CKD Due to a Novel Mitochondrial DNA Mutation: A Case Report

Focus on Mitochondrial Respiratory Chain: Potential Therapeutic Target for Chronic Renal Failure

The function of the respiratory chain is closely associated with kidney function, and the dysfunction of the respiratory chain is a primary pathophysiological change in chronic kidney failure. The incidence of chronic kidney failure caused by defects in respiratory-chain-related genes has frequently been overlooked. Correcting abnormal metabolic reprogramming, rescuing the "toxic respiratory chain", and targeting the clearance of mitochondrial reactive oxygen species are potential therapies for treating chronic kidney failure. These treatments have shown promising results in slowing fibrosis and inflammation progression and improving kidney function in various animal models of chronic kidney failure and patients with chronic kidney disease (CKD). The mitochondrial respiratory chain is a key target worthy of attention in the treatment of chronic kidney failure. This review integrated research related to the mitochondrial respiratory chain and chronic kidney failure, primarily elucidating the pathological status of the mitochondrial respiratory chain in chronic kidney failure and potential therapeutic drugs. It provided new ideas for the treatment of kidney failure and promoted the development of drugs targeting the mitochondrial respiratory chain.

Roles of Mitochondrial DNA Damage in Kidney Diseases: A New Biomarker

The kidney is a mitochondria-rich organ, and kidney diseases are recognized as mitochondria-related pathologies. Intact mitochondrial DNA (mtDNA) maintains normal mitochondrial function. Mitochondrial dysfunction caused by mtDNA damage, including impaired mtDNA replication, mtDNA mutation, mtDNA leakage, and mtDNA methylation, is involved in the progression of kidney diseases. Herein, we review the roles of mtDNA damage in different setting of kidney diseases, including acute kidney injury (AKI) and chronic kidney disease (CKD). In a variety of kidney diseases, mtDNA damage is closely associated with loss of kidney function. The level of mtDNA in peripheral serum and urine also reflects the status of kidney injury. Alleviating mtDNA damage can promote the recovery of mitochondrial function by exogenous drug treatment and thus reduce kidney injury. In short, we conclude that mtDNA damage may serve as a novel biomarker for assessing kidney injury in different causes of renal dysfunction, which provides a new theoretical basis for mtDNA-targeted intervention as a therapeutic option for kidney diseases.

Clinicopathological Features of Mitochondrial Nephropathy

Introduction

The clinicopathologic characteristics of nephropathy associated with mitochondrial disease (MD) remain unknown. We retrospectively analyzed a cohort of patients with proteinuria, decreased glomerular filtration rate, or Fanconi syndrome who had a genetic mutation confirmed as the cause of MD, defined as mitochondrial nephropathy.

Methods

This nationwide survey included 757 nephrology sections throughout Japan, and consequently, data on 81 cases of mitochondrial nephropathy were collected.

Results

The most common renal manifestation observed during the disease course was proteinuria. Hearing loss was the most common comorbidity; a renal-limited phenotype was observed only in mitochondrial DNA (mtDNA) point mutation and COQ8B mutation cases. We found a median time delay of 6.0 years from onset of renal manifestations to diagnosis. Focal segmental glomerular sclerosis (FSGS) was the most common pathologic diagnosis. We then focused on 63 cases with the m.3243A>G mutation. The rate of cases with diabetes was significantly higher among adult-onset cases than among childhood-onset cases. Pathologic diagnoses were more variable in adult-onset cases, including diabetic nephropathy, nephrosclerosis, tubulointerstitial nephropathy, and minor glomerular abnormalities. During the median observation period of 11.0 years from the first onset of renal manifestations in patients with m.3243A>G, renal replacement therapy (RRT) was initiated in 50.8% of patients. Death occurred in 25.4% of the patients during the median observation period of 12.0 years. The median estimated glomerular filtration rate (eGFR) decline was 5.4 ml/min per 1.73 m²/yr in the cases, especially 8.3 ml/min per 1.73 m²/yr in FSGS cases, with m.3243A>G.

Conclusion

Here, we described the clinicopathologic features and prognosis of mitochondrial nephropathy using large-scale data.

Possible role of the mitochondrial genome in the pathogenesis of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenic renal disease in adults and is due to heterozygous germ line variants in either PKD1, PKD2 or rarely other genes. It is characterized by marked intra-familial disease variability suggesting that other genetic and/or environmental factors are involved in determining the lifetime course ADPKD. Recently, research indicates that polycystin-mediated mitochondrial dysfunction and metabolic re-programming contributes to the progression of ADPKD. Although biochemical abnormalities have gained the most interest, variants in the mitochondrial genome could be one of the mechanisms underlying the phenotypic variability in ADPKD. This narrative review aims to evaluate the role of the mitochondrial genome in the pathogenesis of APDKD.

Kidney epithelial targeted mitochondrial transcription factor A deficiency results in progressive mitochondrial depletion associated with severe cystic disease

Abnormal mitochondrial function is a well-recognized feature of acute and chronic kidney diseases. To gain insight into the role of mitochondria in kidney homeostasis and pathogenesis, we targeted mitochondrial transcription factor A (TFAM), a protein required for mitochondrial DNA replication and transcription that plays a critical part in the maintenance of mitochondrial mass and function. To examine the consequences of disrupted mitochondrial function in kidney epithelial cells, we inactivated TFAM in sine oculis-related homeobox 2-expressing kidney progenitor cells. TFAM deficiency resulted in significantly decreased mitochondrial gene expression, mitochondrial depletion, inhibition of nephron maturation and the development of severe postnatal cystic disease, which resulted in premature death. This was associated with abnormal mitochondrial morphology, a reduction in oxygen consumption and increased glycolytic flux. Furthermore, we found that TFAM expression was reduced in murine and human polycystic kidneys, which was accompanied by mitochondrial depletion. Thus, our data suggest that dysregulation of TFAM expression and mitochondrial depletion are molecular features of kidney cystic disease that may contribute to its pathogenesis.