Cellular networks and the aging process.

The most important interactions between cellular molecules have a high affinity, are unique and specific, and require a network approach for a detailed description. After a brief introduction to cellular networks (protein--protein interaction networks, metabolic networks, gene regulatory networks, signalling networks and membrane--organelle networks) an overview is given on the network aspects of the theories on aging. The most important part of the review summarizes our knowledge on the aging of networks. The effects of aging on the general network models are described, as well as the initial findings on the effects of aging on the cellular networks. Finally we suggest a 'weak link theory of aging' linking the random damage of the network constituents to the overwhelming majority of the low affinity, transient interactions (weak links) in the cellular networks. We show that random damage of weak links may lead to an increase of noise and an increased vulnerability of cellular networks, and make a comparison between these predictions and the observed behaviour of the emergent properties of cellular networks in aged organisms.