Mutant Parkin Impairs Mitochondrial Function and Morphology in Human Fibroblasts

Background: Mutations in Parkin are the most common cause of autosomal recessive Parkinson disease (PD). The mitochondrially localized E3 ubiquitin-protein ligase Parkin has been reported to be involved in respiratory chain function and mitochondrial dynamics. More recent publications also described a link between Parkin and mitophagy.Methodology/Principal Findings: In this study, we investigated the impact of Parkin mutations on mitochondrial function and morphology in a human cellular model. Fibroblasts were obtained from three members of an Italian PD family with two mutations in Parkin (homozygous c.1072delT, homozygous delEx7, compound-heterozygous c.1072delT/delEx7), as well as from two relatives without mutations. Furthermore, three unrelated compound-heterozygous patients (delEx3-4/duplEx7-12, delEx4/c.924C>T and delEx1/c.924C>T) and three unrelated age-matched controls were included. Fibroblasts were cultured under basal or paraquat-induced oxidative stress conditions. ATP synthesis rates and cellular levels were detected luminometrically. Activities of complexes I-IV and citrate synthase were measured spectrophotometrically in mitochondrial preparations or cell lysates. The mitochondrial membrane potential was measured with 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide. Oxidative stress levels were investigated with the OxyBlot technique. The mitochondrial network was investigated immunocytochemically and the degree of branching was determined with image processing methods. We observed a decrease in the production and overall concentration of ATP coinciding with increased mitochondrial mass in Parkin-mutant fibroblasts. After an oxidative insult, the membrane potential decreased in patient cells but not in controls. We further determined higher levels of oxidized proteins in the mutants both under basal and stress conditions. The degree of mitochondrial network branching was comparable in mutants and controls under basal conditions and decreased to a similar extent under paraquat-induced stress.Conclusions: Our results indicate that Parkin mutations cause abnormal mitochondrial function and morphology in non-neuronal human cells

Differential response of myeloid-derived suppressor cells to the nonsteroidal anti-inflammatory agent indomethacin in tumor-associated and tumor-free microenvironments

Myeloid-derived suppressor cells (MDSCs) are key regulatory cells that control inflammation and promote tumor-immune escape. To date, no specific immunomodulatory drug has proven efficacy in targeting the expansion and/or function of these cells in different pathophysiologic settings. In this study, we identified a context-dependent effect of the nonsteroidal anti-inflammatory drug indomethacin (IND) on MDSCs, depending on whether they were derived from tumor microenvironments (TME) or from tumor-free microenvironments (TFME). Treatment of mice bearing the LP07 lung adenocarcinoma with IND inhibited the suppressive activity of splenic MDSCs, which restrained tumor growth through mechanisms involving CD8(+) T cells. The same effect was observed when MDSCs were treated with IND and conditioned media from LP07 tumor cells in vitro. However, in the absence of a tumor context, IND enhanced the intrinsic suppressive function of MDSCs and amplified their protumoral activity. In a model of autoimmune neuroinflammation, IND-treated MDSCs differentiated in TFME attenuated inflammation, whereas IND-treated MDSCs differentiated in TME aggravated clinical symptoms and delayed resolution of the disease. Mechanistically, IND reduced arginase activity as well as NO and reactive oxygen species production in MDSCs differentiated in TME but not in TFME. Moreover, expression of the C/EBP-â transcription factor isoforms correlated with the suppressive activity of IND-treated MDSCs. Our study unveils the dual and context-dependent action of IND, a drug that serves both as an anti-inflammatory and anticancer agent, which differentially affects MDSC activity whether these cells are derived from TME or TFME. These results have broad clinical implication in cancer, chronic inflammation and autoimmunityFil: Blidner, Ada Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Oncología "Ángel H. Roffo"; ArgentinaFil: Salatino, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; ArgentinaFil: Mascanfroni, Ivan Darío. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; ArgentinaFil: Diament, Miriam. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Oncología "Ángel H. Roffo"; ArgentinaFil: Bal, Elisa Dora. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Oncología "Ángel H. Roffo"; ArgentinaFil: Maria A. Jasnis. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Oncología "Ángel H. Roffo"; ArgentinaFil: Slobodanka M. Klein. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Oncología "Ángel H. Roffo"; ArgentinaFil: Rabinovich, Gabriel Adrián. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentin

Novel homozygous p.E64D mutation in DJ1 in early onset Parkinson disease (PARK7).

