The influence of intervertebral disc overloading on nociceptor calcium flickering

Abstract

IntroductionMechanical overloading can trigger a degenerative‐like cascade in an organ culture of intervertebral disc (IVD). Whether the overloaded IVD can influence the activation of nociceptors (i.e., the damage sensing neurons) remains unknown. The study aims to investigate the influence of overloaded IVD conditioned medium (CM) on the activation of nociceptors.MethodsIn the static loading regime, force‐controlled loading of 0.2 MPa for 20 h/day representing “long‐term sitting and standing” was compared with a displacement‐controlled loading maintaining original IVD height. In the dynamic loading regime, high‐frequency‐intensity loading representing degenerative “wear and tear” was compared with a lower‐frequency‐intensity loading. CM of differently loaded IVDs were collected to stimulate the primary bovine dorsal root ganglion (DRG) cultures. Calcium imaging (Fluo‐4) and calcitonin gene‐related peptide (CGRP) immunofluorescent labeling were jointly used to record the calcium flickering in CGRP(+) nociceptors.ResultsForce‐controlled loading led to a higher IVD cell death compared to displacement‐controlled loading. Both static and dynamic overloading (force‐controlled and high‐frequency‐intensity loadings) elevated the frequency of calcium flickering in the subsurface space of CGRP(+) nociceptors compared to their mild loading counterparts.ConclusionIn the organ culture system, IVD overloading mediated an altered IVD‐nociceptor communication suggesting a biological mechanism associated with discogenic pain.

Repetitive strikes loading organ culture model to investigate the biological and biomechanical responses of the intervertebral disc

“…The IVD organ culture bioreactor has long been used in basic and translational research for its advantages of precise control in biochemical and biomechanical aspects and is an indispensable tool for bridging in vitro and in vivo models 13,31,32 . Salzer et al observed an increase in the metabolic activity of NP tissue with dynamic loading, coupled with a notable reduction in living cell density by the seventh day 33 .…”

“…In a disc‐like organ model, Gewiess illustrated that extended static loading resulted in a 12.1% reduction in cell viability in the annulus fibrosus (AF) and a 4.2% reduction in the nucleus pulposus (NP). Conversely, dynamic loading had no discernible impact on cell viability in the disc 31 . Salzer et al proposed that dynamic loading acts as an additional stressor, leading to a decrease in nucleus pulposus (NP) cell density 33 .…”

Engineering Sensory Ganglion Multicellular System to Model Tissue Nerve Ingrowth

“…This threshold value has been shown to successfully exclude noise based on our former calcium flickering evaluations in dead neurons. [ 57 ] The capsaicin induced peak height was calculated by subtracting the maximum ΔF / F 0 after adding capsaicin by an average value of ΔF / F 0 over a time window (500 time frames) before capsaicin was added.…”