In vitro simulation of the early proinflammatory phase in fracture healing reveals strong immunomodulatory effects of CD146-positive mesenchymal stromal cells

Revolutionizing bone defect healing: the power of mesenchymal stem cells as seeds

Bone defects can arise from trauma or pathological factors, resulting in compromised bone integrity and the loss or absence of bone tissue. As we are all aware, repairing bone defects is a core problem in bone tissue engineering. While minor bone defects can self-repair if the periosteum remains intact and normal osteogenesis occurs, significant defects or conditions such as congenital osteogenesis imperfecta present substantial challenges to self-healing. As research on mesenchymal stem cell (MSC) advances, new fields of application have emerged; however, their application in orthopedics remains one of the most established and clinically valuable directions. This review aims to provide a comprehensive overview of the research progress regarding MSCs in the treatment of diverse bone defects. MSCs, as multipotent stem cells, offer significant advantages due to their immunomodulatory properties and ability to undergo osteogenic differentiation. The review will encompass the characteristics of MSCs within the osteogenic microenvironment and summarize the research progress of MSCs in different types of bone defects, ranging from their fundamental characteristics and animal studies to clinical applications.

Biologic therapies in stress fractures: Current concepts

Stress fractures, a common overuse injury in physically active individuals, present a significant challenge for athletes and military personnel. Patients who sustain stress fractures have demanding training regimes where periods of rest and immobilisation have unacceptable negative consequences on sports goals and finances. Aside from being an overuse injury, there are various contributing risk factors that put certain individuals at risk of a stress fracture. The main two being nutritional deficiencies and hormonal variations, which have significant effects on bone metabolism and turnover. Historically, treatment of stress fractures focused on conservative strategies such as rest and immobilisation. Calcium and vitamin D deficiencies have been closely linked to stress fractures and so over time supplementation has also played a role in treatment. With the introduction of biologics into orthopaedics, newer treatment strategies have been applied to accelerate fracture healing and perhaps improve fracture callus quality. If such therapies can reduce time spent away from sport and activity, it would be ideal for treating stress fractures. This article aims to offer insights into the evolving landscape of stress fracture management. It investigates the pre-clinical evidence and available published clinical applications. Though fracture healing is well understood, the role of biologics for fracture healing is still indeterminate. Available literature for the use of biologic therapies in stress fractures are restricted and most reports have used biologics as a supplement to surgical fixation in subjects in studies that lack control groups. Randomised control trials have been proposed and registered by a few groups, with results awaited. Assessing individuals for risk factors, addressing hormonal imbalances and nutritional deficiencies seems like an effective approach to addressing the burden of stress fractures. We await better designed trials and studies to accurately determine the clinical benefit of adding biologics to the management of these injuries.

Mesenchymal Stem/Stromal Cells: Immunomodulatory and Bone Regeneration Potential after Tumor Excision in Osteosarcoma Patients

Osteosarcoma (OS) is a type of bone cancer that is derived from primitive mesenchymal cells typically affecting children and young adults. The current standard of treatment is a combination of neoadjuvant chemotherapy and surgical resection of the cancerous bone. Post-resection challenges in bone regeneration arise. To determine the appropriate amount of bone to be removed, preoperative imaging techniques such as bone and CT scans are employed. To prevent local recurrence, the current standard of care suggests maintaining bony and soft tissue margins from 3 to 7 cm beyond the tumor. The amount of bone removed in an OS patient leaves too large of a deficit for bone to form on its own and requires reconstruction with metal implants or allografts. Both methods require the bone to heal, either to the implant or across the allograft junction, often in the setting of marrow-killing chemotherapy. Therefore, the issue of bone regeneration within the surgically resected margins remains an important challenge for the patient, family, and treating providers. Mesenchymal stem/stromal cells (MSCs) are potential agents for enhancing bone regeneration post tumor resection. MSCs, used with scaffolds and growth factors, show promise in fostering bone regeneration in OS cases. We spotlight two MSC types-bone marrow-derived (BM-MSCs) and adipose tissue-derived (ASCs)-highlighting their bone regrowth facilitation and immunomodulatory effects on immune cells like macrophages and T cells, enhancing therapeutic outcomes. The objective of this review is two-fold: review work demonstrating any ability of MSCs to target the deranged immune system in the OS microenvironment, and synthesize the available literature on the use of MSCs as a therapeutic option for stimulating bone regrowth in OS patients post bone resection. When it comes to repairing bone defects, both MB-MSCs and ASCs hold great potential for stimulating bone regeneration. Research has showcased their effectiveness in reconstructing bone defects while maintaining a non-tumorigenic role following wide resection of bone tumors, underscoring their capability to enhance bone healing and regeneration following tumor excisions.

