Myasthenia Gravis Treatment: From Old Drugs to Innovative Therapies with a Glimpse into the Future

Myasthenia gravis (MG) is a rare autoimmune disease that causes debilitating muscle weakness due to impaired neuromuscular transmission. Since most (about 80-90%) MG patients present autoantibodies against the acetylcholine receptor, standard medical therapy consists of symptomatic treatment with acetylcholinesterase inhibitors (e.g., pyridostigmine). In addition, considering the autoimmune basis of MG, standard therapy includes immunomodulating agents, such as corticosteroids, azathioprine, cyclosporine A, and cyclophosphamide. New strategies have been proposed for the treatment of MG and include complement blockade (i.e., eculizumab, ravulizumab, and zilucoplan) and neonatal Fc receptor antagonism (i.e., efgartigimod and rozanolixizumab). The aim of this review is to provide a detailed overview of the pre- and post-marketing evidence on the five pharmacological treatments most recently approved for the treatment of MG, by identifying both preclinical and clinical studies registered in clinicaltrials.gov. A description of the molecules currently under evaluation for the treatment of MG is also provided.

Drosophila Mpv17 forms an ion channel and regulates energy metabolism

Mutations in MPV17 are a major contributor to mitochondrial DNA (mtDNA) depletion syndromes, a group of inherited genetic conditions due to mtDNA instability. To investigate the role of MPV17 in mtDNA maintenance, we generated and characterized a Drosophila melanogaster Mpv17 (dMpv17) KO model showing that the absence of dMpv17 caused profound mtDNA depletion in the fat body but not in other tissues, increased glycolytic flux and reduced lifespan in starvation. Accordingly, the expression of key genes of glycogenolysis and glycolysis was upregulated in dMpv17 KO flies. In addition, we demonstrated that dMpv17 formed a channel in planar lipid bilayers at physiological ionic conditions, and its electrophysiological hallmarks were affected by pathological mutations. Importantly, the reconstituted channel translocated uridine but not orotate across the membrane. Our results indicate that dMpv17 forms a channel involved in translocation of key metabolites and highlight the importance of dMpv17 in energy homeostasis and mitochondrial function.

Generation of mouse hippocampal brain organoids from primary embryonic neural stem cells

Here we present a protocol to generate standardized cerebral organoids with hippocampal regional specification using morphogen WNT3a. We describe steps for isolating mouse embryonic (E14.5) neural stem cells from the brain subgranular zone, preparing organoids samples for immunofluorescence, calcium imaging, and metabolic profiling. This protocol can be used to generate mouse brain organoids for developmental studies, modeling disease, and drug screening. Organoids can be obtained in one month, thus providing a rapid tool for high-throughput data validation. For complete details on the use and execution of this protocol, please refer to Ciarpella et al. "Murine cerebral organoids develop network of functional neurons and hippocampal brain region identity".1.

Advances in Mitochondria-Targeted Drug Delivery

Mitochondria are dynamic organelles that play a crucial role in numerous cellular activities [...].

PPAR-gamma agonist pioglitazone recovers mitochondrial quality control in fibroblasts from PITRM1-deficient patients

Introduction: Biallelic variants in PITRM1 are associated with a slowly progressive syndrome characterized by intellectual disability, spinocerebellar ataxia, cognitive decline and psychosis. The pitrilysin metallopeptidase 1 (PITRM1) is a mitochondrial matrix enzyme, which digests diverse oligopeptides, including the mitochondrial targeting sequences (MTS) that are cleaved from proteins imported across the inner mitochondrial membrane by the mitochondrial processing peptidase (MPP). Mitochondrial peptidases also play a role in the maturation of Frataxin, the protein affected in Friedreich's ataxia. Recent studies in yeast indicated that the mitochondrial matrix protease Ste23, which is a homologue of the human insulin-degrading enzyme (IDE), cooperates with Cym1 (homologue of PITRM1) to ensure the proper functioning of the preprotein processing machinery. In humans, IDE could be upregulated by Peroxisome Proliferator-Activated Receptor Gamma (PPARG) agonists. Methods: We investigated preprotein processing, mitochondrial membrane potential and MTS degradation in control and patients' fibroblasts, and we evaluated the pharmacological effect of the PPARG agonist Pioglitazone on mitochondrial proteostasis. Results: We discovered that PITRM1 dysfunction results in the accumulation of MTS, leading to the disruption and dissipation of the mitochondrial membrane potential. This triggers a feedback inhibition of MPP activity, consequently impairing the processing and maturation of Frataxin. Furthermore, we found that the pharmacological stimulation of PPARG by Pioglitazone upregulates IDE and also PITRM1 protein levels restoring the presequence processing machinery and improving Frataxin maturation and mitochondrial function. Discussion: Our findings provide mechanistic insights and suggest a potential pharmacological strategy for this rare neurodegenerative mitochondrial disease.

