Point mutation in mitochondrial tRNA gene is associated with polycystic ovary syndrome and insulin resistance

Association of Mitochondrial Variants with the Joint Occurrence of Polycystic Ovary Syndrome and Hashimoto's Thyroiditis

BACKGROUND

The prevalence of Hashimoto's thyroiditis (HT) among women with polycystic ovary syndrome (PCOS) is higher than in the general female population, but the factors predisposing to the coexistence of these disorders remain unclear. This study employed whole genome sequencing of mitochondrial DNA to identify genetic variants potentially associated with the development of PCOS and HT and predisposing to their joint occurrence.

RESULTS

A total of 84 women participated, including patients with PCOS, HT, coexisting PCOS and HT (PCOS + HT) and healthy women. Both Fisher's exact and Mann-Whitney U statistical analyses were performed to compare the frequency of variants between groups. Ten differentiating variants were common to both analyses in PCOS + HT vs. PCOS, one in PCOS + HT vs. HT, and six in PCOS + HT vs. control. Several variants differentiating the PCOS + HT group from PCOS and controls were identified, located both in the mitochondrial genes (including the MT-CYB, MT-ND1, MT-ND2, MT-ND4, MT-ND6, MT-CO1, MT-CO3) and the D-loop region. Only two variants differentiated PCOS + HT and HT groups. One variant (13237a in MT-ND5) was common for all three comparisons and underrepresented in the PCOS + HT group. Functional enrichment analysis showed 10 pathways that were unique for the comparison of PCOS + HT and PCOS groups, especially related to ATP production and oxidative phosphorylation, and one pathway, the NADH-quinone oxidoreductase, chain M/4, that was unique for the comparison of PCOS + HT and control groups. Notably, nine pathways shared commonality between PCOS + HT vs. PCOS and PCOS + HT vs. control, related to the biogenesis and assembly of Complex I.

CONCLUSION

This study provides novel insights into the genetic variants associated with oxidative stress in women with coexisting PCOS and HT. Mitochondrial dysfunction and oxidative stress appear to play a role in the pathogenesis of both conditions. However, more mitochondrial variants were found to differentiate women with both PCOS and HT from those with PCOS alone than from those with HT alone.

Polycystic Ovary Syndrome and Oxidative Stress-From Bench to Bedside

Oxidative stress (OS) is a condition that occurs as a result of an imbalance between the production of reactive oxygen species (ROS) and the body's ability to detoxify and neutralize them. It can play a role in a variety of reproductive system conditions, including polycystic ovary syndrome (PCOS), endometriosis, preeclampsia, and infertility. In this review, we briefly discuss the links between oxidative stress and PCOS. Mitochondrial mutations may lead to impaired oxidative phosphorylation (OXPHOS), decreased adenosine triphosphate (ATP) production, and an increased production of ROS. These functional consequences may contribute to the metabolic and hormonal dysregulation observed in PCOS. Studies have shown that OS negatively affects ovarian follicles and disrupts normal follicular development and maturation. Excessive ROS may damage oocytes and granulosa cells within the follicles, impairing their quality and compromising fertility. Impaired OXPHOS and mitochondrial dysfunction may contribute to insulin resistance (IR) by disrupting insulin signaling pathways and impairing glucose metabolism. Due to dysfunctional OXPHOS, reduced ATP production, may hinder insulin-stimulated glucose uptake, leading to IR. Hyperandrogenism promotes inflammation and IR, both of which can increase the production of ROS and lead to OS. A detrimental feedback loop ensues as IR escalates, causing elevated insulin levels that exacerbate OS. Exploring the relations between OS and PCOS is crucial to fully understand the role of OS in the pathophysiology of PCOS and to develop effective treatment strategies to improve the quality of life of women affected by this condition. The role of antioxidants as potential therapies is also discussed.

