PDGFB-based stem cell gene therapy increases bone strength in the mouse

Abstract

Substantial advances have been made in the past two decades in the management of osteoporosis. However, none of the current medications can eliminate the risk of fracture and rejuvenate the skeleton. To this end, we recently reported that transplantation of hematopoietic stem/progenitor cells (HSCs) or Sca1 + cells engineered to overexpress FGF2 results in a significant increase in lamellar bone matrix formation at the endosteum; but this increase was attended by the development of secondary hyperparathyroidism and severe osteomalacia. Here we switch the therapeutic gene to PDGFB, another potent mitogen for mesenchymal stem cells (MSCs) but potentially safer than FGF2. We found that modest overexpression of PDGFB using a relatively weak phosphoglycerate kinase (PGK) promoter completely avoided osteomalacia and secondary hyperparathyroidism, and simultaneously increased trabecular bone formation and trabecular connectivity, and decreased cortical porosity. These effects led to a 45% increase in the bone strength. Transplantation of PGK-PDGFB-transduced Sca1 + cells increased MSC proliferation, raising the possibility that PDGF-BB enhances expansion of MSC in the vicinity of the hematopoietic niche where the osteogenic milieu propels the differentiation of MSCs toward an osteogenic destination. Our therapy should have potential clinical applications for patients undergoing HSC transplantation, who are at high risk for osteoporosis and bone fractures after total body irradiation preconditioning. It could eventually have wider application once the therapy can be applied without the preconditioning.PDGFB | hematopoietic stem cells | bone formation | gene therapy

1,25-Dihydroxyvitamin D suppresses M1 macrophages and promotes M2 differentiation at bone injury sites

“…Femurs with fractures and intact femurs were harvested at day 28, fixed in 4% paraformaldehyde, and subjected to μCT analysis using a Scanco vivaCT μCT system with a voxel size of 10.5 μm. Mineralized callus bone was determined as previously described (49). Each sample was contoured around the periosteal circumference to determine the volume of interest (VOI) at a fracture site.…”

Direct interaction of receptor tyrosine kinases, EphA4 and PDGFRβ, plays an important role in the proliferation of neural stem cells

“…35,[46][47][48] Among the abnormalities during the development, resembling defects in dendritic spine density, impairment in hippocampus-dependent memory formation, and long-term potentiation are caused by deletion of either PDGFRβ or EphA4, suggesting neuron development and maturation require the presence of both PDGFRβ and EphA4. 21,49,50 These findings suggest that the PDGFRβ/EphA4 receptor complex mediates a variety of signals.…”

PDGF-BB and IL-4 co-overexpression is a potential strategy to enhance mesenchymal stem cell-based bone regeneration

“…A slight reduction of PDGF-BB expression was also found in the MSCs-IL-4-PDGF group compared to the MSCs-PDGF group in both BALB/c and C57BL/6 MSCs (Fig. 1C, D), but levels in both strains were also in the therapeutically effective range of expression [8].…”

“…Platelet-derived growth factor (PDGF)-BB stimulates MSCs, resulting in enhanced angiogenesis and osteogenesis in a dose-dependent manner [6,7]. Osteogenesis was enhanced by relatively low doses of PDGF-BB in vitro; in vivo studies showed that trabecular bone formation and trabecular connectivity were increased by overexpression by lentiviral vector of PFGF-BB under a relatively week PGK promoter, completely avoiding osteomalacia and secondary hyperparathyroidism seen with higher doses [8].…”

“…We have generated IL-4 secreting MSCs using a lentiviral vector under a relatively strong CMV promotor [5,9]. In the current study, we constructed a lentiviral vector that produced PDGF-BB under a weak (phosphoglycerate kinase; PGK) promoter [8]. MSCs were infected with the PDGF-BBproducing lentiviruses in combination with the IL-4 lentiviral vector [5] to generate IL-4 only overexpressing MSCs, PDGF-BB only overexpressing MSCs, and co-overexpressing IL-4 and PDGF-BB GM MSCs cell populations.…”