Amore Alessandro, Cirina Paola, Conti Giovanni, Brusa Paola, Peruzzi Licia, Coppo Rosanna
Nephrology, Dialysis and Transplantation Department, Regina Margherita Hospital-Torino, Torino, Italy.
Pharmaceutical Chemistry Science and Technology Institute, University of Torino, Torino, Italy.
J Am Soc Nephrol. 2001 Sep;12(9):1862-1871. doi: 10.1681/ASN.V1291862.
Abnormalities in circulating IgA1 have been demonstrated in patients with IgA nephropathy (IgAN). This study addresses the question of the functional significance of this alteration in creating mesangial injury. Biologic effects of selected IgA glycoforms isolated from serum of IgAN patients and controls and in vitro deglycosylated normal IgA were tested on cultured human mesangial cells (MC). IgA glycoforms, ranging from 250 to 500 kD molecular weight, were isolated by lectin affinity chromatography followed by HPLC. IgA and IgG content was measured by enzyme-linked immunosorbent assay. HPLC fractions were incubated with MC to evaluate proliferation and apoptosis rates and nitric oxide synthesis. Moreover, MC were conditioned with in vitro desialylated and degalactosylated normal IgA. Patients with IgAN displayed increased levels of IgA glycoforms exposing sialic acid in alpha2,6 linkage with N-acetylgalactosamine (Neu5Acalpha2,6GalNAc) (P < 0.02) and GalNAc (P < 0.05), indicating truncation of O-linked glycans of IgA1. Moreover, IgA glycoforms with increased exposure of mannose were observed (P < 0.03), suggesting a defective N-linked glycosylation. No modification in IgG glycosylation was detected. When incubated with MC, the IgA glycoforms isolated from patients with increased exposure of GalNAc, Neu5Acalpha2,6GalNAc, or mannose, significantly depressed the proliferation and increased the apoptotic rate and nitric oxide synthesis activity of cultured MC, in comparison with fractions isolated from controls. Similarly, in vitro desialylated and degalactosylated IgAs significantly depressed the proliferation and enhanced the apoptosis rates of MC. In conclusion, a significant modulation of several human MC functions exerted by serum IgA with increased exposure of GalNAc, Neu5Acalpha2,6GalNAc, and mannose residues isolated from IgAN patients is reported for the first time.
IgA肾病（IgAN）患者体内已证实存在循环IgA1异常。本研究探讨了这种改变在引发系膜损伤中的功能意义问题。对从IgAN患者和对照者血清中分离出的特定IgA糖型以及体外去糖基化的正常IgA对培养的人系膜细胞（MC）的生物学效应进行了测试。通过凝集素亲和层析继以高效液相色谱法（HPLC）分离出分子量在250至500kD之间的IgA糖型。采用酶联免疫吸附测定法测量IgA和IgG含量。将HPLC分离组分与MC共同孵育，以评估增殖率、凋亡率及一氧化氮合成情况。此外，用体外去唾液酸化和去半乳糖基化的正常IgA处理MC。IgAN患者体内暴露有与N - 乙酰半乳糖胺以α2,6键连接的唾液酸（Neu5Acalpha2,6GalNAc）（P < 0.02）和GalNAc（P < 0.05）的IgA糖型水平升高，表明IgA1的O - 连接聚糖截短。此外，还观察到甘露糖暴露增加的IgA糖型（P < 0.03），提示N - 连接糖基化存在缺陷。未检测到IgG糖基化的改变。与从对照者分离出的组分相比，当与MC共同孵育时，从暴露GalNAc、Neu5Acalpha2,6GalNAc或甘露糖增加的患者体内分离出的IgA糖型显著抑制培养的MC的增殖，并增加其凋亡率及一氧化氮合成活性。同样，体外去唾液酸化和去半乳糖基化的IgA显著抑制MC的增殖并提高其凋亡率。总之，首次报道了从IgAN患者体内分离出的暴露GalNAc、Neu5Acalpha2,6GalNAc和甘露糖残基增加的血清IgA对多种人MC功能有显著调节作用。
