De Pace Raffaella, Maroofian Reza, Paimboeuf Adeline, Zamani Mina, Zaki Maha S, Sadeghian Saeid, Azizimalamiri Reza, Galehdari Hamid, Zeighami Jawaher, Williamson Chad D, Fleming Emily, Zhou Dihong, Gannon Jennifer L, Thiffault Isabelle, Roze Emmanuel, Suri Mohnish, Zifarelli Giovanni, Bauer Peter, Houlden Henry, Severino Mariasavina, Patten Shunmoogum A, Farrow Emily, Bonifacino Juan S
Neurosciences and Cellular and Structural Biology Division, Eunice Kennedy Shriver National Institute of Child, Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
Department of Neuromuscular Disorders, UCL Queen Square Institute of Neurology, London WC1N 3BG, UK.
Brain. 2024 May 3;147(5):1751-1767. doi: 10.1093/brain/awad427.
BLOC-one-related complex (BORC) is a multiprotein complex composed of eight subunits named BORCS1-8. BORC associates with the cytosolic face of lysosomes, where it sequentially recruits the small GTPase ARL8 and kinesin-1 and -3 microtubule motors to promote anterograde transport of lysosomes toward the peripheral cytoplasm in non-neuronal cells and the distal axon in neurons. The physiological and pathological importance of BORC in humans, however, remains to be determined. Here, we report the identification of compound heterozygous variants [missense c.85T>C (p.Ser29Pro) and frameshift c.71-75dupTGGCC (p.Asn26Trpfs51)] and homozygous variants [missense c.196A>C (p.Thr66Pro) and c.124T>C (p.Ser42Pro)] in BORCS8 in five children with a severe early-infantile neurodegenerative disorder from three unrelated families. The children exhibit global developmental delay, severe-to-profound intellectual disability, hypotonia, limb spasticity, muscle wasting, dysmorphic facies, optic atrophy, leuko-axonopathy with hypomyelination, and neurodegenerative features with prevalent supratentorial involvement. Cellular studies using a heterologous transfection system show that the BORCS8 missense variants p.Ser29Pro, p.Ser42Pro and p.Thr66Pro are expressed at normal levels but exhibit reduced assembly with other BORC subunits and reduced ability to drive lysosome distribution toward the cell periphery. The BORCS8 frameshift variant p.Asn26Trpfs51, on the other hand, is expressed at lower levels and is completely incapable of assembling with other BORC subunits and promoting lysosome distribution toward the cell periphery. Therefore, all the BORCS8 variants are partial or total loss-of-function alleles and are thus likely pathogenic. Knockout of the orthologous borcs8 in zebrafish causes decreased brain and eye size, neuromuscular anomalies and impaired locomotion, recapitulating some of the key traits of the human disease. These findings thus identify BORCS8 as a novel genetic locus for an early-infantile neurodegenerative disorder and highlight the critical importance of BORC and lysosome dynamics for the development and function of the central nervous system.
BLOC-1相关复合物(BORC)是一种由八个亚基(命名为BORCS1-8)组成的多蛋白复合物。BORC与溶酶体的胞质面结合,在那里它依次招募小GTP酶ARL8以及驱动蛋白-1和驱动蛋白-3微管马达,以促进溶酶体在非神经元细胞中向周边细胞质以及在神经元中向轴突远端的顺向运输。然而,BORC在人类生理和病理方面的重要性仍有待确定。在此,我们报告了在来自三个不相关家庭的五名患有严重早发性婴儿神经退行性疾病的儿童中,鉴定出BORCS8基因的复合杂合变异[错义突变c.85T>C(p.Ser29Pro)和移码突变c.71-75dupTGGCC(p.Asn26Trpfs51)]以及纯合变异[错义突变c.196A>C(p.Thr66Pro)和c.124T>C(p.Ser42Pro)]。这些儿童表现出全面发育迟缓、重度至极重度智力残疾、肌张力减退、肢体痉挛、肌肉萎缩、面部畸形、视神经萎缩、伴有髓鞘形成减少的白质轴索性病变以及以幕上病变为主的神经退行性特征。使用异源转染系统进行的细胞研究表明,BORCS8错义变异p.Ser29Pro、p.Ser42Pro和p.Thr66Pro表达水平正常,但与其他BORC亚基的组装减少,且驱动溶酶体向细胞周边分布的能力降低。另一方面,BORCS8移码变异p.Asn26Trpfs51表达水平较低,完全无法与其他BORC亚基组装,也无法促进溶酶体向细胞周边分布。因此,所有BORCS8变异都是部分或完全功能丧失等位基因,因此可能具有致病性。敲除斑马鱼中的直系同源borcs8会导致脑和眼尺寸减小、神经肌肉异常以及运动能力受损,重现了人类疾病的一些关键特征。这些发现因此确定BORCS8是早发性婴儿神经退行性疾病的一个新的基因位点,并突出了BORC和溶酶体动力学对中枢神经系统发育和功能的至关重要性。