Physiology of aging and reproduction in invertebrates

Our team studies the regulation of lifespan, or aging. Reduced reproduction and reduced feeding extend lifespans in many organisms, but the physiological mechanisms are poorly understood. Using grasshoppers as a model system, we examine the effects of reproduction and feeding rate on lifespan and longevity.

We have shown that ovariectomy and dietary restriction each involve lowered feeding, reduced reproductive output, and extended lifespan. In contrast, ovariectomy doubles fat body mass and hemolymph volume, while dietary restriction does not change either. Hence, these two means of extending lifespan appear to be the same superficially, but must be acting through different mechanisms physiologically. We seek to characterize these differences to identify the effects of reproduction on lifespan while appropriately controlling for dietary intake. 

Research Projects

• Oxidation of amino acids underlying life-extension by reduced reproduction or reduced diet

  Metabolism plays a central role in longevity. Dietary restriction of certain amino acids, and especially the sulfur-containing amino acids methionine and cysteine, can increase lifespan. In collaboration with Marshall McCue , we have begun examining the oxidation and allocation of specific amino acids, upon either ovariectomy or dietary restriction. A ¹³ C-labeled amino acid is force-fed to a grasshopper, and then the appearance of the ¹³ C is measured in either the CO ₂  of the breath (which indicates oxidation) or the muscle, fat body, and other tissues (which indicates allocation). We have shown that leucine oxidation is increased upon ovariectomy, which is consistent with fewer amino acids being used for egg production. Now we are focusing on the sulfur-containing amino acids, in comparison to similar amino acids that lack sulfur. 

• Feeding regulation underlying life extension by reduced reproduction or reduced diet

  Hunger, or the collection of signals that stimulate feeding, may be a vital element of inducing life extension via dietary restriction. In mice, evidence suggests life extension by dietary restriction may require feeding stimulation by the hormone neuropeptide Y (homologous to neuropeptide F in insects). In experiments in our lab, some diet-restricted grasshoppers receive the same daily amount of food that is consumed by ovariectomized grasshoppers, which reduce their feeding rate by ~40%. While these restricted-diet yet reproductive grasshoppers quickly finish their meals, ovariectomized grasshoppers consume this same amount slowly throughout the day. Hence, the stimulation of feeding and regulation of hunger likely differs between these treatments.

   

  Graduate student Matthew Heck is examining the roles of the feeding stimulant Neuropeptide F (NPF) in life-extension by dietary restriction. He is testing various combinations of dietary restriction and NPF. For example, some individuals receive an ad libitum diet plus NPF injection, others receive dietary restriction and a water injection, while others receive dietary restriction plus a supplemental NPF injection. We have recently obtained partial transcriptomes for brain, fat body, and muscle for our grasshopper model. Using this genetic information, Matt plans to measure mRNA levels of a variety of genes are that downstream from NPF and involved in cell protection. 

• Regulation of growth and storage underlying life extension by reduced reproduction or reduced diet

  Reduced growth signals (e.g., Target of Rapamycin, Insulin-like peptides) throughout the lifespan are associated with longevity in several species. Ovariectomized grasshoppers have twice the fat body of dietary restricted grasshoppers, even when eating the same daily amount, suggesting different levels of tissue-specific growth signals between the two treatments. The fat body transcriptome for our grasshopper will facilitate the investigation of these pathways, and others as well. We have identified two 1000 bp segments of the TOR gene for grasshoppers. Using these sequences, we plan to use RNAi to knockdown TOR in grasshoppers. While life-extension upon TOR knockdown has been shown in other species, TOR knockdown in our grasshopper will allow easy measure of physiology parameters not easily studied in flies and worms, such as feeding rates and nutrient-specific oxidation. 

Research Team

• Primary Investigator

  John Hatle

   

  Terry Presidential Professor of Biology Office: Building 59, Room 3314 Phone: (904) 620-2778 Lab: Building 59, Room 2110 E-mail: jhatle@unf.edu   B.A. (Biology) Luther College (1991) Ph.D. (Evolutionary Biology) University of Louisiana-Lafayette (1998) Post-doctoral fellowship – Illinois State University (1998-2003)   Joined UNF faculty in 2003.

