NK1.1- natural killer T cells upregulate interleukin-17 expression in experimental lupus nephritis

Interleukin (IL)-17-secreting invariant natural killer T (NKT) cells are involved in several inflammatory diseases. However, their role in lupus nephritis (LN) has not been fully characterized. Samples from patients with LN or glomerulonephritis and healthy controls were obtained, and elevated IL-17+ NKT cell numbers and IL-17 expression were observed in blood cells and kidneys, respectively, in patients with LN. Comparison of a mouse model of experimental autoimmune LN with the parental strain (NKT-deficient B6.CD1d-/- mice) revealed improved proteinuria, disease severity, and histopathology and decreased levels of chemokine (C-X-C motif) ligand 16 and T cell receptor-α variable 14 expression. Spleens and kidneys of B6.CD1d-/- mice also showed downregulation of inflammatory markers and IL-17. In coculture with renal mesangial and NKT cells, inflammatory markers and IL-17 were upregulated following α-galactosylceramide treatment and downregulated after treatment with IL-17-blocking antibodies. This was most prominent with killer cell lectin-like receptor subfamily B member 1 C (NK1.1)- NKT cells. Thus, IL-17 is upregulated in LN. Activation of NKT cells regulates IL-17-related immune responses systemically and in the kidneys, primarily via NK1.1- NKT cells. IL-17-secreting NK1.1- NKT cells could serve as diagnostic and therapeutic targets for LN.NEW & NOTEWORTHY This study makes a significant contribution to the literature because our results indicate that IL-17 is upregulated in lupus nephritis and that natural killer T (NKT) cells are involved in its pathogenesis. Activation of NKT cells regulates IL-17-related immune responses, both systemically and in the kidney, and this mainly involves NK1.1- NKT cells. Furthermore, IL-17-secreting NK1.1- NKT cells could serve as a diagnostic and therapeutic target for lupus nephritis.

The enhanced expression of IL-17-secreting T cells during the early progression of atherosclerosis in ApoE-deficient mice fed on a western-type diet

Atherosclerosis is a chronic progressive inflammatory disorder and the leading cause of cardiovascular mortality. Here we assessed the dynamic changes of T-cell-derived cytokines, such as inteferon (IFN)-γ, interleukin (IL)-17 and IL-4, during the progression of atherosclerosis in apolipoprotein E-null (ApoE^−/−) mice, to understand the role of immune responses in different stages of atherosclerosis. Male ApoE^−/− mice were fed a high-fat, western-type diet (WD: 21% lipid, 1.5% cholesterol) after 5 weeks of age and were compared with C57BL/6 wild-type control mice fed a standard chow diet. Atherosclerotic lesions appeared in the aortic sinus of ApoE^−/− mice 4 weeks after WD and the lesions progressed and occupied >50% of the total sinus area 16 weeks after WD. Aortic IL-17 mRNA and protein expression started to increase in ApoE^−/− mice after 4 weeks on the WD and peaked at around 8–12 weeks on the WD. In terms of systemic expression of T-cell-derived cytokines, IL-17 production from splenocytes after anti-CD3/CD28 stimuli increased from 4 weeks on the WD, peaked at 12 weeks and returned to control levels at 16 weeks. The production of IFN-γ and IL-4 (Th1 and Th2 cytokines, respectively) from splenocytes was delayed compared with IL-17. Taken together, the present data indicate that Th17 cell response may be involved at an early stage in the development of atherosclerosis.

The association of Klotho polymorphism with disease progression and mortality in IgA nephropathy

BACKGROUNDS

IgA nephropathy (IgAN) is the most common primary glomerulonephritis causing end stage renal disease (ESRD), and vasculopathy is known to involve disease progression. Klotho, a gene related to aging, has been reported to play a role in atherosclerosis and endothelial dysfunction. We investigated whether klotho gene polymorphism affect clinical course of IgAN.

METHODS

The data registered for PREMIER study which enrolled the patients with biopsy proven IgAN were analyzed. Two single nucleotide polymorphisms for klotho gene, G395A of promoter region and C1818T of exon 4, were examined, and investigated the association klotho genotypes with the progression of IgAN and patient survival.

RESULTS

Clinical data from 973 patients confirmed about survival were analyzed. The allele frequency was 0.830 and 0.170 for allele G and A, and 0.816 and 0.184 for allele C and T, which were complied with Hardy-Weinberg equilibrium (p=0.996 and 0.531 respectively). Death was observed more frequently in A-allele carriers of G395A polymorphism (0.7 vs. 2.6 %, GG vs. GA+AA, p=0.022). Renal survival in Kaplan-Meier survival curve was also worse in same group (p=0.04).

CONCLUSION

Klotho gene polymorphism was associated with patient survival and disease progression of IgAN.

Activation of Rice nicotianamine synthase 2 (OsNAS2) enhances iron availability for biofortification

Because micronutrients in human diets ultimately come from plant sources, malnutrition of essential minerals is a significant public health concern. By increasing the expression of nicotianamine synthase (NAS), we fortified the level of bioavailable iron in rice seeds. Activation of iron deficiency-inducible OsNAS2 resulted in a rise in Fe content (3.0-fold) in mature seeds. Its ectopic expression also increased that content. Enhanced expression led to higher tolerance of Fe deficiency and better growth under elevated pH. Mice fed with OsNAS2-D1 seeds recovered more rapidly from anemia, indicating that bioavailable Fe contents were improved by this increase in OsNAS2 expression.

