Renal cortex microperfusion evaluated by laser speckle contrast imaging in an ex vivo perfused kidney model-A proof-of-concept study

BACKGROUND

Validated quantitative biomarkers for assessment of renal graft function during normothermic machine perfusion (NMP) conditions are lacking. The aim of this project was to quantify cortex microperfusion during ex vivo kidney perfusion using laser speckle contrast imaging (LSCI), and to evaluate the sensitivity of LSCI when measuring different levels of renal perfusion. Furthermore, we aimed to introduce LSCI measurements during NMP in differentially damaged kidneys.

METHODS

Eleven porcine kidneys were nephrectomized and perfused ex vivo. Cortex microperfusion was simultaneously monitored using LSCI. First, a flow experiment examined the relationship between changes in delivered renal flow and corresponding changes in LSCI-derived cortex microperfusion. Second, renal cortical perfusion was reduced stepwise by introducing a microembolization model. Finally, LSCI was applied for measuring renal cortex microperfusion in kidneys exposed to minimal damage or 2 h warm ischemia (WI).

RESULTS

Cortex microperfusion was calculated from the LSCI-obtained data. The flow experiment resulted in relatively minor changes in cortex microperfusion compared to the pump-induced changes in total renal flow. Based on stepwise injections of microspheres, we observed different levels of cortex microperfusion that correlated with administrated microsphere dosages (r2 = 0.95-0.99). We found no difference in LSCI measured cortex microperfusion between the kidneys exposed to minimal damage (renal cortex blood flow index, rcBFI = 2090-2600) and 2 h WI (rcBFI = 2189-2540).

CONCLUSIONS

Based on this preliminary study, we demonstrated the feasibility of LSCI in quantifying cortex microperfusion during ex vivo perfusion. Furthermore, based on LSCI-measurements, cortical microperfusion was similar in kidneys exposed to minimal and 2 h WI.

Does the route matter? A preclinical review of mesenchymal stromal cell delivery to the kidney

Mesenchymal stromal/stem cell (MSC) therapy has been thoroughly tested in preclinical animal models and holds great promise for the treatment of kidney diseases. It is becoming increasingly evident that the efficacy of MSC therapy is dependent on several factors including dosage, the tissue source of MSCs, the route of delivery and timing of administration. In a time where MSC therapy is moving from preclinical research to clinically therapeutic use, the importance of choice of delivery method, modality, and administration route increases. In this review, we provide an overview of the different MSC delivery routes used in preclinical kidney disease models, highlight the recent advances in the field, and summarize studies comparing delivery routes of MSCs to the kidney.

Reconstitution and post-thaw storage of cryopreserved human mesenchymal stromal cells: Pitfalls and optimizations for clinically compatible formulants

Introduction

The regenerative and immunomodulatory properties of multipotent mesenchymal stromal cells (MSCs) make them an intriguing asset for therapeutic applications. An off-the-shelf approach, using pre-expanded cryopreserved allogenic MSCs, bypasses many practical difficulties of cellular therapy. Reconstitution of a MSC product away from cytotoxic cryoprotectants towards a preferred administration solution might be favorable for several indications. Variations in MSC handling accompanied by a non-standardized use of reconstitution solutions complicate a general clinical standardization of MSC cellular therapies. In this study, we aimed to identify a simple and clinically compatible approach for thawing, reconstitution, and post-thaw storage of cryopreserved MSCs.

Methods

Human adipose tissue-derived MSCs were expanded in human platelet lysate (hPL) supplemented culture medium and cryopreserved using a dimethyl sulfoxide (DMSO)-based cryoprotectant. Isotonic solutions (saline, Ringer's acetate and phosphate buffered saline (PBS)) with or without 2% human serum albumin (HSA) were used as thawing, reconstitution, and storage solutions. MSCs were reconstituted to 5 × 10⁶ MSCs/mL for evaluating MSC stability. Total MSC numbers and viability were determined using 7-aminoactinomycin D (7-AAD) and flow cytometry.

Results

For thawing cryopreserved MSCs the presence of protein was proven to be essential. Up to 50% of MSCs were lost when protein-free thawing solutions were used. Reconstitution and post-thaw storage of MSCs in culture medium and widely used PBS demonstrated poor MSC stability (>40% cell loss) and viability (<80%) after 1 h of storage at room temperature. Reconstitution in simple isotonic saline appeared to be a good alternative for post-thaw storage, ensuring >90% viability with no observed cell loss for at least 4 h. Reconstitution of MSCs to low concentrations was identified as critical. Diluting MSCs to <10⁵/mL in protein-free vehicles resulted in instant cell loss (>40% cell loss) and lower viability (<80%). Addition of clinical grade HSA could prevent cell loss during thawing and dilution.

Conclusion

This study identified a clinically compatible method for MSC thawing and reconstitution that ensures high MSC yield, viability, and stability. The strength of the method lies within the simplicity of implementation which offers an accessible way to streamline MSC therapies across different laboratories and clinical trials, improving standardization in this field.

H2S-Enriched Flush out Does Not Increase Donor Organ Quality in a Porcine Kidney Perfusion Model

Kidney extraction time has a detrimental effect on post-transplantation outcome. This study aims to improve the flush-out and potentially decrease ischemic injury by the addition of hydrogen sulphide (H2S) to the flush medium. Porcine kidneys (n = 22) were extracted during organ recovery surgery. Pigs underwent brain death induction or a Sham operation, resulting in four groups: donation after brain death (DBD) control, DBD H2S, non-DBD control, and non-DBD H2S. Directly after the abdominal flush, kidneys were extracted and flushed with or without H2S and stored for 13 h via static cold storage (SCS) +/− H2S before reperfusion on normothermic machine perfusion. Pro-inflammatory cytokines IL-1b and IL-8 were significantly lower in H2S treated DBD kidneys during NMP (p = 0.03). The non-DBD kidneys show superiority in renal function (creatinine clearance and FENa) compared to the DBD control group (p = 0.03 and p = 0.004). No differences were seen in perfusion parameters, injury markers and histological appearance. We found an overall trend of better renal function in the non-DBD kidneys compared to the DBD kidneys. The addition of H2S during the flush out and SCS resulted in a reduction in pro-inflammatory cytokines without affecting renal function or injury markers.

Dynamics of circulating dendritic cells and cytokines after kidney transplantation-No effect of remote ischaemic conditioning

Inflammation resulting from ischaemia/reperfusion injury can cause kidney graft dysfunction, increase the risk of delayed graft function and possibly reduce long-term graft survival. Remote ischaemic conditioning may protect against ischaemia/reperfusion injury and mitigate the immunological response to the graft. We investigated the immunological effects of remote ischaemic conditioning on kidney transplantation from deceased donors in the randomized CONTEXT study. Three circulating dendritic cell (DC) subtypes identified in peripheral blood from kidney transplant recipients [myeloid DCs, plasmacytoid DCs and immunoglobulin-like transcript (ILT)3⁺ DCs] were measured at baseline, days 1, 3 and 5 and 1 and 3 months after transplantation. We also quantified 21 cytokines at baseline, days 1 and 5 and 3 months after transplantation. Neither DC counts nor cytokine levels differed between patients receiving remote ischaemic conditioning and controls; however, several parameters exhibited dynamic and parallel alterations in the two groups over time, reflecting the immunological response to the kidney transplantation and immunosuppression.

Mesenchymal stromal cell treatment of donor kidneys during ex vivo normothermic machine perfusion: A porcine renal autotransplantation study

Normothermic machine perfusion (NMP) of injured kidneys offers the opportunity for interventions to metabolically active organs prior to transplantation. Mesenchymal stromal cells (MSCs) can exert regenerative and anti-inflammatory effects in ischemia-reperfusion injury. The aims of this study were to evaluate the safety and feasibility of MSC treatment of kidneys during NMP using a porcine autotransplantation model, and examine potential MSC treatment-associated kidney improvements up to 14 days posttransplant. After 75 min of kidney warm ischemia, four experimental groups of n = 7 underwent 14 h of oxygenated hypothermic machine perfusion. In three groups this was followed by 240 min of NMP with infusion of vehicle, 10 million porcine, or 10 million human adipose-derived MSCs. All kidneys were autotransplanted after contralateral nephrectomy. MSC treatment did not affect perfusion hemodynamics during NMP or cause adverse effects at reperfusion, with 100% animal survival. MSCs did not affect plasma creatinine, glomerular filtration rate, neutrophil gelatinase-associated lipocalin concentrations or kidney damage assessed by histology during the 14 days, and MSCs retention was demonstrated in renal cortex. Infusing MSCs during ex vivo NMP of porcine kidneys was safe and feasible. Within the short posttransplant follow-up period, no beneficial effects of ex vivo MSC therapy could be demonstrated.

