Cl--sensitive with-no-lysine kinase (WNK) plays a key role in regulating the thiazide-sensitive Na+-Cl- cotransporter (NCC) in the distal convoluted tubule (DCT). Cl- enters DCT cells through NCC... Show moreCl--sensitive with-no-lysine kinase (WNK) plays a key role in regulating the thiazide-sensitive Na+-Cl- cotransporter (NCC) in the distal convoluted tubule (DCT). Cl- enters DCT cells through NCC and leaves the cell across the basolateral membrane via the Cl- channel ClC-K2 or K+-Cl- cotransporter (KCC). While KCC is electroneutral, Cl- exit via ClC-K2 is electrogenic. Therefore, an alteration in DCT basolateral K+ channel activity is expected to influence Cl- movement across the basolateral membrane. Although a role for intracellular Cl- in the regulation of WNK and NCC has been established, intracellular Cl- concentrations ([Cl-](i)) have not been directly measured in the mammalian DCT. Therefore. to measure [Cl-](i) in DCT cells, we generated a transgenic mouse model expressing an optogenetic kidney-specific Cl-Sensor and measured Cl- fluorescent imaging in the isolated ix:T. Basal measurements indicated that the mean [Cl-](i) was similar to 7 mM. Stimulation of Cl- exit with low-Cl- hypotonic solutions decreased [Cl-](i), whereas inhibition of KCC by DIOA or inhibition of ClC-K2 by NPPB increased [Cl-](i). suggesting roles for both KCC and ClC-K2 in the modulation of [Cl-](i). Blockade of basolateral K+ channels (Kir4.1/5.1) with barium significantly increased [Cl-](i). Finally, a decrease in extracellular K+ concentration transiently decreased [Cl-](i). whereas raising extracellular K+ transiently increased [Cl-](i), further suggesting a role for Kir4.1/5.1 in the regulation of [Cl-](i). We conclude that the alteration in ClC- K2. KCC, and Kir4.1/5.1 activity influences [Cl-](i) in the DCT. Show less
Everaert, I.; He, J.L.; Hanssens, M.; Stautemas, J.; Bakker, K.; Albrecht, T.; ... ; Derave, W. 2020
doi:10.1152/ajprenal.00329.2019. Manipulation of circulating histidine-containing dipeptides (HCD) has been shown to affect the development of diabetes and early-stage diabetic nephropathy (DN).... Show moredoi:10.1152/ajprenal.00329.2019. Manipulation of circulating histidine-containing dipeptides (HCD) has been shown to affect the development of diabetes and early-stage diabetic nephropathy (DN). The aim of the present study was to investigate whether such interventions, which potentially alter levels of circulating HCD, also affect the development of advanced -stage DN. 'Iwo interventions, aerobic exercise training and overexpression of the human carnosinase-1 (hCNI) enzyme, were tested. BTBR ob/ob mice were either subjected to aerobic exercise training (20 wk) or genetically manipulated to overexpress hCNi, and different diabetes- and DNrelated markers were compared with control ob/ob and healthy (wild type) mice. An acute exercise study was performed to elucidate the effect of obesity, acute running, and hCNI overexpression on plasma HCD levels. Chronic aerobic exercise training did not affect the development of diabetes or DN, but hCNI overexpression accelerated hyperlipidemia and aggravated the development of alburninuria, mesangial matrix expansion, and glomerular hypertrophy- of ob/ob mice. In line, plasma, kidney, and muscle 11CD were markedly lower in oh/oh versus wild -type mice, and plasma and kidney HCD in particular were lower in ob/ob hCNI versus ob/ob mice but were unaffected by aerobic exercise. In conclusion, advanced glomerular damage is accelerated in mice overexpressing the hCNI enzyme but not protected by chronic exercise training. Interestingly, we showed, for the first time, that the development of DN is closely linked to renal HCD availability. Further research will have to elucidate whether the stimulation of renal HCD levels can he a therapeutic strategy to reduce the risk for developing DN. Show less
Proteinuria develops when specific components in the glomerular filtration barrier have impaired function. Although the precise components involved in maintaining this barrier have not been fully... Show moreProteinuria develops when specific components in the glomerular filtration barrier have impaired function. Although the precise components involved in maintaining this barrier have not been fully identified, heparan sulfate proteoglycans are believed to play an essential role in maintaining glomerular filtration. Although in situ studies have shown that a loss of heparan sulfate glycosaminoglycans increases the permeability of the glomerular filtration barrier, recent studies using experimental models have shown that podocyte-specific deletion of heparan sulfate glycosaminoglycan assembly does not lead to proteinuria. However, tubular reabsorption of leaked proteins might have masked an increase in glomerular permeability in these models. Furthermore, not only podocytes but also glomerular endothelial cells are involved in heparan sulfate synthesis in the glomerular filtration barrier. Therefore, we investigated the effect of a global heparan sulfate glycosaminoglycan deficiency on glomerular permeability. We used a zebrafish embryo model carrying a homozygous germline mutation in the ext2 gene. Glomerular permeability was assessed with a quantitative dextran tracer injection method. In this model, we accounted for tubular reabsorption. Loss of anionic sites in the glomerular basement membrane was measured using polyethyleneimine staining. Although mutant animals had significantly fewer negatively charged areas in the glomerular basement membrane, glomerular permeability was unaffected. Moreover, heparan sulfate glycosaminoglycan-deficient embryos had morphologically intact podocyte foot processes. Glomerular filtration remains fully functional despite a global reduction of heparan sulfate. Show less