Bio-available zinc in rice seeds is increased by activation tagging of nicotianamine synthase

We generated rice lines with increased content of nicotianamine (NA), a key ligand for metal transport and homeostasis. This was accomplished by activation tagging of rice nicotianamine synthase 2 (OsNAS2). Enhanced expression of the gene resulted in elevated NA levels, greater Zn accumulations and improved plant tolerance to a Zn deficiency. Expression of Zn-uptake genes and those for the biosynthesis of phytosiderophores (PS) were increased in transgenic plants. This suggests that the higher amount of NA led to greater exudation of PS from the roots, as well as stimulated Zn uptake, translocation and seed-loading. In the endosperm, the OsNAS2 activation-tagged line contained up to 20-fold more NA and 2.7-fold more zinc. Liquid chromatography combined with inductively coupled plasma mass spectrometry revealed that the total content of zinc complexed with NA and 2'-deoxymugineic acid was increased 16-fold. Mice fed with OsNAS2-D1 seeds recovered more rapidly from a zinc deficiency than did control mice receiving WT seeds. These results demonstrate that the level of bio-available zinc in rice grains can be enhanced significantly by activation tagging of OsNAS2.

Sulfatide-reactive natural killer T cells abrogate ischemia-reperfusion injury

There is a significant immune response to ischemia-reperfusion injury (IRI), but the role of immunomodulatory natural killer T (NKT) cell subtypes is not well understood. Here, we compared the severity of IRI in mice deficient in type I/II NKT cells (CD1d(-/-)) or type I NKT cells (Jα18(-/-)). The absence of NKT cells, especially type II NKT cells, accentuated the severity of renal injury, whereas repletion of NKT cells attenuated injury. Adoptively transferred NKT cells trafficked into the tubulointerstitium, which is the primary area of injury. Sulfatide-induced activation of type II NKT cells protected kidneys from IRI, but inhibition of NKT cell recruitment enhanced injury. In co-culture experiments, sulfatide-induced activation of NKT cells from either mice or humans attenuated apoptosis of renal tubular cells after transient hypoxia via hypoxia-inducible factor (HIF)-1α and IL-10 pathways. Renal tissue of patients with acute tubular necrosis (ATN) frequently contained NKT cells, and the number of these cells tended to negatively correlate with ATN severity. In summary, sulfatide-reactive type II NKT cells are renoprotective in IRI, suggesting that pharmacologic modulation of NKT cells may protect against ischemic injury.

Inactivation of Notch signaling in the renal collecting duct causes nephrogenic diabetes insipidus in mice

The heterogeneous cellular composition of the mammalian renal collecting duct enables regulation of fluid, electrolytes, and acid-base homeostasis, but the molecular mechanism of its development has yet to be elucidated. The Notch signaling pathway is involved in cell fate determination and has been implicated in proximal-distal patterning in the mammalian kidney. To investigate the role of Notch signaling in renal collecting duct development, we generated mice in which Mind bomb-1 (Mib1), an E3 ubiquitin ligase required for the initiation of Notch signaling, was specifically inactivated in the ureteric bud of the developing kidney. Mice lacking Mib1 in the renal collecting duct displayed increased urinary production, decreased urinary osmolality, progressive hydronephrosis, sodium wasting, and a severe urinary concentrating defect manifested as nephrogenic diabetes insipidus. Histological analysis revealed a diminished number of principal cells and corresponding increase in the number of intercalated cells. Transgenic overexpression of Notch intracellular domain reversed the altered cellular composition of mutant renal collecting duct, with principal cells occupying the entire region. Our data demonstrate that Notch signaling is required for the development of the mammalian renal collecting duct and principal cell differentiation and indicate that pathway dysregulation may contribute to distal renal tubular disorders.

The heme oxygenase-1 genotype is a risk factor to renal impairment of IgA nephropathy at diagnosis, which is a strong predictor of mortality

The induction of heme oxygenase-1 (HO-1) ameliorates oxidative stress and inflammatory process, which play important roles in IgA nephropathy. We hypothesized length polymorphism in the promoter region of the HO-1 gene, which is related to the level of gene transcription, is associated with disease severity of IgA nephropathy. The subjects comprised 916 patients with IgA nephropathy and gene data. Renal impairment was defined as an estimated glomerular filtration rate less than 60 mL/min/1.73 m(2) at diagnosis. The short (S: <23), medium (M: 23-28), and long (L: >28) (GT) repeats in the HO-1 gene was determined. The frequencies of S/S, S/M, M/M, S/L, L/M, and L/L genotypes were 7.2%, 6.9%, 3.1%, 30.8%, 22.7%, and 29.4%, respectively. The baseline characteristics were not different. In the S/S genotypic group, the renal impairment rate was 18.2%, which was lower than 32.2% in the group with M/M, L/M, or L/L genotype. The odds ratio of renal impairment in S/S genotype, compared to that in M/M, L/M, or L/L genotype, was 0.216 (95% confidence interval, 0.060-0.774, p=0.019). The HO-1 gene promoter length polymorphism was related to the renal impairment of IgA nephropathy at diagnosis, which is an important risk factor for mortality in IgA nephropathy patients.

Effects of thiazide on the expression of TRPV5, calbindin-D28K, and sodium transporters in hypercalciuric rats

TRPV5 is believed to play an important role in the regulation of urinary calcium excretion. We assessed the effects of hydrochlorothiazide (HCTZ) on the expression of TRPV5, calbindin-D(28K), and several sodium transporters in hypercalciuric rats. Sprague-Dawley rats were divided into 4 groups; control, HCTZ, high salt, and high salt with HCTZ group in experiment 1; control, HCTZ, high calcium (Ca), and high Ca with HCTZ group in experiment 2. To quantitate the expression of TRPV5, calbindin-D(28K), and sodium transporters, western blotting was performed. In both experiments, HCTZ significantly decreased urinary calcium excretion. TRPV5 protein abundance decreased in all hypercalciuric rats, and restored by HCTZ in both high salt with HCTZ and high Ca with HCTZ group. Calbindin-D(28K) protein abundance increased in the high salt and high salt with HCTZ groups, but did not differ among groups in experiment 2. Protein abundance of NHE3 and NKCC2 decreased in all hypercalciuric rats, and were restored by HCTZ in only high Ca-induced hypercalciuric rats. In summary, protein abundance of TRPV5, NHE3, and NKCC2 decreased in all hypercalciuric rats. The hypocalciuric effect of HCTZ is associated with increased protein abundance of TRPV5 in high salt or calcium diet-induced hypercalciuric rats.

