An Improved Method for Assessing Macroscale Diffusion through Osteonal Bone

The characterization of diffusion through biological tissues has played an important role in fundamental medical research and product development. Understanding the diffusion phenomena allows for the identification of new concepts in fundamental science, evolving medical knowledge and improving future standards and protocols. To illustrate, the structure of cortical bone changes upon the onset of osteoporosis, altering the limited porous compartment through which nutrients and essential signaling molecules travel to bone cells. Estrogen hormone replacement therapy (HRT) is one of the gold standard treatments to attempt to mitigate the effects that this structural change exerts in menopausal osteoporosis patients; however, HRT effectiveness is often variable in these patients, likely due to variability in bone structure and physiology, and thus transport rates. Scientists have studied diffusion in cortical bone tissue for decades. Current methodological standards include fluorescence recovery after photobleaching and computed tomography finite element analysis. Both techniques limit areas of tissue to microscale (1-100 µm2) analysis - only examining a few osteocytes within the structure at a time - and adopt assumptions that oversimplify in vivo tissue structure and transport phenomena. As well, the range of diffusion tracers is limited by the sensitivities of the analytical equipment, typically requiring tracer concentrations in the micromolar range. Herein is described a novel device for directly assessing the diffusion coefficient of 3H-estradiol at 37°C in macroscale osteonal bone specimens (1.4 cm2) - assessing a much larger portion of the total tissue than previously reported - while using radioisotope tracers for much higher sensitivity, thus achieving physiologically relevant estradiol concentrations. The current diffusion chamber device represents a cost-effective and validated method to mitigate these shortcomings. The device provides long-term diffusion data through macroscale (greater than 1 mm2) tissue areas, presenting a more physiologically accurate way to assess cortical bone diffusion. The device can assess solute diffusion through other tissues or materials and may easily be scaled up to run multiple diffusion experiments simultaneously.

Assessment of Clinical, Tissue, and Cell-Level Metrics Identify Four Biologically Distinct Knee Osteoarthritis Patient Phenotypes

OBJECTIVE

Clinical heterogeneity of primary osteoarthritis (OA) is a major challenge in understanding pathogenesis and development of targeted therapeutic strategies. This study aims to (1) identify OA patient subgroups phenotypes and (2) determine predictors of OA severity and cartilage-derived stem/progenitor concentration using clinical-, tissue-, and cell- level metrics.

DESIGN

Cartilage, synovium (SYN) and infrapatellar fatpad (IPFP) were collected from 90 total knee arthroplasty patients. Clinical metrics (patient demographics, radiograph-based joint space width (JSW), Kellgren and Lawrence score (KL)), tissue metrics (cartilage histopathology grade, glycosaminoglycans (GAGs)) and cell-based metrics (cartilage-, SYN-, and IPFP-derived cell concentration ([Cell], cells/mg), connective tissue progenitor (CTP) prevalence (PCTP, CTPs/million cells plated), CTP concentration, [CTP], CTPs/mg)) were assessed using k-mean clustering and linear regression model.

RESULTS

Four patient subgroups were identified. Clusters 1 and 2 comprised of younger, high body mass index (BMI) patients with healthier cartilage, where Cluster 1 had high CTP in cartilage, SYN, and IPFP, and Cluster 2 had low [CTP] in cartilage, SYN, and IPFP. Clusters 3 and 4 comprised of older, low BMI patients with diseased cartilage where Cluster 3 had low [CTP] in SYN, IPFP but high [CTP] in cartilage, and Cluster 4 had high [CTP] in SYN, IPFP but low [CTP] in cartilage. Age (r = 0.23, P = 0.026), JSW (r = 0.28, P = 0.007), KL (r = 0.26, P = 0.012), GAG/mg cartilage tissue (r = -0.31, P = 0.007), and SYN-derived [Cell] (r = 0.25, P = 0.049) were weak but significant predictors of OA severity. Cartilage-derived [Cell] (r = 0.38, P < 0.001) and PCTP (r = 0.9, P < 0.001) were moderate/strong predictors of cartilage-derived [CTP].

CONCLUSION

Initial findings suggests the presence of OA patient subgroups that could define opportunities for more targeted patient-specific approaches to prevention and treatment.

Influence of Glucose Concentration on Colony-Forming Efficiency and Biological Performance of Primary Human Tissue-Derived Progenitor Cells

OBJECTIVE

Glucose concentrations used in current cell culture methods are a significant departure from physiological glucose levels. The study focuses on comparing the effects of glucose concentrations on primary human progenitors (connective tissue progenitors [CTPs]) used for cartilage repair.

DESIGN

Cartilage- (Outerbridge grade 1, 2, 3; superficial and deep zone cartilage), infrapatellar fatpad-, synovium-, and periosteum-derived cells were obtained from 63 patients undergoing total knee arthroplasty and cultured simultaneously in fresh chondrogenic media containing 25 mM glucose (HGL) or 5 mM glucose (NGL) for pairwise comparison. Automated ASTM-based quantitative image analysis was used to determine colony-forming efficiency (CFE), effective proliferation rates (EPR), and sulfated-proteoglycan (GAG-ECM) staining of the CTPs across tissue sources.

RESULTS

HGL resulted in increased cell cultures with CFE = 0 compared with NGL in all tissue sources (P = 0.049). The CFE in NGL was higher than HGL for superficial cartilage (P < 0.001), and contrary for synovium-derived CTPs (P = 0.046) when CFE > 0. EPR of the CTPs did not differ between the media in the 6-day assay time period (P = 0.082). The GAG-ECM area of the CTPs and their progeny was increased in presence of HGL (P = 0.027).

CONCLUSION

Glucose concentration is critical to progenitor's physiology and should be taken into account in the setting of protocols for clinical or in vitro cell expansion strategies.

KLK6 expression in skin induces PAR1-mediated psoriasiform dermatitis and inflammatory joint disease

Kallikrein-related peptidase 6 (KLK6) is a secreted serine protease hypothesized to promote inflammation via cleavage of protease-activated receptor 1 (PAR1) and PAR2. KLK6 levels are elevated in multiple inflammatory and autoimmune conditions, but no definitive role in pathogenesis has been established. Here, we show that skin-targeted overexpression of KLK6 causes generalized, severe psoriasiform dermatitis with spontaneous development of debilitating psoriatic arthritis-like joint disease. The psoriatic skin and joint phenotypes are reversed by normalization of skin KLK6 levels and attenuated following genetic elimination of PAR1 but not PAR2. Conservation of this regulatory pathway was confirmed in human psoriasis using vorapaxar, an FDA-approved PAR1 antagonist, on explanted lesional skin from patients with psoriasis. Beyond defining a critical role for KLK6/PAR1 signaling in promoting psoriasis, our results demonstrate that KLK6/PAR1-mediated inflammation in the skin alone is sufficient to drive inflammatory joint disease. Further, we identify PAR1 as a promising cytokine-independent target in therapy of psoriasis and psoriatic arthritis.

A comparison of alendronate to varying magnitude PEMF in mitigating bone loss and altering bone remodeling in skeletally mature osteoporotic rats

Pulsed electromagnetic field (PEMF) treatments stimulate bone formation activities though further work is needed to optimize its therapeutic benefit. PEMF can generate local potential gradients and electric currents that have been suggested to mimic bone electrochemical responses to load. In line with this reasoning, a recent publication reported that PEMF application on isolated bone tissue induced detectable micro-vibrations (doi:https://doi.org/10.1109/TMAG.2016.2515069). To determine the ability of PEMF to intervene in a rat model of osteoporosis, we tested its effect on trabecular and cortical bone following ovariectomy. Four PEMF treatments, with increasing sinusoidal amplitude rise with time (3850 Hz pulse frequency and 15 Hz repetition rate at 10 tesla/sec (T/s), 30 T/s, 100 T/s, or 300 T/s), were compared to the efficacy of an osteoporosis drug, alendronate, in reducing levels of trabecular bone loss in the proximal tibia. Herein, the novel findings from our study are: (1) 30 T/s PEMF treatment approached the efficacy of alendronate in reducing trabecular bone loss, but differed from it by not reducing bone formation rates; and (2) 30 T/s and 100 T/s PEMF treatments imparted measurable alterations in lacunocanalicular features in cortical bone, consistent with osteocyte sensitivity to PEMF in vivo. The efficacy of specific PEMF doses may relate to their ability to modulate osteocyte function such that the 30 T/s, and to a lesser extent 100 T/s, doses preferentially antagonize trabecular bone resorption while stimulating bone formation. Thus, PEMF treatments of specific magnetic field magnitudes exert a range of measurable biological effects in trabecular and cortical bone tissue in osteoporotic rats.

