Identification of the LIM kinase-1 as a ceramide-regulated gene in renal mesangial cells

A Rheostat of Ceramide and Sphingosine-1-Phosphate as a Determinant of Oxidative Stress-Mediated Kidney Injury

Reactive oxygen species (ROS) modulate sphingolipid metabolism, including enzymes that generate ceramide and sphingosine-1-phosphate (S1P), and a ROS-antioxidant rheostat determines the metabolism of ceramide-S1P. ROS induce ceramide production by activating ceramide-producing enzymes, leading to apoptosis, while they inhibit S1P production, which promotes survival by suppressing sphingosine kinases (SphKs). A ceramide-S1P rheostat regulates ROS-induced mitochondrial dysfunction, apoptotic/anti-apoptotic Bcl-2 family proteins and signaling pathways, leading to apoptosis, survival, cell proliferation, inflammation and fibrosis in the kidney. Ceramide inhibits the mitochondrial respiration chain and induces ceramide channel formation and the closure of voltage-dependent anion channels, leading to mitochondrial dysfunction, altered Bcl-2 family protein expression, ROS generation and disturbed calcium homeostasis. This activates ceramide-induced signaling pathways, leading to apoptosis. These events are mitigated by S1P/S1P receptors (S1PRs) that restore mitochondrial function and activate signaling pathways. SphK1 promotes survival and cell proliferation and inhibits inflammation, while SphK2 has the opposite effect. However, both SphK1 and SphK2 promote fibrosis. Thus, a ceramide-SphKs/S1P rheostat modulates oxidant-induced kidney injury by affecting mitochondrial function, ROS production, Bcl-2 family proteins, calcium homeostasis and their downstream signaling pathways. This review will summarize the current evidence for a role of interaction between ROS-antioxidants and ceramide-SphKs/S1P and of a ceramide-SphKs/S1P rheostat in the regulation of oxidative stress-mediated kidney diseases.

Podocyte pathology and nephropathy - sphingolipids in glomerular diseases

Sphingolipids are components of the lipid rafts in plasma membranes, which are important for proper function of podocytes, a key element of the glomerular filtration barrier. Research revealed an essential role of sphingolipids and sphingolipid metabolites in glomerular disorders of genetic and non-genetic origin. The discovery that glucocerebrosides accumulate in Gaucher disease in glomerular cells and are associated with clinical proteinuria initiated intensive research into the function of other sphingolipids in glomerular disorders. The accumulation of sphingolipids in other genetic diseases including Tay-Sachs, Sandhoff, Fabry, hereditary inclusion body myopathy 2, Niemann-Pick, and nephrotic syndrome of the Finnish type and its implications with respect to glomerular pathology will be discussed. Similarly, sphingolipid accumulation occurs in glomerular diseases of non-genetic origin including diabetic kidney disease (DKD), HIV-associated nephropathy, focal segmental glomerulosclerosis (FSGS), and lupus nephritis. Sphingomyelin metabolites, such as ceramide, sphingosine, and sphingosine-1-phosphate have also gained tremendous interest. We recently described that sphingomyelin phosphodiesterase acid-like 3b (SMPDL3b) is expressed in podocytes where it modulates acid sphingomyelinase activity and acts as a master modulator of danger signaling. Decreased SMPDL3b expression in post-reperfusion kidney biopsies from transplant recipients with idiopathic FSGS correlates with the recurrence of proteinuria in patients and in experimental models of xenotransplantation. Increased SMPDL3b expression is associated with DKD. The consequences of differential SMPDL3b expression in podocytes in these diseases with respect to their pathogenesis will be discussed. Finally, the role of sphingolipids in the formation of lipid rafts in podocytes and their contribution to the maintenance of a functional slit diaphragm in the glomerulus will be discussed.

Ceramide: a common pathway for atherosclerosis?

Plasma sphingomyelin concentration is correlated with the development of atherosclerosis. It has been found to exist in significantly higher concentrations in aortic plaque. This appears to have clinical relevance as well as it has been shown to be an independent predictor of coronary artery disease. Ceramide, the backbone of sphingolipids, is the key component which affects atherosclerotic changes through its important second-messenger role. This paper sheds light on some of the current literature supporting the significance of ceramide with respect to its interactions with lipids, inflammatory cytokines, homocysteine and matrix metalloproteinases. Furthermore, the potential therapeutic implications of modulating ceramide concentrations are also discussed.

