Update of Mitochondrial Network Analysis by Imaging: Proof of Technique in Schizophrenia

Mitochondria, similar to living cells and organelles, have a negative membrane potential, which ranges between (-108) and (150) mV as compared to (-70) and (-90) mV of the plasma membrane. Therefore, permeable lipophilic cations tend to accumulate in the mitochondria. Those cations which exhibit fluorescence activity after accumulation into energized systems are widely used to decipher changes in membrane potential by imaging techniques. Here we describe the use of two different dyes for labeling mitochondrial membrane potential (Δψ_m) in live cells. One is the lipophilic cation 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazol-carbocyanine iodide (JC-1), which alters reversibly its color from green (J-monomer, at its low concentration in the cytosol) to red (J-aggregates, at its high concentration in active mitochondria) with increasing mitochondrial membrane potential (Δψ_m). The other is MitoTracker^® Orange, a mitochondrion-selective probe which passively diffuses across the plasma membrane and accumulates in active mitochondria depending on their Δψ_m. We show that in addition to changes in Δψ_m, these specific dyes can be used to follow alterations in mitochondrial distribution and mitochondrial network connectivity. We suggest that JC-1 is a preferable probe to compare between different cell types and cell state, as a red to green ratio of fluorescence intensities is used for analysis. This ratio depends only on the mitochondrial membrane potential and not on other cellular and/or mitochondrial-dependent or independent factors that may alter, for example, due to treatment or disease state. However, in cells labeled either with green or red fluorescence protein, JC-1 cannot be used. Therefore, other dyes are preferable. We demonstrate various applications of JC-1 and MitoTracker Orange staining to study mitochondrial abnormalities in different cell types derived from schizophrenia patients and healthy subjects.