Long Noncoding RNA NORAD Promotes Fracture Healing through Interacting with Osteoblast Differentiation via Targeting miR-26a

The present study was designed to evaluate the dynamic expression of lncRNA NORAD in fracture healing of patients with brittle fractures and explore the function and mechanism of NORAD in regulating osteoblastic proliferation, differentiation, and apoptosis. The expression level of NORAD was detected by quantitative real-time PCR. The proliferation, differentiation, and apoptosis of osteoblasts were analyzed by MTT assay, ELISA, and flow cytometry. Luciferase report analysis was used to confirm the interaction between NORAD and its target ceRNA miR-26a. This study showed no significant differences in serum NORAD expression on the 7th day during fracture healing in patients, but increased expression of NORAD was certified on the 14, 21, and 28 days after fixation. Overexpression of NORAD promoted the proliferation and differentiation of osteoblasts and suppressed the apoptosis of osteoblasts. miR-26a proved to be the target gene of NORAD and was inhibited by overexpression of NORAD in osteoblasts. The enhanced expression of miR-26a was negatively linked to the lessened expression of NORAD. NORAD could accelerate the proliferation and differentiation of osteoblasts and inhibit apoptosis, thereby promoting fracture healing.

Enhancement of Immunosuppressive Activity of Mesenchymal Stromal Cells by Platelet-Derived Factors is Accompanied by Apoptotic Priming

The pro-inflammatory phase of bone healing, initiated by platelet activation and eventually hematoma formation, impacts bone marrow mesenchymal stromal cells (MSCs) in unknown ways. Here, we created platelet-rich plasma (PRP) hydrogels to study how platelet-derived factors modulate functional properties of encapsulated MSCs in comparison to a non-inflammatory fibrin (FBR) hydrogel environment. MSCs were isolated from human bone marrow, while PRP was collected from pooled apheresis thrombocyte concentrates and used for hydrogel preparation. After their encapsulation in hydrogels for 72 h, retrieved MSCs were analyzed for immunomodulatory activities, apoptosis, stem cell properties, senescence, CD9+, CD63+ and CD81+ extracellular vesicle (EV) release, and metabolism-related changes. PRP-hydrogels stimulated immunosuppressive functions of MSCs, along with their upregulated susceptibility to cell death in communication with PBMCs and augmented caspase 3/7 activity. We found impaired clonal growth and cell cycle progression, and more pronounced β-galactosidase activity as well as accumulation of LC3-II-positive vacuoles in PRP-MSCs. Stimuli derived from PRP-hydrogels upregulated AKT and reduced mTOR phosphorylation in MSCs, which suggests an initiation of survival-related processes. Our results showed that PRP-hydrogels might represent a metabolically stressful environment, inducing acidification of MSCs, reducing polarization of the mitochondrial membrane and increasing lipid accumulation. These features were not detected in FBR-MSCs, which showed reduced CD63+ and CD81+ EV production and maintained clonogenicity. Our data revealed that PRP-derived hematoma components cause metabolic adaptation of MSCs followed by increased immune regulatory functions. For the first time, we showed that PRP stimuli represent a survival challenge and “apoptotic priming” that are detrimental for stem cell-like growth of MSCs and important for their therapeutic consideration.

Graphical Abstract

Immune and stem cell compartments of acetabular and femoral bone marrow in hip osteoarthritis patients

OBJECTIVE

Hip osteoarthritis (OA) affects all components of the osteochondral unit, leading to bone marrow (BM) lesions, and unknown consequences on BM cell functionality. We analyzed the cellular composition in OA-affected acetabula compared to proximal femur shafts obtained of hip OA patients to reveal yet not explored immune and stem cell compartments.

DESIGN

Combining flow cytometry, cellular assays and transcription analyses, we performed extensive ex vivo phenotyping of acetabular BM cells from 18 hip OA patients, comparing them with their counterparts from patient-matched femoral shaft BM samples. Findings were related to differences in skeletal sites and age.

RESULTS

Acetabular BM had a greater frequency of T-lymphocytes, non-hematopoietic cells and colony-forming units fibroblastic potential than femoral BM. The incidence of acetabular CD45⁺CD3⁺ T-lymphocytes increased (95% CI: 0.1770 to 0.0.8416), while clonogenic hematopoietic progenitors declined (95% CI: -0.9023 to -0.2399) with age of patients. On the other side, in femoral BM, we observed higher B-lymphocyte, myeloid and erythroid cell frequencies. Acetabular mesenchymal stromal cells (MSCs) showed a senescent profile associated with the expression of survival and inflammation-related genes. Efficient osteogenic and chondrogenic differentiation was detected in acetabular MSCs, while adipogenesis was more pronounced in their femoral counterparts.

CONCLUSION

Our results suggest that distinctions in BM cellular compartments and MSCs may be due to the influence of the OA-stressed microenvironment, but also acetabular vs femoral shaft-specific peculiarities cannot be excluded. These results bring new knowledge on acetabular BM cell populations and may be addressed as novel pathogenic mechanisms and therapeutic targets in OA.

