Effects of hedgehog proteins on tissue engineering of cartilage in vitro

Role of Hedgehog Signaling Pathways in Multipotent Mesenchymal Stem Cells Differentiation

Multipotent mesenchymal stem cells (MSCs) have high self-renewal and multi-lineage differentiation potentials and low immunogenicity, so they have attracted much attention in the field of regenerative medicine and have a promising clinical application. MSCs originate from the mesoderm and can differentiate not only into osteoblasts, cartilage, adipocytes, and muscle cells but also into ectodermal and endodermal cell lineages across embryonic layers. To design cell therapy for replacement of damaged tissues, it is essential to understand the signaling pathways, which have a major impact on MSC differentiation, as this will help to integrate the signaling inputs to initiate a specific lineage. Hedgehog (Hh) signaling plays a vital role in the development of various tissues and organs in the embryo. As a morphogen, Hh not only regulates the survival and proliferation of tissue progenitor and stem populations but also is a critical moderator of MSC differentiation, involving tri-lineage and across embryonic layer differentiation of MSCs. This review summarizes the role of Hh signaling pathway in the differentiation of MSCs to mesodermal, endodermal, and ectodermal cells.

Chondrogenic differentiation of bone marrow-derived mesenchymal stem cells following transfection with Indian hedgehog and sonic hedgehog using a rotary cell culture system

Background

Indian hedgehog (IHH) and Sonic hedgehog (SHH) are important regulators of chondrogenesis. However, activation of IHH and SHH also promotes chondrocyte hypertrophy and ossification during chondrogenesis. The aims of this study were to investigate the effect of microgravity on IHH- and SHH-induced chondrogenic differentiation and to elucidate the role of microgravity in this process.

Methods

Adenovirus plasmids encoding the rabbit IHH gene and SHH genes were constructed in vitro and transfected into rabbit bone marrow-derived mesenchymal stem cells (BMSCs). A rotary cell culture system (RCCS), in which a dynamic three-dimensional culture system combines the mechanical environment with a three-dimensional culture surface, was used for cell culture and differentiation. During the induction of differentiation, expression levels of cartilage-related and cartilage hypertrophy-related genes and proteins were detected by quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting, respectively. Toluidine blue and collagen II immunohistochemical staining and annexin V-Cy3 staining were used to indicate investigate cartilage matrix synthesis and hypertrophic hypertrophy, respectively, on day 21 after induction of differentiation.

Results

In this study, IHH and SHH were shown to be equipotent inducers of chondrogenesis in rabbit BMSCs, as evidenced by strong staining for proteoglycans and collagen II, and increased expression of mRNAs and proteins associated with chondrogenesis in an RCCS environment. More importantly, chondrogenic hypertrophy and aging were effectively inhibited in the RCCS environment. In addition, levels of cartilage-related markers in the IHH and SHH transfection groups were initially increased and later decreased in the traditional two-dimensional environment, while cartilage hypertrophy-related factors revealed higher mRNA expression levels during induction.

Conclusions

In summary, microgravity significantly promoted chondrogenic differentiation of BMSCs induced by IHH and SHH and attenuated chondrogenic hypertrophy and aging during chondrogenesis. Furthermore, exogenous IHH and SHH had the same effect on chondrogenic differentiation of BMSCs in the RCCS environment. This study provides further evidence of chondrogenic induction of BMSCs in vitro via IHH and SHH gene delivery.

Electronic supplementary material

The online version of this article (10.1186/s11658-019-0144-2) contains supplementary material, which is available to authorized users.

TGF-β Stimulates Endochondral Differentiation after Denervation

Transforming growth factor beta (TGF-β) is a multifunctional protein that induces gene expression of cartilage-specific molecules, but its exact role in the process of chondrogenesis is unclear. Because recent studies suggest that TGF-β can facilitate chondrogenic precursor cells differentiating into chondrocytes, we sought to determine whether TGF-β prevents denervation-induced reduction of endochondral bone formation in an experimental model. Mice were treated daily with recombinant human TGF-β1 (rhTGF-β1) for 3 weeks. We found that rhTGF-β1 not only prevented denervation-induced reduction of gene expression of type II collagen, type X collagen, aggrecan, Indian hedgehog, and parathyroid hormone-related peptide, but also synergized endochondral differentiation. These results demonstrate that short-term systemic administration of TGF-β substantially prevents denervation-induced reduction of endochondral bone formation via stimulating endochondral differentiation. Potential therapeutic applications will be pursued in further studies that address the molecular biological mechanism of TGF-β on endochodral bone formation after denervation in animal models.

