Prx1+ MPCs Accumulate in the Dura Mater of Wild-Type and p21-/- Mice Followed by a Specific Reduction in p21-/- Dural MPCs.

Epidural fat contains a population of mesenchymal progenitor cells (MPCs), and this study explores the behavior of these cells on the adjacent dura mater during growth and in response to injury in a p21 knockout mouse model. p21-/- mice are known to have increased cell proliferation and enhanced tissue regeneration post-injury. Therefore, it is hypothesized that the process by which epidural fat MPCs maintain the dura mater can be accelerated in p21-/- mice. Using a Prx1 lineage tracing mouse model, the epidural fat MPCs are found to increase in the dura mater over time in both C57BL/6 (p21+/+ ) and p21-/- mice; however, by 3 weeks post-tamoxifen induction, few MPCs are observed in p21-/- mice. These endogenous MPCs also localize to dural injuries in both mouse strains, with MPCs in p21-/- mice demonstrating increased proliferation. When epidural fat MPCs derived from p21-/- mice are transplanted into dural injuries in C57BL/6 mice, these MPCs are found in the injury site. It is demonstrated that epidural fat MPCs play a role in dural tissue maintenance and are able to directly contribute to dural injury repair. This suggests that these MPCs have the potential to treat injuries and/or pathologies in tissues surrounding the spinal cord.

Proteoglycan 4 is present within the dura mater and produced by mesenchymal progenitor cells.

Mesenchymal progenitor cells (MPCs) have been recently identified in human and murine epidural fat and have been hypothesized to contribute to the maintenance/repair/regeneration of the dura mater. MPCs can secrete proteoglycan 4 (PRG4/lubricin), and this protein can regulate tissue homeostasis through bio-lubrication and immunomodulatory functions. MPC lineage tracing reporter mice (Hic1) and human epidural fat MPCs were used to determine if PRG4 is expressed by these cells in vivo. PRG4 expression co-localized with Hic1+ MPCs in the dura throughout skeletal maturity and was localized adjacent to sites of dural injury. When Hic1+ MPCs were ablated, PRG4 expression was retained in the dura, yet when Prx1+ MPCs were ablated, PRG4 expression was completely lost. A number of cellular processes were impacted in human epidural fat MPCs treated with rhPRG4, and human MPCs contributed to the formation of epidural fat, and dura tissues were xenotransplanted into mouse dural injuries. We have shown that human and mouse MPCs in the epidural/dura microenvironment produce PRG4 and can contribute to dura homeostasis/repair/regeneration. Overall, these results suggest that these MPCs have biological significance within the dural microenvironment and that the role of PRG4 needs to be further elucidated.

Sources, Identification, and Clinical Implications of Heterogeneity in Human Umbilical Cord Stem Cells.

Heterogeneity among different subpopulations of human umbilical cord mesenchymal stem cell (hUCMSCs) lines is an ubiquitous phenomenon, with such variability being related to several factors including the identity of the individual donor, tissue source (Wharton's jelly vs. umbilical cord blood), culture conditions, as well as random variations in the cloning expansion process. In this chapter, we provide a general overview on the sources as well as available experimental techniques for proper identification of heterogeneity in hUCMSCs. Finally, we provide a brief discussion on the current scientific evidence regarding the potential superiority of subpopulations of hUCMSCs for specific clinical applications. Taking into account the exponential growth on the available experimental data on hUCMSCs in the past few years, this chapter is not intended to be comprehensive in nature, but rather is intended to provide a general overview about the central role which the topic of heterogeneity has in both basic science and clinical research in umbilical cord stem cells.

Isolation and Characterization of an Adult Stem Cell Population from Human Epidural Fat.

