PDGF receptor beta is a potent regulator of mesenchymal stromal cell function

Fibro-adipogenic progenitors in physiological adipogenesis and intermuscular adipose tissue remodeling

Excessive accumulation of intermuscular adipose tissue (IMAT) is a common pathological feature in various metabolic and health conditions and can cause muscle atrophy, reduced function, inflammation, insulin resistance, cardiovascular issues, and unhealthy aging. Although IMAT results from fat accumulation in muscle, the mechanisms underlying its onset, development, cellular components, and functions remain unclear. IMAT levels are influenced by several factors, such as changes in the tissue environment, muscle type and origin, extent and duration of trauma, and persistent activation of fibro-adipogenic progenitors (FAPs). FAPs are a diverse and transcriptionally heterogeneous population of stromal cells essential for tissue maintenance, neuromuscular stability, and tissue regeneration. However, in cases of chronic inflammation and pathological conditions, FAPs expand and differentiate into adipocytes, resulting in the development of abnormal and ectopic IMAT. This review discusses the role of FAPs in adipogenesis and how they remodel IMAT. It highlights evidence supporting FAPs and FAP-derived adipocytes as constituents of IMAT, emphasizing their significance in adipose tissue maintenance and development, as well as their involvement in metabolic disorders, chronic pathologies and diseases. We also investigated the intricate molecular pathways and cell interactions governing FAP behavior, adipogenesis, and IMAT accumulation in chronic diseases and muscle deconditioning. Finally, we hypothesize that impaired cellular metabolic flexibility in dysfunctional muscles impacts FAPs, leading to IMAT. A deeper understanding of the biology of IMAT accumulation and the mechanisms regulating FAP behavior and fate are essential for the development of new therapeutic strategies for several debilitating conditions.

Cross Talk Between Cells and the Current Bioceramics in Bone Regeneration: A Comprehensive Review

The conventional approach for addressing bone defects and stubborn non-unions typically involves the use of autogenous bone grafts. Nevertheless, obtaining these grafts can be challenging, and the procedure can lead to significant morbidity. Three primary treatment strategies for managing bone defects and non-unions prove resistant to conventional treatments: synthetic bone graft substitutes (BGS), a combination of BGS with bioactive molecules, and the use of BGS in conjunction with stem cells. In the realm of synthetic BGS, a multitude of biomaterials have emerged for creating scaffolds in bone tissue engineering (TE). These materials encompass biometals like titanium, iron, magnesium, and zinc, as well as bioceramics such as hydroxyapatite (HA) and tricalcium phosphate (TCP). Bone TE scaffolds serve as temporary implants, fostering tissue ingrowth and the regeneration of new bone. They are meticulously designed to enhance bone healing by optimizing geometric, mechanical, and biological properties. These scaffolds undergo continual remodeling facilitated by bone cells like osteoblasts and osteoclasts. Through various signaling pathways, stem cells and bone cells work together to regulate bone regeneration when a portion of bone is damaged or deformed. By targeting signaling pathways, bone TE can improve bone defects through effective therapies. This review provided insights into the interplay between cells and the current state of bioceramics in the context of bone regeneration.

MicroRNA-138: an emerging regulator of skeletal development, homeostasis, and disease

Noncoding microRNAs are powerful epigenetic regulators of cellular processes by their ability to target and suppress expression of numerous protein-coding mRNAs. This multitargeting function is a unique and complex feature of microRNAs. It is now well-described that microRNAs play important roles in regulating the development and homeostasis of many cell/tissue types, including those that make up the skeletal system. In this review, we focus on microRNA-138 (miR-138) and its effects on regulating bone and cartilage cell differentiation and function. In addition to its reported role as a tumor suppressor, miR-138 appears to function as an inhibitor of osteoblast differentiation. This review provides additional information on studies that have attempted to alter miR-138 expression in vivo as a means to dampen ectopic calcification or alter bone mass. However, a review of the published literature on miR-138 in cartilage reveals a number of contradictory and inconclusive findings with respect to regulating chondrogenesis and chondrocyte catabolism. This highlights the need for more research in understanding the role of miR-138 in cartilage biology and disease. Interestingly, a number of studies in other systems have reported miR-138-mediated effects in dampening inflammation and pain responses. Future studies will reveal if a multifunctional role of miR-138 involving suppression of ectopic bone, inflammation, and pain will be beneficial in skeletal conditions such as osteoarthritis and heterotopic ossification.

MDA-9/Syntenin in the tumor and microenvironment defines prostate cancer bone metastasis

Bone metastasis is a frequent and incurable consequence of advanced prostate cancer (PC). An interplay between disseminated tumor cells and heterogeneous bone resident cells in the metastatic niche initiates this process. Melanoma differentiation associated gene-9 (mda-9/Syntenin/syndecan binding protein) is a prometastatic gene expressed in multiple organs, including bone marrow-derived mesenchymal stromal cells (BM-MSCs), under both physiological and pathological conditions. We demonstrate that PDGF-AA secreted by tumor cells induces CXCL5 expression in BM-MSCs by suppressing MDA-9-dependent YAP/MST signaling. CXCL5-derived tumor cell proliferation and immune suppression are consequences of the MDA-9/CXCL5 signaling axis, promoting PC disease progression. mda-9 knockout tumor cells express less PDGF-AA and do not develop bone metastases. Our data document a previously undefined role of MDA-9/Syntenin in the tumor and microenvironment in regulating PC bone metastasis. This study provides a framework for translational strategies to ameliorate health complications and morbidity associated with advanced PC.

JAM-A Overexpression in Human Umbilical Cord-Derived Mesenchymal Stem Cells Accelerated the Angiogenesis of Diabetic Wound By Enhancing Both Paracrine Function and Survival of Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) is promising in promoting wound healing mainly due to their paracrine function. Nonetheless, the transplanted MSCs presented poor survival with cell dysfunction and paracrine problem in diabetic environment, thus limiting their therapeutic efficacy and clinical application. JAM-A, an adhesion molecule, has been reported to play multi-functional roles in diverse cells. We therefore investigated the potential effect of JAM-A on MSCs under diabetic environment and explored the underlying mechanism. Indeed, high-glucose condition inhibited MSCs viability and JAM-A expression. However, JAM-A abnormality was rescued by lentivirus transfection and JAM-A overexpression promoted MSCs proliferation, migration and adhesion under hyperglycemia. Moreover, JAM-A overexpression attenuated high-glucose-induced ROS production and MSCs apoptosis. The bio-effects of JAM-A on MSCs under hyperglycemia were confirmed by RNA-seq with enrichment analyses. Moreover, Luminex chip results showed JAM-A overexpression dramatically upregulated PDGF-BB and VEGF in the supernatant of MSCs, which was verified by RT-qPCR and western blotting. The supernatant was further found to facilitate HUVECs proliferation, migration and angiogenesis under hyperglycemia. In vivo experiments revealed JAM-A overexpression significantly enhanced MSCs survival, promoted wound angiogenesis, and thus accelerated diabetic wound closure, partially by enhancing PDGF-BB and VEGF expression. This study firstly demonstrated that JAM-A expression of MSCs was inhibited upon high-glucose stimulation. JAM-A overexpression alleviated high-glucose-induced MSCs dysfunction, enhanced their anti-oxidative capability, protected MSCs from hyperglycemia-induced apoptosis and improved their survival, thus strengthening MSCs paracrine function to promote angiogenesis and significantly accelerating diabetic wound healing, which offers a promising strategy to maximize MSCs-based therapy in diabetic wound.

