ABSTRACT: Proprionibacterium acnes is a Gram positive bacterium found ubiquitously on human skin, where it is typically considered to assume a commensal relationship with its host. However, it is also closely associated with the skin condition acne vulgaris. More controversially, it has a postulated involvement in infections of implanted prosthetic devices and has been isolated from malignant prostate tissues. The role of P. acnes in these pathologies remains undetermined, although both bacterial and host factors are implicated. By microarray analysis, we have identified fundamental differences in the global transcriptional profiles of keratinocyte and prostate cells to P. acnes infection. Notably, P. acnes infection of the keratinocyte cell line, HaCaT, elicited a robust, but acute inflammatory response. By contrast, the inflammatory response of the prostate cell line, RWPE1, was delayed and persisted for longer times. Immunofluorescence and electron microscopy revealed higher numbers of internalized P. acnes bacteria in RWPE1 cells, which could still be detected intracellularly three weeks post infection. This contrasted with HaCaT cells, which P. acnes largely failed to invade. Moreover, P. acnes induced a delayed, sustained activation of NFκB in RWPE1 cells, which was absent in HaCaT cells. Further characterization of the host-cell response to infection revealed that the intermediate filament protein, vimentin, was a key determinant of P. acnes invasion, persistence and inflammatory profile in RWPE1 cells. siRNA mediated knock down of vimentin in RWPE1 cells attenuated bacterial invasion and the inflammatory response to infection; similarly, overexpression of vimentin in HaCaT cells increased bacterial invasion. We conclude that vimentin-dependent host-tissue tropism, in part, determines P. acnes invasion and inflammatory capacity. This could contribute to P. acnes pathology at non-skin infection sites.
