Snapshots of nascent RNA reveal cell- and stimulus-specific responses to acute kidney injury

Abstract

The current strategy to detect acute injury of kidney tubular cells relies on changes in serum levels of creatinine. Yet serum creatinine (sCr) is a marker of both functional and pathological processes and does not adequately assay tubular injury. In addition, sCr may require days to reach diagnostic thresholds, yet tubular cells respond with programs of damage and repair within minutes or hours. To detect acute responses to clinically relevant stimuli, we created Rosa26-floxed-stop uracil phosphoribosyltransferase (Uprt) expressing mice and inoculated 4-thiouracil (TU) to tag nascent RNA at selected time points. Cre-driven TU-tagged RNA was isolated from intact kidneys and demonstrated that volume depletion and ischemia induced different genetic programs in collecting ducts and intercalated cells. Even lineage related cell types expressed different genes in response to the two stressors. TU-tagging also demonstrated the transient nature of the responses. Because we placed Uprt in the ubiquitously active Rosa-26 locus, nascent RNAs from many cell types can be tagged in vivo and their roles interrogated under various conditions. In short, TU labeling identifies stimulus-specific, cell-specific, and time-dependent acute responses that are otherwise difficult to detect with other technologies and are entirely obscured when sCr is the sole metric of kidney damage.

The Pathophysiology of Sepsis-Associated AKI

“…Third, the pathogenesis is complex and, although preclinical studies utilizing various animal models may be useful, it also introduces additional complexities. When examining activated gene sets from a mouse model of prerenal and intrinsic AKI, functionally unrelated signal transduction pathways were identified and were localized in different cell types in the kidney (183,184). Compared with AKI with nonseptic etiologies, the pathophysiology of sepsis-associated AKI is complex; microarray studies using various rodent models of AKI showed that the LPS-induced sepsis-associated AKI had the largest number of uniquely altered genes compared with nonseptic AKI (185).…”