Panoply™ Human PPIA Knockdown Stable Cell Line

Loss of protein function is one of the major drivers of aging. Here, researchers have discovered that peptidyl prolyl isomerase A (PPIA, or cyclosporine A) is a major molecular chaperone in hematopoietic stem cells and progenitor cells. The absence of PPIA accelerates stem cell aging. Researchers found that proteins with intrinsically disordered regions (IDRs) are common substrates for PPIA. IDRs promote interactions with other proteins or nucleic acids and can trigger liquid-liquid phase separation. Over 20% of PPIA substrates are involved in the formation of supramolecular, membrane-free organelles. PPIA promotes phase separation and enhances cellular stress resistance by influencing regulators of stress granules (PABPC1), P-body (DDX6), and nucleolar (NPM1). Hematopoietic stem cell aging is associated with a posttranscriptional decrease in PPIA expression and a reduction in the translation of IDR-rich proteins. Here, researchers link the molecular chaperone PPIA to the synthesis of intrinsically disordered proteins, suggesting that impaired protein interaction networks and macromolecular aggregation may be potential determinants of hematopoietic stem cell aging.

To determine whether proline isomerization affects phase separation of PABPC1, researchers genetically modulated PPIA activity and assessed the dynamics of stress granule formation. Following sodium arsenite-induced stress, the absence of prolyl isomerase activity significantly reduced stress granule formation (Figure 1a), and PPIA knockdown cells were more prone to cell death after sodium arsenite treatment. Furthermore, reintroduction of the molecular chaperone partially restored stress granule formation in PPIA knockdown cells. Similar to the findings on PABPC1, researchers found reduced P-body formation in PPIA knockdown cells, manifested by weakened DDX6 staining (Figure 1b). Additionally, the nucleoli of PPIA knockdown cells were smaller and more fragmented, as evidenced by the nuclear distribution of NPM1 (Figure 1c). The combined data indicate that reduced PPIA activity significantly affected liquid-liquid phase separation in all three tested cases and decreased the ability of cells to form aggregates containing these PPIA substrate proteins.

Figure 1. PPIA regulates protein phase separation of its substrates. (Maneix L, et al., 2024)