Developmental expression of human angiotensinogen in transgenic mice

Long-Range Control of Renin Gene Expression in Tsukuba Hypertensive Mice

Renin, a rate-limiting enzyme in the renin–angiotensin system, is regulated to maintain blood pressure homeostasis: renin gene expression in the kidney is suppressed in a hypertensive environment. We found that expression of a 15-kb human RENIN (hREN) transgene was aberrantly upregulated (>4.2-fold), while the endogenous mouse renin (mRen) gene was suppressed (>1.7-fold) in Tsukuba hypertensive mice (THM), a model for genetically induced hypertension. We then generated transgenic mice using a 13-kb mRen gene fragment that was homologous to the 15-kb hREN transgene and found that its expression was also upregulated (>3.1-fold) in THM, suggesting that putative silencing elements of the renin genes were distally located in the loci. We next examined the possible role of a previously identified mouse distal enhancer (mdE) located outside of the 13-kb mRen gene fragment. Deletion of the mdE in the context of a 156-kb mRen transgene did not affect its transcriptional repression in THM, implying that although the silencing element of the mRen gene is located within the 156-kb fragment tested, it is distinct from the mdE. Consistent with these results, deletion of the 63-kb region upstream of the mdE from the endogenous mRen gene locus abrogated its transcriptional repression in THM. We finally tested whether dysregulation of the short renin transgenes also occurred in the fetal or neonatal kidneys of THM and found that their expression was not aberrantly upregulated, demonstrating that aberrant regulation of short renin transgenes commences sometime between neonate and adult periods.

Salt-Sensitive Hypertension: Perspectives on Intrarenal Mechanisms

Salt sensitive hypertension is characterized by increases in blood pressure in response to increases in dietary salt intake and is associated with an enhanced risk of cardiovascular and renal morbidity. Although researchers have sought for decades to understand how salt sensitivity develops in humans, the mechanisms responsible for the increases in blood pressure in response to high salt intake are complex and only partially understood. Until now, scientists have been unable to explain why some individuals are salt sensitive and others are salt resistant. Although a central role for the kidneys in the development of salt sensitivity and hypertension has been generally accepted, it is also recognized that hypertension is of multifactorial origin and a variety of factors can induce, or prevent, blood pressure responsiveness to the manipulation of salt intake. Excess salt intake in susceptible persons may also induce inappropriate central and sympathetic nervous system responses and increase the production of intrarenal angiotensin II, catecholamines and other factors such as oxidative stress and inflammatory cytokines. One key factor is the concomitant inappropriate or paradoxical activation of the intrarenal renin-angiotensin system, by high salt intake. This is reflected by the increases in urinary angiotensinogen during high salt intake in salt sensitive models. A complex interaction between neuroendocrine factors and the kidney may underlie the propensity for some individuals to retain salt and develop salt-dependent hypertension. In this review, we focus mainly on the renal contributions that provide the mechanistic links between chronic salt intake and the development of hypertension.

Development of fetal brain renin-angiotensin system and hypertension programmed in fetal origins

Since the concept of fetal origins of adult diseases was introduced in 1980s, the development of the renin-angiotensin system (RAS) in normal and abnormal patterns has attracted attention. Recent studies have shown the importance of the fetal RAS in both prenatal and postnatal development. This review focuses on the functional development of the fetal brain RAS, and ontogeny of local brain RAS components in utero. The central RAS plays an important role in the control of fetal cardiovascular responses, body fluid balance, and neuroendocrine regulation. Recent progress has been made in demonstrating that altered fetal RAS development as a consequence of environmental insults may impact on "programming" of hypertension later in life. Given that the central RAS is of equal importance to the peripheral RAS in cardiovascular regulation, studies on the fetal brain RAS development in normal and abnormal patterns could shed light on "programming" mechanisms of adult cardiovascular diseases in fetal origins.

Redox control of renal function and hypertension

Loss of redox homeostasis and formation of excessive free radicals play an important role in the pathogenesis of kidney disease and hypertension. Free radicals such as reactive oxygen species (ROS) are necessary in physiologic processes. However, loss of redox homeostasis contributes to proinflammatory and profibrotic pathways in the kidney, which in turn lead to reduced vascular compliance and proteinuria. The kidney is susceptible to the influence of various extracellular and intracellular cues, including the renin-angiotensin-aldosterone system (RAAS), hyperglycemia, lipid peroxidation, inflammatory cytokines, and growth factors. Redox control of kidney function is a dynamic process with reversible pro- and anti-free radical processes. The imbalance of redox homeostasis within the kidney is integral in hypertension and the progression of kidney disease. An emerging paradigm exists for renal redox contribution to hypertension.

Intrarenal renin-angiotensin system and counteracting protective mechanisms in angiotensin II-dependent hypertension

It is now well accepted that alterations in kidney function, due either to primary renal disease or to inappropriate hormonal influences on the kidney, are a cardinal characteristic in all forms of hypertension, and lead to a reduced ability of the kidneys to excrete sodium and the consequent development of elevated arterial pressures. However, it is also apparent that many extrarenal factors are important contributors to altered kidney function and hypertension. Central to many hypertensinogenic processes is the inappropriate activation of the renin-angiotensin system (RAS) and its downstream consequences by various pathophysiologic mechanisms. There may also be derangements in arachidonic acid metabolites, endothelium derived factors such as nitric oxide and carbon monoxide, and various paracrine and neural systems that normally interact with or provide a counteracting balance to the actions of the RAS. Thus, when the capacity of the kidneys to maintain sodium balance and extracellular fluid volume within appropriate ranges is compromised, increases in arterial pressure become necessary to re-establish normal balance.

Thyroid hormone modulates renin and ANG II receptor expression in fetal sheep

Fetal renin-angiotensin system (RAS) activity is developmentally regulated, increasing in late gestation toward term. At the same time, fetal hemodynamic parameters change, with blood pressure increasing and heart rate decreasing. During this period, fetal plasma thyroid hormone concentrations also increase significantly. In this study we utilized the technique of thyroidectomy (TX), which removes thyroid hormone from the circulation, to investigate the importance of thyroid hormone on the developmental changes in the RAS (in plasma, kidney, heart, and lung) and hemodynamic regulation in fetal sheep. TX was performed at 120 days of gestational age (dGA), and control fetuses were sham operated. Immediately before necropsy (∼137 dGA), fetuses were infused with isoproterenol and the hemodynamic responses were noted. TX significantly decreased plasma thyroid hormone concentrations and renal renin mRNA and renal active renin levels but did not change fetal plasma active renin levels. TX decreased both angiotensin II receptor subtype 1 (AT1) mRNA and protein levels in kidney and lung but not in the left ventricle. TX also was associated with increased ANG II receptor subtype 2 (AT2) mRNA and protein at the 44-kDa band in kidney, whereas AT2 protein was decreased at the 78-kDa level in kidney and lung tissue only. TX fetuses had significantly lower basal mean arterial blood pressures (MAP) and heart rates than controls. Isoproterenol infusion decreased MAP in TX fetuses. These findings support the hypothesis that thyroid hormone is important in modulating maturation of RAS and cardiovascular function in the late-gestation fetal sheep.