Hematopoietic cell regulation of osteoblast proliferation and differentiation

Lineage Differentiation Potential of Different Sources of Mesenchymal Stem Cells for Osteoarthritis Knee

Tissue engineering and regenerative medicine (TERM) have paved a way for treating musculoskeletal diseases in a minimally invasive manner. The regenerative medicine cocktail involves the usage of mesenchymal stem/stromal cells (MSCs), either uncultured or culture-expanded cells along with growth factors, cytokines, exosomes, and secretomes to provide a better regenerative milieu in degenerative diseases. The successful regeneration of cartilage depends on the selection of the appropriate source of MSCs, the quality, quantity, and frequency of MSCs to be injected, and the selection of the patient at an appropriate stage of the disease. However, confirmation on the most favorable source of MSCs remains uncertain to clinicians. The lack of knowledge in the current cellular treatment is uncertain in terms of how beneficial MSCs are in the long-term or short-term (resolution of pain) and improved quality of life. Whether MSCs treatments have any superiority, exists due to sources of MSCs utilized in their potential to objectively regenerate the cartilage at the target area. Many questions on source and condition remain unanswered. Hence, in this review, we discuss the lineage differentiation potentials of various sources of MSCs used in the management of knee osteoarthritis and emphasize the role of tissue engineering in cartilage regeneration.

Сord blood hematopoietic stem cells ex vivo enhance the bipotential commitment of adipose mesenchymal stromal progenitors

AIMS

Stroma-dependent ex vivo expansion of hematopoietic stem progenitor cells (HSPCs) is a valid approach for cell therapy needs. Our goal was to verify whether HSPCs can affect stromal cells to optimize their functions during ex vivo expansion.

MAIN METHODS

HSPCs from cord blood (cb) were cocultured with growth-arrested adipose mesenchymal stromal cells (MSCs). Commitment-related transcriptional and secretory profiles as well as hematopoiesis-supportive activity of intact and osteo-induced MSCs were examined.

KEY FINDINGS

During expansion, cbHSPCs affected the functional state of MSCs, contributing to the formation of early stromal progenitors with a bipotential osteo-adipogenic profile. This was evidenced by the upregulation of certain MSC genes of osteo- and adipodifferentiation (ALPL, RUNX2, BGLAP, CEBPA, ADIPOQ), as well as by elevated alkaline phosphatase activity and altered osteoprotein patterns. Joint paracrine profiles upon coculture were characterized by a balance of "positive" (GM-SCF) and "negative" (IP-10, MIP-1α, MCP-3) myeloid regulators, effectively supporting expansion of both committed and primitive cbHSPCs. Short-term (72 h) osteoinduction prior to coculture resulted in more pronounced shift of the bipotential transcriptomic and osteoprotein profiles. The increased proportions of late primitive CD133^-/CD34⁺cbHSPCs and unipotent CFUs suggested that cbHSPCs after expansion on osteo-MSCs were more committed versus cbHSPCs from coculture with non-differentiated MSCs.

SIGNIFICANCE

During ex vivo expansion, cbHSPCs can drive the bipotential osteo-adipogenic commitment of MSCs, providing a specific hematopoiesis-supportive milieu. Short-term preliminary osteo-induction enhanced the development of the bipotential profile, leading to more pronounced functional polarization of cbHSPCs, which may be of interest in an applied context.

Deterioration of hematopoietic autophagy is linked to osteoporosis

Hematopoietic disorders are known to increase the risk of complications such as osteoporosis. However, a direct link between hematopoietic cellular disorders and osteoporosis has been elusive. Here, we demonstrate that the deterioration of hematopoietic autophagy is coupled with osteoporosis in humans. With a conditional mouse model in which autophagy in the hematopoietic system is disrupted by deletion of the Atg7 gene, we show that incapacitating hematopoietic autophagy causes bone loss and perturbs osteocyte homeostasis. Induction of osteoporosis, either by ovariectomy, which blocks estrogen secretion, or by injection of ferric ammonium citrate to induce iron overload, causes dysfunction in the hematopoietic stem and progenitor cells (HSPCs) similar to that found in autophagy‐defective mice. Transcriptomic analysis of HSPCs suggests promotion of iron activity and inhibition of osteocyte differentiation and calcium metabolism by hematopoietic autophagy defect, while proteomic profiling of bone tissue proteins indicates disturbance of the extracellular matrix pathway that includes collagen family members. Finally, screening for expression of selected genes and an immunohistological assay identifies severe impairments in H vessels in the bone tissue, which results in disconnection of osteocytes from hematopoietic cells in the autophagy‐defective mice. We therefore propose that hematopoietic autophagy is required for the integrity of H vessels that bridge blood and bone cells and that its deterioration leads to osteoporosis.