Association of angiotensin II type 2 receptor gene A1818T polymorphism with progression of immunoglobulin A nephropathy in Korean patients

We determined the relationship between the progression of immunoglobulin A nephropathy (IgAN) and the A1818T polymorphism in intron 2 of Angiotensin II type 2 receptor (AT2R) gene, which might play protective roles in the pathogenesis of IgAN. Patients with biopsy-proven IgAN were recruited from the registry of the Progressive REnal disease and Medical Informatics and gEnomics Research (PREMIER) which was sponsored by the Korean Society of Nephrology. A1818T polymorphism of AT2R gene was analyzed with PCR-RFLP method and the association with the progression of IgAN, which was defined as over 50% increase in baseline serum creatinine level, was analyzed with survival analysis. Among the 480 patients followed for more than 10 months, the group without T allele had significantly higher rates of progression of IgAN than the group with T allele (11.4% vs. 3.9%, p=0.024), although there were no significant differences in the baseline variables such as initial serum creatinine level, the degree of proteinuria, and blood pressure. In the Cox's proportional hazard model, the hazard ratio of disease progression in the patients with T allele was 0.221 (95% confidence interval for Exp(B): 0.052-0.940, p=0.041) compared to that of without T allele. In conclusion, A1818T polymorphism of AT2R gene was associated with the progression of IgAN.

Kidney and calcium homeostasis

Plasma calcium concentration is maintained within a narrow range (8.5-10.5 mg/dL) by the coordinated action of parathyroid hormone (PTH), 1,25(OH)₂D₃, calcitonin, and ionized calcium (iCa²⁺) itself. The kidney plays a key role in this process by the fine regulation of calcium excretion. More than 95% of filtered calcium is reabsorbed along the renal tubules. In the proximal tubules, 60% of filtered calcium is reabsorbed by passive mechanisms. In the thick ascending limb, 15% of calcium is reabsorbed by paracellular diffusion through paracellin-1 (claudin-16). The calcium sensing receptor (CaSR) in the basolateral membrane of the thick ascending limb senses the change in iCa²⁺ and inhibits calcium reabsorption independent to PTH and 1,25(OH)₂D₃. The fine regulation of calcium excretion occurs in the distal convoluted tubules and connecting tubules despite the fact that only 10-15% of filtered calcium is reabsorbed there. Transient receptor potential vanilloid 5 (TRPV5) and 6 (TRPV6) in the apical membrane act as the main portal of entry, calbindin-D_28K delivers Ca²⁺ in the cytoplasm, and then Na²⁺/Ca²⁺ exchanger (NCX1) and plasma membrane Ca²⁺-ATPase in the basolateral membrane serve as an exit. In the cortical collecting duct, TRPV6 is expressed, but the role might be negligible. In addition to PTH and 1,25(OH)₂D₃, acid-base disturbance, diuretics, and estrogen affect on these calcium channels. Recently, klotho and fibroblast growth factor 23 (FGF23) are suggested as new players in the calcium metabolism. Klotho is exclusively expressed in the kidney and co-localized with TRPV5, NCX1, and calbindin-D_28K. Klotho increases calcium reabsorption through trafficking of TRPV5 to the plasma membrane, and also converts FGF receptor to the specific FGF23 receptor. FGF23:klotho complex bound to FGF receptor inhibits 1α-hydroxylase of vitamin D, and contributes to calcium reabsorption and phosphate excretion in the kidney.

NF-kappaB modulates aquaporin-2 transcription in renal collecting duct principal cells

Renal tubulo-interstitial inflammation is frequently associated with polyuria and urine concentration defects. This led us to investigate the effects of the major pro-inflammatory nuclear factor kappaB (NF-kappaB) pathway on aquaporin 2 (AQP2) expression by the collecting duct. Using immortalized collecting duct principal cells (mpkCCDcl4), we found that, acting independently of vasopressin, activation of NF-kappaB by lipopolysaccharide (LPS) decreased AQP2 mRNA and protein levels in a time- and dose-dependent manner but did not decrease AQP2 mRNA stability. Consistently, constitutively active IkappaB kinase beta decreased AQP2 expression. The LPS-induced decrease in AQP2 mRNA levels was confirmed in rat kidney slices and was reproduced both under conditions of elevated cAMP concentration and V(2) receptor antagonism. Computer analysis of the AQP2 promoter revealed two putative kappaB elements. Mutation of either kappaB element abolished the LPS-induced decrease of luciferase activity in cells expressing AQP2 promoter-luciferase plasmid constructs. Chromatin immunoprecipitation revealed that LPS challenge decreased p65, increased p50 and p52, and had no effect on RelB and c-Rel binding to kappaB elements of the AQP2 promoter. RNA-mediated interference silencing of p65, p50, and p52 confirmed controlled AQP2 transcription by these NF-kappaB subunits. We additionally found that hypertonicity activated NF-kappaB in mpkCCDcl4 cells, an effect that may counteract the Tonicity-responsive enhancer binding protein (TonEBP)-dependent increase in AQP2 gene transcription. Taken together, these findings indicate that NF-kappaB is an important physiological regulator of AQP2 transcription.

