Ghrelin protects against nucleus pulposus degeneration through inhibition of NF-κB signaling pathway and activation of Akt signaling pathway

Roles of organokines in intervertebral disc homeostasis and degeneration

The intervertebral disc is not isolated from other tissues. Recently, abundant research has linked intervertebral disc homeostasis and degeneration to various systemic diseases, including obesity, metabolic syndrome, and diabetes. Organokines are a group of diverse factors named for the tissue of origin, including adipokines, osteokines, myokines, cardiokines, gastrointestinal hormones, and hepatokines. Through endocrine, paracrine, and autocrine mechanisms, organokines modulate energy homeostasis, oxidative stress, and metabolic balance in various tissues to mediate cross-organ communication. These molecules are involved in the regulation of cellular behavior, inflammation, and matrix metabolism under physiological and pathological conditions. In this review, we aimed to summarize the impact of organokines on disc homeostasis and degeneration and the underlying signaling mechanism. We focused on the regulatory mechanisms of organokines to provide a basis for the development of early diagnostic and therapeutic strategies for disc degeneration.

Role and molecular mechanism of ghrelin in degenerative musculoskeletal disorders

Ghrelin is a brain-gut peptide, and the first 28-peptide that was found in the gastric mucosa. It has a growth hormone (GH)-releasing hormone-like effect and can potently promote the release of GH from pituitary GH cells; however, it is unable to stimulate GH synthesis. Therefore, ghrelin is believed to play a role in promoting bone growth and development. The correlation between ghrelin and some degenerative diseases of the musculoskeletal system has been reported recently, and ghrelin may be one of the factors influencing degenerative pathologies, such as osteoporosis, osteoarthritis, sarcopenia and intervertebral disc degeneration. With population ageing, the risk of health problems caused by degenerative diseases of the musculoskeletal system gradually increases. In this article, the roles of ghrelin in musculoskeletal disorders are summarized to reveal the potential effects of ghrelin as a key target in the treatment of related bone and muscle diseases and the need for further research.

Metabolomic signature and molecular profile of normal and degenerated human intervertebral disc cells

BACKGROUND CONTEXT

Intervertebral disc degeneration (IVDD) is an incurable, specific treatment-orphan disease with an increasing burden worldwide. Although great efforts have been made to develop new regenerative therapies, their clinical success is limited.

PURPOSE

Characterize the metabolomic and gene expression changes underpinning human disc degeneration. This study also aimed to disclose new molecular targets for developing and optimizing novel biological approaches for IVDD.

STUDY DESIGN

Intervertebral disc cells were obtained from IVDD patients undergoing circumferential arthrodesis surgery or from healthy subjects. Mimicking the harmful microenvironment of degenerated discs, cells isolated from the nucleus pulposus (NP) and annulus fibrosus (AF) were exposed to the proinflammatory cytokine IL-1β and the adipokine leptin. The metabolomic signature and molecular profile of human disc cells were unraveled for the first time.

METHODS

The metabolomic and lipidomic profiles of IVDD and healthy disc cells were analyzed by high-performance liquid chromatography-mass spectrometry (UHPLC-MS). Gene expression was investigated by SYBR green-based quantitative real-time RT-PCR. Altered metabolites and gene expression were documented.

RESULTS

Lipidomic analysis revealed decreased levels of triacylglycerols (TG), diacylglycerol (DG), fatty acids (FA), phosphatidylcholine (PC), lysophosphatidylinositols (LPI) and sphingomyelin (SM), and increased levels of bile acids (BA) and ceramides, likely promoting disc cell metabolism changing from glycolysis to fatty acid oxidation and following cell death. The gene expression profile of disc cells suggests LCN2 and LEAP2/GHRL as promising molecular therapeutic targets for disc degeneration and demonstrates the expression of genes related to inflammation (NOS2, COX2, IL-6, IL-8, IL-1β, and TNF-α) or encoding adipokines (PGRN, NAMPT, NUCB2, SERPINE2, and RARRES2), matrix metalloproteinases (MMP9 and MMP13), and vascular adhesion molecules (VCAM1).

CONCLUSIONS

Altogether, the presented results disclose the NP and AF cell biology changes from healthy to degenerated discs, allowing the identification of promising molecular therapeutic targets for intervertebral disc degeneration.

