Christoph Eisner

Reduced Production of Creatinine Limits Its Use as Marker of Kidney Injury in Sepsis

Although diagnosis and staging of acute kidney injury uses serum creatinine, acute changes in creatinine lag behind both renal injury and recovery. The risk for mortality increases when acute kidney injury accompanies sepsis; therefore, we sought to explore the limitations of serum creatinine in this setting. In mice, induction of sepsis by cecal ligation and puncture in bilaterally nephrectomized mice increased markers of nonrenal organ injury and serum TNF-alpha. Serum creatinine, however, was significantly lower in septic animals than in animals subjected to bilateral nephrectomy and sham cecal ligation and puncture. Under these conditions treatment with chloroquine decreased nonrenal organ injury markers but paradoxically increased serum creatinine. Sepsis dramatically decreased production of creatinine in nephrectomized mice, without changes in body weight, hematocrit, or extracellular fluid volume. In conclusion, sepsis reduces production of creatinine, which blunts the increase in serum creatinine after sepsis, potentially limiting the early detection of acute kidney injury. This may partially explain why small absolute increases in serum creatinine levels are associated with poor clinical outcomes. These data support the need for new biomarkers that provide better measures of renal injury, especially in patients with sepsis.

Functional expression of the olfactory signaling system in the kidney

Olfactory-like chemosensory signaling occurs outside of the olfactory epithelium. We find that major components of olfaction, including olfactory receptors (ORs), olfactory-related adenylate cyclase (AC3) and the olfactory G protein (Golf), are expressed in the kidney. AC3 and Golf colocalize in renal tubules and in macula densa (MD) cells which modulate glomerular filtration rate (GFR). GFR is significantly reduced in AC3−/− mice, suggesting that AC3 participates in GFR regulation. Although tubuloglomerular feedback is normal in these animals, they exhibit significantly reduced plasma renin levels despite up-regulation of COX-2 expression and nNOS activity in the MD. Furthermore, at least one member of the renal repertoire of ORs is expressed in a MD cell line. Thus, key components of olfaction are expressed in the renal distal nephron and may play a sensory role in the MD to modulate both renin secretion and GFR.

Major contribution of tubular secretion to creatinine clearance in mice

This study was performed to quantify the fraction of excreted creatinine not attributable to creatinine filtration for accurately determining the glomerular filtration rate in mice. To measure this we compared creatinine filtration with the simultaneous measurement of inulin clearance using both single-bolus fluorescein isothiocyanate (FITC)-inulin elimination kinetics and standard FITC-inulin infusion. During anesthesia, creatinine filtration was found to be systematically higher than inulin clearance in both male and female C57BL/6J mice. The secretion fraction was significantly less in female mice. Administration of either cimetidine or para-aminohippuric acid, competitors of organic cation and anion transport respectively, significantly reduced the secretion fraction in male and female mice and both significantly increased the plasma creatinine level. Creatinine secretion in both genders was not mediated by the organic cation transporters OCT1 or OCT 2 since secretion fraction levels were identical in FVB wild-type and OCT1/2 knockout mice. Thus, secretion accounts for about 50 and 35% of excreted creatinine in male and female mice, respectively. Increasing plasma creatinine threefold by infusion further increased the secretion fraction. Renal organic anion transporter 1 mRNA expression was higher in male than in female mice, reflecting the gender difference in creatinine secretion. Hence we show that there is a major secretory contribution to creatinine excretion mediated through the organic anion transport system. This feature adds to problems associated with measuring endogenous creatinine filtration in mice.

Sphingosine kinase 1 and sphingosine-1-phosphate receptor 2 are vital to recovery from anaphylactic shock in mice

Sphingosine kinase 1 (SphK1) and SphK2 are ubiquitous enzymes that generate sphingosine-1-phosphate (S1P), a ligand for a family of G protein-coupled receptors (S1PR1-S1PR5) with important functions in the vascular and immune systems. Here we explore the role of these kinases and receptors in recovery from anaphylaxis in mice. We found that Sphk2-/- mice had a rapid recovery from anaphylaxis. In contrast, Sphk1-/- mice showed poor recovery from anaphylaxis and delayed histamine clearance. Injection of S1P into Sphk1-/- mice increased histamine clearance and promoted recovery from anaphylaxis. Adoptive cell transfer experiments demonstrated that SphK1 activity was required in both the hematopoietic and nonhematopoietic compartments for recovery from anaphylaxis. Mice lacking the S1P receptor S1PR2 also showed a delay in plasma histamine clearance and a poor recovery from anaphylaxis. However, S1P did not promote the recovery of S1pr2-/- mice from anaphylaxis, whereas S1pr2+/- mice showed partial recovery. Unlike Sphk2-/- mice, Sphk1-/- and S1pr2-/- mice had severe hypotension during anaphylaxis. Thus, SphK1-produced S1P regulates blood pressure, histamine clearance, and recovery from anaphylaxis in a manner that involves S1PR2. This suggests that specific S1PR2 agonists may serve to counteract the vasodilation associated with anaphylactic shock.

