinical manifestations of all reported cases of CCA caused by splicing-altering pathogenic variants and focused on all the pathogenic variants in FBN2 gene that are associated with severe cardiovascular manifestations.

RESULTS

The splice-altering variant (c.4472-3C>A) in FBN2 was demonstrated to result in the exon 35 skipping and cause an in-frame deletion. Furthermore, we identified exons 31 to 35 may be a hotspot region in FBN2 gene associated with severe cardiovascular phenotype.

CONCLUSIONS

This study enriched the pathogenic spectrum of CCA and identified a hotspot region in FBN2 gene associated with severe cardiovascular manifestations. We recommend that patients carrying pathogenic variants in exons 31 to 35 of FBN2 pay more attention to cardiac evaluation.

The Fibrillin-1/VEGFR2/STAT2 signaling axis promotes chemoresistance via modulating glycolysis and angiogenesis in ovarian cancer organoids and cells

Background

Chemotherapy resistance is a primary reason of ovarian cancer therapy failure; hence it is important to investigate the underlying mechanisms of chemotherapy resistance and develop novel potential therapeutic targets.

Methods

RNA sequencing of cisplatin‐resistant and ‐sensitive (chemoresistant and chemosensitive, respectively) ovarian cancer organoids was performed, followed by detection of the expression level of fibrillin‐1 (FBN1) in organoids and clinical specimens of ovarian cancer. Subsequently, glucose metabolism, angiogenesis, and chemosensitivity were analyzed in structural glycoprotein FBN1‐knockout cisplatin‐resistant ovarian cancer organoids and cell lines. To gain insights into the specific functions and mechanisms of action of FBN1 in ovarian cancer, immunoprecipitation, silver nitrate staining, mass spectrometry, immunofluorescence, Western blotting, and Fӧrster resonance energy transfer‐fluorescence lifetime imaging analyses were performed, followed by in vivo assays using vertebrate model systems of nude mice and zebrafish.

Results

FBN1 expression was significantly enhanced in cisplatin‐resistant ovarian cancer organoids and tissues, indicating that FBN1 might be a key factor in chemoresistance of ovarian cancer. We also discovered that FBN1 sustained the energy stress and induced angiogenesis in vitro and in vivo, which promoted the cisplatin‐resistance of ovarian cancer. Knockout of FBN1 combined with treatment of the antiangiogenic drug apatinib improved the cisplatin‐sensitivity of ovarian cancer cells. Mechanistically, FBN1 mediated the phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR2) at the Tyr1054 residue, which activated its downstream focal adhesion kinase (FAK)/protein kinase B (PKB or AKT) pathway, induced the phosphorylation of signal transducer and activator of transcription 2 (STAT2) at the tyrosine residue 690 (Tyr690), promoted the nuclear translocation of STAT2, and ultimately altered the expression of genes associated with STAT2‐mediated angiogenesis and glycolysis.

Conclusions

The FBN1/VEGFR2/STAT2 signaling axis may induce chemoresistance of ovarian cancer cells by participating in the process of glycolysis and angiogenesis. The present study suggested a novel FBN1‐targeted therapy and/or combination of FBN1 inhibition and antiangiogenic drug for treating ovarian cancer.

Association between anti-fibrillin-2 protein induced retinal degeneration via intravitreous delivery and activated TGF-β signaling in mice

