G-CSF Indirectly Induces Apoptosis of Osteoblasts During Hematopoietic Stem Cell Mobilization

Innovations in hematopoietic stem-cell mobilization: a review of the novel CXCR4 inhibitor motixafortide

Hematopoietic stem-cell transplantation (HCT) and stem-cell-based gene therapies rely on the ability to collect sufficient CD34+ hematopoietic stem and progenitor cells (HSPCs), typically via peripheral blood mobilization. Commonly used HSPC mobilization regimens include single-agent granulocyte colony-stimulating factor (G-CSF), plerixafor, chemotherapy, or a combination of these agents. These regimens, however, frequently require multiple days of injections and leukapheresis procedures to collect adequate HSPCs for HCT (minimum = >2 × 106 CD34+ cells/kg; optimal = 5-6 × 106 CD34+ cells/kg). In addition, these regimens frequently yield suboptimal CD34+ HSPC numbers for HSPC-based gene-edited therapies, given the significantly higher HSPC number needed for successful gene-editing and manufacturing. Meanwhile, G-CSF is associated with common adverse events such as bone pain as well as an increased risk of rare but potentially life-threatening splenic rupture. Moreover, G-CSF is unsafe in patients with sickle-cell disease, a key patient population that may benefit from autologous HSPC-based gene-edited therapies, where it has been associated with unacceptable rates of serious vaso-occlusive and thrombotic events. Motixafortide is a novel CXCR4 inhibitor with extended in vivo activity (>48 h) that has been shown in preclinical and clinical trials to rapidly mobilize robust numbers of HSPCs in preparation for HCT, while preferentially mobilizing increased numbers of more primitive HSPCs by immunophenotyping and single-cell RNA expression profiling. In this review, we present a history of stem-cell mobilization and update of recent innovations in novel mobilization strategies with a specific focus on the development of motixafortide, a long-acting CXCR4 inhibitor, as a novel HSPC mobilizing agent.

G‑CSF delays tooth extraction socket bone healing via the inhibition of bone turnover in mice

Granulocyte colony-stimulating factor (G-CSF) regulates the survival, proliferation and differentiation of all cells in the neutrophil lineage, and is consequently used for neutropenic conditions. Upon G-CSF administration, osteoblasts and osteocytes are suppressed, and the support system allowing hematopoietic stem cells to remain in the microenvironment is diminished. The present study focused on and investigated G-CSF as a regulatory factor of bone remodeling. The aim of the present study was to investigate the effect of G-CSF administration on the bone healing of tooth extraction sockets. Significant differences in the bone volume fraction, and trabecular separation of the proximal femurs and alveolar septa were observed between the G-CSF and control (saline-treated) groups. The trabecular bone of the femur and alveolar septa was reduced in the G-CSF group compared with that in the control group. In addition, serum procollagen type 1 N-terminal propeptide levels, a marker of bone formation, were lower in the G-CSF group compared with in the control group. Fibrous connective tissues and immature bone were observed in the extraction socket, and bone healing was delayed in the G-CSF group compared with that in the control group. The bone area in the extraction socket 6 days after tooth extraction was significantly smaller in the G-CSF group (23.6%) than that in the control group (45.1%). Furthermore, G-CSF administration reduced the number of canaliculi per osteocyte and inhibited the connection of osteocyte networks. Consequently, osteoblast activation was inhibited and bone remodeling changed to a state of low bone turnover in the G-CSG group. Analysis of bone formation parameters revealed that the G-CSF group exhibited a lower mineral apposition rate compared with in the control group. In conclusion, these findings indicated that G-CSF may delay bone healing of the socket after tooth extraction.

Granulocyte colony-stimulating factor (G-CSF) mediates bone resorption in periodontitis

Background

Granulocyte colony-stimulating factor (G-CSF) is an important immune factor that mediates bone metabolism by regulating the functions of osteoclasts and osteoblasts. Bone loss is a serious and progressive result of periodontitis. However, the mechanisms underlying the effects of G-CSF on periodontal inflammation have yet not been completely elucidated. Here, we examined whether an anti-G-CSF antibody could inhibit bone resorption in a model of experimental periodontitis and investigated the local expression of G-CSF in periodontal tissues.

