Molecular and Cellular Approaches to Nutrition
In Chapter 16, metal-regulated gene expression is reviewed. Trace metals can play a role in gene expression in three ways: structural, catalytic, or regulatory. The regulation of gene expression by trace metals is more specific and interactive than the other two levels of interaction. Iron and zinc provide the best examples of metals involved in gene regulation, with the role of zinc being the best understood of any of the metals. The chapter discusses the zinc-finger motif of some proteins that are involved in DNA binding, as well as the role of zinc as an activator of trans-acting factors for regulating specific gene expression.
Chapter 17 provides an overview of the processes that contribute to gene expression and describes techniques used to study the regulation of gene expression associated with nutrient metabolism. While protein synthesis can be regulated at the level of transcription, translation, or posttranslational modification, particular emphasis in this chapter is given to the process of gene transcription and its control, and several model systems are described that show how changes in transcription of specific genes occur in response to nutritional factors.
Chapters 16 and 17 describe molecular techniques that may permit the identification of stress-responsive genes whose expression would be beneficial to control, and the authors indicate that in the future it may be possible to combine nutritional therapy with gene modification. However, the use of techniques to study gene expression is still limited in its application to nutritional problems.
The use of isolated cell techniques to study the cellular uptake and metabolism of naturally occurring glucosides of water-soluble vitamins is the subject of Chapter 18. While micronutrients are clearly essential to performance capability, a number of questions remain to be answered regarding their exact roles. Much work has been done to elucidate the cellular import of water-soluble vitamins, their metabolism, and their bioavailability.
Finally, Chapter 19 examines cellular dysfunction during physiologic stress by discussing the use of isolated cell systems to study the impact of hypoxia and oxidative stress on cellular function. Cellular responses to these stimuli are dependent on the cell type, the nature of the stress, and the environment (cellular, exocrine, and endocrine) of the cells. It is emphasized that if the purpose of using an isolated cell system is to model a more complex in vivo counterpart, the choice of cell system becomes critical. As a general rule, to maximize the utility of a particular cell model, the cell type chosen must display a pattern of response and sensitivity to the stimulus similar to the tissue or system of interest.
These two chapters show how isolated cell systems can be used to examine the effects of stimuli at the organelle or cellular level. Caution is warranted in that care must be taken to choose cell culture models that are as similar in response as possible to the entire organism and situation in question, and like the molecular approaches to nutritional problems, application is still limited.