RESUMO
Aminoacyl-tRNA synthetases (ARS) are ubiquitously expressed, essential enzymes that charge tRNA with cognate amino acids. Variants in genes encoding ARS enzymes lead to myriad human inherited diseases. First, missense alleles cause dominant peripheral neuropathy. Second, missense, nonsense, and frameshift alleles cause recessive multisystem disorders that differentially affect tissues depending on which ARS is mutated. A preponderance of evidence has shown that both phenotypic classes are associated with loss-of-function alleles, suggesting that tRNA charging plays a central role in disease pathogenesis. However, it is currently unclear how perturbation in the function of these ubiquitously expressed enzymes leads to tissue-specific or tissue-predominant phenotypes. Here, we review our current understanding of ARS-associated disease phenotypes and discuss potential explanations for the observed tissue specificity.
Assuntos
Aminoacil-tRNA Sintetases/genética , Predisposição Genética para Doença , Doenças do Sistema Nervoso Periférico/genética , RNA de Transferência/genética , Alelos , Aminoácidos/genética , Humanos , Mutação/genética , Doenças do Sistema Nervoso Periférico/patologia , Fenótipo , Aminoacilação de RNA de Transferência/genéticaRESUMO
Aminoacyl-tRNA synthetases (ARSs) are essential enzymes responsible for charging tRNA molecules with cognate amino acids. Consistent with the essential function and ubiquitous expression of ARSs, mutations in 32 of the 37 ARS-encoding loci cause severe, early-onset recessive phenotypes. Previous genetic and functional data suggest a loss-of-function mechanism; however, our understanding of the allelic and locus heterogeneity of ARS-related disease is incomplete. Cysteinyl-tRNA synthetase (CARS) encodes the enzyme that charges tRNACys with cysteine in the cytoplasm. To date, CARS variants have not been implicated in any human disease phenotype. Here, we report on four subjects from three families with complex syndromes that include microcephaly, developmental delay, and brittle hair and nails. Each affected person carries bi-allelic CARS variants: one individual is compound heterozygous for c.1138C>T (p.Gln380∗) and c.1022G>A (p.Arg341His), two related individuals are compound heterozygous for c.1076C>T (p.Ser359Leu) and c.1199T>A (p.Leu400Gln), and one individual is homozygous for c.2061dup (p.Ser688Glnfs∗2). Measurement of protein abundance, yeast complementation assays, and assessments of tRNA charging indicate that each CARS variant causes a loss-of-function effect. Compared to subjects with previously reported ARS-related diseases, individuals with bi-allelic CARS variants are unique in presenting with a brittle-hair-and-nail phenotype, which most likely reflects the high cysteine content in human keratins. In sum, our efforts implicate CARS variants in human inherited disease, expand the locus and clinical heterogeneity of ARS-related clinical phenotypes, and further support impaired tRNA charging as the primary mechanism of recessive ARS-related disease.
Assuntos
Aminoacil-tRNA Sintetases/genética , Doença de Charcot-Marie-Tooth/etiologia , Deficiências do Desenvolvimento/etiologia , Doenças do Cabelo/etiologia , Microcefalia/etiologia , Mutação , Doenças da Unha/etiologia , Adulto , Sequência de Aminoácidos , Doença de Charcot-Marie-Tooth/enzimologia , Doença de Charcot-Marie-Tooth/patologia , Deficiências do Desenvolvimento/enzimologia , Deficiências do Desenvolvimento/patologia , Feminino , Genes Recessivos , Predisposição Genética para Doença , Doenças do Cabelo/enzimologia , Doenças do Cabelo/patologia , Humanos , Masculino , Microcefalia/enzimologia , Microcefalia/patologia , Doenças da Unha/enzimologia , Doenças da Unha/patologia , Linhagem , Fenótipo , Prognóstico , Homologia de Sequência , Adulto JovemRESUMO
Mutations in histidyl-tRNA synthetase (HARS1), an enzyme that charges transfer RNA with the amino acid histidine in the cytoplasm, have only been associated to date with autosomal recessive Usher syndrome type III and autosomal dominant Charcot-Marie-Tooth disease type 2W. Using massive parallel sequencing, we identified bi-allelic HARS1 variants in a child (c.616G>T, p.Asp206Tyr and c.730delG, p.Val244Cysfs*6) and in two sisters (c.1393A>C, p.Ile465Leu and c.910_912dupTTG, p.Leu305dup), all characterized by a multisystem ataxic syndrome. All mutations are rare, segregate with the disease, and are predicted to have a significant effect on protein function. Functional studies helped to substantiate their disease-related roles. Indeed, yeast complementation assays showing that one out of two mutations in each patient is loss-of-function, and the reduction of messenger RNA and protein levels and enzymatic activity in patient's skin-derived fibroblasts, together support the pathogenicity of the identified HARS1 variants in the patient phenotypes. Thus, our efforts expand the allelic and clinical spectrum of HARS1-related disease.
