bims-curels 2024-08-25 papers

Issue of 2024–08–25
six papers selected by
Cure Mito Foundation

Orphanet J Rare Dis. 2024 Aug 21. 19(1): 305

IARS2 mutations lead to Leigh syndrome with a combined oxidative phosphorylation deficiency.

Qiyu Dong, Xiaojie Yin, Shuanglong Fan, Sheng Zhong, Wenxin Yang, Keer Chen, Qian Wang, Xue Ma, Refiloe Laurentinah Mahlatsi, Yanling Yang, Jianxin Lyu, Hezhi Fang, Ya Wang.

BACKGROUND: Leigh syndrome (LS) is a common mitochondrial disease caused by mutations in both mitochondrial and nuclear genes. Isoleucyl-tRNA synthetase 2 (IARS2) encodes mitochondrial isoleucine-tRNA synthetase, and variants in IARS2 have been reported to cause LS. However, the pathogenic mechanism of IARS2 variants is still unclear.
METHODS: Two unrelated patients, a 4-year-old boy and a 5-year-old boy diagnosed with LS, were recruited, and detailed clinical data were collected. The DNA of the patients and their parents was isolated from the peripheral blood for the identification of pathogenic variants using next-generation sequencing and Sanger sequencing. The ClustalW program, allele frequency analysis databases (gnomAD and ExAc), and pathogenicity prediction databases (Clinvar, Mutation Taster and PolyPhen2) were used to predict the conservation and pathogenicity of the variants. The gene expression level, oxygen consumption rate (OCR), respiratory chain complex activity, cellular adenosine triphosphate (ATP) production, mitochondrial membrane potential (MMP) and mitochondrial reactive oxygen species (ROS) levels were measured in patient-derived lymphocytes and IARS2-knockdown HEK293T cells to evaluate the pathogenicity of the variants.
RESULTS: We reported 2 unrelated Chinese patients manifested with LS who carried biallelic IARS2 variants (c.1_390del and c.2450G > A from a 4-year-old boy, and c.2090G > A and c.2122G > A from a 5-year-old boy), of which c.1_390del and c.2090G > A were novel. Functional studies revealed that the patient-derived lymphocytes carrying c.1_390del and c.2450G > A variants exhibited impaired mitochondrial function due to severe mitochondrial complexes I and III deficiencies, which was also found in IARS2-knockdown HEK293T cells. The compensatory experiments in vitro cell models confirmed the pathogenicity of IARS2 variants since re-expression of wild-type IARS2 rather than mutant IARS2 could rescue complexes I and III deficiency, oxygen consumption, and cellular ATP content in IARS2 knockdown cells.
CONCLUSION: Our results not only expand the gene mutation spectrum of LS, but also reveal for the first time the pathogenic mechanism of IARS2 variants due to a combined deficiency of mitochondrial complexes I and III, which is helpful for the clinical diagnosis of IARS2 mutation-related diseases.

Keywords: IARS2 ; Leigh syndrome; Mitochondrial disease; OXPHOS

DOI: https://doi.org/10.1186/s13023-024-03310-x

EMBO Mol Med. 2024 Aug 21.

Restoration of defective oxidative phosphorylation to a subset of neurons prevents mitochondrial encephalopathy.

Brittni R Walker, Lise-Michelle Theard, Milena Pinto, Monica Rodriguez-Silva, Sandra R Bacman, Carlos T Moraes.

Oxidative Phosphorylation (OXPHOS) defects can cause severe encephalopathies and no effective treatment exists for these disorders. To assess the ability of gene replacement to prevent disease progression, we subjected two different CNS-deficient mouse models (Ndufs3/complex I or Cox10/complex IV conditional knockouts) to gene therapy. We used retro-orbitally injected AAV-PHP.eB to deliver the missing gene to the CNS of these mice. In both cases, we observed survival extension from 5-6 to more than 15 months, with no detectable disease phenotypes. Likewise, molecular and cellular phenotypes were mostly recovered in the treated mice. Surprisingly, these remarkable phenotypic improvements were achieved with only ~30% of neurons expressing the transgene from the AAV-PHP.eB vector in the conditions used. These findings suggest that neurons lacking OXPHOS are protected by the surrounding neuronal environment and that partial compensation for neuronal OXPHOS loss can have disproportionately positive effects.

