PARKIN is not required to sustain OXPHOS function in adult mammalian tissues.

Loss-of-function variants in the PRKN gene encoding the ubiquitin E3 ligase PARKIN cause autosomal recessive early-onset Parkinson's disease (PD). Extensive in vitro and in vivo studies have reported that PARKIN is involved in multiple pathways of mitochondrial quality control, including mitochondrial degradation and biogenesis. However, these findings are surrounded by substantial controversy due to conflicting experimental data. In addition, the existing PARKIN-deficient mouse models have failed to faithfully recapitulate PD phenotypes. Therefore, we have investigated the mitochondrial role of PARKIN during ageing and in response to stress by employing a series of conditional Parkin knockout mice. We report that PARKIN loss does not affect oxidative phosphorylation (OXPHOS) capacity and mitochondrial DNA (mtDNA) levels in the brain, heart, and skeletal muscle of aged mice. We also demonstrate that PARKIN deficiency does not exacerbate the brain defects and the pro-inflammatory phenotype observed in mice carrying high levels of mtDNA mutations. To rule out compensatory mechanisms activated during embryonic development of Parkin-deficient mice, we generated a mouse model where loss of PARKIN was induced in adult dopaminergic (DA) neurons. Surprisingly, also these mice did not show motor impairment or neurodegeneration, and no major transcriptional changes were found in isolated midbrain DA neurons. Finally, we report a patient with compound heterozygous PRKN pathogenic variants that lacks PARKIN and has developed PD. The PARKIN deficiency did not impair OXPHOS activities or induce mitochondrial pathology in skeletal muscle from the patient. Altogether, our results argue that PARKIN is dispensable for OXPHOS function in adult mammalian tissues.

The displacement of frataxin from the mitochondrial cristae correlates with abnormal respiratory supercomplexes formation and bioenergetic defects in cells of Friedreich ataxia patients.

Friedreich ataxia (FRDA) is a neurodegenerative disease resulting from a severe decrease of frataxin (FXN). Most patients carry a GAA repeat expansion in both alleles of the FXN gene, whereas a small fraction of them are compound heterozygous for the expansion and a point mutation in the other allele. FXN is involved in the mitochondrial biogenesis of the FeS-clusters. Distinctive feature of FRDA patient cells is an impaired cellular respiration, likely due to a deficit of key redox cofactors working as electrons shuttles through the respiratory chain. However, a definite relationship between FXN levels, FeS-clusters assembly dysregulation and bioenergetics failure has not been established. In this work, we performed a comparative analysis of the mitochondrial phenotype of cell lines from FRDA patients, either homozygous for the expansion or compound heterozygotes for the G130V mutation. We found that, in healthy cells, FXN and two key proteins of the FeS-cluster assembly machinery are enriched in mitochondrial cristae, the dynamic subcompartment housing the respiratory chain. On the contrary, FXN widely redistributes to the matrix in FRDA cells with defects in respiratory supercomplexes assembly and altered respiratory function. We propose that this could be relevant for the early mitochondrial defects afflicting FRDA cells and that perturbation of mitochondrial morphodynamics could in turn be critical in terms of disease mechanisms.

Metabolic control of DNA methylation in naive pluripotent cells.

Naive epiblast and embryonic stem cells (ESCs) give rise to all cells of adults. Such developmental plasticity is associated with genome hypomethylation. Here, we show that LIF-Stat3 signaling induces genomic hypomethylation via metabolic reconfiguration. Stat3-/- ESCs show decreased α-ketoglutarate production from glutamine, leading to increased Dnmt3a and Dnmt3b expression and DNA methylation. Notably, genome methylation is dynamically controlled through modulation of α-ketoglutarate availability or Stat3 activation in mitochondria. Alpha-ketoglutarate links metabolism to the epigenome by reducing the expression of Otx2 and its targets Dnmt3a and Dnmt3b. Genetic inactivation of Otx2 or Dnmt3a and Dnmt3b results in genomic hypomethylation even in the absence of active LIF-Stat3. Stat3-/- ESCs show increased methylation at imprinting control regions and altered expression of cognate transcripts. Single-cell analyses of Stat3-/- embryos confirmed the dysregulated expression of Otx2, Dnmt3a and Dnmt3b as well as imprinted genes. Several cancers display Stat3 overactivation and abnormal DNA methylation; therefore, the molecular module that we describe might be exploited under pathological conditions.

Insight into the mechanism of cytotoxicity of membrane-permeant psoralenic Kv1.3 channel inhibitors by chemical dissection of a novel member of the family.

