Protein associated with Myc (PAM) is a giant E3 ubiquitin ligase of 510 kDa. Although the role of PAM during neuronal development is well established, very little is known about its function in the regulation of synaptic strength. Here we used multiepitope ligand cartography (MELC) to study protein network profiles associated with PAM during the modulation of synaptic strength. MELC is a novel imaging technology that utilizes biomathematical tools to describe protein networks after consecutive immunohistochemical visualization of up to 100 proteins on the same sample. As an in vivo model to modulate synaptic strength we used the formalin test, a common model for acute and inflammatory pain. MELC analysis was performed with 37 different antibodies or fluorescence tags on spinal cord slices and led to the identification of 1390 PAM-related motifs that distinguish untreated and formalin-treated spinal cords. The majority of these motifs related to ubiquitin-dependent processes and/or the actin cytoskeleton. We detected an intermittent colocalization of PAM and ubiquitin with TSC2, a known substrate of PAM, and the glutamate receptors mGluR5 and GLUR1. Importantly these complexes were detected exclusively in the presence of F-actin. A direct PAM/F-actin interaction was confirmed by colocalization and cosedimentation. The binding of PAM toward F-actin varied strongly between the PAM splice forms found in rat spinal cords. PAM did not ubiquitylate actin or alter actin polymerization and depolymerization. However, F-actin decreased the ubiquitin ligase activity of purified PAM. Because PAM activation is known to involve its translocation, the binding of PAM to F-actin may serve to control its subcellular localization as well as its activity. Taken together we show that defining protein network profiles by topological proteomics analysis is a useful tool to identify previously unknown protein/protein interactions that underlie synaptic processes. Molecular & Cellular Proteomics 7:2475-2485, 2008.Synapses are dynamic structures that expand, retract, and remodel to accomplish activity-dependent modification of neuronal circuits. During peripheral inflammation, the synaptic contacts between primary sensory neurons and dorsal horn neurons are modified in a way that the responsiveness of the system to subsequent stimuli is increased, resulting in hypersensitivity to noxious stimuli (1, 2). These activity-dependent changes in synaptic morphology and strength are based on many different mechanisms including alterations in ion channel and receptor activities due to phosphorylation by protein kinases, the translocation of ␣-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) 1 receptors to the postsynaptic membrane (3, 4), transcription-and translation-dependent changes in protein expression (2, 5), and ubiquitylation-mediated protein degradation (6). Often these changes occur only at a few synapses, making the analysis by common proteomics techniques extremely difficult. Multiepitope ligand cartography (MELC) is a novel i...

Sphingosine 1-Phosphate (S1P) modulates various cellular functions such as apoptosis, cell differentiation, and migration. Although S1P is an abundant signaling molecule in the central nervous system, very little is known about its influence on neuronal functions. We found that S1P concentrations were selectively decreased in the cerebrospinal fluid of adult rats in an acute and an inflammatory pain model. Pharmacological inhibition of sphingosine kinases (SPHK) decreased basal pain thresholds and SphK2 knock-out mice, but not SphK1 knock-out mice, had a significant decrease in withdrawal latency. Intrathecal application of S1P or sphinganine 1-phosphate (dihydro-S1P) reduced the pain-related (nociceptive) behavior in the formalin assay. S1P and dihydro-S1P inhibited cyclic AMP (cAMP) synthesis, a key second messenger of spinal nociceptive processing, in spinal cord neurons. By combining fluorescence resonance energy transfer (FRET)-based cAMP measurements with Multi Epitope Ligand Cartography (MELC), we showed that S1P decreased cAMP synthesis in excitatory dorsal horn neurons. Accordingly, intrathecal application of dihydro-S1P abolished the cAMP-dependent phosphorylation of NMDA receptors in the outer laminae of the spinal cord. Taken together, the data show that S1P modulates spinal nociceptive processing through inhibition of neuronal cAMP synthesis.The bioactive sphingolipid metabolite sphingosine 1-phosphate (S1P) 2 is synthesized by phosphorylation of sphingosine by sphingosine kinases (SPHK) in a wide variety of cell types in response to extracellular stimuli such as nerve growth factor or vascular endothelial growth factor. S1P modulates diverse cellular functions such as apoptosis, cell differentiation, and migration either through the activation of a family of five G-protein-coupled receptors (S1P 1-5 ) or by acting as an intracellular second messenger (1-3). In the central nervous system S1P has been shown to be released by cerebellar granule cells and astrocytes (4 -6). Regarding its function in the central nervous system it is well known that S1P promotes survival of neurons and astrocytes, induces proliferation of neural progenitor cells and astrocytes, and mediates nerve growth factor (NGF)-stimulated neurite outgrowth (2, 3, 7). However, very little is known about the role of S1P in the regulation of neuronal excitability and the mechanisms that mediate these S1P functions. Recently whole cell patch clamp recordings revealed that loss of S1P 2 leads to a large increase in the excitability of neocortical pyramidal neurons (8), suggesting an inhibitory effect of S1P 2 on neuronal excitability. On the other hand, several in vitro studies show that S1P can also increase neuronal functions. For example, S1P receptor activation augments glutamate secretion in hippocampal neurons (9) and elevated intracellular S1P concentrations enhance the spontaneous neurotransmitter release at neuromuscular junctions (10). Furthermore, intra-as well as extracellularly applied S1P facilitated the NGF-induced increas...

