Myocardium-specific Isca1 knockout causes iron metabolism disorder and myocardial oncosis in rat

Iron Dyshomeostasis and Mitochondrial Function in the Failing Heart: A Review of the Literature

Cardiac contraction and relaxation require a substantial amount of energy provided by the mitochondria. The failing heart is adenosine triphosphate (ATP)- and creatine-depleted. Studies have found iron is involved in almost every aspect of mitochondrial function, and previous studies have shown myocardial iron deficiency in heart failure (HF). Many clinicians advocated intravenous iron repletion for HF patients meeting the conventional criteria for systemic iron deficiency. While clinical trials showed improved quality of life, iron repletion failed to significantly impact survival or significant cardiovascular adverse events. There is evidence that in HF, labile iron is trapped inside the mitochondria causing oxidative stress and lipid peroxidation. There is also compelling preclinical evidence demonstrating the detrimental effects of both iron overload and depletion on cardiomyocyte function. We reviewed the mechanisms governing myocardial and mitochondrial iron content. Mitochondrial dynamics (i.e., fusion, fission, mitophagy) and the role of iron were also investigated. Ferroptosis, as an important regulated cell death mechanism involved in cardiomyocyte loss, was reviewed along with agents used to manipulate it. The membrane stability and iron content of mitochondria can be altered by many agents. Some studies are showing promising improvement in the cardiomyocyte function after iron chelation by deferiprone; however, whether the in vitro and in vivo findings will be reflected on on clinical grounds is still unclear. Finally, we briefly reviewed the clinical trials on intravenous iron repletion. There is a need for more well-simulated animal studies to shed light on the safety and efficacy of chelation agents and pave the road for clinical studies.

Expanding DdCBE-mediated targeting scope to aC motif preference in rat

An animal model harboring pathogenic mitochondrial DNA (mtDNA) mutations is important to understand the biological links between mtDNA variation and mitochondrial diseases. DdCBE, a DddA-derived cytosine base editor, has been utilized in zebrafish, mice, and rats for tC sequence-context targeting and human mitochondrial disease modeling. However, human pathogenic mtDNA mutations other than the tC context cannot be manipulated. Here, we screened the combination of different DdCBE pairs at pathogenic mtDNA mutation sites with nC (n for a, g, or c) context and identified that the left-G1333C (L1333C) + right G1333N (R1333N) pair could mediate C⋅G-to-T⋅A conversion effectively at aC sites in rat C6 cells. The editing efficiency at disease-associated mtDNA mutation sites within aC context was further confirmed to be up to 67.89% in vivo. Also, the installed disease-associated mtDNA mutations were germline transmittable. Moreover, the edited rats showed impaired cardiac function and mitochondrial function, resembling human mitochondrial disease symptoms. In summary, for the first time, we expanded the DdCBE targeting scope to an aC motif and installed the pathogenic mutation in rats to model human mitochondrial diseases.

A conditional knockout rat resource of mitochondrial protein-coding genes via a DdCBE-induced premature stop codon

Hundreds of pathogenic variants of mitochondrial DNA (mtDNA) have been reported to cause mitochondrial diseases, which still lack effective treatments. It is a huge challenge to install these mutations one by one. We repurposed the DddA-derived cytosine base editor to incorporate a premature stop codon in the mtProtein-coding genes to ablate mitochondrial proteins encoded in the mtDNA (mtProteins) instead of installing pathogenic variants and generated a library of both cell and rat resources with mtProtein depletion. In vitro, we depleted 12 of 13 mtProtein-coding genes with high efficiency and specificity, resulting in decreased mtProtein levels and impaired oxidative phosphorylation. Moreover, we generated six conditional knockout rat strains to ablate mtProteins using Cre/loxP system. Mitochondrially encoded ATP synthase membrane subunit 8 and NADH:ubiquinone oxidoreductase core subunit 1 were specifically depleted in heart cells or neurons, resulting in heart failure or abnormal brain development. Our work provides cell and rat resources for studying the function of mtProtein-coding genes and therapeutic strategies.

A neuron-specific Isca1 knockout rat developments multiple mitochondrial dysfunction syndromes

BACKGROUND

Multiple mitochondrial dysfunction syndromes (MMDS) are rare mitochondrial diseases caused by mutation of mitochondrial iron-sulfur cluster synthesis proteins. This study established a rat model simulating MMDS5 disease in the nervous system to investigate its pathological features and neuronal death.

METHODS

We generated neuron-specific Isca1 knockout rat (Isca1^flox/flox -NeuN-Cre) using CRISPR-Cas9 technology. The brain structure changes of CKO rats were studied with MRI, and the behavior abnormalities were analyzed through gait analysis and open field tests, Y maze tests and food maze tests. The pathological changes of neurons were analyzed through H&E staining, Nissl staining, and Golgi staining. Mitochondrial damage was assessed by TEM, western blot and ATP assay, and the morphology of neurons was assessed by WGA immunofluorescence to detect the death of neurons.

RESULTS

This study established the disease model of MMDS5 in the nervous system for the first time, and found that after Isca1 loss, the rats suffered from developmental retardation, epilepsy, memory impairment, massive neuronal death, reduced number of Nissl bodies and dendritic spines, mitochondrial fragmentation, cristae fracture, reduced content of respiratory chain complex protein, and reduced production of ATP. Isca1 knockout caused neuronal oncosis.

CONCLUSIONS

This rat model can be used to study the pathogenesis of MMDS. In addition, compared with human MMDS5, the rat model can survive up to 8 weeks of age, effectively extending the window of clinical treatment research, and can be used for the treatment of neurological symptoms in other mitochondrial diseases.

Rodent Models of Dilated Cardiomyopathy and Heart Failure for Translational Investigations and Therapeutic Discovery

Even with modern therapy, patients with heart failure only have a 50% five-year survival rate. To improve the development of new therapeutic strategies, preclinical models of disease are needed to properly emulate the human condition. Determining the most appropriate model represents the first key step for reliable and translatable experimental research. Rodent models of heart failure provide a strategic compromise between human in vivo similarity and the ability to perform a larger number of experiments and explore many therapeutic candidates. We herein review the currently available rodent models of heart failure, summarizing their physiopathological basis, the timeline of the development of ventricular failure, and their specific clinical features. In order to facilitate the future planning of investigations in the field of heart failure, a detailed overview of the advantages and possible drawbacks of each model is provided.