HMGB1 promotes cellular chemokine synthesis and potentiates mesenchymal stromal cell migration via Rap1 activation

Pharmacological activation of mesenchymal stem cells increases gene expression pattern of cell adhesion molecules and fusion with neonatal cardiomyocytes

Cellular therapy is considered a better option for the treatment of degenerative disorders. Different cell types are being used for tissue regeneration. Despite extensive research in this field, several issues remain to be addressed concerning cell transplantation. One of these issues is the survival and homing of administered cells in the injured tissue, which depends on the ability of these cells to adhere. To enhance cell adherence and survival, Rap1 GTPase was activated in mesenchymal stem cells (MSCs) as well as in cardiomyocytes (CMs) by using 8-pCPT-2'-O-Me-cAMP, and the effect on gene expression dynamics was determined through quantitative reverse transcriptase-polymerase chain reaction analysis. Pharmacological activation of MSCs and CMs resulted in the upregulation of connexin-43 and cell adhesion genes, which increased the cell adhesion ability of MSCs and CMs, and increased the fusion of MSCs with neonatal CMs. Treating stem cells with a pharmacological agent that activates Rap1a before transplantation can enhance their fusion with CMs and increase cellular regeneration.

Interplay between mesenchymal stem cells and macrophages: Promoting bone tissue repair

The repair of bone tissue damage is a complex process that is well-orchestrated in time and space, a focus and difficulty in orthopedic treatment. In recent years, the success of mesenchymal stem cells (MSCs)-mediated bone repair in clinical trials of large-area bone defects and bone necrosis has made it a candidate in bone tissue repair engineering and regenerative medicine. MSCs are closely related to macrophages. On one hand, MSCs regulate the immune regulatory function by influencing macrophages proliferation, infiltration, and phenotype polarization, while also affecting the osteoclasts differentiation of macrophages. On the other hand, macrophages activate MSCs and mediate the multilineage differentiation of MSCs by regulating the immune microenvironment. The cross-talk between MSCs and macrophages plays a crucial role in regulating the immune system and in promoting tissue regeneration. Making full use of the relationship between MSCs and macrophages will enhance the efficacy of MSCs therapy in bone tissue repair, and will also provide a reference for further application of MSCs in other diseases.

Interorgan communication in neurogenic heterotopic ossification: the role of brain-derived extracellular vesicles

Brain-derived extracellular vesicles participate in interorgan communication after traumatic brain injury by transporting pathogens to initiate secondary injury. Inflammasome-related proteins encapsulated in brain-derived extracellular vesicles can cross the blood‒brain barrier to reach distal tissues. These proteins initiate inflammatory dysfunction, such as neurogenic heterotopic ossification. This recurrent condition is highly debilitating to patients because of its relatively unknown pathogenesis and the lack of effective prophylactic intervention strategies. Accordingly, a rat model of neurogenic heterotopic ossification induced by combined traumatic brain injury and achillotenotomy was developed to address these two issues. Histological examination of the injured tendon revealed the coexistence of ectopic calcification and fibroblast pyroptosis. The relationships among brain-derived extracellular vesicles, fibroblast pyroptosis and ectopic calcification were further investigated in vitro and in vivo. Intravenous injection of the pyroptosis inhibitor Ac-YVAD-cmk reversed the development of neurogenic heterotopic ossification in vivo. The present work highlights the role of brain-derived extracellular vesicles in the pathogenesis of neurogenic heterotopic ossification and offers a potential strategy for preventing neurogenic heterotopic ossification after traumatic brain injury. Brain-derived extracellular vesicles (BEVs) are released after traumatic brain injury. These BEVs contain pathogens and participate in interorgan communication to initiate secondary injury in distal tissues. After achillotenotomy, the phagocytosis of BEVs by fibroblasts induces pyroptosis, which is a highly inflammatory form of lytic programmed cell death, in the injured tendon. Fibroblast pyroptosis leads to an increase in calcium and phosphorus concentrations and creates a microenvironment that promotes osteogenesis. Intravenous injection of the pyroptosis inhibitor Ac-YVAD-cmk suppressed fibroblast pyroptosis and effectively prevented the onset of heterotopic ossification after neuronal injury. The use of a pyroptosis inhibitor represents a potential strategy for the treatment of neurogenic heterotopic ossification.