Mitochondrial Dysfunction in PCOS: Insights into Reproductive Organ Pathophysiology

Polycystic ovary syndrome (PCOS) is a complex, but relatively common endocrine disorder associated with chronic anovulation, hyperandrogenism, and micro-polycystic ovaries. In addition to reduced fertility, people with PCOS have a higher risk of obesity, insulin resistance, and metabolic disease, all comorbidities that are associated with mitochondrial dysfunction. This review summarizes human and animal data that report mitochondrial dysfunction and metabolic dysregulation in PCOS to better understand how mitochondria impact reproductive organ pathophysiology. This in-depth review considers all the elements regulating mitochondrial quantity and quality, from mitochondrial biogenesis under the transcriptional regulation of both the nuclear and mitochondrial genome to the ultrastructural and functional complexes that regulate cellular metabolism and reactive oxygen species production, as well as the dynamics that regulate subcellular interactions that are key to mitochondrial quality control. When any of these mitochondrial functions are disrupted, the energetic equilibrium within the cell changes, cell processes can fail, and cell death can occur. If this process is ongoing, it affects tissue and organ function, causing disease. The objective of this review is to consolidate and classify a broad number of PCOS studies to understand how various mitochondrial processes impact reproductive organs, including the ovary (oocytes and granulosa cells), uterus, placenta, and circulation, causing reproductive pathophysiology. A secondary objective is to uncover the potential role of mitochondria in the transgenerational transmission of PCOS and metabolic disorders.

The tRNA identity landscape for aminoacylation and beyond

tRNAs are key partners in ribosome-dependent protein synthesis. This process is highly dependent on the fidelity of tRNA aminoacylation by aminoacyl-tRNA synthetases and relies primarily on sets of identities within tRNA molecules composed of determinants and antideterminants preventing mischarging by non-cognate synthetases. Such identity sets were discovered in the tRNAs of a few model organisms, and their properties were generalized as universal identity rules. Since then, the panel of identity elements governing the accuracy of tRNA aminoacylation has expanded considerably, but the increasing number of reported functional idiosyncrasies has led to some confusion. In parallel, the description of other processes involving tRNAs, often well beyond aminoacylation, has progressed considerably, greatly expanding their interactome and uncovering multiple novel identities on the same tRNA molecule. This review highlights key findings on the mechanistics and evolution of tRNA and tRNA-like identities. In addition, new methods and their results for searching sets of multiple identities on a single tRNA are discussed. Taken together, this knowledge shows that a comprehensive understanding of the functional role of individual and collective nucleotide identity sets in tRNA molecules is needed for medical, biotechnological and other applications.

Potential Roles of mtDNA Mutations in PCOS-IR: A Review

Polycystic ovary syndrome (PCOS) is the most common heterogeneous endocrine disease that affecting females in reproductive age. Insulin resistance (IR), an important molecular basis for PCOS, accounts for at least 75% of women carrying this syndrome. Although there have been many studies on PCOS-IR, the detailed mechanisms are not fully understood. As essential hub for energy generation, mitochondria are critical to insulin secretion and normal function, whereas mutations in mitochondrial DNA (mtDNA) result in mitochondrial dysfunctions contributing to the pathophysiology of PCOS-IR via the regulation of balance of oxidative stress (OS), energy deficiency, or hormone metabolism. In the current review, we summarize the clinical and molecular features of PCOS-IR and discuss molecular mechanisms related to mtDNA mutations.

Mitochondrial Dysfunction in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a multi-causal condition. Among the genetic causes, variations in the mitochondrial DNA (mtDNA) are increasingly recognised as causative. PCOS not only occurs in known syndromic mitochondrial disorders due to pathogenic variants in the mtDNA but also in non-syndromic mitochondrial disorders. Additionally, mtDNA variants not causing a multi-system mitochondrial disorder but exclusively PCOS have been reported. Among the syndromic mitochondrial disorders, PCOS has been described in myoclonic epilepsy with ragged-red fibre (MERRF) syndrome. Among the non-syndromic mitochondrial disorders, PCOS has been described in association with insulin resistance. Several other studies suggest that mtDNA point mutations or mtDNA deletions can be associated with PCOS without manifesting in organs other than the ovaries. Evidence from animal studies suggests that function, morphology, and biogenesis of mitochondria in ovarian tissue are generally impaired in PCOS patients. In conclusion, there is increasing evidence that mtDNA variants play a pathophysiological role in the development of PCOS. Further studies are needed to establish the causal link between mtDNA variants and PCOS.

