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Gardner JJ, Cushen SC, Oliveira da Silva RDN, Bradshaw JL, Hula N, Gorham IK, Tucker SM, Zhou Z, Cunningham RL, Phillips NR, Goulopoulou S. Oxidative stress induces release of mitochondrial DNA into the extracellular space in human placental villous trophoblast BeWo cells. Am J Physiol Cell Physiol 2024; 326:C1776-C1788. [PMID: 38738304 PMCID: PMC11371324 DOI: 10.1152/ajpcell.00091.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2024] [Revised: 04/26/2024] [Accepted: 04/26/2024] [Indexed: 05/14/2024]
Abstract
Circulating cell-free mitochondrial DNA (ccf-mtDNA) is an indicator of cell death, inflammation, and oxidative stress. ccf-mtDNA in pregnancies with placental dysfunction differs from that in healthy pregnancies, and the direction of this difference depends on gestational age and method of mtDNA quantification. Reactive oxygen species (ROS) trigger release of mtDNA, yet it is unknown whether trophoblast cells release mtDNA in response to oxidative stress, a common feature of pregnancies with placental pathology. We hypothesized that oxidative stress would induce cell death and release of mtDNA from trophoblast cells. BeWo cells were treated with antimycin A (10-320 µM) or rotenone (0.2-50 µM) to induce oxidative stress. A multiplex real-time quantitative PCR (qPCR) assay was used to quantify mtDNA and nuclear DNA in membrane-bound, non-membrane-bound, and vesicle-bound forms in cell culture supernatants and cell lysates. Treatment with antimycin A increased ROS (P < 0.0001), induced cell necrosis (P = 0.0004) but not apoptosis (P = 0.6471), and was positively associated with release of membrane-bound and non-membrane-bound mtDNA (P < 0.0001). Antimycin A increased mtDNA content in exosome-like extracellular vesicles (vesicle-bound form; P = 0.0019) and reduced autophagy marker expression (LC3A/B, P = 0.0002; p62, P < 0.001). Rotenone treatment did not influence mtDNA release or cell death (P > 0.05). Oxidative stress induces release of mtDNA into the extracellular space and causes nonapoptotic cell death and a reduction in autophagy markers in BeWo cells, an established in vitro model of human trophoblast cells. Intersection between autophagy and necrosis may mediate the release of mtDNA from the placenta in pregnancies exposed to oxidative stress.NEW & NOTEWORTHY This is the first study to test whether trophoblast cells release mitochondrial (mt)DNA in response to oxidative stress and to identify mechanisms of release and biological forms of mtDNA from this cellular type. This research identifies potential cellular mechanisms that can be used in future investigations to establish the source and biomarker potential of circulating mtDNA in preclinical experimental models and humans.