Tissue-engineered cartilage: the crossroads of biomaterials, cells and stimulating factors

Damage to cartilage represents one of the most challenging tasks of musculoskeletal therapeutics due to its limited propensity for healing and regenerative capabilities. Lack of current treatments to restore cartilage tissue function has prompted research in this rapidly emerging field of tissue regeneration of functional cartilage tissue substitutes. The development of cartilaginous tissue largely depends on the combination of appropriate biomaterials, cell source, and stimulating factors. Over the years, various biomaterials have been utilized for cartilage repair, but outcomes are far from achieving native cartilage architecture and function. This highlights the need for exploration of suitable biomaterials and stimulating factors for cartilage regeneration. With these perspectives, we aim to present an overview of cartilage tissue engineering with recent progress, development, and major steps taken toward the generation of functional cartilage tissue. In this review, we have discussed the advances and problems in tissue engineering of cartilage with strong emphasis on the utilization of natural polymeric biomaterials, various cell sources, and stimulating factors such as biophysical stimuli, mechanical stimuli, dynamic culture, and growth factors used so far in cartilage regeneration. Finally, we have focused on clinical trials, recent innovations, and future prospects related to cartilage engineering.

Sonic hedgehog improves redifferentiation of dedifferentiated chondrocytes for articular cartilage repair

Sonic hedgehog (Shh) is involved in the induction of early cartilaginous differentiation of mesenchymal cells in the limb. We investigated whether Shh could promote redifferentiation of dedifferentiated chondrocytes and have a favorable effect on the regeneration of cartilage. Articular chondrocytes of rats were separated and cultured. The redifferentiation of dedifferentiated chondrocytes transfected with Shh was evaluated using monolayer and pellet culture system. The signaling molecules (Ptc 1, Gli 1 and Sox9) of the hedgehog pathway were investigated. A rat model of articular cartilage defect was used to evaluate cartilage repair after transplantation with dedifferentiated chondrocytes. After Shh gene transfer, the hedgehog pathway was upregulated in dedifferentiated chondrocytes. Real time-PCR and western blot analysis verified the stronger expression of Ptc1, Gli1 and Sox9 in Shh transfected cells. Shh upregulates the Shh signaling pathway and multiple cytokines (bone morphogenetic protein 2 and insulin-like growth factor 1) in dedifferentiated chondrocytes. After transplantation in the joint, histologic analysis of the regenerative tissues revealed that significantly better cartilage repair in rats transplanted with Shh transfected cells. These data suggest that Shh could induce redifferentiation of dedifferentiated chondrocytes through up-regulating Shh signaling pathway, and have considerable therapeutic potential in cartilage repair.

Construction of self-assembled cartilage tissue from bone marrow mesenchymal stem cells induced by hypoxia combined with GDF-5

It is widely known that hypoxia can promote chondrogenesis of human bone marrow derived mesenchymal stem cells (hMSCs) in monolayer cultures. However, the direct impact of oxygen tension on hMSC differentiation in three-dimensional cultures is still unknown. This research was designed to observe the direct impact of oxygen tension on the ability of hMSCs to "self assemble" into tissue-engineered cartilage constructs. hMSCs were cultured in chondrogenic medium (CM) containing 100 ng/mL growth differentiation factor 5 (GDF-5) at 5% (hypoxia) and 21% (normoxia) O2 levels in monolayer cultures for 3 weeks. After differentiation, the cells were digested and employed in a self-assembly process to produce tissue-engineered constructs under hypoxic and normoxic conditions in vitro. The aggrecan and type II collagen expression, and type X collagen in the self-assembled constructs were assessed by using immunofluorescent and immunochemical staining respectively. The methods of dimethylmethylene blue (DMMB), hydroxyproline and PicoGreen were used to measure the total collagen content, glycosaminoglycan (GAG) content and the number of viable cells in each construct, respectively. The expression of type II collagen and aggrecan under hypoxic conditions was increased significantly as compared with that under normoxic conditions. In contrast, type X collagen expression was down-regulated in the hypoxic group. Moreover, the constructs in hypoxic group showed more significantly increased total collagen and GAG than in normoxic group, which were more close to those of the natural cartilage. These findings demonstrated that hypoxia enhanced chondrogenesis of in vitro, scaffold-free, tissue-engineered constructs generated using hMSCs induced by GDF-5. In hypoxic environments, the self-assembled constructs have a Thistological appearance and biochemical parameters similar to those of the natural cartilage.

