Enhancing proliferation and optimizing the culture condition for human bone marrow stromal cells using hypoxia and fibroblast growth factor-2

The potential mechanism of hypoxia-induced tenogenic differentiation of mesenchymal stem cell for tendon regeneration

Tendon injuries account up to 50% of all musculoskeletal problems and remains a challenge to treat owing to the poor intrinsic reparative ability of tendon tissues. The natural course of tendon healing is very slow and often leads to fibrosis and disorganized tissues with inferior biomechanical properties. Mesenchymal stem cells (MSC) therapy is a promising alternative strategy to augment tendon repair due to its proliferative and multilineage differentiation potential. Hypoxic conditioning of MSC have been shown to enhance their tenogenic differentiation capacity. However, the mechanistic pathway by which this is achieved is yet to be fully defined. A key factor involved in this pathway is hypoxia-inducible factor-1-alpha (HIF-1α). This review aims to discuss the principal mechanism underlying the enhancement of MSC tenogenic differentiation by hypoxic conditioning, particularly the central role of HIF-1α in mediating activation of tenogenic pathways in the MSC. We focus on the interaction between HIF-1α with fibroblast growth factor-2 (FGF-2) and transforming growth factor-beta 1 (TGF-β1) in regulating MSC tenogenic differentiation pathways in hypoxic conditions. Strategies to promote stabilization of HIF-1α either through direct manipulation of oxygen tension or the use of hypoxia mimicking agents are therefore beneficial in increasing the efficacy of MSC therapy for tendon repair.

Construction of Bone Hypoxic Microenvironment Based on Bone-on-a-Chip Platforms

The normal physiological activities and functions of bone cells cannot be separated from the balance of the oxygenation level, and the physiological activities of bone cells are different under different oxygenation levels. At present, in vitro cell cultures are generally performed in a normoxic environment, and the partial pressure of oxygen of a conventional incubator is generally set at 141 mmHg (18.6%, close to the 20.1% oxygen in ambient air). This value is higher than the mean value of the oxygen partial pressure in human bone tissue. Additionally, the further away from the endosteal sinusoids, the lower the oxygen content. It follows that the construction of a hypoxic microenvironment is the key point of in vitro experimental investigation. However, current methods of cellular research cannot realize precise control of oxygenation levels at the microscale, and the development of microfluidic platforms can overcome the inherent limitations of these methods. In addition to discussing the characteristics of the hypoxic microenvironment in bone tissue, this review will discuss various methods of constructing oxygen gradients in vitro and measuring oxygen tension from the microscale based on microfluidic technology. This integration of advantages and disadvantages to perfect the experimental study will help us to study the physiological responses of cells under more physiological-relevant conditions and provide a new strategy for future research on various in vitro cell biomedicines.

Evaluating the Effect of Hypoxia on Human Adult Mesenchymal Stromal Cell Chondrogenesis In Vitro: A Systematic Review

Human adult mesenchymal stromal cells (MSCs) from a variety of sources may be used to repair defects in articular cartilage by inducing them into chondrogenic differentiation. The conditions in which optimal chondrogenic differentiation takes place are an area of interest in the field of tissue engineering. Chondrocytes exist in vivo in a normally hypoxic environment and thus it has been suggested that exposing MSCs to hypoxia may also contribute to a beneficial effect on their differentiation. There are two main stages in which MSCs can be exposed to hypoxia, the expansion phase when cells are cultured, and the differentiation phase when cells are induced with a chondrogenic medium. This systematic review sought to explore the effect of hypoxia at these two stages on human adult MSC chondrogenesis in vitro. A literature search was performed on PubMed, EMBASE, Medline via Ovid, and Cochrane, and 24 studies were ultimately included. The majority of these studies showed that hypoxia during the expansion phase or the differentiation phase enhances at least some markers of chondrogenic differentiation in adult MSCs. These results were not always demonstrated at the protein level and there were also conflicting reports. Studies evaluating continuous exposure to hypoxia during the expansion and differentiation phases also had mixed results. These inconsistent results can be explained by the heterogeneity of studies, including factors such as different sources of MSCs used, donor variability, level of hypoxia used in each study, time exposed to hypoxia, and differences in culture methodology.

