• NFAT5
• TonEBP
• cell stress
• immune response
• osmolality
• transcription factor

• nephrology
• physiology

Sepsis is one of the leading causes of acute kidney injury (AKI), and several mechanisms including microcirculatory alterations, oxidative stress, and endothelial cell dysfunction are involved. Nitric oxide (NO) is one of the common elements to all these mechanisms. Although all three nitric oxide synthase (NOS) isoforms are constitutively expressed within the kidneys, they contribute in different ways to nitrergic signaling. While the endothelial (eNOS) and neuronal (nNOS) isoforms are likely to be the main sources of NO under basal conditions and participate in the regulation of renal hemodynamics, the inducible isoform (iNOS) is dramatically increased in conditions such as sepsis. The overexpression of iNOS in the renal cortex causes a shunting of blood to this region, with consequent medullary ischemia in sepsis. Differences in the vascular reactivity among different vascular beds may also help to explain renal failure in this condition. While most of the vessels present vasoplegia and do not respond to vasoconstrictors, renal microcirculation behaves differently from nonrenal vascular beds, displaying similar constrictor responses in control and septic conditions. The selective inhibition of iNOS, without affecting other isoforms, has been described as the ideal scenario. However, iNOS is also constitutively expressed in the kidneys and the NO produced by this isoform is important for immune defense. In this sense, instead of a direct iNOS inhibition, targeting the NO effectors such as guanylate cyclase, potassium channels, peroxynitrite, and S-nitrosothiols, may be a more interesting approach in sepsis-AKI and further investigation is warranted.

• endothelial nitric oxide synthase
• guanylate cyclase
• inducible nitric oxide synthase
• peroxynitrite
• potassium channels
• renal haemodynamics

• Animals
• Cell Nucleus/metabolism
• Cell Proliferation
• Cytokines/metabolism
• Diabetes Complications/genetics
• Diabetes Complications/metabolism
• Diabetes Mellitus/drug therapy
• Diabetes Mellitus/genetics
• Diabetes Mellitus/metabolism
• Gene Expression Profiling
• Gene Expression Regulation
• Genetic Therapy
• Homeostasis
• Humans
• Inflammation
• Insulin Resistance
• Medicine, Chinese Traditional
• Mice
• Osmotic Pressure
• Reactive Oxygen Species
• Risk
• Transcription Factors/genetics
• Transcription Factors/physiology
• Transcription, Genetic
• Treatment Outcome

• hypothalamus
• inflammation
• proopiomelanocortin
• sickness responses
• tonicity-responsive enhancer binding protein

• AQP-1
• NFAT5
• UTA-1
• hypoxia
• iNOS

• Active Transport, Cell Nucleus
• Animals
• Aquaporin 1/genetics
• Aquaporin 1/metabolism
• Cell Hypoxia
• Cells, Cultured
• Fibroblasts/enzymology
• Membrane Transport Proteins/genetics
• Membrane Transport Proteins/metabolism
• Mice
• Nitric Oxide/metabolism
• Nitric Oxide Synthase Type II/genetics
• Nitric Oxide Synthase Type II/metabolism
• Signal Transduction
• Transcription Factors/genetics
• Transcription Factors/metabolism
• Urea Transporters

• Countercurrent multiplication
• NFAT5
• SHP-1
• TonEBP
• Vasa recta

• Anemia, Sickle Cell/metabolism
• Anemia, Sickle Cell/urine
• Animals
• Aquaporin 1/metabolism
• Aquaporin 2/genetics
• Aquaporin 2/metabolism
• Epithelial Sodium Channels/genetics
• Epithelial Sodium Channels/metabolism
• Female
• Kidney/metabolism
• Male
• Membrane Transport Proteins/genetics
• Membrane Transport Proteins/metabolism
• Mice
• Protein Tyrosine Phosphatase, Non-Receptor Type 6/genetics
• Protein Tyrosine Phosphatase, Non-Receptor Type 6/metabolism
• Solute Carrier Family 12, Member 1/genetics
• Solute Carrier Family 12, Member 1/metabolism
• Transcription Factors/metabolism
• Up-Regulation
• Vasopressins/metabolism
• Water-Electrolyte Balance
• Urea Transporters