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Affiliation(s)
- Jennifer J Gardner
- Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Spencer C Cushen
- Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
- Texas College of Osteopathic Medicine, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Reneé de Nazaré Oliveira da Silva
- Lawrence D. Longo, MD Center for Perinatal Biology, Departments of Basic Sciences, Gynecology, and Obstetrics, Loma Linda University School of Medicine, Loma Linda, California, United States
| | - Jessica L Bradshaw
- Department of Pharmaceutical Sciences, System College of Pharmacy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Nataliia Hula
- Lawrence D. Longo, MD Center for Perinatal Biology, Departments of Basic Sciences, Gynecology, and Obstetrics, Loma Linda University School of Medicine, Loma Linda, California, United States
| | - Isabelle K Gorham
- Department of Microbiology, Immunology, and Genetics, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Selina M Tucker
- Department of Physiology and Anatomy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Zhengyang Zhou
- Department of Population & Community Health, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Rebecca L Cunningham
- Department of Pharmaceutical Sciences, System College of Pharmacy, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Nicole R Phillips
- Department of Microbiology, Immunology, and Genetics, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - Styliani Goulopoulou
- Lawrence D. Longo, MD Center for Perinatal Biology, Departments of Basic Sciences, Gynecology, and Obstetrics, Loma Linda University School of Medicine, Loma Linda, California, United States
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Gardner JJ, Cushen SC, Oliveira da Silva RDN, Bradshaw JL, Hula N, Gorham IK, Tucker SM, Zhou Z, Cunningham RL, Phillips NR, Goulopoulou S. Oxidative stress induces release of mitochondrial DNA into the extracellular space in human placental villous trophoblast BeWo cells. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.02.578433. [PMID: 38352590 PMCID: PMC10862877 DOI: 10.1101/2024.02.02.578433] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2024]
Abstract
Circulating cell-free mitochondrial DNA (ccf-mtDNA) is an indicator of cell death, inflammation, and oxidative stress. ccf-mtDNA differs in pregnancies with placental dysfunction from healthy pregnancies and the direction of this difference depends on gestational age and method of mtDNA quantification. Reactive oxygen species (ROS) trigger release of mtDNA from non-placental cells; yet it is unknown whether trophoblast cells release mtDNA in response to oxidative stress, a common feature of pregnancies with placental pathology. We hypothesized that oxidative stress would induce cell death and release of mtDNA from trophoblast cells. BeWo cells were treated with antimycin A (10-320 μM) or rotenone (0.2-50 μM) to induce oxidative stress. A multiplex real-time quantitative PCR (qPCR) assay was used to quantify mtDNA and nuclear DNA in membrane bound, non-membrane bound, and vesicular-bound forms in cell culture supernatants and cell lysates. Treatment with antimycin A increased ROS (p<0.0001), induced cell necrosis (p=0.0004) but not apoptosis (p=0.6471) and was positively associated with release of membrane-bound and non-membrane bound mtDNA (p<0.0001). Antimycin A increased mtDNA content in exosome-like extracellular vesicles (vesicular-bound form; p=0.0019) and reduced autophagy marker expression (LC3A/B, p=0.0002; p62, p<0.001). Rotenone treatment did not influence mtDNA release or cell death (p>0.05). Oxidative stress induces release of mtDNA into the extracellular space and causes non-apoptotic cell death and a reduction in autophagy markers in BeWo cells, an established in vitro model of human trophoblast cells. Intersection between autophagy and necrosis may mediate the release of mtDNA from the placenta in pregnancies exposed to oxidative stress. NEW & NOTEWORTHY This is the first study to test whether trophoblast cells release mitochondrial DNA in response to oxidative stress and to identify mechanisms of release and biological forms of mtDNA from this cellular type. This research identifies potential cellular mechanisms that can be used in future investigations to establish the source and biomarker potential of circulating mitochondrial DNA in preclinical experimental models and humans.
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Ito J, Iwata H. Age-related advanced glycation end-product accumulation impairs mitochondrial regulation after vitrification†. Biol Reprod 2023; 109:271-281. [PMID: 37399120 DOI: 10.1093/biolre/ioad070] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Revised: 04/05/2023] [Accepted: 06/26/2023] [Indexed: 07/05/2023] Open
Abstract
Vitrification is an important assisted reproductive technology, although it induces mitochondrial dysfunction in embryos. Herein, we aimed to investigate whether age-associated accumulation of advanced glycation end-products (AGEs) in oocytes impairs the recovery of embryos from cryopreservation-induced mitochondrial dysfunction/damage. Mouse eight-cell stage embryos developed in vitro were vitrified and warmed and incubated up to the blastocyst stage. AGE levels in oocytes were higher in both aged mice and AGE accumulation mouse models (MGO-mice) than those in young and control mice. In addition, the level of SIRT1 upregulation was lower for embryos of aged and MGO-mice than that for embryos of young and control mice. The highest mitochondrial DNA (mtDNA) content was detected in blastocysts derived from vitrified embryos of aged and MGO-mice. The spent culture medium of blastocysts derived from both aged and MGO-mice contained higher mtDNA content than that of the blastocysts derived from young and control mice. EX527 increased mtDNA content in the spent culture medium of vitrified embryos derived from young mice. In addition, p62 aggregate levels were higher in vitrified embryos of control mice than those in vitrified embryos of MGO-mice. The SIRT1 activator, resveratrol, increased p62 aggregation levels in vitrified embryos derived from young and aged mice, whereas vitrification did not affect p62 aggregation levels in embryos from aged mice. Therefore, age-associated AGE accumulation induces decreased responsive SIRT1 upregulation following vitrified-warmed treatment and impairs mitochondrial quality control activity in vitrified embryos.