CLINICAL SIGNIFICANCE

Our results are relevant to improving current biological-based strategies aiming to repair IVD by restoring cellular lipid metabolites as well as adipokines homeostasis. Ultimately, our results will be valuable for successful, long-lasting relief of painful IVDD.

Embelin protects against apoptosis and inflammation by regulating PI3K/Akt signaling in IL-1β-stimulated human nucleus pulposus cells

Embelin is a natural benzoquinone compound that displays a beneficial effect in various inflammatory-related diseases. However, the effect of embelin on degeneration of intervertebral disc (IDD), a chronic inflammatory disorder, has not been reported. This study was attempted to explore the therapeutic action of embelin on IDD in vitro. Network pharmacology analysis was performed for evaluating the link between embelin and IDD. The human nucleus pulposus cells (NPCs) were stimulated with IL-1β to induce inflammation. Cell viability of NPCs was assessed by CCK-8 assay. Western blotting was conducted to detect the expression levels of PI3K, p-PI3K, Akt, p-Akt, cleaved caspase-3, caspase-3, Bax, Bcl-2, p65 and p-p65. Apoptotic deaths of NPCs were examined by TUNEL assay. The production of COX-2, IL-6, IL-8, and TNF-α was examined by ELISA. It can be seen that 16 overlapping genes were selected from 109 possible targets of embelin and 342 possible targets of IDD. KEGG pathway enrichment analysis showed that the PI3K/Akt signaling pathway was a close link between embelin and IDD. We found that embelin dose-dependently improved the cell viability in IL-1β-stimulated NPCs. Embelin elevated the relative levels of p-PI3K/PI3K and p-Akt/Akt in IL-1β-stimulated NPCs. IL-1β induced a significant increase in apoptotic deaths of NPCs, which was attenuated by embelin treatment. IL-1β-induced alternations in expression levels of apoptotic-related proteins including cleaved caspase-3, Bax and Bcl-2 were prevented by embelin treatment. Pretreatment with LY294002 (an inhibitor of PI3K) reversed the inhibitory effect of embelin on IL-1β-induced apoptosis in NPCs. Embelin treatment caused inhibitory effects on the IL-1β-stimulated production of COX-2, IL-6, IL-8, and TNF-α, which were abolished by LY294002 treatment. Furthermore, embelin treatment prevented IL-1β-induced phosphorylation of p65 in NPCs, while LY294002 elevated the embelin-caused decrease in p-p65/p65 level. Overall, embelin protected human NPCs against IL-1β-stimulated apoptosis and inflammation by regulating the PI3K/Akt signaling pathway. These findings provided new ideas for the clinical usage of embelin in the prevention and treatment of IDD.

A new immunometabolic perspective of intervertebral disc degeneration

Intervertebral disc (IVD) degeneration is a common finding on spine imaging that increases in prevalence with age. IVD degeneration is a frequent cause of low back pain, which is a leading cause of disability. The process of IVD degeneration consists of gradual structural change accompanied by severe alterations in metabolic homeostasis. IVD degeneration, like osteoarthritis, is a common comorbidity in patients with obesity and type 2 diabetes mellitus, two metabolic syndrome pathological conditions in which adipokines are important promoters of low-grade inflammation, extracellular matrix degradation and fibrosis. Impairment in white adipose tissue function, due to the abnormal fat accumulation in obesity, is characterized by increased production of specific pro-inflammatory proteins such as adipokines by white adipose tissue and of cytokines such as TNF by immune cells of the stromal compartment. Investigations into the immunometabolic alterations in obesity and type 2 diabetes mellitus and their interconnections with IVD degeneration provide insights into how adipokines might affect the pathogenesis of IVD degeneration and impair IVD function and repair. Toll-like receptor-mediated signalling has also been implicated as a promoter of the inflammatory response in the metabolic alterations associated with IVD and is thus thought to have a role in IVD degeneration. Pathological starvation, obesity and adipokine dysregulation can result in immunometabolic alterations, which could be targeted for the development of new therapeutics.

