Mesenchymal progenitor cells derived from traumatized human muscle

Novel insights from human induced pluripotent stem cells on origins and roles of fibro/adipogenic progenitors as heterotopic ossification precursors

Fibro/adipogenic progenitors (FAPs) that reside in muscle tissue are crucial for muscular homeostasis and regeneration as they secrete signaling molecules and components of the extracellular matrix. During injury or disease, FAPs differentiate into different cell types and significantly modulate muscular function. Recent advances in lineage tracing and single-cell transcriptomics have proven that FAPs are heterogeneous both in resting and post-injury or disease states. Their heterogeneity may be owing to the varied tissue microenvironments and their diverse developmental origins. Therefore, understanding FAPs' developmental origins can help predict their characteristics and behaviors under different conditions. FAPs are thought to be the major cell populations in the muscle connective tissue (MCT). During embryogenesis, the MCT directs muscular development throughout the body and serves as a prepattern for muscular morphogenesis. The developmental origins of FAPs as stromal cells in the MCT were studied previously. In adult tissues, FAPs are important precursors for heterotopic ossification, especially in the context of the rare genetic disorder fibrodysplasia ossificans progressiva. A new developmental origin for FAPs have been suggested that differs from conventional developmental perspectives. In this review, we summarize the developmental origins and functions of FAPs as stromal cells of the MCT and present novel insights obtained by using patient-derived induced pluripotent stem cells and mouse models of heterotopic ossification. This review broadens the current understanding of FAPs and suggests potential avenues for further investigation.

Engineered biochemical cues of regenerative biomaterials to enhance endogenous stem/progenitor cells (ESPCs)-mediated articular cartilage repair

As a highly specialized shock-absorbing connective tissue, articular cartilage (AC) has very limited self-repair capacity after traumatic injuries, posing a heavy socioeconomic burden. Common clinical therapies for small- to medium-size focal AC defects are well-developed endogenous repair and cell-based strategies, including microfracture, mosaicplasty, autologous chondrocyte implantation (ACI), and matrix-induced ACI (MACI). However, these treatments frequently result in mechanically inferior fibrocartilage, low cost-effectiveness, donor site morbidity, and short-term durability. It prompts an urgent need for innovative approaches to pattern a pro-regenerative microenvironment and yield hyaline-like cartilage with similar biomechanical and biochemical properties as healthy native AC. Acellular regenerative biomaterials can create a favorable local environment for AC repair without causing relevant regulatory and scientific concerns from cell-based treatments. A deeper understanding of the mechanism of endogenous cartilage healing is furthering the (bio)design and application of these scaffolds. Currently, the utilization of regenerative biomaterials to magnify the repairing effect of joint-resident endogenous stem/progenitor cells (ESPCs) presents an evolving improvement for cartilage repair. This review starts by briefly summarizing the current understanding of endogenous AC repair and the vital roles of ESPCs and chemoattractants for cartilage regeneration. Then several intrinsic hurdles for regenerative biomaterials-based AC repair are discussed. The recent advances in novel (bio)design and application regarding regenerative biomaterials with favorable biochemical cues to provide an instructive extracellular microenvironment and to guide the ESPCs (e.g. adhesion, migration, proliferation, differentiation, matrix production, and remodeling) for cartilage repair are summarized. Finally, this review outlines the future directions of engineering the next-generation regenerative biomaterials toward ultimate clinical translation.

Investigation of UV-treated mesenchymal stem cells in an in vitro wound model

This study examines the effects of ultraviolet-induced adipose tissue-derived mesenchymal stem cells and their supernatants on wound healing regarding cell viability, percentage of wound healing, released cytokine, and growth factors. It has been reported in previous studies that mesenchymal stem cells are resistant to ultraviolet light and have a protective effect on skin cells against ultraviolet-induced damage. At the same time, there are many studies in the literature about the positive effects of cytokines and growth factors secreted by mesenchymal stem cells. Based on this information, the effects of ultraviolet-induced adipose-derived stem cells and supernatants containing their secreted cytokines and growth factors on an in vitro two-dimensional wound model created with two different cell lines were investigated in this study. It was determined from the results that the highest cell viability and the least apoptotic staining were 100 mJ in mesenchymal stem cells (**p < 0.01). Furthermore, analysis of cytokines and growth factors collected from supernatants also supported 100 mJ as the optimal ultraviolet dose. It was observed that cells treated with ultraviolet and their supernatants significantly increased cell viability and wound-healing rate over time compared to other groups. In conclusion, with this study, it has been shown that adipose-derived stem cells exposed to ultraviolet light can have an important use in wound healing, both with their potential and with the more cytokines and growth factors they secrete. However, further analysis and animal experiments should be performed before clinical use.

Research trends of mesenchymal stem cells application in orthopedics: A bibliometric analysis of the past 2 decades

Background

Bibliometric analysis and visualization tools were used to determine the development trend of mesenchymal stem cells (MSCs) in orthopedics in the past 20 years, so as to guide researchers to explore new directions and hotspots in the field in the future.

Methods

In the Web of Science Core Collection, all articles about the application of MSCs in orthopedics from 2002 to 2021 were searched. The qualitative and quantitative analysis was performed based on Web of Science and CiteSpace software.

Results

A total of 2,207 articles were retrieved. After excluding non-article articles such as review and letter and non-English language articles, 1,489 articles were finally included. Over the past 2 decades, the number of publications on the application of MSCs in orthopedic diseases increased. Among them, the United States, China, Japan and the United Kingdom have made significant contributions in this field. The most productive institution was Shanghai Jiao Tong University. Journal of Orthopedic Research published the largest number of publications. The journal with the highest citation frequency was Experimental Hematology. The authors with the highest output and the highest citation frequency on average were Rochy S. Tuan and Scott A. Rodeo, respectively. "Mesenchymal stem cell", "in vitro" and "Differentiation" were the top three keywords that appeared. From the keyword analysis, the current research trend indicates that the primary research hotspots of MSCs in orthopedics are the source of MSCs, in vitro experiments and the differentiation of MSCs into bone and cartilage. The frontiers of this field are the combination of MSCs and platelet-rich plasma (PRP), the treatment of knee diseases such as osteoarthritis, osteogenic differentiation, and the application of biological scaffolds combined with MSCs.

Conclusion

Over the past 2 decades, the application of MSCs in orthopedic diseases has received increasing attention. Our bibliometric analysis results provide valuable information and research trends for researchers in the field to understand the basic knowledge of the field, identify current research hotspots, potential collaborators, and future research frontiers.

A new perfusion mode of culture for WJ-MSCs expansion in a stirred and online monitored bioreactor

As a clinical dose requires a minimum of 10⁶ cells per kilogram of patients, it is, therefore, crucial to develop a scalable method of production of Wharton Jelly mesenchymal stem cells (WJ-MSCs) with maintained inner characteristics. Scalable expansion of WJ-MSCs on microcarriers usually found in cell culture, involves specific cell detachment using trypsin and could have harmful effects on cells. In this study, the performance of batch, fed-batch, and perfused-continuous mode of culture were compared. The batch and fed-batch modes resulted in expansion factors of 5 and 43, respectively. The perfused-continuous mode strategy consisted of the implementation of a settling tube inside the bioreactor. The diameter of the tube was calculated to maintain microcarriers colonized by cells in the bioreactor whereas empty microcarriers (responsible for potentially damaging collisions) were removed, using a continuous flow rate based on MSCs physiological requirements. Thanks to this strategy, a maximal number of 800 million cells was obtained in a 1.5 L bioreactor in 10 days. Lastly, online dielectric spectroscopy was implemented in the bioreactor and indicated that cell growth could be monitored during the culture.

Three-Dimensional Modeling of the Structural Microenvironment in Post-Traumatic War Wounds

BACKGROUND:

The development of post-traumatic heterotopic ossification (HO) is a common, undesirable sequela in patients with high-energy (war-related) extremity injuries. While inflammatory and osteoinductive signaling pathways are known to be involved in the development and progression of post-traumatic HO, features of the structural microenvironment within which the ectopic bone begins to form remain poorly understood. Thus, increasing our knowledge of molecular and structural changes within the healing wound may help elucidate the pathogenesis of post-traumatic HO and aid in the development of specific treatment and/or prevention strategies.