The versican-hyaluronan complex provides an essential extracellular matrix niche for Flk1+ hematoendothelial progenitors

Little is known about extracellular matrix (ECM) contributions to formation of the earliest cell lineages in the embryo. Here, we show that the proteoglycan versican and glycosaminoglycan hyaluronan are associated with emerging Flk1⁺ hematoendothelial progenitors at gastrulation. The mouse versican mutant Vcan^hdf lacks yolk sac vasculature, with attenuated yolk sac hematopoiesis. CRISPR/Cas9-mediated Vcan inactivation in mouse embryonic stem cells reduced vascular endothelial and hematopoietic differentiation within embryoid bodies, which generated fewer blood colonies, and had an impaired angiogenic response to VEGF₁₆₅. Hyaluronan was severely depleted in Vcan^hdf embryos, with corresponding upregulation of the hyaluronan-depolymerase TMEM2. Conversely, hyaluronan-deficient mouse embryos also had vasculogenic suppression but with increased versican proteolysis. VEGF₁₆₅ and Indian hedgehog, crucial vasculogenic factors, utilized the versican-hyaluronan matrix, specifically versican chondroitin sulfate chains, for binding. Versican-hyaluronan ECM is thus an obligate requirement for vasculogenesis and primitive hematopoiesis, providing a vasculogenic factor-enriching microniche for Flk1⁺ progenitors from their origin at gastrulation.

Native-Osteoarthritic Joint Resident Stem and Progenitor Cells for Cartilage Cell-Based Therapies: A Quantitative Comparison With Respect to Concentration and Biological Performance

BACKGROUND

Cell-based therapy for cartilage repair is a promising approach and is becoming an established technique. Yet, there is no consensus on the optimal cell source.

PURPOSE

To provide a donor-matched quantitative comparison of the connective tissue progenitors (CTPs) derived from cartilage (Outerbridge grade 1-3 [G1-2-3]), bone marrow aspirate concentrate (BMC), infrapatellar fat pad (IPFP), synovium, and periosteum with respect to (1) cell concentration ([Cell], cells/mL), (2) CTP prevalence (P_CTP, colonies per million cells), and (3) biological performance based on in vitro proliferation potential (cells per colony) colony density, and differentiation potential (expression of negatively charged extracellular matrix: glycosaminoglycan-rich extra cellular matrix [GAG-ECM]).

STUDY DESIGN

Descriptive laboratory study.

METHODS

Tissues were obtained from 10 patients undergoing total knee arthroplasty (mean age, 59 years; women, n = 6). Automated quantitative colony-forming unit analysis was used to compare [Cell], P_CTP, and CTP biological performance across tissue sources.

RESULTS

[Cell] was highest in grade 3 cartilage (P = .002) and BMC (P = .001). Median P_CTP was highest in IPFP (P = .001), synovium (P = .003), and G1-2 cartilage (P = .02). Proliferation was highest in synovium-derived CTPs (P < .001). Median colony density was highest in G1-2-3 (P < .001). Median GAG-ECM was highest in G1-2-3 (P < .001). Within each patient, CTPs derived from all tissues were highly heterogeneous in biological performance as determined by cells per colony, density, and GAG-ECM.

CONCLUSION

Tissue sources differ in [Cell], P_CTP, and biological attributes. The data presented in this study suggest that cartilage (G1-2-3) is the preferred tissue source for cartilage repair based on P_CTP and GAG-ECM, followed by synovium, IPFP, BMC, and periosteum. However, due to the heterogeneous mixture of CTPs within each tissue source, there exists a subset of CTPs with biological performance similar to G1-2-3 cartilage, particularly in synovium and IPFP. Performance-based clonal selection and expansion of preferred CTPs and their progeny will potentially lead to improved cell population with predictive future.

CLINICAL RELEVANCE

Optimal tissue regeneration strategies will require informed decisions regarding which of the available tissue sources to use. Optimizing cell sourcing in any tissue may require separation of CTPs with preferred attributes from those with less desirable attributes. The heterogeneity manifest in the early stage of colony formation represents an opportunity for performance-based clone selection for clinical cell processing and manufacturing.

Donor-matched comparison of chondrogenic progenitors resident in human infrapatellar fat pad, synovium, and periosteum - implications for cartilage repair

Purpose: There is a clinical need to better characterize tissue sources being used for stem cell therapies. This study focuses on comparison of cells and connective tissue progenitors (CTPs) derived from native human infrapatellar fatpad (IPFP), synovium (SYN), and periosteum (PERI). Materials and Methods: IPFP, SYN, PERI were harvested from twenty-eight patients undergoing arthroplasty. CTPs were quantitatively characterized using automated colony-forming-unit assay to compare total nucleated cell concentration-[Cell], cells/mg; prevalence-(P_CTP), CTPs/million nucleated cells; CTP concentration-[CTP], CTPs/mg; proliferation and differentiation potential; and correlate outcomes with patient's age and gender. Results: [Cell] did not differ between IPFP, SYN, and PERI. P_CTP was influenced by age and gender: patients >60 years, IPFP and SYN had higher P_CTP than PERI (p < 0.001) and females had higher P_CTP in IPFP (p < 0.001) and SYN (p = 0.001) than PERI. [CTP] was influenced by age: patients <50 years, SYN (p = 0.0165) and PERI (p < 0.001) had higher [CTP] than IPFP; patients between 60 and 69 years, SYN (p < 0.001) had higher [CTP] than PERI; patients >70 years, IPFP (p = 0.006) had higher [CTP] than PERI. In patients >60 years, proliferation potential of CTPs differed significantly (SYN>IPFP>PERI); however, differentiation potentials were comparable between all three tissue sources. Conclusion: SYN and IPFP may serve as a preferred tissue source for patients >60 years, and PERI along with SYN and IPFP may serve as a preferred tissue source for patients <60 years for cartilage repair. However, the heterogeneity among the CTPs in any given tissue source suggests performance-based selection might be useful to optimize cell-sourcing strategies to improve efficacy of cellular therapies for cartilage repair.

High molecular weight hyaluronan ameliorates allergic inflammation and airway hyperresponsiveness in the mouse

Allergic asthma is a major cause of morbidity in both pediatric and adult patients. Recent research has highlighted the role of hyaluronan (HA), an extracellular matrix glycosaminoglycan, in asthma pathogenesis. Experimental allergic airway inflammation and clinical asthma are associated with an increase of shorter fragments of HA (sHA), which complex with inter-α-inhibitor heavy chains (HCs) and induce inflammation and airway hyperresponsiveness (AHR). Importantly, the effects of sHA can be antagonized by the physiological counterpart high molecular weight HA (HMWHA). We used a mouse model of house dust mite-induced allergic airway inflammation and demonstrated that instilled HMWHA ameliorated allergic airway inflammation and AHR, even when given after the establishment of allergic sensitization and after challenge exposures. Furthermore, instilled HMWHA reduced the development of HA-HC complexes and the activation of Rho-associated, coiled-coil containing protein kinase 2. We conclude that airway application of HMWHA is a potential treatment for allergic airway inflammation.

Knockout of hyaluronan synthase 1, but not 3, impairs formation of the retrocalcaneal bursa

Hyaluronan (HA), a high molecular weight non-sulfated glycosaminoglycan, is an integral component of the extracellular matrix of developing and mature connective tissues including tendon. There are few published reports quantifying HA content during tendon growth and maturation, or detailing its effects on the mechanical properties of the tendon extracellular matrix. Therefore, the goal of the current study was to examine the role of HA synthesis during post-natal skeletal growth and maturation, and its influence on tendon structure and biomechanical function. For this purpose, the morphological, biochemical, and mechanical properties of Achilles tendons from wild type (WT) and hyaluronan synthase 1 and 3 deficient mouse strains (Has1-/- (Has1KO), Has3-/- (Has3KO), and Has1-/- 3-/- (Has1/3KO)) were determined at 4, 8, and 12 weeks of age. Overall, HAS-deficient mice did not show any marked differences from WT mice in Achilles tendon morphology or in the HA and chondroitin/dermatan sulfate (CS/DS) contents. However, HAS1-deficiency (in the single or Has1/3 double KO) impeded post-natal formation of the retrocalcaneal bursa, implicating HAS1 in regulating HA metabolism by cells lining the bursal cavity. Together, these data suggest that HA metabolism via HAS1 and HAS3 does not markedly influence the extracellular matrix structure or function of the tendon body, but plays a role in the formation/maintenance of peritendinous bursa. Additional studies are warranted to elucidate the relationship of HA and CS/DS metabolism to tendon healing and repair in vivo. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2622-2632, 2018.

Progenitor cells from different zones of human cartilage and their correlation with histopathological osteoarthritis progression

Cell-based therapies development for the treatment of osteoarthritis (OA) requires an understanding of the disease progression and attributes of the cells resident in cartilage. This study focused on quantitative assessment of the concentration and biological potential of stem and progenitor cells resident in different zones of cartilage displaying macroscopic Outerbridge grade 1-2 OA, and their correlation with OA progression based on established histologic scoring system. Lateral femoral condyles were collected from 15 patients with idiopathic OA and varus knees undergoing total knee arthroplasty. Superficial(C_sp , top ∼ 500 µm) and deep cartilage(C_dp ) was separated. Chondrogenic Connective Tissue Progenitors (CTP-C) were assayed by standardized Colony-Forming-Unit assay using automated image analysis (Colonyze^TM ) based on ASTM standard F-2944-12. Cell concentration (cells/mg) was significantly greater in C_sp (median: 7,000; range: 3,440-17,600) than C_dp (median: 5,340; range: 3,393-9,660), p = 0.039. Prevalence (CTPs/million cells) was not different between C_sp (median: 1,274; range: 0-3,898) and C_dp (median:1,365; range:0-6,330), p = 0.42. In vitro performance of CTP-C progeny varied widely within and between patients, manifest by variation in colony size and morphology. Mean histopathological Mankin score was 4.7 (SD = 1.2), representing mild to moderate OA. Tidemark breach by blood vessels was associated with lower C_sp cell concentration (p = 0.02). Matrix degradation was associated with lower C_dp cell and CTP-C concentration (p = 0.015 and p = 0.095, respectively), independent of articular surface changes. These findings suggest that the initiation of OA may occur in either superficial or deep zones. The pathological changes affect CTP-Cs in C_sp and C_dp cartilage zones differently. The heterogeneity among the available CTP-Cs in C_sp and C_dp suggests performance-based selection to optimize cell-sourcing strategies for therapy. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1728-1738, 2018.

