Osteoprogenitor cells from bone marrow and cortical bone: understanding how the environment affects their fate

Amniotic fluid-derived mesenchymal stem cells as a therapeutic tool against cytokine storm: a comparison with umbilical cord counterparts

BACKGROUND

Several immunosuppressive therapies have been proposed as key treatment options for critically ill patients since the first appearance of severe acute respiratory syndrome coronavirus 2. Mesenchymal stem cells (MSCs) from different sources have been considered for their potential to attenuate the cytokine storm associated to COVID-19 and the consequent multi-organ failure, providing evidence for safe and efficacious treatments. Among them, administration of umbilical cord-derived MSCs (UC-MSCs) has demonstrated a significant increase in survival rates, largely due to their potent immunosuppressive properties.

METHODS

We applied next-generation sequencing (NGS) analysis to compare the transcriptomic profiles of MSCs isolated from two gestational sources: amniotic fluid (AF) obtained during prenatal diagnosis and their clinically relevant umbilical cord counterparts, for which datasets were publicly available. A full meta-analysis was performed to identify suitable GEO and NGS datasets for comparison between AF- and UC-MSC samples.

RESULTS

Transcriptome analysis revelaed significant differences between groups, despite both cell lines being strongly involved in the tissue development, crucial to achieve the complex task of wound healing. Significantly enriched hallmark genes suggest AF-MSC superior immunomodulatory features against signaling pathways actively involved in the cytokine storm (i.e., IL-2/STAT, TNF-a/NFkB, IL-2/STAT5, PI3K/AKT/mTOR).

CONCLUSIONS

The data presented here suggest that AF-MSCs hold significant promise for treating not only COVID-19-associated cytokine storms but also a variety of other inflammatory syndromes (i.e., those induced by bacterial infections, autoimmune disorders, and therapeutic interventions). Realizing the full potential of AF-MSCs as a comprehensive therapeutic approach in inflammatory disease management will require more extensive clinical trials and in-depth mechanistic studies.

Reconstruction of Maxillary Bone Defects With Cellular Bone Matrix Allografts

Study Design

Retrospective Cohort Study.

Objective

Reconstruction of maxillary bone defects can be completed with vascularized and non-vascularized autografts. Cellular bone matrix allografts (CBMs), which have lineage committed bone cells, has risen as an alternative. The purpose of this study was to describe our experience and to determine the success of CBM based maxillary reconstruction in a variety of clinical scenarios.

Methods

A retrospective cohort study was designed and implemented using data from subjects who presented to the University of Louisville and were treated with a CBM for maxillary reconstruction from 2019 to 2023. Subjects were excluded if they were not treated with a CBM, data were not complete, or postoperative follow-up time was less than 3 months. Descriptive statistics were calculated for each variable. To measure the associations between the risk factors and graft success, Fisher's exact test was implemented. A P-value of <0.05 was considered significant.

Results

The sample included 48 subjects. The mean age of all subjects was 43 ± 24 years. Overall, 42 (87.5%) cases were successful. The perioperative antibiotic administered (P = 0.02), etiology (P = 0.021), and the addition of platelet rich fibrin or autograft as an adjunct influenced CBM success (P = 0.039).

Conclusions

CBMs are a viable option for reconstruction of maxillary bone defects. CBMs may be an alternative to autografts.

Comparison between Cancellous Trabecular and Cortical Specimens from Human Lumbar Spine Samples as an Alternative Source of Mesenchymal Stromal Cells

Due to their immunosuppressive potential and ability to differentiate into multiple musculoskeletal cell lineages, mesenchymal stromal cells (MSCs) became popular in clinical trials for the treatment of musculoskeletal disorders. The aim of this study was to isolate and characterize native populations of MSCs from human cortical and cancellous bone from the posterior elements of the lumbar spine and determine what source of MSCs yield better quality and quantity of cells to be potentially use for spinal fusion repair. We were able to show that MSCs from trabecular and cortical spine had the typical MSC morphology and expression markers; the ability to differentiate in adipocyte, chondrocyte, or osteoblast but they did not have a consistent pattern in the expression of the specific differentiation lineage genes. Moreover, MSCs from both sites demonstrated an immune suppression profile suggesting that these cells may have a more promising success in applications related to immunomodulation more than exploring their ability to drive osteogenesis to prevent nonunion in spine fusion procedures.

A novel lineage of osteoprogenitor cells with dual epithelial and mesenchymal properties govern maxillofacial bone homeostasis and regeneration after MSFL

Bone regeneration originates from proliferation and differentiation of osteoprogenitors via either endochondral or intramembranous ossification; and the regeneration capacities decline with age and estrogen loss. Maxillary sinus floor lifting (MSFL) is a commonly used surgical procedure for guiding bone regeneration in maxilla. Radiographic analysis of 1210 clinical cases of maxilla bone regeneration after MSFL revealed that the intrasinus osteogenic efficacy was independent of age and gender, however; and this might be related to the Schneiderian membrane that lines the sinus cavity. In view of the particularity of this biological process, our present study aimed to elucidate the underlying mechanism of MSFL-induced bone regeneration. We first established a murine model to simulate the clinical MSFL. By single-cell RNA-sequencing and flow cytometry-based bulk RNA-sequencing, we identified a novel Krt14⁺Ctsk⁺ subset of cells that display both epithelial and mesenchymal properties and the transcriptomic feature of osteoprogenitors. Dual recombinases-mediated lineage tracing and loss-of-function analyses showed that these Krt14⁺Ctsk⁺ progenitors contribute to both MSFL-induced osteogenesis and physiological bone homeostasis by differentiating into Krt14^-Ctsk⁺ descendants which show robust osteogenic capacity. In addition, we detected a similar population of Krt14⁺Ctsk⁺ cells in human samples of Schneiderian membrane, which show a highly similar osteogenic potential and transcriptomic feature to the corresponding cells in mice. The identification of this Krt14⁺Ctsk⁺ population, featured by osteoprogenitor characteristics and dual epithelial-mesenchymal properties, provides new insight into the understanding of bone regeneration and may open more possibilities for clinical applications.

