The carboxypeptidase U system in atherosclerosis

Subtitle:insights in carboxypeptidase U mediated pleiotropic effects of statins

Carboxypeptidase U (CPU) provides a molecular link between coagulation and fibrinolysis. By cleaving C-terminal lysines from partially degraded fibrin it counteracts efficient plasminogen activation, thereby attenuating the fibrinolytic rate. CPU circulates in plasma as the zymogen procarboxypeptidase U (proCPU). With this doctoral research we aimed to contribute to a better understanding of the clinical context and expression of CPU, mainly focusing on hyperlipidemia & atherosclerosis. In a first part, the influence of statin therapy on proCPU biology in statin-eligible patients with hyperlipidemia was explored in a proof-of-concept observational study. Treatment of hyperlipidemic individuals with statin therapy normalized their proCPU levels and on a functional level a resulting improvement of the fibrinolytic rate was observed. Moreover, this pilot study revealed that the statin-dependent decline in plasma proCPU concentrations is highly different interindividually with the largest improvement in fibrinolysis seen in patients with the highest pre-treatment proCPU levels. Additionally, evidence that the proCPU downregulation in response to statins is a pleiotropic effect of this therapy was also provided in a murine model of atherosclerosis. In a larger clinical study, we confirmed that plasma proCPU concentration and its expected effect on the fibrinolytic rate are increased in hyperlipidemic patients and these effects can be normalized by treatment with atorvastatin. High interindividual variation in proCPU levels was again observed in hyperlipidemic individuals, with proCPU levels up to 80% higher compared to normolipidemic controls. Interestingly, patients with the highest proCPU levels were not necessarily the individuals with the highest cholesterol levels. Lastly, we observed that the proCPU downregulation and the improvement of the plasma fibrinolysis by atorvastatin were dose-dependent. In the second part of this research, the expression of proCPU in (primary) human monocytes and macrophage-subsets was studied. CPB2 mRNA and proCPU protein was detected in all investigated cell types and it was found that CPB2 mRNA expression and proCPU secretion in monocytes and (activated) macrophages are related to the degree to which these cells are differentiated. Moreover, it was demonstrated that proCPU can be activated into functionally active CPU in the in vitro cell culture environment. During the conduct of this PhD research, some very interesting, CPU-related research questions came into the spotlight that we explored further. The first one was the functional characterization of a new mutation in the CPB2 gene of proCPU. This mutation resulted in a proCPU deficiency that was found to be clinically asymptomatic, but accelerated fibrinolysis in vitro. Finally, CPU-related parameters were evaluated in hospitalized COVID-19 patients, showing an initial significant generation of CPU with concomitant proCPU consumption during the early phase of SARS-CoV-2 infection, with a subsequent progressive increase in both proCPU concentration and CPU+CPUi antigen levels.

Publication year:2022

Keywords:Doctoral thesis

Accessibility:Open