A practical guide to culturing mouse and human bone marrow stromal cells

Bone marrow stromal cell-derived hepcidin has antimicrobial and immunomodulatory activities

Bone marrow stromal cells (BMSCs) have immunomodulatory activities in numerous species and have been used in clinical trials. BMSCs also make antibacterial agents. Since hepcidin is known to have antimicrobial effects in fish, we wondered if it might also be used as an antimicrobial agent by mammalian BMSCs. In the present study, we show hepcidin expression in both mouse (mBMSC) and human BMSCs (hBMSC). We observed a hBMSC hepcidin-dependent degradation of ferroportin in HEK-293 reporter cells in vitro. In human and mouse bone marrows (BM) we detected hepcidin-positive BMSCs in close proximity to hematopoietic progenitors. The conditioned culture medium of hBMSCs significantly reduced bacterial proliferation that was partially blocked by a hepcidin-neutralizing antibody. Similarly, medium in which hepcidin-deficient (Hamp-/-) mouse BMSCs had been grown was significantly less effective in reducing bacterial counts than the medium of wild-type cells. In a zymosan-induced peritonitis mouse model we found that mBMSC-derived hepcidin reduced the number of invading polymorphonuclear (PMN) cells in the peritoneal cavity. Our results show that BMSC-derived hepcidin has antimicrobial properties in vitro and also reduces inflammation in vivo. We conclude that hepcidin should be added to the expanding arsenal of agents available to BMSCs to fight infections and inflammation.

An inducible explant model of osteoclast-osteoprogenitor coordination in exacerbated osteoclastogenesis

Elucidating a basic blueprint of osteoclast-osteoblast coordination in skeletal remodeling and understanding how this coordination breaks down with age and disease is essential for addressing the growing skeletal health problem in our aging population. The paucity of simple, activatable, biologically relevant models of osteoclast-osteoblast coordination has hindered our understanding of how skeletal remolding is regulated. Here, we describe an inducible ex vivo model of osteoclast-osteoblast progenitor coordination. Induction activates the release of osteoclastogenic factors from osteoprogenitors, which elicits the differentiation and fusion of neighboring preosteoclasts. In turn, multinucleated osteoclasts release soluble coupling factors, RANK⁺ extracellular vesicles and promote osteoprogenitor proliferation, recapitulating aspects of perturbed coordination in diseases underpinned by excessive osteoclast formation. We expect this model to expedite the investigation of cell-cell fusion, osteoclast-osteoblast progenitor coordination, and extracellular vesicle signaling during bone remodeling and offer a powerful tool for evaluating signaling cascades and novel therapeutic interventions in osteoclast-linked skeletal disease.

Stromal Co-Cultivation for Modeling Breast Cancer Dormancy in the Bone Marrow

Cancers metastasize to the bone marrow before primary tumors can be detected. Bone marrow micrometastases are resistant to therapy, and while they are able to remain dormant for decades, they recur steadily and result in incurable metastatic disease. The bone marrow microenvironment maintains the dormancy and chemoresistance of micrometastases through interactions with multiple cell types and through structural and soluble factors. Modeling dormancy in vitro can identify the mechanisms of these interactions. Modeling also identifies mechanisms able to disrupt these interactions or define novel interactions that promote the reawakening of dormant cells. The in vitro modeling of the interactions of cancer cells with various bone marrow elements can generate hypotheses on the mechanisms that control dormancy, treatment resistance and reawakening in vivo. These hypotheses can guide in vivo murine experiments that have high probabilities of succeeding in order to verify in vitro findings while minimizing the use of animals in experiments. This review outlines the existing data on predominant stromal cell types and their use in 2D co-cultures with cancer cells.

G protein-coupled receptor kinase 3 modulates mesenchymal stem cell proliferation and differentiation through sphingosine-1-phosphate receptor regulation

BACKGROUND

The bone marrow niche supports hematopoietic cell development through intimate contact with multipotent stromal mesenchymal stem cells; however, the intracellular signaling, function, and regulation of such supportive niche cells are still being defined. Our study was designed to understand how G protein receptor kinase 3 (GRK3) affects bone marrow mesenchymal stem cell function by examining primary cells from GRK3-deficient mice, which we have previously published to have a hypercellular bone marrow and leukocytosis through negative regulation of CXCL12/CXCR4 signaling.