Commercial Bone Grafts Claimed as an Alternative to Autografts: Current Trends for Clinical Applications in Orthopaedics

In the last twenty years, due to an increasing medical and market demand for orthopaedic implants, several grafting options have been developed. However, when alternative bone augmentation materials mimicking autografts are searched on the market, commercially available products may be grouped into three main categories: cellular bone matrices, growth factor enhanced bone grafts, and peptide enhanced xeno-hybrid bone grafts. Firstly, to obtain data for this review, the search engines Google and Bing were employed to acquire information from reports or website portfolios of important competitors in the global bone graft market. Secondly, bibliographic databases such as Medline/PubMed, Web of Science, and Scopus were also employed to analyse data from preclinical/clinical studies performed to evaluate the safety and efficacy of each product released on the market. Here, we discuss several products in terms of osteogenic/osteoinductive/osteoconductive properties, safety, efficacy, and side effects, as well as regulatory issues and costs. Although both positive and negative results were reported in clinical applications for each class of products, to date, peptide enhanced xeno-hybrid bone grafts may represent the best choice in terms of risk/benefit ratio. Nevertheless, more prospective and controlled studies are needed before approval for routine clinical use.

Combination of optimized tissue engineering bone implantation with heel-strike like mechanical loading to repair segmental bone defect in New Zealand rabbits

In this study, effects of combining optimized tissue engineering bone (TEB) implantation with heel-strike like mechanical loading to repair segmental bone defect in New Zealand rabbits were investigated. Physiological characteristics of bone marrow mesenchymal stem cells (BMMSCs), compact bone cells (CBCs), and bone marrow and compact bone coculture cells (BMMSC-CBCs) were compared to select the optimal seed cells for optimized TEB construction. Rabbits with segmental bone defects were treated in different ways (cancellous bone scaffold for group A, cancellous bone scaffold and mechanical loading for group B, optimized TEB for group C, optimized TEB and mechanical loading for group D, n = 4), and the bone repair were compared. BMMSC-CBCs showed better proliferation capacity than CBCs (p < 0.01) and stronger osteogenic differentiation ability than BMMSCs (p < 0.05). Heel-strike like mechanical loading improved proliferation and osteogenic differentiation ability and expression levels of TGFβ1 as well as BMP2 of seed cells in vitro (p < 0.05). At week 12 post-operation, group D showed the best bone repair, followed by groups B and C, while group A finished last (p < 0.05). During week 4 to 12 post-operation, group D peaked in terms of expression levels of TGFβ1, BMP2, and OCN, followed by groups B and C, while group A finished last (p < 0.05). Thus, BMMSC-CBCs showed good proliferation and osteogenic differentiation ability, and they were thought to be better as seed cells than BMMSCs and CBCs. The optimized TEB implantation combined with heel-strike like mechanical loading had a synergistic effect on bone defect healing, and enhanced expression of TGFβ1 and BMP2 played an important role in this process.

Effect of TNF-α and IL-6 on Compact Bone-Derived Cells

BACKGROUND

Although bone tissue engineering has already been applied clinically, its regeneration efficacy is not always sufficient. Local inflammatory cytokines are considered as the major factors that induce apoptosis of transplanted cells, thus leading to insufficient new bone formation. In this study, we focused on the effects of interleukin (IL)-6 and tumor necrosis factor-alpha (TNF-α) on differentiation and apoptosis of compact bone-derived cells (CBDCs).

METHODS

CBDCs were obtained from mouse legs and cultured. The effects of TNF-α and/or IL-6 on the osteogenic differentiation and apoptosis of CBDCs were analyzed in vitro. To confirm the expression of local inflammatory cytokines in vivo, CBDCs were transplanted to the back of immunocompetent mice.

RESULTS

IL-6 exerted inconsistent effects on the expression of the different osteogenic markers tested, while significantly upregulating Fas. By contrast, the addition of TNF-α dramatically reduced the expression of all tested osteogenic markers and increased Fas expression. The highest dose of IL-6 could partially reverse the repressive effect of TNF-α, while the addition of IL-6 further increased Fas expression in CBDCs compared to TNF-α alone. The results from in vivo experiments showed the presence of transplants with and without new bone formation. The transplants without bone formation were characterized by higher IL-6 and lower IL-10 expression than those with bone formation, while the expression of TNF-α did not show notable difference.

CONCLUSION

The results of this study suggest an important role for IL-6 in modulating the efficacy of bone tissue engineering, which can affect osteogenic cells both positively and negatively.

