Angiotensin II and the ERK pathway mediate the induction of leptin by mechanical cyclic stretch in cultured rat neonatal cardiomyocytes

Research Progress of Myocardial Fibrosis and Atrial Fibrillation

With the aging population and the increasing incidence of basic illnesses such as hypertension and diabetes (DM), the incidence of atrial fibrillation (AF) has increased significantly. AF is the most common arrhythmia in clinical practice, which can cause heart failure (HF) and ischemic stroke (IS), increasing disability and mortality. Current studies point out that myocardial fibrosis (MF) is one of the most critical substrates for the occurrence and maintenance of AF. Although myocardial biopsy is the gold standard for evaluating MF, it is rarely used in clinical practice because it is an invasive procedure. In addition, serological indicators and imaging methods have also been used to evaluate MF. Nevertheless, the accuracy of serological markers in evaluating MF is controversial. This review focuses on the pathogenesis of MF, serological evaluation, imaging evaluation, and anti-fibrosis treatment to discuss the existing problems and provide new ideas for MF and AF evaluation and treatment.

"Feeding the Foot": Nutritional Influences on Equine Hoof Health

Nutrition plays an important role in equine health, including that of the foot. Deficiencies and excesses of dietary components can affect the growth and function of the foot and have been associated with important podiatric diseases. The recognition, prevention, and treatment of specific notable nutritional diseases of the foot are discussed, as well as information regarding specific ingredients included in supplements meant to improve equine hoof quality. Ensuring provision of a balanced diet, maintaining horses in appropriate body condition, and seeking guidance from an equine nutritionist when creating dietary recommendations will prevent most equine foot disease related to nutrition.

Telmisartan improves myocardial remodeling by inhibiting leptin autocrine activity and activating PPARγ

The mechanism responsible for myocardial remodeling in hypertensive left ventricular hypertrophy (LVH) is complex. This study was designed to investigate the role of telmisartan in improving myocardial remodeling in hypertensive LVH and to explore the molecular mechanisms underlying the effects of telmisartan on hypertensive LVH. Hypertensive LVH was established in eight-week-old male Sprague–Dawley (SD) rats by abdominal aortic constriction. Telmisartan was intragastrically administered six weeks after surgery. Telmisartan improved cardiac dysfunction and myocardial fibrosis and reduced myocardial renin-angiotensin-aldosterone system (RAAS) activity and leptin levels in hypertensive LVH rats. To assess the mechanism underlying hypertensive LVH, cardiac fibroblasts were treated in vitro with angiotensin II (Ang II) or leptin, plus various inhibitors. Ang II stimulated leptin synthesis and secretion in cardiac fibroblasts by promoting AP-1 nuclear translocation via the AT1R-ROS-ERK1/2 pathway. Leptin induced collagen metabolism disorder in cardiac fibroblasts via the JAK2/STAT3 pathway. Telmisartan improved collagen metabolism disorder by inhibiting leptin induced by local Ang II in an autocrine manner. Telmisartan also improved Ang II-induced collagen metabolism disorder by inhibiting STAT3 phosphorylation, a leptin downstream signal, by activating PPAR-γ. Telmisartan therefore improved myocardial remodeling in hypertensive LVH rats by acting as an AT1R antagonist, inhibiting leptin autocrine activity induced by local Ang II and by acting as a PPAR-γ agonist, inhibiting downstream leptin activation of STAT3 phosphorylation. These findings indicate the crosstalk between local myocardial RAAS and leptin and suggest a molecular mechanism by which telmisartan improves myocardial remodeling in hypertensive LVH.

Impact statement

This study shows the crosstalk between local myocardial RAAS and leptin in hypertensive LVH rats; that Ang II induces myocardial remodeling by stimulating leptin autocrine activity by promoting AP-1 nuclear translocation via the AT1R-ROS-ERK1/2 pathway; and that telmisartan improves myocardial remodeling by inhibiting local Ang II-induced leptin autocrine activity and by inhibiting the leptin downstream signal STAT3 phosphorylation by activating PPAR-γ. These findings reveal novel molecular mechanisms by which telmisartan improves myocardial remodeling and could help to identify therapeutic targets for hypertensive LVH.

Cyclic stretch induced oxidative stress by mitochondrial and NADPH oxidase in retinal pigment epithelial cells

Background

Vitreomacular adhesion (VMA) has been reported to associated with age-related macular degeneration (AMD). Understanding the mechanisms underlying cyclic stretch induced in retinal pigment epithelial cells (RPE) may be important for the treatment of VMA-related AMD.

Method

Cyclic stretch (1HZ, 20% elongation) was applied to cultured ARPE-19 cells for 15 min, 2 h, 6 h, 12 h, 24 h by flexcell FX-5000 Tension system. Total reactive oxygen species (ROS) were detected using DCFH-DA. Mitochondrial superoxide were detected using MitoSOX Red mitochondrial superoxide indicator. NADPH oxidases (NOX) and signaling pathways, such as p38 and PKC, were detected using western blot. Apocycin (Apo) were used as NOX inhibitors.

Result

High levels of total ROS were detected from 15 min to 24 h, whereas mitochondrial superoxide were higher only in early time. NOX2 were significantly increased at 24 h. NOX4 were significantly increased at 2 h and reach its peak at 24 h. P-p38 was significantly increased at 12 h and 24 h. P-PKC was significantly increased at 15 min and kept a persistent high level. The upregulated expression of NOX4 by cyclic stretch can be significantly decreased under p-PKC inhibitor other than p-p38 inhibitor.

Conclusion

Cyclic stretch induce oxidative stress from both mitochodrial and NADPH oxidase in RPE cells, which may prompt oxidative damage in VMA-related AMD.

A role for membrane shape and information processing in cardiac physiology

While the heart is a dynamic organ and one of its major functions is to provide the organism with sufficient blood supply, the regulatory feedback systems, which allow adaptation to hemodynamic changes, remain not well understood. Our current description of mechanosensation focuses on stretch-sensitive ion channels, cytoskeletal components, structures such as the sarcomeric Z-disc, costameres, caveolae, or the concept of tensegrity, but these models appear incomplete as the remarkable plasticity of the myocardium in response to biomechanical stress and heart rate variations remains unexplained. Signaling activity at membranes depends on their geometric parameters such as surface area and curvature, which links shape to information processing. In the heart, continuous cycles of contraction and relaxation reshape membrane morphology and hence affect cardio-mechanic signaling. This article provides a brief review on current models of mechanosensation and focuses on how signaling, cardiac myocyte dynamics, and membrane shape interact and potentially give rise to a self-organized system that uses shape to sense the extra- and intracellular environment. This novel concept may help to explain how changes in frequency, and thus membrane shape, affect cardiac plasticity. One of the conclusions is that hypertrophy and associated fibrosis, which have been considered as necessary to cope with increased wall stress, can also be seen as part of complex feedback systems which use local membrane inhomogeneity in different cardiac cell types to influence whole organphysiology and which are predicted to fine-tune and thus regulate membrane-mediated signaling.