Metakaryotic stem cell lineages in organogenesis of humans and other metazoans

A disease-driver population within interstitial cells of human calcific aortic valves identified via single-cell and proteomic profiling

Cellular heterogeneity of aortic valves complicates the mechanistic evaluation of the calcification processes in calcific aortic valve disease (CAVD), and animal disease models are lacking. In this study, we identify a disease-driver population (DDP) within valvular interstitial cells (VICs). Through stepwise single-cell analysis, phenotype-guided omic profiling, and network-based analysis, we characterize the DDP fingerprint as CD44highCD29+CD59+CD73+CD45low and discover potential key regulators of human CAVD. These DDP-VICs demonstrate multi-lineage differentiation and osteogenic properties. Temporal proteomic profiling of DDP-VICs identifies potential targets for therapy, including MAOA and CTHRC1. In vitro loss-of-function experiments confirm our targets. Such a stepwise strategy may be advantageous for therapeutic target discovery in other disease contexts.

Sirolimus-eluting stents: opposite in vitro effects on the clonogenic cell potential on a long-term exposure

We evaluated the long-term effects of sirolimus on three different cell in vitro models, cultured in physiological conditions mimicking sirolimus-eluted stent, in order to clarify the effectiveness of sirolimus in blocking cell proliferation and survival.

Three cells lines (WPMY-1 myofibroblasts, HT-29 colorectal adenocarcinoma, and U2OS osteosarcoma) were selected and growth in 10 ml of Minimum Essential Medium for 5 weeks with serial dilutions of sirolimus. The number of colonies and the number of cells per colony were counted.

As main result, the number of WPMY-1 surviving colonies increased in a dose-dependent manner when treated with sirolimus (p = 0.0011), while the number of U2OS colonies progressively decreased (p = 0.0011). The clonal capacity of HT-29 was not modified by the exposure to sirolimus (p = 0.6679).

In conclusion sirolimus showed the well-known cytostatic effect, but with an effect on clonogenic potential different among the different cell types. In the practice, the plaque typology and composition may influence the response to sirolimus and thus the effectiveness of eluted stent.

Nuclear morphologies: their diversity and functional relevance

Studies of chromosome and genome biology often focus on condensed chromatin in the form of chromosomes and neglect the non-dividing cells. Even when interphase nuclei are considered, they are often then treated as interchangeable round objects. However, different cell types can have very different nuclear shapes, and these shapes have impacts on cellular function; indeed, many pathologies are linked with alterations to nuclear shape. In this review, we describe some of the nuclear morphologies beyond the spherical and ovoid. Many of the leukocytes of the immune system have lobed nuclei, which aid their flexibility and migration; smooth muscle cells have a spindle shaped nucleus, which must deform during muscle contractions; spermatozoa have highly condensed nuclei which adopt varied shapes, potentially associated with swimming efficiency. Nuclei are not passive passengers within the cell. There are clear effects of nuclear shape on the transcriptional activity of the cell. Recent work has shown that regulation of gene expression can be influenced by nuclear morphology, and that cells can drastically remodel their chromatin during differentiation. The link between the nucleoskeleton and the cytoskeleton at the nuclear envelope provides a mechanism for transmission of mechanical forces into the nucleus, directly affecting chromatin compaction and organisation.

The study of calcified atherosclerotic arteries: an alternative to evaluate the composition of a problematic tissue reveals new insight including metakaryotic cells

Background

Calcifications of atherosclerotic plaques represent a controversial issue as they either lead to the stabilization or rupture of the lesion. However, the cellular key players involved in the progression of the calcified plaques have not yet been described. The primary reason for this lacuna is that decalcification procedures impair protein and nucleic acids contained in the calcified tissue. The aim of our study was to preserve the cellular content of heavily calcified plaques with a new rapid fixation in order to simplify the study of calcifications.

Methods

Here we applied a fixation method for fresh calcified tissue using the Carnoy’s solution followed by an enzymatic tissue digestion with type II collagenase. Immunohistochemistry was performed to verify the preservation of nuclear and cytoplasmic antigens. DNA content and RNA preservation was evaluated respectively with Feulgen staining and RT-PCR. A checklist of steps for successful image analysis was provided. To present the basic features of the F-DNA analysis we used descriptive statistics, skewness and kurtosis. Differences in DNA content were analysed with Kruskal-Wallis and Dunn’s post tests. The value of P < 0.05 was considered significant.

Results

Twenty-four vascular adult tissues, sorted as calcified (14) or uncalcified (10), were processed and 17 fetal tissues were used as controls (9 soft and 8 hard). Cells composing the calcified carotid plaques were positive to Desmin, Vimentin, Osteocalcin or Ki-67; the cellular population included smooth muscle cells, osteoblasts and osteoclasts-like cells and metakaryotic cells. The DNA content of each cell type found in the calcified carotid artery was successfully quantified in 7 selected samples. Notably the protocol revealed that DNA content in osteoblasts in fetal control tissues exhibits about half (3.0 ng) of the normal nuclear DNA content (6.0 ng).

Conclusion

Together with standard histology, this technique could give additional information on the cellular content of calcified plaques and help clarify the calcification process during atherosclerosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12907-016-0036-6) contains supplementary material, which is available to authorized users.

