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Altered cellular metabolism in kidney proximal tubule (PT) cells plays a critical role in acute kidney injury (AKI). The transcription factor Krüppel-like factor 6 (KLF6) is rapidly and robustly induced early in the PT after AKI. We found that PT-specific Klf6 knockdown ( Klf6 ) is protective against AKI and kidney fibrosis in mice. Combined RNA and chromatin immunoprecipitation sequencing analysis demonstrated that expression of genes encoding branched-chain amino acid (BCAA) catabolic enzymes was preserved in PTKD ) is protective against AKI and kidney fibrosis in mice. Combined RNA and chromatin immunoprecipitation sequencing analysis demonstrated that expression of genes encoding branched-chain amino acid (BCAA) catabolic enzymes was preserved in Klf6 overexpression suppressed expression of BCAA genes and exacerbated kidney injury and fibrosis in mice. In vitro PTKD mice, with KLF6 occupying the promoter region of these genes. Conversely, inducible KLF6 overexpression suppressed expression of BCAA genes and exacerbated kidney injury and fibrosis in mice. In vitro , , which encodes one subunit of the rate-limiting enzyme in BCAA catabolism, resulted in reduced ATP production, while treatment with BCAA catabolism enhancer BT2 increased metabolism. Analysis of kidney function, KLF6 , and BCAA gene expression in human chronic kidney disease patients showed significant inverse correlations between BCKDHB and both kidney function and BCAA expression. Thus, targeting KLF6-mediated suppression of BCAA catabolism may serve as a key therapeutic target in AKI and kidney fibrosis.KLF6 , and BCAA gene expression in human chronic kidney disease patients showed significant inverse correlations between KLF6 and both kidney function and BCAA expression. Thus, targeting KLF6-mediated suppression of BCAA catabolism may serve as a key therapeutic target in AKI and kidney fibrosis., Competing Interests: Competing interest statement: J.C.H. declares a Shangpharma research grant of $250,000 per year in 2019 to 2020 and is a Scientific Advisory Board member for RenalytixAI.

The renal prostaglandins PGS2 and PGE2 possess potent antihypertensive and vasodepressor activity. The mechanism of blood pressure lowering effect is through peripheral arteriolar dilation with a fall in total peripheral resistance. PGA unlike PGE escape degradation by the lung and thus could circulate as antihypertensive hormones. Since plasma PGA levels rise in humans on a low sodium intake, it has been postulated that the beneficial effects of a low sodium diet in some hypertensives may be the result of an increase in peripheral vasodilating PGA. Support that plasma PGA may be a regulator of systemic blood pressure is also derived from the fact a PGA-secreting renal tumor was associated with a fall in blood pressure and a rise in plasma PGA in a previously hypertensive woman. The removal of the tumor resulted in a return of blood pressure to elevated levels and a concomitant fall in PGA. Recently, a number of human patients with essential hypertension have been infused with PGA1 and PGA2. It was observed that there was an initial increase in renal blood flow, sodium and water excretion which was associated with no change in the elevated blood pressure. When blood pressure ultimately fell, there was a return of renal blood flow, sodium and water excretion to preinfusion levels. It would appear that PGA compounds act as 'ideal' antihypertensive agents since they favorably effect renal resistance, sodium and water homeostasis, plasma volume, total peripheral resistance, blood pressure and indirectly cardiac output through baroreceptor stimulation, all factors known to be important in etiology in human hypertension.

To study the interaction of the prohypertensive renin-angiotensin axis with the antihypertensive renal prostaglandins, angiotensin-converting enzyme inhibition (captopril and teprotide) and angiotensin blockade (Sar1-Ile8-AII) were produced in rabbits in vivo and renal slice prostaglandin E2 was measured in vitro after 30 minutes of incubation in Krebs-Ringer HCO3- buffer. In rabbits with angiotensin-converting enzyme inhibition, de novo prostaglandin E2 synthesis decreased in cortical, outer medullary and papillary slices by 85, 52 and 47 percent, respectively. Similar degrees of inhibition were observed with angiotensin blockade. It is concluded that renal prostaglandin E2 synthesis is angiotensin II dependent under these conditions. This finding suggests that any increase in the prohypertensive antinatriuretic renin-angiotensin axis may be associated with a secondary increase in renal prostaglandin E2 which may be acting in an antihypertensive natriuretic compensatory fashion.

