No abstract

We recently reported that DAG (diacylglycerol) generated during sphingomyelin synthesis plays an important role in protein kinase C activation and cell proliferation in Madin-Darby canine kidney cells [Cerbon and Lopez-Sanchez (2003) Biochem. J. 373, 917-924]. In yeast cells, IPC (inositol phosphoceramide) synthase catalyses the transfer of phosphoinositol from phosphatidylinositol to ceramide to form IPC and generates DAG. In the present study, we found that, during the G1 to S transition after N2-starvation, there was a significant increase in the synthesis of IPC accompanied by a progressive increase (up to 6-fold) in the level of DAG. The increased DAG levels coincided with decrements in ceramide and sphingoid base levels, conditions that are adequate for the activation of putative protein kinase C required for the G1 to S transition and proliferation of yeast cells. To separate the role of DAG generated during IPC synthesis from that originating from other sources, we utilized beta-chloroalanine and myriocin, inhibitors of serine:palmitoyl-CoA transferase, the first committed step in sphingolipid synthesis, to avoid accumulation of sphingolipid intermediates. When the synthesis of sphingolipids was inhibited, DAG accumulation was significantly decreased and the G1 to S transition was blocked; such blockage was avoided by metabolic complementation with phytosphingosine. The DAG/ceramide ratio was 0.27 and it changed to 2.0 during growth re-initiation, suggesting that the synthesis of phosphosphingolipids could act to switch growth arrest (increased ceramide) to a mitogenic signal (increased DAG), and that this signalling process is preserved in yeast and mammalian cells.

Diabetes mellitus is the leading cause of diabetic nephropathy; the early phase of diabetes is associated with kidney growth and hyperfiltration; several factors modulate these changes, among them, prostaglandins and angiotensin II. Previous studies have shown that cyclooxygenase-2 is implicated in experimental models of diabetes. The aim of this work was to study the effect of celecoxib treatment on renal hypertrophy development in early diabetes mellitus. In our rats with early streptozotocin-induced diabetes there was renal hypertrophy, and increased renal expression of cyclooxygenase-2, AT 1 receptor, and transforming growth factor-β 1 . Treatment with the selective cyclooxygenase-2 inhibitor celecoxib reduced the urinary excretion of prostaglandins such as prostaglandin E 2 , 6-keto prostaglandin F 1α , and thromboxane B 2 . Kidney hypertrophy was reversed by the treatment, and the renal expression of cyclooxygenase-2, AT 1 receptor, and transforming growth factor-β 1 decreased. The renoprotective effects of celecoxib were independent of the changes in plasma glucose levels. These results confirm that cyclooxygenase-2 inhibition in rats with streptozotocin-induced diabetes decrease renal hypertrophy; this effect in turn, may be mediated by reduction of the expression of AT 1 receptors and transforming growth factor- 1 in the kidney.

La hipertensión es un síndrome cardiovascular progresivo que surge de etiologías complejas e interrelacionadas. Los marcadores tempranos del síndrome a menudo están presentes antes de que la elevación de la presión sanguínea sea observada. El desarrollo de la hipertensión arterial se asocia con anomalías cardíacas y vasculares funcionales y estructurales que dañan el corazón, los riñones, el cerebro, los vasos, y otros órganos, y conducen a la morbilidad y muerte prematura. El sistema renina angiotensina y los riñones son los principales mecanismos que subyacen para el desarrollo de la hipertensión. La renina es la enzima limitante para la síntesis de la angiotensina II; la liberación de renina está regulada por mecanismos como el barorreceptor intrarrenal, la mácula densa (MD) y el sistema nervioso simpático. Desde la MD son liberadas prostaglandinas vasodilatadoras (PG) como PGI2 y PGE2, generadas por la ciclooxigenasa 2, que inducen la liberación de renina de las células yuxtaglomerulares. En esta revisión, mostramos los mecanismos interrelacionados entre la ciclooxigenasa 2 de la MD y la angiotensina II renal.