Nicole Wagner

Rationale: Cardiac repair and regeneration are severely constrained in adult mammals. Several cell types have been identified as playing a role in cardiac repair. However, our understanding of the regulatory proteins common to these cell types and implicated in cardiac repair remains limited.

The Wilms’ tumor suppressor WT1 is essential for the development of the heart, among other organs such as the kidneys and gonads. The Wt1 gene encodes a zinc finger transcription factor that regulates proliferation, cellular differentiation processes, and apoptosis. WT1 is also involved in cardiac homeostasis and repair. In adulthood, WT1-expression levels are lower compared to those observed through development, and WT1 expression is restricted to a few cell types. However, its systemic deletion in adult mice is lethal, demonstrating that its presence is also key for organ maintenance. In response to injury, the epicardium re-activates the expression of WT1, but little is known about the roles it plays in cardiomyocytes, which are the main cell type affected after myocardial infarction. The fact that cardiomyocytes exhibit a low proliferation rate in the adult heart in mammals highlights the need to explore new approaches for cardiac regeneration. The aim of this review is to emphasize the functions carried out by WT1 in cardiomyocytes in cardiac homeostasis and heart regeneration.

P16Ink4a is a well-established marker of senescence. Although P16Ink4a is expressed in endothelial cells, little is known about its function in these cells. Using isolated liver endothelial cells with silencing or overexpression of P16Ink4a, we show here that dependent on P16Ink4a levels, different pathways and functions are affected. High levels of P16Ink4a reduce proliferation and induce senescence, while low levels have the opposite effects. Only high P16Ink4a expression reduces in vitro angiogenesis. Expression profiling reveals an inflammatory phenotype upon silencing of P16Ink4a, while P16Ink4a overexpression is associated with a profile associated with DNA damage, repair and senescence. Low levels of P16Ink4a induce reactive oxygen species (ROS) generation and increase endothelial cell leakage. Collectively, P16Ink4a represents an “antagonistic pleiotropy” gene, which is, on the one hand, required to prevent ROS generation and endothelial damage and, on the other hand, inhibits angiogenesis through induction of senescence at high levels.

Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that play important roles in cell proliferation, differentiation, metabolism, and cancer

During development, the heart is the first organ to form and function

The Wilms tumor suppressor gene (Wt1) encodes a C2H2-type zinc-finger transcription factor that participates in transcriptional regulation, RNA metabolism, and protein–protein interactions. WT1 is involved in the development of several organs, including the kidneys and gonads, heart, spleen, adrenal glands, liver, diaphragm, and neuronal system. We previously provided evidence of transient WT1 expression in about 25% of cardiomyocytes of mouse embryos. Conditional deletion of Wt1 in the cardiac troponin T lineage caused abnormal cardiac development. A low expression of WT1 has also been reported in adult cardiomyocytes. Therefore, we aimed to explore its function in cardiac homeostasis and in the response to pharmacologically induced damage. Silencing of Wt1 in cultured neonatal murine cardiomyocytes provoked alterations in mitochondrial membrane potential and changes in the expression of genes related to calcium homeostasis. Ablation of WT1 in adult cardiomyocytes by crossing αMHC^MerCreMer mice with homozygous WT1-floxed mice induced hypertrophy, interstitial fibrosis, altered metabolism, and mitochondrial dysfunction. In addition, conditional deletion of WT1 in adult cardiomyocytes increased doxorubicin-induced damage. These findings suggest a novel role of WT1 in myocardial physiology and protection against damage.

P16INK4A is a tumor suppressor and cell cycle regulator that has been linked to aging and senescence. In development, a potential role of p21 and of p19ARF has been postulated, but little is known about p16. Our previous results revealed a highly dynamic expression pattern of p16 in development and in different organs and cell types assessed by qRT-PCR and immunohistochemistry (IHC). In addition, we also noticed through IHC observation that p16 expression in old liver is mainly in the endothelial cells (ECs) compared to parenchymal cells. Therefore, we aimed at better understanding the role of p16 in biological processes of liver ECs, such as proliferation, migration, apoptosis, and tube formation. We also performed RNA sequencing to identify genes differentially expressed between young and old ECs. We used small hairpin (shRNA) constructs and a p16 cDNA-GFP vector to knockdown and overexpress p16 in vitro, in two types of liver ECs, CD31+ vascular ECs and CD146+ sinusoidal endothelial cells. Afterwards, we assessed p16’s down- and up-regulation effect on ECs function. Brdu incorporation assays showed that p16 upregulation was associated with slower proliferation compared to control cells, whereas its downregulation induced higher proliferation compared to control cells. Scratch assay and transwell migration assays showed attenuated migration in p16 overexpressed cells compared to baseline expression, while only transwell assays showed the ameliorated migration of p16 knockdown cells compared to controls. Similar migration between p16 knockdown and control was observed in scratch assays. We also observed in β-gal staining, a marker of senescence, a higher number of stained cells in p16 overexpression conditions compared to controls, while less cells were stained in the case of knockdown. Additional experiments that aim to further decipher p16’s effect in ECs’ tube formation, apoptosis, and telomeres shortening are ongoing, which might contribute to the invention of more specialized anti-aging therapies.

Aging is the leading predictive factor of many chronic diseases that account for most of the morbidity and mortality worldwide, i

Peroxisome proliferator activated receptors, including PPARα, PPARβ/δ, and PPARγ, are ligand-activated transcription factors belonging to the nuclear receptor superfamily. They play important roles in glucose and lipid metabolism and are also supposed to reduce inflammation and atherosclerosis. All PPARs are involved in angiogenesis, a process critically involved in cardiovascular pathology. Synthetic specific agonists exist for all PPARs. PPARα agonists (fibrates) are used to treat dyslipidemia by decreasing triglyceride and increasing high-density lipoprotein (HDL) levels. PPARγ agonists (thiazolidinediones) are used to treat Type 2 diabetes mellitus by improving insulin sensitivity. PPARα/γ (dual) agonists are supposed to treat both pathological conditions at once. In contrast, PPARβ/δ agonists are not in clinical use. Although activators of PPARs were initially considered to have favorable effects on the risk factors for cardiovascular disease, their cardiovascular safety is controversial. Here, we discuss the implications of PPARs in vascular biology regarding cardiac pathology and focus on the outcomes of clinical studies evaluating their benefits in cardiovascular diseases.