METHODS:

In this study, we performed high-resolution microscopy and biochemical analysis of tissues obtained from traumatic war wounds to characterize changes in the structural microenvironment. In addition, using an electrospinning approach, we modeled this microenvironment to reconstitute a three-dimensional type I collagen scaffold with non-woven, randomly oriented nanofibers where we evaluated the performance of primary mesenchymal progenitor cells.

RESULTS:

We found that traumatic war wounds are characterized by a disorganized, densely fibrotic collagen I matrix that influences progenitor cells adhesion, proliferation and osteogenic differentiation potential.

CONCLUSION:

Altogether, these results suggest that the structural microenvironment present in traumatic war wounds has the potential to contribute to the development of post-traumatic HO. Our findings may support novel treatment strategies directed towards modifying the structural microenvironment after traumatic injury.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13770-021-00355-y.

C-terminal domain small phosphatase 1 (CTDSP1) regulates growth factor expression and axonal regeneration in peripheral nerve tissue

Peripheral Nerve Injury (PNI) represents a major clinical and economic burden. Despite the ability of peripheral neurons to regenerate their axons after an injury, patients are often left with motor and/or sensory disability and may develop chronic pain. Successful regeneration and target organ reinnervation require comprehensive transcriptional changes in both injured neurons and support cells located at the site of injury. The expression of most of the genes required for axon growth and guidance and for synapsis formation is repressed by a single master transcriptional regulator, the Repressor Element 1 Silencing Transcription factor (REST). Sustained increase of REST levels after injury inhibits axon regeneration and leads to chronic pain. As targeting of transcription factors is challenging, we tested whether modulation of REST activity could be achieved through knockdown of carboxy-terminal domain small phosphatase 1 (CTDSP1), the enzyme that stabilizes REST by preventing its targeting to the proteasome. To test whether knockdown of CTDSP1 promotes neurotrophic factor expression in both support cells located at the site of injury and in peripheral neurons, we transfected mesenchymal progenitor cells (MPCs), a type of support cells that are present at high concentrations at the site of injury, and dorsal root ganglion (DRG) neurons with REST or CTDSP1 specific siRNA. We quantified neurotrophic factor expression by RT-qPCR and Western blot, and brain-derived neurotrophic factor (BDNF) release in the cell culture medium by ELISA, and we measured neurite outgrowth of DRG neurons in culture. Our results show that CTDSP1 knockdown promotes neurotrophic factor expression in both DRG neurons and the support cells MPCs, and promotes DRG neuron regeneration. Therapeutics targeting CTDSP1 activity may, therefore, represent a novel epigenetic strategy to promote peripheral nerve regeneration after PNI by promoting the regenerative program repressed by injury-induced increased levels of REST in both neurons and support cells.

Origins, potency, and heterogeneity of skeletal muscle fibro-adipogenic progenitors-time for new definitions

Striated muscle is a highly plastic and regenerative organ that regulates body movement, temperature, and metabolism-all the functions needed for an individual's health and well-being. The muscle connective tissue's main components are the extracellular matrix and its resident stromal cells, which continuously reshape it in embryonic development, homeostasis, and regeneration. Fibro-adipogenic progenitors are enigmatic and transformative muscle-resident interstitial cells with mesenchymal stem/stromal cell properties. They act as cellular sentinels and physiological hubs for adult muscle homeostasis and regeneration by shaping the microenvironment by secreting a complex cocktail of extracellular matrix components, diffusible cytokines, ligands, and immune-modulatory factors. Fibro-adipogenic progenitors are the lineage precursors of specialized cells, including activated fibroblasts, adipocytes, and osteogenic cells after injury. Here, we discuss current research gaps, potential druggable developments, and outstanding questions about fibro-adipogenic progenitor origins, potency, and heterogeneity. Finally, we took advantage of recent advances in single-cell technologies combined with lineage tracing to unify the diversity of stromal fibro-adipogenic progenitors. Thus, this compelling review provides new cellular and molecular insights in comprehending the origins, definitions, markers, fate, and plasticity of murine and human fibro-adipogenic progenitors in muscle development, homeostasis, regeneration, and repair.

A microRNA Signature for Impaired Wound-Healing and Ectopic Bone Formation in Humans

BACKGROUND

Heterotopic ossification (HO) is characterized by the abnormal growth of ectopic bone in soft tissues, frequently occurring within the military population because of extensive orthopaedic combat trauma. MicroRNAs (miRNAs) are small noncoding RNAs that act as post-transcriptional regulators of gene expression. We hypothesized that a clinically relevant miRNA signature could be detected in patients following injury that progressed to form HO (HO+) or did not form HO (HO-).

METHODS

Tissue samples were obtained from injured servicemembers during their initial surgical debridements, and miRNA profiling was performed using a real-time miRNA polymerase chain reaction (PCR) array. Primary mesenchymal progenitor cells (MPCs) were harvested from debrided traumatized human muscle tissue, and cells were isolated and cultured in vitro. Mimic miRNAs were transfected into MPCs, followed by downstream in vitro analyses.

RESULTS

The investigation of the miRNA expression profile in the tissue of HO+ compared with HO- patients demonstrated a molecular signature that included the upregulation of miR-1, miR-133a, miR-133b, miR-206, miR-26a, and miR-125b. Transfection of each of these mature miRNAs into MPCs followed by osteogenic induction demonstrated that miR-1, miR-133a, miR-133b, and miR-206 enhanced osteogenic differentiation compared with control treatments. In silico and in vitro analyses identified the transcription factor SOX9 as a candidate downstream target of miR-1 and miR-206 miRNAs.

CONCLUSIONS

Our data demonstrated a molecular signature of miRNAs in the soft tissue of wounded servicemembers that was associated with the development of HO, providing novel insights into the underlying molecular mechanisms associated with posttraumatic HO.

LEVEL OF EVIDENCE

Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Mesenchymal stem cells as a multimodal treatment for nervous system diseases

Neurological disorders are a massive challenge for modern medicine. Apart from the fact that this group of diseases is the second leading cause of death worldwide, the majority of patients have no access to any possible effective and standardized treatment after being diagnosed, leaving them and their families helpless. This is the reason why such great emphasis is being placed on the development of new, more effective methods to treat neurological patients. Regenerative medicine opens new therapeutic approaches in neurology, including the use of cell-based therapies. In this review, we focus on summarizing one of the cell sources that can be applied as a multimodal treatment tool to overcome the complex issue of neurodegeneration-mesenchymal stem cells (MSCs). Apart from the highly proven safety of this approach, beneficial effects connected to this type of treatment have been observed. This review presents modes of action of MSCs, explained on the basis of data from vast in vitro and preclinical studies, and we summarize the effects of using these cells in clinical trial settings. Finally, we stress what improvements have already been made to clarify the exact mechanism of MSCs action, and we discuss potential ways to improve the introduction of MSC-based therapies in clinics. In summary, we propose that more insightful and methodical optimization, by combining careful preparation and administration, can enable use of multimodal MSCs as an effective, tailored cell therapy suited to specific neurological disorders.

CD34 positive cells isolated from traumatized human skeletal muscle require the CD34 protein for multi-potential differentiation

The CD34 protein is regarded as a marker of stem cells from multiple origins. Recently a mesenchymal progenitor CD34 positive cell identified from traumatized human skeletal muscle demonstrates differentiation capability into vascular endothelial cells, osteoblasts and adipocytes. Here they were treated with a small inhibitory RNA for CD34, which significantly reduced the cellular level of the CD34 protein. These treated cells had a reduced capacity to proliferate, and migrate. They were both unable to differentiation down multiple pathways and to undergo vascular endothelial differentiation as reflected by a lack of expression of VE cadherin, Tie 2 and CD31. Additionally the cells were unable to form tube-like structures in an endothelial tube assay. These treated cells were also unable to undergo osteogenesis, as revealed by lack of alizarin red and alkaline phosphatase staining and were unable to undergo adipogenesis as revealed by lack of oil red O staining. Finally, when CD34 was expressed in cells lacking this protein, the cells were able to undergo vascular endothelial differentiation as revealed by expression of Tie2, VE-cadherin and CD31. These data indicate that in cells derived from traumatized muscle the CD34 protein is required for enhanced proliferation, migration and differentiation down multiple pathways.

