Mammalian target of rapamycin complex 1 activation in podocytes promotes cellular crescent formation

Podocytes play a key role in the formation of cellular crescents in experimental and human diseases. However, the underlying mechanisms for podocytes in promoting crescent formation need further investigation. Here, we demonstrated that mammalian target of rapamycin complex 1 (mTORC1) signaling was remarkably activated and hypoxia-inducible factor (HIF) 1α expression was largely induced in cellular crescents from patients with crescentic glomerular diseases. Specific deletion of Tsc1 in podocytes led to mTORC1 activation in podocytes and kidney dysfunction in mice. Interestingly, 33 of 36 knockouts developed cellular or mixed cellular and fibrous crescents at 7 wk of age (14.19±3.86% of total glomeruli in knockouts vs. 0% in control littermates, n=12-36, P=0.04). All of the seven knockouts developed crescents at 12 wk of age (30.92±11.961% of total glomeruli in knockouts vs. 0% in control littermates, n=4-7, P=0.002). Most notably, bridging cells between the glomerular tuft and the parietal basement membrane as well as the cellular crescents were immunostaining positive for WT1, p-S6, HIF1α, and Cxcr4. Furthermore, continuously administrating rapamycin starting at 7 wk of age for 5 wk abolished crescents as well as the induction of p-S6, HIF1α, and Cxcr4 in the glomeruli from the knockouts. Together, it is concluded that mTORC1 activation in podocytes promotes cellular crescent formation, and targeting this signaling may shed new light on the treatment of patients with crescentic glomerular diseases.