İNSAN KAN VE İSKELET KASI ÖRNEKLERİNDE HETEROPLAZMİYLE İLİŞKİLİ MİTOKONDRİYAL DNA VARYANTLARI

Abstract

Amaç: Ökaryotik hücrelerin tanımlanmış bir özelliği olan mitokondriyel heteroplazmi, mitokondriyel hastalıkların fenotipik çeşitliliğinde önemli bir rol oynar. Düşük düzeydeki heteroplazminin tespitindeki hassasiyeti artıran yeni nesil dizileme (YND) teknolojisi, heteroplazmi özellikleri ile ilişkili ultra-düşük düzeydeki (%<1) varyantları saptayabilmektedir. Çalışmamız, fenotiplerine bakılmaksızın, bireylerdeki mitokondriyel varyantların heteroplazmi düzeyleri ile ilişkilendirilebilecek potansiyel genetik ve demografik faktörleri incelemeyi amaçlandı. Gereç ve Yöntem: Cinsiyet dağılımı eşit olan 10 bireyin mitokondriyel genomları üzerinde, yüksek-çıktılı yeni nesil dizileme yöntemi uygulandı. Heteroplazmi oranları %5 ile %95 arasında değişen ve bu aralığın dışında kalan varyantlar, istatistiksel analizler için kullanıldı. Bulgular: Toplamda 194 heteroplazmik varyant tanımlandı, bunlardan 13'ü dişi bireylerin hem kan hem de iskelet kası örneklerinde daha düşük heteroplazmi oranları sergilerken, mitokondrial kontrol bölgesi (D-ilmiği) daha yüksek oranlara sahipti. Sonuç: Çalışma bulguları, önceki araştırmalarla uyumlu olarak m.10398A>G varyantı ile mitokondriyel heteroplazmi düzeyleri arasındaki korelasyonu doğruladı. Ayrıca, MT-RNR2 genindeki m.1811A>G varyantının ve MT-TL2 genindeki m.12308A>G varyantının da yüksek heteroplazmi ile ilişkili olduğu gösterildi. Bunun yanı sıra, hepsi tranzisyon tipinde olan, MT-TF genindeki m.582T>C, MT-TL1 genindeki m.3260A>G, MT-TL1 genindeki m.3302A>G, MT-TM genindeki m.4409T>C ve MT-TI genindeki m.4267A>G varyantlarının ise düşük heteroplazmi oranı ile ilişkili olduğu bulundu. Çalışmamız ayrıca, kontrol bölgesindeki varyant birikimi için potansiyel bir yaş sınır eşiği olabileceğini de işaret etmiştir. Gelecekte, daha büyük örnek sayısı ve gelişmiş analiz yöntemlerinin kullanılacağı çalışmalar, bu bulguların doğrulanması ve geliştirilmesine katkı sağlayacaktır.

Keywords

• Mitokondriyel heteroplazmi
• MT-TL1
• MTTL2
• MT-RNR2
• MT-TM
• MT-TI
• MT-TF

HETEROPLASMY-ASSOCIATED MITOCHONDRIAL DNA VARIANTS IN HUMAN BLOOD AND SKELETAL MUSCLE SAMPLES

Abstract

Objective: Mitochondrial heteroplasmy, a recognized trait in eukaryotic cells, plays a pivotal role in complex disorders like mitochondrial diseases. High-throughput sequencing has improved precision in detecting low-level heteroplasmy and can identify ultra-low-level variants (<1%) associated with heteroplasmy attributes. We aimed to investigate potential genetic and demographic factors associated with heteroplasmy levels in mitochondrial variants by analyzing both blood and muscle tissues in individuals, regardless of their phenotypes. Material and Methods: High-throughput sequencing was conducted on the mitochondrial genomes of 10 individuals, with an equal gender distribution. Variants with heteroplasmy ratios both ranging from 5% to 95% and out of this range were used for statistical analysis. Result: A total of 194 heteroplasmic variants were identified, of which 13 displayed lower heteroplasmy ratios in both blood and skeletal muscle samples from females, while the mitochondrial control region (D-Loop) exhibited higher ratios. Conclusion: The study findings confirm the correlation between the m.10398A>G variant and mitochondrial heteroplasmy levels, consistent with prior research. Additionally, we identified the m.1811A>G variant in MT-RNR2 and the m.12308A>G variant in MT-TL2, both associated with higher heteroplasmy. Conversely, the m.582T>C variant in MT-TF, m.3260A>G in MT-TL1, m.3302A>G in MT-TL1, m.4409T>C in MT-TM, and m.4267A>G in MT-TI were linked to lower heteroplasmy, all involving transition-type alterations. Furthermore, our study hinted at a potential age-related threshold for variant accumulation in the control region. Future studies, involving larger cohorts and advanced expression analysis methods, will further contribute to the validation and enhancement of these findings.

Keywords

• Mitochondrial heteroplasmy
• MT-TL1
• MT-TL2
• MTRNR2
• MT-TM
• MT-TI
• MT-TF

Supporting Institution

This study was supported by the Scientific Research Projects Coordination Unit of Istanbul University, Project No. TYL-2019-33447 and TDK-2018-32544.

Ethical Statement

The study has ethical approval from the Istanbul Faculty of Medicine Ethics Council at Istanbul University (Approval numbers: 1626/2018 and 872/2018.

Thanks

The authors extend their gratitude to the donors for their invaluable participation in this study.

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