Cell-Specific Responses Redefine Acute Kidney Injury

The critical function of the kidney is to regulate the body’s extracellular fluid volume to maintain homeostasis. When insults to the kidney occur, as in the case of kidney ischemia, the function of the kidney to filter metabolic wastes and reabsorb essential solutes is compromised, leading to a variety of clinical manifestations. Current metrics of kidney function are measured by the rise of a single analyte, the serum creatinine, which implies injury of the kidney tubule and its epithelial cells and is encapsulated by the term Acute Kidney Injury (AKI). Yet, creatinine does not specify the etiology, the cell type, or the molecular pathways that are affected by the acute decreases in kidney excretory function. During my thesis work, I hypothesized that there is a pathogenetic heterogeneity of kidney injury and a specificity of location, timing, and molecular mechanisms, unique to each of these three injury models: kidney ischemia, volume depletion, and urinary tract infection. Using genetic mouse models, RNA-sequencing, and a range of molecular biology techniques, I have found (1) kidney ischemia activates inflammatory responses, signal transduction pathways, and epithelial repair and reprogramming, that are not activated in volume depletion, (2) which in contrast, is a transient metabolic condition, inducing genes regulating energy metabolism that were reversible upon rehydration. Lastly, (3) I have found that urinary tract infection, particularly one that invades the kidney, involves a novel heme transport system in the collecting duct of the kidney, that may contribute to nutritional defenses against bacterial pathogens. Each of these findings is explored in specific aims and experiments, which I detail here in my thesis.