Cellular and RAS changes in the hearts of young obese rats

Angiotensin II type 2 receptor mediates high fat diet-induced cardiomyocyte hypertrophy and hypercholesterolemia

Obesity is the major risk factor for several cardiovascular and metabolic disorders. Previous studies reported that deletion of Angiotensin II type 2 receptor (AT2R) protects against metabolic dysfunctions induced by high fat (HF) diet. However, the role of AT2R in obesity-induced cardiac hypertrophy remains unclear. Male AT2R knockout (AT2RKO) and wild type (AT2RWT) mice were fed with control or HF diet for 10 weeks. HF diet increased cardiac expression of AT2R in obese mice. Deletion of AT2R did not affect body weight gain, glucose intolerance and fat mass gain induced by HF feeding. However, loss of AT2R prevented HF diet-induced hypercholesterolemia and cardiac remodeling. Mechanistically, we found that pharmacological inhibition or knockdown of AT2R prevented leptin-induced cardiomyocyte hypertrophy in vitro. Collectively, our results suggest that AT2R is involved in obesity-induced cardiac hypertrophy.

Angiotensin II type 2 receptor (AT2R) in renal and cardiovascular disease

Angiotensin II (Ang II) is well-considered to be the principal effector of the renin-angiotensin system (RAS), which binds with strong affinity to the angiotensin II type 1 (AT1R) and type 2 (AT2R) receptor subtype. However, activation of both receptors is likely to stimulate different signalling mechanisms/pathways and produce distinct biological responses. The haemodynamic and non-haemodynamic effects of Ang II, including its ability to regulate blood pressure, maintain water-electrolyte balance and promote vasoconstriction and cellular growth are well-documented to be mediated primarily by the AT1R. However, its biological and functional effects mediated through the AT2R subtype are still poorly understood. Recent studies have emphasized that activation of the AT2R regulates tissue and organ development and provides in certain context a potential counter-regulatory mechanism against AT1R-mediated actions. Thus, this review will focus on providing insights into the biological role of the AT2R, in particular its actions within the renal and cardiovascular system.

Early life obesity and chronic kidney disease in later life

The prevalence of chronic kidney disease (CKD) has increased considerably with a parallel rise in the prevalence of obesity. It is now recognized that early life nutrition has life-long effects on the susceptibility of an individual to develop obesity, diabetes, cardiovascular disease and CKD. The kidney can be programmed by a number of intrauterine and neonatal insults. Low birth weight (LBW) is one of the most identifiable markers of a suboptimal prenatal environment, and the important intrarenal factors sensitive to programming events include decreased nephron number and altered control of the renin-angiotensin system (RAS). LBW complicated by accelerated catch-up growth is associated with an increased risk of obesity, hypertension and CKD in later life. High birth weight and exposure to maternal diabetes or obesity can enhance the risk for developing CKD in later life. Rapid postnatal growth per se may also contribute to the subsequent development of obesity and CKD regardless of birth weight and prenatal nutrition. Although the mechanisms of renal risks due to early life nutritional programming remain largely unknown, experimental and clinical studies suggest the burdening role of early life obesity in longstanding cardiovascular and renal diseases.

Differential modification of enalapril in the kidneys of lean and 'programmed' obese male young rats

OBJECTIVE

We investigated whether enalapril treatment could have beneficial effects on nutritionally-programmed renal changes in postnatally overfed young rats.

METHODS

Three or 10 male pups per mother were assigned to either the Obese or Lean groups during the first 21 days of life. These pups were treated with enalapril (Obese enalapril, OE; Lean enalapril, LE) or vehicle (Obese control, OC; Lean control, LC) between 15 and 28 days. All pups had their kidneys examined at 29 days.

RESULTS

OC pups weighed more than those in the LC group between 7 and 28 days of age (P<0.05). Enalapril reduced body weights in rats from both the Obese and Lean groups between 22 and 28 days (P<0.05). Renal cell proliferation and apoptosis, glomerulosclerosis, and tubulointerstitial fibrosis were all increased by enalapril (P<0.05). Among the groups, renal cell apoptosis and serum creatinine were the highest in OE pups (P<0.05). Enalapril treatment resulted in contrasting molecular expression profiles involved in renal maturation and repair in the kidneys of the rats from the Lean and Obese groups.

CONCLUSION

Enalapril can differentially modulate renal molecular alterations in lean and postnatally overfed rats and may be not beneficial in obese young male rats.

Postnatal early overnutrition causes long-term renal decline in aging male rats

BACKGROUND

We evaluated the influence of postnatal early overnutrition on renal pathophysiological changes in aging rats.

METHODS

Three or 10 male pups per mother were assigned to either the small litter (SL) or normal litter (control) groups, respectively, during the first 21 d of life. The effects of early postnatal overnutrition were determined at 12 mo.