METHODS

Murine GRK3-deficient bone marrow mesenchymal stromal cells were harvested and cultured to differentiate into three lineages (adipocyte, chondrocyte, and osteoblast) to confirm multipotency and compared to wild type cells. Immunoblotting, modified-TANGO experiments, and flow cytometry were used to further examine the effects of GRK3 deficiency on bone marrow mesenchymal stromal cell receptor signaling. Microcomputed tomography was used to determine trabecular and cortical bone composition of GRK3-deficient mice and standard ELISA to quantitate CXCL12 production from cellular cultures.

RESULTS

GRK3-deficient, bone marrow-derived mesenchymal stem cells exhibit enhanced and earlier osteogenic differentiation in vitro. The addition of a sphingosine kinase inhibitor abrogated the osteogenic proliferation and differentiation, suggesting that sphingosine-1-phosphate receptor signaling was a putative G protein-coupled receptor regulated by GRK3. Immunoblotting showed prolonged ERK1/2 signaling after stimulation with sphingosine-1-phosphate in GRK3-deficient cells, and modified-TANGO assays suggested the involvement of β-arrestin-2 in sphingosine-1-phosphate receptor internalization.

CONCLUSIONS

Our work suggests that GRK3 regulates sphingosine-1-phosphate receptor signaling on bone marrow mesenchymal stem cells by recruiting β-arrestin to the occupied GPCR to promote internalization, and lack of such regulation affects mesenchymal stem cell functionality.

Tryptophan and Kynurenine Enhances the Stemness and Osteogenic Differentiation of Bone Marrow-Derived Mesenchymal Stromal Cells In Vitro and In Vivo

Aging tissues present a progressive decline in homeostasis and regenerative capacities, which has been associated with degenerative changes in tissue-specific stem cells and stem cell niches. We hypothesized that amino acids could regulate the stem cell phenotype and differentiation ability of human bone marrow-derived mesenchymal stromal cells (hBMSCs). Thus, we performed a screening of 22 standard amino acids and found that D-tryptophan (10 μM) increased the number of cells positive for the early stem cell marker SSEA-4, and the gene expression levels of OCT-4, NANOG, and SOX-2 in hBMSCs. Comparison between D- and L-tryptophan isomers showed that the latter presents a stronger effect in inducing the mRNA levels of Oct-4 and Nanog, and in increasing the osteogenic differentiation of hBMSCs. On the other hand, L-tryptophan suppressed adipogenesis. The migration and colony-forming ability of hBMSCs were also enhanced by L-tryptophan treatment. In vivo experiments delivering L-tryptophan (50 mg/kg/day) by intraperitoneal injections for three weeks confirmed that L-tryptophan significantly increased the percentage of cells positive for SSEA-4, mRNA levels of Nanog and Oct-4, and the migration and colony-forming ability of mouse BMSCs. L-kynurenine, a major metabolite of L-tryptophan, also induced similar effects of L-tryptophan in enhancing stemness and osteogenic differentiation of BMSCs in vitro and in vivo, possibly indicating the involvement of the kynurenine pathway as the downstream signaling of L-tryptophan. Finally, since BMSCs migrate to the wound healing site to promote bone healing, surgical defects of 1 mm in diameter were created in mouse femur to evaluate bone formation after two weeks of L-tryptophan or L-kynurenine injection. Both L-tryptophan and L-kynurenine accelerated bone healing compared to the PBS-injected control group. In summary, L-tryptophan enhanced the stemness and osteoblastic differentiation of BMSCs and may be used as an essential factor to maintain the stem cell properties and accelerate bone healing and/or prevent bone loss.

Bone Marrow-Derived Mesenchymal Stromal Cells (MSCs) Modulate the Inflammatory Character of Alveolar Macrophages from Sarcoidosis Patients

Sarcoidosis is a devastating inflammatory disease affecting many organs, especially the lungs and lymph nodes. Bone marrow-derived mesenchymal stromal cells (MSCs) can “reprogram” various types of macrophages towards an anti-inflammatory phenotype. We wanted to determine whether alveolar macrophages from sarcoidosis subjects behave similarly by mounting an anti-inflammatory response when co-cultured with MSCs. Fifteen sarcoidosis and eight control subjects underwent bronchoscopy and bronchoalveolar lavage (BAL). Unselected BAL cells (70–94% macrophages) were isolated and cultured with and without MSCs from healthy adults. Following stimulation of the cultured cells with lipopolysaccharide, the medium was removed to measure interleukin 10 and tumor necrosis factor alpha (IL-10 and TNF-α). In two additional sarcoidosis subjects, flow cytometry was used to study intracellular cytokines and surface markers associated with alveolar macrophages to confirm the results. Unselected BAL cells from sarcoidosis subjects co-cultured with MSCs showed a reduction in TNF-α (pro-inflammatory M1) and an increase in IL-10 (anti-inflammatory M2) in 9 of 11 samples studied. Control subject samples showed few, if any, differences in cytokine production. Unselected BAL cells from two additional patients analyzed by flow cytometry confirmed a switch towards an anti-inflammatory state (i.e., M1 to M2) after co-culture with MSCs. These results suggest that, similarly to other macrophages, alveolar macrophages also respond to MSC contacts by changing towards an anti-inflammatory phenotype. Based on our results, we hypothesize that mesenchymal stromal cells applied to the airways might alleviate lung inflammation and decrease steroid need in patients with sarcoidosis.

