INSERM U1060, Laboratoire Carmen, Université Lyon 1, INRA U1235, INSA de Lyon, CENS, Centre de Recherche en Nutrition Humaine Rhône Alpes, Villeurbanne, Oullins, France; Hospices Civils de Lyon, Centre Hospitalier Lyon-Sud, Centre de Biologie Sud, Laboratoire de Biochimie moléculaire et métabolique, Pierre-Bénite, France.
INSERM U1060, Laboratoire Carmen, Université Lyon 1, INRA U1235, INSA de Lyon, CENS, Centre de Recherche en Nutrition Humaine Rhône Alpes, Villeurbanne, Oullins, France; Service de Biochimie et Biologie moléculaire Grand Est, Hospices Civils de Lyon, Groupement Hospitalier Est, Bron, France.
J Clin Lipidol. 2018 Sep-Oct;12(5):1244-1252. doi: 10.1016/j.jacl.2018.06.018. Epub 2018 Jul 7.
The LMF1 (lipase maturation factor 1) gene encodes a protein involved in lipoprotein lipase and hepatic lipase maturation. Homozygous mutations in LMF1 leading to severe hypertriglyceridemia (SHTG) are rare in the literature. A few additional rare LMF1 variants have been described with poor functional studies.
The aim of this study was to assess the frequency of LMF1 variants in a cohort of 385 patients with SHTG, without homozygous or compound heterozygous deleterious mutations identified in lipoprotein lipase (LPL), apolipoprotein A5 (APOA5), apolipoprotein C2 (APOC2), glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1 (GPIHBP1) genes, and to determine their functionality.
LMF1 coding variants were screened using denaturing high-performance liquid chromatography followed by direct sequencing. In silico studies of LMF1 variants were performed, followed by in vitro functional studies using human embryonic kidney 293T (HEK-293T) cells cotransfected with vectors encoding human LPL and LMF1 cDNA. LPL activity was measured in cell culture medium after heparin addition using human VLDL-TG as substrate.
Nineteen nonsynonymous coding LMF1 variants were identified in 65 patients; 10 variants were newly described in SHTG. In vitro, p.Gly172Arg, p.Arg354Trp, p.Arg364Gln, and p.Arg537Trp LMF1 variants decreased LPL activity, and the p.Trp464Ter variant completely abolished LPL activity. We identified a young girl heterozygote for the p.Trp464Ter variant and a homozygote carrier of the p.Gly172Arg variant with a near 50% decreased LPL activity in vitro and in vivo.
The study confirms the rarity of LMF1 variants in a large cohort of patients with SHTG. LMF1 variants are likely to be involved in multifactorial hyperchylomicronemia. Partial LMF1 defects could be associated with intermittent phenotype as described for p.Gly172Arg homozygous and p.Trp464Ter heterozygous carriers.
LMF1（脂肪酶成熟因子 1）基因编码一种参与脂蛋白脂肪酶和肝脂肪酶成熟的蛋白质。文献中很少报道导致严重高甘油三酯血症（SHTG）的 LMF1 纯合突变。已有少数其他罕见的 LMF1 变体被描述，但功能研究不佳。
本研究旨在评估 385 例 SHTG 患者中 LMF1 变体的频率，这些患者未发现脂蛋白脂肪酶（LPL）、载脂蛋白 A5（APOA5）、载脂蛋白 C2（APOC2）、糖基磷脂酰肌醇锚定高密度脂蛋白结合蛋白 1（GPIHBP1）基因中的纯合或复合杂合有害突变，并确定其功能。
使用变性高效液相色谱法（denaturing high-performance liquid chromatography，dHPLC）结合直接测序筛选 LMF1 编码变异。对 LMF1 变体进行计算机预测分析，然后使用转染编码人 LPL 和 LMF1 cDNA 的载体的人胚肾 293T（HEK-293T）细胞进行体外功能研究。用肝素添加后以人 VLDL-TG 为底物在细胞培养物中测量 LPL 活性。
在 65 例患者中发现了 19 个非同义编码 LMF1 变体；其中 10 个新变体在 SHTG 中被描述。体外研究表明，p.Gly172Arg、p.Arg354Trp、p.Arg364Gln 和 p.Arg537Trp LMF1 变体降低了 LPL 活性，而 p.Trp464Ter 变体完全消除了 LPL 活性。我们鉴定了一名携带 p.Trp464Ter 变体的杂合子年轻女孩和一名携带 p.Gly172Arg 变体的纯合子携带者，他们在体外和体内的 LPL 活性均降低了近 50%。
该研究证实了在一大群 SHTG 患者中 LMF1 变体的罕见性。LMF1 变体可能与多因素高乳糜微粒血症有关。部分 LMF1 缺陷可能与间歇性表型有关，如描述的 p.Gly172Arg 纯合子和 p.Trp464Ter 杂合子携带者。
