Diabetes impairs periosteal progenitor regenerative potential

Skeletal stem and progenitor cells in bone development and repair

Bone development, growth, and repair are complex processes involving various cell types and interactions, with central roles played by skeletal stem and progenitor cells. Recent research brought new insights into the skeletal precursor populations that mediate intramembranous and endochondral bone development. Later in life, many of the cellular and molecular mechanisms determining development are reactivated upon fracture, with powerful trauma-induced signaling cues triggering a variety of postnatal skeletal stem/progenitor cells (SSPCs) residing near the bone defect. Interestingly, in this injury context, the current evidence suggests that the fates of both SSPCs and differentiated skeletal cells can be considerably flexible and dynamic, and that multiple cell sources can be activated to operate as functional progenitors generating chondrocytes and/or osteoblasts. The combined implementation of in vivo lineage tracing, cell surface marker-based cell selection, single-cell molecular analyses, and high-resolution in situ imaging has strongly improved our insights into the diversity and roles of developmental and reparative stem/progenitor subsets, while also unveiling the complexity of their dynamics, hierarchies, and relationships. Albeit incompletely understood at present, findings supporting lineage flexibility and possibly plasticity among sources of osteogenic cells challenge the classical dogma of a single primitive, self-renewing, multipotent stem cell driving bone tissue formation and regeneration from the apex of a hierarchical and strictly unidirectional differentiation tree. We here review the state of the field and the newest discoveries in the origin, identity, and fates of skeletal progenitor cells during bone development and growth, discuss the contributions of adult SSPC populations to fracture repair, and reflect on the dynamism and relationships among skeletal precursors and differentiated cell lineages. Further research directed at unraveling the heterogeneity and capacities of SSPCs, as well as the regulatory cues determining their fate and functioning, will offer vital new options for clinical translation toward compromised fracture healing and bone regenerative medicine.

Tibial transverse transport induces mobilization of endothelial progenitor cells to accelerate angiogenesis and ulcer wound healing through the VEGFA/CXCL12 pathway

BACKGROUND

Tibial transverse transport (TTT) can promote the healing of chronic foot ulcers, but the specific cellular and molecular mechanisms by which TTT promotes wound healing remain unclear.

METHODS

New Zealand White rabbits were selected to induce foot ulcer models. The treatment included unilateral TTT surgery and bilateral TTT surgery. Observation of tissue neovascularization structure by HE staining and CD31 immunofluorescence detection. Collagen fiber formation was detected through the Masson staining. The mobilization of endothelial progenitor cell (EPCs) were analyzed by VEGFR2 immunofluorescence detection and flow cytometry detection of the number of VEGFR2/Tie-2-positive cells in peripheral blood. ELISA and qPCR assay were performed to detect VEGFA and CXCL12 levels.

RESULTS

The complete healing time of ulcer surfaces in sham, unilateral and bilateral TTT groups was about 22 days, 17 days and 13 days, respectively. TTT treatment significantly increased the deposition of granulation tissue and epithelialization of wounds. It also led to an increase in collagen fiber content and the level of the microvascular marker CD31. Furthermore, TTT treatment upregulated the levels of VEGFA and CXCL12 in peripheral blood and wound tissues, as well as increased the expression of VEGFR2 in wound tissues and the proportion of VEGFR2/Tie-2 in peripheral blood. Moreover, these effects of TTT treatment in the bilateral group was more significant than that in the unilateral group.

CONCLUSIONS

TTT may facilitate wound fibroblasts to release VEGFA and CXCL12, causing EPC mobilization, thus promoting angiogenesis and ulcer wound healing.

