Xu Zhen, Jobe Shawn M, Ma Yan-Qing, Shavit Jordan A
Thrombosis and Hemostasis Program, Versiti Blood Research Institute, Milwaukee, Wisconsin, USA.
Department of Pediatrics and Human Development, Michigan State University, Lansing, Michigan, USA.
J Thromb Haemost. 2024 Feb;22(2):558-564. doi: 10.1016/j.jtha.2023.10.013. Epub 2023 Oct 20.
Leukocyte adhesion deficiency III (LAD-III) is a rare autosomal recessive syndrome characterized by functional deficiencies of platelets and leukocytes that occurs due to mutations in the FERMT3 gene encoding kindlin-3. Kindlin-3 is a FERM domain-containing adaptor protein that is essential in integrin activation. We have previously demonstrated that the FERM domain of kindlin-3 is structurally compact and plays an important role in supporting integrin activation in a mouse model. The impact of destabilizing the compact FERM domain in kindlin-3 on the development of LAD-III in humans remains uncertain.
To use primary cells from a patient with LAD-III to validate the role of the compact FERM domain in kindlin-3 function in platelets and leukocytes.
The patient is a 4-year-old girl who since infancy has displayed clinical features of LAD-III. Patient platelets and leukocytes were functionally analyzed, and structural analysis of the kindlin-3 variant was conducted.
We identified a novel homozygous missense mutation in the FERMT3 (c.412G>A, p.E138K) FERM domain. Substantially reduced levels of kindlin-3 were detected in the proband's platelets and leukocytes. Functional evaluation verified that integrin αIIbβ3-mediated platelet activation, spreading, and aggregation and β2-integrin-mediated neutrophil adhesion and spreading were significantly compromised. Structural analysis revealed that this newly identified E138K substitution in kindlin-3 destabilizes the compacted FERM domain, resulting in poor expression of kindlin-3 in blood cells and subsequent LAD-III.
We have identified a novel missense mutation and verified the functional significance of the compact kindlin-3 FERM domain in supporting integrin functions in platelets and leukocytes.
白细胞黏附缺陷III型（LAD-III）是一种罕见的常染色体隐性综合征，其特征为血小板和白细胞功能缺陷，由编码纽带蛋白-3的FERMT3基因突变引起。纽带蛋白-3是一种含FERM结构域的衔接蛋白，在整合素激活中起关键作用。我们之前已经证明，在小鼠模型中，纽带蛋白-3的FERM结构域结构紧密，在支持整合素激活方面发挥重要作用。破坏纽带蛋白-3中紧密的FERM结构域对人类LAD-III发病的影响仍不确定。
利用LAD-III患者的原代细胞，验证紧密的FERM结构域在纽带蛋白-3于血小板和白细胞中功能的作用。
该患者为一名4岁女孩，自婴儿期起就表现出LAD-III的临床特征。对患者的血小板和白细胞进行功能分析，并对纽带蛋白-3变体进行结构分析。
我们在FERMT3（c.412G>A，p.E138K）的FERM结构域中鉴定出一种新的纯合错义突变。在先证者的血小板和白细胞中检测到纽带蛋白-3水平大幅降低。功能评估证实，整合素αIIbβ3介导的血小板激活、铺展和聚集以及β2整合素介导的中性粒细胞黏附和铺展均受到显著损害。结构分析表明，在纽带蛋白-3中新发现的E138K替代使紧密的FERM结构域不稳定，导致纽带蛋白-3在血细胞中表达不佳，进而引发LAD-III。
我们鉴定出一种新的错义突变，并验证了紧密的纽带蛋白-3 FERM结构域在支持血小板和白细胞中整合素功能方面的功能意义。