A selective EP4 PGE2 receptor agonist alleviates disease in a new mouse model of X-linked nephrogenic diabetes insipidus.

X-linked nephrogenic diabetes insipidus (XNDI) is a severe kidney disease caused by inactivating mutations in the V2 vasopressin receptor (V2R) gene that result in the loss of renal urine-concentrating ability. At present,no specific pharmacological therapy has been developed for XNDI, primarily due to the lack of suitable animal models. To develop what we believe to be the first viable animal model of XNDI, we generated mice in which the V2R gene could be conditionally deleted during adulthood by administration of 4-OH-tamoxifen.Radioligand-binding studies confirmed the lack of V2R-binding sites in kidneys following 4-OH-tamoxifen treatment, and further analysis indicated that upon V2R deletion, adult mice displayed all characteristic symptoms of XNDI, including polyuria, polydipsia, and resistance to the antidiuretic actions of vasopressin. Gene expression analysis suggested that activation of renal EP4 PGE2 receptors might compensate for the lack of renal V2R activity in XNDI mice. Strikingly, both acute and chronic treatment of the mutant mice with a selective EP4 receptor agonist greatly reduced all major manifestations of XNDI, including changes in renal morphology.These physiological improvements were most likely due to a direct action on EP4 receptors expressed on collecting duct cells. These findings illustrate the usefulness of the newly generated V2R mutant mice for elucidating and testing new strategies for the potential treatment of humans with XNDI.

Pre-existing renal disease promotes sepsis-induced acute kidney injury and worsens outcome

While it is known that risk of death from sepsis is higher in patients with pre-existing chronic kidney disease its mechanism is unknown. To study this we established a two-stage mouse model where renal disease was first induced by folic acid injection followed by sub-lethal cecal ligation and puncture to induce sepsis. Septic mice with pre-existing renal disease had significantly higher mortality, serum creatinine, vascular permeability, plasma vascular endothelial growth factor (VEGF) levels, bacteremia, serum IL-10, splenocyte apoptosis and more severe septic shock when compared to septic mice without pre-existing disease. To evaluate the contribution of vascular and immunological dysfunction, we treated the folate-septic mice with soluble Flt-1 to bind VEGF and chloroquine to reduce splenocyte apoptosis. These treatments together resulted in a significant improvement in kidney injury, hemodynamics and survival. Our study shows that the sequential mouse model mimics human sepsis frequently complicated by pre-existing renal disease and might be useful in evaluating preventive and therapeutic strategies.

Angiotensin II overcomes strain-dependent resistance of rapid CKD progression in a new remnant kidney mouse model

The remnant kidney model in C57BL/6 mice does not develop progressive chronic kidney disease (CKD). In this study we modified the model to mimic features of human CKD and to define accelerants of disease progression using three strains of mice. Following the procedure, there was a progressive increase in albuminuria, progressive loss in renal function, severe glomerulosclerosis and interstitial fibrosis, hypertension, cardiac fibrosis, and anemia by 4 weeks in CD-1 mice and by 12 weeks in 129S3 mice. In contrast, even after 16 weeks, the C57BL/6 mice with a remnant kidney had modestly increased albuminuria without increased blood pressure and without developing CKD or cardiac fibrosis. The baseline blood pressure, determined by radiotelemetry in conscious animals, correlated with CKD progression rates in each strain. Administering angiotensin II overcame the resistance of C57BL/6 mice to CKD following renal mass reduction, displaying high blood pressure and albuminuria, severe glomerulosclerosis, and loss of renal function by 4 weeks. Decreasing blood pressure with olmesartan, but not hydralazine, in CD-1 mice with a remnant kidney reduced CKD progression and cardiac fibrosis. C57BL/6 mice with a remnant kidney and DOCA-salt hypertension developed modest CKD. Each strain had similar degrees of interstitial fibrosis in three different normotensive models of renal fibrosis. Thus, reducing renal mass in CD-1 or 129S3 mice mimics many features of human CKD. Angiotensin II can convert the C57BL/6 strain from CKD resistant to susceptible in this disease model.

Salt sensitivity of blood pressure in NKCC1-deficient mice.

