TNF inhibits AQP2 expression via a miR137-dependent pathway

As miR-137 is a regulator of aquaporin (AQP)2 expression and tumor necrosis factor (TNF) inhibits the expression of several extrarenal AQPs, we tested the hypothesis that TNF inhibits AQP2 in the kidney via a miR-137-dependent mechanism. AQP2 mRNA and protein expression decreased ∼70% and 53%, respectively, in primary renal inner medullary collecting duct (IMCD) cells transfected with a miRNA mimic of mmu-miR-137, suggesting that miR-137 directly targets AQP2 mRNA in these cells. Exposure of IMCD cells for 2 h to 400 mosmol/kgH2O medium increased mmu-miR-137 mRNA expression about twofold, conditions that also increased TNF production approximately fourfold. To determine if the increase in mmu-miR-137 mRNA expression was related to the concomitant increase in TNF, IMCD cells were transfected with a lentivirus construct to silence TNF. This construct decreased mmu-miR-137 mRNA expression by ∼63%, suggesting that TNF upregulates the expression of miR-137. Levels of miR-137 also increased approximately twofold in IMCD tubules isolated from male mice given 1% NaCl in the drinking water for 3 days. Intrarenal lentivirus silencing of TNF increased AQP2 mRNA levels and protein expression concomitant with a decrease in miR-137 levels in tubules isolated from mice given NaCl. The changes in AQP2 expression levels affected the diluting ability of the kidney, which was assessed by measuring urine osmolality and urine volume, as the decrease in these parameters after renal silencing of TNF was prevented on intrarenal administration of miR-137. The study reveals a novel TNF function via a miR-137-dependent mechanism that regulates AQP2 expression and function.NEW & NOTEWORTHY An emerging intratubular tumor necrosis factor system, functioning during normotensive noninflammatory conditions, acts as a breaking mechanism that attenuates both the increases in Na+-K+-2Cl- cotransporter and aquaporin-2 induced by arginine vasopressin, thereby contributing to the regulation of electrolyte balance and blood pressure. A greater appreciation for the role of cytokines as mediators of immunophysiological responses may help reveal the relationship between the immune system and other physiological systems.

The EP3 receptor regulates water excretion in response to high salt intake

The mechanisms by which prostanoids contribute to the maintenance of whole body water homeostasis are complex and not fully understood. The present study demonstrates that an EP3-dependent feedback mechanism contributes to the regulation of water homeostasis under high-salt conditions. Rats on a normal diet and tap water were placed in metabolic cages and given either sulprostone (20 μg·kg^-1·day^-1) or vehicle for 3 days to activate EP3 receptors in the thick ascending limb (TAL). Treatment was continued for another 3 days in rats given either 1% NaCl in the drinking water or tap water. Sulprostone decreased expression of cyclooxygenase 2 (COX-2) expression by ∼75% in TAL tubules from rats given 1% NaCl concomitant with a ∼60% inhibition of COX-2-dependent PGE₂ levels in the kidney. Urine volume increased after ingestion of 1% NaCl but was reduced ∼40% by sulprostone. In contrast, the highly selective EP3 receptor antagonist L-798106 (100 μg·kg^-1·day^-1), which increased COX-2 expression and renal PGE₂ production, increased urine volume in rats given 1% NaCl. Sulprostone increased expression of aquaporin-2 (AQP2) in the inner medullary collecting duct plasma membrane in association with an increase in phosphorylation at Ser269 and decrease in Ser261 phosphorylation; antagonism of EP3 with L-798106 reduced AQP2 expression. Thus, although acute activation of EP3 by PGE₂ in the TAL and collecting duct inhibits the Na-K-2Cl cotransporter and AQP2 activity, respectively, chronic activation of EP3 in vivo limits the extent of COX-2-derived PGE₂ synthesis, thereby mitigating the inhibitory effects of PGE₂ on these transporters and decreasing urine volume.

Prostaglandin I2 does not contribute to the hypotensive effect of the superoxide dismutase mimetic Tempo in rats with aortic coarctation-induced hypertension

This study was designed to investigate the contribution of prostaglandins to the vasodepressor effect of the superoxide dismutase mimetic Tempo in rats made hypertensive by ligation of the abdominal aorta at a point between the left and right renal arteries. Rings of thoracic aorta taken from rats with aortic coarctation released more 6-keto-PGF1alpha (a non-enzymatic product of PGI2 degradation) in the presence than in the absence of Tempo (1 mmol/L; 35.3 +/- 10.1 versus 13.6 +/- 2.6 pg/mg tissue). However, Tempo administered intravenously (2 mg/kg bolus injection plus infusion at 3 mg/kg/h) to rats with aortic coarctation did not increase significantly the concentration of 6-keto-PGF1alpha in vena cava blood. Treatment with Tempo did not affect the arterial pressure of un-operated normotensive rats but promptly decreased the arterial pressure of rats with aortic coarctation-induced hypertension (from 178 +/- 2 to 125 +/- 6 mmHg). The vasodepressor effect of Tempo in hypertensive animals was not affected by pretreatment with indomethacin to inhibit prostaglandin synthesis. These data argue against the hypothesis that PGI2 contributes to the acute hypotensive effect of Tempo in rats with aortic coarctation.