Mesenchymal Stromal Cell‐Mediated Treatment of Local and Systemic Inflammation through the Triggering of an Anti‐Inflammatory Response

The emergence of cell‐based therapeutics, specifically the use of mesenchymal stromal/stem cells (MSCs), stands to significantly affect the future of targeted drug delivery technologies. MSCs represent a unique cell type, offering more than only regenerative potential but also site‐specific inflammatory targeting and tissue infiltration. In this study, a versatile multicomponent delivery platform, combining MSC tropism with multistage nanovector (MSV)‐mediated payload delivery, is debuted. It is demonstrated that the incorporation of drug‐loaded MSVs bestows MSCs with the ability to transport anti‐inflammatory payloads, achieving a fivefold increase in payload release without negatively impacting cellular functions, viability, extravasation, and inflammatory homing. When incorporated within MSCs, MSVs avoid rapid sequestration by filtering organs and conserve a 15‐fold increase in local inflammatory targeting compared to healthy ears. Furthermore, this MSC‐mediated MSV platform (M&Ms) rapidly triggers a 4.5‐fold reduction of local inflammation compared to free drug and extends survival to 100% of treated mice in a lethal model of systemic inflammation.

Isolation and characterization of mesenchymal stem cells in orthopaedics and the emergence of compact bone mesenchymal stem cells as a promising surgical adjunct

The potential clinical and economic impact of mesenchymal stem cell (MSC) therapy is immense. MSCs act through multiple pathways: (1) as “trophic” cells, secreting various factors that are immunomodulatory, anti-inflammatory, anti-apoptotic, proangiogenic, proliferative, and chemoattractive; (2) in conjunction with cells native to the tissue they reside in to enhance differentiation of surrounding cells to facilitate tissue regrowth. Researchers have developed methods for the extraction and expansion of MSCs from animal and human tissues. While many sources of MSCs exist, including adipose tissue and iliac crest bone graft, compact bone (CB) MSCs have shown great potential for use in orthopaedic surgery. CB MSCs exert powerful immunomodulatory effects in addition to demonstrating excellent regenerative capacity for use in filling boney defects. CB MSCs have been shown to have enhanced response to hypoxic conditions when compared with other forms of MSCs. More work is needed to continue to characterize the potential applications for CB MSCs in orthopaedic trauma.

Improving the immunosuppressive potential of articular chondroprogenitors in a three-dimensional culture setting

Cartilage repair in osteoarthritic patients remains a challenge. Identifying resident or donor stem/progenitor cell populations is crucial for augmenting the low intrinsic repair potential of hyaline cartilage. Furthermore, mediating the interaction between these cells and the local immunogenic environment is thought to be critical for long term repair and regeneration. In this study we propose articular cartilage progenitor/stem cells (CPSC) as a valid alternative to bone marrow-derived mesenchymal stem cells (BMMSC) for cartilage repair strategies after trauma. Similar to BMMSC, CPSC isolated from osteoarthritic patients express stem cell markers and have chondrogenic, osteogenic, and adipogenic differentiation ability. In an in vitro 2D setting, CPSC show higher expression of SPP1 and LEP, markers of osteogenic and adipogenic differentiation, respectively. CPSC also display a higher commitment toward chondrogenesis as demonstrated by a higher expression of ACAN. BMMSC and CPSC were cultured in vitro using a previously established collagen-chondroitin sulfate 3D scaffold. The scaffold mimics the cartilage niche, allowing both cell populations to maintain their stem cell features and improve their immunosuppressive potential, demonstrated by the inhibition of activated PBMC proliferation in a co-culture setting. As a result, this study suggests articular cartilage derived-CPSC can be used as a novel tool for cellular and acellular regenerative medicine approaches for osteoarthritis (OA). In addition, the benefit of utilizing a biomimetic acellular scaffold as an advanced 3D culture system to more accurately mimic the physiological environment is demonstrated.

Nanostructured Biomaterials for Bone Regeneration

This review article addresses the various aspects of nano-biomaterials used in or being pursued for the purpose of promoting bone regeneration. In the last decade, significant growth in the fields of polymer sciences, nanotechnology, and biotechnology has resulted in the development of new nano-biomaterials. These are extensively explored as drug delivery carriers and as implantable devices. At the interface of nanomaterials and biological systems, the organic and synthetic worlds have merged over the past two decades, forming a new scientific field incorporating nano-material design for biological applications. For this field to evolve, there is a need to understand the dynamic forces and molecular components that shape these interactions and influence function, while also considering safety. While there is still much to learn about the bio-physicochemical interactions at the interface, we are at a point where pockets of accumulated knowledge can provide a conceptual framework to guide further exploration and inform future product development. This review is intended as a resource for academics, scientists, and physicians working in the field of orthopedics and bone repair.

Effect of short-term betamethasone administration on the regeneration process of tissue-engineered bone

Local inflammation at the transplanted site of tissue-engineered bone may cause apoptosis of the transplanted cells, thus negatively affecting bone regeneration. To maximize the efficacy of bone tissue engineering, the local effect of short-term corticosteroid administration at the transplanted site of tissue-engineered bone was studied with respect to the expression of inflammatory cytokines. Compact bone-derived cells from mouse leg bones were isolated, cultured and seeded onto β-tricalcium phosphate granules. The constructs were transplanted to the back of syngeneic mice. Betamethasone sodium phosphate was administered intraperitoneally to an experimental (betamethasone) group, whereas the same amount of saline was administered to a control group. When betamethasone was administered three times (immediately after operation and 12 hours and 24 hours after transplantation), the number of SP7/osterix-positive osteoblasts was larger in the betamethasone group. Three times of betamethasone administration (immediately after operation and 12 hours and 24 hours after transplantation) did not change the number of apoptotic cells and osteoclasts, but showed a slight upregulation of IL-4 and a downregulation of IL-6. However, 7 doses of betamethasone administration (over 7 consecutive days) increased the number of apoptotic cells and osteoclasts, which was correlated with a downregulation of IL-4 and an upregulation of IL-6. TNF-α expression levels showed no significant differences between the two groups. The results showed beneficial effects of 3 betamethasone administrations for bone regeneration therapy but contrary effects when betamethasone was administered 7 times due to the downregulation of anti-inflammatory cytokines (IL-4) and the upregulation of inflammatory cytokines (IL-6). As a conclusion, our results suggested the importance of the cautious usage of corticosteroids to control local inflammation at transplanted sites in bone tissue engineering.

