Cultivation of EPC and co-cultivation with MSC on β-TCP granules in vitro is feasible without fibronectin coating but influenced by scaffolds' design

Pretreatment of Mesenchymal Stem Cells with Electrical Stimulation as a Strategy to Improve Bone Tissue Engineering Outcomes

Electrical stimulation (EStim), whether used alone or in combination with bone tissue engineering (BTE) approaches, has been shown to promote bone healing. In our previous in vitro studies, mesenchymal stem cells (MSCs) were exposed to EStim and a sustained, long-lasting increase in osteogenic activity was observed. Based on these findings, we hypothesized that pretreating MSC with EStim, in 2D or 3D cultures, before using them to treat large bone defects would improve BTE treatments. Critical size femur defects were created in 120 Sprague-Dawley rats and treated with scaffold granules seeded with MSCs that were pre-exposed or not (control group) to EStim 1 h/day for 7 days in 2D (MSCs alone) or 3D culture (MSCs + scaffolds). Bone healing was assessed at 1, 4, and 8 weeks post-surgery. In all groups, the percentage of new bone increased, while fibrous tissue and CD68+ cell count decreased over time. However, these and other healing features, like mineral density, bending stiffness, the amount of new bone and cartilage, and the gene expression of osteogenic markers, did not significantly differ between groups. Based on these findings, it appears that the bone healing environment could counteract the long-term, pro-osteogenic effects of EStim seen in our in vitro studies. Thus, EStim seems to be more effective when administered directly and continuously at the defect site during bone healing, as indicated by our previous studies.

Measuring Bone Healing: Parameters and Scores in Comparison

(1) Background: Bone healing is a complex process that can not be replicated in its entirety in vitro. Research on bone healing still requires the animal model. The critical size femur defect (CSFD) in rats is a well-established model for fractures in humans that exceed the self-healing potential. New therapeutic approaches can be tested here in vivo. Histological, biomechanical, and radiological parameters are usually collected and interpreted. However, it is not yet clear to what extent they correlate with each other and how necessary it is to record all parameters. (2) Methods: The basis for this study was data from three animal model studies evaluating bone healing. The µCT and histological (Movat pentachrome, osteocalcin) datasets/images were reevaluated and correlation analyses were then performed. Two image processing procedures were compared in the analysis of the image data. (3) Results: There was a significant correlation between the histologically determined bone fraction (Movat pentachrome staining) and bending stiffness. Bone fraction determined by osteocalcin showed no prognostic value. (4) Conclusions: The evaluation of the image datasets using ImageJ is sufficient and simpler than the combination of both programs. Determination of the bone fraction using Movat pentachrome staining allows conclusions to be drawn about the biomechanics of the bone. A standardized procedure with the ImageJ software is recommended for determining the bone proportion.

Polydopamine-coated 3D-printed β-tricalcium phosphate scaffolds to promote the adhesion and osteogenesis of BMSCs for bone-defect repair: mRNA transcriptomic sequencing analysis

Cellular bioactivity and tissue regeneration can be affected by coatings on tissue-engineered scaffolds. Using mussel-inspired polydopamine (PDA) is a convenient and effective approach to surface modification. Therefore, 3D-printed β-tricalcium phosphate (β-TCP) scaffolds were coated with PDA in this study. The effects of the scaffolds on the adhesion and osteogenic differentiation of seeded bone marrow mesenchymal stem cells (BMSCs) in vitro and on new-bone formation in vivo were investigated. The potential mechanisms and related differential genes were assessed using mRNA sequencing. It was seen that PDA coating increased the surface roughness of the 3D-printed β-TCP scaffolds. Furthermore, it prompted the adhesion and osteogenic differentiation of seeded BMSCs. mRNA sequencing analysis revealed that PDA coating might affect the osteogenic differentiation of BMSCs through the calcium signaling pathway, Wnt signaling pathway, TGF-beta signaling pathway, etc. Moreover, the expression of osteogenesis-related genes, such as R-spondin 1 and chemokine c-c-motif ligand 2, was increased. Finally, both the 3D-printed β-TCP scaffolds and PDA-coated scaffolds could significantly accelerate the formation of new bone in critical-size calvarial defects in rats compared with the control group; and the new bone formation was obviously higher in the PDA-coated scaffolds than in β-TCP scaffolds. In summary, 3D-printed β-TCP scaffolds with a PDA coating can improve the physicochemical characteristics and cellular bioactivity of the scaffold surface for bone regeneration. Potential differential genes were identified, which can be used as a foundation for further research.

Estrogen Facilitates the Healing of Diabetic Wounds via Ameliorating the Function of Bone Marrow Mesenchymal Stem Cells

We inted to elucidate the impacts of estrogen on the bone marrow-originated endothelial progenitor cells (BM-EPC) and mesenchymal stem cells (BM-MSC) as well as on diabetic wound healing. The skin injury models were established using the diabetic mice (db+/db+) and non-diabetic vector mice and then treated with estrogen-based or placebo-based cream. On the 5th day following injury, BM cells were collected for quantification of EPCs and MSCs and colony-forming units along with analysis of wound healing rate and densities of blood vessels and scars following whole-body perfusion. EPCs were identified through staining of VEGFR1 and CD34 by immunohistochemistrical analyses. In contrast to placebo, treatment with estrogen significantly intensified the colony formation of EPC and MSC, and further promoted the viability and proliferation potential of cells. Meanwhile, estrogen-treated mice exhibited increased recruitment of EPC to the diabetic wounds along with increased vascular density. Additionally, on day 6 after injury, estrogen significantly accelerated wound healing, which was mediated by the enhanced collagen deposition through boosting MSC activation and differentiation, resulting in elevated scar density. In conclusion, estrogen prompts wound healing of diabetic mice via ameliorating the function of BM-derived EPC and MSC, so as to accelerate the neovascularization at the sites of wounds in diabetic mice.

