Cyclooxygenase-2 in rat nephron development

Renal Function Underpins the Cyclooxygenase-2: Asymmetric Dimethylarginine Axis in Mouse and Man

Introduction

Through the production of prostacyclin, cyclooxygenase (COX)-2 protects the cardiorenal system. Asymmetric dimethylarginine (ADMA), is a biomarker of cardiovascular and renal disease. Here we determined the relationship between COX-2/prostacyclin, ADMA, and renal function in mouse and human models.

Methods

We used plasma from COX-2 or prostacyclin synthase knockout mice and from a unique individual lacking COX-derived prostaglandins (PGs) because of a loss of function mutation in cytosolic phospholipase A2 (cPLA2), before and after receiving a cPLA2-replete transplanted donor kidney. ADMA, arginine, and citrulline were measured using ultra-high performance liquid-chromatography tandem mass spectrometry. ADMA and arginine were also measured by enzyme-linked immunosorbent assay (ELISA). Renal function was assessed by measuring cystatin C by ELISA. ADMA and prostacyclin release from organotypic kidney slices were also measured by ELISA.

Results

Loss of COX-2 or prostacyclin synthase in mice increased plasma levels of ADMA, citrulline, arginine, and cystatin C. ADMA, citrulline, and arginine positively correlated with cystatin C. Plasma ADMA, citrulline, and cystatin C, but not arginine, were elevated in samples from the patient lacking COX/prostacyclin capacity compared to levels in healthy volunteers. Renal function, ADMA, and citrulline were returned toward normal range when the patient received a genetically normal kidney, capable of COX/prostacyclin activity; and cystatin C positively correlated with ADMA and citrulline. Levels of ADMA and prostacyclin in conditioned media of kidney slices were not altered in tissue from COX-2 knockout mice compared to wildtype controls.

Conclusion

In human and mouse models, where renal function is compromised because of loss of COX-2/PGI2 signaling, ADMA levels are increased.

Hypertension and renal disease programming: focus on the early postnatal period

The developmental origin of hypertension and renal disease is a concept highly supported by strong evidence coming from both human and animal studies. During development there are periods in which the organs are more vulnerable to stressors. Such periods of susceptibility are also called 'sensitive windows of exposure'. It was shown that as earlier an adverse event occurs; the greater are the consequences for health impairment. However, evidence show that the postnatal period is also quite important for hypertension and renal disease programming, especially in rodents because they complete nephrogenesis postnatally, and it is also important during preterm human birth. Considering that the developing kidney is vulnerable to early-life stressors, renal programming is a key element in the developmental programming of hypertension and renal disease. The purpose of this review is to highlight the great number of studies, most of them performed in animal models, showing the broad range of stressors involved in hypertension and renal disease programming, with a particular focus on the stressors that occur during the early postnatal period. These stressors mainly include undernutrition or specific nutritional deficits, chronic behavioral stress, exposure to environmental chemicals, and pharmacological treatments that affect some important factors involved in renal physiology. We also discuss the common molecular mechanisms that are activated by the mentioned stressors and that promote the appearance of these adult diseases, with a brief description on some reprogramming strategies, which is a relatively new and promising field to treat or to prevent these diseases.

Expression of neuronal nitric oxide synthase and renin in dysplastic kidneys of young dogs

Renin and neuronal nitric oxide synthase in the kidney control the renin-angiotensin and tubuloglomerular feedback systems. The present study investigated the expression of renin and neuronal nitric oxide synthase in the dysplastic kidneys of three young dogs. Renin-immunoreactivity, which occurs in the juxtaglomerular and tubular cells of dysplastic kidneys, did not differ from that in the normal kidneys of young dogs. Macula densa cells in the normal kidneys showed neuronal nitric oxide synthase -immunoreactivity, but those in the dysplastic kidneys showed no apparent signals. This observation may be correlated with the pathological mechanisms of renal failure in young dogs.

New insights into the obligatory nature of cyclooxygenase-2 and PGE2 during early chick embryogenesis

Temporal expression patterns and activity of two cyclooxygenase (COX-1 and COX-2) isoforms were analysed during early chick embryogenesis to evaluate their roles in development. COX-2 inhibition with etoricoxib resulted in significant structural anomalies such as anophthalmia (born without one or both eyes), phocomelia (underdeveloped or truncated limbs), and gastroschisis (an opening in the abdominal wall), indicating its significance in embryogenesis. Furthermore, the levels of PGE₂, PGD₂, PGF_2α, and TXB₂ were assessed using quantitative LC-MS/MS to identify which effector prostanoid (s) had their synthesis initiated by COX-2. COX-2 inhibition was only shown to reduce the level of PGE₂ significantly_, and hence it could be inferred that the later could be largely under the regulation of activated COX-2 in chick embryos. The compensatory increase in the activity of COX-1 observed in the etoricoxib-treated group helped to maintain the levels of PGD₂, PGF_2α, and TXB₂. Though the roles of these three prostanoids in embryogenesis need to be further clarified, it appears that their contribution to the observed developmental anomalies is minimal. This study has shown that COX-2 is functionally active during chick embryogenesis, and it plays a central role in the structural configuration of several organs and tissues through its downstream effector molecule PGE₂.

The role of the spinal cyclooxygenase (COX) for incisional pain in rats at different developmental stages

BACKGROUND

Cyclooxygenase enzymes (COX)-1 and COX-2 are important targets for pain relief after surgery, but the spinal contribution of both isoforms is still unclear, e.g., from a developmental point of view. Here, we studied changes of spinal COX-1 and COX-2 expression and their functional relevance in rats of different ages for pain-related behaviour after incision.

METHODS

Mechanical paw withdrawal thresholds (PWT) were assessed before and after incision and after intrathecal administration (IT) of SC-560 (COX-1 inhibitor) or NS-398 (COX-2 inhibitor) in rats aged 5, 14 and 28 days (P5, P14, P28). Furthermore, spinal expressions of COX m-RNA and proteins were investigated.

RESULTS

In P5 rats, only IT-administered NS-398 but not SC-560 significantly reversed the decreased PWT after incision. In P14 rats, none of the substance modified PWT, and in P28 rats, only SC-560 increased PWT. Spinal COX-2 mRNA and protein were increased in P5 but not in P14 and P28 rats after incision. Whereas COX-2 is located in spinal neurons, COX-1 is mainly found in spinal microglia cells.

CONCLUSION

Our results demonstrate a possible developmental transition from COX-2 to COX-1 activation. Whereas in adult rats spinal COX-1 but not COX-2 is involved in pain-related behaviour after incision, it seems opposite in P5 rats. Interestingly, in P14, neither COX-1 nor COX-2 seems to play a role. This switch may relate to altered neuronal/microglia activation. Our findings indicate specific mechanisms to pain after incision that are age-dependent and may guide further research improving paediatric pain management.

SIGNIFICANCE

Postoperative pain in pediatric patients after surgery is still poorly controlled; this might contribute to long-lasting alteration in the nociceptive system and prolonged chronic pain. Here we show a possible developmental switch in the COX-dependent pathway for nociceptive spinal transmission that may explain why pain management in young children needs to be related to age-dependent mechanisms.

Cyclooxygenase-2, Asymmetric Dimethylarginine, and the Cardiovascular Hazard From Nonsteroidal Anti-Inflammatory Drugs

BACKGROUND

Large-scale, placebo-controlled trials established that nonsteroidal anti-inflammatory drugs confer a cardiovascular hazard: this has been attributed to depression of cardioprotective products of cyclooxygenase (COX)-2, especially prostacyclin. An alternative mechanism by which nonsteroidal anti-inflammatory drugs might constrain cardioprotection is by enhancing the formation of methylarginines in the kidney that would limit the action of nitric oxide throughout the vasculature.

METHODS

Targeted and untargeted metabolomics were used to investigate the effect of COX-2 deletion or inhibition in mice and in osteoarthritis patients exposed to nonsteroidal anti-inflammatory drugs on the l-arginine/nitric oxide pathway.

RESULTS

Analysis of the plasma and renal metabolome was performed in postnatal tamoxifen-inducible Cox-2 knockout mice, which exhibit normal renal function and blood pressure. This revealed no changes in arginine and methylarginines compared with their wild-type controls. Moreover, the expression of genes in the l-arginine/nitric oxide pathway was not altered in the renal medulla or cortex of tamoxifen inducible Cox-2 knockout mice. Therapeutic concentrations of the selective COX-2 inhibitors, rofecoxib, celecoxib, and parecoxib, none of which altered basal blood pressure or renal function as reflected by plasma creatinine, failed to elevate plasma arginine and methylarginines in mice. Finally, plasma arginine or methylarginines were not altered in osteoarthritis patients with confirmed exposure to nonsteroidal anti-inflammatory drugs that inhibit COX-1 and COX-2. By contrast, plasma asymmetrical dimethylarginine was increased in mice infused with angiotensin II sufficient to elevate blood pressure and impair renal function. Four weeks later, blood pressure, plasma creatinine, and asymmetrical dimethylarginine were restored to normal levels. The increase in asymmetrical dimethylarginine in response to infusion with angiotensin II in celecoxib-treated mice was also related to transient impairment of renal function.

CONCLUSIONS

Plasma methylarginines are not altered by COX-2 deletion or inhibition but rather are elevated coincident with renal compromise.

Immunohistochemical Staining of CD8α in Diabetic Mouse Kidney

Immune cell infiltration, particularly cytotoxic CD8α lymphocyte infiltration, plays an important role in development of diabetic nephropathy. Although CD8α infiltration can be evaluated by its production of cytokines, its localization in the kidney is of particular importance. The current protocol describes CD8α immunostaining using a Vectastain ABC kit. This protocol works well with most commercially available antibodies, including CD8α antibodies in kidneys of diabetic mice.

