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

Abstract

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 α1 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). Wild-type mice were treated with prazosin 12 hours after CLP or NOS-2 inhibitor, 30 min before and 6 and 12 hours after CLP. In vivo experiments and biochemistry assays were performed 24 hours after CLP. Sepsis decreased the systemic mean arterial pressure 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 decreased in GRK2 level associated to an increase in α1 adrenergic receptor density in the kidney. The disappearance of renal GRK2 was prevented in NOS-2-KO mice or mice treated with 1400W. Treatment of non-septic mice with a NO donor reduced GRK2 content in the kidney. Therefore, our results show that a NO-dependent reduction in GRK2 level in the kidney leads to the maintenance of a normal α1 adrenergic receptor density, probably. 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.

The role of nitric oxide in sepsis-associated kidney injury

“…Corroborating these findings, a recent study showed that renal vascular reactivity to alpha-1-adrenergic agonist is preserved in sepsis due to the NO-dependent G protein-coupled receptor kinase 2 (GRK2) reduction in the kidneys from septic mice. They also showed that reduction of GRK2 is associated with the preservation of renal alpha-1-adrenergic receptor density and function, which is not observed in other tissues such as the heart, and this fact may contribute for the development of S-AKI [ 96 ].…”

“…Even though protein S-nitrosylation is an important mechanism for many beneficial and harmful effects of NO, this post-translational modification has been less explored in the S-AKI context. The already cited reduction in GRK2 levels in the kidney of septic mice is likely to be due to S-nitrosylation of the enzyme [ 96 ]. S-nitrosylation of the transcription factor TonEBP/NFAT5 and the subsequent reduction in its transcriptional activity led to a reduced expression of target genes such as ClC-K1 , Barttin , urea transporter-A1 , and aquaporin 2 , all required for urinary concentration.…”