Ppia, also known as peptidylprolyl isomerase A or cyclophilin A, is a central enzyme in the protein-folding response pathway [3]. It has peptidyl-prolyl cis/trans isomerase activity, which can catalyze the cis-trans isomerization of peptidyl-prolyl bonds in proteins, thus playing a crucial role in protein folding, assembly, and transport. Ppia is involved in multiple biological pathways and is important for normal cellular function [5].

In lung cancer, ablation of Ppia promotes NRF2 protein degradation and blocks NRF2-driven growth, indicating its role in promoting lung cancer progression [1]. Ppia -/- mice have significantly less fat and smaller adipocytes, and silencing Ppia in cell lines impairs adipocyte differentiation, suggesting it is a novel adipogenic factor in obesity [2]. In multiple myeloma, CRISPR-Cas9 deletion of PPIA or its inhibition with a small molecule inhibitor sensitizes tumor cells to proteasome inhibitors, highlighting it as a potential therapeutic target [3]. In oral cancer, reducing PPIA expression and secretion decreases cell invasion and migration, while recombinant PPIA treatment increases these processes, suggesting it may be a novel target and prognostic marker [4].

In conclusion, Ppia is essential for protein-folding-related functions and is involved in various disease-related biological processes. Studies using gene-knockout models, such as Ppia -/- mice, have revealed its role in cancer progression, obesity, and multiple myeloma, providing valuable insights into potential therapeutic strategies for these diseases.