Microbiota control acute arterial inflammation and neointimal hyperplasia development after arterial injury.

BACKGROUND: The microbiome has a functional role in a number of inflammatory processes and disease states. While neointimal hyperplasia development has been linked to inflammation, a direct role of the microbiota in neointimal hyperplasia has not yet been established. Germ-free (GF) mice are an invaluable model for studying causative links between commensal organisms and the host. We hypothesized that GF mice would exhibit altered neointimal hyperplasia following carotid ligation compared to conventionally raised (CONV-R) mice. METHODS: Twenty-week-old male C57BL/6 GF mice underwent left carotid ligation under sterile conditions. Maintenance of sterility was assessed by cultivation and 16S rRNA qPCR of stool. Neointimal hyperplasia was assessed by morphometric and histologic analysis of arterial sections after 28 days. Local arterial cell proliferation and inflammation was assessed by immunofluorescence for Ki67 and inflammatory cell markers at five days. Systemic inflammation was assessed by multiplex immunoassays of serum. CONV-R mice treated in the same manner served as the control cohort. GF and CONV-R mice were compared using standard statistical methods. RESULTS: All GF mice remained sterile during the entire study period. Twenty-eight days after carotid ligation, CONV-R mice had significantly more neointimal hyperplasia development compared to GF mice, as assessed by intima area, media area, intima+media area, and intima area/(intima+media) area. The collagen content of the neointimal lesions appeared qualitatively similar on Masson's trichrome staining. There was significantly reduced Ki67 immunoreactivity in the media and adventitia of GF carotid arteries 5 days after ligation. GF mice also had increased arterial infiltration of anti-inflammatory M2 macrophages compared to CONV-R mouse arteries and a reduced proportion of mature neutrophils. GF mice had significantly reduced serum IFN-γ-inducible protein (IP)-10 and MIP-2 5 days after carotid ligation, suggesting a reduced systemic inflammatory response. CONCLUSIONS: GF mice have attenuated neointimal hyperplasia development compared to CONV-R mice, which is likely related to altered kinetics of wound healing and acute inflammation. Recognizing the role of commensals in the regulation of arterial remodeling will provide a deeper understanding of the pathophysiology of restenosis and support strategies to treat or reduce restenosis risk by manipulating microbiota.

Toll-like receptor 4 signaling has a critical role in Porphyromonas gingivalis-accelerated neointimal formation after arterial injury in mice.

Recently, we reported that a periodontopathic pathogen, Porphyromonas gingivalis (P. gingivalis), infection induced neointimal hyperplasia with enhanced expression of monocyte chemoattractant protein (MCP)-1 after arterial injury in wild-type mice. Toll-like receptor (TLR) 4 is known to be a key receptor for virulence factors of P. gingivalis. The aim of this study is to assess the hypothesis that TLR4 has a critical role in periodontopathic bacteria-induced neointimal formation after an arterial injury. Wild-type and TLR4-deficient mice were used in this study. The femoral arteries were injured, and P. gingivalis or vehicle was injected subcutaneously once per week. Fourteen days after arterial injury, murine femoral arteries were obtained for histopathological and immunohistochemical analyses. The anti-P. gingivalis IgG levels in P. gingivalis-infected groups were significantly increased compared with the anti-P. gingivalis IgG levels of the corresponding non-infected groups in both wild-type and TLR4-deficient mice. TLR4 deficiency negated P. gingivalis-induced neointimal formation compared with that observed in wild-type mice and reduced the number of MCP-1 positive cells in the neointimal area. We conclude that P. gingivalis infection may promote neointimal formation after an arterial injury through TLR4 signaling.

Porphyromonas gingivalis accelerates neointimal formation after arterial injury.

BACKGROUND: Inflammation plays a key role in neointimal hyperplasia after an arterial injury. Chronic infectious disorders, such as periodontitis, are associated with an increased risk of cardiovascular diseases. However, the effects of a periodontal infection on vascular remodeling have not been examined. We assess the hypothesis that periodontal infection could promote neointimal formation after an arterial injury. METHODS: Mice were implanted with subcutaneous chambers (n = 41). Two weeks after implantation, the femoral arteries were injured, and Porphyromonas gingivalis (n = 21) or phosphate-buffered saline (n = 20) was injected into the chamber. The murine femoral arteries were obtained for the histopathological analysis. The expression level of mRNA in the femoral arteries was analyzed using quantitative reverse transcriptase polymerase chain reaction (n = 19-20). RESULTS: The intima/media thickness ratio in the P. gingivalis infected group was found to be significantly increased in comparison to the non-infected group. The expression of matrix metalloproteinase-2 mRNA was significantly increased in the P. gingivalis infected group compared to the non-infected group. CONCLUSION: These findings demonstrate that P. gingivalis injection can promote neointimal formation after an arterial injury. Periodontitis may be a critical factor in the development of restenosis after arterial intervention.