RESULTS

SL rats weighed more than controls between 4 d and 6 mo of age (P < 0.05). However, between 6 and 12 mo, body weights in both groups were not different. In the SL group, at 12 mo, systolic blood pressure was higher and creatinine clearance was lower than the same in controls (P < 0.05). Numbers of CD68 (ED1)-positive macrophages and apoptotic cells in renal cortex were higher in SL rats (P < 0.05). Furthermore, index scores for glomerulosclerosis and tubulointerstitial fibrosis were higher in the SL group (P < 0.05). Significantly less glomeruli per section area were found in aging SL rats (P < 0.05). Immunoblotting and immunohistochemistry showed decreased intrarenal renin expression in SL rats (P < 0.05).

CONCLUSION

Early postnatal overnutrition can potentiate structural and functional abnormalities in the aging kidney and can lead to systolic hypertension with reduced intrarenal renin activity.

Angiotensin II type-2 receptor-specific effects on the cardiovascular system

The renin-angiotensin system (RAS) is intricately involved in cardiovascular homeostasis. It is well known that angiotensin II, the key effector in RAS, contributes to a range of cardiovascular pathologies and diseases via angiotensin II type-1 receptor (AT1R) activation. However, the role of angiotensin II type-2 receptor (AT2R) regulation is less well understood. Recent studies describe the role of the AT2R on cardiovascular function in normal and pathologic conditions. The data describe an important role of AT2R in blood pressure regulation, cardiac hypertrophy and fibrosis, myocardial infarction and vascular homeostasis.

Effects of coronary ischemia-reperfusion in a rat model of early overnutrition. Role of angiotensin receptors

Background

Obesity during childhood has dramatically increased worldwide in the last decades. Environmental factors acting early in life, including nutrition, play an important role in the pathogenesis of obesity and cardiovascular diseases in adulthood.

Aims

To analyze the effects of early overfeeding on the heart and coronary circulation, the effect of ischemia-reperfusion (I/R) and the role of the renin-angiotensin system (RAS) were studied in isolated hearts from control and overfed rats during lactation.

Methods and Results

On the day of birth litters were adjusted to twelve pups per mother (control) or to three pups per mother (overfed). At weaning (21 days) the rats were killed and the heart perfused in a Langendorff system and subjected to 30 min of ischemia followed by 15 min of reperfusion. The contractility (left developed intraventricular pressure) was lower in the hearts from overfed rats, and was reduced by I/R in hearts from control but not from overfed rats. I/R also reduced the coronary vasoconstriction to angiotensin II more in hearts from control than from overfed rats, and the vasodilatation to bradykinin similarly in both experimental groups. The expression of both angiotensin AGTRa and AGTR2 receptors was increased in the myocardium of overfed rats, and I/R increased the expression of both receptors in control rats but reduced it in overfed rats. The expression of apoptotic and antiapoptotic markers was increased in hearts of overfed rats compared with control, and further increased by I/R.

Conclusions

These results suggest that both overfeeding and I/R impair cardiac and coronary function due, at least in part, to activation of the angiotensin pathway. However, overfeeding may reduce the impairment of ventricular contractility by I/R.

Adaptive mechanisms to compensate for overnutrition-induced cardiovascular abnormalities

In conditions of overnutrition, cardiac cells must cope with a multitude of extracellular signals generated by changes in nutrient load (glucose, amino acids, and lipids) and the hormonal milieu [increased insulin (INS), ANG II, and adverse cytokine/adipokine profile]. Herein, we review the diverse compensatory/adaptive mechanisms that counter the deleterious effects of excess nutrients and growth factors. We largely focus the discussion on evidence obtained from Zucker obese (ZO) and Zucker diabetic fatty (ZDF) rats, which are useful models to evaluate adaptive and maladaptive metabolic, structural, and functional cardiac remodeling. One adaptive mechanism present in the INS-resistant ZO, but absent in the diabetic ZDF heart, involves an interaction between the nutrient sensor kinase mammalian target of rapamycin complex 1 (mTORC1) and ANG II-type 2 receptor (AT2R). Recent evidence supports a cardioprotective role for the AT2R; for example, suppression of AT2R activation interferes with antihypertrophic/antifibrotic effects of AT1R blockade, and AT2R agonism improves cardiac structure and function. We propose a scenario, whereby mTORC1-signaling-mediated increase in AT2R expression in the INS-resistant ZO heart is a cardioprotective adaptation to overnutrition. In contrast to the ZO rat, heart tissues of ZDF rats do not show activation of mTORC1. We posit that such a lack of activation of the mTOR↔AT2R integrative pathway in cardiac tissue under conditions of obesity-induced diabetes may be a metabolic switch associated with INS deficiency and clinical diabetes.