Sex Differences in Rat Intervertebral Disc Structure and Function Following Annular Puncture Injury

Abstract

Study Design. A rat puncture injury intervertebral disc (IVD) degeneration model with structural, biomechanical, and histological analyses. Objective. To determine if males and females have distinct responses in the IVD after injury. Summary of Background Data. Low back pain (LBP) and spinal impairments are more common in women than men. However, sex differences in IVD response to injury have been underexplored, particularly in animal models where sex differences can be measured without gender confounds. Methods. Forty-eight male and female Sprague Dawley rats underwent sham, single annular puncture with tumor necrosis factor α (TNFα) injection (1×), or triple annular puncture with TNFα injection (3×) surgery. Six weeks after surgery, lumbar IVDs were assessed by radiologic IVD height, spinal motion segment biomechanical testing, histological degeneration grading, second harmonic generation (SHG) imaging, and immunofluorescence for fibronectin and α-smooth muscle actin. Results. Annular puncture injuries significantly increased degenerative grade and IVD height loss for males and females, but females had increased degeneration grade particularly in the annulus fibrosus (AF). Despite IVD height loss, biomechanical properties were largely unaffected by injury at 6 weeks. However, biomechanical measures sensitive to outer AF differed by sex after 3× injury—male IVDs had greater torsional stiffness, torque range, and viscoelastic creep responses. SHG intensity of outer AF was reduced after injury only in female IVDs, suggesting sex differences in collagen remodeling. Both males and females exhibited decreased cellularity and increased fibronectin expression at injury sites. Conclusion. IVD injury results in distinct degeneration and functional healing responses between males and females. The subtle sex differences identified in this animal model suggest differences in response to IVD injury that might explain some of the variance observed in human LBP, and demonstrate the need to better understand differences in male and female IVD degeneration patterns and pain pathogenesis. Level of Evidence: N/A

Males and females exhibit distinct relationships between intervertebral disc degeneration and pain in a rat model

“…This study identified relationships between structural and functional measures of IVD degeneration and measures of pain by using network analysis to construct sex-specific correlation networks. We hypothesized that females and males would differ in their relationships between IVD injury and pain with more correlation between measures of pain and IVD degeneration in the male network, due to previous findings of subtle sex differences in fibrotic IVD degenerative changes 32 and known sex differences in pain 20,21 . The most important findings were the sex differences between the correlational networks where injury was associated with pain measures in males and not in females.…”

“…Sections were stained for collagen and glycosaminoglycans with picrosirius red and alcian blue (PR/ AB), respectively. PR/AB stained sections were evaluated by three blinded evaluators using a semi-quantitative system to determine degeneration grade, that evaluates annulus fibrosus (AF) integrity, nucleus pulposus (NP) cellularity, NP matrix quality, interruption of AF/NP border, and endplate irregularity, that is sensitive to puncture-induced degenerative changes 32,77 .…”

“…This study determined which measures of structural and functional IVD degeneration are most related to pain measurements in a rat model of low back pain and determined how these relationships between IVD changes and pain assays differ between males and females. A previously developed surgical rat discogenic pain model was used 32,34,35 . We hypothesized that males and females would have distinct correlations within their networks, with more correlations between measures of IVD degeneration and pain found in the male network and estrus stage as a possible confound in the female network.…”

Leptin signaling and the intervertebral disc: Sex dependent effects of leptin receptor deficiency and Western diet on the spine in a type 2 diabetes mouse model

“…The testing protocol was adopted from our previous studies [35–37]. In brief, on the day of testing, after 10 mins in PBS for thawing and hydrating, the motion segment specimens were loaded into parallel-platens of an axial loading machine (Bose ElectroForce 3220; TA Instruments, New Castle, DE, USA) using a custom-designed fixture with a fluid bath of PBS for axial testing.…”

Quantitative analysis of intervertebral disc degeneration using Q‐space imaging in a rat model

“…by averaging disc height measured from the one fourth, middle, and the three-fourths portion of the adjacent endplate width. 28 F I G U R E 2 Sections of histology and magnetic resonance imaging scan with a conventional circularly polarized birdcage resonator. The histology and magnetic resonance imaging in this figure was obtained from the same sample.…”