Immunomodulatory strategies for bone regeneration: A review from the perspective of disease types

Tissue engineering strategies for treating bone loss to date have largely focused on targeting stem cells or vascularization. Immune cells, including macrophages and T cells, can also indirectly enhance bone healing via cytokine secretion to interact with other bone niche cells. Bone niche cues and local immune environment vary depending on anatomical location, size of defects and disease types. As such, it is critical to evaluate the role of the immune system in the context of specific bone niche and different disease types. This review focuses on immunomodulation research for bone applications using biomaterials and cell-based strategies, with a unique perspective from different disease types. We first reviewed applications for prolonging orthopaedic implant lifetime and enhancing fracture healing, two clinical challenges where immunomodulatory strategies were initially developed for orthopedic applications. We then reviewed recent research progress in harnessing immunomodulatory strategies for regenerating critical-sized, long bone or cranial bone defects, and treating osteolytic bone diseases. Remaining gaps in knowledge, future directions and opportunities were also discussed.

NR4A3 and CCL20 clusters dominate the genetic networks in CD146+ blood cells during acute myocardial infarction in humans

BACKGROUND

CD146 is a tight junction-associated molecule involved in maintaining endothelial barrier, and balancing immune-inflammation response, in cardiovascular disease. Notably, peripheral CD146+ cells significantly upsurge under vessel dyshomeostasis such as acute myocardial injury (AMI), appearing to be a promising therapeutic target. In this study, with a new view of gene correlation, we aim at deciphering the complex underlying mechanism of CD146+ cells' impact in the development of AMI.

METHODS

Transcription dataset GSE 66,360 of CD146+ blood cells from clinical subjects was downloaded from NCBI. Pearson networks were constructed and the clustering coefficients were calculated to disclose the differential connectivity genes (DCGs). Analysis of gene connectivity and gene expression were performed to reveal the hub genes and hub gene clusters followed by gene enrichment analysis.

RESULTS AND CONCLUSIONS

Among the total 23,520 genes, 27 genes out of 126 differential expression genes were identified as DCGs. These DCGs were found in the periphery of the networks under normal condition, but transferred to the functional center after AMI. Moreover, it was revealed that DCGs spontaneously crowded together into two functional models, CCL20 cluster and NR4A3 cluster, influencing the CD146-mediated signaling pathways during the pathology of AMI for the first time.

MiR-193a-3p Promotes Fracture Healing via Targeting PTEN Gene

The aim of this study was to investigate the role and potential mechanism of miR-193a-3p in fracture healing. The 70 fragility fracture patients and 45 healthy controls were enrolled in this study. Quantitative real-time PCR (qRT-PCR) was used for the measurement of the expression levels of miR-193a-3p and PTEN. MTT assay and flow cytometry were used to detect cell viability and apoptosis in the mouse osteoblastic cell line MC3T3-E1. Luciferase reporter assay was performed to confirm the correlation of miR-193a-3p with PTEN. The serum expression level of miR-193a-3p showed no significant change in fracture patients 7 days after fixation treatment, but over time, there was a significant decrease in the expression at 14 days and 21 days after treatment (P < 0.01). Overexpression of miR-193a-3p significantly enhanced cell viability and inhibited cell apoptosis in MC3T3-E1 cells (P < 0.001). Serum PTEN level in fracture patients was increased gradually during the fracture healing process (P < 0.01). PTEN was demonstrated to be a target gene of miR-9-5p and reversed the effect of miR-193a-3p on cell viability and apoptosis (P < 0.001). miR-193a-3p promoted fracture healing via regulating PTEN and may serve as a novel potential target for enhancing bone repair of fragility fracture.

Clinical Application of Bone Marrow Mesenchymal Stem/Stromal Cells to Repair Skeletal Tissue

There has been an escalation in reports over the last decade examining the efficacy of bone marrow derived mesenchymal stem/stromal cells (BMSC) in bone tissue engineering and regenerative medicine-based applications. The multipotent differentiation potential, myelosupportive capacity, anti-inflammatory and immune-modulatory properties of BMSC underpins their versatile nature as therapeutic agents. This review addresses the current limitations and challenges of exogenous autologous and allogeneic BMSC based regenerative skeletal therapies in combination with bioactive molecules, cellular derivatives, genetic manipulation, biocompatible hydrogels, solid and composite scaffolds. The review highlights the current approaches and recent developments in utilizing endogenous BMSC activation or exogenous BMSC for the repair of long bone and vertebrae fractures due to osteoporosis or trauma. Current advances employing BMSC based therapies for bone regeneration of craniofacial defects is also discussed. Moreover, this review discusses the latest developments utilizing BMSC therapies in the preclinical and clinical settings, including the treatment of bone related diseases such as Osteogenesis Imperfecta.