Cross-talk between angiotensin II and glucagon receptor signaling mediates phosphorylation of mitogen-activated protein kinases ERK 1/2 in rat glomerular mesangial cells

American Journal of Physiology-Renal Physiology

2012

Self Cite

Li XC, Shao Y, Zhuo JL. AT1a receptor signaling is required for basal and water deprivation-induced urine concentration in AT 1a receptor-deficient mice. Am J Physiol Renal Physiol 303: F746-F756, 2012. First published June 27, 2012 doi:10.1152/ajprenal.00644.2011It is well recognized that ANG II interacts with arginine vasopressin (AVP) to regulate water reabsorption and urine concentration in the kidney. The present study used ANG II type 1a (AT 1a) receptor-deficient (Agtr1a Ϫ/Ϫ ) mice to test the hypothesis that AT 1a receptor signaling is required for basal and water deprivation-induced urine concentration in the renal medulla. Eight groups of wild-type (WT) and Agtr1a Ϫ/Ϫ mice were treated with or without 24-h water deprivation and 1-desamino-8-D-AVP (DDAVP; 100 ng/h ip) for 2 wk or with losartan (10 mg/kg ip) during water deprivation. Under basal conditions, Agtr1a Ϫ/Ϫ mice had lower systolic blood pressure (P Ͻ 0.01), greater than threefold higher 24-h urine excretion (WT mice: 1.3 Ϯ 0.1 ml vs. Agtr1a Ϫ/Ϫ mice: 5.9 Ϯ 0.7 ml, P Ͻ 0.01), and markedly decreased urine osmolality (WT mice: 1,834 Ϯ 86 mosM/kg vs. Agtr1a Ϫ/Ϫ mice: 843 Ϯ 170 mosM/kg, P Ͻ 0.01), without significant changes in 24-h urinary Na ϩ excretion. These responses in Agtr1a Ϫ/Ϫ mice were associated with lower basal plasma AVP (WT mice: 105 Ϯ 8 pg/ml vs. Agtr1a Ϫ/Ϫ mice: 67 Ϯ 6 pg/ml, P Ͻ 0.01) and decreases in total lysate and membrane aquaporin-2 (AQP2; 48.6 Ϯ 7% of WT mice, P Ͻ 0.001) and adenylyl cyclase isoform III (55.6 Ϯ 8% of WT mice, P Ͻ 0.01) proteins. Although 24-h water deprivation increased plasma AVP to the same levels in both strains, 24-h urine excretion was still higher, whereas urine osmolality remained lower, in Agtr1a Ϫ/Ϫ mice (P Ͻ 0.01). Water deprivation increased total lysate AQP2 proteins in the inner medulla but had no effect on adenylyl cyclase III, phosphorylated MAPK ERK1/2, and membrane AQP2 proteins in Agtr1a Ϫ/Ϫ mice. Furthermore, infusion of DDAVP for 2 wk was unable to correct the urine-concentrating defects in Agtr1a Ϫ/Ϫ mice. These results demonstrate that AT 1a receptor-mediated ANG II signaling is required to maintain tonic AVP release and regulate V2 receptormediated responses to water deprivation in the inner medulla. angiotensin II; angiotensin II type 1a receptor; adenylyl cyclases; aquaporin 2; arginine vasopressin; inner medullary collecting ducts; urine concentration WATER REABSORPTION by the inner medulla plays an important role in maintaining basal body electrolytes and fluid balance, urine concentration, and blood pressure homeostasis. Physiologically, water transport in the inner medulla is primarily regulated by the neuropeptide hormone arginine vasopressin ([Arg 8 ]-AVP), which is released from the posterior pituitary in response to changes in extracellular fluid volume and plasma and urine osmolality (1,23,40). In the inner medulla of the kidney, AVP binds to G s protein-coupled type 2 (V 2 ) receptors expressed on basolateral membranes of principal cells, which activates adenylyl cyclases ...

Section: Methodsmentioning

confidence: 99%

“…cAMP is the key second messenger that mediates the translocation of AQP2 from intracellular vesicles to apical membranes (10,11,22). cAMP also activates PKA and MAPK ERK1/2 (19,22,27,28). Activation of ERK1/2 may induce AQP2 phosphorylation, facilitating water transport in the collecting ducts.…”

Section: Or In Agtr1amentioning

confidence: 99%

AT_1a receptor signaling is required for basal and water deprivation-induced urine concentration in AT_1a receptor-deficient mice

Shao

American Journal of Physiology-Renal Physiology

2012

Self Cite

“…Portions (100 μg of protein) from each sample were separated by SDS/PAGE [8-16% (w/v) polyacrylamide gel] and transferred semi-dry on to an Immobilon-P membrane (Millipore). Total and phosphorylated ERK1/2 proteins were detected by immunoblotting using a rabbit polyclonal ERK1/2 antibody (Cell Signaling) and a mouse monoclonal anti-[phospho-ERK1/2 (Tyr 204 )] antibody (Santa Cruz Laboratories), as described previously [29,30]. Total and phospho-Akt (Ser 473 ) proteins were measured by Western blots using specific antibodies against total Akt or phospho-Akt (Ser 473 ) (Cell Signaling).…”