The effects of inhibiting hedgehog signaling pathways by using specific antagonist cyclopamine on the chondrogenic differentiation of mesenchymal stem cells

This study aimed to investigate the effects of cyclopamine, a specific inhibitor of Hedgehog signaling pathways, on the chondrogenic differentiation of mesenchymal stem cells (MSCs). During culture, the experimental groups were treated with cyclopamine and their cell proliferation status was assessed using the MTT test. The extra-bone cellular matrix (ECM) and Collagen II (Col II) was detected by toluidine blue staining and immunohistochemistry of cells. The concentrations of Col II and aggrecan in the culture solution and cytosol were detected using ELISA on the 7th, 14th, and 21st days of cyclopamine induction. Gene and protein expression of Col II and aggrecan were analyzed on the 14th day of cyclopamine induction using real-time PCR and western blot analyses. No significant differences in proliferation of mesenchymal stem cells were found between the control group and the group treated with cyclopamine. Compared to the blank control group, the ECM level was low and the protein and mRNA concentrations of Collagen II (Col II) and aggrecan in the culture solution and cytosol, respectively, were significantly reduced in the experimental group. The Smo acted as a key point in the regulations of Hedgehog signaling pathway on the chondrogenic differentiation of rabbit MSCs.

Indian hedgehog gene transfer is a chondrogenic inducer of human mesenchymal stem cells

Introduction

To date, no single most-appropriate factor or delivery method has been identified for the purpose of mesenchymal stem cell (MSC)-based treatment of cartilage injury. Therefore, in this study we tested whether gene delivery of the growth factor Indian hedgehog (IHH) was able to induce chondrogenesis in human primary MSCs, and whether it was possible by such an approach to modulate the appearance of chondrogenic hypertrophy in pellet cultures in vitro.

Methods

First-generation adenoviral vectors encoding the cDNA of the human IHH gene were created by cre-lox recombination and used alone or in combination with adenoviral vectors, bone morphogenetic protein-2 (Ad.BMP-2), or transforming growth factor beta-1 (Ad.TGF-β1) to transduce human bone-marrow derived MSCs at 5 × 10² infectious particles/cell. Thereafter, 3 × 10⁵ cells were seeded into aggregates and cultured for 3 weeks in serum-free medium, with untransduced or marker gene transduced cultures as controls. Transgene expressions were determined by ELISA, and aggregates were analysed histologically, immunohistochemically, biochemically and by RT-PCR for chondrogenesis and hypertrophy.

Results

IHH, TGF-β1 and BMP-2 genes were equipotent inducers of chondrogenesis in primary MSCs, as evidenced by strong staining for proteoglycans, collagen type II, increased levels of glycosaminoglycan synthesis, and expression of mRNAs associated with chondrogenesis. IHH-modified aggregates, alone or in combination, also showed a tendency to progress towards hypertrophy, as judged by the expression of alkaline phosphatase and stainings for collagen type X and Annexin 5.

Conclusion

As this study provides evidence for chondrogenic induction of MSC aggregates in vitro via IHH gene delivery, this technology may be efficiently employed for generating cartilaginous repair tissues in vivo.