Hydrogel viscoelasticity modulates migration and fusion of mesenchymal stem cell spheroids

Multicellular spheroids made of stem cells can act as building blocks that fuse to capture complex aspects of native in vivo environments, but the effect of hydrogel viscoelasticity on cell migration from spheroids and their fusion remains largely unknown. Here, we investigated the effect of viscoelasticity on migration and fusion behavior of mesenchymal stem cell (MSC) spheroids using hydrogels with a similar elasticity but different stress relaxation profiles. Fast relaxing (FR) matrices were found to be significantly more permissive to cell migration and consequent fusion of MSC spheroids. Mechanistically, inhibition of ROCK and Rac1 pathways prevented cell migration. Moreover, the combination of biophysical and biochemical cues provided by fast relaxing hydrogels and platelet-derived growth factor (PDGF) supplementation, respectively, resulted in a synergistic enhancement of migration and fusion. Overall, these findings emphasize the important role of matrix viscoelasticity in tissue engineering and regenerative medicine strategies based on spheroids.

Administration of stem cells against cardiovascular diseases with a focus on molecular mechanisms: Current knowledge and prospects

Cardiovascular diseases (CVDs) are a serious global concern for public and human health. Despite the emergence of significant therapeutic advances, it is still the leading cause of death and disability worldwide. As a result, extensive efforts are underway to develop practical therapeutic approaches. Stem cell-based therapies could be considered a promising strategy for the treatment of CVDs. The efficacy of stem cell-based therapeutic approaches is demonstrated through recent laboratory and clinical studies due to their inherent regenerative properties, proliferative nature, and their capacity to differentiate into different cells such as cardiomyocytes. These properties could improve cardiovascular functioning leading to heart regeneration. The two most common types of stem cells with the potential to cure heart diseases are induced pluripotent stem cells (iPSCs) and mesenchymal stem cells (MSCs). Several studies have demonstrated the use, efficacy, and safety of MSC and iPSCs-based therapies for the treatment of CVDs. In this study, we explain the application of stem cells, especially iPSCs and MSCs, in the treatment of CVDs with a focus on cellular and molecular mechanisms and then discuss the advantages, disadvantages, and perspectives of using this technology in the treatment of these diseases.

PDGF-BB prevents destructive repair and promotes reparative osteogenesis of steroid-associated osteonecrosis of the femoral head in rabbits

Destructive repair characterized by inadequate angiogenesis and osteogenesis is the main pathological progression in steroid-associated osteonecrosis of the femoral head (SONFH). Platelet-derived growth factor-BB (PDGF-BB) is an "angiogenesis and osteogenesis coupling" factor that has been used for the treatment of bone defects in clinic. This study was designed to analyze the ability of PDGF-BB for preventing destructive repair and promoting reparative osteogenesis in SONFH. Steroid-associated osteonecrosis (SAON) was induced and triggered destructive repair of the femoral head by repeated lipopolysaccharide (LPS) and methylprednisolone (MPS) injections in rabbits. At 2, 4, and 6 weeks after induction, recombinant human PDGF-BB, neutralizing PDGF-BB antibody, or saline was intramedullary injected into the proximal femora. At week 6 after SAON induction, the proximal femora were dissected for bone architecture and histological analysis. C3H10T1/2 cells and HUVECs were used for further mechanistic investigation. After PDGF-BB treatment, type H vessels and leptin receptor-positive (LepR+) mesenchymal stem cells (MSCs) increased in the affected femoral head, and more osteoblastic osteogenesis along the bone surfaces but scattered adipocytes in bone marrow tissue than that in the SAON group. PDGF-BB treatment prevented destructive repair progression and led to 50-70 % of osteonecrotic femoral heads undergoing reparative osteogenesis. In particular, we found that PDGF-BB could mediate MSC self-renewal and maintain their osteogenic potency by activating PDGFR/Akt/GSK3β/CERB signaling in the presence of steroids. Moreover, PDGF-BB also stabled the newly formed vascular tubes by recruiting MSCs for improving intraosseous vascular integration. PDGF-BB may be a candidate for the promotion of reparative osteogenesis in SONFH.

Improved intervertebral bone union in ALIF rat model with porous hydroxyapatite/collagen combined with platelet-rich plasma

BACKGROUND CONTEXT

Platelet-rich plasma (PRP) can accelerate bone union in spinal fusion surgery with an autogenous bone graft. However, it is unclear whether bone union can be obtained by using artificial bone and PRP together in spinal interbody fusion surgery.

PURPOSE

This study aimed to determine whether interbody fusion can be achieved by transplanting porous hydroxyapatite/collagen(HAp/Col) which is an artificial bone material frequently used in spinal fusion surgery, together with PRP in the intervertebral disc space in rats.

STUDY DESIGN AND SETTING

A controlled laboratory study.

METHODS

A total of fourty 10-week old Sprague-Dawley rats were used in this study and assigned to three groups as follow: disc curettage only (control group, n=10), disc curettage + HAp/Col transplant (H group, n=10), and disc curettage + HAp/Col + PRP transplant (H+P group, n=10). The other 10 rats were sacrificed as blood donors for acquisition of PRP. Microcomputed tomography (μCT) examinations were performed to evaluate bone union, bone volume (BV), and bone mineral density (BMD) at 4, 8, and 12 weeks following surgery. Twelve weeks postoperatively, each group of three of L4-L5 spines was harvested to perform histological examination (hematoxylin & eosin stain) and the others were subjected to biomechanical testing (compression properties).

RESULTS

The platelet count in PRP was approximately 4.1 times greater than that in whole blood (260.6±26.2 × 10⁴ mg/dL and 64.3±2.9 × 10⁴ mg/dL in PRP and whole blood, respectively). All the L4-L5 lumbar discs were fused in the H+P group, whereas only one case was fused in the H group and none in the control group at 12 weeks after surgery. BV was significantly higher in the H+P group than in the H group or control groups (both p<.01), although BMD was not significantly different among the three groups. Upon histological analysis, mature bone formation was observed at the transplanted space in all cases in the H+P group, whereas fibrous tissue was observed at the location in the H and control groups. Regarding biomechanical properties, the ultimate load to failure was significantly higher in the H+P group than in the H group or control group (p=.021 and .013, respectively), although stiffness was not significantly different between the three groups.

