Signaling by mitochondria

A resurgence of interest in mitochondrial physiology has recently developed as a result of new experimental data demonstrating that mitochondria function as important participants in a diverse collection of novel intracellular signaling pathways. Recent data demonstrate that mitochondria regulate molecular and cellular responses to low oxygen levels (hypoxia). Hypoxic conditions between 1 and 2% oxygen typically elicit an increase in transcription of over 100 genes. By contrast, oxygen levels close to 0% initiate programmed cell death. Mitochondria release free radicals that are necessary and sufficient to initiate the increase in gene transcription during hypoxia. Mitochondria also regulate the initiation of programmed cell death during anaerobic conditions by releasing cytochrome c, which results in the activation of caspases. Thus, mitochondria serve to integrate changes in environmental conditions such as changes in oxygen levels to the activation of diverse events, such as gene transcription and programmed cell death