Spontaneous redifferentiation of dedifferentiated human articular chondrocytes on hydrogel surfaces

Chondrocytes rapidly dedifferentiate into a more fibroblastic phenotype on a two-dimensional polystyrene substratum. This impedes fundamental research on these cells as well as their clinical application. This study investigated the redifferentiation behavior of dedifferentiated chondrocytes on a hydrogel substratum. Dedifferentiated normal human articular chondrocyte-knee (NHAC-kn) cells were released from the sixth-passage monolayer cultured on a polystyrene surface. These cells were then subcultured on a chemically crosslinked copolymer hydrogel, that is, poly(NaAMPS-co-DMAAm), and the cells thus obtained were used as the seventh-passage cultivation. Copolymer gels were synthesized from a negatively charged monomer, the sodium salt of 2-acrylamido-2-methyl-1-propanesulfonic acid (NaAMPS), and a neutral monomer, N,N-dimethylacrylamide (DMAAm). These gels were of different compositions because the molar fraction (F) of NaAMPS was varied (F = 0, 0.2, 0.4, 0.6, 0.8, and 1.0). The dedifferentiated NHAC-kn cells spontaneously redifferentiated to normal NHAC-kn cells on neutral (F = 0) and poly(NaAMPS-co-DMAAm) hydrogels of low charge density (F = 0.2). This was deduced from the cell morphology and expression of cartilage-specific genes and proteins. These results should enable us to establish a simple and efficient method for preparing large amounts of chondrocytes by cultivation on the surfaces of neutral and low-charge-density hydrogels.

Biomaterial effects in articular cartilage tissue engineering using polyglycolic acid, a novel marine origin biomaterial, IGF-I, and TGF-beta 1

Bovine articular chondrocytes were seeded on either polyglycolic acid (PGA) non-woven mesh scaffolds or a biomatrix from the species Porites lutea (POR). These constructs were cultured for 6 weeks in the presence of insulin-like growth factor (IGF)-I (10 ng/ml or 100 ng/ml) or transforming growth factor (TGF)-beta 1 (5 ng/ml or 30 ng/ml) to determine the in-vitro articular cartilage regeneration capacity of each. Histology, deoxyribonucleic acid content, collagen I and II (immunohistochemistry and enzyme-linked immunosorbent assay), and glycosaminoglycan (GAG) contents were measured at 0 weeks, 2 weeks, and 6 weeks to assess the characteristics of chondrogenesis. Both scaffolds supported the maintenance of the chondrocytic phenotype, as evidenced by the predominance of collagen II and the presence of rounded chondrocytes embedded in lacunae. Regardless of growth factor treatment, cells cultured on PGA scaffolds produced more collagen type II than those cultured on POR. Conversely, by 6 weeks, cells cultured on POR scaffolds produced more GAG than those cultured on PGA scaffolds, again regardless of the growth factor used. Across the two groups, 100 ng/ml of IGF-I had the greatest overall effect in GAG content. This work indicates that PGA and the POR scaffolds are both effective growth matrices for articular cartilage, with each scaffold exhibiting different yet desirable profiles of articular cartilage growth.

Sonic hedgehog protein promotes proliferation and chondrogenic differentiation of bone marrow-derived mesenchymal stem cells in vitro

BACKGROUND

Sonic hedgehog (Shh) protein is known to be an important signaling protein in early embryonic development. Also, Shh is involved in the induction of early cartilaginous differentiation of mesenchymal cells in the limb and in the spine.

METHODS

The impact of Shh on adult stem cells, human bone marrow-derived mesenchymal stem cells (MSCs), was tested. The MSCs were treated either with recombinant Sonic hedgehog protein (r-Shh) or with transforming growth factor-beta 1 (TGF-beta(1)) as a positive control in vitro for 3 weeks. The effects on cartilaginous differentiation and proliferation were assayed.

RESULTS

MSCs when treated with either Shh or TGF-beta(1) showed expression of cartilage markers aggrecan, Sox9, CEP-68, and collagen type II and X within 3 weeks. Only r-Shh-treated cells showed a very strong cell proliferation and much higher BrdU incorporation in cell assay systems.

CONCLUSIONS

These are the first data that indicate an important role of Shh for the induction of cartilage production by MSCs in vitro.

