CROSSTALK BETWEEN THE RENAL SYMPATHETIC NERVE AND INTRARENAL ANGIOTENSIN II MODULATES PROXIMAL TUBULAR SODIUM REABSORPTION Roberto B. Pontes1, Adriana C. C. Girardi2, Erika E. Nishi1, Ruy R. Campos1, Cássia T. Bergamaschi1
1
Department of Physiology, Division of Cardiovascular Physiology, Federal
University of Sao Paulo, São Paulo, SP, Brazil 2
Heart Institute (InCor), University of São Paulo Medical School, São Paulo,
SP, Brazil.
Running Title: Renal nerve stimulation and NHE3-mediated sodium reabsorption.
Author for correspondence: Dr. Cássia T. Bergamaschi Federal University of São Paulo Department of Physiology Rua Botucatu, 862 04023-060, São Paulo, SP, Brazil Tel/Fax: 55 11 5576-4536 This is an Accepted Article that has been peer-reviewed and approved for publication in the Experimental Physiology, but has yet to undergo copy-editing and proof correction. Please cite this article as an Accepted Article; doi:10.1113/EP085075. This article is protected by copyright. All rights reserved.
1
E-mail:
[email protected]
New Findings What is the topic of this review? The sympathetic control of renal sodium tubular reabsorption is dependent on activation of the intrarenal renin angiotensin system and activation of the AT 1 receptor by ANG II.
What advances does it highlight? Despite the fact that the interaction between the sympathetic nervous system (SNS) and ANG II regarding salt reabsorption is a well-known classical mechanism for the maintenance of extracellular volume homeostasis, the underlying molecular signalling is not clearly understood. It has been recently shown that renal nerve stimulation increases intrarenal ANG II and activates the AT 1 receptor, triggering a signalling cascade that leads to elevations of Na+/H+ exchanger isoform 3 (NHE3)mediated tubular transport. In this short review, the crosstalk between intrarenal ANG II and renal nerve activity and its effect on sodium reabsorption is addressed.
Abstract In this review, we address the importance of the interaction between the sympathetic nervous system (SNS) and intrarenal renin-angiotensin system (RAS) in modulating renal tubular handling of sodium and water. We have recently shown that increased Na+/H+ exchanger isoform 3 (NHE3) activity induced by renal nerve stimulation (RNS) depends on the activation of the AT 1 receptor by angiotensin II (ANG II). Low-frequency RNS resulted in higher levels of intrarenal angiotensinogen (AGT) and ANG II independent of changes in blood pressure, the glomerular filtration rate and systemic AGT. ANG II, via the AT1 receptor, triggered an intracellular pathway activating NHE3 in the renal cortex leading to antinatriuresis and antidiuresis. Pharmacological blockade of the AT1 receptor with losartan prior to RNS abolished both the functional and molecular responses, suggesting that intrarenal This article is protected by copyright. All rights reserved.
2
ANG II acting via the AT1 receptor is a major factor for NHE3-mediated sodium and water reabsorption induced by RNS. Introduction The sympathetic nervous system (SNS) plays a pivotal role in the control of renal function during physiological and pathophysiological conditions (DiBona & Kopp, 1997). Altered renal handling of sodium and water accompanied by sympathetic hyperactivity have been demonstrated in various chronic diseases, including hypertension, heart failure and renal insufficiency (Girardi & Di Sole, 2012). Therefore, elucidation of the molecular mechanisms by which the SNS influences renal regulation of the extracellular volume may contribute to treating and/or attenuating the progression of cardiovascular and renal disease. Several distinct techniques have been used to demonstrate that an acute increase in renal sympathetic nerve activity (rSNA) enhances electrolyte and fluid tubular reabsorption by the kidneys (Bell-Reuss et al., 1976; Koepke et al., 1988; Healy et al., 2014), whereas surgical renal denervation has the opposite effect (Bello-Reuss et al., 1975; Healy et al., 2014). In addition to autonomic control, angiotensin II (ANG II) also exerts a myriad of influences on renal function (Baum et al., 1997; Quan & Baum, 2001, 2002). All components required for the formation of ANG II are present in the kidney, allowing the generation of very high concentrations of local ANG II (Braam et al., 1993; Baum et al., 1997; Boer et al., 1997; Navar et al., 2003). The interdependent action between SNS and ANG II has been demonstrated in both the central nervous system and kidney (Li & Guyenet, 1996; Quan & Baum, 2001, 2002). In this review, we address the importance of the interaction between the SNS and ANG II on renal tubular handling of sodium and water.
This article is protected by copyright. All rights reserved.
