The osteogenic response of undifferentiated human adipose-derived stem cells under mechanical stimulation

MicroRNA-503-3p affects osteogenic differentiation of human adipose-derived stem cells by regulation of Wnt2 and Wnt7b under cyclic strain

BACKGROUND

MicroRNAs (miRNAs) play a role in regulating osteogenic differentiation (OD) of mesenchymal stem cells by inhibiting mRNAs translation under cyclic strain. miR-503-3p was downregulated in OD of human adipose-derived stem cells (hASCs) in vivo under cyclic strain in our previous study, while it might target the Wnt/β-catenin (W-β) pathway. In this study, we explored miR-503-3p's role in OD of hASCs under cyclic strain.

METHODS

OD of hASCs was induced by cyclic strain. Bioinformatic and dual luciferase analyses were used to confirm the relationship between Wnt2/Wnt7b and miR-503-3p. Immunofluorescence was used to detect the effect of miR-503-3p on Wnt2/Wnt7b and β-catenin in hASCs transfected with miR-503-3p mimic and inhibitor. Mimic, inhibitor, and small interfering RNA (siRNA) transfected in hASCs to against Wnt2 and Wnt7b. Quantitative real-time PCR (RT-PCR) and western blot were used to examine the OD and W-β pathway at the mRNA and protein levels, respectively. Immunofluorescence was performed to locate β-catenin. ALP activity and calcium were detected by colorimetric assay.

RESULTS

Results of immunophenotypes by flow cytometry and multi-lineage potential confirmed that the cultured cells were hASCs. Results of luciferase reporter assay indicated that miR-503-3p could regulate the expression levels of Wnt2 and Wnt7b by targeting their respective 3'-untranslated region (UTR). Under cyclic strain, gain- or loss-function of miR-503-3p studies by mimic and inhibitor revealed that decreasing expression of miR-503-3p could significantly bring about promotion of OD of hASCs, whereas increased expression of miR-503-3p inhibited OD. Furthermore, miR-503-3p high-expression reduced the activity of the W-β pathway, as indicated by lowering expression of Wnt2 and Wnt7b, inactive β-catenin in miR-503-3p-treated hASCs. By contrast, miR-503-3p inhibition activated the W-β pathway.

CONCLUSIONS

Collectively, our findings indicate that miR-503-3p is a negative factor in regulating W-β pathway by Wnt2 and Wnt7b, which inhibit the OD of hASCs under cyclic strain.

The osteogenic differentiation of human adipose-derived stem cells is regulated through the let-7i-3p/LEF1/β-catenin axis under cyclic strain

Background

The Wnt/β-catenin pathway is involved in the osteogenic differentiation of human adipose-derived stem cells (hASCs) under cyclic strain. Very little is known about the role of microRNAs in these events.

Methods

Cells were obtained using enzyme digestion methods, and proliferation was detected using Cell Counting Kit 8. Cell cycles and immunophenotypes were detected by flow cytometry. The multilineage potential of hASCs was induced by induction media. Cyclic strain was applied to hASCs (0.5 Hz, 2 h/day, 6 days) to induce osteogenic differentiation and miRNA changes. Bioinformatic and dual-luciferase analyses confirmed lymphoid enhancer factor 1 (LEF1) as a potential target of let-7i-3p. The effect of let-7i-3p on LEF1 in hASCs transfected with a let-7i-3p mimic and inhibitor was analyzed by immunofluorescence. hASCs were transfected with a let-7i-3p mimic, inhibitor, or small interfering RNA (siRNA) against LEF1 and β-catenin. Quantitative real-time PCR (qPCR) and western blotting were performed to examine the osteogenic markers and Wnt/β-catenin pathway at the mRNA and protein levels, respectively. Immunofluorescence and western blotting were performed to confirm the activation of the Wnt/β-catenin pathway.