Differential Adaptations of the Musculoskeletal System after Spinal Cord Contusion and Transection in Rats

Spinal cord injury (SCI) causes impaired neuronal function with associated deficits in the musculoskeletal system, which can lead to permanent disability. Here, the impact of SCI on in vivo musculoskeletal adaptation was determined by studying deficits in locomotor function and analyzing changes that occur in the muscle and bone compartments within the rat hindlimb after contusion or transection SCI. Analyses of locomotor patterns, as assessed via the Basso, Beattie, and Bresnahan (BBB) rating scale, revealed that transection animals showed significant deficits, while the contusion group had moderate deficits, compared with naïve groups. Muscle myofiber cross-sectional areas (CSA) of both the soleus and tibialis anterior muscles were significantly decreased three months after contusion SCI. Such decreases in CSA were even more dramatic in the transection SCI group, suggesting a dependence on muscle activity, which is further validated by the correlation analyses between BBB score and myofiber CSA. Bone compartment analyses, however, revealed that transection animals showed the most significant deficits, while contusion animals showed no significant differences in the trabecular bone content within the proximal tibia compartment. In general, values of bone volume per total bone volume (BV/TV) were similar across the SCI groups. Significant decreases were observed, however, in the transection animals for bone mineral content, bone mineral density, and three-dimensional trabecular structure parameters (trabecular number, thickness, and spacing) compared with the naïve and contusion groups. Together, these findings suggest an altered musculoskeletal system can be correlated directly to motor dysfunctions seen after SCI.

High occurrence of osteoarthritic histopathological features unaccounted for by traditional scoring systems in lateral femoral condyles from total knee arthroplasty patients with varus alignment

Background and purpose - A better understanding of the patterns and variation in initiation and progression of osteoarthritis (OA) in the knee may influence the design of therapies to prevent or slow disease progression. By studying cartilage from the human lateral femoral condyle (LFC), we aimed to: (1) assess specimen distribution into early, mild, moderate, and severe OA as per the established histopathological scoring systems (HHGS and OARSI); and (2) evaluate whether these 2 scoring systems provide sufficient tools for characterizing all the features and variation in patterns of OA. Patients and methods - 2 LFC osteochondral specimens (4 x 4 x 8 mm) were collected from 50 patients with idiopathic OA varus knee and radiographically preserved lateral compartment joint space undergoing total knee arthroplasty. These were fixed, sectioned, and stained with HE and Safranin O-Fast Green (SafO). Results - The histopathological OA severity distribution of the 100 specimens was: 6 early, 62 mild, 30 moderate, and 2 severe. Overall, 45/100 specimens were successfully scored by both HHGS and OARSI: 12 displayed low OA score and 33 displayed cartilage surface changes associated with other histopathological features. However, 55/100 samples exhibited low surface structure scores, but were deemed to be inadequately scored by HHGS and OARSI because of anomalous features in the deeper zones not accounted for by these systems: 27 exhibited both SafO and tidemark abnormal features, 16 exhibited only SafO abnormal features, and 12 exhibited tidemark abnormal features. Interpretation - LFC specimens were scored as mild to moderate OA by HHGS and OARSI. Yet, several specimens exhibited deep zone anomalies while maintaining good surface structure, inconsistent with mild OA. Overall, a better classification of these anomalous histopathological features could help better understand idiopathic OA and potentially recognize different subgroups of disease.

Variation in primary and culture-expanded cells derived from connective tissue progenitors in human bone marrow space, bone trabecular surface and adipose tissue

BACKGROUND AIMS

Connective tissue progenitors (CTPs) embody the heterogeneous stem and progenitor cell populations present in native tissue. CTPs are essential to the formation and remodeling of connective tissue and represent key targets for tissue-engineering and cell-based therapies. To better understand and characterize CTPs, we aimed to compare the (i) concentration and prevalence, (ii) early in vitro biological behavior and (iii) expression of surface-markers and transcription factors among cells derived from marrow space (MS), trabecular surface (TS), and adipose tissues (AT).

METHODS

Cancellous-bone and subcutaneous-adipose tissues were collected from 8 patients. Cells were isolated and cultured. Colony formation was assayed using Colonyze software based on ASTM standards. Cell concentration ([Cell]), CTP concentration ([CTP]) and CTP prevalence (P_CTP) were determined. Attributes of culture-expanded cells were compared based on (i) effective proliferation rate and (ii) expression of surface-markers CD73, CD90, CD105, SSEA-4, SSEA-3, SSEA-1/CD15, Cripto-1, E-Cadherin/CD324, Ep-CAM/CD326, CD146, hyaluronan and transcription factors Oct3/4, Sox-2 and Nanog using flow cytometry.

RESULTS

Mean [Cell], [CTP] and P_CTP were significantly different between MS and TS samples (P = 0.03, P = 0.008 and P= 0.0003), respectively. AT-derived cells generated the highest mean total cell yield at day 6 of culture-4-fold greater than TS and more than 40-fold greater than MS per million cells plated. TS colonies grew with higher mean density than MS colonies (290 ± 11 versus 150 ± 11 cell per mm²; P = 0.0002). Expression of classical-mesenchymal stromal cell (MSC) markers was consistently recorded (>95%) from all tissue sources, whereas all the other markers were highly variable.

CONCLUSIONS

The prevalence and biological potential of CTPs are different between patients and tissue sources and lack variation in classical MSC markers. Other markers are more likely to discriminate differences between cell populations in biological performance. Understanding the underlying reasons for variation in the concentration, prevalence, marker expression and biological potential of CTPs between patients and source tissues and determining the means of managing this variation will contribute to the rational development of cell-based clinical diagnostics and targeted cell-based therapies.

TNF-stimulated gene 6 promotes formation of hyaluronan-inter-α-inhibitor heavy chain complexes necessary for ozone-induced airway hyperresponsiveness

Exposure to pollutants, such as ozone, exacerbates airway inflammation and hyperresponsiveness (AHR). TNF-stimulated gene 6 (TSG-6) is required to transfer inter-α-inhibitor heavy chains (HC) to hyaluronan (HA), facilitating HA receptor binding. TSG-6 is necessary for AHR in allergic asthma, because it facilitates the development of a pathological HA-HC matrix. However, the role of TSG-6 in acute airway inflammation is not well understood. Here, we hypothesized that TSG-6 is essential for the development of HA- and ozone-induced AHR. TSG-6^-/- and TSG-6^+/+ mice were exposed to ozone or short-fragment HA (sHA), and AHR was assayed via flexiVent. The AHR response to sHA was evaluated in the isolated tracheal ring assay in tracheal rings from TSG-6^-/- or TSG-6^+/+, with or without the addition of exogenous TSG-6, and with or without inhibitors of Rho-associated, coiled-coil-containing protein kinase (ROCK), ERK, or PI3K. Smooth-muscle cells from mouse tracheas were assayed in vitro for signaling pathways. We found that TSG-6 deficiency protects against AHR after ozone (in vivo) or sHA (in vitro and in vivo) exposure. Moreover, TSG-6^-/- tracheal ring non-responsiveness to sHA was reversed by exogenous TSG-6 addition. sHA rapidly activated RhoA, ERK, and Akt in airway smooth-muscle cells, but only in the presence of TSG-6. Inhibition of ROCK, ERK, or PI3K/Akt blocked sHA/TSG-6-mediated AHR. In conclusion, TSG-6 is necessary for AHR in response to ozone or sHA, in part because it facilitates rapid formation of HA-HC complexes. The sHA/TSG-6 effect is mediated by RhoA, ERK, and PI3K/Akt signaling.

Histopathological assessment of primary osteoarthritic knees in large patient cohort reveal the possibility of several potential patterns of osteoarthritis initiation

OBJECTIVE

The two main objectives of the study include (1) Test the hypothesis that the lateral femoral condyle (LFC) in patients with primary OA and varus knees undergoing total knee arthroplasty (TKA) can be used as a model to better characterize varying histological features of human OA, (2) Correlate characteristic OA features using the established histopathological scoring systems (HHGS and OARSI) to understand potential histopathological patterns of OA initiation.

DESIGN

Two osteochondral specimens (4×4×8mm) were collected from fifty patient's LFC at the time of TKA (total 100 specimens), who presented preserved lateral knee compartment with joint space width>2mm. Three independent readers graded the sections on three different occasions using HHGS and OARSI systems. The correlation between individual parameters of the two scoring systems and their inter- and intra-reader variability, reliability and reproducibility were estimated.

RESULTS

All samples in this cohort showed abnormal histopathological features. Total histopathological scores of the LFC ranged from HHGS median=4.6 (range=0 to 11), and OARSI median=5.2 (range=0 to 19.5). The four individual sub-items of HHGS scoring system (structure, cells, safraninO staining, tidemark) were weakly correlated, with the correlation between structure and cellularity being the strongest (r=0.40). Both the scoring systems had similar repeatability and reproducibility coefficients of<21%.