3
Renal innervation influences renal reabsorption All of the segments of the nephron, and especially the proximal tubule, are richly innervated by the SNS (Müller & Barajas, 1972; Barajas et al., 1992). The physiological importance of the tubular innervation on fluid reabsorption has been demonstrated by experiments using either renal nerve stimulation (RNS) or renal denervation (DiBona & Kopp, 1997; Johns et al., 2011). Denervation been has shown to acutely increase the urinary volume and sodium excretion (Bello-Reuss et al., 1975; Quan & Baum, 2001) that remained over 6 days after surgery (Quan & Baum, 2001). RNS promotes different renal responses in a frequency-dependent manner; low-frequencies (0.5 and 2.0 Hz) causes renin secretion and sodium reabsorption independent of hemodynamic changes, and frequencies above 2.0 Hz cause vasoconstriction (DiBona & Kopp, 1997). The actions of the SNS on renal function are dependent on both alpha and beta-adrenergic receptors. The alpha1adrenoreceptors are mainly confined to the basolateral membrane of the proximal tubule cell. Indeed, it has been demonstrated that intrarenal infusion of alpha adrenergic receptor agonists decreases urinary output and sodium excretion with no changes in glomerular filtration rate and blood pressure (Chan, 1980), indicating that the renal nerve may influence renal tubular function, at least in part, due to the activation of alpha1-adrenoreceptors. In addition, Healy and colleagues have demonstrated that norepinephrine increases brush border NHE3 abundance and activity in primary cultures of proximal tubular cells, and these effects are completely prevented by prior exposure of these cells to prazosin, indicating that norepinephrine upregulates NHE3 via an alpha-1-adrenoceptor-mediated mechanism (Healy et al., 2014). However, it has been shown that activation of beta1-adrenoreceptors in the juxtaglomerular granular cells increases the rate of renin secretion, which may contribute to the activation of systemic RAS (DiBona & Kopp, 1997).
One may
speculate that preferential or simultaneous activation of alpha and/or beta adrenoreceptors in the kidney may be dependent upon time and levels of RNS.
This article is protected by copyright. All rights reserved.
4
It has also been shown that within the kidney, ANG II influences renal tubular reabsorption by acting in the initial (Baum et al., 1997) and distal portions (PetiPeterdi et al., 2002) of the nephron segments. Although in vitro ANG II per se can increase proximal tubular reabsorption (Baum et al., 1997), under physiological conditions, the actions of ANG II seem to be strongly dependent on intact renal innervation (Quan & Baum, 2001). After 6 days of renal denervation, the remaining reduction in proximal tubular reabsorption was restored by intraluminal infusion of ANG II (Quan & Baum, 2001). It has also been shown that ANG II acts on AT1 receptors located at the presynaptic membranes, thereby facilitating norepinephrine release, and losartan has been shown to inhibit this response, further underscoring the physiological importance of the interaction between the SNS and ANG II (DiBona & Kopp, 1997). However, the exact mechanism underlying the intrarenal interaction between SNS-ANG II has not been fully explained. Recently, we have shown that lowfrequency RNS leads to activation of the intrarenal RAS, with no effects on the systemic components of this system. This response was accompanied by increased sodium and water reabsorption independent of hemodynamic changes. Moreover, these effects were completely blunted by AT 1 receptor blockade prior to lowfrequency RNS (Pontes et al., 2015).
Effects of the interaction between SNS and intrarenal ANG II on renal function ANG II is not only generated systemically but also “locally” in a variety of tissues, especially the kidneys. In fact, the concentration of ANG II in the renal interstitial fluid is higher than that in the plasma (Braam et al., 1993; Baum et al., 1997; Boer et al., 1997), reflecting the intrarenal generation of the peptide. Interestingly, local ANG II may act completely independent of systemic ANG II. It has been demonstrated that intrarenally produced ANG II modulates fluid transport in the proximal tubule independent of systemic ANG II (Quan & Baum, 1996; Thomson et al., 2006). Using in vivo microperfusion in the rat, Quan and Baum demonstrated that RNS increased proximal tubular fluid transport, and this effect was blunted by intraluminal perfusion with the ANG II converting enzyme (ACE) inhibitor (Quan & Baum, 2002). Moreover, acute renal denervation or intraluminal perfusion of This article is protected by copyright. All rights reserved.
5
the proximal tubule with the ACE inhibitor equally decreased proximal tubular reabsorption (Quan & Baum, 2002), demonstrating an important role of intrarenal ANG II in the actions mediated by SNS activation on proximal tubule transport. In addition, we have recently found that low-frequency RNS significantly increases intrarenal, but not systemic, ANG II (Pontes et al., 2015). These studies further our understanding regarding the crosstalk between the renal sympathetic nerve and intrarenal ANG II, which influences sodium and water reabsorption. However, the interaction between the SNS and intrarenal ANG II in the long term control of sodium tubule reabsorption remains unclear. The introduction of renal denervation to treat refractory hypertensive subjects underscores the importance of renal nerves in the regulation of renal function and blood pressure control. Renal nerve stimulation increases NHE3 activity: new insights into the role of the AT1 ANG II receptor The proximal tubule reabsorbs the bulk of glomerular filtrate via both transcellular and paracellular mechanisms. Na+/H+ exchanger isoform 3 (NHE3) is an important proximal tubular transporter that substantially contributes to sodium bicarbonate and sodium chloride (Schultheis et al., 1998) reabsorption in this nephron segment. NHE3 regulation may occur by changes in its abundance, activity or redistribution along the microvilli of the brush border membrane (Aronson, 2002; Lee et al., 2009; Brasen et al., 2014). A recent study suggests the influence of the SNS on NHE3-mediated sodium transport. RNS increased NHE3 activity resulting in antidiuresis and antinatriuresis, whereas surgical renal denervation produced the opposite effect (Healy et al., 2014). However, the role of intrarenal ANG II in mediating such molecular responses was not evaluated in this study.