Renal Medullary Interstitial COX-2 (Cyclooxygenase-2) Is Essential in Preventing Salt-Sensitive Hypertension and Maintaining Renal Inner Medulla/Papilla Structural Integrity

COX (cyclooxygenase)-derived prostaglandins regulate renal hemodynamics and salt and water homeostasis. Inhibition of COX activity causes blood pressure elevation. In addition, chronic analgesic abuse can induce renal injury, including papillary necrosis. COX-2 is highly expressed in the kidney papilla in renal medullary interstitial cells (RMICs). However, its role in blood pressure and papillary integrity in vivo has not been definitively studied. In mice with selective, inducible RMIC COX-2 deletion, a high-salt diet led to an increase in blood pressure that peaked at 4 to 5 weeks and was associated with increased papillary expression of AQP2 (aquaporin 2) and ENac (epithelial sodium channel) and decreased expression of cystic fibrosis transmembrane conductance regulator. With continued high-salt feeding, the mice with RMIC COX-2 deletion had progressive decreases in blood pressure from its peak. After return to a normal-salt diet for 3 weeks, blood pressure remained low and was associated with a persistent urinary concentrating defect. Within 2 weeks of institution of a high-salt diet, increased apoptotic RMICs and collecting duct cells could be detected in papillae with RMIC deletion of COX-2, and by 9 weeks of high salt, there was a striking loss of the papillae. Therefore, RMIC COX-2 expression plays a crucial role in renal handling water and sodium homeostasis, preventing salt-sensitive hypertension and maintaining structural integrity of papilla.

Postnatal changes in constitutive cyclooxygenase‑2 expression in the mice hippocampus and its function in synaptic plasticity

Although the expression of cyclooxygenase-2 (COX-2) is closely associated with inflammation in the brain, it is constitutively expressed in the brain, and its expression is regulated by synaptic activity. The present study investigated postnatal expression of COX-2 in the hippocampus in C57BL/6 mice at postnatal days (P) 1, 7, 14, 28, and 56. In addition, the presented study examined the effects of COX-2 on synaptic plasticity through Arc, phosphorylated cAMP response element-binding protein (pCREB), N-methyl-d-aspartate receptor 1 (GluN1), and GluN2A/2B immunohistochemistry, which was performed on COX-2 knockout (KO) and wild-type (WT) mice. Extremely weak COX-2 immunoreactivity was detected in the hippocampal CA1-3 areas in addition to the dentate gyrus at P1. Conversely, COX-2 immunoreactivity was observed in the stratum pyramidale of the CA1-3 regions and in the outer granule cell layer of the dentate gyrus at P7. Additionally, although peak COX-2 immunoreactivity was observed in all hippocampal sub-regions, including the dentate gyrus at P14, it was significantly decreased at P14. Finally, COX-2 immunoreactivity and the distribution pattern seen at P56 in the hippocampal CA1-3 regions were similar to those observed at P28, whereas, they were identified in the inner half of the granule cell layer of the dentate gyrus. The western blot analysis revealed that the COX-2 protein levels peaked at P14 and were decreased at P28 and P56. Additionally, the number of Arc and pCREB immunoreactive cells as well as GluN1 and GluN2A/2B immunoreactivity of COX-2 KO mice were significantly decreased in the dentate gyrus when compared with that in WT mice. Taken together, the results of the present study suggest that COX-2 serves an important role in synaptic plasticity in the dentate gyrus and changes in the levels of its constitutive expression are associated with the hippocampal dentate gyrus postnatal development.

TGF-β promotes fibrosis after severe acute kidney injury by enhancing renal macrophage infiltration

TGF-β signals through a receptor complex composed of 2 type I and 2 type II (TGF-βRII) subunits. We investigated the role of macrophage TGF-β signaling in fibrosis after AKI in mice with selective monocyte/macrophage TGF-βRII deletion (macrophage TGF-βRII-/- mice). Four weeks after injury, renal TGF-β1 expression and fibrosis were higher in WT mice than macrophage TGF-βRII-/- mice, which had decreased renal macrophages. The in vitro chemotactic response to f-Met-Leu-Phe was comparable between bone marrow-derived monocytes (BMMs) from WT and macrophage TGF-βRII-/- mice, but TGF-βRII-/- BMMs did not respond to TGF-β. We then implanted Matrigel plugs suffused with either f-Met-Leu-Phe or TGF-β1 into WT or macrophage TGF-βRII-/- mice. After 6 days, f-Met-Leu-Phe induced similar macrophage infiltration into the Matrigel plugs of WT and macrophage TGF-βRII-/- mice, but TGF-β induced infiltration only in WT mice. We further determined the number of labeled WT or TGF-βRII-/- BMMs infiltrating into WT kidneys 20 days after ischemic injury. There were more labeled WT BMMs than TGF-βRII-/- BMMs. Therefore, macrophage TGF-βRII deletion protects against the development of tubulointerstitial fibrosis following severe ischemic renal injury. Chemoattraction of macrophages to the injured kidney through a TGF-β/TGF-βRII axis is a heretofore undescribed mechanism by which TGF-β can mediate renal fibrosis during progressive renal injury.

Inhibition of Epidermal Growth Factor Receptor Activation Is Associated With Improved Diabetic Nephropathy and Insulin Resistance in Type 2 Diabetes

Previous studies by us and others have indicated that renal epidermal growth factor receptors (EGFR) are activated in models of diabetic nephropathy (DN) and that inhibition of EGFR activity protects against progressive DN in type 1 diabetes. In this study we examined whether inhibition of EGFR activation would affect the development of DN in a mouse model of accelerated type 2 diabetes (BKS db/db with endothelial nitric oxide knockout [eNOS^-/-db/db]). eNOS^-/-db/db mice received vehicle or erlotinib, an inhibitor of EGFR tyrosine kinase activity, beginning at 8 weeks of age and were sacrificed at 20 weeks of age. In addition, genetic models inhibiting EGFR activity (waved 2) and transforming growth factor-α (waved 1) were studied in this model of DN in type 2 diabetes. Compared with vehicle-treated mice, erlotinib-treated animals had less albuminuria and glomerulosclerosis, less podocyte loss, and smaller amounts of renal profibrotic and fibrotic components. Erlotinib treatment decreased renal oxidative stress, macrophage and T-lymphocyte infiltration, and the production of proinflammatory cytokines. Erlotinib treatment also preserved pancreas function, and these mice had higher blood insulin levels at 20 weeks, decreased basal blood glucose levels, increased glucose tolerance and insulin sensitivity, and increased blood levels of adiponectin compared with vehicle-treated mice. Similar to the aforementioned results, both waved 1 and waved 2 diabetic mice also had attenuated DN, preserved pancreas function, and decreased basal blood glucose levels. In this mouse model of accelerated DN, inhibition of EGFR signaling led to increased longevity.

IL-4/IL-13-mediated polarization of renal macrophages/dendritic cells to an M2a phenotype is essential for recovery from acute kidney injury

Cytokines IL-4 and IL-13 play important roles in polarization of macrophages/dendritic cells to an M2 phenotype, which is important for recovery from acute kidney injury. Both IL-4 and IL-13 activate JAK3/STAT6 signaling. In mice with diphtheria toxin receptor expression in proximal tubules (selective injury model), a relatively selective JAK3 inhibitor, tofacitinib, led to more severe kidney injury, delayed recovery from acute kidney injury, increased inflammatory M1 phenotype markers and decreased reparative M2 phenotype markers of macrophages/dendritic cells, and development of more severe renal fibrosis after diphtheria toxin administration. Similarly, there was delayed recovery and increased tubulointerstitial fibrosis in these diphtheria toxin-treated mice following tamoxifen-induced deletion of both IL-4 and IL-13, with increased levels of M1 and decreased levels of M2 markers in the macrophages/dendritic cells. Furthermore, deletion of IL-4 and IL-13 led to a decrease of tissue reparative M2a phenotype markers but had no effect on anti-inflammatory M2c phenotype markers. Deletion of IL-4 and IL-13 also inhibited recovery from ischemia-reperfusion injury in association with increased M1 and decreased M2 markers and promoted subsequent tubulointerstitial fibrosis. Thus, IL-4 and IL-13 are required to effectively polarize macrophages/dendritic cells to an M2a phenotype and to promote recovery from acute kidney injury.

CITED1 confers stemness to Wilms tumor and enhances tumorigenic responses when enriched in the nucleus

Wilms tumor (WT) is the most common childhood kidney cancer and retains gene expression profiles reminiscent of the embryonic kidney. We have shown previously that CITED1, a transcriptional regulator that labels the self-renewing, multipotent nephron progenitor population of the developing kidney, is robustly expressed across all major WT disease and patient characteristics. In this malignant context, CITED1 becomes enriched in the nucleus, which deviates from its cytosolic predominance in embryonic nephron progenitors. We designed the current studies to test the functional and mechanistic effects of differential CITED1 subcellular localization on WT behavior. To mimic its subcellular distribution observed in clinical WT specimens, CITED1 was misexpressed ectopically in the human WT cell line, WiT49, as either a wild-type (predominantly cytosolic) or a mutant, but transcriptionally active, protein (two point mutations in its nuclear export signal, CITED1ΔNES; nuclear-enriched). In vitro analyses showed that CITED1ΔNES enhanced WiT49 proliferation and colony formation in soft agar relative to wild-type CITED1 and empty vector controls. The nuclear-enriched CITED1ΔNES cell line showed the greatest tumor volumes after xenotransplantation into immunodeficient mice (n=15 animals per cell line). To elucidate CITED1 gene targets in this model, microarray profiling showed that wildtype CITED1 foremost upregulated LGR5 (stem cell marker), repressed CDH6 (early marker of epithelial commitment of nephron progenitors), and altered expression of specific WNT pathway participants. In summary, forced nuclear enrichment of CITED1 in a human WT cell line appears to enhance tumorigenicity, whereas ectopic cytosolic expression confers stem-like properties and an embryonic phenotype, analogous to the developmental context.

