A mitochondrial DNA deletion presenting with corneal clouding and severe Fanconi syndrome

Mitochondrial Dysfunction in Kidney Tubulopathies

Mitochondria play a key role in kidney physiology and pathology. They produce ATP to fuel energy-demanding water and solute reabsorption processes along the nephron. Moreover, mitochondria contribute to cellular health by the regulation of autophagy, (oxidative) stress responses, and apoptosis. Mitochondrial abundance is particularly high in cortical segments, including proximal and distal convoluted tubules. Dysfunction of the mitochondria has been described for tubulopathies such as Fanconi, Gitelman, and Bartter-like syndromes and renal tubular acidosis. In addition, mitochondrial cytopathies often affect renal (tubular) tissues, such as in Kearns-Sayre and Leigh syndromes. Nevertheless, the mechanisms by which mitochondrial dysfunction results in renal tubular diseases are only scarcely being explored. This review provides an overview of mitochondrial dysfunction in the development and progression of kidney tubulopathies. Furthermore, it emphasizes the need for further mechanistic investigations to identify links between mitochondrial function and renal electrolyte reabsorption.

Growth Retardation in the Course of Fanconi Syndrome Caused by the 4977-bp Mitochondrial DNA Deletion: A Case Report

Fanconi syndrome is one of the primary renal manifestations of mitochondrial cytopathies caused by mitochondrial DNA (mtDNA) mutation. The common 4977-bp mtDNA deletion has been reported to be associated with aging and diseases involving multiple extrarenal organs. Cases of Fanconi syndrome caused by the 4977-bp deletion were rarely reported previously. Here, we report a 6-year-old girl with growth retardation in the course of Fanconi syndrome. She had mild ptosis and pigmented retinopathy. Abnormal biochemical findings included low-molecular-weight proteinuria, normoglycemic glycosuria, increased urine phosphorus excretion, metabolic acidosis, and hypophosphatemia. Growth records showed that her body weight and height were normal in the first year and failed to thrive after the age of three. Using a highly sensitive mtDNA analysis methodology, she was identified to possess the common 4977-bp mtDNA deletion. The mutation rate was 84.7% in the urine exfoliated cells, 78.67% in the oral mucosal cells, and 23.99% in the blood sample. After three months of oral coenzyme Q10 and levocarnitine treatment in combination with standard electrolyte supplement, her condition was improved. This is a report of growth retardation as the initial major clinical presentation of Fanconi syndrome caused by the deletion of the 4977-bp fragment. Renal tubular abnormality without any other extrarenal dysfunction may be an initial clinical sign of mitochondrial disorders. Moreover, considering the heterogeneity of the phenotypes associated with mtDNA mutations, the risk of developing Kearns–Sayre syndrome (KSS) with age in this patient should be noted because she had ptosis, retinal involvement, and changes in the brain and skeletal muscle.

Transcriptome from opaque cornea of Fanconi anemia patient uncovers fibrosis and two connected players

Congenital corneal opacities (CCO) are a group of blinding corneal disorders, where the underlying molecular mechanisms are poorly understood. Phenotyping through specialized imaging and histopathology analysis, together with assessment of key transcriptomic changes (including glycosaminoglycan metabolic enzymes) in cornea(s) with CCO from a case of Fanconi anemia is the approach taken in this study to identify causal mechanisms. Based on our findings, we propose a novel mechanism and two key players contributing to CCO.

Mitochondrial DNA mutations in renal disease: an overview

Kidneys have a high energy demand to facilitate the reabsorption of the glomerular filtrate. For this reason, renal cells have a high density of mitochondria. Mitochondrial cytopathies can be the result of a mutation in both mitochondrial and nuclear DNA. Mitochondrial dysfunction can lead to a variety of renal manifestations. Examples of tubular manifestations are renal Fanconi Syndrome, which is often found in patients diagnosed with Kearns-Sayre and Pearson's marrow-pancreas syndrome, and distal tubulopathies, which result in electrolyte disturbances such as hypomagnesemia. Nephrotic syndrome can be a glomerular manifestation of mitochondrial dysfunction and is typically associated with focal segmental glomerular sclerosis on histology. Tubulointerstitial nephritis can also be seen in mitochondrial cytopathies and may lead to end-stage renal disease. The underlying mechanisms of these cytopathies remain incompletely understood; therefore, current therapies focus mainly on symptom relief. A better understanding of the molecular disease mechanisms is critical in order to improve treatments.

