Modulation of mesenchymal stem cell genotype and phenotype by extracellular matrix proteins

Viable tendon neotissue from adult adipose-derived multipotent stromal cells

Background: Tendon healing is frequently prolonged, unpredictable, and results in poor tissue quality. Neotissue formed by adult multipotent stromal cells has the potential to guide healthy tendon tissue formation. Objectives: The objective of this study was to characterize tendon neotissue generated by equine adult adipose-derived multipotent stromal cells (ASCs) on collagen type I (COLI) templates under 10% strain in a novel bioreactor. The tested hypothesis was that ASCs assume a tendon progenitor cell-like morphology, express tendon-related genes, and produce more organized extracellular matrix (ECM) in tenogenic versus stromal medium with perfusion and centrifugal fluid motion. Methods: Equine ASCs on COLI sponge cylinders were cultured in stromal or tenogenic medium within bioreactors during combined perfusion and centrifugal fluid motion for 7, 14, or 21 days under 10% strain. Viable cell distribution and number, tendon-related gene expression, and micro- and ultra-structure were evaluated with calcein-AM/EthD-1 staining, resazurin reduction, RT-PCR, and light, transmission, and scanning electron microscopy. Fibromodulin was localized with immunohistochemistry. Cell number and gene expression were compared between culture media and among culture periods (p < 0.05). Results: Viable cells were distributed throughout constructs for up to 21 days of culture, and cell numbers were higher in tenogenic medium. Individual cells had a round or rhomboid shape with scant ECM in stromal medium in contrast to clusters of parallel, elongated cells surrounded by highly organized ECM in tenogenic medium after 21 days of culture. Transcription factor, extracellular matrix, and mature tendon gene expression profiles confirmed ASC differentiation to a tendon progenitor-like cell in tenogenic medium. Construct micro- and ultra-structure were consistent with tendon neotissue and fibromodulin was present in the ECM after culture in tenogenic medium. Conclusion: Long-term culture in custom bioreactors with combined perfusion and centrifugal tenogenic medium circulation supports differentiation of equine adult ASCs into tendon progenitor-like cells capable of neotissue formation.

Tendon-derived matrix crosslinking techniques for electrospun multi-layered scaffolds

Tendon tears are common and healing often occurs incompletely and by fibrosis. Tissue engineering seeks to improve repair, and one approach under investigation uses cell-seeded scaffolds containing biomimetic factors. Retention of biomimetic factors on the scaffolds is likely critical to maximize their benefit, while minimizing the risk of adverse effects, and without losing the beneficial effects of the biomimetic factors. The aim of the current study was to evaluate cross-linking methods to enhance the retention of tendon-derived matrix (TDM) on electrospun poly(ε-caprolactone) (PCL) scaffolds. We tested the effects of ultraviolet (UV) or carbodiimide (EDC:NHS:COOH) crosslinking methods to better retain TDM to the scaffolds and stimulate tendon-like matrix synthesis. Initially, we tested various crosslinking configurations of carbodiimide (2.5:1:1, 5:2:1, and 10:4:1 EDC:NHS:COOH ratios) and UV (30 s 1 J/cm2 , 60 s 1 J/cm2 , and 60 s 4 J/cm2 ) on PCL films compared to un-crosslinked TDM. We found that no crosslinking tested retained more TDM than coating alone (Kruskal-Wallis: p > .05), but that human adipose stem cells (hASCs) spread most on the 60 s 1 J/cm2 UV- and 2.5:1:1 EDC-crosslinked films (Kruskal-Wallis: p < .05). Next, we compared the effects of 60 s 1 J/cm2 UV- and 2.5:1:1 EDC-crosslinked to TDM-coated and untreated PCL scaffolds on hASC-induced tendon-like differentiation. UV-crosslinked scaffolds had greater modulus and stiffness than PCL or TDM scaffolds, and hASCs spread more on UV-crosslinked scaffolds (ANOVA: p < .05). Fourier transform infrared spectra revealed that UV- or EDC-crosslinking TDM did not affect the peaks at wavenumbers characteristic of tendon. Crosslinking TDM to electrospun scaffolds improves tendon-like matrix synthesis, providing a viable strategy for improving retention of TDM on electrospun PCL scaffolds.

Current progress of mesenchymal stem cell membrane-camouflaged nanoparticles for targeted therapy

Nanodrug delivery systems have been widely used in disease treatment. However, weak drug targeting, easy to be cleared by the immune system, and low biocompatibility are great obstacles for drug delivery. As an important part of cell information transmission and behavior regulation, cell membrane can be used as drug coating material which represents a promising strategy and can overcome these limitations. Mesenchymal stem cell (MSC) membrane, as a new carrier, has the characteristics of active targeting and immune escape of MSC, and has broad application potential in tumor treatment, inflammatory disease, tissue regeneration and other fields. Here, we review recent progress on the use of MSC membrane-coated nanoparticles for therapy and drug delivery, aiming to provide guidance for the design and clinical application of membrane carrier in the future.