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Affiliation(s)
- Jun Ito
- Laboratory of Animal Reproduction, Department of Animal Science, Tokyo University of Agriculture, Atsugi, Kanagawa, Japan
| | - Hisataka Iwata
- Laboratory of Animal Reproduction, Department of Animal Science, Tokyo University of Agriculture, Atsugi, Kanagawa, Japan
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Zhou XY, Yang YZ, Zhang J, Zhang XF, Liu YD, Wang Z, Chen SL. Elevated cell-free mitochondria DNA level of patients with premature ovarian insufficiency. BMC Pregnancy Childbirth 2023; 23:462. [PMID: 37349693 DOI: 10.1186/s12884-023-05769-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2023] [Accepted: 06/09/2023] [Indexed: 06/24/2023] Open
Abstract
BACKGROUND Premature ovarian insufficiency (POI) patients present with a chronic inflammatory state. Cell-free mitochondria DNA (cf-mtDNA) has been explored as a reliable biomarker for estimating the inflammation-related disorders, however, the cf-mtDNA levels in POI patients have never been measured. Therefore, in the presenting study, we aimed to evaluate the levels of cf-mtDNA in plasma and follicular fluid (FF) of POI patients and to determine a potential role of cf-mtDNA in predicting the disease progress and pregnancy outcomes. METHODS We collected plasma and FF samples from POI patients, biochemical POI (bPOI) patients and control women. Quantitative real-time PCR was used to measure the ratio of mitochondrial genome to nuclear genome of cf-DNAs extracted from the plasma and FF samples. RESULTS The plasma cf-mtDNA levels, including COX3, CYB, ND1 and mtDNA79, were significantly higher in overt POI patients than those in bPOI patients or control women. The plasma cf-mtDNA levels were weakly correlated with ovarian reserve, and could not be improved by regular hormone replacement therapy. The levels of cf-mtDNA in FF, rather than those in plasma, exhibited the potential to predict the pregnancy outcomes, although they were comparable among overt POI, bPOI and control groups. CONCLUSIONS The increased plasma cf-mtDNA levels in overt POI patients indicated its role in the progress of POI and the FF cf-mtDNA content may hold the value in predicting pregnancy outcomes of POI patients.
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Affiliation(s)
- Xing-Yu Zhou
- Center for Reproductive Medicine, Department of Gynecology and Obstetrics, Nanfang Hospital, Southern Medical University, No. 1838 Guangzhou Northern Road, Guangzhou, 510515, Guangdong, China
| | - Yi-Zhen Yang
- Center for Reproductive Medicine, Department of Gynecology and Obstetrics, Nanfang Hospital, Southern Medical University, No. 1838 Guangzhou Northern Road, Guangzhou, 510515, Guangdong, China
| | - Jun Zhang
- Center for Reproductive Medicine, Department of Gynecology and Obstetrics, Nanfang Hospital, Southern Medical University, No. 1838 Guangzhou Northern Road, Guangzhou, 510515, Guangdong, China
| | - Xiao-Fei Zhang
- Center for Reproductive Medicine, Department of Gynecology and Obstetrics, Nanfang Hospital, Southern Medical University, No. 1838 Guangzhou Northern Road, Guangzhou, 510515, Guangdong, China
| | - Yu-Dong Liu
- Center for Reproductive Medicine, Department of Gynecology and Obstetrics, Nanfang Hospital, Southern Medical University, No. 1838 Guangzhou Northern Road, Guangzhou, 510515, Guangdong, China
| | - Zhe Wang
- Center for Reproductive Medicine, Department of Gynecology and Obstetrics, Nanfang Hospital, Southern Medical University, No. 1838 Guangzhou Northern Road, Guangzhou, 510515, Guangdong, China
| | - Shi-Ling Chen
- Center for Reproductive Medicine, Department of Gynecology and Obstetrics, Nanfang Hospital, Southern Medical University, No. 1838 Guangzhou Northern Road, Guangzhou, 510515, Guangdong, China.
