Bone Marrow-Derived CD44+ Cells Migrate to Tissue-Engineered Constructs via SDF-1/CXCR4-JNK Pathway and Aid Bone Repair

Silicon-substituted calcium phosphate promotes osteogenic-angiogenic coupling by activating the TLR4/PI3K/AKT signaling axis

Silicon-substituted calcium phosphate (Si-CaP) is a promising bioactive material for bone tissue engineering. The mechanism of Si-CaP regulates osteogenic-angiogenic coupling during bone regeneration has not been fully elucidated. In this study, we screened the targets of Si-CaP and osteogenic-angiogenic coupling. 83 common genes were regarded as key targets for Si-CaP regulation of the osteogenic-angiogenic coupling. Then, we performed protein-protein interaction analysis, GO and KEGG enrichment analysis of these 83 targets to further predict their molecular mechanism. Our results showed that Si-CaP treatment could regulate the osteogenic-angiogenic coupling by up-regulating the expression of Toll-like receptor 4 (TLR4), and the phosphorylation of AKT which in turn activating the PI3K/AKT signaling pathway, promoting the expression of RUNX2, OPN, VEGF. In addition, we also found that TLR4 siRNA treatment could block the PI3K/AKT signaling pathway, while inhibiting the promoting effect of Si-CaP. However, although LY294002 can achieve the same inhibitory effect as TLR4 siRNA by blocking the PI3K/AKT signaling pathway, it could not affect the expression of TLR4. This indicates that TLR4 is an upstream activator of PI3K/AKT signaling pathway. These results are highly consistent with the prediction of bioinformatics. In conclusion, we have elucidated the role of TLR4/PI3K/AKT signaling axis in Si-CaP mediated osteogenic-angiogenic coupling for the first time. This study provides new data onto the regulatory role and molecular mechanism of Si-CaP in the process of osteogenic-angiogenic coupling, which strongly supports its wide application for bone tissue engineering.

The CD133+CXCR4+ Colorectal Tumor Cells Promote Colorectal Cancer Progression by PI3K/AKT Signaling

Colorectal cancer (CRC) is one of the most common cancers in the world. Due to its preferential metastasis to the liver, CRC has become one of the leading causes of cancer-related deaths worldwide. There has evidence showing that a variety of subpopulations exist among cancer cells, which play an important role in liver metastasis. Growing evidence suggests that CD133 and C-X-C chemokine receptor type 4 (CXCR-4) are thought to contribute to cancer progression and metastasis. However, it has not been fully characterized in CRC. Here, we found that the expression of CD133 and CXCR4 in metastatic liver cancer tissues was higher than that of the primary tumor tissue and paratumor tissue. Furthermore, CD133⁺CXCR4⁺ cells were found to contribute to colorectal carcinogenesis and liver metastasis in vitro and in vivo. Moreover, CXCR4 blocked significantly inhibited the CD133⁺CXCR4⁺ cells metastatic to the liver in a mouse model. We also showed that CD133⁺CXCR4⁺ induced significant phosphorylation of PI3K/AKT. In conclusion, our data demonstrate that CD133⁺CXCR4⁺ cell subsets play an important role in the development and progression of colon cancer.

Separated parabiont reveals the fate and lifespan of peripheral-derived immune cells in normal and ischaemia-induced injured kidneys

Immune cell infiltration plays a key role in acute kidney injury (AKI) to chronic kidney disease (CKD) progression. T lymphocytes, neutrophils, monocytes/macrophages and other immune cells regulate inflammation, tissue remodelling and repair. To determine the kinetics of accumulation of various immune cell populations, we established an animal model combining parabiosis and separation surgery to explore the fate and lifespan of peripheral leucocytes that migrate to the kidney. We found that peripheral T lymphocytes could survive for a long time (more than 14 days), whereas peripheral neutrophils survived for a short time in both healthy and ischaemia-induced damaged kidneys. Nearly half of the peripheral-derived macrophages disappeared after 14 days in normal kidneys, while their existing time in the inflammatory kidneys was prolonged. A fraction of F4/80^high macrophages were renewed from the circulating monocyte pool. In addition, we found that after renal ischaemia reperfusion, neutrophils increased significantly in the early phase, and T lymphocytes mainly accumulated in the late stage, whereas macrophages infiltrated throughout AKI-CKD progression and were sustained longer in injured as opposed to normal kidneys. In conclusion, peripheral-derived macrophages, T lymphocytes and neutrophils exhibit different lifespans in the kidney, which may play different roles during AKI-CKD progression.

