Lifespan extension and delayed immune and collagen aging in mutant mice with defects in growth hormone production

Abstract

Single-gene mutations that extend lifespan provide valuable tools for the exploration of the molecular basis for age-related changes in cell and tissue function and for the pathophysiology of agedependent diseases. We show here that mice homozygous for loss-of-function mutations at the Pit1 (Snell dwarf) locus show a >40% increase in mean and maximal longevity on the relatively long-lived (C3H͞HeJ ؋ DW͞J)F1 background. Mutant dw J ͞dw animals show delays in age-dependent collagen cross-linking and in six age-sensitive indices of immune system status. These findings thus demonstrate that a single gene can control maximum lifespan and the timing of both cellular and extracellular senescence in a mammal. Pituitary transplantation into dwarf mice does not reverse the lifespan effect, suggesting that the effect is not due to lowered prolactin levels. In contrast, homozygosity for the Ghrhr lit mutation, which like the Pit1 dw mutation lowers plasma growth hormone levels, does lead to a significant increase in longevity. Male Snell dwarf mice, unlike calorically restricted mice, become obese and exhibit proportionately high leptin levels in old age, showing that their exceptional longevity is not simply due to alterations in adiposity per se. Further studies of the Pit1 dw mutant, and the closely related, long-lived Prop-1 df (Ames dwarf) mutant, should provide new insights into the hormonal regulation of senescence, longevity, and late life disease.T he analysis of single-gene mutations in flies (1) and nematode worms (2-4) has begun to yield important clues to the molecular basis of aging and genetic control of longevity in invertebrates. At present there are four examples of single gene mutations that extend longevity in mammals (5-8). The best documented of these is the Ames dwarf mutation, now known as Prop-1 df , which in homozygous form has been shown to extend longevity by Ͼ50% in both males and females (5). Homozygous df͞df mice show defects in embryonic development of the anterior pituitary that lead to an absence of cells responsible for the production of growth hormone (GH), thyroid-stimulating hormone, and prolactin (PRL). The small body size of these mice is apparent within the first 3 weeks of age, and young adults are approximately one-third of the size of ϩ͞df or ϩ͞ϩ littermates, which are themselves phenotypically indistinguishable from one another. Extended longevity (about 20%) and small body size also are seen in transgenic mice that express high brain levels of urokinase-type plasminogen activator (6); in this case the phenotypes are thought to reflect a loss of appetite and diminished food intake similar to that seen in genetically normal mice and rats subjected to involuntary food restriction (9). In a third instance, targeted deletion of the p66 shc signal transduction protein has been shown to lead to increased lifespan presumably mediated by increased cellular resistance to apoptosis (7).The fourth example, the Snell dwarf mutation Pit1 dw and the coallelic mutation Pit1 dwJ are the topic of...

Circulating microRNA signature of genotype‐by‐age interactions in the long‐lived Ames dwarf mouse

“…There is a caveat in our experimental design, which due to the lack of a standardized scale of biological age equivalence between dwarf mice and normal mice considered animals of the same chronological age for each genotype. Normal and df/df mice of the same chronological age do not necessarily represent the same biological age (i.e., df/df mice may represent a younger biological age at an equivalent chronological age compared to normal mice; Flurkey et al ., 2001). However, by focusing on GbA interaction effects, we inherently reduce the risk for biological misinterpretation.…”

Reduced in vivo hepatic proteome replacement rates but not cell proliferation rates predict maximum lifespan extension in mice

“…These data provide evidence that the reduction in hepatic protein RRs in CR and Rapa‐treated mice is due to a reduced demand for protein renewal attributable to a reduction in protein damage, consistent with the model that we propose here. Reduced protein damage has been previously reported in Snell Dwarf mice relative to control counterparts (Flurkey et al ., 2001); however, it remains to be determined whether elongation rates are reduced and translational fidelity is increased in these mice.…”

Genes regulated by caloric restriction have unique roles within transcriptional networks

“…A number of "aging genes" have been identified for which mutations significantly increase mouse lifespan and delay the onset of age-related disease (Prop1, Pit1, Ghr,Ghrhr,Irs1,Irs2,PappA,Clk1,Shc1,Igf1r,Kl,Adcy5,Surf1,Insr,Ucp2,Gpx4) (Brown-Borg et al, 1996;Kopchick and Laron, 1999;Migliaccio et al, 1999;Flurkey et al, 2001;Bluher et al, 2003;Holzenberger et al, 2003;Kurosu et al, 2005;Liu et al, 2005;Conti et al, 2006;Conover and Bale, 2007;Dell'Agnello et al, 2007;Ran et al, 2007;Taguchi et al, 2007;Yan et al, 2007;Selman et al, 2008). The extent to which these genes interact with CR-regulated pathways is unclear (Miller et al, 2002;Tsuchiya et al, 2004;Bonkowski et al, 2006;Swindell, 2007).…”