Results

Flow cytometry showed that 82.12% ± 5.83% of the cells were in G1 phase and 17.88% ± 2.59% of the cells were in S/G2 phase; hASCs were positive for CD29, CD90, and CD105. hASCs could have the potential for osteogenic, chondrogenic, and adipogenic differentiation. MicroRNA screening via microarray showed that let-7i-3p expression was decreased under cyclic strain. Bioinformatic and dual-luciferase analyses confirmed that LEF1 in the Wnt/β-catenin pathway was the target of let-7i-3p. Under cyclic strain, the osteogenic differentiation of hASCs was promoted by overexpression of LEF1and β-catenin and inhibited by overexpression of let-7i-3p. hASCs were transfected with let-7i-3p mimics and inhibitor. Gain- or loss-of-function analyses of let-7i-3p showed that the osteogenic differentiation of hASCs was promoted by decreased let-7i-3p expression and inhibited by increased let-7i-3p expression. Furthermore, high LEF1 expression inactivated the Wnt/β-catenin pathway in let-7i-3p-enhanced hASCs. In contrast, let-7i-3p inhibition activated the Wnt/β-catenin pathway.

Conclusions

Let-7i-3p, acting as a negative regulator of the Wnt/β-catenin pathway by targeting LEF1, inhibits the osteogenic differentiation of hASCs under cyclic strain in vitro.

Uniaxial Cyclic Tensile Stretching at 8% Strain Exclusively Promotes Tenogenic Differentiation of Human Bone Marrow-Derived Mesenchymal Stromal Cells

The present study was conducted to establish the amount of mechanical strain (uniaxial cyclic stretching) required to provide optimal tenogenic differentiation expression in human mesenchymal stromal cells (hMSCs) in vitro, in view of its potential application for tendon maintenance and regeneration. Methods. In the present study, hMSCs were subjected to 1 Hz uniaxial cyclic stretching for 6, 24, 48, and 72 hours; and were compared to unstretched cells. Changes in cell morphology were observed under light and atomic force microscopy. The tenogenic, osteogenic, adipogenic, and chondrogenic differentiation potential of hMSCs were evaluated using biochemical assays, extracellular matrix expressions, and selected mesenchyme gene expression markers; and were compared to primary tenocytes. Results. Cells subjected to loading displayed cytoskeletal coarsening, longer actin stress fiber, and higher cell stiffness as early as 6 hours. At 8% and 12% strains, an increase in collagen I, collagen III, fibronectin, and N-cadherin production was observed. Tenogenic gene expressions were highly expressed (p < 0.05) at 8% (highest) and 12%, both comparable to tenocytes. In contrast, the osteoblastic, chondrogenic, and adipogenic marker genes appeared to be downregulated. Conclusion. Our study suggests that mechanical loading at 8% strain and 1 Hz provides exclusive tenogenic differentiation; and produced comparable protein and gene expression to primary tenocytes.

Equiaxial Strain Modulates Adipose-derived Stem Cell Differentiation within 3D Biphasic Scaffolds towards Annulus Fibrosus

Recurrence of intervertebral disc (IVD) herniation is the most important factor leading to chronic low back pain and subsequent disability after discectomy. Efficacious annulus fibrosus (AF) repair strategy that delivers cells and biologics to IVD injury site is needed to limit the progression of disc degeneration and promote disc self-regeneration capacities after discectomy procedures. In this study, a biphasic mechanically-conditioned scaffold encapsulated with human adipose-derived stem cells (ASCs) is studied as a potential treatment strategy for AF defects. Equiaxial strains and frequencies were applied to ASCs-encapsulated scaffolds to identify the optimal loading modality to induce AF differentiation. Equiaxial loading resulted in 2–4 folds increase in secretion of extracellular matrix proteins and the reorganization of the matrix fibers and elongations of the cells along the load direction. Further, the equiaxial load induced region-specific differentiation of ASCs within the inner and outer regions of the biphasic scaffolds. Gene expression of AF markers was upregulated with 5–30 folds within the equiaxially loaded biphasic scaffolds compared to unstrained samples. The results suggest that there is a specific value of equiaxial strain favorable to differentiate ASCs towards AF lineage and that ASCs-embedded biphasic scaffold can potentially be utilized to repair the AF defects.