USP15 promotes the apoptosis of degenerative nucleus pulposus cells by suppressing the PI3K/AKT signalling pathway

OBJECTIVES

Degenerative disc disease is characterized by an enhanced breakdown of its existing nucleus pulposus (NP) matrix due to the dysregulation of matrix enzymes and factors. Ubiquitin-specific protease 15 (USP15) is reported to be abnormal in certain human diseases. However, its role in NP degeneration remains unclear. Therefore, we aimed to explore the function of USP15 in degenerative NP cell specimens.

METHODS

We induced gene silencing and overexpression of USP15 in degenerative NP cells using RNA interference (RNAi) and a lentiviral vector, respectively. qRT-PCR and Western blotting were used to determine gene and protein expression levels. Cell apoptosis was analysed via flow cytometry. Protein interaction was examined by performing a co-immunoprecipitation assay. Furthermore, the PI3K inhibitor LY294002 and agonist IGF-1 were used to investigate the link between USP15 and AKT in NP degeneration.

RESULTS

We found that USP15 was up-regulated in degenerative NP cells and that its overexpression accelerated the process of apoptosis. Moreover, USP15 expression levels negatively correlated with AKT phosphorylation in degenerative NP cells. Furthermore, targeting and silencing USP15 with miR-338-3p and studying its interaction with FK506-binding protein 5 (FKBP5) revealed enhancement of FKBP5 ubiquitination, indicating that USP15 is a component of the FKBP5/AKT signalling pathway in degenerative NP cells.

CONCLUSIONS

Our results show that USP15 exacerbates NP degradation by deubiquitinating and stabilizing FKBP5. This in turn results in the suppression of AKT phosphorylation in degenerative NP cells. Therefore, our study provides insights into the understanding of USP15 function as a potential molecule in the network of NP degeneration.

Adipocytokines: Are they the Theory of Everything?

INTRODUCTION

Adipose tissue secretes various bioactive peptides/proteins, immune molecules and inflammatory mediators which are known as adipokines or adipocytokines. Adipokines play important roles in the maintenance of energy homeostasis, appetite, glucose and lipid metabolism, insulin sensitivity, angiogenesis, immunity and inflammation. Enormous number of studies from all over the world proved that adipocytokines are involved in the pathogenesis of diseases affecting nearly all body systems, which raises the question whether we can always blame adipocytokines as the triggering factor of every disease that may hit the body.

OBJECTIVE

Our review targeted the role played by adipocytokines in the pathogenesis of different diseases affecting different body systems including diabetes mellitus, kidney diseases, gynecological diseases, rheumatologic disorders, cancers, Alzheimer's, depression, muscle disorders, liver diseases, cardiovascular and lung diseases.

METHODOLOGY

We cited more than 33 recent literature reviews that discussed the role played by adipocytokines in the pathogenesis of different diseases affecting different body systems.

CONCLUSION

More evidence is being discovered to date about the role played by adipocytokines in more diseases and extra research is needed to explore hidden roles played by adipokine imbalance on disease pathogenesis.

[Research progress on the role of adipokines in intervertebral disc degeneration]

OBJECTIVE

To review the research progress of the role and mechanism of adipokines in intervertebral disc degeneration (IVDD) in recent years.

METHODS

The domestic and foreign literature related to adipokines in the process of IVDD was extensively reviewed. The types and functions of adipokines, the role and mechanism in the process of IVDD, and the application prospects of intervertebral disc biotherapy were reviewed.

RESULTS

As a kind of bioactive substance secreted by adipose tissue, adipokine plays an important role in bone and joint diseases, metabolic diseases, and breast cancer. During IVDD, most adipokines can activate multiple signaling pathways by binding to autoreceptors, cause the proliferation and apoptosis of cells and proinflammatory and anti-inflammatory factors parasecretions in the intervertebral disc, and lead to imbalance of intradiscal metabolism and establishment of the initial inflammatory environment, and finally cause the IVDD.

CONCLUSION

Adipokines, as a biologically active substance with metabolic and immunomodulatory functions, play important roles in the occurrence, development, and biological treatment of IVDD.