CONCLUSIONS

OA changes in the LFC are not confined to any one region, and maybe seen in different regions of cartilage, tidemark, subchondral bone, and/or the marrow space vascularity. These variations may point to the possibility of several potential patterns of initiation in OA.

Quantification of hyaluronan (HA) using a simplified fluorophore-assisted carbohydrate electrophoresis (FACE) procedure

Hyaluronan (HA) exhibits numerous important roles in physiology and pathologies, and these facts necessitate an ability to accurately and reproducibly measure its quantities in tissues and cell cultures. Our group previously reported a rigorous and analytical procedure to quantify HA (and chondroitin sulfate, CS) using a reductive amination chemistry and separation of the fluorophore-conjugated, unsaturated disaccharides unique to HA and CS on high concentration acrylamide gels. This procedure is known as fluorophore-assisted carbohydrate electrophoresis (FACE) and has been adapted for the detection and quantification of all glycosaminoglycan types. While this previous FACE procedure is relatively straightforward to implement by carbohydrate research investigators, many nonglycoscience laboratories now studying HA biology might have difficulties establishing this prior FACE procedure as a routine assay for HA. To address this need, we have greatly simplified our prior FACE procedure for accurate and reproducible assessment of HA in tissues and cell cultures. This chapter describes in detail this simplified FACE procedure and, because it uses an enzyme that degrades both HA and CS, investigators will also gain additional insight into the quantities of CS in the same samples dedicated for HA analysis.

cAMP-dependent activation of protein kinase A attenuates respiratory syncytial virus-induced human airway epithelial barrier disruption

Airway epithelium forms a barrier to the outside world and has a crucial role in susceptibility to viral infections. Cyclic adenosine monophosphate (cAMP) is an important second messenger acting via two intracellular signaling molecules: protein kinase A (PKA) and the guanidine nucleotide exchange factor, Epac. We sought to investigate effects of increased cAMP level on the disruption of model airway epithelial barrier caused by RSV infection and the molecular mechanisms underlying cAMP actions. Human bronchial epithelial cells were infected with RSV-A2 and treated with either cAMP releasing agent, forskolin, or cAMP analogs. Structure and functions of the Apical Junctional Complex (AJC) were evaluated by measuring transepithelial electrical resistance and permeability to FITC-dextran, and determining localization of AJC proteins by confocal microscopy. Increased intracellular cAMP level significantly attenuated RSV-induced disassembly of AJC. These barrier-protective effects of cAMP were due to the activation of PKA signaling and did not involve Epac activity. Increased cAMP level reduced RSV-induced reorganization of the actin cytoskeleton, including apical accumulation of an essential actin-binding protein, cortactin, and inhibited expression of the RSV F protein. These barrier-protective and antiviral-function of cAMP signaling were evident even when cAMP level was increased after the onset of RSV infection. Taken together, our study demonstrates that cAMP/PKA signaling attenuated RSV-induced disruption of structure and functions of the model airway epithelial barrier by mechanisms involving the stabilization of epithelial junctions and inhibition of viral biogenesis. Improving our understanding of the mechanisms involved in RSV-induced epithelial dysfunction and viral pathogenesis will help to develop novel anti-viral therapeutic approaches.

Endotoxin free hyaluronan and hyaluronan fragments do not stimulate TNF-α, interleukin-12 or upregulate co-stimulatory molecules in dendritic cells or macrophages

The extracellular matrix glycosaminoglycan, hyaluronan, has been described as a regulator of tissue inflammation, with hyaluronan fragments reported to stimulate innate immune cells. High molecular mass hyaluronan is normally present in tissues, but upon inflammation lower molecular mass fragments are generated. It is unclear if these hyaluronan fragments induce an inflammatory response or are a consequence of inflammation. In this study, mouse bone marrow derived macrophages and dendritic cells (DCs) were stimulated with various sizes of hyaluronan from different sources, fragmented hyaluronan, hyaluronidases and heavy chain modified-hyaluronan (HA-HC). Key pro-inflammatory molecules, tumour necrosis factor alpha, interleukin-1 beta, interleukin-12, CCL3, and the co-stimulatory molecules, CD40 and CD86 were measured. Only human umbilical cord hyaluronan, bovine testes and Streptomyces hyaluronlyticus hyaluronidase stimulated macrophages and DCs, however, these reagents were found to be contaminated with endotoxin, which was not fully removed by polymyxin B treatment. In contrast, pharmaceutical grade hyaluronan and hyaluronan fragments failed to stimulate in vitro-derived or ex vivo macrophages and DCs, and did not induce leukocyte recruitment after intratracheal instillation into mouse lungs. Hence, endotoxin-free pharmaceutical grade hyaluronan does not stimulate macrophages and DCs in our inflammatory models. These results emphasize the importance of ensuring hyaluronan preparations are endotoxin free.

Pathological Hyaluronan Matrices in Cystic Fibrosis Airways and Secretions

Hyaluronan (HA) has been used in treatment of cystic fibrosis (CF) via a nebulizer and has demonstrated success in clinical outcomes. HA is an important glycosaminoglycan that is cross-linked by heavy chains (HCs) from inter-α-inhibitor during inflammation. HC cross-linked HA (HC-HA) becomes significantly more adhesive for leukocytes than non-cross-linked HA, which can enhance inflammation. Our studies tested the hypothesis that HC-HA is present in CF airways and that altered ratios of HC-HA to its degradation into relatively lower molecular weight HA contribute to the pathophysiology of chronic inflammation in CF. We evaluated the distribution, levels, and size of HC-HA within CF, healthy, and diseased control lung, bronchus, and sputum tissues by histological and biochemical approaches. HC-HA was significantly elevated in CF, with deposits around the pulmonary vasculature, airway submucosa, and in the stroma of the submucosal glands. The increased infiltration of leukocyte populations correlated with the distribution of HC-HA matrices in the airways. Elevated lung tissue HC-HA correlated with decreased HA levels in CF mucus and sputum compared with controls, suggesting that aberrant degradation and cross-linking of HA in lung tissue is a unique feature of CF. The accumulation and degradation of proinflammatory HC-HA in CF lung tissue suggests that aberrant HA catabolism and cross-linking may contribute to chronic inflammation in airway tissues and affect mucus viscosity in CF airways.

Deficiency of circadian clock protein BMAL1 in mice results in a low bone mass phenotype

The circadian clock is an endogenous time keeping system that controls the physiology and behavior of many organisms. The transcription factor Brain and Muscle ARNT-like Protein 1 (BMAL1) is a component of the circadian clock and necessary for clock function. Bmal1(-/-) mice display accelerated aging and many accompanying age associated pathologies. Here, we report that mice deficient for BMAL1 have a low bone mass phenotype that is absent at birth and progressively worsens over their lifespan. Accelerated aging of these mice is associated with the formation of bony bridges occurring across the metaphysis to the epiphysis, resulting in shorter long bones. Using micro-computed tomography we show that Bmal1(-/-) mice have reductions in cortical and trabecular bone volume and other micro-structural parameters and a lower bone mineral density. Histology shows a deficiency of BMAL1 results in a reduced number of active osteoblasts and osteocytes in vivo. Isolation of bone marrow derived mesenchymal stem cells from Bmal1(-/-) mice demonstrate a reduced ability to differentiate into osteoblasts in vitro, which likely explains the observed reductions in osteoblasts and osteocytes, and may contribute to the observed osteopenia. Our data support the role of the circadian clock in the regulation of bone homeostasis and shows that BMAL1 deficiency results in a low bone mass phenotype.

Substrate concentration influences effective radial diffusion coefficient in canine cortical bone

Transport of nutrients and waste across osseous tissue is dependent on the dynamic micro and macrostructure of the tissue; however little quantitative data exists examining how this transport occurs across the entire tissue. Here we investigate in vitro radial diffusion across a section of canine tissue, at dimensions of several hundred microns to millimeters, specifically between several osteons connected through a porous microstructure of Volkmann's canals and canaliculi. The effective diffusion coefficient is measured by a "sample immersion" technique presented here, in which the tissue sample was immersed in solution for 18-30 h, image analysis software was used to quantify the solute concentration profile in the tissue, and the data were fit to a mathematical model of diffusion in the tissue. Measurements of the effective diffusivity of sodium fluorescein using this technique were confirmed using a standard two-chamber diffusion system. As the solute concentration increased, the effective diffusivity decreased, ranging from 1.6 × 10(-7) ± 3.2 × 10(-8) cm(2)/s at 0.3 μM to 1.4 × 10(-8) ± 1.9 × 10(-9) cm(2)/s at 300 μM. The results show that there is no significant difference in mean diffusivity obtained using the two measurement techniques on the same sample, 3.3 × 10(-8) ± 3.3 × 10(-9) cm(2)/s (sample immersion), compared to 4.4 × 10(-8) ± 1.1 × 10(-8) cm(2)/s (diffusion chamber).

