During remodelling, osteoclasts produce discrete bone cavities filled with bone and this is associated with the dimensions of the cavity. The aim of this study is to investigate the effect of pores of similar size to those produced by osteoclasts on the morphology, proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) in vitro. The hypothesis is that a porous surface similar in morphology to a bone surface prepared by osteoclasts will increase cell proliferation and osteogenic differentiation of MSCs.

Sheep BMSCs were seeded onto plain titanium surfaces and 100µm, 250µm and 500µm discrete pores surfaces. Cell metabolic activity was investigated using Presto Blue on days 3, 7 and 10. Bone mineralisation was quantified by Alizarin red staining at days 3, 7 and 14. Cell morphology was observed by scanning electron microscopy (SEM). Data was statistically analysed using one-way analysis of variance and a Bonferroni correction method.

Cells on porous discs had a three dimensional phenotype and aligned on the circumference of each pore. Metabolic activity was significantly higher by day 10 on plain discs compared to all porous discs. Bone mineralization was significantly higher on 100µm pores by day 3 (0.545mM±0.66; p=0.047) than plain discs and significantly higher on both 100µm and 250µm pores by day 7(p=0.000 and p=0.005) than plain discs. Substantial mineralised bone matrix was found on 100µm discs without being treated with osteogenic supplements, compared to other control disc types (p=0.043, p=0.003, p=0.000).

The different topographies altered cell behaviour and migration.100µm pores demonstrated earlier and enhanced bone mineralisation even in the absence of osteogenic supplements. This pore size is aligned to the size of individual resorption bays that osteoclasts produce on bone surfaces and is considerably lower than the pore sizes used to enhance osteo-integration of implant surfaces.

A significant number of fractures develop non-union. Stem cell therapy may be beneficial in their treatment, however this requires acquisition, culture and delivery of stem cells. Stem cell homing and migration is regulated through SDF-1 and its receptor CXCR4. Studies have demonstrated endogenous mobilisation of different populations of stem and progenitor cells by administering growth factors with a pharmacological antagonist of CXCR4, AMD3100. This may therefore be a means to improve compromised fracture healing. A 1.5mm femoral osteotomy in adult female Wistar rats was stabilised with an external skeletal fixator. After osteotomy, saline/PBS (P) VEGF (V), IGF-1 (I) or GCSF (G) (100ug/kg, 0.5ml/100g i.p.), were administered daily for 4 days. On day 5, a single 5mg/kg i.p. dose of AMD3100 was given. Control group (C) did not receive growth factors or AMD 3100. At 5 weeks, the femur was retrieved and microCT scanned. Compared to group C (n=7), group P (n=5) had a significant increase in bone volume (P=0.01) 8.9±2.2um∧3 (control 4.3±3.1um∧3) and trabecular thickness (P=0.03). Group I (n=6) also had a significant increase in bone volume (P=0.035) 5.1±4.2um∧3 and trabecular thickness 0.062±0.008um (control 0.042±0.01um) (P=0.01). Group V (n=8), showed a non-significant increase in bone volume; 5.22±1.7um∧3 and trabecular thickness 0.048±0.007um. Group G (n=5) showed a significant decrease in bone volume (2.5±2.6um∧3) (P=0.048). AMD3100 alone and IgF1-AMD3100, showed the greatest increase in bone formation, presumably through mobilisation of beneficial combinations of stem and progenitor cells. GCSF-AMD3100, which is expected to mobilise hematopoietic progenitors inhibited bone healing.

Objectives

Cellular movement and relocalisation are important for many physiologic properties. Local mesenchymal stem cells (MSCs) from injured tissues and circulating MSCs aid in fracture healing. Cytokines and chemokines such as Stromal cell-derived factor 1(SDF-1) and its receptor chemokine receptor type 4 (CXCR4) play important roles in maintaining mobilisation, trafficking and homing of stem cells from bone marrow to the site of injury. We investigated the differences in migration of MSCs from the femurs of young, adult and ovariectomised (OVX) rats and the effect of CXCR4 over-expression on their migration.

