A cost-effective method for the automatic quantitative analysis of fibroblastic colony-forming units

MF2C3: Multi-Feature Fuzzy Clustering to Enhance Cell Colony Detection in Automated Clonogenic Assay Evaluation

A clonogenic assay is a biological technique for calculating the Surviving Fraction (SF) that quantifies the anti-proliferative effect of treatments on cell cultures: this evaluation is often performed via manual counting of cell colony-forming units. Unfortunately, this procedure is error-prone and strongly affected by operator dependence. Besides, conventional assessment does not deal with the colony size, which is generally correlated with the delivered radiation dose or administered cytotoxic agent. Relying upon the direct proportional relationship between the Area Covered by Colony (ACC) and the colony count and size, along with the growth rate, we propose MF2C3, a novel computational method leveraging spatial Fuzzy C-Means clustering on multiple local features (i.e., entropy and standard deviation extracted from the input color images acquired by a general-purpose flat-bed scanner) for ACC-based SF quantification, by considering only the covering percentage. To evaluate the accuracy of the proposed fully automatic approach, we compared the SFs obtained by MF2C3 against the conventional counting procedure on four different cell lines. The achieved results revealed a high correlation with the ground-truth measurements based on colony counting, by outperforming our previously validated method using local thresholding on L*u*v* color well images. In conclusion, the proposed multi-feature approach, which inherently leverages the concept of symmetry in the pixel local distributions, might be reliably used in biological studies.

Cell colony counter called CoCoNut

Clonogenic assays are powerful tools for testing cell reproductive death after biological damage caused by, for example, ionizing radiation. Traditionally, the methods require a cumbersome, slow and eye-straining manual counting of viable colonies under a microscope. To speed up the counting process and minimize those issues related to the subjective decisions of the scoring personnel, we developed a semi-automated, image-based cell colony counting setup, named CoCoNut (Colony Counter developed by the Nutech department at the Technical University of Denmark). It consists in an ImageJ macro and a photographic 3D-printed light-box, conceived and demonstrated to work together for Crystal Violet-stained colonies. Careful attention was given to the image acquisition process, which allows background removal (i.e. any unwanted element in the picture) in a minimally invasive manner. This is mainly achieved by optimal lighting conditions in the light-box and dividing the image of a flask that contains viable colonies by the picture of an empty flask. In this way, CoCoNut avoids using aggressive background removal filters that usually lead to suboptimal colony count recovery. The full method was tested with V79 and HeLa cell survival samples. Results were compared to other freely available tools. CoCoNut proved able to successfully distinguish between single and merged colonies and to identify colonies bordering on flask edges. CoCoNut software calibration is fast; it requires the adjustment of a single parameter that is the smallest colony area to be counted. The employment of a single parameter reduces the risk of subjectivity, providing a robust and user-friendly tool, whose results can be easily compared over time and among different bio-laboratories. The method is inexpensive and easy to obtain. Among its advantages, we highlight the possibility of combining the macro with a perfectly reproducible 3D-printed light-box. The CoCoNut software and the 3D-printer files are provided as supporting information (S1 CoCoNut Files).

Chronic kidney disease and vitamin D metabolism in human bone marrow-derived MSCs

Vitamin D that is synthesized in the skin or is ingested undergoes sequential steps of metabolic activation via a cascade of cytochrome P450 enzymatic hydroxylations in the liver and kidney to produce 1α,25-dihydroxyvitamin D (1α,25(OH)2 D). There are many tissues that are able to synthesize 1α,25(OH)2 D, but the biological significance of extrarenal hydroxylases is unresolved. Human marrow-derived mesenchymal stem cells (marrow stromal cells, hMSCs) give rise to osteoblasts, and their differentiation is stimulated by 1α,25(OH)2 D. In addition to being targets of 1α,25(OH)2 D, hMSCs can synthesize it; on the basis of those observations, we further examined the local autocrine/paracrine role of vitamin D metabolism in osteoblast differentiation. Research with hMSCs from well-characterized subjects provides an innovative opportunity to evaluate the effects of clinical attributes on the regulation of hMSCs. Like the renal 1α-hydroxylase, the enzyme in hMSCs is constitutively decreased with age and chronic kidney disease (CKD); both are regulated by PTH1-34, insulin-like growth factor 1, calcium, 1α,25(OH)2 D, 25(OH)D, and fibroblast growth factor 23. CKD is associated with impaired renal biosynthesis of 1α,25(OH)2 D, low bone mass, and increased fracture risk. Studies with hMSCs from CKD patients or aged subjects indicate that circulating 25(OH)D may have an important role in osteoblast differentiation on vitamin D metabolism and action in hMSCs.

Age-related BMAL1 change affects mouse bone marrow stromal cell proliferation and osteo-differentiation potential

INTRODUCTION

Aging people's bone regeneration potential is always impaired. Bone marrow stromal cells (MSCs) contain progenitors of osteoblasts. Donor age may affect MSCs' proliferation and differentiation potential, but the genomic base is still unknown. Due to recent research's indication that a core circadian component, brain and muscle ARNT-like 1 protein (BMAL1), has a role in premature aging, we investigated the normal aging mechanism in mice with their MSCs and Bmal1 gene/protein level.

