PCSK9 interactions: towards new tools for hypercholesterolemia therapy

Hypercholesterolemia is a pathological status related to high cholesterol level. Such disease is a form of hyperlipidemia and dyslipidemia associated to high-mortality rate complications, such as cardiovascular diseases and heart failure. European Society of Cardiology and Food and Drug Administration guidelines suggest to monitor hypercholesterolemia closely, especially in the case of high-risk patients, whose number is increasing year–by-year due to population aging. Today, available drugs to treat hypercholesterolemia include statins and antibodies that, particularly in the case of high-risk patients, are administered to reduce cholesterol by at least 50%. However, statins show side effects such as diabetes, myopathy, serious kidney problems, and are not recommended during pregnancy, whilst antibodies require parenteral administration and act on proteins involved in cholesterol homeostasis at extracellular level only. PCSK9 protein is a convertase whose level is directly related to cholesterol concentration in the blood and forms protein-protein complexes that are considered potential anti-hypercholesterolemia drug targets. However, till now, structure-based rational drug-design campaigns have relied only on the very poor structural information available for such complexes. This project aims to provide such structural information by combining X-ray based techniques, such as protein crystallography and small angle X-ray scattering, molecular dynamics and state-of-art deep learning protein-modelling techniques. Particularly, it will be investigated the promising interaction between PCSK9 and the N-terminal region of the LDLr, as well as between PCSK9 and selected proteins involved in its secretion, maturation, and degradation. Moreover, by considering that PCSK9 variants are strictly related to hypercholesterolemia onset, selected and already known loss- and gain-of-function PCSK9 variants will be investigated to assess the effect of the carried mutations on protein folding, as well as on the ability of the convertase to form protein-protein complexes associated to cholesterol homeostasis. In silico methods will be exploited to identify conserved residues involved in mutations and potentially related to hypercholesterolemia. Structural information on PCSK9-involving complexes will be exploited to outlines the topology of the molecular contacts, as well as the presence of candidate binding pockets to be screened by virtual screening techniques against drug libraries. Finally, based on such information, a drug-design campaign will be attempted to translate our results in new potential cholesterol lowering molecules.