Ex Vivo Administration of Mesenchymal Stromal Cells in Kidney Grafts Against Ischemia-reperfusion Injury-Effective Delivery Without Kidney Function Improvement Posttransplant

BACKGROUND

Mesenchymal stromal cell (MSC) therapy may improve renal function after ischemia-reperfusion injury in transplantation. Ex vivo renal intraarterial administration is a targeted delivery method, avoiding the lung vasculature, a known barrier for cellular therapies. In a randomized and blinded study, we tested the feasibility and effectiveness of MSC therapy in a donation after circulatory death autotransplantation model to improve posttransplant kidney function, using an ex vivo MSC delivery method similar to the clinical standard procedure of pretransplant cold graft flush.

METHODS

Kidneys exposed to 75 minutes of warm ischemia and 16 hours of static cold storage were intraarterially infused ex vivo with 10 million male porcine MSCs (Tx-MSC, n = 8) or vehicle (Tx-control, n = 8). Afterwards, the kidneys were autotransplanted after contralateral nephrectomy. Biopsies an hour after reperfusion confirmed the presence of MSCs in the renal cortex. Animals were observed for 14 days.

RESULTS

Postoperatively, peak plasma creatinine was 1230 and 1274 µmol/L (Tx-controls versus Tx-MSC, P = 0.69). During follow-up, no significant differences over time were detected between groups regarding plasma creatinine, plasma neutrophil gelatinase-associated lipocalin, or urine neutrophil gelatinase-associated lipocalin/creatinine ratio. At day 14, measured glomerular filtration rates were 40 and 44 mL/min, P = 0.66. Renal collagen content and fibrosis-related mRNA expression were increased in both groups but without significant differences between the groups.

CONCLUSIONS

We demonstrated intraarterial MSC infusion to transplant kidneys as a safe and effective method to deliver MSCs to the graft. However, we could not detect any positive effects of this cell treatment within 14 days of observation.

Activin type IIA decoy receptor and intermittent parathyroid hormone in combination overturns the bone loss in disuse-osteopenic mice

Damage of the lower motor neuron cell bodies or their axons results in reduced or abolished voluntary movement accompanied by a substantial loss of bone and muscle mass. Intermittent parathyroid hormone 1-34 (PTH) (teriparatide) is one of the most potent bone-anabolic treatment regimens. ActRIIA-mFc is an activin type IIA decoy receptor that increases bone mass mediated by inhibition of the activin receptor signaling pathway. We investigated whether PTH or ActRIIA-mFc alone or in combination could prevent loss of bone and muscle mass induced by injecting botulinum toxin A (BTX) into the right hind limb in mice. Seventy-two 16-week-old female C57BL/6 mice were allocated to the following groups: Baseline, Control, BTX, BTX + ActRIIA-mFc (10 mg/kg), BTX + PTH (100 μg/kg), and BTX + ActRIIA-mFc + PTH. The mice were sacrificed after three weeks of disuse and treatment. In contrast to monotherapy with PTH, ActRIIA-mFc alone or in combination with PTH was able partly or completely to prevent disuse-induced loss of whole femoral bone mass, trabecular thickness, and bone strength. Moreover, an additive effect of ActRIIA-mFc and PTH on areal bone mineral density and trabecular bone volume was found. In summary, ActRIIA-mFc and PTH in combination were more effective in preventing disuse-induced bone loss and deterioration of trabecular micro-architecture than either treatment alone.

Inhibition of the activin receptor signaling pathway: A novel intervention against osteosarcoma

Osteosarcoma is a cancer of pathological bone remodeling with high mortality and severe comorbidity. New therapies are urgently needed. Activin A, a member of the transforming growth factor β (TGFβ) superfamily, has been suggested to stimulate proliferation and invasion of osteosarcoma cells in vitro, thus representing a potential therapeutic target. In this study, inhibition of the activin receptor signaling pathway was explored as a therapy for osteosarcoma. In a murine intratibial osteosarcoma xenograft model, two types of inhibitors were tested: (a) a soluble activin type IIA decoy receptor (ActRIIA-mFc), or (b) a modified variant of follistatin (FSTΔHBS -hFc), either alone or in combination with a bisphosphonate. Both inhibitors reduced primary tumor development by nearly 50% compared to vehicle treatment. When ActRIIA-mFc was combined with bisphosphonate, the effect on tumor size became even more pronounced (78% reduction vs. vehicle). Moreover, FSTΔHBS -hFc increased body weight in the face of tumor progression (14% increase vs. vehicle), and ActRIIA-mFc reduced the number of lung metastases when combined with bisphosphonate. The present study demonstrates a novel approach to treating osteosarcoma and encourages further investigation of inhibition of the activin receptor signaling pathway as an intervention against the disease.

Subclinical effects of remote ischaemic conditioning in human kidney transplants revealed by quantitative proteomics

Background

Remote ischaemic conditioning (RIC) is currently being explored as a non-invasive method to attenuate ischaemia/reperfusion injuries in organs. A randomised clinical study (CONTEXT) evaluated the effects of RIC compared to non-RIC controls in human kidney transplants.

Methods

RIC was induced prior to kidney reperfusion by episodes of obstruction to arterial flow in the leg opposite the transplant using a tourniquet (4 × 5 min). Although RIC did not lead to clinical improvement of transplant outcomes, we explored whether RIC induced molecular changes through precision analysis of CONTEXT recipient plasma and kidney tissue samples by high-resolution tandem mass spectrometry (MS/MS).

Results

We observed an accumulation of muscle derived proteins and altered amino acid metabolism in kidney tissue proteomes, likely provoked by RIC, which was not reflected in plasma. In addition, MS/MS analysis demonstrated transient upregulation of several acute phase response proteins (SAA1, SAA2, CRP) in plasma, 1 and 5 days post-transplant in RIC and non-RIC conditions with a variable effect on the magnitude of acute inflammation.

Conclusions

Together, our results indicate sub-clinical systemic and organ-localised effects of RIC.

Treating Ischemically Damaged Porcine Kidneys with Human Bone Marrow- and Adipose Tissue-Derived Mesenchymal Stromal Cells During Ex Vivo Normothermic Machine Perfusion

Pretransplant normothermic machine perfusion (NMP) of donor kidneys offers the unique opportunity to perform active interventions to an isolated renal graft before transplantation. There is increasing evidence that mesenchymal stromal cells (MSCs) could have a paracrine/endocrine regenerative effect on ischemia-reperfusion injury. The purpose of this study was to determine which cytokines are secreted by MSCs during NMP of a porcine kidney. Viable porcine kidneys and autologous whole blood were obtained from a slaughterhouse. Warm ischemia time was standardized at 20 min and subsequent hypothermic machine perfusion was performed during 2-3 h. Thereafter, kidneys were machine perfused at 37°C during 7 h. After 1 h of NMP, 0, 10⁷ cultured human adipose tissue-derived MSCs, or 10⁷ cultured bone marrow-derived MSCs were added (n = 5 per group). In a fourth experimental group, 7-h NMP was performed with 10⁷ adipose tissue-derived MSCs, without a kidney in the circuit. Kidneys perfused with MSCs showed lower lactate dehydrogenase and neutrophil gelatinase-associated lipocalin levels in comparison with the control group. Also, elevated levels of human hepatocyte growth factor, interleukin (IL)-6, and IL-8 were found in the perfusate of the groups perfused with MSCs compared to the control groups. This study suggests that MSCs, in contact with an injured kidney during NMP, could lead to lower levels of injury markers and induce the release of immunomodulatory cytokines.

