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+CD342CD452) and adventitial cells (CD1462CD34+ CD452), 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. STEM CELLS

Pericytes, mesenchymal stem cells and their contributions to tissue repair

“…This is in line with the literature claiming that the quintessential MSC derives from the perivascular niche (Crisan et al, 2008). Their ability to contribute to osteogenic repair has been validated in four distinct models: rat spinal fusion (Chung et al, 2014), murine muscle pouch, murine femoral segmental defect and rat calvarial defect, the latter two of which will not display self-healing due to their critical size (James et al, 2012b). However, although perivascular cells are capable of differentiation into osteoblasts and osteocytes, the majority of neo-bone is of host origin, suggesting that they contribute to bone formation via the secretion of trophic factors (Chung et al, 2014).…”

“…Moreover, the progenitor cell potential and secretion of pro-repair factors by pericytes means that their recruitment to sites of injury is highly desirable. Previously, sources of MSCs for the regeneration of mesenchymal tissue have included the bone marrow, adipose tissue and the stromal vascular fraction (SVF) of adipose tissue (Chung et al, 2014).…”

“…However, these cell types are fraught with disadvantages; it is necessary to expand bone marrowderived MSCs in culture, and they exhibit limited cellular activity in elderly patients; adipose MSCs are immunogenic, and genetically unstable; and SVF MSCs are notoriously heterogeneous, leading to inefficient and unreliable tissue formation (Chung et al, 2014). Therefore, it is desirable to utilise specific cells with MSC capacity from the perivascular niche which are, in theory, obtainable from any microvascularised tissue.…”

“…Their ability to contribute to osteogenic repair has been validated in four distinct models: rat spinal fusion (Chung et al, 2014), murine muscle pouch, murine femoral segmental defect and rat calvarial defect, the latter two of which will not display self-healing due to their critical size (James et al, 2012b). However, although perivascular cells are capable of differentiation into osteoblasts and osteocytes, the majority of neo-bone is of host origin, suggesting that they contribute to bone formation via the secretion of trophic factors (Chung et al, 2014). Furthermore, greater vascularisation occurs with the use of perivascular cells compared to SVF; they did not differentiate into ECs, but rather resume their natural role as vascular mural cells (Askarinam et al, 2013).…”

Human kidney pericytes produce renin

“…prospectively identified human vascular pericytes from multiple human organs based on the expression of CD146 (Mel-CAM), nerve/glial antigen 2 (NG2), and platelet-derived growth factor receptor-β (PDGFR-β), and demonstrated that pericytes are one of the origins of mesenchymal stem cells (MSCs). Pericytes show regenerative potential in injured skeletal muscle,9, 10 ischemic heart,11, 12 bone,13, 14 adipose tissue, 15 and dental pulp 16 ; therefore, they are regarded as a local reservoir of regenerative cells 17, 18. In tissue fibrosis, pericytes have a pathological role in which they proliferate and differentiate into collagen-I–producing myofibroblasts 19, 20.…”