The potassium channel Kv1.3, involved in several important pathologies, is the target of a family of psoralen-based drugs whose mechanism of action is not fully understood. Here we provide evidence for a physical interaction of the mitochondria-located Kv1.3 (mtKv1.3) and Complex I of the respiratory chain and show that this proximity underlies the death-inducing ability of psoralenic Kv1.3 inhibitors. The effects of PAP-1-MHEG (PAP-1, a Kv1.3 inhibitor, with six monomeric ethylene glycol units attached to the phenyl ring of PAP-1), a more soluble novel derivative of PAP-1 and of its various portions on mitochondrial physiology indicate that the psoralenic moiety of PAP-1 bound to mtKv1.3 facilitates the diversion of electrons from Complex I to molecular oxygen. The resulting massive production of toxic Reactive Oxygen Species leads to death of cancer cells expressing Kv1.3. In vivo, PAP-1-MHEG significantly decreased melanoma volume. In summary, PAP-1-MHEG offers insights into the mechanisms of cytotoxicity of this family of compounds and may represent a valuable clinical tool.

Going beyond conventional parameters to unveil sperm quality in fish: the use of fibre optic technology to assess mitochondrial respiratory performance.

Sperm fertilisation success depends on both intrinsic quality and the interactions with the surrounding reproductive fluids. In several fish species, these interactions have a variable effect on sperm performance. Although specific responses to reproductive fluids may depend on intrinsic differences in sperm quality, variations in the traditionally recorded sperm functional traits do not fully account for the observed patterns. New methods to enhance the evaluation of sperm quality may prove to be valuable at both applied and theoretical levels, by improving the breeding protocol of reared species and the understanding of mating success in sperm competition contexts. Here we develop a fibre optic-based technique, also adequate for small ejaculate samples, to test the role of mitochondrial respiratory efficiency in deciphering sperm performance variability. We purposely used as model the grass goby, Zosterisessor ophiocephalus, a fish with guard-sneaker mating tactics where the sperm in each male tactic have similar intrinsic qualities (velocity, viability, ATP content), but sneakers' sperm exploit territorial males' seminal fuid, overall displaying better fertilization ability. We found that sperm differed in their mitochondrial respiratory efficiency, which was higher in sneakers' sperm compared to territorial ones. This result draws the attention to an indicator of sperm quality that might be helpful in disentangling the mechanisms driving sperm-reproductive fluid interactions.

Developmental and Tumor Angiogenesis Requires the Mitochondria-Shaping Protein Opa1.

While endothelial cell (EC) function is influenced by mitochondrial metabolism, the role of mitochondrial dynamics in angiogenesis, the formation of new blood vessels from existing vasculature, is unknown. Here we show that the inner mitochondrial membrane mitochondrial fusion protein optic atrophy 1 (OPA1) is required for angiogenesis. In response to angiogenic stimuli, OPA1 levels rapidly increase to limit nuclear factor kappa-light-chain-enhancer of activated B cell (NFκB) signaling, ultimately allowing angiogenic genes expression and angiogenesis. Endothelial Opa1 is indeed required in an NFκB-dependent pathway essential for developmental and tumor angiogenesis, impacting tumor growth and metastatization. A first-in-class small molecule-specific OPA1 inhibitor confirms that EC Opa1 can be pharmacologically targeted to curtail tumor growth. Our data identify Opa1 as a crucial component of physiological and tumor angiogenesis.

Regulation of Mitochondrial Electron Transport Chain Assembly.

Mitochondrial function depends on the correct synthesis, transport, and assembly of proteins and cofactors of the electron transport chain. The initial idea that the respiratory chain protein complexes (RCCs) were independent structures in the inner mitochondrial membrane evolved after the identification of higher quaternary structures called supercomplexes (SCs), whose formation is dynamically regulated in order to accommodate cellular metabolic demands. Due to the dual genetic origin of the mitochondrial proteome, electron transport chain and SCs formation must be tightly regulated to coordinate the expression and assembly of components encoded by both genomes. This regulation occurs at different levels from gene transcription to protein, complex or SCs assembly, and might involve the participation of factors that contribute to the formation and stability of the RCCs and SCs. Here we review the cellular pathways and assembly factors that regulate RCCs and SCs formation.

Optic Atrophy 1 Is Epistatic to the Core MICOS Component MIC60 in Mitochondrial Cristae Shape Control.

