Francesco Bellomo

Dysfunctions of Cellular Oxidative Metabolism in Patients with Mutations in the NDUFS1 and NDUFS4 Genes of Complex I

The pathogenic mechanism of a G44A nonsense mutation in the NDUFS4 gene and a C1564A mutation in the NDUFS1 gene of respiratory chain complex I was investigated in fibroblasts from human patients. As previously observed the NDUFS4 mutation prevented complete assembly of the complex and caused full suppression of the activity. The mutation (Q522K replacement) in NDUFS1 gene, coding for the 75-kDa Fe-S subunit of the complex, was associated with (a) reduced level of the mature complex, (b) marked, albeit not complete, inhibition of the activity, (c) accumulation of H2O2 and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{O}_{{\dot{2}}}^{-}\) \end{document} in mitochondria, (d) decreased cellular content of glutathione, (e) enhanced expression and activity of glutathione peroxidase, and (f) decrease of the mitochondrial potential and enhanced mitochondrial susceptibility to reactive oxygen species (ROS) damage. No ROS increase was observed in the NDUFS4 mutation. Exposure of the NDUFS1 mutant fibroblasts to dibutyryl-cAMP stimulated the residual NADH-ubiquinone oxidoreductase activity, induced disappearance of ROS, and restored the mitochondrial potential. These are relevant observations for a possible therapeutical strategy in NDUFS1 mutant patients.

Mitochondrial Respiratory Dysfunction in Familiar Parkinsonism Associated with PINK1 Mutation

In the present study mitochondrial respiratory function of fibroblasts from a patient affected by early-onset Parkinsonism carrying the homozygous W437X nonsense mutation in the PINK1 gene has been thoroughly characterized. When compared with normal fibroblasts, the patient’s fibroblast mitochondria exhibited a lower respiratory activity and a decreased respiratory control ratio with cellular ATP supply relying mainly on enhanced glycolytic production. The quantity, specific activity and subunit pattern of the oxidative phosphorylation complexes were normal. However, a significant decrease of the cellular cytochrome c content was observed and this correlated with a reduced cytochrome c oxidase in situ-activity. Measurement of ROS revealed in mitochondria of the patient’s fibroblasts enhanced O2•− and H2O2 production abrogated by inhibition of complex I. No change in the glutathione-based redox buffering was, however, observed.

Stem cell microvesicles transfer cystinosin to human cystinotic cells and reduce cystine accumulation in vitro.

Cystinosis is a rare disease caused by homozygous mutations of the CTNS gene, encoding a cystine efflux channel in the lysosomal membrane. In Ctns knockout mice, the pathologic intralysosomal accumulation of cystine that drives progressive organ damage can be reversed by infusion of wildtype bone marrow-derived stem cells, but the mechanism involved is unclear since the exogeneous stem cells are rarely integrated into renal tubules. Here we show that human mesenchymal stem cells, from amniotic fluid or bone marrow, reduce pathologic cystine accumulation in co-cultured CTNS mutant fibroblasts or proximal tubular cells from cystinosis patients. This paracrine effect is associated with release into the culture medium of stem cell microvesicles (100–400 nm diameter) containing wildtype cystinosin protein and CTNS mRNA. Isolated stem cell microvesicles reduce target cell cystine accumulation in a dose-dependent, Annexin V-sensitive manner. Microvesicles from stem cells expressing CTNSRed transfer tagged CTNS protein to the lysosome/endosome compartment of cystinotic fibroblasts. Our observations suggest that exogenous stem cells may reprogram the biology of mutant tissues by direct microvesicle transfer of membrane-associated wildtype molecules.

cAMP controls oxygen metabolism in mammalian cells

The impact of cAMP on ROS‐balance in human and mammalian cell cultures was studied. cAMP reduced accumulation of ROS induced by serum‐limitation, under conditions in which there was no significant change in the activity of scavenger systems. This effect was associated with cAMP‐dependent activation of the NADH‐ubiquinone oxidoreductase activity of complex I. In fibroblasts from a patient a genetic defect in the 75 kDa FeS‐protein subunit of complex I resulted in inhibition of the activity of the complex and enhanced ROS production, which were reversed by cAMP. A missense genetic defect in the NDUFS4 subunit, putative substrate of PKA, suppressed, on the other hand, the activity of the complex and prevented ROS production.

