Elsevier

Gene

Volume 642, 5 February 2018, Pages 299-306
Gene

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

https://doi.org/10.1016/j.gene.2017.11.049Get rights and content

Highlights

  • Mt-tRNA mutations may be associated with PCOS and MetS.

  • Mt-tRNA mutations may cause the failure in tRNA metabolism.

  • Mt-tRNA mutations may cause mitochondrial dysfunction.

  • Screening for mt-tRNA mutations is recommended for diagnosis of PCOS and MetS.

Abstract

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 tRNALeu(UUR), whereas the T4363C mutation created a new base-pairing (31T-37A) in the anticodon stem of tRNAGln, furthermore, the A8343G mutation occurred at the very conserved position of tRNALys 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.

Introduction

Polycystic ovary syndrome (PCOS) is a serious health problem, according to a recent report, approximately 5%–10% reproductive women suffered from this disorder (Goodarzi et al., 2011). PCOS can be caused by an imbalance of sex hormones, characterized by chronic anovulation, hyperandrogenism, hyperinsulinemia and infertility (Jiao et al., 2014). In addition, patients with this disease are at a risk of type 2 diabetes mellitus (T2DM), cardiovascular events, as well as metabolic syndrome (MetS) (Rajendran et al., 2009, Christakou and Diamanti, 2008). Moreover, in accordance with the national health statistic reports, the percentage of MetS in America was almost 34% in the general population with the age of 20 years old (Ervin, 2009). In particular, it has been estimated that 60–80% DM patients manifestated MetS.

Even today, the molecular mechanism underlying MetS remains poorly understood, but it is believed that the etiology of MetS may be related to the alternations in genetic factors. Mutations in nuclear encoded genes, such as VEGF and PPARD, are considered as susceptibility genes of MetS (Ghazizadeh et al., 2017, Tang et al., 2016). However, the association between variants in mitochondrial genome and MetS is less characterized.

Mitochondrial DNA (mtDNA) is a 16,569 bp molecule that encodes 22 tRNAs, 2 rRNAs, as well as 13 polypeptides which are essential for generation energy in the form of ATP via oxidative phosphorylation (OXPHOS) (Picard et al., 2016). Furthermore, since mtDNA lacks histones protection and does not have a DNA repair system, its mutation rate is much higher than nuclear DNA (Selim and Hassaan, 2017).

Previously, with the purpose of understanding the association between mtDNA mutations and PCOS, we sequenced the complete mitochondrial genomes from 160 PCOS patients and 80 with age- and body mass index (BMI)-matched healthy subjects from Hangzhou First People's Hospital. We found that mutations in mt-tRNA genes may be involved in the development of PCOS. For example, the tRNAGln T4395C, tRNACys G5821A, tRNAAsp A7543G, tRNAArg T10454C, tRNAGlu A14693G, tRNASer(UCN) C7492T and tRNALeu(UUR) A3302G mutations which occurred at the highly evolutionary conserved positions of mt-tRNA, may result in the structural and functional alternations and consequently lead to the failure in mt-tRNAs metabolism (Zhuo et al., 2012, Ding et al., 2016b, Ding et al., 2016c, Ding et al., 2017). In particular, the A3302G mutation on the acceptor arm of tRNALeu(UUR) caused the mitochondrial dysfunction via the reduction of mitochondrial copy number (Ding et al., 2016b). To explore the contribution of mtDNA to PCOS, we enrolled more patients from our Hospital and screened the potential pathogenic mtDNA mutations by PCR-Sanger sequencing. In the present study, we reported a Chinese pedigree with MetS, combined with PCOS. Analysis of the mitochondrial sequence led us to identify the co-existence three tRNA mutations: tRNALeu(UUR) C3275T, tRNAGln T4363C and tRNALys A8343G. To further understand the contributions of these mutations to the clinical phenotypes, we measured the MMP, ATP and ROS levels in PMNs from the individuals carrying these mt-tRNA mutations, moreover, the mtDNA copy number was determined using real-time quantitative PCR.

Section snippets

Subjects

A maternally inherited Chinese pedigree, which manifestated both MetS and PCOS, was ascertained in Hangzhou First People's Hospital (Fig. 1). In addition, 300 age- and gender-matched healthy subjects were enrolled in this investigation. Informed consent was protocol approval by the Ethics Committee of Hangzhou First People's Hospital, affiliated to Nanjing Medical University. Moreover, the written informed consent was obtained from each individual who participated in this study.

Diagnosis of MetS and PCOS

The definition

Clinical and biochemical characteristics

We collected a Chinese family with MetS and PCOS from Hangzhou First People's Hospital, as displayed in Fig. 1. There were seven matrilineal relatives in this pedigree, while three of them affected different phenotypes of endocrine disorders, the sex ratio between male and female was 1:1, with the age ranged from 31 to 66 years old. The proband, aged 31 came to the Department of Gynecological and Obstetrics of Hangzhou First People's Hospital because of her abnormal menstruation. According to

Discussion

The current study reported the molecular and biochemical features of a Chinese pedigree with MetS, combined with PCOS. Many of the anthropometric and metabolic abnormalities of PCOS overlapped with components of the MetS, a clustering of both lipid and non-lipid risk factors that identified individuals at increased risk for coronary heart disease and T2DM (Osei and Gaillard, 2017). However, maternally inherited MetS, especially co-existence with PCOS, was infrequent in general population.

Conclusions

In conclusion, the present study demonstrated the association between mt-tRNA mutations and MetS, combined with PCOS in a Han Chinese family. The tRNALeu(UUR) C3275T, tRNAGln T4363C and tRNALys A8343G mutations should be regarded as risk factors for further molecular diagnosis of MetS and PCOS. Thus, our findings provided novel insight into the molecular mechanism, management of maternally transmitted MetS. The main limitation of the present study was relative small sample size; moreover, the

Conflict of interest

None.

Acknowledgements

This work is supported by the grants from Ministry of Public Health from Zhejiang Province (no. 2013KYA158), Hangzhou Bureau of Science and Technology (no. 20150633B16) and Natural Science Foundation of Zhejiang Province (no. LY14H270008; LY15H280007).

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    The first two authors have contributed equally for this work.

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