Phosphoprotein expression profiles in rat kidney injury: Source for potential mechanistic biomarkers

Acute kidney injury (AKI) is defined by the Acute Kidney Injury Network as “functional and structural disorder or signs of renal damage including any defect from blood or urine test, or tissue imaging that is less than 3 months.” AKI is the most common cause of renal dysfunction.1 Understanding of molecular determinants of AKI induction and development could help to diagnose and monitor kidney injury in the clinic as well as to select safe drug candidates in preclinical drug development. Protein phosphorylation plays a significant role in a wide range of cellular processes and can directly indicate an active/inactive state of cellular enzymes and the signalling pathways in injury initiation and progression. Alteration of phosphorylation of some proteins was already described for kidney injury: MAPK activation in cisplatin‐induced nephrotoxicity,2 increased phosphorylation of moesin and HSP90ɑ in tubular cells in response to TGF‐β3 and increased phosphorylation of lamin A and phospholamban in a salt‐load rat model of kidney damage.4 Our study aimed at identifying changes in phosphoprotein expression and creating comprehensive phosphoprotein profiles of nephron‐specific injuries in a time‐dependent manner. To meet this objective, we utilized rat models of drug‐induced kidney injury (DIKI), which were induced with three nephrotoxicants over a 28‐day period: cisplatin (proximal tubules); puromycin (glomerulus) and N‐phenylanthranylic acid (NPAA, collecting ducts). The phosphoproteins were studied by antibody microarrays in kidney tissue on days 7, day 14 and day 28. We established changes in phosphoprotein expression in response to kidney injury and associated these changes with biological processes. Up‐regulation of MEK2 (pThyr394) on day 14 in cisplatin and puromycin‐induced injuries was confirmed by immunohistochemistry (IHC). Identified phosphoprotein signatures provide a link to molecular mechanisms of kidney injury/recovery as well as a source for potential mechanistic biomarkers.