Genetic associations with polycystic ovary syndrome: the role of the mitochondrial genome; a systematic review and meta-analysis

Background

Polycystic ovary syndrome (PCOS) remains the most common female reproductive endocrine disorder. Genetic studies have predominantly focused on the role of the nuclear genome, while the contribution of mitochondrial genetics in PCOS remains largely unknown.

Aim

This study aims to systematically evaluate the literature regarding the associations between the mitochondrial genome and PCOS.

Methods

A literature search focused on PCOS and mitochondrial genetics was conducted on (1) MEDLINE, (2) EMBASE and (3) The Cochrane Library (CENTRAL and Cochrane Reviews). Search results were screened for eligibility, and data involving genetic variants of mitochondrial DNA (mtDNA) were extracted. Quantitative data were presented in forest plots, and where this was not possible, data were analysed in a qualitative manner. Quality of studies was assessed using the Q-Genie tool.

Results

Of the 13 812 identified studies, 15 studies were eligible for inclusion, with 8 studies suitable for meta-analysis. Women with PCOS showed higher frequencies of a 9 bp deletion, and aberrant single nucleotide polymorphisms (SNPs) in the ND5, A6 and 7 transfer RNA-encoding genes. They also showed lower frequencies of two SNPs in the D-loop of the genome. Women with PCOS also exhibited significantly lowered mtDNA copy number.

Conclusion

Women with PCOS harbour genetic variants in coding and non-coding regions of the mitochondrial genome. This may disrupt the electron transport chain and lead to oxidative stress, causing apoptosis of cells and further genetic damage. However, further studies of higher quality are required to confirm these associations.

PROSPERO registration number

CRD42021267991.

Mitochondrial DNA: Consensuses and Controversies

In the course of its short history, mitochondrial DNA (mtDNA) has made a long journey from obscurity to the forefront of research on major biological processes. mtDNA alterations have been found in all major disease groups, and their significance remains the subject of intense research. Despite remarkable progress, our understanding of the major aspects of mtDNA biology, such as its replication, damage, repair, transcription, maintenance, etc., is frustratingly limited. The path to better understanding mtDNA and its role in cells, however, remains torturous and not without errors, which sometimes leave a long trail of controversy behind them. This review aims to provide a brief summary of our current knowledge of mtDNA and highlight some of the controversies that require attention from the mitochondrial research community.

Maternally transmitted diabetes mellitus may be associated with mitochondrial ND5 T12338C and tRNAAla T5587C variants

INTRODUCTION

Mutations/variants in mitochondrial genomes are found to be associated with type 2 diabetes mellitus (T2DM), but the pathophysiology of this disease remains largely unknown.

AIM

The aim of this study is to investigate the relationship between mitochondrial DNA (mtDNA) variants and T2DM.

METHODOLOGY

A maternally inherited T2DM pedigree is underwent clinical, genetic, and molecular assessment. Moreover, the complete mitochondrial genomes of the matrilineal relatives of this family are PCR amplified and sequenced. We also utilize the phylogenetic conservation analysis, haplogroup classification, and the pathogenicity scoring system to determine the T2DM-associated potential pathogenic mtDNA variants.

RESULT

Four of seven matrilineal relatives of this pedigree suffered from T2DM with variable ages of onset. Screening for the entire mtDNA genes of matrilineal members reveals co-existence of ND5 T12338C and tRNA^Ala T5587C variants, as well as 21 genetic polymorphisms which belong to East Asian haplogroup F2. Interestingly, the T12338C variant causes the alternation of first amino acid Met to Thr, shortened two amino acids of ND5 protein. Furthermore, T5587C variant is located at position 73 in the 3'end of mt-tRNA^Ala and may have structural and functional consequences.

CONCLUSIONS

The co-occurrence of ND5 T12338C and tRNA^Ala T5587C variants may impair the mitochondrial function, which are associated with the development of T2DM in this family.

Mitochondrial function in women with polycystic ovary syndrome

PURPOSE OF REVIEW

To provide an overview of mitochondrial functional alterations in women with polycystic ovary syndrome (PCOS).

