Endothelin A receptor blockade influences apoptosis and cellular proliferation in the developing rat kidney

Hypertension and renal disease programming: focus on the early postnatal period

The developmental origin of hypertension and renal disease is a concept highly supported by strong evidence coming from both human and animal studies. During development there are periods in which the organs are more vulnerable to stressors. Such periods of susceptibility are also called 'sensitive windows of exposure'. It was shown that as earlier an adverse event occurs; the greater are the consequences for health impairment. However, evidence show that the postnatal period is also quite important for hypertension and renal disease programming, especially in rodents because they complete nephrogenesis postnatally, and it is also important during preterm human birth. Considering that the developing kidney is vulnerable to early-life stressors, renal programming is a key element in the developmental programming of hypertension and renal disease. The purpose of this review is to highlight the great number of studies, most of them performed in animal models, showing the broad range of stressors involved in hypertension and renal disease programming, with a particular focus on the stressors that occur during the early postnatal period. These stressors mainly include undernutrition or specific nutritional deficits, chronic behavioral stress, exposure to environmental chemicals, and pharmacological treatments that affect some important factors involved in renal physiology. We also discuss the common molecular mechanisms that are activated by the mentioned stressors and that promote the appearance of these adult diseases, with a brief description on some reprogramming strategies, which is a relatively new and promising field to treat or to prevent these diseases.

Endothelin receptor-specific control of endoplasmic reticulum stress and apoptosis in the kidney

Endothelin-1 (ET-1) promotes renal damage during cardiovascular disease; yet, the molecular mechanisms involved remain unknown. Endoplasmic reticulum (ER) stress, triggered by unfolded protein accumulation in the ER, contributes to apoptosis and organ injury. These studies aimed to determine whether the ET-1 system promotes renal ER stress development in response to tunicamycin. ET_B deficient (ET_B def) or transgenic control (TG-con) rats were used in the presence or absence of ET_A receptor antagonism. Tunicamycin treatment similarly increased cortical ER stress markers in both rat genotypes; however, only ET_B def rats showed a 14-24 fold increase from baseline for medullary GRP78, sXBP-1, and CHOP. Pre-treatment of TG-con rats with the ET_A blocker ABT-627 for 1 week prior to tunicamycin injection significantly reduced the ER stress response in cortex and medulla, and also inhibited renal apoptosis. Pre-treatment with ABT-627 failed to decrease renal ER stress and apoptosis in ET_B def rats. In conclusion, the ET-1 system is important for the development of tunicamycin-induced renal ER stress and apoptosis. ET_A receptor activation induces renal ER stress genes and apoptosis, while functional activation of the ET_B receptor has protective effects. These results highlight targeting the ET_A receptor as a therapeutic approach against ER stress-induced kidney injury.

The Role of Endothelin System in Renal Structure and Function during the Postnatal Development of the Rat Kidney

Renal development in rodents, unlike in humans, continues during early postnatal period. We aimed to evaluate whether the pharmacological inhibition of Endothelin system during this period affects renal development, both at structural and functional level in male and female rats. Newborn rats were treated orally from postnatal day 1 to 20 with vehicle or bosentan (Actelion, 20 mg/kg/day), a dual endothelin receptor antagonist (ERA). The animals were divided in 4 groups: control males, control females, ERA males and ERA females. At day 21, we evaluated renal function, determined the glomerular number by a maceration method and by morphometric analysis and evaluated possible structural renal alterations by three methods: 〈alpha〉-Smooth muscle actin (α-SMA) immunohistochemistry, Masson's trichrome and Sirius red staining. The pharmacological inhibition of Endothelin system with a dual ERA during the early postnatal period of the rat did not leads to renal damage in the kidneys of male and female rats. However, ERA administration decreased the number of glomeruli, the juxtamedullary filtration surface area and the glomerular filtration rate and increased the proteinuria. These effects could predispose to hypertension or renal diseases in the adulthood. On the other hand, these effects were more pronounced in male rats, suggesting that there are sex differences that could be greater later in life. These results provide evidence that Endothelin has an important role in rat renal postnatal development. However these results do not imply that the same could happen in humans, since human renal development is complete at birth.