Applications of functionally-adapted hydrogels in tendon repair

Despite all the efforts made in tissue engineering for tendon repair, the management of tendon injuries still poses a challenge, as current treatments are unable to restore the function of tendons following injuries. Hydrogels, due to their exceptional biocompatibility and plasticity, have been extensively applied and regarded as promising candidate biomaterials in tissue regeneration. Varieties of approaches have designed functionally-adapted hydrogels and combined hydrogels with other factors (e.g., bioactive molecules or drugs) or materials for the enhancement of tendon repair. This review first summarized the current state of knowledge on the mechanisms underlying the process of tendon healing. Afterward, we discussed novel strategies in fabricating hydrogels to overcome the issues frequently encountered during the applications in tendon repair, including poor mechanical properties and undesirable degradation. In addition, we comprehensively summarized the rational design of hydrogels for promoting stem-cell-based tendon tissue engineering via altering biophysical and biochemical factors. Finally, the role of macrophages in tendon repair and how they respond to immunomodulatory hydrogels were highlighted.

Serum deprivation limits loss and promotes recovery of tenogenic phenotype in tendon cell culture systems

Current knowledge gaps on tendon tissue healing can partly be ascribed to the limited availability of physiologically relevant culture models. An unnatural extracellular matrix, high serum levels and random cell morphology in vitro mimic strong vascularization and lost cell elongation in pathology, and discord with a healthy, in vivo cell microenvironment. The thereby induced phenotypic drift in tendon-derived cells (TDCs) compromises the validity of the research model. Therefore, this research quantified the extracellular matrix (ECM)-, serum-, and cell morphology-guided phenotypic changes in tendon cells of whole tendon fascicle explants with intact ECM and TDCs cultured in a controlled microenvironmental niche. Explanted murine tail tendon fascicles were cultured in serum-rich or serum-free medium and phenotype was assessed using transcriptome analysis. Next, phenotypic marker gene expression was measured in in vitro expanded murine tail TDCs upon culture in serum-rich or serum-free medium on aligned or random collagen I patterns. Freshly isolated fascicles or TDCs served as native controls. In both systems, the majority of tendon-specific genes were similarly attenuated in serum-rich culture. Strikingly, 1-week serum-deprived culture-independent of cell morphology-converged TDC gene expression toward native levels. This study reveals a dynamic serum-responsive tendon cell phenotype. Extracting fascicles or TDCs from their native environment causes large changes in cellular phenotype, which can be limited and even reversed by serum deprivation. We conclude that serum-derived factors override matrix-integrity and cell morphology cues and that serum-deprivation stimulates a more physiological microenvironment for in vitro studies.

Collagen type I promotes osteogenic differentiation of amniotic membrane-derived mesenchymal stromal cells in basal and induction media

Collagen has been widely shown to promote osteogenesis of bone marrow mesenchymal stromal cells (BM-MSCs). Due to the invasive procedure of obtaining BM-MSCs, MSCs from other tissues have emerged as a promising alternative for regenerative therapy. MSCs originated from different sources, exhibiting different differentiation potentials. Therefore, the applicability of collagen type I (COL), combining with amniotic membrane (AM)-MSCs was examined through proliferation and differentiation assays together with the expression of surface markers and genes associated with stemness and differentiation under basal or induction conditions. No increase in cell growth was observed because AM-MSCs might be directed toward spontaneous osteogenesis. This was evidenced by the calcium deposition and elevated expression of osteogenic genes when AM-MSCs were cultured in collagen plate with basal media. Under the osteogenic condition, reciprocal expression of OCN and CEBPA suggested a shift toward adipogenesis. Surprisingly, adipogenic genes were not elevated upon adipogenic induction, although oil droplets deposition was observed. In conclusion, our findings demonstrated that collagen causes spontaneous osteogenesis in AM-MSCs. However, the presence of exogenous inductors could shift the direction of adipo-osteogenic gene regulatory network modulated by collagen.

Zonal characterization and differential trilineage potentials of equine intrasynovial deep digital flexor tendon-derived cells

BACKGROUND

Intrasynovial deep digital flexor tendon (DDFT) injuries occur frequently and are often implicated in cases of navicular disease with poor outcomes and reinjuries. Cell-based approaches to tendon healing are gaining traction in veterinary medicine and ultimately may contribute to improved DDFT healing in horses. However, a better understanding of the innate cellular characteristics of equine DDFT is necessary for developing improved therapeutic strategies. Additionally, fibrocartilaginous, intrasynovial tendons like the DDFT are common sites of injury and share a poor prognosis across species, offering translational applications of this research. The objective of this study is to isolate and characterize tendon-derived cells (TDC) from intrasynovial DDFT harvested from within the equine forelimb podotrochlear bursa. TDC from the fibrocartilaginous and tendinous zones are separately isolated and assessed. Flow cytometry is performed for mesenchymal stem cell (MSC) surface markers (CD 29, CD 44, CD 90). Basal tenogenic, osteogenic and chondrogenic markers are assessed via quantitative real time-PCR, and standard trilineage differentiation is performed with third passage TDC from the fibrocartilaginous (fTDC) and tendinous (tTDC) zones of DDFT.

