From the Council of Scientific and Industrial Research-Centre for Cellular and Molecular Biology, Hyderabad 500 007, India.
From the Council of Scientific and Industrial Research-Centre for Cellular and Molecular Biology, Hyderabad 500 007, India.
J Biol Chem. 2013 Nov 8;288(45):32326-32342. doi: 10.1074/jbc.M113.498337. Epub 2013 Sep 27.
Fibril formation of β2-microglobulin and associated inflammation occur in patients on long term dialysis. We show that the plasma protein haptoglobin prevents the fatty acid-promoted de novo fibril formation of β2-microglobulin even at substoichiometric concentration. The fibrils are cytotoxic, and haptoglobin abolishes the cytotoxicity by preventing fibril formation. Haptoglobin does not alleviate the cytotoxicity of preformed fibrils. Fibrillar β2-microglobulin is resistant to lysosomal degradation. However, the species of β2-microglobulin populated in the presence of haptoglobin is susceptible to degradation. We observed that haptoglobin interacts with oligomeric prefibrillar species of β2-microglobulin but not with monomeric or fibrillar β2-microglobulin that may underlie the molecular mechanism. 1,1'-Bis(4-anilino)naphthalene-5,5'-disulfonic acid cross-linking to haptoglobin significantly compromises its chaperone activity, suggesting the involvement of hydrophobic surfaces. Haptoglobin is an acute phase protein whose level increases severalfold during inflammation, where local acidosis can occur. Our data show that haptoglobin prevents fibril formation of β2-microglobulin under conditions of physiological acidosis (between pH 5.5 and 6.5) but with relatively decreased efficiency. However, compromise in its chaperone activity under these conditions is more than compensated by its increased level of expression under inflammation. Erythrolysis is known to release hemoglobin into the plasma. Haptoglobin forms a 1:1 (mol/mol) complex with hemoglobin. This complex, like haptoglobin, interacts with the prefibrillar species of β2-microglobulin, preventing its fibril formation and the associated cytotoxicity and resistance to intracellular degradation. Thus, our study demonstrates that haptoglobin is a potential extracellular chaperone for β2-microglobulin even in moderately acidic conditions relevant during inflammation, with promising therapeutic implications in β2-microglobulin amyloid-related diseases.
β2-微球蛋白的纤维形成和相关炎症发生在长期透析的患者中。我们表明，血浆蛋白触珠蛋白即使在亚化学计量浓度下也能防止脂肪酸促进的β2-微球蛋白的从头纤维形成。纤维是细胞毒性的，触珠蛋白通过防止纤维形成来消除细胞毒性。触珠蛋白不能减轻预先形成的纤维的细胞毒性。纤维状β2-微球蛋白抵抗溶酶体降解。然而，在触珠蛋白存在下存在的β2-微球蛋白的物种易于降解。我们观察到触珠蛋白与寡聚预纤维状β2-微球蛋白相互作用，但不与单体或纤维状β2-微球蛋白相互作用，这可能是其分子机制的基础。1,1'-双（4-苯胺基）萘-5,5'-二磺酸交联到触珠蛋白上会严重损害其伴侣活性，表明涉及疏水面。触珠蛋白是一种急性期蛋白，其水平在炎症期间增加数倍，局部酸中毒可能发生。我们的数据表明，触珠蛋白在生理酸中毒条件下（pH5.5 至 6.5 之间）但效率相对降低的情况下阻止β2-微球蛋白的纤维形成。然而，在这些条件下其伴侣活性的受损被其在炎症下表达水平的增加所补偿。众所周知，红细胞溶解会将血红蛋白释放到血浆中。触珠蛋白与血红蛋白形成 1:1（摩尔/摩尔）的复合物。该复合物与触珠蛋白一样，与β2-微球蛋白的预纤维状物质相互作用，阻止其纤维形成以及相关的细胞毒性和对细胞内降解的抗性。因此，我们的研究表明，触珠蛋白即使在炎症过程中相关的中度酸性条件下也是β2-微球蛋白的潜在细胞外伴侣，在β2-微球蛋白淀粉样相关疾病中有很有前途的治疗意义。
