Irisin Prevents Disuse‐Induced Osteocyte Apoptosis. (6th January 2020)

• Record Type: Journal Article
• Authors: Storlino, Giuseppina; Colaianni, Graziana; Sanesi, Lorenzo; Lippo, Luciana; Brunetti, Giacomina; Errede, Mariella; Colucci, Silvia; Passeri, Giovanni; Grano, Maria
• Is Part Of: Journal of bone and mineral research. Volume 35:Number 4(2020)
• Page Start: 766
• Page End: 775
• Publication Date: 2020-01-06
• Subjects: ANABOLICS -- BONE‐MUSCLE INTERACTIONS -- IRISIN -- OSTEOCYTES -- OSTEOPOROSIS; Bones -- Metabolism -- Periodicals; Mineral metabolism -- Periodicals; 612.392
• DOI: 10.1002/jbmr.3944
• Languages: English
• ISSNs: 0884-0431

Abstract

ABSTRACT: Previous results showed that intermittently administered irisin improves bone mass in normal mice and prevents the development of disuse‐induced osteoporosis and muscular atrophy in hindlimb‐suspended mice, a murine model able to mimic the absence of mechanical loading. A recent study showed that irisin increases survival of osteocytes acting through integrin αV/β5 receptors. To better understand the action of irisin on these cells, we investigated the downstream signaling cascades in osteocyte‐like cells (MLO‐Y4) treated with recombinant irisin (rec‐irisin) in vitro and we analyzed survival of osteocytes and caspase activation in cortical bone of osteoporotic mice treated with rec‐irisin in vivo. Our results revealed that rec‐irisin activated the MAP kinases Erk1 and Erk2 and increased the expression of the transcription factor Atf4 (2.5‐fold, p < .05) through an Erk‐dependent pathway in osteocytes. Some key genes expressed by MLO‐Y4 cells were modulated by long‐term irisin treatment, either continuously administered or given with intermittent short pulses. Interestingly, Sost mRNA was severely downregulated only upon intermittent irisin administration (10‐fold, p < .001). Furthermore, rec‐irisin upregulated Tfam mRNA (fourfold, p < .05) and Bcl2/Bax ratio (twofold, p < .05) in MLO‐Y4 cells. By detecting caspase‐9 and caspase‐3, we also found that rec‐irisin inhibited apoptosis induced by hydrogen peroxide and dexamethasone, respectively. In cortical bone of unloading C57BL6 mice treated with vehicle (unload‐veh), irisin prevented disuse‐induced reduction of viable osteocytes (+30% versus unload‐veh, p < .05) and increase of empty lacunae (+110% versus unload‐veh, p < .05), as well as caspase‐9 (threefold, p < .05) and caspase‐3 (twofold, p < .05) activations. Our findings revealed underlying mechanisms of irisin action on osteocytes, which increases their functions and exerts anti‐apoptotic effects, confirming that mechanosensor cells of bone are sensitive to the exercise‐mimetic myokine irisin. © 2019 American Society for Bone and Mineral Research. Abstract : Schematic representation of irisin's action on osteocytes to activate ERK phosphorylation, which in turn stimulates the increase of Atf4 mRNA levels. A recent study showed that irisin increases survival of osteocytes acting through integrin αV/β5 receptors. To elucidate the action of irisin on osteocytes, we investigated the downstream signaling cascades in MLO‐Y4 cells treated with recombinant irisin (rec‐irisin). We found that rec‐irisin activated the MAP kinases Erk1 and Erk2 and increased the expression of the transcription factor Atf4 through an Erk‐dependent pathway in osteocytes.