Butyrate alleviates inflammatory response and NF-κB activation in human degenerated intervertebral disc tissues

Butyrate has multiple protective effects in inflammation-related intestinal diseases. Previous studies have found that butyrate could inhibit inflammation in rheumatoid arthritis. Inflammation is a pivotal inducement in the degeneration progress of the intervertebral disc. The anti-inflammatory treatment has an apparent curative effect in the symptomatic treatment of spine-related disease. Herein we investigated whether butyrate plays a protective role in degenerated intervertebral disc model. To mimic the lumbar disc local inflammatory environment, human primary nucleus pulposus cells were cultured with interleukin-1β (IL-1β, 10 ng/ml) to build a nucleus pulposus cell inflammation model. Butyrate was added to the cell culture medium to test the effect of butyrate on disc inflammation. Furthermore, a cultured nucleus pulposus tissue model was treated with butyrate (1 mM) to simulate the local treatment of intervertebral disc disease. Herein, we found that butyrate could downregulate the production of the inflammatory mediator caused by IL-1β stimulation in the cell culture model. Additionally, butyrate inhibits the secretion of pro-inflammatory cytokines or graded enzymes in disc tissues from lumbar disc herniation patients. Furthermore, the anti-inflammatory function of butyrate in lumbar disc degenerated model may be caused by inhibiting the activation of the nuclear factor kappa B (NF-κB) signal pathway. This study presents butyrate as a candidate therapeutic method to treat lumbar disc degenerative disease.

Molecular Relationships among Obesity, Inflammation and Intervertebral Disc Degeneration: Are Adipokines the Common Link?

Intervertebral disc degeneration (IVDD) is a chronic, expensive, and high-incidence musculoskeletal disorder largely responsible for back/neck and radicular-related pain. It is characterized by progressive degenerative damage of intervertebral tissues along with metabolic alterations of all other vertebral tissues. Despite the high socio-economic impact of IVDD, little is known about its etiology and pathogenesis, and currently, no cure or specific treatments are available. Recent evidence indicates that besides abnormal and excessive mechanical loading, inflammation may be a crucial player in IVDD. Furthermore, obese adipose tissue is characterized by a persistent and low-grade production of systemic pro-inflammatory factors. In this context, chronic low-grade inflammation associated with obesity has been hypothesized as an important contributor to IVDD through different, but still unknown, mechanisms. Adipokines, such as leptin, produced prevalently by white adipose tissues, but also by other cells of mesenchymal origin, particularly cartilage and bone, are cytokine-like hormones involved in important physiologic and pathophysiological processes. Although initially restricted to metabolic functions, adipokines are now viewed as key players of the innate and adaptative immune system and active modulators of the acute and chronic inflammatory response. The goal of this review is to summarize the most recent findings regarding the interrelationships among inflammation, obesity and the pathogenic mechanisms involved in the IVDD, with particular emphasis on the contribution of adipokines and their potential as future therapeutic targets.

Isofraxidin attenuates IL-1β-induced inflammatory response in human nucleus pulposus cells

Inflammation has been demonstrated to be the key factor for intervertebral disc degeneration (IVD), which remains a major public health problem. Isofraxidin is a coumarin compound that possesses strong anti-inflammatory activity. However, the role of isofraxidin in IVD remains unclear. The aim of this study was to evaluate the effects of isofraxidin on inflammatory response in human nucleus pulposus cells (NPCs) exposed to interleukin-1β (IL-1β). The results proved that isofraxidin attenuated the IL-1β-induced significant increases in inflammatory mediators and cytokines including nitric oxide (NO), inducible NO synthase (iNOS), cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE2), tumor necrosis factor alpha (TNF-α), and IL-6. Besides, isofraxidin also inhibited the induction effect of IL-1β on matrix metalloproteinases (MMP)-3 and MMP-13. Moreover, the NF-κB activation caused by IL-1β was significantly inhibited by isofraxidin treatment. These findings suggested that isofraxidin alleviates IL-1β-induced inflammation in NPCs. Our work provided an idea that isofraxidin might act as a novel preventive role in IVD.

Cortistatin binds to TNF-α receptors and protects against osteoarthritis

Background

Osteoarthritis (OA) is a common degenerative disease, and tumor necrosis factor (TNF-α) is known to play a critical role in OA. Cortistatin (CST) is a neuropeptide discovered over 20  years ago, which plays a vital role in inflammatory reactions. However, it is unknown whether CST is involved in cartilage degeneration and OA development.

