Uncovering a temperature-depending role of the P. anserina i-AAA protease on lifespan

Due to their endosymbiotic origin, mitochondria contain their own protein quality control system to ensure mitochondrial integrity. This includes two membrane-bound proteases, the m-AAA and the i-AAA protease. The i-AAA protease is a conserved protein involved in the proteolytic degradation of polypeptides as well as the dislocation of proteins.

Here we present investigations analyzing the role of the i-AAA protease in the fungal aging model Podospora anserina. A strain was generated lacking the ORF of the i-AAA protease PaIap (ΔPaIap). Unexpectedly, at 27°C, the standard growth temperature of P. anserina, this results in an increased lifespan of ΔPaIap while there are no impairments in growth or fertility. Other components of the molecular quality control system appear not to compensate for the loss of PaIAP as there is no difference in the amounts of PaLON, PaCLPP and PaHSP60 in mitochondria of ΔPaIap.

Interestingly, exposure of ΔPaIap to heat-stress reveals a higher temperature sensitivity of ΔPaIap. This results in a decreased lifespan as well as impaired physiological functions of the deletion strains. The strains show reduced growth rates and an impaired female fertility. A role of PaIAP in heat-stress response is further supported by the ~6 fold up-regulation of the protein in wild-type mitochondria after heat-stress. In addition, mitochondria of strains lacking PaIap show reduced levels of PaHSP60 and PaCLPP under heat-stress.