Effects of intermittent hypoxia with thrombin in an in vitro model of human brain endothelial cells and their impact on PAR-1/PAR-3 cleavage

Hemostasis and endothelial functionality: the double face of coagulation factors

Hemostasis is a sophisticated sequence of events aimed at repairing vessel injury. This process occurs in combination with angiogenesis, which leads to new blood vessel formation, helping in wound repair and facilitating tissue healing. The fine mechanisms that regulate hemostasis and angiogenesis are well described, but for a long time, coagulation factors (CF) have been considered merely players in the coagulation cascade. However, evidence from several experiments highlights the crucial functions of these CF in regulating endothelial functionality, especially in the angiogenic process. Some of these CF (e.g., thrombin and tissue factor) have been widely investigated and have been described as triggering intracellular signaling related to endothelial cell (EC) functionality. For others (e.g., factor VIII and thrombomodulin), potential receptors and molecular mechanisms have not been fully elucidated but some data show their potential to induce EC response. This review focuses on the emerging roles of selected CF in regulating EC functions, highlighting in particular their ability to activate signaling pathways involved in angiogenesis, migration, proliferation and endothelial barrier stability.

Pleiotropic Effects of Direct Oral Anticoagulants in Chronic Heart Failure and Atrial Fibrillation: Machine Learning Analysis

Oral anticoagulant therapy (OAT) for managing atrial fibrillation (AF) encompasses vitamin K antagonists (VKAs, such as warfarin), which was the mainstay of anticoagulation therapy before 2010, and direct-acting oral anticoagulants (DOACs, namely dabigatran etexilate, rivaroxaban, apixaban, edoxaban), approved for the prevention of AF stroke over the last thirteen years. Due to the lower risk of major bleeding associated with DOACs, anticoagulant switching is a common practice in AF patients. Nevertheless, there are issues related to OAT switching that still need to be fully understood, especially for patients in whom AF and heart failure (HF) coexist. Herein, the effective impact of the therapeutic switching from warfarin to DOACs in HF patients with AF, in terms of cardiac remodeling, clinical status, endothelial function and inflammatory biomarkers, was assessed by a machine learning (ML) analysis of a clinical database, which ultimately shed light on the real positive and pleiotropic effects mediated by DOACs in addition to their anticoagulant activity.

Endothelial PDGF-D contributes to neurovascular protection after ischemic stroke by rescuing pericyte functions

Ischemic stroke induces neovascularization of the injured tissue as an attempt to promote structural repair and neurological recovery. Angiogenesis is regulated by pericytes that potently react to ischemic stroke stressors, ranging from death to dysfunction. Platelet-derived growth factor (PDGF) receptor (PDGFR)β controls pericyte survival, migration, and interaction with brain endothelial cells. PDGF-D a specific ligand of PDGFRβ is expressed in the brain, yet its regulation and role in ischemic stroke pathobiology remains unexplored. Using experimental ischemic stroke mouse model, we found that PDGF-D is transiently induced in brain endothelial cells at the injury site in the subacute phase. To investigate the biological significance of PDGF-D post-ischemic stroke regulation, its subacute expression was either downregulated using siRNA or upregulated using an active recombinant form. Attenuation of PDGF-D subacute induction exacerbates neuronal loss, impairs microvascular density, alters vascular permeability, and increases microvascular stalling. Increasing PDGF-D subacute bioavailability rescues neuronal survival and improves neurological recovery. PDGF-D subacute enhanced bioavailability promotes stable neovascularization of the injured tissue and improves brain perfusion. Notably, PDGF-D enhanced bioavailability improves pericyte association with brain endothelial cells. Cell-based assays using human brain pericyte and brain endothelial cells exposed to ischemia-like conditions were applied to investigate the underlying mechanisms. PDGF-D stimulation attenuates pericyte loss and fibrotic transition, while increasing the secretion of pro-angiogenic and vascular protective factors. Moreover, PDGF-D stimulates pericyte migration required for optimal endothelial coverage and promotes angiogenesis. Our study unravels new insights into PDGF-D contribution to neurovascular protection after ischemic stroke by rescuing the functions of pericytes.

Chronic intermittent hypoxia-induced cardiovascular and renal dysfunction: from adaptation to maladaptation