Co-culture of the bone and bone marrow: a novel way to obtain mesenchymal stem cells with enhanced osteogenic ability for fracture healing in SD rats

Background

Mesenchymal stem cells (MSCs) have great potential for the repair and regeneration of bone fracture, but their optimal origins remain controversial.

Methods

Bone marrow-MSCs (BM-MSCs) and bone-bone marrow-MSCs (B-BM-MSCs) were isolated from 12 SD rats, and the morphology, MSC-associated markers, and proliferative capacity of these cells were compared using an inverted microscope, flow cytometry, and CCK-8 assays, respectively. After 14 days of osteoblastic induction, osteoblast phenotypes were detected by ALP and calcium nodule staining, and the expression of BMP-2 and TGF-β1 was observed by western blotting. Then, the rat tibia fracture model was established with 3 groups (n = 6 per group), the control, BM-MSC, and B-BM-MSC groups. Computed tomography (CT) imaging was performed to evaluate fracture healing at weeks 2, 4, and 6. Finally, the fractured bones were removed at weeks 4 and 6, and HE staining was performed to evaluate fracture healing.

Results

Although the 2 types of MSCs shared the same cellular morphology and MSC-associated markers, B-BM-MSCs had a higher proliferative rate than BM-MSCs from day 9 to day 12 (p < 0.05), and the expression levels of ALP and calcium were obviously higher in B-BM-MSCs than in BM-MSCs after osteogenic induction (p < 0.01 and p < 0.001, respectively). Western blot results showed that the expression levels of BMP-2 and TGF-β1 in B-BM-MSCs were higher than in BM-MSCs before and after osteogenic induction (p < 0.01). In the animal experiments, CT imaging and gross observation showed that B-BM-MSCs had a greater capacity than BM-MSCs to promote fracture healing, as the Lane-Sandhu scores of B-BM-MSCs at weeks 4 and 6 after operation (3.00 ± 0.81 and 9.67 ± 0.94, respectively) were higher than those of BM-MSCs (1.33 ± 0.47 and 6.67 ± 1.25, respectively; both p < 0.05). The HE staining results further supported this conclusion.

Conclusions

Taken together, our study results proved that MSCs obtained by co-culturing the bone and bone marrow from SD rats had better proliferative, osteogenic differentiation, and fracture healing capacities than BM-MSCs, perhaps suggesting a novel way to obtain MSCs for bone tissue repair.

Bone Repair and Regenerative Biomaterials: Towards Recapitulating the Microenvironment

Biomaterials and tissue engineering scaffolds play a central role to repair bone defects. Although ceramic derivatives have been historically used to repair bone, hybrid materials have emerged as viable alternatives. The rationale for hybrid bone biomaterials is to recapitulate the native bone composition to which these materials are intended to replace. In addition to the mechanical and dimensional stability, bone repair scaffolds are needed to provide suitable microenvironments for cells. Therefore, scaffolds serve more than a mere structural template suggesting a need for better and interactive biomaterials. In this review article, we aim to provide a summary of the current materials used in bone tissue engineering. Due to the ever-increasing scientific publications on this topic, this review cannot be exhaustive; however, we attempted to provide readers with the latest advance without being redundant. Furthermore, every attempt is made to ensure that seminal works and significant research findings are included, with minimal bias. After a concise review of crystalline calcium phosphates and non-crystalline bioactive glasses, the remaining sections of the manuscript are focused on organic-inorganic hybrid materials.

Spontaneously Formed Spheroids from Mouse Compact Bone-Derived Cells Retain Highly Potent Stem Cells with Enhanced Differentiation Capability

The results from our recent study showed the presence of two distinct spheroid-forming mechanisms, i.e., spontaneous and mechanical. In this study, we focused on the spontaneously formed spheroids, and the character of spontaneously formed spheroids from mouse compact bone-derived cells (CBDCs) was explored. Cells from (C57BL/6J) mouse leg bones were isolated, and compact bone-derived cells were cultured after enzymatic digestion. Spontaneous spheroid formation was achieved on a culture plate with specific water contact angle as reported. The expression levels of embryonic stem cell markers were analyzed using immunofluorescence and quantitative reverse transcription polymerase chain reaction. Then, the cells from spheroids were induced into osteogenic and neurogenic lineages. The spontaneously formed spheroids from CBDCs were positive for ES cell markers such as SSEA1, Sox2, Oct4, and Nanog. Additionally, the expressions of fucosyltransferase 4/FUT4 (SSEA1), Sox2, and Nanog were significantly higher than those in monolayer cultured cells. The gene expression of mesenchymal stem cell markers was almost identical in both spheroids and monolayer-cultured cells, but the expression of Sca-1 was higher in spheroids. Spheroid-derived cells showed significantly higher osteogenic and neurogenic marker expression than monolayer-cultured cells after induction. Spontaneously formed spheroids expressed stem cell markers and showed enhanced osteogenic and neurogenic differentiation capabilities than cells from the conventional monolayer culture, which supports the superior stemness.

