An in vivo method for adenovirus-mediated transduction of thick ascending limbs

Gene and epigenetic editing in the treatment of primary ciliopathies

Primary ciliopathies are inherited human disorders that arise from mutations in ciliary genes. They represent a spectrum of severe, incurable phenotypes, differentially involving several organs, including the kidney and the eye. The development of gene-based therapies is opening up new avenues for the treatment of ciliopathies. Particularly attractive is the possibility of correcting in situ the causative genetic mutation, or pathological epigenetic changes, through the use of gene editing tools. Due to their versatility and efficacy, CRISPR/Cas-based systems represent the most promising gene editing toolkit for clinical applications. However, delivery and specificity issues have so far held back the translatability of CRISPR/Cas-based therapies into clinical practice, especially where systemic administration is required. The eye, with its characteristics of high accessibility and compartmentalization, represents an ideal target for in situ gene correction. Indeed, studies for the evaluation of a CRISPR/Cas-based therapy for in vivo gene correction to treat a retinal ciliopathy have reached the clinical stage. Further technological advances may be required for the development of in vivo CRISPR-based treatments for the kidney. We discuss here the possibilities and the challenges associated to the implementation of CRISPR/Cas-based therapies for the treatment of primary ciliopathies with renal and retinal phenotypes.

Stretch-Induced Increases in Intracellular Ca Stimulate Thick Ascending Limb O2- Production and Are Enhanced in Dahl Salt-Sensitive Rats

Mechanical stretch raises intracellular Ca (Ca_i) in many cell types. Luminal flow-derived stretch stimulates O₂^- production by thick ascending limbs (THALs). Renal O₂^- is greater in Dahl salt-sensitive (SS) than salt-resistant (SR) rats. We hypothesized that mechanical stretch stimulates Ca influx via TRPV4 (transient receptor potential vanilloid type 4) which in turn raises Ca_i in THALs; these increases in Ca_i are necessary for stretch to augment O₂^- production; and stretch-stimulated, and therefore flow-induced, O₂^- production is enhanced in SS compared with SR THALs due to elevated Ca influx and increased Ca_i. Ca_i and O₂^- were measured in SS and SR THALs from rats on normal salt using Fura2-acetoxymethyl ester and dihydroethidium, respectively. Stretch raised Ca_i in SS by 270.4±48.9 nmol/L and by 123.6±27.0 nmol/L in SR THALs (P<0.02). Removing extracellular Ca eliminated the increases and differences in Ca_i between strains. Knocking down TRPV4 in SS THALs reduced stretch-induced Ca_i to SR levels (SS: 92.0±15.9 nmol/L; SR: 123.6±27.0 nmol/L). RN1734, a TRPV4 inhibitor, blunted stretch-elevated Ca_i by ≈75% and ≈66% in SS (P<0.03) and SR (P<0.04), respectively. Stretch augmented O₂^- production by 58.6±10.2 arbitrary fluorescent units/min in SS and by 24.4±2.6 arbitrary fluorescent units/min in SR THALs (P<0.05). Removal of extracellular Ca blunted stretch-induced increases in O₂^- and eliminated differences between strains. RN1734 reduced stretch-induced O₂^- by ≈70% in SS (P<0.005) and ≈60% in SR (P<0.01). Conclusions are as follows: (1) stretch activates TRPV4, which raises Ca_i in THALs; (2) the increase in Ca_i stimulates O₂^- production; and (3) stretch-induced O₂^- production is enhanced in SS THALs due to greater increases in Ca_i.

Gene therapy research for kidney diseases

A resurgence in the development of newer gene therapy systems has led to recent successes in the treatment of B cell cancers, retinal degeneration and neuromuscular atrophy. Gene therapy offers the ability to treat the patient at the root cause of their malady by restoring normal gene function and arresting the pathological progression of their genetic disease. The current standard of care for most genetic diseases is based upon the symptomatic treatment with polypharmacy while minimizing any potential adverse effects attributed to the off-target and drug-drug interactions on the target or other organs. In the kidney, however, the development of gene therapy modifications to specific renal cells has lagged far behind those in other organ systems. Some positive strides in the past few years provide continued enthusiasm to invest the time and effort in the development of new gene therapy vectors for medical intervention to treat kidney diseases. This mini-review will systematically describe the pros and cons of the most commonly tested gene therapy vector systems derived from adenovirus, retrovirus, and adeno-associated virus and provide insight about their potential utility as a therapy for various types of genetic diseases in the kidney.

Role of Alström syndrome 1 in the regulation of blood pressure and renal function

Elevated blood pressure (BP) and renal dysfunction are complex traits representing major global health problems. Single nucleotide polymorphisms identified by genome-wide association studies have identified the Alström syndrome 1 (ALMS1) gene locus to render susceptibility for renal dysfunction, hypertension, and chronic kidney disease (CKD). Mutations in the ALMS1 gene in humans causes Alström syndrome, characterized by progressive metabolic alterations including hypertension and CKD. Despite compelling genetic evidence, the underlying biological mechanism by which mutations in the ALMS1 gene lead to the above-mentioned pathophysiology is not understood. We modeled this effect in a KO rat model and showed that ALMS1 genetic deletion leads to hypertension. We demonstrate that the link between ALMS1 and hypertension involves the activation of the renal Na+/K+/2Cl- cotransporter NKCC2, mediated by regulation of its endocytosis. Our findings establish a link between the genetic susceptibility to hypertension, CKD, and the expression of ALMS1 through its role in a salt-reabsorbing tubular segment of the kidney. These data point to ALMS1 as a potentially novel gene involved in BP and renal function regulation.

Prospects of siRNA applications in regenerative medicine

Small interfering RNA (siRNA) has established its reputation in the field of tissue engineering owing to its ability to silence the proteins that inhibit tissue regeneration. siRNA is capable of regulating cellular behavior during tissue regeneration processes. The concept of using siRNA technology in regenerative medicine derived from its ability to inhibit the expression of target genes involved in defective tissues and the possibility to induce the expression of tissue-inductive factors that improve the tissue regeneration process. To date, siRNA has been used as a suppressive biomolecule in different tissues, such as nervous tissue, bone, cartilage, heart, kidney, and liver. Moreover, various delivery systems have been applied in order to deliver siRNA to the target tissues. This review will provide an in-depth discussion on the development of siRNA and their delivery systems and mechanisms of action in different tissues.

