Schweitzer George G, Collier Sara L, Chen Zhouji, Eaton James M, Connolly Anne M, Bucelli Robert C, Pestronk Alan, Harris Thurl E, Finck Brian N
Department of Medicine, Division of Geriatrics and Nutritional Sciences, Washington University School of Medicine, 660 S. Euclid Ave, Box 8031, St. Louis, MO, 63110, USA.
JIMD Rep. 2015;23:113-22. doi: 10.1007/8904_2015_440. Epub 2015 May 13.
Rhabdomyolysis is an acute syndrome due to extensive injury of skeletal muscle. Recurrent rhabdomyolysis is often caused by inborn errors in intermediary metabolism, and recent work has suggested that mutations in the human gene encoding lipin 1 (LPIN1) may be a common cause of recurrent rhabdomyolysis in children. Lipin 1 dephosphorylates phosphatidic acid to form diacylglycerol (phosphatidic acid phosphohydrolase; PAP) and acts as a transcriptional regulatory protein to control metabolic gene expression. Herein, a 3-year-old boy with severe recurrent rhabdomyolysis was determined to be a compound heterozygote for a novel c.1904T>C (p.Leu635Pro) substitution and a previously reported genomic deletion of exons 18-19 (E766-S838_del) in LPIN1. Western blotting with patient muscle biopsy lysates demonstrated a marked reduction in lipin 1 protein, while immunohistochemical staining for lipin 1 showed abnormal subcellular localization. We cloned cDNAs to express recombinant lipin 1 proteins harboring pathogenic mutations and showed that the E766-S838_del allele was not expressed at the RNA or protein level. Lipin 1 p.Leu635Pro was expressed, but the protein was less stable, was aggregated in the cytosol, and was targeted for proteosomal degradation. Another pathogenic single amino acid substitution, lipin 1 p.Arg725His, was well expressed and retained its transcriptional regulatory function. However, both p.Leu635Pro and p.Arg725His proteins were found to be deficient in PAP activity. Kinetic analyses demonstrated a loss of catalysis rather than diminished substrate binding. These data suggest that loss of lipin 1-mediated PAP activity may be involved in the pathogenesis of rhabdomyolysis in lipin 1 deficiency.
横纹肌溶解症是一种由于骨骼肌广泛损伤引起的急性综合征。复发性横纹肌溶解症通常由中间代谢的先天性缺陷所致，近期研究表明，人类编码脂联素1（LPIN1）基因的突变可能是儿童复发性横纹肌溶解症的常见病因。脂联素1使磷脂酸去磷酸化形成二酰甘油（磷脂酸磷酸水解酶；PAP），并作为转录调节蛋白控制代谢基因的表达。在此，一名患有严重复发性横纹肌溶解症的3岁男孩被确定为LPIN1基因一个新的c.1904T>C（p.Leu635Pro）替换和一个先前报道的外显子18 - 19缺失（E766 - S838_del）的复合杂合子。用患者肌肉活检裂解物进行的蛋白质印迹分析显示脂联素1蛋白显著减少，而脂联素1的免疫组织化学染色显示亚细胞定位异常。我们克隆了cDNA以表达携带致病突变的重组脂联素1蛋白，并表明E766 - S838_del等位基因在RNA或蛋白质水平均未表达。脂联素1 p.Leu635Pro得以表达，但该蛋白稳定性较差，在细胞质中聚集，并被靶向蛋白酶体降解。另一个致病性单氨基酸替换，脂联素1 p.Arg725His，表达良好并保留其转录调节功能。然而，发现p.Leu635Pro和p.Arg725His蛋白均缺乏PAP活性。动力学分析表明是催化作用丧失而非底物结合减少。这些数据表明脂联素1介导的PAP活性丧失可能参与了脂联素1缺乏导致的横纹肌溶解症的发病机制。