Biomimetic Tissue Engineering: Tuning the Immune and Inflammatory Response to Implantable Biomaterials

Regenerative medicine technologies rely heavily on the use of well-designed biomaterials for therapeutic applications. The success of implantable biomaterials hinges upon the ability of the chosen biomaterial to negotiate with the biological barriers in vivo. The most significant of these barriers is the immune system, which is composed of a highly coordinated organization of cells that induce an inflammatory response to the implanted biomaterial. Biomimetic platforms have emerged as novel strategies that aim to use the principle of biomimicry as a means of immunomodulation. This principle has manifested itself in the form of biomimetic scaffolds that imitate the composition and structure of biological cells and tissues. Recent work in this area has demonstrated the promising potential these technologies hold in overcoming the barrier of the immune system and, thereby, improve their overall therapeutic efficacy. In this review, a broad overview of the use of these strategies across several diseases and future avenues of research utilizing these platforms is provided.

IL-17A improves the efficacy of mesenchymal stem cells in ischemic-reperfusion renal injury by increasing Treg percentages by the COX-2/PGE2 pathway

Mesenchymal stem cells (MSCs) are effective for the management of experimental ischemia-reperfusion acute kidney injury (IRI-AKI). Immune modulation is one of the important mechanisms of MSCs treatment. Interleukin-17A (IL-17A) pretreated MSCs are more immunosuppressive with minimal changes in immunogenicity in vitro. Here, we demonstrated that administration of IL-17A-pretreated MSCs resulted in significantly lower acute tubular necrosis scores, serum creatinine, and BUN of mice with IRI-AKI, compared with the administration of MSCs. Of the co-cultured splenocytes, IL-17A-pretreated MSCs significantly increased the percentages of CD4⁺Foxp3⁺ Tregs and decreased concanavalin A-induced T cell proliferation. Furthermore, mice with IRI-AKI that underwent IL-17A-pretreated MSC therapy had significantly lower serum IL-6, TNF-α, and IFN-γ levels, a higher serum IL-10 level, and higher spleen and kidney Treg percentages than the mice that underwent MSCs treatment. Additionally, the depletion of Tregs by PC61 (anti-CD25 antibody) reversed the enhanced treatment efficacy of the IL-17A-pretreatedMSCs on mice with IRI-AKI. Additionally, IL-17A upregulated COX-2 expression and increased PGE2 production. The blockage of COX-2 by celecoxib reversed the benefit of IL-pretreated 17A-MSCs on the serum PGE2 concentration, spleen and kidney Tregs percentages, serum creatinine and BUN levels, renal acute tubular necrosis scores, and serum IL-6, TNF-α, IFN-γ, and IL-10 levels of IRI-pretreated mice with AKI, compared with MSCs. Thus, our results suggest that IL-17A pretreatment enhances the efficacy of MSCs on mice with IRI-AKI by increasing the Treg percentages through the COX-2/PGE2 pathway.

Concise Review: Biomimetic Functionalization of Biomaterials to Stimulate the Endogenous Healing Process of Cartilage and Bone Tissue

Musculoskeletal reconstruction is an ongoing challenge for surgeons as it is required for one out of five patients undergoing surgery. In the past three decades, through the close collaboration between clinicians and basic scientists, several regenerative strategies have been proposed. These have emerged from interdisciplinary approaches that bridge tissue engineering with material science, physiology, and cell biology. The paradigm behind tissue engineering is to achieve regeneration and functional recovery using stem cells, bioactive molecules, or supporting materials. Although plenty of preclinical solutions for bone and cartilage have been presented, only a few platforms have been able to move from the bench to the bedside. In this review, we highlight the limitations of musculoskeletal regeneration and summarize the most relevant acellular tissue engineering approaches. We focus on the strategies that could be most effectively translate in clinical practice and reflect on contemporary and cutting‐edge regenerative strategies in surgery. Stem Cells Translational Medicine2017;6:2186–2196

Comparative analyses of industrial-scale human platelet lysate preparations

BACKGROUND

Efforts are underway to eliminate fetal bovine serum from mammalian cell cultures for clinical use. An emerging, viable replacement option for fetal bovine serum is human platelet lysate (PL) as either a plasma-based or serum-based product.

STUDY DESIGN AND METHODS

Nine industrial-scale, serum-based PL manufacturing runs (i.e., lots) were performed, consisting of an average ± standard deviation volume of 24.6 ± 2.2 liters of pooled, platelet-rich plasma units that were obtained from apheresis donors. Manufactured lots were compared by evaluating various biochemical and functional test results. Comprehensive cytokine profiles of PL lots and product stability tests were performed. Global gene expression profiles of mesenchymal stromal cells (MSCs) cultured with plasma-based or serum-based PL were compared to MSCs cultured with fetal bovine serum.

RESULTS

Electrolyte and protein levels were relatively consistent among all serum-based PL lots, with only slight variations in glucose and calcium levels. All nine lots were as good as or better than fetal bovine serum in expanding MSCs. Serum-based PL stored at -80°C remained stable over 2 years. Quantitative cytokine arrays showed similarities as well as dissimilarities in the proteins present in serum-based PL. Greater differences in MSC gene expression profiles were attributable to the starting cell source rather than with the use of either PL or fetal bovine serum as a culture supplement.

