Endocannabinoids prevent β-amyloid-mediated lysosomal destabilization in cultured neurons

Neuronal cell loss underlies the pathological decline in cognition and memory associated with Alzheimer disease (AD). Recently, targeting the endocannabinoid system in AD has emerged as a promising new approach to treatment. Studies have identified neuroprotective roles for endocannabinoids against key pathological events in the AD brain, including cell death by apoptosis. Elucidation of the apoptotic pathway evoked by β-amyloid (Aβ) is thus important for the development of therapeutic strategies that can thwart Aβ toxicity and preserve cell viability. We have previously reported that lysosomal membrane permeabilization plays a distinct role in the apoptotic pathway initiated by Aβ. In the present study, we provide evidence that the endocannabinoid system can stabilize lysosomes against Aβ-induced permeabilization and in turn sustain cell survival. We report that endocannabinoids stabilize lysosomes by preventing the Aβ-induced up-regulation of the tumor suppressor protein, p53, and its interaction with the lysosomal membrane. We also provide evidence that intracellular cannabinoid type 1 receptors play a role in stabilizing lysosomes against Aβ toxicity and thus highlight the functionality of these receptors. Given the deleterious effect of lysosomal membrane permeabilization on cell viability, stabilization of lysosomes with endocannabinoids may represent a novel mechanism by which these lipid modulators confer neuroprotection.     

A scan for genes associated with cancer mortality and longevity in pedigree dog breeds

Mammalian Genome - Selective breeding of the domestic dog (Canis lupus familiaris) rigidly retains desirable features, and could inadvertently fix disease-causing variants within a breed. We...     

The subtype of GluN2 C-terminal domain determines the response to excitotoxic insults

It is currently unclear whether the GluN2 subtype influences NMDA receptor (NMDAR) excitotoxicity. We report that the toxicity of NMDAR-mediated Ca(2+) influx is differentially controlled by the cytoplasmic C-terminal domains of GluN2B (CTD(2B)) and GluN2A (CTD(2A)). Studying the effects of acute expression of GluN2A/2B-based chimeric subunits with reciprocal exchanges of their CTDs revealed that CTD(2B) enhances NMDAR toxicity, compared to CTD(2A). Furthermore, the vulnerability of forebrain neurons in?vitro and in?vivo to NMDAR-dependent Ca(2+) influx is lowered by replacing the CTD of GluN2B with that of GluN2A by targeted exon exchange in a mouse knockin model. Mechanistically, CTD(2B) exhibits stronger physical/functional coupling to the PSD-95-nNOS pathway, which suppresses protective CREB activation. Dependence of NMDAR excitotoxicity on the GluN2 CTD subtype can be overcome by inducing high levels of NMDAR activity. Thus, the identity (2A versus 2B) of the GluN2 CTD controls the toxicity dose-response to episodes of NMDAR activity.     

Evolution of vertebrate tissues driven by differential modes of gene duplication

In this study, we investigated the evolution of vertebrate tissues by examining the potential association among gene expression, duplication, and base substitution patterns. In particular, we compared whole-genome duplication (WGD) with small-scale duplication (SSD), as well as tissue restricted with ubiquitously expressed genes. All patterns were also analysed in the light of gene evolutionary rates. Among those genes characterized by rapid evolution and expressed in a restricted range of tissues, SSD was represented in a larger proportion than WGD. Conversely, genes with ubiquitous expression were associated with slower evolutionary rates and a larger proportion of WGD. The results also show that evolutionary rates were faster in genes expressed in endodermal tissues and slower in ectodermal genes. Accordingly, the proportion of the SSD and WGD genes was highest in the endoderm and ectoderm, respectively. Therefore, quickly evolving SSD genes might have contributed to the faster evolution of endodermal tissues, whereas the comparatively slowly evolving WGD genes might have functioned to maintain the basic characteristics of ectodermal tissues. Mesenchymal tissues occupied an intermediate position in this regard, whereas the patterns observed for haemocytes were unique. Rapid tissue evolution could be related to a specific gene duplication mode (SSD) and faster molecular evolution in response to exposure to the external environment. These findings reveal general patterns underlying the evolution of tissues and their corresponding genes.     

A role for p53 in the regulation of lysosomal permeability by delta 9-tetrahydrocannabinol in rat cortical neurones: implications for neurodegeneration

The psychoactive ingredient of marijuana, Δ⁹-tetrahydrocannabinol (Δ⁹-THC), can evoke apoptosis in cultured cortical neurones. Whilst the intracellular mechanisms responsible for this apoptotic pathway remain to be fully elucidated, we have recently identified a role for the CB₁ type of cannabinoid (CB) receptor and the tumour suppressor protein, p53. In the current study, we demonstrate the Δ⁹-THC promotes a significant increase in lysosomal permeability in a dose- and time-dependent manner. The increase in lysosomal permeability was blocked by the CB₁ receptor antagonist, AM251. Δ⁹-THC increased the localization of phospho-p53Ser15 at the lysosome and stimulated the release of the lysosomal cathepsin enzyme, cathepsin-D, into the cytosol. The p53 inhibitor, pifithrin-α and small interfering RNA-mediated knockdown of p53 prevented the Δ⁹-THC-mediated increase in lysosomal permeability. Furthermore, the Δ⁹-THC -mediated induction of apoptosis was abrogated by a cell-permeable cathepsin-D inhibitor (10 μM). Thus, the study demonstrates that Δ⁹-THC impacts on the lysosomal system, via p53, to evoke lysosomal instability as an early event in the apoptotic cascade. This provides evidence for a novel link between the CB₁ receptor and the lysosomal branch of the apoptotic pathway which is crucial in regulating neuronal viability following exposure to Δ⁹-THC.     

Interacting gene clusters and the evolution of the vertebrate immune system

Unraveling the "code" of genome structure is an important goal of genomics research. Colocalization of genes in eukaryotic genomes may facilitate preservation of favorable allele combinations between epistasic loci or coregulation of functionally related genes. However, the presence of interacting gene clusters in the human genome has remained unclear. We systematically searched the human genome for evidence of closely linked genes whose protein products interact. We find 83 pairs of interacting genes that are located within 1 Mbp in the human genome or 37 if we exclude hub proteins. This number of interacting gene clusters is significantly more than expected by chance and is not the result of tandem duplications. Furthermore, we find that these clusters are significantly more conserved across vertebrate (but not chordate) genomes than other pairs of genes located within 1 Mbp in the human genome. In many cases, the genes are both present but not clustered in older vertebrate lineages. These results suggest gene cluster creation along the human lineage. These clusters are not enriched for housekeeping genes, but we find a significant contribution from genes involved in "response to stimulus." Many of these genes are involved in the immune response, including, but not limited to, known clusters such as the major histocompatibility complex. That these clusters were formed contemporaneously with the origin of adaptive immunity within the vertebrate lineage suggests that novel evolutionary and regulatory constraints were associated with the operation of the immune system.