NKCC1 is a widely expressed isoform of the Na-2Cl-K cotransporter that mediates several direct and indirect vascular effects and regulates expression and release of renin. In this study, we used NKCC1-deficient (NKCC1-/-) and wild-type (WT) mice to assess day/night differences of blood pressure (BP), locomotor activity, and renin release and to study the effects of high (8%) or low (0.03%) dietary NaCl intake on BP, activity, and the renin/aldosterone system. On a standard diet, 24-h mean arterial blood pressure (MAP) and heart rate determined by radiotelemetry, and their day/night differences, were not different in NKCC1-/- and WT mice. Spontaneous and wheel-running activities in the active night phase were lower in NKCC1-/- than WT mice. In NKCC1-/- mice on a high-NaCl diet, MAP increased by 10 mmHg in the night without changes in heart rate. In contrast, there was no salt-dependent blood pressure change in WT mice. MAP reductions by hydralazine (1 mg/kg) or isoproterenol (10 microg/mouse) were significantly greater in NKCC1-/- than WT mice. Plasma renin (PRC; ng ANG I.ml(-1).h(-1)) and aldosterone (aldo; pg/ml) concentrations were higher in NKCC1-/- than WT mice (PRC: 3,745+/-377 vs. 1,245+/-364; aldo: 763+/-136 vs. 327+/-98). Hyperreninism and hyperaldosteronism were found in NKCC1-/- mice during both day and night. High Na suppressed PRC and aldosterone in both NKCC1-/- and WT mice, whereas a low-Na diet increased PRC and aldosterone in WT but not NKCC1-/- mice. We conclude that 24-h MAP and MAP circadian rhythms do not differ between NKCC1-/- and WT mice on a standard diet, probably reflecting a balance between anti- and prohypertensive factors, but that blood pressure of NKCC1-/- mice is more sensitive to increases and decreases of Na intake.

Stimulation of Renin Secretion by Angiotensin II Blockade is Gsα-Dependent

Angiotensin II converting enzyme inhibitors (ACEI) or angiotensin II receptor blockers (ARB) presumably stimulate renin secretion by interrupting angiotensin II feedback inhibition. The increase in cytosolic calcium caused by activation of Gq-coupled AT1 receptors may mediate the renin-inhibitory effect of angiotensin II at the cellular level, implying that ACEI and ARB may work by reducing intracellular calcium. Here, we investigated whether angiotensin II blockade acts predominantly through Gs-mediated stimulation of adenylyl cyclase (AC) by testing the effect of ACEI and ARB in mice with juxtaglomerular cell-specific deficiency of the AC-stimulatory Gsalpha. The ACEI captopril and quinaprilate and the ARB candesartan significantly increased plasma renin concentration (PRC) to 20 to 40 times basal PRC in wild-type mice but did not significantly alter PRC in Gsalpha-deficient mice. Captopril also completely abrogated renin stimulation in wild-type mice after co-administration of propranolol, indomethacin, and L-NAME. Treatment with enalapril and a low-NaCl diet for 7 days led to a 35-fold increase in PRC among wild-type mice but no significant change in PRC among Gsalpha-deficient mice. Three different pharmacologic inhibitors of AC reduced the stimulatory effect of captopril by 70% to 80%. In conclusion, blockade of angiotensin II stimulates renin synthesis and release indirectly through the action of ligands that activate the cAMP/PKA pathway in a Gsalpha-dependent fashion, including catecholamines, prostaglandins, and nitric oxide.

Deletion of the secretory vesicle proteins IA-2 and IA-2β disrupts circadian rhythms of cardiovascular and physical activity

Targeted deletion of IA‐2 and IA‐2β, major autoantigens in type 1 diabetes and transmembrane secretory vesicle proteins, results in impaired secretion of hormones and neurotransmitters. In the present study, we evaluated the effect of these deletions on daily rhythms in blood pressure, heart rate, core body temperature, and spontaneous physical and neuronal activity. We found that deletion of both IA‐2 and IA‐2β profoundly disrupts the usual diurnal variation of each of these parameters, whereas the deletion of either IA‐2 or IA‐2β alone did not produce a major change. In situ hybridization revealed that IA‐2 and IA‐2β transcripts are highly but nonrhythmically expressed in the suprachiasmatic nuclei, the site of the brains master circadian oscillator. Electrophysiological studies on tissue slices from the suprachiasmatic nuclei showed that disruption of both IA‐2 and IA‐2β results in significant alterations in neuronal firing. From these studies, we concluded that deletion of IA‐2 and IA‐2β, structural proteins of secretory vesicles and modulators of neuroendocrine secretion, has a profound effect on the circadian system.—Kim, S. M., Power, A., Brown, T. M., Constance, C. M., Coon, S. L., Nishimura, T., Hirai, H., Cai, T., Eisner, C., Weaver, D. R., Piggins, H. D., Klein, D. C., Schnermann, J., Notkins, A. L. Deletion of the secretory vesicle proteins IA‐2 and IA‐2β disrupts circadian rhythms of cardiovascular and physical activity. FASEBJ. 23, 3226‐3232 (2009). www.fasebj.org