The Modulatory Role of Heme Oxygenase on Subpressor Angiotensin II-Induced Hypertension and Renal Injury

EET enhances renal function in obese mice resulting in restoration of HO-1-Mfn1/2 signaling, and decrease in hypertension through inhibition of sodium chloride co-transporter

BACKGROUND

We have previously reported that epoxyeicosatrienoic acid (EET) has multiple beneficial effects on renal and adipose tissue function, in addition to its vasodilatory action; it increases insulin sensitivity and inhibits inflammation. In an examination of the signaling mechanisms by which EET reduces renal and peri-renal fat function, we hypothesized that EET ameliorates obesity-induced renal dysfunction by improving sodium excretion, reducing the sodium-chloride cotransporter NCC, lowering blood pressure, and enhancing mitochondrial and thermogenic gene levels in PGC-1α dependent mice.

METHODS

EET-agonist treatment normalized glucose metabolism, renal ENaC and NCC protein expression, urinary sodium excretion and blood pressure in obese (db/db) mice. A marked improvement in mitochondrial integrity, thermogenic genes, and PGC-1α-HO-1-adiponectin signaling occurred. Knockout of PGC-1α in EET-treated mice resulted in a reversal of these beneficial effects including a decrease in sodium excretion, elevation of blood pressure and an increase in the pro-inflammatory adipokine nephroblastoma overexpressed gene (NOV). In the elucidation of the effects of EET on peri-renal adipose tissue, EET increased adiponectin, mitochondrial integrity, thermogenic genes and decreased NOV, i.e. "Browning' peri-renal adipose phenotype that occurs under high fat diets. Taken together, these data demonstrate a critical role of an EET agonist in the restoration of healthy adipose tissue with reduced release of inflammatory molecules, such as AngII and NOV, thereby preventing their detrimental impact on sodium absorption and NCC levels and the development of obesity-induced renal dysfunction.

Heme Oxygenase-1 in Kidney Health and Disease

SIGNIFICANCE

Acute kidney injury (AKI) and chronic kidney disease (CKD) represent a considerable burden in healthcare. The heme oxygenase (HO) system plays an important role in regulating oxidative stress and is protective in a variety of human and animal models of kidney disease. Preclinical studies of the HO system have led to the development of several clinical trials targeting the enzyme or its products.

RECENT ADVANCES

Connection of HO, ferritin, and other proteins involved in iron regulation has provided important insight into mechanisms of damage in AKI. Also, HO-1 expression is important in the pathogenesis of hypertension, diabetic kidney disease, and progression to end-stage renal disease.

CRITICAL ISSUES

Despite intriguing discoveries, no drugs targeting the HO system have been translated to the clinic. Meanwhile, treatments for AKI and CKD are urgently needed. Many factors have likely contributed to challenges in clinical translation, including variation in animal models, difficulties in obtaining human tissue, and complexity of the disease processes being studied.

FUTURE DIRECTIONS

The HO system represents a promising avenue of investigation that may lead to targeted therapeutics. Tissue-specific gene modulation, widening the scope of animal studies, and continued clinical research will provide valuable insight into the role HO plays in kidney homeostasis and disease. Antioxid. Redox Signal. 25, 165-183.

Renal protective effects of induction of haem oxygenase-1 combined with increased adiponectin on the glomerular vascular endothelial growth factor-nitric oxide axis in obese rats

What is the central question of this study? This study aimed to investigate whether induction of haem oxygenase-1 (HO-1) can protect the kidneys of obese rats by regulating the glomerular vascular endothelial growth factor-nitric oxide (VEGF-NO) axis by increasing the adiponectin concentrations. What is the main finding and its importance? Induction of HO-1 reduces the degree of microalbuminuria and has renal protective effects by improving endothelial function and regulating the uncoupled glomerular VEGF-NO axis in diet-induced obese rats. The mechanism may be related to increased activation of the HO-1-adiponectin axis. The glomerular vascular endothelial growth factor-nitric oxide (VEGF-NO) axis plays a critical role in maintenance of normal kidney function in obesity. Induction of haem oxygenase-1 (HO-1) may result in a parallel increase in adiponectin secretion. The aim of this study was to investigate whether induction of HO-1 could protect the kidneys of obese rats by regulating the glomerular VEGF-NO axis by increasing adiponectin levels. Rats received high-fat diets and were injected with either cobalt protoporphyrin to induce HO-1 or stannous protoporphyrin to inhibit HO-1. Blood and urine samples were collected. Endothelial function was determined by measuring the endothelium-dependent vasodilatation of the aorta. Renal tissues were collected for CD34 immunohistochemistry. The glomerular VEGF-NO axis and the AMP kinase-phosphoinositide 3-kinase (PI3K)/Akt-endothelial nitric oxide synthase pathway were measured. Induction of HO-1 by cobalt protoporphyrin decreased microalbuminuria, plasma free fatty acids, serum high-sensitivity C-reactive protein and malondialdehyde levels and increased serum adiponectin levels compared with the untreated obese rats. Severe impairment of endothelium-dependent vasodilatation was observed in the obese rats, which was improved to some extent by HO-1 induction. Induction of HO-1 reduced glomerular CD34 expression and production of reactive oxygen species in obese rats. Obese rats showed increased glomerular VEGF expression and reduced NO levels. This uncoupling of the glomerular VEGF-NO axis was improved to some extent by induction of HO-1, with enhancement of p-AMP kinase, p-Akt and phospho-endothelial nitric oxide synthase in obese rats. These results indicate that induction of HO-1 with cobalt protoporphyrin reduces the degree of microalbuminuria and has renal protective effects by improving endothelial dysfunction and regulating the glomerular VEGF-NO axis in diet-induced obese rats by increasing adiponectin levels.