Mitochondrial Dysfunction in Peripheral Blood Mononuclear Cells as Novel Diagnostic Tools for Non-Alcoholic Fatty Liver Disease: Visualizing Relationships with Known and Potential Disease Biomarkers

Non-alcoholic fatty liver disease (NAFLD) is a health emergency worldwide due to its high prevalence and the lack of specific therapies. Noninvasive biomarkers supporting NAFLD diagnosis are urgently needed. Liver mitochondrial dysfunction is a central NAFLD pathomechanism that changes throughout disease progression. Blood-cell bioenergetics reflecting mitochondrial organ dysfunction is emerging for its potential applications in diagnostics. We measured real-time mitochondrial respirometry in peripheral blood mononuclear cells (PBMCs), anthropometric parameters, routine blood analytes, and circulating cytokines from a cohort of NAFLD patients (N = 19) and non-NAFLD control subjects (N = 18). PBMC basal respiration, ATP-linked respiration, maximal respiration, and spare respiratory capacity were significantly reduced in NAFLD compared to non-NAFLD cases. Correlation plots were applied to visualize relationships between known or potential NAFLD-related biomarkers, while non-parametric methods were applied to identify which biomarkers are NAFLD predictors. Basal and ATP-linked mitochondrial respiration were negatively correlated with triglycerides and fasting insulin levels and HOMA index. Maximal and spare respiratory capacity were negatively correlated with IL-6 levels. All the mitochondrial respiratory parameters were positively correlated with HDL-cholesterol level and negatively correlated with fatty liver index. We propose including blood cell respirometry in panels of NAFLD diagnostic biomarkers to monitor disease progression and the response to current and novel therapies, including mitochondrial-targeted ones.

Effects of Noonan Syndrome-Germline Mutations on Mitochondria and Energy Metabolism

Noonan syndrome (NS) and related Noonan syndrome with multiple lentigines (NSML) contribute to the pathogenesis of human diseases in the RASopathy family. This family of genetic disorders constitute one of the largest groups of developmental disorders with variable penetrance and severity, associated with distinctive congenital disabilities, including facial features, cardiopathies, growth and skeletal abnormalities, developmental delay/mental retardation, and tumor predisposition. NS was first clinically described decades ago, and several genes have since been identified, providing a molecular foundation to understand their physiopathology and identify targets for therapeutic strategies. These genes encode proteins that participate in, or regulate, RAS/MAPK signalling. The RAS pathway regulates cellular metabolism by controlling mitochondrial homeostasis, dynamics, and energy production; however, little is known about the role of mitochondrial metabolism in NS and NSML. This manuscript comprehensively reviews the most frequently mutated genes responsible for NS and NSML, covering their role in the current knowledge of cellular signalling pathways, and focuses on the pathophysiological outcomes on mitochondria and energy metabolism.

Therapeutic Induction of Energy Metabolism Reduces Neural Tissue Damage and Increases Microglia Activation in Severe Spinal Cord Injury