TGF-β1 plays a protective role in glucocorticoid-induced dystrophic calcification

Dystrophic calcification (DC) is the deposition of calcium in degenerated tissue which occurs as a reaction to tissue damage. Sometimes if tissue repair fails, it can progress into heterotopic ossification (HO), a pathological condition of abnormal bone formation. HO happens frequently in severe trauma patients such as in blast injury, central nervous system injury and burn injury, in which excessive endogenous glucocorticoid production has always been found. Glucocorticoids have a big impact on bone and muscle. However, few studies have investigated the impact of glucocorticoids on DC/HO formation in muscle. This study aimed to determine the role of glucocorticoids in DC/HO pathogenesis following muscular injury and the possible underlying mechanism. In this study, we administered a high dose of a synthetic glucocorticoid, dexamethasone (DEX), to animals with muscle injury induced by cardiotoxin (CTX) injection to mimic a glucocorticoid excess state following severe muscle trauma. The findings reported here showed that DEX treatment together with CTX-induced muscle injury led to a significant amount of DC in muscle. This effect was likely related to protein level alterations in the fibrinolytic system and resultant decreased circulating transforming growth factor-beta 1 (TGF-β1), given that supplementation of recombinant TGF-β1 markedly rescued this phenomenon. In summary, our results suggest that glucocorticoid excess impairs muscle regeneration and promotes DC/HO, and that TGF-β1 could be a key factor in modulating this process.

Mesenchymal stromal cells; a new horizon in regenerative medicine

In recent decades, mesenchymal stromal cells (MSCs) biomedical utilizing has attracted worldwide growing attention. After the first report of the human MSCs obtaining from the bone marrow (BM) tissue, these cells were isolated from wide types of the other tissues, ranging from adipose tissue to dental pulp. Their specific characteristics, comprising self-renewality, multipotency, and availability accompanied by their immunomodulatory properties and little ethical concern denote their importance in the context of regenerative medicine. Considering preclinical studies, MSCs can modify immune reactions during tissue repair and restoration, providing suitable milieu for tissue recovery; on the other hand, they can be differentiated into comprehensive types of the body cells, such as osteoblast, chondrocyte, hepatocyte, cardiomyocyte, fibroblast, and neural cells. Though a large number of studies have investigated MSCs capacities in regenerative medicine in varied animal models, the oncogenic capability of unregulated MSCs differentiation must be more assessed to enable their application in the clinic. In the current review, we provide a brief overview of MSCs sources, isolation, and expansion as well as immunomodulatory activities. More important, we try to collect and discuss recent preclinical and clinical research and evaluate current challenges in the context of the MSC-based cell therapy for regenerative medicine.

Bone Substitutes in Orthopaedic Surgery: Current Status and Future Perspectives

Bone replacement materials have been successfully supplied for a long time. But there are cases, especially in critical sized bone defects, in which the therapy is not sufficient. Nowadays, there are multiple bone substitutes available. Autologous bone grafts remain the "gold standard" in bone regeneration. Yet, donor-site morbidity and the available amount of sufficient material are limitations for autologous bone grafting. This study aimed to provide information about the current status in research regarding bone substitutes. We report on the advantages and drawbacks of several bone substitutes. At the end, we discuss the current developments of combining ceramic substitutes with osteoinductive substances.

Impact of the type of microcarrier and agitation modes on the expansion performances of mesenchymal stem cells derived from umbilical cord

The present study proposed to compare the impact of agitation mode (static, orbital, and mechanical) on the culture of mesenchymal stem cells extracted from the Wharton's jelly of umbilical cords (WJ-MSC), in a clinical grade culture medium, using human platelet lysate and different xeno-free microcarriers. Attachment, expansion, and detachment performances were characterized by a new dedicated tool of microscopic image posttreatment, allowing an in situ cell counting without detachment step. Results showed that performances in static mode were not necessarily representative of those obtained in dynamic mode. Moreover, impacts on nutrient consumptions and metabolite productions were identified, such as a higher glutamine consumption when Cytodex-1 microcarriers were used. The detachment strategy used was relatively efficient for Star-Plus, Plastic-Plus, and Hillex II, but not sufficient for Cytodex-1. Despite Cytodex-1 presented promising attachment and expansion performances, Star-Plus and Plastic-Plus showed a better compromise, respectively, for the orbital and the mechanical agitation modes.

Identification and Characterization of Skeletal Muscle Stem Cells from Human Orbicularis Oculi Muscle

Skeletal muscle stem cell (SMSC) transplantation has shown great therapeutical potential in repairing muscle loss and dysfunction, but the muscle acquisition is usually a traumatic procedure causing pain and morbidity to the donor. In this study, we investigated the feasibility of isolating SMSCs from human orbicularis oculi muscle (OOM), which is routinely removed and discarded during ophthalmic cosmetic surgeries. OOM fragments were harvested from 18 female healthy donors undergoing upper eyelid plasties. Plastic-adherent cells were isolated from the muscles using a two-step plating method combined with collagenase digestion. A total of 15 cell cultures were successfully established from the muscle samples. These adherent cells were positive for the specific markers of SMSCs and could be directed toward the osteogenic, adipogenic, chondrogenic, and myogenic phenotypes in the presence of lineage-specific inductive media. Moreover, after cultured in the myogenic inductive medium for 3 weeks, the muscle cells were injected into the tibialis anterior muscles of nude mice and the cell fate was detected using a DiI-labeling technique. In vivo myogenesis was evidenced by the expression of DiI fluorescence after cell transplantation. The donor cells could be found in the satellite cell position and incorporated into the host myofibers. Our results demonstrated that human OOM represents a novel source of myogenic precursors with stem cell-like properties, which may provide a foundation for the SMSC-based therapeutics of skeletal muscle diseases.

Failure of Indomethacin and Radiation to Prevent Blast-induced Heterotopic Ossification in a Sprague-Dawley Rat Model

BACKGROUND

Although use of nonsteroidal antiinflammatory drugs and low-dose irradiation has demonstrated efficacy in preventing heterotopic ossification (HO) after THA and surgical treatment of acetabular fractures, these modalities have not been assessed after traumatic blast amputations where HO is a common complication that can arise in the residual limb.

QUESTIONS/PURPOSES

The purpose of this study was to investigate the effectiveness of indomethacin and irradiation in preventing HO induced by high-energy blast trauma in a rat model.

METHODS

Thirty-six Sprague-Dawley rats underwent hind limb blast amputation with a submerged explosive under water followed by irrigation and primary wound closure. One group (n = 12) received oral indomethacin for 10 days starting on postoperative Day 1. Another group (n = 12) received a single dose of 8 Gy irradiation to the residual limb on postoperative Day 3. A control group (n = 12) did not receive either. Wound healing and clinical course were monitored in all animals until euthanasia at 24 weeks. Serial radiographs were taken immediately postoperatively, at 10 days, and every 4 weeks thereafter to monitor the time course of ectopic bone formation until euthanasia. Five independent graders evaluated the 24-week radiographs to quantitatively assess severity and qualitatively assess the pattern of HO using a modified Potter scale from 0 to 3. Assessment of grading reproducibility yielded a Fleiss statistic of 0.41 and 0.37 for severity and type, respectively. By extrapolation from human clinical trials, a minimum clinically important difference in HO severity was empirically determined to be two full grades or progression of absolute grade to the most severe.

RESULTS

We found no differences in mean HO severity scores among the three study groups (indomethacin 0.90 ± 0.46 [95% confidence interval {CI}, 0.60-1.19]; radiation 1.34 ± 0.59 [95% CI, 0.95-1.74]; control 0.95 ± 0.55 [95% CI, 0.60-1.30]; p = 0.100). For qualitative HO type scores, the radiation group had a higher HO type than both indomethacin and controls, but indomethacin was no different than controls (indomethacin 1.08 ± 0.66 [95% CI, 0.67-1.50]; radiation 1.89 ± 0.76 [95% CI, 1.38-2.40]; control 1.10 ± 0.62 [95% CI, 0.70-1.50]; p = 0.013). The lower bound of the 95% CI on mean severity in the indomethacin group and the upper bound of the radiation group barely spanned a full grade and involved only numeric grades < 2, suggesting that even if a small difference in severity could be detected, it would be less than our a priori-defined minimum clinically important difference and any differences that might be present are unlikely to be clinically meaningful.

