Metabolic shift underlies recovery in reversible infantile respiratory chain deficiency.

Reversible infantile respiratory chain deficiency (RIRCD) is a rare mitochondrial myopathy leading to severe metabolic disturbances in infants, which recover spontaneously after 6-months of age. RIRCD is associated with the homoplasmic m.14674T>C mitochondrial DNA mutation; however, only ~ 1/100 carriers develop the disease. We studied 27 affected and 15 unaffected individuals from 19 families and found additional heterozygous mutations in nuclear genes interacting with mt-tRNAGlu including EARS2 and TRMU in the majority of affected individuals, but not in healthy carriers of m.14674T>C, supporting a digenic inheritance. Our transcriptomic and proteomic analysis of patient muscle suggests a stepwise mechanism where first, the integrated stress response associated with increased FGF21 and GDF15 expression enhances the metabolism modulated by serine biosynthesis, one carbon metabolism, TCA lipid oxidation and amino acid availability, while in the second step mTOR activation leads to increased mitochondrial biogenesis. Our data suggest that the spontaneous recovery in infants with digenic mutations may be modulated by the above described changes. Similar mechanisms may explain the variable penetrance and tissue specificity of other mtDNA mutations and highlight the potential role of amino acids in improving mitochondrial disease.

Variants in EXOSC9 Disrupt the RNA Exosome and Result in Cerebellar Atrophy with Spinal Motor Neuronopathy.

The exosome is a conserved multi-protein complex that is essential for correct RNA processing. Recessive variants in exosome components EXOSC3, EXOSC8, and RBM7 cause various constellations of pontocerebellar hypoplasia (PCH), spinal muscular atrophy (SMA), and central nervous system demyelination. Here, we report on four unrelated affected individuals with recessive variants in EXOSC9 and the effect of the variants on the function of the RNA exosome in vitro in affected individuals' fibroblasts and skeletal muscle and in vivo in zebrafish. The clinical presentation was severe, early-onset, progressive SMA-like motor neuronopathy, cerebellar atrophy, and in one affected individual, congenital fractures of the long bones. Three affected individuals of different ethnicity carried the homozygous c.41T>C (p.Leu14Pro) variant, whereas one affected individual was compound heterozygous for c.41T>C (p.Leu14Pro) and c.481C>T (p.Arg161∗). We detected reduced EXOSC9 in fibroblasts and skeletal muscle and observed a reduction of the whole multi-subunit exosome complex on blue-native polyacrylamide gel electrophoresis. RNA sequencing of fibroblasts and skeletal muscle detected significant >2-fold changes in genes involved in neuronal development and cerebellar and motor neuron degeneration, demonstrating the widespread effect of the variants. Morpholino oligonucleotide knockdown and CRISPR/Cas9-mediated mutagenesis of exosc9 in zebrafish recapitulated aspects of the human phenotype, as they have in other zebrafish models of exosomal disease. Specifically, portions of the cerebellum and hindbrain were absent, and motor neurons failed to develop and migrate properly. In summary, we show that variants in EXOSC9 result in a neurological syndrome combining cerebellar atrophy and spinal motoneuronopathy, thus expanding the list of human exosomopathies.

Side-by-side comparison of next-generation sequencing, cytology, and histology in diagnosing locally advanced pancreatic adenocarcinoma.

BACKGROUND AND AIMS: EUS-guided biopsy sampling is the method of choice for obtaining pancreatic tissue. Next-generation sequencing (NGS) has been applied to EUS-guided biopsy sampling and may classify patients based on specific molecular profiles. Our study aimed to compare side-by-side the diagnostic yield achievable by genetic identification of somatic mutations detected with NGS versus histologic and cytologic typing in locally advanced pancreatic carcinoma (LAPC) in samples acquired under EUS guidance. METHODS: We conducted a prospective comparative pilot study at Humanitas Research Hospital. The study included 33 patients referred for LAPC who underwent EUS-guided tissue acquisition using a 22-gauge Franseen needle. Material was obtained for both pathologic diagnosis and DNA extraction and targeted NGS analysis with the AmpliSeq Comprehensive Panel v3 (Illumina Inc, San Diego, Calif, USA). Twenty-one genes were prioritized for somatic mutation detection. RESULTS: The final diagnosis was pancreatic ductal adenocarcinoma (PDAC) in all patients (100%). A macroscopic core was obtained in 30 patients (91%). In 3 lesions no cores adequate for histologic analysis were obtained, but cytologic analysis revealed tumoral cells from PDAC. DNA was extracted from 32 of 33 samples (97%), most of which (27/32) carried at least 2 clearly pathogenic mutations in different genes. Detection of K-ras mutation allowed for molecular diagnosis of PDAC in most of the patients (30/32). CONCLUSIONS: In our study we demonstrated that proper tissue specimens obtained under EUS guidance allowed DNA sample extraction and subsequent NGS analysis in 97% of cases. These results support the potential role of NGS as a complementary diagnostic test to be implemented in association with standard diagnostic modalities. (Clinical trial registration number: NCT03578939.).

