Mechanical compression simulating orthodontic tooth movement in in vitro models induces pro-inflammatory cytokine expression in periodontal ligament (PDL) cells. Our previous work shows that TLR4 is involved in this process. Here, primary PDL cells are isolated and characterized to better understand the cell signaling downstream of key molecules involved in the process of sterile inflammation via TLR4. The TLR4 monoclonal blocking antibody significantly reverses the upregulation of phospho-AKT, caused by compressive force, to levels comparable to controls by inhibition of TLR4. Phospho-ERK and phospho-p38 are also modulated in the short term via TLR4. Additionally, moderate compressive forces of 2 g/cm², a gold standard for static compressive mechanical stimulation, are not able to induce translocation of Nf-kB and phospho-ERK into the nucleus. Accordingly, we demonstrated for the first time that TLR4 is also one of the triggers for signal transduction under compressive force. The TLR4, one of the pattern recognition receptors, is involved through its specific molecular structures on damaged cells during mechanical stress. Our findings provide the basis for further research on TLR4 in the modulation of sterile inflammation during orthodontic therapy and periodontal remodeling.

Tissue engineering is a steadily growing field of research due to its wide‐ranging applicability in the field of regenerative medicine. Application‐dependent mechanical properties of a scaffold material as well as its biocompatibility and tailored functionality represent particular challenges. Here the properties of fibrin‐based hydrogels reinforced by functional cytocompatible poly( N ‐vinylcaprolactam)‐based (PVCL) microgels are studied and evaluated. The employment of temperature‐responsive microgels decorated by epoxy groups for covalent binding to the fibrin is studied as a function of cross‐linking degree within the microgels, microgel concentration, as well as temperature. Rheology reveals a strong correlation between the mechanical properties of the reinforced fibrin‐based hydrogels and the microgel rigidity and concentration. The incorporated microgels serve as cross‐links, which enable temperature‐responsive behavior of the hydrogels, and slow down the hydrogel degradation. Microgels can be additionally used as carriers for active drugs, as demonstrated for dexamethasone. The microgels’ temperature‐responsiveness allows for triggered release of payload, which is monitored using a bioassay. The cytocompatibility of the microgel‐reinforced fibrin‐based hydrogels is demonstrated by LIVE/DEAD staining experiments using human mesenchymal stem cells. The microgel‐reinforced hydrogels are a promising material for tissue engineering, owing to their superior mechanical performance and stability, possibility of drug release, and retained biocompatibility.

Background: Teeth and supporting oral tissues are attractive and accessible sources of stem cells. Periodontal ligament stem cells (PDLSC) are readily isolated from extracted third molars, and exhibit the ability to self‐renew and differentiate into multiple mesodermal cell fates. Clinical experience suggests that the exact location of periodontal defects affects the oral bone remodeling and wound healing. Compared to the mandible, the maxilla heals quicker and more efficiently. Angiogenesis is key in tissue regeneration including dental tissues, yet few studies focus on the angiogenic potential of PDLSC, none of which considered the differences between upper and lower jaw PDLSC (u‐PDLSC and l‐PDLSC, respectively).Methods: Here we studied the angiogenic potential of u‐PDLSC and l‐PDLSC and compared the results to well‐established mesenchymal stem cells (MSC). Cells were characterized in terms of surface markers, proliferation, and vascular endothelial growth factor (VEGF) secretion, and angiogenic assays were performed. Newly formed capillaries were stained with CD31, and their expression of platelet endothelial cell adhesion molecule (PECAM‐1), angiopoietin 2 (ANGPT2), and vascular endothelial growth factor receptor 1 and 2 (VEGFR‐1, VEGFR‐2) were measured.Results: Periodontal stem cells from the upper jaw showed a higher proliferation capacity, secreted more VEGF, and formed capillary networks faster and denser than l‐PDLSC. Gene expression of angiogenesis‐related genes was significantly higher in u‐PDLSC than in l‐PDLSC or MSC, given that culture conditions were suitable.Conclusion: The oral cavity is a valuable source of stem cells, particularly PDLSC, which are promising for oral tissue engineering due to their robust growth, lifelong accessibility, low immunogenicity, and strong differentiation potential. Notably, u‐PDLSC exhibit higher VEGF secretion and accelerate capillary formation compared to l‐PDLSC or MSC. This study suggests a potential molecular mechanism in capillary formation, emphasizing the significance of precise location isolation of PDLSC.

Within the heterogenous pool of bone marrow stromal cells, mesenchymal stromal cells (MSCs) are of particular interest because of their hematopoiesis-supporting capacities, contribution to disease progression, therapy resistance, and leukemic initiation. Cultured bone marrow-derived stromal cells (cBMSCs) are used for in vitro modeling of hematopoiesis-stroma interactions, validation of disease mechanisms, and screening for therapeutic targets. Here, we place cBMSCs (mouse and human) in a bone marrow tissue context by systematically comparing the transcriptome of plastic-adherent cells on a single-cell level with in vivo counterparts. Cultured BMSCs encompass a rather homogenous cell population, independent of the isolation method used and, although still possessing hematopoiesis-supporting capacity, are distinct from freshly isolated MSCs and more akin to in vivo fibroblast populations. Informed by combined cell trajectories and pathway analyses, we illustrate that TGFb inhibition in vitro can preserve a more "MSC"-like phenotype.

Periodontal defects’ localization affects wound healing and bone remodeling, with faster healing in the upper jaw compared to the lower jaw. While differences in blood supply, innervation, and odontogenesis contribute, cell-intrinsic variances may exist. Few studies explored cell signaling in periodontal ligament stem cells (PDLSC), overlooking mandible-maxilla disparitiesUsing kinomics technology, we investigated molecular variances in PDLSC. Characterization involved stem cell surface markers, proliferation, and differentiation capacities. Kinase activity was analyzed via multiplex kinase profiling, mapping differential activity in known gene regulatory networks. Upstream kinase analysis identified stronger EphA receptor expression in the mandible, potentially inhibiting osteogenic differentiation. The PI3K-Akt pathway showed higher activity in lower-jaw PDLSC. PDLSC from the upper jaw exhibit superior proliferation and differentiation capabilities. Differential activation of gene regulatory pathways in upper vs. lower-jaw PDLSC suggests implications for regenerative therapies.

Article 05-1700-P7 was published on September 1, 2021 in the journal Biomedical Engineering / Biomedizinische Technik (volume 66, issue s1).