Naloxone and Ouabain in Ultralow Concentrations Restore Na+/K+-ATPase and Cytoskeleton in Lipopolysaccharide-treated Astrocytes

Abstract

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)

Glial dysfunction and persistent neuropathic postsurgical pain

“…Naloxone at ultralow concentrations has the ability to block -opioid receptor-coupling to the excitatory G s protein and causes theopioid receptor to couple to the inhibitory G i/o protein [110,111]. Naloxone can also restore to some extent, inflammatory disrupted actin filaments [77].…”

“…In astrocytes, Toll-like receptor 4 (TLR4) is an inflammatory receptor that responds to lipopolysaccharide (LPS) by increasing its expression and activity [76,77]. Activation of TLR4 leads to an increase in the release of the pro-inflammatory cytokines TNF-␣ and IL-1␤ [78].…”

Toll-Like Receptor-Triggered Calcium Mobilization Protects Mice against Bacterial Infection through Extracellular ATP Release

“…Although the recognition of PAMPs is specific to each TLR, individual TLRs mainly activate similar transcription factors, such as NF-B, activating protein 1, and interferon regulatory factors, driving specific immune responses (27). Meanwhile, LPS can also evoke a transient Ca 2ϩ increase in monocytes/macrophages and astrocytes (28,29). LPS induces a Ca 2ϩ increase through release from intracellular Ca 2ϩ stores instead of an extracellular Ca 2ϩ efflux (30).…”

The Role of NO/cGMP Signaling on Neuroinflammation: A New Therapeutic Opportunity

“…Under conditions that lead to neuroinflammation in the CNS, as in exposure to LPS, Ca [58,59], and these effects are hallmarks of astrocyte reaction on neuroinflammation.…”

“…In the astrocytic response, in addition to increased TLR4 levels, leading to the expression of a variety of chemokines and cytokines [55,58], other important processes occur, such as alteration of intracellular calcium signaling. Under conditions that lead to neuroinflammation in the CNS, as in exposure to LPS, Ca [58,59], and these effects are hallmarks of astrocyte reaction on neuroinflammation.…”