Souzan Salemi, Lorenzo Kaeser, Janine Rethage, Beat A. Michel, Renate E. Gay, Steffen Gay, Haiko Sprott, Zurich, Switzerland
Dysregulation of kappa (KOR) and delta opioid (DOR) receptors may be a reason for severe and persistent pain and therapeutical failure in fibromyalgia (FM) patients. The aim of the present study was to localize these receptors in muscle tissues by in-situ RT-PCR and immunohistochemical (IHC) methods.
Muscle biopsies were obtained from 12 patients diagnosed for FM according to the ACR criteria (all women, 30-65 years of age). Normal brain tissue was taken as a positive control. Pieces of muscle samples from each patient were rapidly frozen in isopentane, cooled with liquid nitrogen and covered with OCT (Tissue-Tek®) embedding medium. 6 cryostat sections were fixed and used for further experiments. To search for the cellular localization of the opioid receptors mRNA in the tissues in-situ RT-PCR on muscle tissues and normal brain tissue was performed. Rabbit polyclonal IgG anti-human KOR antibodies (60711A, Pharmingen, San Diego, CA), and rabbit polyclonal IgG anti-human DOR antibodies (DiaSorin, Minnesota) were employed as primary antibodies for IHC. To examine whether opioid receptors are produced in satellite cells, monoclonal antibodies against human CD34 (Pharmingen) a marker of quiescent satellite cells in muscle, were used for double labeling.
DOR mRNA was abundantly expressed in normal brain as well as in the muscle of FM patients detected by in-situ RT-PCR. DOR mRNA was observed on the surface of certain muscle fibers. Immunoreactivity for KOR or DOR was seen in muscle tissues of normal individuals and FM patients. In FM muscle, DOR was distributed more widely than KOR which is in accordance with our previous results showing higher expression of DOR by real-time PCR. These receptors were also found to be expressed on the surface of certain muscle cells. By utilizing antibodies against human CD34 a similar pattern of expression could be observed suggesting the expression of opioid receptors in satellite cells.
Since satellite cells contribute to repair and regeneration of damaged myofibers. The present study for the expression of opioid receptors in muscle satellite cells may help in understanding pathophysiology and pain in FM patients.
Disclosure: Dr. Salemi was supported by the Zurzach foundation and Dr. Sprott by the American Fibromyalgia Syndrome Association and all others by their institutions.