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Sandy Martin, Ph.D.
Professor Emerita
| sandy.martin@cuanschutz.edu | |
| Ph.D., University of California, Berkeley, 1982 |
Humans, as mammals, are homeotherms, i.e., we use energy to maintain our body temperature continuously at ~37oC. Remarkably some mammals are heterotherms, precipitously dropping their body temperature, metabolic, heart and respiratory rates to enter a state known as torpor. In small-bodied mammals, e.g., ground squirrels, torpor is used during fall and winter and can be maintained for as long as 2-3 weeks with a body temperature as low as 0oC and heart and metabolic rates at 1-3% of their active, resting rates. Bouts of torpor end spontaneously and without harm to tissues throughout the body with a rapid burst of metabolic heat production that propels the animal back to ~37oC. The animal remains warm and sleeps for about 12 hours before entering the next bout of torpor. This cycle between long periods of torpor and short periods of rewarming repeats scores of times throughout the winter months without harm to cells, tissues or organs. The ground squirrel emerges from these months of hibernation to spend spring and summer as a homeotherm: reproducing, growing and fattening for the next hibernation season. Numerous aspects of this phenotype hold great promise for application to medicine and space exploration if they could be engineered in humans. The first step towards that goal is understanding in detail how torpor is orchestrated in a natural hibernator like the ground squirrel.
Although retired and no longer running an active research lab, I remain deeply interested in all aspects of hibernation and welcome any opportunity to engage in discussions or collaborations with anyone who shares this interest.
Gillen, A. E., Epperson, L. E., Orlicky, D. J., Fu, R. and Martin, S. L. (2023). Adrenal gene expression dynamics support hibernation in 13-lined ground squirrels. Physiol Genomics 55: 155-167. PMID: 36847440.
Fu, R., Gillen, A.E., Grabek, K.R., Riemondy, K.A., Epperson, L.E., Bustamante, C.D., Hesselberth, J.R. and Martin, S.L. (2021) Dynamic RNA regulation in the brain underlies physiological plasticity in a hibernating mammal. Frontiers in Physiology, 11: 624677, PMID: 33536943.
Gillen, A. E., Fu, R., Riemondy, K.A., Jager, J., Fang,B., Lazar, M.A. and Martin, S.L. (2021). Liver transcriptome dynamics during hibernation are shaped by a shifting balance between transcription and RNA stability. Frontiers in Physiology 12: 662132, PMID: 34093224.
Regan, M.D., Chiang, E., Martin, S.L., Porter, W.P., Assadi-Porter, F.M., Carey, H.V. (2019) Shifts in metabolic fuel use coincide with maximal rates of ventilation and body surface rewarming in an arousing hibernator. Am J Physiol Regul Integr Comp Physiol. 316:R764-R775 PMID:30969844.
Grabek, K.R., Cooke, T.F., Epperson, L.E., Spees, K.K., Cabral, G.F., Sutton, S.C., Merriman, D.K., Martin, S.L. and Bustamante, C.D. (2019) Genetic variation drives seasonal onset of hibernation in the 13-lined ground squirrel. Communications Biology 2: 478. PMID: 31886416.
Riemondy, K.A., Gillen, A.E., White, E.A., Bogren L.K., Hesselberth J.R., and Martin S.L. (2018) Dynamic temperature-sensitive A-to-I RNA editing in the brain of a heterothermic mammal during hibernation. RNA 24, 1481-1495. PMID: 30065024.
D'Alessandro, A., Nemkov, T., Bogren, L.K., Martin, S.L., Hansen, K.C. (2017) Comfortably numb and back: Plasma metabolomics reveals biochemical adaptations in the hibernating thirteen-lined ground squirrel. J Proteome Res. 16:958-969. PubMed PMID: 27991798.
Bogren, L.K., Grabek, K.R., Barsh, G.S., and Martin, S.L. (2017) Comparative tissue transcriptomics highlights dynamic differences among tissues but conserved metabolic transcript prioritization in preparation for arousal from torpor, J. Comp. Phys. B 187:735-748. PMID: 28332019.
Jain S., Keys D., Martin, S.L., Edelstein, C.L., Jani, A. (2016) Protection from apoptotic cell death during cold storage followed by rewarming in 13-lined ground squirrel tubular cells: the role of prosurvival factors X-linked inhibitor of apoptosis and phosphoAkt. Transplantation, 100:538-545. PMID: 26457601.