Aquaporins (AQPs) are a family of highly selective transmembrane channels that mainly transport water across the cell and some facilitate low-molecular-weight solutes. Eight AQPs, including AQP1, AQP2, AQP3, AQP4, AQP5, AQP6, AQP7, and AQP11, are expressed in different segments and various cells in the kidney to maintain normal urine concentration function. AQP2 is critical in regulating urine concentrating ability. The expression and function of AQP2 are regulated by a series of transcriptional factors and post-transcriptional phosphorylation, ubiquitination, and glycosylation. Mutation or functional deficiency of AQP2 leads to severe nephrogenic diabetes insipidus. Studies with animal models show AQPs are related to acute kidney injury and various chronic kidney diseases, such as diabetic nephropathy, polycystic kidney disease, and renal cell carcinoma. Experimental data suggest ideal prospects for AQPs as biomarkers and therapeutic targets in clinic. This review article mainly focuses on recent advances in studying AQPs in renal diseases.

• acute kidney injury
• aquaporin
• diabetic nephropathy
• nephrogenic diabetes insipidus
• polycystic kidney disease
• renal cell carcinoma
• vasopressin

• Denitrosylation
• Nitrosylation
• Organ damage
• Sepsis
• Vascular dysfunction

A growing body of evidence from animal models and cell culture studies indicate an important role of a local regulatory complement system (CS) in peritoneal injury during peritoneal dialysis (PD). We investigated the expression of the local regulatory CS (reflected by CD46,CD55,CD59) in the peritoneal tissue of patients with different membrane function characteristics.

Biopsies from the parietal peritoneum were taken from 24 patients on PD, 22 uremic patients prior to PD. PD patients were grouped according to the dialysate-to-plasma ratio of creatinine (D/P Cre) and ratio of dialysate glucose at 4 hours versus dialysate glucose at time zero (D/D0 glucose) into low or low-average peritoneal transport status (L/LA) and high-average or high-transport status (HA/H) groups. CD46, CD55, and CD59 RNA expression were analyzed by real-time polymerase chain reaction (RT-PCR). Further localization of membrane complement regulators (CRegs) and semiquantitatively analysis was done by immunohistochemistry (IHC).

CD46 and CD59 expression were similar in all groups. CD55 expression was significantly decreased in the HA/H group compared to the L/LA group and to uremic controls (p < 0.05 and p = 0.05, respectively). No statistically significant differences in CD46, CD55, and CD55 expression were detected when considering the history of peritonitis. There was no statistically significant correlation between PD duration and the expressions of CD46, CD55, and CD59. IHC revealed strong CD46, CD55, and CD59 expression in mesothelial cells. CD55 and CD59 were additionally detected in the vasculature. Using IHC, CD46 was lower in PD patients compared to uremic controls (p>0.05), but there was no difference between the L/LA compared to the H/HA group. Moreover IHC confirmed decreased expression of CD55 in the HA/H group compared to the L/LA group and uremic controls (p<0.0001 and p = 0.0001, respectively).

CD55 expression is decreased in patients with fast transporter membrane function, whereas peritonitis and PD duration do not appear to alter CReg expression.

