IntroductionFibromyalgia (FM) is characterized by chronic pain and reduced pain threshold. The pathophysiology involves disturbed neuroendocrine function, including impaired function of the growth hormone/insulin-like growth factor-1 axis. Recently, microRNAs have been shown to be important regulatory factors in a number of diseases.The aim of this study was to try to identify cerebrospinal microRNAs with expression specific for FM and to determine their correlation to pain and fatigue. MethodsThe genome-wide profile of microRNAs in cerebrospinal fluid was assessed in ten women with FM and eight healthy controls using real-time quantitative PCR. Pain thresholds were examined by algometry. Levels of pain (FIQ pain) were rated on a 0-100 mm scale (fibromyalgia impact questionnaire, FIQ). Levels of fatigue (FIQ fatigue) were rated on a 0-100 mm scale using FIQ and by multidimensional fatigue inventory (MFI-20) general fatigue (MFIGF).ResultsExpression levels of nine microRNAs were significantly lower in patients with FM patients compared to healthy controls. The microRNAs identified were miR-21-5p, miR-145-5p, miR-29a-3p, miR-99b-5p, miR-125b-5p, miR-23a-3p, 23b-3p, miR-195-5p, miR-223-3p.The identified microRNAs with significantly lower expression in FM were assessed with regard to pain and fatigue. miR-145-5p correlated positively with FIQ pain (r=0.709, p=0.022, n=10) and with FIQ fatigue (r=0.687, p=0.028, n=10). ConclusionTo our knowledge, this is the first study to show a disease-specific pattern of cerebrospinal microRNAs in FM.We have identified nine microRNAs in cerebrospinal fluid that differed between FM patients and healthy controls. One of the identified microRNAs, miR-145 was associated with the cardinal symptoms of FM, pain and fatigue.

Infection, tissue damage, or other conditions can lead to a neuroinflammatory state. Lipopolysaccharide (LPS) exposure can be used experimentally as a model to generate an inflammatory response both in vitro and in vivo. Endotoxin, or LPS, is a potent inflammatory activator (1) in astrocytes and microglia, with stimulation of Toll-like receptor 4 (TLR4) (2). The expression of TLR4 is up-regulated in astrocytes under neuroinflammatory conditions (3). Activation of TLR4 leads to activation of nuclear factor-B, a factor that regulates expression of genes involved in immune responses, including release of the proinflammatory cytokines tumor necrosis factor-␣ (TNF-␣) and interleukin-1␤ (IL-1␤) (2).Astrocytes in networks, positioned between the vasculature and synapses, monitor neuronal signaling, including rebuilding of synapses (4, 5). Astrocytes express almost the same repertoire of receptors and ion channels as neurons. They regulate synaptic transmission via a bidirectional communication with neurons, and they release gliotransmitters as well as factors, including cytokines, fatty acid metabolites, and free radicals (6 -8).The Ca 2ϩ signaling in astrocytes over long distances is analogous to, but much slower than, the propagation of action potentials in neurons (9). These astrocytic Ca 2ϩ waves (10, 11) can be evoked by transmitters released from neurons and glial cells, followed by activation of especially G protein-coupled receptors. Cytosolic Ca 2ϩ plays a key role as a second messenger, and the control of Ca 2ϩ signals is therefore critical. This involves coordination of Ca 2ϩ entry across the plasma membrane (PM), 2 Ca 2ϩ release from the endoplasmatic reticulum (ER), refilling of the ER stores, and extrusion across the PM (12). The Na ϩ -Ca 2ϩ exchanger, a Ca 2ϩ transporter that controls the intracellular Ca 2ϩ concentrations, is driven by the Na ϩ electrochemical gradient across the PM. This Na ϩ pump, Na ϩ /K ϩ -ATPase, indirectly modulates Ca 2ϩ signaling (13), and inflammatory stimuli influence Ca 2ϩ homeostasis in the astrocyte networks (5, 14 -16).The cytoskeleton seems to be important in this system for controlling of PM microdomains and the ER complex. The adaptor protein ankyrin B is associated with the Na ϩ pump and also with ER proteins, such as the inositol 1,4,5-trisphosphate (IP 3 ) receptor. The main cytoplasmic matrix of proteins, spectrin and actin, are attached to ankyrin B. An intact cytoskeleton is required for the propagation of astrocytic Ca 2ϩ waves (17)

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