Disease Models & Mechanisms最新文献

The translation elongation factor eEF1α (eukaryotic elongation factor 1α) mediates mRNA translation by delivering aminoacyl-tRNAs to ribosomes. eEF1α also has other reported roles, including the regulation of actin dynamics. However, these distinct roles of eEF1α are often challenging to uncouple and remain poorly understood in aging metazoan tissues. The genomes of mammals and Drosophila encode two eEF1α paralogs, with eEF1α1 expressed ubiquitously and eEF1α2 expression more limited to neurons and muscle cells. Here, we report that eEF1α2 plays a unique role in maintaining myofibril homeostasis during aging in Drosophila. Specifically, we generated an eEF1α2 null allele, which was viable and showed two distinct muscle phenotypes. In young flies, the mutants had thinner myofibrils in indirect flight muscles that could be rescued by expressing eEF1α1. With aging, the muscles of the mutant flies began showing abnormal distribution of actin and myosin in muscles, but without a change in actin and myosin protein levels. This age-related phenotype could not be rescued by eEF1α1 overexpression. These findings support an unconventional role of Drosophila eEF1α2 in age-related homeostasis of muscle myofibers.

Epithelial-mesenchymal transitions (EMTs) are thought to promote metastasis via downregulation of E-cadherin (also known as Cdh1) and upregulation of mesenchymal markers such as N-cadherin (Cdh2) and vimentin (Vim). Contrary to this, E-cadherin is retained in many invasive carcinomas and promotes collective cell invasion. To investigate how E-cadherin regulates metastasis, we examined the highly metastatic, E-cadherin-positive murine 4T1 breast cancer model, together with the less metastatic, 4T1-related cell lines 4T07, 168FARN and 67NR. We found that 4T1 cells display a hybrid epithelial/mesenchymal phenotype with co-expression of epithelial and mesenchymal markers, whereas 4T07, 168FARN, and 67NR cells display progressively more mesenchymal phenotypes in vitro that relate inversely to their metastatic capacity in vivo. Using RNA interference and constitutive expression, we demonstrate that the expression level of E-cadherin does not determine 4T1 or 4T07 cell metastatic capacity in mice. Mechanistically, 4T1 cells possess highly dynamic, unstable cell-cell junctions and can undergo collective invasion without E-cadherin downregulation. However, 4T1 orthotopic tumors in vivo also contain subregions of EMT-like loss of E-cadherin. Thus, 4T1 cells function as a model for carcinomas with a hybrid epithelial/mesenchymal phenotype that promotes invasion and metastasis.

The mandible plays an essential part in human life and, thus, defects in this structure can dramatically impair the quality of life in patients. Axolotls, unlike humans, are capable of regenerating their lower jaws; however, the underlying mechanisms and their similarity to those in limb regeneration are unknown. In this work, we used morphological, histological, and transcriptomic approaches to analyze the regeneration of lateral resection defects in the axolotl mandible. We found that this structure can regenerate all missing tissues in 90 days through gap minimization, blastema formation, and finally tissue growth, differentiation, and integration. Moreover, transcriptomic comparisons of regenerating mandibles and limbs showed that they share molecular phases of regeneration, that these similarities peak during blastema stages, and that mandible regeneration occurs at a slower pacing. Altogether, our study demonstrates the existence of a shared regenerative program used in two different regenerating body structures with different embryonic origins in the axolotl, and contributes to our understanding of the minimum requirements for a successful regeneration in vertebrates, bringing us closer to understand similar lesions in human mandibles.

Being a vital cellular process, COPII vesicle trafficking has been found plays a crucial role in liver metabolism. However, its functions and the underlying mechanisms in systemic metabolic homeostasis have not been fully understood. Here, with a newly identified gene trap zebrafish line (sec31anju221), we show that compromised COPII vesicle trafficking leads to biphasic abnormal hepatic metabolism. During the larval stage, deficiency of COPII-mediated trafficking leads to activation of unfolded protein reaction (UPR) and the development of hepatic steatosis. By using epistasis analysis, we found eIF2a/ATF4 branch serves as the primary effector for liver steatosis. In adult sec31anju221 fish, the hepatosteatosis was reversed and the phenotype swing to glycogenic hepatopathy. Proteomic profiling and biochemical assay indicate sec31anju221 fish are in a state of hypothyroidism. Moreover, our study showed thyroid hormone treatment alleviates the metabolic defects. This study provides insights into processes of liver diseases associated with vesicle trafficking impairments and has expanded our understanding of the pathological interplay between thyroid and liver.

Skeletal insufficiency affects all individuals with Down syndrome (DS) or Trisomy 21 (Ts21) and may alter bone strength throughout development due to a reduced period of bone formation and early attainment of peak bone mass compared to typically developing individuals. Appendicular skeletal deficits also appear in males before females with DS. In femurs of male Ts65Dn DS model mice, cortical deficits were pronounced throughout development, but trabecular deficits and Dyrk1a overexpression were transitory until postnatal day (P) 30 when there were persistent trabecular and cortical deficits and Dyrk1a was trending overexpression. Correction of DS-related skeletal deficits by a purported DYRK1A inhibitor or through genetic means beginning at P21 was not effective at P30, but germline normalization of Dyrk1a improved male bone structure by P36. Trabecular and cortical deficits in female Ts65Dn mice were evident at P30 but subsided by P36, typifying periodic developmental skeletal normalizations that progressed to more prominent bone deficiencies. Sex-dependent differences in skeletal deficits with a delayed impact of trisomic Dyrk1a are important to find temporally specific treatment periods for bone and other phenotypes associated with Ts21.

