Partial Netrin-1 Deficiency Aggravates Acute Kidney Injury

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

Histological tissue insure induced by AKI in mice with partial netrin-1 deficiency (<i>Ntn1^+/−</i>) or control mice (<i>Ntn1^+/+</i>).

<p>Renal histology in <i>Ntn1^+/−</i> mice exposed to renal ischemia or age-, weight-, and gender-matched littermate controls (<i>Ntn1^+/+</i>) were subjected to 30 minutes of left renal artery ischemia. Renal histology was obtained after 24 hours of reperfusion. (A–D) Representative H&E staining (400×). Arrow marks destructed tubules. (E) Quantification of histological tissue damage assessed by Jablonski index.</p

Renal inflammatory changes in <i>Ntn1^+/−</i> mice following ischemia.

<p><i>Ntn1^+/−</i> mice and their respective age-, weight-, and gender-matched littermate controls (<i>Ntn1^+/+</i>) were subjected to 30 minutes of left renal artery ischemia. (A–D) Neutrophil staining. Arrows indicate neutrophils (magnification 400×). (E) Quantification of neutrophil tissue accumulation by measurement of myeloperoxidase (MPO). (F) TNF-α and (G) interleukin-6 (IL-6) and (H) interleukin-10 (IL-10) were assessed by real-time RT-PCR from renal tissues. Data were calculated relative to ß-actin and are expressed as fold change compared to sham-operated animals without ischemia (−I). Data are representative of four to six independent experiments for each experimental condition (mean ± SD).</p

<i>In vitro</i> expression of netrin-1 in HK-2 cells.

<p>(A) Expression of netrin-1 in human renal epithelial cells (HK-2 cells) following exposure to hypoxia (1% O₂) for indicated time periods. One representative blot of three is displayed. (B) Quantification or netrin-1 protein in HK-2 cells relative to β-actin.</p

Reconstitution of <i>Ntn1^+/−</i> mice with exogenous netrin-1.

<p>Renal function and inflammation in mice with partial deficiency for netrin-1 (<i>Ntn1^+/−</i>) treated with exogenous netrin (5 µg/mouse I.V.) or vehicle prior to 30 minutes of renal ischemia. (A) Glomerular filtration rate (as measured by FITC-inulin clearance) was measured after 1 hour of reperfusion. (B) Quantification of neutrophil tissue accumulation by measurement of myeloperoxidase (MPO) (mean ± SD; n = 6–8).</p

Equilibrative nucleoside transporter 1 (ENT1) regulates postischemic blood flow during acute kidney injury in mice

View from Jardin Anglais looking over the Etang des Carpes towards the island pavilion; Henry IV made considerable alterations and additions to Fontainebleau. He enclosed a new courtyard (begun 1599) to the north of the Galerie François I and Cour de l'Ovale around the Jardin de la Reine (now the Jardin de Diane). The Jardin de Diane is now named after the Fountain of Diana, the plinth of which bears bronze figures (1603) by Pierre Biard. Outside the château Henry IV created an island garden, the Jardin de l'Etang, in the lake in front of the Cour de la Fontaine, laid out as a parterre de broderie (1595; island destroyed 1713). He also built a pavilion in the middle of the lake (rebuilt 1664; restored ca. 1811) and laid out the Parterre du Tibre south of the Cour de l'Ovale and the Cour des Offices. It was so called because of the statue and fountain at its centre. Under Louis XIII, Louis Le Vau redesigned the Parterre du Tibre (1662) and created an architectural cascade (largely destroyed 1723) at the head of Henry IV's canal. In the grounds Napoleon commissioned (1810) Maximilien-Joseph Hurtault (1765-1824) to remodel the gardens south of the Aile Louis XV into a Jardin Anglais and to restore the Jardin de Diane

Equilibrative nucleoside transporter 1 (ENT1) regulates postischemic blood flow during acute kidney injury in mice

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