From ureteric bud to the first glomeruli: genes, mediators, kidney alterations

The development of the mammalian kidney is a complex and in part unknown process which requires interactions between pluripotential/stem cells, undifferentiated mesenchymal cells, epithelial and mesenchymal components, eventually leading to the coordinate development of multiple different specialized epithelial, endothelial and stromal cell types within the kidney architectural complexity. We will describe the embryology and molecular nephrogenetic mechanisms, a fascinating traffic of cells and tissues which takes place in five stages: (1) ureteric bud (UB) development; (2) cap mesenchyme formation; (3) mesenchymal-epithelial transition (MET); (4) glomerulogenesis and tubulogenesis; (5) interstitial cell development. In particular, we will analyze the multiple cell types involved in these dramatic events as characters moving between different worlds, from the mesenchymal to the epithelial world and back, and will start to define the multiple factors that propel these cells during their travels throughout the developing kidney. Moreover, according with the hypothesis of renal perinatal programing, we will present the results reached in the fields of immunohistochemistry and molecular biology, by means of which we can explain how a loss or excess of molecular factors governing nephrogenesis may cause the onset of pathologies of different gravity, in some cases leading to a chronic kidney disease at different times from birth.

Postnatal regulation of 15-hydroxyprostaglandin dehydrogenase in the rat kidney

Cyclooxygenase 2 (COX-2) has an established role in postnatal kidney development. 15-Hydroxyprostaglandin dehydrogenase (15-PGDH) is recently identified as an endogenous inhibitor of COX-2, limiting the production of COX-2-derived prostanoids in several pathological conditions. The present study was undertaken to examine the regulation of renal 15-PGDH expression during postnatal kidney development in rats compared with COX-2. qRT-PCR and immunoblotting demonstrated that 15-PGDH mRNA and protein in the kidney were present in neonates, peaked in the second postnatal week, and then declined sharply to very low level in adulthood. Immunostaining demonstrated that at the second postnatal week, renal 15-PGDH protein was predominantly found in the proximal tubules stained positive for Na/H exchanger 3 and brush borders (periodic acid-Schiff), whereas COX-2 protein was restricted to macular densa and adjacent thick ascending limbs. Interestingly, in the fourth postnatal week, 15-PGDH protein was redistributed to thick ascending limbs stained positive for the Na-K-2Cl cotransporter. After 6 wk of age, 15-PGDH protein was found in the granules in subsets of the proximal tubules. Overall, these results support a possibility that 15-PGDH may regulate postnatal kidney development through interaction with COX-2.

11β-Hydroxysteroid Dehydrogenase Type II is a Potential Target for Prevention of Colorectal Tumorigenesis

Colorectal cancer (CRC) is a leading cause of cancer death, yet primary prevention remains the best approach to reducing overall morbidity and mortality. There is a clear molecular link between cyclooxygenase-2 (COX-2)-derived prostaglandin E₂ (PGE₂) production and CRC progression. Although selective COX-2 inhibitors as well as non-steroidal anti-inflammatory drugs (NSAIDs) reduce the number and sizes of colonic adenomas, increased cardiovascular risks of selective COX-2 inhibitors and increased gastrointestinal side-effects of NSAIDs limit their use in chemoprevention of CRC. Glucocorticoids induce apoptosis and are endogenous, potent COX-2 inhibitors. Glucocorticoids have been used for the treatment of hematologic malignancies, but not for solid tumors due to adverse side-effects such as immunosuppression and osteoporosis. In tissues, glucocorticoid actions are down-regulated by t y p e 2 1 1 β-hydroxysteroid dehydrogenase (11βHSD2), and inhibition of 11βHSD2 activity will elevate intracellular active glucocorticoid to levels that effectively suppress COX-2 expression. Both COX-2 and 11βHSD2 increase in Apc^+/min mouse intestinal adenomas and human colonic adenomas and either pharmacologic or genetic 11βHSD2 inhibition leads to decreases in COX-2-mediated PGE₂ production in tumors and prevents adenoma formation, tumor growth, and metastasis. 11βHSD2 inhibition may represent a novel approach for CRC chemoprevention by increasing tumor cell intracellular glucocorticoid activity, which in turn inhibits tumor growth by suppressing the COX-2-derived PGE₂ pathway, as well as other pathways, without potential side-effects relating to chronic application of COX-2 inhibitors, NSAIDs and glucocorticoids.

Cyclooxygenase (COX) Inhibitors and the Newborn Kidney

This review summarizes our current understanding of the role of cyclo-oxygenase inhibitors (COXI) in influencing the structural development as well as the function of the developing kidney. COXI administered either during pregnancy or after birth can influence kidney development including nephronogenesis, and can decrease renal perfusion and ultrafiltration potentially leading to acute kidney injury in the newborn period. To date, which COX isoform (COX-1 or COX-2) plays a more important role in during fetal development and influences kidney function early in life is not known, though evidence points to a predominant role for COX-2. Clinical implications of the use of COXI in pregnancy and in the newborn infant are also evaluated herein, with specific reference to the potential effects of COXI on nephronogenesis as well as newborn kidney function.

Temporal expression of the PGE2 synthetic system in the kidney is associated with the time frame of renal developmental vulnerability to cyclooxygenase-2 inhibition

Pharmacological blockade of cyclooxygenase-2 (COX-2) causes impairment of kidney development. The present study was aimed at determining temporal expression pattern and activity of the PGE(2) synthetic pathway during postnatal nephrogenesis in mice and its association to the time window sensitive to COX-2 inhibition. During the first 10 days after birth, we observed transient induction of mRNA and protein for microsomal PGE synthase (mPGES)-1 between postnatal days 4 (P4) and P8, but not for mPGES-2 or cytosolic PGE synthase (cPGES). PGE(2) synthetic activity using arachidonic acid and PGH(2) as substrates and also urinary excretion of PGE(2) were enhanced during this time frame. In parallel to the PGE(2) system, COX-2 but not COX-1 expression was also transiently induced. Studying glomerulogenesis in EP receptor knockout mice revealed a reduction in glomerular size in EP1(-/-), EP2(-/-), and EP4(-/-) mice, supporting the developmental role of PGE(2). The most vulnerable time window to COX-2 inhibition by SC-236 was found closely related to the temporal expression of COX-2 and mPGES-1. The strongest effects of COX-2 inhibition were achieved following 8 days of drug administration. Similar developmental damage was caused by application of rofecoxib, but not by the COX-1-selective inhibitor SC-560. COX-2 inhibition starting after P10 has had no effect on the size of glomeruli or on the relative number of superficial glomeruli; however, growth of the renal cortex was significantly diminished, indicating the requirement of COX-2 activity after P10. Effects of COX-2 inhibition on renal cell differentiation and on renal fibrosis needed a prolonged time of exposition of at least 10 days. In conclusion, temporal expression of the PGE(2) synthetic system coincides with the most vulnerable age interval for the induction of irreversible renal abnormalities. We assume that mPGES-1 is coregulated with COX-2 for PGE(2) synthesis to orchestrate postnatal kidney development and growth.

Hematopoetic prostaglandin D synthase: an ESR1-dependent oviductal epithelial cell synthase

Oviductal disease is a primary cause of infertility, a problem that largely stems from excessive inflammation of this key reproductive organ. Our poor understanding of the mechanisms regulating oviductal inflammation restricts our ability to diagnose, treat, and/or prevent oviductal disease. Using mice, our objective was to determine the spatial localization, regulatory mechanism, and functional attributes of a hypothesized regulator of oviductal inflammation, the hematopoietic form of prostaglandin D synthase (HPGDS). Immunohistochemistry revealed specific localization of HPGDS to the oviduct's epithelium. In the isthmus, expression of HPGDS was consistent. In the ampulla, expression of HPGDS appeared dependent upon stage of the estrous cycle. HPGDS was expressed in the epithelium of immature and cycling mice but not in the oviducts of estrogen receptor α knockouts. Two receptor subtypes bind PGD₂: PGD₂ receptor and G protein-coupled receptor 44. Expression of mRNA for Ptgdr was higher in the epithelial cells (EPI) than in the stroma (P < 0.05), whereas mRNA for Gpr44 was higher in the stroma than epithelium (P < 0.05). Treatment of human oviductal EPI with HQL-79, an inhibitor of HPGDS, decreased cell viability (P < 0.05). Treatment of mice with HQL-79 increased mRNA for chemokine (C-C motif) ligands 3, 4, and 19; chemokine (C-X-C motif) ligands 11 and 12; IL-13 and IL-17B; and TNF receptor superfamily, member 1b (P < 0.02 for each mRNA). Overall, these results suggest that HPGDS may play a role in the regulation of inflammation and EPI health within the oviduct.