The effects of chronic alterations in dietary sodium intake on urinary prostaglandin (PG) E2 and thromboxane (TX) B2 was investigated in the rabbit. Sodium restriction, over a 15-day period, reduced daily urinary PGE2 and TXB2 in concordance with urinary flow (V) and sodium excretion (UNa+V), but increased plasma renin activity (PRA) and plasma aldosterone concentration (PAC). Sodium repletion, on the other hand, increased urinary PGE2 and TXB2 in proportion to the rise in V, but reduced PRA and PAC. During both sodium diets PGE2 and TXB2 correlated positively with V and negatively with PRA. It is concluded that chronic sodium intake produces opposite changes in the renal prostaglandin and the renin-angiotensin systems.

To test the hypothesis that renal PGs may mediate the renal functional defect of potassium depletion, rabbits were placed on normal potassium and potassium-deficient diets for 7 weeks, and measurements were made of urinary PGE2 excretion; renal cortical, medullary, and papillary PGE2 content; and in vitro, de novo PGE2 biosynthesis. In the sixth week maximal urinary osmolality declined significantly, from 1118 +/- 44 mOsm/kg of H2O in controls to 666 +/- 25 in potassium-deficient animals, accompanied by a corresponding decrease in urinary excretion of potassium from 12.2 +/- 0.7 mEq/24 hr to 0.93 +/- 0.1 and in muscle potassium content from 39.0 +/- 1.0 mEq/100 gm to 22.3 +/- 1.9. By 3 weeks urinary excretion of PGE2 was significantly lower in hypokalemic animals than in controls. Renal cortical, medullary, and papillary PGE2 tissue content decreased significantly, from 0.061 +/- 0.01 microgram/gm to 0.022 +/- 0.005, 0.73 +/- 0.09 microgram/gm to 0.267 +/- 0.036, and 8.6 +/- 1.04 microgram/gm to 4.6 +/- 1.4, respectively. In vitro PGE2 biosynthesis by cortical, medullary, and papillary slices from normal animals was 0.102 +/- 0.01, 9.55 +/- 1.7, and 25.5 +/- 2.8 microgram/gm/30 min, whereas corresponding values from hypokalemic rabbits were 0.04 +/- 0.006, 3.9 +/- 0.747, and 14.0 +/- 1.25 microgram/gm/30 min, respectively. These results indicate that renal slices from hypokalemic rabbits synthesize much less PGE2 in vitro than do normal controls. The date do not support the hypothesis that enhanced PGE2 synthesis mediates the renal concentrating defect of chronic potassium deficiency but suggest that decreased renal PGE2 production may underlie the impairment in renal hemodynamics known to exist in this condition.