Reparative effect of mesenchymal stromal cells on endothelial cells after hypoxic and inflammatory injury

Background

The renal endothelium is a prime target for ischemia-reperfusion injury (IRI) during donation and transplantation procedures. Mesenchymal stromal cells (MSC) have been shown to ameliorate kidney function after IRI. However, whether this involves repair of the endothelium is not clear. Therefore, our objective is to study potential regenerative effects of MSC on injured endothelial cells and to identify the molecular mechanisms involved.

Methods

Human umbilical vein endothelial cells (HUVEC) were submitted to hypoxia and reoxygenation and TNF-α treatment. To determine whether physical interaction or soluble factors released by MSC were responsible for the potential regenerative effects of MSC on endothelial cells, dose-response experiments were performed in co-culture and transwell conditions and with secretome-deficient MSC.

Results

MSC showed increased migration and adhesion to injured HUVEC, mediated by CD29 and CD44 on the MSC membrane. MSC decreased membrane injury marker expression, oxidative stress levels, and monolayer permeability of injured HUVEC, which was observed only when allowing both physical and paracrine interaction between MSC and HUVEC. Furthermore, viable MSC in direct contact with injured HUVEC improved wound healing capacity by 45% and completely restored their angiogenic capacity. In addition, MSC exhibited an increased ability to migrate through an injured HUVEC monolayer compared to non-injured HUVEC in vitro.

Conclusions

These results show that MSC have regenerative effects on injured HUVEC via a mechanism which requires both physical and paracrine interaction. The identification of specific effector molecules involved in MSC-HUVEC interaction will allow targeted modification of MSC to apply and enhance the therapeutic effects of MSC in IRI.

Two-day-treatment of Activin-A leads to transient change in SV-HFO osteoblast gene expression and reduction in matrix mineralization

Activins regulate bone formation by controlling osteoclasts and osteoblasts. We investigated Activin‐A mechanism of action on human osteoblast mineralization, RNA and microRNA (miRNA) expression profile. A single 2‐day treatment of Activin‐A at Day 5 of osteoblast differentiation significantly reduced matrix mineralization. Activin A‐treated osteoblasts responded with transient change in gene expression, in a 2‐wave‐fashion. The 38 genes differentially regulated during the first wave (within 8 hr after Activin A start) were involved in transcription regulation. In the second wave (1–2 days after Activin A start), 65 genes were differentially regulated and related to extracellular matrix. Differentially expressed genes in both waves were associated to transforming growth factor beta signaling. We identified which microRNAs modulating osteoblast differentiation were regulated by Activin‐A. In summary, 2‐day treatment with Activin‐A in premineralization period of osteoblast cultures influenced miRNAs, gene transcription, and reduced matrix mineralization. Modulation of Activin A signaling might be useful to control bone quality for therapeutic purposes.

Mesenchymal Stromal Cells Are Retained in the Porcine Renal Cortex Independently of Their Metabolic State After Renal Intra-Arterial Infusion

The regenerative capacities of mesenchymal stromal cells (MSCs) make them suitable for renal regenerative therapy. The most common delivery route of MSC is through intravenous infusion, which is associated with off-target distribution. Renal intra-arterial delivery offers a targeted therapy, but limited knowledge is available regarding the fate of MSCs delivered through this route. Therefore, we studied the efficiency and tissue distribution of MSCs after renal intra-arterial delivery to a porcine renal ischemia-reperfusion model. MSCs were isolated from adipose tissue of healthy male pigs, fluorescently labeled and infused into the renal artery of female pigs. Flow cytometry allowed MSC detection and quantification in tissue and blood. In addition, quantitative polymerase chain reaction was used to trace MSCs by their Y-chromosome. During infusion, a minor number of MSCs left the kidney through the renal vein, and no MSCs were identified in arterial blood. Ischemic and healthy renal tissues were analyzed 30 min and 8 h after infusion, and 1-4 × 10⁴ MSCs per gram of tissue were detected, predominantly, in the renal cortex, with a viability >70%. Confocal microscopy demonstrated mainly glomerular localization of MSCs, but they were also observed in the capillary network around tubuli. The infusion of heat-inactivated (HI) MSCs, which are metabolically inactive, through the renal artery showed that HI-MSCs were distributed in the kidney in a similar manner to regular MSCs, suggesting a passive retention mechanism. Long-term MSC survival was analyzed by Y-chromosome tracing, and demonstrated that a low percentage of the infused MSCs were present in the kidney 14 days after administration, while HI-MSCs were completely undetectable. In conclusion, renal intra-arterial MSC infusion limited off-target engraftment, leading to efficient MSC delivery to the kidney, most of them being cleared within 14 days. MSC retention was independent of the metabolic state of MSC, indicating a passive mechanism.

Infusing Mesenchymal Stromal Cells into Porcine Kidneys during Normothermic Machine Perfusion: Intact MSCs Can Be Traced and Localised to Glomeruli

Normothermic machine perfusion (NMP) of kidneys offers the opportunity to perform active interventions, such as the addition of mesenchymal stromal cells (MSCs), to an isolated organ prior to transplantation. The purpose of this study was to determine whether administering MSCs to kidneys during NMP is feasible, what the effect of NMP is on MSCs and whether intact MSCs are retained in the kidney and to which structures they home. Viable porcine kidneys were obtained from a slaughterhouse. Kidneys were machine perfused during 7 h at 37 °C. After 1 h of perfusion either 0, 10⁵, 10⁶ or 10⁷ human adipose tissue derived MSCs were added. Additional ex vivo perfusions were conducted with fluorescent pre-labelled bone-marrow derived MSCs to assess localisation and survival of MSCs during NMP. After NMP, intact MSCs were detected by immunohistochemistry in the lumen of glomerular capillaries, but only in the 10⁷ MSC group. The experiments with fluorescent pre-labelled MSCs showed that only a minority of glomeruli were positive for infused MSCs and most of these glomeruli contained multiple MSCs. Flow cytometry showed that the number of infused MSCs in the perfusion circuit steeply declined during NMP to approximately 10%. In conclusion, the number of circulating MSCs in the perfusate decreases rapidly in time and after NMP only a small portion of the MSCs are intact and these appear to be clustered in a minority of glomeruli.

Effects of Normothermic Machine Perfusion Conditions on Mesenchymal Stromal Cells

Ex-situ normothermic machine perfusion (NMP) of transplant kidneys allows assessment of kidney quality and targeted intervention to initiate repair processes prior to transplantation. Mesenchymal stromal cells (MSC) have been shown to possess the capacity to stimulate kidney repair. Therefore, the combination of NMP and MSC therapy offers potential to repair transplant kidneys. It is however unknown how NMP conditions affect MSC. In this study the effect of NMP perfusion fluid on survival, metabolism and function of thawed cryopreserved human (h)MSC and porcine (p)MSC in suspension conditions was studied. Suspension conditions reduced the viability of pMSC by 40% in both perfusion fluid and culture medium. Viability of hMSC was reduced by suspension conditions by 15% in perfusion fluid, whilst no differences were found in survival in culture medium. Under adherent conditions, survival of the cells was not affected by perfusion fluid. The perfusion fluid did not affect survival of fresh MSC in suspension compared to the control culture medium. The freeze-thawing process impaired the survival of hMSC; 95% survival of fresh hMSC compared to 70% survival of thawed hMSC. Moreover, thawed MSC showed increased levels of reactive oxygen species, which indicates elevated levels of oxidative stress, and reduced mitochondrial activity, which implies reduced metabolism. The adherence of pMSC and hMSC to endothelial cells was reduced after the thawing process, effect which was particularly profound in in the perfusion fluid. To summarize, we observed that conditions required for machine perfusion are influencing the behavior of MSC. The freeze-thawing process reduces survival and metabolism and increases oxidative stress, and diminishes their ability to adhere to endothelial cells. In addition, we found that hMSC and pMSC behaved differently, which has to be taken into consideration when translating results from animal experiments to clinical studies.