Becker Muscular Dystrophy (BMD) is a rare X-linked recessive neuromuscular disorder frequently caused by in-frame deletions in the DMD gene that result in the production of a truncated, yet functional, dystrophin protein. The consequences of BMD-causing in-frame deletions on the organism are difficult to predict, especially in regard to long-term prognosis. Here, we employed CRISPR-Cas9 to generate a new Dmd del52-55 mouse model by deleting exons 52-55, resulting in a BMD-like in-frame deletion. To delineate the long-term effects of this deletion, we studied these mice over 52 weeks by performing histology and echocardiography analyses and assessing motor functions. Our results suggest that a truncated dystrophin is sufficient to maintain wildtype-like muscle and heart histology and functions in young mice. However, the truncated protein appears insufficient to maintain normal muscle homeostasis and protect against exercise-induced damage at 52 weeks. To further delineate the effects of this exon52-55 in-frame deletion, we performed RNA-Seq pre- and post-exercise and identified several differentially expressed pathways that reflect the abnormal muscle phenotype observed at 52 weeks in the BMD model.

Hypertrophic cardiomyopathy (HCM) is an inherited heart muscle disease that is characterised by left ventricular wall thickening, cardiomyocyte disarray and fibrosis, and is associated with arrhythmias, heart failure and sudden death. However, it is unclear to what extent the electrophysiological disturbances that lead to sudden death occur secondary to structural changes in the myocardium or as a result of HCM cardiomyocyte electrophysiology. In this study, we used an induced pluripotent stem cell model of the R403Q variant in myosin heavy chain 7 (MYH7) to study the electrophysiology of HCM cardiomyocytes in electrically coupled syncytia, revealing significant conduction slowing and increased spatial dispersion of repolarisation - both well-established substrates for arrhythmia. Analysis of rhythmonome protein expression in MYH7 R403Q cardiomyocytes showed reduced expression of connexin-43 (also known as GJA1), sodium channels and inward rectifier potassium channels - a three-way hit that reduces electrotonic coupling and slows cardiac conduction. Our data represent a previously unreported, biophysical basis for arrhythmia in HCM that is intrinsic to cardiomyocyte electrophysiology. Later in the progression of the disease, these proarrhythmic phenotypes may be accentuated by myocyte disarray and fibrosis to contribute to sudden death.

The size and composition of the intracellular DNA precursor pool is integral to the maintenance of genome stability, and this relationship is fundamental to our understanding of cancer. Key aspects of carcinogenesis, including elevated mutation rates and induction of certain types of DNA damage in cancer cells, can be linked to disturbances in deoxynucleoside triphosphate (dNTP) pools. Furthermore, our approaches to treat cancer heavily exploit the metabolic interplay between the DNA and the dNTP pool, with a long-standing example being the use of antimetabolite-based cancer therapies, and this strategy continues to show promise with the development of new targeted therapies. In this Review, we compile the current knowledge on both the causes and consequences of dNTP pool perturbations in cancer cells, together with their impact on genome stability. We outline several outstanding questions remaining in the field, such as the role of dNTP catabolism in genome stability and the consequences of dNTP pool expansion. Importantly, we detail how our mechanistic understanding of these processes can be utilised with the aim of providing better informed treatment options to patients with cancer.

N-methyl-D-aspartate (NMDA)-induced retinal damage has been well studied in rodents, but the detailed mechanisms have not yet been characterized in nonhuman primates. Here, we characterized the retinal degenerative effects of NMDA on rhesus monkeys in vivo. NMDA saline or saline-only control was injected intravitreally to the randomly assigned eyes and contralateral eyes of four rhesus monkeys, respectively. The structural and functional changes of retina were characterized by optical coherence tomography and electroretinography on days 0, 4, 30 and 60 post injection. Both optic discs and macular areas of the NMDA-injected eyes initially presented with a transient retinal thickening, followed by continued retinal thinning. The initial, transient retinal thickening has also been observed in glaucoma patients, but this has not been reported in rodent NMDA models. This initial response was followed by loss of retina ganglion cells (RGCs), which is similar to glaucomatous optic neuropathy and other RGC-related retinal degenerations. The amplitudes of both the photopic negative response and pattern electroretinogram decreased significantly and remained low until the end of the study. Thus, the NMDA monkey model may serve as a more clinically relevant animal model of retinal damage.

A pervasive discussion point within the scientific community is the value of unpublished or unavailable data. Researchers, funders, ethical review bodies, editors and publishers have all highlighted the need to make more data available to enhance experimental planning and interpretation and to prevent others from repeating similar experiments. This is particularly important in the context of experimentation involving animals and efforts towards replacement, refinement and reduction. However, despite this broad agreement, sharing data that show inconclusive, statistically insignificant or unremarkable results is still not common practice. In this Editorial, we will highlight the value of what are often coined negative (or null) data and outline some emerging initiatives to address the gap between data generated in laboratories and data available to the wider scientific community.