Silencing of the nuclear RPS10 gene encoding mitochondrial ribosomal protein alters translation in arabidopsis mitochondria.

Hardly anything is known about translational control of plant mitochondrial gene expression. Here, we provide evidence for differential translation of mitochondrial transcripts in Arabidopsis thaliana. We found that silencing of the nuclear RPS10 gene encoding mitochondrial ribosomal protein S10 disturbs the ratio between the small and large subunits of mitoribosomes, with an excess of the latter. Moreover, a portion of the small subunits are incomplete, lacking at least the S10 protein. rps10 cells also have an increased mitochondrial DNA copy number per cell, causing an upregulation of all mitochondrial transcripts. Mitochondrial translation is also altered so that it largely overrides the hyperaccumulation of transcripts, and as a consequence, only ribosomal proteins are oversynthesized, whereas oxidative phosphorylation subunits are downregulated. Expression of nuclear-encoded components of mitoribosomes and oxidative phosphorylation system (OXPHOS) complexes seems to be less affected. The ultimate coordination of expression of the nuclear and mitochondrial genomes occurs at the complex assembly level. These findings indicate that mitoribosomes can regulate gene expression by varying the efficiency of translation of mRNAs for OXPHOS and ribosomal proteins.

Protein quality control in organelles - AAA/FtsH story.

This review focuses on organellar AAA/FtsH proteases, whose proteolytic and chaperone-like activity is a crucial component of the protein quality control systems of mitochondrial and chloroplast membranes. We compare the AAA/FtsH proteases from yeast, mammals and plants. The nature of the complexes formed by AAA/FtsH proteases and the current view on their involvement in degradation of non-native organellar proteins or assembly of membrane complexes are discussed. Additional functions of AAA proteases not directly connected with protein quality control found in yeast and mammals but not yet in plants are also described shortly. Following an overview of the molecular functions of the AAA/FtsH proteases we discuss physiological consequences of their inactivation in yeast, mammals and plants. The molecular basis of phenotypes associated with inactivation of the AAA/FtsH proteases is not fully understood yet, with the notable exception of those observed in m-AAA protease-deficient yeast cells, which are caused by impaired maturation of mitochondrial ribosomal protein. Finally, examples of cytosolic events affecting protein quality control in mitochondria and chloroplasts are given. This article is part of a Special Issue entitled: Protein Import and Quality Control in Mitochondria and Plastids.

Proteolytic system of plant mitochondria.

The existence of a proteolytic system which can specifically recognize and cleave proteins in mitochondria is now well established. The components of this system comprise processing peptidases, ATP-dependent peptidases and oligopeptidases. A short overview of experimentally confirmed proteases mainly from Arabidopsis thaliana is provided. The role of the mitochondrial peptidases in plant growth and development is emphasized. We also discuss the possibility of existence of as yet unidentified plant homologs of yeast mitochondrial ATP-independent proteases.

ATP-dependent proteases in biogenesis and maintenance of plant mitochondria.

ATP-dependent proteases from three families have been identified experimentally in Arabidopsis mitochondria: four FtsH proteases (AtFtsH3, AtFtsH4, AtFtsH10, and AtFtsH11), two Lon proteases (AtLon1 and AtLon4), and one Clp protease (AtClpP2 with regulatory subunit AtClpX). In this review we discuss their submitochondrial localization, expression profiles and proposed functions, with special emphasis on their impact on plant growth and development. The best characterized plant mitochondrial ATP-dependent proteases are AtLon1 and AtFtsH4. It has been proposed that AtLon1 is necessary for proper mitochondrial biogenesis during seedling establishment, whereas AtFtsH4 is involved in maintaining mitochondrial homeostasis late in rosette development under short-day photoperiod.

Gene polymorphisms predisposing to cardiac hypertrophy in patients with cardiac syndrome X.

Polymorphisms of the angiotensin-converting enzyme gene and endothelial nitric oxide synthase gene have been suggested to be associated with left ventricular hypertrophy. The aim of our study was to asses the association between above polymorphisms and left ventricular hypertrophy in patients with cardiac syndrome X. The presence of allele 4 of eNOS VNTR polymorphism could predispose to cardiac hypertrophy. The pathological course of postprandial lipemia in patients with CSX may add to the understanding of the CSX pathology.