Neural tissue has high metabolic requirements. Following spinal cord injury (SCI), the damaged, tissue suffers from a severe metabolic impairment, which aggravates axonal degeneration and, neuronal loss. Impaired cellular energetic, tricarboxylic acid (TCA) cycle and oxidative, phosphorylation metabolism in neuronal cells has been demonstrated to be a major cause of neural tissue death and regeneration failure following SCI. Therefore, rewiring the spinal cord cell metabolism may be an innovative therapeutic strategy for the treatment of SCI. In this study, we evaluated the therapeutic effect of the recovery of oxidative metabolism in a mouse model of severe contusive SCI. Oral administration of TCA cycle intermediates, co-factors, essential amino acids, and branched-chain amino acids was started 3 days post-injury and continued until the end of the experimental procedures. Metabolomic, immunohistological, and biochemical analyses were performed on the injured spinal cord sections. Administration of metabolic precursors enhanced spinal cord oxidative metabolism. In line with this metabolic shift, we observed the activation of the mTORC1 anabolic pathway, the increase in mitochondrial mass, and ROS defense which effectively prevented the injury-induced neural cell apoptosis in treated animals. Consistently, we found more choline acetyltransferase (ChAT)-expressing motor neurons and increased neurofilament positive corticospinal axons in the spinal cord parenchyma of the treated mice. Interestingly, oral administration of the metabolic precursors increased the number of activated microglia expressing the CD206 marker suggestive of a, pro-resolutive, M2-like phenotype. These molecular and histological modifications observed in treated animals ultimately led to a significant, although partial, improvement of the motor functions. Our data demonstrate that rewiring the cellular metabolism can represent an effective strategy to treat SCI.

Interrupting the nitrosative stress fuels tumor-specific cytotoxic T lymphocytes in pancreatic cancer

Background

Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest tumors owing to its robust desmoplasia, low immunogenicity, and recruitment of cancer-conditioned, immunoregulatory myeloid cells. These features strongly limit the success of immunotherapy as a single agent, thereby suggesting the need for the development of a multitargeted approach. The goal is to foster T lymphocyte infiltration within the tumor landscape and neutralize cancer-triggered immune suppression, to enhance the therapeutic effectiveness of immune-based treatments, such as anticancer adoptive cell therapy (ACT).

Methods

We examined the contribution of immunosuppressive myeloid cells expressing arginase 1 and nitric oxide synthase 2 in building up a reactive nitrogen species (RNS)-dependent chemical barrier and shaping the PDAC immune landscape. We examined the impact of pharmacological RNS interference on overcoming the recruitment and immunosuppressive activity of tumor-expanded myeloid cells, which render pancreatic cancers resistant to immunotherapy.

Results

PDAC progression is marked by a stepwise infiltration of myeloid cells, which enforces a highly immunosuppressive microenvironment through the uncontrolled metabolism of L-arginine by arginase 1 and inducible nitric oxide synthase activity, resulting in the production of large amounts of reactive oxygen and nitrogen species. The extensive accumulation of myeloid suppressing cells and nitrated tyrosines (nitrotyrosine, N-Ty) establishes an RNS-dependent chemical barrier that impairs tumor infiltration by T lymphocytes and restricts the efficacy of adoptive immunotherapy. A pharmacological treatment with AT38 ([3-(aminocarbonyl)furoxan-4-yl]methyl salicylate) reprograms the tumor microenvironment from protumoral to antitumoral, which supports T lymphocyte entrance within the tumor core and aids the efficacy of ACT with telomerase-specific cytotoxic T lymphocytes.

Conclusions

Tumor microenvironment reprogramming by ablating aberrant RNS production bypasses the current limits of immunotherapy in PDAC by overcoming immune resistance.

Murine cerebral organoids develop network of functional neurons and hippocampal brain region identity

Brain organoids are in vitro three-dimensional (3D) self-organized neural structures, which can enable disease modeling and drug screening. However, their use for standardized large-scale drug screening studies is limited by their high batch-to-batch variability, long differentiation time (10-20 weeks), and high production costs. This is particularly relevant when brain organoids are obtained from human induced pluripotent stem cells (iPSCs). Here, we developed, for the first time, a highly standardized, reproducible, and fast (5 weeks) murine brain organoid model starting from embryonic neural stem cells. We obtained brain organoids, which progressively differentiated and self-organized into 3D networks of functional neurons with dorsal forebrain phenotype. Furthermore, by adding the morphogen WNT3a, we generated brain organoids with specific hippocampal region identity. Overall, our results showed the establishment of a fast, robust and reproducible murine 3D in vitro brain model that may represent a useful tool for high-throughput drug screening and disease modeling.

The Impact Of Covid-19 On Logistic Systems: An Italian Case Study

since the beginning of 2020, a new virus named COVID-19 has rapidly spread to a global pandemic. The world economy has been strongly affected and early evidence suggests that its impact has involved all the sectors and business functions. In such context, logistics activities have been severely affected by the COVID-19 pandemic because of the introduction of new strict prevention rules; moreover, purchasing behaviours of customers have changed and systems had to rapidly adapt to unexpected events. This paper aims to investigate the impact of the sanitary emergency on logistics activities. A logistic provider specialized in the food and fast moving consumer goods sector has been involved in the research in order to analyse its activities and the main changes caused by the pandemic. A quantitative survey has been conducted, combining numerical data and qualitative answers. Results confirm strong effects on some sectors and an economic loss mainly due to the new procedures adopted to face the emergency.