Background

Osteoporosis and bone fractures lead to immobility, chronic pain and high patient care costs. Mesenchymal stem cells (MSCs) from postmenopausal women have a slower growth rate and osteogenic differentiation ability causing lower bone density and reduced fracture healing capacity compared to MSCs from premenopausal women. Cellular movement and relocalisation are necessary for many physiologic properties. Local MSCs from injured tissues and circulating MSCs are involved in fracture healing. Cytokines and chemokines such as SDF-1 and its receptor CXCR4 play important roles in maintaining mobilisation, trafficking and homing of stem cells from bone marrow to the site of injury. This study investigated the effect of CXCR4 over-expression on the migration of MSCs from ovariectomised, normal and young rats.

Intermittent parathyroid hormone 1–34 (teriparatide) is the N-fragment terminal of the intact hormone, currently in clinical use to treat osteoporosis. Unlike anti-catabolic agents such as bisphosphonates, PTH 1–34 not only affects the osteoclast, but also up regulates bone formation via both modelling and remodelling mechanisms. The actions of iPTH on mesenchymal stem cell differentiation (MSCs) may underpin a further method in the treatment of osteoporosis specifically, and for fracture healing in general. Stem cells from older female osteoporotic animals have reduced activity and poorer osteogenic potential; additionally, their migration to and retention at sites of increased bone turnover are reduced in comparison to cells from younger animals. The aim of this study was to isolate bone marrow derived MSCs from both young Wild Type (WT) and ovarectomized senile (OVX) rats, then to investigate and compare the effect of pulsatile and continuous PTH administration on migration to SDF-1, proliferation and osteogenic differentiation.

MSCs were harvested from the femora of 6–9week Wistar rats, and from 10–13month ovarectomized rats with established osteopenia. Cells were cultured with 25, 50 and 100nmMol of PTH 1–34 added to osteogenic media either continuously or in a pulsatile fashion for 6 hours in every 72hour cycle. ALP and Alizarin Red were used to assess the optimal concentration of PTH for osteogenic differentiation. Subsequently, proliferation was assessed with Alamar Blue and cells were seeded in a Boyden chamber to quantify the migration to SDF-1. As the data was parametric a student t-test was used to analyse results, and a p value < 0.05 was considered significant.

ALP and Alizarin Red parameters were significantly increased for both WT and OVX groups at 50nmMol of pulsatile PTH in comparison to groups cultured in 25 or 100nmMol. Continuous administration at all concentrations led to reduced calcium phosphate deposition by day 21 in all groups. Interestingly, in comparison to cells cultured in osteogenic media, 50nmMol of pulsatile PTH lead to statistically significant higher ALP and Alizarin Red measurements up to day 10 and 14 respectively in WT cells, and days 10 and 21 in OVX cells. The proliferation rate normalised against DNA was similar for both OVX and WT rats at all-time points. PTH administration did not effect cell proliferation in any group. WT MSCs not only had improved osteogenic differentiation, but also showed increased migration to SDF-1 in comparison to OVX groups. Pulsatile PTH led to further increases in migration of both OVX and WT cells.

Intermittent PTH increases the osteogenic diffrentiation and migration of MSCs from both young and ovarectomised rats, though importantly this effect is not dose dependent. Ultimately, the role of PTH 1–34 on MSCs may lead to improved bone formation and cell homing capacity-particularly in the context of osteoporosis.

Osteoporosis is characterised by an uncoupling of bone formation and resorption resulting in a net reduction in bone density. Stem cells derived from bone marrow in osteoporotic patients typically contain more adipocytes,. Intermittent Parathyroid hormone (iPTH), has been shown to cause the preferential differentiation of mesenchymal stem cells (MSCs) to osteoblasts. We isolated rat bone marrow derived MSCs, investigating the effect of iPTH on adipocyte differentiation.

MSCs were harvested from the femora of 6–10week oldWT rats and cultured to induce adipogenesis for 21 days. Subsequently, cells were continually cultured in adipogenic media, osteogenic media or in osteogenic media supplemented with PTH 1–34 either continuously or intermittently for 6hours in every 72hour cycle. ALP and Alizarin Red assessed osteogenic differentiation, and Oil Red O used to assess intracellular microdroplet formation. A student t-test was used to analyse results, and a p value<0.05 considered significant.