   

• Graduate Research

   

  Matthew Heck spent nearly 2 years in the Hatle lab as an undergraduate. Using 15 N-labelled hydroponic lettuce that he grew himself, Matthew measured the allocation of ingested nitrogen to somatic and reproductive tissues. Testing the disposable soma hypothesis of aging, we found dietary restriction reduced reproductive investment by ~50% but did not alter the proportional allocation of nitrogen to somatic tissues. In addition, Matthew measured levels of protein carbonylation (oxidized proteins) in somatic tissues, and found that dietary restriction reduced protein damage in some, even without a change in nutrient allocation to the same tissue in the same individual. Matt’s graduate project will address the role of feeding regulation in life extension (see above).  Derek Tokar also spent two years in the Hatle lab as an undergraduate. He used RNAi to knock down vitellogenin, and then studied the trade-off between reproductive investment and somatic storage (Tokar et al. 2014. Integrative and Comparative Biology).    Recent alumni  Undergraduate Katie Veleta (now a PhD student in neurobiology at the University of North Carolina) is a co-first author on the Tokar et al. (2014) paper. Following that work, Alicia Linquist (now head technician at NextScience) and Jacob Burnett (now a PhD student in genetics at the University of Georgia) showed that RNAi knockdown of vitellogenin extended lifespan, increased storage, but the life-extension was not additive with that of ovariectomy.   Mirna Pehlivanovic and Jennifer Purcell were essential to the project testing the allocation of nitrogen to reproduction or the soma. Mirna will attend Physician’s Assistant school starting fall 2015, and Jenn is in the DO program at Lake Erie College of Medicine. Mirna was best poster at the 2015 meeting of the Comparative Nutrition Society for this work.

  Matt and Ayesha with Dr. Hatle                     Hatle Research Lab

   

   

Relevant Publications

• Relevant Publications

   

  Heck MJ¹, Pehlivanovic M¹, Purcell JU, Hahn DA, Hatle JD* (2016) Life-extending dietary restriction reduces oxidative damage of proteins in grasshoppers but does not alter allocation of ingested nitrogen to somatic tissues. J Gerontol A Biol Sci Med Sci. doi:10.1093/gerona/glw094 (¹equal contribution)

   

  Tetlak AG, Burnett JB, Hahn DA, Hatle JD* (2015) Vitellogenin-RNAi and ovariectomy each increase lifespan, increase protein storage, and decrease feeding, but are not additive in grasshoppers. Biogerontology. 16:761–774. DOI 10.1007/s10522-015-9599-3

   

  Tokar DR¹, Veleta KA¹, Canzano J, Hahn DA, Hatle JD* (2014) Vitellogenin RNAi halts ovarian growth and diverts reproductive proteins and lipids in young grasshoppers.  Integrative and Comparative Biology 54:931-941. doi:10.1093/icb/icu068 (¹equal contribution)

   

  Hatle JD*, Kellenberger JW, Viray E, Smith AM, Hahn DA (2013) Life-extending ovariectomy in grasshoppers increases somatic storage, but dietary restriction with an equivalent feeding rate does not.  Experimental Gerontology 48: 966-972.

   

  Judd ET, Wessels FJ, Drewry MD, Grove M, Wright K, Hahn DA, Hatle JD* (2011) Ovariectomy in grasshoppers increases somatic storage, but proportional allocation of ingested nutrients to somatic tissues is unchanged. Aging Cell 10:972-979.
  
  Drewry MD, Williams JM, Hatle JD* (2011) Life-extending dietary restriction and ovariectomy result in similar feeding rates but different physiological responses in grasshoppers. Experimental Gerontology 46: 781-786.
  
  Judd ET, Hatle JD*, Drewry MD , Wessels FJ, Hahn DA (2010) Allocation of nutrients to somatic tissues in young ovariectomized grasshoppers. Integrative and Comparative Biology 50:818-828. 

  
  

   

   

   

Support

• Funding Sources

  National Institute on Aging R15 Award (i.e., AREA grant) 2010-2013.

   

  National Science Foundation ($35,000 supplement to Dan Hahn’s award, to fund the transcriptome project) in 2013-14.

   

  UNF Academic Affairs summer research award in 2014.

   

  National Institute on Aging R15 Award (i.e., AREA grant). 2016-2019. Testing direct effects of reproduction on lifespan with controlled feeding in grasshoppers. $432,000.

   

  UNF Terry Presidential Professorship. 2016-2019. $22,500.