MATERIAL AND METHODS

1, 6 and 16 month old C57BL/6 mice were used and the bone marrow stromal cells were gained and cultured at early passage. Bmal1 gene and protein level were detected in these cells. Marrow stromal cells were also induced to differentiate to osteoblasts or adipocytes. Three groups of mice MSCs were compared on proliferation by flow cytometry, on cell senescence by SA-β-gal expression and after osteo-induction on osteogenic potential by the expression of osterix (Osx), alkaline phosphatase (ALP) and osteocalcin (OCN).

RESULTS

Bmal1 gene and protein level as well as S-phase fraction of the cell cycle decreased in MSCs along with the aging process. At the same time, SA-β-gal+ levels increased, especially in the aged mice MSCs. When induced to be osteogenic, Osx gene expression and ALP activity declined in the mid-age and aged mice MSCs, while OCN protein secretion deteriorated in the aged mice MSCs.

CONCLUSIONS

These findings demonstrate that mouse MSCs changed with their proliferation and osteo-differentiation abilities at different aging stages, and that Bmal1 is related to the normal aging process in MSCs.

Single-platform quality control assay to quantify multipotential stromal cells in bone marrow aspirates prior to bulk manufacture or direct therapeutic use

BACKGROUND AIMS

The manufacture of multipotential stromal cell (MSC)-based products is costly; therefore, a rapid evaluation of bone marrow (BM) 'quality' with respect to MSC content is desirable. The aim of this study was to develop a rapid single-platform assay to quantify MSC in BM aspirates.

METHODS

Aspirated MSC were enumerated using the CD45(-/low) CD271(bright) phenotype and AccuCheck counting beads and compared with a classic colony-forming unit-fibroblast (CFU-F) assay. The phenotype of CD45(-/low) CD271(bright) cells was defined using a range of MSC (CD73, CD105, CD90) and non-MSC (CD31, CD33, CD34, CD19) markers. The effect of aspirated BM volume on MSC yield was also determined.

RESULTS

CD45(-/low) CD271(bright) cells had a classic MSC phenotype (CD73(+) CD105(+) CD90(+)). Their numbers correlated positively with CFU-F counted manually (R = 0.81, P < 0.001) or using automatic measurements of surface area occupied by colonies (R = 0.66, P < 0.001). Simultaneous enumeration of CD34(+) cells revealed donor variability ranges compatible with standard International Society of Hematotherapy and Graft Engineering (ISHGE) protocols. Aspirating larger marrow volumes gave a significant several-fold reduction in the frequency of CFU-F and CD45(-/low) CD271(bright) cells per milliliter. Therefore aspirated MSC yields can be maximized through a standardized, low-volume harvesting technique.

CONCLUSIONS

Absolute quantification of CD45(-/low) CD271(bright) cells was found to be a reliable method of predicting CFU-F yields in BM aspirates. This rapid (< 40 min) procedure could be suitable for intra-operative quality control of BM aspirates prior to volume reduction/direct injection in orthopedics. In the production of culture-expanded MSC, this assay could be used to exclude samples containing low numbers of MSC, resulting in improved consistency and quality of manufactured MSC batches.

Low-cost, high-throughput, automated counting of bacterial colonies

Research involving bacterial pathogens often requires enumeration of bacteria colonies. Here, we present a low-cost, high-throughput colony counting system consisting of colony counting software and a consumer-grade digital camera or document scanner. We demonstrate that this software, called "NICE" (NIST's Integrated Colony Enumerator), can count bacterial colonies as part of a high-throughput multiplexed opsonophagocytic killing assay used to characterize pneumococcal vaccine efficacy. The results obtained with NICE correlate well with the results obtained from manual counting, with a mean difference of less than 3%. NICE is also rapid; it can count colonies from multiple reaction wells within minutes and export the results to a spreadsheet for data processing. As this program is freely available from NIST, NICE should be helpful in bacteria colony enumeration required in many microbiological studies, and in standardizing colony counting methods.

Alterations in hematopoietic microenvironment in patients with aplastic anemia

Mechanisms of hematopoietic failure in patients with aplastic anemia (AA) are obscure. We investigate alterations in the hematopoietic microenvironment in AA patients. We present the results of studying mesenchymal stromal cells (MSC), fibroblastic colony-forming units (CFU-F), and adherent cell layers (ACL) of long-term bone marrow cultures (LTBMC) from bone marrow (BM) samples of AA patients. MSC of AA patients proliferated longer than those of donors. In half of the patients' MSC cultures, adipogenesis was impaired. Osteogenic differentiation was not achieved in 36% of AA MSC. CFU-F formed enlarged colonies, and their concentration in the BM of AA patients was significantly increased. Our data suggest that the physiological activation of the stromal microenvironment is characteristic of AA. We detected a decrease in the expression of the angiopoetin-1 (ANG-1) and vascular cell adhesion molecule-1 (VCAM-1) genes, together with an increase in the expression of vascular endothelial growth factor (VEGF) in ACL of AA patients. This indicates abnormal regulatory patterns in both osteoblastic and vascular contexts. Addition of AA patients' serum to donors' LTBMC for 3 weeks induced similar gene expression alterations. The addition of parathyroid hormone (PTH) resulted in the expression levels of analyzed genes returning to normal, in both AA LTBMC and donor cultures treated with AA serum. The physiologic status of the BM stromal microenvironment (MSC, CFU-F, and ACL of LTBMC) of AA patients was altered.