CONCLUSION

The combination of porous HAp/Col and PRP at an appropriate concentration can promote bone union in the intervertebral disc space without using an autologous bone graft in the rat model. Bone tissue formation was histologically confirmed, and it was mechanically strong.

CLINICAL SIGNIFICANCE

This preclinical study showed that porous HAp/Col, when combined with PRP at an appropriate concentration, can induce bone union without autologous bone grafts. The results may eliminate the need for autologous bone collection for spinal fusion surgery in the future.

PDGF inhibits BMP2-induced bone healing

Bone regeneration depends on a pool of bone/cartilage stem/progenitor cells and signaling mechanisms regulating their differentiation. Using in vitro approach, we have shown that PDGF signaling through PDGFRβ inhibits BMP2-induced osteogenesis, and significantly attenuates expression of BMP2 target genes. We evaluated outcomes of treatment with two anabolic agents, PDGF and BMP2 using different bone healing models. Targeted deletion of PDGFRβ in αSMA osteoprogenitors, led to increased callus bone mass, resulting in improved biomechanical properties of fractures. In critical size bone defects BMP2 treatment increased proportion of osteoprogenitors, while the combined treatment of PDGF BB with BMP2 decreased progenitor number at the injury site. BMP2 treatment induced significant bone formation and increased number of osteoblasts, while in contrast combined treatment with PDGF BB decreased osteoblast numbers. This is in vivo study showing that PDGF inhibits BMP2-induced osteogenesis, but inhibiting PDGF signaling early in healing process does not improve BMP2-induced bone healing.

SM22α-lineage niche cells regulate intramembranous bone regeneration via PDGFRβ-triggered hydrogen sulfide production

Bone stromal cells are critical for bone homeostasis and regeneration. Growing evidence suggests that non-stem bone niche cells support bone homeostasis and regeneration via paracrine mechanisms, which remain to be elucidated. Here, we show that physiologically quiescent SM22α-lineage stromal cells expand after bone injury to regulate diverse processes of intramembranous bone regeneration. The majority of SM22α-lineage cells neither act as stem cells in vivo nor show their expression patterns. Dysfunction of SM22α-lineage niche cells induced by loss of platelet-derived growth factor receptor β (PDGFRβ) impairs bone repair. We further show that PDGFRβ-triggered hydrogen sulfide (H₂S) generation in SM22α-lineage niche cells facilitates osteogenesis and angiogenesis and suppresses overactive osteoclastogenesis. Collectively, these data demonstrate that non-stem SM22α-lineage niche cells support the niche for bone regeneration with a PDGFRβ/H₂S-dependent regulatory mechanism. Our findings provide further insight into non-stem bone stromal niche cell populations and niche-regulation strategy for bone repair.

The conditioned medium from mesenchymal stromal cells pretreated with proinflammatory cytokines promote fibroblasts migration and activation

Human dermal fibroblasts (HDFs) play important roles in all stages of wound healing. However, in nonhealing wounds, fibroblasts are prone to aging, resulting in insufficient migration, proliferation and secretion functions. Recent studies have suggested that mesenchymal stromal cells (MSCs) are conducive to wound healing and cell growth through paracrine cytokine signaling. In our studies, we found that conditioned medium of MSCs pretreated with IFN-γ and TNF-α (IT MSC-CM) has abundant growth factors associated with wound repair. Our in vitro results showed that the effects of IT MSC-CM on promoting cell migration, proliferation and activation in HDFs were better than those of conditioned medium from mesenchymal stromal cells (MSC-CM). Moreover, we embedded a scaffold material containing IT MSC-CM and reconfirmed that cell migration and activation were superior to that in the presence of MSC-CM in vivo. Generally, PDGF-BB is perceived as a promoter of the migration and proliferation of HDFs. Moreover, a high level of PDGF-BB in IT MSC-CM was detected, according to which we guess that the effect on HDFs may be mediated by the upregulation of PDGF-BB. These studies all showed the potential of IT MSC-CM to promote rapid and effective wound healing.

Two Hits for Bone Regeneration in Aged Patients: Vertebral Bone Marrow Clot as a Biological Scaffold and Powerful Source of Mesenchymal Stem Cells

Recently, the use of a new formulation of bone marrow aspirate (BMA), the BMA clot, has been described. This product entails a naturally formed clot from the harvested bone marrow, which retains all the BMA components preserved in a matrix biologically molded by the clot. Even though its beneficial effects were demonstrated by some studies, the impact of aging and aging-associated processes on biological properties and the effect of BMA cell-based therapy are currently unknown. The purpose of our study was to compare selected parameters and properties of clotted BMA and BMA-derived mesenchymal stem cells (MSCs) from younger (<45 years) and older (>65 years) female donors. Clotted BMA growth factors (GFs) expression, MSCs morphology and viability, doubling time, surface marker expression, clonogenic potential, three-lineage differentiation, senescence-associated factors, and Klotho synthesis from younger and older donors were analyzed. Results indicated that donor age does not affect tissue-specific BMA clot regenerative properties such as GFs expression and MSCs morphology, viability, doubling time, surface antigens expression, colony-forming units, osteogenic and adipogenic differentiation, and Klotho and senescence-associated gene expression. Only few differences, i.e., increased platelet-derived growth factor-AB (PDGF-AB) synthesis and MSCs Aggrecan (ACAN) expression, were detected in younger donors in comparison with older ones. However, these differences do not interfere with all the other BMA clot biological properties. These results demonstrated that BMA clot can be applied easily, without any sample processing and avoiding potential contamination risks as well as losing cell viability, proliferation, and differentiation ability, for autologous transplantation in aged patients. The vertebral BMA clot showed two successful hits since it works as a biological scaffold and as a powerful source of mesenchymal stem cells, thus representing a novel and advanced therapeutic alternative for the treatment of orthopedic injuries.

In ovariectomy-induced osteoporotic rat models, BMP-2 substantially reversed an impaired alveolar bone regeneration whereas PDGF-BB failed

OBJECTIVES

We previously suggested an ovariectomy (OVX)-induced osteoporotic rat model showing an impaired alveolar bone defect healing. This study aimed to evaluate and compare the effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) and recombinant human platelet-derived growth factor-BB (rhPDGF-BB) on alveolar bone defect healing in OVX-induced osteoporotic rats.

MATERIALS AND METHODS

A total of forty-one female rats were divided into four groups: a collagen group (n=10), a PDGF-BB group (n=11), a BMP-2 group (n=10), and a control group (n=10). Four months after OVX, alveolar bone drill-hole defects were created and grafted with collagen gel, rhPDGF-BB/collagen gel, or rhBMP-2/collagen gel. The defects in the control group were not grafted with any material. Defect healing was evaluated by histological, histomorphometric, and microcomputed tomographic (micro-CT) analyses at 2 and 4 weeks.

RESULTS

According to the micro-CT analysis, the BMP-2 group exhibited the greatest bone volume fraction among all groups, while the PDGF-BB group did not show significant differences compared with the collagen group. The histomorphometric analysis showed a significantly larger amount of new bone area in the BMP-2 group than in the control and collagen groups at 4 weeks; however, the PDGF-BB group did not reach significant superiority compared with the other groups.

