Simultaneous expression of MMB-FOXM1 complex components enables efficient bypass of senescence

Cellular senescence is a stable cell cycle arrest that normal cells undergo after a finite number of divisions, in response to a variety of intrinsic and extrinsic stimuli. Although senescence is largely established and maintained by the p53/p21WAF1/CIP1 and pRB/p16INK4A tumour suppressor pathways, the downstream targets responsible for the stability of the growth arrest are not known. We have employed a stable senescence bypass assay in conditionally immortalised human breast fibroblasts (CL3EcoR) to investigate the role of the DREAM complex and its associated components in senescence. DREAM is a multi-subunit complex comprised of the MuvB core, containing LIN9, LIN37, LIN52, LIN54, and RBBP4, that when bound to p130, an RB1 like protein, and E2F4 inhibits cell cycle-dependent gene expression thereby arresting cell division. Phosphorylation of LIN52 at Serine 28 is required for DREAM assembly. Re-entry into the cell cycle upon phosphorylation of p130 leads to disruption of the DREAM complex and the MuvB core, associating initially to B-MYB and later to FOXM1 to form MMB and MMB-FOXM1 complexes respectively. Here we report that simultaneous expression of MMB-FOXM1 complex components efficiently bypasses senescence with LIN52, B-MYB, and FOXM1 as the crucial components. Moreover, bypass of senescence requires non-phosphorylated LIN52 that disrupts the DREAM complex, thereby indicating a central role for assembly of the DREAM complex in senescence

Variants of PLCXD3 are not associated with variant or sporadic Creutzfeldt-Jakob disease in a large international study

BACKGROUND: Human prion diseases are relentlessly progressive neurodegenerative disorders which include sporadic Creutzfeldt-Jakob disease (sCJD) and variant CJD (vCJD). Aside from variants of the prion protein gene (PRNP) replicated association at genome-wide levels of significance has proven elusive. A recent association study identified variants in or near to the PLCXD3 gene locus as strong disease risk factors in multiple human prion diseases. This study claimed the first non-PRNP locus to be highly significantly associated with prion disease in genomic studies. METHODS: A sub-study of a genome-wide association study with imputation aiming to replicate the finding at PLCXD3 including 129 vCJD and 2500 sCJD samples. Whole exome sequencing to identify rare coding variants of PLCXD3. RESULTS: Imputation of relevant polymorphisms was accurate based on wet genotyping of a sample. We found no supportive evidence that PLCXD3 variants are associated with disease. CONCLUSION: The marked discordance in vCJD genotype frequencies between studies, despite extensive overlap in vCJD cases, and the finding of Hardy-Weinberg disequilibrium in the original study, suggests possible reasons for the discrepancies between studies

Iatrogenic CJD due to pituitary-derived growth hormone with genetically determined incubation times of up to 40 years

Patients with iatrogenic Creutzfeldt-Jakob disease due to administration of cadaver-sourced growth hormone during childhood are still being seen in the UK 30 years after cessation of this treatment. Of the 77 patients who have developed iatrogenic Creutzfeldt-Jakob disease, 56 have been genotyped. There has been a marked change in genotype profile at polymorphic codon 129 of the prion protein gene (PRNP) from predominantly valine homozygous to a mixed picture of methionine homozygous and methionine-valine heterozygous over time. The incubation period of iatrogenic Creutzfeldt-Jakob disease is significantly different between all three genotypes. This experience is a striking contrast with that in France and the USA, which may relate to contamination of different growth hormone batches with different strains of human prions. We describe the clinical, imaging, molecular and autopsy features in 22 of 24 patients who have developed iatrogenic Creutzfeldt-Jakob disease in the UK since 2003. Mean age at onset of symptoms was 42.7 years. Gait ataxia and lower limb dysaesthesiae were the most frequent presenting symptoms. All had cerebellar signs, and the majority had myoclonus and lower limb pyramidal signs, with relatively preserved cognitive function, when first seen. There was a progressive decline in neurological and cognitive function leading to death after 5-32 (mean 14) months. Despite incubation periods approaching 40 years, the clinical duration in methionine homozygote patients appeared to be shorter than that seen in heterozygote patients. MRI showed restricted diffusion in the basal ganglia, thalamus, hippocampus, frontal and the paracentral motor cortex and cerebellar vermis. The electroencephalogram was abnormal in 15 patients and cerebrospinal fluid 14-3-3 protein was positive in half the patients. Neuropathological examination was conducted in nine patients. All but one showed synaptic prion deposition with numerous kuru type plaques in the basal ganglia, anterior frontal and parietal cortex, thalamus, basal ganglia and cerebellum. The patient with the shortest clinical duration had an atypical synaptic deposition of abnormal prion protein and no kuru plaques. Taken together, these data provide a remarkable example of the interplay between the strain of the pathogen and host prion protein genotype. Based on extensive modelling of human prion transmission barriers in transgenic mice expressing human prion protein on a mouse prion protein null background, the temporal distribution of codon 129 genotypes within the cohort of patients with iatrogenic Creutzfeldt-Jakob disease in the UK suggests that there was a point source of infecting prion contamination of growth hormone derived from a patient with Creutzfeldt-Jakob disease expressing prion protein valine 129

