Understanding temperature production and regulation in endotherm organisms becomes a crucial challenge facing the increased frequency and intensity of heat strokes related to global warming.Mitochondria, located at the crossroad of metabolism, respiration, Ca 2+ homeostasis and apoptosis, were recently proposed to further act as cellular radiators, with an estimated inner temperature reaching 50°C in common cell lines. This inner thermogenesis might be further exacerbated in organs devoted to produce consistent efforts as muscles, or heat as brown adipose tissue, in response to acute solicitations. Consequently, pathways promoting respiratory chain uncoupling and mitochondrial activity, such as Ca 2+ uxes, uncoupling proteins, futile cycling and substrate supplies, provide the main processes controlling heat production and cell temperature. The mitochondrial thermogenesis might be further ampli ed by cytoplasmic mechanisms promoting the over-consumption of ATP pools.Considering these new thermic paradigms, we discuss here all conventional wisdoms linking mitochondrial functions to cellular thermogenesis in different physiological conditions.
HighlightsBeyond its role as the principal source of ATP production, mitochondria can be considered as cellular radiators, with a possible local temperature of 50°C. This physiological contribution to heat production is regulated by many mechanisms targeting mitochondrial activity levels, and can be further stimulated by uncoupling the respiratory chain and membrane potential from ATP synthesis, to respond to drastic cold stresses. In addition, exergonic reactions using large ATP amounts in cell functions, like muscle shivering or Ca 2+ leak from the SR, can contribute to generate heat by inducing an over-stimulation of mitochondrial activity to replenish ATP pools. Cell variations in thermal ows might thus promote heterogeneous subcellular temperature gradients that might contribute to novel regulatory pathways controlling cell physiology.
Internal Heat Production In EndothermsBody temperature in endotherms, such as mammals, is crucial for the management of most biological functions. The ability to produce internal heat and maintain a constant body temperature was acquired during animal evolution, and is closely linked to original processes controlling energy metabolism. Indeed, an increased metabolic rate in endotherm species produces su cient heat to raise body temperature, even at rest (Legendre et Davesne 2020).Thermodynamics laws help to understand the link between heat production and energy metabolism.Energetic metabolism combines catabolic reactions, which break down molecules into smaller units, and anabolic reactions, which promote the synthesis of complex molecules from smaller units. Catabolic reactions are spontaneous and exergonic, i.e. more energy is released than consumed, whereas anabolic reactions are non-spontaneous endergonic reactions, requiring energy input from exergonic reactions.
