Age-dependent changes in intervertebral disc cell mitochondria and bioenergetics

Abstract

Robust cellular bioenergetics is vital in the energy-demanding process of maintaining matrix homeostasis in the intervertebral disc. Age-related decline in disc cellular bioenergetics is hypothesised to contribute to the matrix homeostatic perturbation observed in intervertebral disc degeneration. The present study aimed to measure how ageing impacted disc cell mitochondria and bioenergetics. Age-related changes measured included matrix content and cellularity in disc tissue, as well as matrix synthesis, cell proliferation and senescence markers in cell cultures derived from annulus fibrosus (AF) and nucleus pulposus (NP) isolated from the discs of young (6-9 months) and older (36-50 months) New Zealand White rabbits. Cellular bioenergetic parameters were measured using a Seahorse XFe96 Analyzer, in addition to quantitating mitochondrial morphological changes and membrane potential. Ageing reduced mitochondrial number and membrane potential in both cell types. Also, it significantly reduced glycolytic capacity, mitochondrial reserve capacity, maximum aerobic capacity and non-glucose-dependent respiration in NP. Moreover, NP cells exhibited age-related decline in matrix synthesis and reduced cellularity in older tissues. Despite a lack of changes in mitochondrial respiration with age, AF cells showed an increase in glycolysis and altered matrix production. While previous studies report age-related matrix degenerative changes in disc cells, the present study revealed, for the first time, that ageing affected mitochondrial number and function, particularly in NP cells. Consequently, age-related bioenergetic changes may contribute to the functional alterations in aged NP cells that underlie disc degeneration.

Lactate Efflux From Intervertebral Disc Cells Is Required for Maintenance of Spine Health

“…A renewed interest in cellular metabolism has highlighted the importance of bioenergetics in the pathogenesis of chronic skeletal disorders including disc degeneration, osteoporosis, and osteoarthritis . Discogenic back pain and associated disc degeneration are particularly related to pathological decreases in intracellular pH, perhaps secondary to metabolic dysregulation during the disease process .…”

“…(5)(6)(7)(8)(9)(10) A renewed interest in cellular metabolism has highlighted the importance of bioenergetics in the pathogenesis of chronic skeletal disorders including disc degeneration, osteoporosis, and osteoarthritis. (11)(12)(13)(14)(15) Discogenic back pain and associated disc degeneration are particularly related to pathological decreases in intracellular pH, perhaps secondary to metabolic dysregulation during the disease process. (16,17) In fact, lactate, the end product of glycolysis, has been considered a biomarker of disc degeneration since 1968 and was recently proposed as a biomarker of discogenic pain.…”

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

“…Four independent P1 AF cells from four rabbits were cultured in low glucose DMEM containing 5.5 mM glucose and 10% FBS at 5% O 2 in ± 4 mM lactate. AF cell bioenergetic ux in the presence and absence of lactate was measured by using Seahorse XFe96 Analyzer as previously described (23). Oxygen consumption rate (OCR) was calculated and normalized to protein amount as measured using the Crystal Violet dye (C3886, Sigma-Aldrich).…”

“…Oxygen consumption rate (OCR) was calculated and normalized to protein amount as measured using the Crystal Violet dye (C3886, Sigma-Aldrich). Individual parameters of OXPHOS were derived from OCR pro les, including mitochondrial respiration-mediated ATP production, as described (23,24).…”

Aquaporin Expression, Regulation and Function in the Intervertebral Disc

“…Many factors contribute to the correct function of the NP. The environment in which NP cells reside plays a big role in the physiology of the tissue; the correct biomechanical loading, pH, nutrition, O2 tension and adaptation to a diurnal cycle all allow NP tissues to function correctly (McMillan, Garbutt and Adams, 1996;Ishihara et al, 1997;Urban, 2002;Bibby et al, 2005;Hartman et al, 2018). As the NP has a high content of negatively charged, hydrophilic GAGs within its matrix, allowing water and cation retention, this provides a high osmotic pressure environment within the disc (Ishihara et al, 1997;van Dijk, Potier and Ito, 2011;Johnson, Shapiro and Risbud, 2014a).…”