Pre-transplantational Control of the Post-transplantational Fate of Human Pluripotent Stem Cell-Derived Cartilage

Moxibustion ameliorates osteoarthritis by regulating gut microbiota via impacting cAMP-related signaling pathway

BACKGROUND

Osteoarthritis (OA) is a prevalent progressive disorder. Moxibustion has found widespread use in clinical practice for OA, while its underlying mechanism remains elusive.

OBJECTIVE

To investigate whether moxibustion can ameliorate OA by influencing the metabolic processes in OA and to elucidate the specific metabolic mechanisms involved.

METHODS

C57BL/6J WT mice were randomly assigned to one of three groups: the SHAM group, the ACLT group, and the ACLT+M group. In the ACLT+M group, mice underwent moxibustion treatment at acupoints Shenshu (BL23) and Zusanli (ST36) for a continuous period of 28 days, with each session lasting 20 min. We conducted a comprehensive analysis to assess the impact of moxibustion on OA, focusing on pathological changes, intestinal flora composition, and serum metabolites.

RESULTS

Moxibustion treatment effectively mitigated OA-related pathological changes. Specifically, moxibustion treatment resulted in the amelioration of articular cartilage damage, synovial inflammation, subchondral bone sclerosis when compared to the ACLT group. Moreover, 16S rDNA sequencing analysis revealed that moxibustion treatment positively influenced the composition of the flora, making it more similar to that of the SHAM group. Notably, moxibustion treatment led to a reduction in the abundance of Ruminococcus and Proteobacteria in the intestine. In addition, non-targeted metabolomics analysis identified 254 significantly different metabolites between the groups. Based on KEGG pathway analysis and the observed impact of moxibustion on OA-related inflammation, moxibustion therapy is closely associated with the cAMP-related signaling pathway.

CONCLUSION

Moxibustion can relieve OA by regulating intestinal flora and via impacting cAMP-related signaling pathway.

The Origin and Fate of Chondrocytes: Cell Plasticity in Physiological Setting

PURPOSE OF REVIEW

Here, we discuss the origin of chondrocytes, their destiny, and their plasticity in relationship to bone growth, articulation, and formation of the trabeculae. We also consider these processes from a biological, clinical, and evolutionary perspective.

RECENT FINDINGS

Chondrocytes, which provide the template for the formation of most bones, are responsible for skeletal growth and articulation during postnatal life. In recent years our understanding of the fate of these cells has changed dramatically. Current evidence indicates a paradoxical situation during skeletogenesis, with some cells of mesenchymal condensation differentiating directly into osteoblasts, whereas others of the same kind give rise to highly similar osteoblasts via a complex process of differentiation involving several chondrocyte intermediates. The situation becomes even more paradoxical during postnatal growth when stem cells in the growth plate produce differentiated, functional progenies, which thereafter presumably dedifferentiate into another type of stem cell. Such a remarkable transition from one cell type to another under postnatal physiological conditions provides a fascinating example of cellular plasticity that may have valuable clinical implications.

Regenerative engineering of long bones using the small molecule forskolin

Bone grafting procedures have become increasingly common in the United States, with approximately 500,000 cases occurring each year at a societal cost exceeding $2.4 billion. Recombinant human bone morphogenetic proteins (rhBMPs) are therapeutic agents that have been widely used by orthopedic surgeons to stimulate bone tissue formation alone and when paired with biomaterials. However, significant limitations such as immunogenicity, high production cost, and ectopic bone growth from these therapies remain. Therefore, efforts have been made to discover and repurpose osteoinductive small-molecule therapeutics to promote bone regeneration. Previously, we have demonstrated that a single-dose treatment with the small-molecule forskolin for just 24 h induces osteogenic differentiation of rabbit bone marrow-derived stem cells in vitro, while mitigating adverse side effects attributed with prolonged small-molecule treatment schemes. In this study, we engineered a composite fibrin-PLGA [poly(lactide-co-glycolide)]-sintered microsphere scaffold for the localized, short-term delivery of the osteoinductive small molecule, forskolin. In vitro characterization studies showed that forskolin released out of the fibrin gel within the first 24 h and retained its bioactivity toward osteogenic differentiation of bone marrow-derived stem cells. The forskolin-loaded fibrin-PLGA scaffold was also able to guide bone formation in a 3-mo rabbit radial critical-sized defect model comparable to recombinant human bone morphogenetic protein-2 (rhBMP-2) treatment, as demonstrated through histological and mechanical evaluation, with minimal systemic off-target side effects. Together, these results demonstrate the successful application of an innovative small-molecule treatment approach within long bone critical-sized defects.

