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Introduction: Therapeutic interventions for intervertebral disc herniation remain scarce due to the inability of endogenous annulus fibrosus (AF) cells to respond to injury and drive tissue regeneration. Unlike other orthopedic tissues, such as cartilage, delivery of exogenous cells to the site of annular injury remains underdeveloped, largely due to a lack of an ideal cell source and the invasive nature of cell isolation. Human induced pluripotent stem cells (iPSCs) can be differentiated to specific cell fates using biochemical factors and are, therefore, an invaluable tool for cell therapy approaches. While differentiation protocols have been developed for cartilage and fibrous connective tissues (e.g., tendon), the signals that regulate the induction and differentiation of human iPSCs toward the AF fate remain unknown. Methods: iPSC‐derived sclerotome cells were treated with various combinations of developmental signals including transforming growth factor beta 3 (TGF‐β3), connective tissue growth factor (CTGF), platelet derived growth factor BB (PDGF‐BB), insulin‐like growth factor 1 (IGF‐1), or the Hedgehog pathway activator, Purmorphamine, and gene expression changes in major AF‐associated ECM genes were assessed. The top performing combination treatments were further validated by using three distinct iPSC lines and by assessing the production of upregulated ECM proteins of interest. To conduct a broader analysis of the transcriptomic shifts elicited by each factor combination, and to compare genetic profiles of treated cells to mature human AF cells, a 96.96 Fluidigm gene expression array was applied, and principal component analysis was employed to identify the transcriptional signatures of each cell population and treatment group in comparison to native AF cells. Results: TGF‐β3, in combination with PDGF‐BB, CTGF, or IGF‐1, induced an upregulation of key AF ECM genes in iPSC‐derived sclerotome cells. In particular, treatment with a combination of TGF‐β3 with PDGF‐BB for 14 days significantly increased gene expression of collagen II and aggrecan and increased protein deposition of collagen I and elastin compared to other treatment groups. Assessment of genes uniquely highly expressed by AF cells or SCL cells, respectively, revealed a shift toward the genetic profile of AF cells with the addition of TGF‐β3 and PDGF‐BB for 14 days. Discussion: These findings represent an initial approach to guide human induced pluripotent stem cells toward an AF‐like fate for cellular delivery strategies. [ABSTRACT FROM AUTHOR]

Intervertebral disc (IVD) degeneration and associated back pain place a significant burden on the population. IVD degeneration is a progressive cascade of cellular, compositional, and structural changes, which results in a loss of disc height, disorganization of extracellular matrix architecture, tears in the annulus fibrosus which may involve herniation of the nucleus pulposus, and remodeling of the bony and cartilaginous endplates (CEP). These changes to the IVD often occur concomitantly, across the entire motion segment from the disc subcomponents to the CEP and vertebral bone, making it difficult to determine the causal initiating factor of degeneration. Furthermore, assessments of the subcomponents of the IVD have been largely qualitative, with most studies focusing on a single attribute, rather than multiple adjacent IVD substructures. The objective of this study was to perform a multiscale and multimodal analysis of human lumbar motion segments across various length scales and degrees of degeneration. We performed multiple assays on every sample and identified several correlations between structural and functional measurements of disc subcomponents. Our results demonstrate that with increasing Pfirrmann grade there is a reduction in disc height and nucleus pulposus T2 relaxation time, in addition to alterations in motion segment macromechanical function, disc matrix composition and cellular morphology. At the cartilage endplate‐vertebral bone interface, substantial remodeling was observed coinciding with alterations in micromechanical properties. Finally, we report significant relationships between vertebral bone and nucleus pulposus metrics, as well as between micromechanical properties of the endplate and whole motion segment biomechanical parameters, indicating the importance of studying IVD degeneration as a whole organ. [ABSTRACT FROM AUTHOR]

ABSTRACT: Hyaluronic acid (HA) is widely injected as a viscosupplement in the treatment of osteoarthritis. Despite its extensive use, it is not currently known if cartilage degradation alters how HA‐based solutions lubricate the articular surface. In this study we utilized a model of cartilage degradation by IL‐1β along with a recently developed framework to study role of cartilage degradation on lubrication by clinically‐approved HA‐based lubricants with high viscosities. Cartilage explants were cultured up to 8 days with 10 ng/ml IL‐1β. After culture, samples were examined histologically, immunohistochemically, biochemically, mechanically, topographically, and tribologically. The tribological testing analyzed both boundary and mixed lubrication modes to assess individual effects of viscosity and boundary lubricating ability. Friction testing was carried out using PBS and two clinically approved HA‐based viscosupplements in a cartilage‐glass configuration. After culture with IL‐1β, boundary mode friction was elevated after both 4 and 8 days. Additionally, friction in mixed mode lubrication, where HA is most effective as a lubricant, was significantly elevated after 8 days of culture. As cartilage became rougher, softer, and more permeable after culture, the boundary mode plateau was extended, and as a result, significantly increased lubricant viscosities or sliding speeds were necessary to achieve effective mixed lubrication. Overall, this study revealed that lubrication of cartilage by HA is degradation‐dependent and coincides with changes in mechanics and roughness. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1456–1464, 2018. [ABSTRACT FROM AUTHOR]