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The study results from conplastic strains of rat model which provide evidence linking naturally occurring variation in the mitochondrial genome, independent of variation in the nuclear genome and other confounding factors, to inherited variation in known risk factors for type 2 diabetes is presented.

Loss-of-function studies show that the human mitochondrial YME1L protease ensures cell proliferation, maintains normal cristae morphology and complex I activity, acts in an antiapoptotic manner, protects mitochondria from accumulation of oxidatively damaged membrane proteins, and is involved in proteolytic regulation of respiratory chain biogenesis.

A retrospective, multicenter study of 180 children with cytochrome coxidase (COX) deficiency analyzed the clinical features, prognosis, and molecular bases of the COX deficiency. Clinical symptoms including failure to thrive, encephalopathy, hypotony, Leigh syndrome, cardiac involvement, and hepatopathy appeared in most patients early after birth or in early childhood. Two thirds of all children died. Biochemical examination revealed an isolated COX deficiency in 101 children and COX deficiency combined with disturbances of other respiratory chain complexes in 79 children. Blood and cerebrospinal fluid lactate increased in 85% and 81% of examined cases, respectively. Pathogenic mutations in mitochondrial or nuclear DNA were established in 75 patients. Mutations in surfeit locus protein 1 gene (SURF1) were found in 47 children with Leigh syndrome; 2bp deletion 845-846delCT was found in 89% of independent alleles. Mutations in a mitochondrial copper-binding protein (SCO2) gene were found in nine children with encephalomyopathy and/or cardiomyopathy; all of them were homozygotes or heterozygotes for 1541G>A mutation. Different mitochondrial DNA (mtDNA) deletion or depletion were found in nine children, mtDNA mutation 3243A>G in six, mtDNA mutation 8363G>A in two children with Leigh syndrome and mtDNA mutations 8344A>G, and 9205-9206delTA in one child each. COX deficiency represents a heterogeneous group of diseases with unfavorable prognosis. Marked prevalence of two nuclear DNA mutations (845-846delCT in the SURF1gene and 1541G>A in the SCO2gene) associated with COX deficiency in a Slavonic population suggests the existence of regional differences in the genetic basis of COX deficiency.

A retrospective, multicenter study of 180 children with cytochrome c oxidase (COX) deficiency analyzed the clinical features, prognosis, and molecular bases of the COX deficiency. Clinical symptoms including failure to thrive, encephalopathy, hypotony, Leigh syndrome, cardiac involvement, and hepatopathy appeared in most patients early after birth or in early childhood. Two thirds of all children died. Biochemical examination revealed an isolated COX deficiency in 101 children and COX deficiency combined with disturbances of other respiratory chain complexes in 79 children. Blood and cerebrospinal fluid lactate increased in 85% and 81% of examined cases, respectively. Pathogenic mutations in mitochondrial or nuclear DNA were established in 75 patients. Mutations in surfeit locus protein 1 gene (SURF1) were found in 47 children with Leigh syndrome; 2bp deletion 845-846delCT was found in 89% of independent alleles. Mutations in a mitochondrial copper-binding protein (SCO2) gene were found in nine children with encephalomyopathy and/or cardiomyopathy; all of them were homozygotes or heterozygotes for 1541G>A mutation. Different mitochondrial DNA (mtDNA) deletion or depletion were found in nine children, mtDNA mutation 3243A>G in six, mtDNA mutation 8363G>A in two children with Leigh syndrome and mtDNA mutations 8344A>G, and 9205-9206delTA in one child each. COX deficiency represents a heterogeneous group of diseases with unfavorable prognosis. Marked prevalence of two nuclear DNA mutations (845-846delCT in the SURF1 gene and 1541G>A in the SCO2 gene) associated with COX deficiency in a Slavonic population suggests the existence of regional differences in the genetic basis of COX deficiency.

The biogenesis of eukaryotic COX (cytochrome c oxidase) requires several accessory proteins in addition to structural subunits and prosthetic groups. We have analysed the assembly state of COX and SCO2 protein levels in various tissues of six patients with mutations in SCO2 and SURF1. SCO2 is a copper-binding protein presumably involved in formation of the CuA centre of the COX2 subunit. The function of SURF1 is unknown. Immunoblot analysis of native gels demonstrated that COX holoenzyme is reduced to 10–20% in skeletal muscle and brain of SCO2 and SURF1 patients and to 10–30% in heart of SCO2 patients, whereas liver of SCO2 patients' contained normal holoenzyme levels. The steady-state levels of mutant SCO2 protein ranged from 0 to 20% in different SCO2 patient tissues. In addition, eight distinct COX subcomplexes and unassembled subunits were found, some of them identical with known assembly intermediates of the human enzyme. Heart, brain and skeletal muscle of SCO2 patients contained accumulated levels of the COX1·COX4·COX5A subcomplex, three COX1-containing subcomplexes, a COX4·COX5A subcomplex and two subcomplexes composed of only COX4 or COX5A. The accumulation of COX1·COX4·COX5A subcomplex, along with the virtual absence of free COX2, suggests that the lack of the CuA centre may result in decreased stability of COX2. The appearance of COX4·COX5A subcomplex indicates that association of these nucleus-encoded subunits probably precedes their addition to COX1 during the assembly process. Finally, the consequences of SCO2 and SURF1 mutations suggest the existence of tissue-specific functional differences of these proteins that may serve different tissue-specific requirements for the regulation of COX biogenesis.