CONCLUSIONS

Alveolar bone regeneration was significantly enhanced by the local use of rhBMP-2/collagen gel compared with the use of rhPDGF-BB/collagen gel in OVX-induced osteoporotic rats.

CLINICAL RELEVANCE

A treatment modality using rhBMP-2 may be a promising approach to promote alveolar bone regeneration in patients suffering from postmenopausal osteoporosis.

An MSC bone-homing compound, Rab001, increases bone mass and reduces the incidence of osteonecrosis in a glucocorticoid-induced osteonecrosis mouse model

Currently, there are no effective medications to either prevent or slow the progression of atraumatic osteonecrosis (ON). The objective of this study is to determine the effects of bone-targeted delivery of mesenchymal stem cells on the prevalence of ON in a glucocorticoid (GC)-induced mouse model. Eight-week-old male BALB/c mice were randomized into groups that received placebo (PL), prednisolone (GC), or concurrent treatments with GC + mesenchymal stromal cells (MSCs), Rab001 or GC + Rab001 + MSCs. Human parathyroid hormone (hPTH) was used as a positive control for bone anabolism. Mice were killed after 30 days, and quantitative measurements of bone mass, bone strength, prevalent ON at the distal femoral epiphysis (DFE) were performed. Angiogenesis was accessed by RNA-Seq, the circulating angiogenic markers, as well as by immunohistochemical staining. We have showed that a novel agent, Rab001 that can noncovalently bind to mesenchymal stem cells (MSC) and direct them to the bone, prevents the incidence of glucocorticoid-induced osteonecrosis in the mouse. In contrast, PTH, a bone anabolic treatment, preserves bone mass but sustains higher ON incidence than Rab001+/- MSC-treated mice. The results of these experiments reveal that glucocorticoids increase the prevalence of ON, and agents that prevent loss of bone vascularity appear to prevent the development of ON. This intervention might be useful in patients with early stages of atraumatic ON.

Novel hybrid polyester-polyacrylate hydrogels enriched with platelet-derived growth factor for chondrogenic differentiation of adipose-derived mesenchymal stem cells in vitro

Background

The goal of the present study was to create a new biodegradable hybrid PCL-P (HEMA-NIPAAm) thermosensitive hydrogel scaffold by grafting PNIPAAm-based copolymers with biodegradable polyesters to promote the chondrogenic differentiation of human progenitor cells (adipose-derived stem cells-hASCs) in the presence of the platelet-derived growth factor (PDGF-BB). Different mixture ratios including 50 mmol ε-caprolactone and 10 mmol HEMA (S-1), 30 mmol ε-caprolactone and 10 mmol HEMA (S-2), 10 mmol ε-caprolactone and 30 mmol HEMA (S-3) were copolymerized followed by the addition of NIPAAm.

Results

A mild to moderate swelling and wettability rates were found in S-2 group copmpared to the S-1 ans S-3 samples. After 7 weeks, S-2 degradation rate reached ~ 43.78%. According to the LCST values, S-2, reaching 37 °C, was selected for different in vitro assays. SEM imaging showed nanoparticulate structure of the scaffold with particle size dimensions of about 62–85 nm. Compressive strength, Young’s modulus, and compressive strain (%) of S-2 were 44.8 MPa, 0.7 MPa, and 75.5%. An evaluation of total proteins showed that the scaffold had the potential to gradually release PDGF-BB. When hASCs were cultured on PCL-P (HEMA-NIPAAm) in the presence of PDGF-BB, the cells effectively attached and flattened on the scaffold surface for a period of at least 14 days, the longest time point evaluated, with increased cell viability rates as measured by performing an MTT assay (p < 0.05). Finally, a real-time RT-PCR analysis demonstrated that the combination of PCL-P (HEMA-NIPAAm) and PDGF-BB promoted the chondrogenesis of hASCs over a period of 14 days by up-regulating the expression of aggrecan, type-II collagen, SOX9, and integrin β1 compared with the non-treated control group (p < 0.05).

Conclusion

These results demonstrate that the PCL-P(HEMA-NIPAAm) hydrogel scaffold carrying PDGF-BB as a matrix for hASC cell seeding is a valuable system that may be used in the future as a three-dimensional construct for implantation in cartilage injuries.

Tumor to normal single-cell mRNA comparisons reveal a pan-neuroblastoma cancer cell

Neuroblastoma is a childhood cancer that resembles developmental stages of the neural crest. It is not established what developmental processes neuroblastoma cancer cells represent. Here, we sought to reveal the phenotype of neuroblastoma cancer cells by comparing cancer (n = 19,723) with normal fetal adrenal single-cell transcriptomes (n = 57,972). Our principal finding was that the neuroblastoma cancer cell resembled fetal sympathoblasts, but no other fetal adrenal cell type. The sympathoblastic state was a universal feature of neuroblastoma cells, transcending cell cluster diversity, individual patients, and clinical phenotypes. We substantiated our findings in 650 neuroblastoma bulk transcriptomes and by integrating canonical features of the neuroblastoma genome with transcriptional signals. Overall, our observations indicate that a pan-neuroblastoma cancer cell state exists, which may be attractive for novel immunotherapeutic and targeted avenues.

Insights into the mechanism of vascular endothelial cells on bone biology

In the skeletal system, blood vessels not only function as a conduit system for transporting gases, nutrients, metabolic waste, or cells but also provide multifunctional signal molecules regulating bone development, regeneration, and remodeling. Endothelial cells (ECs) in bone tissues, unlike in other organ tissues, are in direct contact with the pericytes of blood vessels, resulting in a closer connection with peripheral connective tissues. Close-contact ECs contribute to osteogenesis and osteoclastogenesis by secreting various cytokines in the paracrine or juxtacrine pathways. An increasing number of studies have revealed that extracellular vesicles (EVs) derived from ECs can directly regulate maturation process of osteoblasts and osteoclasts. The different pathways focus on targets at different distances, forming the basis of the intimate spatial and temporal link between bone tissue and blood vessels. Here, we provide a systematic review to elaborate on the function of ECs in bone biology and its underlying mechanisms based on three aspects: paracrine, EVs, and juxtacrine. This review proposes the possibility of a therapeutic strategy targeting blood vessels, as an adjuvant treatment for bone disorders.