Glomeruli or interstitium targeted by inter-renal injections supplemented by electroporation: Still a useful tool in renal research

BACKGROUND

Studies concerning proteins are always a crucial part of renal research. As a result of current technologies, scientists have mastered several techniques for generating genetically modified animals. However, in most cases, accessing these animals is still time-consuming and often expensive. This makes the alteration of protein expression by in vivo plasmid transfection an easily-accessible alternative. However, there is still no comprehensive study describing where plasmids would be expressed when they are injected into the kidneys.

METHODS

We injected pEGFP-N1 into rats via intra-/inter-renal channels and detected green fluorescent protein (GFP) by immunohistochemistry and immunofluorescence to localize plasmid expression.

RESULTS

Seven days post-injection, we found that GFP was expressed in the glomeruli when pEGFP-N1 was injected via the renal artery or vein enhanced by electroporation and in the interstitium following injection via the ureter. Other channels, including intraperitoneal, subcapsule and parenchymal injection, only led to scattered expression within the kidneys.

CONCLUSIONS

The present study provides evidence that plasmid transfection via the renal vessels is suitable for glomeruli research and that transfection via the ureter is appropriate for studies regarding interstitium lesions. Additionally, we provide evidence that plasmid transfection on live animals is still an applicable and useful tool, as well as being cost-effective and facile.

Vesicle-associated Membrane Protein 3 (VAMP3) Mediates Constitutive Trafficking of the Renal Co-transporter NKCC2 in Thick Ascending Limbs: ROLE IN RENAL FUNCTION AND BLOOD PRESSURE

Renal cells of the thick ascending limb (TAL) reabsorb NaCl via the apical Na⁺/K⁺/2Cl^- co-transporter NKCC2. Trafficking of NKCC2 to the apical surface regulates NKCC2-mediated NaCl absorption and blood pressure. The molecular mechanisms by which NKCC2 reaches the apical surface and their role in renal function and maintenance of blood pressure are poorly characterized. Here we report that NKCC2 interacts with the vesicle fusion protein VAMP3, and they co-localize at the TAL apical surface. We observed that silencing VAMP3 in vivo blocks constitutive NKCC2 exocytic delivery, decreasing the amount of NKCC2 at the TAL apical surface. VAMP3 is not required for cAMP-stimulated NKCC2 exocytic delivery. Additionally, genetic deletion of VAMP3 in mice decreased total expression of NKCC2 in the TAL and lowered blood pressure. Consistent with these results, urinary excretion of water and electrolytes was higher in VAMP3 knock-out mice, which produced more diluted urine. We conclude that VAMP3 interacts with NKCC2 and mediates its constitutive exocytic delivery to the apical surface. Additionally, VAMP3 is required for normal NKCC2 expression, renal function, and blood pressure.

TRPV4 mediates flow-induced increases in intracellular Ca in medullary thick ascending limbs

Medullary thick ascending limbs (mTAL) regulate Na balance and therefore blood pressure. We previously showed that cell swelling and luminal flow activates the mechanosensitive channel TRPV4 in mTAL.

AIM

We hypothesized that TRPV4 mediates flow-induced increases in intracellular Ca (Cai) in rat mTALs.

METHODS

We performed ratiometric measurements of Cai in perfused mTALs.

RESULTS

Increasing luminal flow from 0 to 20 nL min(-1) caused Cai to peak 231 ± 29 nmol L(-1) above basal concentrations (n = 18). The general TRPV inhibitor ruthenium red at 15 and 50 μmol L(-1) reduced peak Cai by 41 ± 9 (P < 0.01; n = 5) and 77 ± 10% (P < 0.02; n = 6). The selective TRPV4 inhibitor RN1734 at 10 and 50 μmol L(-1) reduced peak Cai by 46 ± 11 (P < 0.01; n = 7) and 76 ± 5% (P < 0.02; n = 5) respectively. To specifically target TRPV4, mTALs were transduced with adenoviruses expressing TRPV4 small hairpin (sh) RNA. In non-transduced control mTALs, luminal flow generated a peak increase in Cai of 111 ± 21 nmol L(-1) (n = 8). In TRPV4shRNA-transduced mTALs, the Cai peak was reduced to 56 ± 8 nmol L(-1) (P < 0.03, n = 9). Removing extracellular Ca completely abolished flow-induced increases in Cai. Increasing luminal flow in the presence of hexokinase 20 (U mL(-1) ) to scavenge extracellular ATP did not modify significantly the increases in Cai induced by luminal flow. Finally, we studied the effect of the TRPV4 selective agonist GSK1016790A on Cai. In the absence of luminal flow, GSK1016790A (10 nmol L(-1) ) increased Cai from 60 ± 11 nmol L(-1) to 262 ± 71 nmol L(-1) (P < 0.05; n = 7).

CONCLUSION

We conclude that flow-induced increases in Cai are mediated primarily by TRPV4 in the rat mTAL.

Remedial applications of silencing ribonucleic acids and modalities for its delivery to the kidneys--a review

BACKGROUND

The Kidney has been the target organ for the delivery of silencing ribonucleic acids (silencing RNA) administered systemically in comparison to other body tissues.

MATERIALS AND METHOD

In this review, we discussed different approaches made to delivering proteins to the kidneys in different conditions like normal and pathological defects. Data from clinical experiments have been used to discuss and support the administration of silencing RNA for the treatment of kidney diseases.

RESULTS

Results were achieved using the available genome wide RNA libraries.

CONCLUSION

The research results are helpful in application to 3D and conventional models to find the involvement of signal pathways in kidney diseases.