Altered renal sodium transporter expression in an animal model of type 2 diabetes mellitus

Hemodynamic factors play an important role in the development and/or progression of diabetic nephropathy. We hypothesized that renal sodium transporter dysregulation might contribute to the hemodynamic alterations in diabetic nephropathy. Otsuka Long Evans Tokushima Fatty (OLETF) rats were used as an animal model for type 2 diabetes. Long Evans Tokushima (LETO) rats were used as controls. Renal sodium transporter regulation was investigated by semiquantitative immunoblotting and immunohistochemistry of the kidneys of 40-week-old animals. The mean serum glucose level in OLETF rats was increased to 235+/-25 mg/dL at 25 weeks, and the hyperglycemia continued up to the end of 40 weeks. Urine protein/ creatinine ratios were 10 times higher in OLETF rats than in LETO rats. At 40th week, the abundance of the epithelial sodium channel (ENaC) beta-subunit was increased in OLETF rats, but the abundance of the ENaC gamma-subunit was decreased. No significant differences were observed in the ENaC alpha-subunit or other major sodium transporters. Immunohistochemistry for the ENaC beta-subunit showed increased immunoreactivity in OLETF rats, whereas the ENaC gamma-subunit showed reduced immunoreactivity in these rats. In OLETF rats, ENaC beta-subunit upregulation and ENaC gamma-subunit downregulation after the development of diabetic nephropathy may reflect an abnormal sodium balance.

Reduced urinary excretion of thiazide-sensitive Na-Cl cotransporter in Gitelman syndrome: preliminary data

BACKGROUND

The relationship between SLC12A3 mutations and actual sodium-chloride (Na-Cl) cotransporter (NCC) expression in patients with Gitelman syndrome (GS) was rarely evaluated. Detection of urinary thiazide-sensitive NCC was not tried in patients with GS.

STUDY DESIGN

Case series.

SETTING & PARTICIPANTS

6 patients with GS and 1 patient with surreptitious vomiting.

OUTCOMES & MEASUREMENTS

Renal clearance study, mutation analysis using reverse-transcription polymerase chain reaction and direct sequencing for the SLC12A3 gene, and immunohistochemical staining for NCC, Na-K-2Cl-cotransporter, alpha1-subunit of Na(+),K(+)-ATPase, and calbindin-D(28K) of the renal biopsy specimens were performed. Membrane fractions of urine were obtained by using differential centrifugation and probed with antibodies against human NCC and aquaporin 2.

RESULTS

Results of clearance studies were consistent with GS, showing decreased distal fractional chloride reabsorption with only furosemide. SLC12A3 gene mutations were found in all patients with GS. Immunohistochemistry showed markedly decreased NCC expression in the distal convoluted tubule, whereas expression of other transporters remained intact. Urinary NCC excretion was markedly decreased in patients with GS, but not in the patient with surreptitious vomiting.

LIMITATIONS

Small number of patients and lack of mutation analysis of CLCNKB.

CONCLUSIONS

There were no relations between NCC expression and types of mutations. Detection of urinary NCC might be helpful for the differential diagnosis of GS.

Downregulation of renal TonEBP in hypokalemic rats

Hypokalemia causes a significant decrease in the tonicity of the renal medullary interstitium in association with reduced expression of sodium transporters in the distal tubule. We asked whether hypokalemia caused downregulation of the tonicity-responsive enhancer binding protein (TonEBP) transcriptional activator in the renal medulla due to the reduced tonicity. We found that the abundance of TonEBP decreased significantly in the outer and inner medullas of hypokalemic rats. Underlying mechanisms appeared different in the two regions because the abundance of TonEBP mRNA was lower in the outer medulla but unchanged in the inner medulla. Immunohistochemical examination of TonEBP revealed cell type-specific differences. TonEBP expression decreased dramatically in the outer and inner medullary collecting ducts, thick ascending limbs, and interstitial cells. In the descending and ascending thin limbs, TonEBP abundance decreased modestly. In the outer medulla, TonEBP shifted to the cytoplasm in the descending thin limbs. As expected, transcription of aldose reductase, a target of TonEBP, was decreased since the abundance of mRNA and protein was reduced. Downregulation of TonEBP appeared to have also contributed to reduced expression of aquaporin-2 and UT-A urea transporters in the renal medulla. In cultured cells, expression and activity of TonEBP were not affected by reduced potassium concentrations in the medium. These data support the view that medullary tonicity regulates expression and nuclear distribution of TonEBP in the renal medulla in cell type-specific manners.

Chronic furosemide or hydrochlorothiazide administration increases H+-ATPase B1 subunit abundance in rat kidney

Furosemide administration stimulates distal acidification. This has been attributed to the increased lumen-negative voltage in the distal nephron, but the aspect of regulatory mechanisms of H+-ATPase has not been clear. The purpose of this study is to investigate whether chronic administration of diuretics alters the expression of H+-ATPase and whether electrogenic Na+ reabsorption is involved in this process. A 7-day infusion of furosemide or hydrochlorothiazide (HCTZ) lowered urine pH significantly. However, this effect of furosemide-induced distal acidification was not changed with amiloride-blocking electrogenic Na+ reabsorption. On immunoblotting, a polyclonal antibody against the H+-ATPase B1 subunit recognized a specific ∼56-kDa band in membrane fractions from the kidney. The protein abundance of H+-ATPase was significantly increased by furosemide and HCTZ infusion in both the cortex and outer medulla. Furosemide plus amiloride administration also increased the H+-ATPase protein abundance significantly. However, no definite subcellular redistribution of H+-ATPase was observed by furosemide ± amiloride infusion with immunohistochemistry. Chronic furosemide ± amiloride administration induced a translocation of pendrin to the apical membrane, while total protein abundance was not increased. The mRNA expression of H+-ATPase was not altered by furosemide ± amiloride infusion. We conclude that chronic administration of diuretics enhances distal acidification by increasing the abundance of H+-ATPase irrespective of electrogenic Na+ reabsorption. This upregulation of H+-ATPase in the intercalated cells may be the result of tubular hypertrophy by diuretics.

