Supplementary Material for: The Role of Extracellular Phosphate Levels on Kidney Disease Progression in a Podocyte Injury Mouse Model

<b><i>Background:</i></b> Hyperphosphatemia is a major accelerator of complications in chronic kidney disease and dialysis, and phosphate (Pi) binders have been shown to regulate extracellular Pi levels. Research on hyperphosphatemia in mouse models is scarce, and few models display hyperphosphatemia induced by glomerular injury, despite its relevance to human glomerular disease conditions. In this study, we investigated the involvement of hyperphosphatemia in kidney disease progression using a mouse model in which hyperphosphatemia is induced by focal segmental glomerulosclerosis (FSGS). <b><i>Methods:</i></b> We established the NEP25 mouse model in which FSGS-hyperphosphatemia is induced by podocyte injury and evaluated the effect of a Pi binder, sevelamer. <b><i>Results:</i></b> After disease induction, we confirmed a gradual increase in serum Pi accompanied by reduced renal function and observed increases in serum FGF23 and PTH. Treatment with sevelamer significantly reduced serum Pi and urinary Pi fractional excretion and suppressed increases in serum FGF23 and PTH. A high dose improved serum creatinine and tubular injury markers, and pathological analysis confirmed amelioration of glomerular and tubular damage. Gene expression and marker analysis suggested protective effects on tubular epithelial cells in the diseased kidney. Compared to disease control, NEP25 mice treated with sevelamer retained their mRNA expression of Klotho, a known FGF23 co-receptor and renoprotective factor. <b><i>Conclusions:</i></b> Hyperphosphatemia caused by renal function decline was observed in a FSGS-induced NEP25 mouse model. Studies using this model showed that Pi regulation had a positive impact on kidney disease progression, and notably on tubular epithelial cell injury, which indicates the importance of Pi regulation in the treatment of kidney disease progression.

**背景：** 高磷血症是慢性肾脏病及透析患者并发症发生的核心促进因素，磷（Pi）结合剂已被证实可有效调控细胞外磷（Pi）水平。目前针对小鼠模型中高磷血症的研究较为匮乏，且鲜有能够模拟肾小球损伤诱导的高磷血症模型，尽管该模型与人类肾小球疾病状态密切相关。本研究通过局灶节段性肾小球硬化症（focal segmental glomerulosclerosis, FSGS）诱导的高磷血症小鼠模型，探究了高磷血症在肾脏病进展中的作用。
**方法：** 本研究构建了足细胞损伤诱导局灶节段性肾小球硬化症-高磷血症的NEP25小鼠模型，并评估了磷（Pi）结合剂司维拉姆（sevelamer）的干预效果。
**结果：** 造模成功后，我们确认血清磷水平随病程逐渐升高，同时伴随肾功能下降，并观察到血清成纤维细胞生长因子23（FGF23）与甲状旁腺激素（PTH）水平上升。司维拉姆治疗可显著降低血清磷水平及尿磷排泄分数，同时抑制血清FGF23与PTH的升高。高剂量司维拉姆可改善血清肌酐水平及肾小管损伤标志物水平，病理分析证实其可缓解肾小球及肾小管损伤。基因表达与标志物分析显示，司维拉姆对患病肾脏中的肾小管上皮细胞具有保护作用。与疾病对照组相比，接受司维拉姆治疗的NEP25小鼠保留了Klotho的mRNA表达水平——Klotho是已知的FGF23共受体及肾脏保护因子。
**结论：** 本研究在FSGS诱导的NEP25小鼠模型中观察到肾功能下降引发的高磷血症。利用该模型开展的研究表明，磷水平调控对肾脏病进展具有积极影响，尤其可改善肾小管上皮细胞损伤，这提示磷水平调控在肾脏病进展治疗中的重要价值。