RECENT FINDINGS

Although numerous studies have focused on PCOS, the pathophysiological mechanisms that cause this common disease remain unclear. Mitochondria play a central role in energy production, and mitochondrial dysfunction may underlie several abnormalities observed in women with PCOS. Recent studies associated mtDNA mutations and low mtDNA copy number with PCOS, and set out to characterize the potential protective role of mitochondrial and endoplasmic reticulum unfolded protein responses (UPR and UPR).

SUMMARY

Mitochondrial dysfunction likely plays a role in the pathogenesis of PCOS by increasing reactive oxygen (ROS) and oxidative stress. This occurs in a metabolic milieu often affected by insulin resistance, which is a common finding in women with PCOS, especially in those who are overweight or obese. Mutations in mtDNA and low mtDNA copy number are found in these patients and may have potential as diagnostic modalities for specific PCOS phenotypes. More recently, UPR and UPR are being investigated as potential cellular rescue mechanisms in PCOS, the failure of which may lead to apoptosis, and contribute to decreased reproductive potential.

Mitochondrial Dysfunction and Chronic Inflammation in Polycystic Ovary Syndrome

Polycystic ovarian syndrome (PCOS) is the most common endocrine-metabolic disorder affecting a vast population worldwide; it is linked with anovulation, mitochondrial dysfunctions and hormonal disbalance. Mutations in mtDNA have been identified in PCOS patients and likely play an important role in PCOS aetiology and pathogenesis; however, their causative role in PCOS development requires further investigation. As a low-grade chronic inflammation disease, PCOS patients have permanently elevated levels of inflammatory markers (TNF-α, CRP, IL-6, IL-8, IL-18). In this review, we summarise recent data regarding the role of mtDNA mutations and mitochondrial malfunctions in PCOS pathogenesis. Furthermore, we discuss recent papers dedicated to the identification of novel biomarkers for early PCOS diagnosis. Finally, traditional and new mitochondria-targeted treatments are discussed. This review intends to emphasise the key role of oxidative stress and chronic inflammation in PCOS pathogenesis; however, the exact molecular mechanism is mostly unknown and requires further investigation.

Mitochondrial DNA 4977 bp Deletion in Peripheral Blood Is Associated With Polycystic Ovary Syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS) is a common endocrine disorder worldwide. We aimed to examine the associations of two mitochondrial DNA (mtDNA) biomarkers in the peripheral blood, mtDNA copy number (CN), and mtDNA⁴⁹⁷⁷ deletion rate (DR), with PCOS in a clinical setting.

METHODS

We performed a study involving 263 women with PCOS and 326 age-matched controls between June 2015 and June 2019. The mtDNA CN and mtDNA⁴⁹⁷⁷ DR were measured using multiplex probe-based qPCR. The associations of the mtDNA CN and mtDNA⁴⁹⁷⁷ DR with the risk of PCOS were estimated using logistic regression.

RESULTS

Analysis of the associations between mtDNA biomarkers and PCOS indicate that the mtDNA CN (P = 0.003) and mtDNA⁴⁹⁷⁷ DR (P < 0.001) in PCOS patients were significantly higher than those in the controls. After adjusting for the body mass index, luteinizing hormone/follicle-stimulating hormone ratio, and testosterone level, only higher mtDNA⁴⁹⁷⁷ DR was associated with PCOS (odds ratio 1.053, 95% confidence interval 1.024 to 1.083; P < 0.001). The linear dose-response trends of the mtDNA⁴⁹⁷⁷ DR were also supported by the quartile analysis.

CONCLUSION

Multivariable models suggest that mtDNA⁴⁹⁷⁷ DR levels are strongly associated with PCOS and represent an independent risk factor for PCOS. Further investigation of the utility of mtDNA as a biomarker for PCOS is warranted.

A mitochondrial myopathy-associated tRNASer(UCN) 7453G>A mutation alters tRNA metabolism and mitochondrial function

BACKGROUND

Mitochondrial disorders are a group of heterogeneous diseases characterized by biochemical disturbances in oxidative phosphorylation (OXPHOS). Mutations in mitochondrial transfer RNA (mt-tRNA) genes are the most frequently in mitochondrial disease. However, few studies have detailed the molecular mechanisms behind these mutations.

