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Autophagy induced by type III secretion system toxins enhances clearance of Pseudomonas aeruginosa from human corneal epithelial cells

Mohankumar, Vidyarani, Ramalingam, Sangeetha, Chidambaranathan, Gowri Priya, Prajna, Lalitha
Biochemical and biophysical research communications 2018 v.503 no.3 pp. 1510-1515
Pseudomonas aeruginosa, Western blotting, autophagy, bacterial toxins, cornea, epithelial cells, fluorescent antibody technique, gene expression, genotype, humans, mutants, quantitative polymerase chain reaction, tissues, type III secretion system
Corneal ulcers caused by Pseudomonas aeruginosa may lead to severe visual disability due to impaired bacterial clearance from corneal tissues. Our purpose was to study the role of autophagy in the intracellular clearance of P. aeruginosa from human corneal epithelial cells (HCET) and its regulation by the bacterial type III secretion system (T3SS) toxins. Nine different corneal ulcer isolates of P. aeruginosa, PAO1 and T3SS mutants of PAO1 were used to infect HCET cells. Induction of autophagy (Immunofluorescence and Western blot) and pro-inflammatory gene expression (real time PCR) by P. aeruginosa and the role of autophagy in intracellular bacterial clearance were studied in the context of T3SS genotypes. The clinical isolates and PAO1 induced autophagy irrespective of the T3SS genotype, whereas the T3SS mutants were relatively defective in inducing autophagy and becn1 gene expression. External induction of autophagy significantly reduced the intracellular load of P. aeruginosa strains that were associated with worst clinical outcomes. The T3SS negative isolate and PAO1ΔexoST were less sensitive to pharmacological modulation of autophagy and had relatively higher replication potential, suggesting a possible mechanism of bacterial survival in the absence of T3SS toxins. Overall, our results highlight a selective role for autophagy in bacterial clearance from corneal epithelial cells and emphasize the pro-autophagic role of bacterial toxins in the context of corneal ulcers.