CONCLUSION

Using a large-scale, standardized method, lot-to-lot variations were noted for industrial-scale preparations of serum-based PL products. However, all lots performed as well as or better than fetal bovine serum in supporting MSC growth. Together, these data indicate that off-the-shelf PL is a feasible substitute for fetal bovine serum in MSC cultures.

Heparan Sulfate: A Potential Candidate for the Development of Biomimetic Immunomodulatory Membranes

Clinical trials have demonstrated that heparan sulfate (HS) could be used as a therapeutic agent for the treatment of inflammatory diseases. Its anti-inflammatory effect makes it suitable for the development of biomimetic innovative strategies aiming at modulating stem cells behavior toward a pro-regenerative phenotype in case of injury or inflammation. Here, we propose collagen type I meshes fabricated by solvent casting and further crosslinked with HS (HS-Col) to create a biomimetic environment resembling the extracellular matrix of soft tissue. HS-Col meshes were tested for their capability to provide physical support to stem cells’ growth, maintain their phenotypes and immunosuppressive potential following inflammation. HS-Col effect on stem cells was investigated in standard conditions as well as in an inflammatory environment recapitulated in vitro through a mix of pro-inflammatory cytokines (tumor necrosis factor-α and interferon-gamma; 20 ng/ml). A significant increase in the production of molecules associated with immunosuppression was demonstrated in response to the material and when cells were grown in presence of pro-inflammatory stimuli, compared to bare collagen membranes (Col), leading to a greater inhibitory potential when mesenchymal stem cells were exposed to stimulated peripheral blood mononuclear cells. Our data suggest that the presence of HS is able to activate the molecular machinery responsible for the release of anti-inflammatory cytokines, potentially leading to a faster resolution of inflammation.

Hyaluronic acid coatings as a simple and efficient approach to improve MSC homing toward the site of inflammation

A major challenge in regenerative medicine is to improve therapeutic cells' delivery and targeting using an efficient and simple protocol. Mesenchymal stem cells (MSC) are currently employed for the treatment of inflammatory-based diseases, due to their powerful immunosoppressive potential. Here we report a simple and versatile method to transiently overexpress the hyaluronic acid (HA) receptor, CD44, on MSC membranes, to improve their homing potential towards an inflammatory site without affecting their behavior. The effect of HA-coatings on murine MSC was functionally determined both, in vitro and in vivo as a consequence of the transient CD44 overexpression induced by HA. Data obtained from the in vitro migration assay demonstrated a two-fold increase in the migratory potential of HA-treated MSC compared to untreated cells. In an LPS-induced inflamed ear murine model, HA-treated MSC demonstrated a significantly higher inflammatory targeting as observed at 72 hrs as compared to untreated cells. This increased accumulation for HA-treated MSC yielded a substantial reduction in inflammation as demonstrated by the decrease in the expression of pro-inflammatory markers and by the induction of a pro-regenerative environment.

Enhancing Vascularization through the Controlled Release of Platelet-Derived Growth Factor-BB

Using delivery systems to control the in vivo release of growth factors (GFs) for tissue engineering applications is extremely desirable as the clinical use of GFs is limited by their fast in vivo turnover. Hence, the development of effective platforms that are able to finely control the release of GFs in vivo remains a challenge. Herein, we investigated the ability of multiscale microspheres, composed by a nanostructured silicon multistage vector (MSV) core and a poly(dl-lactide-co-glycolide) acid (PLGA) forming outer shell (PLGA-MSV), to release functional platelet-derived growth factor-BB (PDGF-BB) to induce in vivo localized neovascularization. The in vitro release of PDGF-BB was assessed by enzyme-linked immunosorbent assay (ELISA) over 2 weeks and showed a sustained, zero-order release kinetics. The ability to promote in vivo localized neovascularization was investigated in a subcutaneous injection model in BALB/c mice and followed by intravital microscopy up to 2 weeks. Fully functional newly formed vessels were found within the area where PLGA-MSVs were localized and covered 3.0 ± 0.9 and 19 ± 5.1% at 7 and 14 days, respectively, showing a 6-fold increase in 1 week. The distribution of CD31⁺ and α-SMA⁺ cells was detected by immunofluorescence on harvested tissues. CD31 was significantly more expressed (4-fold increase) compared to the untreated control. Finally, the level of up-regulation of angiogenesis-associated genes (Vegfa, Vwf, and Col3a1) was assessed by q-PCR, resulting in a significantly higher expression where PLGA-MSVs were localized (Vegfa: 2.32 ± 0.50 at 7 days and 4.37 ± 0.75 at 14 days; Vwf: 4.13 ± 0.82 and 7.74 ± 0.91; Col3a1: 5.43 ± 0.37 and 6.66 ± 0.89). Altogether, our data supported the conclusion that the localized delivery of PDGF-BB from PLGA-MSVs induced the localized de novo formation of fully functional vessels in vivo. With this study, we demonstrated that PLGA-MSV holds promise for accomplishing the controlled localized in vivo release of GFs for the design of innovative tissue engineering strategies.