Quantitatively measurements of Alizarin Red staining significantly increased in all adipocytes grown in osteogenic media compared to the cells continually cultured in adipogenic media. Calcium phosphate deposition continued to increase significantly in these groups up to day 14. At day 14, Alizarin Red staining from cells cultured in iPTH were significantly higher than osteogenic media alone. ALP expression was significantly higher for cells cultured in osteogenic media and iPTH compared to adipogenic media at days 3–14. Expression peaked at day 7, at this timepoint cells cultured in iPTH expressed significantly more ALP than other groups. Oil Red O measurements were significantly reduced from days 7–14 for all osteogenic groups, this significance was greatest for the iPTH group at day 7.

iPTH increased the transdifferentiation of adipocytes derived from MSCs into osteoblasts, this effect was most significant after 7 days. Ultimately, the role of iPTH on adipocytes may lead to improved bone formation with many orthopaedic applications.

The current treatment for osteoporosis such as bisphosphonates inhibits the catabolic activity of osteoclasts and subsequent bone resorption, but does not increase bone formation. There is therefore interest in using anabolic factors such as stem cells to augment fracture repair. The poor bone formation in postmenopausal women could be due to poor retention and function of Mesenchymal stem cells (MSCs) resulting into delayed unions. Another factor associated with fracture healing is the retention and migration of stem cells to the site of injury (1–3). The aim of this study was to isolate stem cells from osteopenic rats and investigate and compare the CD marker expression, proliferation, migration, osteogenic and adipogenic differentiation. The hypothesis of this study is that the migration of MSCs from young, adult and ovariectomised (OVX) rats will have different proliferation, differentiation and migratory abilities.

Ovariectomy was performed in 6–9 month old Wistar rats and osteopenia developed over a 4 month post-op period. MSCs were harvested from the femora of young, adult and osteopenic Wistar rats. Proliferation of the these MSCs from the three group of rats was measured using Alamar blue, osteogenic differentiation was measured using ALP expression at day 0, 7, 14 and 21 and alizarin red at day 21. Adipogenic differentiation was measured at day 7, 14 and 21 using Oil red O. Cells were incubated in Boyden chambers to quantify their migration towards SDF1. For analysis, the number of cells migrating across the membrane was expressed as a percentage of the cells remaining on the upper membrane surface. Data was analysed using a Student t-test where p values < 0.05 were considered significant.

The stem cells from all 3 groups of rats expressed on average the same amount of CD29 (>90%), CD90 (>96%), CD34 (<5%) and CD45 (approx 10%). The proliferation rate measured by Alamar blue normalised against DNA was also similar at day 3, 7, 10 and 14. However, interestingly the migration and differentiation ability was significantly different between the MSCs from the 3 groups of rats. The young MSCs were not only better at differentiating into bone and fat as well, but they also migrated significantly more towards SDF1. The migration of SDF-1 doubled with young rats compared to the adult rats (p = 0.023) and it was four times higher when compared to cells isolated from OVX rats (p = 0.013).

MSCs from OVX rats are similar to MSCs from young rats. However when induced to turn into bone, fat and migrate towards SDF1, young MSCs are significantly more responsive than MSCs from OVX and adult control rats. The poor homing ability and differentiation of the stem cells and their retention may result in a reduction in bone formation leading to delayed union in fractures of osteoporotic patients(4).

Intermittently administered parathyroid hormone (PTH 1-34) has been shown to promote bone formation in both human and animal studies. The hormone and its analogues stimulate both bone formation and resorption, and as such at low doses are now in clinical use for the treatment of severe osteoporosis. By varying the duration of exposure, parathyroid hormone can modulate genes leading to increased bone formation within a so-called ‘anabolic window’. The osteogenic mechanisms involved are multiple, affecting the stimulation of osteoprogenitor cells, osteoblasts, osteocytes and the stem cell niche, and ultimately leading to increased osteoblast activation, reduced osteoblast apoptosis, upregulation of Wnt/β-catenin signalling, increased stem cell mobilisation, and mediation of the RANKL/OPG pathway. Ongoing investigation into their effect on bone formation through ‘coupled’ and ‘uncoupled’ mechanisms further underlines the impact of intermittent PTH on both cortical and cancellous bone. Given the principally catabolic actions of continuous PTH, this article reviews the skeletal actions of intermittent PTH 1-34 and the mechanisms underlying its effect.