Environmental Enrichment Induces Meningeal Niche Remodeling through TrkB-Mediated Signaling

Neural precursors (NPs) present in the hippocampus can be modulated by several neurogenic stimuli, including environmental enrichment (EE) acting through BDNF-TrkB signaling. We have recently identified NPs in meninges; however, the meningeal niche response to pro-neurogenic stimuli has never been investigated. To this aim, we analyzed the effects of EE exposure on NP distribution in mouse brain meninges. Following neurogenic stimuli, although we did not detect modification of the meningeal cell number and proliferation, we observed an increased number of neural precursors in the meninges. A lineage tracing experiment suggested that EE-induced β3-Tubulin⁺ immature neuronal cells present in the meninges originated, at least in part, from GLAST⁺ radial glia cells. To investigate the molecular mechanism responsible for meningeal reaction to EE exposure, we studied the BDNF-TrkB interaction. Treatment with ANA-12, a TrkB non-competitive inhibitor, abolished the EE-induced meningeal niche changes. Overall, these data showed, for the first time, that EE exposure induced meningeal niche remodeling through TrkB-mediated signaling. Fluoxetine treatment further confirmed the meningeal niche response, suggesting it may also respond to other pharmacological neurogenic stimuli. A better understanding of the neurogenic stimuli modulation for meninges may be useful to improve the effectiveness of neurodegenerative and neuropsychiatric treatments.

Defective metabolic programming impairs early neuronal morphogenesis in neural cultures and an organoid model of Leigh syndrome

Leigh syndrome (LS) is a severe manifestation of mitochondrial disease in children and is currently incurable. The lack of effective models hampers our understanding of the mechanisms underlying the neuronal pathology of LS. Using patient-derived induced pluripotent stem cells and CRISPR/Cas9 engineering, we developed a human model of LS caused by mutations in the complex IV assembly gene SURF1. Single-cell RNA-sequencing and multi-omics analysis revealed compromised neuronal morphogenesis in mutant neural cultures and brain organoids. The defects emerged at the level of neural progenitor cells (NPCs), which retained a glycolytic proliferative state that failed to instruct neuronal morphogenesis. LS NPCs carrying mutations in the complex I gene NDUFS4 recapitulated morphogenesis defects. SURF1 gene augmentation and PGC1A induction via bezafibrate treatment supported the metabolic programming of LS NPCs, leading to restored neuronal morphogenesis. Our findings provide mechanistic insights and suggest potential interventional strategies for a rare mitochondrial disease.

Therapeutic Approaches to Treat Mitochondrial Diseases: "One-Size-Fits-All" and "Precision Medicine" Strategies

Primary mitochondrial diseases (PMD) refer to a group of severe, often inherited genetic conditions due to mutations in the mitochondrial genome or in the nuclear genes encoding for proteins involved in oxidative phosphorylation (OXPHOS). The mutations hamper the last step of aerobic metabolism, affecting the primary source of cellular ATP synthesis. Mitochondrial diseases are characterized by extremely heterogeneous symptoms, ranging from organ-specific to multisystemic dysfunction with different clinical courses. The limited information of the natural history, the limitations of currently available preclinical models, coupled with the large variability of phenotypical presentations of PMD patients, have strongly penalized the development of effective therapies. However, new therapeutic strategies have been emerging, often with promising preclinical and clinical results. Here we review the state of the art on experimental treatments for mitochondrial diseases, presenting "one-size-fits-all" approaches and precision medicine strategies. Finally, we propose novel perspective therapeutic plans, either based on preclinical studies or currently used for other genetic or metabolic diseases that could be transferred to PMD.