Endothelium-derived ET-1 and the development of renal injury

The role of the vasoactive peptide endothelin-1 (ET-1) in renal injury is not fully understood. In this review, we examine the genetic models available to understand the autocrine/paracrine mechanisms by which ET-1 leads to renal injury and propose the working hypothesis that endothelium-derived ET-1 induces renal injury by initiating renal tubular apoptosis in a paracrine manner.

Ontogeny of endothelin receptors in the brain, heart, and kidneys of neonatal rats

BACKGROUND

Endothelin (ET) plays an important role in many physiological functions. It has been demonstrated that endogenous ET-1 concentration in the central nervous system (CNS) changes with age; however the ontogeny of ETA and ETB receptors in the brain, heart, and kidneys during postnatal development has not been studied.

METHODS

Brains, hearts and kidneys of rats at postnatal days 1, 7, 14 and 28 were evaluated for the expression of ETA and ETB receptors via Western blot. ETB receptors within the developing brain were further accessed via immunofluorescence.

RESULTS

The mean organ and body weights increased proportionally with advancing age demonstrating normal growth. The expression of ETA receptors in the brain, heart, and kidneys and ETB receptor expression in the heart and kidneys was similar in these rats at postnatal ages 1, 7, 14 and 28days. However, brain ETB receptor expression significantly (P<0.001) decreased by 72% on day 28 compared to the levels on postnatal day 1. Upon immunofluorescent analysis, the intensity of ETB staining in the cerebral cortex and subventricular zones of the developing rat brain decreased significantly from day 1 to day 7 (P<0.001) and from day 7 to day 14 (P<0.0001). There was no further decrease in ETB intensity noted in the cerebral cortex and subventricular zones between day 14 and day 28 of postnatal age. The intensity of ETB receptor staining within the cerebrovasculature, on the other hand, increased significantly (P<0.05) from days 1 and 7 to day 14.

CONCLUSIONS

These results demonstrate that expression of ETA receptors does not change with postnatal development. On the other hand ETB receptors in the cerebral cortex and subventricular zones of the brain decrease with age, while ETB receptors in the cerebrovasculature increase with age, implicating ETB receptor involvement in the structural maturity and development of the CNS.

The role of endothelin receptor A during myelination of developing oligodendrocytes

Endothelin (ET)-1 and its receptors (ETA and ETB receptor) are present in the central nervous system. ET exerts biological effects on gliogenesis and glial cell functions. In order to define a possible mechanism of ETA receptor signaling, the distribution of the ETA receptor in developing oligodendrocytes and the effects of ET-1 on the myelination of oligodendrocytes were examined. ETA receptor immunoreactivity was confined to the perivascular elements of the blood vessels during early postnatal development. However later in development, ETA receptor immunoreactivity was no longer observed in the vessels but became localized to the myelinating oligodendrocytes of the primitive corpus callosum of the white matter, apart from the vessels. ET-1 induced myelin basic protein (MBP) in primary oligodendrocyte precursor cell culture though the ETA receptor and was blocked by an ETA receptor antagonist. In addition, ET-1 evoked the release of Ca(2+) which is a central regulator of oligodendrocyte differentiation. Our results provide a link between ET-1 and its ETA receptor and myelination during oligodendrocyte differentiation.

Activated protein C protects myocardium via activation of anti-apoptotic pathways of survival in ischemia-reperfused rat heart

Activated protein C (APC) is known to be beneficial on ischemia reperfusion injury in myocardium. However, the protection mechanism of APC is not fully understood. The purpose of this study was to investigate the effects and possible mechanisms of APC on myocardial ischemic damage. Artificially ventilated anaesthetized Sprague-Dawley rats were subjected to a 30 min of left anterior descending coronary artery occlusion followed by 2 hr of reperfusion. Rats were randomly divided into four groups; Sham, I/R, APC preconditioning and postconditioning group. Myocardial infarct size, apoptosis index, the phosphorylation of ERK1/2, Bcl-2, Bax and cytochrome c genes and proteins were assessed. In APC-administrated rat hearts, regardless of the timing of administration, infarct size was consistently reduced compared to ischemia/reperfusion (I/R) rats. APC improved the expression of ERK1/2 and anti-apoptotic protein Bcl-2 which were significantly reduced in the I/R rats. APC reduced the expression of pro-apoptotic genes, Bax and cytochrome c. These findings suggest that APC produces cardioprotective effect by preserving the expression of proteins and genes involved in anti-apoptotic pathways, regardless of the timing of administration.