This article is protected by copyright. All rights reserved.
6
We have recently shown that increased NHE3 activity induced by RNS depends on intrarenal ANG II binding to AT 1 receptors. In our study, low-frequency RNS resulted in higher levels of intrarenal AGT and ANG II independent of changes in blood pressure, renal function and systemic RAS. ANG II via the AT 1 receptor triggered the intracellular pathway activating NHE3, which resulted in antinatriuresis and antidiuresis. Pharmacological blockade of the AT 1 receptor with losartan prior to RNS abolished both the functional and molecular responses induced by RNS, suggesting that intrarenal ANG II acting via the AT 1 receptor was a major factor that influenced NHE3-mediated sodium and water reabsorption (Pontes et al., 2015). Following ANG II binding to AT1 receptors, intracellular pathway activation was dependent on the inhibition of adenylyl cyclase and the reduction of protein kinase A (PKA) activity, leading to NHE3 activation with consequently greater Na+ reabsorption. Previously, this pathway was demonstrated by Thekkumkara and Linas (Thekkumkara & Linas, 2002). Considering that NHE3 is endogenously inhibited by protein kinase A (PKA) (Zhao et al., 1999), a decrease in cAMP levels and PKA activity resulting in translocation of NHE3 from the base to the body of the microvilli may explain how ANG II activates NHE3 (Woodcock & Johnston, 1982; Liu & Cogan, 1989). Our findings suggested that acute low-frequency RNS leads to a preferential increase in the formation of intrarenal ANG II, which binds to the AT 1 receptor, triggering inhibitory G protein (Gi) signalling, which reduces cAMP generation and consequently decreases PKA-mediated inhibition of NHE3, resulting in antidiuresis and antinatriuresis, as demonstrated in Figure 1.
This article is protected by copyright. All rights reserved.
7
Conclusions Taken together it is very likely that under physiological conditions, acute rSNA modulates sodium reabsorption by increasing intrarenal ANG II generation and activation of the luminal membrane AT1 receptor. However, further studies are necessary to better understand the role of renal nerves in sodium and water reabsorption along the other nephron segments during physiological and pathophysiological conditions. The understanding of the molecular mechanism involved may contribute to the development of more refined tools to treat several pathological conditions such as systemic hypertension and heart failure.
Disclosures None declared.
Sources of funding This study was supported by grants from the São Paulo Research Foundation (FAPESP), National Counsel of Technological and Scientific Development (CNPq) and Coordenação de Aperfeiçoamento de Pessoal de Nivel Superior (CAPES). CTB, ACG and RRC are recipients of CNPq fellowships.
This article is protected by copyright. All rights reserved.
8
References
Aronson PS (2002). Ion exchangers mediating NaCl transport in the renal proximal tubule. Cell Biochem Biophys 36, 147-153. Barajas L, Liu L & Powers K (1992). Anatomy of the renal innervation: intrarenal aspects and ganglia of origin. Can J Physiol Pharmacol 70, 735-749. Baum M, Quigley R & Quan A (1997). Effect of luminal angiotensin II on rabbit proximal convoluted tubule bicarbonate absorption. Am J Physiol 273, F595600. Bell-Reuss E, Trevino DL & Gottschalk CW (1976). Effect of renal sympathetic nerve stimulation on proximal water and sodium reabsorption. J Clin Invest 57, 1104-1107. Bello-Reuss E, Colindres RE, Pastoriza-Munoz E, Mueller RA & Gottschalk CW (1975). Effects of acute unilateral renal denervation in the rat. J Clin Invest 56, 208-217. Boer WH, Braam B, Fransen R, Boer P & Koomans HA (1997). Effects of reduced renal perfusion pressure and acute volume expansion on proximal tubule and whole kidney angiotensin II content in the rat. Kidney Int 51, 44-49. Braam B, Mitchell KD, Fox J & Navar LG (1993). Proximal tubular secretion of angiotensin II in rats. Am J Physiol 264, F891-898. Brasen JC, Burford JL, McDonough AA, Holstein-Rathlou NH & Peti-Peterdi J (2014). Local pH domains regulate NHE3-mediated Na⁺ reabsorption in the renal proximal tubule. Am J Physiol Renal Physiol 307, F1249-1262. Chan YL (1980). The role of norepinephrine in the regulation of fluid absorption in the rat proximal tubule. J Pharmacol Exp Ther 215, 65-70. DiBona GF & Kopp UC (1997). Neural control of renal function. Physiol Rev 77, 75197. Girardi AC & Di Sole F (2012). Deciphering the mechanisms of the Na+/H+ exchanger-3 regulation in organ dysfunction. Am J Physiol Cell Physiol 302, C1569-1587. Healy V, Thompson C & Johns EJ (2014). The adrenergic regulation of proximal tubular Na⁺/H⁺ exchanger 3 in the rat. Acta Physiol (Oxf) 210, 678-689. Johns EJ, Kopp UC & DiBona GF (2011). Neural control of renal function. Compr Physiol 1, 731-767.
