PINK1 deficiency alters muscle stem cell fate decision and muscle regenerative capacity.

Maintenance of mitochondrial function plays a crucial role in the regulation of muscle stem cell (MuSC), but the underlying mechanisms remain ill defined. In this study, we monitored mitophagy in MuSCS under various myogenic states and examined the role of PINK1 in maintaining regenerative capacity. Results indicate that quiescent MuSCs actively express mitophagy genes and exhibit a measurable mitophagy flux and prominent mitochondrial localization to autophagolysosomes, which become rapidly decreased during activation. Genetic disruption of Pink1 in mice reduces PARKIN recruitment to mitochondria and mitophagy in quiescent MuSCs, which is accompanied by premature activation/commitment at the expense of self-renewal and progressive loss of muscle regeneration, but unhindered proliferation and differentiation capacity. Results also show that impaired fate decisions in PINK1-deficient MuSCs can be restored by scavenging excess mitochondrial ROS. These data shed light on the regulation of mitophagy in MuSCs and position PINK1 as an important regulator of their mitochondrial properties and fate decisions.

Adaptive optimization of the OXPHOS assembly line partially compensates lrpprc-dependent mitochondrial translation defects in mice.

Mouse models of genetic mitochondrial disorders are generally used to understand specific molecular defects and their biochemical consequences, but rarely to map compensatory changes allowing survival. Here we took advantage of the extraordinary mitochondrial resilience of hepatic Lrpprc knockout mice to explore this question using native proteomics profiling and lipidomics. In these mice, low levels of the mtRNA binding protein LRPPRC induce a global mitochondrial translation defect and a severe reduction (>80%) in the assembly and activity of the electron transport chain (ETC) complex IV (CIV). Yet, animals show no signs of overt liver failure and capacity of the ETC is preserved. Beyond stimulation of mitochondrial biogenesis, results show that the abundance of mitoribosomes per unit of mitochondria is increased and proteostatic mechanisms are induced in presence of low LRPPRC levels to preserve a balance in the availability of mitochondrial- vs nuclear-encoded ETC subunits. At the level of individual organelles, a stabilization of residual CIV in supercomplexes (SCs) is observed, pointing to a role of these supramolecular arrangements in preserving ETC function. While the SC assembly factor COX7A2L could not contribute to the stabilization of CIV, important changes in membrane glycerophospholipid (GPL), most notably an increase in SC-stabilizing cardiolipins species (CLs), were observed along with an increased abundance of other supramolecular assemblies known to be stabilized by, and/or participate in CL metabolism. Together these data reveal a complex in vivo network of molecular adjustments involved in preserving mitochondrial integrity in energy consuming organs facing OXPHOS defects, which could be therapeutically exploited.

Successful Management of Internal Carotid Artery Transection Secondary to a Gunshot Wound and Subsequent Malignant MCA Syndrome.

There are over 100,000 strokes each year in the UK. A very small proportion of these can be attributed to gunshot wounds and subsequent surgical intervention. We present a rare case of a 24-year-old male patient admitted to the Emergency Department having sustained a gunshot wound to the left side of his neck. Initial imaging and surgical exploration revealed significant left-sided vertebral artery damage and a complete transection of the internal carotid artery. Following damage control surgery (DCS), the patient was admitted to ITU but had an acute neurological deterioration and was found to have suffered malignant middle cerebral artery (MCA) syndrome, requiring an urgent decompressive craniectomy. The patient's National Institutes of Health Stroke Scale (NIHSS) at this stage was 26. After a prolonged ITU stay and repatriation to a local stroke unit for intensive therapies input, the patient walked out of the hospital independently on day 106, with an improved NIHSS of 3. This case report aims to highlight the rarity of an ischaemic stroke, secondary to the DCS required for a near fatal gunshot wound, along with the importance of timely recognition of an acute deterioration following artery ligation. Additionally, it aims to examine the lifesaving surgical management of malignant MCA syndrome and in turn the significance of the shared decision-making process between clinicians, the patient, and family members, due to the high rate of poor functional outcomes following this major surgery.

Mitophagy: A New Player in Stem Cell Biology.

The fundamental importance of functional mitochondria in the survival of most eukaryotic cells, through regulation of bioenergetics, cell death, calcium dynamics and reactive oxygen species (ROS) generation, is undisputed. However, with new avenues of research in stem cell biology these organelles have now emerged as signaling entities, actively involved in many aspects of stem cell functions, including self-renewal, commitment and differentiation. With this recent knowledge, it becomes evident that regulatory pathways that would ensure the maintenance of mitochondria with state-specific characteristics and the selective removal of organelles with sub-optimal functions must play a pivotal role in stem cells. As such, mitophagy, as an essential mitochondrial quality control mechanism, is beginning to gain appreciation within the stem cell field. Here we review and discuss recent advances in our knowledge pertaining to the roles of mitophagy in stem cell functions and the potential contributions of this specific quality control process on to the progression of aging and diseases.

Modulation of Agrin and RhoA Pathways Ameliorates Movement Defects and Synapse Morphology in MYO9A-Depleted Zebrafish.

