Interaction between bacteria and cholesterol crystals: Implications for endocarditis and atherosclerosis

Clinical correlates of circulating small dense low-density lipoproteins in acute infective endocarditis

BACKGROUND AND AIM

Infective endocarditis (IE) is a complex thrombo-inflammatory disorder, the pathogenesis of which involves a multifaceted interplay between vascular damage and bacterial virulence factors. This study aimed to assess the prognostic role of small dense low-density lipoprotein (sdLDL) cholesterol in patients with IE and its correlation with various disease-related features.

METHODS

A cohort of 198 patients with definite IE was included in this study. Clinical, laboratory, and echocardiographic parameters were meticulously analyzed, with a specific focus on comorbidities. sdLDL levels were measured using stored plasma samples obtained upon admission during the acute phase of the disease.

RESULTS

The median level of sdLDL was 24 mg/dL [with an interquartile range of 17.9-35.2 mg/dL], and this value showed a statistically significant positive correlation with LDL/HDL cholesterol and triglycerides (p < 0.01 for all). Furthermore, a remarkable inverse correlation between C-reactive protein and D-dimer levels was observed (p < 0.0001). Univariate analysis revealed that patients with sdLDL levels ≤ 24 mg/dL had 2.75 times higher odds of in-hospital mortality (95% Confidence Interval:1.08-6.98, p = 0.031). In addition, nonsurvivors had significantly lower median sdLDL levels (19.7 vs. 26.0 mg/dL, p = 0.041). Lower sdLDL levels were also associated with embolic complications, larger vegetation size, and positive blood cultures for Staphylococci (p = 0.019, p = 0.022, and p < 0.001, respectively).

CONCLUSIONS

Low circulating sdLDL levels in the acute phase of IE were significantly correlated with unfavorable clinical outcomes. These results suggest that the sdLDL level may serve as an important marker of disease severity in IE and may represent a link between vascular damage, embolic complications, and disease progression.

Untargeted and temporal analysis of retinal lipidome in bacterial endophthalmitis

Bacterial endophthalmitis is a blinding infectious disease typically acquired during ocular surgery. We previously reported significant alterations in retinal metabolism during Staphylococcus (S) aureus endophthalmitis. However, the changes in retinal lipid composition during endophthalmitis are unknown. Here, using a mouse model of S. aureus endophthalmitis and an untargeted lipidomic approach, we comprehensively analyzed temporal alterations in total lipids and oxylipin in retina. Our data showed a time-dependent increase in the levels of lipid classes, sphingolipids, glycerolipids, sterols, and non-esterified fatty acids, whereas levels of phospholipids decreased. Among lipid subclasses, phosphatidylcholine decreased over time. The oxylipin analysis revealed increased prostaglandin-E2, hydroxyeicosatetraenoic acids, docosahexaenoic acid, eicosapentaenoic acid, and α-linolenic acid. In-vitro studies using mouse bone marrow-derived macrophages showed increased lipid droplets and lipid-peroxide formation in response to S. aureus infection. Collectively, these findings suggest that S. aureus-infection alters the retinal lipid profile, which may contribute to the pathogenesis of bacterial endophthalmitis.

Flagellar hook protein FlgE promotes macrophage activation and atherosclerosis by targeting ATP5B

BACKGROUND AND AIMS

Pseudomonas aeruginosa (P. aeruginosa) infections are strongly linked to the development of cardiovascular disease and atherosclerosis; however, the underlying mechanisms remain unclear. We previously confirmed that the flagellar hook protein FlgE in P. aeruginosa has immunostimulatory effects. This study investigated the effects and mechanisms of action of FlgE on atherogenesis.

METHODS

ApoE-/- mice were intravenously challenged with FlgE or FlgEM recombinant proteins for eight weeks. A murine model of chronic lung colonization was established using beads containing either mutable- or wild-type bacteria. Aortic sinus sections were stained to assess atherosclerosis progression. THP-1 macrophages exposed to FlgE or FlgEM were evaluated for their effects on lipid uptake and inflammation in vitro. Western blotting and pull-down assays were used to identify the binding proteins and signaling pathways involved, and specific blocking experiments were performed to confirm these effects.

RESULTS

FlgE accelerated atherosclerosis progression by triggering lipid deposition and inflammatory responses in high-fat diet (HFD)-fed ApoE-/- mice. In comparison to infection with wild-type PAO1, infection with PAO1/flgEΔBmF resulted in reduced atherosclerosis. Mechanistic analysis indicated that FlgE exacerbated lipoprotein uptake and foam cell formation by upregulating SR-A1 expression. Moreover, FlgE activated NF-κB and MAPK signaling, which subsequently led to inflammatory responses in THP-1-derived macrophages. Pull-down assays revealed that FlgE directly interacted with ATP5B, whereas blocking ATP5B attenuated FlgE-induced responses in macrophages.

CONCLUSIONS

FlgE induces macrophage lipid uptake and pro-inflammatory responses mediated by ATP5B/NF-kB/AP-1 signaling, which eventually results in atherosclerosis. These findings support the development of therapeutic strategies for P. aeruginosa infection-induced atherosclerosis.

Wall Teichoic Acid Mediates Staphylococcus aureus Binding to Endothelial Cells via the Scavenger Receptor LOX-1

The success of Staphylococcus aureus as a major cause for endovascular infections depends on effective interactions with blood-vessel walls. We have previously shown that S. aureus uses its wall teichoic acid (WTA), a surface glycopolymer, to attach to endothelial cells. However, the endothelial WTA receptor remained unknown. We show here that the endothelial oxidized low-density lipoprotein receptor 1 (LOX-1) interacts with S. aureus WTA and permits effective binding of S. aureus to human endothelial cells. Purified LOX-1 bound to isolated S. aureus WTA. Ectopic LOX-1 expression led to increased binding of S. aureus wild type but not of a WTA-deficient mutant to a cell line, and LOX-1 blockage prevented S. aureus binding to endothelial cells. Moreover, WTA and LOX-1 expression levels correlated with the efficacy of the S. aureus-endothelial interaction. Thus, LOX-1 is an endothelial ligand for S. aureus, whose blockage may help to prevent or treat severe endovascular infections.