Cerebral vasomotor reactivity and extent of white matter lesions in middle-aged men with arterial hypertension: a pilot study.

BACKGROUND: Cerebrovascular reactivity (CVR) impairment and cerebral white matter lesions (WMLs) are associated in elderly or patients with overt cerebral ischemia. Such association has not been confirmed for asymptomatic middle-aged individuals with risk factors for stroke. We assessed the relationship between the CVR and the presence of WMLs in a middle-aged population-based cohort of hypertensive men. METHODS: Magnetic resonance imaging (MRI) and transcranial Doppler (TCD) examination were performed in 54 hypertensive men, all at 60 years of age, without a history of stroke, neurologic deficits, or carotid stenosis. The CVR of the middle cerebral artery (MCA) was expressed as the vasomotor reactivity reserve (VMRr). RESULTS: WMLs were detected in 22 men (40.7%); all WMLs were classified as mild (first grade of the Fazekas modified scale). The VMRr was lower in patients with WMLs (mean 55%; s.e. 3%) compared to those without WMLs (mean 65%; s.e. 3%; P = 0.03). The lower VMRr in patients with WMLs was consistent after controlling for confounders. A higher pulsatility index (PI) in subjects with WMLs (mean 1.08; s.e. 0.05) compared to those without WMLs (mean 0.90; s.e. 0.05; P = 0.01) was not consistent after controlling for confounders. CONCLUSIONS: The CVR was lower in middle-aged hypertensive men with WMLs compared to those without WMLs indicating that even a low load of WMLs may reflect some functional impairment of the cerebral microvasculature.

Human mitochondrial RNA turnover caught in flagranti: involvement of hSuv3p helicase in RNA surveillance.

The mechanism of human mitochondrial RNA turnover and surveillance is still a matter of debate. We have obtained a cellular model for studying the role of hSuv3p helicase in human mitochondria. Expression of a dominant-negative mutant of the hSUV3 gene which encodes a protein with no ATPase or helicase activity results in perturbations of mtRNA metabolism and enables to study the processing and degradation intermediates which otherwise are difficult to detect because of their short half-lives. The hSuv3p activity was found to be necessary in the regulation of stability of mature, properly formed mRNAs and for removal of the noncoding processing intermediates transcribed from both H and L-strands, including mirror RNAs which represent antisense RNAs transcribed from the opposite DNA strand. Lack of hSuv3p function also resulted in accumulation of aberrant RNA species, molecules with extended poly(A) tails and degradation intermediates truncated predominantly at their 3'-ends. Moreover, we present data indicating that hSuv3p co-purifies with PNPase; this may suggest participation of both proteins in mtRNA metabolism.

[Lung microangiopathy in diabetes]. / Mikroangiopatia plucna w przebiegu cukrzycy.

Diabetes mellitus (DM) is the metabolic disorder, which is characterised by persistent hyperglycaemia and abnormal metabolism of carbohydrates, proteins and lipids. These metabolic disorders result from impaired insulin secretion, altered tissue sensitivity to insulin or the coexistence of both these mechanisms. Chronic DM usually results in micro- and macroangiopathy, which in turn may have a negative impact on the function of internal organs. Microangiopathy specifically affects eyes (retinopathy), kidney (nephropathy) and peripheral nervous system (neuropathy). Little is known about the influence of diabetic microangiopathy on lung function. A few available papers describe lung function and lung diffusing capacity for carbon monoxide (DLCO) impairment in patients with both DM type 1 and type 2. Reduction of DLCO can indicate, however, that DM leads to alveolar-capillary barrier damage in the lung. In this paper authors review available literature on microangiopathy and its influence on the lung function.

Down-regulation of human RNA/DNA helicase SUV3 induces apoptosis by a caspase- and AIF-dependent pathway.

BACKGROUND INFORMATION: The nuclear gene hSUV3 (human SUV3) encodes an ATP-dependent DNA/RNA helicase. In the yeast Saccharomyces cerevisiae the orthologous Suv3 protein is localized in mitochondria, and is a subunit of the degradosome complex which regulates RNA surveillance and turnover. In contrast, the functions of human SUV3 are not known to date. RESULTS: In the present study, we show that a fraction of human SUV3 helicase is localized in the nucleus. Using small interfering RNA gene silencing in HeLa cells, we demonstrate that down-regulation of hSUV3 results in cell cycle perturbations and in apoptosis, which is both AIF- and caspase-dependent, and proceeds with the induction of p53. CONCLUSIONS: In addition to its mitochondrial localization, human SUV3 plays an important role in the nucleus and is probably involved in chromatin maintenance.

Differential stability of mitochondrial mRNA in HeLa cells.

The physiological significance and metabolism of oligoadenylated and polyadenylated human mitochondrial mRNAs are not known to date. After study of eight mitochondrial transcripts (ND1, ND2, ND3, ND5, CO1, CO2, ATP6/8 and Cyt. b) we found a direct correlation between the half-lives of mitochondrial mRNAs and their steady-state levels. Investigation of the mt-mRNA decay after thiamphenicol treatment indicated that three transcripts (ND2, ND3 and Cyt. b) are significantly stabilized after inhibition of mitochondrial translation. Careful analysis one of them, ND3, showed that inaccurate processing of the H-strand RNA precursor may occasionally occur between the ND3 and tRNA(Arg) locus leading to synthesis of ND3 mRNAs lacking the STOP codon. However, analysis of the oligo(A) fraction observed in case of the ND3 indicates that partially polyadenylated mRNAs are linked rather to the transcription process than to the translation-dependent deadenylation. Analysis of ND3 mRNA turnover in cells with siRNA-mediated knock-down of the mitochondrial poly(A) polymerase shows that strongly decreased polyadenylation does not markedly affect the decay of this transcript. We present a model where oligoadenylated mitochondrial transcripts are precursors of molecules containing full length poly(A) tails.