GDF5+ chondroprogenitors derived from human pluripotent stem cells preferentially form permanent chondrocytes

It has been established in the mouse model that during embryogenesis joint cartilage is generated from a specialized progenitor cell type, distinct from that responsible for the formation of growth plate cartilage. We recently found that mesodermal progeny of human pluripotent stem cells gave rise to two types of chondrogenic mesenchymal cells in culture: SOX9+ and GDF5+ cells. The fast-growing SOX9+ cells formed in vitro cartilage that expressed chondrocyte hypertrophy markers and readily underwent mineralization after ectopic transplantation. In contrast, the slowly growing GDF5+ cells derived from SOX9+ cells formed cartilage that tended to express low to undetectable levels of chondrocyte hypertrophy markers, but expressed PRG4, a marker of embryonic articular chondrocytes. The GDF5+-derived cartilage remained largely unmineralized in vivo. Interestingly, chondrocytes derived from the GDF5+ cells seemed to elicit these activities via non-cell-autonomous mechanisms. Genome-wide transcriptomic analyses suggested that GDF5+ cells might contain a teno/ligamento-genic potential, whereas SOX9+ cells resembled neural crest-like progeny-derived chondroprogenitors. Thus, human pluripotent stem cell-derived GDF5+ cells specified to generate permanent-like cartilage seem to emerge coincidentally with the commitment of the SOX9+ progeny to the tendon/ligament lineage.

Human adipose-derived stromal/stem cells expressing doublecortin improve cartilage repair in rabbits and monkeys

Localized cartilage lesions in early osteoarthritis and acute joint injuries are usually treated surgically to restore function and relieve pain. However, a persistent clinical challenge remains in how to repair the cartilage lesions. We expressed doublecortin (DCX) in human adipose-derived stromal/stem cells (hASCs) and engineered hASCs into cartilage tissues using an in vitro 96-well pellet culture system. The cartilage tissue constructs with and without DCX expression were implanted in the knee cartilage defects of rabbits (n = 42) and monkeys (n = 12). Cohorts of animals were euthanized at 6, 12, and 24 months after surgery to evaluate the cartilage repair outcomes. We found that DCX expression in hASCs increased expression of growth differentiation factor 5 (GDF5) and matrilin 2 in the engineered cartilage tissues. The cartilage tissues with DCX expression significantly enhanced cartilage repair as assessed macroscopically and histologically at 6, 12, and 24 months after implantation in the rabbits and 24 months after implantation in the monkeys, compared to the cartilage tissues without DCX expression. These findings suggest that hASCs expressing DCX may be engineered into cartilage tissues that can be used to treat localized cartilage lesions.

Induction and expansion of human PRRX1+ limb-bud-like mesenchymal cells from pluripotent stem cells

Current protocols for the differentiation of human pluripotent stem cells (hPSCs) into chondrocytes do not allow for the expansion of intermediate progenitors so as to prospectively assess their chondrogenic potential. Here we report a protocol that leverages PRRX1-tdTomato reporter hPSCs for the selective induction of expandable and ontogenetically defined PRRX1⁺ limb-bud-like mesenchymal cells under defined xeno-free conditions, and the prospective assessment of the cells' chondrogenic potential via the cell-surface markers CD90, CD140B and CD82. The cells, which proliferated stably and exhibited the potential to undergo chondrogenic differentiation, formed hyaline cartilaginous-like tissue commensurate to their PRRX1-expression levels. Moreover, we show that limb-bud-like mesenchymal cells derived from patient-derived induced hPSCs can be used to identify therapeutic candidates for type II collagenopathy and we developed a method to generate uniformly sized hyaline cartilaginous-like particles by plating the cells on culture dishes coated with spots of a zwitterionic polymer. PRRX1⁺ limb-bud-like mesenchymal cells could facilitate the mass production of chondrocytes and cartilaginous tissues for applications in drug screening and tissue engineering.

Comparative evaluation of isogenic mesodermal and ectomesodermal chondrocytes from human iPSCs for cartilage regeneration

Generating phenotypic chondrocytes from pluripotent stem cells is of great interest in the field of cartilage regeneration. In this study, we differentiated human induced pluripotent stem cells into the mesodermal and ectomesodermal lineages to prepare isogenic mesodermal cell-derived chondrocytes (MC-Chs) and neural crest cell-derived chondrocytes (NCC-Chs), respectively, for comparative evaluation. Our results showed that both MC-Chs and NCC-Chs expressed hyaline cartilage-associated markers and were capable of generating hyaline cartilage-like tissue ectopically and at joint defects. Moreover, NCC-Chs revealed closer morphological and transcriptional similarities to native articular chondrocytes than MC-Chs. NCC-Ch implants induced by our growth factor mixture demonstrated increased matrix production and stiffness compared to MC-Ch implants. Our findings address how chondrocytes derived from pluripotent stem cells through mesodermal and ectomesodermal differentiation are different in activities and functions, providing the crucial information that helps make appropriate cell choices for effective regeneration of articular cartilage.