Assuntos
Ataxia/genética , Histidina-tRNA Ligase/genética , Adulto , Alelos , Criança , Feminino , Humanos , Masculino , Mutação de Sentido IncorretoRESUMO
Aminoacyl-tRNA synthetases (ARSs) are ubiquitously expressed enzymes implicated in several dominant and recessive disease phenotypes. The canonical function of ARSs is to couple an amino acid to a cognate transfer RNA (tRNA). We identified three novel disease-associated missense mutations in the alanyl-tRNA synthetase (AARS) gene in three families with dominant axonal Charcot-Marie-Tooth (CMT) disease. Two mutations (p.Arg326Trp and p.Glu337Lys) are located near a recurrent pathologic change in AARS, p.Arg329His. The third (p.Ser627Leu) is in the editing domain of the protein in which hitherto only mutations associated with recessive encephalopathies have been described. Yeast complementation assays demonstrated that two mutations (p.Ser627Leu and p.Arg326Trp) represent loss-of-function alleles, while the third (p.Glu337Lys) represents a hypermorphic allele. Further, aminoacylation assays confirmed that the third mutation (p.Glu337Lys) increases tRNA charging velocity. To test the effect of each mutation in the context of a vertebrate nervous system, we developed a zebrafish assay. Remarkably, all three mutations caused a pathological phenotype of neural abnormalities when expressed in zebrafish, while expression of the human wild-type messenger RNA (mRNA) did not. Our data indicate that not only functional null or hypomorphic alleles, but also hypermorphic AARS alleles can cause dominantly inherited axonal CMT disease.
Assuntos
Alanina-tRNA Ligase/genética , Aminoacil-tRNA Sintetases/genética , Doença de Charcot-Marie-Tooth/genética , RNA de Transferência/genética , Adulto , Alelos , Aminoácidos/genética , Animais , Doença de Charcot-Marie-Tooth/patologia , Feminino , Regulação Enzimológica da Expressão Gênica/genética , Heterogeneidade Genética , Humanos , Masculino , Pessoa de Meia-Idade , Mutação/genética , Linhagem , Leveduras/genética , Peixe-Zebra/genéticaRESUMO
Mutations in the mitochondrial alanyl-tRNA synthetase gene, AARS2, have been reported to cause leukoencephalopathy associated with early ovarian failure, a clinical presentation described as "ovarioleukodystrophy." We present a sibling pair: one with cerebellar ataxia and one with vision loss and cognitive impairment in addition to ataxia. Neither shows evidence of leukoencephalopathy on MRI imaging. Exome sequencing revealed that both siblings are compound heterozygous for AARS2 variants (p.Phe131del and p.Ile328Met). Yeast complementation assays indicate that p.Phe131del AARS2 dramatically impairs gene function and that p.Ile328Met AARS2 is a hypomorphic allele. This work expands the phenotypic spectrum of AARS2-associated disease to include ataxia without leukoencephalopathy.
Assuntos
Alanina-tRNA Ligase/genética , Ataxia/diagnóstico por imagem , Ataxia/genética , Leucoencefalopatias/diagnóstico por imagem , Leucoencefalopatias/genética , Adulto , Sequência de Aminoácidos , Feminino , Humanos , Masculino , Linhagem , IrmãosRESUMO
The majority of patients with spinal muscular atrophy (SMA) identified to date harbor a biallelic exonic deletion of SMN1. However, there have been reports of SMA-like disorders that are independent of SMN1, including those due to pathogenic variants in the glycyl-tRNA synthetase gene (GARS1). We report three unrelated patients with de novo variants in GARS1 that are associated with infantile-onset SMA (iSMA). Patients were ascertained during inpatient hospital evaluations for complications of neuropathy. Evaluations were completed as indicated for clinical care and management and informed consent for publication was obtained. One newly identified, disease-associated GARS1 variant, identified in two out of three patients, was analyzed by functional studies in yeast complementation assays. Genomic analyses by exome and/or gene panel and SMN1 copy number analysis of three patients identified two previously undescribed de novo missense variants in GARS1 and excluded SMN1 as the causative gene. Functional studies in yeast revealed that one of the de novo GARS1 variants results in a loss-of-function effect, consistent with other pathogenic GARS1 alleles. In sum, the patients' clinical presentation, assessments of previously identified GARS1 variants and functional assays in yeast suggest that the GARS1 variants described here cause iSMA. GARS1 variants have been previously associated with Charcot-Marie-Tooth disease (CMT2D) and distal SMA type V (dSMAV). Our findings expand the allelic heterogeneity of GARS-associated disease and support that severe early-onset SMA can be caused by variants in this gene. Distinguishing the SMA phenotype caused by SMN1 variants from that due to pathogenic variants in other genes such as GARS1 significantly alters approaches to treatment.