In-vitro screen of prion disease susceptibility genes using the scrapie cell assay.

Prion diseases (transmissible spongiform encephalopathies) are fatal neurodegenerative diseases including Creutzfeldt-Jakob disease (CJD) in humans, scrapie in sheep and bovine spongiform encephalopathy (BSE) in cattle. While genome-wide association studies in human and quantitative trait loci mapping in mice have provided evidence for multiple susceptibility genes, few of these have been confirmed functionally. Phenotyping mouse models is generally the method of choice. However, this is not a feasible option where many novel genes, without pre-existing models, would need to be tested. We have therefore developed and applied an in-vitro screen to triage and prioritise candidate modifier genes for more detailed future studies which is faster, far more cost effective and ethical relative to mouse bioassay models. An in vitro prion bioassay, the scrapie cell assay (SCA), uses a neuroblastoma derived cell line (PK1) that is susceptible to RML prions and able to propagate prions at high levels. In this study, we have generated stable gene silencing and/or overexpressing PK1-derived cell lines to test whether perturbation of 14 candidate genes affects prion susceptibility. While no consistent differences were determined for seven genes, highly significant changes were detected for Zbtb38, Sorcs1, Stmn2, Hspa13, Fkbp9, Actr10 and Plg, suggesting that they play key roles in the fundamental processes of prion propagation or clearance. Many neurodegenerative diseases involve the accumulation of misfolded protein aggregates and "prion-like" seeding and spread has been implicated in their pathogenesis. It is therefore expected that some of these prion-modifier genes may be of wider relevance in neurodegeneration

Sod1 deficiency reduces incubation time in mouse models of prion disease.

Prion infections, causing neurodegenerative conditions such as Creutzfeldt-Jakob disease and kuru in humans, scrapie in sheep and BSE in cattle are characterised by prolonged and variable incubation periods that are faithfully reproduced in mouse models. Incubation time is partly determined by genetic factors including polymorphisms in the prion protein gene. Quantitative trait loci studies in mice and human genome-wide association studies have confirmed that multiple genes are involved. Candidate gene approaches have also been used and identified App, Il1-r1 and Sod1 as affecting incubation times. In this study we looked for an association between App, Il1-r1 and Sod1 representative SNPs and prion disease incubation time in the Northport heterogeneous stock of mice inoculated with the Chandler/RML prion strain. No association was seen with App, however, significant associations were seen with Il1-r1 (P = 0.02) and Sod1 (P<0.0001) suggesting that polymorphisms at these loci contribute to the natural variation observed in incubation time. Furthermore, following challenge with Chandler/RML, ME7 and MRC2 prion strains, Sod1 deficient mice showed highly significant reductions in incubation time of 20, 13 and 24%, respectively. No differences were detected in Sod1 expression or activity. Our data confirm the protective role of endogenous Sod1 in prion disease

Expression of NDRG2 is down-regulated in high-risk adenomas and colorectal carcinoma

<p>Abstract</p> <p>Background</p> <p>It has recently been shown that <it>NDRG2 </it>mRNA is down-regulated or undetectable in several human cancers and cancer cell-lines. Although the function of NDRG2 is unknown, high <it>NDRG2 </it>expression correlates with improved prognosis in high-grade gliomas. The aim of this study has been to examine <it>NDRG2 </it>mRNA expression in colon cancer. By examining affected and normal tissue from individuals with colorectal adenomas and carcinomas, as well as in healthy individuals, we aim to determine whether and at which stages <it>NDRG2 </it>down-regulation occurs during colonic carcinogenesis.</p> <p>Methods</p> <p>Using quantitative RT-PCR, we have determined the mRNA levels for <it>NDRG2 </it>in low-risk (n = 15) and high-risk adenomas (n = 57), colorectal carcinomas (n = 50) and corresponding normal tissue, as well as control tissue from healthy individuals (n = 15). <it>NDRG2 </it>levels were normalised to <it>β-actin</it>.</p> <p>Results</p> <p><it>NDRG2 </it>mRNA levels were lower in colorectal carcinomas compared to normal tissue from the control group (p < 0.001). When comparing adenomas/carcinomas with adjacent normal tissue from the same individual, <it>NDRG2 </it>expression levels were significantly reduced in both high-risk adenoma (p < 0.001) and in colorectal carcinoma (p < 0.001). There was a trend for <it>NDRG2 </it>levels to decrease with increasing Dukes' stage (p < 0.05).</p> <p>Conclusion</p> <p>Our results demonstrate that expression of <it>NDRG2 </it>is down-regulated at a late stage during colorectal carcinogensis. Future studies are needed to address whether <it>NDRG2 </it>down-regulation is a cause or consequence of the progression of colorectal adenomas to carcinoma.</p