Compact and ultrastable photonic microwave oscillator.

Frequency comb synthesized microwaves have been so far realized with tabletop systems, operated in well-controlled environments. Here, we demonstrate state-of-the-art ultrastable microwave synthesis with a compact rack-mountable apparatus. We present absolute phase noise characterization of a 12 GHz signal using an ultrastable laser at $\sim{194}\;{\rm THz}$∼194THz and an Er:fiber comb divider, obtaining $ - {83}\;{\rm dBc/Hz}$-83dBc/Hz at 1 Hz and $ \lt - {166}\;{\rm dBc/Hz}$<-166dBc/Hz for offsets greater than 5 kHz. Employing semiconductor coating mirrors for the same type of transportable optical frequency reference, we show that $ - {105}\;{\rm dBc/Hz}$-105dBc/Hz at 1 Hz is supported by demonstrating a residual noise limit of division and detection process of $ - {115}\;{\rm dBc/Hz}$-115dBc/Hz at 1 Hz. This level of fidelity paves the way for the deployment of ultrastable photonic microwave oscillators and for operating transportable optical clocks.

Altered RNA metabolism due to a homozygous RBM7 mutation in a patient with spinal motor neuropathy.

The exosome complex is the most important RNA processing machinery within the cell. Mutations in its subunits EXOSC8 and EXOSC3 cause pontocerebellar hypoplasia, spinal muscular atrophy (SMA) and central nervous system demyelination. We present a patient with SMA-like phenotype carrying a homozygous mutation in RBM7-a subunit of the nuclear exosome targeting (NEXT) complex-which is known to bind and carry specific subtypes of coding and non-coding RNAs to the exosome. The NEXT complex with other protein complexes is responsible for the substrate specificity of the exosome. We performed RNA-sequencing (RNA-seq) analysis on primary fibroblasts of patients with mutations in EXOSC8 and RBM7 and gene knock-down experiments using zebrafish as a model system. RNA-seq analysis identified significantly altered expression of 62 transcripts shared by the two patient cell lines. Knock-down of rbm7, exosc8 and exosc3 in zebrafish showed a common pattern of defects in motor neurons and cerebellum. Our data indicate that impaired RNA metabolism may underlie the clinical phenotype by fine tuning gene expression which is essential for correct neuronal differentiation.

Distal femur periprosthetic knee fractures in elderly patients: clinical and radiographic outcome after internal fixation.

BACKGROUND AND AIM OF THE WORK: The incidence of periprosthetic knee fractures is steadily increasing, especially in the geriatric population. Surgical treatment in these patients must consider the poor bone quality and the risks of general complications related to age and comorbidities. The aim of the present study is to analyze the clinical and radiographic outcome of internal fixation for periprosthetic knee fractures of the distal femur in elderly patients (>75aa). METHODS: All patients treated at the Orthopedic and Traumatology Unit of Cattinara Hospital-ASUGI (Trieste, Italy) between September 2014 and September 2019 for distal femur periprosthetic fracture after total knee replacement were included in the study. Mortality, complications, radiographic healing and functional outcomes were retrospectively evaluated. Data collection was conducted by clinical database searching and telephone interview. Results were compared with the literature. RESULTS: The study population included 19 patients, F:M 16:3, mean age 84 years. Plate fixation was used in the majority of cases (90%). One-year mortality was 21.05%. Radiographic healing of the fracture occurred in 92% of cases. Nonetheless, 61% of patients saw a worsening in their functional outcome. CONCLUSION: Internal fixation is a valuable and safe option for distal femur periprosthetic fracture treatment in the elderly. The significant impact of periprosthetic knee fractures on the medium- to long-term survival and quality of life of the elderly patient is confirmed.

Post-Biopsy Cell-Free DNA From Blood: An Open Window on Primary Prostate Cancer Genetics and Biology.

Circulating cell-free DNA (ccfDNA), released from normal and cancerous cells, is a promising biomarker for cancer detection as in neoplastic patients it is enriched in tumor-derived DNA (ctDNA). ctDNA contains cancer-specific mutations and epigenetic modifications, which can have diagnostic/prognostic value. However, in primary tumors, and in particular in localized prostate cancer (PCa), the fraction of ctDNA is very low and conventional strategies to study ccfDNA are unsuccessful. Here we demonstrate that prostate biopsy, by causing multiple injuries to the organ, leads to a significant increase in plasma concentration of ccfDNA (P<0.0024) in primary PCa patients. By calculating the minor allele fraction at patient-specific somatic mutations pre- and post-biopsy, we show that ctDNA is significantly enriched (from 3.9 to 164 fold) after biopsy, representing a transient "molecular window" to access and analyze ctDNA. Moreover, we show that newly released ccfDNA contains a larger fraction of di-, tri- and multi-nucleosome associated DNA fragments. This feature could be exploited to further enrich prostate-derived ccfDNA and to analyze epigenetic markers. Our data represent a proof-of-concept that liquid tumor profiling from peripheral blood performed just after the biopsy procedure can open a "valuable molecular metastatic window" giving access to the tumor genetic asset, thus providing an opportunity for early cancer detection and individual genomic profiling in the view of PCa precision medicine.