Assuntos
Predisposição Genética para Doença , Glicina-tRNA Ligase/genética , Atrofias Musculares Espinais da Infância/genética , Proteína 1 de Sobrevivência do Neurônio Motor/genética , Doença de Charcot-Marie-Tooth/genética , Doença de Charcot-Marie-Tooth/fisiopatologia , Pré-Escolar , Feminino , Humanos , Lactente , Recém-Nascido , Masculino , Atrofia Muscular Espinal/genética , Atrofia Muscular Espinal/fisiopatologia , Mutação de Sentido Incorreto/genética , Fenótipo , Atrofias Musculares Espinais da Infância/diagnóstico por imagem , Atrofias Musculares Espinais da Infância/fisiopatologiaRESUMO
Alpha satellite is a tandemly organized type of repetitive DNA that comprises 5% of the genome and is found at all human centromeres. A defined number of 171-bp monomers are organized into chromosome-specific higher-order repeats (HORs) that are reiterated thousands of times. At least half of all human chromosomes have two or more distinct HOR alpha satellite arrays within their centromere regions. We previously showed that the two alpha satellite arrays of Homo sapiens Chromosome 17 (HSA17), D17Z1 and D17Z1-B, behave as centromeric epialleles, that is, the centromere, defined by chromatin containing the centromeric histone variant CENPA and recruitment of other centromere proteins, can form at either D17Z1 or D17Z1-B. Some individuals in the human population are functional heterozygotes in that D17Z1 is the active centromere on one homolog and D17Z1-B is active on the other. In this study, we aimed to understand the molecular basis for how centromere location is determined on HSA17. Specifically, we focused on D17Z1 genomic variation as a driver of epiallele formation. We found that D17Z1 arrays that are predominantly composed of HOR size and sequence variants were functionally less competent. They either recruited decreased amounts of the centromere-specific histone variant CENPA and the HSA17 was mitotically unstable, or alternatively, the centromere was assembled at D17Z1-B and the HSA17 was stable. Our study demonstrates that genomic variation within highly repetitive, noncoding DNA of human centromere regions has a pronounced impact on genome stability and basic chromosomal function.
Assuntos
Centrômero/genética , Cromossomos Humanos Par 17/genética , DNA Satélite , Instabilidade Genômica , Polimorfismo Genético , Alelos , Proteína Centromérica A/genética , Cromatina/genética , Células HCT116 , HumanosRESUMO
Alanyl-tRNA synthetase 1 (AARS1) encodes the enzyme that ligates tRNA molecules to alanine in the cytoplasm, which is required for protein translation. Variants in AARS1 have been implicated in early-onset, multi-system recessive phenotypes and in later-onset dominant peripheral neuropathy; to date, no single variant has been associated with both dominant and recessive diseases raising questions about shared mechanisms between the two inheritance patterns. AARS1 variants associated with recessive disease are predicted to result in null or hypomorphic alleles and this has been demonstrated, in part, via yeast complementation assays. However, pathogenic alleles have not been assessed in a side-by-side manner to carefully scrutinize the strengths and limitations of this model system. To address this, we employed a humanized yeast model to evaluate the functional consequences of all AARS1 missense variants reported in recessive disease. The majority of variants showed variable loss-of-function effects, ranging from no growth to significantly reduced growth. These data deem yeast a reliable model to test the functional consequences of human AARS1 variants; however, our data indicate that this model is prone to false-negative results and is not informative for genotype-phenotype studies. We next tested missense variants associated with no growth for dominant-negative effects. Interestingly, K81T AARS1, a variant implicated in recessive disease, demonstrated loss-of-function and dominant-negative effects, indicating that certain AARS1 variants may be capable of causing both dominant and recessive disease phenotypes.