Advantages and Limitations of Diabetic Bone Healing in Mouse Models: A Narrative Review

Diabetes represents a major risk factor for impaired fracture healing. Type 2 diabetes mellitus is a growing epidemic worldwide, hence an increase in diabetes-related complications in fracture healing can be expected. However, the underlying mechanisms are not yet completely understood. Different mouse models are used in preclinical trauma research for fracture healing under diabetic conditions. The present review elucidates and evaluates the characteristics of state-of-the-art murine diabetic fracture healing models. Three major categories of murine models were identified: Streptozotocin-induced diabetes models, diet-induced diabetes models, and transgenic diabetes models. They all have specific advantages and limitations and affect bone physiology and fracture healing differently. The studies differed widely in their diabetic and fracture healing models and the chosen models were evaluated and discussed, raising concerns in the comparability of the current literature. Researchers should be aware of the presented advantages and limitations when choosing a murine diabetes model. Given the rapid increase in type II diabetics worldwide, our review found that there are a lack of models that sufficiently mimic the development of type II diabetes in adult patients over the years. We suggest that a model with a high-fat diet that accounts for 60% of the daily calorie intake over a period of at least 12 weeks provides the most accurate representation.

A Model of Immediate Implant Placement to Evaluate Early Osseointegration in 129/Sv Diabetic Mice

PURPOSE

To analyze the process of early oral osseointegration of titanium (Ti) implants in diabetic 129/Sv mice through microCT and histologic and immunohistochemical analysis.

MATERIALS AND METHODS

A group of 30 male 129/Sv mice was equally subdivided into two groups: (1) nondiabetic (ND), in which mice did not undergo systemic alterations and received a standard diet, and (2) diabetic (D), in which mice were provided a high-fat diet from the age of 6 weeks until the conclusion of the study and received two intraperitoneal (IP) injections of streptozotocin (STZ) at a concentration of 100 mg/Kg each. Each mouse underwent extraction of a maxillary first molar, and customized Ti screws (0.50 mm diameter, 1.5 mm length) were placed in the residual alveolar sockets of the palatal roots. At 7 and 21 days after implant placement, the animals were euthanized for maxilla and pancreas collection. Maxillae containing Ti implants were analyzed with microCT, histology, and immunohistochemistry for cells that were positive for F4/80, CD146, runt-related transcription factor 2 (Runx2), and proliferating cell nuclear antigen (PCNA). Pancreata were histologically analyzed. Quantitative data were statistically analyzed with a significance level at 5% (P < .05).

RESULTS

ND mice presented successful healing and osseointegration, with a significantly higher fraction of bone volume compared to D mice, both at the alveolar sockets (53.39 ± 5.93 and 46.08 ± 3.18, respectively) and at the implant sites (68.88 ± 7.07 and 44.40 ± 6.98, respectively) 21 days after implant placement. Histologic evaluation revealed that the ND mice showed a significant decrease in inflammatory infiltrate and a significant increase in newly formed bone matrix at 21 days, whereas peri-implant sites in the D mice were predominantly encapsulated by fibrous tissue and chronic inflammatory infiltrate. Immunohistochemical characterization revealed higher Runx2 osteoblast differentiation and higher cell proliferation activity in the ND mice at 7 days, while higher amounts of macrophages were present in D mice at 7 and 21 days. Interestingly, no differences were found in CD146-positive cells when comparing ND and D mice.

CONCLUSIONS

This study evaluated the effects of immediate dental implant placement in 129/Sv diabetic mice by using specific healing markers to identify changes in cellular events involved in early oral osseointegration. This approach may serve as tool to evaluate new materials and surface coatings to improve osseointegration in diabetic patients.

Wnt-associated adult stem cell marker Lgr6 is required for osteogenesis and fracture healing

Despite the remarkable regenerative capacity of skeletal tissues, nonunion of bone and failure of fractures to heal properly presents a significant clinical concern. Stem and progenitor cells are present in bone and become activated following injury; thus, elucidating mechanisms that promote adult stem cell-mediated healing is important. Wnt-associated adult stem marker Lgr6 is implicated in the regeneration of tissues with well-defined stem cell niches in stem cell-reliant organs. Here, we demonstrate that Lgr6 is dynamically expressed in osteoprogenitors in response to fracture injury. We used an Lgr6-null mouse model and found that Lgr6 expression is necessary for maintaining bone volume and efficient postnatal bone regeneration in adult mice. Skeletal progenitors isolated from Lgr6-null mice have reduced colony-forming potential and reduced osteogenic differentiation capacity due to attenuated cWnt signaling. Lgr6-null mice consist of a lower proportion of self-renewing stem cells. In response to fracture injury, Lgr6-null mice have a deficiency in the proliferation of periosteal progenitors and reduced ALP activity. Further, analysis of the bone regeneration phase and remodeling phase of fracture healing in Lgr6-null mice showed impaired endochondral ossification and decreased mineralization. We propose that in contrast to not being required for successful skeletal development, Lgr6-positive cells have a direct role in endochondral bone repair.