Since recent investigations have shown elevated urinary PGE2 and polyuria in hypokalemic animals which were reversed by PG synthesis inhibition with indomethacin, studies were undertaken to examine the effects of extracellular [K+] on renomedullary PG production in vitro. Slices of rabbit and human renal papilla were incubated in Krebs-Ringer HCO3- buffer, 95% O2-5% CO2, glucose 10 mM, HSA 4 gm/100 ml, for 30 min at 38 degrees C, with and without 1-14C-AA (10 micrometer). Measurments were made of total endogenous iPGE2 and iPGF2alpha production and radioactive AA leads to PGE2. In rabbit renal medulla values for iPGE2 (nmol/gm/30 min) were 252 +/- 20 at [K+] 0; 182 +/- 17 at [K+] 2.5 mEq/L; 163 +/- 18 at [K+] 5.5; and 129 +/- 17 [K+] 9.0 (p less than 0.005). iPGF2alpha was unaltered by changes in media potassium concentrations (6.8 +/- 0.9 nmol/gm/30 min at [K+] 0 and 6.2 +/- 0.8 at [K+] 9.0 MEq/L). In the human renal medulla iPGE2 was 9.5 +/- 1.6 nmol/gm/30 min at [K+] 0; 5.0 +/- 0.7 at [K+] 2.5 mEq/L; 5.3 +/- 0.3 at [K+] 5.5; and 4.6 +/- 1.0 at [K+] 9.0 (p less than 0.05). AA leads to PGE2 (nmol/gm/30 min) was 3.21 +/- 0.92 at [K+] 0; 2.47 +/- 0.57 at [K+] 2.5 mEq/L; 1.30 +/- 0.30 at [K+] 5.5; and 0.76 +/- 0.4 at [K+] 9.0 in rabbit medulla (P less than 0.005). It is postulated that direct stimulation of papillary PGE2 biosynthesis by low extracellular [K+] impairing the cAMP-generating response to vasopressin could represent the initial event in the pathogenesis of vasopressin-resistant polyuria.

To test the hypothesis that renal prostaglandin (PG) biosynthesis is regulated by angiotensin (AII), rabbits were given prolonged treatment with the AII analogue, Sar1-Ileu8AII (200 micrograms/kg/4 hr, subcutaneously), for 2 days during a low, normal, and high sodium intake. Sodium restriction augmented plasma renin activity (PRA), which was associated with a rise in basal renal PGE2 synthesis and urinary excretion, whereas sodium supplementation attenuated PRA with a decrease in renal PGE2 synthesis and urinary excretion. Sar1-Ileu8AII administration, with either a low, normal, or high salt intake, suppressed PRA. Sar1-Ileu8AII injection with a low sodium intake also suppressed renal PGE2 synthesis and excretion that was associated with a fall in blood pressure, suggesting an antagonistic action of this agent on vascular beds and renal PGE2 synthesis. On the other hand, with a high sodium intake Sar1-Ileu8-AII increased renal PGE2 synthesis and excretion as well as blood pressure, revealing an agonistic action of this compound under these conditions. The results suggest that exogenous AII analogue may act as an antagonist or agonist depending on sodium intake and endogenous AII levels, renal PGE2 synthesis is dependent on AII levels, either endogenously produced or exogenously administered (as an AII agonist), and the action of AII analogue on vascular beds and renal PGE2 synthesis does not appear to parallel its action on renin-AII feedback regulation at the juxtaglomerular cell especially under conditions of high sodium intake.

Studies were conducted to investigate the interaction of renal prostaglandin E2 (PGE2) production and the renin-angiotensin system in the mechanism of furosemide-induced natriuresis. In conscious rabbits with permanent urinary bladder cannulation, furosemide in vivo (10 mg/kg) increased urinary water, sodium, and PGE2 excretion and plasma renin activity (PRA) over 50 min. Furosemide administered in vivo enhanced renal papillary but not cortical in vitro PGE2 biosynthesis. Prior administration of indomethacin at 2 mg/kg augmented the saluretic effect of furosemide, decreased its effect on UPGE2 V, abolished the rise in PRA, and reduced cortical but not papillary PGE2 biosynthesis. However, at 10 mg/kg, indomethacin reduced the saluretic effect of furosemide and eliminated the increase in UPGE2 V with continued suppression of PRA. Direct addition of furosemide in vitro to the incubation medium (10(-5) and 10(-3) M) markedly augmented papillary PGE2 synthesis. It is concluded that furosemide stimulates renal papillary PGE2 biosynthesis directly without mediation by angiotensin II, resulting in an increase in UPGE2 V, and the enhanced or inhibitory effect of indomethacin on furosemide-induced natriuresis is dose related and dependent on the degree of PGE2 synthesis inhibition in the presence of suppressed PRA, which occurred at all doses studied.