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.
Ovariectomized grasshoppers are long-lived and obese, while
diet-restricted grasshoppers are long-lived and lean, suggesting their
metabolisms are different. To address this, we tracked individual 13C-labeled
nutrients from ingestion to exhalation as CO2. Any 13C
that appeared in exhaled CO2 must have come from the 13C-enriched
nutrient, allowing a measurement of metabolism of that particular nutrient over
time. In summer 2013, we tested oxidation of glucose, leucine (an amino acid),
and oleic acid (a fatty acid). Our preliminary results suggest that ovariectomy
reduces glucose oxidation and delays leucine oxidation, while dietary
restriction appears to speed leucine oxidation. To our surprise, oleic acid
oxidation was not altered by either treatment. Next, we plan to identify the
tissues to which the 13C labels were allocated, and follow up by testing
oxidation of additional amino acids.
Undergraduates Ayesha Awan and Justin Nicholas have led this
project. This work is in collaboration with Marshall McCue, Dan Hahn, and CarolineWilliams.
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 our lab, some diet-restricted grasshoppers receive
the same daily amount of food that is consumed by ovariectomized grasshoppers. While
these restricted-diet grasshoppers quickly finish their meals within an hour, ovariectomized
grasshoppers consume this same amount slowly throughout the day. Hence, the
stimulation of feeding and regulation of hunger likely differs between these
We have recently obtained transcriptomes for brain, fat
body, and muscle from our grasshopper model. Using this genetic information, we
intend to characterize differences in the expression of mRNAs underlying
feeding regulation (e.g., Npf, sNPF, and
for). We plan to use RNAi to
knockdown key molecules involved in feeding stimulation pathways. Next, we will
analyze a host of molecular and physiological changes upon those knockdowns,
including differential gene expression, feeding rate, fecundity, and lifespan.
Office: Building 59, Room 3314
Phone: (904) 620-2778
Lab: Building 59, Room 2110
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.
Matthew Heck spent nearly 2 years in the Hatle lab as an
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).
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
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.
Tokar DR, Veleta KA, 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.
Hatle JD*, Kellengerber 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. (1equal contribution)
Hatle JD*, Paterson CS, Jawaid I, Lentz C, Wells SM, Fronstin RB (2008) Protein accumulation underlying lifespan extension via ovariectomy in grasshoppers is consistent with the disposable soma hypothesis but is not due to dietary restriction. Experimental Gerontology 43:900-908.
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.
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