Confronting cellular heterogeneity in studies of protein metabolism and homeostasis in aging research.

In this chapter we review the different technologies that can be applied in the analysis of protein homeostasis and metabolism in aging research. Special focus will be on technologies with a potential to circumvent the problems associated with cell heterogeneity in biomarker discovery. Often studies aimed at increasing our understanding of cellular senescence take advantage of model systems. This can be in the form of cell culture, where specific celllines are cultivated, thus undergoing cellular senescence according to the Hayflick phenomenon. Alternatively, model organisms can be included, such as yeast, nematodes and zebra fish. Even though such model systems allow the researcher to control many parameters of the system, it is well established that even in a simple cell culture system the individual cells are morphologically and functionally different. The heterogeneity observed even within the least complex systems, makes it a difficult task to identify biomarkers of cellular senescence and to fully understand the various molecular networks. The complexity is further increased when taking the step from model systems of aging to human aging.