Abstract
There are two well-described thermogenic sites; brown adipose tissue (BAT) and skeletal muscle, which utilize distinct mechanisms of heat production. In BAT, mitochondrial metabolism is the molecular basis of heat generation, while it serves only a secondary role in supplying energy for thermogenesis in muscle. Here, we wanted to document changes in mitochondrial ultrastructure in these two tissue types based upon adaptation to mild (16°C) and severe (4°C) cold in mice. When reared at thermoneutrality (29°C), mitochondria in both tissues were loosely packed with irregular cristae. Interestingly, adaptation to even mild cold initiated ultrastructural remodeling of mitochondria including acquisition of more elaborate cristae structure in both thermogenic sites. The shape of mitochondria in the BAT remained mostly circular, whereas the intermyofibrilar mitochondria in the skeletal muscle became more elongated and tubular. The most dramatic remodeling of mitochondrial architecture was observed upon adaptation to severe cold. In addition, we report cold-induced alteration in levels of humoral factors: fibroblast growth factor 21 (FGF21), IL1α, peptide YY (PYY), tumor necrosis factor α (TNFα), and interleukin 6 (IL6) were all induced whereas both insulin and leptin were down-regulated. In summary, adaptation to cold leads to enhanced cristae formation in mitochondria in skeletal muscle as well as the BAT. Further, the present study indicates that circulating cytokines might play an important role in the synergistic recruitment of the thermogenic program including cross-talk between muscle and BAT.
Highlights
Mitochondria are very dynamic organelles that undergo dramatic remodeling in response to increase in local energy demand within a cell
All the nonshivering thermogenesis (NST) mechanisms are intricately associated with mitochondrial metabolism, connected to mitochondrial architecture
The data showing similar level of long-range physical activity compared with thermoneutrality suggest that NST is a major component of energy expenditure during mild cold adaptation
Summary
Mitochondria are very dynamic organelles that undergo dramatic remodeling in response to increase in local energy demand within a cell. Two well-known sites of thermogenesis are brown adipose tissue (BAT) and skeletal muscle [1,2,3,4,5] Both tissues use energy substrates such as fatty acids and glucose to convert the chemical energy generated in cells into heat as well as utilizing it for core body temperature (Tc) maintenance. Skeletal muscle possesses multiple mechanisms of heat production including shivering and nonshivering thermogenesis (NST) [10,11,12,13,14]. These mechanisms employ futile ATP hydrolysis by various ATPases [15,16,17,18,19,20]. BAT-based thermogenesis is directly reliant on mitochondrial metabolism, whereas skeletal muscle based thermogenesis is indirectly linked to mitochondrial metabolism
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