Proliferative effects of nanobubbles on fibroblasts

In recent years, the potential of nanobubbles (NBs) for biological activation has been actively investigated. In this study, we investigated the proliferative effects of nitrogen NBs (N-NBs) on fibroblast cells using cell assays with image analysis and flow cytometry. A high concentration of N-NBs (more than 4 × 10⁸ NBs/mL) was generated in Dulbecco’s modified Eagle’s medium (DMEM) using a gas–liquid mixing method. In image analysis, the cells were counted and compared, which showed an 11% increase in cell number in the culture medium with N-NBs. However, in two further cell cytometry analyses, the effect of nanobubbles on cell division was found to be insignificant (approximately 2%); as there is insufficient evidence that N-NB is involved in cell division mechanism, further studies are needed to determine whether NB affects other cellular mechanisms such as apoptosis. This study presents the first successful attempt of directly generating and quantifying N-NBs in a culture medium for cell culture. The findings suggest that the N-NBs in the culture medium can potentially facilitate cell proliferation.

The Choice of Anticoagulant Influences the Characteristics of Bone Marrow Aspirate Concentrate and Mesenchymal Stem Cell Bioactivity In Vitro

Bone marrow aspirate concentrate (BMC) is commonly used as a therapeutic agent to resolve orthopedic injuries, using its unique cellularity to reduce inflammation and prime the region for repair. The aspiration of the bone marrow is performed using either sodium citrate (SC) or heparin sodium (HS) as an anticoagulant and processed via centrifugation to concentrate the cellular constituents. To date, the consideration of the impact of the two commonly used anticoagulants on the mesenchymal stem/stromal cell (MSC) population has been overlooked. The current study assesses the differences in the BMCs produced using 15% SC and HS at 1,000 U/mL or 100 U/mL final v./v. as an anticoagulant using in vitro metrics including total nucleated cell counts (TNC) and viability, the ability for mesenchymal stromal/stem cells (MSCs) to establish colony-forming units with fibroblast morphology (CFU-f), and cytokine expression profile of the MSC cultures. Our findings demonstrate that HS-derived BMC cultures result in higher CFU-f formation and CFU-f frequency at both concentrations assessed compared to SC-derived BMC cultures. In addition, there were significant differences in 27% (7 of 26) of the cytokines quantified in HS-derived BMC cultures compared to SC-derived BMC cultures with implications for MSC plasticity and self-renewal.

Endogenous FGF-2 levels impact FGF-2/BMP-2 growth factor delivery dosing in aged murine calvarial bone defects

Bone repair in elderly mice has been shown to be improved or negatively impacted by supplementing the highly osteogenic bone morphogenetic protein-2 (BMP-2) with fibroblast growth factor-2 (FGF-2). To better predict the outcome of FGF-2 supplementation, we investigated whether endogenous levels of FGF-2 play a role in optimal dosing of FGF-2 for augmenting BMP-2 activity in elderly mice. In vivo calvarial bone defect studies in Fgf2 knockout mice with wildtype controls were conducted with the growth factors delivered in a highly localized manner from a biomimetic calcium phosphate/polyelectrolyte multilayer coating applied to a bone graft substitute. Endogenous FGF-2 levels were measured in old mice versus young and found to decrease with age. Optimal dosing for improving bone defect repair correlated with levels of endogenous FGF-2, with a larger dose of FGF-2 required to have a positive effect on bone healing in the Fgf2 knockout mice. The same dose in wildtype old mice, with higher levels of FGF-2, promoted chondrogenesis and increased osteoclast activity. The results suggest a personalized medicine approach, based on a knowledge of endogenous levels of FGF-2, should guide FGF-2 supplementation in order to avoid provoking excessive bone resorption and cartilage formation, both of which inhibited calvarial bone repair.