A follistatin-based molecule increases muscle and bone mass without affecting the red blood cell count in mice

Inhibitors of the activin receptor signaling pathway (IASPs) have become candidate therapeutics for sarcopenia and bone remodeling disorders because of their ability to increase muscle and bone mass. However, IASPs utilizing activin type IIA and IIB receptors are also potent stimulators of erythropoiesis, a feature that may restrict their usage to anemic patients because of increased risk of venous thromboembolism. Based on the endogenous TGF-β superfamily antagonist follistatin (FST), a molecule in the IASP class, FST_ΔHBS-mFc, was generated and tested in both ovariectomized and naive BALB/c and C57BL/6 mice. In ovariectomized mice, FST_ΔHBS-mFc therapy dose-dependently increased cancellous bone mass up to 42% and improved bone microstructural indices. For the highest dosage of FST_ΔHBS-mFc (30 mg/kg, 2 times/wk), the increase in cancellous bone mass was similar to that observed with parathyroid hormone therapy (1-34, 80 µg/kg, 5 times/wk). Musculus quadriceps femoris mass dose-dependently increased up to 21% in ovariectomized mice. In both ovariectomized and naive mice, FST_ΔHBS-mFc therapy did not influence red blood cell count or hematocrit or hemoglobin levels. If the results are reproduced, a human FST_ΔHBS-mFc version could be applicable in patients with musculoskeletal conditions irrespective of hematocrit status.-Lodberg, A., van der Eerden, B. C. J., Boers-Sijmons, B., Thomsen, J. S., Brüel, A., van Leeuwen, J. P. T. M., Eijken, M. A follistatin-based molecule increases muscle and bone mass without affecting the red blood cell count in mice.

Isolation of Adipose Tissue-Derived Stem Cells: Enzymatic Digestion in Combination with Mechanical Distortion to Increase Adipose Tissue-Derived Stem Cell Yield from Human Aspirated Fat

Mesenchymal stem cells (MSCs) are of great interest due to their properties of immune modulation, tissue regeneration, and multipotent differentiation. Future developments of clinical applications, however, require a higher yield of MSCs, lower number of passages of cells in culture, and shorter time from harvest to use. Optimization and standardization of techniques for mesenchymal adipose tissue-derived stem cell isolation offers solutions to current bottlenecks as a larger amount of MSCs can be isolated. These improvements result in shorter expansion time, fewer passages, less donor material needed, and higher MSC yield. This paper describes an MSC isolation method combining enzymatic digestion with mechanic disruption. This protocol is a standardized and easy-to-implement method for reaching significantly higher MSC yields compared to conventional enzymatic isolation protocols. Based on the results presented, we hypothesize that the combined enzymatic and mechanical method increases the surface area of the adipose tissue, facilitating digestion by enzymes. This approach reduces the amount of adipose tissue and in vitro expansion time needed to reach sufficient amounts of MSCs for clinical purposes. Importantly, the method does not require increased amounts of collagenase, nor does it impair the viability or differentiability of the MSCs. Using this protocol increases MSC yield by a factor of three. As a consequence, these results indicate that the physiological concentration of MSCs in adipose tissue is higher than previously assumed. © 2018 by John Wiley & Sons, Inc.

A soluble activin type IIA receptor mitigates the loss of femoral neck bone strength and cancellous bone mass in a mouse model of disuse osteopenia

Disuse causes a rapid and substantial bone loss distinct in its pathophysiology from the bone loss associated with cancers, age, and menopause. While inhibitors of the activin-receptor signaling pathway (IASPs) have been shown to prevent ovariectomy- and cancer-induced bone loss, their application in a model of disuse osteopenia remains to be tested. Here, we show that a soluble activin type IIA receptor (ActRIIA-mFc) increases diaphyseal bone strength and cancellous bone mass, and mitigates the loss of femoral neck bone strength in the Botulinum Toxin A (BTX)-model of disuse osteopenia in female C57BL/6J mice. We show that ActRIIA-mFc treatment preferentially stimulates a dual-effect (anabolic-antiresorptive) on the periosteal envelope of diaphyseal bone, demonstrating in detail the effects of ActRIIA-mFc on cortical bone. These observations constitute a previously undescribed feature of IASPs that mediates at least part of their ability to mitigate detrimental effects of unloading on bone tissue. The study findings support the application of IASPs as a strategy to combat bone loss during disuse.

Using the Connectivity Map to discover compounds influencing human osteoblast differentiation

Osteoporosis is a common skeletal disorder characterized by low bone mass leading to increased bone fragility and fracture susceptibility. Identification of factors influencing osteoblast differentiation and bone formation is very important. Previously, we identified parbendazole to be a novel compound that stimulates osteogenic differentiation of human mesenchymal stromal cells (hMSCs), using gene expression profiling and bioinformatic analyzes, including the Connectivity Map (CMap), as an in-silico approach. The aim for this paper is to identify additional compounds affecting osteoblast differentiation using the CMap. Gene expression profiling was performed on hMSCs differentiated to osteoblasts using Illumina microarrays. Our osteoblast gene signature, the top regulated genes 6 hr after induction by dexamethasone, was uploaded into CMap (www.broadinstitute.org/cmap/). Through this approach we identified compounds with gene signatures positively correlating (withaferin-A, calcium folinate, amylocaine) or negatively correlating (salbutamol, metaraminol, diprophylline) to our osteoblast gene signature. All positively correlating compounds stimulated osteogenic differentiation, as indicated by increased mineralization compared to control treated cells. One of three negatively correlating compounds, salbutamol, inhibited dexamethasone-induced osteoblastic differentiation, while the other two had no effect. Based on gene expression data of withaferin-A and salbutamol, we identified HMOX1 and STC1 as being strongly differentially expressed . shRNA knockdown of HMOX1 or STC1 in hMSCs inhibited osteoblast differentiation. These results confirm that the CMap is a powerful approach to identify positively compounds that stimulate osteogenesis of hMSCs, and through this approach we can identify genes that play an important role in osteoblast differentiation and could be targets for novel bone anabolic therapies.

Mesenchymal Stromal Cells as Anti-Inflammatory and Regenerative Mediators for Donor Kidneys During Normothermic Machine Perfusion

There is great demand for transplant kidneys for the treatment of end-stage kidney disease patients. To expand the donor pool, organs from older and comorbid brain death donors, so-called expanded criteria donors (ECD), as well as donation after circulatory death donors, are considered for transplantation. However, the quality of these organs may be inferior to standard donor organs. A major issue affecting graft function and survival is ischemia/reperfusion injury, which particularly affects kidneys from deceased donors. The development of hypothermic machine perfusion has been introduced in kidney transplantation as a preservation technique and has improved outcomes in ECD and marginal organs compared to static cold storage. Normothermic machine perfusion (NMP) is the most recent evolution of perfusion technology and allows assessment of the donor organ before transplantation. The possibility to control the content of the perfusion fluid offers opportunities for damage control and reparative therapies during machine perfusion. Mesenchymal stromal cells (MSC) have been demonstrated to possess potent regenerative properties via the release of paracrine effectors. The combination of NMP and MSC administration at the same time is a promising procedure in the field of transplantation. Therefore, the MePEP consortium has been created to study this novel modality of treatment in preparation for human trials. MePEP aims to assess the therapeutic effects of MSC administered ex vivo by NMP in the mechanisms of injury and repair in a porcine kidney autotransplantation model.