Targeting Multiple Mitochondrial Processes by a Metabolic Modulator Prevents Sarcopenia and Cognitive Decline in SAMP8 Mice

The age-dependent declines of skeletal muscle and cognitive functions often coexist in elderly subjects. The underlying pathophysiological mechanisms share common features of mitochondrial dysfunction, which plays a central role in the development of overt sarcopenia and/or dementia. Dietary supplementation with formulations of essential and branched-chain amino acids (EAA-BCAA) is a promising preventive strategy because it can preserve mitochondrial biogenesis and function. The senescence-accelerated mouse prone 8 (SAMP8) is considered an accurate model of age-related muscular and cognitive alterations. Hence, we aimed to investigate the progression of mitochondrial dysfunctions during muscular and cognitive aging of SAMP8 mice and to study the effects of a novel EAA-BCAA-based metabolic modulator on these changes. We evaluated body condition, motor endurance, and working memory of SAMP8 mice at 5, 9, 12, and 15 months of age. Parallel changes in protein levels of mitochondrial respiratory chain subunits, regulators of mitochondrial biogenesis and dynamics, and the antioxidant response, as well as respiratory complex activities, were measured in the quadriceps femoris and the hippocampus. The same variables were assessed in 12-month-old SAMP8 mice that had received dietary supplementation with the novel EAA-BCAA formulation, containing tricarboxylic acid cycle intermediates and co-factors (PD-0E7, 1.5 mg/kg/body weight/day in drinking water) for 3 months. Contrary to untreated mice, which had a significant molecular and phenotypic impairment, PD-0E7-treated mice showed preserved healthy body condition, muscle weight to body weight ratio, motor endurance, and working memory at 12 months of age. The PD-0E7 mixture increased the protein levels and the enzymatic activities of mitochondrial complex I, II, and IV and the expression of proliferator-activated receptor γ coactivator-1α, optic atrophy protein 1, and nuclear factor, erythroid 2 like 2 in muscles and hippocampi. The mitochondrial amyloid-β-degrading pitrilysin metallopeptidase 1 was upregulated, while amyloid precursor protein was reduced in the hippocampi of PD-0E7 treated mice. In conclusion, we show that a dietary supplement tailored to boost mitochondrial respiration preserves skeletal muscle and hippocampal mitochondrial quality control and health. When administered at the early onset of age-related physical and cognitive decline, this novel metabolic inducer counteracts the deleterious effects of precocious aging in both domains.

Expanding the molecular and phenotypic spectrum of truncating MT-ATP6 mutations

Objective

To describe the clinical and functional consequences of 1 novel and 1 previously reported truncating MT-ATP6 mutation.

Methods

Three unrelated probands with mitochondrial encephalomyopathy harboring truncating MT-ATP6 mutations are reported. Transmitochondrial cybrid cell studies were used to confirm pathogenicity of 1 novel variant, and the effects of all 3 mutations on ATPase 6 and complex V structure and function were investigated.

Results

Patient 1 presented with adult-onset cerebellar ataxia, chronic kidney disease, and diabetes, whereas patient 2 had myoclonic epilepsy and cerebellar ataxia; both harbored the novel m.8782G>A; p.(Gly86*) mutation. Patient 3 exhibited cognitive decline, with posterior white matter abnormalities on brain MRI, and severely impaired renal function requiring transplantation. The m.8618dup; p.(Thr33Hisfs*32) mutation, previously associated with neurogenic muscle weakness, ataxia, and retinitis pigmentosa, was identified. All 3 probands demonstrated a broad range of heteroplasmy across different tissue types. Blue-native gel electrophoresis of cultured fibroblasts and skeletal muscle tissue confirmed multiple bands, suggestive of impaired complex V assembly. Microscale oxygraphy showed reduced basal respiration and adenosine triphosphate synthesis, while reactive oxygen species generation was increased. Transmitochondrial cybrid cell lines studies confirmed the deleterious effects of the novel m.8782 G>A; p.(Gly86*) mutation.

Conclusions

We expand the clinical and molecular spectrum of MT-ATP6-related mitochondrial disorders to include leukodystrophy, renal disease, and myoclonic epilepsy with cerebellar ataxia. Truncating MT-ATP6 mutations may exhibit highly variable mutant levels across different tissue types, an important consideration during genetic counseling.