Identification and subcellular localization of a new cystinosin isoform

Nephropathic cystinosis is a lysosomal disorder caused by functional defects of cystinosin, which mediates cystine efflux into the cytosol. The protein sequence contains at least two signals that target the protein to the lysosomal compartment, one of which is located at the carboxy terminal tail (GYDQL). We have isolated from a human kidney cDNA library a cystinosin isoform, which is generated by an alternative splicing of exon 12 that removes the GYDQL motif. Based on its last three amino acids, we have termed this protein cystinosin-LKG. Contrary to the lysosomal cystinosin isoform, expression experiments performed by transient transfection of green fluorescent protein fusion plasmids in HK2 cells showed that cystinosin-LKG is expressed in the plasma membrane, in lysosomes, and in other cytosolic structures. This subcellular localization of the protein was confirmed by transmission electron microscopy. In addition, immunogold labeling was observed in the endoplasmic reticulum and in the Golgi apparatus. Expression of the protein in renal tubular structures was also directly demonstrated by immunostaining of normal human kidney sections. The plasma membrane localization of cystinosin-LKG was directly tested by [(35)S]cystine flux experiments in COS-1 cells. In the presence of a proton gradient, a marked enhancement of intracellular cystine transport was observed in cells overexpressing this isoform. These data indicate that the expression of the gene products encoded by the CTNS gene is not restricted to the lysosomal compartment. These finding may help elucidate the mechanisms of cell dysfunction in this disorder.

Modulation of CTNS gene expression by intracellular thiols

The cysteine/cystine (Cys/CySS) couple represents one of the major cell thiol/disulfide systems and is involved in the regulation of several metabolic pathways and the cell redox state. Nephropathic cystinosis (NC) is an autosomal recessive disease characterized by renal cellular dysfunction due to mutations in the CTNS gene, which encodes cystinosin, a CySS lysosomal transporter. To analyze the mechanisms involved in cell damage in NC, we have investigated the effects of CTNS gene overexpression or inhibition on cell thiol/disulfide systems and vice versa. Overexpression of the CTNS gene had no remarkable effect on intracellular Cys/CySS and GSH/GSSG redox state. Silencing the CTNS gene increased cell CySS and Cys and decreased cell GSH and GSSG and increased mildly the redox state of the Cys/CySS-couple. Extracellular CySS and Cys deprivation for 48 h caused an oxidation of the Cys/CySS (73 mV) and GSH/GSSG (100 mV) redox couples and increased CTNS mRNA levels by 1.9+/-0.2-fold (p<0.001). Conversely, a reduced cell environment associated with a GSH/GSSG reduction from -250.1+/-3.10 to -330.6+/-4.70 mV (p<0.001) and a Cys/CySS reduction from -167.0+/-11.30 to -240.0+/-8.17 mV (p<0.005) was associated with a 40% decrease in CTNS mRNA levels (p<0.05). By regression analysis, CTNS gene expression was correlated with intracellular Cys level and with Cys/CySS redox state.

Differential effects of all-trans retinoic acid on the growth of human keratinocytes and mouth carcinoma epidermoid cultures. Involvement of GRIM-19 and complex I of the respiratory chain.

Squamous cell carcinoma (SSC) is the most frequent malignant tumor of the oral cavity. A study on the effect of all-trans retinoic acid (RA) on cell growth, expression of GRIM-19 and content and activity of complex I of the mitochondrial respiratory chain in normal human keratinocytes (NHEK) and mouth carcinoma cells with low (HN) and high (KB) transformation grade was carried out. In NHEK cells, RA treatment resulted in growth suppression, significant overexpression of GRIM-19 protein, enhanced content of complex I but depressed activity of NADH-UQ oxidoreductase activity of the complex. In HN cells, RA treatment depressed cell growth, inhibited the enzymatic activity of complex I but had no significant effect on the levels of GRIM-19 and complex I. In KB cells RA had no effect on cell growth, GRIM-19 expression, content and activity of complex I.

