Mitochondrial DNA mutations in focal segmental glomerular sclerotic lesions

肾小球上皮细胞(GEPC)是局灶性节段性肾小球硬化(FGS)病变的主要致病部位。GEPC被认为是终末分化的细胞，不会增殖。神经细胞和肌肉细胞的这一特征是相同的，这两个细胞是mtDNA突变积累的主要部位。我们筛查了来自原发FGS患者和IgA肾病患者的肾活检标本中的线粒体DNA(MtDNA)突变，作为继发性FGS受试者和对照。从肾活检组织中提取线粒体DNA，用合适的引物对其进行扩增，以研究线粒体DNA点突变3243A~G、3271T~C、8344A~G、8993T~G、C以及常见的缺失(跨越线粒体DNA核苷酸对8469~13447的4977bp缺失)。还进行了总mtDNA的原位扩增和常见缺失。2例FGS患者有3243个A-G点突变，12例FGS患者，7例伴有肾小球硬化性病变的IgA肾病患者的肾脏组织中存在共同缺失。未发现3271T~C、8344A~G、8993T~G或8993T~G突变。3243A~G点突变异质性大于85%，而常见缺失的异质性小于1%。原位聚合酶链式反应显示，正常mtDNA主要分布于肾小管上皮细胞，常见缺失的mtDNA主要分布于肾小管上皮细胞。提示在部分原发性FGS和继发性FGS合并IgA肾病患者中，mtDNA突变主要分布于GEPC。这些突变可能与GEPC损伤有关。

Glomerular epithelial cells (GEpC) are primary pathogenic sites in focal segmental glomerular sclerosis (FGS) lesions. GEpCs are regarded as terminally differentiated cells and do not proliferate. This characteristic is the same for neuron cells and muscular cells, which are major sites of mtDNA mutations accumulation. We screened for mitochondrial DNA (mtDNA) mutations in renal biopsy specimens from primary FGS patients and also from IgA nephropathy patients as a secondary FGS subject and as a control. MtDNA extracted from kidney biopsy specimens was amplified with appropriate primer pairs for studying mtDNA point mutations 3243 A to G, 3271 T to C, 8344 A to G, 8993 T to G, C and the common deletion (a 4977-bp deletion spanning mtDNA nucleotide pairs 8469 to 13447). In situ amplification of both total mtDNA and the common deletion were also performed. Two patients with FGS had a 3243 A to G point mutation and 12 patients with FGS, and 7 patients with IgA nephropathy accompanied by glomerular sclerotic lesions, had the common deletion in their kidney tissue. No patient showed mtDNA mutations 3271 T to C, 8344 A to G or 8993 T to G or C. The degree of heteroplasmy for 3243 A to G point mutation was more than 85%, however, the heteroplasmy for the common deletion was less than 1%. Using in situ PCR, normal mtDNA was mainly distributed to the tubular epithelium, and mtDNA with the common deletion was mainly distributed among GEpC. In conclusion, it is suggested that mtDNA mutations are distributed to the GEpC in some patients with primary FGS and secondary FGS with IgA nephropathy. These mutations may be related to GEpC damage.