DDIT3 and diabetes mellitus: Importantly, the expression of CHOP, a marker of the apoptotic response in UPR, and apoptosis marker cleaved caspase-3 was significantly elevated in DM+uIRI kidneys in comparison with uIRI kidneys, indicative of increased RTEC apoptosis in DM+uIRI mice (Figure 5, A and B), while RTN1A knockdown effectively reduced RTEC apoptosis.