In Vitro Insights Into the Influence of Marrow Mesodermal/Mesenchymal Progenitor Cells on Acute Myelogenous Leukemia and Myelodysplastic Syndromes

The study of marrow-resident mesodermal progenitors can provide important insight into their role in influencing normal and aberrant hematopoiesis as occurs in acute myelogenous leukemia (AML) and myelodysplastic syndromes (MDS). In addition, the chemokine competency of these cells provides links to the inflammatory milieu of the marrow microenvironment with additional implications for normal and malignant hematopoiesis. While in vivo studies have elucidated the structure and function of the marrow niche in murine genetic models, corollary human studies have not been feasible, and thus the use of culture-adapted mesodermal cells has provided insights into the role these rare endogenous niche cells play in physiologic, malignant, and inflammatory states. This review focuses on culture-adapted human mesenchymal stem/stromal cells (MSCs) as they have been utilized in understanding their influence in AML and MDS as well as on their chemokine-mediated responses to myeloid malignancies, injury, and inflammation. Such studies have intrinsic limitations but have provided mechanistic insights and clues regarding novel druggable targets.

In situ self-assembled organoid for osteochondral tissue regeneration with dual functional units

The regeneration of hierarchical osteochondral units is challenging due to difficulties in inducing spatial, directional and controllable differentiation of mesenchymal stem cells (MSCs) into cartilage and bone compartments. Emerging organoid technology offers new opportunities for osteochondral regeneration. In this study, we developed gelatin-based microcryogels customized using hyaluronic acid (HA) and hydroxyapatite (HYP), respectively for inducing cartilage and bone regeneration (denoted as CH-Microcryogels and OS-Microcryogels) through in vivo self-assembly into osteochondral organoids. The customized microcryogels showed good cytocompatibility and induced chondrogenic and osteogenic differentiation of MSCs, while also demonstrating the ability to self-assemble into osteochondral organoids with no delamination in the biphasic cartilage-bone structure. Analysis by mRNA-seq showed that CH-Microcryogels promoted chondrogenic differentiation and inhibited inflammation, while OS-Microcryogels facilitated osteogenic differentiation and suppressed the immune response, by regulating specific signaling pathways. Finally, the in vivo engraftment of pre-differentiated customized microcryogels into canine osteochondral defects resulted in the spontaneous assembly of an osteochondral unit, inducing simultaneous regeneration of both articular cartilage and subchondral bone. In conclusion, this novel approach for generating self-assembling osteochondral organoids utilizing tailor-made microcryogels presents a highly promising avenue for advancing the field of tissue engineering.

Stem Cells and Their Derivatives: An Implication for the Regeneration of Nonunion Fractures

Despite advances in biomedical research, fracture nonunion rates have remained stable throughout the years. Long-bone fractures have a high likelihood of nonunion, but the specific biological pathways involved in this severe consequence are unknown. Fractures often heal in an organized sequence, including the production of a hematoma and an early stage of inflammation, the development of a soft callus and hard callus, and eventually the stage of bone remodeling. Deficient healing can result in a persistent bone defect with instability, discomfort, and loss of function. In the treatment of nonunions, mesenchymal stem cells (MSCs) prove to be a promising and safe alternative to the standard therapeutic strategies. Moreover, novel scaffolds are being created in order to use a synergistic biomimetic technique to rapidly generate bone tissue. MSCs respond to acellular biomimetic matrices by regenerating bone. Extracellular vesicles (EVs) derived from MSCs have recently gained interest in the field of musculoskeletal regeneration. Although many of these techniques and technologies are still in the preclinical stage and have not yet been approved for use in humans, novel approaches to accelerate bone healing via MSCs and/or MSC derivatives have the potential to reduce the physical, economic, and social burdens associated with nonhealing fractures and bone defects. In this review, we focus on providing an up-to-date summary of recent scientific studies dealing with the treatment of nonunion fractures in clinical and preclinical settings employing MSC-based therapeutic techniques.

