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The triad composed by α-Klotho, fibroblast growth factor-23, and its receptor are involved in the pathogenesis of chronic kidney disease–mineral and bone disorder. A disintegrin and metalloproteinase 17 (ADAM17) is a metalloproteinase causing the proteolytic shedding of α-Klotho from the cell membrane, and its role in chronic kidney disease–mineral and bone disorder is not yet known. We studied the circulating levels of the above-mentioned mediators in patients with secondary hyperparathyroidism due to uremia, compared to control subjects, as well as in patients with primary hyperparathyroidism. We also measured the immunofluorescence pattern of the relevant tissue proteins in specimens obtained from patients undergoing parathyroid surgery for secondary compared to primary hyperparathyroidism. Results showed that α-Klotho tissue levels are reduced, in the presence of increased ADAM17 tissue levels. In addition, we showed increased serum levels of the main product of ADAM17 proteolytic activity, tumor necrosis factor-α. Thus, we found a paradoxical situation, in secondary compared to primary hyperparathyroidism, that is, that in the face of increased tumor necrosis factor-α in circulation, both soluble and tissue α-Klotho are reduced significantly, despite increased tissue ADAM17. In conclusion, tissue and serum levels of α-Klotho seem to have become independent from the regulation induced by ADAM17, which constitutes therefore another tassel in the impaired α-Klotho–FGF23 receptor axis present in uremia.

Dialysis patients display a high cardiovascular mortality, the causes of which are still not completely explained, but are related to uremic toxicity. Among uremic toxins, homocysteine and cysteine are both substrates of cystathionine beta-synthase and cystathionine gamma-lyase in hydrogen sulfide biosynthesis, leading to the formation of two sulfur metabolites, lanthionine and homolanthionine, considered stable indirect biomarkers of its production. Hydrogen sulfide is involved in the modulation of multiple pathophysiological responses. In uremia, we have demonstrated low plasma total hydrogen sulfide levels, due to reduced cystathionine gamma-lyase expression.Plasma hydrogen sulfide levels were measured in hemodialysis patients and healthy controls with three different techniques in comparison, allowing to discern the different pools of this gas. The protein bound (the one thought to be the most active) and acid-labile forms are significantly decreased, while homolanthionine, but especially lanthionine, accumulate in the blood of uremic patients. The hemodialysis regimen plays a role in determining sulfur compounds levels, and lanthionine is partially removed by a single dialysis session. Lanthionine inhibits hydrogen sulfide production in cell cultures under conditions comparable to in vivo ones. We therefore propose that lanthionine is a novel uremic toxin. The possible role of high lanthionine as a contributor to the genesis of hyperhomocysteinemia in uremia is discussed. (C) 2016 Elsevier B.V. and Societe Francaise de Biochimie et Biologie Moleculaire (SFBBM). All rights reserved.

PLoS one 10(1), 1-17 (2015). doi:10.1371/journal.pone.0116468, Published by PLoS, Lawrence, Kan.

Endocannabinoids are lipid signaling mediators that exert an important neuromodulatory role and confer neuroprotection in several types of brain injury. Neuroinflammation, microglial activation, oxidative stress, and excitotoxicity are variably combined in neurodegenerative diseases following trauma and can be modulated by endocannabinoids (for review, Rossi et al., Exp. Neurol. 2010). Unlike mammalian, the nervous system of low vertebrates (fish, amphibians and reptilia) is promptly able to regenerate neurons and spinal nerves after unjury. In the lizards, tail loss transects spinal nerves and the cut axons elongate in the regrowing tail, providing a natural paradigm of robust regenerative response of injured spinal motoneurons (Terni, Arch Ital Anat Embriol., 1920). On this basis we have investigated the possible involvement of the endocannabinoid system in the survival of motoneurons committed to axonal elongation in the context of the neuroregenerative response that follows caudotomy. By our previous investigations, a typical chromatolytic reaction to axotomy (cellular hypertrophy and nuclear eccentricity) was mostly showed in the first two weeks after caudotomy (reactive phase) (Cristino et al., J. Comp. Neurol. 2000). On this basis, in the present work, we compared the endocannabinoid system of regenerating motoneurons, at 10 days (reactive phase) and at 4 months after caudotomy (regenerative phase), to those of intact motoneurons. Single and multiple immunohystochemistry were performed for CB1 and CB2 receptors, 2-AG endocannabinoid synthesizing (DAGL alpha) and degrading (MAGL) enzymes, for glutamate and GABA vescicular transmitter transportes (VGluT1 and VGAT, respectively) and for the glial marker GFAP and for the activated microglia Iba-1. Intact motoneurons exhibited DAGL- immunoreactivity (-ir) in the somatodendritic compartment and were immersed in a meshwork of MAGL/CB1-ir puncta on VGluT1-ir fibers. Very low CB2-ir expression was found in the gray matter of intact spinal cord which showed an intense and diffuse GFAP-ir and the lowest Iba-1 reactivity. During the reactive fase to axotomy, a general decrease of markers of the endocannabinoid system was observed, except for CB2-ir which, diffusely, colocalize with Iba-1-ir microglial cells. In the regenerative phase a strong DAGL-and CB1-ir, on both glutamatergic and GABAergic axon terminals surrounding motoneurons, was observed. CB-2-ir and Iba-1-ir came back to normal levels. Our data suggest a model of retrograde control by CB1 over glutamate release. In the reactive phase the wide-ranging temporary loss of contact between some presynaptic axons and the motoneurons could explain the endocannabinoid system down regulation. Cannabinoids exert anti-glutamatergic and anti-inflammatory actions through activation of the CB1 and CB2 receptors, respectively. Activation of CB1 receptors may therefore inhibit glutamate release from presynaptic nerve terminals and reduce the postsynaptic calcium influx in response to glutamate receptor stimulation. Meanwhile, CB2 receptors may influence inflammation, whereby receptor activation reduces microglial activation, resulting in a decrease in microglial secretion of neurotoxic mediators. These results collectively lead to a model of the motoneuron survival and axonal regeneration whereby 2-AG mediates the CB1-induced inhibition of glutammate release.