Institute of Clinical Biochemistry.
Institute of Functional and Applied Anatomy.
J Am Soc Nephrol. 2019 Jun;30(6):1021-1035. doi: 10.1681/ASN.2018090951. Epub 2019 Apr 30.
The etiology of steroid-resistant nephrotic syndrome, which manifests as FSGS, is not completely understood. Aberrant glycosylation is an often underestimated factor for pathologic processes, and structural changes in the glomerular endothelial glycocalyx have been correlated with models of nephrotic syndrome. Glycans are frequently capped by sialic acid (Sia), and sialylation's crucial role for kidney function is well known. Human podocytes are highly sialylated; however, sialylation's role in podocyte homeostasis remains unclear.
We generated a podocyte-specific sialylation-deficient mouse model ( ) by targeting CMP-Sia synthetase, and used histologic and ultrastructural analysis to decipher the phenotype. We applied CRISPR/Cas9 technology to generate immortalized sialylation-deficient podocytes (asialo-podocytes) for functional studies.
Progressive loss of sialylation in mice resulted in onset of proteinuria around postnatal day 28, accompanied by foot process effacement and loss of slit diaphragms. Podocyte injury led to severe glomerular defects, including expanded capillary lumen, mesangial hypercellularity, synechiae formation, and podocyte loss. , loss of sialylation resulted in mislocalization of slit diaphragm components, whereas podocalyxin localization was preserved. , asialo-podocytes were viable, able to proliferate and differentiate, but showed impaired adhesion to collagen IV.
Loss of cell-surface sialylation in mice resulted in disturbance of podocyte homeostasis and FSGS development. Impaired podocyte adhesion to the glomerular basement membrane most likely contributed to disease development. Our data support the notion that loss of sialylation might be part of the complex process causing FSGS. Sialylation, such as through a Sia supplementation therapy, might provide a new therapeutic strategy to cure or delay FSGS and potentially other glomerulopathies.
表现为 FSGS 的激素耐药性肾病综合征的病因尚不完全清楚。异常糖基化是病理过程中经常被低估的一个因素，肾小球内皮糖萼的结构变化与肾病综合征模型有关。聚糖经常被唾液酸 (Sia) 封顶，Sia 对肾功能的关键作用是众所周知的。人类足细胞高度唾液酸化；然而，足细胞内稳态中 Sia 的作用仍不清楚。
我们通过靶向 CMP-Sia 合成酶生成了一种足细胞特异性 Sia 缺陷型小鼠模型 ( )，并应用组织学和超微结构分析来破译表型。我们应用 CRISPR/Cas9 技术生成了永生化的 Sia 缺陷型足细胞（asialo-podocytes）用于功能研究。
小鼠中 Sia 的逐渐缺失导致出生后第 28 天左右出现蛋白尿，伴有足突融合和裂孔隔膜丢失。足细胞损伤导致严重的肾小球缺陷，包括扩张的毛细血管腔、系膜细胞增生、粘连形成和足细胞丢失。 ，Sia 的缺失导致裂孔隔膜成分的定位错误，而 podocalyxin 的定位得到保留。 ，asialo-podocytes是存活的，能够增殖和分化，但对胶原蛋白 IV 的黏附能力受损。
小鼠细胞表面 Sia 的缺失导致足细胞内稳态紊乱和 FSGS 的发展。足细胞黏附至肾小球基底膜的受损可能是疾病发展的主要原因。我们的数据支持这样一种观点，即 Sia 的缺失可能是导致 FSGS 的复杂过程的一部分。Sia 修饰，例如通过 Sia 补充治疗，可能为治疗或延缓 FSGS 以及潜在的其他肾小球疾病提供新的治疗策略。
