Atractylenolide I mitigates Alzheimer’s disease pathology in ApoE–/– mice via ARG1/nNOS axis and lipid homeostasis regulation

Abstract

Apolipoprotein E (ApoE) serves as a critical molecular nexus between Alzheimer’s disease (AD) and atherosclerosis, two age-associated inflammatory disorders that share vascular pathology, amyloid-beta (Aβ) deposition, and lipid dysregulation. Atractylenolide I (AI), a promising therapeutic candidate derived from Atractylodes macrocephala Koidz., exhibits multimodal bioactivities with demonstrated anti-inflammatory and neuroprotective properties. To explore its therapeutic potential against AD pathology, we use high-fat diet (HFD)-fed ApoE knockout (ApoE–/–) mice treated with or without AI for 12 weeks. Integrated bioinformatics analyses and experimental validation reveal that AI treatment markedly attenuates systemic lipid dyshomeostasis, particularly cerebral lipid deposition, suppresses neuroinflammation via downregulation of M1 macrophage polarization markers, and restores cognitive function through neuronal preservation in hippocampal regions. Mechanistically, AI orchestrates cholesterol efflux by up-regulating ATP-binding cassette transporter A1 (ABCA1) and liver X receptor (LXR) expression, while concurrently modulating the abundance of arginine biosynthesis metabolites (urea, malic acid, and creatinine) to rebalance neurovascular homeostasis. Notably, western blot and RT-qPCR analyses reveal that AI differentially regulates key enzymes including arginase 1 (ARG1) and simultaneously upregulates the expression of neuronal nitric oxide synthase (nNOS). Further molecular docking and surface plasmon resonance (SPR) analyses confirm the direct binding of AI to ARG1, indicating a novel neuroprotective mechanism involving the modulation of arginine metabolism. These findings delineate the pleiotropic effects of AI against AD pathology and establish a preclinical foundation for the development of AI-based therapeutics targeting neurodegenerative-cardiovascular comorbidities.

1. Introduction

Alzheimer’s disease (AD), the most prevalent neurodegenerative disorder, is characterized by the progressive accumulation of amyloid-β (Aβ) plaques and intraneuronal neurofibrillary tangles (NFTs), both of which are pathological hallmarks associated with chronic neuroinflammation and sustained neuronal degeneration [1]. In turn, atherosclerosis, a systemic inflammatory vasculopathy, shares overlapping pathophysiological mechanisms with AD, particularly their mutual association with Aβ metabolism and apolipoprotein E (ApoE) polymorphism [2,3]. The polymorphic ApoE protein, which exists as three major isoforms (ε2, ε3, and ε4), plays critical roles in cholesterol homeostasis, blood-brain barrier (BBB) integrity maintenance, and Aβ clearance, thereby implicating it in both AD pathogenesis and atherosclerotic progression [4–7].

Notably, transgenic models expressing human amyloid precursor protein (APP) variants exhibit accelerated atherogenesis, revealing mechanistic intersections between cerebral amyloidosis and vascular inflammation [8]. Genome-wide association studies further substantiate molecular crosstalk between these conditions through shared susceptibility loci [9]. Emerging evidence implicates Aβ-mediated macrophage activation as a critical amplifier of neurovascular inflammation. Specifically, cytotoxic Aβ species activate cerebral macrophages, triggering self-perpetuating neuroinflammation via cytokine overproduction and neuronal apoptosis [10].

Macrophage polarization dynamics underpin this pathological crosstalk [11,12]. Proinflammatory M1 polarization, characterized by increased tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1β secretion, as well as inducible nitric oxide synthase (iNOS) overexpression [13,14], exacerbates both neurotoxicity and vascular inflammation. Liver X receptors (LXRs) orchestrate inflammatory resolution through the dual regulation of cholesterol efflux (via ABCA1 induction) and the suppression of proinflammatory cytokines [15,16], emerging as key modulators of macrophage immune-metabolism [17]. Arginase 1 (ARG1), a cytoplasmic enzyme, acts as a pivotal regulator of macrophage functionality by regulating L-arginine metabolism, nitric oxide (NO) generation, inflammation, and oxidative stress. Neuronal nitric oxide synthase (nNOS), the primary NO-producing enzyme in the brain, mediates various functions, including learning, memory, synaptic plasticity, and neuronal development. It is also implicated in AD, psychiatric illnesses, and cognitive deficits [18]. The ARG1/NOS axis critically balances inflammatory responses through competitive substrate utilization, while ARG1 catalyzes the conversion of L-arginine to urea and L-ornithine, thus competing with NOS for substrate and modulating NO production.