Mitoribosomal regulation of OXPHOS biogenesis in plants.

The ribosome filter hypothesis posits that ribosomes are not simple non-selective translation machines but may also function as regulatory elements in protein synthesis. Recent data supporting ribosomal filtering come from plant mitochondria where it has been shown that translation of mitochondrial transcripts encoding components of oxidative phosphorylation complexes (OXPHOS) and of mitoribosomes can be differentially affected by alterations in mitoribosomes. The biogenesis of mitoribosome was perturbed by silencing of a gene encoding a small-subunit protein of the mitoribosome in Arabidopsis thaliana. As a consequence, the mitochondrial OXPHOS and ribosomal transcripts were both upregulated, but only the ribosomal proteins were oversynthesized, while the OXPHOS subunits were actually depleted. This finding implies that the heterogeneity of plant mitoribosomes found in vivo could contribute to the functional selectivity of translation under distinct conditions. Furthermore, global analysis indicates that biogenesis of OXPHOS complexes in plants can be regulated at different levels of mitochondrial and nuclear gene expression, however, the ultimate coordination of genome expression occurs at the complex assembly level.

Phospholamban gene mutations are not associated with hypertrophic cardiomyopathy in patients from southern Poland.

BACKGROUND: Hypertrophic cardiomyopathy (HCM) is a genetic disease. The role of phospholamban (PLN) gene mutations is the development of HCM has not been established. AIM: To screen for PLN gene mutations in a group of HCM patients from the southern Poland. METHODS: We included 50 consecutive patients (31 males, mean age 42 ± 14 years) diagnosed with HCM on the basis of typical clinical, echocardiographic, and haemodynamic features. The control group consisted of 50 (sex-, age-matched) healthy subjects with normal echocardiograms. RESULTS: The genetic analysis was focused on R9C mutation with the ability to block PLN phosphorylation leading to chronic inhibition of SERCA2a activity. Another analysed mutation causing the alteration of PLN level in cells was related to the substitution of a leucine residue at position 39 with a premature stop codon (L39X). The sequence analysis of selected coding regions of the PLN gene did not show the presence of mutations in either the patients or the control subpopulations. CONCLUSIONS: Systematic mutation screening did not reveal any mutation in the selected regions of the PLN gene. Additionally, no polymorphisms were detected in any patients. Therefore, PLN gene mutations were not found to be associated with HCM in the study group.

Evaluation of genetic predisposition to insulin resistance by nutrient-induced insulin output ratio (NIOR).

BACKGROUND: New tools to identify genotype-phenotype interactions need to be described and implemented. The aim of this study was to identify correlation between the risk originating from gene variation and diet-dependent development of insulin resistance. METHODS: Insulin output in terms of area under the curve after an oral glucose tolerance test (AUC Ins OGTT) and lipid tolerance tests (AUC Ins OLTT) were measured in 167 overweight/obese patients. Estimation of the 18 common gene polymorphisms for obesity risk and standard phenotyping were performed. RESULTS: Insulin output (AUC Ins OGTT) correlated strongly between both insulin treatments across the whole group. However, within the genotype sub-groups, correlation was lower or did not exist. Using a nutrient-induced insulin output ratio (NIOR), calculated as AUC Ins OLTT/AUC Ins OGTT, values ranged from 0.42 to 5.83 and correlated significantly with body mass index (BMI) and leptin, but not with age, gender, waist-to-hip ratio (WHR) and homeostasis model assessment of insulin resistance (HOMA-IR) or plasma adiponectin. High NIOR was found in a subgroup of carriers of rare allelic variants of genes characteristic for poorer tolerance to lipids in the diet. Low NIOR values were found within a sub-group with rare genetic variants regulating carbohydrate metabolism. Thus, the new insulin index NIOR may distinguish gene variant carriers into groups of glucose- or lipid-sensitive phenotypes. CONCLUSIONS: We suggest that the OLTT/OGTT insulin output ratio (NIOR) may be predictive for identifying individuals who are phenotypically susceptible to insulin resistance in response to high fat or carbohydrate in their habitual diet.