Differential expression and effect analysis of lncRNA-mRNA in congenital pseudarthrosis of the tibia

Background: To analyze the lncRNA-mRNA differential expression and co-expression network of periosteal stem cells (PSCs) from congenital pseudarthrosis of the tibia (CPT) and normal patients, and to explore the role of key lncRNAs. Methods: Differentially expressed lncRNAs and mRNAs in PSCs were obtained by sequencing, and biological functions of differentially expressed mRNAs were detected by gene ontology (GO), Kyoto encyclopedia of genes and genomes (KEGG) pathway and protein -protein interaction (PPI) analysis. The co-expression network of lncRNA-mRNA was constructed by correlation analysis of differentially expressed lncRNAs and mRNAs, and the key lncRNAs were screened according to the connectivity degree. After that, the cis-regulated target genes of differential expressed lncRNAs and mRNAs were predicted. Results: A total of 194 differentially expressed lncRNAs were identified, including 73 upregulated and 121 downregulated genes. A total of 822 differentially expressed mRNAs were identified, including 311 upregulated and 511 downregulated genes. GO, KEGG and PPI enrichment analysis showed that the regulatory function of differentially expressed mRNAs were mainly gathered in skeletal system development and tissue morphogenesis. The co-expression network with 226 nodes and 3,390 edges was constructed based on correlation analysis. A total of 10 key lncRNAs, including FAM227B, POM121L9P, AF165147 and AC103702, were screened according to connectivity degree. Prediction of target genes indicated that FAM227B-FGF7 and AC103702-HOXB4/5/6 may play an important role in the pathogenesis of CPT. Conclusion: A total of 10 key lncRNAs, including FAM227B, POM121L9P, AF165147, and AC103702, occupy the core position in the co-expression network, suggesting that these lncRNAs and their target genes may play an important role in the pathogenesis of CPT.

Adipose-derived stem cell spheroid-laden microbial transglutaminase cross-linked gelatin hydrogel for treating diabetic periodontal wounds and craniofacial defects

BACKGROUND

Diabetes mellitus deteriorates the destruction and impairs the healing of periodontal wounds and craniofacial defects. This study is to evaluate the potential of self-assembled adipose-derived stem cell spheroids (ADsp) in microbial transglutaminase cross-linked gelatin hydrogel (mTG) for treating diabetic periodontal wounds and craniofacial defects.

METHODS

Human adipose-derived stem cells (ADSCs) were isolated by lipoaspiration, pluripotent genes and trilineage differentiation were examined, and the maintenance of ADsp properties in mTG was verified. Oral mucosal wounds and calvarial osseous defects were created in diabetic rats. Gross observation, histologic evaluation, and immunohistochemistry for proliferating cells and keratinization were conducted in the mucosal wounds within 4-28 days. Micro-CT imaging, histologic evaluation, and immunohistochemistry for proliferating cells and osteogenic differentiation were conducted in the osseous defects at 7 and 28 days.

RESULTS

ADSCs expressed pluripotent genes and were capable of trilineage differentiation. ADsp retained morphology and stemness in mTG. In diabetic mucosal wounds, wound closure, epithelization, and keratinization were accelerated in those with ADsp and ADsp-mTG. In diabetic osseous defects, osteogenic differentiation markers were evidently expressed, cell proliferation was promoted from day 7, and bone formation was significantly promoted at day 28 in those with osteogenically pretreated ADsp-mTG.

CONCLUSIONS

ADsp-mTG accelerated diabetic oral mucosal wound healing, and osteogenically pretreated ADsp-mTG promoted diabetic osseous defect regeneration, proving that ADsp-mTG facilitated diabetic periodontal wound healing and craniofacial osseous defect regeneration.