Vesicle-associated membrane protein 2 (VAMP2) but Not VAMP3 mediates cAMP-stimulated trafficking of the renal Na+-K+-2Cl- co-transporter NKCC2 in thick ascending limbs

In the kidney, epithelial cells of the thick ascending limb (TAL) reabsorb NaCl via the apical Na⁺/K⁺/2Cl⁻ co-transporter NKCC2. Steady-state surface NKCC2 levels in the apical membrane are maintained by a balance between exocytic delivery, endocytosis, and recycling. cAMP is the second messenger of hormones that enhance NaCl absorption. cAMP stimulates NKCC2 exocytic delivery via protein kinase A (PKA), increasing steady-state surface NKCC2. However, the molecular mechanism involved has not been studied. We found that several members of the SNARE family of membrane fusion proteins are expressed in TALs. Here we report that NKCC2 co-immunoprecipitates with VAMP2 in rat TALs, and they co-localize in discrete domains at the apical surface. cAMP stimulation enhanced VAMP2 exocytic delivery to the plasma membrane of renal cells, and stimulation of PKA enhanced VAMP2-NKCC2 co-immunoprecipitation in TALs. In vivo silencing of VAMP2 but not VAMP3 in TALs blunted cAMP-stimulated steady-state surface NKCC2 expression and completely blocked cAMP-stimulated NKCC2 exocytic delivery. VAMP2 was not involved in constitutive NKCC2 delivery. We concluded that VAMP2 but not VAMP3 selectively mediates cAMP-stimulated NKCC2 exocytic delivery and surface expression in TALs. We also demonstrated that cAMP stimulation enhances VAMP2 exocytosis and promotes VAMP2 interaction with NKCC2.

TRPV4 activation mediates flow-induced nitric oxide production in the rat thick ascending limb

Nitric oxide (NO) regulates renal function. Luminal flow stimulates NO production in the thick ascending limb (TAL). Transient receptor potential vanilloid 4 (TRPV4) is a mechano-sensitive channel activated by luminal flow in different types of cells. We hypothesized that TRPV4 mediates flow-induced NO production in the rat TAL. We measured NO production in isolated, perfused rat TALs using the fluorescent dye DAF FM. Increasing luminal flow from 0 to 20 nl/min stimulated NO from 8 ± 3 to 45 ± 12 arbitrary units (AU)/min (n = 5; P < 0.05). The TRPV4 antagonists, ruthenium red (15 μmol/l) and RN 1734 (10 μmol/l), blocked flow-induced NO production. Also, luminal flow did not increase NO production in the absence of extracellular calcium. We also studied the effect of luminal flow on NO production in TALs transduced with a TRPV4shRNA. In nontransduced TALs luminal flow increased NO production by 47 ± 17 AU/min (P < 0.05; n = 5). Similar to nontransduced TALs, luminal flow increased NO production by 39 ± 11 AU/min (P < 0.03; n = 5) in TALs transduced with a control negative sequence-shRNA while in TRPV4shRNA-transduced TALs, luminal flow did not increase NO production (Δ10 ± 15 AU/min; n = 5). We then tested the effect of two different TRPV4 agonists on NO production in the absence of luminal flow. 4α-Phorbol 12,13-didecanoate (1 μmol/l) enhanced NO production by 60 ± 11 AU/min (P < 0.002; n = 7) and GSK1016790A (10 ηmol/l) increased NO production by 52 ± 15 AU/min (P < 0.03; n = 5). GSK1016790A (10 ηmol/l) did not stimulate NO production in TRPV4shRNA-transduced TALs. We conclude that activation of TRPV4 channels mediates flow-induced NO production in the rat TAL.

In vivo and ex vivo analysis of tubule function

Analysis of tubule function with in vivo and ex vivo approaches has been instrumental in revealing renal physiology. This work allows assignment of functional significance to known gene products expressed along the nephron, primary of which are proteins involved in electrolyte transport and regulation of these transporters. Not only we have learned much about the key roles played by these transport proteins and their proper regulation in normal physiology but also the combination of contemporary molecular biology and molecular genetics with in vivo and ex vivo analysis opened a new era of discovery informative about the root causes of many renal diseases. The power of in vivo and ex vivo analysis of tubule function is that it preserves the native setting and control of the tubule and proteins within tubule cells enabling them to be investigated in a "real-life" environment with a high degree of precision. In vivo and ex vivo analysis of tubule function continues to provide a powerful experimental outlet for testing, evaluating, and understanding physiology in the context of the novel information provided by sequencing of the human genome and contemporary genetic screening. These tools will continue to be a mainstay in renal laboratories as this discovery process continues and as we continue to identify new gene products functionally compromised in renal disease.

An adenovirus vector incorporating carbohydrate binding domains utilizes glycans for gene transfer

BACKGROUND

Vectors based on human adenovirus serotype 5 (HAdV-5) continue to show promise as delivery vehicles for cancer gene therapy. Nevertheless, it has become clear that therapeutic benefit is directly linked to tumor-specific vector localization, highlighting the need for tumor-targeted gene delivery. Aberrant glycosylation of cell surface glycoproteins and glycolipids is a central feature of malignant transformation, and tumor-associated glycoforms are recognized as cancer biomarkers. On this basis, we hypothesized that cancer-specific cell-surface glycans could be the basis of a novel paradigm in HAdV-5-based vector targeting.

METHODOLOGY/PRINCIPAL FINDINGS

As a first step toward this goal, we constructed a novel HAdV-5 vector encoding a unique chimeric fiber protein that contains the tandem carbohydrate binding domains of the fiber protein of the NADC-1 strain of porcine adenovirus type 4 (PAdV-4). This glycan-targeted vector displays augmented CAR-independent gene transfer in cells with low CAR expression. Further, we show that gene transfer is markedly decreased in cells with genetic glycosylation defects and by inhibitors of glycosylation in normal cells.

CONCLUSIONS/SIGNIFICANCE

These data provide the initial proof-of-concept for HAdV-5 vector-mediated gene delivery based on the presence of cell-surface carbohydrates. Further development of this new targeting paradigm could provide targeted gene delivery based on vector recognition of disease-specific glycan biomarkers.

