Age-dependent changes in protein interaction partners of protein C

Protein C is a critical regulator of haemostasis, exerting anticoagulant, anti-inflammatory and cytoprotective effects through tightly coordinated interactions within the coagulation system. Protein C activity is dependent not only on circulating concentration, but also on its structure and functional interactions with other proteins. The plasma concentration, structure and functional activity of Protein C is known to change with age, but changes in protein-protein interactions (PPIs) of Protein C with age have not been investigated. Co-immunoprecipitation (coIP) was performed on plasma samples pooled in age groups spanning from neonates to adults using an anti-Protein C antibody. Eluates were subjected to LC-MS/MS, enriched and depleted proteins identified, and multivariate analysis, pair-wise comparisons, and functional enrichment analysis was performed. The Protein C co-precipitating proteome was found to change across development, with the most pronounced differences in the enrichment of Protein C seen in the youngest cohorts, the largest number of Protein C interaction partners identified in the 11–16 year-old group and the smallest number identified in the 6–10 year-old group. Protein C appears to associate with age-specific haemostatic, platelet, complement, and immune-related protein networks, suggesting that the surrounding protein context of Protein C differs across age. However, pathway analysis identified significant cross-over of pathways in which Protein C and interactors are involved in across age ranges, despite different proteins being identified as participating in these pathways. The findings of this study highlight global differences in the haemostatic system across normal development, and the complex and shifting role of the plasma proteome with age. Data are available via ProteomeXchange with identifier PXD077907.