Exploring a Chemotactic Role for EVs from Progenitor Cell Populations of Human Exfoliated Deciduous Teeth for Promoting Migration of Naïve BMSCs in Bone Repair Process

Mobilization of naïve bone marrow mesenchymal stromal cells (BMSCs) is crucial to desired bone regeneration in both orthopedic and dental contexts. In such conditions, mesenchymal progenitor cell populations from human exfoliated deciduous teeth (SHEDs) present advantageous multipotent properties with easy accessibility which makes them a good candidate in both bone and periodontal tissue regeneration. Extracellular vesicles (EVs) are a functional membranous structure which could participate in multiple cell interactions and imitate the biological functions of their parenting cells largely. To assess their ability to mobilize naïve BMSCs in the bone repair process, Nanosight Tracking Analysis (NTA) and Enzyme-Linked Immunosorbent Assays (ELISA) were performed to illustrate the composition and functional contents of EV samples derived from SHEDs with different culturing time (24 h, 48 h, and 72 h). Afterwards, the Boyden chamber assay was performed to compare their capacity for mobilizing naïve BMSCs. One-way analysis of variance (ANOVA) with a post hoc Turkey test was performed for statistical analysis. SHEDs-derived EVs collected from 24 h, 48 h, and 72 h time points, namely, EV24, EV48, and EV72, were mainly secreted as exosomes and tended to reform into smaller size as a result of sonication indicated by NTA results. Moreover, different EV groups were found to be abundant with multiple growth factors including transforming growth factor-β1 (TGF-β1), platelet-derived growth factor (PDGF), insulin-like growth factor-1 (IGF-1), and fibroblast growth factor-2 (FGF-2) given the detections through ELISA. Boyden chamber assays implied the migratory efficiency of BMSCs driven by EVs at varying concentrations. However, the results showed that migration of BMSCs driven by different EV groups was not statistically significant even with chemotactic factors contained (P > 0.05). Taken together, these data suggest that EVs derived from SHEDs are secreted in functional forms and present a potential of mobilizing naïve BMSCs, which may propose their relevance in assisting bone regeneration.

The biological role of the CXCL12/CXCR4 axis in esophageal squamous cell carcinoma

Esophageal cancer is the eighth most common malignant tumor and the sixth leading cause of cancer-related death worldwide. Esophageal squamous cell carcinoma (ESCC) is the main histological type of esophageal cancer, and accounts for 90% of all cancer cases. Despite the progress made in surgery, chemotherapy, and radiotherapy, the mortality rate from esophageal cancer remains high, and the overall 5-year survival rate is less than 20%, even in developed countries. The C-X-C motif chemokine ligand 12 (CXCL12) is a member of the CXC chemokine subgroup, which is widely expressed in a variety of tissues and cells. CXCL12 participates in the regulation of many physiological and pathological processes by binding to its specific receptor, C-X-C motif chemokine receptor type 4 (CXCR4), where it causes embryonic development, immune response, and angiogenesis. In addition, increasing evidence indicates that the CXCL12/CXCR4 axis plays an important role in the biological processes of tumor cells. Studies have shown that CXCL12 and its receptor, CXCR4, are highly expressed in ESCC. This abnormal expression contributes to tumor proliferation, lymph node and distant metastases, and worsening prognosis. At present, antagonists and imaging agents against CXCL12 or CXCR4 have been developed to interfere with the malignant process and monitor metastasis of tumors. This article summarizes the structure, function, and regulatory mechanism of CXCL12/CXCR4 and its role in the malignancy of ESCC. Current results from preclinical research targeting CXCL12/CXCR4 are also summarized to provide a reference for the clinical diagnosis and treatment of ESCC.

The negative charge of the 343 site is essential for maintaining physiological functions of CXCR4

BACKGROUND

Warts, hypogammaglobulinemia, recurrent bacterial infections and myelokathexis (WHIM) syndrome is a primary immunodeficiency disease (PID) usually caused by autosomal dominant mutations in the chemokine receptor CXCR4 gene. To date, a total of nine different mutations including eight truncation mutations and one missense mutation (E343K, CXCR4^E343K) distributed in the C-terminus of CXCR4 have been identified in humans. Studies have clarified that the loss of phosphorylation sites in the C-terminus of truncated CXCR4 impairs the desensitization process, enhances the activation of G-protein, prolongs downstream signaling pathways and introduces over immune responses, thereby causing WHIM syndrome. So far, there is only one reported case of WHIM syndrome with a missense mutation, CXCR4^E343K, which has a full length of C-terminus with entire phosphorylation sites, no change in all potential phosphorylation sites. The mechanism of the missense mutation (CXCR4^E343K) causing WHIM syndrome is unknown. This study aimed to characterize the effect of mutation at the 343 site of CXCR4 causing the replacement of arginine/E with glutamic acid/K on the receptor signal transduction, and elucidate the mechanism underling CXCR4^E343K causing WHIM in the reported family.

RESULTS

We completed a series of mutagenesis to generate different mutations at the 343 site of CXCR4 tail, and established a series of HeLa cell lines stably expressing CXCR4^WT or CXCR4^E343D (glutamic acid/E replaced with aspartic acid/D) or CXCR4^E343K (glutamic acid/E replaced with lysine/K) or CXCR4^E343R (glutamic acid/E replaced with arginine/R) or CXCR4^E343A (glutamic acid/E replaced with alanine/A) and then systematically analyzed functions of the CXCR4 mutants above. Results showed that the cells overexpressing of CXCR4^E343D had no functional changes with comparison that of wild type CXCR4. However, the cells overexpressing of CXCR4^E343K or CXCR4^E343R or CXCR4^E343A had enhanced cell migration, prolonged the phosphorylation of ERK1/2, p38, JNK1/2/3, aggravated activation of PI3K/AKT/NF-κB signal pathway, introduced higher expression of TNFa and IL6, suggesting over immune response occurred in CXCR4 mutants with charge change at the 343 site of receptor tail, as a result, causing WHIM syndrome. Biochemical analysis of those mutations at the 343 site of CXCR4 above shows that CXCR4 mutants with no matter positive or neutral charge have aberrant signal pathways downstream of activated mutated CXCR4, only CXVR4 with negative charge residues at the site shows normal signal pathway post activation with stromal-derived factor (SDF1, also known as CXCL12).

