Department of Pharmaceutical Biochemistry, Wroclaw Medical University, Borowska 211A, 50-556 Wrocław, Poland.
Int J Mol Sci. 2021 May 28;22(11):5809. doi: 10.3390/ijms22115809.
Albumin is the main protein of blood plasma, lymph, cerebrospinal and interstitial fluid. The protein participates in a variety of important biological functions, such as maintenance of proper colloidal osmotic pressure, transport of important metabolites and antioxidant action. Synthesis of albumin takes place mainly in the liver, and its catabolism occurs mostly in vascular endothelium of muscle, skin and liver, as well as in the kidney tubular epithelium. Long-lasting investigation in this area has delineated the principal route of its catabolism involving glomerular filtration, tubular endocytic uptake via the multiligand scavenger receptor tandem-megalin and cubilin-amnionless complex, as well as lysosomal degradation to amino acids. However, the research of the last few decades indicates that also additional mechanisms may operate in this process to some extent. Direct uptake of albumin in glomerular podocytes via receptor for crystallizable region of immunoglobulins (neonatal FC receptor) was demonstrated. Additionally, luminal recycling of short peptides into the bloodstream and/or back into tubular lumen or transcytosis of whole molecules was suggested. The article discusses the molecular aspects of these processes and presents the major findings and controversies arising in the light of the research concerning the last decade. Their better characterization is essential for further research into pathophysiology of proteinuric renal failure and development of effective therapeutic strategies.
白蛋白是血浆、淋巴液、脑脊液和间质液的主要蛋白质。该蛋白质参与多种重要的生物学功能，如维持适当的胶体渗透压、转运重要的代谢物和抗氧化作用。白蛋白的合成主要发生在肝脏，其分解代谢主要发生在肌肉、皮肤和肝脏的血管内皮以及肾小管上皮细胞中。在这一领域的长期研究已经描绘了其分解代谢的主要途径，包括肾小球滤过、通过多配体 scavenger 受体 tandem-megalin 和 cubilin-amnionless 复合物的管状内吞摄取，以及溶酶体降解为氨基酸。然而，过去几十年的研究表明，在这个过程中，还可能在某种程度上存在其他机制。已经证明了肾小球足细胞通过免疫球蛋白可结晶区域受体（新生儿 FC 受体）直接摄取白蛋白。此外，还提出了短肽从腔侧回收至血液以及/或再回到管状腔或整个分子的胞转的观点。本文讨论了这些过程的分子方面，并根据过去十年的研究提出了主要的发现和争议。进一步研究蛋白尿性肾衰竭的病理生理学和开发有效的治疗策略，需要对这些过程进行更好的描述。