Zebrafish as a Model to Investigate Dynamin 2-Related Diseases.

Mutations in the dynamin-2 gene (DNM2) cause autosomal dominant centronuclear myopathy (CNM) and dominant intermediate Charcot-Marie-Tooth (CMT) neuropathy type B (CMTDIB). As the relation between these DNM2-related diseases is poorly understood, we used zebrafish to investigate the effects of two different DNM2 mutations. First we identified a new alternatively spliced zebrafish dynamin-2a mRNA (dnm2a-v2) with greater similarity to human DNM2 than the deposited sequence. Then we knocked-down the zebrafish dnm2a, producing defects in muscle morphology. Finally, we expressed two mutated DNM2 mRNA by injecting zebrafish embryos with human mRNAs carrying the R522H mutation, causing CNM, or the G537C mutation, causing CMT. Defects arose especially in secondary motor neuron formation, with incorrect branching in embryos injected with CNM-mutated mRNA, and total absence of branching in those injected with CMT-mutated mRNA. Muscle morphology in embryos injected with CMT-mutated mRNA appeared less regularly organized than in those injected with CNM-mutated mRNA. Our results showing, a continuum between CNM and CMTDIB phenotypes in zebrafish, similarly to the human conditions, confirm this animal model to be a powerful tool to investigate mutations of DNM2 in vivo.

Exosomal Protein Deficiencies: How Abnormal RNA Metabolism Results in Childhood-Onset Neurological Diseases.

Defects of RNA metabolism have been increasingly identified in various forms of inherited neurological diseases. Recently, abnormal RNA degradation due to mutations in human exosome subunit genes has been shown to cause complex childhood onset neurological presentations including spinal muscular atrophy, pontocerebellar hypoplasia and myelination deficiencies. This paper summarizes our current knowledge about the exosome in human neurological disease and provides some important insights into potential disease mechanisms.

Investigating the role of the physiological isoform switch of cytochrome c oxidase subunits in reversible mitochondrial disease.

Reversible infantile respiratory chain deficiency is characterised by spontaneous recovery of mitochondrial myopathy in infants. We studied whether a physiological isoform switch of nuclear cytochrome c oxidase subunits contributes to the age-dependent manifestation and spontaneous recovery in reversible mitochondrial disease. Some nuclear-encoded subunits of cytochrome c oxidase are present as tissue-specific isoforms. Isoforms of subunits COX6A and COX7A expressed in heart and skeletal muscle are different from isoforms expressed in the liver, kidney and brain. Furthermore, in skeletal muscle both the heart and liver isoforms of subunit COX7A have been demonstrated with variable levels, indicating that the tissue-specific expression of nuclear-encoded subunits could provide a basis for the fine-tuning of cytochrome c oxidase activity to the specific metabolic needs of the different tissues. We demonstrate a developmental isoform switch of COX6A and COX7A subunits in human and mouse skeletal muscle. While the liver type isoforms are more present soon after birth, the heart/muscle isoforms gradually increase around 3 months of age in infants, 4 weeks of age in mice, and these isoforms persist in muscle throughout life. Our data in follow-up biopsies of patients with reversible infantile respiratory chain deficiency indicate that the physiological isoform switch does not contribute to the clinical manifestation and to the spontaneous recovery of this disease. However, understanding developmental changes of the different cytochrome c oxidase isoforms may have implications for other mitochondrial diseases. This article is part of a Directed Issue entitled: Energy Metabolism Disorders and Therapies.

EXOSC8 mutations alter mRNA metabolism and cause hypomyelination with spinal muscular atrophy and cerebellar hypoplasia.

The exosome is a multi-protein complex, required for the degradation of AU-rich element (ARE) containing messenger RNAs (mRNAs). EXOSC8 is an essential protein of the exosome core, as its depletion causes a severe growth defect in yeast. Here we show that homozygous missense mutations in EXOSC8 cause progressive and lethal neurological disease in 22 infants from three independent pedigrees. Affected individuals have cerebellar and corpus callosum hypoplasia, abnormal myelination of the central nervous system or spinal motor neuron disease. Experimental downregulation of EXOSC8 in human oligodendroglia cells and in zebrafish induce a specific increase in ARE mRNAs encoding myelin proteins, showing that the imbalanced supply of myelin proteins causes the disruption of myelin, and explaining the clinical presentation. These findings show the central role of the exosomal pathway in neurodegenerative disease.