Intrarenal dopamine modulates progressive angiotensin II-mediated renal injury

It is well-recognized that excessive angiotensin II (ANG II) can mediate progressive renal injury. Previous studies by us and others have indicated that dopamine may modulate actions of ANG II in the kidney. The current studies investigated whether altering intrarenal dopamine levels affected ANG II-mediated renal fibrosis. We utilized a model of increased intrarenal dopamine, catechol-O-methyl-transferase knockout (COMT KO) mice, which have increased kidney dopamine levels due to deletion of a major intrarenal dopamine-metabolizing enzyme. In wild-type mice, chronic ANG II infusion increased renal expression of both of the major dopamine-metabolizing enzymes, COMT and monoamine oxidase. After 8 wk of ANG II infusion, there were no significant differences in blood pressure between wild-type and COMT KO mice. Compared with wild-type, COMT KO mice had decreased albuminuria and tubulointerstitial injury. In response to ANG II infusion, there was decreased expression of both glomerular and tubulointerstitial injury markers (fibronectin, connective tissue growth factor, fibroblast-specific protein-1, collagen I, podocyte vascular endothelial growth factor) in COMT KO mice. We recently reported that ANG II-mediated tubulointerstitial fibrosis is mediated by src-dependent epidermal growth factor receptor (EGFR) activation. In aromatic l-amino acid decarboxylase knockout (AADC KO) mice, a model of intrarenal dopamine deficiency due to selective proximal tubule AADC deletion, which inhibits intrarenal dopamine synthesis, ANG II infusion further increased expression of p-src and pTyr845-EGFR. In contrast, their expression was markedly attenuated in COMT KO mice. These results demonstrate a role for intrarenal dopamine to buffer the detrimental effects of ANG II upon the kidney.

COX-2 disruption leads to increased central vasopressin stores and impaired urine concentrating ability in mice

It was hypothesized that cyclooxygenase-2 (COX-2) activity promotes urine concentrating ability through stimulation of vasopressin (AVP) release after water deprivation (WD). COX-2-deficient (COX-2(-/-), C57BL/6) and wild-type (WT) mice were water deprived for 24 h, and water balance, central AVP mRNA and peptide level, AVP plasma concentration, and AVP-regulated renal transport protein abundances were measured. In male COX-2(-/-), basal urine output and water intake were elevated while urine osmolality was decreased compared with WT. Water deprivation resulted in lower urine osmolality, higher plasma osmolality in COX-2(-/-) mice irrespective of gender. Hypothalamic AVP mRNA level increased and was unchanged between COX-2(-/-) and WT after WD. AVP peptide content was higher in COX-2(-/-) compared with WT. At baseline, plasma AVP concentration was elevated in conscious chronically catheterized COX-2(-/-) mice, but after WD plasma AVP was unchanged between COX-2(-/-) and WT mice (43 ± 11 vs. 70 ± 16 pg/ml). Renal V2 receptor abundance was downregulated in COX-2(-/-) mice. Medullary interstitial osmolality increased and did not differ between COX-2(-/-) and WT after WD. Aquaporin-2 (AQP2; cortex-outer medulla), AQP3 (all regions), and UT-A1 (inner medulla) protein abundances were elevated in COX-2(-/-) at baseline and further increased after WD. COX-2(-/-) mice had elevated plasma urea and creatinine and accumulation of small subcapsular glomeruli. In conclusion, hypothalamic COX-2 activity is not necessary for enhanced AVP expression and secretion in response to water deprivation. Renal medullary COX-2 activity negatively regulates AQP2 and -3. The urine concentrating defect in COX-2(-/-) is likely caused by developmental glomerular injury and not dysregulation of AVP or collecting duct aquaporins.

Immunohistochemical Expressions of Main PGE(2) Biosynthesis-related Enzymes and PGE(2) Receptor in Rat Nephrogenesis

Endogenous prostaglandin (PG) E(2) plays important roles in renal homeostasis. Immunoexpressions of PGE(2) biosynthesis-related enzymes, cyclooxygenase (COX)-2 and microsomal PGE(2) synthetase (mPGES)-1 and EP4 (a PGE(2) receptor), were investigated in renal development. Kidney tissues were obtained from fetuses on gestation days 18 and 21 and neonates on days 1 to 18. In fetuses and early neonates, the expressions of COX-2, mPGES-1 and EP4 were observed in developing renal tubules, indicating that COX-2 and its product, PGE(2), play important roles in blastemal cell-derived renal tubular development via EP4. Cyclin D1 expression was seen in both the nucleus and cytoplasm of the developing tubules. These findings differed from the decreased COX-2 expression and exclusive nuclear expression of cyclin D1 seen in abnormal epithelial regeneration of injured renal tubules in cisplatin-treated rats in our previous articles. Collectively, PGE(2), induced by COX-2, regulates renal tubular epithelial formation via EP4.

Eicosanoids and tumor necrosis factor-alpha in the kidney

The thick ascending limb of Henle's loop (TAL) is capable of metabolizing arachidonic acid (AA) by cytochrome P450 (CYP450) and cyclooxygenase (COX) pathways and has been identified as a nephron segment that contributes to salt-sensitive hypertension. Previous studies demonstrated a prominent role for CYP450-dependent metabolism of AA to products that inhibited ion transport pathways in the TAL. However, COX-2 is constitutively expressed along all segments of the TAL and is increased in response to diverse stimuli. The ability of Tamm-Horsfall glycoprotein, a selective marker of cortical TAL (cTAL) and medullary (mTAL), to bind TNF and localize it to this nephron segment prompted studies to determine the capacity of mTAL cells to produce TNF and determine its effects on mTAL function. The colocalization of calcium-sensing receptor (CaR) and COX-2 in the TAL supports the notion that activation of CaR induces TNF-dependent COX-2 expression and PGE₂ synthesis in mTAL cells. Additional studies showed that TNF produced by mTAL cells inhibits ⁸⁶Rb uptake, an in vitro correlate of natriuresis, in an autocrine- and COX-2-dependent manner. The molecular mechanism for these effects likely includes inhibition of Na⁺-K⁺-2Cl⁻ cotransporter (NKCC2) expression and trafficking.

The adverse renal effects of prostaglandin-synthesis inhibition in the fetus and the newborn

OBJECTIVES

To summarize experimental animal data and to provide a limited literature review on the adverse renal effects of nonsteroidal anti-inflammatory drugs (NSAIDs) on the developing fetus and the maturing newborn.

DATA

The experimental data were obtained from anesthetized, ventilated, six- to eight-day-old rabbits that received an intravenous bolus of either acetylsalicylic acid (ASA), ibuprofen (IBU) or indomethacin (INDO). In one set of experiments, ASA was also tested in 12-week-old (young adult) rabbits. Renal function was monitored with inulin and para-aminohippuric acid clearances measuring glomerular filtration rate (GFR) and renal blood flow. The renal vascular resistance was calculated. All three nonspecific cyclo-oxygenase-1 or -2 (COX-1/2) inhibitors caused remarkably similar reversible, oliguric, acute renal failure (ARF). In young adult animals, the side effects were attenuated. The underlying pathophysiology is related to the carefully maintained low GFR of the fetus and the newborn, dependent on a delicate interplay between vasoconstriction (angiotensin II) and vasodilation (prostaglandins [PGs]). When PG-synthesis is inhibited, the vasoconstriction is relatively unopposed, causing ARF.

LITERATURE REVIEW

The renal effects of fetal exposure to NSAIDs are discussed, as are new insights into the role of COX-1/2 for a normal nephrogenesis. COX-nil or COX-inhibited animals have long lasting renal structural injury. Fetuses exposed in utero to significant amounts of NSAIDs have at birth various degrees of renal insufficiency and structural renal defects with a very high mortality.

CONCLUSIONS

All NSAIDs, both specific and nonspecific COX inhibitors, have renal side effects in the immediate post-natal period and should, therefore, be given with the utmost caution. NSAIDs given during pregnancy for the prevention of toxemia, polyhydramnios and premature labour may affect fetal renal function and structure. In animal experiments, IBU was not less nephrotoxic than INDO, as suggested recently by human premature neonates.

Intrarenal dopamine deficiency leads to hypertension and decreased longevity in mice

In addition to its role as an essential neurotransmitter, dopamine serves important physiologic functions in organs such as the kidney. Although the kidney synthesizes dopamine through the actions of aromatic amino acid decarboxylase (AADC) in the proximal tubule, previous studies have not discriminated between the roles of extrarenal and intrarenal dopamine in the overall regulation of renal function. To address this issue, we generated mice with selective deletion of AADC in the kidney proximal tubules (referred to herein as ptAadc-/- mice), which led to selective decreases in kidney and urinary dopamine. The ptAadc-/- mice exhibited increased expression of nephron sodium transporters, decreased natriuresis and diuresis in response to l-dihydroxyphenylalanine, and decreased medullary COX-2 expression and urinary prostaglandin E2 excretion and developed salt-sensitive hypertension. They had increased renin expression and altered renal Ang II receptor (AT) expression, with increased AT1b and decreased AT2 and Mas expression, associated with increased renal injury in response to Ang II. They also exhibited a substantially shorter life span compared with that of wild-type mice. These results demonstrate the importance of the intrarenal dopaminergic system in salt and water homeostasis and blood pressure control. Decreasing intrarenal dopamine subjects the kidney to unbuffered responses to Ang II and results in the development of hypertension and a dramatic decrease in longevity.

