Sensory innervation in porous endplates by Netrin-1 from osteoclasts mediates PGE2-induced spinal hypersensitivity in mice

Abstract

Spinal pain is a major clinical problem, however, its origins and underlying mechanisms remain unclear. Here we report that in mice, osteoclasts induce sensory innervation in the porous endplates which contributes to spinal hypersensitivity in mice. Sensory innervation of the porous areas of sclerotic endplates in mice was confirmed. Lumbar spine instability (LSI), or aging, induces spinal hypersensitivity in mice. In these conditions, we show that there are elevated levels of PGE2 which activate sensory nerves, leading to sodium influx through Na v 1.8 channels. We show that knockout of PGE2 receptor 4 in sensory nerves significantly reduces spinal hypersensitivity. Inhibition of osteoclast formation by knockout Rankl in the osteocytes significantly inhibits LSI-induced porosity of endplates, sensory innervation, and spinal hypersensitivity. Knockout of Netrin-1 in osteoclasts abrogates sensory innervation into porous endplates and spinal hypersensitivity. These findings suggest that osteoclast-initiated porosity of endplates and sensory innervation are potential therapeutic targets for spinal pain.

Sensory neurons sprouting is dependent on osteoclast-derived extracellular vesicles involving the activation of epidermal growth factor receptors

“…BMSC are known to promote axon growth through the secretion of neurotrophins (Cantinieaux et al, 2013; Gu et al, 2012, 2010) and osteoclasts where described to induce nerve outgrowth through netrin-1 action (Ni et al, 2019; Zhu et al, 2019). To assess if the osteoclast secretome observed effect follow similar mechanisms, we measured in the conditioned medium the levels of NGF, BDNF, NT-3, NT-4/5 and netrin-1, by enzyme-linked immunosorbent assay (ELISA).…”

“…Different studies point to a parallel between osteoclast activity and sensory neurons outgrowth in physiological and pathological conditions (Cheung et al, 2009; Clarke, 2008; Gajda et al, 2005; Kumar et al, 2011; Mediati et al, 2014; Nagae et al, 2006; Ni et al, 2019; Reddy et al, 1999; Riminucci et al, 2003; Sisask et al, 1996, 2013; Zhu et al, 2019). Several reports have described that during embryonic long bone development, osteoclasts are found in the process of endochondral ossification, degrading the newly formed trabecular bone, creating the bone marrow space (Clarke, 2008).…”

“…have shown that osteoclasts can actively promote axonal growth on subchondral bone, through netrin-1 signaling, in an osteoarthritis model (Zhu et al, 2019). Moreover, osteoclasts-derived netrin-1 was also linked to an increase in the sensory innervation of porous endplates of intervertebral disc (Ni et al, 2019). We were unable to detect NGF, BDNF, NT-3, NT4/5 nor netrin-1 in the osteoclast secretome by using comparable settings for osteoclast in vitro differentiation and netrin-1 quantification (mass spectrometry analysis and ELISA (data not shown)).…”

“…The greater effect observed in the increasing of the MFR was related to the secretome from osteoclasts cultured on mineralized substrates, as expected. Osteoclasts were shown to increase the expression of sodium channel Na v 1.8 in sensory nerve endings in the endplates leading to spinal hypersensitivity (Ni et al, 2019). Protons released by the osteoclasts upon matrix degradation are known to stimulate the acid-sensing ions channels contributing to the activation of nociceptors on the nerve terminals (Hiasa et al, 2017; Yoneda et al, 2015a).…”

“…have shown that osteoclasts can actively promote axonal growth on subchondral bone, through netrin-1 signaling, in an osteoarthritis model (Zhu et al, 2019). Moreover, osteoclast-derived netrin-1 was also linked to an increase in the sensory innervation of porous endplates of intervertebral disc, causing an low back pain (Ni et al, 2019). Therefore, deciphering the mechanisms by which peripheral innervation can be controlled by the osteoclasts constitute a major advantage for developing new strategies to tackle bone pain.…”