Nonviral delivery of basic fibroblast growth factor gene to bone marrow stromal cells

Basic fibroblast growth factor (bFGF) is capable of stimulating osteogenic differentiation of preosteoblast cells in vitro and new bone tissue deposition in vivo. Delivering the gene for the protein, rather than the protein itself, is considered advantageous for bone repair since gene delivery obviates the need to produce the protein in pharmaceutical quantities. To explore the feasibility of bFGF gene delivery by nonviral methods, we transfected primary rat bone marrow stromal cells (BMSC) using cationic polymers (polyethylenimine and poly(L-lysine)-palmitic acid) in vitro. After delivering a bFGF-expression plasmid (pFGF2-IRES-AcGFP) to BMSC, the presence of bFGF in culture supernatants was detected by a commercial ELISA. As much as 0.3 ng bFGF/10(6) cells/day was obtained from the BMSC under optimal conditions. This secretion rate was approximately 100-fold lower than the secretion obtained from immortal, and easy-to-transfect, human 293T cells. These data suggest the feasibility of modifying BMSC with nonviral delivery systems for bFGF expression, but also highlight the need for substantial improvement in transfection rate for an effective therapy.

The effect of oxygen tension on the in vitro assay of human osteoblastic connective tissue progenitor cells

Connective tissue progenitors (CTPs) are defined as the heterogeneous set of stem and progenitor cells that reside in native tissues and are capable of proliferation and differentiation into one or more connective tissue phenotypes. CTPs play important roles in tissue formation, repair, and remodeling. Therefore, in vitro assays of CTP prevalence and biological potential have important scientific and clinical relevance. This study evaluated oxygen tension as an important variable in optimizing in vitro conditions for quantitative assays of human CTPs. Bone marrow aspirates were collected from 20 human subjects and cultured using established medium conditions at ambient oxygen tensions of 1, 5, 10, and 20%. Colony-forming efficiency (CFE), proliferation, and colony density were assessed. CFE and proliferation were greatest at 5% O(2). Traditional conditions using atmospheric oxygen tension (20% O(2)) reduced CFE by as much as 32%. CFE and proliferation at 1% O(2) were less than 5% O(2) but comparable to that seen at 20% O(2), suggesting that CTPs are relatively resilient under hypoxic conditions, a fact that may be relevant to their function in wound repair and their potential use in tissue engineering applications involving transplantation into settings of moderate to severe hypoxia. These data demonstrate that optimization of quantitative assays for CTPs will require control of oxygen tension.

Age-related intrinsic changes in human bone-marrow-derived mesenchymal stem cells and their differentiation to osteoblasts

In vivo and in vitro studies indicate that a subpopulation of human marrow-derived stromal cells (MSCs, also known as mesenchymal stem cells) has potential to differentiate into multiple cell types, including osteoblasts. In this study, we tested the hypothesis that there are intrinsic effects of age in human MSCs (17-90 years). We tested the effect of age on senescence-associated beta-galactosidase, proliferation, apoptosis, p53 pathway genes, and osteoblast differentiation in confluent monolayers by alkaline phosphatase activity and osteoblast gene expression analysis. There were fourfold more human bone MSCs (hMSCs) positive for senescence-associated beta-galactosidase in samples from older than younger subjects (P < 0.001; n = 17). Doubling time of hMSCs was 1.7-fold longer in cells from the older than the younger subjects, and was positively correlated with age (P = 0.002; n = 19). Novel age-related changes were identified. With age, more cells were apoptotic (P = 0.016; n = 10). Further, there were age-related increases in expression of p53 and its pathway genes, p21 and BAX. Consistent with other experiments, there was a significant age-related decrease in generation of osteoblasts both in the STRO-1+ cells (P = 0.047; n = 8) and in adherent MSCs (P < 0.001; n = 10). In sum, there is an age-dependent decrease in proliferation and osteoblast differentiation, and an increase in senescence-associated beta-galactosidase-positive cells and apoptosis in hMSCs. Up-regulation of the p53 pathway with age may have a critical role in mediating the reduction in both proliferation and osteoblastogenesis of hMSCs. These findings support the view that there are intrinsic alterations in human MSCs with aging that may contribute to the process of skeletal aging in humans.

Scoring CFU-GM colonies in vitro by data fusion: A first account

OBJECTIVE

In vitro models of hematopoiesis used in investigative hematopathology and in safety studies on candidate drugs, involve clonogenic assays on colony-forming unit granulocyte macrophage (CFU-GM). These assays require live and unstained colonies to be counted. Most laboratories still rely on visual scoring, which is time-consuming and error-prone. As a consequence, automated scoring is highly desired. An algorithm that recognizes and scores CFU-GM colonies by data fusion has been developed. Some preliminary results are presented in this article.

METHODS

CFU-GM assays were carried out on hematopoietic progenitors (human umbilical cord blood cells) grown in methylcellulose. Colony images were acquired by a digital camera and stored.