In vitro toxicity in long-term cell culture of MR contrast agents targeted to cartilage evaluation

OBJECTIVE

Contrast-enhanced magnetic resonance (MR) imaging methods have been proposed for non-invasive evaluation of osteoarthritis (OA). We measured cell toxicities of cartilage-targeted low-generation dendrimer-linked nitroxide MR contrast agents and gadopentetate dimeglumine (Gd-DTPA) on cultured chondrocytes.

DESIGN

A long-term Swarm rat chondrosarcoma chondrocyte-like cell line was exposed for 48-h to different salts (citrate, maleate, tartrate) and concentrations of generation one or two diaminobutyl-linked nitroxides (DAB4-DLN or DAB8-DLN), Gd-DTPA, or staurosporine (positive control). Impact on microscopic cell appearance, MTT spectrophotometric assays of metabolic activity, and quantitative PicoGreen assays of DNA content (cell proliferation) were measured and compared to untreated cultures.

RESULTS

Chondrocyte cultures treated with up to 7.5 mM Gd-DTPA for 48-h had no statistical differences in DNA content or MTT reaction compared to untreated cultures. At all doses, DAB4-DLN citrate treated cultures had results similar to untreated and Gd-DTPA-treated cultures. At doses >1 mM, DAB4-DLN citrate treated cultures showed statistically greater DNA and MTT reaction than maleate and tartrate DAB4-DLN salts. Cultures exposed to 5 mM or 7.5 mM DAB8-DLN citrate exhibited rounded cells, poor cell proliferation, and barely detectable MTT reaction. Treatment with 0.1 μM staurosporine caused chondrocyte death.

CONCLUSION

Long-term exposure, greater than clinically expected, to either DAB4-DLN citrate or Gd-DTPA had no detectable toxicity with results equivalent to untreated cultures. DAB4-DLN citrate was more biocompatible than either the maleate or tartrate salts. Cells exposed for 48-h to 5 mM or 7.5 mM DAB8-DLN salts demonstrated significant cell toxicity. Further evaluation of DAB8-DLN with clinically appropriate exposure times is required to determine the maximum useful concentration.

Hyperglycemia diverts dividing osteoblastic precursor cells to an adipogenic pathway and induces synthesis of a hyaluronan matrix that is adhesive for monocytes

Isolated rat bone marrow stromal cells cultured in osteogenic medium in which the normal 5.6 mm glucose is changed to hyperglycemic 25.6 mm glucose greatly increase lipid formation between 21-31 days of culture that is associated with decreased biomineralization, up-regulate expression of cyclin D3 and two adipogenic markers (CCAAT/enhancer binding protein α and peroxisome proliferator-activated receptor γ) within 5 days of culture, increase neutral and polar lipid synthesis within 5 days of culture, and form a monocyte-adhesive hyaluronan matrix through an endoplasmic reticulum stress-induced autophagic mechanism. Evidence is also provided that, by 4 weeks after diabetes onset in the streptozotocin-induced diabetic rat model, there is a large loss of trabecular bone mineral density without apparent proportional changes in underlying collagen matrices, a large accumulation of a hyaluronan matrix within the trabecular bone marrow, and adipocytes and macrophages embedded in this hyaluronan matrix. These results support the hypothesis that hyperglycemia in bone marrow diverts dividing osteoblastic precursor cells (bone marrow stromal cells) to a metabolically stressed adipogenic pathway that induces synthesis of a hyaluronan matrix that recruits inflammatory cells and establishes a chronic inflammatory process that demineralizes trabecular cancellous bone.

Separation of newly formed bone from older compact bone reveals clear compositional differences in bone matrix

In long bone diaphyses, woven bone forms first and then transitions into a more mineralized compact bone tissue. Prior evidence suggests that the non-collagenous protein composition of woven bone may be distinct from that of more mature bone tissue, particularly with respect to a diverse group of phosphorylated, extracellular matrix proteins. To critically test this hypothesis, we developed an in situ approach to isolate newly formed bone from more mature bone within the same long bone, and combine this anatomical approach with Western blotting to make relative comparisons of 7 phosphorylated matrix proteins important for bone physiology and biomineralization. Interestingly, 75 kDa bone sialoprotein (BSP), 63 kDa osteopontin, and the 75 kDa form of bone acidic glycoprotein-75 (BAG-75) were enriched in primary bone as opposed to more mature cortical bone, while osteonectin, fetuin A, matrix extracellular phosphoglycoprotein (MEPE) and dentin matrix protein-1 (DMP-1) appeared to be equally distributed between these two bone tissue compartments. Analyses also revealed the presence of larger sized forms of osteopontin (and to a lesser degree BSP) mostly in newly formed bone, while larger forms of BAG-75 were mostly detected in more mature cortical bone. Smaller sized forms of DMP-1 and BAG-75 were detected in both newly formed and more mature bone tissue extracts, and they are likely the result of proteolytic processing in vivo. Intact DMP-1 (97 kDa) was only detected in unmineralized matrix extracts. These findings indicate that newly formed bone exhibits a non-collagenous matrix protein composition distinct from that of more mature compact bone even within the same long bone, and suggest that the temporal fate of individual non-collagenous proteins is variable in growing bone.

Stromal cell-derived factor-1 and monocyte chemotactic protein-3 improve recruitment of osteogenic cells into sites of musculoskeletal repair

Homing of osteogenic cells through the systemic circulation represents an alternative to traditional orthopedic tissue engineering approaches that focus on local cell populations. We hypothesize that expression of the chemokine, stromal cell-derived factor-1 (SDF-1) or monocyte chemotactic protein-3 (MCP-3) may enhance homing of osteogenic cells into sites of fracture repair, as both have demonstrated promise in recruitment of marrow stromal cells (MSCs). This hypothesis was tested by transplantation of culture expanded MSCs expressing these factors adjacent to a fracture site on a collagen scaffold. One green fluorescent protein positive (GFP+) and one wild-type mouse were surgically conjoined as parabiots at 7-8 weeks of age. Fibular osteotomy was performed 4 weeks after parabiosis on the hind limb of the wild-type mouse. Mice were randomly allocated to receive one of the following five treatments: control (no scaffold), empty scaffold (no cells), or scaffold containing MSCs, scaffold containing MSCs expressing SDF-1, or scaffold containing MSCs expressing MCP-3. Fracture callus was harvested 2 weeks after injury, and analyzed with confocal microscopy and cell-counting software. When compared to fracture callus treated with nontransfected MSCs, the fracture callus of mice treated with both SDF-1 and MCP-3 secreting MSCs demonstrated a significant increase in the number of both GFP+ cells (p = 0.0003, p = 0.02) and GFP+ /AP+ cells (p = 0.0005, p = 0.01). These data suggest that homing of osteogenic cells from systemic circulation participate in fracture repair and that homing pathways might be modulated to enhance the contribution of circulating progenitors at the site of skeletal injury.

Inhibition of proprotein convertase SKI-1 blocks transcription of key extracellular matrix genes regulating osteoblastic mineralization

Mineralization, a characteristic phenotypic property of osteoblastic lineage cells, was blocked by 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride (AEBSF) and decanoyl-Arg-Arg-Leu-Leu-chloromethyl ketone (dec-RRLL-cmk), inhibitors of SKI-1 (site 1; subtilisin kexin like-1) protease. Because SKI-1 is required for activation of SREBP and CREB (cAMP-response element-binding protein)/ATF family transcription factors, we tested the effect of these inhibitors on gene expression. AEBSF decreased expression of 140 genes by 1.5-3.0-fold including Phex, Dmp1, COL1A1, COL11A1, and fibronectin. Direct comparison of AEBSF and dec-RRLL-cmk, a more specific SKI-1 inhibitor, demonstrated that expression of Phex, Dmp1, COL11A1, and fibronectin was reduced by both, whereas COL1A2 and HMGCS1 were reduced only by AEBSF. AEBSF and dec-RRLL-cmk decreased the nuclear content of SKI-1-activated forms of transcription factors SREBP-1, SREBP-2, and OASIS. In contrast to AEBSF, the actions of dec-RRLL-cmk represent the sum of its direct actions on SKI-1 and indirect actions on caspase-3. Specifically, dec-RRLL-cmk reduced intracellular caspase-3 activity by blocking the formation of activated 19-kDa caspase-3. Conversely, overexpression of SKI-1-activated SREBP-1a and CREB-H in UMR106-01 osteoblastic cells increased the number of mineralized foci and altered their morphology to yield mineralization nodules, respectively. In summary, SKI-1 regulates the activation of transmembrane transcription factor precursors required for expression of key genes required for mineralization of osteoblastic cultures in vitro and bone formation in vivo. Our results indicate that the differentiated phenotype of osteoblastic cells and possibly osteocytes depends upon the non-apoptotic actions of SKI-1.

Lipids and collagen matrix restrict the hydraulic permeability within the porous compartment of adult cortical bone

In vivo the hydraulic permeability of cortical bone influences the transport of nutrients, waste products and signaling molecules, thus influencing the metabolic functions of osteocytes and osteoblasts. In the current study two hypotheses were tested: the presence of (1) lipids and (2) collagen matrix in the porous compartment of cortical bone restricts its permeability. Our approach was to measure the radial permeability of adult canine cortical bone before and after extracting lipids with acetone-methanol, and before and after digesting collagen with bacterial collagenase. Our results showed that the permeability of adult canine cortical bone was below 4.0x10(-17) m2, a value consistent with prior knowledge. After extracting lipids, permeability increased to a median value of 8.6x10(-16) m2. After further digesting with collagenase, permeability increased to a median value of 1.4x10(-14) m2. We conclude that the presence of both lipids and collagen matrix within the porous compartment of cortical bone restricts its radial permeability. These novel findings suggest that the chemical composition of the tissue matrix within the porous compartment of cortical bone influences the transport and exchange of nutrients and waste products, and possibly influences the metabolic functions of osteocytes and osteoblasts.