Keywords: Gene Therapy; Mitochondria; Mitochondrial Disease; Oxidative Phosphorylation

DOI: https://doi.org/10.1038/s44321-024-00111-4

Neurobiol Dis. 2024 Aug 20. pii: S0969-9961(24)00244-4. [Epub ahead of print] 106644

Phenotyping mitochondrial glutamyl-tRNA synthetase deficiency (EARS2): A case series and systematic literature review.

Gonçalo Pelayo, Margarida Paiva Coelho, Joana Correia, Anabela Bandeira, Célia Nogueira, Laura Vilarinho, Esmeralda Martins.

Mitochondrial glutamyl-aminoacyl tRNA synthetase deficiency, stemming from biallelic mutations in the EARS2 gene, was first described in 2012. With <50 cases reported globally, this condition exhibits a distinct phenotype of neonatal or childhood-onset, often referred to as leukoencephalopathy with thalamus and brainstem involvement and high lactate (LTBL). It has also been one of the few reversible mitochondrial disorders described. The natural history of these patients is poorly documented, ranging from clinical and radiological improvement to early death. Herein, we detail three cases from our centre, including follow-up on the Portuguese patient reported by Steenweg et al., These cases illustrate the phenotypic spectrum: i) rapidly progressive neonatal presentation with lactic acidemia and corpus callosum agenesis, leading to early death; ii) early onset with a severe, slowly progressive course; iii) early onset with a milder phenotype, showing some improvement and mild neurological symptoms. Additionally, we conducted a systematic literature review on cases of EARS2-deficient patients, focusing on clinical manifestations, laboratory findings, radiological aspects, and disease progression over time, along with respective data analysis. "Patients with EARS2 deficiency typically present within the first year of life with a well-defined neurometabolic disorder picture, often including hypotonia and/or spasticity, along with neurodevelopmental delay or regression. There are no pathognomonic features specific to EARS2 deficiency, and no genotype-phenotype correlation has been identified." Comparing to initial characterization by Steenweg et al., this analysis reveals an expanded disease spectrum. We propose a novel strategy for clustering phenotypes into severe, moderate, or mild disease based on initial presentation, seemingly correlating with disease progression. The paucity of data on the disease's natural history highlights the need for a multicentric approach to enhance understanding and management. TAKE-HOME MESSAGE: Analysis of all cases published with EARS2 deficiency allows for establish disease spectrum and a novel strategy for clustering phenotypes which correlate to disease progression.

Keywords: EARS2 protein; Glutamyl-tRNA synthetase 2; Human; Mitochondrial; Mitochondrial diseases

DOI: https://doi.org/10.1016/j.nbd.2024.106644

Rev Neurosci. 2024 Aug 20.

Unraveling mitochondrial dysfunction: comprehensive perspectives on its impact on neurodegenerative diseases.

Abdul Aziz Mohamed Yusoff, Siti Zulaikha Nashwa Mohd Khair.

Neurodegenerative diseases represent a significant challenge to modern medicine, with their complex etiology and progressive nature posing hurdles to effective treatment strategies. Among the various contributing factors, mitochondrial dysfunction has emerged as a pivotal player in the pathogenesis of several neurodegenerative disorders. This review paper provides a comprehensive overview of how mitochondrial impairment contributes to the development of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis, driven by bioenergetic defects, biogenesis impairment, alterations in mitochondrial dynamics (such as fusion or fission), disruptions in calcium buffering, lipid metabolism dysregulation and mitophagy dysfunction. It also covers current therapeutic interventions targeting mitochondrial dysfunction in these diseases.

Keywords: mitochondrial bioenergetics and biogenesis; mitochondrial dynamics and mitophagy; mitochondrial dysfunctions; neurodegenerative diseases; therapy

DOI: https://doi.org/10.1515/revneuro-2024-0080