PDGF Receptor Signaling in Osteoblast Lineage Cells Controls Bone Resorption Through Upregulation of Csf1 Expression

The physiological functions of platelet-derived growth factor receptors (PDGFRs) α and β in osteoblast biology and bone metabolism remain to be established. Here, we show that PDGFRA and PDGFRB genes are expressed by osteoblast-lineage canopy and reversal cells in close proximity to PDGFB-expressing osteoclasts within human trabecular bone remodeling units. We also report that, although removal of only one of the two PDGFRs in Osterix-positive cells does not affect bone phenotype, suppression of both PDGFRs in those osteoblast lineage cells increases trabecular bone volume in male mice as well as in female gonad-intact and ovariectomized mice. Furthermore, osteoblast lineage-specific suppression of PDGFRs reduces Csf1 expression, bone marrow level of macrophage colony-stimulating factor (M-CSF), number of osteoclasts, and, therefore, bone resorption, but does not change bone formation. Finally, abrogation of PDGFR signaling in osteoblasts blocks PDGF-induced ERK1/2-mediated Csf1 expression and M-CSF secretion in osteoblast cultures and calcitriol-mediated osteoclastogenesis in co-cultures. In conclusion, our results indicate that PDGFR signaling in osteoblast lineage cells controls bone resorption through ERK1/2-mediated Csf1 expression. © 2020 American Society for Bone and Mineral Research (ASBMR).

Identification of biological pathways and genes associated with neurogenic heterotopic ossification by text mining

Background

Neurogenic heterotopic ossification is a disorder of aberrant bone formation affecting one in five patients sustaining a spinal cord injury or traumatic brain injury (SCI-TBI-HO). However, the underlying mechanisms of SCI-TBI-HO have proven difficult to elucidate. The aim of the present study is to identify the most promising candidate genes and biological pathways for SCI-TBI-HO.

Methods

In this study, we used text mining to generate potential explanations for SCI-TBI-HO. Moreover, we employed several additional datasets, including gene expression profile data, drug data and tissue-specific gene expression data, to explore promising genes that associated with SCI-TBI-HO.

Results

We identified four SCI-TBI-HO-associated genes, including GDF15, LDLR, CCL2, and CLU. Finally, using enrichment analysis, we identified several pathways, including integrin signaling, insulin pathway, internalization of ErbB1, urokinase-type plasminogen activator and uPAR-mediated signaling, PDGFR-beta signaling pathway, EGF receptor (ErbB1) signaling pathway, and class I PI3K signaling events, which may be associated with SCI-TBI-HO.

Conclusions

These results enhance our understanding of the molecular mechanisms of SCI-TBI-HO and offer new leads for researchers and innovative therapeutic strategies.

Current and Future Concepts for the Treatment of Impaired Fracture Healing

Bone regeneration represents a complex process, of which basic biologic principles have been evolutionarily conserved over a broad range of different species. Bone represents one of few tissues that can heal without forming a fibrous scar and, as such, resembles a unique form of tissue regeneration. Despite a tremendous improvement in surgical techniques in the past decades, impaired bone regeneration including non-unions still affect a significant number of patients with fractures. As impaired bone regeneration is associated with high socio-economic implications, it is an essential clinical need to gain a full understanding of the pathophysiology and identify novel treatment approaches. This review focuses on the clinical implications of impaired bone regeneration, including currently available treatment options. Moreover, recent advances in the understanding of fracture healing are discussed, which have resulted in the identification and development of novel therapeutic approaches for affected patients.

Bone marrow osteoprogenitors are depleted whereas osteoblasts are expanded independent of the osteogenic vasculature in response to zoledronic acid

Zoledronic acid (ZOL) is an antiresorptive drug used to prevent bone loss in a variety of conditions, acting mainly through suppression of osteoclast activity. There is growing evidence that ZOL can also affect cells of the mesenchymal lineage in bone. We present novel data revealing significant changes in the abundance of perivascular mesenchymal stromal cells (MSCs)/osteoprogenitors and osteoblasts following the injection of ZOL, in vivo. In young mice with high bone turnover and an abundance of perivascular osteoprogenitors, ZOL significantly (P < 0.0001) increased new bone formation. This was accompanied by a decline in osterix-positive osteoprogenitors and a corresponding increase in osteoblasts. However, these effects were not observed in mature mice with low bone turnover. Interestingly, the ZOL-induced changes in cells of the mesenchymal lineage occurred independently of effects on the osteogenic vasculature. Thus, we demonstrate that a single, clinically relevant dose of ZOL can induce new bone formation in microenvironments enriched for perivascular MSC/osteoprogenitors and high osteogenic potential. This arises from the differentiation of perivascular osterix-positive MSC/osteoprogenitors into osteoblasts at sites that are innately osteogenic. Collectively, our data demonstrate that ZOL affects multiple cell types in bone and has differential effects depending on the level of bone turnover.-Hughes, R., Chen, X., Hunter, K. D., Hobbs, J. K., Holen, I., Brown, N. J. Bone marrow osteoprogenitors are depleted whereas osteoblasts are expanded independent of the osteogenic vasculature in response to zoledronic acid.

A PDGFRβ-PI3K signaling axis mediates periosteal cell activation during fracture healing

Insufficient and delayed fracture healing remain significant public health problems with limited therapeutic options. Phosphoinositide 3-kinase (PI3K) signaling, a major pathway involved in regulation of fracture healing, promotes proliferation, migration, and differentiation of osteoprogenitors. We have recently reported that knock-in mice with a global increase in PI3K signaling (gCbl^YF) show enhanced femoral fracture healing characterized by an extraordinary periosteal response to injury. Interestingly, of all growth factor receptors involved in fracture healing, PI3K directly binds only to PDGFR. Given these findings, we hypothesized a PDGFR-PI3K interaction is necessary for mediating robust periosteal cell activation following fracture. In this study, we isolated primary periosteal cells from gCbl^YF mice to analyze cross-talk between the PDGFRβ and PI3K signaling pathways. We found PDGFRβ signaling contributes to robust Akt phosphorylation in periosteal cells in comparison with other growth factor signaling pathways. Additionally, we performed femoral fractures on gCbl^YF mice with a conditional removal of PDGFRβ in mesenchymal progenitors using inducible alpha smooth muscle actin (αSMA) CreER^T2 mice. Our studies showed that depletion of PDGFRβ signaling within these progenitors in the early phase of fracture healing significantly abrogates PI3K-mediated periosteal activation and proliferation three days after fracture. Combined, these results suggest that PDGFRβ signaling through PI3K is necessary for robust periosteal activation in the earliest phases of fracture healing.

Platelet-rich plasma enhances bone union in posterolateral lumbar fusion: A prospective randomized controlled trial

BACKGROUND CONTEXT

Platelet-rich plasma (PRP) accelerates bone union in vivo in a rodent model of spinal fusion surgery. However, PRP's effect on bone union after spinal surgery remains unclear.

PURPOSE

The objective of this study was to evaluate the efficacy of PRP after posterolateral lumbar fusion (PLF) surgery.

STUDY DESIGN/SETTING

Single-center prospective randomized controlled clinical trial with 2-year follow-up.

PATIENT SAMPLE

The patient sample included a total 62 patients (31 patients in the PRP group or 31 patients in the control group).

OUTCOME MEASURES

The outcome measures included the bone fusion rate, the area of bone fusion mass, the duration of bone fusion, and the clinical score using the visual analog scale (VAS).