Phosphate glass fibers facilitate proliferation and osteogenesis through Runx2 transcription in murine osteoblastic cells

Cell-material interactions and compatibility are important aspects of bioactive materials for bone tissue engineering. Phosphate glass fiber (PGF) is an attractive inorganic filler with fibrous structure and tunable composition, which has been widely investigated as a bioactive filler for bone repair applications. However, the interaction of osteoblasts with PGFs has not been widely investigated to elucidate the osteogenic mechanism of PGFs. In this study, different concentrations of short PGFs with interlaced oriented topography were cocultured with MC3T3-E1 cells for different periods, and the synergistic effects of fiber topography and ionic product of PGFs on osteoblast responses including cell adhesion, spreading, proliferation, and osteogenic differentiation were investigated. It was found that osteoblasts were more prone to adhere on PGFs through Vinculin protein, leading to enhanced cell proliferation with polygonal cell shape and spreading cellular actin filaments. In addition, osteoblasts incubated on PGF meshes showed enhanced alkaline phosphatase activity, extracellular matrix mineralization, and increased expression of osteogenesis-related marker genes, which could be attributed to the Wnt/β-catenin/Runx2 signaling pathway. This study elucidated the possible mechanism of PGF on triggering specific osteoblast behavior, which would be highly beneficial for designing PGF-based bone graft substitutes with excellent osteogenic functions.

Pharmacological and transcriptome profiling analyses of Fufang E'jiao Jiang during chemotherapy-induced myelosuppression in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Fufang E'jiao Jiang (FEJ), a famous traditional Chinese medicine formula from "Liangyi Ointment", consists of five crude drugs, Colla corii asini, Radix Ginseng Rubra, Radix Rehmanniae Preparata, Codonopsis pilosula, and Crataegus pinnatifida Bge. It has pronounced functions of qi-nourishing and blood-activating. Recently, it has been widely used in China as a medication against myelosuppression in cancer treatment.

AIM OF THE STUDY

We aimed to investigate the complex mode of action and underlying mechanisms of Fufang E'jiao Jiang (FEJ) regarding its hematopoietic effect.

MAIN METHODS

Mice were divided into 5 groups of control, model, high dose FEJ (HFEJ), medium dose FEJ (MFEJ) and low dose FEJ (LFEJ). After 10 days from the administration, bone marrow cells (BMCs) were extracted for nucleated cells counts, flow cytometry analysis of hematopoietic stem cells (HSCs) population, as well as hematopoietic progenitor cells (HPCs) colony-forming unit (CFU) assay. A portion of bone marrow nucleated cells (BMNCs) of MFEJ group were prepared for RNA sequencing (RNA-Seq). The transcriptome data were analyzed based on the differentially expressed genes (DEGs). The molecular mechanisms of FEJ were deducted based on the biological processes and protein-protein interaction (PPI) network.

RESULTS

FEJ could significantly increase the percentage of HSCs and the quantities of BFU-E and CFU-GM in BMSCs. FEJ could stimulate the proliferation of HSC and the differentiation of HPC to all lineages, which may thereby accelerate the recovery of hematopoietic function in myelosuppressive mice. By providing transcriptome profile we highlighted several genes and biological processes that might be applicable for FEJ to treat chemotherapy-induced myelosuppression. GO analysis showed that the co-expressed DEGs in FEJ vs model and model vs control group were involved in biological processes including ossification, osteoblast differentiation, bone mineralization and bone development. The KEGG pathway analysis pointed out ECM-receptor interaction and PI3K-AKT signaling pathway as the most relevant pathways to the function of FEJ on myelosuppression. PPI network showed MMP2 and COL1A1 were the relatively large nodes.

CONCLUSION

FEJ has the hematopoietic effect in chemotherapy-induced myelosuppression mice. It might be achieved by improving the proliferative capacity of HSCs and the differentiation ability of HPCs. The molecular mode of action of FEJ might be the improvement of the bone marrow microenvironment via ECM-receptor interaction, the promoted proliferation of HSC through regulation of PI3K-AKT signaling pathway, and the involvement of osteoblasts and osteoclasts. MMP2 and COL1A1 appear to be the key relevant regulatory molecules. These results provide significant insight into the hematopoietic effects of FEJ in myelosuppression and point out novel targets for future validating analyses.

