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

Role of epidural fat in the local milieu: what we know and what we don't

PURPOSE

Traditionally, the epidural fat (EF) is known as a physical buffer for the dural sac against the force and a lubricant facilitating the relative motion of the latter on the osseous spine. Along with the development of the studies on EF, controversies still exist on vital questions, such as the underlying mechanism of the spinal epidural lipomatosis. Meanwhile, the scattered and fragmented researches hinder the global insight into the seemingly dispensable tissue.

METHODS

Herein, we reviewed literature on the EF and its derivatives to elucidate the dynamic change and complex function of EF in the local milieu, especially at the pathophysiological conditions. We start with an introduction to EF and the current pathogenic landscape, emphasizing the interlink between the EF and adjacent structures. We generally categorize the major pathological changes of the EF into hypertrophy, atrophy, and inflammation.

RESULTS AND CONCLUSIONS

It is acknowledged that not only the EF (or its cellular components) may be influenced by various endogenic/exogenic and focal/systematic stimuli, but the adjacent structures can also in turn be affected by the EF, which may be a hidden pathogenic clue for specific spinal disease. Meanwhile, the unrevealed sections, which are also the directions the future research, are proposed according to the objective result and rational inference. Further effort should be taken to reveal the underlying mechanism and develop novel therapeutic pathways for the relevant diseases.

The Mysterious Role of Epidural Fat Tissue in Spine Surgery: A Comprehensive Descriptive Literature Review

BACKGROUND

Though both neurosurgeons and orthopedic spinal surgeons are keenly aware of the clinical importance of epidural fat (EF), surgical practice varies amongst individual surgeons and across both fields. Thus, an in-depth understanding of the anatomical structure and composition of EF is vital, as it will play a significant role in the therapeutic management and the surgical choice of treatment.

OBJECTIVE

We aim to extensively review the anatomical and biological properties of EF and further outline the surgical importance of EF management.

STUDY METHODOLOGY

(i) MEDLINE search 1966-July 2019. Keywords: Review of the Literature. Authorship, Meta-analysis, Descriptive/Narrative overview; (ii) CINAHL search from 1982 to May 2019. Keywords: Review of the Literature spinal epidural fat; Authorship; Meta-analysis; Descriptive/Narrative overview; (iii) Hand searches of the references of retrieved literature; (iv) Personal and college libraries were searched for texts on research methods and literature reviews; and (v) 200 articles were downloaded, 50 were excluded because of similarity of topics and also because of new update on the same topics. (vi) Discussions with experts in the field of reviews of the literature.

DISCUSSION

Though excessive or reductive amounts of EF usually exacerbates neurological symptoms and lead to various pathologic conditions such as spinal epidural lipomatosis, but there is no basic science, experimental, or clinical research that proves the role of EF in the aforementioned pathologic situations.

CONCLUSION

Anatomical illustration, biological function and properties of EF knowledge may lead to changes in the stages of the surgical approach to avoid postoperative complications. However, the role of EF is exclusively bound to a scientific hypothesis as one cannot be sure if an excessive or reductive amount in EF is entirely responsible for the pathologic findings, or just only an incidental finding.

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.

Fibrotic and inflammatory characteristics of epidural fat adjacent to the ossification area in patients with ossification of the ligament flavum

Objectives

To observe histological and inflammatory characteristics of epidural fat (EF) adjacent to the ossification area in patients with ossification of the thoracic ligament flavum (TOLF) and provide a preliminary research basis for investigating the impact of the EF on OLF.

Methods

Samples of EF and autologous subcutaneous adipose tissue (SCAT) from TOLF patients (n = 26) and non-TOLF patients (n = 23) were harvested during posterior thoracic spine surgery. Adipocyte size and fibrosis were measured by histology. Vascularization and inflammatory cell infiltration were evaluated by immunohistochemical staining. Adipogenesis-related genes were assessed by real-time quantitative PCR. Conditioned media from cultured EF were evaluated via enzyme-linked immunosorbent assay to detect the secretion of inflammatory cytokines, including interleukin-6 (IL-6), tumor necrosis factor (TNF-α), and leptin. The phosphorylated STAT3 protein level in ligament flavum (LF) was examined using Western blot.

