Lan Xiqian, Wen Hongxiu, Saleem Moin A, Mikulak Joanna, Malhotra Ashwani, Skorecki Karl, Singhal Pravin C
Renal Molecular Research Laboratory, Feinstein Institute for Medical Research, Department of Medicine, Hofstra North Shore LIJ Medical School, NY, USA.
Renal Academic Unit, Department of Pediatrics, University of Bristol, Bristol, UK.
Exp Mol Pathol. 2015 Jun;98(3):491-501. doi: 10.1016/j.yexmp.2015.03.020. Epub 2015 Mar 18.
Clinical reports have demonstrated that higher rates of non-diabetic glomerulosclerosis in African Americans can be attributed to two coding sequence variants (G1 and G2) in the APOL1 gene; however, the underlying mechanism is still unknown. Kidney biopsy data suggest enhanced expression of APOL1/APOL1 variants (Vs) in smooth muscle cells (SMCs) of renal vasculature. Since APOL1 is a secretory protein of relatively low molecular weight (41kDa), SMCs may be a contributory endocrine/paracrine source of APOL1 wild type (WT)/APOL1Vs in the glomerular capillary perfusate percolating podocytes. In the present study, we tested the hypothesis that an HIV milieu stimulated secretion of APOL1 and its risk variants by arterial SMCs contributes to podocyte injury. Human umbilical artery smooth muscle cells (HSMCs)-treated with conditioned media (CM) of HIV-infected peripheral mononuclear cells (PBMC/HIV-CM), CM of HIV-infected U939 cells, or recombinant IFN-γ displayed enhanced expression of APOL1. Podocytes co-cultured in trans-wells with HSMCs-over expressing APOL1WT showed induction of injury; however, podocytes co-cultured with HSMC-over expressing either APOL1G1 or APOL1G2 showed several folds greater injury when compared to HSMC-over expressing APOL1WT. Conditioned media collected from HSMC-over-expressing APOL1G1/APOL1G2 (HSMC/APOL1G1-CM or HSMC/APOL1G2-CM) also displayed higher percentages of injured podocytes in the form of swollen cells, leaky lysosomes, loss of viability, and enhanced sensitivity to adverse host factors when compared to HSMC/APOL1WT-CM. Notably, HSMC/APOL1WT-CM promoted podocyte injury only at a significantly higher concentrations compared to HSMC/APOL1G1/G2-CM. We conclude that HSMCs could serve as an endocrine/paracrine source of APOL1Vs, which mediate accelerated podocyte injury in HIV milieu.
临床报告表明，非裔美国人中较高的非糖尿病性肾小球硬化率可归因于载脂蛋白L1（APOL1）基因中的两个编码序列变异（G1和G2）；然而，其潜在机制仍不清楚。肾活检数据表明，肾血管平滑肌细胞（SMC）中APOL1/APOL1变异体（Vs）的表达增强。由于APOL1是一种相对低分子量（41kDa）的分泌蛋白，因此SMC可能是肾小球毛细血管灌流足细胞中APOL1野生型（WT）/APOL1Vs的内分泌/旁分泌来源。在本研究中，我们测试了以下假设：HIV环境刺激动脉SMC分泌APOL1及其风险变异体，从而导致足细胞损伤。用人脐动脉平滑肌细胞（HSMC）分别处理HIV感染的外周单核细胞的条件培养基（PBMC/HIV-CM）、HIV感染的U939细胞的条件培养基或重组干扰素-γ，结果显示APOL1的表达增强。与过表达APOL1WT的HSMC在转孔中共培养的足细胞显示出损伤诱导；然而，与过表达APOL1G1或APOL1G2的HSMC共培养的足细胞相比过表达APOL1WT的HSMC，损伤程度高出数倍。与HSMC/APOL1WT-CM相比，从过表达APOL1G1/APOL1G2的HSMC（HSMC/APOL1G1-CM或HSMC/APOL1G2-CM）收集的条件培养基也显示出更高比例的足细胞损伤，表现为细胞肿胀、溶酶体渗漏、活力丧失以及对不良宿主因素的敏感性增强。值得注意的是，与HSMC/APOL1G1/G2-CM相比，HSMC/APOL1WT-CM仅在显著更高的浓度下才促进足细胞损伤。我们得出结论，HSMC可作为APOL1Vs的内分泌/旁分泌来源，在HIV环境中介导加速的足细胞损伤。