MATERIALS AND METHODS

We randomized 62 patients who underwent one- or two-level instrumented PLF for lumbar degenerative spondylosis with instability to either the PRP (31 patients) or the control (31 patients) groups. Platelet-rich plasma-treated patients underwent surgery using an autograft bone chip (local bone), and PRP was prepared from patient blood samples immediately before surgery; patients from the control group underwent PLF without PRP treatment. We assessed platelet counts and growth factor concentrations in PRP prepared immediately before surgery. The duration of bone union, the postoperative bone fusion rate, and the area of fusion mass were assessed using plain radiography every 3 months after surgery and by computed tomography at 12 or 24 months. The duration of bone fusion and the clinical scores for low back pain, leg pain, and leg numbness before and 3, 6, 12, and 24 months after surgery were evaluated using VAS.

RESULTS

Data from 50 patients with complete data were included. The bone union rate at the final follow-up was significantly higher in the PRP group (94%) than in the control group (74%) (p=.002). The area of fusion mass was significantly higher in the PRP group (572 mm²) than in the control group (367 mm²) (p=.02). The mean period necessary for union was 7.8 months in the PRP group and 9.8 months in the control group (p=.013). In the PRP, the platelet count was 7.7 times higher and the growth factor concentrations were 50 times higher than those found in plasma (p<.05). There was no significant difference in low back pain, leg pain, and leg numbness in either group at any time evaluated (p>.05).

CONCLUSIONS

Patients treated with PRP showed a higher fusion rate, greater fusion mass, and more rapid bone union after spinal fusion surgery than patients not treated with PRP.

PDGF Modulates BMP2-Induced Osteogenesis in Periosteal Progenitor Cells

BMPs are used in various clinical applications to promote bone formation. The limited success of the BMPs in clinical settings and supraphysiological doses required for their effects prompted us to evaluate the influence of other signaling molecules, specifically platelet‐derived growth factor (PDGF) on BMP2‐induced osteogenesis. Periosteal cells make a major contribution to fracture healing. We detected broad expression of PDGF receptor beta (PDGFRβ) within the intact periosteum and healing callus during fracture repair. In vitro, periosteum‐derived progenitor cells were highly responsive to PDGF as demonstrated by increased proliferation and decreased apoptosis. However, PDGF blocked BMP2‐induced osteogenesis by inhibiting the canonical BMP2/Smad pathway and downstream target gene expression. This effect is mediated via PDGFRβ and involves ERK1/2 MAPK and PI3K/AKT signaling pathways. Therapeutic targeting of the PDGFRβ pathway in periosteum‐mediated bone repair might have profound implications in the treatment of bone disease in the future. © 2018 The Authors JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Mesenchymal Stem Cell Functionalization for Enhanced Therapeutic Applications

IMPACT STATEMENT

Culture expansion of MSCs has detrimental effects on various cell characteristics and attributes (e.g., phenotypic changes and senescence), which, in addition to inherent interdonor variability, negatively impact the standardization and reproducibility of their therapeutic potential. The identification of innate distinct functional MSC subpopulations, as well as the description of ex vivo protocols aimed at maintaining phenotypes and enhancing specific functions have the potential to overcome these limitations. The incorporation of those approaches into cell-based therapy would significantly impact the field, as more reproducible clinical outcomes may be achieved.

From "Bench to Bedside": Current Advancement on Large-Scale Production of Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are the primary cell source in cell therapy and regenerative medicine due to its extraordinary self-renewing capacity and multilineage differentiation potential. Clinical trials involving MSCs are being conducted in a range of human diseases and the number of registered cases is continuously increasing. However, a wide gap exists between the number of MSCs obtainable from the donor site and the number required for implantation to damage tissues, and also between MSC scalability and MSC phenotype stability. The clinical translation of MSCs necessitates a scalable expansion bioprocess for the biomanufacturing of therapeutically qualified cells. This review presents current achievements for expansion of MSCs. Issues involving culture condition modification, bioreactor systems, as well as microcarrier and scaffold platforms for optimal MSC systems are discussed. Most importantly, the gap between current MSC expansion and clinical application, as well as outbreak directions for the future are discussed. The present systemic review will bring new insights into future large-scale MSC expansion and clinical application.

CD140b (PDGFRβ) signaling in adipose-derived stem cells mediates angiogenic behavior of retinal endothelial cells

Adipose-derived stem cells (ASCs) are multipotent mesenchymal progenitor cells that have functional and phenotypic overlap with pericytes lining microvessels in adipose tissue. The role of CD140b [platelet-derived growth factor receptor- β (PDGFR-β)], a constitutive marker expressed by ASCs, in the angiogenic behavior of human retinal endothelial cells (HREs) is not known. CD140b was knocked down in ASCs using targeted siRNA and lipofectamine transfection protocol. Both CD140b+ and CD140b- ASCs were tested for their proliferation (WST-1 reagent), adhesion (laminin-1 coated plates), and migration (wound-scratch assay). Angiogenic effect of CD140b+ and CD140b- ASCs on HREs was examined by co-culturing ASCs:HREs in 12:1 ratio for 6 days followed by visualization of vascular network by Isolectin B4 staining. The RayBio® Membrane-Based Antibody Array was used to assess differences in human cytokines released by CD140b+ or CD140b- ASCs. Knockdown of CD140b in ASCs resulted in a significant 50% decrease in proliferation rate, 25% decrease in adhesion ability to Laminin-1, and 50% decrease in migration rate, as compared to CD140b+ ASCs. Direct contact of ASCs expressing CD140b+ with HREs resulted in robust vascular network formation that was significantly reduced with using CD140b- ASCs. Of the 80 proteins tested, 45 proteins remained unchanged (>0.5-<1.5 fold), 6 proteins including IL-10 downregulated (<0.5 fold) and 29 proteins including IL-16 & TNF-β were upregulated (>1.5 fold) in CD140b- ASCs compared to CD140b+ ASCs. Our data demonstrate a substantial role for CD140b in the intrinsic abilities of ASCs and their angiogenic influence on HREs. Future studies are needed to fully explore the signaling of CD140b in ASCs in vivo for retinal regeneration.

Enhanced cellular uptake and osteogenic differentiation efficiency of melatonin by inclusion complexation with 2-hydroxypropyl β-cyclodextrin

Melatonin (MLT), a hormone secreted from the pineal gland, is recognized as a potential candidate for stimulation of bone regeneration. However, because of its hydrophobicity, the administration of MLT to stimulate bone regeneration is difficult. In this study, an inclusion complex of MLT with 2-hydroxypropyl β-cyclodextrin (HP-β-CD) was prepared to improve the water solubility, and the osteogenic differentiation ability of the inclusion complex was investigated in MC3T3-E1 cells. The formation of HP-β-CD/MLT inclusion complex was confirmed by ¹H and ¹³C nuclear magnetic resonance spectroscopy and wide-angle X-ray diffraction. The water solubility of MLT increased linearly upon addition of HP-β-CD because of the formation of the inclusion complex. Additionally, treatment of the cells with HP-β-CD/MLT inclusion complex showed higher uptake amount of MLT than that treated with free MLT. In addition, treatment of MC3T3-E1 cells with HP-β-CD/MLT inclusion complex increased alkaline phosphatase activity and mineralized matrix deposition, compared to that in free MLT-treated and untreated cells. Furthermore, cells treated with HP-β-CD/MLT inclusion complex exhibited higher expression levels of osteogenic differentiation genes than those in the untreated and free MLT-treated cells. Accordingly, these results suggested that inclusion complexation of MLT with HP-β-CD would be a potential formulation for bone regeneration because of its improved solubility and enhanced osteogenic differentiation efficiency.

