PIMT/NCOA6IP Deletion in the Mouse Heart Causes Delayed Cardiomyopathy Attributable to Perturbation in Energy Metabolism

Detection, Isolation and Quantification of Myocardial Infarct with Four Different Histological Staining Techniques

Precise quantification of myocardial infarction is crucial for evaluating the therapeutic strategies. We developed a robust, color-based semi-automatic algorithm capable of infarct region detection, isolation and quantification with four different histological staining techniques, and the isolation and quantification of diffuse fibrosis in the heart. Our method is developed based on the color difference in the infarct and non-infarct regions after histological staining. Mouse cardiac tissues stained with Masson's trichrome (MTS), hematoxylin and eosin (H&E), 2,3,5-Triphenyltetrazolium chloride and picrosirius red were included to demonstrate the performance of our method. We demonstrate that our algorithm can effectively identify and produce a clear visualization of infarct tissue for the four staining techniques. Notably, the infarct region on a H&E-stained tissue section can be clearly visualized after processing. The MATLAB-based program we developed holds promise in the infarct quantification. Additionally, our program can isolate and quantify the diffuse fibrotic elements from an MTS-stained cardiac section, which suggested the algorithm's potential for evaluating pathological cardiac fibrosis in diseased cardiac tissues. In conclusion, we demonstrate that this color-based algorithm is capable of accurately identifying, isolating and quantifying cardiac infarct regions with different staining techniques, as well as the diffuse and patchy fibrosis in MTS-stained cardiac tissues.

Cardiac-Specific Expression of Cre Recombinase Leads to Age-Related Cardiac Dysfunction Associated with Tumor-like Growth of Atrial Cardiomyocyte and Ventricular Fibrosis and Ferroptosis

Transgenic expression of Cre recombinase driven by a specific promoter is normally used to conditionally knockout a gene in a tissue- or cell-type-specific manner. In αMHC-Cre transgenic mouse model, expression of Cre recombinase is controlled by the myocardial-specific α-myosin heavy chain (αMHC) promoter, which is commonly used to edit myocardial-specific genes. Toxic effects of Cre expression have been reported, including intro-chromosome rearrangements, micronuclei formation and other forms of DNA damage, and cardiomyopathy was observed in cardiac-specific Cre transgenic mice. However, mechanisms associated with Cardiotoxicity of Cre remain poorly understood. In our study, our data unveiled that αMHC-Cre mice developed arrhythmias and died after six months progressively, and none of them survived more than one year. Histopathological examination showed that αMHC-Cre mice had aberrant proliferation of tumor-like tissue in the atrial chamber extended from and vacuolation of ventricular myocytes. Furthermore, the αMHC-Cre mice developed severe cardiac interstitial and perivascular fibrosis, accompanied by significant increase of expression levels of MMP-2 and MMP-9 in the cardiac atrium and ventricular. Moreover, cardiac-specific expression of Cre led to disintegration of the intercalated disc, along with altered proteins expression of the disc and calcium-handling abnormality. Comprehensively, we identified that the ferroptosis signaling pathway is involved in heart failure caused by cardiac-specific expression of Cre, on which oxidative stress results in cytoplasmic vacuole accumulation of lipid peroxidation on the myocardial cell membrane. Taken together, these results revealed that cardiac-specific expression of Cre recombinase can lead to atrial mesenchymal tumor-like growth in the mice, which causes cardiac dysfunction, including cardiac fibrosis, reduction of the intercalated disc and cardiomyocytes ferroptosis at the age older than six months in mice. Our study suggests that αMHC-Cre mouse models are effective in young mice, but not in old mice. Researchers need to be particularly careful when using αMHC-Cre mouse model to interpret those phenotypic impacts of gene responses. As the Cre-associated cardiac pathology matched mostly to that of the patients, the model could also be employed for investigating age-related cardiac dysfunction.

Trimethylguanosine synthase 1 is a novel regulator of pancreatic beta-cell mass and function

Type 2 diabetes is a metabolic disorder associated with abnormal glucose homeostasis and is characterized by intrinsic defects in β-cell function and mass. Trimethylguanosine synthase 1 (TGS1) is an evolutionarily conserved enzyme that methylates small nuclear and nucleolar RNAs and that is involved in pre-mRNA splicing, transcription, and ribosome production. However, the role of TGS1 in β-cells and glucose homeostasis had not been explored. Here, we show that TGS1 is upregulated by insulin and upregulated in islets of Langerhans from mice exposed to a high-fat diet and in human β-cells from type 2 diabetes donors. Using mice with conditional (βTGS1KO) and inducible (MIP-Cre^ERT-TGS1KO) TGS1 deletion, we determined that TGS1 regulates β-cell mass and function. Using unbiased approaches, we identified a link between TGS1 and endoplasmic reticulum stress and cell cycle arrest, as well as and how TGS1 regulates β-cell apoptosis. We also found that deletion of TGS1 results in an increase in the unfolded protein response by increasing XBP-1, ATF-4, and the phosphorylation of eIF2α, in addition to promoting several changes in cell cycle inhibitors and activators such as p27 and Cyclin D2. This study establishes TGS1 as a key player regulating β-cell mass and function. We propose that these observations can be used as a stepping-stone for the design of novel strategies focused on TGS1 as a therapeutic target for the treatment of diabetes.

