THE ROLE OF PERIVASCULAR CELL (PERICYTE) DYSFUNCTION IN HEPATIC COMPLICATIONS OF SEVERE DENGUE

The World Health Organisation listed dengue as one of its top ten threats to global public health in 2019, comparable to climate change and antimicrobial resistance, and one of only three infectious diseases on the list. Half of the world's population is at risk of dengue virus infection, mostly in low- and middle-income countries. Dengue disease normally manifest as a febrile syndrome, but in some patients the disease progresses into a severe phase presenting with generalised and acute blood and fluid leakage from blood vessels that can lead to systemic shock and death. With the current vaccine unsuitable for use in all settings, no specific antiviral drugs, and no prognostic markers to identify patients that will progress to severe disease, dengue poses an enormous health, economic and social burden on the affected countries and individuals. The liver is often compromised in severe dengue patients, leading to fluid accumulation in the abdomen and local haemorrhage; indeed, biomarkers of liver dysfunction correlate with dengue disease severity and a poor prognostic outcome. The ways in which severe dengue disease affects the liver, and in particular its vasculature, are not entirely understood at a mechanistic level and might provide important clues to identify patients at high risk of developing severe disease, and new ways of developing drugs to improve patient outcomes. This project will focus on understanding the development of blood vessel malfunction in the liver of severe dengue patients by focusing on the biology of the blood vessels affected by dengue haemorrhage. Liver blood vessels are formed of two cell types, endothelial cells lining the inner surface of the vessel and perivascular cells (hepatic stellate cells) enveloping the endothelial tubes. The function of pericytes is to closely regulate the function of endothelial cells and modulate the integrity of blood vessel. Our own research has shown for the first time that the presence of a viral protein called 'NS1', which is present in high concentration in the blood of severe dengue patients, prevents pericytes from performing this regulatory function. Indeed, our experiments showed that the NS1 protein disrupts the interaction between endothelial cells and pericytes, leaving the endothelial vessels naked and leaky because they lack pericytes. In this grant, we propose to study three separate ways in which dengue virus might be causing the dysfunction of liver hepatic stellate cells, and therefore provoking vessel leakage: (1) the impact of the NS1 protein present in patient blood, (2) direct infection of hepatic stellate cells by dengue virus, and (3) the release of inflammatory substances by infected liver cells (hepatocytes). While investigating these mechanisms, we will focus on how they change the identity of the hepatic stellate cells by causing their differentiation into different cell type and how they modify the hepatic stellate cells' relationship with blood vessels, affecting the integrity of the blood vessel barrier. Furthermore, we will investigate the behaviour of all four variants dengue viruses (serotypes) as the presentation of severe symptoms has been reported to differ depending on the predominant variant in each outbreak.