Biology subjects

Witten, A.

Publications and source records attributed to Witten, A..

7 recordsLinked to original sources

bioRxiv2025

Contractility governs cardiomyocyte cell cycle activity

The hearts rhythmic contractions keep blood flowing to deliver the oxygen and nutrients that sustain life, but this very strength may also explain why the heart has so little capacity to regenerate. Whereas embryonic and neonatal hearts can repair themselves, this ability is rapidly lost after birth as heart muscle cells (cardiomyocytes) exit the cell cycle. We tested whether the force-generating machinery of the heart acts as a barrier to regeneration. Across human cardiomyocytes, engineered heart tissue, and myocardial slices, we found that active force generation suppresses proliferation, whereas its inhibition, through chemogenetic or pharmacological modulation, enabled cell cycle re-entry. These findings identify contractility as a central regulator of regenerative potential, highlighting new directions for strategies to restore repair in the diseased heart.

cell biology↗

bioRxiv2023

LncRNA Bigheart trans-activates gene expression in a feed forward mechanism that facilitates calcineurin-NFAT signaling in myocardial hypertrophy

Terminally differentiated cardiomyocytes exhibit hypertrophy as a default response to injury by translating biomechanical stress into a complex network of intracellular signaling events. The molecular intricacies how calcium-dependent signaling engage molecular circuits and epigenetic modifications to activate deleterious gene programs remain enigmatic. Here we report on the re-activation of the evolutionarily conserved lncRNA "Bigheart", which is repressed in the postnatal myocardium and quickly re-activated in a calcineurin-NFAT-dependent fashion in the diseased myocardium in man and mouse. In line, AAV9-mediated overexpression of lncRNA Bigheart in otherwise healthy primary cardiomyocytes or mouse hearts suffices to drive maladapative hypertrophy. Conversely, mice receiving a "Gapmer" antisense oligonucleotide designed to specifically silence endogenous lncRNA Bigheart display resistance to biomechanical stress-induced myocardial remodeling, indicating its requirement in left ventricular hypertrophy. Mechanistically, lncRNA Bigheart recruits the RNA binding proteins hnRNP-F1 and HMGB1 to modulate the local chromatin environment and trans-activate Bigheart target genes including Rcan1 to stimulate calcineurin-NFAT coupling. Our observations confirm that human heart failure arises from specific susceptibilities in gene regulatory circuits that are amenable for therapeutic intervention using RNA-based therapeutics.

molecular biology↗

bioRxiv2022

Male sex hormone and reduced plakoglobin jointly impair atrial conduction and cardiac sodium currents

Androgenic anabolic steroids (AAS) are commonly abused by young men. Male sex associates with earlier manifestation of common and rare cardiac conditions including atrial fibrillation and arrhythmogenic right ventricular cardiomyopathy (ARVC). Clinical data suggest an atrial involvement in ARVC. The disease is caused by desmosomal gene defects such as reduced plakoglobin expression. Analysis of clinical records from 146 ARVC patients identified male preponderance and increased prevalence of atrial arrhythmias in patients with definite ARVC. Definite patients displayed ECG changes suggesting atrial remodelling. To study mechanisms of atrial remodelling due to desmosomal vulnerability and AAS, young adult male mice, heterozygously deficient for plakoglobin (Plako+/-) and wildtype (WT) littermates, were chronically exposed to 5-dihydrotestosterone (DHT) or placebo. DHT increased atrial expression of pro-hypertrophic, fibrotic and inflammatory transcripts. DHT caused atrial conduction slowing, decreased peak sodium current density, reduced action potential amplitude and lowered the peak depolarisation rate in Plako+/- but not WT atria. Super-resolution microscopy revealed a reduction in Nav1.5 clustering in Plako+/- atrial cardiomyocytes following DHT exposure. These data reveal that AAS combined with plakoglobin deficiency cause pathological atrial electrical remodelling in young male hearts. AAS abuse may increase the risk of atrial myopathy in males with desmosomal gene variants.

molecular biology↗

bioRxiv2021

C/EBPδ-induced epigenetic changes control the dynamic gene transcription of S100A8 and S100A9

The proinflammatory alarmins S100A8 and S100A9 are among the most abundant proteins in neutrophils and monocytes but completely silenced after differentiation to macrophages. The molecular mechanisms of the extraordinarily dynamic transcriptional regulation of s100a8 and s100a9 genes, however, are only barely understood. Using an unbiased genome-wide CRISPR/Cas9 knockout based screening approach in immortalized murine monocytes we identified the transcription factor C/EBP{delta} as a central regulator of S100A8 and S100A9 expression. S100a8 and S100a9 expression was further controlled by the C/EBP{delta}-antagonists ATF3 and FBXW7. We confirmed the clinical relevance of this regulatory network in subpopulations of human monocytes in a clinical cohort of cardiovascular patients. Moreover, we identified specific C/EBP{delta}-binding sites within s100a8 and s100a9 promoter regions, and demonstrated that C/EBP{delta}-dependent JMJD3-mediated demethylation of H3K27me3 is indispensable for their expression. Overall, our work uncovered C/EBP{delta} as a novel regulator of S100A8 and S100A9 expression. Therefore, C/EBP{delta} represents a promising target for modulation of inflammatory conditions that are characterised by S100A8 and S100A9 overexpression.