CONCLUSIONS

This work unexpectedly demonstrated that, compared with controls, indomethacin and irradiation provide no effective prophylaxis against HO in the residual limb after high-energy blast amputation in a rat model. Such an observation is contrary to the civilian experience and may be potentially explained by either a different pathogenesis for blast-induced HO or a stimulus that overwhelms conventional regimens used to prevent HO in the civilian population.

CLINICAL RELEVANCE

HO in the residual limb after high-energy traumatic blast amputation will likely require novel approaches for prevention and management.

In Vitro and In Vivo Osteogenesis of Human Orbicularis Oculi Muscle-Derived Stem Cells

BACKGROUND

Cell-based therapies for treating bone defects require a source of stem cells with osteogenic potential. There is evidence from pathologic ossification within muscles that human skeletal muscles contain osteogenic progenitor cells. However, muscle samples are usually acquired through a traumatic biopsy procedure which causes pain and morbidity to the donor. Herein, we identified a new alternative source of skeletal muscle stem cells (SMSCs) without conferring morbidity to donors.

METHODS

Adherent cells isolated from human orbicularis oculi muscle (OOM) fragments, which are currently discarded during ophthalmic cosmetic surgeries, were obtained using a two-step plating method. The cell growth kinetics, immunophenotype and capabilities of in vitro multilineage differentiation were evaluated respectively. Moreover, the osteogenically-induced cells were transduced with GFP gene, loaded onto the porous β-tricalcium phosphate (β-TCP) bioceramics, and transplanted into the subcutaneous site of athymic mice. Ectopic bone formation was assessed and the cell fate in vivo was detected.

RESULTS

OOM-derived cells were fibroblastic in shape, clonogenic in growth, and displayed phenotypic and behavioral characteristics similar to SMSCs. In particular, these cells could be induced into osteoblasts in vitro evidenced by the extracellular matrix calcification and enhanced alkaline phosphatase (ALP) activity and osteocalcin (OCN) production. New bone formation was found in the cell-loaded bioceramics 6 weeks after implantation. By using the GFP-labeling technique, these muscle cells were detected to participate in the process of ectopic osteogenesis in vivo.

CONCLUSION

Our data suggest that human OOM tissue is a valuable and noninvasive resource for osteoprogenitor cells to be used in bone repair and regeneration.

Skin-derived mesenchymal stem cells as quantum dot vehicles to tumors

Purpose

Cell-mediated delivery of nanoparticles is emerging as a new method of cancer diagnostics and treatment. Due to their inherent regenerative properties, adult mesenchymal stem cells (MSCs) are naturally attracted to wounds and sites of inflammation, as well as tumors. Such characteristics enable MSCs to be used in cellular hitchhiking of nanoparticles. In this study, MSCs extracted from the skin connective tissue were investigated as transporters of semiconductor nanocrystals quantum dots (QDs).

Materials and methods

Cytotoxicity of carboxylated CdSe/ZnS QDs was assessed by lactate dehydrogenase cell viability assay. Quantitative uptake of QDs was determined by flow cytometry; their intracellular localization was evaluated by confocal microscopy. In vitro tumor-tropic migration of skin-derived MSCs was verified by Transwell migration assay. For in vivo migration studies of QD-loaded MSCs, human breast tumor-bearing immunodeficient mice were used.

Results

QDs were found to be nontoxic to MSCs in concentrations no more than 16 nM. The uptake studies showed a rapid QD endocytosis followed by saturating effects after 6 h of incubation and intracellular localization in the perinuclear region. In vitro migration of MSCs toward MDA-MB-231 breast cancer cells and their conditioned medium was up to nine times greater than the migration toward noncancerous breast epithelial cells MCF-10A. In vivo, systemically administered QD-labeled MSCs were mainly located in the tumor and metastatic tissues, evading most healthy organs with the exception being blood clearance organs (spleen, kidneys, liver).

Conclusion

Skin-derived MSCs demonstrate applicability in cell-mediated delivery of nanoparticles. The findings presented in this study promise further development of a cell therapy and nanotechnology-based tool for early cancer diagnostics and therapy.

Neurotrophic support by traumatized muscle-derived multipotent progenitor cells: Role of endothelial cells and Vascular Endothelial Growth Factor-A

BACKGROUND

Adult mesenchymal stem cells (MSCs) have been shown to increase nerve regeneration in animal models of nerve injury. Traumatized muscle-derived multipotent progenitor cells (MPCs) share important characteristics with MSCs and are isolated from severely damaged muscle tissue following surgical debridement. Previous investigations have shown that MPCs may be induced to increase production of several neurotrophic factors, suggesting the possible utility of autologous MPCs in peripheral nerve regeneration following injury. Recent findings have also shown that components of the vascular niche, including endothelial cells (ECs) and vascular endothelial growth factor (VEGF)-A, regulate neural progenitor cells and sensory neurons.

METHODS

In this study, we have investigated the neuroinductive activities of MPCs, particularly MPC-produced VEGF-A, in the context of an aligned, neuroconductive nerve guide conduit and the endothelial component of the vascular system. Embryonic dorsal root ganglia (DRG) seeded on poly-ϵ-caprolactone aligned nanofibrous scaffold (NF) constructs and on tissue culture plastic, were cocultured with induced MPCs or treated with their conditioned medium (MPC-CM).

RESULTS

Increased neurite extension was observed on both NF and tissue culture plastic in the presence of MPC-CM versus cell-free control CM. The addition of CM from ECs significantly increased the neurotrophic activity of induced MPC-CM, suggesting that MPC and EC neurotrophic activity may be synergistic. Distinctly higher VEGF-A production was seen in MPCs following neurotrophic induction versus culture under normal growth conditions. Selective removal of VEGF-A from MPC-CM reduced the observed DRG neurite extension length, indicating VEGF-A involvement in neurotrophic activity of the CM.

CONCLUSIONS

Taken together, these findings suggest the potential of MPCs to encourage nerve growth via a VEGF-A-dependent action, and the use of MPC-CM or a combination of MPC and CM from ECs for peripheral nerve repair in conjunction with NFs in a nerve guide conduit. Due to the ease of use, application of bioactive agents derived from cultured cells to enhance neurotrophic support presents a promising line of research into peripheral nerve repair.

Concise Review: Mesenchymal Stem Cells in Cardiovascular Regeneration: Emerging Research Directions and Clinical Applications

Experimental and early clinical data suggest that, due to several unique properties, mesenchymal stem cells (MSCs) may be more effective than other cell types for diseases that are difficult to treat or untreatable. Owing to their ease of isolation and culture as well as their secretory and immunomodulatory abilities, MSCs are the most promising option in the field of cell-based therapies. Although MSCs from various sources share several common characteristics, they also exhibit several important differences. These variations may reflect, in part, specific regional properties of the niches from which the cells originate. Moreover, morphological and functional features of MSCs are susceptible to variations across isolation protocols and cell culture conditions. These observations suggest that careful preparation of manufacturing protocols will be necessary for the most efficient use of MSCs in future clinical trials. A typical human myocardial infarct involves the loss of approximately 1 billion cardiomyocytes and 2-3 billion other (mostly endothelial) myocardial cells, leading (despite maximized medical therapy) to a significant negative impact on the length and quality of life. Despite more than a decade of intensive research, search for the "best" (safe and maximally effective) cell type to drive myocardial regeneration continues. In this review, we summarize information about the most important features of MSCs and recent discoveries in the field of MSCs research, and describe current data from preclinical and early clinical studies on the use of MSCs in cardiovascular regeneration. Stem Cells Translational Medicine 2017;6:1859-1867.

Progenitors in Peripheral Nerves Launch Heterotopic Ossification

Studies presented here, using a murine model of bone morphogenetic protein type 2 (BMP2)-induced heterotopic ossification (HO) show that the protein initiates HO by signaling through progenitors in the endoneurium of peripheral nerves. In the mouse, these cells were identified in the endoneurium one day after BMP2 induction using antibody against phosphoSMAD (PS) 1, 5, and 8. Studies conducted in a tracking mouse that contains a tamoxifen-regulated Wnt1-Cre recombinase crossed with a td Tomato red (TR) reporter (Wnt1^CreErt :Ai9Tm) confirmed their neural origin. In this model both BMP2 induction and tamoxifen are absolutely required to induce TR. SP7⁺ (osterix⁺ )TR⁺ cells were found in the endoneurium on day 1 and associated with bone on day 7. Quantification of TR⁺ and TR^- cells isolated by fluorescence-activated cell sorting showed that all SP7⁺ cells were found in the TR⁺ population, whereas only about 80% of the TR⁺ cells expressed SP7. Pre-chondrocytes (Sox 9⁺ ) and transient brown fat (tBAT, UCP1⁺ ) also coexpressed TR, suggesting that the progenitor in nerves is multi-potential. The endoneurium of human nerves near the site of HO contained many PS⁺ cells, and SP7⁺ cells were found in nerves and on bone in tissue from patients with HO. Control tissues and nerves did not contain these PS⁺ and SP7⁺ cells. Some osteoblasts on bone from patients with HO were positive for PS, suggesting the continued presence of BMP during bone formation. The data suggests that the progenitors for HO are derived from the endoneurium in both the mouse model of HO and in humans with HO. Stem Cells Translational Medicine 2017;6:1109-1119.

