Liver Research Center, Beijing Friendship Hospital, Beijing Key Laboratory of Translational Medicine on Liver Cirrhosis, Capital Medical University, Beijing, 100050, China.
Beijing Institute of Clinical Medicine, Beijing Friendship Hospital, Capital Medical University, Beijing, 100050, China.
Hepatol Int. 2023 Jun;17(3):648-661. doi: 10.1007/s12072-022-10474-w. Epub 2023 Feb 2.
Pathogenic variants in HFE and non-HFE genes have been identified in hereditary hemochromatosis (HH) in different patient populations, but there are still a considerable proportion of patients with unexplained primary iron overload. We recently identified in Chinese patients with unexplained primary iron overload a recurrent p.L708V variant in the differentially expressed in normal and neoplastic cells domain 3 (DENND3) gene, functioning as a guanine nucleotide exchange factor for small GTpase Rab12 which down-regulates TfR expression in mice. We aim to investigate the pathogenicity and the underlying mechanism of the DENND3 p.L708V variant in HH patients.
Patients with primary iron overload were analyzed for DENND3 p.L708V. TFR2 and hepcidin expression in livers were examined in HH patients harboring DENND3 p.L708V. The effects of DENND3 p.L708V on RAB12/TFR2 and downstream iron metabolic pathways were investigated in vitro and in vivo.
Six of 31 patients with HH (19.35%) harbored the DENND3 p.L708V variant. The expression of TFR2 and hepcidin was decreased in the liver of HH patients with DENND3 p.L708V. Cells transfected with the DENND3 p.L708V vector showed up-regulation of RAB12 expression and TFR2 degradation in lysosomes, and down-regulation of the pSMAD1/5 and hepcidin. Mice models infected with adeno-associated virus expressing DENND3 p.L708V variant showed higher total serum iron concentrations and decreased HAMP level, increased amount of iron accumulation and the down-regulated of TFR2 expression in the liver.
The DENND3 p.L708V activating variant down-regulates hepcidin expression through the DENND3/RAB12/TFR2 axis, which may represent a potential novel pathogenic factor of HH.
在不同患者群体的遗传性血色素沉着症（HH）中，已经鉴定出 HFE 和非 HFE 基因的致病性变异，但仍有相当一部分患者的原发性铁过载原因不明。我们最近在患有原因不明的原发性铁过载的中国患者中发现，差异表达正常和肿瘤细胞域 3（DENND3）基因中的反复出现的 p.L708V 变异，作为小 GTpase Rab12 的鸟嘌呤核苷酸交换因子，下调小鼠中的 TfR 表达。我们旨在研究 HH 患者中 DENND3 p.L708V 变异的致病性和潜在机制。
分析原发性铁过载患者的 DENND3 p.L708V。研究携带 DENND3 p.L708V 的 HH 患者肝脏中 TFR2 和铁调素的表达。在体外和体内研究 DENND3 p.L708V 对 RAB12/TFR2 和下游铁代谢途径的影响。
31 名 HH 患者中有 6 名（19.35%）携带 DENND3 p.L708V 变异。携带 DENND3 p.L708V 的 HH 患者肝脏中 TFR2 和铁调素的表达减少。转染 DENND3 p.L708V 载体的细胞在溶酶体中显示 RAB12 表达上调和 TFR2 降解，以及 pSMAD1/5 和铁调素下调。感染表达 DENND3 p.L708V 变异的腺相关病毒的小鼠模型显示总血清铁浓度升高和 HAMP 水平降低，肝脏中铁积累增加和 TFR2 表达下调。
DENND3 p.L708V 激活变异通过 DENND3/RAB12/TFR2 轴下调铁调素表达，这可能代表 HH 的潜在新致病因素。
