One factor that impacts on microglial activation is the interaction between the ubiquitously expressed CD200 and CD200R, which is expressed only on microglia in the brain. Decreased signalling through CD200R, when CD200 expression is reduced, results in microglial activation and may, at least in part, explain the increased cell activity that is observed with age, in models of Alzheimer’s and Parkinson’s disease as well as in the human diseases. There is evidence of increased microglial activation in CD200-deficient mice, and isolated microglia prepared from these mice are more reactive to inflammatory stimuli like Toll-like receptor 2 and 4 agonists, and interferon-γ. Here, we examined the impact of CD200 deficiency on amyloid-β (Aβ)-induced changes in microglia and report, perhaps unexpectedly, that the effect of Aβ was attenuated in microglia prepared from CD200-deficient mice. The evidence indicates that this is a consequence of increased phagocytosis, associated with increased lysosomal activity in CD200-deficient microglia. The data suggest that mTOR-related signalling is decreased in these cells and that inhibiting mTOR by rapamycin increases phagocytosis. Thus, while the findings to date have emphasized the anti-inflammatory effects of CD200-CD200R interaction, the present evidence indicates a previously unreported impact on lysosomal function.

Mechanical priming can be employed in tissue engineering strategies to control the fate and differentiation pattern of mesenchymal stromal cells. This is relevant to regenerative medicine whereby mechanical cues can promote the regeneration of a specific tissue type from mesenchymal precursors. The ability of cells to respond to mechanical forces is dependent upon mechanotransduction pathways that involve membrane-associated proteins, such as integrins. During the aging process changes in the mechanotransduction machinery may influence how cells from aged individuals respond to mechanical priming. In this study mesenchymal stromal cells were prepared from young adult and aged rats and exposed to uniaxial tensile strain at 5% and 10% for 3 days, or 2.5% for 7 days. Application of 5% tensile strain had no impact on cell viability. In contrast, application of 10% tensile strain evoked apoptosis and the strain-induced apoptosis was significantly higher in the mesenchymal stromal cells prepared from the aged rats. In parallel to the age-related difference in cellular responsiveness to strain, an age-related decrease in expression of α2 integrin and actin, and enhanced lipid peroxidation was observed. This study demonstrates that mesenchymal stem cells from aged animals have an altered membrane environment, are more vulnerable to the pro-apoptotic effects of 10% tensile strain and less responsive to the pro-osteogenic effects of 2.5% tensile strain. Thus, it is essential to consider how aged cells respond to mechanical stimuli in order to identify optimal mechanical priming strategies that minimise cell loss, particularly if this approach is to be applied to an aged population.

The classical endogenous cannabinoid (CB) system is composed of the endocannabinoid signalling molecules, 2-arachidonoyl glycerol (2-AG) and anandamide (AEA) and their G-protein coupled receptors (GPCR), CB1 and CB2 which together constitutes the endocannabinoid system (ECS). However, putative, novel lipid-sensing CB receptors have recently been identified, including the orphan GPR55 and GPR18 receptors that are regulated by cannabinoid-like molecules and interact with CB system. CB receptors and associated orphan GPCRs are expressed at high levels in the immune and/or central nervous systems (CNS) and regulate a number of neurophysiological processes, including key events involved in neuroinflammation. As such, these receptors have been identified as emerging therapeutic targets for a number of brain disorders in which neuroinflammation is a key feature, including multiple sclerosis (MS) and Alzheimer's disease (AD). This review will consider the role of the wider cannabinoid receptor superfamily in mediating immune function with a focus on the immune processes that contribute to neuroinflammatory conditions.

Alzheimer’s disease is a complex age-related neurodegenerative disease characterized by the progressive loss of memory and cognitive function. Approximately 36 million people worldwide suffer from Alzheimer’s disease and with an increasingly aged global population that number is estimated to triple by 2050. Deterioration in the health of patients with Alzheimer’s disease leads to death within 3 to 9 years. The accumulation of misfolded proteins in the brain results in chronic activation of the immune response, oxidative damage, and excitotoxicity leading to neurodegeneration. The endocannabinoid system is an evolutionarily conserved neuromodulatory system that has a number of anti-inflammatory, antioxidant, and neurogenic effects and clinical studies have already reported positive behavioral effects in Alzheimer’s patients. Pharmacological modulation of the endocannabinoid system is emerging as a viable therapeutic target for the treatment of Alzheimer’s disease.

