AFM-based nanoindentation indicates an impaired cortical stiffness in the AAV-PCSK9DY atherosclerosis mouse model

Incidence of microvascular dysfunction is increased in hyperlipidemic mice, reducing cerebral blood flow and impairing remote memory

Introduction

The development of cognitive dysfunction is not necessarily associated with diet-induced obesity. We hypothesized that cognitive dysfunction might require additional vascular damage, for example, in atherosclerotic mice.

Methods

We induced atherosclerosis in male C57BL/6N mice by injecting AAV-PCSK9DY (2x1011 VG) and feeding them a cholesterol-rich Western diet. After 3 months, mice were examined for cognition using Barnes maze procedure and for cerebral blood flow. Cerebral vascular morphology was examined by immunehistology.

Results

In AAV-PCSK9DY-treated mice, plaque burden, plasma cholesterol, and triglycerides are elevated. RNAseq analyses followed by KEGG annotation show increased expression of genes linked to inflammatory processes in the aortas of these mice. In AAV-PCSK9DY-treated mice learning was delayed and long-term memory impaired. Blood flow was reduced in the cingulate cortex (-17%), caudate putamen (-15%), and hippocampus (-10%). Immunohistological studies also show an increased incidence of string vessels and pericytes (CD31/Col IV staining) in the hippocampus accompanied by patchy blood-brain barrier leaks (IgG staining) and increased macrophage infiltrations (CD68 staining).

Discussion

We conclude that the hyperlipidemic PCSK9DY mouse model can serve as an appropriate approach to induce microvascular dysfunction that leads to reduced blood flow in the hippocampus, which could explain the cognitive dysfunction in these mice.

Mouse models of atherosclerosis in translational research

Atherosclerotic cardiovascular disease (CVD), the major cause of premature human mortality, is a chronic and progressive metabolic and inflammatory disease in large- and medium-sized arteries. Mouse models are widely used to gain mechanistic insights into the pathogenesis of atherosclerosis and have facilitated the discovery of anti-atherosclerotic drugs. Despite promising preclinical studies, many drug candidates have not translated to clinical use because of the complexity of disease patho-mechanisms including lipid metabolic traits and inflammatory, genetic, and hemodynamic factors. We review the current preclinical utility and translation potential of traditional [apolipoprotein E (APOE)- and low-density lipoprotein (LDL) receptor (LDLR)-deficient mice] and emerging mouse models that include partial carotid ligation and AAV8-Pcsk9-D377Y injection in atherosclerosis research and drug discovery. This article represents an important resource in atherosclerosis research.

A novel mouse model of diabetes, atherosclerosis and fatty liver disease using an AAV8-PCSK9-D377Y injection and dietary manipulation in db/db mice

Preclinical mouse models of cardiometabolic diseases are crucial to study the pathological mechanisms of cardiometabolic diseases and to explore potential new therapeutic agents. Using double-knockouts in the background of ApoE^-/- or Ldlr^-/- mice requires an extensive amount of breeding and is costly. A significant breakthrough in atherosclerosis research is the use of AAV8-PCSK9-D377Y (a gain-of-function mutant of PCSK9 which promotes LDLR degradation) injection which can induce hyperlipidemia, increased endothelial stiffness, vascular calcification, aneurysm, and atherosclerotic plaque development in normal C57BL/6J mice. The purpose of this study was to assess the possibility that the injection of AAV8-PCSK9 vectors in db/db mice (a well-established animal model of type 2 diabetes mellitus) produces a novel mouse model of diabetes, atherosclerosis and fatty liver disease to study the pathomechanisms of cardiometabolic disease and its complications. Db/db mice were injected with AAV8-PCSK9-D377Y (AAV8-PCSK9 for simplicity) or AAV8-control and fed with high-cholesterol diets for 8 weeks. Levels of total cholesterol (TC) and triglyceride (TG) were significantly elevated in AAV8-PCSK9-injected mice compared to the controls. AAV8-PCSK9 injection led to increased serum level of PCSK9, serious liver steatosis, hypercholesterolemia and atherosclerotic plaque as determined by aortic arch/roots histopathological staining, with Oil Red O, Masson-trichrome and hematoxylin-eosin staining. RNA sequencing and bioinformatics were used to assess the global gene expression in liver tissues. We conclude that AAV8-PCSK9 injection in db/db mice is a promising and time-efficient approach to induce diabetic atherosclerosis with fatty liver. This mouse model can be a new one to investigate the etiology and therapeutics of atherosclerosis with diabetes and fatty liver beyond the traditional model established in ApoE^-/- mice or LDLR^-/- mice receiving streptozotocin (STZ) injection.