Long-term selective estrogen receptor-beta agonist treatment modulates gene expression in bone and bone marrow of ovariectomized rats

Gonadal hormones including 17β-estradiol exert important protective functions in skeletal homeostasis. However, numerous details of ovarian hormone deficiency in the common bone marrow microenvironment have not yet been revealed and little information is available on the tissue-specific acts either, especially those via estrogen receptor beta (ERβ). The aim of the present study was therefore to examine the bone-related gene expression changes after ovariectomy (OVX) and long-term ERβ agonist diarylpropionitrile (DPN) administration. We found that OVX produced strong and widespread changes of gene expression in both femoral bone and bone marrow. In the bone out of 22 genes, 20 genes were up- and 2 were downregulated after OVX. It is noteworthy that DPN restored mRNA expression of 10 OVX-induced changes (Aldh2, Col1a1, Daam1, Fgf12, Igf1, Il6r, Nfkb1, Notch1, Notch2 and Psen1) suggesting a modulatory role of ERβ in bone physiology. In bone marrow, out of 37 categorized genes, transcription of 25 genes were up- and 12 were downregulated indicating that the marrow is highly responsive to gonadal hormones. DPN modestly affected transcription, only expression of two genes (Nfatc1 and Tgfb1) was restored by DPN action. The PI3K/Akt signaling pathway was the most affected gene cluster following the interventions in bone and bone marrow, as demonstrated by canonical variates analysis (CVA). We suggested that our results contribute to a deeper understanding of alterations in gene expression of bone and bone marrow niche elicited by ERβ and selective ERβ analogs.

Direct conversion of human fibroblasts into functional osteoblasts by defined factors

Osteoblasts produce calcified bone matrix and contribute to bone formation and remodeling. In this study, we established a procedure to directly convert human fibroblasts into osteoblasts by transducing some defined factors and culturing in osteogenic medium. Osteoblast-specific transcription factors, Runt-related transcription factor 2 (Runx2), and Osterix, in combination with Octamer-binding transcription factor 3/4 (Oct4) and L-Myc (RXOL) transduction, converted ∼ 80% of the fibroblasts into osteocalcin-producing cells. The directly converted osteoblasts (dOBs) induced by RXOL displayed a similar gene expression profile as normal human osteoblasts and contributed to bone repair after transplantation into immunodeficient mice at artificial bone defect lesions. The dOBs expressed endogenous Runx2 and Osterix, and did not require continuous expression of the exogenous genes to maintain their phenotype. Another combination, Oct4 plus L-Myc (OL), also induced fibroblasts to produce bone matrix, but the OL-transduced cells did not express Osterix and exhibited a more distant gene expression profile to osteoblasts compared with RXOL-transduced cells. These findings strongly suggest successful direct reprogramming of fibroblasts into functional osteoblasts by RXOL, a technology that may provide bone regeneration therapy against bone disorders.

Acute exposure to high dose γ-radiation results in transient activation of bone lining cells

The present studies investigated the cellular mechanisms for the detrimental effects of high dose whole body γ-irradiation on bone. In addition, radioadaptation and bone marrow transplantation were assessed as interventions to mitigate the skeletal complications of irradiation. Increased trabecular thickness and separation and reduced cancellous bone volume fraction, connectivity density, and trabecular number were detected in proximal tibia and lumbar vertebra 14days following γ-irradiation with 6Gy. To establish the cellular mechanism for the architectural changes, vertebrae were analyzed by histomorphometry 1, 3, and 14days following irradiation. Marrow cell density decreased within 1day (67% reduction, p<0.0001), reached a minimum value after 3days (86% reduction, p<0.0001), and partially rebounded by 14days (30% reduction, p=0.0025) following irradiation. In contrast, osteoblast-lined bone perimeter was increased by 290% (1day, p=0.04), 1230% (3days, p<0.0001), and 530% (14days, p=0.003), respectively. There was a strong association between radiation-induced marrow cell death and activation of bone lining cells to express the osteoblast phenotype (Pearson correlation -0.85, p<0.0001). An increase (p=0.004) in osteoclast-lined bone perimeter was also detected with irradiation. A priming dose of γ-radiation (0.5mGy), previously shown to reduce mortality, had minimal effect on the cellular responses to radiation and did not prevent detrimental changes in bone architecture. Bone marrow transplantation normalized marrow cell density, bone turnover, and most indices of bone architecture following irradiation. In summary, radiation-induced death of marrow cells is associated with 1) a transient increase in bone formation due, at least in part, to activation of bone lining cells, and 2) an increase in bone resorption due to increased osteoclast perimeter. Bone marrow transplantation is effective in mitigating the detrimental effects of acute exposure to high dose whole body γ-radiation on bone turnover.

