Abstract Background Systemic administration of atherogenic, electronegative very-low-density lipoprotein (VLDL), which does not penetrate the blood-brain barrier (BBB), has been shown to induce parenchymal inflammation and behavioral disorders in mice. Similarly, human plasma high-density lipoprotein (HDL) can be chromatographically separated into five subfractions (H1 to H5), with H5 being the most electronegative and proinflammatory. Accumulating evidence suggests that Alzheimer’s disease is a brain manifestation of systemic metabolic derangement. It is therefore critical to determine whether dysfunctional HDL, such as H5, contributes to neuronal damage by disrupting the BBB. Purpose To test this hypothesis, we investigated whether H5—but not H1, the least electronegative and most health-beneficial HDL subfraction—can disrupt the BBB by inducing vascular endothelial cell (EC) death, thereby leading to neuronal DNA damage, axonopathy, and senescence. Methods We investigated the apoptotic effects of H5 and H1 in aortic and brain microvascular ECs to prepare for an isolated brain microvessel (IBM) study. Subsequently, we examined the impact of H1 and H5 on neuronal cells, using solvent-treated cells as a control. We used differentiated SH-SY5Y human neuronal cells and primary mouse neuronal cells (from newborn mice) to assess cell apoptosis (PI/Calcein staining), dendritic arborization (Sholl analysis), and length (Sholl analysis in primary mouse neuronal cells). Furthermore, we monitored reactive oxygen species (ROS) accumulation (MitoSox), DNA damage (8-oxodG), cellular senescence (β-gal), and cytosolic β-amyloid (Aβ)40 and Aβ42 production (ELISA). Finally, transcriptomics analysis was performed to identify the signaling pathways involved in H5-induced pathology. Results In a cohort, H5% (H5/HDL%) was greater in patients with metabolic syndrome (MetS; 3.0 ± 1.7%; n=34) than in healthy controls (2.3 ± 1.2%; n=46; p=0.01). We thus used the MetS-H1 and H5. H5 induces apoptosis in both aortic and brain microvascular ECs in a concentration-dependent manner. H5% increased with increases in systolic BP, total cholesterol, triglycerides, and Lp(a) (Fig. 1). Of great significance, proteomics revealed a significantly greater Lp(a) content in H5 than in H1. H5, but not H1, increased apoptosis in both human and primary mouse neuronal cells, as well as reducing dendritic arborization and length. Moreover, H5 induced cellular DNA damage, ROS accumulation, and senescence, potentially due to H5-induced production of Aβ40 and Aβ42 (Fig. 2). Transcriptomics indicated that H5-induced neuronal cell senescence was mediated by p21-dependent pathways. Conclusion This is the first report that apo(a) is associated with an electronegative HDL subfraction (H5), other than the well-described Lp(a). By potentially disrupting the BBB, H5 may contribute to neurodegeneration by directly damaging neuronal DNA and increasing proinflammatory mitochondrial ROS with subsequent neuronopathy.Fig 1 Fig 2
Hsu et al. (Sat,) studied this question.