NADPH oxidase 4 mediates flow-induced superoxide production in thick ascending limbs

We previously showed that luminal flow stimulates thick ascending limb (TAL) superoxide (O(2)(-)) production by stretching epithelial cells and increasing NaCl transport, and reported that the major source of flow-induced O(2)(-) is NADPH oxidase (Nox). However, the specific Nox isoform involved is unknown. Of the three isoforms expressed in the kidney-Nox1, Nox2, and Nox4-we hypothesized that Nox4 is responsible for flow-induced O(2)(-) production in TALs. Measurable flow-induced O(2)(-) production at physiological flow rates of 0, 5, 10, and 20 nl/min was 5 ± 1, 9 ± 2, 36 ± 6, and 66 ± 8 AU/s, respectively. RT-PCR detected mRNA for all three Nox isoforms in the TAL. The order of RNA abundance was Nox2 > Nox4 >>> Nox1. Since all three isoforms are expressed in TALs and pharmacological inhibitors are not selective, we used rats transduced with siRNA and knockout mice. Nox4 siRNA knocked down Nox4 mRNA expression by 63 ± 7% but did not reduce Nox1 or Nox2 mRNA. Flow-induced O(2)(-) was 18 ± 9 AU/s in TALs transduced with Nox4 siRNA compared with 77 ± 9 AU/s in tubules transduced with scrambled siRNA. Flow-induced O(2)(-) was 81 ± 5 AU/s in Nox2 knockout mice compared with 83 ± 13 AU/s in wild-type mice. In TALs transduced with Nox1 siRNA, flow-induced O(2)(-) was 82 ± 7 AU/s. We conclude that Nox4 mediates flow-induced O(2)(-) production in TALs.

Dynamin2, clathrin, and lipid rafts mediate endocytosis of the apical Na/K/2Cl cotransporter NKCC2 in thick ascending limbs

Steady-state surface levels of the apical Na/K/2Cl cotransporter NKCC2 regulate NaCl reabsorption by epithelial cells of the renal thick ascending limb (THAL). We reported that constitutive endocytosis of NKCC2 controls NaCl absorption in native THALs; however, the pathways involved in NKCC2 endocytosis are unknown. We hypothesized that NKCC2 endocytosis at the apical surface depends on dynamin-2 and clathrin. Measurements of steady-state surface NKCC2 and the rate of NKCC2 endocytosis in freshly isolated rat THALs showed that inhibition of endogenous dynamin-2 with dynasore blunted NKCC2 endocytosis by 56 ± 11% and increased steady-state surface NKCC2 by 67 ± 27% (p < 0.05). Expression of the dominant negative Dyn2K44A in THALs slowed the rate of NKCC2 endocytosis by 38 ± 8% and increased steady-state surface NKCC2 by 37 ± 8%, without changing total NKCC2 expression. Inhibition of clathrin-mediated endocytosis with chlorpromazine blunted NKCC2 endocytosis by 54 ± 6%, while preventing clathrin from interacting with synaptojanin also blunted NKCC2 endocytosis by 52 ± 5%. Disruption of lipid rafts blunted NKCC2 endocytosis by 39 ± 4% and silencing caveolin-1 by 29 ± 4%. Simultaneous inhibition of clathrin- and lipid raft-mediated endocytosis completely blocked NKCC2 internalization. We concluded that dynamin-2, clathrin, and lipid rafts mediate NKCC2 endocytosis and maintain steady-state apical surface NKCC2 in native THALs. These are the first data identifying the endocytic pathway for apical NKCC2 endocytosis.

Angiotensin II stimulates superoxide production in the thick ascending limb by activating NOX4

Angiotensin II (ANG II) stimulates production of superoxide (O(2)(-)) by NADPH oxidase (NOX) in medullary thick ascending limbs (TALs). There are three isoforms of the catalytic subunit (NOX1, 2, and 4) known to be expressed in the kidney. We hypothesized that NOX2 mediates ANG II-induced O(2)(-) production by TALs. To test this, we measured NOX1, 2, and 4 mRNA and protein by RT-PCR and Western blot in TAL suspensions from rats and found three catalytic subunits expressed in the TAL. We measured O(2)(-) production using a lucigenin-based assay. To assess the contribution of NOX2, we measured ANG II-induced O(2)(-) production in wild-type and NOX2 knockout mice (KO). ANG II increased O(2)(-) production by 346 relative light units (RLU)/mg protein in the wild-type mice (n = 9; P < 0.0007 vs. control). In the knockout mice, ANG II increased O(2)(-) production by 290 RLU/mg protein (n = 9; P < 0.007 vs. control). This suggests that NOX2 does not contribute to ANG II-induced O(2)(-) production (P < 0.6 WT vs. KO). To test whether NOX4 mediates the effect of ANG II, we selectively decreased NOX4 expression in rats using an adenovirus that expresses NOX4 short hairpin (sh)RNA. Six to seven days after in vivo transduction of the kidney outer medulla, NOX4 mRNA was reduced by 77%, while NOX1 and NOX2 mRNA was unaffected. In control TALs, ANG II stimulated O(2)(-) production by 96%. In TALs transduced with NOX4 shRNA, ANG II-stimulated O(2)(-) production was not significantly different from the baseline. We concluded that NOX4 is the main catalytic isoform of NADPH oxidase that contributes to ANG II-stimulated O(2)(-) production by TALs.