Oxidative status in the macula densa modulates tubuloglomerular feedback responsiveness in angiotensin II-induced hypertension

AIM

Tubuloglomerular feedback (TGF) is an important mechanism in control of signal nephron glomerular filtration rate. The oxidative stress in the macula densa, primarily determined by the interactions between nitric oxide (NO) and superoxide (O2-), is essential in maintaining the TGF responsiveness. However, few studies examining the interactions between and amount of NO and O2- generated by the macula densa during normal and hypertensive states.

METHODS

In this study, we used isolated perfused juxtaglomerular apparatus to directly measure the amount and also studied the interactions between NO and O2- in macula densa in both physiological and slow pressor Angiotensin II (Ang II)-induced hypertensive mice.

RESULTS

We found that slow pressor Ang II at a dose of 600 ng kg(-1) min(-1) for two weeks increased mean arterial pressure by 26.1 ± 5.7 mmHg. TGF response increased from 3.4 ± 0.2 μm in control to 5.2 ± 0.2 μm in hypertensive mice. We first measured O2- generation by the macula densa and found it was undetectable in control mice. However, O2- generation by the macula densa increased to 21.4 ± 2.5 unit min(-1) in Ang II-induced hypertensive mice. We then measured NO generation and found that NO generation by the macula densa was 138.5 ± 9.3 unit min(-1) in control mice. The NO was undetectable in the macula densa in hypertensive mice infused with Ang II.

CONCLUSIONS

Under physiological conditions, TGF response is mainly controlled by the NO generated in the macula densa; in Ang II induced hypertension, the TGF response is mainly controlled by the O2- generated by the macula densa.

Beneficial effects of diminished production of hydrogen sulfide or carbon monoxide on hypertension and renal injury induced by NO withdrawal

BACKGROUND AND PURPOSE

Whether NO, carbon monoxide (CO) and hydrogen sulfide (H2 S) compensate for each other when one or more is depleted is unclear. Inhibiting NOS causes hypertension and kidney injury. Both global depletion of H2 S by cystathionine γ-lyase (CSE) gene deletion and low levels of exogenous H2 S cause hypertension. Inhibiting CO-producing enzyme haeme oxygenase-1 (HO-1) makes rodents hypersensitive to hypertensive stimuli. We hypothesized that combined inhibition of NOS and HO-1 exacerbates hypertension and renal injury, but how combined inhibition of NOS and CSE affect hypertension and renal injury was unclear.

EXPERIMENTAL APPROACH

Rats were treated with inhibitors of NOS (L-nitroarginine; LNNA), CSE (DL-propargylglycine; PAG), or HO-1 (tin protoporphyrin; SnPP) singly for 1 or 4 weeks or in combinations for 4 weeks.

KEY RESULTS

LNNA always reduced NO, decreased H2 S and increased CO after 4 weeks. PAG abolished H2 S, always enhanced CO and reduced NO, but not when used in combination with other inhibitors. SnPP always increased NO, enhanced H2 S and inhibited CO after 1 week. Rats treated with LNNA, but not PAG and SnPP, rapidly developed hypertension followed by renal dysfunction. LNNA-induced hypertension was ameliorated and renal dysfunction prevented by all additional treatments. Renal HO-1 expression was increased by LNNA in injured tubules and increased in all tubules by all other treatments.

CONCLUSIONS AND IMPLICATIONS

The amelioration of LNNA-induced hypertension and renal injury by additional inhibition of H2 S and/or CO-producing enzymes appeared to be associated with secondary increases in renal CO or NO production.

Enhanced expression and activity of Nox2 and Nox4 in the macula densa in ANG II-induced hypertensive mice

NAD(P)H oxidase (Nox)2 and Nox4 are the isoforms of Nox expressed in the macula densa (MD). MD-derived superoxide (O₂⁻), primarily generated by Nox2, is enhanced by acute ANG II stimulation. However, the effects of chronic elevations in ANG II during ANG II-induced hypertension on MD-derived O₂⁻ are unknown. We infused a slow pressor dose of ANG II (600 ng·min⁻¹·kg⁻¹) for 2 wk in C57BL/6 mice and found that mean arterial pressure was elevated by 22.3 ± 3.4 mmHg (P < 0.01). We measured O₂⁻ generation in isolated and perfused MDs and found that O₂⁻ generation by the MD was increased from 9.4 ± 0.9 U/min in control mice to 34.7 ± 1.8 U/min in ANG II-induced hypertensive mice (P < 0.01). We stimulated MMDD1 cells, a MD-like cell line, with ANG II and found that O₂⁻ generation increased from 921 ± 91 to 3,687 ± 183 U·min⁻¹·10⁵ cells⁻¹, which was inhibited with apocynin, oxypurinol, or NS-398 by 46%, 14%, and 12%, respectively. We isolated MD cells using laser capture microdissection and measured mRNA levels of Nox. Nox2 and Nox4 levels increased by 3.7 ± 0.17- and 2.6 ± 0.15-fold in ANG II-infused mice compared with control mice. In MMDD1 cells treated with Nox2 or Nox4 small interfering (si)RNAs, ANG II-stimulated O₂⁻ generation was blunted by 50% and 41%, respectively. In cells treated with p22(phox) siRNA, ANG II-stimulated O₂⁻ generation was completely blocked. In conclusion, we found that a subpressor dose of ANG II enhances O₂⁻ generation in the MD and that the sources of this O₂⁻ are primarily Nox2 and Nox4.