Parathyroid hormone suppresses osteoblast apoptosis by augmenting DNA repair

Daily injection of parathyroid hormone (PTH) is a clinically approved treatment for osteoporosis. It suppresses apoptosis of bone-forming osteoblasts although its exact anti-apoptotic mechanism(s) is incompletely understood. In this study, PTH treatment of cultured osteoblasts blocked the pro-apoptotic effects of serum withdrawal and nutrient deprivation; hydrogen peroxide induced oxidative stress, and UV irradiation. We hypothesized that PTH might suppress osteoblast apoptosis by enhancing DNA repair. Evidence is provided showing that post-confluent, non-proliferating osteoblasts treated with PTH exhibited a protein kinase A-mediated activation of two proteins that regulate DNA repair processes (proliferating cell nuclear antigen and forkhead box transcription factor 3a) as well as a suppression of the pro-apoptotic growth arrest and DNA damage protein 153. Additional proof of a connection between DNA damage and osteoblast apoptosis came from an unexpected finding whereby a majority of fixed PTH-treated osteoblasts scored weakly positive for Terminal Deoxynucleotidyl dUTP Nick-End Labeling (TUNEL), even though similar cultures were determined to be viable via a trypsin replating strategy. TUNEL identifies DNA excision repair, not just apoptotic DNA fragmentation, and the most likely explanation of these TUNEL results is that PTH's activation of DNA repair processes would permit nucleotide incorporation as a result of enhanced excision repair. This explanation was confirmed by an enhanced incorporation of bromodeoxyuridine in PTH-treated cells even though a majority of the cell population was determined to be non-replicating. An augmentation of DNA repair by PTH is an unreported finding, and provides an additional explanation for its anti-apoptotic mechanism(s).

Regulation of heparan sulfate and chondroitin sulfate glycosaminoglycan biosynthesis by 4-fluoro-glucosamine in murine airway smooth muscle cells

The importance of the pathological changes in proteoglycans has driven the need to study and design novel chemical tools to control proteoglycan synthesis. Accordingly, we tested the fluorinated analogue of glucosamine (4-fluoro-N-acetyl-glucosamine (4-F-GlcNAc)) on the synthesis of heparan sulfate (HS) and chondroitin sulfate (CS) by murine airway smooth muscle (ASM) cells in the presence of radiolabeled metabolic precursors. Secreted and cell-associated CS and HS were assessed for changes in size by Superose 6 chromatography. Treatment of ASM cells with 4-F-GlcNAc (100 microM) reduced the quantity (by 64.1-76.6%) and decreased the size of HS/CS glycosaminoglycans associated with the cell layer (K(av) shifted from 0.30 to 0.45). The quantity of CS secreted into the medium decreased by 65.7-73.0%, and the size showed a K(av) shift from 0.30 to 0.50. Treatment of ASM cells with 45 microM and 179 microM 4-F-GlcNAc in the presence of a stimulator of CS synthesis, 4-methylumbelliferyl-beta-D-xyloside, reduced the amount of the xyloside-CS chains by 65.4 and 87.0%, respectively. The size of xyloside-CS chains synthesized in the presence of 4-F-GlcNAc were only slightly larger than those with xyloside treatment alone (K(av) of 0.55 compared with that of 0.6). The effects of 4-F-GlcNAc to inhibit CS synthesis were not observed with equimolar concentrations of glucosamine. We propose that 4-F-GlcNAc inhibits CS synthesis by inhibiting 4-epimerization of UDP-GlcNAc to UDP-GalNAc, thereby depleting one of the substrates required, whereas HS elongation is inhibited by truncation when the nonreducing terminus of the growing chain is capped with 4-F-GlcNAc.

Confocal laser Raman microspectroscopy of biomineralization foci in UMR 106 osteoblastic cultures reveals temporally synchronized protein changes preceding and accompanying mineral crystal deposition

Mineralization in UMR 106-01 osteoblastic cultures occurs within extracellular biomineralization foci (BMF) within 12 h after addition of beta-glycerol phosphate to cells at 64 h after plating. BMF are identified by their enrichment with an 85-kDa glycoprotein reactive with Maackia amurensis lectin. Laser Raman microspectroscopic scans were made on individual BMF at times preceding (64-76 h) and following the appearance of mineral crystals (76-88 h). The range of variation between spectra for different BMF in the same culture was rather small. In contrast, significant differences were observed for spectral bands at 957-960, 1004, and 1660 cm(-1) when normalized BMF spectra at different times were compared. Protein-dependent spectral bands at 1004 and 1660 cm(-1) increased and then decreased preceding the detection of hydroxyapatite crystals via the phosphate stretching peak at 959-960 cm(-1). When sodium phosphate was substituted for beta-glycerol phosphate, mineralization occurred 3-6 h earlier. Irrespective of phosphate source, the Raman full peak width at half-maximum ratio for 88 h cultures was similar to that for 10-day-old marrow ablation primary bone. However, if mineralization was blocked with serine protease inhibitor 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride, 64-88-h BMF spectra remained largely invariant. In summary, Raman spectral data demonstrate for the first time that formation of hydroxyapatite crystals within individual BMF is a multistep process. Second, changes in protein-derived signals at 1004 and 1660 cm(-1) reflect events within BMFs that precede or accompany mineral crystal production because they are blocked by mineralization inhibitor 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride. Finally, the low extent of spectral variability detected among different BMF at the same time point indicates that mineralization of individual BMF within a culture is synchronized.

Isolation of calcospherulites from the mineralization front of bone

Calcium-containing spherical bodies (calcospherulites) exist along the mineralization front of bone and are thought to play a role in bone formation. Existing methods to isolate calcospherulites involve harsh treatments that remove much of their organic matter. This study sought to isolate them using a less destructive approach to better preserve their organic components. Juvenile rats were injected with a low dose of calcein to label the newly formed mineral at the mineralization front of bone in vivo. Periosteum was completely dissected from the tibial diaphysis and unmineralized osteoid matrix was removed by collagenase in order to expose calcospherulites. Calcein-labeled calcospherulites of approximately 0.5 mum average diameter were observed all along the mineralization front and they exhibited a Ca/P ratio of 1.3 in situ. Calcospherulites were released from the mineralization front by a short dispase digestion and isolated via fluorescence flow sorting. X-ray diffraction revealed they contained apatite crystals (c-axis length of 17.5 +/- 0.2 nm) and their Ca/P ratio was preserved during isolation. Calcospherulites treated with ice-cold ethanol exhibited a Ca/P ratio of 1.6, suggesting the presence of some extractable phospholipids. Proteins extracted from isolated calcospherulites were resolved by SDS-PAGE into more than 20 distinct bands. Western blot analyses showed the presence of matrix proteins in these preparations. These results indicate that calcospherulites can be isolated from the mineralization front of bone in a form that can be used to study their proteome and lipid composition.

Potential role of proprotein convertase SKI-1 in the mineralization of primary bone

The biochemical mechanism controlling nucleation of mineral crystals in developing bone, along with the growth and propagation of these crystals once formed, remains poorly understood. To define the nucleation mechanism, a proteomics analysis was begun on isolated biomineralization foci (BMF), sites of initial crystal nucleation in osteoblastic cell cultures and in primary bone. Comparative analyses of the protein profile for mineralized BMF with that for total osteoblast cultures revealed the latter were enriched in several proteins including BAG-75 and BSP, as well as fragments of each. When 12 protease inhibitors were added separately to UMR 106-01 osteoblastic cultures, only the serine protease inhibitor 4-(2-aminoethyl) benzenesulfonyl fluoride hydrochloride (AEBSF) blocked cleavage of BAG-75 and BSP, and prevented mineral crystal nucleation within BMF. Consideration of the specificities of the inhibitors tested and the fact that AEBSF inhibition was not dependent upon inclusion of FBS in the culture media indicated that mineral nucleation does not require serine protease plasmin, thrombin, kallikrein, urokinase, C1s or furin. In contrast, SKI-1 (S1P or site-1) is a membrane-bound serine protease inhibitable by AEBSF. We show here for the first time that mineralizing UMR 106 cells express a 98-kDa active, soluble form of SKI-1 within BMF. In contrast, nonmineralizing UMR cells appear to differentially process SKI-1 into smaller immunoreactive fragments (<35 kDa). These findings suggest that SKI-1 plays a direct or indirect role in assembly of functional nucleation complexes containing BAG-75 and BSP and their fragments, thus facilitating initial mineral nucleation within these biomineralization foci.