Targeting HIF-1α Regulatory Pathways as a Strategy to Hamper Tumor-Microenvironment Interactions in CLL

The hypoxia-inducible factor 1 (HIF-1) and the CXCL12/CXCR4 axis regulate the interaction of chronic lymphocytic leukemia cells and the tumor microenvironment. However, the interconnections occurring between HIF-1 and the CXCL12/CXCR4 axis are not fully elucidated. Here, we demonstrate that the CXCL12/CXCR4 axis plays a pivotal role in the positive regulation of the α subunit of HIF-1 (HIF-1α) that occurs in CLL cells co-cultured with stromal cells (SC). Inhibitors acting at different levels on CXCR4 downstream signalling counteract the SC-induced HIF-1α upregulation in CLL cells, also hindering the SC-mediated pro-survival effect. HIF-1α inhibition also exerts off-tumor effects on the SC component, inducing the downregulation of target genes, including CXCL12. Consistently, our data show that pretreatment of leukemic cells and/or SC with idelalisib effectively abrogates the SC-mediated survival support. A combined on-tumor and off-tumor inhibition of HIF-1α was also observed in idelalisib-treated patients, who showed, along with a downregulation of HIF-1α target genes in leukemic cells, a significant decrease in CXCL12 serum concentration and changes in the bone marrow microenvironment. Our data demonstrate that the targeting of HIF-1α or its regulatory pathways acts at the tumor- and SC-level, and may be an appealing strategy to overcome the microenvironment-mediated protection of CLL cells.

Partial hepatectomy enhances the growth of CC531 rat colorectal cancer cells both in vitro and in vivo

Partial hepatectomy (PHx) is the gold standard for the treatment of colorectal cancer liver metastases. However, after removing a substantial amount of hepatic tissue, growth factors are released to induce liver regeneration, which may promote the proliferation of liver micrometastases or circulating tumour cells still present in the patient. The aim of this study is to assess the effect of PHx on the growth of liver metastases induced by intrasplenic cell inoculation as well as on in vitro proliferation of the same cancer cell line. Liver tumours were induced in 18 WAG/RijHsd male rats, by seeding 250,000 syngeneic colorectal cancer cells (CC531) into the spleen. The left lateral lobe of the liver was mobilized and in half of the animals it was removed to achieve a 40% hepatectomy. Twenty-eight days after tumour induction, the animals were sacrificed and the liver was removed and sliced to assess the relative tumour surface area (RTSA%). CC531 cells were cultured in presence of foetal calf serum, non-hepatectomised (NRS) or hepatectomized rat serum (HRS), and their proliferation rate at 24, 48, and 72 h was measured. RTSA% was significantly higher in animals which had undergone PHx than in the controls (non-hepatectomised) (46.98 ± 8.76% vs. 18.73 ± 5.65%; p < 0.05). Analysing each lobe separately, this difference in favour of hepatectomized animals was relevant and statistically significant in the paramedian and caudate lobes. But in the right lobe the difference was scarce and not significant. In vitro, 2.5% HRS achieved stronger proliferative rates than the control cultures (10% FCS) or their equivalent of NRS. In this experimental model, a parallelism has been shown between the effect of PHx on the growth of colorectal cancer cells in the liver and the effect of the serum on those cells in vitro.

Fibroblast growth factor-2 ameliorates tumor necrosis factor-alpha-induced osteogenic damage of human bone mesenchymal stem cells by improving oxidative phosphorylation

