Heavy metals such as cadmium (Cd), mercury (Hg), lead (Pb), chromium (Cr) and platinum (Pt) are a major environmental and occupational hazard. Unfortunately, these non-essential elements are toxic at very low doses and non-biodegradable with a very long biological half-life. Thus, exposure to heavy metals is potentially harmful. Because of its ability to reabsorb and accumulate divalent metals, the kidney is the first target organ of heavy metal toxicity. The extent of renal damage by heavy metals depends on the nature, the dose, route and duration of exposure. Both acute and chronic intoxication have been demonstrated to cause nephropathies, with various levels of severity ranging from tubular dysfunctions like acquired Fanconi syndrome to severe renal failure leading occasionally to death. Very varied pathways are involved in uptake of heavy metals by the epithelium, depending on the form (free or bound) of the metal and the segment of the nephron where reabsorption occurs (proximal tubule, loop of Henle, distal tubule and terminal segments). In this review, we address the putative uptake pathways involved along the nephron, the mechanisms of intracellular sequestration and detoxification and the nephropathies caused by heavy metals. We also tackle the question of the possible therapeutic means of decreasing the toxic effect of heavy metals by increasing their urinary excretion without affecting the renal uptake of essential trace elements. We have chosen to focus mainly on Cd, Hg and Pb and on in vivo studies.

Hypertension in patients with chronic kidney disease (CKD) strongly associates with cardiovascular events. Among patients with CKD, reducing the accumulation of uremic toxins may protect against the development of hypertension and progression of renal damage, but there are no established therapies to accomplish this. Here, overexpression of human kidney-specific organic anion transporter SLCO4C1 in rat kidney reduced hypertension, cardiomegaly, and inflammation in the setting of renal failure. In addition, SLCO4C1 overexpression decreased plasma levels of the uremic toxins guanidino succinate, asymmetric dimethylarginine, and the newly identified trans-aconitate. We found that xenobiotic responsive element core motifs regulate SLCO4C1 transcription, and various statins, which act as inducers of nuclear aryl hydrocarbon receptors, upregulate SLCO4C1 transcription. Pravastatin, which is cardioprotective, increased the clearance of asymmetric dimethylarginine and trans-aconitate in renal failure. These data suggest that drugs that upregulate SLCO4C1 may have therapeutic potential for patients with CKD.

The pattern of occludin distribution is present from the neonatal age. Claudins-7 and -8 are up-regulated after birth. Each tubular segment expresses a peculiar set of claudins that might be responsible for the permeability properties of their TJs.

The acid-and volume-sensitive TASK2 K ؉ channel is strongly expressed in renal proximal tubules and papillary collecting ducts. This study was aimed at investigating the role of TASK2 in renal bicarbonate reabsorption by using the task2 ؊͞؊ mouse as a model. After backcross to C57BL6, task2 ؊͞؊ mice showed an increased perinatal mortality and, in adulthood, a reduced body weight and arterial blood pressure. Patch-clamp experiments on proximal tubular cells indicated that TASK2 was activated during HCO 3 ؊ transport. In control inulin clearance measurements, task2 ؊͞؊ mice showed normal NaCl and water excretion. During i.v. NaHCO3 perfusion, however, renal Na ؉ and water reabsorption capacity was reduced in ؊͞؊ animals. In conscious task2 ؊͞؊ mice, blood pH, HCO 3 ؊ concentration, and systemic base excess were reduced but urinary pH and HCO 3 ؊ were increased. These data suggest that task2 ؊͞؊ mice exhibit metabolic acidosis caused by renal loss of HCO 3 ؊ . Both in vitro and in vivo results demonstrate the specific coupling of TASK2 activity to HCO 3 ؊ transport through external alkalinization. The consequences of the task2 gene inactivation in mice are reminiscent of the clinical manifestations seen in human proximal renal tubular acidosis syndrome.

Mechanical forces associated with fluid flow and/or circumferential stretch are sensed by renal epithelial cells and contribute to both adaptive or disease states. Non-selective stretch-activated ion channels (SACs), characterized by a lack of inactivation and a remarkably slow deactivation, are active at the basolateral side of renal proximal convoluted tubules. Knockdown of Piezo1 strongly reduces SAC activity in proximal convoluted tubule epithelial cells. Similarly, overexpression of Polycystin-2 (PC2) or, to a greater extent its pathogenic mutant PC2-740X, impairs native SACs. Moreover, PC2 inhibits exogenous Piezo1 SAC activity. PC2 coimmunoprecipitates with Piezo1 and deletion of its N-terminal domain prevents both this interaction and inhibition of SAC activity. These findings indicate that renal SACs depend on Piezo1, but are critically conditioned by PC2.

