Mitochondrial DNA content and expression of genes involved in mtDNA transcription, regulation and maintenance during human fetal development.

The mitochondrial biogenesis and adequate energy production are important for fetal growth and early postnatal adaptation. The aim of the study was to characterize mitochondrial DNA (mtDNA) content and expression patterns of POLG, TFAM, NRF1,NRF2 and PGC1 family of regulated coactivators (PGC1A, PGC1B and PRC) involved in the mtDNA transcription, regulation and maintenance in human fetal tissues during second trimester of gestation. Further the mRNA expression profiles of selected cytochrome c oxidase (COX) subunits were analysed. Moreover enzyme activities of COX and CS and protein levels of COX subunits were analysed. DNA, RNA and proteins were isolated from 26 pairs of fetal liver and muscle samples obtained at autopsy after termination of pregnancy for genetic indications unrelated to OXPHOS deficiency between 13th and 28th week of gestation. This work offers a broad view on the mtDNA content changes in two different tissues during the second trimester of gestation and in the corresponding tissues after birth. The important differences in expression of POLG, TFAM, NRF2 genes and family PGC1 coactivators were found between the fetal tissues. The significant tissue-specific changes in expression of selected COX subunits on mRNA level (COX4 and MTCO2) were observed. Further the considerable differences in enzyme activities of COX and CS are demonstrated between fetal and postnatal phase. In conclusion our study indicates that the fetal developing tissues might differ in the control of mitochondrial biogenesis depending on their energy demand and the age of gestation. Moreover the gene expression is changed mainly on transcriptional level through fetal period.

Activities of respiratory chain complexes and pyruvate dehydrogenase in isolated muscle mitochondria in premature neonates.

BACKGROUND AND AIMS: Most diseases in premature neonates are secondary to immaturity of various organ systems. Also the inadequate capacity of mitochondrial energy production may play an important role in the neonatal morbidity. SUBJECTS AND METHODS: The activities and amount of respiratory chain (RC) complexes, pyruvate dehydrogenase (PDH) and citrate synthase (CS) were analysed in isolated muscle mitochondria obtained at autopsy in 19 premature neonates using spectrophotometric and radioenzymatic methods and blue-native electrophoresis and Western blotting. Two groups of children recommended for muscle biopsy at the age of 0.5-2 and 3-18 years served as controls. RESULTS: In premature neonates, the activities of RC complexes III, IV, PDH and CS were markedly lower in comparison with older children. On the contrary, the activity of complex I was higher in premature neonates than in older children. The ratios between RC complexes I, II and III and CS were significantly higher in premature neonates in comparison with older children. In addition, the protein amount of RC complexes and PDH subunits were lower in premature neonates in comparison with older children. CONCLUSION: The results of our study document the age-dependent differences in activities of PDH and respiratory chain complexes in early childhood. Lower functional capacity of mitochondrial energy-providing system in critically ill neonates may be explained by combination of various factors including the delay in maturation of PDH and respiratory chain complexes in very premature neonates and increased degradation of mitochondrial proteins in connection with sepsis, tissue hypoperfusion or hypoxemia.

The developmental changes in mitochondrial DNA content per cell in human cord blood leukocytes during gestation.

The mitochondrial DNA (mtDNA) amount in cells as the basis for mitochondrial energy generating system, which produces ATP, plays an important role in the fetal development and postnatal morbidity. Isolated human cord blood leukocytes (HCBL) contribute very little to the overall metabolic turnover, but they may serve as easily available marker cells for the study of the mtDNA amount changes in cord blood during fetal development. The aim of our study was to analyze the mtDNA amount in HCBL. HCBL were isolated from cord blood samples of 107 neonates born between the 25th and 41st week of gestation. The mtDNA amount was analyzed by the real-time PCR method. The significant negative correlations were found between the relative mtDNA amount in HCBL and gestational age (r = -0.54, p<0.01) and birth weight (r = -0.43, p<0.01), respectively. The results revealed that the mtDNA content per cell decreases in HCBL with progressing fetal development. This may be explained by gradual shift of the hematopoiesis from fetal liver to bone marrow during the second half of pregnancy presumably accompanied by decreasing cell volume of HCBL as it was shown similarly in red blood cells.