Protection of eukaryotic cells against pore-forming toxins from pathogenic bacteria

Bacterial infections are a leading cause of mortality and morbidity. Many species of pathogenic bacteria secrete pore-forming toxins to damage eukaryotic cells and facilitate pathogen invasion. Although cells can repair this damage, little is known about the intrinsic protection of cells against these toxins. Side-chain oxysterols and steroids can reduce the severity of bacterial diseases by suppressing immunity. Here we tested the hypothesis that oxysterols and steroids might also enhance the intrinsic protection of eukaryotic cells against pore-forming toxins. We first used the cholesterol-dependent cytolysin pyolysin, which forms pores in bovine endometrial cells. We found that 25-hydroxycholesterol or 27-hydroxycholesterol treatment protected bovine endometrial cells against pyolysin, and that these oxysterols are present in the reproductive tract. The oxysterols reduced pyolysin-induced leakage of potassium and lactate dehydrogenase by > 65%, limited changes to the actin cytoskeleton, and prevented cytolysis. The oxysterols also protected human cervical, lung, and liver epithelial cells against pyolysin damage, and protected cells against Staphylococcus aureus α-hemolysin. Mechanistically, oxysterol cytoprotection was partially dependent on activating acetyl-coenzyme A acetyltransferase and liver X receptors. The steroids, progesterone, oestradiol, or hydrocortisone were not protective in bovine endometrial cells. However, hydrocortisone and dexamethasone protected several types of human cells against pyolysin, reducing cytolysis from > 75% to < 25%, via a glucocorticoid receptor dependent mechanism. Treatment with these glucocorticoids also protected human cells against α-hemolysin and another cholesterol-dependent cytolysin, streptolysin O. However, glucocorticoid cytoprotection was reversibly blocked by the presence of ≥ 4% serum, which led to the discovery that glucocorticoid cytoprotection depended on the rate limiting enzyme of cholesterol biosynthesis, 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase. In conclusion, side-chain oxysterols and glucocorticoids enhance the intrinsic protection of eukaryotic cells against pore-forming toxins. These findings imply that oxysterols and glucocorticoids could help limit the severity of disease caused by pathogens that secrete pore-forming toxins.