Dynamics of GRK2 in the kidney: a putative mechanism for sepsis-associated kidney injury

Renal vascular reactivity to vasoconstrictors is preserved in sepsis in opposition to what happens in the systemic circulation. We studied whether this distinct behavior was related to alpha 1 adrenergic receptor density, G protein-coupled receptor kinase 2 (GRK2) and the putative role of nitric oxide (NO). Sepsis was induced in female mice by cecal ligation and puncture (CLP). Wildtype mice were treated with prazosin 12 h after CLP or nitric oxide synthase 2 (NOS-2) inhibitor, 30 min before and 6 and 12 h after CLP. In vivo experiments and biochemistry assays were performed 24 h after CLP. Sepsis decreased the systemic mean arterial pressure (MAP) and the vascular reactivity to phenylephrine. Sepsis also reduced basal renal blood flow which was normalized by treatment with prazosin. Sepsis led to a substantial decrease in GRK2 level associated with an increase in alpha 1 adrenergic receptor density in the kidney. The disappearance of renal GRK2 was prevented in NOS-2-KO mice or mice treated with 1400 W. Treatment of non-septic mice with an NO donor reduced GRK2 content in the kidney. Therefore, our results show that an NO-dependent reduction in GRK2 level in the kidney leads to the maintenance of a normal alpha 1 adrenergic receptor density. The preservation of the density and/or functionality of this receptor in the kidney together with a higher vasoconstrictor tonus in sepsis lead to vasoconstriction. Thus, the increased concentration of vasoconstrictor mediators together with the preservation (and even increase) of the response to them may help to explain sepsis-induced acute kidney injury.