Traumatized muscle-derived multipotent progenitor cells recruit endothelial cells through vascular endothelial growth factor-A action

Traumatized muscle, such as that debrided from blast injury sites, is considered a promising and convenient tissue source for multipotent progenitor cells (MPCs), a population of adult mesenchymal stem cell (MSC)-like cells. The present study aimed to assess the regenerative therapeutic potential of human traumatized muscle-derived MPCs, e.g., for injury repair in the blast-traumatized extremity, by comparing their pro-angiogenic potential in vitro and capillary recruitment activity in vivo to those of MSCs isolated from human bone marrow, a widely-used tissue source. MPCs were tested for their direct and indirect effects on human microvascular endothelial cells (ECs) in vitro. The findings reported here showed that MPC-conditioned culture medium (MPC-CM), like MSC-CM, promoted EC-cord network branching. Silent (si)RNA-mediated silencing of vascular endothelial growth factor-A (VEGF-A) expression in MPCs attenuated this effect. In a chick embryonic chorioallantoic membrane in vivo angiogenesis assay, MPCs encapsulated in photocrosslinked gelatin scaffold recruited blood vessels more efficiently than either MSCs or human foreskin fibroblasts. Together, these findings support the potential application of traumatized muscle-derived MPCs in cell-based regenerative medicine therapies as a result of their influence on EC organization. Copyright © 2017 John Wiley & Sons, Ltd.

Do skeletal muscle MSCs in humans contribute to bone repair? A systematic review

Mesenchymal stem cells (MSC) from bone marrow and periosteum are known to be heavily involved in fracture repair and bone regeneration is thought to be impaired when the surrounding skeletal muscle is damaged. Recent literature from mouse in vivo models suggest that cells originating from skeletal muscle can occupy a fracture callus during open fracture repair when periosteum is compromised. This systematic review set out to ascertain whether there are MSCs residing in human skeletal muscle and whether cells from human skeletal muscle are capable of forming bone in vitro and in vivo. Original journal articles were selected if they included the terms "skeletal muscle" and "mesenchymal" and used human skeletal muscle samples. Between January 2005 and September 2016, 1000 articles were screened of which, 16 studies met the inclusion criteria for this review. Human skeletal muscle derived cells (SMDC) had the MSC phenotype, positive for CD73, CD90 and CD105 and negative for CD34 and CD45 as well as the potential to differentiate into osteoblasts, chondrocytes and adipocytes in vitro. In addition, SMDC could form bone in vivo when seeded onto an osteoinductive scaffold. A subset of SMDC expressing a pericyte marker (PDGFRα) also expressed the MSC phenotype and were more osteogenic in vivo in comparison to SMDC expressing a satellite cell marker (CD56). The studies included were limited through variation of SMDC extraction methods and tissue culture conditions, which causes heterogeneuous cell cultures. Also, in vitro differentiation assays were not always carried out with bone marrow MSC positive controls. Current evidence suggests that cells with the MSC phenotype reside within human skeletal muscle and are capable of in vivo bone formation in combination with osteoinductive bone scaffolds. This has implications of future development of guided bone regeneration strategies to enhance large bone defect repair, whereby more thought into whether the fracture site should be "blocked" from the skeletal muscle should be carried out.

Secreted trophic factors of mesenchymal stem cells support neurovascular and musculoskeletal therapies

Adult mesenchymal stem cells (MSCs) represent a subject of intense experimental and biomedical interest. Recently, trophic activities of MSCs have become the topic of a number of revealing studies that span both basic and clinical fields. In this review, we focus on recent investigations that have elucidated trophic mechanisms and shed light on MSC clinical efficacy relevant to musculoskeletal applications. Innate differences due to MSC sourcing may play a role in the clinical utility of isolated MSCs. Pain management, osteochondral, nerve, or blood vessel support by MSCs derived from both autologous and allogeneic sources have been examined. Recent mechanistic insights into the trophic activities of these cells point to ultimate regulation by nitric oxide, nuclear factor-kB, and indoleamine, among other signaling pathways. Classic growth factors and cytokines-such as VEGF, CNTF, GDNF, TGF-β, interleukins (IL-1β, IL-6, and IL-8), and C-C ligands (CCL-2, CCL-5, and CCL-23)-serve as paracrine control molecules secreted or packaged into extracellular vesicles, or exosomes, by MSCs. Recent studies have also implicated signaling by microRNAs contained in MSC-derived exosomes. The response of target cells is further regulated by their microenvironment, involving the extracellular matrix, which may be modified by MSC-produced matrix metalloproteinases (MMPs) and tissue inhibitor of MMPs. Trophic activities of MSCs, either resident or introduced exogenously, are thus intricately controlled, and may be further fine-tuned via implant material modifications. MSCs are actively being investigated for the repair and regeneration of both osteochondral and other musculoskeletal tissues, such as tendon/ligament and meniscus. Future rational and effective MSC-based musculoskeletal therapies will benefit from better mechanistic understanding of MSC trophic activities, for example using analytical "-omics" profiling approaches.

Heterotopic Ossification Circumferentia Articularis (HOCA) of Both Knee Joints After Guillain-Barré Syndrome

Heterotopic ossification (HO) is the abnormal development of bone within soft tissue. It is a frequent complication after traumatic as well as atraumatic central nervous system (CNS) insult. It has rarely been found to be associated with Guillain-Barré syndrome (GBS). Only a few cases of HO associated with GBS have been reported so far in medical literature. We present a 30-year-old female patient with severe bilateral knee stiffness following axonal polyneuropathy type of GBS that developed 10 months ago in her immediate post-partum period. She was put on mechanical ventilation for two weeks. She was diagnosed as HO based on clinical and radiological studies. This is an extremely unusual presentation of HO encircling both the knees following GBS without any other well-known risk factors. We have coined a new nomenclature—Heterotopic Ossification Circumferentia Articularis (HOCA)—for this type of presentation. In our patient, various factors such as prolonged ICU stay, mechanical ventilation, hypoxia, and long-standing hypomobility could be attributed to the development of this severe form of HO.

Insight into Reepithelialization: How Do Mesenchymal Stem Cells Perform?

Wound reepithelialization is a cooperative multifactorial process dominated by keratinocyte migration, proliferation, and differentiation that restores the intact epidermal barrier to prevent infection and excessive moisture loss. However, in wounds that exhibit impaired wound healing, such as chronic nonhealing wounds or hypertrophic scars, the reepithelialization process has failed. Thus, it is necessary to explore a suitable way to mitigate these abnormalities to promote reepithelialization and achieve wound healing. Mesenchymal stem cells (MSCs) have the capacity for self-renewal as well as potential multipotency. These cells play important roles in many biological processes, including anti-inflammation, cell migration, proliferation, and differentiation, and signal pathway activation or inhibition. The mechanism of the involvement of MSCs in reepithelialization is still not fully understood. An abundance of evidence has shown that MSCs participate in reepithelialization by inhibiting excessive inflammatory responses, secreting important factors, differentiating into multiple skin cell types, and recruiting other host cells. This review describes the evidence for the roles that MSCs appear to play in the reepithelialization process.

Current therapeutic strategies of heterotopic ossification--a survey amongst orthopaedic and trauma departments in Germany

Background

Heterotopic ossification (HO) is a complication after tissue trauma, fracture and surgery (i.e. total hip arthroplasty). Prophylaxis is the most effective therapy. If HO formations become symptomatic and limit patients’ quality of life, revision surgery is indicated and is usually combined with a perioperative oral prophylaxis (NSAIDs) and/or irradiation. However, a long-term use of NSAIDs can induce gastro-intestinal or cardiac side-effects and possible bony non-unions during fracture healing. Subject of this study was to assess the current status of HO prophylaxis after injuries or fractures and to evaluate current indications and strategies for excision of symptomatic HO.

