ABSTRACT
A complex biologic network regulates kidney perfusion under physiologic conditions. This system is profoundly perturbed following renal ischemia, a leading cause of acute kidney injury (AKI) - a life-threatening condition that frequently complicates the care of hospitalized patients. Therapeutic approaches to prevent and treat AKI are extremely limited. Better understanding of the molecular pathways promoting postischemic reflow could provide new candidate targets for AKI therapeutics. Due to its role in adapting tissues to hypoxia, we hypothesized that extracellular adenosine has a regulatory function in the postischemic control of renal perfusion. Consistent with the notion that equilibrative nucleoside transporters (ENTs) terminate adenosine signaling, we observed that pharmacologic ENT inhibition in mice elevated renal adenosine levels and dampened AKI. Deletion of the ENTs resulted in selective protection in Ent1-/- mice. Comprehensive examination of adenosine receptor-knockout mice exposed to AKI demonstrated that renal protection by ENT inhibitors involves the A2B adenosine receptor. Indeed, crosstalk between renal Ent1 and Adora2b expressed on vascular endothelia effectively prevented a postischemic no-reflow phenomenon. These studies identify ENT1 and adenosine receptors as key to the process of reestablishing renal perfusion following ischemic AKI. If translatable from mice to humans, these data have important therapeutic implications.
Subject(s)
Acute Kidney Injury/metabolism , Equilibrative Nucleoside Transporter 1/metabolism , Ischemia/metabolism , Regional Blood Flow/physiology , Acute Kidney Injury/drug therapy , Acute Kidney Injury/pathology , Adenosine/metabolism , Animals , Cell Line , Chimerism , Dipyridamole/therapeutic use , Equilibrative Nucleoside Transporter 1/antagonists & inhibitors , Equilibrative Nucleoside Transporter 1/genetics , Humans , Kidney/metabolism , Kidney/pathology , Mice , Mice, Inbred C57BL , Mice, Knockout , No-Reflow Phenomenon , Nucleoside Transport Proteins/antagonists & inhibitors , Nucleoside Transport Proteins/metabolism , Phosphodiesterase Inhibitors/therapeutic use , Receptors, Purinergic P1/genetics , Receptors, Purinergic P1/metabolismABSTRACT
The netrin family of secreted proteins provides migrational cues in the developing central nervous system. Recently, netrins have also been shown to regulate diverse processes beyond their functions in the brain, incluing the ochrestration of inflammatory events. Particularly netrin-1 has been implicated in dampening hypoxia-induced inflammation. Here, we hypothesized an anti-inflammatory role of endogenous netrin-1 in acute kidney injury (AKI). As homozygous deletion of netrin-1 is lethal, we studied mice with partial netrin-1 deletion (Ntn-1(+/-) mice) as a genetic model. In fact, Ntn-1(+/-) mice showed attenuated Ntn-1 levels at baseline and following ischemic AKI. Functional studies of AKI induced by 30 min of renal ischemia and reperfusion revealed enhanced kidney dysfunction in Ntn-1(+/-) mice as assessed by measurements of glomerular filtration, urine flow rate, urine electrolytes, serum creatinine and creatinine clearance. Consistent with these findings, histological studies indicated a more severe degree kidney injury. Similarly, elevations of renal and systemic inflammatory markers were enhanced in mice with partial netrin-1 deficiency. Finally, treatment of Ntn-1(+/-) mice with exogenous netrin-1 restored a normal phenotype during AKI. Taking together, these studies implicate endogenous netrin-1 in attenuating renal inflammation during AKI.
Subject(s)
Acute Kidney Injury/etiology , Acute Kidney Injury/pathology , Nerve Growth Factors/metabolism , Nerve Growth Factors/physiology , Tumor Suppressor Proteins/metabolism , Tumor Suppressor Proteins/physiology , Acute Kidney Injury/metabolism , Animals , Blotting, Western , Cells, Cultured , Creatinine/blood , Disease Models, Animal , Enzyme-Linked Immunosorbent Assay , Glomerular Filtration Rate , Humans , Immunoenzyme Techniques , Kidney/cytology , Kidney/metabolism , Kidney Function Tests , Mice , Mice, Knockout , Nerve Growth Factors/genetics , Netrin-1 , Phenotype , RNA, Messenger/genetics , Reverse Transcriptase Polymerase Chain Reaction , Tumor Suppressor Proteins/geneticsABSTRACT
Intestinal ischemia/reperfusion injury (IR) is characterized by intermittent loss of perfusion to the gut, resulting in dramatic increases in morbidity and mortality. Based on previous studies indicating an anti-inflammatory role for hypoxia-inducible factor (HIF)-1-elicited enhancement of extracellular adenosine production via ecto-5'-nucleotidase (CD73) and signaling through the A2B adenosine receptor (A2BAR), we targeted HIF-1 during IR using pharmacological or genetic approaches. Initial studies with pharmacological HIF activation indicated attenuation of intestinal injury with dimethyloxallyl glycine (DMOG) treatment during murine IR. Although DMOG treatment was associated with induction of CD73 transcript and protein, DMOG protection was abolished in cd73(-/-) mice. Similarly, DMOG treatment enhanced A2BAR transcript and protein levels, whereas DMOG protection was abolished in A2BAR(-/-) mice. Finally, studies of mice with conditional HIF-1α deletion in intestinal epithelia or pharmacological inhibition of HIF-1 with 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin revealed enhanced tissue injury during IR. These studies indicated a tissue-protective role of HIF-dependent enhancement of intestinal adenosine generation and signaling during intestinal IR.