Identification of Chloride Intracellular Channel Protein 3 as a Novel Gene Affecting Human Bone Formation

Osteoporosis is a common skeletal disorder characterized by low bone mass leading to increased bone fragility and fracture susceptibility. The bone building cells, osteoblasts, are derived from mesenchymal stromal cells (MSCs); however, with increasing age osteogenic differentiation is diminished and more adipocytes are seen in the bone marrow, suggesting a shift in MSC lineage commitment. Identification of specific factors that stimulate osteoblast differentiation from human MSCs may deliver therapeutic targets to treat osteoporosis. The aim of this study was to identify novel genes involved in osteoblast differentiation of human bone marrow–derived MSCs (hMSCs). We identified the gene chloride intracellular channel protein 3 (CLIC3) to be strongly upregulated during MSC‐derived osteoblast differentiation. Lentiviral overexpression of CLIC3 in hMSCs caused a 60% increase of matrix mineralization. Conversely, knockdown of CLIC3 in hMSCs using two short‐hairpin RNAs (shRNAs) against CLIC3 resulted in a 69% to 76% reduction in CLIC3 mRNA expression, 53% to 37% less alkaline phosphatase (ALP) activity, and 78% to 88% less matrix mineralization compared to scrambled control. Next, we used an in vivo human bone formation model in which hMSCs lentivirally transduced with the CLIC3 overexpression construct were loaded onto a scaffold (hydroxyapatite‐tricalcium‐phosphate), implanted under the skin of NOD‐SCID mice, and analyzed for bone formation 8 weeks later. CLIC3 overexpression led to a 15‐fold increase in bone formation (0.33% versus 5.05% bone area relative to scaffold). Using a Clic3‐His‐tagged pull‐down assay and liquid chromatography–mass spectrometry (LS/MS)‐based proteomics analysis in lysates of osteogenically differentiated hMSCs, we showed that CLIC3 interacts with NIMA‐related kinase 9 (NEK9) and phosphatidylserine synthase 1 (PTDSS1) in vitro, and this finding was supported by immunofluorescent analysis. In addition, inhibition of NEK9 or PTDSS1 gene expression by shRNAs inhibited osteoblast differentiation and mineralization. In conclusion, we successfully identified CLIC3 to be a lineage‐specific gene regulating osteoblast differentiation and bone formation through its interaction with NEK9 and PTDSS1. © The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Connectivity Map-based discovery of parbendazole reveals targetable human osteogenic pathway

Osteoporosis is a common skeletal disorder characterized by low bone mass leading to increased bone fragility and fracture susceptibility. In this study, we have identified pathways that stimulate differentiation of bone forming osteoblasts from human mesenchymal stromal cells (hMSCs). Gene expression profiling was performed in hMSCs differentiated toward osteoblasts (at 6 h). Significantly regulated genes were analyzed in silico, and the Connectivity Map (CMap) was used to identify candidate bone stimulatory compounds. The signature of parbendazole matches the expression changes observed for osteogenic hMSCs. Parbendazole stimulates osteoblast differentiation as indicated by increased alkaline phosphatase activity, mineralization, and up-regulation of bone marker genes (alkaline phosphatase/ALPL, osteopontin/SPP1, and bone sialoprotein II/IBSP) in a subset of the hMSC population resistant to the apoptotic effects of parbendazole. These osteogenic effects are independent of glucocorticoids because parbendazole does not up-regulate glucocorticoid receptor (GR) target genes and is not inhibited by the GR antagonist mifepristone. Parbendazole causes profound cytoskeletal changes including degradation of microtubules and increased focal adhesions. Stabilization of microtubules by pretreatment with Taxol inhibits osteoblast differentiation. Parbendazole up-regulates bone morphogenetic protein 2 (BMP-2) gene expression and activity. Cotreatment with the BMP-2 antagonist DMH1 limits, but does not block, parbendazole-induced mineralization. Using the CMap we have identified a previously unidentified lineage-specific, bone anabolic compound, parbendazole, which induces osteogenic differentiation through a combination of cytoskeletal changes and increased BMP-2 activity.

Calcifying vascular smooth muscle cells and osteoblasts: independent cell types exhibiting extracellular matrix and biomineralization-related mimicries

BACKGROUND

Ectopic vascular calcifications represent a major clinical problem associated with cardiovascular disease and mortality. However, the mechanisms underlying pathological vascular calcifications are largely unknown hampering the development of therapies to tackle this life threatening medical condition.

RESULTS

In order to gain insight into the genes and mechanisms driving this pathological calcification process we analyzed the transcriptional profile of calcifying vascular smooth muscle cells (C-VSMCs). These profiles were compared to differentiating osteoblasts, cells that constitute their physiological calcification counterparts in the body. Overall the transcriptional program of C-VSMC and osteoblasts did not overlap. Several genes, some of them relevant for bone formation, were distinctly modulated by C-VSMCs which did not necessarily lose their smooth muscle cell markers while calcifying. Bioinformatics gene clustering and correlation analysis disclosed limited bone-related mechanisms being shared by two cell types. Extracellular matrix (ECM) and biomineralization genes represented common denominators between pathological vascular and physiological bone calcifications. These genes constitute the strongest link between these cells and represent potential drivers for their shared end-point phenotype.

CONCLUSIONS

The analyses support the hypothesis that VSMC trans-differentiate into C-VSMCs keeping their own identity while using mechanisms that osteoblasts use to mineralize. The data provide novel insights into groups of genes and biological processes shared in MSC and VSMC osteogenic differentiation. The distinct gene regulation between C-VSMC and osteoblasts might hold clues to find cell-specific pathway modulations, opening the possibility to tackle undesired vascular calcifications without disturbing physiologic bone formation and vice versa.

Protein kinase C-induced activin A switches adrenocortical steroidogenesis to aldosterone by suppressing CYP17A1 expression

Functional zonation of the adrenal cortex is a consequence of the zone-specific expression of P450c17 (CYP17A1) and its cofactors. Activin and inhibin peptides are differentially produced within the zones of the adrenal cortex and have been implicated in steroidogenic control. In this study, we investigated whether activin and inhibin can function as intermediates in functional zonation of the human adrenal cortex. Activin A suppressed CYP17A1 expression and P450c17 function in adrenocortical cell lines as well as in primary adrenal cell cultures. Inhibin βA-subunit mRNA and activin A protein levels were found to be increased up to 1,900-fold and 49-fold, respectively, after protein kinase C (PKC) stimulation through PMA or angiotensin II in H295R adrenocortical carcinoma cells. This was confirmed in HAC15 cells and for PMA in primary adrenal cell cultures. Both PMA and Ang II decreased CYP17A1 expression in the adrenocortical cell lines, whereas PMA concurrently suppressed CYP17A1 levels in the primary cultures. Inhibition of activin signaling during PKC stimulation through silencing of the inhibin βA-subunit or blocking of the activin type I receptor opposed the PMA-induced downregulation of CYP17A1 expression and P450c17 function. In contrast, PKA stimulation through adrenocorticotrophin or forskolin increased expression of the inhibin α-subunit and betaglycan, both of which are antagonists of activin action. These data indicate that activin A acts as a PKC-induced paracrine factor involved in the suppression of CYP17A1 in the zona glomerulosa and can thereby contribute to functional adrenocortical zonation.

Activin A suppresses osteoblast mineralization capacity by altering extracellular matrix (ECM) composition and impairing matrix vesicle (MV) production

During bone formation, osteoblasts deposit an extracellular matrix (ECM) that is mineralized via a process involving production and secretion of highly specialized matrix vesicles (MVs). Activin A, a transforming growth factor-β (TGF-β) superfamily member, was previously shown to have inhibitory effects in human bone formation models through unclear mechanisms. We investigated these mechanisms elicited by activin A during in vitro osteogenic differentiation of human mesenchymal stem cells (hMSC). Activin A inhibition of ECM mineralization coincided with a strong decline in alkaline phosphatase (ALP(1)) activity in extracellular compartments, ECM and matrix vesicles. SILAC-based quantitative proteomics disclosed intricate protein composition alterations in the activin A ECM, including changed expression of collagen XII, osteonectin and several cytoskeleton-binding proteins. Moreover, in activin A osteoblasts matrix vesicle production was deficient containing very low expression of annexin proteins. ECM enhanced human mesenchymal stem cell osteogenic development and mineralization. This osteogenic enhancement was significantly decreased when human mesenchymal stem cells were cultured on ECM produced under activin A treatment. These findings demonstrate that activin A targets the ECM maturation phase of osteoblast differentiation resulting ultimately in the inhibition of mineralization. ECM proteins modulated by activin A are not only determinant for bone mineralization but also possess osteoinductive properties that are relevant for bone tissue regeneration.