Identification of a novel human nuclear-encoded mitochondrial poly(A) polymerase.

We report here on the identification of a novel human nuclear-encoded mitochondrial poly(A) polymerase. Immunocytochemical experiments confirm that the enzyme indeed localizes to mitochondrial compartment. Inhibition of expression of the enzyme by RNA interference results in significant shortening of the poly(A) tails of the mitochondrial ND3, COX III and ATP 6/8 transcripts, suggesting that the investigated protein represents a bona fide mitochondrial poly(A) polymerase. This is in agreement with our sequencing data which show that poly(A) tails of several mitochondrial messengers are composed almost exclusively of adenosine residues. Moreover, the data presented here indicate that all analyzed mitochondrial transcripts with profoundly shortened poly(A) tails are relatively stable, which in turn argues against the direct role of long poly(A) extensions in the stabilization of human mitochondrial messengers.

RNA degradation in yeast and human mitochondria.

RNA turnover in yeast mitochondria is controlled by the complex called degradosome, which consists of two nuclear-encoded proteins: the SUV3 gene codes for an RNA helicase and the DSS1 gene codes for an RNase. In contrast to yeast, much less is known about RNA degradation in human mitochondria. We suggest that the key enzyme involved in this process is nuclear-encoded polynucleotide phosphorylase, hPNPase.

Human polynucleotide phosphorylase, hPNPase, is localized in mitochondria.

The human gene encoding a polynucleotide phosphorylase (hPNPase) has been recently identified as strongly up-regulated in two processes leading to irreversible arrest of cell division: progeroid senescence and terminal differentiation. Here, we demonstrate that the hPNPase is localized in mitochondria. Our finding suggests the involvement of mitochondrial RNA metabolism in cellular senescence.

The yeast mitochondrial degradosome. Its composition, interplay between RNA helicase and RNase activities and the role in mitochondrial RNA metabolism.

The yeast mitochondrial degradosome (mtEXO) is an NTP-dependent exoribonuclease involved in mitochondrial RNA metabolism. Previous purifications suggested that it was composed of three subunits. Our results suggest that the degradosome is composed of only two large subunits: an RNase and a RNA helicase encoded by nuclear genes DSS1 and SUV3, respectively, and that it co-purifies with mitochondrial ribosomes. We have found that the purified degradosome has RNA helicase activity that precedes and is essential for exoribonuclease activity of this complex. The degradosome RNase activity is necessary for mitochondrial biogenesis but in vitro the degradosome without RNase activity is still able to unwind RNA. In yeast strains lacking degradosome components there is a strong accumulation of mitochondrial mRNA and rRNA precursors not processed at 3'- and 5'-ends. The observed accumulation of precursors is probably the result of lack of degradation rather than direct inhibition of processing. We suggest that the degradosome is a central part of a mitochondrial RNA surveillance system responsible for degradation of aberrant and unprocessed RNAs.

Localisation of the human hSuv3p helicase in the mitochondrial matrix and its preferential unwinding of dsDNA.

We characterised the human hSuv3p protein belonging to the family of NTPases/helicases. In yeast mitochondria the hSUV3 orthologue is a component of the degradosome complex and participates in mtRNA turnover and processing, while in Caenorhabditis elegans the hSUV3 orthologue is necessary for viability of early embryos. Using immunofluorescence analysis, an in vitro mitochondrial uptake assay and sub-fractionation of human mitochondria we show hSuv3p to be a soluble protein localised in the mitochondrial matrix. We expressed and purified recombinant hSuv3p protein from a bacterial expression system. The purified enzyme was capable of hydrolysing ATP with a K(m) of 41.9 micro M and the activity was only modestly stimulated by polynucleotides. hSuv3p unwound partly hybridised dsRNA and dsDNA structures with a very strong preference for the latter. The presented analysis of the hSuv3p NTPase/helicase suggests that new functions of the protein have been acquired in the course of evolution.

Overexpressed yeast mitochondrial putative RNA helicase Mss116 partially restores proper mtRNA metabolism in strains lacking the Suv3 mtRNA helicase.

RNA helicase, encoded by the Saccharomyces cerevisiae nuclear gene SUV3, is a subunit of the mitochondrial (mt) degradosome: an enzyme complex that takes part in turnover of mtRNAs. Deletion of the SUV3 gene leads to a variety of disturbances in mtRNA metabolism and results in respiratory incompetence of yeast cells. Here we show that the nuclear gene MSS116, which codes for a mitochondrial putative RNA helicase necessary for splicing of several mt introns, can suppress the lack of the SUV3 gene. Overexpression of the Mss116 putative helicase from a multicopy plasmid present in the SUV3-deleted strains partially restores respiratory competence, brings the steady-state levels of COB and ATP6/8 mRNA back almost to normal and lowers the accumulation of 21S rRNA and ATP6/8 RNA precursors to the wild-type levels. To the best of our knowledge, this is the first reported case of a substitution of one RNA helicase by another, belonging to a different class of RNA helicases.