This article is protected by copyright. All rights reserved.
9
Kocinsky HS, Girardi AC, Biemesderfer D, Nguyen T, Mentone S, Orlowski J & Aronson PS (2005). Use of phospho-specific antibodies to determine the phosphorylation of endogenous Na+/H+ exchanger NHE3 at PKA consensus sites. Am J Physiol Renal Physiol 289, F249-258. Koepke JP, Jones S & DiBona GF (1988). Stress increases renal nerve activity and decreases sodium excretion in Dahl rats. Hypertension 11, 334-338. Lee DH, Riquier AD, Yang LE, Leong PK, Maunsbach AB & McDonough AA (2009). Acute hypertension provokes acute trafficking of distal tubule Na-Cl cotransporter (NCC) to subapical cytoplasmic vesicles. Am J Physiol Renal Physiol 296, F810-818. Li YW & Guyenet PG (1996). Angiotensin II decreases a resting K+ conductance in rat bulbospinal neurons of the C1 area. Circ Res 78, 274-282. Liu FY & Cogan MG (1989). Angiotensin II stimulates early proximal bicarbonate absorption in the rat by decreasing cyclic adenosine monophosphate. J Clin Invest 84, 83-91. Müller J & Barajas L (1972). Electron microscopic and histochemical evidence for a tubular innervation in the renal cortex of the monkey. J Ultrastruct Res 41, 533-549. Navar LG, Kobori H & Prieto-Carrasquero M (2003). Intrarenal angiotensin II and hypertension. Curr Hypertens Rep 5, 135-143. Peti-Peterdi J, Warnock DG & Bell PD (2002). Angiotensin II directly stimulates ENaC activity in the cortical collecting duct via AT(1) receptors. J Am Soc Nephrol 13, 1131-1135. Pontes RB, Crajoinas RO, Nishi EE, Oliveira-Sales EB, Girardi AC, Campos RR & Bergamaschi CT (2015). Renal nerve stimulation leads to the activation of the Na+/H+ exchanger isoform 3 via angiotensin II type I receptor. Am J Physiol Renal Physiol, ajprenal.00515.02014. Quan A & Baum M (1996). Endogenous production of angiotensin II modulates rat proximal tubule transport. J Clin Invest 97, 2878-2882. Quan A & Baum M (2001). The renal nerve is required for regulation of proximal tubule transport by intraluminally produced ANG II. Am J Physiol Renal Physiol 280, F524-529. Quan A & Baum M (2002). Renal nerve stimulation augments effect of intraluminal angiotensin II on proximal tubule transport. Am J Physiol Renal Physiol 282, F1043-1048. Schultheis PJ, Clarke LL, Meneton P, Miller ML, Soleimani M, Gawenis LR, Riddle TM, Duffy JJ, Doetschman T, Wang T, Giebisch G, Aronson PS, Lorenz JN & This article is protected by copyright. All rights reserved.
10
Shull GE (1998). Renal and intestinal absorptive defects in mice lacking the NHE3 Na+/H+ exchanger. Nat Genet 19, 282-285.
Thekkumkara T & Linas SL (2002). Role of internalization in AT(1A) receptor function in proximal tubule epithelium. Am J Physiol Renal Physiol 282, F623629.
Thomson SC, Deng A, Wead L, Richter K, Blantz RC & Vallon V (2006). An unexpected role for angiotensin II in the link between dietary salt and proximal reabsorption. J Clin Invest 116, 1110-1116.
Woodcock EA & Johnston CI (1982). Inhibition of adenylate cyclase by angiotensin II in rat renal cortex. Endocrinology 111, 1687-1691.
Zhao H, Wiederkehr MR, Fan L, Collazo RL, Crowder LA & Moe OW (1999). Acute inhibition of Na/H exchanger NHE-3 by cAMP. Role of protein kinase a and NHE-3 phosphoserines 552 and 605. J Biol Chem 274, 3978-3987.
This article is protected by copyright. All rights reserved.
11
Figure 1: Schematic model depicting the molecular mechanism by which the interplay between RNS and intrarenal RAS activation increases proximal tubule sodium reabsorption. A) Under baseline conditions, NHE3 is equally distributed between the body and the base of the proximal tubule brush border microvilli (Girardi & Di Sole, 2012). B) Acute RNS stimulates basolateral adrenoreceptors which leads to increased expression of AGT and generation of intrarenal ANG II. Further activation of the AT 1 receptor by ANG II stimulates NHE3-mediated sodium reabsorption in the proximal tubule. Upregulation of NHE3 transport activity seems to be due, at least in part, to redistribution of the transporter from the base to the body of the micrilovilli, which may be dependent on lowering the levels of NHE3 phosphorylation at the PKA consensus site serine 552 (Kocinsky et al., 2005). Consequently, the acute increase on NHE3-mediated sodium reabsorption in the proximal tubule will lead to anti-diuresis, anti-natriuresis and fluid retention.
