Stroke leads to brain damage with subsequent slow and incomplete recovery of lost brain functions. Enriched housing of stroke-injured rats provides multi-modal sensorimotor stimulation, which improves recovery, although the specific mechanisms involved have not been identified. In rats housed in an enriched environment for two weeks after permanent middle cerebral artery occlusion, we found increased sigma-1 receptor expression in peri-infarct areas. Treatment of rats subjected to permanent or transient middle cerebral artery occlusion with 1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)piperazine dihydrochloride, an agonist of the sigma-1 receptor, starting two days after injury, enhanced the recovery of lost sensorimotor function without decreasing infarct size. The sigma-1 receptor was found in the galactocerebroside enriched membrane microdomains of reactive astrocytes and in neurons. Sigma-1 receptor activation increased the levels of the synaptic protein neurabin and neurexin in membrane rafts in the peri-infarct area, while sigma-1 receptor silencing prevented sigma-1 receptor-mediated neurite outgrowth in primary cortical neuronal cultures. In astrocytic cultures, oxygen and glucose deprivation induced sigma-1 receptor expression and actin dependent membrane raft formation, the latter blocked by sigma-1 receptor small interfering RNA silencing and pharmacological inhibition. We conclude that sigma-1 receptor activation stimulates recovery after stroke by enhancing cellular transport of biomolecules required for brain repair, thereby stimulating brain plasticity. Pharmacological targeting of the sigma-1 receptor provides new opportunities for stroke treatment beyond the therapeutic window of neuroprotection.

expressed on the leading edge of membrane filopodia and colocalizes with a-actinin. Purified recombinant GPR56 extracellular domain protein inhibits glioma cell adhesion and causes abnormal cytoskeletal morphology and cell rounding. These results indicate that the extracellular domain may compete for unidentified ligand(s), and block the normal function of GPR56 in cell attachment. In reporter assays, overexpression of GPR56 activates the NF-jB, PAI-1 and TCF transcriptional response elements. These pathways have been implicated in cytoskeletal signaling, adhesion and tumor biology. The above results indicate that GPR56 serves as an adhesion GPCR and is involved in adhesion signaling.

The acute-phase reactant rabbit serum amyloid A 3 (SAA3) was identified as the major difference product in Ag-induced arthritis in the rabbit, a model resembling in many aspects the clinical characteristics of rheumatoid arthritis (RA) in humans. In Ag-induced arthritis, up-regulated SAA3 transcription in vivo was detected in cells infiltrating into the inflamed joint, in the area where pannus formation starts and, most notably, also in chondrocytes. The proinflammatory cytokine IL-1β induced SAA3 transcription in primary rabbit chondrocytes in vitro. Furthermore, rSAA3 protein induced transcription of matrix metalloproteinases in rabbit chondrocytes in vitro. In the human experimental system, IL-1β induced transcription of acute-phase SAA (A-SSA; encoded by SAA1/SAA2) in primary chondrocytes. Similar to the rabbit system, recombinant human A-SAA protein was able to induce matrix metalloproteinases’ transcription in chondrocytes. Further, immunohistochemistry demonstrated that A-SAA was highly expressed in human RA synovium. A new finding of our study is that A-SSA expression was also detected in cartilage in osteoarthritis. Our data, together with previous findings of SAA expression in RA synovium, suggest that A-SAA may play a role in cartilage destruction in arthritis.

Survival and maintenance of vertebrate neurons are influenced by neurotrophic factors which mediate their signal by binding to specific cell surface receptors. We determined the binding sites of human neurotrophin‐3 (NT‐3) to its receptors trkC and gp75 by mutational analysis and compared them to the analogous interactions of nerve growth factor (NGF) with trkA and gp75. The trkC binding site extends around the central beta‐strand bundle and in contrast to NGF does not make use of non‐conserved loops and the six N‐terminal residues. The gp75 epitope is dominated by loop residues and the C‐terminus of NT‐3. A novel rapid biological screening procedure allowed the identification of NT‐3 mutants that are able to signal efficiently through the non‐preferred receptors trkA and trkB, which are specific for NGF and BDNF respectively. Mutation of only seven residues in NT‐3 resulted in a human neurotrophin variant which bound to all receptors of the trk family with high affinity and efficiently supported the survival of NGF‐, BDNF‐ and NT‐3‐dependent neurons. Our results suggest that the specificity among neurotrophic factors is not solely encoded in sequence diversity, but rather in the way each neurotrophin interacts with its preferred receptor.

Death-associated protein kinase (DAPK) is a calcium calmodulin-regulated serine/threonine protein kinase involved in ischemic neuronal death. In situ hybridization experiments show that DAPK mRNA expression is up-regulated in brain following a global ischemic insult and down-regulated in ischemic tissues after focal ischemia. DAPK is inactive in normal brain tissues, where it is found in its phosphorylated state and becomes rapidly and persistently dephosphorylated and activated in response to ischemia in vivo. A similar dephosphorylation pattern is detected in primary cortical neurons subjected to oxygen glucose deprivation or N-methyl-D-aspartate (NMDA)-induced toxicity. Both a calcineurin inhibitor, FK506, and a selective NMDA receptor antagonist, MK-801, inhibit the dephosphorylation of DAPK after in vitro ischemia. This indicates that DAPK could be activated by NMDA receptor-mediated calcium flux, activation of calcineurin, and subsequent DAPK dephosphorylation. Moreover, concomitantly to dephosphorylation, DAPK is proteolytically processed by cathepsin after ischemia. Furthermore, a selective DAPK inhibitor is neuroprotective in both in vitro and in vivo ischemic models. These results indicate that DAPK plays a key role in mediating ischemic neuronal injury.Ischemic stroke is characterized by apoptotic and necrotic cell death leading to neuronal loss (1). To date, there is no effective neuroprotective drug in clinical use for the treatment of acute ischemic neuronal damage (2). Several biological processes have been proposed to contribute to ischemic cell death, including excitotoxicity, ionic imbalance, oxidative stress, and apoptosis (3). These pathological events in the brain trigger aberrant cell signaling (4) and subsequent gene expression (5), which have been studied to understand the pathophysiology of stroke. We have identified DAPK 2 as a protein regulated by ischemic conditions both in vitro and in vivo.DAPK is a Ca 2ϩ /calmodulin-regulated serine/threonine kinase that acts as a positive mediator of apoptotic pathways, including those involved in neuronal cell death. It is involved in Fas-, INF-␥-, tumor necrosis factor-(6), ceramide- (7), and p53-mediated apoptosis (8), as well as in the disruption of matrix survival signals and suppression of integrin-mediated cell adhesion (9). DAPK appears to function early in the apoptotic pathway prior to the commitment of the cells to apoptosis. DAPK has also been extensively implicated as a tumor suppressor whose inactivation predicts malignancy, as DAPK expression is frequently lost in tumors due to hypermethylation of the DAPK gene (10, 11).DAPK has a unique multidomain structure containing a kinase domain, a calmodulin regulatory segment, eight ankyrin repeats, a cytoskeleton binding region, and a death domain (12). DAPK is negatively regulated by autophosphorylation on serine 308 in the Ca 2ϩ /CaM regulatory domain. This autoregulation of DAPK serves as an inhibitory mechanism in the basal state (13). Dephosphorylation relieves autoinhibition and stim...