RESULTS

The classifier was designed to process images of layers sampled from a three-dimensional (3D) domain and forming a stack. Structure and texture information was extracted from each image. Classifier training was based on a 3D colony model applied to the image stack. The number of scored colonies (assigned class) was required to match the count supplied by the human expert (class of belonging). The trained classifier was validated on one more stack and then applied to a stack with overlapping colonies. Scoring in distortion- and caustic-affected border areas was also successfully demonstrated. Because of hardware limitations, compact colonies in some cases were missed.

CONCLUSIONS

The industry's scoring methods all rely on structure alone and process 2D data. Instead, the classifier here fuses data from a whole stack and is capable, in principle, of high-throughput screening.

Cannabinoids stimulate fibroblastic colony formation by bone marrow cells indirectly via CB2 receptors

Recently, the cannabinoid receptors CB(1) and CB(2) were shown to modulate bone formation and resorption in vivo, although little is known of the mechanisms underlying this. The effects of cannabinoids on mesenchymal stem cell (MSC) recruitment in whole bone marrow were investigated using either the fibroblastic colony-forming unit (CFU-f) assay or high-density cultures of whole bone marrow. Levels of the CB(1) and CB(2) receptors were assessed by flow cytometry. Treatment of CFU-f cultures with the endocannabinoid 2-arachidonylglycerol (2-AG) dose-dependently increased fibroblastic and differentiated colony formation along with colony size. The nonspecific agonists CP 55,940 and WIN 55,212 both increased colony numbers, as did the CB(2) agonists BML190 and JWH015. The CB(1)-specific agonist ACEA had no effect, whereas the CB(2) antagonist AM630 blocked the effect of the natural cannabinoid tetrahydrocannabivarin, confirming mediation via the CB(2) receptor. Treatment of primary bone marrow cultures with 2-AG stimulated proliferation and collagen accumulation, whereas treatment of subcultures of MSC had no effect, suggesting that the target cell is not the MSC but an accessory cell present in bone marrow. Subcultures of MSCs were negative for CB(1) and CB(2) receptors as shown by flow cytometry, whereas whole bone marrow contained a small population of cells positive for both receptors. These data suggest that cannabinoids may stimulate the recruitment of MSCs from the bone marrow indirectly via an accessory cell and mediated via the CB(2) receptor. This recruitment may be one mechanism responsible for the increased bone formation seen after cannabinoid treatment in vivo.

In vitro osteogenic response of rat bone marrow cells to bFGF and BMP-2 treatments

Basic fibroblast growth factor (bFGF) and bone morphogenetic protein-2 (BMP-2) are actively pursued for stimulation of bone formation. To assess their promise for systemic therapy of osteoporosis, we ascertained the effects of bFGF and BMP-2 on bone marrow cells in vitro. Bone marrow cells were obtained from young (8 weeks) and adult (32 weeks) rats by femoral aspiration and were exposed to osteogenic medium (ie, basal medium with 10 mM beta-glycerolphosphate and 100 nM dexamethasone) containing the growth factors. The cell viability in osteogenic medium was reduced after 3 weeks but not if the concentration of beta-glycerolphosphate/dexamethasone was reduced to 3 mM/30 nM. Unlike BMP-2, bFGF at 2-50 ng/mL was capable of enhancing long-term cell viability. Continuous treatment of bone marrow cells for 3 weeks resulted in dose-dependent stimulation of mineralization by BMP-2, but not by bFGF, whose activity was optimal at 2-10 ng/mL. To explore the effect of short-term exposure, bone marrow cells were treated with growth factors for 1 week and subsequent mineralization was investigated. BMP-2 exposure increased the extent of mineralization, but bFGF was not effective after the short exposure. We concluded bFGF was more potent (ie, required lower concentration) for stimulating osteogenic parameters, but BMP-2 effects were lasting on the bone marrow cells.

Osteogenic potential of adult human stem cells of the lumbar vertebral body and the iliac crest

STUDY DESIGN

Marrow was aspirated from the vertebral body (VB) and iliac crest (IC) of patients undergoing lumbar spinal surgery, following an approved protocol. Progenitor cells were isolated using standard culture conditions and their osteogenic potential evaluated.

OBJECTIVE

To evaluate the osteogenic potential of mesenchymal stem cells (MSCs) isolated from the bone marrow of the human VB.

SUMMARY OF BACKGROUND DATA

IC marrow grafting during cervical discectomy and fusion procedure is associated with donor site morbidity. Since the VB contains marrow cells, it may be possible to circumvent this problem by using this tissue for osseous graft supplementation. However, there is paucity of information concerning the osteogenic potential of non-IC-derived progenitor cells. Herein, we address this issue.

METHODS

Marrow samples from VB of patients undergoing lumbar spinal surgery were collected; marrow was also harvested from the IC. Progenitor cells were isolated and the number of colony forming unit-fibroblastic (CFU-F) determined. The osteogenic potential of the cells was characterized using biochemical and molecular biology techniques.

