Purinergic P2X1 receptor, purinergic P2X7 receptor, and angiotensin II type 1 receptor interactions in the regulation of renal afferent arterioles in angiotensin II-dependent hypertension

Purinergic Receptor Activation Protects Glomerular Microvasculature from Increased Mechanical Stress in Angiotensin II-Induced Hypertension: A Modeling Study

Angiotensin II (Ang II)-induced hypertension increases afferent (AA) and efferent (EA) arteriole resistances via the actions of Ang II on the AT1 receptor. In addition to the increased interstitial levels of Ang II, the increased arterial pressure increases interstitial ATP concentrations. In turn, ATP acts on the purinergic receptors P2X1 and P2X7 to constrict the AA, preventing increases in plasma flow and single-nephron GFR (SNGFR). While the hemodynamic effects of P2 activation have been characterized, the resulting increases in mechanical stresses (shear stress and circumferential hoop stress) on the glomerular microvasculature have not been quantified. A mathematical microvascular hemodynamic glomerular model was developed to simulate blood flow and plasma filtration in an anatomically accurate rat glomerular capillary network. AA and EA resistances were adjusted to match glomerular hemodynamic data for control, Ang II-induced hypertension, and P2X1-blocked conditions. A blockade of the purinergic receptors reduced both afferent and efferent resistances, maintaining glomerular pressure at hypertensive levels but increasing blood flow and sheer stress significantly. Because glomerular pressure was maintained, hoop stress barely changed. Our results indicate that the activation of the purinergic system protects the glomerular microvasculature from elevated shear stress caused by increased blood flow that would occur in the absence of purinergic stimulation.

Cardiac surgery-associated acute kidney injury in cardiopulmonary bypass: a focus on sex differences and preventive strategies

Cardiac surgery-associated acute kidney injury (CSA-AKI) is a high-risk complication with well-recognized increased morbidity and mortality after cardiac surgery attributable in large part to cardiopulmonary bypass (CPB)-associated factors contributing to AKI including hemodilution, hypothermia, hypotension, and exposure to artificial surfaces. These conditions disrupt the renal microcirculation and activate local and systemic inflammatory responses to nonpulsatile flow and low perfusion pressure. The underlying mechanisms of CSA-AKI in CPB are not fully understood, and the incidence of CSA-AKI remains high at around 30%. Furthermore, women appear to be more vulnerable than men to the renal injury associated with CPB even though the overall incidence of cardiovascular and kidney diseases is lower in premenopausal women. Nevertheless, estrogen elicits renoprotective effects in several ways including mitigating inflammation, promoting natriuresis, and endothelial protection as shown in preclinical studies. However, women have higher rates of CSA-AKI and these are exacerbated in postmenopausal women. This leads to the conundrum of whether sex, age, and hormonal status differences influence CSA-AKI. In this review, we briefly discuss the pathophysiology of CSA-AKI in CPB and sex differences in kidney functions with a focus on the possible role of estrogen-specific effects in CPB and also possible differences in CPB in women including greater hemodilution. Furthermore, we review strategies to prevent CSA-AKI in CPB with a highlight for potential sex-specific strategies. Improving our understanding of the impact of sex and sex hormones on CSA-AKI initiation and development will allow us to better manage the CPB strategies delivered to all patients.

Role of local angiotensin II signaling in bladder function

Angiotensin II signaling plays a crucial role in many different diseases. Although it has been known for several decades that local angiotensin II signaling molecules are present in the bladder, the understanding of their functions there is still limited, especially compared with other organ systems such as cardiovascular and respiratory systems. This article reviews current literature regarding local angiotensin II signaling in the urinary bladder. By reviewing several decades of literature, the field has provided strong evidence to support the presence of local angiotensin II signaling in the bladder, including the expression of angiotensin type 1 receptor and angiotensin type 2 receptor in both human and animal tissues. In addition, evidence suggests a functional role of angiotensin type 1 receptor in mediating bladder contractions. In bladder disease models, angiotensin II signaling can be upregulated, and angiotensin type 1 receptor activity is associated with increases in inflammation, fibrosis, and oxidative stress. We also address the gaps in knowledge that remain in understanding local angiotensin II signaling in the bladder, including limitations on clinical translatability. Although there is a strong foundation regarding the local presence and role of angiotensin II signaling in the bladder, further research is needed to support translational applications.

