De novo disruptive heterozygous MMP21 variants are potential predisposing genetic risk factors in Chinese Han heterotaxy children.

BACKGROUND: Heterotaxy syndrome (HTX) is caused by aberrant left-right patterning early in embryonic development, which results in abnormal positioning and morphology of the thoracic and abdominal organs. Currently, genetic testing discerns the underlying genetic cause in less than 20% of sporadic HTX cases, indicating that genetic pathogenesis remains poorly understood. In this study, we aim to garner a deeper understanding of the genetic factors of this disease by documenting the effect of different matrix metalloproteinase 21 (MMP21) variants on disease occurrence and pathogenesis. METHODS: Eighty-one HTX patients with complex congenital heart defects and 89 healthy children were enrolled, and we investigated the pathogenetic variants related to patients with HTX by exome sequencing. Zebrafish splice-blocking Morpholino oligo-mediated transient suppression assays were performed to confirm the potential pathogenicity of missense variants found in these patients with HTX. RESULTS: Three MMP21 heterozygous non-synonymous variants (c.731G > A (p.G244E), c.829C > T (p.L277F), and c.1459A > G (p.K487E)) were identified in three unrelated Chinese Han patients with HTX and complex congenital heart defects. Sanger sequencing confirmed that all variants were de novo. Cell transfection assay showed that none of the variants affect mRNA and protein expression levels of MMP21. Knockdown expression of mmp21 by splice-blocking Morpholino oligo in zebrafish embryos revealed a heart looping disorder, and mutant human MMP21 mRNA (c.731G > A, c.1459A > G, heterozygous mRNA (wild-type&c.731G > A), as well as heterozygous mRNA (wild-type& c.1459A > G) could not effectively rescue the heart looping defects. A patient with the MMP21 p.G244E variant was identified with other potential HTX-causing missense mutations, whereas the patient with the MMP21 p.K487E variant had no genetic mutations in other causative genes related to HTX. CONCLUSION: Our study highlights the role of the disruptive heterozygous MMP21 variant (p.K487E) in the etiology of HTX with complex cardiac malformations and expands the current mutation spectrum of MMP21 in HTX.

Exosomes as mediators and biomarkers in fibrosis.

Fibrosis is characterized by aberrant myofibroblast accumulation and excessive extracellular matrix deposition, which leads to organ failure and significantly contributes to mortality worldwide. Exosomes, which are extracellular nanovesicles with a diameter of 30-100 nm that are secreted into the extracellular space by various types of cells, facilitate intercellular communication by delivering different cargos such as proteins, mRNAs and microRNAs. Growing evidence indicates that exosomes play an important role in various fibrotic diseases. A deeper understanding of the effects of exosomes in fibrosis may help in exploring new diagnostic and therapeutic targets. In this review, we summarize recent findings on exosomes in fibrotic diseases, with a special focus on exosomal cargo dysregulation and their potential diagnostic and therapeutic value in fibrosis.