Congenital myasthenic syndromes (CMS) are a group of rare, inherited disorders characterised by impaired function of the neuromuscular junction (NMJ). This is due to defects in one of the many proteins associated with the NMJ. In three patients with CMS, missense mutations in a gene encoding an unconventional myosin protein, MYO9A, were identified as likely causing their disorder. Preliminary studies revealed a potential involvement of the RhoA/ROCK pathway and of a key NMJ protein, agrin, in the pathophysiology of MYO9A-depletion. In this study, a CRISPR/Cas9 approach was used to generate genetic mutants of MYO9A zebrafish orthologues, myo9aa/ab, to expand and refine the morphological analysis of the NMJ. Injection of NT1654, a synthetic agrin fragment compound, improved NMJ structure and zebrafish movement in the absence of Myo9aa/ab. In addition, treatment of zebrafish with fasudil, a ROCK inhibitor, also provided improvements to the morphology of NMJs in early development, as well as rescuing movement defects, but not to the same extent as NT1654 and not at later time points. Therefore, this study highlights a role for MYO9A at the NMJ, the first unconventional myosin motor protein associated with a neuromuscular disease, and provides a potential mechanism of action of MYO9A-pathophysiology.

ARL3 Mutations Cause Joubert Syndrome by Disrupting Ciliary Protein Composition.

Joubert syndrome (JBTS) is a genetically heterogeneous autosomal-recessive neurodevelopmental ciliopathy. We investigated further the underlying genetic etiology of Joubert syndrome by studying two unrelated families in whom JBTS was not associated with pathogenic variants in known JBTS-associated genes. Combined autozygosity mapping of both families highlighted a candidate locus on chromosome 10 (chr10: 101569997-109106128, UCSC Genome Browser hg 19), and exome sequencing revealed two missense variants in ARL3 within the candidate locus. The encoded protein, ADP ribosylation factor-like GTPase 3 (ARL3), is a small GTP-binding protein that is involved in directing lipid-modified proteins into the cilium in a GTP-dependent manner. Both missense variants replace the highly conserved Arg149 residue, which we show to be necessary for the interaction with its guanine nucleotide exchange factor ARL13B, such that the mutant protein is associated with reduced INPP5E and NPHP3 localization in cilia. We propose that ARL3 provides a potential hub in the network of proteins implicated in ciliopathies, whereby perturbation of ARL3 leads to the mislocalization of multiple ciliary proteins as a result of abnormal displacement of lipidated protein cargo.

Therapeutic interventions in children and adolescents with patellar tendon related pain: a systematic review.

OBJECTIVE: Evaluate effectiveness and harms of interventions for patellar tendon related pain in children and adolescents. DESIGN: Systematic review and meta-analysis. DATA SOURCES: Medline via Pubmed, Embase via OVID, CINAHL via Ebsco, SportDiscus up until 24 November 2017 were searched. ELIGIBILITY CRITERIA FOR SELECTING STUDIES: Inclusion criteria were (1) controlled or randomised controlled clinical trials (RCTs), (2) participants with diagnosis of patellar tendon related disorder, (3) participants≤18 years of age at enrolment and (4) published in a peer-reviewed English or Scandinavian language journal. RESULTS: Of 530 studies identified, eight were included after screening, with three included in data synthesis. To be included in data synthesis, we required studies to have included (and have data available for) a minimum of 10 participants under 18 years. All studies were rated as being at high risk of bias. For adolescents with patellar tendinopathy, one RCT compared eccentric exercises to usual care and found no difference between groups. In adolescents with Osgood-Schlatter disease (OSD), injection of local anaesthetic with dextrose proved superior to either usual care or local anaesthetic alone (three armed RCTs). In a retrospective case controlled study in adolescents with OSD, surgery provided no benefit over conservative management in terms of persistent symptoms and had a higher complication rate. CONCLUSION: There is weak evidence to support the use of dextrose injection with local anaesthetic and no evidence to support the use of specific types of exercises to treat children/adolescents with OSD/patellar tendinopathy. Until further evidence arises, clinicians should include load modification and advise on a return to sport based on symptoms.

MYO9A deficiency in motor neurons is associated with reduced neuromuscular agrin secretion.

Congenital myasthenic syndromes (CMS) are a group of rare, inherited disorders characterized by compromised function of the neuromuscular junction, manifesting with fatigable muscle weakness. Mutations in MYO9A were previously identified as causative for CMS but the precise pathomechanism remained to be characterized. On the basis of the role of MYO9A as an actin-based molecular motor and as a negative regulator of RhoA, we hypothesized that loss of MYO9A may affect the neuronal cytoskeleton, leading to impaired intracellular transport. To investigate this, we used MYO9A-depleted NSC-34 cells (mouse motor neuron-derived cells), revealing altered expression of a number of cytoskeletal proteins important for neuron structure and intracellular transport. On the basis of these findings, the effect on protein transport was determined using a vesicular recycling assay which revealed impaired recycling of a neuronal growth factor receptor. In addition, an unbiased approach utilizing proteomic profiling of the secretome revealed a key role for defective intracellular transport affecting proper protein secretion in the pathophysiology of MYO9A-related CMS. This also led to the identification of agrin as being affected by the defective transport. Zebrafish with reduced MYO9A orthologue expression were treated with an artificial agrin compound, ameliorating defects in neurite extension and improving motility. In summary, loss of MYO9A affects the neuronal cytoskeleton and leads to impaired transport of proteins, including agrin, which may provide a new and unexpected treatment option.