Downregulation of renal sodium transporters and tonicity-responsive enhancer binding protein by long-term treatment with cyclosporin A

Tonicity-responsive enhancer binding protein (TonEBP) is a transcriptional activator that is regulated by ambient tonicity. TonEBP protects the renal medulla from the deleterious effects of hyperosmolality and regulates the urinary concentration by stimulating aquaporin-2 and urea transporters. The therapeutic use of cyclosporin A (CsA) is limited by nephrotoxicity that is manifested by reduced GFR, fibrosis, and tubular defects, including reduced urinary concentration. It was reported recently that long-term CsA treatment was associated with decreased renal expression of TonEBP target genes, including aquaporin-2, urea transporter, and aldose reductase. This study tested the hypothesis that long-term CsA treatment reduces the salinity/tonicity of the renal medullary interstitium as a result of inhibition of active sodium transporters, leading to downregulation of TonEBP. CsA treatment for 7 d did not affect TonEBP or renal function. Whereas expression of sodium transporters was altered, the medullary tonicity seemed unchanged. Conversely, 28 d of CsA treatment led to downregulation of TonEBP and overt nephrotoxicity. The downregulation of TonEBP involved reduced expression, cytoplasmic shift, and reduced transcription of its target genes. This was associated with reduced expression of active sodium transporters-sodium/potassium/chloride transporter type 2 (NKCC2), sodium/chloride transporter, and Na(+),K(+)-ATPase-along with increased sodium excretion and reduced urinary concentration. Infusion of vasopressin restored the expression of NKCC2 in the outer medulla as well as the expression and the activity of TonEBP. It is concluded that the downregulation of TonEBP in the setting of long-term CsA administration is secondary to the reduced tonicity of the renal medullary interstitium.

Transcriptional activator TonE-binding protein in cellular protection and differentiation

The TonE-binding protein (TonEBP) is a transcriptional activator in the Rel family that includes NFkappaB and NFAT. TonEBP is critical for the development and function of the renal medulla, which is a major regulator of water homeostasis. TonEBP is also implicated in diabetic nephropathy and inflammation. Established methods for biochemical and histochemical detection and functional analysis of TonEBP, including identification of novel TonEBP target genes, are described for those who are interested in investigating function and regulation of TonEBP.

Comparison of experimental lung injury from acute renal failure with injury due to sepsis

BACKGROUND

Acute renal failure (ARF) and acute respiratory distress syndrome (ARDS) coexist frequently, and the mortality rate of this combination is very high. It is well established that cytokines and chemokines play a major role in the pathogenesis of ARDS. In addition, heat shock proteins (HSPs) have been shown to be protective against ARDS.

OBJECTIVES

The purpose of this study was to investigate the pathophysiology of ARDS in two different conditions, sepsis and ARF.

METHODS

We examined five different rat animal models including sham-operated control, sepsis and three ARF models induced by renal ischemia/reperfusion injury, bilateral nephrectomy or bilateral ligation of renal pedicles. We analyzed pulmonary histology, pulmonary vascular permeability, cellular infiltration, and expression of cytokines, chemokines and HSPs.

RESULTS

Like sepsis, the three forms of ARF led to ARDS, as manifested by increased pulmonary vascular permeability and histological changes consistent with ARDS. On the other hand, ARF and sepsis differed in that ARF was associated with markedly lower levels of pulmonary cellular infiltration. Furthermore, while pulmonary expression of tumor necrosis factor-alpha increased in sepsis, cytokine-induced neutrophil chemoattractant 2 increased in nephrectomized rats indicating that different inflammatory mediators were involved in the injury mechanism. Finally, pulmonary expression of multiple HSPs including HSP27-1, HSP70, HSP70-4, HSP70-8 and HSP90 was significantly different between the two conditions.

CONCLUSIONS

We conclude that the pathophysiology of ARDS following ARF is distinct from that in sepsis. ARF-induced ARDS is characterized by a low level of cellular infiltration, induction of cytokine-induced neutrophil chemoattractant 2, and a discrete expression profile of HSPs.

How tonicity regulates genes: story of TonEBP transcriptional activator

TonEBP stimulates genes whose products drive cellular accumulation of organic osmolytes and HSP70, which protect cells from the deleterious effects of hypertonicity and urea, respectively. Mice deficient in the TonEBP gene display severe atrophy of the renal medulla because cells failed to adapt to the hyperosmolality. Emerging data suggest that TonEBP plays a key role in the urinary concentrating mechanism by stimulating the UT-A urea transporters and possibly AQP2 water channel. Thus, TonEBP is an essential regulator in the urinary concentrating mechanism. Studies on structural basis of TonEBP function have revealed the structure of the DNA binding domain, and defined the transactivation domains. Molecular mechanisms underlying the nucleocytoplasmic trafficking, transactivation, and phosphorylation in response to changes in tonicity need to be understood in molecular detail. Such knowledge is needed for the identification of the sensor that detects changes in ambient tonicity and signals to TonEBP.

Tonicity-responsive enhancer binding protein is an essential regulator of aquaporin-2 expression in renal collecting duct principal cells

Tonicity-responsive enhancer binding protein (TonEBP) plays a key role in protecting renal cells from hypertonic stress by stimulating transcription of specific genes. Under hypertonic conditions, TonEBP activity is enhanced via increased nuclear translocation, transactivation, and abundance. It was reported previously that hypertonicity exerted a dual, time-dependent effect on vasopressin-inducible aquaporin-2 (AQP2) expression in immortalized mouse collecting duct principal cells (mpkCCDcl4). Whereas AQP2 abundance decreased after 3 h of hyperosmotic challenge, it increased after 24 h of hypertonic challenge. This study investigated the role that TonEBP may play in these events by subjecting mpkCCDcl4 cells to 3 or 24 h of hypertonic challenge. Hypertonic challenge increased TonEBP mRNA and protein content and enhanced TonEBP activity as illustrated by both increased TonEBP-dependent luciferase activity and mRNA expression of several genes that are targeted by TonEBP. Irrespective of the absence or presence of vasopressin, decreased TonEBP activity in cells that were transfected with either TonEBP small interfering RNA or an inhibitory form of TonEBP strongly reduced AQP2 mRNA and protein content under iso-osmotic conditions and blunted the increase of AQP2 abundance that was induced after 24 h of hypertonic challenge. Conversely, decreased TonEBP activity did not significantly alter reduced expression of AQP2 mRNA that was induced by 3 h of hypertonic challenge. Mutation of a TonE enhancer element located 489 bp upstream of the AQP2 transcriptional start site abolished the hypertonicity-induced increase of luciferase activity in cells that expressed AQP2 promoter-luciferase plasmid constructs, indicating that TonEBP influences AQP2 transcriptional activity at least partially by acting directly on the AQP2 promoter. These findings demonstrate that in collecting duct principal cells, TonEBP plays a central role in regulating AQP2 expression by enhancing AQP2 gene transcription.