Intrarenal transfer of an intracellular fluorescent fusion of angiotensin II selectively in proximal tubules increases blood pressure in rats and mice

The present study tested the hypothesis that intrarenal adenoviral transfer of an intracellular cyan fluorescent fusion of angiotensin II (ECFP/ANG II) selectively in proximal tubules of the kidney increases blood pressure by activating AT(1) (AT(1a)) receptors. Intrarenal transfer of ECFP/ANG II was induced in the superficial cortex of rat and mouse kidneys, and the sodium and glucose cotransporter 2 (sglt2) promoter was used to drive ECFP/ANG II expression selectively in proximal tubules. Intrarenal transfer of ECFP/ANG II induced a time-dependent, proximal tubule-selective expression of ECFP/ANG II in the cortex, which peaked at 2 wk and was sustained for 4 wk. ECFP/ANG II expression was low in the glomeruli and the entire medulla and was absent in the contralateral kidney or extrarenal tissues. At its peak of expression in proximal tubules at day 14, ANG II was increased by twofold in the kidney (P < 0.01) and more than threefold in proximal tubules (P < 0.01), but remained unchanged in plasma or urine. Systolic blood pressure was increased in ECFP/ANG II-transferred rats by 28 ± 6 mmHg (P < 0.01), whereas fractional sodium excretion was decreased by 20% (P < 0.01) and fractional lithium excretion was reduced by 24% (P < 0.01). These effects were blocked by losartan and prevented in AT(1a) knockout mice. Transfer of a scrambled ECFP/ANG IIc had no effects on blood pressure, kidney, and proximal tubule ANG II, or sodium excretion. These results provide evidence that proximal tubule-selective transfer of an intracellular ANG II fusion protein increases blood pressure by activating AT(1a) receptors and increasing sodium reabsorption in proximal tubules.

Angiotensin II stimulates thick ascending limb superoxide production via protein kinase C(α)-dependent NADPH oxidase activation

Angiotensin II (Ang II) stimulates thick ascending limb (TAL) O₂ production, but the receptor(s) and signaling mechanism(s)involved are unknown. The effect of Ang II on O₂. is generally attributed to the AT₁receptor. In some cells, Ang II stimulates protein kinase C (PKC), whose α isoform (PKCα) can activate NADPH oxidase. We hypothesized that in TALs, Ang II stimulates O₂. via AT₁and PKC α-dependent NADPH oxidase activation.In rat TALs, 1 nM Ang II stimulated O₂. from 0.760.17 to 1.97 0.21 nmol/min/mg (p < 0.001). An AT₁antagonist blocked the stimulatory effect of Ang II on O₂. (0.87 0.25 nmol/min/mg; p < 0.006), whereas an AT₂ antagonist had no effect (2.16 0.133 nmol/min/mg; p < 0.05 versus vehicle). Apocynin, an NADPH oxidase inhibitor, blocked Ang II-stimulated O₂by 90% (p <0.01). Ang II failed to stimulate O₂. in TALs from p47(phox) -/- mice (p < 0.02). Monitored by fluorescence resonance energy transfer, Ang II increased PKC activity from 0.02 0.03 to 0.13 0.02 arbitrary units (p < 0.03). A general PKC inhibitor, GF109203X, blocked the effect of Ang II on O₂(1.47 +/- .21 versus 2.72 +/- .47 nmol/min/mg with Ang II alone; p < 0.03). A PKCα- and ß-selective inhibitor, Gö6976, also blocked the stimulatory effect of Ang II on O₂. (0.59 +/- 0.15 versus 2.05 +/- 0.28 nmol/min/mg with Ang II alone; p < 0.001). To distinguish between PKC α and PKC ß, we used tubules expressing dominant-negative PKC α or -ß. In control TALs, Ang II stimulated O2. by 2.17 0.44 nmol/min/mg (p < 0.011). In tubules expressing dominant-negative PKC α, Ang II failed to stimulate O2. (change: -0.30 +/- 0.27 nmol/min/mg). In tubules expressing dominant-negative PKC ß1, Ang II stimulated O2. by 2.080.69 nmol/min/mg (p < 0.002). We conclude that Ang II stimulates TAL O₂production via activation of AT₁receptors and PKC α-dependent NADPH oxidase.

PKC-alpha mediates flow-stimulated superoxide production in thick ascending limbs

We showed that luminal flow increases net superoxide (O(2)(-)) production via NADPH oxidase in thick ascending limbs. Protein kinase C (PKC) activates NADPH oxidase activity in phagocytes, cardiomyocytes, aortic endothelial cells, vascular smooth muscle cells, and renal mesangial cells. However, the flow-activated pathway that induces NADPH oxidase activity in thick ascending limbs is unclear. We hypothesized that PKC mediates flow-stimulated net O(2)(-) production by thick ascending limbs. Initiation of flow (20 nl/min) increased net O(2)(-) production from 4 +/- 1 to 61 +/- 12 AU/s (P < 0.007; n = 5). The NADPH oxidase inhibitor apocynin completely blocked the flow-induced increase in net O(2)(-) production (2 +/- 1 vs. 1 +/- 1 AU/s; P > 0.05; n = 5). Flow-stimulated O(2)(-) was also blocked in p47(phox)-deficient mice. We measured flow-stimulated PKC activity with a fluorescence resonance energy transfer (FRET)-based membrane-targeted PKC activity reporter and found that the FRET ratio increased from 0.87 +/- 0.02 to 0.96 +/- 0.04 AU (P < 0.05; n = 6). In the absence of flow, the PKC activator phorbol 12-myristate 13-acetate (200 nM) enhanced net O(2)(-) production from 5 +/- 2 to 92 +/- 6 AU/s (P < 0.001; n = 6). The PKC-alpha- and betaI-selective inhibitor Gö 6976 (100 nM) decreased flow-stimulated net O(2)(-) production from 54 +/- 15 to 2 +/- 1 AU/s (P < 0.04; n = 5). Flow-induced net O(2)(-) production was inhibited in thick ascending limbs transduced with dominant-negative (dn)PKC-alpha but not dnPKCbetaI or LacZ (Delta = 11 +/- 3 AU/s for dnPKCalpha, 55 +/- 7 AU/s for dnPKCbetaI, and 63 +/- 7 AU/s for LacZ; P < 0.001; n = 6). We concluded that flow stimulates net O(2)(-) production in thick ascending limbs via PKC-alpha-mediated activation of NADPH oxidase.