Novel allelic variants in the canine cyclooxgenase-2 (Cox-2) promoter are associated with renal dysplasia in dogs

Renal dysplasia (RD) in dogs is a complex disease with a highly variable phenotype and mode of inheritance that does not follow a simple Mendelian pattern. Cox-2 (Cyclooxgenase-2) deficient mice have renal abnormalities and a pathology that has striking similarities to RD in dogs suggesting to us that mutations in the Cox-2 gene could be the cause of RD in dogs. Our data supports this hypothesis. Sequencing of the canine Cox-2 gene was done from clinically affected and normal dogs. Although no changes were detected in the Cox-2 coding region, small insertions and deletions of GC boxes just upstream of the ATG translation start site were found. These sequences are putative SP1 transcription factor binding sites that may represent important cis-acting DNA regulatory elements that govern the expression of Cox-2. A pedigree study of a family of Lhasa apsos revealed an important statistical correlation of these mutant alleles with the disease. We examined an additional 22 clinical cases from various breeds. Regardless of the breed or severity of disease, all of these had one or two copies of the Cox-2 allelic variants. We suggest that the unusual inheritance pattern of RD is due to these alleles, either by changing the pattern of expression of Cox-2 or making Cox-2 levels susceptible to influences of other genes or environmental factors that play an unknown but important role in the development of RD in dogs.

Gαo represses insulin secretion by reducing vesicular docking in pancreatic beta-cells

OBJECTIVE

Pertussis toxin uncoupling-based studies have shown that Gαi and Gαo can inhibit insulin secretion in pancreatic β-cells. Yet it is unclear whether Gαi and Gαo operate through identical mechanisms and how these G-protein-mediated signals inhibit insulin secretion in vivo. Our objective is to examine whether/how Gαo regulates islet development and insulin secretion in β-cells.

RESEARCH DESIGN AND METHODS

Immunoassays were used to analyze the Gαo expression in mouse pancreatic cells. Gαo was specifically inactivated in pancreatic progenitor cells by pancreatic cell-specific gene deletion. Hormone expression and insulin secretion in response to different stimuli were assayed in vivo and in vitro. Electron microscope and total internal reflection fluorescence-based assays were used to evaluate how Gαo regulates insulin vesicle docking and secretion in response to glucose stimulation.

RESULTS

Islet cells differentiate properly in Gαo(-/-) mutant mice. Gαo inactivation significantly enhances insulin secretion both in vivo and in isolation. Gαo nullizygous β-cells contain an increased number of insulin granules docked on the cell plasma membrane, although the total number of vesicles per β-cell remains unchanged.

CONCLUSIONS

Gαo is not required for endocrine islet cell differentiation, but it regulates the number of insulin vesicles docked on the β-cell membrane.

Nonsteroidal Anti-Inflammatory Drugs and the Kidney

Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit the isoenzymes COX-1 and COX-2 of cyclooxygenase (COX). Renal side effects (e.g., kidney function, fluid and urinary electrolyte excretion) vary with the extent of COX-2-COX-1 selectivity and the administered dose of these compounds. While young healthy subjects will rarely experience adverse renal effects with the use of NSAIDs, elderly patients and those with co-morbibity (e.g., congestive heart failure, liver cirrhosis or chronic kidney disease) and drug combinations (e.g., renin-angiotensin blockers, diuretics plus NSAIDs) may develop acute renal failure. This review summarizes our present knowledge how traditional NSAIDs and selective COX-2 inhibitors may affect the kidney under various experimental and clinical conditions, and how these drugs may influence renal inflammation, water transport, sodium and potassium balance and how renal dysfunction or hypertension may result.

Assessing the application of tissue microarray technology to kidney research

Tissue microarray (TMA) is a new high-throughput method that enables simultaneous analysis of the profiles of protein expression in multiple tissue samples. TMA technology has not previously been adapted for physiological and pathophysiological studies of rodent kidneys. We have evaluated the validity and reliability of using TMA to assess protein expression in mouse and rat kidneys. A representative TMA block that we have produced included: (1) mouse and rat kidney cortex, outer medulla, and inner medulla fixed with different fixatives; (2) rat kidneys at different stages of development fixed with different fixatives; (3) mouse and rat kidneys with different physiological or pathophysiological treatments; and (4) built-in controls. As examples of the utility, immunostaining for cyclooxygenase-2, renin, Tamm Horsfall protein, aquaporin-2, connective tissue growth factor, and synaptopodin was carried out with kidney TMA slides. Quantitative analysis of cyclooxygense-2 expression in kidneys confirms that individual cores provide meaningful representations comparable to whole-kidney sections. These studies show that kidney TMA technique is a promising and useful tool for investigating the expression profiles of proteins of interest in rodent kidneys under different physiological and pathophysiological conditions.

Intrarenal dopamine attenuates deoxycorticosterone acetate/high salt-induced blood pressure elevation in part through activation of a medullary cyclooxygenase 2 pathway

Locally produced dopamine in the renal proximal tubule inhibits salt and fluid reabsorption, and a dysfunctional intrarenal dopaminergic system has been reported in essential hypertension and experimental hypertension models. Using catechol-O-methyl-transferase knockout (COMT(-/-)) mice, which have increased renal dopamine because of deletion of the major renal dopamine-metabolizing enzyme, we investigated the effect of intrarenal dopamine on the development of hypertension in the deoxycorticosterone acetate/high-salt (DOCA/HS) model. DOCA/HS led to significant increases in systolic blood pressure in wild-type mice (from 115+/-2 to 153+/-4 mm Hg), which was significantly attenuated in COMT(-/-) mice (from 114+/-2 to 135+/-3 mm Hg). In DOCA/HS COMT(-/-) mice, the D1-like receptor antagonist SCH-23390 increased systolic blood pressure (156+/-2 mm Hg). DOCA/HS COMT(-/-) mice also exhibited more urinary sodium excretion (COMT(-/-) versus wild-type: 3038+/-430 versus 659+/-102 micromol/L per 24 hours; P<0.01). Furthermore, DOCA/HS-induced renal oxidative stress was significantly attenuated in COMT(-/-) mice. COX-2-derived prostaglandins in the renal medulla promote sodium excretion, and dopamine stimulates medullary prostaglandin production. Renal medullary COX-2 expression and urinary prostaglandin E2 excretion were significantly higher in COMT(-/-) than in wild-type mice after DOCA/HS treatment. In DOCA/HS-treated COMT(-/-) mice, the COX-2 inhibitor SC-58236 reduced urinary sodium and prostaglandin E(2) excretion and increased systolic blood pressure (153+/-2 mm Hg). These studies indicate that an activated renal dopaminergic system attenuates the development of hypertension, at least in large part through activating medullary COX-2 expression/activity, and also decreases oxidative stress resulting from DOCA/HS.

Intrarenal dopaminergic system regulates renin expression

Dopamine is a major regulator of proximal tubule salt reabsorption and is a modulator of renin release. Dopamine has been reported to stimulate renin release in vitro through activation of D1-like receptors. However, previous studies investigating dopamine regulation of renin release in vivo have provided contradictory results, indicating stimulation, inhibition, or no effect. We have reported previously that macula densa cyclooxygenase-2 (COX-2) is suppressed by dopamine. Because macula densa COX-2 stimulates renal renin expression, our current studies investigated dopamine regulation of renal renin release and synthesis in vivo. Acute treatment with a D1-like receptor agonist, fenoldopam, significantly inhibited renin release, as did acute inhibition of proximal tubule salt reabsorption with acetazolamide. In catechol-O-methyl transferase knockout (COMT(-/-)) mice, which have increased kidney dopamine levels because of deletion of the major intrarenal dopamine metabolizing enzyme, there was attenuation in response to a low-salt diet of the increases of renal cortical COX-2 and renin expression and renin release. A high-salt diet led to significant decreases in renal renin expression but much less significant decreases in COMT(-/-) mice than wild type mice, resulting in higher renal renin expression in COMT(-/-) mice. In high salt-treated wild-type mice or COX-2 knockout mice on a normal salt diet, fenoldopam stimulated renal renin expression. These results suggest that dopamine predominantly inhibits renal renin expression and release by inhibiting macula densa COX-2, but suppression of renal cortical COX-2 activity reveals a contrasting effect of dopamine to stimulate renal renin expression through activation of D1-like receptors.

Hypertension and sex differences in the age-related renal changes when cyclooxygenase-2 activity is reduced during nephrogenesis

Several studies have proposed that cyclooxygenase-2 (COX2) is involved in the regulation of nephrogenesis and that an impaired nephrogenesis may induce the development of hypertension. This study was designed to test the hypothesis that the decrease of COX2 activity leads to a reduction in nephron number, an increase in arterial pressure, and age-dependent renal alterations that are greater in male than in female rats. Arterial pressure was measured from the first to the 16th month of life in rats treated with vehicle or a COX2 inhibitor during the nephrogenic period. Stereological and histological evaluations and renal function studies were performed at different ages. Arterial pressure increased (14%; P<0.05) and nephron number decreased (17%; P<0.05) to similar levels in male and female COX2-treated rats. However, glomerular filtration rate (31%) and renal plasma flow (25%) decreased (P<0.05) in male but not in female COX2-treated rats. A greater (P<0.05) age-dependent elevation in glomerular hypertrophy was also found in male COX2-treated rats compared with their female littermates. Glomerulosclerosis and tubulointerstitial damage in renal cortex and medulla were also significantly enhanced in male but not in female aged COX2-treated rats. Our results demonstrate that the decrease in COX2 activity during renal development leads to a reduction in nephron number and to an elevation in arterial pressure that are similar in males and females. However, the consequent age-dependent deterioration of the renal structure and renal function is only significantly enhanced in male rats.