The effect of equiaxial stretching on the osteogenic differentiation and mechanical properties of human adipose stem cells

Although mechanical cues are known to affect stem cell fate and mechanobiology, the significance of such stimuli on the osteogenic differentiation of human adipose stem cells (hASCs) remains unclear. In this study, we investigated the effect of long-term mechanical stimulation on the attachment, osteogenic differentiation and mechanical properties of hASCs. Tailor-made, pneumatic cell stretching devices were used to expose hASCs to cyclic equiaxial stretching in osteogenic medium. Cell attachment and focal adhesions were visualised using immunocytochemical vinculin staining on days 3 and 6, and the proliferation and alkaline phosphatase activity, as a sign of early osteogenic differentiation, were analysed on days 0, 6 and 10. Furthermore, the mechanical properties of hASCs, in terms of apparent Young's modulus and normalised contractility, were obtained using a combination of atomic force microscopy based indentation and computational approaches. Our results indicated that cyclic equiaxial stretching delayed proliferation and promoted osteogenic differentiation of hASCs. Stretching also reduced cell size and intensified focal adhesions and actin cytoskeleton. Moreover, cell stiffening was observed during osteogenic differentiation and especially under mechanical stimulation. These results suggest that cyclic equiaxial stretching modifies cell morphology, focal adhesion formation and mechanical properties of hASCs. This could be exploited to enhance osteogenic differentiation.

The Diverse Roles of Hydrogel Mechanics in Injectable Stem Cell Transplantation

Stem cell delivery by local injection has tremendous potential as a regenerative therapy but has seen limited clinical success. Several mechanical challenges hinder therapeutic efficacy throughout all stages of cell transplantation, including mechanical forces during injection and loss of mechanical support post-injection. Recent studies have begun exploring the use of biomaterials, in particular hydrogels, to enhance stem cell transplantation by addressing the often-conflicting mechanical requirements associated with each stage of the transplantation process. This review explores recent biomaterial approaches to improve the therapeutic efficacy of stem cells delivered through local injection, with a focus on strategies that specifically address the mechanical challenges that result in cell death and/or limit therapeutic function throughout the stages of transplantation.

Mechanoresponsive musculoskeletal tissue differentiation of adipose-derived stem cells

Musculoskeletal tissues are constantly under mechanical strains within their microenvironment. Yet, little is understood about the effect of in vivo mechanical milieu strains on cell development and function. Thus, this review article outlines the in vivo mechanical environment of bone, muscle, cartilage, tendon, and ligaments, and tabulates the mechanical strain and stress in these tissues during physiological condition, vigorous, and moderate activities. This review article further discusses the principles of mechanical loading platforms to create physiologically relevant mechanical milieu in vitro for musculoskeletal tissue regeneration. A special emphasis is placed on adipose-derived stem cells (ADSCs) as an emerging valuable tool for regenerative musculoskeletal tissue engineering, as they are easily isolated, expanded, and able to differentiate into any musculoskeletal tissue. Finally, it highlights the current state-of-the art in ADSCs-guided musculoskeletal tissue regeneration under mechanical loading.

