Comparison of Transforming Growth Factor-Beta1 and Lovastatin on Differentiating Mesenchymal Stem Cells toward Nucleus Pulposus-like Phenotype: An In Vitro Cell Culture Study

Lipid metabolism disorder promotes the development of intervertebral disc degeneration

Lipid metabolism is a complex process that maintains the normal physiological function of the human body. The disorder of lipid metabolism has been implicated in various human diseases, such as cardiovascular diseases and bone diseases. Intervertebral disc degeneration (IDD), an age-related degenerative disease in the musculoskeletal system, is characterized by high morbidity, high treatment cost, and chronic recurrence. Lipid metabolism disorder may promote the pathogenesis of IDD, and the potential mechanisms are complex. Leptin, resistin, nicotinamide phosphoribosyltransferase (NAMPT), fatty acids, and cholesterol may promote the pathogenesis of IDD, while lipocalin, adiponectin, and progranulin (PGRN) exhibit protective activity against IDD development. Lipid metabolism disorder contributes to extracellular matrix (ECM) degradation, cell apoptosis, and cartilage calcification in the intervertebral discs (IVDs) by activating inflammatory responses, endoplasmic reticulum (ER) stress, and oxidative stress and inhibiting autophagy. Several lines of agents have been developed to target lipid metabolism disorder. Inhibition of lipid metabolism disorder may be an effective strategy for the therapeutic management of IDD. However, an in-depth understanding of the molecular mechanism of lipid metabolism disorder in promoting IDD development is still needed.

Nucleus pulposus cell-derived efficient microcarrier for intervertebral disc tissue engineering

Adipose-derived stem cells (ADSCs) show great potential for the treatment of intervertebral disc (IVD) degeneration. An ideal carrier is necessary to transplant ADSCs into degenerated IVDs without influencing cell function. Nucleus pulposus cells (NPCs) can synthesize and deposit chondroitin sulfate and type II collagen which are NP-specific extracellular matrix (ECM) and can also regulate the NP-specific differentiation of stem cells. Bioscaffolds fabricated based on the ECM synthesis functions of NPCs have possible roles in cell transplantation and differentiation induction, but it has not been studied. In this study, we first aggregated NPCs into pellets, and then, NPC-derived efficient microcarriers (NPCMs) were fabricated by pellet cultivation under specific conditions and optimized decellularization. Thirdly, we evaluated the microstructure, biochemical composition, biostability and cytotoxicity of the NPCMs. Finally, we investigated the NP-specific differentiation of ADSCs induced by the NPCMsin vitroand NP regeneration induced by the ADSC-loaded NPCMs in a rabbit model. The results indicated that the injectable NPCMs retained maximal ECM and minimal cell nucleic acid after optimized decellularization and had good biostability and no cytotoxicity. The NPCMs also promoted the NP-specific differentiation of ADSCsin vitro. In addition, the results of MRI, x-ray, and the structure and ECM content of NP showed that the ADSCs-loaded NPCMs can partly restored the degenerated NPin vivo. Our injectable NPCMs regenerated the degenerated NP and provide a simplified and efficient strategy for treating IVD degeneration.

Cell sources proposed for nucleus pulposus regeneration

Lower back pain (LBP) occurs in 80% of adults in their lifetime; resulting in LBP being one of the biggest causes of disability worldwide. Chronic LBP has been linked to the degeneration of the intervertebral disc (IVD). The current treatments for chronic back pain only provide alleviation of symptoms through pain relief, tissue removal, or spinal fusion; none of which target regenerating the degenerate IVD. As nucleus pulposus (NP) degeneration is thought to represent a key initiation site of IVD degeneration, cell therapy that specifically targets the restoration of the NP has been reviewed here. A literature search to quantitatively assess all cell types used in NP regeneration was undertaken. With key cell sources: NP cells; annulus fibrosus cells; notochordal cells; chondrocytes; bone marrow mesenchymal stromal cells; adipose-derived stromal cells; and induced pluripotent stem cells extensively analyzed for their regenerative potential of the NP. This review highlights: accessibility; expansion capability in vitro; cell survival in an IVD environment; regenerative potential; and safety for these key potential cell sources. In conclusion, while several potential cell sources have been proposed, iPSC may provide the most promising regenerative potential.

Mesenchymal stem cells regulate inflammatory milieu within degenerative nucleus pulposus cells via p38 MAPK pathway

It has been established that excessive apoptosis of nucleus pulposus cells (NPCs) are responsible for pathogenesis of human intervertebral disc degeneration (IDD). The present study aimed to shed light on the molecular mechanisms underlying the protective effects of mesenchymal stem cells (MSCs) on NPCs in an inflammatory environment. NPCs were treated with TNF-α to induce inflammation and then co-cultured with Wharton's Jelly-derived MSCs (WJ-MSCs)without direct interaction. The levels of inflammation markers (IL-1β, IL-6 and IL-8) in NPCs were detected by performing enzyme-linked immunosorbent assay (ELISA), and expression of metalloproteases and aggrecan, as well as the activity of p38 MAPK pathway were determined through immunoblotting. SB-203580 was used to inhibit p38 signaling, prior to evaluation of the effects of Wharton's Jelly-derived MSCs (WJ-MSCs) on inflammatory response within the co-cultured NPCs. After TNF-α treatment, the levels of inflammatory cytokines, MMP-3, and MMP-13 in NPCs were increased whereas aggrecan was decreased, which was then dramatically reversed by WJ-MSCs co-culture. Likewise, WJ-MSCs suppressed TNF-α-induced phosphorylation of p38 MAPK signaling components including p38, ASK-1, MKK-3 and MKK-6. Blocking p38 MAPK pathway enhanced the anti-inflammatory impact of WJ-MSCs, and there was no significant difference between NPCs co-cultured with WJ-MSCs or the cells cultured alone. WJ-MSCs co-culture mitigate TNF-α-induced inflammatory response and ECM degeneration in NPCs, the major pathological events are implicated in IDD development, probably by suppressing the p38 MAPK signaling cascade.

Bone Morphogenetic Proteins for Nucleus Pulposus Regeneration

Matrix production by nucleus pulposus (NP) cells, the cells residing in the center of the intervertebral disc, can be stimulated by growth factors. Bone morphogenetic proteins (BMPs) hold great promise. Although BMP2 and BMP7 have been used most frequently, other BMPs have also shown potential for NP regeneration. Heterodimers may be more potent than single homodimers, but it is not known whether combinations of homodimers would perform equally well. In this study, we compared BMP2, BMP4, BMP6, and BMP7, their combinations and heterodimers, for regeneration by human NP cells. The BMPs investigated induced variable matrix deposition by NP cells. BMP4 was the most potent, both in the final neotissue glysosaminoglycan content and incorporation efficiency. Heterodimers BMP2/6H and BMP2/7H were more potent than their respective homodimer combinations, but not the BMP4/7H heterodimer. The current results indicate that BMP4 might have a high potential for regeneration of the intervertebral disc. Moreover, the added value of BMP heterodimers over their respective homodimer BMP combinations depends on the BMP combination applied.