This article is protected by copyright. All rights reserved.
12
1
Department of Physiology, Division of Cardiovascular Physiology, Federal
University of Sao Paulo, São Paulo, SP, Brazil 2
Heart Institute (InCor), University of São Paulo Medical School, São Paulo,
SP, Brazil.
Running Title: Renal nerve stimulation and NHE3-mediated sodium reabsorption.
Author for correspondence: Dr. Cássia T. Bergamaschi Federal University of São Paulo Department of Physiology Rua Botucatu, 862 04023-060, São Paulo, SP, Brazil Tel/Fax: 55 11 5576-4536 This is an Accepted Article that has been peer-reviewed and approved for publication in the Experimental Physiology, but has yet to undergo copy-editing and proof correction. Please cite this article as an Accepted Article; doi:10.1113/EP085075. This article is protected by copyright. All rights reserved.
1
E-mail:
[email protected]
New Findings What is the topic of this review? The sympathetic control of renal sodium tubular reabsorption is dependent on activation of the intrarenal renin angiotensin system and activation of the AT 1 receptor by ANG II.
What advances does it highlight? Despite the fact that the interaction between the sympathetic nervous system (SNS) and ANG II regarding salt reabsorption is a well-known classical mechanism for the maintenance of extracellular volume homeostasis, the underlying molecular signalling is not clearly understood. It has been recently shown that renal nerve stimulation increases intrarenal ANG II and activates the AT 1 receptor, triggering a signalling cascade that leads to elevations of Na+/H+ exchanger isoform 3 (NHE3)mediated tubular transport. In this short review, the crosstalk between intrarenal ANG II and renal nerve activity and its effect on sodium reabsorption is addressed.
Abstract In this review, we address the importance of the interaction between the sympathetic nervous system (SNS) and intrarenal renin-angiotensin system (RAS) in modulating renal tubular handling of sodium and water. We have recently shown that increased Na+/H+ exchanger isoform 3 (NHE3) activity induced by renal nerve stimulation (RNS) depends on the activation of the AT 1 receptor by angiotensin II (ANG II). Low-frequency RNS resulted in higher levels of intrarenal angiotensinogen (AGT) and ANG II independent of changes in blood pressure, the glomerular filtration rate and systemic AGT. ANG II, via the AT1 receptor, triggered an intracellular pathway activating NHE3 in the renal cortex leading to antinatriuresis and antidiuresis. Pharmacological blockade of the AT1 receptor with losartan prior to RNS abolished both the functional and molecular responses, suggesting that intrarenal This article is protected by copyright. All rights reserved.
2
ANG II acting via the AT1 receptor is a major factor for NHE3-mediated sodium and water reabsorption induced by RNS. Introduction The sympathetic nervous system (SNS) plays a pivotal role in the control of renal function during physiological and pathophysiological conditions (DiBona & Kopp, 1997). Altered renal handling of sodium and water accompanied by sympathetic hyperactivity have been demonstrated in various chronic diseases, including hypertension, heart failure and renal insufficiency (Girardi & Di Sole, 2012). Therefore, elucidation of the molecular mechanisms by which the SNS influences renal regulation of the extracellular volume may contribute to treating and/or attenuating the progression of cardiovascular and renal disease. Several distinct techniques have been used to demonstrate that an acute increase in renal sympathetic nerve activity (rSNA) enhances electrolyte and fluid tubular reabsorption by the kidneys (Bell-Reuss et al., 1976; Koepke et al., 1988; Healy et al., 2014), whereas surgical renal denervation has the opposite effect (Bello-Reuss et al., 1975; Healy et al., 2014). In addition to autonomic control, angiotensin II (ANG II) also exerts a myriad of influences on renal function (Baum et al., 1997; Quan & Baum, 2001, 2002). All components required for the formation of ANG II are present in the kidney, allowing the generation of very high concentrations of local ANG II (Braam et al., 1993; Baum et al., 1997; Boer et al., 1997; Navar et al., 2003). The interdependent action between SNS and ANG II has been demonstrated in both the central nervous system and kidney (Li & Guyenet, 1996; Quan & Baum, 2001, 2002). In this review, we address the importance of the interaction between the SNS and ANG II on renal tubular handling of sodium and water.
This article is protected by copyright. All rights reserved.