Rejuvenated Stem/Progenitor Cells for Cartilage Repair Using the Pluripotent Stem Cell Technology

It is widely accepted that chondral defects in articular cartilage of adult joints are never repaired spontaneously, which is considered to be one of the major causes of age-related degenerative joint disorders, such as osteoarthritis. Since mobilization of subchondral bone (marrow) cells and addition of chondrocytes or mesenchymal stromal cells into full-thickness defects show some degrees of repair, the lack of self-repair activity in adult articular cartilage can be attributed to lack of reparative cells in adult joints. In contrast, during a fetal or embryonic stage, joint articular cartilage has a scar-less repair activity, suggesting that embryonic joints may contain cells responsible for such activity, which can be chondrocytes, chondroprogenitors, or other cell types such as skeletal stem cells. In this respect, the tendency of pluripotent stem cells (PSCs) to give rise to cells of embryonic characteristics will provide opportunity, especially for humans, to obtain cells carrying similar cartilage self-repair activity. Making use of PSC-derived cells for cartilage repair is still in a basic or preclinical research phase. This review will provide brief overviews on how human PSCs have been used for cartilage repair studies.

Recent progress of animal transplantation studies for treating articular cartilage damage using pluripotent stem cells

Focal articular cartilage damage can eventually lead to the onset of osteoarthritis with degradation around healthy articular cartilage. Currently, there are no drugs available that effectively repair articular cartilage damage. Several surgical techniques exist and are expected to prevent progression to osteoarthritis, but they do not offer a long-term clinical solution. Recently, regenerative medicine approaches using human pluripotent stem cells (PSCs) have gained attention as new cell sources for therapeutic products. To translate PSCs to clinical application, appropriate cultures that produce large amounts of chondrocytes and hyaline cartilage are needed. So too are assays for the safety and efficacy of the cellular materials in preclinical studies including animal transplantation models. To confirm safety and efficacy, transplantation into the subcutaneous space and articular cartilage defects have been performed in animal models. All but one study we reviewed that transplanted PSC-derived cellular products into articular cartilage defects found safe and effective recovery. However, for most of those studies, the quality of the PSCs was not verified, and the evaluations were done with small animals over short observation periods. Large animals and longer observation times are preferred. We will discuss the recent progress and future direction of the animal transplantation studies for the treatment of focal articular cartilage damages using PSCs.

Human pluripotent stem cell-derived chondroprogenitors for cartilage tissue engineering

The cartilage of joints, such as meniscus and articular cartilage, is normally long lasting (i.e., permanent). However, once damaged, especially in large animals and humans, joint cartilage is not spontaneously repaired. Compensating the lack of repair activity by supplying cartilage-(re)forming cells, such as chondrocytes or mesenchymal stromal cells, or by transplanting a piece of normal cartilage, has been the basis of therapy for biological restoration of damaged joint cartilage. Unfortunately, current biological therapies face problems on a number of fronts. The joint cartilage is generated de novo from a specialized cell type, termed a 'joint progenitor' or 'interzone cell' during embryogenesis. Therefore, embryonic chondroprogenitors that mimic the property of joint progenitors might be the best type of cell for regenerating joint cartilage in the adult. Pluripotent stem cells (PSCs) are expected to differentiate in culture into any somatic cell type through processes that mimic embryogenesis, making human (h)PSCs a promising source of embryonic chondroprogenitors. The major research goals toward the clinical application of PSCs in joint cartilage regeneration are to (1) efficiently generate lineage-specific chondroprogenitors from hPSCs, (2) expand the chondroprogenitors to the number needed for therapy without loss of their chondrogenic activity, and (3) direct the in vivo or in vitro differentiation of the chondroprogenitors to articular or meniscal (i.e., permanent) chondrocytes rather than growth plate (i.e., transient) chondrocytes. This review is aimed at providing the current state of research toward meeting these goals. We also include our recent achievement of successful generation of "permanent-like" cartilage from long-term expandable, hPSC-derived ectomesenchymal chondroprogenitors.