METHODS

We performed clinical evaluation, genetic analysis, muscle histochemistry, and molecular and biochemical investigations in muscle tissue and proband-derived cybrid cell lines.

RESULTS

We found a mitochondrial tRNA^Ser(UCN) mutation (m.7453G>A) in a 15-year-old patient with severe mitochondrial myopathy. We demonstrated that this mutation caused impairment of mitochondrial translation, respiratory deficiency, overproduction of reactive oxygen species (ROS), and decreased mitochondrial membrane potential (MMP), which ultimately led to severe mitochondrial myopathy.

CONCLUSION

Our findings offer valuable new insights into the tRNA^Ser(UCN) m.7453G>A mutation for both the pathogenic mechanism and functional consequences.

Melatonin ameliorates excessive PINK1/Parkin-mediated mitophagy by enhancing SIRT1 expression in granulosa cells of PCOS

Mitochondrial injury in granulosa cells is associated with the pathogenesis of polycystic ovary syndrome (PCOS). However, the protective effects of melatonin against mitochondrial injury in the granulosa cells of PCOS remain unclear. In this study, decreased mitochondrial membrane potential and mtDNA content, increased number of autophagosomes were found in the granulosa cells of PCOS patients and the dihydrotestosterone (DHT)-treated KGN cells, with decreased protein level of the autophagy substrate p62 and increased levels of the cellular autophagy markers Beclin 1 and LC3B-II, while the protein levels of PTEN-induced kinase-1 (PINK1) and Parkin were increased and the level of sirtuin 1 (SIRT1) was decreased. DHT-induced PCOS-like mice also showed enhanced mitophagy and decreased SIRT1 mRNA expression. Melatonin treatment significantly increased the protein level of SIRT1 and decreased the levels of PINK1/Parkin, whereas it ameliorated the mitochondrial dysfunction and PCOS phenotype in vitro and in vivo. However, when the KGN cells were treated with SIRT1 siRNA to knock down SIRT1 expression, melatonin treatment failed to repress the excessive mitophagy. In conclusion, melatonin protects against mitochondrial injury in granulosa cells of PCOS by enhancing SIRT1 expression to inhibit excessive PINK1/Parkin-mediated mitophagy.

Screening for mitochondrial 12S rRNA C1494T mutation in 655 patients with non-syndromic hearing loss: An observational study

Mutations in mitochondrial DNA, especially in 12S rRNA gene, are the most important causes for hearing loss. In particular, the A1555G and C1494T mutations have been found to be associated with both aminoglycoside-induced and non-syndromic hearing loss in many families worldwide. To determine the frequency of C1494T mutation in deaf patients, in the current study, we screened this mutation in 655 patients with non-syndromic hearing loss and 300 control subjects. After PCR amplification of mitochondrial 12S rRNA gene and direct sequence analysis, we found that there were 2 patients carrying the C1494T mutation; however, this mutation was not detected in 300 healthy subjects. Further genetic counseling suggested that only 1 patient had an obvious family history of hearing impairment. Clinical evaluation showed that 3 of 10 matrilineal relatives suffered from hearing loss, with different age at onset of hearing loss. Molecular analysis revealed the presence of homoplasmic 12S rRNA C1494T and ND5 T12338C mutations, together with a set of polymorphisms belonging to human mitochondrial haplogroup F2. Interestingly, T12338C mutation resulted in the replacement of the first amino acid, a translation-initiating methionine with a threonine, shortening 2 amino acids of ND5 polypeptide. Moreover, this mutation is located in 2 nucleotides adjacent to the 3' end of the mt-tRNALeu(CUN) gene. Therefore, this mutation may alter ND5 mRNA metabolism and the processing of RNA precursors. Thus, the combination of T12338C and C1494T mutations may contribute to deafness expression in this family. Taken together, our data suggested that the C1494T mutation was the molecular basis for hearing loss, screening for the mitochondrial DNA pathogenic mutations was recommended for early detection, prevention, and diagnosis of mitochondrial deafness.