SURF1 knockout cloned pigs: Early onset of a severe lethal phenotype

Leigh syndrome (LS) associated with cytochrome c oxidase (COX) deficiency is an early onset, fatal mitochondrial encephalopathy, leading to multiple neurological failure and eventually death, usually in the first decade of life. Mutations in SURF1, a nuclear gene encoding a mitochondrial protein involved in COX assembly, are among the most common causes of LS. LSSURF1 patients display severe, isolated COX deficiency in all tissues, including cultured fibroblasts and skeletal muscle. Recombinant, constitutive SURF1-/- mice show diffuse COX deficiency, but fail to recapitulate the severity of the human clinical phenotype. Pigs are an attractive alternative model for human diseases, because of their size, as well as metabolic, physiological and genetic similarity to humans. Here, we determined the complete sequence of the swine SURF1 gene, disrupted it in pig primary fibroblast cell lines using both TALENs and CRISPR/Cas9 genome editing systems, before finally generating SURF1-/- and SURF1-/+ pigs by Somatic Cell Nuclear Transfer (SCNT). SURF1-/- pigs were characterized by failure to thrive, muscle weakness and highly reduced life span with elevated perinatal mortality, compared to heterozygous SURF1-/+ and wild type littermates. Surprisingly, no obvious COX deficiency was detected in SURF1-/- tissues, although histochemical analysis revealed the presence of COX deficiency in jejunum villi and total mRNA sequencing (RNAseq) showed that several COX subunit-encoding genes were significantly down-regulated in SURF1-/- skeletal muscles. In addition, neuropathological findings, indicated a delay in central nervous system development of newborn SURF1-/- piglets. Our results suggest a broader role of sSURF1 in mitochondrial bioenergetics.

TTC19 Plays a Husbandry Role on UQCRFS1 Turnover in the Biogenesis of Mitochondrial Respiratory Complex III

Loss-of-function mutations in TTC19 (tetra-tricopeptide repeat domain 19) have been associated with severe neurological phenotypes and mitochondrial respiratory chain complex III deficiency. We previously demonstrated the mitochondrial localization of TTC19 and its link with complex III biogenesis. Here we provide detailed insight into the mechanistic role of TTC19, by investigating a Ttc19?/? mouse model that shows progressive neurological and metabolic decline, decreased complex III activity, and increased production of reactive oxygen species. By using both the Ttc19?/? mouse model and a range of human cell lines, we demonstrate that TTC19 binds to the fully assembled complex III dimer, i.e., after the incorporation of the iron-sulfur Rieske protein (UQCRFS1). The in situ maturation of UQCRFS1 produces N-terminal polypeptides, which remain bound to holocomplex III. We show that, in normal conditions, these UQCRFS1 fragments are rapidly removed, but when TTC19 is absent they accumulate within complex III, causing its structural and functional impairment.

FGF21 is a biomarker for mitochondrial translation and mtDNA maintenance disorders

OBJECTIVE

To validate new mitochondrial myopathy serum biomarkers for diagnostic use.

METHODS

We analyzed serum FGF21 (S-FGF21) and GDF15 from patients with (1) mitochondrial diseases and (2) nonmitochondrial disorders partially overlapping with mitochondrial disorder phenotypes. We (3) did a meta-analysis of S-FGF21 in mitochondrial disease and (4) analyzed S-Fgf21 and skeletal muscle Fgf21 expression in 6 mouse models with different muscle-manifesting mitochondrial dysfunctions.

RESULTS

We report that S-FGF21 consistently increases in primary mitochondrial myopathy, especially in patients with mitochondrial translation defects or mitochondrial DNA (mtDNA) deletions (675 and 347 pg/mL, respectively; controls: 66 pg/mL, p < 0.0001 for both). This is corroborated in mice (mtDNA deletions 1,163 vs 379 pg/mL, p < 0.0001). However, patients and mice with structural respiratory chain subunit or assembly factor defects showed low induction (human 335 pg/mL, p < 0.05; mice 335 pg/mL, not significant). Overall specificities of FGF21 and GDF15 to find patients with mitochondrial myopathy were 89.3% vs 86.4%, and sensitivities 67.3% and 76.0%, respectively. However, GDF15 was increased also in a wide range of nonmitochondrial conditions.

CONCLUSIONS

S-FGF21 is a specific biomarker for muscle-manifesting defects of mitochondrial translation, including mitochondrial transfer-RNA mutations and primary and secondary mtDNA deletions, the most common causes of mitochondrial disease. However, normal S-FGF21 does not exclude structural respiratory chain complex or assembly factor defects, important to acknowledge in diagnostics.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that elevated S-FGF21 accurately distinguishes patients with mitochondrial myopathies from patients with other conditions, and FGF21 and GDF15 mitochondrial myopathy from other myopathies.

