Profound Length Heteroplasmic Alterations in Mitochondrial DNA Control Region From Primary AML Cells: Implication of Impaired Mitochondrial Replication and Demonstration of ‘vicious cycle’ Hypothesis.

Abstract 3116

Poster Board III-53

Mitochondrial DNA (mtDNA) control region (displacement (D)-loop including HV1 and HV2) is a non-coding region of 1124 bp (nucleotide positions, np 16 024–576), which acts as a promoter for both the heavy and light strands of mtDNA, and contains essential transcription and replication elements (Blood 2004;103:4466-77). Importantly, mutations in the D-loop regulatory region might change mtDNA replication rate by modifying the binding affinity of significant trans-activating factors (Eur J Cancer 2004;40:2519-24). Thus, length heteroplasmic alterations of mtDNA control region may be related with mitochondrial dysfunction resulting in ‘vicious cycle’ (Mol Med Today 2000;6:425-32). In an attempt to investigate profiling of mtDNA length heteroplasmic alterations in primary AML cells, we carried out a quantitative size-based PCR product separation by capillary electrophoresis (ABI 3130XL Genetic Analyzer and ABI Prism Genotyper version 3.1) using six targets (np 303-315 poly C, np 16184-16193 poly C, np 514-511 CA repeats, np 3566-3572 poly C, np 12385-12391 poly C and np 12418-12426 poly A). Length heteroplasmy was further confirmed by cloning and sequencing. Quantitative analysis of mtDNA molecules was performed using the QuantiTect SYBR Green PCR kit (Qiagen) and Rotor-Gene 3000 (Corbett Research). Forty-eight AML bone marrow samples were collected after receiving Institutional Review Board approval and informed consent. There were profound alterations of mtGI in 303 poly C, 16184 poly C and 514 CA repeats. The length heteroplasmy pattern of 303 poly C tract in the HV2 region disclosed mixture of 7C, 8C, 9C and 10C mtDNA types. In the HV2 region, length heteroplasmy in poly-C tract at np 303 - 309 exhibited 5 variant peak patterns: 7CT6C+8CT6C (50.0%), 8CT6C+9CT6C (14.0%), 8CT6C+ 9CT6C+ 10CT6C (10.4%), 9CT6C+10CT6C+11CT6C (8.3%) 9CT6C + 10CT6C + 11CT6C+12CT6C (2.1%). The length heteroplasmy pattern of 514-523 CA repeats in the HV2 region exhibited 2 variant peak patterns: CACACACACA (56.3%) and CACACACA (43.7%). In the HV1 region, length heteroplasmy in the poly-C tract at np 16184 - 16193 exhibited 9 variant peak patterns: 5CT4C+5CT3C (31.0%), 6CT4C+6CT3C (2.1%), 9C+10C+11C+12C (16.7%), 9C+10C+11C (2.1%), T4CT4C+5CT3C (4.2%), 9C+10C+11C+12C+13C (2.1%), 3CTC4C+5CT3C (2.1%), 10C+11C+12C+13C (4.2%), 8C+9C+10+11C (2.1%). Primary AML cells revealed decreased enzyme activity in respiratory chain complex I, II and III. AML cells had about a two-fold decrease in mtDNA copy number compared with normal blood mononuclear cells. Current study demonstrates that profound length heteroplasmic alterations in mtDNA control region of primary AML cells may lead to impairment of mitochondrial biogenesis (reduction of mtDNA copy number) and derangement of mitochondrial ATP synthesis. During this perturbation, mitochondria in primary AML cells might produce a large amount of reactive oxygen species, which causes the vicious cycle observed in chronic inflammatory diseases and cancers as well.