Methods

Experimental periodontitis was induced in mice using ligatures. The levels of G-CSF in serum and bone marrow were measured; immunofluorescence was then performed to analyze the localization and expression of G-CSF in periodontal tissues. Mice with periodontitis were administered anti-G-CSF antibody by tail vein injection to assess the inhibition of bone resorption. Three-dimensional reconstruction was performed to measure bone destruction‐related parameters via micro-computed tomography analysis. Immunofluorescence staining was used to investigate the presence of osteocalcin-positive osteoblasts; tartrate-resistant acid phosphatase (TRAP) staining was used to observe osteoclast activity in alveolar bone.

Results

The level of G-CSF in serum was significantly elevated in mice with periodontitis. Immunofluorescence analyses showed that G-CSF was mostly expressed in the cell membrane of gingival epithelial cells; this expression was enhanced in the periodontitis group. Additionally, systemic administration of anti-G-CSF antibody significantly inhibited alveolar bone resorption, as evidenced by improvements in bone volume/total volume, bone surface area/bone volume, trabecular thickness, trabecular spacing, and trabecular pattern factor values. Immunofluorescence analysis revealed an enhanced number of osteocalcin-positive osteoblasts, while TRAP staining revealed reduction of osteoclast activity.

Conclusions

G-CSF expression levels were significantly up-regulated in the serum and gingival epithelial cells. Together, anti-G-CSF antibody administration could alleviates alveolar bone resorption, suggesting that G-CSF may be one of the essential immune factors that mediate the bone loss in periodontitis.

Insensitive to PTH of CD8+ T cells regulate bone marrow mesenchymal stromal cell in aplastic anemia patients

Aplastic anemia (AA) is a rare disorder characterized by the suppression of bone marrow function resulting in progressive pancytopenia. The pathogenesis of AA is complex and involves an abnormal hematopoietic microenvironment, hematopoietic stem cell/progenitor cell deficiencies, and immunity disorders. However, the underlying mechanism of the disease is still not fully uncovered. In this research, we collected both donor and patient samples and found suppressed proliferation, abnormal differentiation as well as increased apoptosis of patient mesenchymal stem cells (MSCs). Considering the close relationship of parathyroid hormone (PTH) and MSCs differentiation, further studies showed that although patients maintained normal serum PTH level, their CD8⁺ T cells possessed lower PTH receptors. The insensitive to PTH of patients' CD8⁺ T cells finally lead to reduced expression of key Wnt factors. In all, bone marrow CD8⁺ T cells may play an important role in inducing MSCs adipogenesis and osteogenesis imbalancement.

Effect of lipopolysaccharide derived from surabaya isolates of Actinobacillus actinomycetemcomitans on alveolar bone destruction

Background:

Actinobacillus actinomycetemcomitans’ lipopolysaccharide (LPS) has a high virulence factor. It interacts with serum protein through receptors on the epithelial cell surface, thereby increasing both interleukin (IL)-1β, and IL-6 which results in damage to periodontal tissue.

Aim:

The aim of the study was to identify and evaluate the effect of LPS derived from local isolates (A. actinomycetemcomitans) on the destruction of alveolar bone by means of several biomarkers, including; the number of osteoblasts and osteoclasts, the expression of IL-6, matrix metallopeptidase 1 (MMP-1), and receptor activator of nuclear factor kappa-Β ligand (RANKL).

Materials and Methods:

The isolation of LPS from A. actinomycetemcomitans was calculated using phenol, while purification was performed using Sephadex C-18 column chromatography. 40 Wistar rats were divided into four groups of 10. Each treatment was divided into two groups which were 0.9% NaCl and LPS induced for 7 and 14 days, respectively. Gingival and alveolar bones were further introduced into the induction area, followed by the measuring of osteoblast and osteoclast with hematoxylin-eosin staining, IL-6, MMP-1 and RANKL expression with immunohistochemical.

Results:

Reduced numbers of osteoblasts at the 7^th and 14^th day of treatment were detected, while those of osteoclasts increased. There was an increased expression of IL-6, MMP-1, and RANKL in the 7^th and 14^th-day treatment group. Treatment of LPS from A. actinomycetemcomitans over 7 and 14 days resulted in damage to periodontal tissue and alveolar bone in Wistar rats.

Conclusion:

LPS of A. actinomycetemcomitans administration for 7 and 14 days causes periodontal and alveolar tissue destruction in Wistar rats.