Expression of HIF‑1α in cycling stretch‑induced osteogenic differentiation of bone mesenchymal stem cells

During orthodontic treatment, mechanical force is applied to the teeth, and following a series of complex metabolism changes, the position of the teeth in the alveolar bone change. This process is closely associated with primitive bone mesenchymal stem cells (BMSCs), which may differentiate into osteoblasts precursor cell. A hypoxic microenvironment may be caused by orthodontic mechanical forces between the alveolar bone and the root. Hypoxia-inducible factor 1α (HIF-1α) is a specific receptor that adapts to a hypoxic environment. The present study was designed to investigate whether HIF-1α was involved in the osteoblastic differentiation of BMSCs induced by cyclic tensile stress. During this process, HIF-1α mRNA and protein expression were detected using a reverse transcription-quantitative polymerase chain reaction and western blotting. It was revealed that alkaline phosphatase activity increased in a time-dependent manner in three different stretching strength groups, which indicates that cyclic stretch promotes the osteogenic differentiation of BMSCs. The optimal force stage of osteogenesis was an unexpected discovery, which will provide theoretical guidance for selecting the most suitable orthodontic force for tooth movement in clinical orthodontic treatment. Most importantly, all experiments revealed that HIF-1α mRNA and protein were significantly increased following stretching treatment in BMSCs. It was therefore concluded that HIF-1α may be involved in BMSCs modulating osteogenic metabolism during exposure to cyclic stretch and a hypoxic microenvironment, which may prove useful for the reconstruction of a jaw during orthodontic treatment.

Erythropoietin modulates bone marrow stromal cell differentiation

Erythropoietin is essential for bone marrow erythropoiesis and erythropoietin receptor on non-erythroid cells including bone marrow stromal cells suggests systemic effects of erythropoietin. Tg6 mice with chronic erythropoietin overexpression have a high hematocrit, reduced trabecular and cortical bone and bone marrow adipocytes, and decreased bone morphogenic protein 2 driven ectopic bone and adipocyte formation. Erythropoietin treatment (1 200 IU·kg^–1) for 10 days similarly exhibit increased hematocrit, reduced bone and bone marrow adipocytes without increased osteoclasts, and reduced bone morphogenic protein signaling in the bone marrow. Interestingly, endogenous erythropoietin is required for normal differentiation of bone marrow stromal cells to osteoblasts and bone marrow adipocytes. ΔEpoR_E mice with erythroid restricted erythropoietin receptor exhibit reduced trabecular bone, increased bone marrow adipocytes, and decreased bone morphogenic protein 2 ectopic bone formation. Erythropoietin treated ΔEpoR_E mice achieved hematocrit similar to wild-type mice without reduced bone, suggesting that bone reduction with erythropoietin treatment is associated with non-erythropoietic erythropoietin response. Bone marrow stromal cells from wild-type, Tg6, and ΔEpoR_E-mice were transplanted into immunodeficient mice to assess development into a bone/marrow organ. Like endogenous bone formation, Tg6 bone marrow cells exhibited reduced differentiation to bone and adipocytes indicating that high erythropoietin inhibits osteogenesis and adipogenesis, while ΔEpoR_E bone marrow cells formed ectopic bones with reduced trabecular regions and increased adipocytes, indicating that loss of erythropoietin signaling favors adipogenesis at the expense of osteogenesis. In summary, endogenous erythropoietin signaling regulates bone marrow stromal cell fate and aberrant erythropoietin levels result in their impaired differentiation.

Reawakening of dormant estrogen-dependent human breast cancer cells by bone marrow stroma secretory senescence

Background

Dormant estrogen receptor positive (ER+) breast cancer micrometastases in the bone marrow survive adjuvant chemotherapy and recur stochastically for more than 20 years. We hypothesized that inflammatory cytokines produced by stromal injury can re-awaken dormant breast cancer cells.