Methods

Between 2013 and 2014, a questionnaire was sent to 119 orthopaedic and trauma surgery departments in Germany. Participation was voluntary and all acquired data was given anonymously.

Results

The cumulative feedback rate was 71 %. Trauma and orthopaedic surgery departments in Germany recommend oral HO prophylaxis after acetabulum and femoral neck fractures, elbow dislocation, and fracture or dislocation of the radial head. Pain upon movement and an increasing loss of range of motion in the affected joint are considered to be clear indications for HO surgery. A partial removal of ROM-limiting HO formations was also considered important. The vast majority of all departments include perioperative oral HO prophylaxis and/or irradiation if surgical HO removal is planned. The choice and duration of NSAIDs is highly variable.

Conclusion

HO is of clinical significance in current traumatology and orthopaedics. Certain fractures and injuries are prone to HO, and prophylactic measures should be taken. The respondents in this survey assessed current therapeutic strategies for HO formations similarly. These concepts are in line with the literature. However, the duration of perioperative oral HO prophylaxis varied greatly among the specialist centres. This is significant as a long-term use of NSAIDs fosters a potential risk for the patients’ safety and could influence the clinical outcome. National and international guidelines need to be developed to further reduce HO rates and improve patients’ safety in trauma and orthopaedic surgery.

Pathogenesis and prevention strategies of heterotopic ossification in total hip arthroplasty: a narrative literature review and results of a survey in Germany

INTRODUCTION

Heterotopic ossification (HO) after THA can lead to pain, impaired range of motion and possibly revision surgery. This article summarizes current literature on the pathogenesis of HO in THA and trauma. Second, it presents the results of a survey on prophylactic concepts for HO in Germany.

MATERIALS AND METHODS

A narrative literature review was conducted by searching three databases (Pubmed, ScienceDirect, the Cochrane library) on the aetiology of HO. Between 2013 and 2014, a questionnaire was sent to 119 orthopaedic and trauma surgery departments in Germany.

RESULTS

The acquired form of HO seems to develop after tissue trauma, which induces a local inflammation. A change in tissue conditions, multiple signalling pathways and involvement of several different cell types seem to promote enchondral ossification and finally HO formation. The feed back rate of the survey was 67%. Eighty-seven percent of all departments currently administer NSAIDs with a mean time span of 3 weeks after surgery for oral prophylaxis. Prophylactic perioperative irradiation is performed in 64% of trauma/orthopaedic departments if the patient is at risk for HO with a mean dosage of 7 Gy.

CONCLUSIONS

Basic research detected new pathways and cell signalling mechanisms of HO pathogenesis, which could offer new treatment and prophylaxis options in the near future. So far, there is no uniform strategy for the clinical prophylaxis of HO in THA. Guidelines and new clinical trials need to be developed to further reduce HO rates in THA.

Quality of healing: defining, quantifying, and enhancing skeletal muscle healing

Skeletal muscle injury is common in everyday physical activity and athletics, as well as in orthopedic trauma and disease. The overall functional disability resulting from muscle injury is directly related to the intrinsic healing properties of muscle and extrinsic treatment options designed to maximize repair and/or regeneration of muscle tissue all while minimizing pathologic healing pathways. It is important to understand the injury and repair pathways in order to improve the speed and quality of recovery. Recent military conflicts in Iraq and Afghanistan have highlighted the importance of successfully addressing muscular injury and showed the need for novel treatment options that will maximize functional regeneration of the damaged tissue. These severe, wartime injuries, when juxtaposed to peacetime, sports-related injuries, provide us with interesting case examples of the two extreme forms of muscular damage. Comparing and contrasting the differences in these healing pathways will likely provide helpful cues that will help physicians recapitulate the near complete repair and regeneration in less traumatic injuries in addition to more severe cases.

The Neuro-Immune Pathophysiology of Central and Peripheral Fatigue in Systemic Immune-Inflammatory and Neuro-Immune Diseases

Many patients with systemic immune-inflammatory and neuro-inflammatory disorders, including depression, rheumatoid arthritis, systemic lupus erythematosus, Sjögren's disease, cancer, cardiovascular disorder, Parkinson's disease, multiple sclerosis, stroke, and chronic fatigue syndrome/myalgic encephalomyelitis, endure pathological levels of fatigue. The aim of this narrative review is to delineate the wide array of pathways that may underpin the incapacitating fatigue occurring in systemic and neuro-inflammatory disorders. A wide array of immune, inflammatory, oxidative and nitrosative stress (O&NS), bioenergetic, and neurophysiological abnormalities are involved in the etiopathology of these disease states and may underpin the incapacitating fatigue that accompanies these disorders. This range of abnormalities comprises: increased levels of pro-inflammatory cytokines, e.g., interleukin-1 (IL-1), IL-6, tumor necrosis factor (TNF) α and interferon (IFN) α; O&NS-induced muscle fatigue; activation of the Toll-Like Receptor Cycle through pathogen-associated (PAMPs) and damage-associated (DAMPs) molecular patterns, including heat shock proteins; altered glutaminergic and dopaminergic neurotransmission; mitochondrial dysfunctions; and O&NS-induced defects in the sodium-potassium pump. Fatigue is also associated with altered activities in specific brain regions and muscle pathology, such as reductions in maximum voluntary muscle force, downregulation of the mitochondrial biogenesis master gene peroxisome proliferator-activated receptor gamma coactivator 1-alpha, a shift to glycolysis and buildup of toxic metabolites within myocytes. As such, both mental and physical fatigue, which frequently accompany immune-inflammatory and neuro-inflammatory disorders, are the consequence of interactions between multiple systemic and central pathways.

Characterization of discrete subpopulations of progenitor cells in traumatic human extremity wounds

Here we show that distinct subpopulations of cells exist within traumatic human extremity wounds, each having the ability to differentiate into multiple cells types in vitro. A crude cell suspension derived from traumatized muscle was positively sorted for CD29, CD31, CD34, CD56 or CD91. The cell suspension was also simultaneously negatively sorted for either CD45 or CD117 to exclude hematopoietic stem cells. These subpopulations varied in terms their total numbers and their abilities to grow, migrate, differentiate and secrete cytokines. While all five subpopulations demonstrated equal abilities to undergo osteogenesis, they were distinct in their ability to undergo adipogenesis and vascular endotheliogenesis. The most abundant subpopulations were CD29+ and CD34+, which overlapped significantly. The CD29+ and CD34+ cells had the greatest proliferative and migratory capacity while the CD56+ subpopulation produced the highest amounts of TGFß1 and TGFß2. When cultured under endothelial differentiation conditions the CD29+ and CD34+ cells expressed VE-cadherin, Tie2 and CD31, all markers of endothelial cells. These data indicate that while there are multiple cell types within traumatized muscle that have osteogenic differentiation capacity and may contribute to bone formation in post-traumatic heterotopic ossification (HO), the major contributory cell types are CD29+ and CD34+, which demonstrate endothelial progenitor cell characteristics.

A comparison of bone regeneration with human mesenchymal stem cells and muscle-derived stem cells and the critical role of BMP

Adult multipotent stem cells have been isolated from a variety of human tissues including human skeletal muscle, which represent an easily accessible source of stem cells. It has been shown that human skeletal muscle-derived stem cells (hMDSCs) are muscle-derived mesenchymal stem cells capable of multipotent differentiation. Although hMDSCs can undergo osteogenic differentiation and form bone when genetically modified to express BMP2; it is still unclear whether hMDSCs are as efficient as human bone marrow mesenchymal stem cells (hBMMSCs) for bone regeneration. The current study aimed to address this question by performing a parallel comparison between hMDSCs and hBMMSCs to evaluate their osteogenic and bone regeneration capacities. Our results demonstrated that hMDSCs and hBMMSCs had similar osteogenic-related gene expression profiles and had similar osteogenic differentiation capacities in vitro when transduced to express BMP2. Both the untransduced hMDSCs and hBMMSCs formed very negligible amounts of bone in the critical sized bone defect model when using a fibrin sealant scaffold; however, when genetically modified with lenti-BMP2, both populations successfully regenerated bone in the defect area. No significant differences were found in the newly formed bone volumes and bone defect coverage between the hMDSC and hBMMSC groups. Although both cell types formed mature bone tissue by 6 weeks post-implantation, the newly formed bone in the hMDSCs group underwent quicker remodelling than the hBMMSCs group. In conclusion, our results demonstrated that hMDSCs are as efficient as hBMMSCs in terms of their bone regeneration capacity; however, both cell types required genetic modification with BMP in order to regenerate bone in vivo.

