P2A289: A Novel Surgical Model of Acute Kidney Injury in Neonatal Rats Results in Pulmonary Inflammation

Background: Acute kidney injury (AKI) commonly affects critically ill neonates, particularly those with pathologies that induce ischemia-reperfusion injury such as hypotension, sepsis, and acute blood loss. Premature neonates are at higher risk of AKI due to incomplete nephrogenesis. AKI produces a systemic pro-inflammatory state that can lead to dysfunction of other distant organs through complex biological communications known as “organ crosstalk.” Clinically, AKI in critically ill neonates has been associated with significant pulmonary morbidity and mortality. However, this relationship has yet to be replicated in a preclinical neonatal model. Adult models have described the association between AKI-induced lung injury and systemic inflammation, but there is little known about the interaction between the developing lungs and kidneys in neonates. We therefore hypothesized that upregulation of inflammatory pathways secondary to AKI in a neonatal rat model would produce increased pulmonary proinflammatory gene expression and subsequent inflammation.

Methods: Sprague-Dawley rat pups underwent either bilateral ischemia-reperfusion injury (bIRI) (n=13) or sham surgery (n=11) on day of life (DOL) 5 to replicate premature neonatal physiology. First, each kidney was surgically isolated. In the bIRI cohort, a microvascular clamp was applied to the renal vascular bundles for 40 minutes. In the sham cohort, kidneys were left exposed for 40 minutes but without vascular clamping. Control pups (n=15) underwent no surgical intervention. On DOL6, the pups were euthanized, and the lungs were collected and processed for total RNA extraction. AKI was confirmed by elevated plasma BUN and creatinine and positive KIM-1 immunohistochemical staining. Real-time quantitative polymerase chain reaction (RT-qPCR) analysis was performed to evaluate gene expression levels of microRNA(miR)146a, a “regulatory brake” that inhibits the NFkB inflammatory pathway, as well as the pro-inflammatory cytokines IRAK1, TRAF6, NFkB, and IL-6.

Results: We found that pulmonary gene expression levels of miR146a were significantly lower in the bIRI model compared to both shams (p < 0.0001) and controls (p=0.007). Pulmonary gene expression levels of pro-inflammatory cytokines were also significantly elevated in the bIRI model compared to both shams and controls, consistent with a state of increased inflammation (Figure). There was no significant difference in inflammatory cytokine levels when comparing shams to controls, suggesting that the ischemia-reperfusion injury is responsible for subsequent pulmonary inflammation.

Conclusion: We have demonstrated that AKI induced in a neonatal rodent model is associated with dysregulation of miR146a and subsequent increased expression levels of pulmonary inflammatory mediators, which may in part explain the mechanism through which AKI contributes to distant organ injury. Additionally, the dysregulation of miR146a offers a target for potential therapies that could suppress the inflammatory response produced by AKI.