To investigate the role of butyric acid-producing bacteria in long bone homeostasis in mice with periodontitis under a high-fat/high-sugar diet and to provide new insights for the prevention and treatment of periodontitis and related bone metabolic diseases.

This study has been approved by the Animal Welfare and Ethics Committee of the Experimental Animal Center. Initially, 14 mice were randomly divided into the CON group (the control group) and the LIG group (the periodontitis group). Mice in the LIG group had experimental periodontitis induced by ligating the second maxillary molars bilaterally and were fed a high-fat and high-sugar diet. After 8 weeks, samples were collected. Micro-computed tomography (Micro-CT) was used to analyze alveolar bone resorption and various parameters of the proximal tibia trabecular bone, including bone mineral density (BMD), bone volume per tissue volume (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp). After decalcification, hematoxylin and eosin (HE) staining was performed on maxillary bone sections to assess periodontal tissue inflammation and connective tissue destruction. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect related genes in the distal femur and proximal tibia bone tissues, including osteocalcin (OCN), osteogenic transcription factor (Osterix), osteoprotegerin (OPG), tartrate resistant acid phosphatase (TRAP), osteoclast-associated receptor (OSCAR), receptor activator of nuclear factor kappa-B (RANK), and receptor activator of nuclear factor kappa-B ligand (RANK-L). Subsequently, the other 28 mice were randomly divided into the CON group (the control group), LIG group (the periodontitis group), CON + butyric acid-producing bacteria (BP) group, and LIG + BP group. The breeding, sampling, and sample detection methods remained the same. Finally, the other 28 mice were randomly divided into the CON group (the control group), LIG group (the periodontitis group), CON + sodium butyrate (SB) group, and LIG + SB group. The breeding, sampling, and sample detection methods remained the same.

①Periodontitis modeling was successful. Compared with the CON group, the LIG group exhibited significant alveolar bone resorption of the maxillary second molar, aggravated periodontal tissue inflammation, and connective tissue destruction. ②Periodontitis exacerbated long bone resorption in mice fed a high-fat high-sugar diet. Compared with the CON group, the LIG group had significantly lower BMD, BV/TV, Tb.N, and Tb.Th (P＜0.05), and significantly higher Tb.Sp (P＜0.05). HE staining of the proximal tibia showed that the trabeculae in the LIG group were sparse and disordered, with some areas showing fractures or dissolution. The expression of osteoblast markers (OCN, Osterix, OPG) was significantly lower in the LIG group (P＜0.05), while the expression of the osteoclast marker TRAP showed an increasing trend (P＞0.05). The ratio of RANK-L/OPG was significantly higher in the LIG group compared with the CON group (P＜0.05). ③ Supplementation with butyric acid-producing bacteria alleviates periodontitis-induced disruption of long bone homeostasis in mice fed a high-fat/high-sugar diet. Compared with the LIG group, BMD and Tb. Th were significantly higher in the LIG + BP group. HE staining of the proximal tibia showed that bone resorption was mitigated in the LIG + BP group compared with the LIG group. The expression of OCN and Osterix was significantly higher in the LIG + BP group, while the expression of osteoclast-specific genes (OSCAR, RANK, RANK-L) was significantly lower (P＜0.05). ④ Supplementation with butyrate alleviates periodontitis-induced disruption of long bone homeostasis in mice fed a high-fat/high-sugar diet. Compared with the LIG group, BV/TV and Tb.N were significantly higher in the LIG + SB group, and Tb.Sp was significantly lower (P＜0.05). HE staining of the proximal tibia showed that bone resorption was mitigated in the LIG + SB group compared with the LIG group. The expression of Osterix, OPG, OSCAR, TRAP, and RANK was significantly lower in the LIG + SB group compared with the LIG group (P＜0.05).

Periodontitis disrupts the long bone homeostasis of mice fed a high-fat high-sugar diet, aggravating long bone resorption. Supplementation with butyric acid-producing bacteria or butyrate can effectively alleviate the disruption of long bone homeostasis caused by periodontitis.

To examine the effect of intracellular vesicles (IVs) and extracellular vesicles (EVs) that originated from periodontal ligament stem cells (PDLSCs) on the osteogenic differentiation of PDLSCs within a lipopolysaccharide (LPS)-simulated inflammatory microenvironment, and to provide new insights for the application of IVs in the repair and regeneration of periodontal tissue in periodontitis.

Ethical approval was obtained from the institution. Human-origin PDLSCs were extracted, and the IVs and EVs from PDLSCs at the 3rd-6th passages were gathered and identified using transmission electron microscopy, nano flow cytometry (Nano FCM) analysis, and Western Blot. The 3rd-6th generations of PDLSCs were categorized into the following groups: Control group, LPS group, LPS + 100 μg/mL EVs group (LPS+EVs group), and LPS + 100 μg/mL IVs group (LPS+IVs group). The effects of the IVs and EVs on the anti-inflammatory and osteogenic differentiation of PDLSCs in an inflammatory microenvironment were assessed by using a Cell Counting Kit-8 (CCK-8), enzyme-linked immunosorbent assay (ELISA), quantitative real-time polymerase chain reaction (qRT-PCR), Western Blot, alkaline phosphatase (ALP) staining, and alizarin red staining (ARS).

Under transmission electron microscopy, the IVs and EVs derived from PDLSCs displayed a double-layer membrane structure. NanoFCM analysis revealed that the average diameters of the IVs and EVs were 79.6 nm and 82.1 nm, respectively. Western Blot analysis indicated that the surface proteins CD9, CD63, and CD81 of the IVs and EVs were positively expressed, while calnexin was negatively expressed, indicating that IVs and EVs were successfully obtained. Compared with the Control group, the proliferation of PDLSCs in the LPS group was reduced, while the levels of inflammatory cytokine interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) in the cell supernatant were increased, the mRNA expressions of osteogenic differentiation-related genes, including osteoblast-related genes runt-related transcription factor 2 (RUNX2), alkaline phosphatase (ALP), osteocalcin (OCN) of PDLSCs were reduced, the protein expressions of RUNX2 and osteopontin (OPN) were also decreased (P < 0.05); compared with the LPS group, the proliferation of PDLSCs in the LPS+EVs group and LPS+IVs group were significantly increased, while the levels of IL-6, TNF-α were significantly reduced, and the mRNA expressions of RUNX2, ALP, OCN were significantly increased, the protein expressions of RUNX2 and OPN were also significantly increased (P < 0.05). Further, in the inflammatory microenvironment, Compared with EVs, IVs more significantly promote the proliferation of PDLSCs, inhibit TNF-α expression, enhance the expression of RUNX2 mRNA, upregulate the expression of RUNX2 and OPN proteins, increase ALP activity, and promote the formation of mineralized nodules (P < 0.05).

IVs and EVs derived from PDLSCs can boost the proliferation of PDLSCs in an inflammatory microenvironment, inhibit the expression of inflammatory factors, and advance the osteogenic differentiation of PDLSCs. The anti-inflammatory and osteogenic effects of IVs are superior to those of EVs.