Evidence for NOS-containing renal neuronal somata transiently expressing a catecholaminergic phenotype during development in the rat

Pathophysiological mechanisms of calcineurin inhibitor-induced nephrotoxicity and arterial hypertension

Solid organ transplantation is an established treatment modality in patients with end-stage organ damage in cases where other therapeutic options fail. The long-term outcomes of solid organ transplant recipients have improved considerably since the introduction of the first calcineurin inhibitor (CNI) - cyclosporine. In 1984, the potent immunosuppressive properties of another CNI, tacrolimus, were discovered. The immunosuppressive effects of CNIs result from the inhibition of interleukin-2 synthesis and reduced proliferation of T cells due to calcineurin blockade. The considerable side effects that are associated with CNIs therapy include arterial hypertension and nephrotoxicity. The focus of this article was to review the available literature on the pathophysiological mechanisms of CNIs that induce chronic nephrotoxicity and arterial hypertension. CNIs lead to activation of the major vasoconstriction systems, such as the renin-angiotensin and endothelin systems, and increase sympathetic nerve activity. On the other hand, CNIs are known to inhibit NO synthesis and NO-mediated vasodilation and to increase free radical formation. Altogether, these processes cause endothelial dysfunction and contribute to the impairment of organ function. A better insight into the mechanisms underlying CNI nephrotoxicity could assist in developing more targeted therapies of arterial hypertension or preventing CNI nephrotoxicity in organ transplant recipients, including heart transplantation.

Neuronal nitric oxide synthase and renin stimulation by sodium deprivation are dependent on the renal nerves

OBJECTIVE

The aim of the present study was to evaluate the role of the renal nerves in the regulation of neuronal nitric oxide synthase (nNOS) gene expression in normotensive rats on different sodium balance.

METHODS

Thirty-six male Sprague-Dawley rats were divided into six experimental groups combining three diets with different NaCl content (normal, 0.4%; low, 0.04%; or high, 4.0%), and bilateral renal denervation or sham denervation. After 7 days of dietary treatment, all rats were sacrificed and plasma renin activity (PRA) measured. The nNOS and renin messenger RNA (mRNA) levels in the renal cortex were determined by semiquantitative polymerase chain reaction.

RESULTS

PRA was higher in animals with low sodium diet compared with those with standard diet, while it was lower in animals with high sodium diet. Renal denervation decreased PRA in normal and low sodium groups, while it did not alter the PRA values in the high sodium group. The nNOS gene expression significantly increased in rats fed with the low sodium diet compared with the standard diet group, and it significantly decreased in rats with the high sodium diet. Renal denervation significantly reduced nNOS mRNA levels in rats receiving the low sodium diet, but did not significantly influence nNOS mRNA in normal and high sodium groups. Renin mRNA was influenced by diets and denervation in a parallel way to nNOS mRNA.

CONCLUSION

The renal nerves mediate the increase of renin and nNOS mRNA during sodium restriction, while the suppression of nNOS and renin gene expression during a sodium load is independent of the presence of the renal nerves. The parallel changes in renin and nNOS mRNA during different sodium intakes suggest that nNOS can be part of the complex, and still largely unclarified, macula densa mechanism of renin regulation.

Preferential transformation of human neuronal cells by human adenoviruses and the origin of HEK 293 cells

The 293 cell line was derived by transformation of primary cultures of human embryonic kidney (HEK) cells with sheared adenovirus (Ad)5 DNA. A combination of immunostaining, immunoblot, and microarray analysis showed that 293 cells express the neurofilament (NF) subunits NF-L, NF-M, NF-H, and a-internexin as well as many other proteins typically found in neurons. Three other independently derived HEK lines, two transformed by Ad5 and one by Ad12, also expressed NFs, as did one human embryonic retinal cell line transformed with Ad5. Two rodent kidney lines transformed with Ad12 were also found to express NF proteins, although several rodent kidney cell lines transformed by Ad5 DNA and three HEK cell lines transformed by the SV40 early region did not express NFs. These results suggest that human Ads preferentially transform human neuronal lineage cells. We also demonstrate that the widely used HEK293 cells have an unexpected relationship to neurons, a finding that may require reinterpretation of many previous studies in which it was assumed that HEK293 cells resembled more typical kidney epithelial cells.