IFNβ impairs extracellular matrix formation leading to inhibition of mineralization by effects in the early stage of human osteoblast differentiation

Osteoimmunology is an emerging field of research focused on the interaction of the immune system and bone. In this study we demonstrate that human osteoblasts are sensitive to the immune cytokine interferon (IFN)β. Osteoblasts respond to IFNβ as shown by the induction of several known IFN target genes such as interferon-induced (IFI) proteins (IFIT1, IFI44L), interferon-stimulated gene factor 3 (ISGF3) complex and the induction of IFNβ itself. We demonstrated that IFNβ has severe inhibitory effects on mineralization of osteoblast-derived extracellular matrix (ECM). Analysis of the timing of the IFNβ effects revealed that committed osteoblasts in early stage of differentiation are most sensitive to IFNβ inhibition of mineralization. A single IFNβ treatment was as effective as multiple treatments. During the progress of differentiation osteoblasts become desensitized for IFNβ. This pinpoints to a complex pattern of IFNβ sensitivity in osteoblasts. Focusing on early osteoblasts, we showed that IFNβ decreased gene expression of ECM-related genes, such as type I Collagen (COL1A1), fibronectin (FN1), fibullin (FBLN1), fibrillin (FBN2), and laminin (LAMA1). Additionally, ECM produced by IFNβ-treated osteoblasts contained less collagen protein. IFNβ stimulated gene expression of osteopontin (OPN), annexin2 (ANXA2), and hyaluronan synthase 1 (HAS1), which are important factors in the adhesion of hematopoietic stem cells (HSC) in the HSC niche. In conclusion, IFNβ directly modifies human osteoblast function by inhibiting ECM synthesis eventually resulting in delayed bone formation and mineralization and induces a HSC niche supporting phenotype. These effects are highly dependent on timing of treatment in the early phase of osteoblast differentiation.

Basic techniques in human mesenchymal stem cell cultures: differentiation into osteogenic and adipogenic lineages, genetic perturbations, and phenotypic analyses

This unit describes basic techniques in human mesenchymal stem cell (hMSC) cultures. It includes protocols for the differentiation of hMSCs into osteogenic and adipogenic lineages, genetic perturbations, and phenotypic analyses. hMSCs can be differentiated with dexamethasone and β-glycerophosphate into mineralizing osteoblasts within 2 to 3 weeks, or with dexamethasone, indomethacin, and 3-isobutyl-1-methylxanthine into lipid vesicle-containing adipocytes within 1 to 2 weeks. Phenotypic changes during those highly dynamic differentiation processes can be detected by biochemical and histological assays and gene expression analyses of differentiation markers. In addition, this unit describes an electroporation method that allows the transient genetic perturbation of hMSCs.

Unraveling the human bone microenvironment beyond the classical extracellular matrix proteins: a human bone protein library

A characteristic feature of bone, differentiating it from other connective tissues, is the mineralized extracellular matrix (ECM). Mineral accounts for the majority of the bone tissue volume, being the remainder organic material mostly derived from collagen. This, and the fact that only a limited number of noncollagenous ECM proteins are described, provides a limited view of the bone tissue composition and bone metabolism, the more so considering the increasing understanding of ECM significance for cellular form and function. For this reason, we set out to analyze and extensively characterize the human bone proteome using large-scale mass spectrometry-based methods. Bone samples of four individuals were analyzed identifying 3038 unique proteins. A total of 1213 of these were present in at least 3 out of 4 bone samples. For quantification purposes, we were limited to noncollagenous proteins (NCPs) and we could quantify 1051 NCPs. Most classical bone matrix proteins mentioned in literature were detected but were not among the highly abundant ones. Gene ontology analyses identified high-abundance groups of proteins with a functional link to mineralization and mineral metabolism such as transporters, pyrophosphatase activity, and Ca(2+)-dependent phospholipid binding proteins. ECM proteins were as well overrepresented together with nucleosome and antioxidant activity proteins, which have not been extensively characterized as being important for bone. In conclusion, our data clearly demonstrates that human bone tissue is a reservoir of a wide variety of proteins. In addition to the classical osteoblast-derived ECM, we have identified many proteins from different sources and of unknown function in bone. Thus, this study represents an informative library of bone proteins forming a source for novel bone formation modulators as well as biomarkers for bone diseases such as osteoporosis.

GPM6B regulates osteoblast function and induction of mineralization by controlling cytoskeleton and matrix vesicle release

Neuronal membrane glycoprotein gene (GPM6B) encodes a membrane glycoprotein that belongs to the proteolipid protein family. We identified GPM6B as a gene that is strongly upregulated during osteoblast differentiation. To investigate the role of GPM6B in the process of bone formation, we silenced GPM6B expression during osteogenic differentiation of human mesenchymal stem cells (hMSCs). GPM6B silencing in hMSCs resulted in reduced alkaline phosphate (ALP) activity along with reduced mineralization of extracellular matrix (ECM). Microarray expression analysis of GPM6B-depleted osteogenic hMSCs revealed significant changes in genes involved in cytoskeleton organization and biogenesis. Immunocytochemistry results confirm changes in the distribution of actin filaments, as well as the shape and size of focal adhesions on GPM6B silencing. Moreover, we demonstrated that production and release of ALP-positive matrix vesicles (MVs) were reduced. In conclusion, we identified GPM6B as a novel regulator of osteoblast function and bone formation. This finding demonstrates the significance of cytoskeleton organization for MV production and subsequent mineralization.

Effects of dexamethasone-loaded PLGA microspheres on human fetal osteoblasts

Integration of a drug delivery function into implantable medical devices enables local release of specific bioactives to control cells–surface interactions. One alternative to achieve this biofunctionality for bone implants is to incorporate particulate drug delivery systems (DDSs) into the rough or porous implant surfaces. The scope of this study was to assess the effects of a model DDS consisting of poly(D,L-lactide-co-glycolide) (PLGA) microspheres loaded with an anti-inflammatory drug, dexamethasone (DXM), on the response of Simian Virus-immortalized Human Fetal Osteoblast (SV-HFO) cells. The microspheres were prepared by the oil-in-water emulsion/solvent evaporation method, whereas cells response was investigated by Alamar Blue test for viability, alkaline phosphatase (ALP) activity for differentiation, and Alizarin Red staining for matrix mineralization. Cell viability was not affected by the presence of increased concentrations of polymeric microspheres in the culture media. Furthermore, in the cultures with DXM-loaded microspheres, ALP activity was expressed at levels similar with those obtained under osteogenic conditions, indicating that DXM released from the microsphere-stimulated cell differentiation. Matrix mineralization occurred preferentially around the DXM-loaded microspheres confirming that the released DXM could act as osteogenic supplement for the cells. These in vitro findings suggest that a particulate PLGA-DXM DDS may actually provide dual, anti-inflammatory and osteogenic functions when incorporated on the surface of bone implants.

Proteomic analysis of human osteoblastic cells: relevant proteins and functional categories for differentiation

Osteoblasts are the bone forming cells, capable of secreting an extracellular matrix with mineralization potential. The exact mechanism by which osteoblasts differentiate and form a mineralized extracellular matrix is presently not fully understood. To increase our knowledge about this process, we conducted proteomics analysis in human immortalized preosteoblasts (SV-HFO) able to differentiate and mineralize. We identified 381 proteins expressed during the time course of osteoblast differentiation. Gene ontology analysis revealed an overrepresentation of protein categories established as important players for osteoblast differentiation, bone formation, and mineralization such as pyrophosphatases. Proteins involved in antigen presentation, energy metabolism and cytoskeleton rearrangement constitute other overrepresented processes, whose function, albeit interesting, is not fully understood in the context of osteoblast differentiation and bone formation. Correlation analysis, based on quantitative data, revealed a biphasic osteoblast differentiation, encompassing a premineralization and a mineralization period. Identified differentially expressed proteins between mineralized and nonmineralized cells include cytoskeleton (e.g., CCT2, PLEC1, and FLNA) and extracellular matrix constituents (FN1, ANXA2, and LGALS1) among others. FT-ICR-MS data obtained for FN1, ANXA2, and LMNA shows a specific regulation of these proteins during the different phases of osteoblast differentiation. Taken together, this study increases our understanding of the proteomics changes that accompany osteoblast differentiation and may permit the discovery of novel modulators of bone formation.