CONCLUSION

Taken together, our results demonstrated that the negative charge at the 343 site of CXCR4 plays an essential role in regulating the down-stream signal transduction of CXCR4 for physiological events, and residue charge changes, no matter positive or neutral introduce aberrant activities and functions of CXCR4, thus consequently lead to WHIM syndrome.

Effects of Edaravone on Functional Recovery of a Rat Model with Spinal Cord Injury Through Induced Differentiation of Bone Marrow Mesenchymal Stem Cells into Neuron-Like Cells

Edaravone can induce differentiation of bone marrow mesenchymal stem cells (BMSCs) into neuron-like cells and replace lost cells by transplanting neuron-like cells to repair spinal cord injury (SCI). In this study, BMSCs were derived from the bone marrow of male Wistar rats (4 weeks old) through density gradient centrifugation (1.073 g/mL), and the cell purity of BMSCs was up to 95%. The combined injection of basic fibroblast growth factor and edaravone was conducted to differentiate BMSCs into neuron-like cells. In this study, 120 male Wistar rats were used to establish the model of semitransverse SCI; on the seventh day, neuron-like cells were labeled by BrdU and then injected into the epicenter of the injury of rats. On the 14th day after cell transplantation, the biotin dextran amine (BDA) fluorescent agent was used to track the repair of nerve damage. At 7, 14, 21, and 30 days after SCI, the Basso, Beattie, and Bresnahan (BBB) locomotor scale method was used to measure the functional recovery of hind limbs in rats. Additionally, hematoxylin and eosin (H&E) staining, Nissl staining, immunohistochemistry, transmission electron microscopy (TEM), Western blotting, and Real-time quantitative reverse transcripion PCR (qRT-PCR) were used to observe the regeneration of nerve cells. In the edaravone+BMSC group, behavioral analysis of locomotor function showed that functional recovery was significantly enhanced after transplantation of the cells, BrdU-positive cells could be observed scattered in the injured area and extended to both the head and tail, and the BDA tracer shows that the edaravone+BMSC group emits more fluorescent signals. Additionally, H&E staining, Nissl staining, and immunohistochemistry revealed that the space of spinal cord tissue was attenuated and the neurons were increased. Western blotting and qRT-PCR showed that the expression levels of neuron-specific enolase (NSE), Nestin, and neurofilament 200 (NF) were increased, while the expression of glial fibrillary acidic protein (GFAP) was decreased. TEM showed that cytoplasmic edema was reduced, mitochondrial vacuoles were attenuated, and nuclear chromatin concentration was declined after transplantation of neuron-like cells. Moreover, with the extension of time of edaravone+BMSC transplantation, the structures of mitochondria and endoplasmic reticulum tended to be normal. In summary, the induced differentiation of BMSC transplantation can significantly promote the functional repair of SCI.

Mesenchymal Stem Cells Attract Endothelial Progenitor Cells via a Positive Feedback Loop between CXCR2 and CXCR4

Mesenchymal stem cells (MSCs) can attract host endothelial progenitor cells (EPCs) to promote vascularization in tissue-engineered constructs (TECs). Nevertheless, the underlying mechanism remains vague. This study is aimed at investigating the roles of CXCR2 and CXCR4 in the EPC migration towards MSCs. In vitro, Transwell assays were performed to evaluate the migration of EPCs towards MSCs. Antagonists and shRNAs targeting CXCR2, CXCR4, and JAK/STAT3 were applied for the signaling blockade. Western blot and RT-PCR were conducted to analyze the molecular events in EPCs. In vivo, TECs were constructed and subcutaneously implanted into GFP⁺ transgenic mice. Signaling inhibitors were injected in an orientated manner into TECs. Recruitment of host CD34⁺ cells was evaluated by immunofluorescence. Eventually, we demonstrated that CXCR2 and CXCR4 were both highly expressed in migrated EPCs and indispensable for MSC-induced EPC migration. CXCR2 and CXCR4 strongly correlated with each other in the way that the expression of CXCR2 and CXCR2-mediated migration depends on the activity of CXCR4 and vice versa. Further studies documented that both of CXCR2 and CXCR4 activated STAT3 signaling, which in turn regulated the expression of CXCR2 and CXCR4, as well as cell migration. In summary, we firstly introduced a reciprocal crosstalk between CXCR2 and CXCR4 in the context of EPC migration. This feedback loop plays critical roles in the migration of EPCs towards MSCs.