Evidence for pericyte origin of TSC-associated renal angiomyolipomas and implications for angiotensin receptor inhibition therapy.

Nearly all patients with tuberous sclerosis complex (TSC) develop renal angiomyolipomas, although the tumor cell of origin is unknown. We observed decreased renal angiomyolipoma development in patients with TSC2- polycystic kidney disease 1 deletion syndrome and hypertension that were treated from an early age with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers compared with patients who did not receive this therapy. TSC-associated renal angiomyolipomas expressed ANG II type 1 receptors, platelet-derived growth factor receptor-ß, desmin, α-smooth muscle actin, and VEGF receptor 2 but did not express the adipocyte marker S100 or the endothelial marker CD31. Sera of TSC patients exhibited increased vascular mural cell-secreted peptides, such as VEGF-A, VEGF-D, soluble VEGF receptor 2, and collagen type IV. These findings suggest that angiomyolipomas may arise from renal pericytes. ANG II treatment of angiomyolipoma cells in vitro resulted in an exaggerated intracellular Ca(2+) response and increased proliferation, which were blocked by the ANG II type 2 receptor antagonist valsartan. Blockade of ANG II signaling may have preventative therapeutic potential for angiomyolipomas.

Human TSC-associated renal angiomyolipoma cells are hypersensitive to ER stress.

Tuberous sclerosis complex (TSC), an inherited tumor predisposition syndrome associated with mutations in TSC1 or TSC2, affects ∼1 in 6,000 individuals. Eighty percent of TSC patients develop renal angiomyolipomas, and renal involvement is a major contributor to patient morbidity and mortality. Recent work has shown that mammalian target of rapamycin complex 1 (mTORC1) inhibition caused angiomyolipoma shrinkage but that this treatment may cause cytostatic not a cytotoxic effect. Endoplasmic reticulum (ER) stress can develop in TSC-associated cells due to mTORC1-driven protein translation. We hypothesized that renal angiomyolipoma cells experience ER stress that can be leveraged to result in targeted cytotoxicity. We used immortalized human angiomyolipoma cells stably transfected with empty vector or TSC2 (encoding tuberin). Using cell number quantification and cell death assays, we found that mTORC1 inhibition with RAD001 suppressed angiomyolipoma cell proliferation in a cytostatic manner. Angiomyolipoma cells exhibited enhanced sensitivity to proteasome inhibitor-induced ER stress compared with TSC2-rescued cells. After proteasome inhibition with MG-132, Western blot analyses showed greater induction of C/EBP-homologous protein (CHOP) and more poly (ADP-ribose) polymerase (PARP) and caspase-3 cleavage, supporting ER stress-induced apoptosis. Live cell numbers also were decreased and cell death increased by MG-132 in angiomyolipoma cells compared with TSC2 rescued. Intriguingly, while pretreatment of angiomyolipoma cells with RAD001 attenuated CHOP and BiP induction, apoptotic markers cleaved PARP and caspase-3 and eukaryotic translation initiation factor 2α phosphorylation were increased, along with evidence of increased autophagy. These results suggest that human angiomyolipoma cells are uniquely susceptible to agents that exacerbate ER stress and that additional synergy may be achievable with targeted combination therapy.