Creation of Cultures Containing Mutations Linked with Cardiovascular Diseases using Transfection and Genome Editing

OBJECTIVE

In this review article, we analyzed the literature on the creation of cultures containing mutations associated with cardiovascular diseases (CVD) using transfection, transduction and editing of the human genome.

METHODS

We described different methods of transfection, transduction and editing of the human genome, used in the literature.

RESULTS

We reviewed the researches in which the creation of сell cultures containing mutations was described. According to the literature, system CRISPR/Cas9 proved to be the most preferred method for editing the genome. We found rather promising and interesting a practically undeveloped direction of mitochondria transfection using a gene gun. Such a gun can direct a genetically-engineered construct containing human DNA mutations to the mitochondria using heavy metal particles. However, in human molecular genetics, the transfection method using a gene gun is unfairly forgotten and is almost never used. Ethical problems arising from editing the human genome were also discussed in our review. We came to a conclusion that it is impossible to stop scientific and technical progress. It is important that the editing of the genome takes place under the strict control of society and does not bear dangerous consequences for humanity. To achieve this, the constant interaction of science with society, culture and business is necessary.

CONCLUSION

The most promising methods for the creation of cell cultures containing mutations linked with cardiovascular diseases, were system CRISPR/Cas9 and the gene gun.

The Emerging Role of Mitochondrial Targeting in Kidney Disease

Renal disease affects millions of people worldwide, imposing an enormous financial burden for health-care systems. Recent evidence suggests that mitochondria play an important role in the pathogenesis of different forms of renal disease, including genetic defects, acute kidney injury, chronic kidney disease, aging, renal tumors, and transplant nephropathy. Renal mitochondrial abnormalities and dysfunction affect several cellular pathways, leading to increased oxidative stress, apoptosis, microvascular loss, and fibrosis, all of which compromise renal function. Over recent years, compounds that specifically target mitochondria have emerged as promising therapeutic options for patients with renal disease. Although the most compelling evidence is based on preclinical studies, several compounds are currently being tested in clinical trials. This chapter provides an overview of the involvement of mitochondrial dysfunction in renal disease and summarizes the current knowledge on mitochondria-targeted strategies to attenuate renal disease.

Hepatocyte Nuclear Factor-1β Controls Mitochondrial Respiration in Renal Tubular Cells

AKI is a frequent condition that involves renal microcirculation impairment, infiltration of inflammatory cells with local production of proinflammatory cytokines, and subsequent epithelial disorders and mitochondrial dysfunction. Peroxisome proliferator-activated receptor γ coactivator 1-α (PPARGC1A), a coactivator of the transcription factor PPAR-γ that controls mitochondrial biogenesis and function, has a pivotal role in the early dysfunction of the proximal tubule and the subsequent renal repair. Here, we evaluated the potential role of hepatocyte nuclear factor-1β (HNF-1β) in regulating PPARGC1A expression in AKI. In mice, endotoxin injection to induce AKI also induced early and transient inflammation and PPARGC1A inhibition, which overlapped with downregulation of the HNF-1β transcriptional network. In vitro, exposure of proximal tubule cells to the inflammatory cytokines IFN-γ and TNF-α led to inhibition of HNF-1β transcriptional activity. Moreover, inhibition of HNF-1β significantly reduced PPARGC1A expression and altered mitochondrial morphology and respiration in proximal tubule cells. Chromatin immunoprecipitation assays and PCR analysis confirmed HNF-1β binding to the Ppargc1a promoter in mouse kidneys. We also demonstrated downregulation of renal PPARGC1A expression in a patient with an HNF1B germinal mutation. Thus, we propose that HNF-1β links extracellular inflammatory signals to mitochondrial dysfunction during AKI partly via PPARGC1A signaling. Our findings further strengthen the view of HNF1B-related nephropathy as a mitochondrial disorder in adulthood.

Coenzyme Q10 in the Treatment of Corneal Edema in Kearns-Sayre: Is There an Application in Fuchs Endothelial Corneal Dystrophy?