MiR-154-5p regulates osteogenic differentiation of adipose-derived mesenchymal stem cells under tensile stress through the Wnt/PCP pathway by targeting Wnt11

Mechanical stress is a well-acknowledged positive regulatory factor for osteogenic differentiation of adipose- derived mesenchymal stem cells (ADSCs). However, the molecular mechanisms associated with micro-RNAs (miRNAs) whereby ADSCs respond to mechanical stimuli remain elusive. We investigated the mechanism of mechanotransduction from the miRNA perspective in the osteogenic differentiation of ADSCs under tensile stress. Microarray analysis showed that miR-154-5p was remarkably downregulated when ADSCs were subjected to mechanical tension. Bioinformatics analysis with luciferase reporter assays demonstrated that Wnt11 3'UTR was a new direct target of miR-154-5p. Under tensile stress, lentivirus-mediated gain- or loss-of-function studies revealed that forced expression of miR-154-5p inhibited osteogenic differentiation of ADSCs, whereas inhibition of endogenous miR-154-5p with its antisense oligonucleotide (ASO-154-5p) obviously promoted osteogenic differentiation. Furthermore, miR-154-5p overexpression decreased activity of the non-canonical Wnt/PCP (RhoA-ROCK) pathway, as indicated by lower expression of Wnt11, active RhoA and ROCKII in miR-154-5p-treated ADSCs. By contrast, miR-154-5p inhibition activated the Wnt/PCP signals. Taken together, these results demonstrate that, under tensile stress, miR-154-5p negatively regulates ADSCs osteogenic differentiation through the Wnt/PCP pathway by directly targeting Wnt11. This novel regulatory pathway provides new insights into the molecular mechanism of mechanotransduction in osteogenic differentiation of ADSCs.

New bone formation enhanced by ADSCs overexpressing hRunx2 during mandibular distraction osteogenesis in osteoporotic rabbits

Promoting new bone formation during distraction osteogenesis (DO) in elderly patients with osteoporosis is still a challenge. In this study, we investigated the effect of gene therapy using local Runt-related gene 2 on new bone formation during osteoporotic mandibular DO in rabbits. First, we successfully established a mandibular osteoporotic animal model by ovariectomizing rabbits. Second, the right mandibles of the osteoporotic rabbits were distracted after corticotomy. The distraction gap of the rabbits in Group A2 and B2 were injected with Adv-hRunx2-GFP-transfected adipose-derived stromal cells (ADSCs) and Adv-GFP-transfected ADSCs, respectively. Rabbits in Groups C2 (ovariectomized control) and D2 (sham surgery control) were injected with physiologic saline. New-generation bone tissue in the distraction gap was analyzed via plain radiographic examinations, micro-computed tomography, histological examinations, and biomechanical testing at weeks 3, 6, and 9 of the consolidation period. Results of above examinations showed that no ideal new bone formation was observed in Groups B2 and C2, but obvious ideal new bone formation was observed in Group A2 and D2. The results suggested that gene therapy using rhRunx2-modified ADSCs promoted new bone formation during osteoporotic mandibular DO and effectively compensated for the detrimental effects of systemic osteoporosis on new bone formation.

Biophysical cues enhance myogenesis of human adipose derived stem/stromal cells

Adipose-derived stem/stromal cell (ASC)-based tissue engineered muscle grafts could provide an effective alternative therapy to autografts - which are limited by their availability - for the regeneration of damaged muscle. However, the current myogenic potential of ASCs is limited by their low differentiation efficiency into myoblasts. The aim of this study was to enhance the myogenic response of human ASCs to biochemical cues by providing biophysical stimuli (11% cyclic uniaxial strain, 0.5 Hz, 1h/day) to mimic the cues present in the native muscle microenvironment. ASCs elongated and fused upon induction with myogenic induction medium alone. Yet, their myogenic characteristics were significantly enhanced with the addition of biophysical stimulation; the nuclei per cell increased approximately 4.5-fold by day 21 in dynamic compared to static conditions (23.3 ± 7.3 vs. 5.2 ± 1.6, respectively), they aligned at almost 45° to the direction of strain, and exhibited significantly higher expression of myogenic proteins (desmin, myoD and myosin heavy chain). These results demonstrate that mimicking the biophysical cues inherent to the native muscle microenvironment in monolayer ASC cultures significantly improves their differentiation along the myogenic lineage.