Department of Cell Biology and Biophysics, Faculty of Biology, University of Athens, Panepistimiopolis, Athens, Greece.
PLoS One. 2011;6(10):e26032. doi: 10.1371/journal.pone.0026032. Epub 2011 Oct 6.
Secretory Apolipoprotein J/Clusterin (sCLU) is a ubiquitously expressed chaperone that has been functionally implicated in several pathological conditions of increased oxidative injury, including aging. Nevertheless, the biological role of sCLU in red blood cells (RBCs) remained largely unknown. In the current study we identified sCLU as a component of human RBCs and we undertook a detailed analysis of its cellular topology. Moreover, we studied the erythrocytic membrane sCLU content during organismal aging, in conditions of increased organismal stress and accelerated RBCs senescence, as well as during physiological in vivo cellular senescence.
METHODOLOGY/PRINCIPAL FINDINGS: By using a combination of molecular, biochemical and high resolution microscopical methods we found that sCLU is a novel structural component of RBCs extra- and intracellular plasma membrane and cytosol. We observed that the RBCs membrane-associated sCLU decreases during organismal aging or exposure to acute stress (e.g. smoking), in patients with congenital hemolytic anemia, as well as during RBCs in vivo senescence. In all cases, sCLU reduction paralleled the expression of typical cellular senescence, redox imbalance and erythrophagocytosis markers which are also indicative of the senescence- and oxidative stress-mediated RBCs membrane vesiculation.
CONCLUSIONS/SIGNIFICANCE: We propose that sCLU at the mature RBCs is not a silent remnant of the erythroid precursors, but an active component being functionally implicated in the signalling mechanisms of cellular senescence and oxidative stress-responses in both healthy and diseased organism. The reduced sCLU protein levels in the RBCs membrane following cell exposure to various endogenous or exogenous stressors closely correlates to the levels of cellular senescence and redox imbalance markers, suggesting the usefulness of sCLU as a sensitive biomarker of senescence and cellular stress.
分泌载脂蛋白 J/ 簇蛋白 (sCLU) 是一种普遍表达的伴侣蛋白，它在多种氧化损伤增加的病理条件下具有功能，包括衰老。然而，sCLU 在红细胞 (RBC) 中的生物学作用在很大程度上仍然未知。在目前的研究中，我们鉴定 sCLU 为人类 RBC 的一个组成部分，并对其细胞拓扑结构进行了详细分析。此外，我们研究了在机体老化过程中、在机体应激增加和加速 RBC 衰老的情况下以及在生理体内细胞衰老过程中红细胞膜 sCLU 的含量。
方法/主要发现：通过使用分子、生化和高分辨率显微镜方法的组合，我们发现 sCLU 是 RBC 质膜和细胞溶质的新型结构成分。我们观察到，在机体老化或暴露于急性应激（例如吸烟）、先天性溶血性贫血患者以及体内 RBC 衰老期间，RBC 膜相关 sCLU 减少。在所有情况下，sCLU 的减少与典型细胞衰老、氧化还原失衡和红细胞吞噬的标志物表达平行，这也表明了衰老和氧化应激介导的 RBC 膜囊泡化。
结论/意义：我们提出，成熟 RBC 中的 sCLU 不是红细胞前体的沉默残留物，而是一种活跃的成分，它在细胞衰老和氧化应激反应的信号机制中具有功能，无论是在健康还是患病的机体中。细胞暴露于各种内源性或外源性应激源后，RBC 膜中的 sCLU 蛋白水平降低与细胞衰老和氧化还原失衡标志物的水平密切相关，这表明 sCLU 作为衰老和细胞应激的敏感生物标志物具有实用性。
