Different cardiac tissue plasminogen activator release patterns by local stimulation of the endothelium and sympathetic nerves in pigs

Increased Prolylcarboxypeptidase Expression Can Serve as a Biomarker of Senescence in Culture

Prolylcarboxypeptidase (PRCP, PCP, Lysosomal Pro-X-carboxypeptidase, Angiotensinase C) controls angiotensin- and kinin-induced cell signaling. Elevation of PRCP appears to be activated in chronic inflammatory diseases [cardiovascular disease (CVD), diabetes] in proportion to severity. Vascular endothelial cell senescence and mitochondrial dysfunction have consistently been shown in models of CVD in aging. Cellular senescence, a driver of age-related dysfunction, can differentially alter the expression of lysosomal enzymes due to lysosomal membrane permeability. There is a lack of data demonstrating the effect of age-related dysfunction on the expression and function of PRCP. To explore the changes in PRCP, the PRCP-dependent prekallikrein (PK) pathway was characterized in early- and late-passage human pulmonary artery endothelial cells (HPAECs). Detailed kinetic analysis of cells treated with high molecular weight kininogen (HK), a precursor of bradykinin (BK), and PK revealed a mechanism by which senescent HPAECs activate the generation of kallikrein upon the assembly of the HK-PK complex on HPAECs in parallel with an upregulation of PRCP and endothelial nitric oxide (NO) synthase (eNOS) and NO formation. The NO production and expression of both PRCP and eNOS increased in early-passage HPAECs and decreased in late-passage HPAECs. Low activity of PRCP in late-passage HPAECs was associated with rapid decreased telomerase reverse transcriptase mRNA levels. We also found that, with an increase in the passage number of HPAECs, reduced PRCP altered the respiration rate. These results indicated that aging dysregulates PRCP protein expression, and further studies will shed light into the complexity of the PRCP-dependent signaling pathway in aging.

Histone deacetylase inhibition enhances tissue plasminogen activator release capacity in atherosclerotic man

The expression of the tissue plasminogen activator (t-PA) gene appears to be under epigenetic control and can be affected by histone deacetylation inhibition. The study aimed to test if histone deacetalyase inhibitor treatment lead to increased t-PA release or reduced exhaustion in t-PA release in response to stimulation, as well as change in plasminogen activator inhibitor-1 (PAI-1) in subjects with coronary disease. In this clinical study, 16 post-myocardial infarction subjects, the perfused forearm model was used with isoprenaline provocation during 20 minutes, to stimulate local t-PA release. Each subject was measured twice on the same day (repeated stimuli sequences) as well as on two different occasions, without treatment and after four weeks of treatment with valproic acid (500 mg, twice daily). Net forearm release for t-PA in response to isoprenaline at minutes 1.5, 3, 6, 9, 12, 15 and 18 was measured, allowing assessment of cumulative t-PA release. There was a reduction in the exhaustion of cumulative t-PA release during repeated and prolonged stimulation with valproic acid treatment compared to non-treatment. Plasma PAI-1 antigen was decreased following treatment compared to non-treatment (18.4 ± 10.0 vs. 11.0 ± 7.1 nanograms/ml respectively, mean with 95% confidence interval). These findings demonstrate that histone deacetylation inhibition increases the capacity for endogenous t-PA release in subjects with vascular disease. Furthermore, the fibrinolytic balance is favored with suppressed PAI-1 levels. More studies are needed to establish the clinical relevance of these findings.

TRIAL REGISTRATION

EU Clinical Trials Register 2012-004950-27.

β-blockade abolishes the augmented cardiac tPA release induced by transactivation of heterodimerised bradykinin receptor-2 and β2-adrenergic receptor in vivo

Bradykinin (BK) receptor-2 (B2R) and β2-adrenergic receptor (β2AR) have been shown to form heterodimers in vitro. However, in vivo proofs of the functional effects of B2R-β2AR heterodimerisation are missing. Both BK and adrenergic stimulation are known inducers of tPA release. Our goal was to demonstrate the existence of B2R-β2AR heterodimerisation in myocardium and to define its functional effect on cardiac release of tPA in vivo. We further investigated the effects of a non-selective β-blocker on this receptor interplay. To investigate functional effects of B2R-β2AR heterodimerisation (i. e. BK transactivation of β2AR) in vivo, we induced serial electrical stimulation of cardiac sympathetic nerves (SS) in normal pigs that underwent concomitant BK infusion. Both SS and BK alone induced increases in cardiac tPA release. Importantly, despite B2R desensitisation, simultaneous BK infusion and SS (BK+SS) was characterised by 2.3 ± 0.3-fold enhanced tPA release compared to SS alone. When β-blockade (propranolol) was introduced prior to BK+SS, tPA release was inhibited. A persistent B2R-β2AR heterodimer was confirmed in BK-stimulated and non-stimulated left ventricular myocardium by immunoprecipitation studies and under non-reducing gel conditions. All together, these results strongly suggest BK transactivation of β2AR leading to enhanced β2AR-mediated release of tPA. Importantly, non-selective β-blockade inhibits both SS-induced release of tPA and the functional effects of B2R-β2AR heterodimerisation in vivo, which may have important clinical implications.

Histone deacetylase inhibitor treatment increases coronary t-PA release in a porcine ischemia model

Background

The expression of the tissue plasminogen activator gene can be affected by histone deacetylation inhibition and thus appears to be under epigenetic control.

Objectives

The study aimed to test if in vivo pharmacological intervention by valproic acid treatment would lead to increase in tissue plasminogen activator release capacity.

Methods

In an anaesthetized pig model, a controlled transient coronary occlusion was used to stimulate coronary tissue plasminogen activator release in a valproic acid treated (one week) and a non-treated group. Coronary venous blood samples from the ischemic region were collected, great cardiac vein thermodilution flow measurements were performed, and trans-coronary tissue plasminogen activator fluxes were calculated. Plasminogen activator inhibitor-1 was also measured.

Results

Adequate sampling from the affected area after the 10 minute ischemic period was confirmed by lactate measurements. Fluxes for tissue plasminogen activator at minutes 1, 3, 5, 7 and 10 were measured and then used to present cumulative net tissue plasminogen activator release for the whole measurement period for both groups. Area under the curve was higher for the valproic acid treated group at 10 minutes; 932±173 nanograms (n = 12) compared to the non-treated group, 451±78 nanograms (n = 10, p = 0.023). There was no difference in levels of plasminogen activator inhibitor-1 between groups.

Conclusions

These findings support a proof of concept for histone deacetylation inhibition positive effect on tissue plasminogen activator expression in an in vivo setting. Further studies are needed to find an optimal way to implement histone deacetylation inhibition to achieve desired clinical changes in tissue plasminogen activator expression.