The following is a summary of “C1 inhibitor and prolylcarboxypeptidase modulate prekallikrein activation on endothelial cells,” published in the OCTOBER 2023 issue of Allergy & Immunology by Merkulova, et al.
For a study, researchers sought to investigate the regulation of prekallikrein (PK) activation on human microvascular endothelial cells (HMVECs) concerning the ambient levels of C1 inhibitor (C1INH) and prolylcarboxypeptidase (PRCP). They aimed to assess the specificity of PK activation on HMVECs by PRCP and to explore the role of C1INH in its regulation, as well as its impact on high-molecular-weight kininogen (HK) cleavage and the release of bradykinin (BK).
The research involved cultured HMVECs and employed various techniques, including immunofluorescence, enzymatic activity assays, immunoblots, small interfering RNA knockdowns, and cell transfections.
The cultured HMVECs were found to express PK, HK, C1INH, and PRCP consistently. The concentration of ambient C1INH influenced PK activation on HMVECs. In the absence of C1INH, activated PK (PKa) on HMVECs fully cleaved 120-kDa HK into a 65-kDa H-chain and a 46-kDa L-chain within 60 minutes. In the presence of 2 μM C1INH, only 50% of HK underwent cleavage. Different concentrations of C1INH (ranging from 0.0-2.5 μM) decreased but did not eliminate BK liberation from HK by activated PK. Furthermore, when incubated with HMVECs alone for 1 hour, factor XII did not activate. However, in the presence of HK and PK, factor XII became activated. The specificity of PK activation on HMVECs by PRCP was established through various inhibitors for each enzyme. Additionally, PRCP small interfering RNA knockdowns heightened the inhibitory effect of C1INH on PK activation, and PRCP transfections reduced C1INH inhibition at any given concentration.
The findings suggested that on HMVECs, PK activation and the cleavage of HK to release BK were subject to modulation based on local concentrations of C1INH and PRCP. The study sheds light on the intricate regulatory mechanisms governing these processes on endothelial cells.