Although mitochondrial deficiency in cancer has been described by Warburg, many years ago, the mechanisms underlying this impairment remain essentially unknown. Many types of cancer cells are concerned and, in particular, clear cell renal carcinoma (CCRC). In this cancer, the tumor suppressor gene, VHL (von Hippel-Lindau factor) is invalidated. Previous studies have shown that the transfection of the VHL gene in VHL-deficient cells originating from CCRCs could suppress their ability to form tumors when they were injected into nude mice. However, various additional genetic alterations are observed in such cancer cells. In order to investigate whether VHL invalidation was related to the mitochondrial impairment, we have studied the effects of wild-type VHL transfection into VHL-deficient 786-0 or RCC10 cells on their oxidative phosphorylation (OXPHOS) subunit contents and functions. We show that the presence of wild-type VHL protein (pVHL) increased mitochondrial DNA and respiratory chain protein contents and permitted the cells to rely on their mitochondrial ATP production to grow in the absence of glucose. In parallel to mtDNA increase, the presence of pVHL up regulated the mitochondrial transcription factor A, as shown by western blot analysis. In conclusion, in CCRCs, pVHL deficiency is one of the factors responsible for down-regulation of the biogenesis of OXPHOS complexes.

Based on electrophoretic mobility-shift assays and UV cross-linking experiments, we present evidence in the present work for the existence of two mammalian cytosolic proteins that selectively interact with the 3ʹ-untranslated region of the mRNA coding for the catalytic β-subunit of mitochondrial ATP synthase (β-mtATPase). One of the proteins, β-mtATPase mRNA-binding protein (BARB)1, is a novel poly(A)-binding protein that specifically binds the poly(A) tail of the β-mtATPase transcript. BARB1 achieves this mRNA selectivity through its interaction with a second protein, BARB2, that binds the β-mtATPase mRNA through a 22-bp element with a uridylate core, located 75 bp upstream of the poly(A) tail. Conversely, in the absence of BARB1, BARB2 is still able to bind the β-mtATPase mRNA, but does so with lower affinity. Thus the interaction between BARB1 and BARB2 and β-mtATPase mRNA involves the formation of a complex between the two BARB proteins. We conclude that BARB1 and BARB2 selectively bind the 3ʹ-untranslated region of β-mtATPase mRNA in a novel and interdependent manner. The complex between these two proteins may be involved in post-transcriptional regulation of gene expression.

ABSTRACT: Brown adipose tissue (BAT) produces heat by oxidation of fatty acids. This takes place when the tissue is stimulated by norepinephrine; the molecular background for the ability of BAT to produce heat is the tissue‐specific mitochondrial protein UCP1. In the classic view of BAT with respect to fever, BAT is an effector organ, producing heat especially during the onset phase of the fever. There is good evidence that BAT thermogenesis is stimulated via a lipopolysaccharide (LPS), interleukin (IL)‐1β, IL‐6, prostaglandin E cascade. Under physiologic conditions of constantly stimulated activity, BAT is expected to be recruited, but in fevers this is only evident in thyroxine fever. However, BAT may be more than merely an effector. There are indications of a correlation between the amount of BAT and the intensity of fevers, and brown adipocytes can indeed produce IL‐1α and IL‐6. Furthermore, brown adipocytes are directly sensitive to LPS; this LPS sensitivity is augmented in brown adipocytes from IL‐1β‐deficient mice. Thus, BAT may also have a controlling role in thermoregulation. The existence of transgenic mice with ablations of proteins central in fever and in BAT thermogenesis opens up possibilities for identification and elucidation of this putative new role for brown adipose tissue as an endocrine organ involved in the control of fever.

A low content of mitochondrial ATPase in brown adipose tissue (BAT) has previously been found to contrast with high levels of the transcripts of the β-subunit of the F1part of the ATPase and of the transcripts of the mitochondrial encoded subunits (Houstek, J., Tvrdík, P., Pavelka, S., and Baudysová, M.(1991) FEBS Lett.294, 191-194). To delineate which subunit limits the synthesis of the ATPase complex, we have studied the expression of the nuclear genes encoding subunits α, β, and γ of the catalytic F1part and the b, c, d, and OSCP subunits of the F0part of the ATPase.