Human Perivascular Stem Cell-Based Bone Graft Substitute Induces Rat Spinal Fusion

Abstract

Adipose tissue is an attractive source of mesenchymal stem cells (MSCs) because of its abundance and accessibility. We have previously defined a population of native MSCs termed perivascular stem cells (PSCs), purified from diverse human tissues, including adipose tissue. Human PSCs (hPSCs) are a bipartite cell population composed of pericytes (CD146+CD34-CD45-) and adventitial cells (CD146-CD34+CD45-), isolated by fluorescence-activated cell sorting and with properties identical to those of culture identified MSCs. Our previous studies showed that hPSCs exhibit improved bone formation compared with a sample-matched unpurified population (termed stromal vascular fraction); however, it is not known whether hPSCs would be efficacious in a spinal fusion model. To investigate, we evaluated the osteogenic potential of freshly sorted hPSCs without culture expansion and differentiation in a rat model of posterolateral lumbar spinal fusion. We compared increasing dosages of implanted hPSCs to assess for dose-dependent efficacy. All hPSC treatment groups induced successful spinal fusion, assessed by manual palpation and microcomputed tomography. Computerized biomechanical simulation (finite element analysis) further demonstrated bone fusion with hPSC treatment. Histological analyses showed robust endochondral ossification in hPSC-treated samples. Finally, we confirmed that implanted hPSCs indeed differentiated into osteoblasts and osteocytes; however, the majority of the new bone formation was of host origin. These results suggest that implanted hPSCs positively regulate bone formation via direct and paracrine mechanisms. In summary, hPSCs are a readily available MSC population that effectively forms bone without requirements for culture or predifferentiation. Thus, hPSC-based products show promise for future efforts in clinical bone regeneration and repair.

Brief Report: Human Perivascular Stem Cells and Nel-Like Protein-1 Synergistically Enhance Spinal Fusion in Osteoporotic Rats

“…Among seven groups, High P+N group exhibited significantly increased palpation scores (4.7) with the highest fusion rate at 83.3% compared to the other study groups (p<0.01). Notably, neither the regular dose which was effective for healthy rats [12, 15] nor high dose of hPSCs or NELL-1 alone could produce a significant fusion rate in OVX rats, with only 20–28.6% spinal fusion (Table 1). …”

“…Induction of osteoporosis was confirmed by dual energy X-ray absorptiometry 4 weeks post-OVX. The implants were prepared using 2 different doses of hPSCs and NELL-1 based on our previous studies: (1) Regular dose: 0.25×10 6 cells/ml of hPSCs or 33.3 μg/ml of NELL-1 that demonstrated the successful fusion in non-osteoporotic models [12, 15]; (2) High dose: 0.75×10 6 cells/ml of hPSCs or 66.6 μg/ml of NELL-1. Finally animals were organized into the following 7 implant groups: (1) Regular P: Regular dose of hPSCs alone; (2) Regular N: Regular dose of NELL-1 alone; (3) Regular P+N: Combination of regular dose of hPSCs and NELL-1; (4) High P: High dose of hPSCs alone; (5) High N: High dose of NELL-1 alone; (6) High P+N: Combination of high dose of hPSCs and NELL-1; (7) Control.…”

“…A detailed discussion of each of the implant constituents is presented in Table 1. Spinal fusion surgeries were performed as previously described [12]. Animals were harvested 4 weeks post-surgery.…”

“…MicroCT analyses including bone volume (BV) and bone mineral density (BMD) were performed using CT-Analyzer software (SkyScan 1172, Belgium) as described previously [12]. …”

“…Interestingly, we observed an additive effect of NELL-1 and human perivascular stem cells (hPSCs), a prospectively purified mesenchymal stem cell population with perivascular distribution and pro-osteogenic / pro-angiogenic properties, in an ectopic bone formation model [10, 11]. Additionally, hPSC alone has demonstrated pro-osteogenic effects in non-osteoporotic models including spinal fusion with non-osteoporotic rats [12]. …”