The mitochondrial contact site and cristae organizing system (MICOS) and Optic atrophy 1 (OPA1) control cristae shape, thus affecting mitochondrial function and apoptosis. Whether and how they physically and functionally interact is unclear. Here, we provide evidence that OPA1 is epistatic to MICOS in the regulation of cristae shape. Proteomic analysis identifies multiple MICOS components in native OPA1-containing high molecular weight complexes disrupted during cristae remodeling. MIC60, a core MICOS protein, physically interacts with OPA1, and together, they control cristae junction number and stability, OPA1 being epistatic to MIC60. OPA1 defines cristae width and junction diameter independently of MIC60. Our combination of proteomics, biochemistry, genetics, and electron tomography provides a unifying model for mammalian cristae biogenesis by OPA1 and MICOS.

Relationship Between Primary Stability and Crestal Bone Loss of Implants Placed with High Insertion Torque: A 3-Year Prospective Study.

PURPOSE: Concerns have been expressed about the possibility of high insertion torque (IT) causing necrosis, impaired osseointegration, and crestal bone loss over time. The present study investigated the relationship between primary stability and implant success, including early and late maintenance of crestal bone levels. MATERIALS AND METHODS: Implants were placed in patients at three study centers. Every effort was made to achieve the highest possible primary stability, which was measured with IT and implant stability quotient (ISQ). The IT and ISQ at insertion and reopening (3 to 4 months), as well as bone levels at several points in time, were recorded. The correlations between IT, ISQ, and immediate and 3-year crestal bone loss were investigated through linear regression analyses. RESULTS: Average IT was 76.1 ± 20.8 Ncm, while the average ISQ score was 80.4 ± 8.4. The implant success rate at 36 months was 98.6%. The crestal bone loss around most implants (41.0%) ranged from 0.05 to 0.5 mm. None of the osseointegrated implants had crestal bone loss greater than 2.5 mm. The linear regression analysis showed no correlation among early or 3-year crestal bone loss and IT, ISQ at surgery, and ISQ at reopening. CONCLUSION: The implants studied avoided any negative effects deriving from the high IT values (≥ 50 Ncm) applied during 3 years of follow-up.

Short implants with oxidized surface in posterior areas of atrophic jaws: 3- to 5-year results of a multicenter study.

BACKGROUND: The loss of one or more teeth has always been a reason for bone resorption and it can lead to a condition of "alveolar atrophy" that could make implant rehabilitation difficult. PURPOSE: The aim of this prospective study was to observe crestal bone loss and implant success of short implants with oxidized surfaces in patients with partially edentulous jaws after a 3- to 5-year follow-up. MATERIALS AND METHODS: Forty-six patients with single or partial edentulism were treated consecutively from 2006 to 2008 using 107 short implants with oxidized surfaces, which were restored with a single crown or a partial fixed denture. Clinical and radiographic examinations were scheduled after functional loading of implants according to a well-established protocol generally applied to determine implant success rates and crestal bone levels. Statistical analysis was used to determine significant differences or correlations between variables (p = .05). RESULTS: After a 3- to 5-year follow-up, 44 patients with 102 implants were still followed up according to previously established study protocol, because two patients with five implants dropped out. Ninety-eight out of 102 implants are still functioning: four implants have been lost, with a survival rate of 96.1%. Moreover, a total of seven implants failed to meet the success criteria, resulting in a success rate of 93.1%. The mean bone loss was 0.9 ± 0.6 mm. CONCLUSIONS: Many authors had recently demonstrated the predictability of short implants in different clinical conditions after a short-term follow-up. After 3 to 5 years of functional loading, short implants used to restore posterior teeth seems to be a viable solution in order to simplify and shorten the treatment of patients with partial edentulous jaws. Long-term follow-up is recommended to definitively establish the predictability and efficiency of this kind of implant-supported rehabilitation.

"Evidence-based dentistry in oral surgery: could we do better?".

Evidence-based Dentistry (EBD), like Evidence-based Medicine (EBM), was born in order to seek the "best available research evidence" in the field of dentistry both in research and clinical routine.BUT EVIDENCE IS NOT CLEARLY MEASURABLE IN ALL FIELDS OF HEALTHCARE: in particular, while drug effect is rather independent from clinician's characteristics, the effectiveness of surgical procedures is strictly related to surgeon's expertise, which is difficult to quantify. The research problems of dentistry have a lot in common with other surgical fields, where at the moment the best therapeutic recommendations and guidelines originates from an integration of evidence-based medicine and data from consensus conferences.To cope with these problems, new instruments have been developed, aimed at standardizing clinical procedures (CAD-CAM technology) and at integrating EBM achievements with the opinions of expert clinicians (GRADE System).ONE THING WE HAVE TO REMEMBER HOWEVER: it is necessary to use the instruments developed by evidence-based medicine but is impossible to produce sound knowledge without considering clinical expertise and quality of surgical procedures simultaneously. Only in this way we will obtain an evidence-based dentistry both in dental research and clinical practice, which is up to third millennium standards.