Project Details
Projekt
SP7 In vivo mechanical loading and tissue adaptation in vertebrae: Inflammation, pain and opioid effects
Subject Area
Orthopaedics, Traumatology, Reconstructive Surgery
Term
since 2021
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 439742772
We investigate how mechanical spinal (over)loading drives tissue adaptation and remodeling, ultimately impacting inflammation and nociceptive sensitization. We hypothesize that mechanically induced tissue adaptations, locally altered immune balance, and disrupted nociceptive signaling contribute to the development of low back pain (LBP) and its chronification (cLBP). Within this context, we study mu-opioid receptors (MOR) as key mediators of both endogenous and pharmacological analgesia. During the first funding period, we developed and validated an in vivo mouse tail-loading model that mimics human sagittal alignment and allows controlled adaptation of spinal tissues. Longitudinal µCT imaging and histology revealed site-specific bone remodeling, identifying the endplate as a critical locus of load-induced changes. We also observed increased expression of the nociceptive neuropeptide CGRP and its receptor components (CRLR, RAMP1), suggesting that local mechanical strain and microvascular adaptation may trigger nociceptive responses. Ex vivo analyses of spinal tissues from cLBP patients confirmed co-localization of inflammatory markers with opioid receptor (OR) clustering. Additionally, we found altered stress-relaxation properties in the ligament extracellular matrix due to modified water uptake in regions of high load and inflammation. We further showed that inflammation-associated factors modulate MOR via distinct mechanisms. Reactive oxygen species (ROS) modified transmembrane cysteine residues, disrupting disulfide bonds and impairing G-protein signaling. In contrast, extracellular acidosis enhanced activation of the pH-sensitive MOR ligand NFEPP without altering receptor structure. NFEPP remained effective even under high ROS levels typical of inflamed tissues, highlighting its potential as a site-specific analgesic. However, the direct link between mechanical adaptation, local immune dysregulation, and OR clustering remains to be confirmed as a therapeutic target. In the next funding period, we will investigate the mechanistic basis of this mechano-inflammatory link to pain and assess whether these mechanically induced neuroimmune changes are reversible. Using our tail-loading model with altered spinal curvature, we will study the temporal dynamics between bone remodeling, immune infiltration, and nociceptive signaling. Our model mimics human spinal curvature and replicates the heterogeneity of strain-induced tissue adaptations, including effects on adjacent spinal segments. We will elucidate the spatial resolution of load-induced tissue adaptations regarding their co-localization with macrophages, CD8 vs. CD4 T cells, and OR expression in affected and adjacent tissues. Murine findings will be validated through ex vivo analyses of spinal tissues from cLBP patients. We will also extend OR modulation studies to include extracellular purines and reactive nitrogen species, based on our clinical data linking them to the cLBP microenvironment.
DFG Programme
Research Units
Subproject of
FOR 5177:
The Dynamics of the Spine: Mechanics, Morphology and Motion towards a comprehensive Diagnosis of Low Back Pain
Co-Investigators
Professorin Dr. Sara Checa Esteban; Dr. Sandra Reitmaier
