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Rajaii F, Kim DW, Pan J, Mahoney NR, Eberhart CG, Qian J, Blackshaw S. Temperature and species-dependent regulation of browning in retrobulbar fat. Sci Rep 2021; 11:3094. [PMID: 33542375 PMCID: PMC7862600 DOI: 10.1038/s41598-021-82672-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2020] [Accepted: 01/18/2021] [Indexed: 01/30/2023] Open
Abstract
Retrobulbar fat deposits surround the posterior retina and optic nerve head, but their function and origin are obscure. We report that mouse retrobulbar fat is a neural crest-derived tissue histologically and transcriptionally resembles interscapular brown fat. In contrast, human retrobulbar fat closely resembles white adipose tissue. Retrobulbar fat is also brown in other rodents, which are typically housed at temperatures below thermoneutrality, but is white in larger animals. We show that retrobulbar fat in mice housed at thermoneutral temperature show reduced expression of the brown fat marker Ucp1, and histological properties intermediate between white and brown fat. We conclude that retrobulbar fat can potentially serve as a site of active thermogenesis, that this capability is both temperature and species-dependent, and that this may facilitate regulation of intraocular temperature.
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Affiliation(s)
- Fatemeh Rajaii
- grid.21107.350000 0001 2171 9311Department of Ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD USA
| | - Dong Won Kim
- grid.21107.350000 0001 2171 9311Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD USA
| | - Jianbo Pan
- grid.21107.350000 0001 2171 9311Department of Ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD USA
| | - Nicholas R. Mahoney
- grid.21107.350000 0001 2171 9311Department of Ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD USA
| | - Charles G. Eberhart
- grid.21107.350000 0001 2171 9311Department of Ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD USA ,grid.21107.350000 0001 2171 9311Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD USA
| | - Jiang Qian
- grid.21107.350000 0001 2171 9311Department of Ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD USA
| | - Seth Blackshaw
- grid.21107.350000 0001 2171 9311Department of Ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, MD USA ,grid.21107.350000 0001 2171 9311Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD USA ,grid.21107.350000 0001 2171 9311Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD USA ,grid.21107.350000 0001 2171 9311Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD USA ,grid.21107.350000 0001 2171 9311Kavli Neuroscience Discovery Institute, Johns Hopkins University School of Medicine, Baltimore, MD USA
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Fu R, Gillen AE, Grabek KR, Riemondy KA, Epperson LE, Bustamante CD, Hesselberth JR, Martin SL. Dynamic RNA Regulation in the Brain Underlies Physiological Plasticity in a Hibernating Mammal. Front Physiol 2021; 11:624677. [PMID: 33536943 PMCID: PMC7848201 DOI: 10.3389/fphys.2020.624677] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Accepted: 12/29/2020] [Indexed: 12/13/2022] Open
Abstract
Hibernation is a physiological and behavioral phenotype that minimizes energy expenditure. Hibernators cycle between profound depression and rapid hyperactivation of multiple physiological processes, challenging our concept of mammalian homeostasis. How the hibernator orchestrates and survives these extremes while maintaining cell to organismal viability is unknown. Here, we enhance the genome integrity and annotation of a model hibernator, the 13-lined ground squirrel. Our new assembly brings this genome to near chromosome-level contiguity and adds thousands of previously unannotated genes. These new genomic resources were used to identify 6,505 hibernation-related, differentially-expressed and processed transcripts using RNA-seq data from three brain regions in animals whose physiological status was precisely defined using body temperature telemetry. A software tool, squirrelBox, was developed to foster further data analyses and visualization. SquirrelBox includes a comprehensive toolset for rapid visualization of gene level and cluster group dynamics, sequence scanning of k-mer and domains, and interactive exploration of gene lists. Using these new tools and data, we deconvolute seasonal from temperature-dependent effects on the brain transcriptome during hibernation for the first time, highlighting the importance of carefully timed samples for studies of differential gene expression in hibernation. The identified genes include a regulatory network of RNA binding proteins that are dynamic in hibernation along with the composition of the RNA pool. In addition to passive effects of temperature, we provide evidence for regulated transcription and RNA turnover during hibernation. Significant alternative splicing, largely temperature dependent, also occurs during hibernation. These findings form a crucial first step and provide a roadmap for future work toward defining novel mechanisms of tissue protection and metabolic depression that may 1 day be applied toward improving human health.