RESULTS

Both the VB and IC marrow generated small, medium, and large sized CFU-F. Higher numbers of CFU-F were obtained from the VB marrow than the IC (P < 0.05). Progenitor cells from both anatomic sites expressed comparable levels of CD166, CD105, CD49a, and CD63. Moreover, progenitor cells from the VB exhibited an increased level of alkaline phosphatase activity. MSCs of the VB and the IC displayed similar levels of expression of Runx-2, collagen Type I, CD44, ALCAM, and ostecalcin. The level of expression of bone sialoprotein was higher in MSC from the IC than the VB. VB and IC cells mineralized their extracellular matrix to a similar extent.

CONCLUSIONS

Our studies show that CFU-F frequency is higher in the marrow of the VB than the IC. Progenitor cells isolated from both sites respond in a similar manner to an osteogenic stimulus and express common immunophenotypes. Based on these findings, we propose that progenitor cells from the lumbar vertebral marrow would be suitable candidate for osseous graft supplementation in spinal fusion procedures. Studies must now be conducted using animal models to ascertain if cells of the VB are as effective as those of the IC for the fusion applications.

Osteogenic progenitors in bone marrow aspirates from smokers and nonsmokers

Bone marrow aspirates contain connective tissue progenitor cells which can proliferate to form cell colonies that express connective tissue phenotypes. The number of osteogenic connective tissue progenitor cells can be estimated by counting colonies that express alkaline phosphatase, an early marker of osteoblastic differentiation. Because tobacco use is associated with decreased bone mass and fracture nonunion, we tested the hypothesis that current or previous tobacco use is an independent determinant of marrow cellularity or prevalence of osteogenic connective tissue progenitor cells among marrow-derived cells. Marrow aspirates were obtained from the anterior iliac crest of 62 patients who were grouped as never smoked, past smokers, or current smokers. The number of nucleated cells per aspirate was determined. Cells were cultured for 6 days in osteogenic media. The prevalence of osteogenic connective tissue progenitor cells was determined by counting colony forming units. The area of each colony was assessed using quantitative image analysis. Cellularity of bone marrow was found to decrease with age. We observed no relationship between smoking status and marrow cellularity, colony prevalence, or colony area. This suggests that tobacco use is not associated with a change in prevalence of osteogenic connective tissue progenitor cells in bone marrow, or their intrinsic biologic capacity to undergo early osteoblastic differentiation.

LEVEL OF EVIDENCE

Diagnostic Study, Level I (testing of previously developed diagnostic criteria on consecutive patients--with universally applied reference "gold" standard). See the Guidelines for Authors for a complete description of levels of evidence.

Automated counting of mammalian cell colonies by means of a flat bed scanner and image processing

BACKGROUND

Clonogenic assays are used frequently to measure the cell killing and mutagenic effects of radiation and other agents. Clonogenic assays carried out manually are tedious and time-consuming and involve a significant element of subjectivity. However, several commercial automatic colony counters are available. Based on CCD video imaging and image analysis they are relatively expensive and can analyze only one petri dish at a time.

METHOD

We have developed a cheaper and more efficient device, which employs a flat bed scanner to image 12 60-mm petri dishes at a time. Two major problems in automated colony counting are the clustering of colonies and edge effects. By using standard image analysis and implementing an inflection point algorithm, these problems were greatly diminished. The resulting system was compared with two manual colony counts, as well as with automated counts with the Oxford Optronix ColCount colony counter for cell lines V79 and HaCaT.

RESULTS

Comparisons assuming the manual counts to be correct showed that our automatic counter was slightly more accurate than the commercial unit.

CONCLUSIONS

As a whole, our automated colony counter performed significantly better than the commercial unit with regard to processing time, cost and accuracy.

Bone Marrow Cells from Normal and Ovariectomized Rats Respond Differently to Basic Fibroblast Growth Factor and Bone Morphogenetic Protein 2 Treatmentin Vitro

The protein growth factors basic fibroblast growth factor (bFGF) and bone morphogenetic protein 2 (BMP-2) are being actively pursued for bone tissue engineering. Although both proteins are capable of stimulating osteogenic activity of bone marrow cells (BMCs), no studies have addressed the effect of estrogen deficiency on the growth factor responsiveness of BMCs. This study investigated the osteogenic response of BMCs from normal and ovariectomized (OVX) rats to bFGF and BMP- 2. In the absence of growth factors, a higher number of total colony-forming units (t-CFU) and alkaline phosphatase-expressing CFU (ALP-CFU) were obtained with BMCs derived from OVX rats. The percentage of ALP-CFU, however, was not significantly different between BMCs from the two groups of rats. Whereas BMP-2 did not influence the t-CFU and percentage of ALP-CFU, bFGF decreased t-CFU in BMCs derived from OVX rats and reduced the percentage of ALP-CFU in BMCs from both types of rats. Consistent with the higher t-CFU, the number of mineralized colonies (min-CFU) was also higher for BMCs derived from OVX rats. The number of min-CFU was not influenced by BMP-2 treatment, but was reduced with bFGF treatment. Comparison of the growth factor effects on a per-cell (DNA) basis confirmed the expected stimulatory effect of BMP-2 on ALP activity and mineralization in BMCs from normal rats, but these two parameters were not unequivocally stimulated in BMCs from OVX rats. We conclude that BMCs derived from normal and OVX rats exhibited significant differences in their osteogenic response to bFGF and BMP-2 treatment.