Degradation of signaling proteins is one of the most powerful tumor suppressive mechanisms by which a cell can control its own growth. Here, we identify RHOA as the molecular target by which autophagy maintains genomic stability. Specifically, inhibition of autophagosome degradation by the loss of the v-ATPase a3 (TCIRG1) subunit is sufficient to induce aneuploidy. Underlying this phenotype, active RHOA is sequestered via p62 (SQSTM1) within autolysosomes, and fails to localize to the plasma membrane or to the spindle midbody. Conversely, inhibition of autophagosome formation by ATG5 shRNA dramatically increases localization of active RHOA at the midbody, followed by diffusion to the flanking zones. As a result, all of the approaches we examined that compromise autophagy (irrespective of the defect: autophagosome formation, sequestration or degradation) drive cytokinesis failure, multinucleation, and aneuploidy, processes that directly have an impact upon cancer progression. Consistently, we report a positive correlation between autophagy defects and the higher expression of RHOA in human lung carcinoma. We therefore propose that autophagy may act in part as a safeguard mechanism that degrades and thereby maintains the appropriate level of active RHOA at the midbody for faithful completion of cytokinesis and genome inheritance.

The present study directly tested the hypothesis that deletion of the Na+/H+ exchanger 3 (NHE3) selectively in the proximal tubules of the kidney lowers basal blood pressure by increasing the pressure natriuresis response in mice. Adult male and female, age-matched wild-type littermates (WT) and proximal tubule-specific NHE3-knockout mice (PT-Nhe3−/−) (n=6–16 per group) were studied for 1) basal phenotypes of electrolytes and pH, blood pressure, and kidney function, 2) the pressure natriuresis response using the mesenteric, celiac and abdominal arterial occlusion technique, and 3) the natriuretic responses to acute saline expansion (0.9% NaCl, 10% body wt., i.p.) or 2-week of 2% NaCl diet. Under basal conditions, PT-Nhe3−/− mice showed significantly lower systolic, diastolic, and mean arterial blood pressure (p<0.01) than WT mice (p<0.01). PT-Nhe3−/− mice also exhibited significantly greater diuretic (p<0.01) and natriuretic responses than WT mice (p<0.01), without altering 24 h fecal Na+ excretion, plasma pH, Na+, and bicarbonate levels. In response to increased renal perfusion pressure by 30 mmHg, the pressure natriuresis response increased 5-fold in WT mice (p<0.01), but it increased 8-fold in PT-Nhe3−/− mice (p<0.01). In response to 10% acute saline expansion or 2-week 2% NaCl diet, more pronounced natriuretic responses were demonstrated in PT-Nhe3−/− than WT mice (p<0.01). Our results support the scientific premise and physiological relevance that NHE3 in the proximal tubules plays an essential role in maintaining basal blood pressure homeostasis, and genetic deletion of NHE3 selectively in the proximal tubules of the kidney lowers blood pressure by increasing the pressure natriuretic response.

Li XC, Cook JL, Rubera I, Tauc M, Zhang F, Zhuo JL. Intrarenal transfer of an intracellular fluorescent fusion of angiotensin II selectively in proximal tubules increases blood pressure in rats and mice. Am J Physiol Renal Physiol 300: F1076 -F1088, 2011. First published February 9, 2011 doi:10.1152/ajprenal.00329.2010.-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 AT1 (AT1a) 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 Ͻ 0.01) and more than threefold in proximal tubules (P Ͻ 0.01), but remained unchanged in plasma or urine. Systolic blood pressure was increased in ECFP/ANG II-transferred rats by 28 Ϯ 6 mmHg (P Ͻ 0.01), whereas fractional sodium excretion was decreased by 20% (P Ͻ 0.01) and fractional lithium excretion was reduced by 24% (P Ͻ 0.01). These effects were blocked by losartan and prevented in AT1a 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 AT1a receptors and increasing sodium reabsorption in proximal tubules. adenoviral gene delivery; G protein-coupled receptors; intracrine peptides; losartan; renin-angiotensin-aldosterone system; urinary sodium excretion THE RENIN-ANGIOTENSIN SYSTEM (RAS) is long recognized to exist and function as dual extracellular (endocrine and/or paracrine) and intracellular (or intracrine) vasoactive hormonal systems. The extracellular system includes circulating and local tissue ANG II, which plays the classic roles of ANG II through activation of cell surface G protein-coupled ANG II receptors (GPCRs) (6,21,30,35). The intracellular system includes intracellularly formed ANG II (1-5, 8 -10, 12, 19, 40) and extracellular ANG II internalized through type 1 (AT 1 ) receptor-mediated endocytosis (14,15,18,19,25,27,39). The roles of circulating and paracrine ANG II and G protein-coupled signaling transduction mechanisms via activation of cell surface receptors have been extensively studied (6,21,30,35). By contrast, whether intracellular ANG II may induce any physiological effects remains largely unknown. The slow progress in our under...