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

Abstract

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.

Oral Cell Lysates Reduce the Inflammatory Response of Activated Macrophages

“…However, ST2 and IDG-SW3 cell lines do not necessarily represent the necrotic cell damage in the oral cavity; hence, we have extended the original work, now including gingival fibroblasts and the oral squamous carcinoma cell lines HSC2 and TR146 to represent the oral epithelial cell lineage. Consistent with our findings obtained with ST2 and IDG-SW3 cells, necrotic cell lysates from gingival fibroblasts and the oral epithelial cell lines HSC2 and TR146 greatly diminished the LPS as well as the poly (1:C) HMW-induced inflammatory response of RAW264.7 macrophages—and again [ 24 ], using sonication, which is more potent compared to freezing/thawing, to prepare the necrotic cell lysates.…”

“…In contrast, however, extracellular vesicles released from damaged mesenchymal cells can prevent the M1 polarization in LPS-stimulated RAW264.7 macrophages [ 21 , 22 ]. This aspect supports our recent observations that lysates prepared from necrotic murine bone marrow stromal ST2 and the osteocytic cell line IDG-SW3 are polarization inhibitors of LPS-induced RAW264.7 macrophages [ 24 ]. Thus, necrotic cell lysates are potential modulators of inflammatory activity.…”

“…If we relate our findings to those of others, we have to acknowledge our recent work on necrotic cell lysates prepared from the murine bone marrow mesenchymal cell line ST2 cell and the osteocytic cell line IDG-SW3; these cell lysates clearly show anti-inflammatory activity indicated by the dampening of the LPS-induced macrophage polarization [ 24 ]. However, ST2 and IDG-SW3 cell lines do not necessarily represent the necrotic cell damage in the oral cavity; hence, we have extended the original work, now including gingival fibroblasts and the oral squamous carcinoma cell lines HSC2 and TR146 to represent the oral epithelial cell lineage.…”

“…We were surprised to learn that all the cell lysates can lower LPS and poly (I:C) HMW-induced inflammatory response in a macrophage cell line. Actually, this paper is a continuation and more of a refinement of our original observation with mouse mesenchymal cells (ST2 bone marrow stromal cells and IDG-SW3 osteocytic cells) [ 24 ]. Here, we have mainly focused on oral cells of human origin, thus confirming and strengthening our previous observation.…”