Section: Assessment Of Glomerular Injurymentioning

confidence: 99%

“…Western blot analysis of ERK1/2 (extracellular-signal-regulated kinase 1/2) and Akt phosphorylation Liver and kidney samples were lysed with Nonidet P40 lysis buffer [50 mmol/l Tris/HCl (pH 7.4), 150 mmol/l NaCl, 1 mmol/l EDTA, 0.25% sodium deoxycholate, 1 mmol/l PMSF, 1 mmol/l sodium orthovanadate, 1 mmol/l sodium fluoride and 1% Nonidet P40] containing a protease inhibitor cocktail (1 μg/ml each of aprotinin, leupeptin and pepstatin), as described previously for rat glomerular mesangial cells [29,30]. Protein concentrations were measured using a BCA (bicinchoninic acid) protein assay kit (Pierce).…”

Section: Assessment Of Glomerular Injurymentioning

confidence: 99%

“…Western blotting of β-actin (Sigma) on the same membranes was used to confirm equal protein loading. Immunoblots were visualized by enhanced chemiluminescence using HRP (horseradish peroxidase)-conjugated secondary antibodies (Santa Cruz Laboratories), scanned and analysed using a microcomputer imaging device (MCID; Imaging Research) [29,30].…”

Section: Assessment Of Glomerular Injurymentioning

confidence: 99%

See 1 more Smart Citation

Long-term hyperglucagonaemia induces early metabolic and renal phenotypes of Type 2 diabetes in mice

Liao

2008

Clinical Science

Clinical studies have shown that patients with early Type 2 diabetes often have elevated serum glucagon rather than insulin deficiency. Imbalance of insulin and glucagon in favouring the latter may contribute to impaired glucose tolerance, persistent hyperglycaemia, microalbuminuria and glomerular injury. In the present study, we tested the hypothesis that long-term glucagon infusion induces early metabolic and renal phenotypes of Type 2 diabetes in mice by activating glucagon receptors. Five groups of adult male C57BL/6J mice were treated with vehicle, glucagon alone (1 μg/h via an osmotic minipump, intraperitoneally), glucagon plus the glucagon receptor antagonist [Des-His 1 -Glu 9 ]glucagon (5 μg/h via an osmotic minipump), [Des-His 1 -Glu 9 ]glucagon alone or a high glucose load alone (2 % glucose in the drinking water) for 4 weeks. Glucagon infusion increased serum glucagon by 129 % (P < 0.05), raised systolic BP (blood pressure) by 21 mmHg (P < 0.01), elevated fasting blood glucose by 42 % (P < 0.01), impaired glucose tolerance (P < 0.01), increased the kidney weight/body weight ratio (P < 0.05) and 24 h urinary albumin excretion by 108 % (P < 0.01) and induced glomerular mesangial expansion and extracellular matrix deposition. These responses were associated with marked increases in phosphorylated ERK1/2 (extracellular-signalregulated kinase 1/2) and Akt signalling proteins in the liver and kidney (P < 0.01). Serum insulin did not increase proportionally. Concurrent administration of [Des-His 1 -Glu 9 ]glucagon with glucagon significantly attenuated glucagon-increased BP, fasting blood glucose, kidney weight/body weight ratio and 24 h urinary albumin excretion. [Des-His 1 -Glu 9 ]glucagon also improved glucagoninpaired glucose tolerance, increased serum insulin by 56 % (P < 0.05) and attenuated glomerular injury. However, [Des-His 1 -Glu 9 ]glucagon or high glucose administration alone did not elevate fasting blood glucose levels, impair glucose tolerance or induce renal injury. These results demonstrate for the first time that long-term hyperglucagonaemia in mice induces early metabolic and renal phenotypes of Type 2 diabetes by activating glucagon receptors. This supports the idea that glucagon receptor blockade may be beneficial in treating insulin resistance and Type 2 diabetic renal complications.

Current Insights and New Perspectives on the Roles of Hyperglucagonemia in Non-Insulin–Dependent Type 2 Diabetes

2013

Curr Hypertens Rep

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Type 2 diabetes is well recognized as a noninsulin-dependent diabetic disease. Clinical evidence indicates that the level of circulating insulin may be normal, subnormal, and even elevated in type 2 diabetic patients. Unlike type 1 diabetes, the key problem for type 2 diabetes is not due to the absolute deficiency of insulin secretion, but because the body are no longer sensitive to insulin. Thus insulin resistance is increased and the sensitivity to insulin is reset, so increasing levels of insulin are required to maintain body glucose and metabolic homeostasis. How insulin resistance is increased and what factors contribute to its development in type 2 diabetes remain incompletely understood. Overemphasis of insulin deficiency alone may be too simplistic for us to understand how type 2 diabetes is developed and should be treated, since glucose metabolism and homeostasis are tightly controlled by both insulin and glucagon. Insulin acts as a YIN factor to lower blood glucose level by increasing cellular glucose uptake, whereas glucagon acts as a YANG factor to counter the action of insulin by increasing glucose production. Furthermore, other humoral factors other than insulin and glucagon may also directly or indirectly contribute to increased insulin resistance and the development of hyperglycemia. The purpose of this article is to briefly review recently published animal and human studies in this field, and provide new insights and perspectives on recent debates on whether hyperglucagonemia and/or glucagon receptors should be targeted to treat insulin resistance and target organ injury in type 2 diabetes.