Upregulation of profilin, cofilin-2 and LIMK2 in cultured pulmonary artery smooth muscle cells and in pulmonary arteries of monocrotaline-treated rats

Pulmonary hypertension is associated with remodeling of the smooth muscle layer of pulmonary arteries, manifested by reduced smooth muscle cell (SMC) contractility and enhanced motility and growth. These responses are underlied by increased dynamics of the peripheral actin network. Thus, we hypothesized that pulmonary hypertension is associated with upregulation of two proteins that regulate the dynamics of peripheral actin filaments, i.e., profilin and cofilin. We also analyzed the expression of LIMK2, which regulates the actin remodeling capacity of cofilin by phosphorylation. Experimental inflammation was induced by incubation of cultured pulmonary artery SMCs (PASMCs) with inflammatory mediators in vitro, and by subcutaneous administration of monocrotaline to Sprague-Dawley rats in vivo. Expression of messenger RNA (mRNA) was assessed by quantitative RT-PCR, protein levels and phosphorylation were analyzed by immunoblotting. Immune and Masson trichrome stained lung cryosections were analyzed by microscopy. PDGF, IL-1beta, ET-1 and TNFalpha upregulated the profilin, cofilin-2 and LIMK2 mRNA in cultured pulmonary artery SMCs (PASMCs). Along with the development of rat pulmonary artery and right ventricular hypertrophy, monocrotaline treatment also induced the mRNA and protein contents of profilin, cofilin-2 and LIMK2 in PASMCs. The cofilin upregulation was paralleled by a relative decrease of the phospho-cofilin content. The upregulation of profilin, cofilin and LIMK2 in experimental inflammation suggests that by intensifying the remodeling of subcortical actin filaments these proteins may contribute to the enhanced invasiveness and growth of SMCs, and to the development of increased vascular resistance and pulmonary hypertension.

ClC-3 chloride channel is upregulated by hypertrophy and inflammation in rat and canine pulmonary artery

Cl- channels have been implicated in essential cellular functions including volume regulation, progression of cell cycle, cell proliferation and contraction, but the physiological functions of the ClC-3 channel are controversial. We tested the hypothesis that the ClC-3 gene (ClCn-3) is upregulated in hypertensive pulmonary arteries of monocrotaline-treated rats, and upregulated ClC-3 channel aids viability of pulmonary artery smooth muscle cells (PASMCs). Experimental pulmonary hypertension was induced in rats by a single subcutaneous administration of monocrotaline (60 mg kg(-1)). Injected animals developed characteristic features of pulmonary hypertension including medial hypertrophy of pulmonary arteries and right ventricular hypertrophy. Reverse transcriptase-polymerase chain reaction (RT-PCR), immunohistochemistry and Western immunoblot analysis indicated that histopathological alterations were associated with upregulation of the ClC-3 mRNA and protein expression in both smooth muscle cells of hypertensive pulmonary arteries and in cardiac myocytes. RT-PCR analysis of mRNA, extracted from canine cultured PASMCs, indicated that incubation with the inflammatory mediators endothelin-1 (ET-1), platelet-derived growth factor (PDGF), interleukin-1beta (IL-1beta) and tumor necrosis factor alpha (TNF alpha), but not transforming growth factor beta (TGFbeta), upregulated ClC-3 mRNA. Adenovirus-mediated delivery and overexpression of ClC-3 in canine PASMCs improved cell viability against increasing concentrations of hydrogen peroxide (H2O2, range 50-250 microM). In conclusion, upregulation of ClC-3 in rat hypertensive lung and heart is a novel observation. Our functional data suggest that upregulation of ClC-3 is an adaptive response of inflamed pulmonary artery, which enhances the viability of PASMCs against reactive oxygen species.

Clinical manifestations and molecular investigation of 50 patients with Williams syndrome in the Greek population

Williams syndrome (WS) is a well-recognized neurodevelopmental disorder manifested by both connective tissue and CNS abnormalities. The study depicts the 8-y experience and follow-up of 50 Greek children with the clinical diagnosis of WS. Clinical data on the facial features and cardiovascular, endocrinologic, and neurodevelopmental evaluation are presented. The most consistent findings were dysmorphic features (100%), followed by dental anomalies (90%) and hyperacousis (90%). Only eight of 50 children had severe cardiovascular defects that required surgical intervention during the first year of life. Supravalvular aortic stenosis was less frequent (28%) than shown in the literature. Severe hypertension was noticed in 22% of our patients, and infantile hypercalcemia was noticed in 6%. Twelve percent of our patients showed an elevation of CPK. Most children presented with moderate to severe mental retardation with IQ ranging from 20 to 85. Elastin hemizygosity was detected by fluorescence in situ hybridization. Dinucleotide repeat polymorphism analysis was performed in an attempt to correlate phenotype with genotype. The origin of deletions was more frequently maternal (59%), and a more severe phenotype seemed to be associated with those deletions. This is the first report on WS patients in the Greek population.

