Critical roles of extracellular vesicles in periodontal disease and regeneration

Abstract

Extracellular vesicles (EVs) are evolutionarily conserved communication mediators that play key roles in the development of periodontal disease as well as in regeneration processes. This concise review first outlines the pathogenic mechanisms through which EVs derived from bacteria lead to the progression of periodontitis, with a focus on the enrichment of virulence factors, the amplification of immune responses, and the induction of bone destruction as key aspects influenced by bacterial EVs. This review aims to elucidate the positive effects of EVs derived from mesenchymal stem cells (MSC-EVs) on periodontal tissue regeneration. In particular, the anti-inflammatory properties of MSC-EVs and their impact on the intricate interplay between MSCs and various immune cells, including macrophages, dendritic cells, and T cells, are described. Moreover, recent advancements regarding the repair-promoting functions of MSC-EVs are detailed, highlighting the mechanisms underlying their ability to promote osteogenesis, cementogenesis, angiogenesis, and the homing of stem cells, thus contributing significantly to periodontal tissue regeneration. Furthermore, this review provides insights into the therapeutic efficacy of MSC-EVs in treating periodontitis within a clinical context. By summarizing the current knowledge, this review aims to provide a comprehensive understanding of how MSC-EVs can be harnessed for the treatment of periodontal diseases. Finally, a discussion is presented on the challenges that lie ahead and the potential practical implications for translating EV-based therapies into clinical practices for the treatment of periodontitis.

Keywords: MSC- mesenchymal stem cells-extracellular vesicles; extracellular vesicles; mesenchymal stem cells; periodontal disease; periodontal regeneration.

Graphical Abstract

Figure 1.

Pathogenic roles of extracellular vesicles in the pathogenesis of periodontal disease. (A) The biogenesis of bacterial-derived extracellular vesicles (BEVs) containing various types of virulence factors. Outer membrane vesicles (OMVs) and outer-inner membrane vesicles (OIMVs) are generated by gram-negative bacteria, whereas cytoplasmic membrane vesicles (CMVs) originate from gram-positive bacteria. All of these BEVs are capable of transporting virulence factors. For example, OMVs from T. forsythia are known to carry BspA and sialidase, which induce inflammation by activating Toll-like receptor 2 (TLR2). Additionally, P. gingivalis-derived periplasmic vesicles (Pg EVs) contain virulence factors such as gingipain (GP) and lipopolysaccharide (LPS), which increase the expression of tumor necrosis factor-alpha (TNF-α) and interleukin-13 (IL-13) and increase the number of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB)-positive CD11c cells within periodontal tissues. (B) Amplification of the immune response mediated by BEVs released from periodontal pathogens. BEVs can bind to host cells (epithelial cells, neutrophils, and macrophages) through interactions with pattern recognition receptors (PRRs), such as TLR2, TLR4, NOD1, and NOD2, thereby initiating the activation of downstream proinflammatory signaling pathways. (C) BEVs induce bone resorption by activating TLR2 in bone mesenchymal stem cells (BMSCs) and osteoclasts, thereby playing dual regulatory roles in bone metabolism. BEVs inhibit osteoblast differentiation by modulating the RANKL-RANK-OPG signaling axis while promoting osteoclast differentiation by upregulating factors for osteoclast precursor cells. (D) Cellular extracellular vesicles (CEVs) originating from host cells infected by bacteria or their products exacerbate the progression of periodontitis. Host cells exposed to bacteria, BMVs, or LPS release CEVs enriched with proinflammatory cytokines and mediators, including TNF-α and interleukin-6 (IL-6). These CEVs further act on recipient cells to intensify inflammation and promote tissue destruction. Abbreviations: CM, cytoplasmic membrane; ERK, extracellular signal-regulated kinase; Fa, Fusobacterium nucleatum; FOXP3, Forkhead Box P3; G-CSF, granulocyte colony-stimulating facto; GSDMD, Gasdermin D; IL-10, interleukin-10; IL-17, interleukin-17; IL-1ra, interleukin-1ra; JNK, c-Jun N-terminal kinase; MAPK, mitogen-activated protein kinase; MIP-1α, macrophage inflammation protein-1α; MMP1, matrix metalloproteinase-1; MMP3, matrix metalloproteinase-3; MMP9, matrix metalloproteinase-9; NLRP3, NOD-like Receptor Family Pyrin Domain Containing 3. OM, outer membrane; OPG, osteoprotegerin; RANK, receptor activator of nuclear factorκB; RANKL, the receptor activator of nuclear factorκB ligand; RORC, Retinoic Acid Receptor-related Orphan Receptor C; SIRT1, Sirtuin-1; SPP1, Secreted Phosphoprotein 1; Tf, Treponema denticola