Megakaryocyte-bone marrow stromal cell aggregates demonstrate increased colony formation and alkaline phosphatase expression in vitro

Bone marrow stromal cells (BMSCs) possess certain stem celllike properties and can differentiate to adopt a number of mesenchymal phenotypes. BMSCs are usually investigated in vitro as homogeneous single-cell suspensions; however, these preparations lose much of their osteogenic capacity. Using the fibroblastic colony-forming unit assay, we have compared the proliferation and capacity to express alkaline phosphatase of BMSC-containing aggregates of bone marrow cells with single-cell suspensions of bone marrow cells from the same source. Aggregates were separated from single cells by density gradient centrifugation or cell sieving. The aggregate and single-cell preparations gave rise to similar numbers of colonies; however, the colonies produced by the aggregates were larger and expressed higher levels of alkaline phosphatase. When the aggregates were dissociated, colonies still formed; however, they expressed negligible levels of alkaline phosphatase. Immunomagnetic selection and immunofluorescent staining for CD61, N-methyl-D-aspartate (NMDA) receptor subunit 1, and acetylcholinesterase showed that the majority of the aggregates giving rise to osteoblastic colonies contained megakaryocytes. These data demonstrate that removing BMSCs from their normal environment reduces their osteoblastic capacity and that to achieve their maximal differentiation, BMSCs require direct physical contact with accessory cells such as megakaryocytes. These findings may be of direct relevance to the use of BMSCs for tissue-engineering purposes.

Chemically modified tetracyclines act through multiple mechanisms directly on osteoclast precursors

Chemically modified tetracyclines (CMTs) are thought to inhibit bone resorption primarily through their ability to inhibit matrix metalloproteinases (MMPs). We have previously demonstrated that some tetracycline compounds (TCs) induce apoptosis in mature rabbit osteoclasts and inhibit osteoclastic resorption in mouse osteoblast/marrow co-cultures in vitro. In this report, we now show that non-antibiotic analogues of doxycycline (CMT-3) and minocycline (CMT-8) are potent inhibitors of osteoclastogenesis in vitro from human peripheral blood mononuclear cells (PBMC) stimulated with macrophage colony stimulating factor (MCSF) and receptor activator of NF-kappaB ligand (RANKL), through an action that is independent of osteoblast-osteoclast interactions. Osteoclast formation over 20 days was completely abrogated when CMT-3 or CMT-8 were included in PBMC cultures at a concentration of 250 ng/ml, although doxycycline at this concentration reduced osteoclast formation to ca. 50% of control. CMT-3 and CMT-8 also significantly induced apoptosis over 24 h in mature osteoclasts generated over 20 days when added to cultures at 5 microg/ml or more. In a time-course experiment, apoptosis was evident after a delay of 1-2 h following treatment of mature osteoclasts with CMT-3 at 20 microg/ml. The broad-spectrum MMP inhibitor BB94 (Batimastat) did not recapitulate the apoptosis induced by CMT-3, even at a concentration where MMP-13 activity was completely inhibited. There was no evidence for an anabolic effect of any of the TCs on osteoblast lineage cells in a calcifying fibroblastic colony (CFU-f) formation assay, where CMT-3 partially inhibited CFU-f formation at 5 microg/ml. Our data indicate that inhibition of osteoclast formation and induction of osteoclast apoptosis are pharmacologically significant actions of CMTs in inhibiting bone resorption, and that osteoclast apoptosis cannot be attributed to the ability of CMTs to inhibit MMPs or to actions mediated by osteoblastic lineage cells.

EMD273316 & EMD95833, type 4 phosphodiesterase inhibitors, stimulate fibroblastic-colony formation by bone marrow cells via direct inhibition of PDE4 and the induction of endogenous prostaglandin synthesis

Background

Type 4 phosphodiesterase (PDE4) inhibitors have been shown to stimulate bone formation in vivo and to stimulate osteoblastic differentiation in vitro. As one possible mechanism for the stimulation of bone formation is the recruitment of osteoprogenitor cells from the bone marrow, we have investigated the effect of the PDE4 inhibitors EMD273316, EMD95833, EMD249615 and EMD 219906 on fibroblastic colony formation by whole bone marrow cells and on the ability of these colonies to adopt an osteoblastic phenotype.

Results

All four agents stimulated colony formation in a concentration dependent manner, however, in the case of EMD273316 & EMD95833, the effect was evident at lower concentrations and the addition of prostaglandin E₂ (PGE₂) was not necessary for maximal stimulation. It was subsequently found that co-incubation with indomethacin reduced the stimulatory effects of EMD273316 & EMD95833 but had no effect on the actions of EMD249615 and EMD 219906 and that EMD273316 & EMD95833 stimulated the synthesis of endogenous PGE₂ by whole bone marrow cells whereas EMD249615 and EMD 219906 had no significant effect.