Mitochondrial Dysfunction in Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is one of the most common female reproductive metabolisms. It is an endocrine disease that affects reproductive women and often exhibits with hyperandrogenemia, insulin resistance (IR), low inflammation, and an increased risk of type 2 diabetes mellitus, metabolic syndrome, and cardiovascular events such as hypertension and dyslipidemia in patients. However, the molecular mechanism of PCOS is still unclear. Recently, an increasing number of studies have shown that the oxidative stress induced by mitochondrial dysfunction has negative effects on IR, lipid metabolism, and follicular development, suggesting that mitochondrial dysfunction plays an essential role in the development of PCOS. Abnormal mitochondrial DNA copy number in patients with PCOS, and mitochondrial gene mutations, has been the focus of research in recent years, and functional mitochondrial diseases have been gradually accepted as a related factor in PCOS. This review is intended to summarize and discuss previous and recent studies and findings on the connections between mitochondrial dysfunction and PCOS.

Mitochondrial dysfunction: An emerging link in the pathophysiology of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a common endocrine disorder characterized by irregular menstrual cycles, hyperandrogenism and subfertility. Due to its complex manifestation, the pathogenic mechanism of PCOS is not well defined. Cumulative effect of altered genetic and epigenetic factors along with environmental factors may play a role in the manifestation of PCOS leading to systemic malfunction. With failure of genome-wide association study (GWAS) and other studies performed on nuclear genome to provide any clue for precise mechanism of PCOS pathogenesis, attention has been diverted to mitochondria. Mitochondrion plays an important role in cellular metabolic functions and is linked to Insulin Resistance (IR). Recently, increasing reports suggest that mitochondrial dysfunction may be a contributing factor in the pathogenesis of PCOS. Hence, in this review, we have discussed mitochondrial biology in brief and emphasizes on genetic and epigenetic aspects of mitochondrial dysfunction studied in PCOS women and PCOS-like animal models. We also highlight underlying mechanism behind mitochondrial dysfunction contributing to PCOS and its related complications such as obesity, diabetes, cardiovascular diseases, metabolic syndrome, non-alcoholic fatty liver disease (NAFLD) and cancer. Furthermore, contrasting remarks against involvement of mitochondrial dysfunction in PCOS pathophysiology have also been presented. This review enhances our understanding in relation to mitochondrial dysfunction in the etiology of PCOS and stimulates further research to explore a clear link between mitochondrial dysfunction and PCOS pathogenesis and progression. Understanding pathogenic mechanisms underlying PCOS will open new windows to develop promising therapeutic strategies against PCOS.

The tRNA-associated dysregulation in diabetes mellitus

Diabetes mellitus (DM) is a complex endocrine and metabolic disorder for human health and well-being. Deregulated glucose and lipid metabolism are the primary underlying manifestations associated with this disease. Transfer RNAs (tRNAs) are considered to mainly participate in protein translation and may contribute to complex human pathologies. Although the molecular mechanisms remain, for the most part, unknown, accumulating evidence indicates that tRNAs play a vital role in the pathogenesis of DM. This paper reviews different aspects of tRNA-associated dysregulation in DM, such as tRNA mutations, tRNA modifications, tRNA aminoacylation and tRNA derivatives, aiming at a better understanding of the pathogenesis of DM and providing new ideas for the personalized treatment of this metabolism-associated disease.

Polymorphism of mitochondrial tRNA genes associated with the number of pigs born alive

Background

Mutations in mitochondrial tRNA genes have been widely reported association with human reproductions. It is also important to explore the effect on the number of piglets born alive (NBA). Here, 1017 sows were used to investigate the association between polymorphisms in mitochondrial tRNA genes and NBA.

Results

In total, 16 mutations were found in mitochondrial tRNA genes, of which 13 mutations were significantly associated with NBA (P < 0.05). The reproductions of mutant carriers were significantly greater than that of wild carriers by 0.989 piglets born alive/sow farrowing. To test whether the mutations altered the structure of mitochondrial tRNAs, the secondary and tertiary structures were predicted. In result, C2255T changed the secondary structure of tRNA-Val by elongating the T stem and shrinking the T loop, and C2255T and G2259A in the tRNA-Val gene, C6217T and T6219C in the tRNA-Ala gene, and T15283C in the tRNA-Glu gene altered the tertiary structure of their tRNAs, respectively by changing the folding form of the T arm, and C16487T in the tRNA-Thr gene changed the tertiary structure of mitochondrial tRNA-Thr by influencing the folding form of the acceptor arm.

