Host cell tropism of Propionibacterium acnes: infection scenarios differ on skin and prostate epithelia. Homo sapiens

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. Overall design: Microarray experiments were performed as dual-color hybridizations. In order to compensate specific effects of the dyes and to ensure statistically relevant data analysis, a color-swap dye-reversal was performed.

痤疮丙酸杆菌（Proprionibacterium acnes）是一种广泛定植于人体皮肤表面的革兰氏阳性细菌（Gram-positive bacterium），通常被认为与宿主形成偏利共生关系（commensal relationship）。然而，该菌也与寻常痤疮（acne vulgaris）密切相关。更具争议的是，有研究推测其可参与植入式假体装置（implanted prosthetic devices）的感染，并已从恶性前列腺组织（malignant prostate tissues）中分离得到。尽管细菌与宿主双方的因素均被认为参与致病过程，但痤疮丙酸杆菌在上述病理状态中的具体作用仍未明确。
通过微阵列分析，我们鉴定出角质形成细胞（keratinocyte）与前列腺细胞（prostate cells）在痤疮丙酸杆菌感染后的全局转录谱（global transcriptional profiles）存在根本性差异。值得注意的是，痤疮丙酸杆菌感染角质形成细胞系HaCaT后，可引发强烈但短暂的炎症应答（inflammatory response）。与之形成鲜明对比的是，前列腺细胞系RWPE1的炎症应答则出现延迟且持续时间更长。免疫荧光（immunofluorescence）与电子显微镜（electron microscopy）检测显示，RWPE1细胞内被内化的痤疮丙酸杆菌数量更多，且在感染三周后仍可在细胞内被检出。而HaCaT细胞则基本无法被痤疮丙酸杆菌侵袭，二者形成显著差异。此外，痤疮丙酸杆菌可在RWPE1细胞中诱导延迟且持续的NFκB激活，而该现象在HaCaT细胞中并未出现。
对宿主细胞感染应答的进一步表征发现，中间丝蛋白（intermediate filament protein）波形蛋白（vimentin）是决定RWPE1细胞中痤疮丙酸杆菌侵袭、定植及炎症表型的关键调控因子。在RWPE1细胞中通过小干扰RNA（siRNA）介导的基因敲低（knock down），可减弱细菌侵袭能力并抑制感染诱导的炎症应答；与之类似，在HaCaT细胞中过表达波形蛋白，则可增强细菌的侵袭能力。我们由此得出结论：依赖波形蛋白的宿主组织嗜性（tropism），在一定程度上决定了痤疮丙酸杆菌的侵袭能力与炎症潜能，这或许可解释痤疮丙酸杆菌在非皮肤感染部位的病理作用。
实验整体设计：本研究采用双色杂交（dual-color hybridization）开展微阵列实验。为抵消染料带来的特异性效应并确保数据分析的统计学可靠性，我们设置了染料反转（color-swap dye-reversal）对照实验。