Hindle, A.G., Otis, J.P., Epperson, L.E., Hornberger, T.A., Goodman, C.A., Carey, H.V., and Martin, S.L. Prioritization of skeletal muscle regrowth for emergence from hibernation. (2015) J Exp Biol 218:276-284. PMID: 25452506.
Grabek, K.R., Diniz Behn, C., Barsh, G.S., Hesselberth, J.R. and Martin, S.L. Enhanced stability and polyadenylation of select mRNAs support rapid thermogenesis in the brown fat of a hibernator. (2015) eLIFE 4:e04517. PMID: 25626169.
Hindle, A.G. and Martin, S.L. (2013) Cytoskeletal regulation dominates temperature-sensitive proteomic changes of hibernation in forebrain of 13-lined ground squirrels. PLoS ONE 8: e71627. PMID: 23951209.
Hindle, A.G. and Martin, S.L. (2014) Intrinsic circannual regulation of brown adipose tissue form and function in tune with hibernation. Am J Physiol Endocrinol Metab 306:E284-99. PMID: 24326419.
Hindle, A.G., Grabek, K.R., Epperson, L.E, Karimpour-Fard, A. and Martin, S.L. The liver proteome in hibernating ground squirrels is dominated by metabolic changes associated with the long winter fast. (2014) Physiol Genomics 46:348-61. PMID: 24642758.
Carey, H.V., Martin, S.L., Horwitz, B.A., Yan, L., Bailey, S.M., Podrabsky, J., Ortiz, R.M., Storz, J.F., Wong, R.P., and Lathrop, D.A. (2012) Elucidating Nature’s Solutions to Heart, Lung, and Blood Diseases and Sleep Disorders. Circ. Res. 110, 915-921. PMID: 22461362.
Jani, A., Orlicky, D.J., Karimpour-Fard, A., Epperson, L.E., Russell, R.L., Hunter, L.E., and Martin, S.L. (2012) Kidney proteome changes provide evidence for a dynamic metabolism and regional redistribution of plasma proteins during torpor-arousal cycles of hibernation. Physiol Genomics 44: 717-727. PMID: 22643061.
Epperson, L.E., Karimpour-Fard, A., Hunter, L.E. and Martin, S.L. (2011) Metabolic cycles in a circannual hibernator. Physiol. Genomics 43, 799-807. PMID:21540299.
Hindle, A.G., Karimpour-Fard, A., Epperson, L.E., Hunter, L.E., and Martin, S.L. (2011) Skeletal muscle proteomics: Carbohydrate metabolism oscillates with seasonal and torpor-arousal physiology of hibernation. Am J Physiol Regul Integr Comp Physiol, 301, R1440–R1452. PMID:21914784.
Jani, A., Epperson, E., Martin, J., Pacic, A., Ljubanovic, D., Martin, S.L., and Edelstein, C.L. (2011) Renal protection from prolonged cold ischemia and warm reperfusion in hibernating squirrels. Transplantation, 92, 1215-1221. PMID: 22082817.
Grabek, K.R., Karimpour-Fard, A., Epperson, L.E., Hindle, A.G., Hunter, L.E., and Martin, S.L. (2011) A multi-state proteomics analysis reveals novel strategies used by a hibernator to precondition the heart and conserve ATP for winter heterothermy. Physiol Genomics 43, 1263-1275. PMID: 2191478.
Russell, R.L., O'Neill, P.H., Epperson, L.E. and Martin, S.L. (2010) Extensive use of torpor in 13-lined ground squirrels in the fall prior to cold exposure. J Comp Physiol B 180, 1165–1172. PMID: 20556614.
van Breukelen, F. and Martin, S.L. (2001) Translational initiation is uncoupled from elongation at 18°C during mammalian hibernation, Am. J. Physiol. 281, R1374-R1379. PMID: 11641105.
van Breukelen, F. and Martin, S.L. (2002) Reversible depression of transcription during hibernation. J. Comp. Physiol. 172, 355-361. PMID: 12122451.
Srere, H.K., Wang, W.H.C. and Martin, S.L. (1992) A central role for differential gene expression during mammalian hibernation. Proc. Natl. Acad. Sci., USA 89, 7119-7123. PMID:1379733.