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De Gaetano A, Solodka K, Zanini G, Selleri V, Mattioli AV, Nasi M, Pinti M. Molecular Mechanisms of mtDNA-Mediated Inflammation. Cells 2021; 10:2898. [PMID: 34831121 PMCID: PMC8616383 DOI: 10.3390/cells10112898] [Citation(s) in RCA: 87] [Impact Index Per Article: 29.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Revised: 10/25/2021] [Accepted: 10/26/2021] [Indexed: 12/12/2022] Open
Abstract
Besides their role in cell metabolism, mitochondria display many other functions. Mitochondrial DNA (mtDNA), the own genome of the organelle, plays an important role in modulating the inflammatory immune response. When released from the mitochondrion to the cytosol, mtDNA is recognized by cGAS, a cGAMP which activates a pathway leading to enhanced expression of type I interferons, and by NLRP3 inflammasome, which promotes the activation of pro-inflammatory cytokines Interleukin-1beta and Interleukin-18. Furthermore, mtDNA can be bound by Toll-like receptor 9 in the endosome and activate a pathway that ultimately leads to the expression of pro-inflammatory cytokines. mtDNA is released in the extracellular space in different forms (free DNA, protein-bound DNA fragments) either as free circulating molecules or encapsulated in extracellular vesicles. In this review, we discussed the latest findings concerning the molecular mechanisms that regulate the release of mtDNA from mitochondria, and the mechanisms that connect mtDNA misplacement to the activation of inflammation in different pathophysiological conditions.
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Affiliation(s)
- Anna De Gaetano
- Department of Life Sciences, University of Modena and Reggio Emilia, 41125 Modena, Italy; (A.D.G.); (K.S.); (G.Z.); (V.S.)
- National Institute for Cardiovascular Research-INRC, 40126 Bologna, Italy;
| | - Kateryna Solodka
- Department of Life Sciences, University of Modena and Reggio Emilia, 41125 Modena, Italy; (A.D.G.); (K.S.); (G.Z.); (V.S.)
| | - Giada Zanini
- Department of Life Sciences, University of Modena and Reggio Emilia, 41125 Modena, Italy; (A.D.G.); (K.S.); (G.Z.); (V.S.)
| | - Valentina Selleri
- Department of Life Sciences, University of Modena and Reggio Emilia, 41125 Modena, Italy; (A.D.G.); (K.S.); (G.Z.); (V.S.)
| | - Anna Vittoria Mattioli
- National Institute for Cardiovascular Research-INRC, 40126 Bologna, Italy;
- Department of Surgery, Medicine, Dentistry and Morphological Sciences, University of Modena and Reggio Emilia, 41125 Modena, Italy;
| | - Milena Nasi
- Department of Surgery, Medicine, Dentistry and Morphological Sciences, University of Modena and Reggio Emilia, 41125 Modena, Italy;
| | - Marcello Pinti
- Department of Life Sciences, University of Modena and Reggio Emilia, 41125 Modena, Italy; (A.D.G.); (K.S.); (G.Z.); (V.S.)