Physiological regulation of prostaglandins in the kidney

Cyclooxygenase-derived prostanoids exert complex and diverse functions within the kidney. The biological effect of each prostanoid is controlled at multiple levels, including (a) enzymatic reactions catalyzed sequentially by cyclooxygenase and prostanoid synthase for the synthesis of bioactive prostanoid and (b) the interaction with its receptors that mediate its functions. Cyclooxygenase-derived prostanoids act in an autocrine or a paracrine fashion and can serve as physiological buffers, protecting the kidney from excessive functional changes during physiological stress. Through these actions, prostanoids play important roles in maintaining renal function, body fluid homeostasis, and blood pressure. Renal cortical COX2-derived prostanoids, particularly PGI2 and PGE2, play critical roles in maintaining blood pressure and renal function in volume-contracted states. Renal medullary COX2-derived prostanoids appear to have an antihypertensive effect in individuals challenged with a high-salt diet. Loss of EP2 or IP receptor is associated with salt-sensitive hypertension. COX2 also plays a role in maintaining renal medullary interstitial cell viability in the hypertonic environment of the medulla. Cyclooxygenase-derived prostanoids also are involved in certain pathological processes. The cortical COX2-derived PGI2 participates in the pathogenesis of renal vascular hypertension through stimulating renal renin synthesis and release. COX-derived prostanoids also appear to be involved in the pathogenesis of diabetic nephropathy. COXs, prostanoid synthases, and prostanoid receptors should provide fruitful targets for intervention in the pharmacological treatment of renal disease.

Developmental regulation of calcineurin isoforms in the rodent kidney: association with COX-2

Calcineurin (Cn)-Aα-deficient mice develop abnormalities of postnatal kidney development, similar to that of cyclooxygenase (COX)-2-deficient mice. The present study was undertaken to examine expression and regulation of Cn isoforms in the developing kidney during the postnatal period and further characterize the relationship between Cn and COX-2. The protein expressions of all three Cn isoforms, including Cn-Aα, -Aβ, and -B, as determined by immunoblotting, increased in parallel in the first postnatal week and declined gradually with age. Renal Cn-Aα and -Aβ mRNA expressions were both developmentally regulated in the same fashion as their protein expressions, whereas renal Cn-B1 mRNA was not obviously induced in the first postnatal week. Immunohistochemistry demonstrated colocalization of Cn-Aα, Cn-Aβ, and COX-2 in the same cells of thick ascending limb and macula densa. Administration with cyclosporine A (2.5 mg·kg−1·day−1) during the postnatal period remarkably suppressed renal COX-2 expression as assessed by both immunoblotting and immunohistochemistry. Deletion of Cn-Aα but not Cn-Aβ in mice significantly reduced renal COX-2 expression at the postnatal period. Together, these data suggest that renal Cn isoforms are subject to normal developmental regulation and they may play a role in postnatal kidney development via interaction with COX-2.

Loss of Myt1 function partially compromises endocrine islet cell differentiation and pancreatic physiological function in the mouse

Myelin transcription factor 1 (Myt1) is one of the three vertebrate C2HC-type zinc finger transcription factors that include Myt1 (Nzf1), Myt1L (Png1), and Myt3 (Nzf3, St18). All three paralogs are widely expressed in developing neuronal cells. Yet their function for mammalian development has not been investigated directly. Here we report that only Myt1 is expressed in the embryonic pancreas, in both endocrine progenitors and differentiated islet cells. Myt1(-/-) animals die postnatally, likely due to confounding effects in multiple tissues. The endocrine tissues in the embryonic Myt1(-/-) pancreas contained abnormal islet cells that expressed multiple hormones; although hormone levels were normal. We also created pancreas-specific Myt1 knockout mice. These mutant animals had no obvious physical defects from their wild-type littermates. Male mutant animals had reduced glucose-clearing abilities and abnormal multi-hormone-expressing cells present in their endocrine islets. In addition, they also had reduced Glut2 expression, and attenuated glucose-induced insulin secretion in the adult islets. Surprisingly, the expression of the Myt1 paralogs, Myt1l and Myt3, was induced in the embryonic Myt1(-/-) pancreas. The consequences of Myt1 inactivation in the developing pancreas could be masked by activation of its paralogs, Myt1l and Myt3. These findings suggest Myt1 is involved in proper endocrine differentiation and function.

Inhibition of prostate carcinogenesis in probasin/SV40 T antigen transgenic rats by raloxifene, an antiestrogen with anti-androgen action, but not nimesulide, a selective cyclooxygenase-2 inhibitor

The chemopreventive efficacies of raloxifene and nimesulide, an anti-estrogen but with anti-androgen action and a cyclooxygenase-2 (COX-2) selective inhibitor, respectively, were evaluated in probasin/SV40 T antigen (Tag) transgenic (TG) rats. The treatment groups were placebo, nimesulide (400 p.p.m. in basal diet p.o.), raloxifene (slow-release pellets implanted s.c., 5 mg/kg/day), raloxifene (5 mg/kg/day) plus nimesulide (400 p.p.m.), and raloxifene (10 mg/kg/day) plus nimesulide (400 p.p.m.). Animals were killed at 17 weeks of age, and prostate tissues were harvested and weighed by lobes. Tissues were evaluated by histology, immunohistochemistry, and western blot analyses and blood was collected to measure the testosterone levels. All the animals in the placebo group had tumors in each lobe compared with only 43% each in the dorsolateral (DLP) and anterior prostate (AP) of the animals treated with raloxifene (10 mg/kg/day) plus nimesulide. The total prostate weights and adenocarcinoma portions were significantly reduced in the three raloxifene-treated groups, whereas atrophic glands were increased. There were no significant differences between the nimesulide alone and placebo groups or between the raloxifene (5 mg/kg/day) alone and raloxifene (5 mg/kg/day) plus nimesulide group, suggesting a lack of cancer preventive effects of the COX-2 inhibitor in this animal model. PCNA positive rates in ventral prostate (VP) and DLP, and androgen receptor (AR) levels in VP were significantly reduced in the three raloxifene-treated groups. Furthermore, circulating testosterone was decreased after raloxifene (10 mg/kg/day) plus nimesulide treatment. These results demonstrate that raloxifene, but not nimesulide, inhibits prostate carcinogenesis in SV40 Tag TG rats associated with a decline in circulating testosterone levels and a loss of AR expression, as well as an inhibition of cell proliferation.

Cross talk between the intrarenal dopaminergic and cyclooxygenase-2 systems

In mammalian kidney, dopamine produced in the proximal tubule (PT) acts as an autocrine/paracrine natriuretic hormone that inhibits salt and fluid reabsorption in the PT. In high-salt-treated animals, PT dopamine activity increases and inhibits reabsorption, leading to increased salt and fluid delivery to the macula densa (MD) and subsequent natriuresis and diuresis. Regulated cyclooxygenase-2 (COX-2) in the MD represents another intrinsic system mediating renal salt and water homeostasis. Renal cortical COX-2 is inversely related to salt intake, and decreased extracellular NaCl stimulates COX-2 expression in cultured MD/cortical thick ascending limb cells. The current study investigated interactions between renal dopamine and cortical COX-2 systems. In rats fed a control diet, the dopamine precursor l-dihydroxyphenylalanine (l-DOPA) or the DA1 receptor agonist SKF-81297 suppressed cortical COX-2 expression. High salt suppressed cortical COX-2 expression, which was attenuated by inhibition of dopamine production with benserazide or the DA1 receptor antagonist, SCH-23390. In contrast, l-DOPA or the dopamine-metabolizing enzyme inhibitor entacapone suppressed low-salt-induced cortical COX-2 expression. Inhibition of PT reabsorption with the carbonic anhydrase inhibitor acetazolamide suppressed cortical COX-2 expression. In contrast, treatment with distally acting diuretics led to elevation of cortical COX-2. These results indicate that dopamine modulates renal cortical COX-2 expression by modifying PT reabsorption.

Bradykinin regulates cyclooxygenase-2 in rat renal thick ascending limb cells

Cyclooxygenase-2 (COX-2) is constitutively expressed in a subset of thick ascending limb cells in the cortex and medulla and increases when the renin-angiotensin and kallikrein-kinin systems are activated. Although the contribution of angiotensin II to the regulation of COX-2 is known, the effects of bradykinin on COX-2 expression have not been determined in this nephron segment. We evaluated expression of B2 bradykinin receptors in thick ascending limb cells containing COX-2 and the effect of bradykinin on COX-2 expression in primary cultured medullary thick ascending cells. The presence of B2 receptors was studied in renal sections by immunohistochemistry with antibodies against B2, COX-2, and Tamm-Horsfall glycoprotein. B2 receptors were detected on the apical and basolateral portion of the thick ascending cells. These cells also contained COX-2, suggesting that COX-2 expression may be regulated via B2 receptor. Incubation of cultured medullary thick ascending cells with bradykinin (10(-7) to 10(-5) mol/L) induced a significant increase on COX-2 protein expression. Maximal expression of COX-2 was observed 4 hours after exposure to bradykinin (10(-7) mol/L), effect abolished by a B2 receptor antagonist (HOE-140; 10(-6) mol/L). Prostaglandin E2 production increased when these cells were challenged with bradykinin for 4 hours, indicating that COX-2 was enzymatically active. We have demonstrated (1) the presence of B2 receptors in thick ascending limb cells expressing COX-2 and (2) the stimulatory effect of bradykinin on COX-2 protein expression, via B2 receptors, in cultured medullary thick ascending cells. We suggest that bradykinin can affect ion transport in the thick ascending limb via a COX-2-mediated mechanism.