HECTD2 Is Associated with Susceptibility to Mouse and Human Prion Disease

Prion diseases are fatal transmissible neurodegenerative disorders, which include Scrapie, Bovine Spongiform Encephalopathy (BSE), Creutzfeldt-Jakob Disease (CJD), and kuru. They are characterised by a prolonged clinically silent incubation period, variation in which is determined by many factors, including genetic background. We have used a heterogeneous stock of mice to identify Hectd2, an E3 ubiquitin ligase, as a quantitative trait gene for prion disease incubation time in mice. Further, we report an association between HECTD2 haplotypes and susceptibility to the acquired human prion diseases, vCJD and kuru. We report a genotype-associated differential expression of Hectd2 mRNA in mouse brains and human lymphocytes and a significant up-regulation of transcript in mice at the terminal stage of prion disease. Although the substrate of HECTD2 is unknown, these data highlight the importance of proteosome-directed protein degradation in neurodegeneration. This is the first demonstration of a mouse quantitative trait gene that also influences susceptibility to human prion diseases. Characterisation of such genes is key to understanding human risk and the molecular basis of incubation periods

HTT-lowering reverses Huntington's disease immune dysfunction caused by NF kappa B pathway dysregulation

Huntington’s disease is an inherited neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin gene. The peripheral innate immune system contributes to Huntington’s disease pathogenesis and has been targeted successfully to modulate disease progression, but mechanistic understanding relating this to mutant huntingtin expression in immune cells has been lacking. Here we demonstrate that human Huntington’s disease myeloid cells produce excessive inflammatory cytokines as a result of the cell-intrinsic effects of mutant huntingtin expression. A direct effect of mutant huntingtin on the NFκB pathway, whereby it interacts with IKKγ, leads to increased degradation of IκB and subsequent nuclear translocation of RelA. Transcriptional alterations in intracellular immune signalling pathways are also observed. Using a novel method of small interfering RNA delivery to lower huntingtin expression, we show reversal of disease-associated alterations in cellular function–the first time this has been demonstrated in primary human cells. Glucan-encapsulated small interfering RNA particles were used to lower huntingtin levels in human Huntington’s disease monocytes/macrophages, resulting in a reversal of huntingtin-induced elevated cytokine production and transcriptional changes. These findings improve our understanding of the role of innate immunity in neurodegeneration, introduce glucan-encapsulated small interfering RNA particles as tool for studying cellular pathogenesis ex vivo in human cells and raise the prospect of immune cell-directed HTT-lowering as a therapeutic in Huntington’s disease

Predictors for a dementia gene mutation based on gene-panel next-generation sequencing of a large dementia referral series

Next-generation genetic sequencing (NGS) technologies facilitate the screening of multiple genes linked to neurodegenerative dementia, but there is little guidance available about their use in clinical practice. Guidelines on which patients would most profit from testing, and information on the likelihood of discovery of a causal variant in a clinical syndrome, are conspicuously absent from the literature, mostly for a lack of large-scale studies. We applied a validated NGS dementia panel to 3241 patients with dementia and healthy aged controls; 13,152 variants were classified by likelihood of pathogenicity. We identified 354 deleterious variants (DV, 12.6% of patients); 39 were novel DVs. Age at clinical onset, clinical syndrome and family history each strongly predict the likelihood of finding a DV, but healthcare setting and gender did not. DVs were frequently found in genes not usually associated with the clinical syndrome. Patients recruited from primary referral centres were compared to those seen at higher-level research centres and a national clinical neurogenetic laboratory; rates of discovery were comparable, making selection bias unlikely and the results generalizable to clinical practice. We estimated penetrance of DVs using large-scale online genomic population databases and found 71 with evidence of reduced penetrance. Two DVs in the same patient were found more frequently than expected. These publicly-available data should provide a basis for informed counselling and clinical decision making