Current update on theranostic roles of cyclophilin A in kidney diseases.

Cyclophilin A (CyPA) or peptidylprolyl isomerase A (PPIA), an immunophilin with peptidyl-prolyl isomerase (PPIase) activity, is an abundant cellular protein widely expressed across various cell types and tissues, including the kidney. Expression of CyPA in the kidney is relatively higher in proximal tubular epithelial cells than others along the nephron. Alterations in expression and secretion of CyPA play important roles in physiological processes and pathophysiology of several diseases affecting the kidney. Herein, we provide a brief overview of CyPA structural biology and present the current update on its theranostic roles in various kidney diseases, including diabetic nephropathy, acute kidney injury, chronic kidney disease, renal fibrosis, and nephrotoxicity associated with organ transplantation. Notably, the diagnostic/prognostic role for urinary CyPA in several of these kidney diseases is promising. Finally, future perspectives on the CyPA research, especially targeting CyPA for therapeutics, are discussed. A comprehensive understanding of the theranostic roles of CyPA in kidney diseases is expected to provide novel insights into the design of new therapeutic interventions and prevention strategies.