Cite this article: L. Osagie-Clouard, A. Sanghani, M. Coathup, T. Briggs, M. Bostrom, G. Blunn. Parathyroid hormone 1-34 and skeletal anabolic action: The use of parathyroid hormone in bone formation. Bone Joint Res 2017;6:14–21. DOI: 10.1302/2046-3758.61.BJR-2016-0085.R1.

Osteoporosis is characterised by an uncoupling of bone formation and resorption resulting in net resorption. Stem cells derived from bone marrow in osteoporotic patients typically contain more adipocytes. Intermittent Parathyroid hormone (iPTH), has been shown to cause the preferential differentiation of mesenchymal stem cells (MSCs) to osteoblasts. We isolated rat bone marrow derived MSCs, investigating the effect of iPTH on adipocyte differentiation.

MSCs were harvested from the femora of 6–10week oldWT rats and cultured to induce adipogenesis for 21 days. Subsequently, cells were continually cultured in adipogenic media, osteogenic media or in osteogenic media supplemented with PTH 1–34 either continuously or intermittently for 6hours in every 72hour cycle. ALP and Alizarin Red assessed osteogenic differentiation, and Oil Red O used to assess intracellular microdroplet formation. A student t-test was used to analyse results, and a p value<0.05 considered significant.

Quantitatively measurements of Alizarin Red staining significantly increased in all adipocytes grown in osteogenic media compared to the cells continually cultured in adipogenic media. Calcium phosphate deposition continued to increase significantly in these groups up to day 14. At day 14, Alizarin Red staining from cells cultured in iPTH were significantly higher than osteogenic media alone.

ALP expression was significantly higher for cells cultured in osteogenic media and iPTH compared to adipogenic media at days 3–14. Expression peaked at day 7, at this timepoint cells cultured in iPTH expressed significantly more ALP than other groups (Figure 2). Oil Red O measurements were significantly reduced from days 7–14 for all osteogenic groups, this significance was greatest for the iPTH group at day 7.

iPTH increased the transdifferentiation of adipocytes derived from MSCs into osteoblasts, this effect was most significant after 7 days. Ultimately, the role of iPTH on adipocytes may lead to improved bone formation with many orthopaedic applications.

Intermittent parathyroid hormone (iPTH 1–34) increases bone formation via modelling and remodelling mechanisms and as such is used to treat osteoporosis. The actions of iPTH on mesenchymal stem cell (MSCs) may underpin a further treatment option.

We isolated bone marrow derived MSCs from young (WT) and ovarectomized senile (OVX) rats, investigating the effect of intermittent and continuous PTH administration on migration to SDF-1, proliferation and osteogenic differentiation.

MSCs were harvested from the femora of 6–10week old WT rats and 10–13month old OVX rats. Cells were cultured with 25,50 and 100nmMol of PTH 1–34 added to osteogenic media either continuously or intermittently for 6hours in every 72hour cycle. ALP and Alizarin Red assessed osteogenic differentiation, and Alamar Blue- proliferation. Cells were seeded in a Boyden chamber to quantify SDF-1 migration. A student t-test was used to analyse results, and a p value<0.05 considered significant.

ALP and Alizarin Red were significantly increased for WT and OVX groups at 50nmMol of iPTH. Continuous administration at all concentrations reduced calcium phosphate deposition by day 21 in all groups.

In comparison to cells cultured in osteogenic media, 50nmMol of iPTH led to significantly higher ALP and Alizarin Red measurements up to days 10 and 7 respectively (figure 1). There was no change in proliferation between the groups, and PTH had no effect (figure 2.)

WT MSCs not only had improved osteogenic differentiation, but also showed increased migration to SDF-1 in comparison to OVX groups. iPTH led to further increases in migration of both OVX and WT cells.

iPTH increases the osteogenic differentiation and migration of MSCs from both young and ovarectomised rats, though this effect is not dose dependent. Ultimately, the role of iPTH on MSCs may lead to improved bone formation and cell homing capacity-particularly in the context of osteoporosis.