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Affiliation(s)
- Rui Fu
- RNA Bioscience Initiative, University of Colorado School of Medicine, Aurora, CO, United States
| | - Austin E Gillen
- RNA Bioscience Initiative, University of Colorado School of Medicine, Aurora, CO, United States
| | - Katharine R Grabek
- Fauna Bio Incorporated, Emeryville, CA, United States.,Department of Biomedical Data Science, Stanford University, Stanford, CA, United States
| | - Kent A Riemondy
- RNA Bioscience Initiative, University of Colorado School of Medicine, Aurora, CO, United States
| | - L Elaine Epperson
- Center for Genes, Environment & Health, National Jewish Health, Denver, CO, United States
| | - Carlos D Bustamante
- Department of Biomedical Data Science, Stanford University, Stanford, CA, United States
| | - Jay R Hesselberth
- RNA Bioscience Initiative, University of Colorado School of Medicine, Aurora, CO, United States.,Department of Biochemistry and Molecular Genetics, School of Medicine, University of Colorado, Aurora, CO, United States
| | - Sandra L Martin
- RNA Bioscience Initiative, University of Colorado School of Medicine, Aurora, CO, United States.,Department of Cell & Developmental Biology, School of Medicine, University of Colorado, Aurora, CO, United States
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Regan MD, Chiang E, Martin SL, Porter WP, Assadi-Porter FM, Carey HV. 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 2019; 316:R764-R775. [PMID: 30969844 DOI: 10.1152/ajpregu.00379.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
It is well established that hibernating mammals rely predominantly on lipid stores to fuel metabolism throughout the hibernation season. However, it is unclear if other endogenous fuels contribute to the rapid, ~400-fold increase in metabolic rate during the early phase of arousal from torpor. To investigate this issue, we used cavity ring-down spectroscopy, a technique that provides a real-time indication of fuel use by measuring the ratio of 13C to 12C in the exhaled CO2 of arousing 13-lined ground squirrels (Ictidomys tridecemlineatus). We used infrared thermography to simultaneously measure ventilation and surface temperature change in various body regions, and we interpreted these data in light of changing plasma metabolite abundances at multiple stages of arousal from torpor. We found that hibernating squirrels use a combination of lipids and, likely, carbohydrates to fuel the initial ~60 min of arousal before switching to predominantly lipid oxidation. This fuel switch coincided with times of maximal rates of ventilation and rewarming of different body surface regions, including brown adipose tissue. Infrared thermography revealed zonal rewarming, whereby the brown adipose tissue region was the first to warm, followed by the thoracic and head regions and, finally, the posterior half of the body. Consistent with the results from cavity ring-down spectroscopy, plasma metabolite dynamics during early arousal suggested a large reliance on fatty acids, with a contribution from carbohydrates and glycerol. Because of their high oxidative flux rates and efficient O2 use, carbohydrates might be an advantageous metabolic fuel during the early phase of arousal, when metabolic demands are high but ventilation rates and, thus, O2 supply are relatively low.
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Affiliation(s)
- Matthew D Regan
- Department of Comparative Biosciences, University of Wisconsin-Madison , Madison, Wisconsin
| | - Edna Chiang
- Department of Comparative Biosciences, University of Wisconsin-Madison , Madison, Wisconsin.,Department of Bacteriology, University of Wisconsin-Madison , Madison, Wisconsin
| | - Sandra L Martin
- Department of Cell and Developmental Biology, University of Colorado School of Medicine , Aurora, Colorado
| | - Warren P Porter
- Deparment of Integrative Biology, University of Wisconsin-Madison , Madison, Wisconsin
| | - Fariba M Assadi-Porter
- Department of Comparative Biosciences, University of Wisconsin-Madison , Madison, Wisconsin.,Deparment of Integrative Biology, University of Wisconsin-Madison , Madison, Wisconsin
| | - Hannah V Carey
- Department of Comparative Biosciences, University of Wisconsin-Madison , Madison, Wisconsin
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