3
Renal innervation influences renal reabsorption All of the segments of the nephron, and especially the proximal tubule, are richly innervated by the SNS (Müller & Barajas, 1972; Barajas et al., 1992). The physiological importance of the tubular innervation on fluid reabsorption has been demonstrated by experiments using either renal nerve stimulation (RNS) or renal denervation (DiBona & Kopp, 1997; Johns et al., 2011). Denervation been has shown to acutely increase the urinary volume and sodium excretion (Bello-Reuss et al., 1975; Quan & Baum, 2001) that remained over 6 days after surgery (Quan & Baum, 2001). RNS promotes different renal responses in a frequency-dependent manner; low-frequencies (0.5 and 2.0 Hz) causes renin secretion and sodium reabsorption independent of hemodynamic changes, and frequencies above 2.0 Hz cause vasoconstriction (DiBona & Kopp, 1997). The actions of the SNS on renal function are dependent on both alpha and beta-adrenergic receptors. The alpha1adrenoreceptors are mainly confined to the basolateral membrane of the proximal tubule cell. Indeed, it has been demonstrated that intrarenal infusion of alpha adrenergic receptor agonists decreases urinary output and sodium excretion with no changes in glomerular filtration rate and blood pressure (Chan, 1980), indicating that the renal nerve may influence renal tubular function, at least in part, due to the activation of alpha1-adrenoreceptors. In addition, Healy and colleagues have demonstrated that norepinephrine increases brush border NHE3 abundance and activity in primary cultures of proximal tubular cells, and these effects are completely prevented by prior exposure of these cells to prazosin, indicating that norepinephrine upregulates NHE3 via an alpha-1-adrenoceptor-mediated mechanism (Healy et al., 2014). However, it has been shown that activation of beta1-adrenoreceptors in the juxtaglomerular granular cells increases the rate of renin secretion, which may contribute to the activation of systemic RAS (DiBona & Kopp, 1997).
One may
speculate that preferential or simultaneous activation of alpha and/or beta adrenoreceptors in the kidney may be dependent upon time and levels of RNS.
This article is protected by copyright. All rights reserved.
4
It has also been shown that within the kidney, ANG II influences renal tubular reabsorption by acting in the initial (Baum et al., 1997) and distal portions (PetiPeterdi et al., 2002) of the nephron segments. Although in vitro ANG II per se can increase proximal tubular reabsorption (Baum et al., 1997), under physiological conditions, the actions of ANG II seem to be strongly dependent on intact renal innervation (Quan & Baum, 2001). After 6 days of renal denervation, the remaining reduction in proximal tubular reabsorption was restored by intraluminal infusion of ANG II (Quan & Baum, 2001). It has also been shown that ANG II acts on AT1 receptors located at the presynaptic membranes, thereby facilitating norepinephrine release, and losartan has been shown to inhibit this response, further underscoring the physiological importance of the interaction between the SNS and ANG II (DiBona & Kopp, 1997). However, the exact mechanism underlying the intrarenal interaction between SNS-ANG II has not been fully explained. Recently, we have shown that lowfrequency RNS leads to activation of the intrarenal RAS, with no effects on the systemic components of this system. This response was accompanied by increased sodium and water reabsorption independent of hemodynamic changes. Moreover, these effects were completely blunted by AT 1 receptor blockade prior to lowfrequency RNS (Pontes et al., 2015).
Effects of the interaction between SNS and intrarenal ANG II on renal function ANG II is not only generated systemically but also “locally” in a variety of tissues, especially the kidneys. In fact, the concentration of ANG II in the renal interstitial fluid is higher than that in the plasma (Braam et al., 1993; Baum et al., 1997; Boer et al., 1997), reflecting the intrarenal generation of the peptide. Interestingly, local ANG II may act completely independent of systemic ANG II. It has been demonstrated that intrarenally produced ANG II modulates fluid transport in the proximal tubule independent of systemic ANG II (Quan & Baum, 1996; Thomson et al., 2006). Using in vivo microperfusion in the rat, Quan and Baum demonstrated that RNS increased proximal tubular fluid transport, and this effect was blunted by intraluminal perfusion with the ANG II converting enzyme (ACE) inhibitor (Quan & Baum, 2002). Moreover, acute renal denervation or intraluminal perfusion of This article is protected by copyright. All rights reserved.
5
the proximal tubule with the ACE inhibitor equally decreased proximal tubular reabsorption (Quan & Baum, 2002), demonstrating an important role of intrarenal ANG II in the actions mediated by SNS activation on proximal tubule transport. In addition, we have recently found that low-frequency RNS significantly increases intrarenal, but not systemic, ANG II (Pontes et al., 2015). These studies further our understanding regarding the crosstalk between the renal sympathetic nerve and intrarenal ANG II, which influences sodium and water reabsorption. However, the interaction between the SNS and intrarenal ANG II in the long term control of sodium tubule reabsorption remains unclear. The introduction of renal denervation to treat refractory hypertensive subjects underscores the importance of renal nerves in the regulation of renal function and blood pressure control. Renal nerve stimulation increases NHE3 activity: new insights into the role of the AT1 ANG II receptor The proximal tubule reabsorbs the bulk of glomerular filtrate via both transcellular and paracellular mechanisms. Na+/H+ exchanger isoform 3 (NHE3) is an important proximal tubular transporter that substantially contributes to sodium bicarbonate and sodium chloride (Schultheis et al., 1998) reabsorption in this nephron segment. NHE3 regulation may occur by changes in its abundance, activity or redistribution along the microvilli of the brush border membrane (Aronson, 2002; Lee et al., 2009; Brasen et al., 2014). A recent study suggests the influence of the SNS on NHE3-mediated sodium transport. RNS increased NHE3 activity resulting in antidiuresis and antinatriuresis, whereas surgical renal denervation produced the opposite effect (Healy et al., 2014). However, the role of intrarenal ANG II in mediating such molecular responses was not evaluated in this study.