Mechanisms Mediating the Regulation of Peroxisomal Fatty Acid Beta-Oxidation by PPARα

In mammalian cells, two cellular organelles, mitochondria and peroxisomes, share the ability to degrade fatty acid chains. Although each organelle harbors its own fatty acid β-oxidation pathway, a distinct mitochondrial system feeds the oxidative phosphorylation pathway for ATP synthesis. At the same time, the peroxisomal β-oxidation pathway participates in cellular thermogenesis. A scientific milestone in 1965 helped discover the hepatomegaly effect in rat liver by clofibrate, subsequently identified as a peroxisome proliferator in rodents and an activator of the peroxisomal fatty acid β-oxidation pathway. These peroxisome proliferators were later identified as activating ligands of Peroxisome Proliferator-Activated Receptor α (PPARα), cloned in 1990. The ligand-activated heterodimer PPARα/RXRα recognizes a DNA sequence, called PPRE (Peroxisome Proliferator Response Element), corresponding to two half-consensus hexanucleotide motifs, AGGTCA, separated by one nucleotide. Accordingly, the assembled complex containing PPRE/PPARα/RXRα/ligands/Coregulators controls the expression of the genes involved in liver peroxisomal fatty acid β-oxidation. This review mobilizes a considerable number of findings that discuss miscellaneous axes, covering the detailed expression pattern of PPARα in species and tissues, the lessons from several PPARα KO mouse models and the modulation of PPARα function by dietary micronutrients.

Targeting peroxisome proliferator-activated receptors: A new strategy for the treatment of cardiac fibrosis

Cardiac fibrosis is a pathogenic factor of many cardiovascular diseases (CVD), which seriously affects people's life, and health and causes huge economic losses. Increasing evidence has shown that peroxisome proliferator-activated receptors (PPARs) can regulate the progression of cardiac fibrosis. For the first time, this review systematically summarizes the literature on cardiac fibrosis from the perspective of PPARs from 2010 to 2020. Moreover, the role of each PPARs in cardiac fibrosis was clarified in this scientific revision from the perspectives of pharmacologically active substances, known agonists, natural extract compounds, and nucleic-acid-based drugs in different CVD models. Furthermore, the combination of multiple PPARs on the treatment of cardiac fibrosis is discussed. This scientific review provides new ideas for targeting PPARs in the treatment of cardiac fibrosis and provides strategies for the development of new, safe, and effective pharmacological antagonists against cardiac fibrosis based on PPAR activity.

Thyroxine Alleviates Energy Failure, Prevents Myocardial Cell Apoptosis, and Protects against Doxorubicin-Induced Cardiac Injury and Cardiac Dysfunction via the LKB1/AMPK/mTOR Axis in Mice

Background

Previous studies have demonstrated that energy failure is closely associated with cardiac injury. Doxorubicin (DOX) is a commonly used clinical chemotherapy drug that can mediate cardiac injury through a variety of mechanisms. Thyroxine is well known to play a critical role in energy generation; thus, this study is aimed at investigating whether thyroxine can attenuate DOX-induced cardiac injury by regulating energy generation.

Methods

First, the effect of DOX on adenosine diphosphate (ADP) and adenosine triphosphate (ATP) ratios in mice was assessed. In addition, thyroxine was given to mice before they were treated with DOX to investigate the effects of thyroxine on DOX-induced cardiac injury. Furthermore, to determine whether the liver kinase b1 (LKB1)/adenosine 5′-monophosphate-activated protein kinase (AMPK)/mammalian target of rapamycin (mTOR) axis mediated the effect of thyroxine on DOX-induced cardiac injury, thyroxine was given to DOX-treated LKB1 knockout (KO) mice.

Results

DOX treatment time- and dose-dependently increased the ADP/ATP ratio. Thyroxine treatment also reduced lactate dehydrogenase (LDH) and creatine kinase myocardial band (CK-MB) levels in both serum and heart tissue and alleviated cardiac dysfunction in DOX-treated mice. Furthermore, thyroxine reversed DOX-induced reductions in LKB1 and AMPK phosphorylation; mitochondrial complex I, III, and IV activity; and mitochondrial swelling and reversed DOX-induced increases in mTOR pathway phosphorylation and myocardial cell apoptosis. These effects of thyroxine on DOX-treated mice were significantly attenuated by LKB1 KO.

Conclusions

Thyroxine alleviates energy failure, reduces myocardial cell apoptosis, and protects against DOX-induced cardiac injury via the LKB1/AMPK/mTOR axis in mice. Thyroxine may be a new agent for the clinical prevention of cardiac injury in tumor patients undergoing chemotherapy with DOX.