Abstract

The importance of altered glycosphingolipid (GSL) metabolism is increasingly gaining attention as a characteristic of multiple chronic kidney diseases. Previously, we reported elevated levels of GSLs and neuraminidase (NEU) enzyme activity/expression in the urine or kidney of lupus patients and lupus-prone mice, and demonstrated NEU activity mediates the production of cytokines by lupus-prone mouse primary mesangial cells. This mediation occurs in part through TLR4 and p38/ERK MAPK signalling in response to lipopolysaccharide (LPS) and lupus serum (LS). However, the precise role of NEU1, the most abundant NEU in the kidney, is incompletely known. In this study, we investigated the effect of genetically reduced Neu1 levels in vitro and in vivo. Mesangial cells from non-autoimmune prone Neu1+/− C57BL/6 mice had significantly reduced NEU activity, cytokine expression and cytokine secretion in response to LS and LPS, thereby suggesting reducing Neu1 expression may reduce the inflammatory response in lupus nephritis. Disease was assessed in female B6.SLE1/2/3 lupus-prone mice with genetically reduced levels (Neu1+/−) or wild-type levels (Neu1+/+) of Neu1 from 28 to 44 weeks of age along with aged-matched C57BL/6 controls. Renal disease was unexpectedly mild in all B6.SLE1/2/3 mice despite evidence of systemic disease. B6.SLE1/2/3 Neu1+/− mice exhibited significantly reduced levels of renal NEU1 expression and changes in renal α-2,6 linked sialylated N-glycans compared to the Neu1+/+ or healthy C57BL/6 mice, but measures of renal and systemic disease were similar between the B6.SLE1/2/3 Neu1+/+ and Neu1+/− mice. We conclude that NEU1 is the NEU largely responsible for mediating cytokine release by mesangial cells, at least in vitro, but may not be involved in modulating renal GSL levels in vivo or impact onset of nephritis in lupus-prone mice. However, the effect of reduced NEU1 levels on disease may not be appreciated in the mild disease expression in our colony of B6.SLE1/2/3 mice. The impact of the altered renal sialylated N-glycan levels and potential role of NEU1 with respect to established nephritis (late disease) in lupus-prone mice bears further investigation.

摘要

改变鞘糖脂 (GSL) 代谢的重要性作为多种慢性肾脏疾病的一个特征越来越受到关注。以前，我们报道了狼疮患者和狼疮易发小鼠的尿液或肾脏中 GSL 和神经氨酸酶 (NEU) 酶活性/表达水平升高，并证明 NEU 活性介导了狼疮易发小鼠原代系膜细胞产生细胞因子。这种介导部分通过 TLR4 和 p38/ERK MAPK 信号传导以响应脂多糖 (LPS) 和狼疮血清 (LS)。然而，肾脏中最丰富的 NEU NEU1 的确切作用尚不完全清楚。在这项研究中，我们研究了基因降低的Neu1水平在体外和体内的影响. 来自非自身免疫倾向Neu1 +/- C57BL / 6 小鼠的系膜细胞响应 LS 和 LPS 显着降低 NEU 活性、细胞因子表达和细胞因子分泌，从而表明降低Neu1表达可能会降低狼疮性肾炎的炎症反应。疾病在雌性B6.SLE1 / 2/3狼疮易感小鼠评估与基因降低的水平（Neu1 +/-）或野生型水平（Neu1 + / +）的Neu1从28至44周龄aged-沿匹配的 C57BL/6 控件。尽管有全身性疾病的证据，但所有 B6.SLE1/2/3 小鼠的肾脏疾病出乎意料地轻微。B6.SLE1 / 2/3 Neu1 +/-与Neu1 + / +或健康 C57BL / 6 小鼠相比，小鼠表现出肾脏 NEU1 表达水平显着降低和肾脏 α-2,6 连接的唾液酸化 N-聚糖的变化，但 B6 之间肾脏和全身疾病的测量值相似。 SLE1 / 2/3 Neu1 + / +和Neu1 +/- 小鼠。我们得出结论，NEU1 是主要负责介导系膜细胞释放细胞因子的 NEU，至少在体外，但可能不参与调节体内肾 GSL 水平。或影响易患狼疮的小鼠肾炎的发作。然而，在我们的 B6.SLE1 / 2/3 小鼠群中的轻度疾病表达中，可能无法理解降低 NEU1 水平对疾病的影响。改变肾脏唾液酸化 N-聚糖水平的影响和 NEU1 对狼疮易发小鼠肾炎（晚期疾病）的潜在作用有待进一步研究。