This article is protected by copyright. All rights reserved.
6
We have recently shown that increased NHE3 activity induced by RNS depends on intrarenal ANG II binding to AT 1 receptors. In our study, low-frequency RNS resulted in higher levels of intrarenal AGT and ANG II independent of changes in blood pressure, renal function and systemic RAS. ANG II via the AT 1 receptor triggered the intracellular pathway activating NHE3, which resulted in antinatriuresis and antidiuresis. Pharmacological blockade of the AT 1 receptor with losartan prior to RNS abolished both the functional and molecular responses induced by RNS, suggesting that intrarenal ANG II acting via the AT 1 receptor was a major factor that influenced NHE3-mediated sodium and water reabsorption (Pontes et al., 2015). Following ANG II binding to AT1 receptors, intracellular pathway activation was dependent on the inhibition of adenylyl cyclase and the reduction of protein kinase A (PKA) activity, leading to NHE3 activation with consequently greater Na+ reabsorption. Previously, this pathway was demonstrated by Thekkumkara and Linas (Thekkumkara & Linas, 2002). Considering that NHE3 is endogenously inhibited by protein kinase A (PKA) (Zhao et al., 1999), a decrease in cAMP levels and PKA activity resulting in translocation of NHE3 from the base to the body of the microvilli may explain how ANG II activates NHE3 (Woodcock & Johnston, 1982; Liu & Cogan, 1989). Our findings suggested that acute low-frequency RNS leads to a preferential increase in the formation of intrarenal ANG II, which binds to the AT 1 receptor, triggering inhibitory G protein (Gi) signalling, which reduces cAMP generation and consequently decreases PKA-mediated inhibition of NHE3, resulting in antidiuresis and antinatriuresis, as demonstrated in Figure 1.
This article is protected by copyright. All rights reserved.
7
Conclusions Taken together it is very likely that under physiological conditions, acute rSNA modulates sodium reabsorption by increasing intrarenal ANG II generation and activation of the luminal membrane AT1 receptor. However, further studies are necessary to better understand the role of renal nerves in sodium and water reabsorption along the other nephron segments during physiological and pathophysiological conditions. The understanding of the molecular mechanism involved may contribute to the development of more refined tools to treat several pathological conditions such as systemic hypertension and heart failure.
Disclosures None declared.
Sources of funding This study was supported by grants from the São Paulo Research Foundation (FAPESP), National Counsel of Technological and Scientific Development (CNPq) and Coordenação de Aperfeiçoamento de Pessoal de Nivel Superior (CAPES). CTB, ACG and RRC are recipients of CNPq fellowships.
This article is protected by copyright. All rights reserved.
8
References
Aronson PS (2002). Ion exchangers mediating NaCl transport in the renal proximal tubule. Cell Biochem Biophys 36, 147-153. Barajas L, Liu L & Powers K (1992). Anatomy of the renal innervation: intrarenal aspects and ganglia of origin. Can J Physiol Pharmacol 70, 735-749. Baum M, Quigley R & Quan A (1997). Effect of luminal angiotensin II on rabbit proximal convoluted tubule bicarbonate absorption. Am J Physiol 273, F595600. Bell-Reuss E, Trevino DL & Gottschalk CW (1976). Effect of renal sympathetic nerve stimulation on proximal water and sodium reabsorption. J Clin Invest 57, 1104-1107. Bello-Reuss E, Colindres RE, Pastoriza-Munoz E, Mueller RA & Gottschalk CW (1975). Effects of acute unilateral renal denervation in the rat. J Clin Invest 56, 208-217. Boer WH, Braam B, Fransen R, Boer P & Koomans HA (1997). Effects of reduced renal perfusion pressure and acute volume expansion on proximal tubule and whole kidney angiotensin II content in the rat. Kidney Int 51, 44-49. Braam B, Mitchell KD, Fox J & Navar LG (1993). Proximal tubular secretion of angiotensin II in rats. Am J Physiol 264, F891-898. Brasen JC, Burford JL, McDonough AA, Holstein-Rathlou NH & Peti-Peterdi J (2014). Local pH domains regulate NHE3-mediated Na⁺ reabsorption in the renal proximal tubule. Am J Physiol Renal Physiol 307, F1249-1262. Chan YL (1980). The role of norepinephrine in the regulation of fluid absorption in the rat proximal tubule. J Pharmacol Exp Ther 215, 65-70. DiBona GF & Kopp UC (1997). Neural control of renal function. Physiol Rev 77, 75197. Girardi AC & Di Sole F (2012). Deciphering the mechanisms of the Na+/H+ exchanger-3 regulation in organ dysfunction. Am J Physiol Cell Physiol 302, C1569-1587. Healy V, Thompson C & Johns EJ (2014). The adrenergic regulation of proximal tubular Na⁺/H⁺ exchanger 3 in the rat. Acta Physiol (Oxf) 210, 678-689. Johns EJ, Kopp UC & DiBona GF (2011). Neural control of renal function. Compr Physiol 1, 731-767.