Evaluation of zinc-doped mesoporous hydroxyapatite microspheres for the construction of a novel biomimetic scaffold optimized for bone augmentation

Biomaterials with high osteogenic activity are desirable for sufficient healing of bone defects resulting from trauma, tumor, infection, and congenital abnormalities. Synthetic materials mimicking the structure and composition of human trabecular bone are of considerable potential in bone augmentation. In the present study, a zinc (Zn)-doped mesoporous hydroxyapatite microspheres (Zn-MHMs)/collagen scaffold (Zn-MHMs/Coll) was developed through a lyophilization fabrication process and designed to mimic the trabecular bone. The Zn-MHMs were synthesized through a microwave-hydrothermal method by using creatine phosphate as an organic phosphorus source. Zn-MHMs that consist of hydroxyapatite nanosheets showed relatively uniform spherical morphology, mesoporous hollow structure, high specific surface area, and homogeneous Zn distribution. They were additionally investigated as a drug nanocarrier, which was efficient in drug delivery and presented a pH-responsive drug release behavior. Furthermore, they were incorporated into the collagen matrix to construct a biomimetic scaffold optimized for bone tissue regeneration. The Zn-MHMs/Coll scaffolds showed an interconnected pore structure in the range of 100-300 μm and a sustained release of Zn ions. More importantly, the Zn-MHMs/Coll scaffolds could enhance the osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells. Finally, the bone defect repair results of critical-sized femoral condyle defect rat model demonstrated that the Zn-MHMs/Coll scaffolds could enhance bone regeneration compared with the Coll or MHMs/Coll scaffolds. The results suggest that the biomimetic Zn-MHMs/Coll scaffolds may be of enormous potential in bone repair and regeneration.

A nanofibrous electrospun patch to maintain human mesenchymal cell stemness

Mesenchymal stem cells (MSCs) have been extensively investigated in regenerative medicine because of their crucial role in tissue healing. For these properties, they are widely tested in clinical trials, usually injected in cell suspension or in combination with tridimensional scaffolds. However, scaffolds can largely affect the fates of MSCs, inducing a progressive loss of functionality overtime. The ideal scaffold must delay MSCs differentiation until paracrine signals from the host induce their change. Herein, we proposed a nanostructured electrospun gelatin patch as an appropriate environment where human MSCs (hMSCs) can adhere, proliferate, and maintain their stemness. This patch exhibited characteristics of a non-linear elastic material and withstood degradation up to 4 weeks. As compared to culture and expansion in 2D, hMSCs on the patch showed a similar degree of proliferation and better maintained their progenitor properties, as assessed by their superior differentiation capacity towards typical mesenchymal lineages (i.e. osteogenic and chondrogenic). Furthermore, immunohistochemical analysis and longitudinal non-invasive imaging of inflammatory response revealed no sign of foreign body reaction for 3 weeks. In summary, our results demonstrated that our biocompatible patch favored the maintenance of undifferentiated hMSCs for up to 21 days and is an ideal candidate for tridimensional delivery of hMSCs. The present work reports a nanostructured patch gelatin-based able to maintain in vitro hMSCs stemness features. Moreover, hMSCs were able to differentiate toward osteo- and chondrogenic lineages once induces by differentiative media, confirming the ability of this patch to support stem cells for a potential in vivo application. These attractive properties together with the low inflammatory response in vivo make this patch a promising platform in regenerative medicine.

Copper-doped mesoporous hydroxyapatite microspheres synthesized by a microwave-hydrothermal method using creatine phosphate as an organic phosphorus source: application in drug delivery and enhanced bone regeneration

The development of multifunctional biomaterials with drug delivery ability, and pro-osteogenic and pro-angiogenic activities has garnered increasing interest in the field of regenerative medicine. In the present study, hypoxia-mimicking copper (Cu)-doped mesoporous hydroxyapatite (HAP) microspheres (Cu-MHMs) were successfully synthesized through a microwave-hydrothermal method by using creatine phosphate as an organic phosphorus source. The Cu-MHMs doped with 0.2, 0.5 and 1 mol% Cu were prepared. The Cu-MHMs consisting of HAP nanorods or nanosheets exhibited a hierarchically mesoporous hollow structure and a high specific surface area. Then the Cu-MHMs were investigated as a drug nanocarrier using doxorubicin hydrochloride (DOX) as a model drug. The Cu-MHMs showed a relatively high drug-loading capacity and a pH-responsive drug release behavior. Furthermore, the Cu-MHMs were incorporated into a chitosan (CS) matrix to construct a biomimetic scaffold optimized for bone regeneration. The Cu-MHM/CS composite scaffolds maintained high degrees of porosity and showed a sustained release of Cu ions. More importantly, the Cu-MHM/CS scaffolds not only enhanced the osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (rBMSCs) but also promoted the migration and tube formation of EA.hy926 cells. When implanted in rat critical-sized calvarial defects, the Cu-MHM/CS scaffolds significantly enhanced bone regeneration accompanied by more new blood vessel formation at 8 weeks post-operation compared with the MHM/CS scaffolds. These results suggest that the hypoxia-mimicking Cu-MHM/CS scaffolds could encourage bone regeneration by enhancing osteogenesis and angiogenesis simultaneously, which bodes well for the reconstruction of vascularized tissue-engineered bone.