A new concept underlying stem cell lineage skewing that explains the detrimental effects of thiazolidinediones on bone

Bone-marrow adipogenesis is an aging-related phenomenon and is correlated with osteoporosis. The latter is a prevalent bone disease in the elderly leading to increased fracture risk and mortality. It is widely hypothesized that the underlying molecular mechanism includes a shift in the commitment of mesenchymal stem cells (MSCs) from the osteogenic lineage to the adipogenic lineage. Lineage skewing is at least partially a result of transcriptional changes. The nuclear transcription factor peroxisome proliferator-activated receptor gamma (PPAR-gamma) has been proposed as a major decision factor in MSC lineage commitment, promoting adipogenesis at the expense of osteogenesis. Here we found that PPAR-gamma acted unexpectedly to stimulate osteoblast differentiation from human bone marrow-derived MSCs. Both rosiglitazone-mediated activation and overexpression of PPAR-gamma caused acceleration of osteoblast differentiation. Conversely, shRNAi-mediated PPAR-gamma knockdown diminished osteoblast differentiation. MSCs that were treated with rosiglitazone did not preferentially differentiate into adipocytes. However, the rosiglitazone-mediated acceleration of osteoblast differentiation was followed by increased accumulation of reactive oxygen species and apoptosis. In contrast to the osteogenic lineage, cells of the adipogenic lineage were protected from this. Our data support a new concept on bone health that adds to the explanation of the clinically observed suppressive action of activated PPAR-gamma on bone and the associated phenomenon of bone marrow adipogenesis. This concept is based on a higher susceptibility of the osteogenic than the adipogenic lineage to oxidative stress and apoptosis that is preferentially triggered in the osteoblasts by activated PPAR-gamma.

1Alpha,25-(OH)2D3 acts in the early phase of osteoblast differentiation to enhance mineralization via accelerated production of mature matrix vesicles

1Alpha,25-dihydroxyitamin D(3) (1,25D3) deficiency leads to impaired bone mineralization. We used the human pre-osteoblastic cell line SV-HFO, which forms within 19 days of culture an extracellular matrix that starts to mineralize around day 12, to examine the mechanism by which 1,25D3 regulates osteoblasts and directly stimulates mineralization. Time phase studies showed that 1,25D3 treatment prior to the onset of mineralization, rather than during mineralization led to accelerated and enhanced mineralization. This is supported by the observation of unaltered stimulation by 1,25D3 even when osteoblasts were devitalized just prior to onset of mineralization and after 1,25D3 treatment. Gene Chip expression profiling identified the pre-mineralization and mineralization phase as two strongly distinctive transcriptional periods with only 0.6% overlap of genes regulated by 1,25D3. In neither phase 1,25D3 significantly altered expression of extracellular matrix genes. 1,25D3 significantly accelerated the production of mature matrix vesicles (MVs) in the pre-mineralization. Duration rather than timing determined the extent of the 1,25D3 effect. We propose the concept that besides indirect effects via intestinal calcium uptake 1,25D3 directly accelerates osteoblast-mediated mineralization via increased production of mature MVs in the period prior to mineralization. The accelerated deposition of mature MVs leads to an earlier onset and higher rate of mineralization. These effects are independent of changes in extracellular matrix protein composition. These data on 1,25D3, mineralization, and MV biology add new insights into the role of 1,25D3 in bone metabolism and emphasize the importance of MVs in bone and maintaining bone health and strength by optimal mineralization status.

Stretch-induced inhibition of Wnt/beta-catenin signaling in mineralizing osteoblasts

Wnt signaling is important for bone formation and osteoblastic differentiation. Recent findings indicate a stimulating role of Wnt signaling in bone mechanotransduction. However, negative effects of Wnt signaling on osteoblast differentiation and mineralization have been described as well. We conducted in vitro stretch experiments using human pre-osteoblasts to study short- and long-term effects of mechanical loading on Wnt/beta-catenin signaling. As the extracellular regulated kinase (ERK) pathway is known to be involved in mechanotransduction in osteoblasts, we also evaluated its role in Wnt/beta-catenin signaling. Stretch experiments up to 21 days (using stretch episodes of 15 min, alternated with 90 min rest) resulted in higher mineralization compared to static control cultures. We found that 15 min of stretch initially increased nuclear beta-catenin, but ultimately resulted in significant decrease at 12 and 40 h after stretch. Downregulation of Wnt-responsive element activity 16 h after stretch, using a luciferase construct, further supported these findings. The presence of the ERK inhibitor U0126 did not alter the stretch-induced decrease of beta-catenin levels. Our data indicate a biphasic effect of mechanical loading on beta-catenin in mineralizing human differentiating osteoblasts, which is independent of the ERK pathway. The osteogenic potential of our loading regime was confirmed by an increase in osteogenic differentiation markers such as alkaline phosphatase activity and calcium deposition after 3 weeks of culture. We conjecture that the biphasic aspect of Wnt/beta-catenin signaling with a strong decrease up to 40 h after the stretch induction, is important for the anabolic effects of mechanical stretch on bone.

Synergistic induction of local glucocorticoid generation by inflammatory cytokines and glucocorticoids: implications for inflammation associated bone loss

Objectives

Synovial fibroblasts and osteoblasts generate active glucocorticoids by means of the 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) enzyme. This activity increases in response to proinflammatory cytokines or glucocorticoids. During inflammatory arthritis synovium and bone are exposed to both these factors. This study hypothesised that glucocorticoids magnify the effects of inflammatory cytokines on local glucocorticoid production in both synovium and bone.

Methods

The effects of inflammatory cytokines (IL-1β/tumour necrosis factor alpha; TNFα) and glucocorticoids, alone or combined, were assessed on the expression and activity of 11β-HSD1 in primary synovial fibroblasts, primary human osteoblasts and MG-63 osteosarcoma cells. A range of other target genes and cell types were used to examine the specificity of effects. Functional consequences were assessed using IL-6 ELISA.

Results

In synovial fibroblasts and osteoblasts, treatment with cytokines or glucocorticoids in isolation induced 11β-HSD1 expression and activity. However, in combination, 11β-HSD1 expression, activity and functional consequences were induced synergistically to a level not seen with isolated treatments. This effect was seen in normal skin fibroblasts but not foreskin fibroblasts or adipocytes and was only seen for the 11β-HSD1 gene. Synergistic induction had functional consequences on IL-6 production.

Conclusions

Combined treatment with inflammatory cytokines and glucocorticoids synergistically induces 11β-HSD1 expression and activity in synovial fibroblasts and osteoblasts, providing a mechanism by which synovium and bone can interact to enhance anti-inflammatory responses by increasing localised glucocorticoid levels. However, the synergistic induction of 11β-HSD1 might also cause detrimental glucocorticoid accumulation in bone or surrounding tissues.

Donor-derived mesenchymal stem cells remain present and functional in the transplanted human heart

Mesenchymal stem cells (MSC) are characterized by their multilineage differentiation capacity and immunosuppressive properties. They are resident in virtually all tissues and we have recently characterized MSC from the human heart. Clinical heart transplantation offers a model to study the fate of transplanted human MSC. In this study, we isolated and expanded MSC from heart tissue taken before, and 1 week up to 6 years after heart transplantation. MSC from posttransplantation tissue were all of donor origin, demonstrating the longevity of endogenous MSC and suggesting an absence of immigration of recipient MSC into the heart. MSC isolated from transplanted tissue showed an immunophenotype that was characteristic for MSC and maintained cardiomyogenic and osteogenic differentiation capacity. They furthermore preserved their ability to inhibit the proliferative response of donor-stimulated recipient peripheral blood mononuclear cells. In conclusion, functional MSC of donor origin remain present in the heart for several years after transplantation.

Evidence for multiple peroxisome proliferator-activated receptor gamma transcripts in bone: fine-tuning by hormonal regulation and mRNA stability

The expression, regulation and functional significance of multiple peroxisome proliferator-activated receptor gamma transcript variants in bone were studied. PPARG transcripts giving rise to PPARg-1 protein were expressed in human osteoblasts, whereas PPARG-2 transcript and protein remained virtually absent. PPARG expression underwent homologous regulation, was upregulated during differentiation and directly induced by the osteogenic hormone dexamethasone, suggesting a role for PPARg-1 in osteogenesis. Differences between the stabilities of PPARG-1, -3 and -4 were observed. We hypothesize that cell-specific expression patterns of multiple PPARG transcript variants encoding for the same protein but differing in mRNA stabilities enable a fine-tuning of PPARG action, which eventually supports a well-adjusted signal transduction between the cell and its environment.

