Enamel Matrix Derivative Suppresses Chemokine Expression in Oral Epithelial Cells

Epithelial cells in periodontitis patients increasingly express chemokines, suggesting their active involvement in the inflammatory process. Enamel matrix derivative (EMD) is an extract of porcine fetal tooth germs clinically applied to support the regrowth of periodontal tissues. Periodontal regeneration might benefit from the potential anti-inflammatory activity of EMD for epithelial cells. Our aim was, therefore, to set up a bioassay where chemokine expression is initiated in the HSC2 oral squamous carcinoma cell line and then test EMD for its capacity to lower the inflammatory response. To establish the bioassay, HSC2 cells being exposed to TNFα and LPS from E. coli (Escherichia coli) or P. gingivalis (Porphyromonas gingivalis) were subjected to RNAseq. Here, TNFα but not LPS caused a robust increase of chemokines, including CXCL1, CXCL2, CXCL8, CCL5, and CCL20 in HSC2 cells. Polymerase chain reaction confirmed the increased expression of the respective chemokines in cells exposed to TNFα and IL-1β. Under these conditions, EMD reduced the expression of all chemokines at the transcriptional level and CXCL8 by immunoassay. The TGF-β receptor type I kinase-inhibitor SB431542 reversed the anti-inflammatory activity. Moreover, EMD-activated TGF-β-canonical signaling was visualized by phosphorylation of smad3 and nuclear translocation of smad2/3 in HSC2 cells and blocked by SB431542. This observation was confirmed with primary oral epithelial cells where EMD significantly lowered the SB431542-dependent expression of CXCL8. In summary, our findings suggest that TGF-β signaling mediates the effects of EMD to lower the forced expression of chemokines in oral epithelial cells.

Bone Allograft Acid Lysates Change the Genetic Signature of Gingival Fibroblasts

Bone allografts are widely used as osteoconductive support to guide bone regrowth. Bone allografts are more than a scaffold for the immigrating cells as they maintain some bioactivity of the original bone matrix. Yet, it remains unclear how immigrating cells respond to bone allografts. To this end, we have evaluated the response of mesenchymal cells exposed to acid lysates of bone allografts (ALBA). RNAseq revealed that ALBA has a strong impact on the genetic signature of gingival fibroblasts, indicated by the increased expression of IL11, AREG, C11orf96, STC1, and GK-as confirmed by RT-PCR, and for IL11 and STC1 by immunoassays. Considering that transforming growth factor-β (TGF-β) is stored in the bone matrix and may have caused the expression changes, we performed a proteomics analysis, TGF-β immunoassay, and smad2/3 nuclear translocation. ALBA neither showed detectable TGF-β nor was the lysate able to induce smad2/3 translocation. Nevertheless, the TGF-β receptor type I kinase inhibitor SB431542 significantly decreased the expression of IL11, AREG, and C11orf96, suggesting that other agonists than TGF-β are responsible for the robust cell response. The findings suggest that IL11, AREG, and C11orf96 expression in mesenchymal cells can serve as a bioassay reflecting the bioactivity of the bone allografts.

Blocking of Caspases Exerts Anti-Inflammatory Effects on Periodontal Cells

Periodontitis is an inflammatory process that is associated with caspase activity. Caspases could thus become molecular targets for the modulation of the inflammatory response to harmful factors, such as lipopolysaccharides (LPS) and TNFα. Here, the impact of the pan-caspase inhibitor Z-VAD-FMK (carbobenzoxy-valyl-alanyl-aspartyl-[O-methyl]-fluoro-methyl ketone) on the modulation of the LPS-induced inflammatory response of murine RAW 264.7 cells and primary macrophages was examined. Moreover, the inflammatory responses of human gingival fibroblasts, HSC2 oral squamous carcinoma cells and murine ST2 mesenchymal fibroblasts when exposed to TNFα were studied. Data showed that Z-VAD-FMK significantly lowered the inflammatory response of RAW 264.7 cells and primary macrophages, as indicated by the expression of IL1 and IL6. In murine ST2 mesenchymal fibroblasts, the TNFα-induced expression of CCL2 and CCL5 was significantly reduced. In human gingival fibroblasts and HSC2 cells, Z-VAD-FMK considerably reduced the TNFα-induced expression of CXCL8 and CXCL10. These findings suggest that pharmacological blocking of caspases in an inflammatory environment lowers the expression of cytokines and chemokines in periodontal cells.

