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Mechanical Strain Accelerates Intervertebral Disc Degeneration Through Circadian Rhythm Disruption

Circadian Rhythm

Goal of the Study?

The intervertebral disc often plays a role in back pain. In this study1 researchers were curious about how disrupting the natural circadian clock could influence the intervertebral disc and its degeneration. It is known that the intervertebral disc experiences night/day variations of load. During the night, the disc experiences significantly reduced internal stress when a person is lying down, while during waking hours of standing/walking or sitting, there is considerable higher stress. Excessive overload, commonly seen in night-shift workers, has been demonstrated to have more low back pain problems. These researchers wanted to answer whether disrupting an animal model’s circadian rhythm would affect the disc genetic expression through excessive mechanical loading.

 

Why are they doing this study?

The intervertebral disc and its tendency to degenerate is common in the human population. Those degenerative changes have been linked to those that get back pain but not in all cases. To take a closer look at the relationship between disc degeneration and back pain under the overarching theme of disturbed circadian rhythms, these researchers looked to gene expression deep within the disc’s extracellular matrix.

What was done?

Nucleus pulposus specimens were collected from twenty-one humans with disc degeneration and without disc degeneration (normal) according to the Pfiirrmann classification. mRNA sequencing of nine of these twenty-one patients was conducted. An animal experiment was conducted mimicking an upright posture by amputating the forelimbs of Sprague-Dawley Rats (SD).

Mechanical loading rat model

Forty-eight 3wk-old male SD rats were randomly divided into four different groups:

  1. non-shifted crawl group
  2. non-shifted upright group
  3. shifted crawl group
  4. shifted upright group

For the non-shifted groups, rats were placed under a constant 12:12 hr light/dark cycle. For the shifted groups, rats were exposed to a 24:24 hr light/dark cycle for three weeks and then changed to a 12:12 hr cycle fr one week. Food was elevated for the mechanical loading group, so the rats were forced to reach in a vertical orientation to obtain their meals. All rats were sacrificed at the nine and twelve-month point after operations for the disc nucleus extraction for immunochemical analysis.

What did they find?

Overall, the results demonstrated that excessive and prolonged mechanical loading of the intervertebral disc does influence by disrupting the intrinsic circadian rhythm of the intervertebral disc in the upright posture. Disc heights were significantly reduced in both the upright shifted and upright non-shifted rats when compared to matched controls. Interestingly, in the shifted group, there was no pronounced decrease in disc height. The authors speculated that shift work, by itself, did not disrupt the disc height and offered a comment that more time may be needed to see the effect of changing the light/day cycle on disc height or, more likely, that the upright mechanical load plays an important effect on disc height loss.

Overall, these researchers discussed that shift work could disrupt the circadian rhythm, leading to changes in disc degeneration. Furthermore, they also demonstrated how an upright posture animal model accelerated intervertebral disc degeneration.

 

Why do these findings matter?

As night-shift work appears to be related to intervertebral disc progression in some studies, learning what can help slow or even prevent back problems in this human workforce can be helpful to reduce disability and improve overall production.

 

At Dynamic Disc Designs, we believe that teaching the impact of mechanical load to patients can have an effect on changing behaviour to help mitigate back pain sources. Explore our dynamic disc models to help educate patients about load management of the spine.

 

 

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