Methods

We used an established in vitro dormancy model of Michigan Cancer Foundation-7 (MCF-7) breast cancer cells incubated at clonogenic density on fibronectin-coated plates to determine the effects of inflammatory cytokines on reactivation of dormant ER+ breast cancer cells. We measured induction of a mesenchymal phenotype, motility and the capacity to re-enter dormancy. We induced secretory senescence in murine stromal monolayers by oxidation, hypoxia and estrogen deprivation with hydrogen peroxide (H₂O₂), carbonyl-cyanide m-chlorophenylhydrazzone (CCCP) and Fulvestrant (ICI 182780), respectively, and determined the effects on growth of co-cultivated breast cancer cells.

Results

Exogenous recombinant human (rh) interleukin (IL)-6, IL-8 or transforming growth factor β1 (TGFβ1) induced regrowth of dormant MCF-7 cells on fibronectin-coated plates. Dormant cells had decreased expression of E-cadherin and estrogen receptor α (ERα) and increased expression of N-cadherin and SNAI2 (SLUG). Cytokine or TGFβ1 treatment of dormant clones induced formation of growing clones, a mesenchymal appearance, increased motility and an impaired capacity to re-enter dormancy. Stromal injury induced secretion of IL-6, IL-8, upregulated tumor necrosis factor alpha (TNFα), activated TGFβ and stimulated the growth of co-cultivated MCF-7 cells. MCF-7 cells induced secretion of IL-6 and IL-8 by stroma in co-culture.

Conclusions

Dormant ER+ breast cancer cells have activated epithelial mesenchymal transition (EMT) gene expression programs and downregulated ERα but maintain a dormant epithelial phenotype. Stromal inflammation reactivates these cells, induces growth and a mesenchymal phenotype. Reactivated, growing cells have an impaired ability to re-enter dormancy. In turn, breast cancer cells co-cultured with stroma induce secretion of IL-6 and IL-8 by the stroma, creating a positive feedback loop.

Hypothetical endogenous SIV-like antigens in Mauritian cynomolgus macaques

Simian immunodeficiency virus (SIV) infection of Mauritian cynomolgus macaques (MCMs) is an increasingly important nonhuman primate model for HIV vaccine research. We previously reported that in MCMs anti-SIV antibodies can be naturally developed without exogenous infection or vaccination, and that a vaccine targeting SIV protease cleavage sites (PCS) can cross-induce antibodies to non-PCS SIV antigens. We speculate that this is potentially caused by the existence of endogenous SIV-like antigens. External stimuli (such as environmental factors and vaccination) may induce expression of endogenous SIV-like antigens to elicit these antibodies. Database and mass spectrometry analyses were conducted to search for such antigens. We identified endogenous SIV-like DNA sequences in cynomolgus macaque genome and non-PCS peptide homologous to SIV Env protein in PBMCs of a PCS-vaccinated monkey. Our preliminary insights suggest that endogenous SIV-like antigens may be one of the possible reasons for the natural and cross-inducible SIV antibodies in MCMs.

Expression of an active Gαs mutant in skeletal stem cells is sufficient and necessary for fibrous dysplasia initiation and maintenance

Fibrous dysplasia (FD) is a disease caused by postzygotic activating mutations of GNAS (R201C and R201H) that encode the α-subunit of the Gs stimulatory protein. FD is characterized by the development of areas of abnormal fibroosseous tissue in the bones, resulting in skeletal deformities, fractures, and pain. Despite the well-defined genetic alterations underlying FD, whether GNAS activation is sufficient for FD initiation and the molecular and cellular consequences of GNAS mutations remains largely unresolved, and there are no currently available targeted therapeutic options for FD. Here, we have developed a conditional tetracycline (Tet)-inducible animal model expressing the GαsR201C in the skeletal stem cell (SSC) lineage (Tet-GαsR201C/Prrx1-Cre/LSL-rtTA-IRES-GFP mice), which develops typical FD bone lesions in both embryos and adult mice in less than 2 weeks following doxycycline (Dox) administration. Conditional GαsR201C expression promoted PKA activation and proliferation of SSCs along the osteogenic lineage but halted their differentiation to mature osteoblasts. Rather, as is seen clinically, areas of woven bone admixed with fibrous tissue were formed. GαsR201C caused the concomitant expression of receptor activator of nuclear factor kappa-B ligand (Rankl) that led to marked osteoclastogenesis and bone resorption. GαsR201C expression ablation by Dox withdrawal resulted in FD-like lesion regression, supporting the rationale for Gαs-targeted drugs to attempt FD cure. This model, which develops FD-like lesions that can form rapidly and revert on cessation of mutant Gαs expression, provides an opportunity to identify the molecular mechanism underlying FD initiation and progression and accelerate the development of new treatment options.

