Targeting mTOR Signaling Can Prevent the Progression of FSGS

Mammalian target of rapamycin (mTOR) signaling is involved in a variety of kidney diseases. Clinical trials administering mTOR inhibitors to patients with FSGS, a prototypic podocyte disease, led to conflicting results, ranging from remission to deterioration of kidney function. Here, we combined complex genetic titration of mTOR complex 1 (mTORC1) levels in murine glomerular disease models, pharmacologic studies, and human studies to precisely delineate the role of mTOR in FSGS. mTORC1 target genes were significantly induced in microdissected glomeruli from both patients with FSGS and a murine FSGS model. Furthermore, a mouse model with constitutive mTORC1 activation closely recapitulated human FSGS. Notably, the complete knockout of mTORC1 by induced deletion of both Raptor alleles accelerated the progression of murine FSGS models. However, lowering mTORC1 signaling by deleting just one Raptor allele ameliorated the progression of glomerulosclerosis. Similarly, low-dose treatment with the mTORC1 inhibitor rapamycin efficiently diminished disease progression. Mechanistically, complete pharmacologic inhibition of mTOR in immortalized podocytes shifted the cellular energy metabolism toward reduced rates of oxidative phosphorylation and anaerobic glycolysis, which correlated with increased production of reactive oxygen species. Together, these data suggest that podocyte injury and loss is commonly followed by adaptive mTOR activation. Prolonged mTOR activation, however, results in a metabolic podocyte reprogramming leading to increased cellular stress and dedifferentiation, thus offering a treatment rationale for incomplete mTOR inhibition.