Research

Group of pathology and pharmacology of cardiovascular system

Main object of the research:
Our research group participates on the study of endothelial dysfunction, atherosclerosis and liver metabolism in experimental in vitro and in vivo models.

  • Our primary objective is the study of tissue and soluble endoglin (CD105, TGF-βRIII) and its related signaling in endothelial dysfunction and atherogenesis in mouse model of atherosclerosis and in vitro in endothelial cells.
  • Moreover, we study the effects of statins on tissue and soluble endoglin related signaling both in vivo and in vitro.
  • More recently we study the effects of soluble endoglin on cholesterol and bile acids metabolism in liver.

TISSUE AND SOLUBLE ENDOGLIN AS BIOMARKER OR INDUCER OF ENDOTHELIAL DYSFUNCTION

Endoglin (CD 105, TGF-β receptor III) is a homodimeric transmembrane glycoprotein that plays a regulatory role in TGF-β signaling. Endoglin expression was demonstrated in atherosclerotic vessels predominantly in endothelial cells and smooth muscle cells in various types of blood vessels in mice and humans, suggesting its participation on atherogenesis. Endoglin expression was also related to the expression of eNOS in endothelium, repair of the vessel wall, plaque neoangiogenesis, production of collagen and stabilization of atherosclerotic lesions. In addition, increased levels of soluble endoglin were associated with hypercholesterolemia, acute myocardial infarction and diabetes mellitus in humans. Moreover shedding of tissue endoglin and increased levels of soluble endoglin were related to inhibition of tissue TGF-β signaling in patients with preeclampsia and cancer.

Hypothetical model of endoglin role in atherosclerosis:
Endoglin expression by smooth muscle cells was suggested to be a response to injury of the vessel wall to atherogenic stimuli. Endoglin forms a functional complex with TGFβR II and TGF-β1 in vivo. This complex might activate either ALK-1/Smad1/5 signaling pathway or ALK-5/Smad2/3 signaling pathway. Activation of ALK-1/Smad1/5 signaling pathway might be related to plaque neovascularization and/or protection of endothelium due to increase in eNOS expression by VEGF. The role of activation of this pathway with respect to atherosclerosis is unclear.  On the other hand, activation of ALK-5/Smad2/3 signaling may result in increased eNOS production, anti-inflammatory effects via inhibition of NF-κB signaling, activation of transcription factor early growth response-1 (EGR-1), collagen production and plaque stabilization. Activation of endoglin/ALK-5/Smad2/3 signaling might represent an athero-protective mechanism in the vessel wall.

 

Soluble endoglin generation to the circulation. 

A soluble form of endoglin (sEng) is known to be an extracellular domain of the full-length membrane endoglin entering the systemic circulation in various conditions related to endothelial injury, activation, inflammation and senescence of endothelium. After testing several matrix metalloproteinases (MMPs) in HUVECs, sEng has been proposed as an N-terminal endoglin cleavage product chipped at position 586 predominantly by membrane-type metalloproteinase-14 (MMP-14).

Please see the mechanism below. ( Lopez-Novoa JM, Bernabeu C (2010). The physiological role of endoglin in the cardiovascular system. Am J Physiol Heart Circ Physiol 299(4): H959-974.)

<>

Tissue and soluble endoglin role in various pathological conditions

Endoglin plays dual role in various pathological conditions. Endoglin increases eNOS expression and protect vascular endothelium, whcich is important athero-protection, but on the other hand simulate neoangiogenesis which is important for cancerogenesis. Endoglin promotes fibrous tissue production, which may result in stabilization of atherosclerotic plaque, but on the other hand to cardiac or kidney fibrosis. Soluble endoglin might be considered as biomarker of altered function of endothelium or possibly inducer endothelial dysfunction in various cardivascular diseases.

 

Soluble endoglin as possible biomarker and/or inducer of endothelial dysfunction

Hypercholesterolemia, endothelial dysfunction, inflammation, atherosclerosis, type II diabetes mellitus, arterial hypertension, oxidative stress and changes in membrane endoglin expression were related to increased levels of sEng in blood. Soluble endoglin levels might be considered as a biomarker in diseases related to endothelial dysfunction and may reflect therapeutical intervention efficacy. To date, statins and LDL apheresis were shown to reduce sEng levels. Soluble endoglin might affect TGF-β/eNOS and/or BMP-9 signaling, suggesting its role in the development of endothelial dysfunction, as demonstrated in the microcirculation so far.

schema

Soluble endoglin and cholesterol and bile acids metabolism

Significantly elevated serum levels of sEng have been found in patients suffering from cystic fibrosis associated liver disease, Hepatitis C virus coupled with cirrhosis or in patients with hepatocellular carcinoma combined with cirrhosis. As there are currently no data focusing on functional aspects of sEng in the liver, we study the effects of sEng on the cholesterol and bile acids turnover in this organ. 

Cholesterol metabolism

Biliary cholesterol secretion is an important route for excretion of cholesterol. Biliary cholesterol output is driven by biliary bile acid secretion and is dependent as well on the expression and activity of canalicular ATP-binding cassette sub-family G member 5/8 (ABCG5/8) and multidrug resistance protein 2 (MDR2). MDR2 serves as a key phospholipid transporter. HDL cholesterol and LDL cholesterol are taken up from the blood by scavenger receptor class B type1 (SR-B1) and LDL receptor, respectively. 3-Hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, an early rate-limiting step in cholesterol biosynthesis catalyzes conversion of HMG CoA to mevalonate. SREBP-2 transcription factor binds and activates the promoters of SREBP-2-regulated genes of LDL receptor and HMG-CoA-reductase. The major enzyme of cholesterol esterification in the liver is acyl-CoA cholesterol acyltransferase 2 (ACAT2).

 

Bile acids metabolism

Bile formation is one of the essential functions of the liver. Bile plays a vital role in digestion and absorption of lipids in the intestine and bile serves for elimination of endogenous compounds and their metabolites, such as bilirubin or cholesterol. Moreover, bile also provides an important excretory route for exogenous substances, toxins, drugs and their metabolites. The key step in the whole process is secretion of osmotically active compounds, especially bile acids and glutathione, across the hepatocyte canalicular membrane into the bile capillaries, followed by passive movement of water. To generate the driving force for bile flow, solutes are transported into bile against a concentration gradient by energy-dependent transporters; bile salt exporting pump (BSEP) is essential for bile acid-dependent bile flow and multidrug resistance-associated protein (MRP 2) is crucial for bile acid-independent bile flow, which is based on the transport of glutathione and glutathione conjugates.

Na+taurocholate cotransporting polypeptide (NTCP) mediates sodium-dependent uptake of bile acids from the sinusoidal blood into hepatocytes. Sodium-independent basolateral uptake of bile acids is executed by transporters from organic anion transporting polypeptide (OATP) family. Bile acid efflux from hepatocytes back to blood is mediated by transporters from multidrug resistance-associated protein (MRP) family (MRP3, MRP4). BSEP and MRP2 are the major canalicular transporters for bile acid and glutathione excretion into bile, respectively. At least 14 enzymes have been shown to take part in the bile acid synthesis. Among these, cholesterol 7α-hydroxylase (CYP7A1) is a critical enzyme as it catalyzes the first and rate-limiting step of the classic pathway, which accounts for ~90% of bile acid synthesis.

 

© 2017 Charles University, Faculty of Pharmacy in Hradec Králové, Akademika Heyrovského 1203, 500 05 Hradec Králové, Czech Republic
Website information | Powered by Kentico