CCL13 and human diseases

CCL13/MCP-4 belongs to the CC chemokine family, which induces chemotaxis in many immune cells. Despite extensive research into its function in numerous disorders, a thorough analysis of CCL13 is not yet accessible. The role of CCL13 in human disorders and existing CCL13-focused therapies are outlined in this study. The function of CCL13 in rheumatic diseases, skin conditions, and cancer is comparatively well-established, and some studies also suggest that it may be involved in ocular disorders, orthopedic conditions, nasal polyps, and obesity. We also give an overview of research that found very little evidence of CCL13 in HIV, nephritis, and multiple sclerosis. Even though CCL13-mediated inflammation is frequently linked to disease pathogenesis, it's fascinating to note that in some conditions, like primary biliary cholangitis (PBC) and suicide, it might even act as a preventative measure.

Regulation of the release of damage-associated molecular patterns from necroptotic cells

Damage-associated molecular patterns (DAMPs) are molecules within living cells that are released when cell membranes are ruptured. Although DAMPs have physiological functions inside the cell, once DAMPs are released extracellularly, they elicit various biological responses, including inflammation, proliferation, tissue damage, and tissue repair, in a context-dependent manner. In past decades, it was assumed that the release of DAMPs was induced by a membrane rupture, caused by passive ATP depletion, or by chemical or mechanical damage to the membrane. However, that concept has been challenged by recent advancements in understanding the regulation of cell death. Necroptosis is a form of regulated cell death, where cells show necrotic morphology. Necroptosis is triggered by death receptors, toll-like receptors, and some viral infections. The membrane rupture is executed by the mixed lineage-like kinase domain-like pseudokinase (MLKL), which forms oligomers that translocate to the plasma membrane during necroptosis. Although the causal relationship between MLKL function and membrane rupture has been extensively investigated, the detailed molecular mechanisms by which oligomerized MLKL induces membrane rupture are not fully understood. This review summarizes recent advances in understanding how MLKL regulates DAMP release and new technologies for visualizing DAMP release at single-cell resolution.

High Mobility Group Box 1 Protein in Osteoarthritic Knee Tissue and Chondrogenic Progenitor Cells: An Ex Vivo and In Vitro Study

OBJECTIVE

In osteoarthritis (OA), a loss of healthy cartilage extracellular matrix (ECM) results in cartilage degeneration. Attracting chondrogenic progenitor cells (CPCs) to injury sites and stimulating them toward chondrogenic expression profiles is a regenerative approach in OA therapy. High mobility group box 1 protein (HMGB1) is associated with chemoattractant and proinflammatory effects in various pathological processes. Here, we investigate the migratory effects of HMGB1 in knee OA and CPCs for the first time.

DESIGN

Immunohistochemistry, immunoblotting, and immunocytochemistry were performed to identify HMGB1 and its receptors, receptor for advanced glycation end products (RAGE) and toll-like receptor 4 (TLR4) in OA knee tissue, chondrocytes, and CPCs. In situ hybridization for HMGB1 mRNA was performed in CPCs ex vivo. The chemoattractant effects of HMGB1 on CPCs were analyzed in cell migration assays.

RESULTS

HMGB1 expression in OA tissue and OA chondrocytes was higher than in healthy specimens and cells. HMGB1, RAGE, and TLR4 were expressed in CPCs and chondrocytes. In situ hybridization revealed HMGB1 mRNA in CPCs after migration into OA knee tissue, and immunohistochemistry confirmed HMGB1 expression at the protein level. Stimulation via HMGB1 significantly increased the migration of CPCs.

CONCLUSIONS

Our results show the chemoattractant role of HMGB1 in knee OA. HMGB1 is released by chondrocytes and has migratory effects on CPCs. These effects might be mediated via RAGE and TLR4. The in vitro and ex vivo results of this study need to be confirmed in vivo.