This article is protected by copyright. All rights reserved.
9
Kocinsky HS, Girardi AC, Biemesderfer D, Nguyen T, Mentone S, Orlowski J & Aronson PS (2005). Use of phospho-specific antibodies to determine the phosphorylation of endogenous Na+/H+ exchanger NHE3 at PKA consensus sites. Am J Physiol Renal Physiol 289, F249-258. Koepke JP, Jones S & DiBona GF (1988). Stress increases renal nerve activity and decreases sodium excretion in Dahl rats. Hypertension 11, 334-338. Lee DH, Riquier AD, Yang LE, Leong PK, Maunsbach AB & McDonough AA (2009). Acute hypertension provokes acute trafficking of distal tubule Na-Cl cotransporter (NCC) to subapical cytoplasmic vesicles. Am J Physiol Renal Physiol 296, F810-818. Li YW & Guyenet PG (1996). Angiotensin II decreases a resting K+ conductance in rat bulbospinal neurons of the C1 area. Circ Res 78, 274-282. Liu FY & Cogan MG (1989). Angiotensin II stimulates early proximal bicarbonate absorption in the rat by decreasing cyclic adenosine monophosphate. J Clin Invest 84, 83-91. Müller J & Barajas L (1972). Electron microscopic and histochemical evidence for a tubular innervation in the renal cortex of the monkey. J Ultrastruct Res 41, 533-549. Navar LG, Kobori H & Prieto-Carrasquero M (2003). Intrarenal angiotensin II and hypertension. Curr Hypertens Rep 5, 135-143. Peti-Peterdi J, Warnock DG & Bell PD (2002). Angiotensin II directly stimulates ENaC activity in the cortical collecting duct via AT(1) receptors. J Am Soc Nephrol 13, 1131-1135. Pontes RB, Crajoinas RO, Nishi EE, Oliveira-Sales EB, Girardi AC, Campos RR & Bergamaschi CT (2015). Renal nerve stimulation leads to the activation of the Na+/H+ exchanger isoform 3 via angiotensin II type I receptor. Am J Physiol Renal Physiol, ajprenal.00515.02014. Quan A & Baum M (1996). Endogenous production of angiotensin II modulates rat proximal tubule transport. J Clin Invest 97, 2878-2882. Quan A & Baum M (2001). The renal nerve is required for regulation of proximal tubule transport by intraluminally produced ANG II. Am J Physiol Renal Physiol 280, F524-529. Quan A & Baum M (2002). Renal nerve stimulation augments effect of intraluminal angiotensin II on proximal tubule transport. Am J Physiol Renal Physiol 282, F1043-1048. Schultheis PJ, Clarke LL, Meneton P, Miller ML, Soleimani M, Gawenis LR, Riddle TM, Duffy JJ, Doetschman T, Wang T, Giebisch G, Aronson PS, Lorenz JN & This article is protected by copyright. All rights reserved.
10
Shull GE (1998). Renal and intestinal absorptive defects in mice lacking the NHE3 Na+/H+ exchanger. Nat Genet 19, 282-285.
Thekkumkara T & Linas SL (2002). Role of internalization in AT(1A) receptor function in proximal tubule epithelium. Am J Physiol Renal Physiol 282, F623629.
Thomson SC, Deng A, Wead L, Richter K, Blantz RC & Vallon V (2006). An unexpected role for angiotensin II in the link between dietary salt and proximal reabsorption. J Clin Invest 116, 1110-1116.
Woodcock EA & Johnston CI (1982). Inhibition of adenylate cyclase by angiotensin II in rat renal cortex. Endocrinology 111, 1687-1691.
Zhao H, Wiederkehr MR, Fan L, Collazo RL, Crowder LA & Moe OW (1999). Acute inhibition of Na/H exchanger NHE-3 by cAMP. Role of protein kinase a and NHE-3 phosphoserines 552 and 605. J Biol Chem 274, 3978-3987.
This article is protected by copyright. All rights reserved.
11
Figure 1: Schematic model depicting the molecular mechanism by which the interplay between RNS and intrarenal RAS activation increases proximal tubule sodium reabsorption. A) Under baseline conditions, NHE3 is equally distributed between the body and the base of the proximal tubule brush border microvilli (Girardi & Di Sole, 2012). B) Acute RNS stimulates basolateral adrenoreceptors which leads to increased expression of AGT and generation of intrarenal ANG II. Further activation of the AT 1 receptor by ANG II stimulates NHE3-mediated sodium reabsorption in the proximal tubule. Upregulation of NHE3 transport activity seems to be due, at least in part, to redistribution of the transporter from the base to the body of the micrilovilli, which may be dependent on lowering the levels of NHE3 phosphorylation at the PKA consensus site serine 552 (Kocinsky et al., 2005). Consequently, the acute increase on NHE3-mediated sodium reabsorption in the proximal tubule will lead to anti-diuresis, anti-natriuresis and fluid retention.
This article is protected by copyright. All rights reserved.
12