Results

Adipocytes size in EF was similar between in the TOLF and non-TOLF groups, but significantly smaller than that from autologous SCAT. Adipogenesis-related mRNA expression in EF was lower than that in SCAT. More fibrosis and vascularization were found in TOLF than in non-TOLF. EF in the TOLF group exhibited more macrophages and B lymphocytes infiltrated. The levels of cytokines such as IL-6, TNF-α, and leptin secreted by EF were significantly higher in the TOLF group than non-TOLF. The level of phosphorylated STAT3 in LF was significantly upregulated in the TOLF group.

Conclusions

Morphologically, EF adjacent to the ossification area is smaller and more uniform than autologous SCAT, exhibiting a characteristic similarity to visceral fat. EF in the TOLF group shows a more fibrotic, vascularized, and inflammatory phenotype, which secretes multiple cytokines. The phosphorylated STAT3 protein was significantly upregulated in the TOLF group. Whether these properties of EF directly affect the process of OLF needs to be further explored.

Synovial fluid mesenchymal progenitor cells from patients with juvenile idiopathic arthritis demonstrate limited self-renewal and chondrogenesis

Juvenile idiopathic arthritis (JIA) is a heterogeneous group of inflammatory diseases affecting joints with a prevalence of one in a thousand children. There is a growing body of literature examining the use of mesenchymal stem/progenitor cells (MPCs) for the treatment of adult and childhood arthritis, however, we still lack a clear understanding of how these MPC populations are impacted by arthritic disease states and how this could influence treatment efficacy. In the current study we examined the immunophenotyping, self-renewal ability and chondrogenic capacity (in vitro and in vivo) of synovial derived MPCs from normal, JIA and RA joints. Synovial MPCs from JIA patients demonstrated reduced self-renewal ability and chondrogenic differentiation capacity. Furthermore, they did not induce cartilage regeneration when xenotransplanted in a mouse cartilage injury model. Synovial MPCs from JIA patients are functionally compromised compared to MPCs from normal and/or RA joints. The molecular mechanisms behind this loss of function remain elusive. Further study is required to see if these cells can be re-functionalized and used in cell therapy strategies for these JIA patients, or if allogenic approaches should be considered.

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.

Isolation and Characterization of Extracellular Vesicle from Mesenchymal Stem Cells of the Epidural Fat of the Spine

Study Design

An experimental study with extracellular vesicles (EVs) from mesenchymal stem cell (MSC) of the epidural fat (EF) of the spine.

Purpose

This study aims to isolate the exosomes from epidural fat-derived mesenchymal stem cells (EF-MSCs) and fully characterize the EF-MSC-EVs.

Overview of Literature

EF-MSCs were reported in 2019, and a few studies have shown the positive outcomes of using EF-MSCs to treat specific spine pathologies. However, MSCs have significant limitations for conducting basic studies or developing therapeutic agents. Although EVs are an emerging research topic, no studies have focused on EVs, especially exosomes, from EF and EF-MSCs.

Methods

In this study, we isolated the exosomes using the tangential flow filtration (TFF) system with exosome-depleted fetal bovine serum and performed the characterization tests via western blotting, reverse transcription–polymerase chain reaction, nanoparticle tracking analysis (NTA), and transmission electron microscopy.

Results

In transmission electron microscopy, the exosome had a diameter of approximately 100–200 nm and had a spherical shape, whereas in the NTA, the exosome had an average diameter of 142.8 nm with a concentration of 1.27×10¹⁰ particles/mL. The flow cytometry analysis showed the expression of CD63 and CD81. The western blotting analysis showed the positive markers.

Conclusions

These findings showed that isolating the exosomes via TFF resulted in high-quality EF-MSC exosome yield. Further studies with exosomes from EF-MSC are needed to evaluate the function and role of the EF tissue.