Upregulation of macula densa cyclooxygenase-2 expression is not dependent on glomerular filtration

Although the regulation of cyclooxygenase-2 (COX-2) expression in the kidney cortex has been extensively characterized, the physiological control mechanisms of COX-2 expression at the level of the kidney and at the level of the tubular cells are not well understood. Based on the current hypothesis that tubular salt transport might be a crucial regulator of COX-2 expression, this study aimed to determine the impact of salt delivery to the tubules (glomerular filtration) for the regulation of COX-2 in the kidney cortex in vivo. To this end, glomerular filtration of the right kidney was abrogated by the ligation of the right ureter of male Sprague-Dawley rats. After 1 wk of ligation, the animals were treated with subcutaneous infusions of furosemide (12 mg·kg−1·day−1) or with a low-salt or a high-salt diet (0.02% wt/wt; 8% wt/wt), and COX-2 as well as renin mRNA expression were determined in the ligated and the nonligated contralateral kidney. During ureteral ligation, hydronephrosis developed with a reduction of medullary mass, while the cortex was preserved. Expressions of the Na-K-2Cl cotransporter isoforms A and B were both reduced in the hydronephrotic cortex to 70 and 35% of the corresponding contralateral intact kidney. Despite the abrogation of glomerular filtration, detected by inulin clearance measurements, renocortical COX-2 mRNA abundance was stimulated by furosemide treatment (3.2-fold) or low-salt diet (2.9-fold) to similar degrees compared with the intact contralateral kidney (2.7-fold for both treatments), whereas a high-salt diet did not significantly suppress COX-2 mRNA in the macula densa region of either kidney. Renin mRNA expression was regulated strictly in parallel in both kidneys, a low-salt diet or furosemide treatment stimulating and a high-salt diet suppressing it. We conclude from these findings that salt delivery to the tubules is not an essential requirement for the upregulation of COX-2 by salt deficiency or by loop diuretics in the rat kidney cortex nor is it for chronic stimulation of renin mRNA expression.

Neonatal RAS inhibition changes the phenotype of the developing thick ascending limb of Henle

Pharmacological interruption of angiotensin II type 1 (AT(1)) receptor signaling during nephrogenesis in rats perturbs renal tubular development. Perturbed tubulogenesis may contribute to long-term impairment of urinary concentrating ability, which is the main functional irreversible defect. The aim of this study was to further characterize tubular developmental deficits in neonatal rats, focusing on the thick ascending limb of Henle (TALH), known to undergo profound developmental changes and to be involved in urine-concentrating mechanisms. We have carried out immunohistochemistry and Western immunoblotting using antibodies directed against the major histocompatibility complex class II (MHC II) molecule and different TALH-specific markers, namely, cyclooxygenase-2 (COX-2), Tamm-Horsfall glycoprotein (THP), and the bumetanide-sensitive Na(+)-K(+)-2Cl(-) cotransporter (BSC-1/NKCC2). Immunohistochemistry demonstrated expression of MHC II, COX-2, THP, and BSC-1/NKCC2 proteins in normally developing TALH cells. The AT(1)-receptor antagonist losartan abolished MHC II expression exclusively in the developing TALH cells. Increased expression of COX-2 and THP was observed in the TALH cells of losartan-treated rats. Western immunoblotting confirmed increases in cortical and medullary COX-2 and THP abundance and revealed a decrease in cortical BSC-1/NKCC2 abundance in response to losartan treatment. We conclude that neonatal losartan treatment causes significant changes in the phenotype of the developing TALH in the rat.

Low endogenous glucocorticoid allows induction of kidney cortical cyclooxygenase-2 during postnatal rat development

In postnatal weeks 2-4, cyclooxygenase-2 (COX-2) is induced in the rat kidney cortex where it is critically involved in final stages of kidney development. We examined whether changes in circulating gluco- or mineralocorticosteroids or in their renal receptors regulate postnatal COX-2 induction. Plasma corticosterone concentration peaked at birth, decreased to low levels at days 3-13, and increased to adult levels from day 22. Aldosterone peaked at birth and then stabilized at adult levels. Gluco- and mineralocorticoid receptor (GR and MR) mRNAs were expressed stably in kidney before, during, and after COX-2 induction. 11 beta-hydroxysteroid dehydrogenase 2 was induced shortly after birth and was widely distributed in the whole collecting duct system in the suckling period and then returned to an adult pattern. Supplementation with corticosterone (20 mg.kg-1.day-1) or GR-specific dexamethasone (1 mg.kg-1.day-1) during low endogenous corticosterone suppressed renal COX-2 mRNA and protein and led to a restricted distribution of COX-2 immunolabeling. The ability of glucocorticoids to affect COX-2 was reflected in colocalization of GR-alpha and COX-2 immunoreactivity and mRNAs in thick ascending limb of Henle's loop. The MR antagonist potassium canrenoate (20 mg.kg-1.day-1) enhanced COX-2 expression from days 5 to 10, but low MR-specific concentrations of DOCA (1 mg.kg-1.day-1) had no effect on COX-2. Renomedullary interstitial cells expressed GR-alpha and COX-2. Dexamethasone suppressed COX-2 in these cells. Thus low plasma concentrations of corticosterone allowed for cortical and medullary COX-2 induction during postnatal kidney development. Increased circulating glucocorticoid in the postnatal period may damage late renal development through inhibition of COX-2.

Regulation of renal cortical cyclooxygenase-2 in young rats

Cyclooxygenase-2 (COX-2) is involved in kidney morphogenesis and is transiently elevated in the immature kidney. In adult rats, renal cortical COX-2 expression is tonically suppressed by mineralocorticoids (MC) and glucocorticoids (GC) and induced by chronic salt restriction. Young rats have low levels of GC and are in a state of relative volume depletion. The present study was designed to investigate the mechanisms underlying elevated cortical COX-2 expression in the immature kidney. Supplementation of GC or MC suppressed cortical COX-2 expression in suckling rats. GC suppression was significantly, but not completely, prevented by either an MC receptor antagonist or a GC receptor antagonist. MC suppression was completely prevented by a mineralocorticoid receptor antagonist. Salt supplementation suppressed cortical COX-2 expression in a dose- and time-dependent pattern in the suckling rats. Cortical COX-2 expression in the weanling rats was upregulated by a low-salt diet and downregulated by a high-salt diet. These results suggest that relative volume depletion and reduced GC levels are involved in elevated cortical COX-2 expression in the immature rodent kidney.

Key enzymes for renal prostaglandin synthesis: site-specific expression in rodent kidney (rat, mouse)

Prostanoids derived from endogenous cylooxygenase (COX)-mediated arachidonic acid metabolism play important roles in the maintenance of renal blood flow and salt and water homeostasis. The relative importance of COX-1 and COX-2 isoforms is under active investigation. We have performed a comprehensive histochemical analysis by comparing rat and mouse kidneys for cellular and subcellular localization of COX-1 and -2 and microsomal-type PGE synthase (PGES), the rate-limiting biosynthetic enzyme in PGE2 synthesis. A choice of different sera was compared, and the results were confirmed by antigen-retrieval techniques, in situ hybridization, RT-PCR, and the use of COX knockout mice. In the glomerulus, significant COX-1 expression was detected in a subset of mesangial cells. Along the renal tubule, the known COX-2 expression in cTAL and macula densa was paralleled by PGES staining. In the terminal distal convoluted tubule, connecting tubule, and cortical and medullary collecting ducts, a significant COX-1 signal was colocalized with PGES; COX-2 was not found in these sites. Intercalated cells were generally negative. Cortical fibroblasts were COX-1 and PGES positive in mice, whereas in rats only PGES could be reliably detected. Lipid-laden interstitial cells of the inner medulla were COX-1, -2, and PGES positive. Vascular smooth muscle cells were not stained. The present data support prominent functions of renal prostanoids, predominantly PGE2, by defining expression sites of the key enzymes for their biosynthesis in the rat and mouse. Results define the renal cell types involved in prostaglandin autacoid functions within spatially restricted sites such as the juxtaglomerular apparatus, mesangium, distal convolutions and collecting duct, and in compartments of the renal interstitium.

Cyclooxygenase-2 contributes to elevated renin in the early postnatal period in rats

We asked whether cyclooxygenase (COX) activity controls the renin-angiotensin system in the postnatal period. During kidney development, renin peaked at postnatal days 0-1 at the mRNA, tissue protein [renal renin concentration (RRC)], and plasma renin concentration (PRC) levels and was widely expressed along preglomerular vessels. PRC and renin mRNA expression was elevated until weaning in the 4th postnatal week compared with adult rats. Renocortical COX-2 was restricted to Tamm-Horsfall protein-positive cells in the thick ascending limb of Henle's loop, and cortical COX-2 mRNA and protein expression were elevated along with PRC in the 2nd and 3rd postnatal weeks. In contrast, cortical COX-1 expression was constant, but medullary COX-1 expression increased eightfold from the 1st to 4th postnatal week. A COX-2-selective blocker, parecoxib, and a nonselective blocker, indomethacin, given in a period with COX-2 induction from postnatal day 6 to day 12, markedly decreased PRC, but not renin mRNA or RRC. Inhibition of angiotensin AT(1) receptors by candesartan from postnatal day 1 to day 5 increased COX-2 mRNA (2.5-fold), protein, and distribution, renin mRNA (7-fold) and PRC (20- to 70-fold), but had no influence on COX-1 mRNA. Thus, due to very low levels of expression, COX-2 is unlikely to be responsible for the birth peak of renin, but COX-2 activity supports renin secretion later in the suckling period. ANG II negatively feeds back on renocortical COX-2 expression in the 1st postnatal days with high activity of the renin system. We suggest that suckling in the rat is correlated to an enhanced, COX-2-mediated, secretory activity of renin-producing juxtaglomerular cells.

