Viswanathan Pragasam, Rimer Jeffrey D, Kolbach Ann M, Ward Michael D, Kleinman Jack G, Wesson Jeffrey A
The Nephrology Division of the Medical College of Wisconsin, Department of Veterans Affairs Medical Center, 111K, 5000 West National Ave, Milwaukee, WI 53295, USA.
Urol Res. 2011 Aug;39(4):269-82. doi: 10.1007/s00240-010-0353-7. Epub 2011 Jan 13.
Tamm-Horsfall protein (THP) is thought to protect against calcium oxalate monohydrate (COM) stone formation by inhibiting COM aggregation. Several studies reported that stone formers produce THP with reduced levels of glycosylation, particularly sialic acid levels, which leads to reduced negative charge. In this study, normal THP was treated with neuraminidase to remove sialic acid residues, confirmed by an isoelectric point shift to higher pH. COM aggregation assays revealed that desialylated THP (ds-THP) promoted COM aggregation, while normal THP inhibited aggregation. The appearance of protein aggregates in solutions at ds-THP concentrations ≥1 μg/mL in 150 mM NaCl correlated with COM aggregation promotion, implying that ds-THP aggregation induced COM aggregation. The aggregation-promoting effect of the ds-THP was independent of pH above its isoelectric point, but was substantially reduced at low ionic strength, where protein aggregation was much reduced. COM aggregation promotion was maximized at a ds-THP to COM mass ratio of ~0.025, which can be explained by a model wherein partial COM surface coverage by ds-THP aggregates promotes crystal aggregation by bridging opposing COM surfaces, whereas higher surface coverage leads to repulsion between adsorbed ds-THP aggregates. Thus, desialylation of THP apparently abrogates a normal defensive action of THP by inducing protein aggregation, and subsequently COM aggregation, a condition that favors kidney stone formation.
Tamm-Horsfall蛋白（THP）被认为可通过抑制一水草酸钙（COM）聚集来预防COM结石形成。多项研究报告称，结石形成者产生的THP糖基化水平降低，尤其是唾液酸水平降低，这导致负电荷减少。在本研究中，用神经氨酸酶处理正常THP以去除唾液酸残基，通过等电点向更高pH值的偏移得以证实。COM聚集试验表明，去唾液酸化THP（ds-THP）促进COM聚集，而正常THP抑制聚集。在150 mM NaCl中，ds-THP浓度≥1 μg/mL的溶液中出现蛋白质聚集体与COM聚集促进相关，这意味着ds-THP聚集诱导了COM聚集。ds-THP的聚集促进作用在其等电点以上与pH无关，但在低离子强度下显著降低，此时蛋白质聚集也大大减少。当ds-THP与COM的质量比约为0.025时，COM聚集促进作用达到最大，这可以用一个模型来解释，即ds-THP聚集体对COM表面的部分覆盖通过桥接相对的COM表面促进晶体聚集，而更高的表面覆盖导致吸附的ds-THP聚集体之间的排斥。因此，THP的去唾液酸化显然通过诱导蛋白质聚集，进而诱导COM聚集，从而消除了THP正常的防御作用，而这种情况有利于肾结石形成。