Antidiuretic action of oxytocin is associated with increased urinary excretion of aquaporin-2

BACKGROUND

The antidiuretic effect of oxytocin in humans is controversial. Urinary excretion of aquaporin-2 (AQP2) can be used as an index of the action of vasopressin on the kidney. We investigated whether exogenous oxytocin affects urinary concentration and urinary AQP2 excretion in human beings.

METHODS

Oxytocin was administered intravenously at a rate of 20 mU/min in 10 healthy volunteers, seven patients with central diabetes insipidus (CDI) and three patients with nephrogenic diabetes insipidus (NDI). On the next day, 2 micro g of 1-desamino-8-d-arginine vasopressin (dDAVP) was injected subcutaneously. Two-hour urine was collected before and after the administration of oxytocin and dDAVP, and urinary AQP2 was measured semi-quantitatively by western analysis.

RESULTS

Urine volume and free water clearance were decreased, and urine osmolality was increased by the administration of oxytocin or dDAVP in the normal volunteers and CDI patients. Urinary AQP2 excretion was increased by oxytocin infusion in the normal volunteers (from 34+/-12 to 326+/-120 densitometry unit (DU)/2 h) and in the CDI group (from 8+/-2 to 227+/-92 DU/2 h) (P<0.05), but not in the NDI group. dDAVP also had a similar but more potent effect on the urinary excretion of AQP2 in the normal and CDI groups.

CONCLUSIONS

Oxytocin has an antidiuretic effect and increases the urinary excretion of AQP2 in humans whose urinary concentration mechanism is preserved. These results suggest that AQP2 might have a regulatory role in the antidiuretic action of oxytocin in humans.

Oxytocin induces apical and basolateral redistribution of aquaporin-2 in rat kidney

The aquaporin-2 (AQP2) water channel is mainly located in the apical plasma membrane of collecting duct epithelial cells, but there has been some evidence of a moderate amount of basolateral localization of AQP2 at least in the inner medullary collecting duct (IMCD). Previous in vitro microperfusion studies showed that oxytocin has an antidiuretic action, most likely mediated by the vasopressin V2 receptor (V2R) in rat IMCD. By using immunohistochemistry in kidneys from male Sprague-Dawley rats, we observed acute effects of oxytocin on AQP2 localization which were prevented by a V2R antagonist. After intraperitoneal administration of oxytocin (10 U), immunohistochemistry of IMCD revealed that AQP2 was shifted from diffuse cytoplasmic localization in controls to the apical and basolateral membrane domains in oxytocin-treated rats. This pattern of AQP2 redistribution was noted in connecting tubule, cortical collecting duct and outer medullary collecting duct as well as in IMCD, although the tendency to basolateral localization was somewhat less. The pretreatment using a V2R antagonist blocked redistribution of AQP2 in response to oxytocin. We conclude that oxytocin induces a V2R-mediated redistribution of AQP2-containing cytoplasmic vesicles to both apical and basolateral plasma membrane domains in rat kidney. Oxytocin may be one of the factors that accounts for vasopressin-independent AQP2 targeting in the kidney.

Secretory-defect distal renal tubular acidosis is associated with transporter defect in H(+)-ATPase and anion exchanger-1

Recent progress in molecular physiology has permitted us to understand pathophysiology of various channelopathies at a molecular level. The secretion of H(+) from alpha-intercalated cells is mediated by apical plasma membrane H(+)-ATPase and basolateral plasma membrane anion exchanger-1 (AE1). Studies have demonstrated the lack of H(+)-ATPase immunostaining in the intercalated cells in a few patients with distal renal tubular acidosis (dRTA). Mutations in H(+)-ATPase and AE1 gene have recently been reported to cause dRTA. This study extends the investigation of the role of transporter defect in dRTA by using immunohistochemical methods. Eleven patients with hyperchloremic metabolic acidosis were diagnosed functionally to have secretory-defect dRTA: urine pH >5.5 during acidemia, normokalemia or hypokalemia, and urine-to-blood pCO(2) <25 mmHg during bicarbonaturia. Renal biopsy tissue was obtained from each patient, and immunohistochemistry was carried out using antibodies to H(+)-ATPase and AE1. For comparison, renal tissues from the patients who had no evidences of distal acidification defect by functional studies were used: four with glomerulopathy or tubulointerstitial nephritis (disease controls) and three from nephrectomized kidneys for renal cell carcinoma (normal controls). The H(+)-ATPase immunoreactivity in alpha-intercalated cells was almost absent in all of the 11 patients with secretory-defect dRTA. In addition, 7 of 11 patients with secretory-defect dRTA were accompanied by negative AE1 immunoreactivity. In both disease controls and normal controls, the immunoreactivity of H(+)-ATPase and AE1 was strong in alpha-intercalated cells. In conclusion, significant defect in acid-base transporters is the major cause of secretory-defect dRTA.

Does albumin preinfusion potentiate diuretic action of furosemide in patients with nephrotic syndrome?