cell biology↗

bioRxiv2021

A genetic variant alters the secondary structure of the lncRNA H19 and is associated with Dilated Cardiomyopathy

lncRNAs are at the core of many regulatory processes and have also been recognized to be involved in various complex diseases. They affect gene regulation through direct interactions with RNA, DNA or proteins. Accordingly, lncRNAs structure is likely to be essential for their regulatory function. Point mutations, which manifest as SNPs (single nucleotide polymorphisms) in genome screens, can substantially alter their function and, subsequently, the expression of their down-stream regulated genes. To test the effect of SNPs on structure, we investigated lncRNAs associated with dilated cardiomyopathy. Among 322 human candidate lncRNAs we demonstrate first the significant association of a SNP located in lncRNA H19 using data from 1084 diseased and 751 control patients. H19 is generally highly expressed in the heart, with a complex expression pattern during heart development. Next, we used MFE (minimum free energy) folding to demonstrate a significant refolding in the secondary structure of this 861 nt long lncRNA. Since MFE folding may overlook the importance of sub-optimal structures, we showed that this refolding also manifests in the overall Boltzmann structure ensemble. There, the composition of structures is tremendously affected in their thermodynamic probabilities through the genetic variant. Finally, we confirmed these results experimentally, using SHAPE-Seq, corroborating that SNPs affecting such structures may explain hidden genetic variance not accounted for through genome wide association studies. Our results suggest that structural changes in lncRNAs, and lncRNA H19 in particular, affect regulatory processes and represent optimal targets for further in-depth studies probing their molecular interactions.

genetics↗

bioRxiv2021

Evolutionarily conserved transcriptional landscape of the heart defining the chamber specific physiology

Cardiovascular disease (CVD) remains the leading cause of death worldwide. A deeper characterization of the regional transcription patterns within different heart chambers may aid to improve our understanding of the molecular mechanisms involved in the function of the heart as well as our ability to develop novel therapeutic strategies. Here, we determined differentially expressed protein coding, long non-coding (lncRNA) and circular RNA (CircRNA) genes within various heart chambers across seven vertebrate species. We identified chamber specific genes, lncRNAs and pathways that are evolutionarily conserved in vertebrates. Further, we identified lncRNA homologs based on sequence, secondary structure, synteny and expressional conservation. Interestingly, most lncRNAs were found to be syntenically conserved. Various factors affect the co-expression patterns of transcripts including (i) genomic overlap, (ii) strandedness and (iii) transcript biotype. We also provide a catalogue of CircRNAs which are abundantly expressed across vertebrate hearts. Finally, we established a repository called EvoACTG (http://evoactg.uni-muenster.de/), which provides information about the conserved expression patterns for both PC genes and non-coding RNAs (ncRNAs) in the various heart chambers, and may serve as a community resource for investigators interested in the (patho)-physiology of CVD. We believe that this study will inform researchers working in the field of cardiovascular biology to explore the conserved yet intertwined nature of both coding and non-coding cardiac transcriptome across various popular model organisms in CVD research.

genomics↗

bioRxiv2017

Signature Of Co-Evolution Between Defense And Vegetative Lifespan Strategies In Arabidopsis thaliana

The selective impact of pathogen epidemics on host defenses can be strong but remains transient. By contrast, life-history shifts can durably and continuously modify the balance between costs and benefits of immunity, which arbitrates the evolution of host defenses. Their impact on the evolutionary dynamics of host immunity, however, has seldom been documented. Optimal investment into immunity is expected to decrease with shortening lifespan, because a shorter life decreases the probability to encounter pathogens or enemies. Here, we document that in natural populations of Arabidopsis thaliana, the expression levels of immunity genes correlate positively with flowering time, which in annual species is a proxy for lifespan. Using a novel genetic strategy based on bulk-segregants, we partitioned flowering time-dependent from - independent immunity genes and could demonstrate that this positive co-variation can be genetically separated. It is therefore not explained by the pleiotropic action of some major regulatory genes controlling both immunity and lifespan. Moreover, we find that immunity genes containing variants reported to impact fitness in natural field conditions are among the genes whose expression co-varies most strongly with flowering time. Taken together, these analyses reveal that natural selection has likely assorted alleles promoting lower expression of immunity genes with alleles that decrease the duration of vegetative lifespan in A. thaliana and vice versa. This is the first study documenting a pattern of variation consistent with the impact that selection on flowering time is predicted to have on diversity in host immunity.

evolutionary biology↗