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Background  Inhibition of angiotensin II (AngII) signaling, a therapeutic mainstay of glomerular kidney diseases, is thought to act primarily through regulating glomerular blood flow and reducing filtration pressure. Although extravascular actions of AngII have been suggested, a direct effect of AngII on podocytes has not been demonstrated  in vivo .    Methods  To study the effects of AngII on podocyte calcium levels  in vivo , we used intravital microscopy of the kidney in mice expressing the calcium indicator protein GCaMP3.    Results  In healthy animals, podocytes displayed limited responsiveness to AngII stimulation. In contrast, in animals subjected to either adriamycin-induced acute chemical injury or genetic deletion of the podocin-encoding gene  Nphs2 , the consequent podocyte damage and proteinuria rendered the cells responsive to AngII and resulted in AngII-induced calcium transients in significantly more podocytes. The angiotensin type 1 receptor blocker losartan could fully inhibit this response. Also, responsiveness to AngII was at least partly mediated through the transient receptor potential channel 6, which has been implicated in podocyte calcium handling. Interestingly, loss of a single  Nphs2  allele also increased podocytes’ responsiveness to AngII signaling. This direct effect of AngII on injured podocytes results in increased calcium transients, which can further aggravate the underlying kidney disease.    Conclusions  Our discovery that podocytes become sensitized to AngII-induced calcium signaling upon injury might explain results from large, randomized, controlled trials in which improved renal outcomes occur only in the subgroup of patients with proteinuria, indicating podocyte damage. Our findings also emphasize the need to treat every patient with a glomerular disease with either an angiotensin-converting enzyme inhibitor or an angiotensin type 1 receptor blocker.

Injured Podocytes Are Sensitized to Angiotensin II–Induced Calcium Signaling