PURPOSE

Corneal involvement in mitochondrial disease is seldom described. Kearns-Sayre syndrome (KSS) is a mitochondrial disorder characterized by retinitis pigmentosa, external ophthalmoplegia, and heart block. We report 2 patients with KSS with corneal lesions involving the endothelium, which improved with Coenzyme Q10 (CoQ10). Based on recent research regarding the role of dysfunctional oxidative metabolism in Fuchs Endothelial Corneal Dystrophy (FECD), we propose that mitochondrial diseases and FECD share a final pathway.

METHODS

A chart review was performed and a review of the literature was completed with a PubMed search using the terms "Kearns-Sayre Syndrome", "mitochondria", "endothelium", "Fuchs endothelial corneal dystrophy", and "cornea".

RESULTS

There are 19 reports of corneal involvement in clinical phenotypes of mitochondrial disease. Nine of these 19 cases had findings consistent with KSS. Our patients with KSS had microcystic changes throughout the cornea and excrescences on the endothelial surface seen with ultrasound biomicroscopy, similar to the clinical findings in FECD. CoQ10 improved corneal disease in both children. CoQ10 deficiency has been reported in a variety of mitochondrial diseases, and efficacy of supplementation has been demonstrated. It may be beneficial in these patients because of its antioxidant properties and role in oxidative phosphorylation.

CONCLUSIONS

The common deletion found in patients with KSS has recently been implicated in FECD, which has recently been shown to be a disease related to dysfunctional oxidative metabolism. Future research should explore the use of antioxidants, such as CoQ10 in patients with FECD.

The Eye on Mitochondrial Disorders

Ophthalmologic manifestations of mitochondrial disorders are frequently neglected or overlooked because they are often not regarded as part of the phenotype. This review aims at summarizing and discussing the etiology, pathogenesis, diagnosis, and treatment of ophthalmologic manifestations of mitochondrial disorders. Review of publications about ophthalmologic involvement in mitochondrial disorders by search of Medline applying appropriate search terms. The eye is frequently affected by syndromic as well as nonsyndromic mitochondrial disorders. Primary and secondary ophthalmologic manifestations can be differentiated. The most frequent ophthalmologic manifestations of mitochondrial disorders include ptosis, progressive external ophthalmoplegia, optic atrophy, retinopathy, and cataract. More rarely occurring are nystagmus and abnormalities of the cornea, ciliary body, intraocular pressure, the choroidea, or the brain secondarily affecting the eyes. It is important to recognize and diagnose ophthalmologic manifestations of mitochondrial disorders as early as possible because most are accessible to symptomatic treatment with partial or complete short-term or long-term beneficial effect. Ophthalmologic manifestations of mitochondrial disorders need to be appropriately diagnosed to initiate the most effective management and guarantee optimal outcome.

Mitochondrial dysfunction in the pathophysiology of renal diseases

Mitochondrial dysfunction has gained recognition as a contributing factor in many diseases. The kidney is a kind of organ with high energy demand, rich in mitochondria. As such, mitochondrial dysfunction in the kidney plays a critical role in the pathogenesis of kidney diseases. Despite the recognized importance mitochondria play in the pathogenesis of the diseases, there is limited understanding of various aspects of mitochondrial biology. This review examines the physiology and pathophysiology of mitochondria. It begins by discussing mitochondrial structure, mitochondrial DNA, mitochondrial reactive oxygen species production, mitochondrial dynamics, and mitophagy, before turning to inherited mitochondrial cytopathies in kidneys (inherited or sporadic mitochondrial DNA or nuclear DNA mutations in genes that affect mitochondrial function). Glomerular diseases, tubular defects, and other renal diseases are then discussed. Next, acquired mitochondrial dysfunction in kidney diseases is discussed, emphasizing the role of mitochondrial dysfunction in the pathogenesis of chronic kidney disease and acute kidney injury, as their prevalence is increasing. Finally, it summarizes the possible beneficial effects of mitochondrial-targeted therapeutic agents for treatment of mitochondrial dysfunction-mediated kidney injury-genetic therapies, antioxidants, thiazolidinediones, sirtuins, and resveratrol-as mitochondrial-based drugs may offer potential treatments for renal diseases.