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.