The results showed a possible mechanism of interaction between MSCs and NP cells mediated by secreted factors. The most significant effect on NP cells was enhancement of cellular proliferation when they were cocultured with even a small number of MSCs. To differentiate MSCs into NP-like cells with heightened collagen II expression, MSCs must be in an environment containing numerous NP cells.

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Nucleus pulposus (NP) cells, sourced from herniation surgeries, may be used as a cell-based therapy for intervertebral disc (IVD) degeneration. But, both the regenerative potential of these degenerative adult NP cells and how to stimulate optimum matrix synthesis is not yet clear. The purpose of the current study was to understand the different phenotypic behaviors between degenerative adult NP cells and normal adolescent NP cells. Degenerative adult NP cells produced a significantly higher amount of proteoglycans and collagens than adolescent cells. Insulin-like growth factor-1 was the only anabolic cytokine with increased endogenous expression in degenerative adult NP cells. TGF-b1 treatment of degenerative NP cells promoted matrix synthesis but stimulated too much type I collagen and suppressed type II collagen and aggrecan. Adult degenerative NP cells possess upregulated regenerative potential, but stimulation in addition to TGF-b1 is needed to enhance matrix productivity and optimize the collagen expression profile. The intervertebral disc (IVD) is comprised of the nucleus pulposus (NP) core, the multilaminar anulus fibrosus, and cartilaginous endplates. Degeneration of the IVD and associated spinal disorders are leading causes of morbidity, resulting in substantial pain and increased health costs. 1 Pathophysiologic evidence indicates that IVD degeneration originates from the NP, 2,3 where the proteoglycan content and type II collagen synthesis decrease, while denaturation of type II collagen and synthesis of type I collagen increase. 4 As the NP loses its osmotic properties and becomes fibrotic, the IVD cannot transmit intervertebral forces optimally, and various degenerative processes subsequently occur.Regeneration of the NP tissues in the early stages of degeneration can theoretically retard or even reverse the degenerative process and possibly restore a healthy IVD. The approval of autologous disc chondrocyte transplantation (ADCT) in Germany demonstrated the potential for cell-based therapies of IVD degeneration. 5,6 The most clinically applicable source of cells is the tissues obtained in surgeries to treat lumbar disc herniation and degenerative disc disease. Cells harvested from degenerative IVD tissues are not completely healthy and have an altered phenotype. 7,8 Because the IVD cells are continuously exposed to hypoxia, low pH, low nutrition, and high pressure, 9 age-related changes of the IVD cells may reflect a response to the intradiscal environment. Thus, the IVD tissue and cells undergo continuous adaptive changes during the aging process regardless of any superimposed injury which may stimulate degeneration. 10 The purpose of the current study was to understand the differences of phenotypic behaviors between degenerative NP cells of human adults and NP cells of adolescents. Assessments included cellular proliferation, productivity of extracellular matrix (ECM), endogenous expression of anabolic cytokines, and responsiveness to transforming growth factor (TGF)-b1. Results of this ...

To acquire the capacities for matrix production and preservation of an expanded volume within a damaged intervertebral disc (IVD), cells isolated from human nucleus pulposus (NP) tissues must undergo several passages in monolayer culture. However, chondrocytes and IVD cells in monolayer culture undergo "dedifferentiation," characterized by decreased synthesis of type II collagen and increased synthesis of type I collagen, thereby compromising the properties of regenerative tissues. The present study was undertaken to ascertain whether lovastatin reverses "dedifferentiation" of human NP cells during monolayer expansion. Expression of genes encoding type II collagen and transcription factor SOX9 in these cells was upregulated by lovastatin, with maximal stimulations observed at 5 µM, whereas type I collagen gene expression was suppressed by the drug, with maximal inhibitions observed at 5-10 µM. At lovastatin concentrations ≥1 µM, expression of genes encoding the bone morphogenetic proteins BMP-2 and BMP-7 was also significantly enhanced. Furthermore, the number of NP cells exhibiting a rounded shape and positive staining for S-100 protein and type II collagen protein increased during treatment with lovastatin. These findings strongly support the induction by lovastatin of "redifferentiation" of human NP cells during their expansion in monolayer culture.

Annulus fibrosus (AF) damage is proven to prompt intervertebral disc (IVD) degeneration, and unrepaired AF lesions after surgical discectomy may boost herniation of the nucleus pulposus (NP) which may lead to further compression of neural structures. Moreover, vascular and neural ingrowth may occur within the defect which is known as a possible reason for discogenic pain. Due to a limited healing capacity, an effective strategy to repair and close the AF defect is necessary. In this study, using electrospinning technology, two nature polymers, silk fibroin and gelatin, were linked to imitate the unique lamellae structure of native AF. Our findings revealed that a multilayer electrospun-aligned fibroin/gelatin scaffold with mechanical and morphological properties mimicking those of native AF lamellae have been developed. The average diameter of the nanofiber is 162.9 ± 38.8 nm. The young’s modulus is around 6.70 MPa with an ultimate tensile strength of around 1.81 MP along preferred orientation. The in vitro test confirmed its biocompatibility and ability to maintain cell viability and colonization. Using a porcine model, we demonstrated that the multilayer-aligned scaffold offered a crucial microenvironment to induce collagen fibrous tissue production within native AF defect. In the implant-repaired AF, H&E staining showed homogeneous fibroblast-like cell infiltration at the repaired defect with very little vascular ingrowth, which was confirmed by magnetic resonance imaging findings. Picrosirius red staining and immunohistochemical staining against type I collagen revealed positively stained fibrous tissue in an aligned pattern within the implant-integrated site. Relative to the intact control group, the disc height index of the serial X-ray decreased significantly in both the injury control and implant group at 4 weeks and 8 weeks (p < 0.05) which indicated this scaffold may not reverse the degenerative process. However, the results of the discography showed that the effectiveness of annulus repair of the implant group is much superior to that of the untreated group. The scaffold, composed with nature fibroin/gelatin polymers, could potentially enhance AF healing that could prevent IVD recurrent herniation, as well as neural and neovascular ingrowth after discectomy surgeries.