Emerging concepts in the therapy of mitochondrial disease

Mitochondrial disorders are an important group of genetic conditions characterized by impaired oxidative phosphorylation. Mitochondrial disorders come with an impressive variability of symptoms, organ involvement, and clinical course, which considerably impact the quality of life and quite often shorten the lifespan expectancy. Although the last 20 years have witnessed an exponential increase in understanding the genetic and biochemical mechanisms leading to disease, this has not resulted in the development of effective therapeutic approaches, amenable of improving clinical course and outcome of these conditions to any significant extent. Therapeutic options for mitochondrial diseases still remain focused on supportive interventions aimed at relieving complications. However, new therapeutic strategies have recently been emerging, some of which have shown potential efficacy at the pre-clinical level. This review will present the state of the art on experimental therapy for mitochondrial disorders.

AAV-mediated liver-specific MPV17 expression restores mtDNA levels and prevents diet-induced liver failure

Mutations in human MPV17 cause a hepatocerebral form of mitochondrial DNA depletion syndrome (MDS) hallmarked by early-onset liver failure, leading to premature death. Liver transplantation and frequent feeding using slow-release carbohydrates are the only available therapies, although surviving patients eventually develop slowly progressive peripheral and central neuropathy. The physiological role of Mpv17, including its functional link to mitochondrial DNA (mtDNA) maintenance, is still unclear. We show here that Mpv17 is part of a high molecular weight complex of unknown composition, which is essential for mtDNA maintenance in critical tissues, i.e. liver, of a Mpv17 knockout mouse model. On a standard diet, Mpv17-/- mouse shows hardly any symptom of liver dysfunction, but a ketogenic diet (KD) leads these animals to liver cirrhosis and failure. However, when expression of human MPV17 is carried out by adeno-associated virus (AAV)-mediated gene replacement, the Mpv17 knockout mice are able to reconstitute the Mpv17-containing supramolecular complex, restore liver mtDNA copy number and oxidative phosphorylation (OXPHOS) proficiency, and prevent liver failure induced by the KD. These results open new therapeutic perspectives for the treatment of MPV17-related liver-specific MDS.

In vivo correction of COX deficiency by activation of the AMPK/PGC-1α axis

Increased mitochondrial biogenesis by activation of PPAR- or AMPK/PGC-1α-dependent homeostatic pathways has been proposed as a treatment for mitochondrial disease. We tested this hypothesis on three recombinant mouse models characterized by defective cytochrome c-oxidase (COX) activity: a knockout (KO) mouse for Surf1, a knockout/knockin mouse for Sco2, and a muscle-restricted KO mouse for Cox15. First, we demonstrated that double-recombinant animals overexpressing PGC-1α in skeletal muscle on a Surf1 KO background showed robust induction of mitochondrial biogenesis and increase of mitochondrial respiratory chain activities, including COX. No such effect was obtained by treating both Surf1(-/-) and Cox15(-/-) mice with the pan-PPAR agonist bezafibrate, which instead showed adverse effects in either model. Contrariwise, treatment with the AMPK agonist AICAR led to partial correction of COX deficiency in all three models, and, importantly, significant motor improvement up to normal in the Sco2(KO/KI) mouse. These results open new perspectives for therapy of mitochondrial disease.

Isolation, growth and differentiation of equine mesenchymal stem cells: effect of donor, source, amount of tissue and supplementation with basic fibroblast growth factor

Mesenchymal stem cells (MSC) are increasingly used as therapeutical aid for the orthopaedic injuries in the horse. MSC populate different tissues but the most commonly used for clinical purposes are isolated from bone marrow or adipose tissue. The first objective of this study was to investigate if the donor animal, the tissue of origin and the technique of isolation could influence the number of MSC available for transplantation after a short-term expansion. The second aim was to devise a culture system capable of increasing MSC lifespan and we tested the effect of basic fibroblast growth factor (bFGF). Results indicate that MSC can be efficiently isolated from both sources and supplementation of bFGF enhances proliferation rate maintaining differentiation potential. In addition, this study shows that collection, expansion and storage of frozen MSC can be performed for later therapeutic use.