Synthesized HMGB1 peptide attenuates liver inflammation and suppresses fibrosis in mice

The liver has a high regenerative ability and can induce spontaneous regression of fibrosis when early liver damage occurs; however, these abilities are lost when chronic liver damage results in decompensated cirrhosis. Cell therapies, such as mesenchymal stem cell (MSC) and macrophage therapies, have attracted attention as potential strategies for mitigating liver fibrosis. Here, we evaluated the therapeutic effects of HMGB1 peptide synthesized from box A of high mobility group box 1 protein. Liver damage and fibrosis were evaluated using a carbon tetrachloride (CCl₄)-induced cirrhosis mouse model. The effects of HMGB1 peptide against immune cells were evaluated by single-cell RNA-seq using liver tissues, and those against monocytes/macrophages were further evaluated by in vitro analyses. Administration of HMGB1 peptide did not elicit a rapid response within 36 h, but attenuated liver damage after 1 week and suppressed fibrosis after 2 weeks. Fibrosis regression developed over time, despite continuous liver damage, suggesting that administration of this peptide could induce fibrolysis. In vitro analyses could not confirm a direct effect of HMGB1 peptide against monocyte/macrophages. However, macrophages were the most affected immune cells in the liver, and the number of scar-associated macrophages (Trem2+Cd9+ cells) with anti-inflammatory markers increased in the liver following HMGB1 treatment, suggesting that indirect effects of monocytes/macrophages were important for therapeutic efficacy. Overall, we established a new concept for cell-free therapy using HMGB1 peptide for cirrhosis through the induction of anti-inflammatory macrophages.

TNF-α-mediated m6A modification of ELMO1 triggers directional migration of mesenchymal stem cell in ankylosing spondylitis

Ankylosing spondylitis (AS) is a type of rheumatic disease characterized by chronic inflammation and pathological osteogenesis in the entheses. Previously, we demonstrated that enhanced osteogenic differentiation of MSC from AS patients (AS-MSC) resulted in pathological osteogenesis, and that during the enhanced osteogenic differentiation course, AS-MSC induced TNF-α-mediated local inflammation. However, whether TNF-α in turn affects AS-MSC remains unknown. Herein, we further demonstrate that a high-concentration TNF-α treatment triggers enhanced directional migration of AS-MSC in vitro and in vivo, which enforces AS pathogenesis. Mechanistically, TNF-α leads to increased expression of ELMO1 in AS-MSC, which is mediated by a METTL14 dependent m⁶A modification in ELMO1 3′UTR. Higher ELMO1 expression of AS-MSC is found in vivo in AS patients, and inhibiting ELMO1 in SKG mice produces therapeutic effects in this spondyloarthritis model. This study may provide insight into not only the pathogenesis but also clinical therapy for AS.

Abnormal functions of mesenchymal stem cells (MSC) contribute into the pathogenensis of ankylosing spondylitis (AS). Here, the authors show that TNF-α at high concentration induces enhances migration of AS-MSC through METTL14 mediated m6A modification of the ELMO1 3′ UTR.

Macrophages at the nexus of mesenchymal stromal cell potency: The emerging role of chemokine cooperativity

Pharmacological depletion of macrophages in vivo with liposomal clodronate renders mice unresponsive to adoptive transfer of mesenchymal stromal cells (MSCs) for affecting outcomes of acute inflammatory pathology. This experimental observation identifies host macrophages as necessary in mediating the salutary anti-inflammatory properties of MSCs as a cellular pharmaceutical. This theory is supported by the observation that transfusion of MSCs leads to the prompt phagocytosis of nearly half of lung entrapped MSCs by lung resident macrophages, triggering an interleukin (IL)-10 suppressive efferocytotic response. In addition, non-phagocytosed MSCs with COX2 competency shape the immune milieu by inducing tissue macrophages to express IL-10. Additional experimental evidence identifies MSC-borne IL-6, IDO and TSG-6 as directly involved in macrophage polarization. Along similar lines of functional convergence, implantation of CCL2⁺ MSCs in the extravascular space where interaction with lung resident perivascular macrophages is not operative, also leads to IL-10 polarization of CCR2⁺ macrophages within acute injured tissue far removed from MSC depot. Intriguingly, MSC-derived CCL2 on its own is not sufficient to polarize macrophages and requires heterodimerization with MSC-borne CXCL12 to trigger macrophage IL-10 polarization via CCR2, but not CXCR4. Such chemokine cooperativity opens a new venue for analysis of MSC potency especially considering the rich chemokine secretome of MSC exposed to inflammatory stimulus. As an aggregate, these data highlight a necessary MSC and host macrophage functional dyad that may inform potency attribute analysis of MSCs-including the chemokine interactome-that may be directly linked to in vivo clinical anti-inflammatory and regenerative response.

