Mutational Analysis of Mitochondria DNA in Children with IgA Nephropathy

PURPOSE: The association of mitochondrial DNA (mtDNA) mutations, deletions and copy number with progressive changes in patients with some glomerular disease and end-stage renal disease have been reported. In this study, we performed mtDNA mutation analysis in children with IgA nephropathy to investigate its role in progressive clinical course. METHODS: Seven children with IgA nephropathy were involved in this study. MtDNA isolated from platelet was amplified by PCR and sequenced entirely. RESULTS: The mean age at renal biopsy was 11.5+/-2.2 year and the mean age at latest evaluation was 17.9+/-3.2 year. The mean follow-up period were 7.8+/-3.1 years. Patients was divided into 2 groups according to the amount of proteinuria at presenting manifestation. Group 2 patients were nephrotic syndrome. Renal function reveals within normal range in all patients. In group 2 patients, the mean serum albumin level was significantly lower than those of group 1 (3.7+/-0.6 g/dL vs. 4.7+/-0.2 g/dL, P=0.0241) and the mean total cholesterol level was significantly higher than those of group 1 (222.7+/-35.7 mg/dL vs. 148.3+/-29.1 mg/dL, P=0.0283). In Group 2 patients, total amount of protein of 24 hour collected urine also significantly higher than those of group 1 (1,466.0+/-742.5 mg vs. 122.5+/-48.1 mg, P=0.0135). Pr/Cr ratio in random urine sample was also higher in group 2 than those of group 1 but the statistical significance was not noted (1.8+/-1.6 vs. 0.2+/-0.2, P=0.0961). Deletion of mtDNA nt 8272-8281 were observed in two patients, one patient in each groups, respectively. This is non-coding lesion. No patients demonstrated the mtDNA mutations. CONCLUSIONS: We have identified a deletion of mtDNA nt 8272-8281 in two children with IgA nephropathy. Further studies are needed to clarify the role of mitochondrial function in the progressive change of IgA nephropathy.

A Computational Model of Cytosolic and Mitochondrial Ca2+ in Paced Rat Ventricular Myocytes

We carried out a series of experiment demonstrating the role of mitochondria in the cytosolic and mitochondrial Ca2+ transients and compared the results with those from computer simulation. In rat ventricular myocytes, increasing the rate of stimulation (1~3 Hz) made both the diastolic and systolic [Ca2+] bigger in mitochondria as well as in cytosol. As L-type Ca2+ channel has key influence on the amplitude of Ca2+-induced Ca2+ release, the relation between stimulus frequency and the amplitude of Ca2+ transients was examined under the low density (1/10 of control) of L-type Ca2+ channel in model simulation, where the relation was reversed. In experiment, block of Ca2+ uniporter on mitochondrial inner membrane significantly reduced the amplitude of mitochondrial Ca2+ transients, while it failed to affect the cytosolic Ca2+ transients. In computer simulation, the amplitude of cytosolic Ca2+ transients was not affected by removal of Ca2+ uniporter. The application of carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (FCCP) known as a protonophore on mitochondrial membrane to rat ventricular myocytes gradually increased the diastolic [Ca2+] in cytosol and eventually abolished the Ca2+ transients, which was similarly reproduced in computer simulation. The model study suggests that the relative contribution of L-type Ca2+ channel to total transsarcolemmal Ca2+ flux could determine whether the cytosolic Ca2+ transients become bigger or smaller with higher stimulus frequency. The present study also suggests that cytosolic Ca2+ affects mitochondrial Ca2+ in a beat-to-beat manner, however, removal of Ca2+ influx mechanism into mitochondria does not affect the amplitude of cytosolic Ca2+ transients.