The mitochondria of cultured mammalian cells: I. Analysis by immunofluorescence microscopy, histochemistry, subcellular fractionation, and cell fusion

A cellular assay to determine the fusion capacity of MFN2 variants linked to Charcot-Marie-Tooth disease of type 2 A

Charcot-Marie-Tooth Disease (CMT) is an inherited peripheral neuropathy with two main forms: demyelinating CMT1 and axonal CMT2. The most frequent subtype of CMT2 (CMT2A) is linked to mutations of MFN2, encoding a ubiquitously expressed GTP-binding protein anchored to the mitochondrial outer membrane and essential for mitochondrial fusion. The use of Next-Generation Sequencing has led to the identification of increasing numbers of MFN2 variants, yet many of them remain of unknown significance, depriving patients of a clear diagnosis. In this work, we establish a cellular assay allowing to assess the impact of 12 known MFN2 variants linked to CMT2A on mitochondrial fusion. The functional analysis revealed that out of the 12 selected MFN2 mutations, only six exhibited reduced fusion activity. The classification of MFN2 variants according to the results of the functional assay revealed a correlation between the fusion capacity, the age at onset of CMT2A and computational variant effect predictions relying on the analysis of the protein sequence. The functional assay and the results obtained will assist and improve the classification of novel MFN2 variants identified in patients.

A systematic review and meta-analysis on the prevalence of Dupuytren disease in the general population of Western countries

BACKGROUND

Dupuytren disease is a fibroproliferative disease of palmar fascia of the hand. Its prevalence has been the subject of several reviews; however, an accurate description of the prevalence range in the general population--and of the relation between age and disease--is lacking.

METHODS

Embase and PubMed were searched using database-specific Medical Subject Headings; titles and abstracts were searched for the words "Dupuytren," "incidence," and "prevalence." Two reviewers independently assessed the articles using inclusion and exclusion criteria, and rated the included studies with a quality assessment instrument. In a meta-analysis, the median prevalence, as a function of age by sex, was estimated, accompanied by 95 percent prediction intervals. The observed heterogeneity in prevalence was investigated with respect to study quality and geographic location.

RESULTS

Twenty-three of 199 unique identified articles were included. The number of participants ranged from 37 to 97,537, and age ranged from 18 to 100 years. Prevalence varied from 0.6 to 31.6 percent. The quality of studies differed but could not explain the heterogeneity among studies. Mean prevalence was estimated as 12, 21, and 29 percent at ages 55, 65, and 75 years, respectively, based on the relation between age and prevalence determined from 10 studies.

CONCLUSIONS

The authors describe a prevalence range of Dupuytren disease in the general population of Western countries. The relation between age and prevalence of Dupuytren disease is given according to sex, including 95 percent prediction intervals. It is possible to determine disease prevalence at a certain age for the total population, and for men and women separately.

A systematic review and meta-analysis on the prevalence of Dupuytren disease in the general population of Western countries

BACKGROUND

Dupuytren disease is a fibroproliferative disease of palmar fascia of the hand. Its prevalence has been the subject of several reviews; however, an accurate description of the prevalence range in the general population--and of the relation between age and disease--is lacking.

METHODS

Embase and PubMed were searched using database-specific Medical Subject Headings; titles and abstracts were searched for the words "Dupuytren," "incidence," and "prevalence." Two reviewers independently assessed the articles using inclusion and exclusion criteria, and rated the included studies with a quality assessment instrument. In a meta-analysis, the median prevalence, as a function of age by sex, was estimated, accompanied by 95 percent prediction intervals. The observed heterogeneity in prevalence was investigated with respect to study quality and geographic location.

RESULTS

Twenty-three of 199 unique identified articles were included. The number of participants ranged from 37 to 97,537, and age ranged from 18 to 100 years. Prevalence varied from 0.6 to 31.6 percent. The quality of studies differed but could not explain the heterogeneity among studies. Mean prevalence was estimated as 12, 21, and 29 percent at ages 55, 65, and 75 years, respectively, based on the relation between age and prevalence determined from 10 studies.