Fibrillin-2 (FBN2) is a major component of tissue microfibrils, and the decrease of FBN2 perturbs the signaling events mediated by TGF-β, thereby playing a role in macular degeneration. However, the association between the retinal degeneration resulting from the abnormality of FBN2 and the activation of TGF-β signaling has not been fully addressed. In the present study, the mice were divided into a normal control group (NC group), a phosphate-buffered saline (PBS) injection group (PBS group), and an anti-FBN2 protein injection group (anti-FBN2 group), and the mice in PBS and anti-FBN2 groups received the relevant treatment via the intravitreal injection once a week for three consecutive weeks. One week later after injection, the retinal morphology and visual function of the fundus were detected. Further, the expression of FBN2, TGF-β1, TGF-β2 and TGF-β3 in retina was measured using quantitative polymerase chain reaction (Q-PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. As a result, fundus examination suggests that after intravitreous injection of anti-FBN2 protein, there were a large patchy yellow white degeneration region and numerous pigmentations in the retina in anti-FBN2-treated mice; by contrast, there was no apparent change in mice from the NC and PBS groups. The retina suffered markedly damage, and the thickness of whole retina and outer nuclear layer markedly thinned. The expression of FBN2 was decreased whereas the levels of TGF-β1, TGF-β2, and TGF-β3 were upregulated. Together, our findings indicate that the intravitreous delivery of anti-FBN2 protein could induce retina degeneration in mice, accompanied by the higher activated TGF-β. The retinal degeneration mouse model established will provide a platform for the investigation of the retinal diseases.

AP-1 Oligodeoxynucleotides Reduce Aortic Elastolysis in a Murine Model of Marfan Syndrome

Marfan syndrome is characterized by high expression of matrix metalloproteinases (MMPs) in aortic smooth muscle cells (AoSMCs) associated with medial elastolysis and aortic root aneurysm. We aimed to reduce aortic elastolysis through decrease of MMP expression with decoy oligodeoxynucleotides (dODNs) neutralizing the transcription factor activating factor-1 (AP-1). AP-1 abundance in nuclear extracts as well as MMP-2 and MMP-9 expression were significantly increased in isolated mAoSMC of mgR/mgR Marfan mice compared to wild-type cells. Exposure to AP-1 neutralizing dODNs resulted in a significant reduction of basal and interleukin-1β-stimulated MMP expression and activity in mAoSMCs. Moreover, increased migration and formation of superoxide radical anions was substantially decreased in mAoSMCs by AP-1 dODN treatment. Aortic grafts from donor Marfan mice were treated with AP-1- dODN ex vivo and implanted as infrarenal aortic interposition grafts in mgR/mgR mice. Pretreatment of aortic grafts with AP-1 dODN led to reduced elastolysis, macrophage infiltration, and MMP activity. Permeability of the endothelial monolayer was increased for dODN in mgR/mgR aortae with observed loss of tight junction proteins ZO-1 and occludin, enabling dODN to reach the tunica media. Targeting AP-1 activity offers a new potential strategy to treat the vascular phenotype associated with Marfan syndrome.

Fibrillin-1, induced by Aurora-A but inhibited by BRCA2, promotes ovarian cancer metastasis

While Aurora-A (Aur A) provokes, BRCA2 restrains primary tumorigenesis, the roles of Aur A and BRCA2 in cancer metastasis remains unclear. Here, we show that the metastatic promoting markers SLUG, FBN1, and MMP2, 9, 13 are either stimulated or suppressed by Aur A or BRCA2, but the metastatic suppressors E-cadherin, β-catenin, and p53 are either inhibited or promoted by Aur A or BRCA2, leading to enhanced or reduced cell migration and invasion. Further study suggests that FBN1 inhibits E-cadherin and β-catenin, but stimulates MMP2, 9, 13. Depletion of SLUG abrogates FBN1 and MMP9, but increases E-cadherin, while p53 decreases both SLUG and FBN1. Animal assays demonstrate that FBN1 promotes both ovarian tumorigenesis and metastasis. Clinically, overexpression of BRCA2 or Aur A in ovarian cancer tissues predicts good or poor overall and disease free survivals. High expression of SLUG or FBN1 indicates poor overall survivals, whereas high expression of FBN1 but not of SLUG predicts poor disease free survival. No significant associations between p53 expression and patient survivals were found. Overall, FBN1, acts at the downstream of Aur A and BRCA2, promotes ovarian cancer metastasis through the p53 and SLUG-associated signaling, which may be useful for ovarian cancer diagnosis and treatment.