Cysteamine treatment restores the in vitro ability to differentiate along the osteoblastic lineage of mesenchymal stromal cells isolated from bone marrow of a cystinotic patient

BackgroundCystinosis is a rare autosomal recessive disease caused by mutations of the CTNS gene, which encodes for a lysosomal cystine/H+ symporter. In mice, inactivation of the CTNS gene causes intralysosomal cystine accumulation and progressive organ damage that can be reversed, at least in part, by infusion of mesenchymal stromal cells (MSCs). Little is known on the mesenchymal compartment of cystinotic patients. The aim of the study was to test the phenotypical and functional properties of cystinotic MSCs (Cys-MSCs) isolated from bone marrow (BM) aspirate of a patient with nephropathic cystinosis.MethodsMorphology, proliferative capacity (measured as population doublings), immunophenotype (by flow-cytometry) and immunomodulatory properties (as phytohemagglutinin-induced peripheral blood mononuclear cell proliferation) were analyzed. The osteogenic differentiation potential of Cys-MSCs was evaluated by histological staining (alkaline phosphatase activity, Alzarin Red and von Kossa staining) spectrophotometry and Quantitative Reverse Transcriptase Polymerase Chain Reaction for osteigenic markers in the presence and in the absence of cysteamine. Cys-MSCs were compared with those isolated and expanded ex vivo from three healthy donors (HD-MSCs).ResultsDespite a slightly lower proliferative capacity, Cys-MSCs displayed a characteristic spindle-shaped morphology and similar immunephenotype as HD-MSCs. Cys-MSCs and HD-MSCs prevented proliferation of PHA-stimulated allogeneic peripheral blood mononuclear cells to the same extent. After in vitro induction into osteoblasts, Cys-MSCs showed reduced alkaline phosphatase (ALP) activity, calcium depositions and expression of ALP and collagen type 1. When Cys-MSCs were treated in vitro with increasing doses of cysteamine (50-100-200 μM/L) during the differentiation assay, recovery of Cys-MSCs differentiation capacity into osteoblasts was observed. No difference in adipogenic differentiation was found between Cys-MSCs and HD-MSCs.ConclusionsOur results indicate that, as compared to HD-MSCs, Cys-MSCs show reduced ability to differentiate into osteoblasts, which can be reverted after cysteamine treatment.

High-content drug screening for rare diseases

Per definition, rare diseases affect only a small number of subjects within a given population. Taken together however, they represent a considerable medical burden, which remains poorly addressed in terms of treatment. Compared to other diseases, obstacles to the development of therapies for rare diseases include less extensive physiopathology knowledge, limited number of patients to test treatments, and poor commercial interest from the industry. Recently, advances in high-throughput and high-content screening (HTS and HCS) have been fostered by the development of specific routines that use robot- and computer-assisted technologies to automatize tasks, allowing screening of a large number of compounds in a short period of time, using experimental model of diseases. These approaches are particularly relevant for drug repositioning in rare disease, which restricts the search to compounds that have already been tested in humans, thereby reducing the need for extensive preclinical tests. In the future, these same tools, combined with computational modeling and artificial neural network analyses, may also be used to predict individual clinical responses to drugs in a personalized medicine approach.

Transcriptional and Posttranscriptional Regulation of the CTNS Gene

Cell cysteine (Cys) levels and/or the [Cys/CySS] redox potential have been shown to regulate mRNA levels of the CTNS gene, which encodes for a lysosomal cystine (CySS) carrier that is defective in cystinosis. To investigate the mechanisms involved CTNS mRNA regulation, different portions of the CTNS promotor were cloned into a luciferase vector and transfected in HK2 cells. A 1.5–2.4-fold increase in luciferase activity was observed when cells were incubated in culture medium containing low CySS concentrations. Conversely, CTNS mRNA levels decreased by 47–56% in the presence of N-acetyl-l-cysteine (NAC). Chase experiments with actinomycin D (ActD) demonstrated a 3-fold stabilization of the CTNS mRNA when cells were cultured in low CySS medium for 48 h. Treatment of control cells with cyclohexamide (CHX) increased CTNS mRNA levels, suggesting that CHX blocked the synthesis of proteins involved in mRNA degradation or in repression of the CTNS gene. Finally, in vitro binding assays showed increased binding (30–110%) of the Sp-1 transcription factor to two regions of the CTNS promotor when cells were incubated in low CySS medium. These results indicate that the CTNS gene is actively regulated at the transcriptional and posttranscriptional levels and suggest that CTNS plays a pivotal role in regulating cell thiol concentrations.