Evolving DNA methylation and gene expression markers of B-cell chronic lymphocytic leukemia are present in pre-diagnostic blood samples more than 10 years prior to diagnosis

Background B-cell chronic lymphocytic leukemia (CLL) is a common type of adult leukemia. It often follows an indolent course and is preceded by monoclonal B-cell lymphocytosis, an asymptomatic condition, however it is not known what causes subjects with this condition to progress to CLL. Hence the discovery of prediagnostic markers has the potential to improve the identification of subjects likely to develop CLL and may also provide insights into the pathogenesis of the disease of potential clinical relevance. Results We employed peripheral blood buffy coats of 347 apparently healthy subjects, of whom 28 were diagnosed with CLL 2.0–15.7 years after enrollment, to derive for the first time genome-wide DNA methylation, as well as gene and miRNA expression, profiles associated with the risk of future disease. After adjustment for white blood cell composition, we identified 722 differentially methylated CpG sites and 15 differentially expressed genes (Bonferroni-corrected p < 0.05) as well as 2 miRNAs (FDR < 0.05) which were associated with the risk of future CLL. The majority of these signals have also been observed in clinical CLL, suggesting the presence in prediagnostic blood of CLL-like cells. Future CLL cases who, at enrollment, had a relatively low B-cell fraction (<10%), and were therefore less likely to have been suffering from undiagnosed CLL or a precursor condition, showed profiles involving smaller numbers of the same differential signals with intensities, after adjusting for B-cell content, generally smaller than those observed in the full set of cases. A similar picture was obtained when the differential profiles of cases with time-to-diagnosis above the overall median period of 7.4 years were compared with those with shorted time-to-disease. Differentially methylated genes of major functional significance include numerous genes that encode for transcription factors, especially members of the homeobox family, while differentially expressed genes include, among others, multiple genes related to WNT signaling as well as the miRNAs miR-150-5p and miR-155-5p. Conclusions Our findings demonstrate the presence in prediagnostic blood of future CLL patients, more than 10 years before diagnosis, of CLL-like cells which evolve as preclinical disease progresses, and point to early molecular alterations with a pathogenetic potential

Impact of Single Links in Competitive Percolation -- How complex networks grow under competition

How a complex network is connected crucially impacts its dynamics and function. Percolation, the transition to extensive connectedness upon gradual addition of links, was long believed to be continuous but recent numerical evidence on "explosive percolation" suggests that it might as well be discontinuous if links compete for addition. Here we analyze the microscopic mechanisms underlying discontinuous percolation processes and reveal a strong impact of single link additions. We show that in generic competitive percolation processes, including those displaying explosive percolation, single links do not induce a discontinuous gap in the largest cluster size in the thermodynamic limit. Nevertheless, our results highlight that for large finite systems single links may still induce observable gaps because gap sizes scale weakly algebraically with system size. Several essentially macroscopic clusters coexist immediately before the transition, thus announcing discontinuous percolation. These results explain how single links may drastically change macroscopic connectivity in networks where links add competitively.Comment: non-final version, for final see Nature Physics homepag

Alterations in population dynamics of arterial smooth muscle cells during atherogenesis. IV. Evidence for a polyclonal origin of hypercholesterolemic diet induced atherosclerotic lesions in young swine

The purpose of this study was to determine whether atherosclerotic lesions developing in young swine fed hypercholesterolemic (HC) diets were monoclonal or polyclonal in origin. The approach involved labeling arterial cells with tritiated thymidine prior to feeding the HC diet. Baseline swine were sacrificed and radioautography studies carried out to determine baseline labeling indices and grain number distributions in media and in intimal cellular masses (cushions). Remaining swine were then fed an HC diet for 30-60 days before sacrificing and making the same type determinations as with the baseline swine on putative active lesions and media. If a lesion arose from a single cell (or multiple unlabeled cells) labeling indices would be expected to be greatly reduced without a change in grain number patterns. This was not observed in any of the 14 putative lesions that were studied. If the lesion arose from divisions by multiple cells including labeled cells one would expect the proportion of cells with a high number of grains to be decreased, those with low numbers to be increased (since with division half the isotope goes to each daughter cell) and this to be reflected in the grain count. This occurred in 9 of the putative lesions, indicating multicellular origin. In 5 there were neither change in grain number distributions nor reduction in labeling indices. Hence, these showed no division activity during the period of study; they were classified as inactive lesions or preexisting cushions and provide no pertinent information for this study. The final conclusion was that all active lesions observed were polyclonal in origin. Further information was obtained by mathematical analysis on number of divisions made by the originally labeled cells; and considerable heterogeneity was observed, with some not dividing at all and others with progeny going through as many as 4 divisions.link_to_subscribed_fulltex

Population dynamics of arterial cells during atherogenesis. VII. Comparison of loss of endothelial cells over abdominal aortic intimal cellular masses (ICM) with that over non-ICM areas in swine fed a hyperlipidemic diet for 60 days

One of the earliest events in the development of an intimal atherosclerotic lesion may be an alteration in the endothelial cell barrier, allowing the entry of injurious or mitogenic substances, resulting in proliferation of arterial smooth muscle cells. Intimal smooth muscle cell proliferation in atherosclerosis appears to begin in intimal cellular masses (ICM), which are normally occurring intimal structures made up of 2 to 10 layers of smooth muscle cells found in predominantly in relation to branching points of arteries. If endothelial cell loss is a precursor of overt atherosclerotic lesions, the loss should be greater over ICM than over areas showing no ICM. This study presents evidence suggesting that in swine the endothelial cell barrier is compromised over intimal cell masses more than in non-ICM regions prior to development of overt atherosclerotic lesions. The method used was to label swine aortic endothelium and ICM using tritiated thymidine. All swine were then placed on a low-fat, low-cholesterol diet for 15 days, at which time five baseline animals were sacrificed; the remaining five were placed on a hyperlipidemic (HL) diet and sacrificed 60 days later. The rate of endothelial cell growth, division patterns, and loss of labeled endothelial cells in the HL swine was determined by comparing the findings in this group with the baseline group. Smooth muscle cells of ICM and non-ICM medial regions were similar in regard to labeling indices in the baseline swine and in regard to division patterns in 60 day HL diet swine, except one which was an active lesion. None of the remaining ICM were active lesions and thus were suitable for study of the covering endothelial cells in what can be assumed to be the prodromal stage of lesion development. The approximate area of the abdominal aorta occupied by intimal cell mass was considerably more than we had anticipated, averaging more than 20%. The labeling indices and endothelial cell division patterns over ICM and non-ICM in the baseline swine were similar. In contrast, the labeling index was lower, and grain count changes indicated more endothelial cell divisions over ICM areas than over non ICM areas in the hypercholesterolemic swine. Calculation showed that the percentage of endothelial cell loss over ICM in the HL swine was more than twice as great as endothelial cell loss over non-ICM areas. The results of this study suggest the possibility that in the assumed prodromal phase of experimental aortic atherosclerosis in young swine, the endothelial cell barrier may be compromised selectively over areas of predilection for the future development of atherosclerotic lesions. This occurs before there is any evidence of focal increase in intimal smooth muscle cell proliferation, which we regard as the earliest detectable stage of lesion development.link_to_subscribed_fulltex