Urinary ACE2 protein could originate at least partly from plasma (via filtration at the glomerulus), or it could be derived via excretion from renal cells. Although Mizuiri et al. found higher urinary ACE2 levels in CKD patients, there was no difference in plasma ACE2 protein between CKD patients and healthy subjects [14] . However, the CKD patients in their study had significant albuminuria, suggesting that ACE2 may have leaked into the urine across the glomerular barrier. In the present study, we found no association between albuminuria and either urinary ACE2 activity or protein levels by western analysis. The data suggest that urinary ACE2 protein likely derives via shedding from cells along the nephron, and not from filtration from plasma. In support of this hypothesis, soluble ACE2 is shed from the plasma membrane in cell culture systems, via cleavage at its ectodomain by the protease enzyme ADAM-17 [11] [12] [13] . Interestingly, renal ADAM-17 is upregulated in Ang II-induced kidney injury [25] , and de novo expression occurs in human kidney disease, in proximal tubule, podocytes, and mesangial cells [26] . Whether ADAM-17 is activated in the transplant kidney in the presence of diabetes, and mediates shedding of soluble ACE2 into the urine requires further study. Two bands for ACE2 were detected by immunoblot of urine samples in the current study. One band was found at 120 kDA, consistent with the full-length protein, and the other at 90 kDa, which is likely a cleaved ACE2 fragment. Thus, the 90 kDa fragment does not simply represent a deglycosylated form of fulllength ACE2, since incubation with PNGase F resulted in a further reduction in its size, as shown in Figure 2D . To determine if this 90 kDa fragment is generated by ADAM-17-mediated cleavage of ACE2, further characterization is required, including use of antibodies directed against the cytoplasmic carboxyterminus of ACE2 (which may be lacking in this fragment), and/or direct sequence analysis of the polypeptide. Furthermore, although shedding of ACE2 fragments may occur via ADAM-17 in transplant subjects, proteomic analysis has identified ACE2 as one of the 1132 proteins present in urinary exosomes isolated from human urine [27] , suggesting that membrane-bound full-length ACE2 may also be a source of urinary ACE2.