Differential stem- and progenitor-cell trafficking by prostaglandin E2

To maintain lifelong production of blood cells, hematopoietic stem cells (HSC) are tightly regulated by inherent programs and extrinsic regulatory signals received from their microenvironmental niche. Long-term repopulating HSC (LT-HSC) reside in several, perhaps overlapping, niches that produce regulatory molecules/signals necessary for homeostasis and increased output following stress/injury ^1–5. Despite significant advances in specific cellular or molecular mechanisms governing HSC/niche interactions, little is understood about regulatory function within the intact mammalian hematopoietic niche. Recently, we and others described a positive regulatory role for Prostaglandin E₂ (PGE₂) on HSC function ex vivo^6,7. While exploring the role of endogenous PGE₂ we unexpectedly observed hematopoietic egress after nonsteroidal anti-inflammatory drug (NSAID) treatment. Surprisingly, this was independent of the SDF-1/CXCR4 axis. Stem and progenitor cells were found to have differing mechanisms of egress, with HSC transit to the periphery dependent on niche attenuation and reduction in the retentive molecule osteopontin (OPN). Hematopoietic grafts mobilized with NSAIDs had superior repopulating ability and long-term engraftment. Treatment of non-human primates and healthy human volunteers confirmed NSAID-mediated egress in higher species. PGE₂ receptor knockout mice demonstrated that progenitor expansion and stem/progenitor egress resulted from reduced EP4 receptor signaling. These results not only uncover unique regulatory roles for EP4 signaling in HSC retention in the niche but also define a rapidly translatable strategy to therapeutically enhance transplantation.

Megakaryocytes regulate expression of Pyk2 isoforms and caspase-mediated cleavage of actin in osteoblasts

The proliferation and differentiation of osteoblast (OB) precursors are essential for elaborating the bone-forming activity of mature OBs. However, the mechanisms regulating OB proliferation and function are largely unknown. We reported that OB proliferation is enhanced by megakaryocytes (MKs) via a process that is regulated in part by integrin signaling. The tyrosine kinase Pyk2 has been shown to regulate cell proliferation and survival in a variety of cells. Pyk2 is also activated by integrin signaling and regulates actin remodeling in bone-resorbing osteoclasts. In this study, we examined the role of Pyk2 and actin in the MK-mediated increase in OB proliferation. Calvarial OBs were cultured in the presence of MKs for various times, and Pyk2 signaling cascades in OBs were examined by Western blotting, subcellular fractionation, and microscopy. We found that MKs regulate the temporal expression of Pyk2 and its subcellular localization. We also found that MKs regulate the expression of two alternatively spliced isoforms of Pyk2 in OBs, which may regulate OB differentiation and proliferation. MKs also induced cytoskeletal reorganization in OBs, which was associated with the caspase-mediated cleavage of actin, an increase in focal adhesions, and the formation of apical membrane ruffles. Moreover, BrdU incorporation in MK-stimulated OBs was blocked by the actin-polymerizing agent, jasplakinolide. Collectively, our studies reveal that Pyk2 and actin play an important role in MK-regulated signaling cascades that control OB proliferation and may be important for therapeutic interventions aimed at increasing bone formation in metabolic diseases of the skeleton.

Neoplastic bone marrow niche: hematopoietic and mesenchymal stem cells

The neoplastic niche comprises complex interactions between multiple cell types and molecules requiring cell-cell signaling as well as local secretion. These niches are important for both the maintenance of cancer stem cells and the induction of neoplastic cells survival and proliferation. Each niche contains a population of tumor stem cells supported by a closely associated vascular bed comprising mesenchyme-derived cells and extracellular matrix. Targeting cancer stem cells and neoplastic niche may provide new therapies to eradicate tumors. Much progress has been very recently made in the understanding of the cellular and molecular interactions in the microenvironment of neoplastic niches. This review article provides an overview of the neoplastic niches in the bone marrow. In addition to highlighting recent advances in the field, we will also discuss components of the niche and their signaling pathways.