This study focuses on the effect of -opioid receptor agonists on CXCR4 signaling in neurons and the mechanisms involved in regulation of neuronal CXCR4 by opiates. The data show that CXCR4 is negatively modulated by long-term morphine treatments both in vitro and in vivo; CXCR4 inhibition is caused by direct stimulation of -opioid receptors in neurons, leading to alterations of ligand-induced CXCR4 phosphorylation and upregulation of protein ferritin heavy chain (FHC), a negative intracellular regulator of CXCR4. Reduced coupling of CXCR4 to G-proteins was found in the brain of morphine-treated rats, primarily cortex and hippocampus. CXCR4-induced G␣ i /G␤␥ activities were suppressed after 24 h treatment of cortical neurons with morphine or the selective -opioid agonist DAMGO (D-Ala2-NMe-Phe 4 -glycol 5 -enkephalin), as shown by analysis of downstream targets of CXCR4 (i.e., cAMP, Akt, and ERK1/2). These agonists also prevented CXCL12-induced phosphorylation of CXCR4, indicating a deficit of CXCR4 activation in these conditions. Indeed, morphine (or DAMGO) inhibited prosurvival signaling in neurons. These effects are not attributable to a reduction in CXCR4 expression or surface levels but rather to upregulation of FHC by opioids. The crucial role of FHC in inhibition of neuronal CXCR4 was confirmed by in vitro and in vivo RNA interference studies. Overall, these findings suggest that opiates interfere with normal CXCR4 function in the brain. By this mechanism, opiates could reduce the neuroprotective functions of CXCR4 and exacerbate neuropathology in opiate abusers who are affected by neuroinflammatory/infectious disorders, including neuroAIDS.

Postmitotic neurons need to keep their cell cycle under control to survive and maintain a differentiated state. This study aims to test the hypothesis that the chemokine CXCL12 regulates neuronal survival and differentiation by promoting Rb function, as suggested by previous studies showing that CXCL12 protects neurons from apoptosis induced by Rb loss. To this end, the effect of CXCL12 on Rb expression and transcriptional activity and the role of Rb in CXCL12-induced neuronal survival were studied. CXCL12 increases Rb protein and RNA levels in rat cortical neurons. The chemokine also stimulates an exogenous Rb promoter expressed in these neurons and counteracts the inhibition of the Rb promoter induced by E2F1 overexpression. Furthermore CXCL12 stimulates Rb activity as a transcription repressor. The effects of CXCL12 are mediated by its specific receptor CXCR4, and do not require the presence of glia. Finally, shRNA studies show that Rb expression is crucial to the neuroprotective activity of CXCL12 as indicated by NMDA-neurotoxicity assays. These findings suggest that proper CXCR4 stimulation in the mature CNS can prevent impairment of the Rb-E2F pathway and support neuronal survival. This is important to maintain CNS integrity in physiological conditions and prevent neuronal injury and loss typical of many neurodegenerative and neuroinflammatory conditions. Cell Death and Differentiation ( 1,2 Stimulation of CXCR4 by its endogenous ligand leads to activation of intracellular pathways affecting neuronal survival, migration, and neurotransmission.1,3 For instance, CXCR4 stimulates the PI3K/Akt pathway and regulates cell-cycle proteins in neurons. [3][4][5][6] Under pathological conditions at least some of these essential CXCR4 functions are compromised, leading to neuronal dysfunction/death. 1,7 Thus, a complete understanding of the effects of CXCR4 activation in the brain has important physiological and pathological implications.Rb is a well-known transcriptional repressor, which controls cell-cycle progression, differentiation/survival, and genomic integrity. Rb is also implicated in fundamental CNS developmental processes such as, neuronal migration, differentiation, and neurite extension. 8,9 The effects of Rb on cell survival are primarily due to regulation of members of the E2F family of transcription factors, though Rb can also directly inactivate proapoptotic proteins, such as pp32.10 E2F proteins stimulate expression of genes promoting cell-cycle progression in proliferating cells, whereas they induce apoptotic genes in differentiated cells, including neurons.11 Rb is phosphorylated at several phosphoacceptor sites by specific kinases. 12 Hence, the immediate effect of Rb phosphorylation is to remove Rb from its specific promoters, leading to inhibition of Rb-dependent gene repression. Rb phosphorylation results in enhanced E2F1 transcriptional activity culminating in death of postmitotic neurons.11 Alterations of Rb/E2F pathway were reported in various neuropathologies, such as Parkinson's and Alzhei...

We have previously shown that the chemokine fractalkine promotes the adhesion of human prostate cancer cells to bone marrow endothelial cells as well as their migration toward human osteoblasts in vitro. Thus, the interaction of fractalkine with its receptor CX3CR1 could play a crucial role in vivo by directing circulating prostate cancer cells to the bone. We found that although CX3CR1 is minimally detectable in epithelial cells of normal prostate glands, it is overexpressed upon malignant transformation. Interestingly, osteoblasts, stromal and mesenchymal cells derived from human bone marrow aspirates express the cell-bound form of fractalkine, whereas the soluble form of the chemokine is detected in bone marrow supernatants. To investigate the mechanisms regulating the levels of soluble fractalkine in the bone marrow, we focused on androgens, which play a critical role in both prostate cancer progression and skeletal metastasis. Here, we show that dihydrotestosterone dramatically increases the cleavage of fractalkine from the plasma membrane of bone cells and its action is reversed by nilutamide-an antagonist of the androgen receptor-as well as the wide-spectrum inhibitor of matrix metalloproteases, GM6001. However, dihydrotestosterone was unable to induce fractalkine-cleavage from human bone marrow endothelial cells. Thus, androgens could promote the extravasation of CX3CR1-bearing cancer cells on a fractalkine concentration gradient, while leaving unaltered their ability to adhere to the bone marrow endothelium. In conclusion, our results indicate that CX3CR1, fractalkine, and the enzymes responsible for its cleavage might represent suitable targets for therapies aiming to counteract skeletal secondary tumors from prostate adenocarcinoma. [Cancer Res 2008;68(6):1715-22]

These 2 cases are clinicopathologically distinct from typical dura-associated cases of CJD. They may be a subtype with florid-type plaques in dura-associated CJD.

We sought to evaluate the potential of C17.2 neural progenitor cells (NPCs) engineered to secrete glial cell line-derived neurotrophic factor (GDNF) to survive, differentiate and promote functional recovery following engraftment into the brains of adult male Sprague-Dawley rats subjected to lateral fluid percussion brain injury. First, we demonstrated continued cortical expression of GDNF receptor components (GFRalpha-1, c-Ret), suggesting that GDNF could have a physiological effect in the immediate post-traumatic period. Second, we demonstrated that GDNF over-expression reduced apoptotic NPC death in vitro. Finally, we demonstrated that GDNF over-expression improved survival, promoted neuronal differentiation of GDNF-NPCs at 6 weeks, as compared with untransduced (MT) C17.2 cells, following transplantation into the perilesional cortex of rats at 24 h post-injury, and that brain-injured animals receiving GDNF-C17.2 transplants showed improved learning compared with those receiving vehicle or MT-C17.2 cells. Our results suggest that transplantation of GDNF-expressing NPCs in the acute post-traumatic period promotes graft survival, migration, neuronal differentiation and improves cognitive outcome following traumatic brain injury.