Isolating Embryonic Cardiac Progenitors and Cardiac Myocytes by Fluorescence-Activated Cell Sorting

The zebrafish grime mutant uncovers an evolutionarily conserved role for Tmem161b in the control of cardiac rhythm

The establishment of cardiac function in the developing embryo is essential to ensure blood flow and, therefore, growth and survival of the animal. The molecular mechanisms controlling normal cardiac rhythm remain to be fully elucidated. From a forward genetic screen, we identified a unique mutant, grime, that displayed a specific cardiac arrhythmia phenotype. We show that loss-of-function mutations in tmem161b are responsible for the phenotype, identifying Tmem161b as a regulator of cardiac rhythm in zebrafish. To examine the evolutionary conservation of this function, we generated knockout mice for Tmem161b. Tmem161b knockout mice are neonatal lethal and cardiomyocytes exhibit arrhythmic calcium oscillations. Mechanistically, we find that Tmem161b is expressed at the cell membrane of excitable cells and live imaging shows it is required for action potential repolarization in the developing heart. Electrophysiology on isolated cardiomyocytes demonstrates that Tmem161b is essential to inhibit Ca²⁺ and K⁺ currents in cardiomyocytes. Importantly, Tmem161b haploinsufficiency leads to cardiac rhythm phenotypes, implicating it as a candidate gene in heritable cardiac arrhythmia. Overall, these data describe Tmem161b as a highly conserved regulator of cardiac rhythm that functions to modulate ion channel activity in zebrafish and mice.

Maternal obesity persistently alters cardiac progenitor gene expression and programs adult-onset heart disease susceptibility

Objective

Heart disease risk can be programmed by intrauterine exposure to obesity. Dysregulating key transcription factors in cardiac progenitors can cause subsequent adult-onset heart disease. In this study, we investigated the transcriptional pathways that are altered in the embryonic heart and linked to heart disease risk in offspring exposed to obesity during pregnancy.

Methods

Female mice were fed an obesogenic diet and mated with males fed a control diet. Heart function and genome-wide gene expression were analyzed in adult offspring born to obese and lean mice at baseline and in response to stress. Cross-referencing with genes dysregulated genome-wide in cardiac progenitors from embryos of obese mice and human fetal hearts revealed the transcriptional events associated with adult-onset heart disease susceptibility.

Results

We found that adult mice born to obese mothers develop mild heart dysfunction consistent with early stages of disease. Accordingly, hearts of these mice dysregulated genes controlling extracellular matrix remodeling, metabolism, and TGF-β signaling, known to control heart disease progression. These pathways were already dysregulated in cardiac progenitors in embryos of obese mice. Moreover, in response to cardiovascular stress, the heart of adults born to obese dams developed exacerbated myocardial remodeling and excessively activated regulators of cell-extracellular matrix interactions but failed to activate metabolic regulators. Expression of developmentally regulated genes was altered in cardiac progenitors of embryos of obese mice and human hearts of fetuses of obese donors. Accordingly, the levels of Nkx2-5, a key regulator of heart development, inversely correlated with maternal body weight in mice. Furthermore, Nkx2-5 target genes were dysregulated in cardiac progenitors and persistently in adult hearts born to obese mice and human hearts from pregnancies affected by obesity.

Conclusions

Obesity during pregnancy alters Nkx2-5-controlled transcription in differentiating cardiac progenitors and persistently in the adult heart, making the adult heart vulnerable to dysregulated stress responses.

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Maternal obesity programs progressive heart dysfunction in adult offspring.

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Offspring of obese dams are prone to dysregulated stress responses in the heart.

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Nkx2-5-controlled transcription is dysregulated in hearts exposed to obesity in utero.

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Obesity during pregnancy broadly affects gene expression in the embryonic heart.

Cardiac, renal and uterine hemodynamics changes throughout pregnancy in rats with a prolonged high fat diet from an early age

Objective

To examine whether the cardiac, renal and uterine physiological hemodynamic changes during gestation are altered in rats with an early and prolonged exposure to a high fat diet (HFD).

Methods

Arterial pressure and cardiac, renal, uterine and radial arteries hemodynamic changes during gestation were examined in adult SD rats exposed to normal (13%) (n = 8) or high (60%) (n = 8) fat diets from weaning. Plethysmography, high-resolution high-frequency ultrasonography and clearance of an inulin analog were used to evaluate the arterial pressure and hemodynamic changes before and at days 7, 14 and 19 of gestation.

Results

Arterial pressure was higher (P<0.05) in rats with high than in those with normal (NFD) fat diet before pregnancy (123 ±3 and 110 ±3 mmHg, respectively) and only decreased at day 14 of gestation in rats with NFD (98±4 mmHg, P<0.05). A significant increment in stroke volume (42 ±10%) and cardiac output (51 ±12%) was found at day 19 of pregnancy in rats with NFD. The changes in stroke volume and cardiac output were similar in rats with NFD and HFD. When compared to the values obtained before pregnancy, a transitory elevation in renal blood flow was found at day 14 of pregnancy in both groups. However, glomerular filtration rate only increased (P<0.05) in rats with NFD at days 14 (20 ±7%) and 19 (27 ±8%) of gestation. The significant elevations of mean velocity, and velocity time integral throughout gestation in radial (127 ±26% and 111 ±23%, respectively) and uterine (91 ±16% and 111 ±25%, respectively) arteries of rats with NFD were not found in rats with an early and prolonged HFD.

Summary

This study reports novel findings showing that the early and prolonged exposure to a HFD leads to a significant impairment in the renal, uterine and radial arteries hemodynamic changes associated to gestation.