Collagen content in skin and internal organs of the tight skin mouse: an animal model of scleroderma

The Tight Skin mouse is a genetically induced animal model of tissue fibrosis caused by a large in-frame mutation in the gene encoding fibrillin-1 (Fbn-1). We examined the influence of gender on the collagen content of tissues in C57BL/6J wild type (+/+) and mutant Tight Skin (Tsk/+) mice employing hydroxyproline assays. Tissue sections were stained with Masson's trichrome to identify collagen in situ. Adult Tsk/+ mice skin contains ~15% more collagen, on average, than skin from +/+ mice of the same gender. The heart of Tsk/+ males had significantly more collagen than that of +/+ males. No significant gender differences were found in lungs and kidney collagen content. Overall, the collagen content of Tsk/+ males and +/+ males was higher than that of their Tsk/+ and +/+ female counterparts, respectively. Our data confirm increased deposition of collagen in skin and hearts of Tsk/+ mice; however, the effects of the Tsk mutation on collagen content are both tissue specific and gender specific. These results indicate that comparative studies of collagen content between normal and Tsk/+ mice skin and internal organs must take into account gender differences caused by expression of the androgen receptor.

Association of microsatellite markers near the fibrillin 1 gene on human chromosome 15q with scleroderma in a Native American population

OBJECTIVE

To localize disease genes for scleroderma, or systemic sclerosis (SSc), in a population of Choctaw Native Americans with a high prevalence of SSc, in which there is evidence of a possible founder effect.

METHODS

A candidate gene approach was used in which microsatellite alleles on human chromosomes 15q and 2q, homologous to the murine tight skin 1 (tsk1) and tsk2 loci, respectively, were analyzed in Choctaw SSc cases and race-matched normal controls for possible disease association. Genotyping first-degree relatives of the cases identified potential disease haplotypes, and haplotype frequencies were obtained by expectation-maximization and maximum-likelihood estimation methods. Simultaneously, the ancestral origins of contemporary Choctaw SSc cases were ascertained using census and historical records.

RESULTS

A multilocus 2-cM haplotype was identified on human chromosome 15q homologous to the murine tsk1 region, which showed a significantly increased frequency in SSc cases compared with controls. This haplotype contains 2 intragenic markers for the fibrillin 1 (FBN1) gene. Genealogical studies demonstrated that the SSc cases were distantly related, and their ancestry could be traced back to 5 founding families in the mid-eighteenth century. The probability that the SSc cases share this haplotype due to familial aggregation effects alone was calculated and found to be very low. There was no evidence of any microsatellite allele disturbances on chromosome 2q in the region homologous to the tsk2 locus or the region containing the interleukin-1 family.

CONCLUSION

A 2-cM haplotype on chromosome 15q that contains FBN1 is associated with scleroderma in Choctaw Native Americans from Oklahoma. This haplotype may have been inherited from common founders about 10 generations ago and may contribute to the high prevalence of SSc that is now seen.

B-cell deficiency does not abrogate development of cutaneous hyperplasia in mice inheriting the defective fibrillin-1 gene

Tight-skin (TSK) mouse, the experimental model for scleroderma, develops cutaneous hyperplasia, cardiac hypertrophy, pulmonary emphysema and autoimmunity against scleroderma target autoantigens. The cutaneous hyperplasia is associated with the accumulation of microfibrils and elastic fibers in the middle and deep dermis. Fibrillin-1 (Fbn-1) is a major component of the 10-12 nm microfibrils found in the extracellular matrix. In this study we report the identification of a genetic marker in the Fbn-1 gene that can distinguish the mutant phenotype. TSK mice exhibit an unique polymorphism in the Fbn-1 gene. RNA analysis, PCR analysis and sequence determination of the mutant gene showed that the Fbn-1 gene polymorphism is due to intragenic duplication of a segment of the gene coding for 3.0 Kb of mRNA sequence (10 Kb of the genome). Histological analysis of skin samples from F1 progeny obtained by crossing TSK mice with JH-/-, RAG2-/- or vit/vit showed a significant correlation between the inheritance of the defective Fbn-1 gene and the development of cutaneous hyperplasia. Further, our results also show that in mice deficient in mature B cells inheriting the defective Fbn-1 gene, development of cutaneous hyperplasia is not abrogated. Thus, production of autoantibodies or the presence of mature B lymphocytes do not play an integral role in the pathogenesis of cutaneous hyperplasia.