P2X7 receptor knockout does not alter renal function or prevent angiotensin II-induced kidney injury in F344 rats

P2X7 receptors mediate immune and endothelial cell responses to extracellular ATP. Acute pharmacological blockade increases renal blood flow and filtration rate, suggesting that receptor activation promotes tonic vasoconstriction. P2X7 expression is increased in kidney disease and blockade/knockout is renoprotective. We generated a P2X7 knockout rat on F344 background, hypothesising enhanced renal blood flow and protection from angiotensin-II-induced renal injury. CRISPR/Cas9 introduced an early stop codon into exon 2 of P2rx7, abolishing P2X7 protein in kidney and reducing P2rx7 mRNA abundance by ~ 60% in bone-marrow derived macrophages. The M1 polarisation response to lipopolysaccharide was unaffected but P2X7 receptor knockout suppressed ATP-induced IL-1β release. In male knockout rats, acetylcholine-induced dilation of the renal artery ex vivo was diminished but not the response to nitroprusside. Renal function in male and female knockout rats was not different from wild-type. Finally, in male rats infused with angiotensin-II for 6 weeks, P2X7 knockout did not reduce albuminuria, tubular injury, renal macrophage accrual, and renal perivascular fibrosis. Contrary to our hypothesis, global P2X7 knockout had no impact on in vivo renal hemodynamics. Our study does not indicate a major role for P2X7 receptor activation in renal vascular injury.

Interaction of Angiotensin II AT1 Receptors with Purinergic P2X Receptors in Regulating Renal Afferent Arterioles in Angiotensin II-Dependent Hypertension

In angiotensin II (Ang II)-dependent hypertension, Ang II activates angiotensin II type 1 receptors (AT1R) on renal vascular smooth muscle cells, leading to renal vasoconstriction with eventual glomerular and tubular injury and interstitial inflammation. While afferent arteriolar vasoconstriction is initiated by the increased intrarenal levels of Ang II activating AT1R, the progressive increases in arterial pressure stimulate the paracrine secretion of adenosine triphosphate (ATP), leading to the purinergic P2X receptor (P2XR)-mediated constriction of afferent arterioles. Thus, the afferent arteriolar tone is maintained by two powerful systems eliciting the co-existing activation of P2XR and AT1R. This raises the conundrum of how the AT1R and P2XR can both be responsible for most of the increased renal afferent vascular resistance existing in angiotensin-dependent hypertension. Its resolution implies that AT1R and P2XR share common receptor or post receptor signaling mechanisms which converge to maintain renal vasoconstriction in Ang II-dependent hypertension. In this review, we briefly discuss (1) the regulation of renal afferent arterioles in Ang II-dependent hypertension, (2) the interaction of AT1R and P2XR activation in regulating renal afferent arterioles in a setting of hypertension, (3) mechanisms regulating ATP release and effect of angiotensin II on ATP release, and (4) the possible intracellular pathways involved in AT1R and P2XR interactions. Emerging evidence supports the hypothesis that P2X1R, P2X7R, and AT1R actions converge at receptor or post-receptor signaling pathways but that P2XR exerts a dominant influence abrogating the actions of AT1R on renal afferent arterioles in Ang II-dependent hypertension. This finding raises clinical implications for the design of therapeutic interventions that will prevent the impairment of kidney function and subsequent tissue injury.

Purinoceptor: a novel target for hypertension

Hypertension is the leading cause of morbidity and mortality globally among all cardiovascular diseases. Purinergic signalling plays a crucial role in hypertension through the sympathetic nerve system, neurons in the brain stem, carotid body, endothelium, immune system, renin-angiotensin system, sodium excretion, epithelial sodium channel activity (ENaC), and renal autoregulation. Under hypertension, adenosine triphosphate (ATP) is released as a cotransmitter from the sympathetic nerve. It mediates vascular tone mainly through P2X1R activation on smooth muscle cells and activation of P2X4R and P2YR on endothelial cells and also via interaction with other purinoceptors, showing dual effects. P2Y1R is linked to neurogenic hypertension. P2X7R and P2Y11R are potential targets for immune-related hypertension. P2X3R located on the carotid body is the most promising novel therapeutic target for hypertension. A₁R, A_2AR, A_2BR, and P2X7R are all related to renal autoregulation, which contribute to both renal damage and hypertension. The main focus is on the evidence addressing the involvement of purinoceptors in hypertension and therapeutic interventions.