Proteinuria develops when specific components in the glomerular filtration barrier have impaired function. Although the precise components involved in maintaining this barrier have not been fully... Show moreProteinuria develops when specific components in the glomerular filtration barrier have impaired function. Although the precise components involved in maintaining this barrier have not been fully identified. heparan sulfate proteoglycans are believed to play an essential role in maintaining glomerular filtration. Although in situ studies have shown that a loss of heparan sulfate glycosaminoglycans increases the permeability of the glomerular filtration barrier. recent studies using experimental models have shown that podocyte-specific deletion of heparan sulfate glycosaminoglycan assembly does not lead to proteinuria. However, tubular reabsorption of leaked proteins might have masked an increase in glomerular permeability in these models. Furthermore, not only podocytes but also glomerular endothelial cells are involved in heparan sulfate synthesis in the glomerular filtration barrier. Therefore, we investigated the effect of a global heparan sulfate glycosaminoglycan deficiency on glomerular permeability. We used a zebrafish embryo model carrying a homozygous germline mutation in the ext2 gene. Glomerular permeability was assessed with a quantitative dextran tracer injection method. In this model, we accounted for tubular reabsorption. Loss of anionic sites in the glomerular basement membrane was measured using polyethyleneimine staining. Although mutant animals had significantly fewer negatively charged areas in the glomerular basement membrane. glomerular permeability was unaffected. Moreover, heparan sulfate glycosaminoglycan-deficient embryos had morphologically intact podocyte foot processes. Glomerular filtration remains fully functional despite a global reduction of heparan sulfate. Show less
Vascular access is the lifeline for patients on hemodialysis. Arteriovenous fistulas (AVFs) are the preferred vascular access, but AVF maturation failure remains a significant clinical problem.... Show moreVascular access is the lifeline for patients on hemodialysis. Arteriovenous fistulas (AVFs) are the preferred vascular access, but AVF maturation failure remains a significant clinical problem. Currently, there are no effective therapies available to prevent or treat AVF maturation failure. AVF maturation failure frequently results from venous stenosis at the AVF anastomosis, which is secondary to poor outward vascular remodeling and excessive venous intimal hyperplasia that narrows the AVF lumen. Arteriovenous grafts (AVGs) are the next preferred vascular access when an AVF creation is not possible. AVG failure is primarily the result of venous stenosis at the vein-graft anastomosis, which originates from intimal hyperplasia development. Although there has been advancement in our knowledge of the pathophysiology of AVF maturation and AVG failure, this has not translated into effective therapies for these two important clinical problems. Further work will be required to dissect out the mechanisms of AVF maturation failure and AVG failure to develop more specific therapies. This review highlights the major recent advancements in AVF and AVG biology, reviews major clinical trials, and discusses new areas for future research. Show less
Autosomal dominant polycystic kidney disease (ADPKD) caused by mutations in either the PKD1 or PKD2 gene is a major cause of end-stage renal failure. A number of compounds targeting specific... Show moreAutosomal dominant polycystic kidney disease (ADPKD) caused by mutations in either the PKD1 or PKD2 gene is a major cause of end-stage renal failure. A number of compounds targeting specific signaling pathways were able to inhibit cystogenesis in rodent models and are currently being tested in clinical trials. However, given the complex signaling in ADPKD, an ideal therapy would likely have to comprise several pathways at once. Therefore, multitarget compounds may provide promising therapeutic interventions for the treatment of ADPKD. To test this hypothesis, we treated Pkd1-deletion mice with diferuloylmethane (curcumin), a compound without appreciable side effects and known to modulate several pathways that are also altered in ADPKD, e.g., mammalian target of rapamycin (mTOR) and Wnt signaling. After conditional inactivation of Pkd1, mTOR signaling was indeed elevated in cystic kidneys. Interestingly, also activation of signal transducers and activator of transcription 3 (STAT3) strongly correlated with cyst progression. Both pathways were effectively inhibited in vitro by curcumin. Importantly, Pkd1-deletion mice that were treated with curcumin and killed at an early stage of PKD displayed improved renal histology and reduced STAT3 activation, proliferation index, cystic index, and kidney weight/body weight ratios. In addition, renal failure was significantly postponed in mice with severe PKD. These data suggest that multitarget compounds hold promising potential for safe and effective treatment of ADPKD. Show less
Leonhard, W.N.; Wal, A. van der; Novalic, Z.; Kunnen, S.J.; Gansevoort, R.T.; Breuning, M.H.; ... ; Peters, D.J.M. 2011
