This study examined the impact of chronic pain from spinal cord injury on two skeletal muscle proteins, desmin and αB-crystallin, in a rat model. The researchers hypothesized the proteins' concentrations would change compared to controls based on previous human research. However, the results found no significant differences in the concentrations of desmin or αB-crystallin between control rats and rats with spinal cord injury. This disagrees with the previous human study and may be due to differences between rodent models of pain and human chronic pain conditions.

1. Skeletal Muscle Response to Systemic Inflammation from Chronic Pain
and its Impact on Functional Proteins
Kristian A. Spirakis1, Kaitlin A. Letsinger1, Sonja K. Bareiss1, Kori L. Brewer2, Terry E. Jones1
Depts. of Physical Therapy1 and Emergency Medicine2, East Carolina University, Greenville, NC
INTRODUCTION
RESULTS
SUMMARY OF RESULTS
REFERENCES
ACKNOWLEDGEMENTS
MATERIALS & METHODS
Clinicians treat an extensive number of patients with chronic
pain that present with muscle weakness and gait disturbances.
Exercise is typically prescribed as a way to alleviate pain but
alterations in muscle function and structure may provide
limitations. An additional effect of pain due to an injury is an
inflammatory response. We examined the relative change in
two proteins, αB-crystallin and desmin, that are involved with
inflammation and force in skeletal muscle. Previous research
on the impact of chronic pain on skeletal muscle suggests that
αB-crystallin concentration increases and desmin
concentration decreases compared to controls (1). Therefore
we hypothesized that there will be similar trends in the
content of desmin and αB-crystallin in a rat model of chronic
pain. αB-crystallin makes up the core of many heat shock
proteins, which are abundant in skeletal muscle and
upregulated with stress conditions. The main role of αB-
crystallin is to prevent aggregation of faulty proteins.
Specifically in skeletal muscle, αB-crystallin functions to
protect and stabilize sarcomeric units and are involved in Z-
disk maintenance (2). Desmin is an intermediate filament
protein found outside the sarcomeres at Z-disks to link the
sarcomeres together and to the muscle membrane. It is
responsible for organization and stabilization of the
sarcomeres and effective force transmission (3). Together these
proteins function to maintain myofibril structure by keeping
the Z-disks in alignment resulting in proper muscle
contraction.
Thank you to Mary Greyard, Michaela Morris, Jordan Griffin,
and Carter Smith for technical assistance. Funding was
provided by Craig H Neilsen Foundation to SKB and KLB.
Rats were randomly assigned to control or spinal cord injury
(SCI) groups. Animals in the SCI group underwent excitotoxic
(quis) injury which is a chronic pain model. Twenty-two days
after injury EDL muscles were excised, weighed, and
homogenized. The muscle homogenates were used for Western
blot analysis probing for αB-crystallin and desmin. SCI animals
exhibiting pain behavior (PB) were analyzed separately from SCI
animals not exhibiting pain behaviors. Films were scanned and
analyzed using Sigma Scan (Jandel Scientific). Statistical analysis
was completed by a single factor ANOVA.
There is no significant difference in desmin or αB-
crystallin content in skeletal muscle.
(1) Olausson, P. (2015) Scientific Reports, 5:11894: 1-14
(2) Dubinska-Magiera, M. (2014) FEBS Letters, 517-530
(3) Meyer, G. (2012) AJP – Cell Physiol, 302, C1609-C1620.
DISCUSSION
Figure 3: Normalized αB-crystallin protein content in EDL muscle. Values
represent means ± SE (P < 0.05). n=8-15 for all groups.
The research into the effects of chronic pain on skeletal
muscle is relatively new. Our results showed no
differences in the skeletal muscle content of desmin and
αB-crystallin which does not agree with the one study in
humans with fibromyalgia. There may be several
reasons for this including:
• shorter pain duration
• unknown frequency and pattern of movement
between rats and humans that have pain
• unknown consequence of pain on muscle peripheral
to the source of pain
• difference in SCI model of pain in animals compared
to fibromyalgia in humans
As physical therapy students, we chose to examine these
two proteins because of their large impact on function;
however, these proteins may not be affected by chronic
pain of this duration. The literature describes that
muscles adaptation to a chronic stimulus is seen in
energy systems before force producing systems. Thus,
research into energy system changes in a chronic pain
model may be warranted. The literature suggests that
generally fast muscle is more affected by pathologies
than slow muscle, therefore, we examined EDL. Future
research should look to see if there are changes seen in a
slow muscle.
Figure 1: Desmin and αB-crystallin location in the muscle cell (1).
Figure 2: Normalized desmin protein content in EDL muscle. Values
represent means ± SE (P<0.05). n=5-12 for all groups.
0
0.2
0.4
0.6
0.8
1
1.2
Sham Quis Quis-PB
NormalizedAU
αB-crystallin
0
0.2
0.4
0.6
0.8
1
1.2
Sham Quis Quis-PB
NormalizedAU
Desmin