Periodontitis is a disease of the supporting structures of the teeth, characterized by tissue inflammation and destruction. While periodontitis is initiated by periodontal pathogens, diabetes and metabolic syndrome (MetS), which is considered as prediabetes, aggravate its progression. The finding that MetS exacerbates periodontitis is of importance because about 34% of adult Americans have MetS. However, the mechanisms whereby MetS interacts with periodontal pathogens to aggravate periodontitis remain largely unknown. To better study the interaction between MetS and periodontitis, we successfully developed a mouse model with periodontitis and high-fat diet (HFD)-induced MetS to demonstrate that MetS is associated with increased periodontal tissue inflammation and alveolar bone loss. Since the HFD is enriched in saturated fatty acid (SFA), which is increased in the plasma of patients with MetS, we tested our hypothesis that SFA boosts macrophage inflammatory response triggered by periodontal pathogen-derived virulence factors such as lipopolysaccharide (LPS). Results showed that palmitic acid (PA), the most abundant SFA, amplifies LPS- induced inflammatory cytokine expression in macrophages by 3-4 folds. More interestingly, we found that acid sphingomyelinase (ASMase)-mediated sphingomyelin hydrolysis and resulting increased ceramide (CER) production (ASMase-CER pathway) plays a key role in the upregulation of inflammatory cytokines by PA and LPS. Based on our above findings and the notions from the literature that CER and its downstream products such as sphingosine-1-phosphate play a vital role in many pathobiological processes such as inflammation, proliferation and apoptosis, we proposed this study with the following 3 specific aims: 1. To determine the role of ASMase in periodontal inflammation and alveolar bone loss in mice with or without MetS. We hypothesized that ASMase is a potential target to reduce MetS-related alveolar bone loss. 2. To determine the role of ASMase in the stimulation of osteoclast formation and fibroblast apoptosis by LPS and PA. We hypothesized that ASMase-CER pathway mediates the stimulatory actions of LPS and PA on osteoclast formation by enhancing RANKL-RANK interaction and on fibroblast apoptosis by increasing release of macrophage-derived pro-apoptotic cytokines. 3. To determine the mechanisms by which ASMase-CER pathway mediates PA- amplified TLR4 signaling in macrophages. We hypothesized that ASMase-CER pathway mediates the stimulation by LPS and PA of NF?B signaling via CD36/MyD88-independent pathway and inflammasome.
Periodontitis, an oral disease characterized by periodontal inflammation and alveolar bone loss, is aggravated by systemic disease such as diabetes and metabolic syndrome (MetS). In this study, we will test our hypothesis that targeting acid sphingomyelinase (ASMase) to reduce ceramide (CER) generation is associated with an improvement of periodontal tissue inflammation and alveolar bone loss in mice with or without MetS. We will also investigate the mechanisms whereby ASMase-CER pathway mediates osteoclastogenesis, apoptosis and inflammatory signaling.
|Li, Guang; Robles, Samantha; Lu, Zhongyang et al. (2018) Upregulation of free fatty acid receptors in periodontal tissues of patients with metabolic syndrome and periodontitis. J Periodontal Res :|
|Jin, Junfei; Lu, Zhongyang; Li, Yanchun et al. (2018) LPS and palmitate synergistically stimulate sphingosine kinase 1 and increase sphingosine 1 phosphate in RAW264.7 macrophages. J Leukoc Biol 104:843-853|