STUDY DESIGN: Isolation and characterization of human epidural fat (HEF) stem/progenitor cells. OBJECTIVE: To identify a progenitor population within HEF and to determine if they meet the minimal criteria of a mesenchymal stem cell (MSC). SUMMARY OF BACKGROUND DATA: The biological function, if any, has yet to be determined for HEF. The presence of MSCs within HEF may indicate a regenerative potential within the HEF. METHODS: HEF was isolated from 10 patients during elective spinal surgery. HEF cells were differentiated along osteo-, adipo-, and chondrogenic lineages, with differentiation analyzed via qPCR and histology. The cell surface receptor profile of HEF cells was examined by flow cytometry. HEF cells were also assayed through the collagen contraction assay. Prx1 CreERT2GFP:R26R TdTomato MSC lineage-tracking mice were employed to identify EF MSCs in vivo. RESULTS: HEF cell lines were obtained from all 10 patients in the study. Cells from 2/10 patients demonstrated full MSC potential, while cells from 6/10 patients demonstrated progenitor potential; 2/10 patients presented with cells that retained only adipogenic potential. HEF cells demonstrated MSC surface marker expression. All patient cell lines contracted collagen gels. A Prx1-positive population in mouse epidural fat that appeared to contribute to the dura of the spinal cord was observed in vivo. CONCLUSIONS: MSC and progenitor populations are present within HEF. MSCs were not identified in all patients examined in the current study. Furthermore, all patient lines demonstrated collagen contraction capacity, suggesting either a contaminating activated fibroblast population or HEF MSCs/progenitors also demonstrating a fibroblast-like phenotype. In vivo analysis suggests that these cell populations may contribute to the dura. Overall, these results suggest that cells within epidural fat may play a biological role within the local environment above providing a mechanical buffer.

Anterior Versus Posterior Thoracic Discectomy: A Systematic Review.

STUDY DESIGN: Systematic literature review. OBJECTIVE: The aim of this study was to systematically review the current evidence in the literature on thoracic discectomies, to compare the clinical outcomes, and to determine whether there is evidence to support the use of either the anterior or posterior approach. SUMMARY OF BACKGROUND DATA: Thoracic disc herniations (TDHs) often present with myelopathy, radiculopathy, or a combination of both. The posterior approach for thoracic discectomy has been associated with a lower complication rate, but no systematic review exists comparing the clinical outcomes. METHODS: MEDLINE, EMBASE, and The Cochrane Library databases were searched in accordance with the PRISMA guidelines for studies performing an anterior or posterior thoracic discectomy. The methodological quality was assessed using the Methodological Index for Non-Randomized Studies checklist. The reported clinical outcomes were evaluated using risk ratio, with a P < 0.05 being considered statistically significant. RESULTS: Thirty-seven clinical studies with 1156 patients with 1300 TDHs were included in this review. There was no statistically significant difference in the total neurological improvement or neurological worsening using either an anterior approach or a posterior approach (P = 0.02812 and P = 0.5232, respectively). However, there was a statistically significant higher rate of total complications in the anterior approach (P = 0.0024). CONCLUSION: The anterior approach and posterior approach have been shown to be very similar in terms of neurological outcomes. Although the posterior approach was shown to have a lower rate of total complications, this was largely because of a decrease in minor respiratory complications seen in the anterior approach. The optimal approach may therefore be based on surgeon preference as well as patient factors, specifically cardiorespiratory with American Society of Anaesthesiologists grading. LEVEL OF EVIDENCE: 4.

Novel microhydroxyapatite particles in a collagen scaffold: a bioactive bone void filler?