Chronic intermittent hypoxia (CIH) is the dominant pathological feature of human obstructive sleep apnoea (OSA), which is highly prevalent and associated with cardiovascular and renal diseases. CIH causes hypertension, centred on sympathetic nervous overactivity, which persists following removal of the CIH stimulus. Molecular mechanisms contributing to CIH-induced hypertension have been carefully delineated. However, there is a dearth of knowledge on the efficacy of interventions to ameliorate high blood pressure in established disease. CIH causes endothelial dysfunction, aberrant structural remodelling of vessels and accelerates atherosclerotic processes. Pro-inflammatory and pro-oxidant pathways converge on disrupted nitric oxide signalling driving vascular dysfunction. In addition, CIH has adverse effects on the myocardium, manifesting atrial fibrillation, and cardiac remodelling progressing to contractile dysfunction. Sympatho-vagal imbalance, oxidative stress, inflammation, dysregulated HIF-1α transcriptional responses and resultant pro-apoptotic ER stress, calcium dysregulation, and mitochondrial dysfunction conspire to drive myocardial injury and failure. CIH elaborates direct and indirect effects in the kidney that initially contribute to the development of hypertension and later to chronic kidney disease. CIH-induced morphological damage of the kidney is dependent on TLR4/NF-κB/NLRP3/caspase-1 inflammasome activation and associated pyroptosis. Emerging potential therapies related to the gut-kidney axis and blockade of aryl hydrocarbon receptors (AhR) are promising. Cardiorenal outcomes in response to intermittent hypoxia present along a continuum from adaptation to maladaptation and are dependent on the intensity and duration of exposure to intermittent hypoxia. This heterogeneity of OSA is relevant to therapeutic treatment options and we argue the need for better stratification of OSA phenotypes.

Distinct pleiotropic effects of direct oral anticoagulants on cultured endothelial cells: a comprehensive review

Direct Oral Anticoagulants (DOACs) have simplified the treatment of thromboembolic disease. In addition to their established anticoagulant effects, there are indications from clinical and preclinical studies that DOACs exhibit also non-anticoagulant actions, such as anti-inflammatory and anti-oxidant actions, advocating overall cardiovascular protection. In the present study, we provide a comprehensive overview of the existing knowledge on the pleiotropic effects of DOACs on endothelial cells (ECs) in vitro and their underlying mechanisms, while also identifying potential differences among DOACs. DOACs exhibit pleiotropic actions on ECs, such as anti-inflammatory, anti-atherosclerotic, and anti-fibrotic effects, as well as preservation of endothelial integrity. These effects appear to be mediated through inhibition of the proteinase-activated receptor signaling pathway. Furthermore, we discuss the potential differences among the four drugs in this class. Further research is needed to fully understand the pleiotropic effects of DOACs on ECs, their underlying mechanisms, as well as the heterogeneity between various DOACs. Such studies can pave the way for identifying biomarkers that can help personalize pharmacotherapy with this valuable class of drugs.

Does Perinatal Intermittent Hypoxia Affect Cerebrovascular Network Development?

Perinatal hypoxia is an inadequate delivery of oxygen to the fetus in the period immediately before, during, or after the birth process. The most frequent form of hypoxia occurring in human development is chronic intermittent hypoxia (CIH) due to sleep-disordered breathing (apnea) or bradycardia events. CIH incidence is particularly high with premature infants. During CIH, repetitive cycles of hypoxia and reoxygenation initiate oxidative stress and inflammatory cascades in the brain. A dense microvascular network of arterioles, capillaries, and venules is required to support the constant metabolic demands of the adult brain. The development and refinement of this microvasculature is orchestrated throughout gestation and in the initial weeks after birth, at a critical juncture when CIH can occur. There is little knowledge on how CIH affects the development of the cerebrovasculature. However, since CIH (and its treatments) can cause profound abnormalities in tissue oxygen content and neural activity, there is reason to believe that it can induce lasting abnormalities in vascular structure and function at the microvascular level contributing to neurodevelopmental disorders. This mini-review discusses the hypothesis that CIH induces a positive feedback loop to perpetuate metabolic insufficiency through derailment of normal cerebrovascular development, leading to long-term deficiencies in cerebrovascular function.

Loss of Blood-Brain Barrier Integrity in an In Vitro Model Subjected to Intermittent Hypoxia: Is Reversion Possible with a HIF-1α Pathway Inhibitor?

Several sleep-related breathing disorders provoke repeated hypoxia stresses, which potentially lead to neurological diseases, such as cognitive impairment. Nevertheless, consequences of repeated intermittent hypoxia on the blood-brain barrier (BBB) are less recognized. This study compared two methods of intermittent hypoxia induction on the cerebral endothelium of the BBB: one using hydralazine and the other using a hypoxia chamber. These cycles were performed on an endothelial cell and astrocyte coculture model. Na-Fl permeability, tight junction protein, and ABC transporters (P-gp and MRP-1) content were evaluated with or without HIF-1 inhibitors YC-1. Our results demonstrated that hydralazine as well as intermittent physical hypoxia progressively altered BBB integrity, as shown by an increase in Na-Fl permeability. This alteration was accompanied by a decrease in concentration of tight junction proteins ZO-1 and claudin-5. In turn, microvascular endothelial cells up-regulated the expression of P-gp and MRP-1. An alteration was also found under hydralazine after the third cycle. On the other hand, the third intermittent hypoxia exposure showed a preservation of BBB characteristics. Furthermore, inhibition of HIF-1α with YC-1 prevented BBB dysfunction after hydralazine treatment. In the case of physical intermittent hypoxia, we observed an incomplete reversion suggesting that other biological mechanisms may be involved in BBB dysfunction. In conclusion, intermittent hypoxia led to an alteration of the BBB model with an adaptation observed after the third cycle.