Mitochondrial permeability transition and its regulatory components are implicated in apoptosis of primary cultures of rat proximal tubular cells exposed to lead

Previous studies have already demonstrated that mitochondria play a key role in Pb-induced apoptosis in primary cultures of rat proximal tubular (rPT) cells. To further clarify the underlying mechanism of Pb-induced mitochondrial apoptosis, this study was designed to investigate the role of mitochondrial permeability transition (MPT) and its regulatory components in Pb-induced apoptosis in rPT cells. Mitochondrial permeability transition pore (MPTP) opening together with disruption of mitochondrial ultrastructure, translocation of cytochrome c from mitochondria to cytoplasm and subsequent caspase-3 activation were observed in this study, suggesting that MPT is involved in Pb-induced apoptosis in rPT cells. Simultaneously, Pb-induced caspase-3 activation and apoptosis can be significantly inhibited by three MPTP inhibitors (CsA, DIDS, BA), which target different regulatory components of MPTP (Cyp-D, VDAC, ANT), respectively, demonstrating that Cyp-D, VDAC and ANT participate in MPTP regulation during lead exposure. Moreover, decreased ATP levels and increased ADP/ATP ratio induced by lead treatment can be significantly reversed by BA, indicating that Pb-mediated ANT dysfunction resulted in ATP depletion. In addition, up-regulation of VDAC-1, ANT-1 together with down-regulation of Cyp-D, VDAC-2 and ANT-2 at both the levels of transcription and translation were revealed in rPT cells under lead exposure conditions. In conclusion, Pb-mediated mitochondrial apoptosis in rPT cells is dependent on MPTP opening. Different expression levels in each isoform of three regulatory components contribute to alteration in their functions, which may promote the MPTP opening.