The osteogenic differentiation of human bone marrow stromal cells induced by nanofiber scaffolds using bioinformatics

This article aims to investigate the mechanism of behaviors of human bone marrow stromal cells (hBMSCs) affected by scaffold structure combining Monte Carlo feature selection (MFCS), incremental feature selection (IFS) and support vector machine (SVM). The specific differentially expressed genes (DEGs) of hBMSCs cultured on nanofiber (NF) scaffolds and freeform fabrication (FFF) scaffolds were obtained. Key genes were screened from common genes between osteogenic DEGs and NF specific DEGs with MFCS, IFS and SVM. The results demonstrated that NF scaffolds induced hBMSCs to express more genes related to osteogenic differentiation. Finally, 16 key genes were identified among the common genes. The common genes were significantly enriched in Rap1 signaling pathway, extracellular matrix and ossification. The results in this study suggested that the gene expression of hBMSCs was sensitive to NF scaffolds and FFF scaffolds, and the osteogenic differentiation of hBMSCs could be enhanced by NF scaffolds.

Temozolomide Treatment Induces HMGB1 to Promote the Formation of Glioma Stem Cells via the TLR2/NEAT1/Wnt Pathway in Glioblastoma

Formation of glioma stem cells (GSCs) is considered as one of the main reasons of temozolomide (TMZ) resistance in glioma patients. Recent studies have shown that tumor microenvironment-derived signals could promote GSCs formation. But the critical molecule and underlying mechanism for GSCs formation after TMZ treatment is not entirely identified. Our study showed that TMZ treatment promoted GSCs formation by glioma cells; TMZ treatment of biopsy-derived glioblastoma multiforme cells upregulated HMGB1; HMGB1 altered gene expression profile of glioma cells with respect to mRNA, lncRNA and miRNA. Furthermore, our results showed that TMZ-induced HMGB1 increased the formation of GSCs and when HMGB1 was downregulated, TMZ-mediated GSCs formation was attenuated. Finally, we showed that the effect of HMGB1 on glioma cells was mediated by TLR2, which activated Wnt/β-catenin signaling to promote GSCs. Mechanistically, we found that HMGB1 upregulated NEAT1, which was responsible for Wnt/β-catenin activation. In conclusion, TMZ treatment upregulates HMGB1, which promotes the formation of GSCs via the TLR2/NEAT1/Wnt pathway. Blocking HMGB1-mediated GSCs formation could serve as a potential therapeutic target for preventing TMZ resistance in GBM patients.

Functional Diversity of Non-Histone Chromosomal Protein HmgB1

The functioning of DNA in the cell nucleus is ensured by a multitude of proteins, whose interactions with DNA as well as with other proteins lead to the formation of a complicated, organized, and quite dynamic system known as chromatin. This review is devoted to the description of properties and structure of the progenitors of the most abundant non-histone protein of the HMGB family-the HmgB1 protein. The proteins of the HMGB family are also known as "architectural factors" of chromatin, which play an important role in gene expression, transcription, DNA replication, and repair. However, as soon as HmgB1 goes outside the nucleus, it acquires completely different functions, post-translational modifications, and change of its redox state. Despite a lot of evidence of the functional activity of HmgB1, there are still many issues to be solved related to the mechanisms of the influence of HmgB1 on the development and treatment of different diseases-from oncological and cardiovascular diseases to pathologies during pregnancy and childbirth. Here, we describe molecular structure of the HmgB1 protein and discuss general mechanisms of its interactions with other proteins and DNA in cell.