• Antigens, CD/genetics
• Antigens, CD/metabolism
• Cell Membrane/metabolism
• Female
• Gene Expression Regulation
• Humans
• Male
• Membrane Transport Proteins/genetics
• Membrane Transport Proteins/metabolism
• Middle Aged
• Peritoneal Dialysis
• Peritoneum/cytology
• Peritonitis/metabolism
• RNA, Messenger/genetics
• RNA, Messenger/metabolism

• Else Kröner-Fresenius Stiftung
• Fundação Pesquisa e Desenvolvimento Humanitario
• Robert Bosch Foundation

NFAT5 plays a critical role in maintaining the renal functions. Its dis-regulation in the kidney leads to or is associated with certain renal diseases or disorders, most notably the urinary concentration defect. Hypertonicity, which the kidney medulla is normally exposed to, activates NFAT5 through phosphorylation of a signaling molecule or NFAT5 itself. Hypotonicity inhibits NFAT5 through a similar mechanism. More than a dozen of protein and lipid kinases have been identified to contribute to tonicity-dependent regulation of NFAT5. Hypertonicity activates NFAT5 by increasing its nuclear localization and transactivating activity in the early phase and protein abundance in the late phase. The known mechanism for inhibition of NFAT5 by hypotonicity is a decrease of nuclear NFAT5. The present article reviews the effect of each kinase on NFAT5 nuclear localization, transactivation and protein abundance, and the relationship among these kinases, if known. Cyclosporine A and tacrolimus suppress immune reactions by inhibiting the phosphatase calcineurin-dependent activation of NFAT1. It is hoped that this review would stimulate the interest to seek explanations from the NFAT5 regulatory pathways for certain clinical presentations and to explore novel therapeutic approaches based on the pathways. On the basic science front, this review raises two interesting questions. The first one is how these kinases can specifically signal to NFAT5 in the context of hypertonicity or hypotonicity, because they also regulate other cellular activities and even opposite activities in some cases. The second one is why these many kinases, some of which might have redundant functions, are needed to regulate NFAT5 activity. This review reiterates the concept of signaling through cooperation. Cells need these kinases working in a coordinated way to provide the signaling specificity that is lacking in the individual one. Redundancy in regulation of NFAT5 is a critical strategy for cells to maintain robustness against hypertonic or hypotonic stress.

• Tonicity enhancer binding protein
• Osmotic response element binding protein
• Phosphorylation
• Kidney
• Urinary concentration
• Signal transduction
• Nephropathy
• Hypertonicity
• Hypotonicity

Lithium salts are used widely for treatment of bipolar and other mental disorders. Lithium therapy is accompanied frequently by renal side effects, such as nephrogenic diabetes insipidus or chronic kidney disease (CKD), but the molecular mechanisms underlying these effects are still poorly understood. In the present study we examined the effect of lithium on the activity of the osmosensitive transcriptional activator nuclear factor of activated T cells 5 (NFAT5, also known as TonEBP), which plays a key role in renal cellular osmoprotection and urinary concentrating ability. Interestingly, we found different effects of lithium on NFAT5 activity, depending on medium osmolality and incubation time. When cells were exposed to lithium for a relative short period (24 h), NFAT5 activity was significantly increased, especially under isosmotic conditions, resulting in an enhanced expression of the NFAT5 target gene heat shock protein 70 (HSP70). Further analysis revealed that the increase of NFAT5 activity depended primarily on an enhanced activity of the c-terminal transactivation domain (TAD), while NFAT5 protein abundance was largely unaffected. Enhanced activity of the TAD is probably mediated by lithium-induced inhibitory phosphorylation of glycogen synthase kinase 3β (GSK-3β), which is in accordance with previous studies. When cells were exposed to lithium for a longer period (96 h), cellular NFAT5 activity and subsequently expression of HSP70 significantly decreased under hyperosmotic conditions, due to diminished NFAT5 protein abundance, also resulting from GSK-3β inhibition. Taken together, our results provide evidence that lithium has opposing effects on NFAT5 activity, depending on environmental osmolality and exposure duration. The potential impacts of these observations on the diverse effects of lithium on kidney function are discussed.