Distinct osteogenic effect of different periosteum derived cells via Hippo-YAP cascade signaling

Periosteum is expected for bone repairing due to excellent regenerative potential. PDCs are the main source of cells for promoting bone repair. However, PDCs from different sites have been confirmed to be site specific due to their distinct embryonic origin and the methods of bone formation. Hippo-YAP pathway is proved to play a critical role in fate decision of mesenchymal stem cells. The effect of Hippo-YAP on PDCs has not been reported so far. Hence, we aim to explore the differences of PDCs from mandible and femur along with their possible responses to YAP signaling. mPDCs and fPDCs were obtained and tested through flow cytometry for identification. Follow-up results illustrated mPDCs was cubic shape and with better proliferation while fPDCs preferred slender cell shape with worse cell viability compared with mPDCs. mPDCs was superior to fPDCs in ALP activity, related mRNA expression and calcium deposits in late stage. Interestingly, downregulation of YAP promoted the ALP activity, related mRNA expression and calcium deposits of fPDCs while hindered that of mPDCs in vitro. Moreover, implant animal model in mandible and femur were constructed for evaluation in vivo. Histological results were similar to the results in vitro. We speculate this may result from their different embryonic origin and the way of bone formation. Taken together, results available suggested that mPDCs may serve as more optimal seed cells for tissue engineering compared with fPDCs; however, considering their different response to YAP signaling, to ensure sufficient YAP expression in mPDCs and appropriate declining YAP expression in fPDCs may establish better osteogenesis.

Periosteal Skeletal Stem and Progenitor Cells in Bone Regeneration

PURPOSE OF REVIEW

The periosteum, the outer layer of bone, is a major source of skeletal stem/progenitor cells (SSPCs) for bone repair. Here, we discuss recent findings on the characterization, role, and regulation of periosteal SSPCs (pSSPCs) during bone regeneration.

RECENT FINDINGS

Several markers have been described for pSSPCs but lack tissue specificity. In vivo lineage tracing and transcriptomic analyses have improved our understanding of pSSPC functions during bone regeneration. Bone injury activates pSSPCs that migrate, proliferate, and have the unique potential to form both bone and cartilage. The injury response of pSSPCs is controlled by many signaling pathways including BMP, FGF, Notch, and Wnt, their metabolic state, and their interactions with the blood clot, nerve fibers, blood vessels, and macrophages in the fracture environment. Periosteal SSPCs are essential for bone regeneration. Despite recent advances, further studies are required to elucidate pSSPC heterogeneity and plasticity that make them a central component of the fracture healing process and a prime target for clinical applications.

Diabetes and Impaired Fracture Healing: A Narrative Review of Recent Literature

PURPOSE OF THE REVIEW

Diabetes mellitus is a chronic metabolic disorder commonly encountered in orthopedic patients. Both type 1 and type 2 diabetes mellitus increase fracture risk and impair fracture healing. This review examines complex etiology of impaired fracture healing in diabetes.

RECENT FINDINGS

Recent findings point to several mechanisms leading to orthopedic complications in diabetes. Hyperglycemia and chronic inflammation lead to increased formation of advanced glycation end products and generation of reactive oxygen species, which in turn contribute to the disruption in osteoblast and osteoclast balance leading to decreased bone formation and heightening the risk of nonunion or delayed union as well as impaired fracture healing. The mechanisms attributing to this imbalance is secondary to an increase in pro-inflammatory mediators leading to premature resorption of callus cartilage and impaired bone formation due to compromised osteoblast differentiation and their apoptosis. Other mechanisms include disruption in the bone's microenvironment supporting different stages of healing process including hematoma and callus formation, and their resolution during bone remodeling phase. Complications of diabetes including peripheral neuropathy and peripheral vascular disease also contribute to the impairment of fracture healing. Certain diabetic drugs may have adverse effects on fracture healing. The pathophysiology of impaired fracture healing in diabetic patients is complex. This review provides an update of the most recent findings on how key mediators of bone healing are affected in diabetes.