Lactate oxidative phosphorylation by annulus fibrosus cells: evidence for lactate-dependent metabolic symbiosis in intervertebral discs

Arthritis Research & Therapy

Michael J. Jurczak¹  Chao-ming Zhou²  Chao Han²  Dong Wang²  Robert Hartman²  Brandon Couch²  Matias Malkamaki²  Gwendolyn Sowa²  Nam Vo²  Joon Lee²  James Kang³  Vera Roginskaya⁴  Steven J. Mullett⁴  Stacy G. Wendell⁴  Bennett Van Houten⁴ 

[1] Department of Medicine, Division of Endocrinology and Metabolism, University of Pittsburgh;Department of Orthopaedic Surgery, Ferguson Laboratory for Orthopedic and Spine Research, University of Pittsburgh;Department of Orthopedics, Brigham and Women’s Hospital, School of Medicine, Harvard University;Department of Pharmacology and Chemical Biology, University of Pittsburgh;

关键词: Lactate;    Lactic acid;    Intervertebral disc;    Annulus fibrosus;    Nucleus pulpous;    Glycolysis;   

DOI  :  10.1186/s13075-021-02501-2

来源: DOAJ

【 摘 要 】

Abstract Background Intervertebral disc degeneration contributes to low back pain. The avascular intervertebral disc consists of a central hypoxic nucleus pulpous (NP) surrounded by the more oxygenated annulus fibrosus (AF). Lactic acid, an abundant end-product of NP glycolysis, has long been viewed as a harmful waste that acidifies disc tissue and decreases cell viability and function. As lactic acid is readily converted into lactate in disc tissue, the objective of this study was to determine whether lactate could be used by AF cells as a carbon source rather than being removed from disc tissue as a waste byproduct. Methods Import and conversion of lactate to tricarboxylic acid (TCA) cycle intermediates and amino acids in rabbit AF cells were measured by heavy-isotope (13C-lactate) tracing experiments using mass spectrometry. Levels of protein expression of lactate converting enzymes, lactate importer and exporter in NP and AF tissues were quantified by Western blots. Effects of lactate on proteoglycan (35S-sulfate) and collagen (3H-proline) matrix protein synthesis and oxidative phosphorylation (Seahorse XFe96 Extracellular Flux Analyzer) in AF cells were assessed. Results Heavy-isotope tracing experiments revealed that AF cells imported and converted lactate into TCA cycle intermediates and amino acids using in vitro cell culture and in vivo models. Addition of exogenous lactate (4 mM) in culture media induced expression of the lactate importer MCT1 and increased oxygen consumption rate by 50%, mitochondrial ATP-linked respiration by 30%, and collagen synthesis by 50% in AF cell cultures grown under physiologic oxygen (2-5% O2) and glucose concentration (1-5 mM). AF tissue highly expresses MCT1, LDH-H, an enzyme that preferentially converts lactate to pyruvate, and PDH, an enzyme that converts pyruvate to acetyl-coA. In contrast, NP tissue highly expresses MCT4, a lactate exporter, and LDH-M, an enzyme that preferentially converts pyruvate to lactate. Conclusions These findings support disc lactate-dependent metabolic symbiosis in which lactate produced by the hypoxic, glycolytic NP cells is utilized by the more oxygenated AF cells via oxidative phosphorylation for energy and matrix production, thus shifting the current research paradigm of viewing disc lactate as a waste product to considering it as an important biofuel. These scientifically impactful results suggest novel therapeutic targets in disc metabolism and degeneration.

【 授权许可】

Unknown