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Khan HL, Bhatti S, Abbas S, Kaloglu C, Qurat-Ul-Ain Zahra S, Khan YL, Hassan Z, Turhan NÖ, Aydin HH. Melatonin levels and microRNA (miRNA) relative expression profile in the follicular ambient microenvironment in patients undergoing in vitro fertilization process. J Assist Reprod Genet 2021; 38:443-459. [PMID: 33226531 PMCID: PMC7884535 DOI: 10.1007/s10815-020-02010-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Accepted: 11/09/2020] [Indexed: 02/08/2023] Open
Abstract
PURPOSE Intrafollicular fluid (IFF) melatonin plays a decisive role in maintaining granulosa cells' DNA integrity and protects them against apoptosis. It reduces oxidative stress and improves the oocyte quality with a higher fertilization rate. METHOD This prospective study investigated the antioxidant property of IFF melatonin and its impact on IVF outcome parameters. We also explored the relative expression of five microRNAs (miR-663b, miR-320a, miR-766-3p, miR-132-3p, miR-16-5p) and levels of cell-free DNA (cfDNA) by real-time PCR in unexplained infertile patients. We collected 425 follicular fluid (FF) samples containing mature oocytes from 295 patients undergoing IVF. RESULTS Patients were subgrouped based on IFF melatonin concentration (group A ≤ 30 pg/mL, group B > 70 to ≤ 110 pg/mL, group C > 111 to ≤ 385 pg/mL). Our results showed that patients with ≤ 30 pg/mL IFF melatonin levels have significantly higher oxidative stress markers, cfDNA levels, and lower relative expression of miR-663b, miR-320a, miR-766-3p, miR-132-3p, and miR-16-5p compared to other subgroups (p < 0.001). Similarly, they have a low fertilization rate and a reduced number of high-quality day 3 embryos. CONCLUSION Findings suggest that the therapeutic use of melatonin produces a considerable rise in the number of mature oocytes retrieved, fertilization rate, and good-quality embryo selection. Furthermore, miRNA signature enhances the quality of embryo selection, thus, may allow us to classify them as non-invasive biomarkers to identify good-quality embryos.
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Affiliation(s)
- Haroon Latif Khan
- Lahore Institute of Fertility and Endocrinology, Hameed Latif Hospital, 14-Abu Bakar Block, New Garden Town, Lahore, 54800, Pakistan
| | - Shahzad Bhatti
- Lahore Institute of Fertility and Endocrinology, Hameed Latif Hospital, 14-Abu Bakar Block, New Garden Town, Lahore, 54800, Pakistan.
- Department of Human Genetics and Molecular biology, University of Health Sciences, Lahore, 54600, Pakistan.
- Department of Medical Education, Rashid Latif Medical College, Lahore, Pakistan.
- Department of Human Genetics and Molecular Biology, University of Health Sciences, Lahore, 54800, Pakistan.