Adult Stem Cells and Diseases of Aging

Preservation of adult stem cells pools is critical for maintaining tissue homeostasis into old age. Exhaustion of adult stem cell pools as a result of deranged metabolic signaling, premature senescence as a response to oncogenic insults to the somatic genome, and other causes contribute to tissue degeneration with age. Both progeria, an extreme example of early-onset aging, and heritable longevity have provided avenues to study regulation of the aging program and its impact on adult stem cell compartments. In this review, we discuss recent findings concerning the effects of aging on stem cells, contributions of stem cells to age-related pathologies, examples of signaling pathways at work in these processes, and lessons about cellular aging gleaned from the development and refinement of cellular reprogramming technologies. We highlight emerging therapeutic approaches to manipulation of key signaling pathways corrupting or exhausting adult stem cells, as well as other approaches targeted at maintaining robust stem cell pools to extend not only lifespan but healthspan.

Bone Marrow Mesenchymal Stem Cells Increase Survival after Ionizing Irradiation Combined with Wound Trauma: Characterization and Therapy

The aim of this study was to investigate whether treatment with mesenchymal stem cells (MSCs) could improve survival after radiation combined injury. Bone marrow MSCs (BMSCs) were isolated from femurs of B6D2F1/J female mice and were expanded and cultivated in hypoxic conditions (5% O₂, 10% CO₂, 85% N₂) over 30 days. BMSCs were transfused to mice 24 hr after combined injury due to ⁶⁰Co-γ-photon irradiation (9.25 and 9.75 Gy, 0.4 Gy/min, bilateral) followed by skin wounding (CI). Water consumption, body weight, wound healing, and survival tallies were monitored during observation period. Mice subjected to CI experienced a dramatic moribundity over a 30-day observation period. Thus, CI (9.25 Gy)-animal group was characterized by 40% mortality rate while CI (9.75 Gy)-animal group had 100% mortality rate. CI-induced sickness was accompanied by body weight loss, increased water intake, and delayed wound healing. At the 30th day post-injury, bone marrow cell depletion still remained in surviving CI mice. Treatment of CI (9.25 Gy)-animal group with BMSCs led to an increase in 30-day survival rate by 30%, attenuated body weight loss, accelerated wound healing rate, and ameliorated bone-marrow cell depletion. Our novel results are the first to suggest that BMSC therapy is efficacious to sustain animal survival after CI.

Promotion of skeletal muscle repair in a rat skeletal muscle injury model by local injection of human adipose tissue-derived regenerative cells

Human adipose tissue-derived regenerative cells (ADRCs) can be isolated easily and aseptically from unwanted subcutaneous fat without culturing. ADRCs have been used in clinical cosmetic therapy. In addition, they are expected to be an attractive and feasible source of cell-based therapies in regenerative medicine. Therefore, this paper investigates whether transplantation of human adult ADRCs into skeletal muscle injury models promotes the repair of muscle tissues. This was done by locally injecting human ADRCs into an injured site after laceration of the nude-rat tibialis anterior muscle. Phosphate-buffered saline (PBS) and bone marrow mononuclear cells (MNCs) were injected as negative and positive controls, respectively. After injury, recovery of muscle strength was accelerated by transplantation of ADRCs compared to administration of PBS and MNCs. Moreover, transplantation of ADRCs also enhanced angiogenesis and myogenesis, but the number of vascular and muscular cells labeled with the human cell-specific maker was limited at the injury site. Results showed that transplantation of ADRCs into a skeletal muscle injury model promoted repair of muscle tissues in a paracrine manner rather than differentiation of itself into blood vessels and myofibres. Thus, it is believed that ADRCs are a useful and feasible cell source not only for cosmetic therapy but also for regenerative therapy.

Fibroregulation of mesenchymal progenitor cells by BMP-4 after traumatic muscle injury

OBJECTIVES

Traumatized muscle is a complex healing environment containing cells with robust reparative and regenerative potential interacting in a cytokine milieu that influences the function and differentiation of these cells, leading to a spectrum of healing responses. In particular, bone morphogenetic protein-4 (BMP-4) is of interest as a potential modulator of healing because its dysregulation has been associated with fibrosis and heterotopic ossification formation. We propose a descriptive study of altered BMP-4 expression in traumatized muscle tissue and to evaluate its role in the fibroregulatory function of resident mesenchymal progenitor cells (MPCs) at the protein- and gene-expression levels.

METHODS

Protein-level expression of BMP-4 from cells resident in traumatized muscle specimens was evaluated using ELISA and also using sodium dodecyl sulfate-polyacrylamide gel electrophoresis to compare BMP-4 in homogenized muscle tissue specimens. BMP-4, cartilage oligomeric matrix protein (COMP), and osteocalcin expression localization was analyzed via immunohistochemistry. Reverse transcription-polymerase chain reaction was performed to evaluate fibroregulatory gene expression in MPCs after treatment with BMP-4.

RESULTS

BMP-4 was present in all traumatized muscle tissue specimens. Immunohistochemistry demonstrated that traumatized muscle fibers contained greater number of cells expressing BMP-4 in a more disorganized fashion compared with control samples. Reverse transcription-polymerase chain reaction demonstrated that COMP, growth and differentiation factor-10, and integrin beta-2 were up-regulated, whereas tumor necrosis factor-alpha was significantly down-regulated. COMP expression was colocalized in the traumatized muscle tissue with osteocalcin.

CONCLUSIONS

BMP-4 has an effect on MPCs that seems to promote fibrotic tissue formation. These findings suggest that BMP-4, while promoting osteoinduction, may also act on MPCs to promote formation of a fibrotic osteoinductive matrix. Thus, this signaling axis might be a potential target for heterotopic ossification prevention.

Human stem cells and articular cartilage regeneration

The regeneration of articular cartilage damaged due to trauma and posttraumatic osteoarthritis is an unmet medical need. Current approaches to regeneration and tissue engineering of articular cartilage include the use of chondrocytes, stem cells, scaffolds and signals, including morphogens and growth factors. Stem cells, as a source of cells for articular cartilage regeneration, are a critical factor for articular cartilage regeneration. This is because articular cartilage tissue has a low cell turnover and does not heal spontaneously. Adult stem cells have been isolated from various tissues, such as bone marrow, adipose, synovial tissue, muscle and periosteum. Signals of the transforming growth factor beta superfamily play critical roles in chondrogenesis. However, adult stem cells derived from various tissues tend to differ in their chondrogenic potential. Pluripotent stem cells have unlimited proliferative capacity compared to adult stem cells. Chondrogenesis from embryonic stem (ES) cells has been studied for more than a decade. However, establishment of ES cells requires embryos and leads to ethical issues for clinical applications. Induced pluripotent stem (iPS) cells are generated by cellular reprogramming of adult cells by transcription factors. Although iPS cells have chondrogenic potential, optimization, generation and differentiation toward articular chondrocytes are currently under intense investigation.

