Human annulus progenitor cells: Analyses of this viable endogenous cell population.

Back pain and intervertebral disc degeneration have growing socioeconomic/health care impacts. Increasing research efforts address use of stem and progenitor cell-based replacement therapies to repopulate and regenerate the disc. Data presented here on the innate human annulus progenitor cells: (i) assessed osteogenic, chondrogenic and adipogenic potentials of cultured human annulus cells; and (ii) defined progenitor-cell related gene expression patterns. Verification of the presence of progenitor cells within primary human disc tissue also used immunohistochemical identification of cell surface markers and microarray analyses. Differentiation analysis in cell cultures demonstrated a viable progenitor cell pool within Thompson grades III-IV discs. Osteogenesis was present in 8 out of 11 cultures (73%), chondrogenesis in 8 of 11 (73%), and adipogenesis in 6 of 6 (100%). Immunolocalization was positive for CD29, CD44, CD105, and CD14 (mean values 80.2%, 81.5%, 85.1%, and 88.6%, respectively); localization of CD45 and CD34 was negative in disc tissue. Compared to controls, surgical discs showed significantly downregulated genes with recognized progenitor cell functions: TCF7L2 (2.7 fold), BMI1 (3.8 fold), FGF receptor 2 (2 fold), PAFAH1B1 (2.3 fold), and GSTP1 (9 fold). Compared to healthier grade I/II discs, grade III/IV discs showed significantly upregulated XRCC5 (3.6 fold), TCF7L2 (6 fold), GSTP1 (3.7 fold), and BMI1 (3 fold). Additional significant cell marker analyses showed expression of platelet-derived growth factor receptor alpha, CD90, CD73, and STRO-1. Statement of Clinical Significance: Findings provide the first identification of progenitor cells in annulus specimens from older, more degenerate discs (in contrast to earlier studies of healthier discs or nondegenerative specimens from teenagers). Findings also increase knowledge on progenitor cells present in the disc and suggest their value in potential future utilization for regeneration and disc cell therapy. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1351-1360, 2016.

Human annulus signaling cues for nerve outgrowth: In vitro studies.

The relationship between neurotrophins produced by human annulus cells, such as neurotrophin-4 (NT4) and brain-derived neurotrophic factor (BDNF) which function in neurite survival and outgrowth, and nerve ingrowth into the disc remains poorly understood. In this work, we tested F11 neurite growth during exposure to control media, media with added nerve growth factor (NGF), conditioned media (CM) harvested from previous human annulus culture, or co-culture with annulus cells. Co-culture of F11 cells with annulus cells significantly increased media levels of amphiregulin, BDNF, glial-derived neurotrophic factor, and vascular endothelial growth factor compared to levels from in culture of F11 cells alone (p ≤ 0.04). Cell-based assays of neurite growth revealed that BDNF levels present in CM bore a significant (p = 0.01) positive relationship to neurite length and accounted for 38.5% of the change in neurite length. NT4 levels produced during co-culture with annulus cells bore a significant (p = 0.04) positive relationship to neurite length and accounted for 40.9% of the change in length. Statement of clinical significance: In vitro findings point to a potential role of annulus cells related to nerve ingrowth in vivo, and may have relevance in the outer annulus (where cell numbers are high) or in regions where nerves penetrate into annular tears or fissures. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1456-1465, 2016.