EPR study of annexin V-cardiolipin Ca-mediated interaction in phospholipid vesicles and isolated mitochondria

Exogenous cardiolipin localizes to mitochondria and prevents TAZ knockdown-induced apoptosis in myeloid progenitor cells

The concentration and composition of cardiolipin (CL) in mitochondria are altered in age-related heart disease, Barth Syndrome, and other rare genetic disorders, resulting in mitochondrial dysfunction. To explore whether exogenous CL can be delivered to cells, CL was combined with apolipoprotein A-I to generate water-soluble, nanoscale complexes termed nanodisks (ND). Mass spectrometry of HL60 myeloid progenitor cell extracts revealed a 30-fold increase in cellular CL content following incubation with CL-ND. When CL-ND containing a fluorescent CL analogue was employed, confocal microscopy revealed CL localization to mitochondria. The ability of CL-ND to elicit a physiological response was examined in an HL60 cell culture model of Barth Syndrome neutropenia. siRNA knockdown of the phospholipid transacylase, tafazzin (TAZ), induced apoptosis in these cells. When TAZ knockdown cells were incubated with CL-ND, the apoptotic response was attenuated. Thus, CL-ND represent a potential intervention strategy for replenishment of CL in Barth Syndrome, age-related heart disease, and other disorders characterized by depletion of this key mitochondrial phospholipid.

Modeling the calcium sequestration system in isolated guinea pig cardiac mitochondria

Under high Ca(2+) load conditions, Ca(2+) concentrations in the extra-mitochondrial and mitochondrial compartments do not display reciprocal dynamics. This is due to a paradoxical increase in the mitochondrial Ca(2+) buffering power as the Ca(2+) load increases. Here we develop and characterize a mechanism of the mitochondrial Ca(2+) sequestration system using an experimental data set from isolated guinea pig cardiac mitochondria. The proposed mechanism elucidates this phenomenon and others in a mathematical framework and is integrated into a previously corroborated model of oxidative phosphorylation including the Na(+)/Ca(2+) cycle. The integrated model reproduces the Ca(2+) dynamics observed in both compartments of the isolated mitochondria respiring on pyruvate after a bolus of CaCl2 followed by ruthenium red and a bolus of NaCl. The model reveals why changes in mitochondrial Ca(2+) concentration of Ca(2+) loaded mitochondria appear significantly mitigated relative to the corresponding extra-mitochondrial Ca(2+) concentration changes after Ca(2+) efflux is initiated. The integrated model was corroborated by simulating the set-point phenomenon. The computational results support the conclusion that the Ca(2+) sequestration system is composed of at least two classes of Ca(2+) buffers. The first class represents prototypical Ca(2+) buffering, and the second class encompasses the complex binding events associated with the formation of amorphous calcium phosphate. With the Ca(2+) sequestration system in mitochondria more precisely defined, computer simulations can aid in the development of innovative therapeutics aimed at addressing the myriad of complications that arise due to mitochondrial Ca(2+) overload.