Inhibition of the Akt1-mTORC1 Axis Alters Venous Remodeling to Improve Arteriovenous Fistula Patency

Abstract

Arteriovenous fistulas (AVFs) are the most common access created for hemodialysis, but approximately 40% fail to mature, suggesting a clinical need. In a mouse model, reduced Akt1 expression reduces AVF wall thickness and diameter. We hypothesized that inhibition of Akt1-mTORC1 axis alters venous remodeling associated with failure of AVF. A C57BL6/J mouse aortocaval fistula model was used (male, 9-12 weeks). Mice were injected with 100 μg of vehicle or rapamycin (intraperitoneal) daily. The AVFs were harvested at days 3, 7, and 21 for comparison of wall thickness, macrophage markers, and expression level of mTOR signaling proteins using Western blot and immunofluorescence intensity. AVF patency and diameter were assessed with ultrasound. Rapamycin reduced AVF wall thickness at days 7 and 21 (P < .05; n = 6) with no change in AVF diameter (P = .5). Rapamycin decreased the proliferation rate of smooth muscle cells (SMCs) and macrophages (P < .05), with reduced M1 (inducible nitric oxide synthase, tumor necrosis factor α) and M2 (interleukin 10, CD206) macrophages at days 3 and 7 (P < .05). Rapamycin treatment was associated with diminished phosphorylation of Akt1 and the mTORC1 pathway members mTOR (Ser2481), 4EBP1, and p70S6K (P < .05; n =6) but not of the mTORC2 pathway members mTOR (Ser2448) and serum and glucocorticoid-regulated kinase 1 (P > .4). With rapamycin treatment, there was decreased p-Akt1 and p-mTORC1 intensity in SMCs and macrophages at days 3, 7, and 21 (P < .05). There was also reduced p-endothelial nitric oxide synthase intensity in SMCs but not in endothelial cells. After depletion of macrophages with clodronate liposomes, there was reduced wall thickness (P < .01, day 21), SMC proliferation, and p-mTORC1 intensity in SMCs (P = .001); however, AVF patency was reduced (P < .05). Rapamycin improved AVF patency by day 42 (P = .04; n = 14); these AVFs showed less thickening (P < .05) and had similar p-Akt1 and p-mTORC1 intensity in macrophages compared with control (P > .5). However, rapamycin treatment initiated after day 21 did not improve patency (P = .62). Rapamycin improves AVF patency by reducing early inflammation and wall thickening while attenuating the Akt1-mTORC1 signaling pathway in SMCs and macrophages. Macrophages are associated with AVF wall thickening, and M2-type macrophages may play a mechanistic role in AVF maturation. Rapamycin is a potential translational strategy to improve AVF patency.