Co-cultivation of progenitor cells enhanced osteogenic gene expression and angiogenesis potential in vitro

Objectives

The efficiencies of osteogenesis and angiogenesis present challenges that need to be overcome before bone tissue engineering can be widely applied to clinical uses. We aimed to optimize an in vitro culture system to enhance osteogenesis and angiogenesis. We investigated if hematopoietic stem cells (HSCs) promoted osteogenesis in vitro when co-cultured with mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs).

Methods

MSC/HSC, MSC/EPC/HSC, and MSC/EPC co-cultures were incubated for 21 days. Alkaline phosphatase (ALP) activity and calcium content were analyzed to assess mineralization. Expression levels of genes encoding osteogenesis-related proteins (ALP (ALPL), collagen type IA (COL1A1), osteocalcin (BGLAP), and osteopontin (OSTP)) were also evaluated by measuring mRNA levels at day 28. Angiogenesis was evaluated by tube-formation assay.

Results

COL1A1, OSTP, ALPL, and BGLAP genes were upregulated in MSC/HSC and MSC/EPC/HSC co-cultures compared with the MSC/EPC group. Upregulation was strongest in the MSC/EPC/HSC co-cultures. There were no significant changes in ALP levels and calcium content, but ALP activity was slightly higher and calcium content was relatively lower in the MSC/EPC and MSC/EPC/HSC groups.

Conclusions

Co-culture of MSCs with HSCs or EPCs/HSCs upregulated the expression of osteogenesis-related genes but did not affect the efficiency of osteogenesis.

Determination of the effective dose of bone marrow mononuclear cell therapy for bone healing in vivo

Introduction

Cell-based therapy by bone marrow mononuclear cells (BMC) in a large-sized bone defect has already shown improved vascularization and new bone formation. First clinical trials are already being conducted. BMC were isolated from bone marrow aspirate and given back to patients in combination with a scaffold within some hours. However, the optimal concentration of BMC has not yet been determined for bone healing. With this study, we want to determine the optimal dosage of the BMC in the bone defect to support bone healing.

Material and methods

Scaffolds with increasing BMC concentrations were inserted into a 5 mm femoral defect, cell concentrations of 2 × 10⁶ BMC/mL, 1 × 10⁷ BMC/mL and 2 × 10⁷ BMC/mL were used. Based on the initial cell number used to colonize the scaffolds, the groups are designated 1 × 10⁶, 5 × 10⁶ and 1 × 10⁷ group. Bone healing was assessed biomechanically, radiologically (µCT), and histologically after 8 weeks healing time.

Results

Improved bone healing parameters were noted in the 1 × 10⁶ and 5 × 10⁶ BMC groups. A significantly higher BMD was observed in the 1 × 10⁶ BMC group compared to the other groups. Histologically, a significantly increased bone growth in the defect area was observed in group 5 × 10⁶ BMC. This finding could be supported radiologically.

Conclusion

It was shown that the effective dose of BMC for bone defect healing ranges from 2 × 10⁶ BMC/mL to 1 × 10⁷ BMC/mL. This concentration range seems to be the therapeutic window for BMC-supported therapy of large bone defects. However, further studies are necessary to clarify the exact BMC-dose dependent mechanisms of bone defect healing and to determine the therapeutically effective range more precisely.

Decreased numbers of circulating endothelial progenitor cells are associated with hyperglycemia in patients with traumatic brain injury

Hyperglycemia reduces the number of circulating endothelial progenitor cells, accelerates their senescence and impairs their function. However, the relationship between blood glucose levels and endothelial progenitor cells in peripheral blood of patients with traumatic brain injury is unclear. In this study, 101 traumatic brain injury patients admitted to the Department of Neurosurgery, Tianjin Medical University General Hospital or the Department of Neurosurgery, Tianjin Huanhu Hospital, China, were enrolled from April 2005 to March 2007. The number of circulating endothelial progenitor cells and blood glucose levels were measured at 1, 4, 7, 14 and 21 days after traumatic brain injury by flow cytometry and automatic biochemical analysis, respectively. The number of circulating endothelial progenitor cells and blood sugar levels in 37 healthy control subjects were also examined. Compared with controls, the number of circulating endothelial progenitor cells in traumatic brain injury patients was decreased at 1 day after injury, and then increased at 4 days after injury, and reached a peak at 7 days after injury. Compared with controls, blood glucose levels in traumatic brain injury patients peaked at 1 day and then decreased until 7 days and then remained stable. At 1, 4, and 7 days after injury, the number of circulating endothelial progenitor cells was negatively correlated with blood sugar levels (r = −0.147, P < 0.05). Our results verify that hyperglycemia in patients with traumatic brain injury is associated with decreased numbers of circulating endothelial progenitor cells. This study was approved by the Ethical Committee of Tianjin Medical University General Hospital, China (approval No. 200501) in January 2015.