Conclusions

These data suggest that EMD249615, EMD 219906, EMD273316 & EMD95833 can promote the recruitment of bone marrow osteoprogenitor cells leading to a stimulation of bone formation via their direct inhibitory effects on PDE4. The actions of EMD273316 & EMD95833 however, are augmented by their ability to stimulate endogenous prostanoids synthesis which acts synergistically with their direct effects on PDE4.

Practical Modeling Concepts for Connective Tissue Stem Cell and Progenitor Compartment Kinetics

Stem cell activation and development is central to skeletal development, maintenance, and repair, as it is for all tissues. However, an integrated model of stem cell proliferation, differentiation, and transit between functional compartments has yet to evolve. In this paper, the authors review current concepts in stem cell biology and progenitor cell growth and differentiation kinetics in the context of bone formation. A cell-based modeling strategy is developed and offered as a tool for conceptual and quantitative exploration of the key kinetic variables and possible organizational hierarchies in bone tissue development and remodeling, as well as in tissue engineering strategies for bone repair.

An objective method to measure cell survival by computer-assisted image processing of numeric images of Petri dishes

This work establishes an objective method to measure cell clonogenic survival by computer-assisted image processing using images of cell cultures fixed and stained in Petri dishes. The procedure, developed by Samba Technologies, consists of acquiring Petri dish pictures with a desktop scanner and analysing them by computer, using algorithms based on the 'top hat' filter. The results from the automated count for the cell line SQ20B are compared with those found by two observers, before and after normalization of the counting. After normalization, the shape of the survival curves of the 'manual' counting of the Petri dishes shows a good correlation between both observers. The software enables the small visible differences in count between observers to be eliminated. The comparison between the absolute number of colonies shows an increased difference between the two manual scorings that can be as great as 67 colonies, whereas the difference between the two automated counts is never greater than 8 colonies. These results demonstrate that the 'manual' count is inter- and intraobserver variable, whereas the automatic count performs reproducible cell colony counts, thereby minimizing user-generated bias. The large amount of data produced also gives information about cell and colony characteristics. Thus, this computer-assisted method has considerably improved the reliability of our statistical results.

Connective tissue progenitors: practical concepts for clinical applications

Tissue engineering can be defined as any effort to create or induce the formation of a specific tissue in a specific location through the selection and manipulation of cells, matrices, and biologic stimuli. The biologic concepts and the biochemical and biophysical principles on which these efforts are based have become an exciting and rapidly evolving field of biomedical research. More importantly, tissue engineering is becoming a clinical reality in the practice of orthopaedic surgery, providing patients and physicians with an expanding set of practical tools for effective therapy. New and improved matrices and bioactive factors inevitably will play important roles in the evolution of orthopaedic tissue engineering. However, tissue engineering never can stray far from fundamental biologic principles, and one of these is that cells do all the work. No new tissue forms except through the activity of living cells. No bone graft, no matrix, no growth factor, no cytokine can contribute to the generation or integration of new tissue, except through the influence it has on the behavior of cells. The efficacy of all current clinical tools depends entirely on the cells in the grafted site, particularly the small subset of stem cells and progenitor cells that are capable of generating new tissue. The current authors review a series of key biologic concepts related to the rational design and selection of composites of cells and matrices in contemporary bone grafting and tissue engineering efforts. The functional paradigms of stem cell biology are reviewed, including self renewal, asymmetric and symmetric mitosis, and lineage restriction. Several potential sources for autogenous stem cells for connective tissues are discussed. Finally, a simple mathematical model is introduced as a tool for understanding the functional demands placed on stem cells and progenitors in a graft site and to provide a conceptual framework for the rational design of cell matrix composite grafts.

Age-related osteoporosis in biglycan-deficient mice is related to defects in bone marrow stromal cells

Biglycan (bgn) is an extracellular matrix proteoglycan that is enriched in bone and other skeletal connective tissues. Previously, we generated bgn-deficient mice and showed that they developed age-dependent osteopenia. To identify the cellular events that might contribute to this progressive osteoporosis, we measured the number of osteogenic precursors in the bone marrow of normal and mutant mice. The number of colonies, indicative of the colony-forming unit potential of fibroblasts (CFU-F), gradually decreased with age. By 24 weeks of age, colony formation in the bgn knockout (KO) mice was significantly more reduced than that in the wild type (wt) mice. This age-related reduction was consistent with the extensive osteopenia previously shown by X-ray analysis and histological examination of 24-week-old bgn KO mice. Because bgn has been shown previously to bind and regulate transforming growth factor beta (TGF-beta) activity, we also asked whether this growth factor would affect colony formation. TGF-beta treatment significantly increased the size of the wt colonies. In contrast, TGF-beta did not significantly influence the size of the bgn colonies. An increase in apoptosis in bgn-deficient bone marrow stromal cells (BMSCs) was observed also. The combination of decreased proliferation and increased apoptosis, if it occurred in vivo, would lead to a deficiency in the generation of mature osteoblasts and would be sufficient to account for the osteopenia developed in the bgn KO mice. The bgn KO mice also were defective in the synthesis of type I collagen messenger RNA (mRNA) and protein. This result supports the suggestion that the composition of the extracellular matrix may be regulated by specific matrix components including bgn.