• GSK3β
• NFAT5
• chronic kidney disease
• lithium
• nephrogenic diabetes insipidus
• urinary concentrating mechanism

The osmosensitive transcription factor nuclear factor of activated T-cells 5 (NFAT5), also known as tonicity enhancer element binding protein (TonEBP) plays a crucial role in protection of renal medullary cells against hyperosmotic stress, urinary concentration, the adaptive immune response, and other physiological systems. Since it is also important for development, conventional homozygous-null mutations result in perinatal death, which hinders the analysis of NFAT5 function in specific tissues in vivo. Here we describe the generation of mice with a conditional-null allele, in which loxP sites are inserted around exon 4. Mice harboring the floxed allele (NFAT5^flx) were mated to a strain expressing a tamoxifen-inducible derivative of the Cre-recombinase (Cre⁺) under the control of the ubiqitinC promoter. The resultant homozygous conditional knockout mice (Cre⁺ NFAT5^flx/flx) are viable, fertile, and show normal expression of NFAT5 and NFAT5 target genes, indicating that the conditional alleles retain their wild-type function. Induction of Cre-mediated recombination by administration of tamoxifen in 8-week-old mice resulted in a decrease in NFAT5 expression of about 70–90% in all tested tissues (renal cortex, renal outer medulla, renal inner medulla, heart, lung, spleen, skeletal muscle). Accordingly, the expression of the NFAT5 target genes aldose reductase and heat shock protein 70 in the renal medulla was also significantly decreased. Mice harboring this conditional knockout allele should be useful in future studies for gaining a better understanding of tissue and cell-type specific functions of NFAT5 in adult animals under physiological and pathophysiological conditions.

• NFAT5
• TonEBP
• kidney physiology
• knockout mouse model
• osmosensing

• ERK1/2
• aquaporin-2
• leishmaniasis
• urinary concentration
• virulence factors

TonEBP/NFAT5 is a major regulator of the urinary concentrating process and is essential for the osmoadaptation of renal medullary cells. Focal adhesion kinase (FAK) is a mechanosensitive non-receptor protein tyrosine kinase expressed abundantly in the renal medulla. Since osmotic stress causes cell shrinkage, the present study investigated the contribution of FAK on TonEBP/NFAT5 activation. Osmotic stress induced time-dependent activation of FAK as evidenced by phosphorylation at Tyr-397, and furosemide reduces FAK Tyr-397 phosphorylation in the rat renal medulla. Both pharmacological inhibition of FAK and siRNA-mediated knockdown of FAK drastically reduced TonEBP/NFAT5 transcriptional activity and target gene expression in HEK293 cells. This effect was not mediated by impaired nuclear translocation or by reduced transactivating activity of TonEBP/NFAT5. However, TonEBP/NFAT5 abundance under hypertonic conditions was diminished by 50% by FAK inhibition or siRNA knockdown of FAK. FAK inhibition only marginally reduced transcription of the TonEBP/NFAT5 gene. Rather, TonEBP/NFAT5 mRNA stability was diminished significantly by FAK inhibition, which correlated with reduced reporter activity of the TonEBP/NFAT5 mRNA 3′ untranslated region (3′-UTR). In conclusion, FAK is a major regulator of TonEBP/NFAT5 activity by increasing its abundance via stabilization of the mRNA. This in turn, depends on the presence of the TonEBP/NFAT5 3′-UTR.

• TonEBP/NFAT5
• focal adhesion kinase
• gene regulation
• osmotic stress
• renal medulla

• Animals
• Biological Transport
• Humans
• Kidney Tubules, Collecting/metabolism
• Membrane Transport Proteins/genetics
• Membrane Transport Proteins/metabolism
• Urea/metabolism
• Urea Transporters

• R03-DK91501 NIDDK NIH HHS
• K01 DK082733 NIDDK NIH HHS
• R01 DK041707 NIDDK NIH HHS
• R21-DK91147 NIDDK NIH HHS
• R01 DK089828 NIDDK NIH HHS
• R01-DK89828 NIDDK NIH HHS
• K01-DK82733 NIDDK NIH HHS
• R21 DK091147 NIDDK NIH HHS
• R03 DK091501 NIDDK NIH HHS
• UL1 TR000454 NCATS NIH HHS
• R01 DK41707 NIDDK NIH HHS