Comparisons of Extracellular Vesicles from Human Epidural Fat-Derived Mesenchymal Stem Cells and Fibroblast Cells

Extracellular vesicles (EVs) are generated and secreted by cells into the circulatory system. Stem cell-derived EVs have a therapeutic effect similar to that of stem cells and are considered an alternative method for cell therapy. Accordingly, research on the characteristics of EVs is emerging. EVs were isolated from human epidural fat-derived mesenchymal stem cells (MSCs) and human fibroblast culture media by ultracentrifugation. The characterization of EVs involved the typical evaluation of cluster of differentiation (CD antigens) marker expression by fluorescence-activated cell sorting, size analysis with dynamic laser scattering, and morphology analysis with transmission electron microscopy. Lastly, the secreted levels of cytokines and chemokines in EVs were determined by a cytokine assay. The isolated EVs had a typical size of approximately 30–200 nm, and the surface proteins CD9 and CD81 were expressed on human epidural fat MSCs and human fibroblast cells. The secreted levels of cytokines and chemokines were compared between human epidural fat MSC-derived EVs and human fibroblast-derived EVs. Human epidural fat MSC-derived EVs showed anti-inflammatory effects and promoted macrophage polarization. In this study, we demonstrated for the first time that human epidural fat MSC-derived EVs exhibit inflammatory suppressive potency relative to human fibroblast-derived EVs, which may be useful for the treatment of inflammation-related diseases.

Epidural fat mesenchymal stem cells: Important microenvironmental regulators in health, disease, and regeneration: Do EF-MSCs play a role in dural homeostasis/maintenance?

Mesenchymal stem cells (MSCs) are present in fat tissues throughout the body, yet little is known regarding their biological role within epidural fat. We hypothesize that debridement of epidural fat and/or subsequent loss of MSCs within this tissue, disrupts homeostasis in the vertebral environment resulting in increased inflammation, fibrosis, and decreased neovascularization leading to poorer functional outcomes post-injury/operatively. Clinically, epidural fat is commonly considered a space-filling tissue with limited functionality and therefore typically discarded during surgery. However, the presence of MSCs within epidural fat suggests that itis more biologically active than historically believed and may contribute to the regulation of homeostasis and regeneration in the dural environment. While the current literature supports our hypothesis, it will require additional experimentation to determine if epidural fat is an endogenous driver of repair and regeneration and if so, this tissue should be minimally perturbed from its original location in the spinal canal. Also see the video abstract here https://youtu.be/MIol_IWK1os.

Differentiation Potential and Tumorigenic Risk of Rat Bone Marrow Stem Cells Are Affected By Long-Term In Vitro Expansion

Objective:

Mesenchymal stem cells (MSCs) have the capacity for extensive expansion and adipogenic, osteogenic, chondrogenic, myogenic, and neural differentiation in vitro. The aim of our study was to determine stemness, differentiation potential, telomerase activity, and ultrastructural characteristics of long-term cultured rat bone marrow (rBM)-MSCs.

Materials and Methods:

rBM-MSCs from passages 3, 50, and 100 (P3, P50, and P100) were evaluated through immunocytochemistry, reverse transcription-polymerase chain reaction, telomerase activity assays, and electron microscopy.

Results:

A dramatic reduction in the levels of myogenic markers actin and myogenin was detected in P100. Osteogenic markers Coll1, osteonectin (Sparc), and osteocalcin as well as neural marker c-Fos and chondrogenic marker Coll2 were significantly reduced in P100 compared to P3 and P50. Osteogenic marker bone morphogenic protein-2 (BMP2) and adipogenic marker peroxisome proliferator-activated receptor gamma (Pparγ) expression was reduced in late passages. The expression of stemness factor Rex-1 was lower in P100, whereas Oct4 expression was decreased in P50 compared to P3 and P100. Increased telomerase activity was observed in long-term cultured cells, signifying tumorigenic risk. Electron microscopic evaluations revealed ultrastructural changes such as smaller number of organelles and increased amount of autophagic vacuoles in the cytoplasm in long-term cultured rBM-MSCs.

Conclusion:

This study suggests that long-term culture of rBM-MSCs leads to changes in differentiation potential and increased tumorigenic risk.