CONCLUSIONS

The authors describe a prevalence range of Dupuytren disease in the general population of Western countries. The relation between age and prevalence of Dupuytren disease is given according to sex, including 95 percent prediction intervals. It is possible to determine disease prevalence at a certain age for the total population, and for men and women separately.

Nuclear outsourcing of RNA interference components to human mitochondria

MicroRNAs (miRNAs) are small non-coding RNAs that associate with Argonaute proteins to regulate gene expression at the post-transcriptional level in the cytoplasm. However, recent studies have reported that some miRNAs localize to and function in other cellular compartments. Mitochondria harbour their own genetic system that may be a potential site for miRNA mediated post-transcriptional regulation. We aimed at investigating whether nuclear-encoded miRNAs can localize to and function in human mitochondria. To enable identification of mitochondrial-enriched miRNAs, we profiled the mitochondrial and cytosolic RNA fractions from the same HeLa cells by miRNA microarray analysis. Mitochondria were purified using a combination of cell fractionation and immunoisolation, and assessed for the lack of protein and RNA contaminants. We found 57 miRNAs differentially expressed in HeLa mitochondria and cytosol. Of these 57, a signature of 13 nuclear-encoded miRNAs was reproducibly enriched in mitochondrial RNA and validated by RT-PCR for hsa-miR-494, hsa-miR-1275 and hsa-miR-1974. The significance of their mitochondrial localization was investigated by characterizing their genomic context, cross-species conservation and instrinsic features such as their size and thermodynamic parameters. Interestingly, the specificities of mitochondrial versus cytosolic miRNAs were underlined by significantly different structural and thermodynamic parameters. Computational targeting analysis of most mitochondrial miRNAs revealed not only nuclear but also mitochondrial-encoded targets. The functional relevance of miRNAs in mitochondria was supported by the finding of Argonaute 2 localization to mitochondria revealed by immunoblotting and confocal microscopy, and further validated by the co-immunoprecipitation of the mitochondrial transcript COX3. This study provides the first comprehensive view of the localization of RNA interference components to the mitochondria. Our data outline the molecular bases for a novel layer of crosstalk between nucleus and mitochondria through a specific subset of human miRNAs that we termed 'mitomiRs'.

V-fusion: a convenient, nontoxic method for cell fusion

Cell-to-cell fusion (cell fusion) is a fundamental biological process that also has been used as a versatile experimental tool to dissect a variety of cellular mechanisms, including the consequences of cell fusion itself, and to produce cells with desired properties, such as hybridomas and reprogrammed progenitors. However, current methods of cell fusion are not satisfactory because of their toxicity, inefficiency, or lack of flexibility. We describe a simple, versatile, scalable, and nontoxic approach that we call V-fusion, as it is based on the ability of the vesicular stomatitis virus G protein (VSV-G), a viral fusogen of broad tropism, to become rapidly and reversibly activated. We suggest that this approach will benefit a broad array of studies that investigate consequences of cell fusion or use cell fusion as an experimental tool.

Inhibition of mitochondrial fusion by α-synuclein is rescued by PINK1, Parkin and DJ-1

Aggregation of α-synuclein (αS) is involved in the pathogenesis of Parkinson's disease (PD) and a variety of related neurodegenerative disorders. The physiological function of αS is largely unknown. We demonstrate with in vitro vesicle fusion experiments that αS has an inhibitory function on membrane fusion. Upon increased expression in cultured cells and in Caenorhabditis elegans, αS binds to mitochondria and leads to mitochondrial fragmentation. In C. elegans age-dependent fragmentation of mitochondria is enhanced and shifted to an earlier time point upon expression of exogenous αS. In contrast, siRNA-mediated downregulation of αS results in elongated mitochondria in cell culture. αS can act independently of mitochondrial fusion and fission proteins in shifting the dynamic morphologic equilibrium of mitochondria towards reduced fusion. Upon cellular fusion, αS prevents fusion of differently labelled mitochondrial populations. Thus, αS inhibits fusion due to its unique membrane interaction. Finally, mitochondrial fragmentation induced by expression of αS is rescued by coexpression of PINK1, parkin or DJ-1 but not the PD-associated mutations PINK1 G309D and parkin Δ1-79 or by DJ-1 C106A.