To address the molecular mechanisms by which Chop deficiency attenuates UUO-induced renal fibrosis, we first examined the impact of Chop deficiency on UUO-induced tubular apoptosis as UUO-induced ER stress in the tubular compartment is known to cause cell injury and death, which serves as the initial step to the development of renal fibrosis.7 Indeed, TUNEL analysis of renal sections revealed extensive tubular apoptosis following UUO induction, but loss of Chop attenuated UUO-induced tubular apoptosis by twofold. The gene discussed is DDIT3; the disease is renal fibrosis.