Calcospherulites isolated from the mineralization front of bone induce the mineralization of type I collagen

Previous work has suggested that "calcospherulites" actively participate in the mineralization of developing and healing bone. This study sought to directly test this hypothesis by developing a method to isolate calcospherulites and analyzing their capacity to seed mineralization of fibrillar collagen. The periosteal surface of juvenile rat tibial diaphysis was enriched in spherulites of approximately 0.5-mum diameter exhibiting a Ca/P ratio of 1.3. Their identity as calcospherulites was confirmed by their uptake of calcein at the tibial mineralization front 24 h following in vivo injection. Periosteum was dissected and unmineralized osteoid removed by collagenase in order to expose calcospherulites. Calcein-labeled calcospherulites were then released from the mineralization front by dispase digestion and isolated via fluorescence flow sorting. X-ray diffraction analysis revealed they contained apatite crystals (c-axis length of 17.5+/-0.2 nm), though their Ca/P ratio of 1.3 is lower than that of hydroxyapatite. Much of their non-mineral phosphorous content was removed by ice-cold ethanol, elevating their Ca/P ratio to 1.6, suggesting the presence of phospholipids. Western blot analyses showed the presence of bone matrix proteins and type I collagen in these preparations. Incubating isolated calcospherulites in collagen hydrogels demonstrated that they could seed a mineralization reaction on type I collagen fibers in vitro. Ultrastructural analyses revealed crystals on the collagen fibers that were distributed rather uniformly along the fiber lengths. Furthermore, crystals were observed at distances well away from the observed calcospherulites. Our results directly support an active role for calcospherulites in inducing the mineralization of type I collagen fibers at the mineralization front of bone.

Association of specific proteolytic processing of bone sialoprotein and bone acidic glycoprotein-75 with mineralization within biomineralization foci

Mineral crystal nucleation in UMR 106-01 osteoblastic cultures occurs within 15-25-microm extracellular vesicle-containing biomineralization foci (BMF) structures. We show here that BAG-75 and BSP, biomarkers for these foci, are specifically enriched in laser capture microscope-isolated mineralized BMF as compared with the total cell layer. Unexpectedly, fragments of each protein (45-50 kDa in apparent size) were also enriched within captured BMF. When a series of inhibitors against different protease classes were screened, serine protease inhibitor 4-(2-aminoethyl)benzenesulfonylfluoride HCl (AEBSF) was the only one that completely blocked mineral nucleation within BMF in UMR cultures. AEBSF appeared to act on an osteoblast-derived protease at a late differentiation stage in this culture model just prior to mineral deposition. Similarly, mineralization of bone nodules in primary mouse calvarial osteoblastic cultures was completely blocked by AEBSF. Cleavage of BAG-75 and BSP was also inhibited at the minimum dosage of AEBSF sufficient to completely block mineralization of BMF. Two-dimensional SDS-PAGE comparisons of AEBSF-treated and untreated UMR cultures showed that fragmentation/activation of a limited number of other mineralization-related proteins was also blocked. Taken together, our results indicate for the first time that cleavage of BAG-75 and BSP by an AEBSF-sensitive, osteoblast-derived serine protease is associated with mineral crystal nucleation in BMF and suggest that such proteolytic events are a permissive step for mineralization to proceed.

Pulsed electromagnetic fields rapidly modulate intracellular signaling events in osteoblastic cells: comparison to parathyroid hormone and insulin

Pulsed electromagnetic field (PEMF) devices are approved for the healing of bone nonunions, but there is a lack of understanding as to their mechanism of action at the cell and molecular level. Intermittent parathyroid hormone (PTH) therapy is currently utilized for treatment of osteoporosis, and is also being investigated for the purpose of augmenting fracture healing. Insulin and IGF-1 are also thought to play important anabolic roles in osteogenesis. In this report, signaling pathways activated by acute PTH or insulin treatments were compared to those activated by PEMF treatment in osteoblast-like cells. Some signaling molecules like the extracellular response kinases 1/2 (Erk1/2) and the cAMP response element binding protein (CREB) were activated by insulin and PTH, respectively, but not by PEMF treatment. Other signaling molecules like the insulin receptor substrate-1 (IRS-1), the S6 ribosomal subunit kinase, and the endothelial nitric oxide synthase (eNOS) were phosphorylated by PTH, insulin, and PEMF to the same relative extent and within the same time frame. IRS-1, eNOS, and S6 have been implicated in bone anabolism, and our results suggest that the anabolic effects of PEMF may be mediated, in part, through the activation of these proteins.

Decibel Attenuation of Pulsed Electromagnetic Field (PEMF) in Blood and Cortical Bone Determined Experimentally and from the Theory of Ohmic Losses

We studied the PEMF power attenuation in tissues representative of clinical applications (blood and cortical bone) to determine the amount of power available for PEMF purported biological effects. The experimental system consisted of a pair of nearly circular, parallel and coaxial coils separated by a distance of one coil diameter. The power attenuation was measured using a small search coil connected to a digital oscilloscope. The coils were powered by a voltage switch operating at two different frequencies (3.8 and 63 kHz) producing bursts of pulses (numbering 21 and 1619) and triggered at two different frequencies (1.5 and 15 Hz, respectively). The tissue samples were placed inside the coils so as to expose them to either transverse electric field (at the center of coils) or the transverse magnetic field (at the coil wire). The cylindrical coil geometry yielded closed-form expressions for power attenuation based on magnetic diffusion equation and ohmic losses due to bulk tissue magnetic permeability and electrical conductivity. The measured power attenuation at these PEMF frequencies of not more than one decibel (1 dB) was well explained by the theory for the 3.8 kHz but less so for the 63 kHz frequency PEMF. The results provide important insights regarding physical mechanism of weak PEMF power dissipation in tissues.

Exposure of mouse preosteoblasts to pulsed electromagnetic fields reduces the amount of mature, type I collagen in the extracellular matrix

We tested the hypothesis that exposure of a mouse preosteoblast cell line to pulsed electromagnetic fields (PEMF) would affect components of the extracellular matrix. We report that exposure of MC3T3-E1 cells to a single PEMF waveform significantly reduced the amount of mature, alpha1(I) collagen in the extracellular matrix (ECM) and the conditioned medium, without affecting the amount of total ECM protein. This decrease was not due to changes in the steady-state level of Col1A1 mRNA or to degradation of mature collagen. We then tested the effect of three distinct PEMF waveforms, two orthogonal coil orientations, and two waveform amplitude levels on the amount of alpha1(I) collagen in the conditioned medium. A sequence of factorial ANOVAs and stepwise regression modeling revealed that the period (duration) of the individual pulses accounted for a significant proportion of the variance associated with the amount of alpha1(I) collagen in the conditioned medium. The total variance accounted for, however, was small (R(2)=0.155, p<0.001 and R(2)=0.172, p<0.001, in the horizontal and vertical orientations, respectively). The positive and negative regression coefficients for the coil orientations revealed that the influence of pulse period was significantly different for the orthogonal coil orientations (p<0.001). The findings imply that the dominant influence of PEMF on the amount of mature, alpha1(I) collagen in the ECM is related to variables other than those expressed in the time-amplitude domain. The results provide objective direction toward identifying waveform characteristics that contribute to the observed between-waveform differences with regard to collagen. Advances in this area may lead toward improving waveforms and waveform delivery protocols.

Exposure of murine cells to pulsed electromagnetic fields rapidly activates the mTOR signaling pathway

Murine pre-osteoblasts and fibroblast cell lines were used to determine the effect of pulsed electromagnetic field (PEMF) exposure on the production of autocrine growth factors and the activation of early signal transduction pathways. Exposure of pre-osteoblast cells to PEMF minimally increased the amount of secreted TGF-beta after 1 day, but had no significant effects thereafter. PEMF exposure of pre-osteoblast cells also had no effect on the amount of prostaglandin E(2) in the conditioned medium. Exposure of both pre-osteoblasts and fibroblasts to PEMF rapidly activated the mTOR signaling pathway, as evidenced by increased phosphorylation of mTOR, p70 S6 kinase, and the ribosomal protein S6. Inhibition of PI3-kinase activity with the chemical inhibitor LY294002 blocked PEMF-dependent activation of mTOR in both the pre-osteoblast and fibroblast cell lines. These findings suggest that PEMF exposure might function in a manner analogous to soluble growth factors by activating a unique set of signaling pathways, inclusive of the PI-3 kinase/mTOR pathway.

Pulsed electromagnetic field treatments enhance the healing of fibular osteotomies

This study tested the hypothesis that pulsed electromagnetic field (PEMF) treatments augment and accelerate the healing of bone trauma. It utilized micro-computed tomography imaging of live rats that had received bilateral 0.2 mm fibular osteotomies (approximately 0.5% acute bone loss) as a means to assess the in vivo rate dynamics of hard callus formation and overall callus volume. Starting 5 days post-surgery, osteotomized right hind limbs were exposed 3 h daily to Physio-Stim PEMF, 7 days a week for up to 5 weeks of treatment. The contralateral hind limbs served as sham-treated, within-animal internal controls. Although both PEMF- and sham-treatment groups exhibited similar onset of hard callus at approximately 9 days after surgery, a 2-fold faster rate of hard callus formation was observed thereafter in PEMF-treated limbs, yielding a 2-fold increase in callus volume by 13-20 days after surgery. The quantity of the new woven bone tissue within the osteotomy sites was significantly better in PEMF-treated versus sham-treated fibulae as assessed via hard tissue histology. The apparent modulus of each callus was assessed via a cantilever bend test and indicated a 2-fold increase in callus stiffness in the PEMF-treated over sham-treated fibulae. PEMF-treated fibulae exhibited an apparent modulus at the end of 5-weeks that was approximately 80% that of unoperated fibulae. Overall, these data indicate that Physio-Stim PEMF treatment improved osteotomy repair. These beneficial effects on bone healing were not observed when a different PEMF waveform, Osteo-Stim, was used. This latter observation demonstrates the specificity in the relationship between waveform characteristics and biological outcomes.