Rac1 mediates NaCl-induced superoxide generation in the thick ascending limb

Superoxide (O(2)(-)) produced by NADPH oxidase regulates Na absorption and renal hemodynamics. Increased NaCl in the thick ascending limb (TAL) stimulates O(2)(-) generation. However, we do not know whether physiological changes in NaCl concentration augment O(2)(-) generation, nor do we know the mediator(s) involved. In other cells, Rac1, a regulatory subunit of NADPH oxidase, is activated by elevated NaCl. We hypothesized that increasing luminal NaCl within the physiological range activates Rac1 and NADPH oxidase and, thereby, increases O(2)(-) production. We increased NaCl from 10 to 57 mM in medullary TAL suspensions and used lucigenin to measure O(2)(-) generation and Western blot to measure Rac1 activity. Increasing NaCl stimulated O(2)(-) generation from 1.41 +/- 0.16 to 2.71 +/- 0.30 nmol O(2)(-) x min(-1) x mg protein(-1) (n = 6, P < 0.05). This increase was blocked by the Na-K-2Cl cotransporter inhibitor furosemide and the NADPH oxidase inhibitor apocynin. To examine the role of Rac1 in NaCl-induced O(2)(-) production, we measured Rac1 translocation by Western blot. When we added NaCl, Rac1 in the particulate fraction increased from 6.8 +/- 0.8 to 11.7 +/- 2.4% of total Rac1 (n = 7, P < 0.05). Then we measured O(2)(-) generation in the presence and absence of the Rac1 inhibitor. In the absence of the Rac1 inhibitor, NaCl increased O(2)(-) generation from 1.07 +/- 0.24 to 2.02 +/- 0.49 nmol O(2)(-) x min(-1) x mg protein(-1), and this increase was completely blocked by the inhibitor. Similarly, in vivo treatment of TALs with adenovirus expressing dominant-negative Rac1 decreased NaCl-induced O(2)(-) generation by 60% compared with control (0.33 +/- 0.04 vs. 0.81 +/- 0.17 nmol O(2)(-) x min(-1) x mg protein(-1), n = 6, P < 0.05). We concluded that physiological increases in NaCl stimulate TAL O(2)(-) generation by activating Rac1.

Akt1 mediates purinergic-dependent NOS3 activation in thick ascending limbs

Extracellular ATP regulates many physiological processes via release of nitric oxide (NO). ATP stimulates NO in thick ascending limbs (TALs), but the signaling cascade involved in the cells of this nephron segment, as well as many other types of cells, is poorly understood. We hypothesized that ATP enhances NO synthase (NOS) activity by stimulating PI3 kinase and Akt. We measured 1) NO in TALs using the NO-sensitive dye DAF-2 DA and 2) Akt activity by fluorescence resonance energy transfer and phosphorylation of Akt isoforms. ATP (100 microM) stimulated NO in wild-type mice [26 +/- 4 arbitrary units (AU)], but not in NOS3 -/- mice (2 +/- 2 AU; P < 0.04). In the presence of the NOS1- and NOS2-selective inhibitors 7-NI and 1400W, ATP stimulated NO by 30 +/- 2 and 33 +/- 3 AU, respectively (not significant vs. control). In the presence of the PI3 kinase inhibitor LY294002, ATP-increased NO was reduced by 85% (5 +/- 2 vs. 28 +/- 4 AU; P < 0.02). ATP alone increased Akt activity and this effect was significantly blocked by suramin, a P2 receptor antagonist. In the presence of an Akt-selective inhibitor, ATP-induced NO was blocked by 90 +/- 4%. ATP significantly stimulated Akt1 phosphorylation at Ser(473) by 91 +/- 13%, whereas Akt2 phosphorylation remained unchanged and Akt3 phosphorylation decreased. In vivo transduction of TALs with a dominant-negative Akt1 significantly decreased ATP-induced NO by 88 +/- 6%. We concluded that ATP increases NOS3-derived NO via Akt1 activation in the TAL.

Endothelin-1 inhibits thick ascending limb transport via Akt-stimulated nitric oxide production

Endothelin-1 inhibits sodium reabsorption in the thick ascending limb (THAL) via stimulation of nitric oxide (NO) production. The mechanism whereby endothelin-1 stimulates THAL NO is unknown. We hypothesized that endothelin-1 stimulates THAL NO production by activating phosphatidylinositol 3-kinase (PI3K), stimulating Akt activity, and phosphorylating NOS3 at Ser1177. This enhances NO production and inhibits sodium transport. We measured 1) NO production by fluorescence microscopy using DAF2-DA, 2) Akt activity using a fluorescence resonance energy transfer-based Akt reporter, 3) phosphorylated NOS3 and Akt by Western blotting, and 4) NKCC2 activity by fluorescence microscopy. In isolated THAL, endothelin-1 (1 nmol/liter) increased NO production from 0.23 +/- 0.24 to 2.81 +/- 0.32 fluorescence units/min (p < 0.001; n = 5) but failed to stimulate NO production in THALs isolated from NOS3-/- mice. Wortmannin (150 nmol/liter), a PI3K inhibitor, reduced endothelin-1-stimulated NO by 83% (0.49 +/- 0.13 versus 3.31 +/- 0.49 fluorescence units/min for endothelin-1 alone; p < 0.006; n = 5). Endothelin-1 stimulated Akt activity by 0.16 +/- 0.02 arbitrary units as measured by fluorescence resonance energy transfer (p < 0.001; n = 5) and increased phosphorylation of Akt at Ser473 by 56 +/- 11% (p < 0.002; n = 7). Dominant-negative Akt blocked endothelin-1-induced NO by 60 +/- 8% (p < 0.001 versus control; n = 6), and an Akt inhibitor had a similar effect. Endothelin-1 increased phosphorylation of NOS3 at Ser1177 by 89 +/- 24% (p < 0.01; n = 7) but had no effect on Ser633. Endothelin-1 inhibited NKCC2 activity, an effect that was blocked by dominant-negative Akt and NOS inhibition. We conclude that endothelin-1 stimulates THAL NO production by activating PI3K, stimulating Akt activity, and phosphorylating NOS3 at Ser1177. This enhances NO production and inhibits sodium transport.