The aim of this cross-over study was to investigate whether albumin infusion before furosemide administration could potentiate the diuretic action of furosemide. Seven patients with nephrotic syndrome were given the following infusions in random order on two separate days: 1) a sham solution followed by 160 mg of furosemide, 2) 100 ml of 20% human albumin followed by 160 mg of furosemide. Urine and serum furosemide concentrations were measured by high-performance liquid chromatography. The increment of urine volume was greater in albumin preinfusion than in furosemide alone. However, the increments of sodium and chloride excretions between furosemide alone and albumin preinfusion were not different. No significant differences in the pharmacokinetic parameters between the two treatments were observed: area under the concentration-time curve (AUC: 12.7+/-2.2 vs 15.1+/-4.4 g/ml hr), total plasma clearance (253+/-41 vs 256+/-54 ml/min), volume of distribution (341+/-34 vs 494+/-153 ml/kg), elimination half life (4.0+/-1.1 vs 4.6+/-0.8 hr), and urine furosemide excretion of the administered amount (16.5+/-7.3 vs 7.5+/-1.6%). In conclusion, these data show that albumin preinfusion potentiated diuresis, but not natriuresis, of furosemide without any change in the pharmacokinetics of the agent in patients with nephrotic syndrome.

Clinical significance of the fractional excretion of anions in metabolic acidosis

The fractional excretion of anions has been proposed as a new index for the differential diagnosis of metabolic acidosis, identifying the properties of the conjugate base by examining the renal handling of the anion. Here, we investigated clinical significance of the fractional excretion of anions in pathophysiologic diagnosis of metabolic acidosis by measuring urine ammonium (NH4+) excretion, the ratio of A plasma anion gap/delta plasma HCO3- concentration (deltaAG/deltaHCO3-), and fractional excretion of anions in three different groups of metabolic acidosis: acid overproduction (8 patients with lactic acidosis, 8 with diabetic ketoacidosis, 3 with hippuric acidosis following glue sniffing), acid underexcretion (10 patients with chronic renal failure) and normal controls (10 normal volunteers who underwent 3-day NH4Cl loading). As expected, urine NH4+ excretion was higher in overproduction acidosis than in acid-loaded normal controls (88.1 +/- 12.3 vs. 54.0 +/- 3.7 mmol/day, p < 0.05), and it was lower in chronic renal failure than in acid-loaded normal controls (12.8 +/- 1.7 vs. 54.0 +/- 3.7 mmol/day, p < 0.05). The fractional excretion of anions had no difference between overproduction acidosis and chronic renal failure (41.2 +/- 42.8% vs. 41.0 +/- 8.1%). However, the fractional excretion of anions showed significant differences between the subgroups in acid overproduction (lactic acidosis, 4.7 +/- 0.3%; diabetic ketoacidosis, 45.8 +/- 3.1%; hippuric acidosis, 126.0 +/- 14.4%; p < 0.05). The ratio of plasma deltaAG/deltaHCO3- also exhibited significant differences between the subgroups in acid overproduction (lactic acidosis, 1.5 +/- 0.1; diabetic ketoacidosis, 1.0 +/- 0.1; hippuric acidosis, 0.3 +/- 0.1; p < 0.05). There was an inverse linear correlation between the fractional excretion of anions and the ratio of plasma deltaAG/deltaHCO3- (r2 =-0.89, p < 0.05). In conclusion, determination of the fractional excretion of anions may provide a useful clue to the differential diagnosis of metabolic acidosis caused by acid overproduction.

Evaluation of renal tubular functions in convalescent phase of hemorrhagic fever with renal syndrome

To evaluate renal tubular functions and to investigate the causative factors of urinary-concentrating defects in the late stage of hemorrhagic fever with renal syndrome (HFRS), 11 HFRS patients in the convalescent phase were studied and compared with 8 acute renal failure (ARF) patients in convalescence (disease controls) and 9 healthy adults preparing for kidney donation (normal controls, NC). Minimal urine osmolality induced by water loading was higher (p < 0.05) in HFRS (89.5 +/- 22.1 mosm/kg) and ARF patients (84.8 +/- 14.7 mosm/ kg) than in NC (47.8 +/- 4.6 mosm/kg), but the solute-free water clearance of HFRS patients (9.0 +/- 1.3%), measured at maximal diuresis, was not different from that of ARF patients (6.7 +/- 1.2%) or NC (10.5 +/- 1.4%). After 12-hour water deprivation + vasopressin stimulation, HFRS had lower urine osmolality (433.7 +/- 31.1 versus 850.0 +/- 35.1 mosm/kg; p < 0.05), urine-to-plasma osmolality ratio (1.47 +/- 0.11 versus 2.91 +/- 0.11; p < 0.05), and solute-free water reabsorption (0.53 +/- 0.07 versus 0.91 +/- 0.12%; p < 0.05) than NC. As compared with ARF patients (1.09 +/- 0.16%) or NC (1.49 +/- 0.16%), HFRS patients (0.43 +/- 0.20%) had lower solute-free water reabsorption measured at maximal antidiuresis induced by water deprivation + vasopressin stimulation + hypertonic saline infusion (p < 0.05). In HFRS, the plasma vasopressin level and plasma vasopressin/osmolality ratio increased from 3.9 +/- 0.8 to 6.1 +/- 1.1 pg/ml and from 0.013 +/- 0.003 to 0.020 +/- 0.004 pg/ml/mosm/kg after 12-hour water deprivation, respectively (p < 0.01). However, neither basal nor stimulated values of the plasma vasopressin level or plasma vasopressin/osmolality ratio was different among the 3 groups. HFRS patients were not different from ARF patients or NC in lithium clearance, urinary-acidifying capacity, and fractional excretions of sodium, potassium and bicarbonate. We conclude that in the convalescent phase of HFRS, the urinary-acidifying ability is not disturbed, the urinary-diluting defect is mild, and the urinary-concentrating capacity is obviously impaired. This study suggests that the most important factor contributing to the urinary-concentrating defect in HFRS is the reduced collecting duct responsiveness to vasopressin.

