Library

Notes: Sphingosine-1-phosphate (SPP), a bioactive sphingolipid metabolite, suppresses apoptosis of many types of cells, including rat pheochromocytoma PC12 cells. Elucidating the molecular mechanism of action of SPP is complicated by many factors, including uptake and metabolism, as well as activation of specific G-protein-coupled SPP receptors, known as the endothelial differentiation gene-1 (EDG-1) family. In this study, we overexpressed type 1 sphingosine kinase (SPHK1), the enzyme that converts sphingosine to SPP, in order to examine more directly the role of intracellularly generated SPP in neuronal survival. Enforced expression of SPHK1 in PC12 cells resulted in significant increases in kinase activity, with corresponding increases in intracellular SPP levels and concomitant decreases in both sphingosine and ceramide, and marked suppression of apoptosis induced by trophic factor withdrawal or by C2-ceramide. NGF, which protects PC12 cells from serum withdrawal-induced apoptosis, also stimulated SPHK1 activity. Surprisingly, overexpression of SPHK1 had no effect on activation of two known NGF-stimulated survival pathways, extracellular signal regulated kinase ERK 1/2 and Akt. However, trophic withdrawal-induced activation of the stress activated protein kinase, c-Jun amino terminal kinase (SAPK/JNK), and activation of the executionary caspases 2, 3 and 7, were markedly suppressed. Moreover, this abrogation of caspase activation, which was prevented by the SPHK inhibitor N,N-dimethylsphingosine, was not affected by pertussis toxin treatment, indicating that the cytoprotective effect was likely not mediated by binding of SPP to cell surface Gi-coupled SPP receptors. In agreement, there was no detectable release of SPP into the culture medium, even after substantially increasing cellular SPP levels by NGF or sphingosine treatment. In contrast to PC12 cells, C6 astroglioma cells secreted SPP, suggesting that SPP might be one of a multitude of known neurotrophic factors produced and secreted by glial cells. Collectively, our results indicate that SPHK/SPP may play an important role in neuronal survival by regulating activation of SAPKs and caspases.

Notes: Background:  Calciphylaxis and metastatic calcification are known complications of chronic renal failure. Recently, a sclerosing condition of the skin termed nephrogenic fibrosing dermopathy (NFD) has been described in patients with renal disease, many of whom have undergone hemodialysis and/or renal transplantation. To our knowledge, the simultaneous occurrence of both conditions in the same patient, in the same lesion, has not been previously reported.Case report:  We report the clinical, microscopic, and immunohistochemical features of two patients with chronic renal failure whose lesional skin biopsies showed both subcutaneous calcification and NFD. We consider the possible mechanisms that might explain the coexistence of these two disorders.Results:  Both patients presented with erythematous, indurated skin over the lower extremities. Purpuric, reticulated patches, necrosis, or ulceration were not observed. Microscopic examination showed the characteristic changes of NFD involving dermis and subcutaneous septa. In addition, biopsies of both individuals showed subcutaneous calcification, one in a diffuse distribution and the other involving the walls of subcutaneous vessels, as seen in calciphylaxis. Calcification was not suspected clinically in either case.Conclusions:  Metastatic calcification or calciphylaxis and NFD can occur simultaneously in patients with chronic renal failure and may be found together in the same lesion. Because subcutaneous calcification may not be suspected clinically in these cases, and in view of the adverse outcomes frequently associated with calciphylaxis, we recommend deep incisional biopsy of patients presenting with the clinical features of NFD. Both the fibrosis and the calcification of chronic renal failure may be related to the activity of transforming growth factor-β/Smad signaling cascades.