A new dawn for eosinophils in the tumour microenvironment

Eosinophils are evolutionarily conserved, pleotropic cells that display key effector functions in allergic diseases, such as asthma. Nonetheless, eosinophils infiltrate multiple tumours and are equipped to regulate tumour progression either directly by interacting with tumour cells or indirectly by shaping the tumour microenvironment (TME). Eosinophils can readily respond to diverse stimuli and are capable of synthesizing and secreting a large range of molecules, including unique granule proteins that can potentially kill tumour cells. Alternatively, they can secrete pro-angiogenic and matrix-remodelling soluble mediators that could promote tumour growth. Herein, we aim to comprehensively outline basic eosinophil biology that is directly related to their activity in the TME. We discuss the mechanisms of eosinophil homing to the TME and examine their diverse pro-tumorigenic and antitumorigenic functions. Finally, we present emerging data regarding eosinophils as predictive biomarkers and effector cells in immunotherapy, especially in response to immune checkpoint blockade therapy, and highlight outstanding questions for future basic and clinical cancer research.

High-mobility group box 1 protein antagonizes the immunosuppressive capacity and therapeutic effect of mesenchymal stem cells in acute kidney injury

Background

Kidney ischemia reperfusion injury (IRI) is a common cause of acute kidney injury and an unavoidable consequence of kidney transplantation and still lacks specific therapeutics. Recently, mesenchymal stem cell (MSC) has been emerging as a promising cell-based therapy for IRI in the context of transplantation. MSC negatively regulates the secretion of pro-inflammatory as well as the activation of immune cells during IRI through its unique immunosuppressive property.

Methods

We employed mice kidney IRI model and MSC cell line to monitor the IRI related checkpoints. siRNAs were utilized to knock down the potential key factors for mechanistic analysis. Statistical analysis was performed by using one-way ANOVA with Tukey’s post hoc procedure by SPSS.

Results

The expression of high-mobility group box 1 protein (HMGB1) is increased in the acute phase as well as the recovery stage of IRI. Importantly, the HMGB1 upregulation is correlated with the injury severity. HMGB1 diminishes the MSC induced immunosuppressive capacity in the presence of pro-inflammatory cytokines in vitro. Toll like receptor 4 (TLR4)-mediated inducible nitric oxide synthase (iNOS) inhibition contributes to the negative effect of HMGB1 on MSCs. HMGB1-TLR4 signaling inhibition augments the therapeutic efficacy of MSCs in mice renal IRI model.

Conclusions

These findings demonstrate that HMGB1 plays a crucial role in shaping the immunoregulatory property of MSCs within the microenvironments, providing novel insights into the crosstalk between MSCs and microenvironment components, suggesting HMGB1 signals as a promising target to improve MSC-based therapy.

The circular RNA CDR1as regulate cell proliferation via TMED2 and TMED10

Background

Circular RNAs (CircRNAs) are biologically active RNAs. CDR1as is one such circRNA previously reported to be a microRNA-7 (miR-7) sponge, thereby regulating associated gene expression. The specific underlying molecular mechanisms of CDR1as biology, however, remain largely unknown.

Methods

We performed CDR1as knockdown in order to explore its function in cell proliferation, migration, the cell cycle, and tumorigenesis. We further employed quantitative proteomic analyses and associated bioinformatics strategies to globally assess CDR1as-regulated proteins (CRPs). Western blotting and immunofluorescence staining were used to validate the proteomic results. We additionally investigated a specific link between TMED2, TMED10, and miR-7 via a dual-luciferase reporter system, and generated CDR1as knockout cell lines via CRISPR/Cas9 editing.

Results

We identified 353 proteins dysregulated upon CDR1as knockdown in 293 T cells. These CRPs were found to interact with one another and to play key roles in certain cellular pathways. Two such proteins, TMED2 and TMED10, were found to specifically contribute to the influence of CDR1as on cell proliferation. CDR1as may regulate these two TMED proteins through miR-7 sponging. We were able to further confirm these results using both CRISPRi cell lines and nude mouse models.

Conclusion

This study suggested that CDR1as may regulate cell proliferation via serving as a miR-7 sponge, thereby regulating TMED2 and TMED10 expression. These results are an invaluable template for future streamlined studies of circRNAs.