Mutations in the parkin gene have been identified as a common cause of autosomal recessive inherited Parkinson disease (PD) associated with early disease manifestation. However, based on linkage data, mutations in other genes contribute to the genetic heterogeneity of early-onset PD (EOPD). Recently, two mutations in the DJ1 gene were described as a second cause of autosomal recessive EOPD (PARK7). Analyzing the PARK7/DJ1 gene in 104 EOPD patients, we identified a third mutation, c.192G>C (p.E64D), associated with EOPD in a patient of Turkish ancestry and characterized the functional significance of this amino acid substitution. In the patient, a substantial reduction of dopamine uptake transporter (DAT) binding was found in the striatum using [(18)F]FP-CIT and PET, indicating a serious loss of presynaptic dopaminergic afferents. His sister, homozygous for E64D, was clinically unaffected but showed reduced dopamine uptake when compared with a clinically unaffected brother, who is heterozygous for E64D. We demonstrate by crystallography that the E64D mutation does not alter the structure of the DJ1 protein, however we observe a tendency towards decreased levels of the mutant protein when overexpressed in HEK293 or COS7 cells. Using immunocytochemistry in contrast to the homogenous nuclear and cytoplasmic staining in HEK293 cells overexpressing wild-type DJ1, about 5% of the cells expressing E64D and up to 80% of the cells expressing the recently described L166P mutation displayed a predominant nuclear localization of the mutant DJ1 protein

Morphology of the mitochondrial network.

<p>(A) Images of the mitochondrial network in control and patient fibroblasts demonstrating similar degrees of branching under basal culturing conditions. (B) After treatment with paraquat, the network was less branched in patients and controls. (C) The degree of mitochondrial branching (form factor) was comparable in patients (median [IQR]: 78% [66%, 90%]) and controls (median [IQR]: 100% [73%, 105%]) under standard cell culturing conditions. When treated with paraquat (shaded boxes), the form factor decreased significantly in the mutant samples (median [IQR]: 46% [43%, 54%]). By contrast, a drop seen in controls (median [IQR]: 70% [32%, 84%]) was not significant. (D) Citrate synthase activity in cell lysates. <i>Parkin</i> mutants (median [IQR]: 183% [125%, 232%]) showed significantly higher citrate synthase activities than controls (median [IQR]: 100% [43%, 101%]), indicative of increased mitochondrial mass per cell in the former. Citrate synthase activity in cell lysates was normalized for protein concentration. The median, the interquartile range (IQR), the minimum and the maximum value of the investigated groups of individuals are shown.</p

Mitochondrial function.

<p>(A) Basal ATP synthesis rates. The assay demonstrated a significant reduction in ATP production in the <i>Parkin</i>-mutant patients (median [IQR]: 39% [23%, 55%]) compared to controls (set to 100%). (B) Basal ATP levels. Quantifying the overall cellular ATP concentration showed significantly lower levels in the mutants (median [IQR]: 69% [58%, 75%]) than in controls (set to 100%). (C) Mitochondrial membrane potential under basal and oxidative stress conditions. Control (median [IQR]: 100% [94%, 115%]) and patient fibroblasts (median [IQR]: 113% [93%, 128%]) with <i>Parkin</i> mutations show similar membrane potential under basal conditions. When the cells were treated with paraquat (shaded boxes), no relevant changes were detected in the controls (median [IQR]: 102% [100%, 118%]). In the <i>Parkin</i> mutants, a significant drop of the membrane potential was observed (median [IQR]: 84% [81%, 103%]). The median, the interquartile range (IQR), the minimum and the maximum value of 6 (A) or 4 (B) independent experimental runs are plotted. In each experimental run the average ATP level in the controls was set to 100%.</p

Table 1. Genotypic and phenotypic characterisation of investigated individuals.

<p>Table 1. Genotypic and phenotypic characterisation of investigated individuals.</p

Protein oxidation under basal and stress conditions.

<p>Oxidation of proteins in <i>Parkin</i>-mutant fibroblasts and controls was determined by means of an OxyBlot. (A) When quantifying the protein oxidation in each individual using an antibody against DNP, the <i>Parkin</i> mutants (median [IQR]: 123% [113%, 136%]) showed significantly higher levels of oxidation than the controls (median [IQR]: 100% [97%, 105%]). After treatment of the cells with paraquat (shaded boxes), the difference in oxidation between mutants (median [IQR]: 131% [96%, 172%]) and controls (median [IQR]: 100% [90%, 102%]) increased, but was no longer significant. Equal protein loading was verified with an antibody against β-actin. Expression ratios of oxidized proteins vs. β-actin were calculated. The median, the interquartile range (IQR), the minimum and the maximum value of the investigated groups of individuals are given. (B) OxyBlot of pooled protein samples before and after paraquat treatment showing a similar trend as identified by individual measurements.</p