The Effect of Irisin on Human Nucleus Pulposus Cells: New Insights into the Biological Crosstalk between the Muscle and Intervertebral Disc

Abstract

Study Design. In vitro study. Objective. To investigate the effect of irisin on human nucleus pulposus cells (hNPCs) in vitro. Summary of Background Data. Physical exercise (PE) favours weight loss and ameliorates function in patients with low back pain. Although there is no biological evidence that the intervertebral disk (IVD) can respond to PE, recent studies have shown that running is associated with increased IVD hydration and hypertrophy. Irisin, a myokine released upon muscle contraction, has demonstrated anabolic effects on different cell types, including chondrocytes. Materials and Methods. hNPCs were exposed to 5, 10, and 25 ng/mL irisin. Cell proliferation, glycosaminoglycan (GAG) content, metabolic activity, gene expression of collagen type II (COL2), matrix metalloproteinase (MMP)-13, tissue inhibitor of matrix metalloproteinase (TIMP)-1 and TIMP-3, aggrecan (ACAN), interleukin (IL)-1β, a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-5 were assessed. In addition, MTT assay and ADAMTS-5, COL2, TIMP-1, and IL-1β gene expression were evaluated following incubation with irisin for 24 hours and subsequent culture with 10 ng/mL IL-1β and vice versa (incubation for 24 hours with IL-1β and subsequent culture with irisin). Results. Irisin increased hNPC proliferation, metabolic activity, and GAG content, as well as COL2, ACAN, TIMP-1 and TIMP-3 gene expression, while decreasing MMP-13 and IL-1β mRNA levels. Irisin pretreatment of hNPCs cultured in proinflammatory conditions resulted in a rescue of metabolic activity and a decrease of IL-1β levels. Similarly, incubation of hNPCs with IL-1β and subsequent exposure to irisin led to an increment of metabolic activity, COL2 gene expression, and a reduction of IL-1β and ADAMTS-5 levels. Conclusions. Irisin increases hNPC proliferation, GAG content, metabolic activity, and promotes anabolic gene expression while reducing catabolic markers. Irisin may be one of the mediators by which PE and muscle tissues modulate IVD metabolism, suggesting the existence of a biological cross-talk between the muscle and IVD.

Irisin inhibits tenocyte response to inflammation in vitro: New insights into tendon‐muscle cross‐talk

“…Indeed, both the addition of irisin to hTCs cultured in proinflammatory conditions and the later introduction of IL‐1β and TNF‐α in a hTC culture preconditioned with irisin resulted in an increase of mitochondrial activity and decrease of NO concentration, until reaching levels encountered with the standard medium alone. Altogether, these data suggest that irisin may protect hTCs from oxidative stress and blunt the detrimental effects of IL‐1β and TNF‐α in vitro, which have also been shown in other cell types 12,25,26 . Indeed, it has been recently reported that irisin enhanced mitochondrial membrane potential and ATP synthesis while attenuating IL‐1β‐mediated reactive oxygen species production, mitochondrial fusion, mitophagy, and autophagosome formation 27 .…”

“…Apart from its beneficial effects on several tissues, 9 the anabolic role of irisin has been recently elucidated in the musculoskeletal system 8 . Our group was the first to describe the effect of irisin on human articular chondrocytes 11 and nucleus pulposus cells 12 in vitro. In these studies, we found that such a myokine was able to increment cell proliferation, metabolism, and production of anabolic ECM markers while dampening the effect of in vitro inflammation.…”

“…Altogether, these data suggest that irisin may protect hTCs from oxidative stress and blunt the detrimental effects of IL-1β and TNF-α in vitro, which have also been shown in other cell types. 12,25,26 Indeed, it has been recently reported that irisin enhanced mitochondrial membrane potential and ATP synthesis while attenuating IL-1βmediated reactive oxygen species production, mitochondrial fusion, mitophagy, and autophagosome formation. 27 Such effects may be exerted by direct interaction with the αVβ5 receptor, which has been detected on hTCs plasma membrane by our immunohistochemical analysis.…”

“…8 Collectively, this multifunctional peptide showed promising anabolic, antiapoptotic and antioxidative properties with regenerative potential. 9,10 We were the first to report the effect of irisin on human articular chondrocytes 11 and nucleus pulposus cells in vitro, 12 showing that such a myokine was able to enhance cell proliferation and metabolism while reducing the detrimental effects of in vitro inflammation. Recently, the αVβ5 integrin has been identified as the major irisin receptor, through which the myokine is able to regulate several intracellular pathways, including p38 and ERK, thus resulting in its multiple biological functions.…”

Mesenchymal stem cell-derived secretome enhances nucleus pulposus cell metabolism and modulates extracellular matrix gene expression in vitro

“…hNPCs were isolated from IVD tissues of patients undergoing discectomy due to lumbar disc herniation ( n = 5, mean age = 57 ± 17 years old, Table 1 ) as previously described ( Vadalà et al, 2022 ). Tissue specimens were washed, annulus fibrosus and cartilaginous endplate tissues were carefully removed, and the NP tissue was minced and digested overnight in DMEM (Corning) with 1% P/S (Sigma), 5% FBS, and 0.01% collagenase type II (Worthington).…”