Tumor necrosis factor-alpha (TNF-α) has been shown to have an inhibitory effect on the osteogenic differentiation of mesenchymal stem cells. The metabolic switch from glycolysis to oxidative phosphorylation (OXPHOS) is vital for energy supply during osteogenic differentiation. However, the metabolic switch is inhibited under inflammatory stimulation. FGF2 has shown that it can improve osteogenic differentiation and promote autoimmune inflammation. In this study, we investigated whether FGF2 can ameliorate TNF-a-inhibited osteogenic damage by improving OXPHOS. Effects of TNF-α or FGF2 on the proliferation and osteogenic differentiation of hBMSCs were evaluated by MTT assay, qRT-PCR, and ALP activity tests. The function of FGF2 on the TNF-a-inhibited metabolic switch was determined by Mito Stress test. The results showed that TNF-α was able to inhibit the osteogenic differentiation and OXPHOS of hBMSCs. FGF2 has no obvious function in improving the osteogenic-related genes, but it can ameliorate the impaired osteogenesis and OCR value caused by TNF-α. These findings suggest that FGF2 can prevent the impaired osteogenic differentiation and metabolic switch of hBMSCs under inflammatory stimulation, which might enhance the regeneration capacity of hBMSCs.

Physioxia Has a Beneficial Effect on Cartilage Matrix Production in Interleukin-1 Beta-Inhibited Mesenchymal Stem Cell Chondrogenesis

Osteoarthritis (OA) is a degenerative condition that involves the production of inflammatory cytokines (e.g., interleukin-1β (IL-1β), tumour necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6)) that stimulate degradative enzymes, matrix metalloproteinases (MMPs) and aggrecanases (ADAMTS) resulting in articular cartilage breakdown. The presence of interleukin-1β (IL-1β) is one reason for poor clinical outcomes in current cell-based tissue engineering strategies for treating focal early osteoarthritic defects. Mesenchymal stem cells (MSCs) are a potential cell source for articular cartilage regeneration, although IL-1β has been shown to inhibit in vitro chondrogenesis. In vivo, articular chondrocytes reside under a low oxygen environment between 2–5% oxygen (physioxia) and have been shown to enhance in vitro MSC chondrogenic matrix content with reduced hypertrophic marker expression under these conditions. The present investigation sought to understand the effect of physioxia on IL-1β inhibited MSC chondrogenesis. MSCs expanded under physioxic (2% oxygen) and hyperoxic (20%) conditions, then chondrogenically differentiated as pellets in the presence of TGF-β1 and either 0.1 or 0.5 ng/mL IL-1β. Results showed that there were donor variations in response to physioxic culture based on intrinsic GAG content under hyperoxia. In physioxia responsive donors, MSC chondrogenesis significantly increased GAG and collagen II content, whilst hypertrophic markers were reduced compared with hyperoxia. In the presence of IL-1β, these donors showed a significant increase in cartilage matrix gene expression and GAG content relative to hyperoxic conditions. In contrast, a set of MSC donors were unresponsive to physioxia and showed no significant increase in matrix production independent of IL-1β presence. Thus, physioxia has a beneficial effect on MSC cartilage matrix production in responsive donors with or without IL-1β application. The mechanisms controlling the MSC chondrogenic response in both physioxia responsive and unresponsive donors are to be elucidated in future investigations.

Evaluation of fibroblast growth factor-2 on the proliferation of osteogenic potential and protein expression of stem cell spheroids composed of stem cells derived from bone marrow