Mesenchymal stem cells from cortical bone demonstrate increased clonal incidence, potency, and developmental capacity compared to their bone marrow-derived counterparts

In this study, we show that matrix dense cortical bone is the more potent compartment of bone than bone marrow as a stromal source for mesenchymal stem cells as isolated from adult rats. Lineage-depleted cortical bone-mesenchymal stem cells demonstrated >150-fold enrichment of colony forming unit-fibroblasts per cell incidence. compared to lineage-depleted bone marrow-mesenchymal stem cells, corresponding to a 70-fold increase in absolute recovered colony forming unit-fibroblasts. The composite phenotype Lin(-)/CD45(-)/CD31(-)/VLA-1(+)/Thy-1(+) enriched for clonogenic mesenchymal stem cells solely from cortical bone-derived cells from which 70% of clones spontaneously differentiated into all lineages of bone, cartilage, and adipose. Both populations generated vascularized bone tissue within subcutaneous implanted collagen scaffolds; however, cortical bone-derived cells formed significantly more osteoid than bone marrow counterparts, quantified by histology. The data demonstrate that our isolation protocol identifies and validates mesenchymal stem cells with superior clonal, proliferative, and developmental potential from cortical bone compared to the bone marrow niche although marrow persists as the typical source for mesenchymal stem cells both in the literature and current pre-clinical therapies.

Nanotechnology for mesenchymal stem cell therapies

Mesenchymal stem cells (MSC) display great proliferative, differentiative, chemotactic, and immune-modulatory properties required to promote tissue repair. Several clinical trials based on the use of MSC are currently underway for therapeutic purposes. The aim of this article is to examine the current trends and potential impact of nanotechnology in MSC-driven regenerative medicine. Nanoparticle-based approaches are used as powerful carrier systems for the targeted delivery of bioactive molecules to ensure MSC long-term maintenance in vitro and to enhance their regenerative potential. Nanostructured materials have been developed to recapitulate the stem cell niche within a tissue and to instruct MSC toward the creation of regeneration-permissive environment. Finally, the capability of MSC to migrate toward the site of injury/inflammation has allowed for the development of diagnostic imaging systems able to monitor transplanted stem cell bio-distribution, toxicity, and therapeutic effectiveness.

Enhanced osteogenic potential of mesenchymal stem cells from cortical bone: a comparative analysis

Introduction

Mesenchymal stem cells (MSCs) hold great promise for regenerative therapies in the musculoskeletal system. Although MSCs from bone marrow (BM-MSCs) and adipose tissue (AD-MSCs) have been extensively characterized, there is still debate as to the ideal source of MSCs for tissue-engineering applications in bone repair.

Methods

MSCs were isolated from cortical bone fragments (CBF-MSCs) obtained from patients undergoing laminectomy, selected by fluorescence-activated cell sorting analysis, and tested for their potential to undergo mesodermic differentiation. CBF-MSCs were then compared with BM-MSCs and AD-MSCs for their colony-forming unit capability and osteogenic potential in both normoxia and hypoxia. After 2 and 4 weeks in inducing media, differentiation was assessed qualitatively and quantitatively by the evaluation of alkaline phosphatase (ALP) expression and mineral deposition (Von Kossa staining). Transcriptional activity of osteoblastogenesis-associated genes (Alp, RUNX2, Spp1, and Bglap) was also analyzed.

Results

The cortical fraction of the bone contains a subset of cells positive for MSC-associated markers and capable of tri-lineage differentiation. The hypoxic conditions were generally more effective in inducing osteogenesis for the three cell lines. However, at 2 and 4 weeks, greater calcium deposition and ALP expression were observed in both hypoxic and normoxic conditions in CBF-MSCs compared with AD- and BM-MSCs. These functional observations were further corroborated by gene expression analysis, which showed a significant upregulation of Bglap, Alp, and Spp1, with a 22.50 (±4.55)-, 46.56 (±7.4)-, 71.46 (±4.16)-fold increase compared with their uninduced counterparts.

Conclusions

This novel population of MSCs retains a greater biosynthetic activity in vitro, which was found increased in hypoxic conditions. The present study demonstrates that quantitative differences between MSCs retrieved from bone marrow, adipose, and the cortical portion of the bone with respect to their osteogenic potential exist and suggests the cortical bone as suitable candidate to use for orthopedic tissue engineering and regenerative medicine.

Evaluation of the osteoinductive potential of a bio-inspired scaffold mimicking the osteogenic niche for bone augmentation

Augmentation of regenerative osteogenesis represents a premier clinical need, as hundreds of thousands of patients are left with insufficient healing of bony defects related to a host of insults ranging from congenital abnormalities to traumatic injury to surgically-induced deficits. A synthetic material that closely mimics the composition and structure of the human osteogenic niche represents great potential to successfully address this high demand. In this study, a magnesium-doped hydroxyapatite/type I collagen scaffold was fabricated through a biologically-inspired mineralization process and designed to mimic human trabecular bone. The composition of the scaffold was fully characterized by XRD, FTIR, ICP and TGA, and compared to human bone. Also, the scaffold microstructure was evaluated by SEM, while its nano-structure and nano-mechanical properties were evaluated by AFM. Human bone marrow-derived mesenchymal stem cells were used to test the in vitro capability of the scaffold to promote osteogenic differentiation. The cell/scaffold constructs were cultured up to 7 days and the adhesion, organization and proliferation of the cells were evaluated. The ability of the scaffold to induce osteogenic differentiation of the cells was assessed over 3 weeks and the correlate gene expression for classic genes of osteogenesis was assessed. Finally, when tested in an ectopic model in rabbit, the scaffold produced a large volume of trabecular bone in only two weeks, that subsequently underwent maturation over time as expected, with increased mature cortical bone formation, supporting its ability to promote bone regeneration in clinically-relevant scenarios. Altogether, these results confirm a high level of structural mimicry by the scaffold to the composition and structure of human osteogenic niche that translated to faster and more efficient osteoinduction in vivo--features that suggest such a biomaterial may have great utility in future clinical applications where bone regeneration is required.