Modulation of P2X4 receptor activity by ivermectin and 5-BDBD has no effect on the development of ARPKD in PCK rats

Autosomal recessive polycystic kidney disease (ARPKD) is an inherited pathology caused mainly by mutations of the polycystic kidney and hepatic disease 1 (PKHD1) gene, which usually leads to end-stage renal disease. Previous studies suggested that the P2X purinoreceptor 4 (P2X4 R) may play an important role in the progression of ARPKD. To test this hypothesis, we assessed the chronic effects of ivermectin (P2X4 R allosteric modulator) and 5-BDBD (P2X4 R antagonist) on the development of ARPKD in PCK/CrljCrl-Pkhd1pck/CRL (PCK) rats. Our data indicated that activation of ATP-mediated P2X4 R signaling with ivermectin for 6 weeks in high dose (50 mg/L; water supplementation) decreased the total body weight of PCK rats while the heart and kidney weight remained unaffected. Smaller doses of ivermectin (0.5 or 5 mg/L, 6 weeks) or the inhibition of P2X4 R signaling with 5-BDBD (18 mg/kg/day, food supplement for 8 weeks) showed no effect on electrolyte balance or the basic physiological parameters. Furthermore, cystic index analysis for kidneys and liver revealed no effect of smaller doses of ivermectin (0.5 or 5 mg/L) and 5-BDBD on the cyst development of PCK rats. We observed a slight increase in the cystic liver index on high ivermectin dose, possibly due to the cytotoxicity of the drug. In conclusion, this study revealed that pharmacological modulation of P2X4 R by ivermectin or 5-BDBD does not affect the development of ARPKD in PCK rats, which may provide insights for future studies on investigating the therapeutic potential of adenosine triphosphate (ATP)-P2 signaling in PKD diseases.

Purinergic signalling in the kidney: In physiology and disease

Historically, the control of renal vascular and tubular function has, for the most part, concentrated on neural and endocrine regulation. However, in addition to these extrinsic factors, it is now appreciated that several complex humoral control systems exist within the kidney that can act in an autocrine and/or paracrine fashion. These paracrine systems complement neuroendocrine regulation by dynamically fine-tuning renal vascular and tubular function to buffer rapid changes in nephron perfusion and flow rate of tubular fluid. One of the most pervasive is the extracellular nucleotide/P2 receptor system, which is central to many of the intrinsic regulatory feedback loops within the kidney such as renal haemodynamic autoregulation and tubuloglomerular feedback (TGF). Although physiological actions of extracellular adenine nucleotides were reported almost 100 years ago, the conceptual framework for purinergic regulation of renal function owes much to the work of Geoffrey Burnstock. In this review, we reflect on our >20-year collaboration with Professor Burnstock and highlight the research that is still unlocking the potential of the renal purinergic system to understand and treat kidney disease.

The Role of P2X7 Purinergic Receptors in the Renal Inflammation Associated with Angiotensin II-induced Hypertension

Purinergic receptors play a central role in the renal pathophysiology of angiotensin II-induced hypertension, since elevated ATP chronically activates P2X7 receptors in this model. The changes induced by the P2X antagonist Brilliant blue G (BBG) in glomerular hemodynamics and in tubulointerstitial inflammation resulting from angiotensin II infusion were studied. Rats received angiotensin II (435 ng·kg^-1·min^-1, 2 weeks) alone or in combination with BBG (50 mg/kg/day intraperitoneally). BBG did not modify hypertension (214.5 ± 1.4 vs. 212.7 ± 0.5 mmHg), but restored to near normal values afferent (7.03 ± 1.00 to 2.97 ± 0.27 dyn.s.cm^-5) and efferent (2.62 ± 0.03 to 1.29 ± 0.09 dyn.s.cm^-5) arteriolar resistances, glomerular plasma flow (79.23 ± 3.15 to 134.30 ± 1.11 nl/min), ultrafiltration coefficient (0.020 ± 0.002 to 0.036 ± 0.003 nl/min/mmHg) and single nephron glomerular filtration rate (22.28 ± 2.04 to 34.46 ± 1.54 nl/min). Angiotensin II induced overexpression of P2X7 receptors in renal tubular cells and in infiltrating T and B lymphocytes and macrophages. All inflammatory cells were increased by angiotensin II infusion and reduced by 20% to 50% (p < 0.05) by BBG administration. Increased IL-2, IL-6, TNFα, IL-1β, IL-18 and overexpression of NLRP3 inflammasome were induced by angiotensin II and suppressed by BBG. These studies suggest that P2X7 receptor-mediated renal vasoconstriction, tubulointerstitial inflammation and activation of NLRP3 inflammasome are associated with angiotensin II-induced hypertension.