| | - Sana Abbas
- Lahore Institute of Fertility and Endocrinology, Hameed Latif Hospital, 14-Abu Bakar Block, New Garden Town, Lahore, 54800, Pakistan
| | - Celal Kaloglu
- Department of Histology and Embryology, Faculty of Medicine, Sivas-Cumhuriyet University, 58140, Sivas, Turkey
| | | | - Yousaf Latif Khan
- Lahore Institute of Fertility and Endocrinology, Hameed Latif Hospital, 14-Abu Bakar Block, New Garden Town, Lahore, 54800, Pakistan
- Department of Gynecology and Obstetrics, Hameed Latif Hospital, 14 - Abu Bakar Block, New Garden Town, Lahore, 54800, Pakistan
| | - Zahira Hassan
- Department of Cellular Pathology, Royal Free Hospital, London, NW3 2QG, UK
| | - Nilgün Öztürk Turhan
- Bayındır Hastanesi, Department of Obstetrics and Gynecology, Nispetiye Mah. Aydın sokak No:8, 34340, Beşiktaş, Istanbul, Turkey
| | - Hikmet Hakan Aydin
- Department of Medical Biochemistry, Ege University School of Medicine, Bornova, Izmir, Turkey
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Ichikawa K, Shibahara H, Shirasuna K, Kuwayama T, Iwata H. Cell-free DNA content in follicular fluid: A marker for the developmental ability of porcine oocytes. Reprod Med Biol 2020; 19:95-103. [PMID: 31956291 PMCID: PMC6955585 DOI: 10.1002/rmb2.12309] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 11/01/2019] [Accepted: 11/26/2019] [Indexed: 01/18/2023] Open
Abstract
PURPOSE The present study examined the relationships among the amount of cell-free-DNA (cfDNA) in porcine follicular fluid (FF), the developmental ability of enclosed oocytes, and characteristics of granulosa cells and examined the effect of cfDNA content in maturation medium on the developmental ability of the oocytes. METHODS Oocytes and FF were collected from individual gilts, and the gilts were rated based on the ability of their oocytes to develop to the blastocyst stage and the amount of cfDNA in the FF. The copy numbers of mitochondrial DNA (Mt-DNA) and nuclear DNA (N-DNA) were measured by real-time PCR and the DNA sequence. FF or cfDNA was added to the maturation medium, and the developmental ability of the oocytes was examined. RESULTS The amount of cfDNA was associated with apoptosis of the granulosa cells, and high-cfDNA content in FF was associated with low developmental ability of oocytes. Supplementation of the maturation medium with FF containing high cf-Mt-DNA or with DNA extracted from the FF did not affect oocyte developmental competence. CONCLUSIONS Cell-free DNA content in FF is a marker for oocyte competence, but cfDNA in the oocyte maturation environment did not affect oocyte developmental ability.
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Affiliation(s)
- Kana Ichikawa
- Department of Animal ScienceTokyo University of AgricultureKanagawaJapan
| | - Hidenori Shibahara
- Department of Animal ScienceTokyo University of AgricultureKanagawaJapan
| | - Komei Shirasuna
- Department of Animal ScienceTokyo University of AgricultureKanagawaJapan
| | - Takehito Kuwayama
- Department of Animal ScienceTokyo University of AgricultureKanagawaJapan
| | - Hisataka Iwata
- Department of Animal ScienceTokyo University of AgricultureKanagawaJapan
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Abstract
Several studies have proposed that cell-free DNA (cfDNA) is a potential biomarker present in follicular fluid (FF) for oocyte quality. Recently we reported that mitochondria-derived cfDNA (mt-cfDNA) closely reflects the amount of cfDNA in FFs. The present study investigated the mechanism regulating mt-cfDNA secretion from porcine granulosa cells. Oocytes and cumulus cell complexes or granulosa cells (GCs) were cultured in maturation medium for 24 or 48 h respectively. Then, nuclear-derived cell-free DNA (n-cfDNA) or mt-cfDNA contents in the spent medium were examined using real-time polymerase chain reaction. When 10 μM of MG132, a proteasome inhibitor, was added to the culture medium, cellular viability of both COCs and GCs decreased and n-cfDNA significantly increased in the culture medium, whereas mt-cfDNA significantly decreased. Supplementation of the culture medium with GW4869, an inhibitor of intracellular vesicle formation, significantly decreased the mt-cfDNA, whereas no effect was observed on n-cfDNA in the medium of both COCs and GCs. Furthermore, the addition of bafilomycin, an inhibitor of autophagy to the culture medium significantly increased mt-cfDNA in the culture medium. After filtration (0.22 μm) and centrifugation (23,000 g), the mt-cfDNA content of the medium decreased significantly. In conclusion, the proteasomal mitochondrial quality control system is upstream of mt-cfDNA secretion and autophagy plays a role in cellular digestion of mitochondrial DNA in the cytoplasm. It is further suggested that dsDNA is enclosed in certain vesicles or associated with small molecules and secreted into the medium.
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