BACKGROUND: Treatment of segmental bone loss remains a major challenge in orthopaedic surgery. Traditional techniques (eg, autograft) and newer techniques (eg, recombinant human bone morphogenetic protein-2 [rhBMP-2]) have well-established performance limitations and safety concerns respectively. Consequently there is an unmet need for osteoinductive bone graft substitutes that may eliminate or reduce the use of rhBMP-2. QUESTIONS/PURPOSES: Using an established rabbit radius osteotomy defect model with positive (autogenous bone graft) and negative (empty sham) control groups, we asked: (1) whether a collagen-glycosaminoglycan scaffold alone can heal the defect, (2) whether the addition of hydroxyapatite particles to the collagen scaffold promote faster healing, and (3) whether the collagen-glycosaminoglycan and collagen-hydroxyapatite scaffolds are able to promote faster healing (by carrying a low dose rhBMP-2). METHODS: A 15-mm transosseous radius defect in 4-month-old skeletally mature New Zealand White rabbits were treated with either collagen-hydroxyapatite or collagen-glycosaminoglycan scaffolds with and without rhBMP-2. Autogenous bone graft served as a positive control. Time-series radiographs at four intervals and postmortem micro-CT and histological analysis at 16 weeks were performed. Qualitative histological analysis of postmortem explants, and qualitative and volumetric 3-D analysis of standard radiographs and micro-CT scans enabled direct comparison of healing between test groups. RESULTS: Six weeks after implantation the collagen-glycosaminoglycan group had callus occupying greater than ½ the defect, whereas the sham (empty) control defect was still empty and the autogenous bone graft defect was completely filled with unremodeled bone. At 6 weeks, the collagen-hydroxyapatite scaffold groups showed greater defect filling with dense callus compared with the collagen-glycosaminoglycan controls. At 16 weeks, the autogenous bone graft groups showed evidence of early-stage medullary canal formation beginning at the proximal and distal defect borders. The collagen-glycosaminoglycan and collagen-glycosaminoglycan-rhBMP-2 groups had nearly complete medullary canal formation and anatomic healing at 16 weeks. However, collagen-hydroxyapatite-rhBMP-2 scaffolds showed the best levels of healing, exhibiting a dense callus which completely filled the defect. CONCLUSIONS: The collagen-hydroxyapatite scaffold showed comparable healing to the current gold standard of autogenous bone graft. It also performed comparably to collagen-glycosaminoglycan-rhBMP-2, a representative commercial device in current clinical use, but without the cost and safety concerns. CLINICAL RELEVANCE: The collagen-glycosaminoglycan scaffold may be suitable for a low load-bearing defect. The collagen-hydroxyapatite scaffold may be suitable for a load-bearing defect. The rhBMP-2 containing collagen-glycosaminoglycan and collagen-hydroxyapatite scaffolds may be suitable for established nonunion defects.

Innovative collagen nano-hydroxyapatite scaffolds offer a highly efficient non-viral gene delivery platform for stem cell-mediated bone formation.

The ability of nano-hydroxyapatite (nHA) particles developed in-house to act as non-viral delivery vectors is assessed. These nHA particles are combined with collagen to yield bioactive, biodegradable collagen nano-hydroxyapatite (coll-nHA) scaffolds. Their ability to act as gene-activated matrices for BMP2 delivery is demonstrated with successful transfection of mesenchymal stem cells (MSCs) resulting in high calcium production.

The healing of bony defects by cell-free collagen-based scaffolds compared to stem cell-seeded tissue engineered constructs.

One of the key challenges in tissue engineering is to understand the host response to scaffolds and engineered constructs. We present a study in which two collagen-based scaffolds developed for bone repair: a collagen-glycosaminoglycan (CG) and biomimetic collagen-calcium phosphate (CCP) scaffold, are evaluated in rat cranial defects, both cell-free and when cultured with MSCs prior to implantation. The results demonstrate that both cell-free scaffolds showed excellent healing relative to the empty defect controls and somewhat surprisingly, to the tissue engineered (MSC-seeded) constructs. Immunological analysis of the healing response showed higher M1 macrophage activity in the cell-seeded scaffolds. However, when the M2 macrophage response was analysed, both groups (MSC-seeded and non-seeded scaffolds) showed significant activity of these cells which are associated with an immunomodulatory and tissue remodelling response. Interestingly, the location of this response was confined to the construct periphery, where a capsule had formed, in the MSC-seeded groups as opposed to areas of new bone formation in the non-seeded groups. This suggests that matrix deposited by MSCs during in vitro culture may adversely affect healing by acting as a barrier to macrophage-led remodelling when implanted in vivo. This study thus improves our understanding of host response in bone tissue engineering.