RESULTS

Low-density plating isolated homogenous TDC populations from both zones. During monolayer passage, both TDC subpopulations exhibited clonogenicity, high in vitro proliferation rate, and fibroblast-like morphology. fTDC and tTDC were positive for MSC surface markers CD90 and CD29 and negative for CD44. There were no significant differences in basal tenogenic, osteogenic or chondrogenic marker expression between zones. While fTDC were largely restricted to chondrogenic differentiation, tTDC underwent osteogenic and chondrogenic differentiation. Both TDC subpopulations displayed weak adipogenic differentiation potentials.

CONCLUSIONS

TDC at the level of the podotrochlear bursa, that potentially could be targeted for enhancing DDFT injury healing in horses were identified and characterized. Pending further investigation, promoting chondrogenic properties in cells administered exogenously into the intrasynovial space may be beneficial for intrasynovial tendon regeneration.

Temporal changes guided by mesenchymal stem cells on a 3D microgel platform enhance angiogenesis in vivo at a low-cell dose

Therapeutic factors secreted by mesenchymal stem cells (MSCs) promote angiogenesis in vivo. However, delivery of MSCs in the absence of a cytoprotective environment offers limited efficacy due to low cell retention, poor graft survival, and the nonmaintenance of a physiologically relevant dose of growth factors at the injury site. The delivery of stem cells on an extracellular matrix (ECM)-based platform alters cell behavior, including migration, proliferation, and paracrine activity, which are essential for angiogenesis. We demonstrate the biophysical and biochemical effects of preconditioning human MSCs (hMSCs) for 96 h on a three-dimensional (3D) ECM-based microgel platform. By altering the macromolecular concentration surrounding cells in the microgels, the proangiogenic phenotype of hMSCs can be tuned in a controlled manner through cell-driven changes in extracellular stiffness and "outside-in" integrin signaling. The softest microgels were tested at a low cell dose (5 × 10⁴ cells) in a preclinical hindlimb ischemia model showing accelerated formation of new blood vessels with a reduced inflammatory response impeding progression of tissue damage. Molecular analysis revealed that several key mediators of angiogenesis were up-regulated in the low-cell-dose microgel group, providing a mechanistic insight of pathways modulated in vivo. Our research adds to current knowledge in cell-encapsulation strategies by highlighting the importance of preconditioning or priming the capacity of biomaterials through cell-material interactions. Obtaining therapeutic efficacy at a low cell dose in the microgel platform is a promising clinical route that would aid faster tissue repair and reperfusion in "no-option" patients suffering from peripheral arterial diseases, such as critical limb ischemia (CLI).

Glaucoma, Stem Cells, and Gene Therapy: Where Are We Now?

Glaucoma is the second most common cause of blindness, affecting 70∼80 million people around the world. The death of retinal ganglion cells (RGCs) is the main cause of blindness related to this disease. Current therapies do not provide enough protection and regeneration of RGCs. A novel opportunity for treatment of glaucoma is application of technologies related to stem cell and gene therapy. In this perspective we will thus focus on emerging approaches to glaucoma treatment including stem cells and gene therapy.

Cryopreservation of canine cardiosphere-derived cells: Implications for clinical application

The clinical application of cardiosphere-derived cells (CDCs) to treat cardiac disease has gained increasing interest over the past decade. Recent clinical trials confirm their regenerative capabilities, although much remains to be elucidated about their basic biology. To develop this new treatment modality, in a cost effective and standardized workflow, necessitates the creation of cryopreserved cell lines to facilitate access for cardiac patients requiring urgent therapy. Cryopreservation may however lead to alterations in cell behavior and potency. The aim of this study was to investigate the effect of cryopreservation on canine CDCs. CDCs and mesenchymal stem cells (MSCs) isolated from five dogs were characterized. CDCs demonstrated a population doubling time that was unchanged by cryopreservation (fresh vs. cryopreserved; 57.13 ± 5.27 h vs. 48.94 ± 9.55 h, P = 0.71). This was slower than for MSCs (30.46 h, P < 0.05). The ability to form clones, self-renew, and commit to multiple lineages was unaffected by cryopreservation. Cryopreserved CDCs formed larger cardiospheres compared to fresh cells (P < 0.0001). Fresh CDCs showed a high proportion of CD105⁺ (89.0% ± 4.98) and CD44⁺ (99.68% ± 0.13) cells with varying proportions of CD90⁺ (23.36% ± 9.78), CD34⁺ (7.18% ± 4.03) and c-Kit⁺ (13.17% ± 8.67) cells. CD45⁺ (0.015% ± 0.005) and CD29⁺ (2.92% ± 2.46) populations were negligible. Increasing passage number of fresh CDCs correlated with an increase in the proportion of CD34⁺ and a decrease in CD90⁺ cells (P = 0.003 and 0.03, respectively). Cryopreserved CDCs displayed increased CD34⁺ (P < 0.001) and decreased CD90⁺ cells (P = 0.042) when compared to fresh cells. Overall, our study shows that cryopreservation of canine CDCs is feasible without altering their stem characteristics, thereby facilitating their utilization for clinical trials. © 2017 International Society for Advancement of Cytometry.