Effects of amino acids and glucose on mesangial cell aminopeptidase a and angiotensin receptors

Effects of amino acids and glucose on mesangial cell aminopeptidase a and angiotensin receptors. Background High protein diets and diabetes increase renal renin angiotensin system (RAS) activity, which is associated with glomerular injury. Aminopeptidase A (APA) is a cell surface metalloprotease that degrades angiotensin II (AII) in the mesangium. Mesangial cells (MC) also possess receptors for AII; the type 1 (AT 1 receptor) promotes proliferation and fibrosis, while the type 2 (AT 2 receptor) opposes these effects. We evaluated whether amino acids and glucose alter expression of APA, AT 1 receptor and AT 2 receptor in a manner that further augments RAS activity. Methods Confluent rat MC were grown in serum-free media for 48 hours prior to exposing to experimental conditions: control (C), high amino acids (HA, mixed amino acid solution added to raise concentrations 5- to 6-fold over C), high glucose (HG 30, mM glucose). Semi-quantitative RT-PCR was used to assess mRNA for APA, AT 1 receptor, AT 2 receptor, and β-actin. Values are expressed relative to βbgr; actin. Results Both HA and HG reduced APA mRNA (HG 1.13 ± 0.19, HA 1.12 ± 0.16 versus C 1.27 ± 0.16 P N = 8). HA increased AT 1 receptor mRNA (HA 2.11 ± 0.43 versus C 1.14 ± 0.28 P N = 8). HG increased AT 2 receptor mRNA (HG 1.31 ± 0.43 versus C 0.82 ± 0.33 P N = 6). Conclusions A reduction of APA, in response to high levels of amino acids or glucose, could contribute to increased AII as a result of decreased degradation in MC. The effect of amino acids to increase AT 1 receptor expression may further enhance adverse hemodynamic and pro-fibrotic actions of AII. Conversely, glucose increased AT 2 receptor expression, which could modulate responses mediated by the AT 1 receptor.