Conclusions

Results highlight the effect of mitochondrial tRNA genes on the number of piglets born alive, and suggest that polymorphic sites of the tRNA genes be genetic markers for selection of pig reproduction.

Electronic supplementary material

The online version of this article (10.1186/s40104-018-0299-0) contains supplementary material, which is available to authorized users.

Advances in PCOS Pathogenesis and Progression-Mitochondrial Mutations and Dysfunction

Polycystic ovary syndrome (PCOS) is a common female endocrine disorder, which still remains largely unsolved in terms of etiology and pathogenesis despite important advances in our understanding of its genetic, epigenetic, or environmental factor implications. It is a heterogeneous disease, frequently associated with insulin resistance, chronic inflammation, and oxidative stress and probably accompanied with subclinical cardiovascular disease (CVD) and some malignant lesions as well, such as endometrial cancer. Discrepancies in the clinical phenotype and progression of PCOS exist between different population groups, which nuclear genetic studies have so far failed to explain. Over the last years, mitochondrial dysfunction has been increasingly recognized as an important contributor to an array of diseases. Because mitochondria are under the dual genetic control of both the mitochondrial and nuclear genomes, mutations within either DNA molecule may result in deficiency in respiratory chain function that leads to a reduced ability to produce cellular adenosine-5'-triphosphate and to an excessive production of reactive oxygen species. However, the association between variants in mitochondrial genome, mitochondrial dysfunction, and PCOS has been investigated to a lesser extent. May mutations in mitochondrial DNA (mtDNA) become an additional target of investigations on the missing PCOS heritability? Are mutations in mtDNA implicated in the initiation and progression of PCOS complications, e.g., CVDs, diabetes mellitus, cancers?

Mitochondrial tRNALeu(UUR) C3275T, tRNAGln T4363C and tRNALys A8343G mutations may be associated with PCOS and metabolic syndrome

Polycystic ovary syndrome (PCOS) is a very prevalent endocrine disease affecting reproductive women. Clinically, patients with this disorder are more vulnerable to develop type 2 diabetes mellitus (T2DM), cardiovascular events, as well as metabolic syndrome (MetS). To date, the molecular mechanism underlying PCOS remains largely unknown. Previously, we showed that mitochondrial dysfunction caused by mitochondrial DNA (mtDNA) mutation was an important cause for PCOS. In the current study, we described the clinical and biochemical features of a three-generation pedigree with maternally transmitted MetS, combined with PCOS. A total of three matrilineal relatives exhibited MetS including obesity, high triglyceride (TG) and Hemoglobin A1c (HbA1c) levels, and hypertension. Whereas one patient from the third generation manifestated PCOS. Mutational analysis of the whole mitochondrial genes from the affected individuals identified a set of genetic variations belonging to East Asia haplogroup B4b1c. Among these variants, the homoplasmic C3275T mutation disrupted a highly evolutionary conserved base-pairing (28A-46C) on the variable region of tRNA^Leu(UUR), whereas the T4363C mutation created a new base-pairing (31T-37A) in the anticodon stem of tRNA^Gln, furthermore, the A8343G mutation occurred at the very conserved position of tRNA^Lys and may result the failure in mitochondrial tRNAs (mt-tRNAs) metabolism. Biochemical analysis revealed the deficiency in mitochondrial functions including lower levels of mitochondrial membrane potential (MMP), ATP production and mtDNA copy number, while a significantly increased reactive oxygen species (ROS) generation was observed in polymononuclear leukocytes (PMNs) from the individuals carrying these mt-tRNA mutations, suggesting that these mutations may cause mitochondrial dysfunction that was responsible for the clinical phenotypes. Taken together, our data indicated that mt-tRNA mutations were associated with MetS and PCOS in this family, which shaded additional light into the pathophysiology of PCOS that were manifestated by mitochondrial dysfunction.