RESUMO
Ataxia-telangiectasia (A-T) is an autosomal recessive, multisystem disorder characterized by cerebellar degeneration, cancer predisposition, and immune system defects. A major cause of mortality in A-T patients is severe pulmonary disease; however, the underlying causes of the lung complications are poorly understood, and there are currently no curative therapeutic interventions. In this study, we examined the lung phenotypes caused by ATM-deficient immune cells using a mouse model of A-T pulmonary disease. In response to acute lung injury, ATM-deficiency causes decreased survival, reduced blood oxygen saturation, elevated neutrophil recruitment, exaggerated and prolonged inflammatory responses and excessive lung injury compared to controls. We found that ATM null bone marrow adoptively transferred to WT recipients induces similar phenotypes that culminate in impaired lung function. Moreover, we demonstrated that activated ATM-deficient macrophages exhibit significantly elevated production of harmful reactive oxygen and nitrogen species and pro-inflammatory cytokines. These findings indicate that ATM-deficient immune cells play major roles in causing the lung pathologies in A-T. Based on these results, we examined the impact of inhibiting the aberrant inflammatory responses caused by ATM-deficiency with reparixin, a CXCR1/CXCR2 chemokine receptor antagonist. We demonstrated that reparixin treatment reduces neutrophil recruitment, edema and tissue damage in ATM mutant lungs. Thus, our findings indicate that targeted inhibition of CXCR1/CXCR2 attenuates pulmonary phenotypes caused by ATM-deficiency and suggest that this treatment approach represents a viable therapeutic strategy for A-T lung disease.
Assuntos
Ataxia Telangiectasia/complicações , Ataxia Telangiectasia/genética , Biomarcadores , Suscetibilidade a Doenças , Mediadores da Inflamação/metabolismo , Pneumopatias/etiologia , Pneumopatias/metabolismo , Lesão Pulmonar Aguda/etiologia , Lesão Pulmonar Aguda/metabolismo , Lesão Pulmonar Aguda/patologia , Animais , Proteínas Mutadas de Ataxia Telangiectasia/deficiência , Proteínas Mutadas de Ataxia Telangiectasia/genética , Bleomicina/efeitos adversos , Citocinas/metabolismo , Dano ao DNA , Reparo do DNA , Modelos Animais de Doenças , Pneumopatias/mortalidade , Pneumopatias/patologia , Camundongos , Fenótipo , PrognósticoRESUMO
Purpose: Diversity at all levels of medical training remains relatively stagnant, despite efforts to address equity in medical schools. Early career-specific mentoring may address barriers to the pursuit of medical education for students underrepresented in medicine (URiM). By surveying a program that engages medical students as drivers of career-specific mentorship for URiM high school students, this study evaluates medical student mentors' experiences mentoring and seeks to develop a mentorship curriculum. Methods: The authors describe a medical student-led pipeline program, which connects medical students with URiM high school students. Medical student mentors participated in focus groups and gave written responses evaluating reasons for involvement, sociocultural attitudes, and skills needed for mentoring. Thematic analysis was applied. Results: Themes that emerged in this analysis include motivation to mentor, skills used to approach the mentoring relationship, and benefits to the mentor. Mentors felt their experiences had a high impact factor, and they employed dynamic discovery. It provided personal reward and a deeper understanding of disparities. Conclusion: Bringing medical school mentors together for peer to peer idea sharing, creating communities of practice, will help these students develop effective mentorship skills. A curriculum based on appreciative inquiry of mentors' strengths will enrich idea sharing, fostering cultural humility and avoiding burnout. Medical students involved in this program believe they gained benefits, including improving their mentorship skills, expanding their cultural humility, increasing their comfort with caring for underserved populations, and improving their ability to recognize health disparities.
RESUMO
The short arms of the ten acrocentric human chromosomes share several repetitive DNAs, including ribosomal RNA genes (rDNA). The rDNA arrays correspond to nucleolar organizing regions that coalesce each cell cycle to form the nucleolus. Telomere disruption by expressing a mutant version of telomere binding protein TRF2 (dnTRF2) causes non-random acrocentric fusions, as well as large-scale nucleolar defects. The mechanisms responsible for acrocentric chromosome sensitivity to dysfunctional telomeres are unclear. In this study, we show that TRF2 normally associates with the nucleolus and rDNA. However, when telomeres are crippled by dnTRF2 or RNAi knockdown of TRF2, gross nucleolar and chromosomal changes occur. We used the controllable dnTRF2 system to precisely dissect the timing and progression of nucleolar and chromosomal instability induced by telomere dysfunction, demonstrating that nucleolar changes precede the DNA damage and morphological changes that occur at acrocentric short arms. The rDNA repeat arrays on the short arms decondense, and are coated by RNA polymerase I transcription binding factor UBF, physically linking acrocentrics to one another as they become fusogenic. These results highlight the importance of telomere function in nucleolar stability and structural integrity of acrocentric chromosomes, particularly the rDNA arrays. Telomeric stress is widely accepted to cause DNA damage at chromosome ends, but our findings suggest that it also disrupts chromosome structure beyond the telomere region, specifically within the rDNA arrays located on acrocentric chromosomes. These results have relevance for Robertsonian translocation formation in humans and mechanisms by which acrocentric-acrocentric fusions are promoted by DNA damage and repair.