Age-related decline in the osteogenic potential of human bone marrow cells cultured in three-dimensional collagen sponges

Studies with human and animal culture systems indicate that a sub-population of bone marrow stromal cells has the potential to differentiate into osteoblasts. There are conflicting reports on the effects of age on human marrow-derived osteogenic cells. In this study, we used a three dimensional (3D) culture system and quantitative RT-PCR methods to test the hypothesis that the osteogenic potential of human bone marrow stromal cells decreases with age. Marrow was obtained from 39 men aged 37 to 86 years, during the course of total hip arthroplasty. Low-density mononuclear cells were seeded onto 3D collagen sponges and cultured for 3 weeks. Histological sections of sponges were stained for alkaline phosphatase activity and were scored as positive or negative. In the group < or = 50 years, 7 of 11 samples (63%) were positive, whereas only 5 of 19 (26%) of the samples in the group > or = 60 years were positive (p = 0.0504). As revealed by RT-PCR, there was no expression of alkaline phosphatase or collagen type I mRNA before culture, however there were strong signals after 3 weeks, an indication of osteoblast differentiation in vitro. We performed a quantitative, competitive RT-PCR assay with 8 samples (age range 38-80) and showed that the group < or = 50 years had 3-fold more mRNA for alkaline phosphatase than the group > or = 60 years (p = 0.021). There was a significant decrease with age (r = - 0.78, p = 0.028). These molecular and histoenzymatic data indicate that the osteogenic potential of human bone marrow cells decreases with age.

Stimulation of CFU-f formation by prostaglandin E2 is mediated in part by its degradation product, prostaglandin A2

Prostaglandins (PG) of the E series are known to rapidly undergo non-enzymatic dehydration in culture medium containing serum albumin to produce the cyclopentenone PGs of the A series. We investigated the actions of PGA1 and A2 in the in vitro calcifying fibroblastic-colony forming unit assay which can partially mimic the in vivo anabolic effects of PGE2. It was found that PGA1 and A2 both stimulated colony formation in a dose-dependent manner with a maximum at 10(-6) M and to a similar degree to PGE2. In contrast to PGE2, PGA1 and PGA2 both caused an inhibition of cAMP accumulation. Furthermore, the addition of protein kinase A inhibitors, H8 and H89, had no significant effect on the stimulation of colony number by PGE2. These data suggest that (a) the bone anabolic effects of PGE1 and E2 are, in part at least, mediated by their dehydration products PGA1 and A2 and (b) that they are mediated via pathways not necessarily involving the cAMP/protein kinase A cascade.

Automated counting of mammalian cell colonies

Investigating the effect of low-dose radiation exposure on cells using assays of colony-forming ability requires large cell samples to maintain statistical accuracy. Manually counting the resulting colonies is a laborious task in which consistent objectivity is hard to achieve. This is true especially with some mammalian cell lines which form poorly defined or 'fuzzy' colonies, typified by glioma or fibroblast cell lines. A computer-vision-based automated colony counter is presented in this paper. It utilizes novel imaging and image-processing methods involving a modified form of the Hough transform. The automated counter is able to identify less-discrete cell colonies typical of these cell lines. The results of automated colony counting are compared with those from four manual (human) colony counts for the cell lines HT29, A172, U118 and IN1265. The results from the automated counts fall well within the distribution of the manual counts for all four cell lines with respect to surviving fraction (SF) versus dose curves, SF values at 2 Gy (SF2) and total area under the SF curve (Dbar). From the variation in the counts, it is shown that the automated counts are generally more consistent than the manual counts.

Human myeloma cells promote the recruitment of osteoblast precursors: mediation by interleukin-6 and soluble interleukin-6 receptor

Multiple myeloma is associated with the development of osteolytic bone disease characterized by a disruption to normal bone resorption and bone formation. Although studies have shown that myeloma cells produce factors that promote bone resorption little data are available examining the mechanism of decreased bone formation or the factors that mediate this effect. In the present study we describe a novel in vitro coculture system in which to investigate the effect of myeloma cells on osteoblast recruitment and differentiation. Under appropriate conditions mesenchymal stem cells were shown to differentiate into colonies of cells, a proportion of which show characteristics of osteoblasts, in that they express alkaline phosphatase activity and stain positively for collagen and calcium. The addition of the human myeloma cells JJN-3, RPMI-8226, or NCI-H929 to these cultures stimulated a significant increase in the total number of colonies (p < 0.005) and the proportion of osteoblastic colonies (p < 0.005). Media conditioned by these cells also were able to promote the formation of both total and osteoblastic colonies (p < 0.005). The addition of an antibody against the interleukin-6 receptor (IL-6R) blocked myeloma cell and myeloma cell-conditioned media induced osteoblast recruitment (p < 0.01). Furthermore, media conditioned by myeloma cells incubated with phorbol ester, which promotes IL-6R shedding, or a metalloproteinase inhibitor, which inhibits IL-6R shedding, were able to stimulate (p < 0.005) and inhibit osteoblast recruitment (p < 0.005), respectively. In addition, soluble IL-6R (sIL-6R) and IL-6 together, but not alone, were able to promote osteoblastic colony formation (p < 0.01). Taken together these data show that myeloma cells promote osteoblast recruitment by release of sIL-6R from myeloma cells.