Leukocyte-Poor Platelet-Rich Plasma-Derived Growth Factors Enhance Human Fibroblast Proliferation In Vitro

Background

Leukocyte-poor platelet-rich plasma (LP-PRP) from peripheral blood is currently used as a concentrated source of growth factors to stimulate repair at sites of soft tissue injury. Fibroblasts are primary mediators of wound healing. Thus, we aimed to assess the positive effect of LP-PRP on human fibroblast proliferation in vitro.

Methods

LP-PRP was prepared from 49 donors. The fibroblasts were seeded, and at 24 hours after seeding, 1 × 10⁷/10 µL LP-PRP was added once to each well. The cells were harvested 10 times during study period at our planned points, and we examined cell proliferation using the water-soluble tetrazolium salt-1 assay. We collected the supernatants and measured the amount of growth factors such as platelet-derived growth factor (PDGF)-AB/BB, insulin-like growth factor-1 (IGF-1), transforming growth factor-β1 (TGF-β1), and vascular endothelial growth factor (VEGF), which are known to be involved in wound healing processes, by multiplex assay.

Results

Human fibroblasts treated with LP-PRP showed a significant increase in proliferation when compared to untreated controls (p < 0.001 at days 4, 6, and 8). Multiplex cytokine assays revealed various secretion patterns. PDGF-AB/BB appeared at early time points and peaked before fibroblast proliferation. IGF-1 and TGF-β1 secretion gradually increased and peaked on days 4 and 6 post-treatment. The early VEGF concentration was lower than the concentration of other growth factors but increased along with cell proliferation.

Conclusions

Platelets in LP-PRP release growth factors such as PDGF, IGF-1, TGF-β1 and VEGF, and these growth factors have a promoting effect for human fibroblast proliferation, one of the important mediators of wound healing. These results suggest that growth factors derived from LP-PRP enhance the proliferation of human fibroblast.

Substrate stiffness modulates the multipotency of human neural crest derived ectomesenchymal stem cells via CD44 mediated PDGFR signaling

Mesenchymal stem cells (MSCs) have been isolated from various mesodermal and ectodermal tissues. While the phenotypic and functional heterogeneity of MSCs stemming from their developmental origins has been acknowledged, the genetic and environmental factors underpinning these differences are not well-understood. Here, we investigated whether substrate stiffness mediated mechanical cues can directly modulate the development of ectodermal MSCs (eMSCs) from a precursor human neural crest stem cell (NCSC) population. We showed that NCSC-derived eMSCs were transcriptionally and functionally distinct from mesodermal bone marrow MSCs. eMSCs derived on lower substrate stiffness specifically increased their expression of the MSC marker, CD44 in a Rho-ROCK signaling dependent manner, which resulted in a concomitant increase in the eMSCs' adipogenic and chondrogenic differentiation potential. This mechanically-induced effect can only be maintained for short-term upon switching back to a stiff substrate but can be sustained for longer-term when the eMSCs were exclusively maintained on soft substrates. We also discovered that CD44 expression modulated eMSC self-renewal and multipotency via the downregulation of downstream platelet-derived growth factor receptor beta (PDGFRβ) signaling. This is the first instance demonstrating that substrate stiffness not only influences the differentiation trajectories of MSCs but also their derivation from upstream progenitors, such as NCSCs.

Platelet-derived growth factor receptor beta identifies mesenchymal stem cells with enhanced engraftment to tissue injury and pro-angiogenic property

Mesenchymal stem cells (MSCs) are heterogeneous likely consisting of subpopulations with various therapeutic potentials. Here we attempted to acquire a subset of MSCs with enhanced effect in wound healing. We found that human placental MSCs expressing platelet-derived growth factor (PDGF) receptor (PDGFR)-β exhibited greater proliferation rates and generated more colony-forming unit-fibroblast (CFU-F), compared to PDGFR-β- MSCs. Notably, PDGFR-β+ MSCs expressed higher levels of pro-angiogenic factors such as Ang1, Ang2, VEGF, bFGF and PDGF. When 106 GFP-expressing MSCs were topically applied into excisional wounds in mice, PDGFR-β+ MSCs actively incorporated into the wound tissue, resulting in enhanced engraftment (3.92 ± 0.31 × 105 remained in wound by 7 days) and accelerated wound closure; meanwhile, PDGFR-β- MSCs tended to remain on the top of the wound bed with significantly fewer cells (2.46 ± 0.26 × 105) engrafted into the wound, suggesting enhanced chemotactic migration and engraftment of PDGFR-β+ MSCs into the wound. Real-Time PCR and immunostain analyses revealed that the expression of PDGF-B was upregulated after wounding; transwell migration assay showed that PDGFR-β+ MSCs migrated eightfold more than PDGFR-β- MSCs toward PDGF-BB. Intriguingly, PDGFR-β+ MSC-treated wounds showed significantly enhanced angiogenesis compared to PDGFR-β- MSC- or vehicle-treated wounds. Thus, our results indicate that PDGFR-β identifies a subset of MSCs with enhanced chemotactic migration to wound injury and effect in promoting angiogenesis and wound healing, implying a greater therapeutic potential for certain diseases.

Allograft Bone: What Is the Role of Platelet-Derived Growth Factor in Hindfoot and Ankle Fusions

Arthrodesis of the ankle or foot is a common procedure for chronic pain and disability. Nonunion remains a prevalent complication among arthrodesis procedures. Some patients present with an inherent risk of developing a nonunion. Allograft biologics have gained popularity in an effort to reduce complications such as nonunion. Various biologics bring unique properties while maintaining a singular purpose. Platelet-derived growth factor (PDGF) may be introduced into a fusion site to facilitate healthy bony consolidation. The purpose of this article is to review the benefits and modalities of PDGF and how it can improve patient outcomes in ankle and hindfoot fusions.