Preparation of Plasma Membrane Vesicles from Bone Marrow Mesenchymal Stem Cells for Potential Cytoplasm Replacement Therapy

We have previously reported on the generation of plasma membrane vesicles (PMVs) through the mechanical extrusion of mammalian cells. The fusion of PMVs with mitochondrial deficient Rho0 cells restored mitotic activity under normal culture conditions. Atherosclerosis, type 2 diabetes, Alzheimer's disease, and cancer are age-related diseases that have been reported to be associated with multiple mechanical and functional defects in the cytosol and organelles of a variety of cell types. Bone marrow mesenchymal stem cells (BMSCs) represent a unique cell population from the bone marrow that possess self-renewal capabilities while maintaining their multipotency. The supplementation of senescence cells with young cytoplasm from autologous BMSCs via the fusion of PMVs provides a promising approach to ameliorate or even reverse age-associated phenotypes. This protocol describes how to prepare PMVs from BMSCs via extrusion through a polycarbonate membrane with 3 µm pores, determine the existence of mitochondria and examine the maintenance of membrane potential within PMVs using a confocal microscope, concentrate PMVs by centrifugation, and carry out the in vivo injection of PMVs into the gastrocnemius muscle of mice.

Follistatin-like protein 1 modulates IL-17 signaling via IL-17RC regulation in stromal cells

Follistatin-like protein 1 (FSTL-1) possesses several newly identified roles in mammalian biology, including IL-17 driven inflammation, though the mechanism underlying FSTL-1 influence on IL-17 mediated cytokine production is unknown. Using parallel in vitro bone marrow stromal cell models of FSTL-1 suppression we employed unbiased microarray analysis to identify FSTL-1 regulated genes and pathways that could influence IL-17 dependent production of IL-6 and G-CSF. We discovered that FSTL-1 modulates Il17rc gene expression. Specifically, FSTL-1 was necessary for Il17rc gene transcription, IL-17RC surface protein expression and IL-17-dependent cytokine production. This work identifies a mechanism by which FSTL-1 influences IL-17 driven inflammatory signalingin vitro and reveals a novel function for FSTL-1, as a modulator of gene expression. Thus, enhanced understanding of the interplay between FSTL-1 and IL-17 mediated inflammation may provide insight into potential therapeutic targets of IL-17 mediated diseases and warrants ongoing study of in vivo models and clinical scenarios of FSTL-1-influenced diseases.

Shrinkage-mediated imaging of entire organs and organisms using uDISCO

Recent tissue-clearing approaches have become important alternatives to standard histology approaches. However, light scattering in thick tissues and the size restrictions on samples that can be imaged with standard light-sheet microscopy pose limitations for analyzing large samples such as an entire rodent body. We developed 'ultimate DISCO' (uDISCO) clearing to overcome these limitations in volumetric imaging. uDISCO preserves fluorescent proteins over months and renders intact organs and rodent bodies transparent while reducing their size up to 65%. We used uDISCO to image neuronal connections and vasculature from head to toe over 7 cm and to perform unbiased screening of transplanted stem cells within the entire body of adult mice. uDISCO is compatible with diverse labeling methods and archival human tissue, and it can readily be used in various biomedical applications to study organization of large organ systems throughout entire organisms.

Impaired function of bone marrow stromal cells in systemic mastocytosis

Patients with systemic mastocytosis (SM) have a wide variety of problems, including skeletal abnormalities. The disease results from a mutation of the stem cell receptor (c-kit) in mast cells and we wondered if the function of bone marrow stromal cells (BMSCs; also known as MSCs or mesenchymal stem cells) might be affected by the invasion of bone marrow by mutant mast cells. As expected, BMSCs from SM patients do not have a mutation in c-kit, but they proliferate poorly. In addition, while osteogenic differentiation of the BMSCs seems to be deficient, their adipogenic potential appears to be increased. Since the hematopoietic supportive abilities of BMSCs are also important, we also studied the engraftment in NSG mice of human CD34(+) hematopoietic progenitors, after being co-cultured with BMSCs of healthy volunteers vs. BMSCs derived from patients with SM. BMSCs derived from the bone marrow of patients with SM could not support hematopoiesis to the extent that healthy BMSCs do. Finally, we performed an expression analysis and found significant differences between healthy and SM derived BMSCs in the expression of genes with a variety of functions, including the WNT signaling, ossification, and bone remodeling. We suggest that some of the symptoms associated with SM might be driven by epigenetic changes in BMSCs caused by dysfunctional mast cells in the bone marrow of the patients.