Methods

The interaction between CST and TNF-α receptors was investigated through Coimmunoprecipitation and Biotin-based solid-phase binding assay. Western blot, Real-time PCR, ELISA, immunofluorescence staining, nitrite production assay and DMMB assay of GAG were performed for the primary chondrocyte experiments. Surgically induced and spontaneous OA models were established and western blot, flow cytometry, Real-time PCR, ELISA, immunohistochemistry and fluorescence in vivo imaging were performed for in vivo experiments.

Findings

CST competitively bound to TNFR1 as well as TNFR2. CST suppressed proinflammatory function of TNF-α. Both spontaneous and surgically induced OA models indicated that deficiency of CST led to an accelerated OA-like phenotype, while exogenous CST attenuated OA development in vivo. Additionally, TNFR1- and TNFR2-knockout mice were used for analysis and indicated that TNFRs might be involved in the protective role of CST in OA. CST inhibited activation of the NF-κB signaling pathway in OA.

Interpretation

This study provides new insight into the pathogenesis and therapeutic strategy of cartilage degenerative diseases, including OA.

Fund

The National Natural Science Foundation of China, the Natural Science Foundation of Shandong Province, Key Research and Development Projects of Shandong Province and the Cross-disciplinary Fund of Shandong University.

Ghrelin protects against contact dermatitis and psoriasiform skin inflammation by antagonizing TNF-α/NF-κB signaling pathways

Contact dermatitis and psoriasis are skin disorders caused by immune dysregulation, yet much remains unknown about their underlying mechanisms. Ghrelin, a recently discovered novel peptide and potential endogenous anti-inflammatory factor expressed in the epidermis, is involved in skin repair and disease. In this study, we investigated the expression pattern and therapeutic effect of ghrelin in both contact dermatitis and psoriasis mouse models induced by oxazolone (OXA) and imiquimod (IMQ), respectively, and in TNF-α-stimulated RAW264.7 macrophages, NHEKs and skin fibroblasts. Ghrelin expression was reduced in both the OXA-induced contact dermatitis and IMQ-induced psoriasis mouse models. Furthermore, treatment with ghrelin attenuated skin inflammation in both the contact dermatitis and psoriasis mouse models. Mice administered PBS after OXA- or IMQ-induced model generation exhibited typical skin inflammation, whereas ghrelin treatment in these mouse models substantially decreased the dermatitis phenotype. In addition, exogenous ghrelin attenuated the inflammatory reaction induced by TNF-α in RAW264.7 cells. Moreover, ghrelin administration limited activation of NF-κB signaling. In summary, ghrelin may represent a potential molecular target for the prevention and treatment of inflammatory skin diseases, including contact dermatitis and psoriasis.

Potential therapeutic role of Co-Q10 in alleviating intervertebral disc degeneration and suppressing IL-1β-mediated inflammatory reaction in NP cells

Coenzyme Q10 (Co-Q10) is extraordinarily popular and has been used in abundant interventions as an antioxidant reagent that participates in numerous oxidation reactions. According to substantial evidence previously reported, interleukin-1β (IL-1β) is deemed to be one of the chief orchestrator molecules in the degeneration of intervertebral disc (IVD). However, it is unknown whether Co-Q10 is able to protect against IVD degeneration. In the current study, mouse-derived IVDs as well as primary human nucleus pulposus (NP) cells were isolated and cultured. NP cells were stimulated with IL-1β, with or without selective addition of Co-Q10 to investigate the therapeutic effect of Co-Q10 on IVD degeneration. Levels of IL-1β-induced inflammatory biomarkers including TNF-α, COX-2, IL-6 and iNOS were reduced by Co-Q10, which was possibly associated with inhibition of NF-κB signaling activation. Furthermore, Co-Q10 maintained the production of anabolic biomarkers in NP cells such as collagen 2, aggrecan and Sox-9 and altered the enhanced catabolism induced by IL-1β. Moreover, the therapeutic role of Co-Q10 in sustaining IVD tissue-enhanced anabolism is potentially dependent on activation of the Akt signaling pathway. In summary, Co-Q10 may potentially represent an available molecular target that may shed light on approaches to the prevention and treatment of IVD degeneration in the future.