Strategies for MSC expansion and MSC-based microtissue for bone regeneration

Mesenchymal stem cells (MSCs) have gained increasing attention as a potential approach for the treatment of bone injuries due to their multi-lineage differentiation potential and also their ability to recognize and home to damaged tissue sites, secreting bioactive factors that can modulate the immune system and enhance tissue repair. However, a wide gap between the number of MSCs obtainable from the donor site and the number required for implantation, as well as the lack of understanding of MSC functions under different in vitro and in vivo microenvironment, hinders the progression of MSCs toward clinical settings. The clinical translation of MSCs pre-requisites a scalable expansion process for the biomanufacturing of therapeutically qualified cells. This review briefly introduces the features of implanted MSCs to determine the best strategies to optimize their regenerative capacity, as well as the current MSC implantation for bone diseases. Current achievements for expansion of MSCs using various culturing methods, bioreactor technologies, biomaterial platforms, as well as microtissue-based expansion strategies are also discussed, providing new insights into future large-scale MSC expansion and clinical applications.

Bone intramedullary reaming grafts the fracture site with CD146+ skeletal progenitors and downmodulates the inflammatory environment

INTRODUCTION

Femoral shaft fractures generally occur in young adults following a high-energy trauma and are prone to delayed union/non-union. Novel therapies to stimulate bone regeneration will have to mimic some of the aspects of the biology of fracture healing; however, which are these aspects is unclear. Locked intramedullary nailing is the current treatment of choice for the stabilisation of femur shaft fractures, and it is associated with accelerated healing and increased union rates. These benefits were partially attributed to the reaming procedure, which, regardless of significantly destroying the haematoma, stimulates the healing response. To better understand how reaming influences healing, we evaluated the viability of the nucleated cell fraction and the frequency of CD146⁺ skeletal progenitors, which contain multipotent cells, in the post-reaming haematoma. We also screened the concentrations of inflammatory mediators and growth factors in the fracture site after reaming compared with those in the original haematoma.

METHODS

Pre- and post-reaming haematomas were percutaneously aspirated from the fracture site of 15 patients with closed femoral shaft fractures. Cellular viability and the percentage of CD146+ progenitors were analysed by flow cytometry. The concentrations of cytokines and growth factors were determined by ELISA.

RESULTS

AnnexinV/Pi analysis showed that the viability of the total nucleated cell fraction was decreased in the post-reaming haematoma. However, the procedure increased the percentage of CD146+ skeletal progenitors in the fracture site. Analysis of cytokines and growth factors in supernatants showed a decreased concentration of the inflammatory mediators IL-6, CCL-4, and MCP-1, along with an increase of anti-inflammatory IL-10, and the growth factors bFGF and PDGF-AB.

CONCLUSION

These findings support the view that the positive effects of reaming on fracture healing might result from mechanically grafting the fracture site with a population of skeletal progenitors that contain multipotent cells; transitioning the signalling environment to a less inflammatory state, and enhancing the availability of specific osteogenic and angiogenic factors. A better understanding of the requisite stimuli for optimal bone repair, considering the disturbances made by orthopaedic treatments, will be determinant for the development of innovative treatments for bone repair.

STAT1 modulates tissue wasting or overgrowth downstream from PDGFRβ

In this study, He et al. investigated how gain-of-function PDGFRβ mutations cause human disease, specifically whether PDGFRB mutations alone are responsible for genetic diseases characterized by musculoskeletal wasting or overgrowth. Using a genetic approach, their findings suggest a molecular mechanism by which STAT1 suppresses PDGFRβ-driven fibrosis and bone growth.

Platelet-derived growth factor (PDGF) acts through two conserved receptor tyrosine kinases: PDGFRα and PDGFRβ. Gain-of-function mutations in human PDGFRB have been linked recently to genetic diseases characterized by connective tissue wasting (Penttinen syndrome) or overgrowth (Kosaki overgrowth syndrome), but it is unclear whether PDGFRB mutations alone are responsible. Mice with constitutive PDGFRβ signaling caused by a kinase domain mutation (D849V) develop lethal autoinflammation. Here we used a genetic approach to investigate the mechanism of autoinflammation in Pdgfrb^+/D849V mice and test the hypothesis that signal transducer and activator of transcription 1 (STAT1) mediates this phenotype. We show that Pdgfrb^+/D849V mice with Stat1 knockout (Stat1^−/−Pdgfrb^+/D849V) are rescued from autoinflammation and have improved life span compared with Stat1^+/−Pdgfrb^+/D849V mice. Furthermore, PDGFRβ–STAT1 signaling suppresses PDGFRβ itself. Thus, Stat1^−/−Pdgfrb^+/D849V fibroblasts exhibit increased PDGFRβ signaling, and mice develop progressive overgrowth, a distinct phenotype from the wasting seen in Stat1^+/−Pdgfrb^+/D849V mice. Deletion of interferon receptors (Ifnar1 or Ifngr1) does not rescue wasting in Pdgfrb^+/D849V mice, indicating that interferons are not required for autoinflammation. These results provide functional evidence that elevated PDGFRβ signaling causes tissue wasting or overgrowth reminiscent of human genetic syndromes and that the STAT1 pathway is a crucial modulator of this phenotypic spectrum.

Incorporation of Human-Platelet-Derived Growth Factor-BB Encapsulated Poly(lactic-co-glycolic acid) Microspheres into 3D CORAGRAF Enhances Osteogenic Differentiation of Mesenchymal Stromal Cells

Tissue engineering aims to generate or facilitate regrowth or healing of damaged tissues by applying a combination of biomaterials, cells, and bioactive signaling molecules. In this regard, growth factors clearly play important roles in regulating cellular fate. However, uncontrolled release of growth factors has been demonstrated to produce severe side effects on the surrounding tissues. In this study, poly(lactic-co-glycolic acid) (PLGA) microspheres (MS) incorporated three-dimensional (3D) CORAGRAF scaffolds were engineered to achieve controlled release of platelet-derived growth factor-BB (PDGF-BB) for the differentiation of stem cells within the 3D polymer network. Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and microtomography were applied to characterize the fabricated scaffolds. In vitro study revealed that the CORAGRAF-PLGA-PDGF-BB scaffold system enhanced the release of PDGF-BB for the regulation of cell behavior. Stromal cell attachment, viability, release of osteogenic differentiation markers such as osteocalcin, and upregulation of osteogenic gene expression exhibited positive response. Overall, the developed scaffold system was noted to support rapid cell expansion and differentiation of stromal cells into osteogenic cells in vitro for bone tissue engineering applications.

Mesenchymal stem cell subpopulations: phenotype, property and therapeutic potential

Mesenchymal stem cells (MSC) are capable of differentiating into cells of multiple cell lineages and have potent paracrine effects. Due to their easy preparation and low immunogenicity, MSC have emerged as an extremely promising therapeutic agent in regenerative medicine for diverse diseases. However, MSC are heterogeneous with respect to phenotype and function in current isolation and cultivation regimes, which often lead to incomparable experimental results. In addition, there may be specific stem cell subpopulations with definite differentiation capacity toward certain lineages in addition to stem cells with multi-differentiation potential. Recent studies have identified several subsets of MSC which exhibit distinct features and biological activities, and enhanced therapeutic potentials for certain diseases. In this review, we give an overview of these subsets for their phenotypic, biological and functional properties.