Naringin promotes cellular chemokine synthesis and potentiates mesenchymal stromal cell migration via the Ras signaling pathway

Directional migration of mesenchymal stem cells (MSCs) is known to serve roles in bone fracture healing. Naringin is a traditional medicine used in China to treat bone injury and has been confirmed to act as a chemoattractant to MSCs. In the present study, the secretion of chemokines and stimulation of relevant signaling pathways by naringin were detected to determine the molecular mechanism of naringin-induced MSC migration. In these experiments, Quantibody^® arrays were used to detect chemokines secreted by MSCs with or without the addition of naringin. The results revealed differential naringin-induced chemokine secretion of C-X-C motif chemokine (CXCL)5, CXCL6 and C-C motif chemokine 20. Furthermore, the Ras signaling pathway was markedly activated in the naringin-treated groups, suggesting that naringin may enhance the migrational ability of MSCs via Ras activation. Furthermore, naringin was able to promote the secretion of various chemokines derived from MSCs, which would, in turn, increase the mobility of MSCs. The aim of the present study was to provide novel candidate agents for clinical orthopedics and theoretical basis for the future improvement of adjunctive medication for bone fracture healing.

Local delivery of HMGB1 in gelatin sponge scaffolds combined with mesenchymal stem cell sheets to accelerate fracture healing

Fracture nonunion and delayed union continue to pose challenges for orthopedic surgeons. In the present study, we combined HMGB1 gelatin sponges with MSC sheets to promote bone healing after surgical treatment of rat tibial fractures. The HMGB1 gelatin sponge scaffolds supported the expansion of mesenchymal stem cells (MSCs) and promoted the osteogenic differentiation of MSCs and MSC sheets. Lentiviral vectors were then used to overexpress HMGB1 in MSCs. The results indicated that HMGB1 promotes the osteogenic differentiation of MSCs through the STAT3 pathway. Both siRNA and a STAT3 inhibitor downregulated STAT3, further confirming that HMGB1 induces the osteogenic differentiation of MSCs partly via the STAT3 signal pathway. In a rat tibial osteotomy model, we demonstrated the ability of HMGB1 gelatin sponge scaffolds to increase bone formation. The addition of MSC sheets further enhanced fracture healing. These findings support the use of HMGB1-loaded gelatin sponge scaffolds combined with MSC sheets to enhance fracture healing after surgical intervention.

MCPIP1-induced autophagy mediates ischemia/reperfusion injury in endothelial cells via HMGB1 and CaSR

Monocyte chemotactic protein-1-induced protein 1 (MCPIP1) plays a important role in ischemia/reperfusion (I/R) injury. Autophagy is involved in activating endothelial cells in response to I/R. However, researchers have not clearly determined whether MCPIP1 mediates I/R injury in endothelial cells via autophagy, and its downstream mechanism remains unclear. Western blotting analyses and immunocytochemistry were applied to detect protein levels were detected in HUVECs. An in vitro scratch assay was used to detect cell migration. Cells were transfected with siRNAs to knockdown MCPIP1 and high mobility group box 1 (HMGB1) expression. The pharmacological activator of autophagy rapamycin and the specific calcium-sensing receptor (CaSR) inhibitor NPS-2143 were used to confirm the roles of autophagy and CaSR in I/R injury. I/R induced HMGB1 and CaSR expression, which subsequently upreguated the migration and apoptosis of HUVECs and coincided with the increase of autophagy. HMGB1 was involved in cell migration, whereas CaSR specifically participated in I/R-induced HUVEC apoptosis. Based on these findings, I/R-induced MCPIP1 expression regulates the migration and apoptosis of HUVECs via HMGB1 and CaSR, respectively, suggesting a new therapeutic targetof I/R injury.

Potential Role of Chemokines in Fracture Repair

Chemokines are a family of small cytokines that share a typical key structure that is stabilized by disulfide bonds between the cysteine residues at the NH₂-terminal of the protein, and they are secreted by a great variety of cells in several different conditions. Their function is directly dependent on their interactions with their receptors. Chemokines are involved in cell maturation and differentiation, infection, autoimmunity, cancer, and, in general, in any situation where immune components are involved. However, their role in postfracture inflammation and fracture healing is not yet well established. In this article, we will discuss the response of chemokines to bone fracture and their potential roles in postfracture inflammation and healing based on data from our studies and from other previously published studies.