Statin-Conferred Enhanced Cellular Resistance against Bacterial Pore-Forming Toxins in Airway Epithelial Cells

Abstract

Statins are widely used to prevent cardiovascular disease. In addition to their inhibitory effects on cholesterol synthesis, statins have beneficial effects in patients with sepsis and pneumonia, although molecular mechanisms have mostly remained unclear. Using human airway epithelial cells as a proper in vitro model, we show that prior exposure to physiological nanomolar serum concentrations of simvastatin (ranging from 10-1,000 nM) confers significant cellular resistance to the cytotoxicity of pneumolysin, a pore-forming toxin and the main virulence factor of Streptococcus pneumoniae. This protection could be demonstrated with a different statin, pravastatin, or on a different toxin, a-hemolysin. Furthermore, through the use of gene silencing, pharmacological inhibitors, immunofluorescence microscopy, and biochemical and metabolic rescue approaches, we demonstrate that the mechanism of protection conferred by simvastatin at physiological nanomolar concentrations could be different from the canonical mevalonate pathways seen in most other mechanistic studies conducted with statins at micromolar levels. All of these data are integrated into a protein synthesis-dependent, calcium-dependent model showing the interconnected pathways used by statins in airway epithelial cells to elicit an increased resistance to pore-forming toxins. This research fills large gaps in our understanding of how statins may confer host cellular protection against bacterial infections in the context of airway epithelial cells without the confounding effect from the presence of immune cells. In addition, our discovery could be potentially developed into a host-centric strategy for the adjuvant treatment of pore-forming toxin associated bacterial infections.Keywords: airway epithelium; pneumolysin; simvastatin; cholesterol; pneumonia Clinical RelevanceOur study dissects the cellular and molecular protection mechanisms of statins in an isolated airway epithelial cell-bacterial pore-forming toxin context. This research can fill large gaps in our understanding of how statins contribute to the reduced pathology observed during pneumonia and other bacterial infections. The better understanding of the molecular mechanisms in the statin-mediated protection will further affect the therapeutic development of host-centric approach therapies in combating microbial infections.

Statins influence epithelial expression of the anti-microbial peptide LL-37/hCAP-18 independently of the mevalonate pathway

“…In contrast, neither simvastatin nor TSA increased expression of LL‐37/hCAP‐18 in A549 cells investigated in our study. Statt et al observed a mevalonate‐dependent induction of CAMP gene expression by simvastatin in airway epithelial cells . However, this effect was demonstrated at a concentration of 1 µM simvastatin, while we applied concentrations in the nanomolar range as these are concentrations obtained in serum from patients receiving statin therapy .…”

“…A linkage between statins and the expression of the anti‐microbial peptide LL‐37/hCAP‐18 has previously been described in airway epithelial cells . In addition, pravastatin has been suggested to reduce the recurrence of urinary tract infections , but clinical data on the overall effect of statins on urinary tract infections are limited and inconsistent .…”

“…In addition to anti-inflammatory effects, statins have been described to promote the activity of immune cells such as macrophages [5,6], monocytes [7] and neutrophils [8]. The impact of statins on epithelial cells in this context is, however, less well covered [9,10].…”

Statin Use Is Associated With Reduced Mortality On Mechanically Ventilated Patients: A Retrospective Propensity-Matched Analysis Of MIMIC-III Database

“…Sarah et al showed that prior exposure to physiological nanomolar serum concentrations of simvastatin confers significant cellular resistance to the cytotoxicity of pneumolysin, which revealed how statins contribute to the reduced pathology observed in the context of pneumonia and other bacterial infections [37].…”

The Role of Streptococcus pneumoniae in Community-Acquired Pneumonia

“…Although not yet demonstrated in neutrophils or platelets, statins, specifically simvastatin, and also pravastatin, have been reported to protect both isolated human airway epithelial cells 151 and microvascular endothelial cells 152 against the cytotoxic actions of Ply. The latter study also documented a survival benefit of administration of simvastatin to pneumococcus infection-prone sickle-cell disease mice experimentally infected with the pathogen.…”