Department of Endocrinology and Metabolism, Shandong Provincial Hospital, Cheeloo College of Medicine, Shandong University, Jinan, 250021 Shandong, China.
Department of Endocrinology and Metabolism, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, 250021 Shandong, China.
Oxid Med Cell Longev. 2022 Jul 4;2022:8956636. doi: 10.1155/2022/8956636. eCollection 2022.
Mutations of filamin B () gene can lead to a spectrum of autosomal skeletal malformations including spondylocarpotarsal syndrome (SCT), Larsen syndrome (LRS), type I atelosteogenesis (AO1), type III atelosteogenesis (AO3), and boomerang dysplasia (BD). Among them, LRS is milder while BD causes a more severe phenotype. However, the molecular mechanism underlying the differences in clinical phenotypes of different variants has not been fully determined. Here, we presented two patients suffering from autosomal dominant LRS and autosomal recessive vitamin D-dependent rickets type IA (VDDR-IA). Whole-exome sequencing revealed two novel missense variants in , c.4846A>G (p.T1616A) and c.7022T>G (p.I2341R), which are located in repeat 15 and 22 of filamin B, respectively. The expression of FLNB in the muscle tissue from our LRS patient was remarkably increased. And in vitro studies showed that both variants led to a lack of filopodia and accumulation of the mutants in the perinuclear region in HEK293 cells. We also found that c.4846A>G (p.T1616A) and c.7022T>G (p.I2341R) regulated endochondral osteogenesis in different ways. c.4846A>G (p.T1616A) activated AKT pathways through inhibiting SHIP2, suppressed the Smad3 pathway, and impaired the expression of Runx2 in both Saos-2 and ATDC5 cells. c.7022T>G (p.I2341R) activated both AKT and Smad3 pathways and increased the expression of Runx2 in Saos-2 cells, while in ATDC5 cells it activated AKT pathways through inhibiting SHIP2, suppressed the Smad3 pathway, and reduced the expression of Runx2. Our study demonstrated the pathogenic mechanisms of two novel variants in two different clinical settings and proved that variants could not only directly cause skeletal malformations but also worsen skeletal symptoms in the setting of other skeletal diseases. Besides, variants differentially affect skeletal development which contributes to clinical heterogeneity of FLNB-related disorders.
纤连蛋白 B () 基因突变可导致一系列常染色体骨骼畸形，包括脊椎颅面发育不良综合征（SCT）、拉森综合征（LRS）、I 型成骨不全症（AO1）、III 型成骨不全症（AO3）和回旋镖发育不良（BD）。其中，LRS 较轻，而 BD 则导致更严重的表型。然而，不同变异导致的临床表型差异的分子机制尚未完全确定。在这里，我们介绍了两名患有常染色体显性 LRS 和常染色体隐性维生素 D 依赖性佝偻病 I 型（VDDR-IA）的患者。全外显子组测序显示，在纤连蛋白 B 中发现了两个新的错义变异，c.4846A>G（p.T1616A）和 c.7022T>G（p.I2341R），分别位于纤连蛋白 B 的重复 15 和 22 中。我们 LRS 患者的肌肉组织中 FLNB 的表达显著增加。体外研究表明，这两种变异都导致缺乏丝状伪足和突变体在 HEK293 细胞的核周区域积聚。我们还发现，c.4846A>G（p.T1616A）和 c.7022T>G（p.I2341R）以不同的方式调节软骨内骨化。c.4846A>G（p.T1616A）通过抑制 SHIP2 激活 AKT 途径，抑制 Smad3 途径，并在 Saos-2 和 ATDC5 细胞中损害 Runx2 的表达。c.7022T>G（p.I2341R）激活 AKT 和 Smad3 途径，并增加 Saos-2 细胞中 Runx2 的表达，而在 ATDC5 细胞中，它通过抑制 SHIP2 激活 AKT 途径，抑制 Smad3 途径，并减少 Runx2 的表达。我们的研究证明了两种不同临床环境中两种新型 变异的致病机制，并证明 变异不仅可以直接导致骨骼畸形，还可以在其他骨骼疾病的背景下加重骨骼症状。此外， 变异差异影响骨骼发育，导致 FLNB 相关疾病的临床异质性。