Lipoxygenase-dependent mechanisms in hypertension

This study was designed to examine the contribution of lipoxygenase products to mechanisms of vascular contraction and elevated blood pressure in rats with aortic coarctation-induced hypertension. In cytosolic fractions of aortae taken from hypertensive rats, 12-lipoxygenase protein was increased as compared to normotensive controls. Aortic rings from hypertensive, but not from normotensive rats, exhibited a basal tone which was reduced 74+/-12 and 71+/-22%, respectively, by the lipoxygenase inhibitors cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate (CDC, 10(-5) mol/L) and 5,8,11-eicosatriynoic acid (ETI, 10(-5) mol/L). CDC (8 mg/kg s.c.) did not affect the blood pressure of normotensive rats but decreased that of hypertensive rats from 182+/-6 to 151+/-10 mm Hg. The blood pressure lowering effect of CDC was blunted in hypertensive rats pretreated with indomethacin or antibodies against 5,6-dihydro-prostaglandin I2. These data suggest contribution of lipoxygenase-derived products to mechanisms underlying aortic smooth muscle basal tone and elevated blood pressure in rats with aortic coarctation-induced hypertension. The vasodepressor effect of CDC depends on a mechanism involving vasodilatory prostaglandins.

A return to the past: a student perspective on medical school pharmacology

In 1989, the second-year medical school pharmacology course at New York Medical College was revised to help improve student and faculty morale, improve scores on class exams and the U.S. Medical Licensing Examination (USMLE), and encourage more active student participation in the course. Rather than incorporating new and innovative teaching techniques, the course adapted a more classical presentation of material. Traditional blackboard lectures replaced lectures aided by the use of slides, overheads, and extensive handouts. Transcripts and the tape recording of lectures were prohibited. Higher standards for students were set with the implementation of a passing grade, initially set at 65% and increased to 66%. Review sessions with senior graduate students were incorporated, and the use of live animal demonstrations was continued. Despite the return toward a more traditional classroom, students' satisfaction with the course continues to be high, with an overall 80% satisfaction rating. Attendance at lectures is quite high (> or = 80%). In addition, student scores on the USMLE continue to improve, and the number of students failing pharmacology continues to decrease. Overall, these trends indicate that the changes implemented in the pharmacology course at New York Medical College in 1989 successfully improved student participation in class and performance in the course and on the USMLE.

Involvement of nitric oxide and potassium channels in the reduction of basal tone produced by blockade of thromboxane A2/prostaglandin H2 receptors in aortic rings of hypertensive rats

This study was designed to investigate involvement of potassium channels in the action of nitric oxide facilitating reduction of basal tone by thromboxane A2/prostaglandin H2 receptor blockade with ifetroban in rings of thoracic aorta taken from rats with aortic coarctation-induced hypertension. Ifetroban-induced reduction of basal tone in aortic rings without drug pretreatment was attenuated (P<0.05) in rings pretreated with the nitric oxide synthesis inhibitor N(omega-nitro-L-arginine methyl ester (L-NAME; 3 x 10(-4) mol/L; 0.55+/-0.09 g versus 0.23+/-0.07 g). The vasorelaxing effect of ifetroban also was decreased (P<0.05) in preparations pretreated with a potassium channel blocker, either tetraethylammonium (TEA; 10(-2) mol/L) or 4-aminopyridine (4-AP; 3 x 10(-3) mol/L). Ifetroban-induced reduction of basal tone was not attenuated in preparations pretreated first with L-NAME and then with sodium nitroprusside (SNP; 6+/-1 nmol/L) to compensate for the loss of endogenous nitric oxide. However, the facilitatory effect of SNP on ifetroban-induced relaxation of aortic rings pretreated with L-NAME alone was not demonstrable in rings pretreated with L-NAME plus TEA or 4-AP. These observations suggest that a mechanism involving nitric oxide and potassium channels facilitates the reduction in basal tone produced by ifetroban in aortic rings of rats with aortic coarctation-induced hypertension.

Effect of tumor necrosis factor-alpha and interferon-gamma on the growth of human prostate cancer cell lines

Human recombinant tumor necrosis factor-alpha (rTNF-alpha, 10(-12)-10(-8) M) inhibited the proliferation of androgen-dependent LNCaP cells by 32-56%. In contrast, proliferation of androgen-independent PC-3 and JCA-1 cells was only slightly inhibited, or not inhibited at all, respectively. Human recombinant interferon-gamma (rIFN-gamma, 500 U/ml) decreased proliferation of PC-3 and JCA-1 cells by 35% and 53%, respectively, but had no effect on LNCaP cells. Interestingly, the combination of rIFN-gamma and TNF-alpha had greater antiproliferative effects on JCA-1 cells than treatment with either cytokine alone. However, the antiproliferative effects of this combination were similar to those observed for PC-3 or LNCaP cells treated with rIFN-gamma or TNF-alpha alone, respectively. These data suggest that some forms of androgen-independent prostate cancer may benefit from a combination therapy of IFN-gamma and TNF-alpha, while the use of IFN-gamma alone may be more efficacious in others.