BMP2 is superior to BMP4 for promoting human muscle-derived stem cell-mediated bone regeneration in a critical-sized calvarial defect model

Muscle-derived cells have been successfully isolated using a variety of different methods and have been shown to possess multilineage differentiation capacities, including an ability to differentiate into articular cartilage and bone in vivo; however, the characterization of human muscle-derived stem cells (hMDSCs) and their bone regenerative capacities have not been fully investigated. Genetic modification of these cells may enhance their osteogenic capacity, which could potentially be applied to bone regenerative therapies. We found that hMDSCs, isolated by the preplate technique, consistently expressed the myogenic marker CD56, the pericyte/endothelial cell marker CD146, and the mesenchymal stem cell markers CD73, CD90, CD105, and CD44 but did not express the hematopoietic stem cell marker CD45, and they could undergo osteogenic, chondrogenic, adipogenic, and myogenic differentiation in vitro. In order to investigate the osteoinductive potential of hMDSCs, we constructed a retroviral vector expressing BMP4 and GFP and a lentiviral vector expressing BMP2. The BMP4-expressing hMDSCs were able to undergo osteogenic differentiation in vitro and exhibited enhanced mineralization compared to nontransduced cells; however, when transplanted into a calvarial defect, they failed to regenerate bone. Local administration of BMP4 protein and cell pretreatment with N-acetylcysteine (NAC), which improves cell survival, did not enhance the osteogenic capacity of the retro-BMP4-transduced cells. In contrast, lenti-BMP2-transduced hMDSCs not only exhibited enhanced in vitro osteogenic differentiation but also induced robust bone formation and nearly completely healed a critical-sized calvarial defect in CD-1 nude mice 6 weeks following transplantation. Herovici's staining of the regenerated bone demonstrated that the bone matrix contained a large amount of type I collagen. Our findings indicated that the hMDSCs are likely mesenchymal stem cells of muscle origin and that BMP2 is more efficient than BMP4 in promoting the bone regenerative capacity of the hMDSCs in vivo.

Inducible expression of neurotrophic factors by mesenchymal progenitor cells derived from traumatically injured human muscle

Peripheral nerve damage frequently accompanies musculoskeletal trauma and repair of these nerves could be enhanced by the targeted application of neurotrophic factors (NTFs), which are typically expressed by endogenous cells that support nerve regeneration. Injured muscle tissues express NTFs to promote reinnervation as the tissue regenerates, but the source of these factors from within the muscles is not fully understood. We have previously identified a population of mesenchymal progenitor cells (MPCs) in traumatized muscle tissue with properties that support tissue regeneration, and our hypothesis was that MPCs also secrete the NTFs that are associated with muscle tissue reinnervation. We determined that MPCs express genes associated with neurogenic function and measured the protein-level expression of specific NTFs with known functions to support nerve regeneration. We also demonstrated the effectiveness of a neurotrophic induction protocol to enhance the expression of the NTFs, which suggests that the expression of these factors may be modulated by the cellular environment. Finally, neurotrophic induction affected the expression of cell surface markers and proliferation rate of the MPCs. Our findings indicate that traumatized muscle-derived MPCs may be useful as a therapeutic cell type to enhance peripheral nerve regeneration following musculoskeletal injury.

Exosomes for drug delivery - a novel application for the mesenchymal stem cell

Exosomes are the most extensively characterized class of secreted membrane vesicles that carry proteins and RNAs for intercellular communication. They are increasingly seen as possible alternatives to liposomes as drug delivery vehicles. Like liposomes, they could deliver their cargo across the plasma membrane and provide a barrier against premature transformation and elimination. In addition, these naturally-occurring secreted membrane vesicles are less toxic and better tolerated in the body as evidenced by their ubiquitous presence in biological fluids, and have an intrinsic homing ability. They are also amenable to in vivo and in vitro loading of therapeutic agents, and membrane modifications to enhance tissue-specific homing. Here we propose human mesenchymal stem cells as the ideal cell source of exosomes for drug delivery. Mesenchymal stem cell transplantation for various disease indications has been extensively tested and shown to be safe in numerous clinical trials. These cells are also prolific producers of immunologically inert exosomes. Immortalization of these cells does not compromise the quantity or quality of exosome production, thus enabling infinite and reproducible exosome production from a single cell clone.

Blast injuries and heterotopic ossification

Heterotopic ossification (HO) is perhaps the single most significant obstacle to independence, functional mobility, and return to duty for combat-injured veterans of Operation Enduring Freedom and Operation Iraqi Freedom. Recent research into the cause(s) of HO has been driven by a markedly higher prevalence seen in these wounded warriors than encountered in previous wars or following civilian trauma. To that end, research in both civilian and military laboratories continues to shed light onto the complex mechanisms behind HO formation, including systemic and wound specific factors, cell lineage, and neurogenic inflammation. Of particular interest, non-invasive in vivo testing using Raman spectroscopy may become a feasible modality for early detection, and a wound-specific model designed to detect the early gene transcript signatures associated with HO is being tested. Through a combined effort, the goals of early detection, risk stratification, and development of novel systemic and local prophylaxis may soon be attainable.

Mesenchymal stem cell therapy for attenuation of scar formation during wound healing

Scars are a consequence of cutaneous wound healing that can be both unsightly and detrimental to the function of the tissue. Scar tissue is generated by excessive deposition of extracellular matrix tissue by wound healing fibroblasts and myofibroblasts, and although it is inferior to the uninjured skin, it is able to restore integrity to the boundary between the body and its environment. Scarring is not a necessary process to repair the dermal tissues. Rather, scar tissue forms due to specific mechanisms that occur during the adult wound healing process and are modulated primarily by the inflammatory response at the site of injury. Adult tissue-derived mesenchymal stem cells, which participate in normal wound healing, are trophic mediators of tissue repair. These cells participate in attenuating inflammation in the wound and reprogramming the resident immune and wound healing cells to favor tissue regeneration and inhibit fibrotic tissue formation. As a result, these cells have been considered and tested as a likely candidate for a cellular therapy to promote scar-less wound healing. This review identifies specific mechanisms by which mesenchymal stem cells can limit tissue fibrosis and summarizes recent in vivo studies where these cells have been used successfully to limit scar formation.

Mesenchymal progenitor cells derived from traumatized muscle enhance neurite growth

The success of peripheral nerve regeneration is governed by the rate and quality of axon bridging and myelination that occurs across the damaged region. Neurite growth and the migration of Schwann cells is regulated by neurotrophic factors produced as the nerve regenerates, and these processes can be enhanced by mesenchymal stem cells (MSCs), which also produce neurotrophic factors and other factors that improve functional tissue regeneration. Our laboratory has recently identified a population of mesenchymal progenitor cells (MPCs) that can be harvested from traumatized muscle tissue debrided and collected during orthopaedic reconstructive surgery. The objective of this study was to determine whether the traumatized muscle-derived MPCs exhibit neurotrophic function equivalent to that of bone marrow-derived MSCs. Similar gene- and protein-level expression of specific neurotrophic factors was observed for both cell types, and we localized neurogenic intracellular cell markers (brain-derived neurotrophic factor and nestin) to a subpopulation of both MPCs and MSCs. Furthermore, we demonstrated that the MPC-secreted factors were sufficient to enhance in vitro axon growth and cell migration in a chick embryonic dorsal root ganglia (DRG) model. Finally, DRGs in co-culture with the MPCs appeared to increase their neurotrophic function via soluble factor communication. Our findings suggest that the neurotrophic function of traumatized muscle-derived MPCs is substantially equivalent to that of the well-characterized population of bone marrow-derived MPCs, and suggest that the MPCs may be further developed as a cellular therapy to promote peripheral nerve regeneration.

Differentiation and regeneration potential of mesenchymal progenitor cells derived from traumatized muscle tissue

Mesenchymal stem cell (MSC) therapy is a promising approach to promote tissue regeneration by either differentiating the MSCs into the desired cell type or by using their trophic functions to promote endogenous tissue repair. These strategies of regenerative medicine are limited by the availability of MSCs at the point of clinical care. Our laboratory has recently identified multipotent mesenchymal progenitor cells (MPCs) in traumatically injured muscle tissue, and the objective of this study was to compare these cells to a typical population of bone marrow derived MSCs. Our hypothesis was that the MPCs exhibit multilineage differentiation and expression of trophic properties that make functionally them equivalent to bone marrow derived MSCs for tissue regeneration therapies. Quantitative evaluation of their proliferation, metabolic activity, expression of characteristic cell-surface markers and baseline gene expression profile demonstrate substantial similarity between the two cell types. The MPCs were capable of differentiation into osteoblasts, adipocytes and chondrocytes, but they appeared to demonstrate limited lineage commitment compared to the bone marrow derived MSCs. The MPCs also exhibited trophic (i.e. immunoregulatory and pro-angiogenic) properties that were comparable to those of MSCs. These results suggest that the traumatized muscle derived MPCs may not be a direct substitute for bone marrow derived MSCs. However, because of their availability and abundance, particularly following orthopaedic injuries when traumatized muscle is available to harvest autologous cells, MPCs are a promising cell source for regenerative medicine therapies designed to take advantage of their trophic properties.