PDGF and IL-1β Upregulate Cofilin and LIMK2 in Canine Cultured Pulmonary Artery Smooth Muscle Cells

Actin cytoskeleton reorganization is regulated by various actin-binding proteins. Cofilin is the principal filament-depolymerizing protein, whose activity is reduced upon phosphorylation by LIMK. Thus, LIMK and cofilin comprise a signal transduction module regulating actin turnover and myogenic tone in healthy vasculature. Novel functions of smooth muscle cells (SMCs) in the hypertensive pulmonary artery, such as increased motility and proliferation, are supported by the actin cytoskeleton. We therefore hypothesized that bioactive peptides that affect these SMC functions may also result in an upregulation of LIMK and cofilin expression. Semiquantitative RT-PCR and immunoblotting indicated that LIMK2 and cofilin mRNA and protein expression is upregulated in canine pulmonary artery SMCs (PASMCs) exposed to PDGF or IL-1beta (10 ng/ml). Inhibition of ERK MAPKs (U-0126, 10 muM) or p38 MAPK (PD-169316, 10 muM), but not PI3Ks (LY-294002, 50 muM), reduced LIMK2 and cofilin gene expression stimulated by PDGF or IL-1beta. Inhibition of ROCK (Y-27632, 10 muM) reduced only the IL-1beta-stimulated LIMK2 and cofilin expression. These novel observations in PASMCs indicate that LIMK2 and cofilin expression can be induced by PDGF or IL-1beta. This parallel upregulation of LIMK2 and cofilin may have potentially broad functional significance for the progress of pulmonary artery disease.

Pressor responses to platelet-activating factor and thromboxane are mediated by Rho-kinase

Platelet-activating factor (PAF) contracts smooth muscle of airways and vessels primarily via release of thromboxane. Contraction of smooth muscle is thought to be mediated either by calcium and inositol trisphosphate (IP(3))-dependent activation of the myosin light chain kinase or, alternatively, via the recently discovered Rho-kinase pathway. Here we investigated the contribution of these two pathways to PAF and thromboxane receptor-mediated broncho- and vasoconstriction in two different rat models: the isolated perfused lung (IPL) and precision-cut lung slices. Inhibition of the IP(3) receptor (1-10 microM xestospongin C) or inhibition of phosphatidylinositol-specific PLC (30 microM L-108) did not affect bronchoconstriction but attenuated the sustained vasoconstriction by PAF. Inhibition of myosin light chain kinase (35 microM ML-7) or of calmodulin kinase kinase (26 microM STO609), which regulates the phosphorylation of the myosin light chain, had only a small effect on PAF- or thromboxane-induced pressor responses. Similarly, calmidazolium (10 microM), which inhibits calmodulin-dependent proteins, only weakly reduced the airway responses. In contrast, Y-27632 (10 microM), a Rho-kinase inhibitor, attenuated the thromboxane release triggered by PAF and provided partial or complete inhibition against PAF- and thromboxane-induced pressor responses, respectively. Together, our data indicate that PAF- and thus thromboxane receptor-mediated smooth muscle contraction depends largely on the Rho-kinase pathway.

Cofilin interacts with ClC-5 and regulates albumin uptake in proximal tubule cell lines

Receptor-mediated endocytosis is a constitutive high capacity pathway for the reabsorption of proteins from the glomerular filtrate by the renal proximal tubule. ClC-5 is a voltage-gated chloride channel found in the proximal tubule where it has been shown to be essential for protein uptake, based on evidence from patients with Dent's disease and studies in ClC-5 knockout mice. To further delineate the role of ClC-5 in albumin uptake, we performed a yeast two-hybrid screen with the C-terminal tail of ClC-5 to identify any interactions of the channel with proteins involved in endocytosis. We found that the C-terminal tail of ClC-5 bound the actin depolymerizing protein, cofilin, a result that was confirmed by GST-fusion pulldown assays. In cultured proximal tubule cells, cofilin was distributed in nuclear, cytoplasmic, and microsomal fractions and co-localized with ClC-5. Phosphorylation of cofilin by overexpressing LIM kinase 1 resulted in a stabilization of the actin cytoskeleton. Phosphorylation of cofilin in two proximal tubule cell models (porcine renal proximal tubule and opossum kidney) was also accompanied by a pronounced inhibition of albumin uptake. This study identifies a novel interaction between the C-terminal tail of ClC-5 and cofilin, an actin-associated protein that is crucial in the regulation of albumin uptake by the proximal tubule.

Nitric Oxide Signalling with a Special Focus on Lipid-Derived Mediators

The ways in which cells communicate among each other concerns all aspects of biology, from developmental processes to diseases. Nitric oxide (NO) is one of the most remarkable and unusual regulatory molecules. It is a labile free radical gas that is not stored but generated on demand, and has been implicated in an extraordinarily diverse range of physiological and pathophysiological functions. The modulation of cell signalling by free radicals is an emerging area of research that provides insight into the orchestration of cell adaptation to a changing microenvironment. In a multicellular organism this serves to coordinate complex physiological responses, such as inflammation. Cell signalling is also accompanied by rapid remodelling of membrane lipids by activated lipases. The discovery that NO, which does not reversibly interact with membrane receptors like conventional hormones and growth factors, targets enzymes such as phospholipase A2, sphingomyelinases or ceramidases, has stimulated growing interest in the crosstalk between redox and lipid signalling.