Defective fluid and HCO(3)(-) absorption in proximal tubule of neuronal nitric oxide synthase-knockout mice

Using renal clearance techniques and in situ microperfusion of proximal tubules, we examined the effects of N(G)-monomethyl-L-arginine methyl ester (L-NAME) on fluid and HCO(3)(-) transport in wild-type mice and also investigated proximal tubule transport in neuronal nitric oxide synthase (nNOS)-knockout mice. In wild-type mice, administration of L-NAME (3 mg/kg bolus iv) significantly increased mean blood pressure, urine volume, and urinary Na(+) excretion. L-NAME, given by intravenous bolus and added to the luminal perfusion solution, decreased absorption of fluid (60%) and HCO(3)(-) (49%) in the proximal tubule. In nNOS-knockout mice, the urinary excretion of HCO(3)(-) was significantly higher than in the wild-type mice (3.12 +/- 0.52 vs. 1. 40 +/- 0.33 mM) and the rates of HCO(3)(-) and fluid absorption were 62 and 72% lower, respectively. Both arterial blood HCO(3)(-) concentration (20.7 vs. 25.7 mM) and blood pH (7.27 vs. 7.34) were lower, indicating a significant metabolic acidosis in nNOS-knockout mice. Blood pressure was lower in nNOS-knockout mice (76.2 +/- 4.6 mmHg) than in wild-type control animals (102.9 +/- 8.4 mmHg); however, it increased in response to L-NAME (125.5 +/- 5.07 mmHg). Plasma Na(+) and K(+) were not significantly different from control values. Our data show that a large component of HCO(3)(-) and fluid absorption in the proximal tubule is controlled by nNOS. Mice without this isozyme are defective in absorption of fluid and HCO(3)(-) in the proximal tubule and develop metabolic acidosis, suggesting that nNOS plays an important role in the regulation of acid-base balance.

Sympathoadrenal hyperplasia causes renal malformations in Ret(MEN2B)-transgenic mice

The tyrosine kinase receptor Ret is expressed in the ureteric bud and is required for normal renal development. Constitutive loss of Ret, its co-receptor gfralpha-1, or the ligand glial cell line-derived neurotrophic factor results in renal agenesis. Transgenic embryos that express a constitutively active form of Ret (Ret(MEN2B)) under the control of the dopamine-beta-hydroxylase (DbetaH) promoter develop profound neuroglial hyperplasia of their sympathetic ganglia and adrenal medullae. Embryos from two independent DbetaH-Ret(MEN2B)-transgenic lines exhibit renal malformations. In contrast with ret-/- embryos, renal maldevelopment in DbetaH-Ret(MEN2B)-transgenic embryos results from primary changes in sympathoadrenal organs extrinsic to the kidney. The ureteric bud invades the metanephric mesenchyme normally, but subsequent bud branching and nephrogenesis are retarded, resulting in severe renal hypoplasia. Ablation of sympathoadrenal precursors restores normal renal growth in vivo and in vitro. We postulate that disruption of renal development results because Ret(MEN2B) derived from the hyperplastic nervous tissue competes with endogenous renal Ret for gfralpha-1 or other signaling components. This hypothesis is supported by the observation that renal malformations, which do not normally occur in a transgenic line with low levels of DbetaH-Ret(MEN2B) expression, arise in a gdnf+/- background. However, renal maldevelopment was not recapitulated in kidneys that were co-cultured with explanted transgenic ganglia in vitro. Our observations illustrate a novel pathogenic mechanism for renal dysgenesis that may explain how putative activating mutations of the RET gene can produce a phenotype usually associated with RET deficiency.