Evaporative cooling provides a major metabolic energy sink

Ildiko Kasza, Doug Adler, David W. Nelson, C.-L. Eric Yen, Sabrina Dumas, James M. Ntambi, Ormond A. MacDougald, Diego Hernando, Warren P. Porter, Fred A. Best, C.M. Alexander

Thermogenesis could be harnessed to prevent obesity, which makes it important to understand sources of heat loss to maintain normothermia. Trans-epidermal water loss (TEWL) through perspiration is a cooling mechanism for over-heated mammalian bodies, but also occurs at low ambient temperatures. Kasza and colleagues calculated the energy dissipation created by evaporative cooling through mouse skin and show that increased rates of evaporative cooling account for increased energy expenditure reported in mouse strains with deficient lipid layers. They also show that obese mice show lower trans-epidermal water loss. This raises the possibility that evaporative cooling could be a significant player in energy expenditure to avoid obesity.

Objective: Elimination of food calories as heat could help redress the excess accumulation of metabolic energy exhibited as obesity. Prior studies have focused on the induction of thermogenesis in beige and brown adipose tissues as the application of this principle, particularly because the β-adrenergic environment associated with thermogenic activation has been shown to have positive health implications. The counterpoint to this strategy is the regulation of heat loss; we propose that mammals with inefficient heat conservation will require more thermogenesis to maintain body temperature.

Methods: Surface temperature thermography and rates of trans-epidermal water loss were integrated to profile the total heat transfer of genetically-engineered and genetically variable mice.

Results: These data were incorporated with energy expenditure data to generate a biophysical profile to test the significance of increased rates of evaporative cooling.

Conclusions: We show that mouse skins vary considerably in their heat retention properties, whether because of naturally occurring variation (SKH-1 mice), or genetic modification of the heat-retaining lipid lamellae (SCD1, DGAT1 or Agouti Ay obese mice). In particular, we turn attention to widely different rates of evaporative cooling as the result of trans-epidermal water loss; higher rates of heat loss by evaporative cooling leads to increased demand for thermogenesis. We speculate that this physiology could be harnessed to create an energy sink to assist with strategies aimed at treating metabolic diseases.