Figure 2.

Anti-inflammatory effects of MSC-EVs on immune cells. MSC-EVs can transfer diverse cargoes (such as miRNAs and proteins) to different immune cells (including macrophages, T cells, and dendritic cells). These cargoes can activate various signaling pathways to exert anti-inflammatory effects on immune cells. Abbreviations: CCL21, C-C motif chemokine ligand 21; CCR7, chemokine receptor 7; ERK, extracellular signal-regulated kinase; GSH, glutathione; GSR, glutathione reductase; GSSG, glutathione disulfide; IL-12, interleukin-12; IL-1β, interleukin-1β; IL-6, interleukin-6; IκB, Inhibitor of κB; MyD88, Myeloid Differentiation Primary Response 88; NFAT5, Nuclear Factor of Activated T-cells 5; NF-κB, the nuclear factor kappa-light-chain-enhancer of activated B cells; PD-1, programmed cell death protein 1; PD-L1, programmed death ligand 1; ROS, reactive oxygen species; SIRT1, Sirtuin 1 SOD1, superoxide dismutase 1; TLR4, Toll-like receptor 4; TNF-α, tumor necrosis factor-alpha.

Figure 3.

The therapeutic effects of MSC-EVs on periodontitis. MSC-EVs deliver multiple cargoes (eg, miRNAs, proteins, etc.) to different recipient cells, including osteoblasts, cementoblasts, MSCs, and ECs. Multiple underlying mechanisms are involved in MSC-EV-mediated osteogenesis, angiogenesis, cell migration/proliferation, and cementogenesis. These signaling pathways regulate biological processes in recipient cells to exert therapeutic effects on periodontitis. Abbreviations: AKT, protein kinase B; AMP, adenosine monophosphate; AMPK, AMP-activated protein kinase; BMP2, bone morphogenetic protein 2; Ckip-1, casein kinase 2 interacting protein-1 EGF, epidermal growth factor; ERK, extracellular signal-regulated kinase; HIF-1α, hypoxia-inducible factor 1-alpha; IGFBP-3/5/6, insulin-like growth factor binding protein-3/5/6; MAPK, mitogen-activated protein kinase; NF-κB, the nuclear factor kappa-light-chain-enhancer of activated B cells; OPG, osteoprotegerin; p-AKT, the phosphorylation of AKT; p-AMPK, the phosphorylation of AMPK; PI3K, phosphoinositide 3-kinase; p-JNK, the phosphorylation of c-Jun N-terminal kinase; PKC, protein kinase C; PLC, phospholipase C; p-Smad1/5/8/9, the phosphorylation of Smad1/5/8/9; RANK, receptor activator of nuclear factor κB; RANKL, the receptor activator of nuclear factor κ ligand; STAT1, signal transducer and activator of transcription 1; TUFM, Tu translation elongation factor; VCAM-1, vascular cell adhesion molecule-1; VEGF, vascular endothelial growth factor; Wnts, wingless protein.

Figure 4.

The main strategies for promoting the repair-promoting functions of MSC-EVs paves the way for their clinical application in periodontitis. By preconditioning MSCs, engineering MSC-EVs through cargo loading or membrane modification, and developing local delivery systems for MSC-EVs, researchers can increase the therapeutic efficacy of MSC-EVs, rendering them potentially suitable for the treatment of periodontitis.