Low amplitude, high frequency strains imposed by electrically stimulated skeletal muscle retards the development of osteopenia in the tibiae of hindlimb suspended rats

The purpose of this study was to determine the extent to which high frequency, low amplitude skeletal muscle contractions, induced using electrical stimulation, could prevent or retard disuse osteopenia. Ten minutes of 30 Hz electrical stimulation was delivered, 5 days a week, during a 4 week rat-hindlimb suspension protocol. Each pulse generated a peak compressive dynamic strain on the tibia of approximately 200 microepsilon. We hypothesized that the electrical stimulation protocol would significantly reduce the loss of tibial bone mineral density compared to the contralateral control tibia that did not receive electrical stimulation. Compared to the contralateral control limb, the tibia of the stimulated limb had significantly higher bone mineral density and enhanced newly formed bone in the tibial diaphysis. The diaphysis, specifically the posterior bone cortex, of the tibia of the limb receiving the stimulation also demonstrated substantially larger mineral-binding fluorochrome biomarker within the osteocyte lacunae and canalicular volumes. Although the protocol did not prevent disuse osteopenia the evidence suggests that it was effective at reducing the extent of the osteopenia. One possibility for this outcome may be the insensitivity of bone to static, compared to dynamic compressive loads. In the present study there was a considerable static component to the compressive loads that accounted for a large component of the peak load generated by the stimulated skeletal muscle. Nevertheless, the results provide impetus for further development of the methods by which muscle contraction-induced loading of bone can be clinically exploited.

In vivo longitudinal assessment of bone resorption in a fibular osteotomy model using micro-computed tomography

Longitudinal in vivo micro-computerized tomography (CT) imaging was used to monitor bone resorption in a rat fibula osteotomy model. Quantitative image post-processing techniques were developed for spatially aligning the longitudinal data sets. Nominal length and bone volume in the proximal and distal segments of the fibula after the osteotomy were measured, and quantitative comparisons of bone loss over a 13-week period post-surgery were made in five individual rats. A significant decrease in nominal length and bone volume of the distal segment was observed 13 weeks post surgery. A significant decrease in bone volume was also observed in the proximal segment. However, no change in nominal length was observed for the proximal segment of the fibula. This study illustrates the power of this non-invasive technology to measure in vivo small changes in bone length and volume using just a small cohort of animals.

Bone mass is preserved in a critical-sized osteotomy by low energy pulsed electromagnetic fields as quantitated by in vivo micro-computed tomography

The effectiveness of non-invasive pulsed electromagnetic fields (PEMF) on stimulating bone formation in vivo to augment fracture healing is still controversial, largely because of technical ambiguities in data interpretation within several previous studies. To address this uncertainty, we implemented a rigorously controlled, blinded protocol using a bilateral, mid-diaphyseal fibular osteotomy model in aged rats that achieved a non-union status within 3-4 weeks post-surgery. Bilateral osteotomies allowed delivery of a PEMF treatment protocol on one hind limb, with the contralateral limb representing a within-animal sham-treatment. Bone volumes in both PEMF-treated and sham-treated fibulae were assessed simultaneously in vivo using highly sensitive, high-resolution micro-computed tomography (microCT) over the course of treatment. We found a significant reduction in the amount of time-dependent bone volume loss in PEMF-treated, distal fibular segments as compared to their contralateral sham-treated bones. Osteotomy gap size was significantly smaller in hind limbs exposed to PEMF over sham-treatment. Therefore, our data demonstrate measurable biological consequences of PEMF exposure on in vivo bone tissue.

Bone Acidic Glycoprotein-75 Delineates the Extracellular Sites of Future Bone Sialoprotein Accumulation and Apatite Nucleation in Osteoblastic Cultures

Addition of an organophosphate source to UMR osteoblastic cultures activates a mineralization program in which BSP localizes to extracellular matrix sites where hydroxyapatite crystals are subsequently nucleated. This study identifies for the first time novel extracellular spherical structures, termed biomineralization foci (BMF), containing bone acidic glycoprotein-75 (BAG-75), bone sialoprotein (BSP), and alkaline phosphatase that are the exclusive sites of initial nucleation of hydroxyapatite crystals in the UMR model. Importantly, in the absence of added phosphate, UMR cultures after reaching confluency contain two size populations of morphologically identifiable BMF precursors enriched in BAG-75 (15-25 and 150-250 microm in diameter). The shape and size of the smaller population are similar to structures assembled in vitro through self-association of purified BAG-75 protein. After organophosphate addition, BSP accumulates within these BAG-75-containing BMF precursors, with hydroxyapatite crystal nucleation occurring subsequently. In summary, BAG-75 is the earliest detectable biomarker that accurately predicts the extracellular sites of de novo biomineralization in UMR cultures. We hypothesize that BAG-75 may perform a key structural role in the assembly of BMF precursors and the recruitment of other proteins such as alkaline phosphatase and BSP. Furthermore, we propose a hypothetical mechanism in which BAG-75 and BSP function actively in nucleation of apatite within BMF.

Extracellular Bone Acidic Glycoprotein-75 Defines Condensed Mesenchyme Regions to be Mineralized and Localizes with Bone Sialoprotein during Intramembranous Bone Formation

Bone acidic glycoprotein-75 is expressed very early during in vivo models of intramembranous bone formation, highly enriched in condensing osteogenic mesenchyme after marrow ablation and the osteoprogenitor layer of tibial periosteum. Bone sialoprotein accumulates within bone acidic glycoprotein-75-enriched matrix areas at a later stage in both models. Decalcification of initial sites of mineralization consistently revealed focal immunostaining for bone acidic glycoprotein-75 underneath these sites suggesting that mineralization occurs within bone acidic glycoprotein-75-enriched matrix areas. Ultrastructural immunolocalization of bone acidic glycoprotein-75 does not support a direct association with banded collagen fibrils, but rather suggests it is a component of a separate, amorphous scaffold occupying interfibrillar spaces. Double immunogold labeling demonstrated that a sizeable proportion of bone sialoprotein particles were located within a 50-nm radius of bone acidic glycoprotein-75. These results define bone acidic glycoprotein-75 as the earliest bone-restricted, extracellular marker of osteogenic mesenchyme. Based on this early bone-restricted expression pattern and a previously documented propensity of bone acidic glycoprotein-75 to form supramolecular complexes through self-association, bone acidic glycoprotein-75 may serve a key structural role in setting boundary limits of condensing osteogenic mesenchyme.

Osteoblast attachment to a textured surface in the absence of exogenous adhesion proteins

The present study investigated whether osteoblasts could attach to a culture substratum through a surface texture-dependent mechanism. Four test groups were used: (A) untextured, and three texture groups with maximum feature sizes of (B) <0.5 microm, (C) 2 microm, and (D) 4 microm, respectively. All surfaces were coated with the nonadhesive protein bovine serum albumin (BSA). Osteoblasts were allowed to adhere in serum-free medium for either 1 or 4 h, at which time nonadherent cells were removed. At 4 h, untextured surface A exhibited no cell attachment, while textured surfaces B, C, and D exhibited 9%, 32%, and 16% cell adhesion, respectively. At 16 h of incubation, adherent osteoblasts on textured surface C exhibited focal adhesion contacts and microfilament stress-fiber bundles. These results indicate that microtextured surfaces in the absence of exogenous adhesive proteins can facilitate osteoblast adhesion.

Parathyroid Hormone Rapidly Stimulates Hyaluronan Synthesis by Periosteal Osteoblasts in the Tibial Diaphysis of the Growing Rat

Short term treatment (3-24 h) with parathyroid hormone (PTH) stimulated the synthesis and accumulation of hyaluronan (HyA) in explant cultures of tibial diaphyses from young rats. PTH increased the overall HyA content of periosteum 5-fold, with the basal cambium layer exhibiting the greatest enhancement ( approximately 8-fold). PTH increased the HyA content of cortical bone by 2-fold while not affecting the HyA content of bone marrow. PTH treatment greatly enhanced HyA staining throughout all layers of the periosteum, although its most dramatic effect occurred in the basal cambium layer. Here, unlike in the control tissue sections, nearly all cambium-lining osteoblasts stained intensely positive for HyA. PTH treatment enhanced the HyA staining of osteocytes in cortical bone tissue sections to the extent that the lacunocanalicular system became visualized. Three significant findings were revealed in this study. First, mature periosteal osteoblasts, under natural conditions, do not contain much HyA in their surrounding extracellular matrix but dramatically enhance their matrix HyA content when treated with PTH. Second, pre-osteocytes and osteocytes contain more HyA in their natural matrix than mature lining osteoblasts, and they appear to have functional PTH receptors because they responded to PTH treatment with an enhancement of HyA content. Finally, it was observed that the lining cells along the endosteal surface of the diaphysis did not stain strongly positive for HyA either naturally or when exposed to PTH treatment. This indicates that periosteal and endosteal osteoblastic cell populations exhibit metabolic differences in their extracellular matrix responses to PTH.