Dynamic mechanical loading and growth factors influence chondrogenesis of induced pluripotent mesenchymal progenitor cells in a cartilage-mimetic hydrogel

Human induced pluripotent stem cells (iPSCs) have emerged as a promising alternative to bone-marrow derived mesenchymal stem/stromal cells for cartilage tissue engineering. However, the effect of biochemical and mechanical cues on iPSC chondrogenesis remains understudied. This study evaluated chondrogenesis of induced pluripotent mesenchymal progenitor cells (iPS-MPs) encapsulated in a cartilage-mimetic hydrogel under different culture conditions: free swelling versus dynamic compressive loading and different growth factors (TGFβ3 and/or BMP2). Human iPSCs were differentiated into iPS-MPs and chondrogenesis was evaluated by gene expression (qPCR) and protein expression (immunohistochemistry) after three weeks. In pellet culture, both TGFβ3 and BMP2 were required to promote chondrogenesis. However, the hydrogel in growth factor-free conditions promoted chondrogenesis, but rapidly progressed to hypertrophy. Dynamic loading in growth factor-free conditions supported chondrogenesis, but delayed the transition to hypertrophy. Findings were similar with TGFβ3, BMP2, and TGFβ3 + BMP2. Dynamic loading with TGFβ3, regardless of BMP2, was the only condition that promoted a stable chondrogenic phenotype (aggrecan + collagen II) accompanied by collagen X down-regulation. Positive TGFβRI expression with load-enhanced Smad2/3 signaling and low SMAD1/5/8 signaling was observed. In summary, this study reports a promising cartilage-mimetic hydrogel for iPS-MPs that when combined with appropriate biochemical and mechanical cues induces a stable chondrogenic phenotype.

Thalidomide Inhibits Human iPSC Mesendoderm Differentiation by Modulating CRBN-dependent Degradation of SALL4

Exposure to thalidomide during a critical window of development results in limb defects in humans and non-human primates while mice and rats are refractory to these effects. Thalidomide-induced teratogenicity is dependent on its binding to cereblon (CRBN), the substrate receptor of the Cul4A-DDB1-CRBN-RBX1 E3 ubiquitin ligase complex. Thalidomide binding to CRBN elicits subsequent ubiquitination and proteasomal degradation of CRBN neosubstrates including SALL4, a transcription factor of which polymorphisms phenocopy thalidomide-induced limb defects in humans. Herein, thalidomide-induced degradation of SALL4 was examined in human induced pluripotent stem cells (hiPSCs) that were differentiated either to lateral plate mesoderm (LPM)-like cells, the developmental ontology of the limb bud, or definitive endoderm. Thalidomide and its immunomodulatory drug (IMiD) analogs, lenalidomide, and pomalidomide, dose-dependently inhibited hiPSC mesendoderm differentiation. Thalidomide- and IMiD-induced SALL4 degradation can be abrogated by CRBN V388I mutation or SALL4 G416A mutation in hiPSCs. Genetically modified hiPSCs expressing CRBN E377V/V388I mutant or SALL4 G416A mutant were insensitive to the inhibitory effects of thalidomide, lenalidomide, and pomalidomide on LPM differentiation while retaining sensitivity to another known limb teratogen, all-trans retinoic acid (atRA). Finally, disruption of LPM differentiation by atRA or thalidomide perturbed subsequent chondrogenic differentiation in vitro. The data here show that thalidomide, lenalidomide, and pomalidomide affect stem cell mesendoderm differentiation through CRBN-mediated degradation of SALL4 and highlight the utility of the LPM differentiation model for studying the teratogenicity of new CRBN modulating agents.

Enhancement of the chondrogenic differentiation of mesenchymal stem cells and cartilage repair by ghrelin

Transforming growth factor beta (TGF-β) is commonly utilized in chondrogenic differentiation protocols, but this often results in incomplete maturation of the derived chondrocytes. Gene expression analysis, quantitation of sulfated glycosaminoglycan and collagen, and histological staining were performed to assess the effects of ghrelin. The signaling pathways involved were investigated with inhibitors or targeted by shRNAs. Joint cavity delivery of TGF-β with or without ghrelin, within a rat cartilage defect model was performed to evaluate the in vivo effects of ghrelin. Ghrelin dramatically enhanced gene expression levels of SOX9, ACAN, and COL II and resulted in increased synthesis of sulfated glycosaminoglycan (sGAG) and collagen in vitro. Combined treatment with TGF-β and ghrelin synergistically enhanced the phosphorylation of ERK1/2 and DMNT3A, which accounted for increased expression of chondrogenic genes. Delivery of ghrelin in combination with TGF-β after MSC implantation within a rat osteochondral defect model significantly enhanced de novo cartilage regeneration, as compared to delivery with TGF-β alone. In conclusion, ghrelin could significantly enhance MSC chondrogenic differentiation in vitro and can also enhance cartilage regeneration in vivo when used in combination with TGF-β. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1387-1397, 2019.