Molecular pathways regulating pro-migratory effects of Hedgehog signaling

The Hedgehog proteins play a crucial role in metazoan embryo development. Constitutive activation of the pathway is associated with multiple types of cancer. Recent experimental data suggest involvement of Hedgehog signaling in vascular remodeling, germ cell migration, and axon guidance. The molecular mechanisms underlying these effects remain elusive. Here we show that yolk sac-derived endothelial cells and embryonic fibroblasts can directly respond to the Hedgehog signal by increased migration in an in vitro scratch (wound) assay. We also identify Hedgehog transcriptional target genes in these cells, many of which participate in cell migration, axon guidance, and angiogenesis processes. Inhibition of one such molecular pathway, neuropilin-flavomonooxygenase, blocks Hedgehog-induced cell migration. These findings suggest that Hedgehog signaling directly affects embryonic endothelial and fibroblast cell migration via molecules and pathways known to regulate cell migration in response to a variety of environmental cues.

A self-assembling process in articular cartilage tissue engineering

Current therapies for articular cartilage defects often result in fibrocartilaginous tissue. To achieve regeneration with hyaline articular cartilage, tissue-engineering approaches employing cell-seeded scaffolds have been investigated. However, limitations of scaffolds include phenotypic alteration of cells, stress-shielding, hindrance of neotissue organization, and degradation product toxicity. This study employs a self-assembling process to produce tissue-engineered constructs over agarose in vitro without using a scaffold. Compared to past studies using various meshes and gels as scaffolding materials, the self-assembly method yielded constructs with comparable GAG and collagen content. By 12 weeks, the self-assembling process resulted in tissue-engineered constructs that were hyaline- like in appearance with histological, biochemical, and biomechanical properties approaching those of native articular cartilage. Overall, constructs contained two thirds more GAG per dry weight than calf articular cartilage. Collagen per dry weight reached more than one third the level of native tissue. IHC and gel electrophoresis showed collagen type II production and absence of collagen type I. More importantly, self-assembled constructs reached well over one third the stiffness of native tissue.

Low-density cultures of bovine chondrocytes: effects of scaffold material and culture system

Chondrocytes were seeded on either agarose or polyglycolic acid (PGA) unwoven meshes at 10 million cells/ml of scaffold volume to evaluate the effect that these two biomaterials have on the low-density culture of chondrocytes in a rotating-wall bioreactor. For both static and bioreactor culture, agarose constructs contained more glycosaminoglycan than their PGA counterparts. However, the PGA constructs contained more collagen for both culture conditions when compared to agarose. For the low seeding density of this study, PGA constructs cultured in the bioreactor did not outperform static cultures when comparing collagen content after 8 weeks. The mechanical properties of the PGA constructs also did not improve with culture time. Similar results were observed with the agarose culture, though both static- and bioreactor-culture agarose constructs exhibited increases in aggregate modulus at the end of the culture period. As in PGA culture, chondrocytes cultured in agarose may require a higher density to reap the benefits of the bioreactor environment.

PEGylation Does Not Impair Insulin Efficacy in Three-Dimensional Cartilage Culture: An Investigation toward Biomimetic Polymers

A major goal in tissue engineering is the controlled application of growth factors. As a novel application system, we are currently developing biomimetic polymers that are processed into three-dimensional scaffolds. Bioactive proteins will be covalently bound to the polymers via a poly(ethylene glycol) (PEG) linker. Of paramount importance is the maintenance of the biological activity of the protein after PEGylation and covalent binding to the polymer. Therefore, within this study, insulin used as a model protein was PEGylated with an active succinimidyl ester of poly(ethylene glycol) (SS-NH-PEG) (MW ~2000) and biological effects of the protein-PEG conjugate were monitored in comparison with unmodified insulin. No significant differences in chondrocyte proliferation were observed in a conventional proliferation assay after treatment with insulin or PEGylated insulin. In a complex three-dimensional cartilage-engineering model the effects of insulin and PEGylated insulin were investigated over a wide concentration range (0.025-25 microg/mL). Insulin and PEGylated insulin at equivalent concentrations resulted in cartilaginous tissue constructs exhibiting identical wet weight, cell number, biochemical composition of the extracellular matrix, and histological appearance, both compounds significantly improving tissue quality as compared with control constructs. In conclusion, the presented study demonstrates that PEGylation of insulin using SS-NH-PEG did not change the activity of the protein in a complex biological environment and is regarded as a step toward the development of biomimetic polymers.