Fibroblast growth factor-2 (FGF-2) is reported to have various functions and is considered a key human mesenchymal stem cell mitogen, often supplemented to increase human mesenchymal stem cell growth rates. The purpose of this study was to evaluate the effects of FGF-2 on cellular viability and osteogenic differentiation using three-dimensional cell spheroids of stem cells. Three-dimensional cell spheroids were fabricated using concave silicon elastomer-based microwells in the presence of FGF-2 at concentrations of 0, 30, 60 and 90 ng/ml. Qualitative cellular viability was determined with a confocal microscope, and quantitative cellular viability was evaluated using a Cell Counting Kit-8 assay. Alkaline phosphatase activity and Alizarin Red S staining were used to assess osteogenic differentiation. Spheroids were well formed in silicon elastomer-based concave microwells on Day 1. The average spheroid diameters at Day 1 for FGF-2 at 0, 30, 60 and 90 ng/ml were 202.2±3.0, 206.6±22.6, 208.8±6.8 and 196.6±26.7 µm, respectively (P>0.05). The majority of the cells in the cell spheroids emitted green fluorescence. The relative Cell Counting Kit-8 assay values for FGF-2 at 0, 30, 60 and 90 ng/ml at Day 1 were 100.0±5.5, 101.8±8.8, 99.2±4.8 and 103.4±9.6% (P>0.05). The addition of FGF-2 at 60 ng/ml concentration produced the highest value for alkaline phosphatase activity. Mineralized extracellular deposits were evenly observed in each group, and the highest value was identified for FGF-2 groups at 60 ng/ml concentration for Alizarin Red S staining. Based on these findings, it was concluded that FGF-2 may increase alkaline phosphatase activity or Alizarin Red S staining, and further studies are needed to fully elucidate the mechanisms of FGF-2.

Effects of NSAIDs and environmental oxygen pressure on bone regeneration

Objective: To evaluate the effects of administering diclofenac and ketoprofen, as well as the effects of environmental oxygen pressure variation on mandibular bone regeneration. Methods: Thirty-six guinea pigs were distributed into two equal groups. Mandibular bone defects were performed on both groups. Group A was monitored under oxygen pressure at altitude (3320msl, 107mm Hg). Group B was monitored at sea level oxygen pressure (150msl, 157mm Hg). Each group was subdivided into 3 equal groups (A1, A2, A3 and B1, B2, B3). Subgroups A1 and B1 were given diclofenac; subgroups A2 and B2 ketoprofen; subgroups A3 and B3 NaCl. Bone regeneration was evaluated histologically on days 15 and 30. Results: After 15 days in the group controlled at sea level, the level of osteoblasts presented by the control subgroup was significantly higher (28.00±2.65) compared to the diclofenac subgroup (16.00±6.25) and to the ketoprofen subgroup (18.00±4.36); (p=0.041). After 15 days in the group controlled at altitude, the level of osteoblasts was significantly higher in the control subgroup (38.00±5.29) compared to the diclofenac subgroup (21.67±6.35) and to the ketoprofen subgroup (19.33±2.52); p=0.007. After 30 days in the group at sea level there was no difference found in the cell counting; p>0.05. After 30 days in the group controlled at altitude, the level of osteoblast was significantly higher in the control subgroup (58.00±4.58) compared to the diclofenac subgroup (34.33±4.73) and the ketoprofen subgroup (34.00±11.14); (p=0.003). Conclusion: The administration of diclofenac and ketoprofen produced lower mandibular bone regeneration, the effect being significantly more negative at sea level.

The Importance of Physioxia in Mesenchymal Stem Cell Chondrogenesis and the Mechanisms Controlling Its Response

Articular cartilage covers the surface of synovial joints and enables joint movement. However, it is susceptible to progressive degeneration with age that can be accelerated by either previous joint injury or meniscectomy. This degenerative disease is known as osteoarthritis (OA) and it greatly affects the adult population. Cell-based tissue engineering provides a possible solution for treating OA at its earliest stages, particularly focal cartilage lesions. A candidate cell type for treating these focal defects are Mesenchymal Stem Cells (MSCs). However, present methods for differentiating these cells towards the chondrogenic lineage lead to hypertrophic chondrocytes and bone formation in vivo. Environmental stimuli that can stabilise the articular chondrocyte phenotype without compromising tissue formation have been extensively investigated. One factor that has generated intensive investigation in MSC chondrogenesis is low oxygen tension or physioxia (2⁻5% oxygen). In vivo articular cartilage resides at oxygen tensions between 1⁻4%, and in vitro results suggest that these conditions are beneficial for MSC expansion and chondrogenesis, particularly in suppressing the cartilage hypertrophy. This review will summarise the current literature regarding the effects of physioxia on MSC chondrogenesis with an emphasis on the pathways that control tissue formation and cartilage hypertrophy.