Physiology of aging and reproduction in invertebrates

Our team studies the regulation of lifespan, or aging. Reduced reproduction and reduced feeding extend lifespan in many organisms. The physiological mechanisms underlying life-extension by reduced reproduction are poorly understood, while the mechanisms underlying reduced feeding are clearer but still an active area of study. Grasshoppers have proven to be an excellent model system for studying the organismal physiology underlying longevity. 

Dr. Hatle works with undergraduate research student, Jillian Eisenhauer, in his lab.  

Research Projects

• Oxidation of amino acids underlying life-extension

  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. Therefore, these two means of extending lifespan result in very different levels of storage and must be acting through different physiological mechanisms. We seek to characterize these differences to identify life-extension mechanisms that may be additive. Due to the differences in energy storage for grasshoppers upon ovariectomy compared to those on dietary restriction, we have searched for metabolic differences underlying these two routes to longevity.

   

  In collaboration with Marshall McCue, we have begun examining the oxidation and allocation of specific amino acids upon either ovariectomy or dietary restriction. A ¹³C-labeled amino acid is force-fed to a grasshopper, and then the appearance of the ¹³C is measured in either the CO₂ of the breath (which indicates oxidation) or the muscle, fat body, and other tissues (which indicates allocation).

   

  The branched-chain amino acids (leucine, isoleucine, valine) play important roles in life-extension via dietary restriction. They are especially potent at stimulating the Target of Rapamycin pathway (TOR), which accelerates cellular growth and shortens organismal lifespan. Undergraduates Ayesha Awan and Justin Nicholas have shown that leucine oxidation is increased upon ovariectomy, which is consistent with less leucine being available for TOR stimulation or egg production. At the same time, allocation of leucine to the muscle is decreased, consistent with a reduced investment in locomotion. These alterations in leucine dynamics may be an underappreciated component of life-extension. This work has been provisionally accepted pending minor revision.

   

  The sulfur-containing amino acids (methionine and cysteine) also play important roles in longevity. They provide the sulfur needed for production of cellular H₂S, which turns on cell proteostasis pathways, enhancing longevity. Counterintuitively, dietary restriction of sulfur-containing amino acids actually increases the production of H₂S in mice. Our early results suggest that life-extending ovariectomy actually decreases H­₂S production in grasshoppers. We have also measured another potential fate for dietary cysteine. Undergraduate Ryan Koch has shown that organismal oxidation of cysteine was not affected by either ovariectomy or dietary restriction. Dr. Cathy Paterson from Florida State College at Jacksonville is joining the project to search for potential roles of anti-oxidants and lipid peroxidation. 

    

  John Hatle and Ryan Koch at the National WW II museum in New Orleans, visited while attending the annual meeting of the Society for Integrative and Comparative Biology.

  Hatle lab after a kayaking trip. Front row, left to right: Ryan Koch, Saskia (guest), Lauren Milano, John Hatle. 2nd row: Melissa Leen (Ryan’s wife), Amra Karjasevic. 3rd row: Jillian Eisenhauer, Matthew Heck.

   

• Feeding regulation and protein oxidation underlying life extension

  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). To avoid starvation, NPY/NPF increases feeding on substandard food, and simultaneously reduces response to stressful inputs.   Graduate student Matthew Heck hypothesized that this preparation for stress could lead to reduced molecular oxidation in tissues. He is testing combinations of feeding levels and NPF injection. For example, some individuals receive an ad libitum diet plus NPF injection, others receive an ad libitum diet and a water injection, while others receive dietary restriction plus a supplemental NPF injection. Matt has found that NPF provides protection against protein oxidation (i.e., carbonylation) upon dietary restriction, but not upon ad libitum feeding. This protection is pronounced in the fat body, moderated in the gut, and absent in the brain.

  Matt Heck showing protein carbonylation results at the gel imager

   

   

   

• Effects of dietary branched-chain amino acids on reproduction and lifespan

   

  The role of branched-chain amino acids (BCAAs) like leucine in stimulation of cellular growth is well accepted, but the role of dietary BCAA in organismal responses like lifespan is controversial. Indeed, testing the role of dietary leucine on longevity in mice has been proposed to the NIA’s Intervention Testing Program. We plan to conduct a similar study, force-feeding extra quantities of all three BCAAs to grasshoppers throughout the lifespan. Grasshopper lifespan is about 6 months, about 2 years shorter than mice, so our results should be available sooner. Undergraduates Amra Karjasevic and Lauren Milano, and post-bac Sophie Nagle, are conducting this study. 

  
  

   

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 (see Feeding regulation and protein oxidation underlying life extension above) spent 2 years in the Hatle lab as an undergraduate. Using 15 N-labelled hydroponic lettuce that he grew, Matt and fellow undergraduate Mirna Pehlivanovic measured the allocation of ingested nitrogen to somatic and reproductive tissues. Testing the disposable soma hypothesis of aging, we found that life-extending dietary restriction did not alter the proportional allocation of nitrogen to somatic tissues, but did reduce protein oxidation in some tissues. See below for the 2016 publication in Journal of Gerontology: Biological Sciences. Derek Tokar aalso 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). His graduate project is involves using RNAi to knockdown the grasshopper Target of Rapamycin.

  Matt Heck

   

   

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.