Damaged Mesenchymal Cells Dampen the Inflammatory Response of Macrophages and the Formation of Osteoclasts

Damage to mesenchymal cells occurs by dental implant drills as a consequence of shear forces and heat generation. However, how the damaged mesenchymal cells can affect the polarization of macrophages and their differentiation into osteoclastogenesis is not fully understood. To simulate cell damage, we exposed suspended ST2 murine bone marrow stromal cells to freeze/thawing or sonication cycles, followed by centrifugation. We then evaluated the lysates for their capacity to modulate lipopolysaccharide-induced macrophage polarization and RANKL-MCSF-TGF-β-induced osteoclastogenesis. We report that lysates of ST2, particularly when sonicated, greatly diminished the expression of inflammatory IL6 and COX2 as well as moderately increased arginase 1 in primary macrophages. That was confirmed by lysates obtained from the osteocytic cell line IDG-SW3. Moreover, the ST2 lysate lowered the phosphorylation of p65 and p38 as well as the nuclear translocation of p65. We further show herein that lysates of damaged ST2 reduced the formation of osteoclast-like cells characterized by their multinuclearity and the expression of tartrate-resistant phosphatase and cathepsin K. Taken together, our data suggest that thermal and mechanical damage of mesenchymal cells causes the release of as-yet-to-be-defined molecules that dampen an inflammatory response and the formation of osteoclasts in vitro.

Gingival Fibroblasts Are Sensitive to Oral Cell Lysates Indicated by Their IL11 Expression

Damaged cells that appear as a consequence of invasive dental procedures or in response to dental materials are supposed to release damage-associated signals. These damage-associated signals not only support tissue regeneration but might also contribute to unwanted fibrosis. The aim of this study was to identify a molecular target that reflects how fibroblasts respond to necrotic oral tissue cells. To simulate the cell damage, we prepared necrotic cell lysates by sonication of the osteocytic cell line IDG-SW3 and exposed them to gingival fibroblasts. RNAseq revealed a moderate increase in IL11 expression in the gingival fibroblasts, a pleiotropic cytokine involved in fibrosis and inflammation, and also in regeneration following trauma. Necrotic lysates of the human squamous carcinoma cell lines HSC2 and TR146, as well as of gingival fibroblasts, however, caused a robust increase in IL11 expression in the gingival fibroblasts. Consistently, immunoassay revealed significantly increased IL11 levels in the gingival fibroblasts when exposed to the respective lysates. Considering that IL11 is a TGF-β target gene, IL11 expression was partially blocked by SB431542, a TGF-β receptor type I kinase inhibitor. Moreover, lysates from the HSC2, TR146, and gingival fibroblasts caused a moderate smad2/3 nuclear translocation in the gingival fibroblasts. Taken together and based on IL11 expression, our findings show that fibroblasts are sensitive to damaged oral tissue cells.

Oral cell lysates reduce osteoclastogenesis in murine bone marrow cultures

Mechanical and thermal cell damage can occur due to invasive procedures related to drilling, the insertion of dental implants, and periodontal treatments. Necrotic cells release the content of their cytoplasm and membrane fragments, thereby signaling the need for repair, which includes bone resorption by osteoclasts and inflammation. Here we screened lysates from human gingival fibroblasts, HSC2 and TR146 oral squamous carcinoma cell lines, as well as murine IDG-SW3 osteocytic and RAW264.7 macrophage cell lines for their potential to modulate in vitro osteoclastogenesis in murine bone marrow cultures. We also tested the impact of necrotic lysates on modulating the expression of inflammatory cues in murine ST2 bone marrow stromal cells. We report here that independent of human or murine origin, all cell lysates significantly reduced in vitro osteoclastogenesis in bone marrow cultures, as indicated by the expression of the osteoclast marker genes cathepsin K and tartrate-resistant acid phosphatase and the respective histochemical staining in multinucleated cells. We also found that lysates from HSC2 and TR146 cells significantly pushed the expression of CCL2, CCL5, CXCL1, IL1, and IL6 in ST2 cells. These findings suggest that oral cell lysates reduce in vitro osteoclastogenesis, but only damaged oral squamous carcinoma cells can force murine stromal cells to produce an inflammatory environment.