Cyclooxygenase-2 (COX-2)-dependent prostaglandin (PG) E2 synthesis in the spinal cord plays a major role in the development of inflammatory hyperalgesia and allodynia. Microsomal PGE2 synthase-1 (mPGES-1) isomerizes COX-2-derived PGH2 to PGE2. Here, we evaluated the effect of mPGES-1-deficiency on the noci-ceptive behavior in various models of nociception that depend on PGE2 synthesis. Surprisingly, in the COX-2-dependent zymosan-evoked hyperalgesia model, the nociceptive behavior was not reduced in mPGES-1-deficient mice despite a marked decrease of the spinal PGE2 synthesis. Similarly, the nociceptive behavior was unaltered in mPGES-1-deficient mice in the formalin test. Importantly, spinal cords and primary spinal cord cells derived from mPGES-1-deficient mice showed a redirection of the PGE2 synthesis to PGD2, PGF2α and 6-keto-PGF1α (stable metabolite of PGI2). Since the latter prostaglandins serve also as mediators of noci-ception they may compensate the loss of PGE2 synthesis in mPGES-1-deficient mice.

Multi-Epitope-Ligand-Carthography (MELC) allows consecutive immunohistochemical visualization of up to 100 proteins on the same tissue sample. Subsequent biomathematical analysis of these images allows a quantitative description of changes in protein networks. We used the MELC technology to study the effect of the nonopioid analgesic drug dipyrone on protein network profiles associated with arachidonic acid-dependent signaling pathways. MELC analysis with 31 different fluorescence-labeled tags was used to compare the effect of dipyrone on protein networks in spinal cords of mice with zymosan-induced hyperalgesia, a common model for inflammatory pain. We found that the number of motifs which describe the colocalization of 5-lipoxygenase (5-LO) or 12-LO with other proteins increased disproportionally after dipyrone treatment. Activation of 5-LO and 12-LO induces their translocation to membrane compartments which was also reflected by MELC results. Although no changes in 5-LO or 12-LO expression were seen by Western blot analysis or by immunohistochemistry in spinal cords of dipyrone-treated mice, the activation of both enzymes was verified by determining LO-products. Spinal amounts of 5(S)-hydroxyeicosatetraenoic acid (HETE) and 12(S)-HETE, which are generated by 5-LO and 12-LO, respectively, were significantly increased in spinal cords of dipyrone-treated animals. In primary spinal cord neurons, dipyrone selectively and dose-dependently increased 5(S)-(HETE) and 12(S)-HETE synthesis. Thus, we show for the first time that monitoring protein network profiles by topological proteomic analysis is a useful tool to identify mechanisms of drug actions.

These findings illustrate that impaired monocyte/macrophage recruitment is responsible for reduced collateral growth under diabetic conditions but not in arterial hypertension suggesting that diabetes mellitus in particular affects early stages of collateral growth whereas hypertension has its impact on later remodeling stages. Successful pro-arteriogenic treatment strategies in a patient population that presents with diabetes mellitus and arterial hypertension need to address different stages of collateral growth and thus different molecular and cellular targets simultaneously.