Alzheimer's disease is an age-related neurodegenerative disease characterized by the progressive deterioration of cognition andmemory resulting from synaptic loss and neuronal death. The accumulation of toxic amyloid-beta oligomers results in chronic neuroinflammation leading to synaptic dysfunction and severe neurodegeneration. Modulation of the endocannabinoid system has been shown to confer neuroprotection against amyloid-beta-induced neurotoxicity through the inhibition of Ca permeable channels, apoptotic cascades and blocking the activation and subsequent release of pro-inflammatory cytokines from microglia. A recently identified membrane channel, PanX1, has been implicated in the release of ATP from damaged cells as well as activation of the NLRP3 inflammasome and the resulting processing of IL-1beta in immune cells. The aim of this study was to investigate the involvement of PanX1 in cannabinoid-mediated neuroprotection against amyloid-beta. Cultured primary rat cortical neurons treated with amyloid-beta release chemoattractant signals that induced the migration of BV2 microglial cells using a Boyden chamber assay. Both the pharmacological inhibition of PanX1 by mimetic peptide panx and treatment with URB597, an inhibitor of cannabinoid degradation, significantly reduced the microglial migration that is stimulated by amyloid-betaprimed neuronal media. Furthermore, no additive effect from cotreating neurons with both panx and URB597 on microglial migration was found indicating a possible overlap in the two pathways. Amyloid-beta has no effect on total neuronal expression of PanX1, however increased levels of mature membrane bound PanX1 have been observed. Application of URB597 or probenecid, an inhibitor of PanX1 gating, reduced membrane PanX1 to control levels. Current experiments are aimed at investigating the link between the endocannabinoid systems anti-apoptotic effects and neuronal PanX1 regulation as well as elucidating the involvement of PanX1 in microglial activation. Funding received from the Higher Education Authority (HEA) under the Program for Research in Third Level Institutes (PRTLI) cycle 5 and co-funded by the Irish government and the European Union.

In an increasingly ageing population, the incidence of neurodegenerative disorders such as A lzheimer's disease, P arkinson's disease and H untington's disease are rising. While the aetiologies of these disorders are different, a number of common mechanisms that underlie their neurodegenerative components have been elucidated; namely neuroinflammation, excitotoxicity, mitochondrial dysfunction and reduced trophic support. Current therapies focus on treatment of the symptoms and attempt to delay the progression of these diseases but there is currently no cure. Modulation of the endogenous cannabinoid system is emerging as a potentially viable option in the treatment of neurodegeneration. Endocannabinoid signalling has been found to be altered in many neurodegenerative disorders. To this end, pharmacological manipulation of the endogenous cannabinoid system, as well as application of phytocannabinoids and synthetic cannabinoids have been investigated. Signalling from the CB 1 and CB 2 receptors are known to be involved in the regulation of Ca 2+ homeostasis, mitochondrial function, trophic support and inflammatory status, respectively, while other receptors gated by cannabinoids such as PPAR γ, are gaining interest in their anti‐inflammatory properties. Through multiple lines of evidence, this evolutionarily conserved neurosignalling system has shown neuroprotective capabilities and is therefore a potential target for neurodegenerative disorders. This review details the mechanisms of neurodegeneration and highlights the beneficial effects of cannabinoid treatment. Linked Articles This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue‐6

Significant loss of bone due to trauma, underlying metabolic disease, or lack of repair due to old age surpasses the body's endogenous bone repair mechanisms. Mesenchymal stem cells (MSCs) are adult stem cells which may represent an ideal cell type for use in cell-based tissue engineered bone regeneration strategies. The body's endocannabinoid system has been identified as a central regulator of bone metabolism. The aim of the study was to elucidate the role of the cannabinoid receptor type 1 in the differentiation and survival of MSCs. We show that the cannabinoid receptor type 1 has a prosurvival function during acute cell stress. Additionally, we show that the phytocannabinoid, Δ(9)-Tetrahydrocannabinol, has a negative impact on MSC survival and osteogenesis. Overall, these results show the potential for the modulation of the cannabinoid system in cell-based tissue engineered bone regeneration strategies whilst highlighting cannabis use as a potential cause for concern in the management of orthopaedic patients.

A finite element model of a single cell was created and used to compute the biophysical stimuli generated within a cell under mechanical loading. Major cellular components were incorporated in the model: the membrane, cytoplasm, nucleus, microtubules, actin filaments, intermediate filaments, nuclear lamina and chromatin. The model used multiple sets of tensegrity structures. Viscoelastic properties were assigned to the continuum components. To corroborate the model, a simulation of atomic force microscopy indentation was performed and results showed a force/indentation simulation with the range of experimental results. A parametric analysis of both increasing membrane stiffness (thereby modelling membrane peroxidation with age) and decreasing density of cytoskeletal elements (thereby modelling reduced actin density with age) was performed. Comparing normal and aged cells under indentation predicts that aged cells have a lower membrane area subjected to high strain as compared with young cells, but the difference, surprisingly, is very small and may not be measurable experimentally. Ageing is predicted to have a more significant effect on strain deep in the nucleus. These results show that computation of biophysical stimuli within cells are achievable with single-cell computational models; correspondence between computed and measured force/displacement behaviours provides a high-level validation of the model. Regarding the effect of ageing, the models suggest only small, although possibly physiologically significant, differences in internal biophysical stimuli between normal and aged cells.