Metabolic acidosis and urinary acidification defect during the course of hemorrhagic fever with renal syndrome

To evaluate urinary acidification defect and its contribution to metabolic acidosis (MA) during hemorrhagic fever with renal syndrome (HFRS), we serially analyzed acid-base balance and urinary acidification indices in 10 HFRS patients. Data of the patients were compared with those of 8 normal volunteers (NC). MA was observed in 6 of 8 patients in the oliguric phase, 5 of 7 in the early diuretic phase, 8 of 10 in the late diuretic phase and 2 of 9 in the convalescent phase. HFRS patients with MA had a higher plasma anion gap in the oliguric and early diuretic phases than NC and a higher plasma Cl/Na ratio in the late diuretic phase than NC. As compared with acid-loaded NC, HFRS patients had a higher urine pH in the oliguric, early diuretic and late diuretic phases, a higher urine anion gap (UAG) in the oliguric and early diuretic phases and a lower urinary NH4+ excretory rate in the oliguric, early diuretic and late diuretic phases. Overt distal acidification defect was observed in 6 of 8 patients in the oliguric phase, 3 of 7 in the early diuretic phase, 5 of 10 in the late diuretic phase and none of 9 in the convalescent phase. None of the convalescent patients had latent acidification defect. In conclusion, urinary acidification defect is marked in the oliguric and diuretic phases of severe HFRS and may play a role in the development of a high anion gap (AG) metabolic acidosis in the earlier phase and hyperchloremic MA in the later phase, but rapidly recovers in the convalescent phase.

Absence of H(+)-ATPase in the intercalated cells of renal tissues in classic distal renal tubular acidosis

Proton-secretory defect is thought to be a major pathophysiologic mechanism leading to classic distal renal tubular acidosis (dRTA). However, there have been only two case reports demonstrating the absence of proton pump in renal tissues of the patients with Sjögren's syndrome. This study presents two cases of classic dRTA in which the absence of intact H(+)-ATPase was shown in their renal biopsy tissues by immunohistochemistry using a rabbit polyclonal antibody against the 70 kDa catalytic subunit of H(+)-ATPase from bovine brain clathrin-coated vesicles; one of the cases is diagnosed as subclinical Sjögren's syndrome and the other is idiopathic dRTA. A normal human kidney (NC) and the renal biopsy tissues from a patient with chronic tubulointerstitial nephritus whose proton secretory capacity was intact (DC) were compared as controls. The first patient, a 26-year-old woman, presented with quadriparesis. Her serologic tests revealed positive autoantibodies (ANA, SSA; SSB & RF), and a lower lip biopsy confirmed the diagnosis of Sjögren's syndrome. The second patient, a 43-year-old woman, who initially presented with a pathologic fracture of both femoral necks was referred for an evaluation for hypokalemia by the Department of Orthopedic Surgery. Her renal ultrasonography showed medullary calcification, and no autoantibodies were positive. Serum electrolytes and blood gas analyses of the two patients indicated severe hypokalemia and metabolic acidosis, and proton secretory defects were shown by a failure to lower the urine pH during marked acidemia induced by NH4Cl loading and an abnormally low urine-blood pCO2 difference during bicarbonate administration. While stainings with the anti-H(+)-ATPase antibody in NC and DC were strongly positive in intercalated cells in the connecting tubules and collecting ducts, the tissues from both patients with dRTA were devoid of any anti-H(+)-ATPase staining in the intercalated cells. These results support that the pathophysiologic basis of impaired H+ secretion in idiopathic classic dRTA as well as Sjögren's syndrome is the absence of intact H(+)-ATPase pumps in the intercalated cells.

Temporal changes and reversibility of carbamylated hemoglobin in renal failure

The detection of carbamylated hemoglobin (CarHb) is known to be useful in determination of the chronicity of uremia. However, the time course of the in vivo reaction between isocyanic acid and terminal valine residues of the hemoglobin chain is not clearly defined. To assess the temporal relationship and reversibility of carbamylation, we prospectively measured CarHb as micrograms of valine hydantoin per gram of hemoglobin (microg VH/g Hb) by high-performance liquid chromatography in 37 patients with acute renal failure (ARF), 53 patients with chronic renal failure (CRF), and six patients with successful kidney transplant. Patients with ARF had a lower median CarHb concentration (53.2 microg VH/g Hb; range, 24.6 to 97.1 microg VH/g Hb) than those with CRF (115.0 microg VH/g Hb; range, 34.6 to 286.5 microg VH/g Hb; P < 0.01), but had a higher value (53.2 microg VH/g Hb; range, 24.6 to 97.1 microg VH/g Hb) than 31 normal controls (36.6 microg VH/g Hb; range, 19.9 to 62.9 microg VH/g Hb; P < 0.05). In patients with ARF, the CarHb concentration positively correlated with the number of days of illness (r = 0.74; P < 0.01). The patients with ARF of 10 or more days' duration had a higher CarHb concentration (68.7 microg VH/g Hb; range, 36.0 to 93.9 microg VH/g Hb) than those with a shorter duration of ARF (33.7 microg VH/g Hb; range, 24.6 to 55.8 microg VH/g Hb; P < 0.01) despite similar blood urea nitrogen and serum creatinine values. However, they had a lower concentration of CarHb (68.7 microg VH/g Hb; range, 36.0 to 93.9 microg VH/g Hb) than CRF patients with comparable serum creatinine values (112.5 microg VH/g Hb; range, 34.6 to 286.5 microg VH/g Hb; P < 0.01). In patients with a kidney transplant, CarHb concentration declined by 19.7% (range, 12.3% to 35.6%) within 2 to 3 weeks after receiving the graft, while the level of hemoglobin increased by 25% (range, 4.0% to 46.6%) during the same period. Therefore, the total blood CarHb (CarHb x hemoglobin concentration) was not significantly changed. We concluded that the in vivo reaction of carbamylation of hemoglobin progressed during the period of uremia, and there might exist some irreversible preformed CarHb in advanced stages of CRF.