Mechanistic studies revealed that worsening kidney injury in ACE2 knockout mice was associated with an increase in Smurf2 (Smad-specific E3 ubiquitin protein ligase 2), a decrease in renal Smad7, and marked activation of TGF-β (transforming growth factor β)/Smad3 and NF-κB (nuclear factor κ-light-chain-enhancer of activated B cells) signaling, suggesting that Smurf2-dependent Smad7 ubiquitin degradation may be a key mechanism whereby loss of ACE2 promotes angiotensin II-induced TGF-β/Smad3 and NF-κB-mediated hypertensive nephropathy.