Identification of a conserved family of Meis1-related homeobox genes

Meis1 locus was isolated as a common site of viral integration involved in myeloid leukemia in BXH-2 mice. Meis1 encodes a novel homeobox protein belonging to the TALE (three amino acid loop extension) family of homeodomain-containing proteins. The homeodomain of Meis1 is the only known motif within the entire 390-amino-acid protein. Southern blot analyses using the Meis1 homeodomain as a probe revealed the existence family of Meis1-related genes (Mrgs) in several diverged species. In addition, the 3' untranslated region (UTR) Meis1 was remarkably conserved in evolution. To gain a further understanding of the role Meis1 plays in leukemia and development, as well as to identify conserved regions of the protein that might reveal function, we cloned and characterized Mrgs from the mouse and human genomes. We report the sequence of Mrg1 and MRG2 as well as their chromosomal locations in murine and human genomes. Both Mrgs share a high degree of sequence identity with the protein coding region of Meis1. We have also cloned the Xenopus laevis ortholog of (XMeis1). Sequence comparison of the murine and Xenopus clones reveals that Meis1 is highly conserved throughout its coding sequence as well as the 3' UTR. Finally, comparison of Meis1 and the closely related Mrgs to known homeoproteins suggests that Meis1 represents a new subfamily of TALE homeobox genes.

Fibrillin and elastin expression in skin regenerating from cultured keratinocyte autografts: morphogenesis of microfibrils begins at the dermo-epidermal junction and precedes elastic fiber formation

The temporo-spatial expression of fibrillin and elastin in skin regenerating from autologous keratinocyte grafts was studied in three burned children. Skin biopsies taken between 5 days and 17 months after grafting were investigated by conventional immunofluorescence, confocal laser scanning, and electron microscopy. Fibrillin, the major component of 10-12nm microfibrils, appeared 5 days after grafting in a band-like fashion similar to collagen VII at the prospective basement membrane, and the formed the characteristic microfibrillar candelabra at the dermo-epidermal junction by fusion of several fine microfibrils to communicating microfibrils projecting downward into the reticular layer of the neodermis. Four to five months after grafting, several communicating microfibrils were connected to a web of horizontally undulating microfibrils of the neodermis which had developed independently. Elastin was first identified in the deeper neodermis 1 month after grafting as granular aggregates and 4 months after grafting on fibrillar structures and surrounding capillaries of the upper neodermis. Association of elastin with microfibrils in the papillary dermis was not detectable before month 17. Our findings suggest that the cutaneous microfibrillar apparatus develops simultaneously at both the dermo-epidermal junction and the reticular dermis and is a prerequisite for elastic fiber formation. In addition, it might be a driving force for the formation of the papilla-rete ridge pattern.

A tandem duplication within the fibrillin 1 gene is associated with the mouse tight skin mutation

Mice carrying the Tight skin (Tsk) mutation have thickened skin and visceral fibrosis resulting from an accumulation of extracellular matrix molecules. These and other connective tissue abnormalities have made Tskl + mice models for scleroderma, hereditary emphysema, and myocardial hypertrophy. Previously we localized Tsk to mouse chromosome 2 in a region syntenic with human chromosome 15. The microfibrillar glycoprotein gene, fibrillin 1 (FBN1), on human chromosome 15q, provided a candidate for the Tsk mutation. We now demonstrate that the Tsk chromosome harbors a 30- to 40-kb genomic duplication within the Fbn1 gene that results in a larger than normal in-frame Fbn1 transcript. These findings provide hypotheses to explain some of the phenotypic characteristics of Tskl + mice and the lethality of Tsk/Tsk embryos.