[Development of nucleic acid transfection technology to the kidney]

The kidney is one of the most important organs that play a crucial role in homeostasis and, therefore, congenital or acquired renal dysfunction causes refractory diseases, i.e., Alport's syndrome, Fabry's disease, diabetic nephropathy, IgA nephropathy, kidney cancer, transplant glomerulopathy. Nucleic acid transfection technology to the kidney is indispensable for the progress of biomedical research and the realization of gene therapy and nucleic acid drug for renal diseases. Control of renal nucleic acid transfection was difficult because of the structural complexity; however, the study of recombinant virus, synthetic carrier and physical force-mediated nucleic acid transfection to the kidney has advanced. Recombinant virus and synthetic carrier-mediated methods require long-term block of the blood or urinary flow for efficient transfection of nucleic acid because of the rich blood flow of the kidney. In contrast, physical force-mediated methods that transfect with nucleic acid via transient membrane permeability do not apprehend ischemia-reperfusion injury and, therefore, may be beneficial for nucleic acid transfection to the kidney. In this article, we collect the information of therapeutic gene, target molecule of the nucleic acid drug and target cells for renal diseases and structural property of the kidney from the point of view of nucleic acid transfection. Additively, current status of nucleic acid transfection technology to the kidney is reviewed.

TRPV4 mediates hypotonicity-induced ATP release by the thick ascending limb

Extracellular ATP is an autocrine/paracrine factor that regulates renal function. Transient receptor potential vanilloid (TRPV) 4 is a cation channel that mediates release of autocrine/paracrine factors by acting as an osmosensor. The renal medulla, and therefore the thick ascending limb, is exposed to osmotic stress. We hypothesize that reduced osmolality stimulates ATP release from the thick ascending limb via transient receptor potential vanilloid (TRPV) 4 activation. We measured ATP release by medullary thick ascending limb suspensions after reducing bath osmolality from 350 to 323 mosmol/kgH2O, using the luciferin-luciferase assay. Decreasing osmolality stimulated ATP release compared with control (38.9+/-7.2 vs. 2.4+/-1.0 pmol/mg protein; n=6, P<0.01). To examine the role of TRPV4, we used 1) Ca-free solutions, 2) a TRPV4 inhibitor, 3) small interfering (si) RNA against TRPV4, and 4) a TRPV4 activator. Removal of Ca completely blocked osmolality-induced ATP release (42.2+/-5.9 vs. 2.6+/-1.5 pmol/mg protein; n=6, P<0.01). In the presence of the TRPV4-selective inhibitor ruthenium red, osmolality-induced ATP release was blocked by 73% (56.4+/-19.9 vs. 8.8+/-2.3 pmol/mg protein; n=6; P<0.03). In vivo treatment of thick ascending limbs with siRNA against TRPV4 decreased osmolality-induced ATP release by 62% (31.5+/-3.4 vs. 12.4+/-1.1 pmol/mg protein; n=6; P<0.01), while reducing TRPV4 expression by 74% compared with the nontreated kidney. Treatment with scrambled siRNA did not affect TRPV4 expression and/or osmolality-induced ATP release. Finally, in the absence of changes in osmolality, the specific TRPV4 agonist 4alpha-PDD increased ATP release (3.6+/-0.9 vs. 25.4+/-7.4 pmol/mg protein; n=6; P<0.04). We concluded that decreases in osmolality stimulate ATP release by thick ascending limbs and this effect is mediated by TRPV4 activation.

Regulation of thick ascending limb transport: role of nitric oxide

Nitric oxide (NO) plays a role in many physiological and pathophysiological processes. In the kidney, NO reduces renal vascular resistance, increases glomerular filtration rate, alters renin release, and inhibits transport along the nephron. The thick ascending limb is responsible for absorbing 20-30% of the filtered load of NaCl, much of the bicarbonate that escapes the proximal nephron, and a significant fraction of the divalent cations reclaimed from the forming urine. Additionally, this nephron segment plays a role in K+ homeostasis. This article will review recent advances in our understanding of the role NO plays in regulating the transport processes of the thick ascending limb. NO has been shown to inhibit NaCl absorption primarily by reducing Na+-K+-2Cl- cotransport activity. NO also inhibits bicarbonate absorption by reducing Na+/H+ exchange activity. It has also been reported to enhance luminal K+ channel activity and thus is likely to alter K+ secretion. The source of NO may be vascular structures such as the afferent arteriole or vasa recta, or the thick ascending limb itself. NO is produced by NO synthase 3 in this segment, and several factors that regulate its activity both acutely and chronically have recently been identified. Although the effects of NO on thick ascending limb transport have received a great deal of attention recently, its effects on divalent ion absorption and many other issues remain unexplored.

An adenovirus serotype 5 vector with fibers derived from ovine atadenovirus demonstrates CAR-independent tropism and unique biodistribution in mice

Many clinically important tissues are refractory to adenovirus (Ad) infection due to negligible levels of the primary Ad5 receptor the coxsackie and adenovirus receptor CAR. Thus, development of novel CAR-independent Ad vectors should lead to therapeutic gain. Ovine atadenovirus type 7, the prototype member of genus Atadenovirus, efficiently transduces CAR-deficient human cells in vitro, and systemic administration of OAdV is not associated with liver sequestration in mice. The penton base of OAdV7 does not contain an RGD motif, implicating the long-shafted fiber molecule as a major structural dictate of OAdV tropism. We hypothesized that replacement of the Ad5 fiber with the OAdV7 fiber would result in an Ad5 vector with CAR-independent tropism in vitro and liver "detargeting" in vivo. An Ad5 vector displaying the OAdV7 fiber was constructed (Ad5Luc1-OvF) and displayed CAR-independent, enhanced transduction of CAR-deficient human cells. When administered systemically to C57BL/6 mice, Ad5Luc1-OvF reporter gene expression was reduced by 80% in the liver compared to Ad5 and exhibited 50-fold higher gene expression in the kidney than the control vector. To our knowledge, this is the first report of a fiber-pseudotyped Ad vector that simultaneously displays decreased liver uptake and a distinct organ tropism in vivo. This vector may have future utility in murine models of renal disease.