Analysis of candidate genes in Polish families with obesity.

This study analyzes the relationship between risk factors related to overweight/obesity, insulin resistance, lipid tolerance, hypertension, endothelial function and genetic polymorphisms associated with: i) appetite regulation (leptin, melanocortin-3-receptor (MCR-3), dopamine receptor 2 (D2R)); ii) adipocyte differentiation and insulin sensitivity (peroxisome proliferator-activated receptor-gamma2 (PPAR-gamma2), tumor necrosis factor-alpha (TNF-alpha)); iii) thermogenesis and free fatty acid (FFA) transport/catabolism (uncoupling protein-1 (UCP1), lipoprotein lipase (LPL), beta2- and beta3-adrenergic receptor (beta2AR, beta3AR), fatty acid transport protein-1 (FATP-1) and iv) lipoproteins (apoliprotein E (apoE), apo CIII). The 122 members of 40 obese Caucasian families from southern Poland participated in the study. The genotypes were analyzed by restriction fragment length polymorphism-polymerase chain reaction (RFLP-PCR) or by direct sequencing. Phenotypes related to obesity (body mass index (BMI), fat/lean body mass composition, waist-to-hip ratio (WHR)), fasting lipids, glucose, leptin and insulin, as well as insulin during oral glucose tolerance test (OGTT) (4 points within 2 hours) and during oral lipid tolerance test (OLTT) (5 points within 8 hours) were assessed. The insulin sensitivity indexes: homeostasis model assessment of insulin resistance, whole body insulin sensitivity index, hepatic insulin sensitivity and early secretory response to an oral glucose load (HOMA-IR, ISI-COMP, ISI-HOMA and DELTA) were calculated. The single gene mutations such as C105 T OB and Pro115 Gln PPAR-gamma2 linked to morbid obesity were not detected in our group. A weak correlation between obesity and certain gene polymorphisms was observed. Being overweight (25 < BMI > or = 30 kg/m2) significantly correlated with worse FFA tolerance in male PPAR-gamma2 12Pro, LPL-H (G) allele carriers. Insulin resistance was found in female PPAR-gamma2 Pro12, TNF-alpha (-308A) and LPL-H (G) allele carriers. Hypertension linked to the PPAR-gamma2 Pro allele carriers was characterized by high leptin output during OLTT. We conclude that the polymorphisms we investigated were weakly correlated with obesity but significantly modified the risk factors of the metabolic syndrome.

An analysis of the link between polymorphisms of the beta2 and beta3 adrenergic receptor gene and metabolic parameters among Polish Caucasians with familial obesity.

BACKGROUND: Previous studies have suggested that genetic variation in the beta2 (b2-AR) and beta3 (b3-AR) adrenergic receptor genes are associated with obesity and insulin resistance. The aim of this study was to evaluate the influence of beta2 (Gln27>Glu) and beta3 (Trp64>Arg) adrenoreceptor gene polymorphisms on BMI and carbohydrate-lipid metabolism in Polish obese families. MATERIAL/METHODS: 122 persons (84 women, 38 men) from 40 obese families (BMI 33.5I7.7) were included. PCR-RFLP analysis of genotype was plotted against anthropometric parameters and the results of glucose and lipid oral tolerance tests. Venous blood samples were analysed for concentrations of glucose, insulin, free fatty acids, triglycerides, total cholesterol, HDL-chol, LDL-chol, leptin, and vWF. RESULTS: We found 39% Glu27 with 8% Arg64 allele frequencies. The blood glucose and insulin concentration during OGTT and blood FFA and TG level during OLTT was lower in patients with the Glu/Glu b2-AR polymorphism than Glu/Gln and Gln/Gln. In the obese patients the same effect was observed; however, the percent of fat body mass, leptin concentration, and BMI was higher in this group. Patients with the Trp/Trp polymorphism in the b3-AR gene were characterized by higher glucose and insulin concentration during OGTT and higher blood concentration of FFA and TG during OLTT. These results were independent of BMI value. CONCLUSIONS: The b2-AR 27Glu and b3-AR 64Arg alleles have a protective effect against metabolic disorders in obese families from southern Poland.