We have characterized the expression and secretion of the acute kidney injury (AKI) biomarkers insulin-like growth factor binding protein 7 (IGFBP7) and tissue inhibitor of metalloproteinases-2 (TIMP-2) in human kidney epithelial cells in primary cell culture and tissue. We established cell culture model systems of primary kidney cells of proximal and distal tubule origin and observed that both proteins are indeed expressed and secreted in both tubule cell types in vitro. However, TIMP-2 is both expressed and secreted preferentially by cells of distal tubule origin, while IGFBP7 is equally expressed across tubule cell types yet preferentially secreted by cells of proximal tubule origin. In human kidney tissue, strong staining of IGFBP7 was seen in the luminal brush-border region of a subset of proximal tubule cells, and TIMP-2 stained intracellularly in distal tubules. Additionally, while some tubular colocalization of both biomarkers was identified with the injury markers kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin, both biomarkers could also be seen alone, suggesting the possibility for differential mechanistic and/or temporal profiles of regulation of these early AKI biomarkers from known markers of injury. Last, an in vitro model of ischemia-reperfusion demonstrated enhancement of secretion of both markers early after reperfusion. This work provides a rationale for further investigation of these markers for their potential role in the pathogenesis of acute kidney injury.

Sepsis-associated acute kidney injury (S-AKI) independently predicts mortality among critically ill patients. The role of innate immunity in this process is unclear, and there is an unmet need for S-AKI models to delineate the pathophysiological response. Mammals and zebrafish ( Danio rerio) share a conserved nephron structure and homologous innate immune systems, making the latter suitable for S-AKI research. We introduced Edwardsiella tarda to the zebrafish. Systemic E. tarda bacteremia resulted in sustained bacterial infection and dose-dependent mortality. A systemic immune reaction was characterized by increased mRNA expressions of il1b, tnfa, tgfb1a, and cxcl8-l1 ( P < 0.0001, P < 0.001, P < 0.001, and P < 0.01, respectively). Increase of host stress response genes ccnd1 and tp53 was observed at 24 h postinjection ( P < 0.0001 and P < 0.05, respectively). Moderate E. tarda infection induced zebrafish mortality of over 50% in larvae and 20% in adults, accompanied by pericardial edema in larvae and renal dysfunction in both larval and adult zebrafish. Expression of AKI markers insulin-like growth factor-binding protein-7 (IGFBP7), tissue inhibitor of metalloproteinases 2 (TIMP-2), and kidney injury molecule-1 (KIM-1) was found to be significantly increased in the septic animals at the transcription level ( P < 0.01, P < 0.05, and P < 0.05) and in nephric tubules compared with noninfected animals. In conclusion, we established a zebrafish model of S-AKI induced by E. tarda injection, with both larval and adult zebrafish showing nephron injury in the setting of infection.

Introduction: Sexual dimorphism in pulmonary arterial hypertension (PAH) is attributed, in part, to estrogen signaling. 16α-hydroxyestrone (16αOHE) is considered a major contributor to PAH pathogenesis. Recent genetic studies have also suggested that deficiency of SOX17, an endothelial cell (EC)-specific transcription factor, contributes to PAH risk. While functional studies of SOX17 are absent, we hypothesized that 16αOHE contributes to PAH, in part, via, SOX17 downregulation. Methods/Results: Sox17 expression was reduced in 3 animal PAH models and in human pulmonary artery ECs (HPAECs) isolated from patients with PAH (vs controls). Inducible Tie2-specific Sox17 knockout ( Sox17 EC-/- ) mice exhibited increased right ventricular systolic pressure (RVSP), RV hypertrophy (RVH), and PA wall thickness (PAWT) after chronic hypoxia (CH) (Fig 1A). Inducible Tie2- Sox17 transgenic overexpressing ( Sox17 Tg ) mice attenuated CH-induced PH (Fig 1B). While not evident across murine sex, Sox17 expression was increased in baseline lungs from male compared to female rats. Supporting in silico evidence of estrogen response elements (ERE) on the SOX17 promoter, HPAECs exposed to 16αOHE reduced SOX17 expression and promoter luciferase activity via ERα, which was partly negated by serial ERE mutagenesis (Fig 1C ) . Lungs from ERα loss-of-function mutant rats (vs control) confirmed in vivo reductions of Sox17 expression. Sox17 Tg mice attenuated 16αOHE-mediated PH after CH (Fig 1D). To translate these data, we identified a functional coding SNP in the ESR1 gene (encoding ERα), rs746432, previously shown to reduce transcriptional activity of ERα. The SNP was associated with reduced pulmonary vascular resistance in patients with PAH (n=702, Fig 1E) in adjusted analyses. Conclusion: Validating genetic studies, SOX17 deficiency augments preclinical PAH. 16αOHE mediates PH development via downregulation of SOX17, linking SOX17 genetics with the observed sexual dimorphism.