Expression of human heme oxygenase-1 in the thick ascending limb attenuates angiotensin II-mediated increase in oxidative injury

BACKGROUND

Heme oxygenase-1 (HO-1) catalyzes the conversion of heme to bilirubin, carbon monoxide (CO), and free iron, thus controlling the level of cellular heme. The medullary thick ascending limb of the loop of Henle (TALH) is situated in a site of markedly diminished oxygen tension and, as such, is highly vulnerable to ischemic insult. We hypothesize that selective upregulation of HO-1 in TALH by gene transfer attenuates oxidative stress caused by angiotensin II (Ang II).

METHODS

An adenoviral vector expressing the human HO-1 under the control of the TALH-specific promoter [Na(+)-K(+)-Cl(-) cotransporter (NKCC2 promoter)] was constructed and the cell specific expression of the recombinant adenovirus was examined using several types of cells, including endothelial, vascular smooth muscle, and TALH cells. The effects of HO-1 transduction on HO-1 expression, HO activity and the response to Ang II with respect to cyclooxygenase-2 (COX-2) up-regulation and oxidative injury [growth-stimulating hormone (GSH) levels and cell death] were determined.

RESULTS

Western blot and reverse transcription-polymerase chain reaction (RT-PCR) revealed that human HO-1 was selectively expressed in primary cultured TALH cells following infection with Ad-NKCC2-HO-1. In TALH cells infected with Ad-NKCC2-HO-1, Ang II-stimulated prostaglandin E(2) (PGE(2)) levels were reduced by 40%. Ang II caused a marked decrease in GSH levels and this decrease was greatly attenuated in TALH cells transduced with Ad-NKCC2-HO-1. Moreover, Ang II-mediated DNA degradation was completely blocked by the site-specific expression of human HO-1 gene.

CONCLUSION

These results indicate that TALH cell survival after exposure to oxidative stress injury may be facilitated by selective upregulation of HO-1, thusly blocking inflammation and apoptosis.

Approaches and methods in gene therapy for kidney disease

Renal gene therapy may offer new strategies to treat diseases of native and transplanted kidneys. Several experimental techniques have been developed and employed using nonviral, viral, and cellular vectors. The most efficient vector for in vivo transfection appears to be adenovirus. Glomeruli, blood vessels, interstitial cells, and pyelum can be transfected with high efficiency. In addition, electroporation and microbubbles with ultrasound, both being enhanced naked plasmid techniques, offer good opportunities. Trapping of mesangial cells into the glomeruli as well as natural targeting of monocytes or macrophages to inflamed kidneys are elegant methods for site-specific delivery of genes. For gene therapy in kidney transplantation, hemagglutinating virus of Japan liposomes are efficient vectors for tubular transfection, whereas enhanced naked plasmid techniques are suitable for glomerular transfection. However, adenovirus offers the best opportunities in a renal transplantation setup because varying parameters of graft perfusion allows targeting of different cell types. In renal grafts, lymphocytes can be used for selective targeting to sites of inflammation. In conclusion, for both in vivo and ex vivo renal transfection, enhanced naked plasmids and adenovirus offer the best perspectives for effective clinical application. Moreover, the development of safer, nonimmunogenic vectors and the large-scale production could make clinical renal gene therapy a realistic possibility for the near future.

Perspectives for gene therapy in renal diseases

Somatic cell gene therapy has made considerable progress last five years and has shown clear success in some clinical trials. In the field of nephrology, both the elucidation of pathophysiology of renal diseases and the development of gene transfer technique have become driving force for new therapy of incurable renal diseases, such as Alport syndrome and polycystic kidney disease. Gene therapy of renal cancer, although its application is limited to advanced cancer, is the front-runner of clinical application. Erythropoietin gene therapy has provided encouraging results for the treatment of anemia in uremic rats and recently progressed to the inducible one in response to hypoxia. Gene therapy for glomerulonephritis and renal fibrosis showed prominent impact on experimental models, although the safety must be confirmed for prolonged treatment. Transplant kidney is an ideal material for gene modification and induction of tolerance in the transplant kidney is an attractive challenge. Emerging techniques are becoming available such as stem cell technology and messenger RNA silencing strategies. We believe that the future of gene therapy research is exciting and promising and it holds an enormous potential for clinical application.

Gene transfer of eNOS to the thick ascending limb of eNOS-KO mice restores the effects of L-arginine on NaCl absorption

The thick ascending limb of the loop of Henle (THAL) plays an essential role in the regulation of sodium and water homeostasis by the kidney. l-Arginine, the substrate for nitric oxide synthase (NOS), decreases NaCl absorption by THALs. We hypothesized that eNOS produces the NO that regulates THAL NaCl transport and that selective expression of eNOS in the THAL of eNOS knockout(-/-) mice would restore the effects of l-arginine on NaCl absorption. eNOS-/- mice were anesthetized, the left kidney was exposed, and the renal interstitium was injected with recombinant adenoviral vectors that expressed green fluorescent protein (GFP) or eNOS driven by the promoter of the Na/K/2Cl cotransporter Ad-NKCC2GFP and Ad-NKCC2eNOS, respectively. In Ad-NKCC2eNOS-transduced kidneys, eNOS expression was detected 7 days after injection but was absent in Ad-NKCC2GFP-transduced kidneys. In THALs from eNOS-/- mice transduced with Ad-NKCC2eNOS, adding L-arginine increased DAF-2DA fluorescence, a measure of NO production, by 9.1+/-1.1% (P<0.05; n=5), but not in THALs transduced with Ad-NKCC2GFP. In THALs from eNOS-/- mice transduced with Ad-NKCC2eNOS, Cl absorption averaged 85.9+/-11.8 pmol/min per millimeter. Adding l-arginine (1 mmol/L) to the bath decreased Cl absorption to 59.7+/-11.0 pmol/min per millimeter (P<0.05; n=6). In THALs transduced with Ad-NKCC2GFP, Cl absorption averaged 96.0+/-21.0 pmol/min per millimeter. Adding L-arginine to the bath did not significantly affect Cl absorption (100.6+/-20.6 pmol/min per millimeter; n=4). We concluded that gene transfer of eNOS to the THAL of eNOS-/- mice restores L-arginine-induced inhibition of NaCl transport and NO production. These data indicate that eNOS is essential for the regulation of THAL NaCl transport by NO.