Inhibition of cyclooxygenase-2: effects on renin secretion and expression in fetal lambs

The importance of prostaglandins in the regulation of the renin-angiotensin system during development is not known. These experiments were conducted to examine the effects of prostaglandin synthesis inhibitors on basal and isoproterenol-induced plasma renin concentration and renin gene expression in the late-gestation fetal lamb. Eighteen lamb fetuses ranging in gestational age from 129 to 138 days underwent surgical insertion of femoral arterial and venous catheters under general endotracheal anesthesia. After a period of recovery, animals underwent an infusion of isoproterenol after administration of a saline bolus (control experiments); 24-48 h later a second study was performed after administration of NS-398, a cyclooxygenase (COX)-2 inhibitor, or saline for a second control study. Administration of COX-2 inhibitor significantly reduced baseline plasma renin levels and attenuated responses in fetal renin secretion to isoproterenol infusions. Renal cortical cells from animals receiving COX-2 inhibitor had significantly lower levels of renin mRNA compared with animals receiving only saline. Renal cortical cells in culture from animals receiving only saline exhibited increased levels of renin mRNA when treated with isoproterenol, forskolin, or IBMX. Only forskolin increased renin mRNA levels in renal cortical cells in culture from animals receiving COX-2 inhibitor. We conclude that prostaglandins play a stimulatory role in the regulation of the renin-angiotensin system and are necessary for beta-adrenergic stimulation of renin secretion and gene expression in the late-gestation fetal lamb.

Alterations in renal cytosolic phospholipase A2 and cyclooxygenases in polycystic kidney disease

Cytosolic phospholipase A2 (cPLA2), cyclooxygenase-1 (COX-1), and cyclooxygenase-2 (COX-2) regulate the formation of physiologically active prostaglandins, the production of which is known to be elevated in several renal disorders. We studied the relevance of these enzymes in polycystic kidney disease (PKD) by using two models of the disease: a model in which decline in renal function begins in adulthood (CD1-pcy/pcy mouse) and one in which it occurs early, during growth (Han:SPRD-cy rat). Immunoblotting analyses of cytosolic and particulate kidney fractions revealed that cPLA2 levels are significantly higher (by 34-131%) in the latter stages of the disease in both models. Renal COX enzymes were found only in the particulate fractions, with COX-1 87% higher in 6-month-old CD1-pcy/pcy mice compared with normal controls, and 110% higher in male 70-day-old Han:SPRD-cy rats with cystic kidneys compared with controls. Renal COX-2 was detected only in the rats and was 58% lower in diseased kidneys of 70-day-old male Han:SPRD-cy rats, indicating that cPLA2 is coupled to COX-1 in the kidney. The altered levels of these eicosanoid-regulating enzymes has implications for the use of NSAIDS and specific COX inhibitors in individuals with this disorder.

Mineralocorticoid regulation of cyclooxygenase-2 expression in rat renal medulla

The renal inner medulla and its distal one-third, the papilla, are major sites of prostanoid synthesis involved in water and electrolyte homeostasis. These sites contain variable levels of cyclooxygenase (COX)-2, a key prostaglandin synthase enzyme that is sensitive to adrenal steroids. Immunoreactive renal medullary COX-2, restricted to interstitial cells in control adult rats, shows a gradient of intense staining at the tip of the papilla that gradually diminishes to undetectable levels in the proximal inner medulla. We used adrenalectomy (ADX) and steroid replacement to investigate the effects of steroids on papillary COX-2. Immunoblots demonstrate that papillary COX-2 was reduced by one-half after 2 wk ADX; glucocorticoid replacement ameliorated the decline but not to control levels. Mineralocorticoid (deoxycorticosterone acetate; DOCA) replacement stimulated papillary COX-2 more than fivefold over control; both the intensity of immunostaining and the numbers of COX-2-positive cells in the inner medulla increased. Similar stimulation of papillary COX-2 resulted from DOCA treatment of normal control rats, but the response was blunted in rats fed a low-salt diet and absent in Brattleboro rats. DOCA treatment of mouse renal medullary interstitial cells in culture had no effect, but increased tonicity of the culture medium with NaCl caused strong upregulation of COX-2. Urea, a permeant molecule, had no effect. Together, these results suggest that mineralocorticoids lead to upregulation of COX-2 in rat renal medulla by indirect pathways, probably involving induced electrolyte hypertonicity in the interstitial fluid.

Renal cyclooxygenase-2: evidence for recruitment of thick ascending limb of henle cells in microdissected nephron segments

Prostaglandins participate in the regulation of sodium and water renal excretion. They are synthesized by cyclooxygenases (COX): the constitutive isoform and the enzyme regulated by physiological stimuli (COX-2). Our previous immunohistochemical studies have demonstrated the presence of COX-2 in a subset of thick ascending limb (TAL) of Henle cells and its induction during the postnatal period and after adrenalectomy. Previous results suggested that this induction phenomenon proceeds by recruitment of TAL cells from the cortex to the outer medulla. The present work aimed to specifically address these preliminary observations by using immunohistochemical techniques in single microdissected nephron segments. Normal adult rats, adrenalectomized rats, adrenalectomized rats on dexamethasone and 5, 10, and 15 days postnatal age were used (Sprague-Dawley rats, n= 5 each group). Glomeruli and different segments of nephron were microdissected from collagenase-treated kidney tissue. Tubules were immunostained with specific antibodies against COX-2. We confirmed that COX-2 was localized exclusively in TAL segments; it was induced after adrenalectomy and during postnatal age, peaking at 15 days after birth. We provided morphological evidence that the induction of COX-2 along TAL proceeded in a defined pattern by recruitment of cells from the cortical portion close to the glomeruli toward the outer medulla. No COX-2 was observed in the post-macula densa portion of the segments. Our results provide the anatomical basis for the contribution of COX-2 in physiological mechanisms such as renin secretion, tubuloglomerular feedback, and the interaction with neuronal NO synthase at the juxtaglomerular apparatus.

Physiological regulation of cyclooxygenase-2 in the kidney

In adult mammalian kidney, cyclooxygenase-2 (COX-2) expression is found in a restricted subpopulation of cells. The two sites of renal COX-2 localization detected in all species to date are the macula densa (MD) and associated cortical thick ascending limb (cTALH) and medullary interstitial cells (MICs). Physiological regulation of COX-2 in these cellular compartments suggests functional roles for eicosanoid products of the enzyme. COX-2 expression increases in high-renin states (salt restriction, angiotensin-converting enzyme inhibition, renovascular hypertension), and selective COX-2 inhibitors significantly decrease plasma renin levels, renal renin activity, and mRNA expression. There is evidence for negative regulation of MD/cTALH COX-2 by angiotensin II and by glucocorticoids and mineralocorticoids. Conversely, nitric oxide generated by neuronal nitric oxide synthase is a positive modulator of COX-2 expression. Decreased extracellular chloride increases COX-2 expression in cultured cTALH, an effect mediated by increased p38 mitogen-activated protein kinase activity, and, in vivo, a sodium-deficient diet increases expression of activated p38 in MD/cTALH. In contrast to COX-2 in MD/cTALH, COX-2 expression increases in MICs in response to a high-salt diet as well as water deprivation. Studies in cultured MICs have confirmed that expression is increased in response to hypertonicity and is mediated, at least in part, by nuclear factor-kappaB activation. COX-2 inhibition leads to apoptosis of MICs in response to hypertonicity in vitro and after water deprivation in vivo. In addition, COX-2 metabolites appear to be important mediators of medullary blood flow and renal salt handling. Therefore, there is increasing evidence that COX-2 is an important physiological mediator of kidney function.

Genetic deletion of COX-2 prevents increased renin expression in response to ACE inhibition

Cyclooxygenase-2 (COX-2) is expressed in macula densa (MD) and surrounding cortical thick ascending limb of the loop of Henle (cTALH) and is involved in regulation of renin production. We and others have previously found that selective COX-2 inhibitors can inhibit renal renin production (Cheng HF, Wang JL, Zhang MZ, Miyazaki Y, Ichikawa I, McKanna JA, and Harris RC. J Clin Invest 103: 953-961, 1999; Harding P, Sigmon DH, Alfie ME, Huang PL, Fishman MC, Beierwaltes WH, and Carretero OA. Hypertension 29: 297-302, 1997; Traynor TR, Smart A, Briggs JP, and Schnermann J. Am J Physiol Renal Physiol 277: F706-F710, 1999; Wang JL, Cheng HF, and Harris RC. Hypertension 34: 96-101, 1999). In the present studies, we utilized mice with genetic deletions of the COX-2 gene in order to investigate further the potential role of COX-2 in mediation of the renin-angiotensin system (RAS). Age-matched wild-type (+/+), heterozygotes (+/-), and homozygous null mice (-/-) were administered the angiotensin-converting enzyme inhibitor (ACEI), captopril, for 7 days. ACEI failed to significantly increase plasma renin activity, renal renin mRNA expression, and renal renin activity in (-/-) mice. ACEI increased the number of cells expressing immunoreactive renin in the (+/+) mice both by inducing more juxtaglomerular cells to express immunoreactive renin and by recruiting additional renin-expressing cells in the more proximal afferent arteriole. In contrast, there was minimal recruitment of renin-expressing cells in the more proximal afferent arteriole of the -/- mice. In summary, these results indicate that ACEI-mediated increases in renal renin production were defective in COX-2 knockout (K/O) mice and provide further indication that MD COX-2 is an important mediator of the renin-angiotensin system.