Systems biology towards life in silico: mathematics of the control of living cells

Systems Biology is the science that aims to understand how biological function absent from macromolecules in isolation, arises when they are components of their system. Dedicated to the memory of Reinhart Heinrich, this paper discusses the origin and evolution of the new part of systems biology that relates to metabolic and signal-transduction pathways and extends mathematical biology so as to address postgenomic experimental reality. Various approaches to modeling the dynamics generated by metabolic and signal-transduction pathways are compared. The silicon cell approach aims to describe the intracellular network of interest precisely, by numerically integrating the precise rate equations that characterize the ways macromolecules' interact with each other. The non-equilibrium thermodynamic or 'lin-log' approach approximates the enzyme rate equations in terms of linear functions of the logarithms of the concentrations. Biochemical Systems Analysis approximates in terms of power laws. Importantly all these approaches link system behavior to molecular interaction properties. The latter two do this less precisely but enable analytical solutions. By limiting the questions asked, to optimal flux patterns, or to control of fluxes and concentrations around the (patho)physiological state, Flux Balance Analysis and Metabolic/Hierarchical Control Analysis again enable analytical solutions. Both the silicon cell approach and Metabolic/Hierarchical Control Analysis are able to highlight where and how system function derives from molecular interactions. The latter approach has also discovered a set of fundamental principles underlying the control of biological systems. The new law that relates concentration control to control by time is illustrated for an important signal transduction pathway, i.e. nuclear hormone receptor signaling such as relevant to bone formation. It is envisaged that there is much more Mathematical Biology to be discovered in the area between molecules and Life.

The activin A-follistatin system: potent regulator of human extracellular matrix mineralization

Bone quality is an important determinant of osteoporosis, and proper osteoblast differentiation plays an important role in the control and maintenance of bone quality. We investigated the impact of activin signaling on human osteoblast differentiation, extracellular matrix formation, and mineralization. Activins belong to the transforming growth factor-beta superfamily and activin A treatment strongly inhibited mineralization in osteoblast cultures, whereas the activin antagonist follistatin increased mineralization. Osteoblasts produced activin A and follistatin in a differentiation-dependent manner, leading to autocrine regulation of extracellular matrix formation and mineralization. In addition, mineralization in a vascular smooth muscle cell-based model for pathological calcification was inhibited. Comparative activin A and follistatin gene expression profiling showed that activin signaling changes the expression of a specific range of extracellular matrix proteins prior to the onset of mineralization, leading to a matrix composition with reduced or no mineralizing capacity. These findings demonstrate the regulation of osteoblast differentiation and matrix mineralization by the activin A-follistatin system, providing the possibility to control bone quality as well as pathological calcifications such as atherosclerosis by using activin A, follistatin, or analogs thereof.

The essential role of glucocorticoids for proper human osteoblast differentiation and matrix mineralization

Glucocorticoids (GCs) exert profound effects on bone and are essential for human osteoblast differentiation. However, GCs are still interpreted as negative regulators of bone formation, mainly caused by the detrimental effects on bone after clinical use of GCs. In this paper we emphasize the importance of GCs for proper human osteoblast differentiation and matrix mineralization. We show that human osteoblast differentiation needs to be triggered by GCs in a specific time-window during the early stages of development. Exposure to GCs in the beginning of osteoblast development induces a dose dependent increase in alkaline phosphatase activity and matrix mineralization. GC-induced differentiation stimulated expression of genes involved in bone formation and suppressed genes that negatively regulate bone formation and mineralization. Furthermore we highlight the importance of local cortisol activation in osteoblasts by expression of 11beta-hydroxysteroid dehydrogenase 1 (11beta-HSD1).

11β-Hydroxysteroid Dehydrogenase Expression and Glucocorticoid Synthesis Are Directed by a Molecular Switch during Osteoblast Differentiation

11β-Hydroxysteroid dehydrogenase type 1 (11β-HSD1) plays an important role in the prereceptor regulation of corticosteroids by locally converting cortisone into active cortisol. To investigate the impact of this mechanism on osteoblast development, we have characterized 11β-HSD1 activity and regulation in a differentiating human osteoblast cell line (SV-HFO). Continuous treatment with the synthetic glucocorticoid dexamethasone induces differentiation of SV-HFO cells during 21 d of culture. Using this cell system, we showed an inverse relationship between 11β-HSD1 activity and osteoblast differentiation. 11β-HSD1 mRNA expression and activity were low and constant in differentiating osteoblasts. However, in the absence of differentiation (no dexamethasone), 11β-HSD1 mRNA and activity increased strongly from d 12 of culture onward, with a peak around d 19. Promoter reporter studies provided evidence that specific regions of the 11β-HSD1 gene are involved in this differentiation controlled regulation of the enzyme. Functional implication of these changes in 11β-HSD1 is shown by the induction of osteoblast differentiation in the presence of cortisone. The current study demonstrates the presence of an intrinsic differentiation-driven molecular switch that controls expression and activity of 11β-HSD1 and thereby cortisol production by human osteoblasts. This efficient mechanism by which osteoblasts generate cortisol in an autocrine fashion to ensure proper differentiation will help to understand the complex effects of cortisol on bone metabolism.

Tonoplast anion channel activity modulation by pH in Chara corallina

The patch-clamp technique was used to investigate regulation of anion channel activity in the tonoplast of Chara corallina in response to changing proton and calcium concentrations on both sides of the membrane. These channels are known to be Ca2+-dependent, with conductances in the range of 37 to 48 pS at pH 7.4. By using low pH at the vacuolar side (either pH(vac) 5.3 or 6.0) and a cytosolic pH (pH(cyt)) varying in a range of 4.3 to 9.0, anion channel activity and single-channel conductance could be reversibly modulated. In addition, Ca2+-sensitivity of the channels was markedly influenced by pH changes. At pH(cyt) values of 7.2 and 7.4 the half-maximal concentration (EC50) for calcium activation was 100-200 microm, whereas an EC(50) of about 5 microm was found at a pH(cyt) of 6.0. This suggests an improved binding of Ca2+ ions to the channel protein at more acidic cytoplasm. At low pH(cyt), anion channel activity and mean open times were voltage-dependent. At pipette potentials (V(p)) of +100 mV, channel activity was approximately 15-fold higher than activity at negative pipette potentials and the mean open time of the channel increased. In contrast, at pH(cyt) 7.2, anion channel activity and the opening behavior seemed to be independent of the applied V(p). The kinetics of the channel could be further controlled by the Ca2+ concentration at the cytosolic membrane side: the mean open time significantly increased in the presence of a high cytosolic Ca2+ concentration. These results show that tonoplast anion channels are maintained in a highly active state in a narrow pH range, below the resting pH(cyt). A putative physiological role of the pH-dependent modulation of these anion channels is discussed.

Membrane orientation of droplets prepared from Chara corallina internodal cells

It is generally accepted that the membrane surrounding droplets from characean cells originates from the tonoplast, but there is some uncertainty regarding droplet membrane sidedness. This issue was addressed directly by combining two different droplet isolation methods and the patch clamp technique. Neutral red accumulation was used to demonstrate the presence of H(+)-transport over the membrane and to predict membrane orientation. Two types of droplet populations with differently oriented membranes could be formed in an iso-osmotic bath solution. Cytoplasmic droplets (cytosolic side of the tonoplast inside) contained cytoplasm, while the second type of droplet population contained vacuolar sap (vacuolar droplets, vacuolar side of the tonoplast inside). Smaller vesicels also appeared inside the droplets, with an apparently inversely oriented membrane. Confocal laser scanning microscopy indirectly demonstrated that, at least with one of the droplet isolation methods, the plasma membrane entirely remains in the internodal cell after intracellular perfusion. Both types of droplet populations allowed the formation of excised patches and single-channel measurements by the patch clamp technique. Properties of anion channels in the tonoplast could be used to prove the predicted membrane orientation, knowing that Ca2+ can only activate these channels from the cytosolic side. These results provide useful data for studies addressing ligand-binding, block and modulation, organization and interaction of proteins within the membrane or with other regulatory factors, where it is important to control membrane orientation.