The overall goal of the proposed research is to identify the genes in energy metabolism and stress response that are crucial for life span extension using two mammalian model systems, food restriction (FR) and the Ames dwarf (df) mouse. Although many changes in physiologic function and gene expression have been found through the analysis of rodents subjected to food restriction, it is difficult to identify which changes contribute significantly to life span extension. A much needed additional model is the Ames dwarf mouse. These mutant mice have pituitary insufficiency leading to reduced growth hormone, prolactin, and thyrotropin. The df mouse model has a dramatically extended life span--the greatest extension of any mammalian model (Brown-Borg, Nature, 1996). The hypothesis that directs the proposed studies is that downstream target genes altered by the pituitary insufficiency state are candidate genes for longevity. Genes that are similarly expressed in the genetic (df) and in the adaptive (FR) animals compared to ad libitum fed mice, will have a high probability of being critical for the life span extension.
Specific Aim 1 will be to compare the levels of expression of three categories of known genes in liver, muscle, and adipose tissues of the Ames dwarf animals to that of the FR and ad libitum fed control litter mates. The known genes to be examined are those that are 1) involved in energy metabolism 2) transcription factor genes known to regulate the nutritional response of metabolic genes in these tissues and 3) genes involved in stress response pathways. These genes are chosen based on previous descriptions of enzymatic activities found to differ in either the FR or df animals.
Specific Aim 2 will expand the screen for genes whose levels are similarly altered in the FR and df mice by using micro array of the UniGene Mus musculus cDNA set. This comparison of known and unknown genes whose expression is similar in dwarf and FR mice, but differs from ad lib fed animals will suggest categories of genes that are most relevant to the extension of life span. A third specific aim will be to determine whether additional models of hormonal insufficiency have extended life spans. We will initiate the housing of two mutant mouse strains in order to determine their longevity; i.e. the Tshb mouse (deficient in the beta subunit of thyrotropin resulting in thyroid hormone deficiency) and the Little mouse (lacking the growth hormone releasing hormone receptor and deficient in growth hormone). Each of these animals is growth retarded, but their longevity is unknown. If either of these strains has increased longevity, they should share the phenotype of altered gene expression for loci relevant to longevity and will serve as an additional model to delineate patterns of gene expression that increase life span.
