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. 2015 Jul 16;48(10):2210-3.
doi: 10.1016/j.jbiomech.2015.03.029. Epub 2015 Apr 3.

Lubricin deficiency in the murine lumbar intervertebral disc results in elevated torsional apparent modulus

Erin Teeple  1 , Koosha Aslani  2 , Matthew R Shalvoy  2 , Jade E Medrano  2 , Ling Zhang  3 , Jason T Machan  4 , Braden C Fleming  5 , Gregory D Jay  6
Affiliations

Lubricin deficiency in the murine lumbar intervertebral disc results in elevated torsional apparent modulus

Erin Teeple et al. J Biomech. .

Abstract

The purpose of this study was to investigate the mechanical consequences of proteoglycan 4 (Prg4) deficiency on intervertebral disc mechanics using a Prg4 knockout mouse model. Prg4, also called lubricin, was first identified as the boundary lubricant in synovial fluid but has subsequently been localized within a number of musculoskeletal tissues in areas subjected to shear and tensile stresses, including the intervertebral disc. The function of lubricin in the intervertebral disc has not been determined. Lumbar level 1-2 vertebral body-disc-vertebral body motion segments were isolated from Prg4 null mice and wild type (WT) litter mate controls. Disc dimensions were measured and motion segments were tested in axial loading and torsion. Torque measurements and disc dimensions were used to calculate the torsional apparent modulus for discs from Prg4 null and WT discs. Discs from Prg4 null mice had a significantly smaller mean transverse disc area (p=0.0057), with a significantly larger proportion of this area occupied by the nucleus pulposus (p<0.0001), compared to WT specimens. Apparent torsional moduli were found to be elevated in Prg4 null lumbar discs compared to WT controls at 10-10° (p=0.0048) and 10-30° (p=0.0127) rotation. This study suggests a functional role for Prg4 in the murine intervertebral disc. The absence of Prg4 was associated with an increased apparent torsional modulus and the structural consequences of Prg4 deficiency in the intervertebral disc, with expansion of the area of the nucleus pulposus relative to the transverse disc area in Prg4 null specimens.

Keywords: Apparent torsional modulus; Disc; Lubricin; Prg4; Proteoglycan 4.

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Conflict of interest statement

Conflict of Interest: G.D.J. has authored patents on lubricin and PRG4. Patent numbers are USPTO#6743774, 6960562, and 7001881. Other authors have no conflicts of interest.

Figures

Figure 1
Figure 1
Gross dissection of the thoracolumbar spine for 10-week-old male mice, WT (A, C) and PRG4 −/−(B, D). Note the scoliosis (B, arrow) and kyphosis (D, arrow) of the PRG 4 −/− specimen.
Figure 2
Figure 2
Testing apparatus for torsional modulus calculations: Axial load cell (A), Torsion load cell (B), Mounted vertebral body-disc-vertebral body segment (C), and Torsional actuator (D).
Figure 3
Figure 3
Rotational Stiffness (A) and Apparent Torsional Modulus (B).
See this image and copyright information in PMC

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