Autophagy Induced by Intracellular Infection of Propionibacterium acnes

Abstract

BackgroundSarcoidosis is caused by Th1-type immune responses to unknown agents, and is linked to the infectious agent Propionibacterium acnes. Many strains of P. acnes isolated from sarcoid lesions cause intracellular infection and autophagy may contribute to the pathogenesis of sarcoidosis. We examined whether P. acnes induces autophagy.MethodsThree cell lines from macrophages (Raw264.7), mesenchymal cells (MEF), and epithelial cells (HeLa) were infected by viable or heat-killed P. acnes (clinical isolate from sarcoid lymph node) at a multiplicity of infection (MOI) of 100 or 1000 for 1 h. Extracellular bacteria were killed by washing and culturing infected cells with antibiotics. Samples were examined by colony assay, electron-microscopy, and fluorescence-microscopy with anti-LC3 and anti-LAMP1 antibodies. Autophagy-deficient (Atg5-/-) MEF cells were also used.ResultsSmall and large (≥5 μm in diameter) LC3-positive vacuoles containing few or many P. acnes cells (LC3-positive P. acnes) were frequently found in the three cell lines when infected by viable P. acnes at MOI 1000. LC3-positive large vacuoles were mostly LAMP1-positive. A few small LC3-positive/LAMP1-negative vacuoles were consistently observed in some infected cells for 24 h postinfection. The number of LC3-positive P. acnes was decreased at MOI 100 and completely abolished when heat-killed P. acnes was used. LC3-positive P. acnes was not found in autophagy-deficient Atg5-/- cells where the rate of infection was 25.3 and 17.6 times greater than that in wild-type Atg5+/+ cells at 48 h postinfection at MOI 100 and 1000, respectively. Electron-microscopic examination revealed bacterial cells surrounded mostly by a single-membrane including the large vacuoles and sometimes a double or multi-layered membrane, with occasional undigested bacterial cells in ruptured late endosomes or in the cytoplasm.ConclusionAutophagy was induced by intracellular P. acnes infection and contributed to intracellular bacterial killing as an additional host defense mechanism to endocytosis or phagocytosis.

Propionibacterium acnes Induces Autophagy in Keratinocytes: Involvement of Multiple Mechanisms

“…The data demonstrated that, at 3 and 6 hpi, P. acnes strain 889 triggers the accumulation of autophagosome-stage vacuoles, which subsequently evolve into degradative autolysosomes, suggesting that these bacteria trigger a transient increase in autophagic activity at the early phase of incubation, which declines thereafter. It was earlier reported that an invasive P. acnes strain induces autophagy in Raw 264.7 macrophages, mesenchymal cells, and HeLa cell line (Nakamura et al, 2016). Overall, our experiments demonstrate that P. acnes can stimulate autophagy in keratinocytes when it is present extracellularly, as the level of bacterial invasion was negligible at the low multiplicity of infection used.…”

“…A recent study has demonstrated that a cell-invasive P. acnes strain triggers the accumulation of autophagosomes in Raw 264.7 macrophages, mesenchymal cells, and the HeLa cell line (Nakamura et al, 2016). Further observations have indicated that propionic acid is a powerful autophagy inducer in the HCT116 cell line.…”

Propionibacterium acnes induces intervertebral disc degeneration by promoting nucleus pulposus cell apoptosis via the TLR2/JNK/mitochondrial-mediated pathway

“…Autophagy is a conserved function in many cells, and NPCs also use this function to counteract different types of harmful extracellular stimuli 22 . A previous study has suggested that P. acnes have the ability to induce autophagy in cell lines of macrophages (Raw264.7), mesenchymal cells (MEF), and epithelial cells (HeLa) 46 . However, P. acnes -induced autophagy in NPCs was not demonstrated.…”

Chronic inflammation evoked by pathogenic stimulus during carcinogenesis

“…It was coined by Christian de Duve in 1963 [230, reviewed in 229]. Intracellular bacterial infections [231] such as propionibacterium acne [232], Shigella and Salmonella [233], H. pylori [234], and viruses [235] can generate autophagy. The accumulation of intracellular amino acids induces a dissociation of mTOR from the membrane with downregulation of its activity.…”