Volume VI, 2007
Dr. John D. Hatle
Consuming fewer calories while maintaining adequate nutrition (i.e. calorie restriction), even if that diet is started late in life, rapidly increases longevity by slowing the aging process (Mair et al. 2003). The mechanisms underlying rapidly reduced mortality rate in response to late-onset calorie restriction are largely unknown. Calorie restriction is associated with lower insulin-like peptides (ILP) levels in many organisms (Tater et al. 2003). We have shown that calorie restriction throughout adulthood, and late-onset calorie restriction, increases longevity in female grasshoppers (Wells et al. 2005; Hatle et al. 2006). The exact role of ILP in the enhanced longevity due to late-onset calorie restriction is unclear. Consequently, there is a need for experiments in which insulin signaling is manipulated only late in life.
Insulin is the hormone secreted by the pancreas of vertebrates that aids in the membrane transport of glucose from the blood into the body cells (Marieb 2005). More generally, insulin directs the absorptive state. Typically, insulin levels increase upon feeding, at which time energy is available for cells to grow. In this role, insulin acts as a growth regulator and signals cells to divide. In lower organisms like insects, ILP are present and appear to act primarily as growth regulators, with little role in glucose metabolism (Ebberink et al. 1989). Previous research on fruit flies has shown that removal of insulin-producing cells causes developmental delays and growth retardation (Rulifson et al. 2002). Hence, we sought to develop an experimental system to test the role of insulin signaling in calorie restriction. The duration of the 5th instar (the stage prior to adulthood) is affected by diet level in juvenile male lubber grasshoppers (Hatle et al. 2003). Developmental events that are affected by calorie intake likely are affected by insulin signaling. To determine whether maturation to adult molt in grasshoppers can be affected by insulin signaling, we injected grasshoppers with an antibody to human insulin (anti-insulin) and measured developmental timing.
Wright, E M. and Gordy, L J., "Tests of Diet and Insulin-like Peptides on the Duration of the 5th Instar of Male Lubber Grasshoppers" (2007). All Volumes (2001-2008). 47.