BACKGROUND:Several factors contribute to the deterioration in synaptic plasticity which accompanies age and one of these is neuroinflammation. This is characterized by increased microglial activation associated with increased production of proinflammatory cytokines like interleukin-1β (IL-1β). In aged rats these neuroinflammatory changes are associated with a decreased ability of animals to sustain long-term potentiation (LTP) in the dentate gyrus. Importantly, treatment of aged rats with agents which possess anti-inflammatory properties to decrease microglial activation, improves LTP. It is known that endocannabinoids, such as anandamide (AEA), have anti-inflammatory properties and therefore have the potential to decrease the age-related microglial activation. However, endocannabinoids are extremely labile and are hydrolyzed quickly after production. Here we investigated the possibility that inhibiting the degradation of endocannabinoids with the fatty acid amide hydrolase (FAAH) inhibitor, URB597, could ameliorate age-related increases in microglial activation and the associated decrease in LTP.METHODS:Young and aged rats received subcutaneous injections of the FAAH inhibitor URB597 every second day and controls which received subcutaneous injections of 30% DMSO-saline every second day for 28 days. Long-term potentiation was recorded on day 28 and the animals were sacrificed. Brain tissue was analyzed for markers of microglial activation by PCR and for levels of endocannabinoids by liquid chromatography coupled to tandem mass spectrometry.RESULTS:The data indicate that expression of markers of microglial activation, MHCII, and CD68 mRNA, were increased in the hippocampus of aged, compared with young, rats and that these changes were associated with increased expression of the proinflammatory cytokines interleukin (IL)-1β and tumor necrosis factor-α (TNFα) which were attenuated by treatment with URB597. Coupled with these changes, we observed an age-related decrease in LTP in the dentate gyrus which was partially restored in URB597-treated aged rats. The data suggest that enhancement of levels of endocannabinoids in the brain by URB597 has beneficial effects on synaptic function, perhaps by modulating microglial activation.

Aberrant Notch signaling has recently emerged as a possible mechanism for the altered neurogenesis, cognitive impairment, and learning and memory deficits associated with Alzheimer disease (AD). Recently, targeting the endocannabinoid system in models of AD has emerged as a potential approach to slow the progression of the disease process. Although studies have identified neuroprotective roles for endocannabinoids, there is a paucity of information on modulation of the pro-survival Notch pathway by endocannabinoids. In this study the influence of the endocannabinoids, anandamide (AEA) and 2-arachidonoylglycerol, on the Notch-1 pathway and on its endogenous regulators were investigated in an in vitro model of AD. We report that AEA up-regulates Notch-1 signaling in cultured neurons. We also provide evidence that although A beta(1-42) increases expression of the endogenous inhibitor of Notch-1, numb (Nb), this can be prevented by AEA and 2-arachidonoylglycerol. Interestingly, AEA up-regulated Nct expression, a component of gamma-secretase, and this was found to play a crucial role in the enhanced Notch-1 signaling mediated by AEA. The stimulatory effects of AEA on Notch-1 signaling persisted in the presence of A beta(1-42). AEA was found to induce a preferential processing of Notch-1 over amyloid precursor protein to generate A beta(1-40). Aging, a natural process of neurodegeneration, was associated with a reduction in Notch-1 signaling in rat cortex and hippocampus, and this was restored with chronic treatment with URB 597. In summary, AEA has the proclivity to enhance Notch-1 signaling in an in vitro model of AD, which may have relevance for restoring neurogenesis and cognition in AD.

Neurodegenerative disorders carry a significant social and economic burden, and the effective treatment of such illnesses remains a challenge for neuroscientists and neurologists. Although significant advances have been made on our understanding of the molecular mechanisms underlying neurodegenerative diseases, the translation of this knowledge into effective therapeutic treatments has been limited. There is still a dearth of curative treatments for most neurodegenerative disorders, with symptomatic relief being the principal target for drug action. Endocannabinoids belong to an evolutionary conserved neuro-signaling system and certain endogenous and exogenous components of this system are emerging as clinically promising neuroprotective agents due to their anti-oxidative, anti-excitotoxic, and anti-inflammatory properties. The cannabinoid system is, therefore, a potential target for several neurodegenerative conditions, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Research on the therapeutic potential of drugs that modulate endogenous cannabinoid tone is intense. Recent evidence implicates the endocannabinoid system as a potential pharmacological target to circumvent neurodegenerative disease pathology. WIREs Membr Transp Signal 2012, 1:633–639. doi: 10.1002/wmts.64 For further resources related to this article, please visit the WIREs website.