Arterial calcification: Finger-pointing at resident and circulating stem cells

The term ‘‘Stammzelle’’ (stem cells) originally appeared in 1868 in the works of Ernst Haeckel who used it to describe the ancestor unicellular organism from which he presumed all multicellular organisms evolved. Since then stem cells have been studied in a wide spectrum of normal and pathological conditions; it is remarkable to note that ectopic arterial calcification was considered a passive deposit of calcium since its original discovering in 1877; in the last decades, resident and circulating stem cells were imaged to drive arterial calcification through chondro-osteogenic differentiation thus opening the idea that an active mechanism could be at the basis of the process that clinically shows a Janus effect: calcifications either lead to the stabilization or rupture of the atherosclerotic plaques. A review of the literature underlines that 130 years after stem cell discovery, antigenic markers of stem cells are still debated and the identification of the osteoprogenitor phenotype is even more elusive due to tissue degradation occurring at processing and manipulation. It is necessary to find a consensus to perform comparable studies that implies phenotypic recognition of stem cells antigens. A hypothesis is based on the singular morphology and amitotic mechanism of division of osteoclasts: it constitutes the opening to a new approach on osteoprogenitors markers and recognition. Our aim was to highlight all the present evidences of the active calcification process, summarize the different cellular types involved, and discuss a novel approach to discover osteoprogenitor phenotypes in arterial wall.

Metakaryotic stem cell nuclei use pangenomic dsRNA/DNA intermediates in genome replication and segregation

Bell shaped nuclei of metakaryotic cells double their DNA content during and after symmetric and asymmetric amitotic fissions rather than in the separate, pre-mitotic S-phase of eukaryotic cells. A parsimonious hypothesis was tested that the two anti-parallel strands of each chromatid DNA helix were first segregated as ssDNA-containing complexes into sister nuclei then copied to recreate a dsDNA genome. Metakaryotic nuclei that were treated during amitosis with RNase A and stained with acridine orange or fluorescent antibody to ssDNA revealed large amounts of ssDNA. Without RNase treatment metakaryotic nuclei in amitosis stained strongly with an antibody complex specific to dsRNA/DNA. Images of amitotic figures co-stained with dsRNA/DNA antibody and DAPI indicated that the entire interphase dsDNA genome (B-form helices) was transformed into two dsRNA/DNA genomes (A-form helices) that were segregated in the daughter cell nuclei then retransformed into dsDNA. As this process segregates DNA strands of opposite polarity in sister cells it hypothetically offers a sequential switching mechanism within the diverging stem cell lineages of development.

Mutator/Hypermutable fetal/juvenile metakaryotic stem cells and human colorectal carcinogenesis

Adult age-specific colorectal cancer incidence rates increase exponentially from maturity, reach a maximum, then decline in extreme old age. Armitage and Doll (1) postulated that the exponential increase resulted from "n" mutations occurring throughout adult life in normal "cells at risk" that initiated the growth of a preneoplastic colony in which subsequent "m" mutations promoted one of the preneoplastic "cells at risk" to form a lethal neoplasia. We have reported cytologic evidence that these "cells at risk" are fetal/juvenile organogenic, then preneoplastic metakaryotic stem cells. Metakaryotic cells display stem-like behaviors of both symmetric and asymmetric nuclear divisions and peculiarities such as bell shaped nuclei and amitotic nuclear fission that distinguish them from embryonic, eukaryotic stem cells. Analyses of mutant colony sizes and numbers in adult lung epithelia supported the inferences that the metakaryotic organogenic stem cells are constitutively mutator/hypermutable and that their contributions to cancer initiation are limited to the fetal/juvenile period. We have amended the two-stage model of Armitage and Doll and incorporated these several inferences in a computer program CancerFit v.5.0. We compared the expectations of the amended model to adult (15-104 years) age-specific colon cancer rates for European-American males born 1890-99 and observed remarkable concordance. When estimates of normal colonic fetal/juvenile APC and OAT gene mutation rates (∼2-5 × 10(-5) per stem cell doubling) and preneoplastic colonic gene loss rates (∼8 × 10(-3)) were applied, the model was in accordance only for the values of n = 2 and m = 4 or 5.

Human fetal/tumor metakaryotic stem cells: pangenomic homologous pairing and telomeric end-joining of chromatids

Metakaryotic cells and syncytia with large, hollow, bell-shaped nuclei demonstrate symmetrical and asymmetrical amitotic nuclear fissions in microanatomical positions and numbers expected of stem cell lineages in tissues of all three primordial germ layers and their derived tumors. Using fluorescence in situ hybridization, mononuclear metakaryotic interphase cells have been found with only 23 centromeric and 23 telomeric staining regions. Syncytial bell-shaped nuclei found approximately during weeks 5-12 of human gestation display 23 centromeric and either 23 or 46 telomeric staining regions. These images suggest that (1) homologous chromatids pair at centromeres and telomeres, (2) all paired telomeres join end-to-end with other paired telomeres in all mononuclear and some syncytial metakaryotic cells, and (3) telomere junctions may open and close during the syncytial phase of development. Twenty-three telomeric joining figures could be accounted by 23 rings of one chromatid pair each, a single pangenomic ring of 23 joined chromatid pairs, or any of many possible sets of oligo-chromatid pair rings. As telomeric end-joining may affect peri-telomeric gene expression, a programmed sequence of telomeric end-joining associations in metakaryotic stem cells could guide developmental arboration and errors in, or interruptions of, this program could contribute to carcinogenesis.